ASSAYS AND METHODS OF DIAGNOSIS AND TREATMENT BASED ON USE OF SODIUM CHANNELS AS TARGETS FOR AMYLOID beta OR ITS AGGREGATES

Abstract: Among other things, assays and methods of diagnosis and treatment of disease (<i>e.g.</i>, Alzheimer's disease) based on the surprsing observation of an interaction between amyloid or its aggregates with the sodium channel are provided. In particular, methods to identify compounds that modulate this interaction are provided, as well as methods of diagnosis and treatment that are based on this interaction.

Description: Assay s and Methods of Diagnosis and Treatment Based on Use of Sodium Channels As Targets for Ar loid β or its Aggregates TECHNICAL FIELD OF THE INVENTION The present invention provides, among other things, assays and methods of diagnosis and treatment that are based on the surprising observation of an lntei action between amyloid β or its aggiegates with sodium channels In paiticular, the present invention provides methods to identify compounds that modulate this interaction, and methods of diagnosis and ti eatment that are based on this interaction BACKGROUND OF THE INVENTION Certain neurodegencrative diseases such as Alzheimer's disease and Down s syndrome are charactenzed by the presence of insoluble aggregates of amyloid β (Aβ) This 39-43 am o acid peptide is derived by abnormal proteolysis from the Amyloid Precursor Protein (APP) It is well known that the amyloid β aggregates/plaques widely found in the brain and intraneuronal neurofibπllary tangles of Alzheimer's disease patients can modulate neurite outgrowth, synaptogenesis, synaptic plasticity or cause neuronal death (Mattson et al, T ends Neurosct , 16, 406- 415 (1993)) The mechanιsm(s) by which these effects are accomplished remain elusive, however (Frazer et al, Trends Neurosct , 20, 67-72 (1997)) Presently, one theory maintains that these deleterious effects may originate from amyloid β's ability to promote chronic calcium influx into neurons thiough modulation of neuronal calcium ion channels (Daidson et al , Biatn Res 643, 324- 327 (1994)), or to form transmembrane cation-permeable channels (Kawahara et al , Biophvsiol J , 73, 67-75 (1997)) that indiscriminately allow calcium, sodium, and other cations to flood a cell's interioi and destioy its calcium homeostasis Calcium channel blockers such as mmodipine that can cross the blood-biain baπier have been shown to slow the progression of Alzheimei 's disease in some patients (Tollefson, Biol Psy chiatry , 27, 1 133-1 142 (1990)) Similarly, zinc cation, which is known to bind at specific amyloid β 1 -40 sites (Bush et al, Science, 265, 1464-1467 ( 1994)), can block the calcium influx through amyloid β 1 -40 channels (Arispe et al., Proc. Nut I. Acad. ScL , 93, 1710- 1715 ( 1996)). In addition, amyloid β aggregates have been shown to induce abnormal potassium ion channel activity. In cultured hippocampal neurons, amyloid β opens a calcium-sensitive, large conductance potassium channel (i.e. , iberitoxin-sensitive BK) (Furukawa et al., Nature, 379, 74-78 (1996)), which could lead to chronic loss of cytoplasmic potassium and destroy the ability of the neurons to generate and propagate action potentials critical for brain signaling functions. Such aberrant potassium channel activity has in fact been noted in Alzheimer's disease patients (Etchebemgaray et al., Proc. Nad. Acad. ScL , 90, 8209-8213 ( 1993)). Likewise, in the cultured cholinergic septal cell line SN56. amyloid β (e.g., amyloid β 1 -40) causes cell death by impacting a TEA-sensitive potassium channel (Colom et al., J. Nenrochemistry, 70, 1925-1934 (1998)). These studies suggest that amyloid β aggregates exert their effects through multiple targets. None of the targets that have been described, however, would result in the rapid and complete inhibition of neuronal electrical impulses critical for brain function that is observed with advanced stage Alzheimer's disease. Furthermore, the ion channel studies described above were performed on cultured neurons, whose properties may have been changed significantly through dedifferentiation in culture conditions. Therefore, the data currently available likely does not represent the true response of native neurons. Recent genetic studies have shown that mutations in the amyloid protein precursor and presenilin genes affect the processing and production of amyloid β and thus are related to age of onset and susceptibility to Alzheimer's disease. Additional studies have shown that variants in ApoE genes also affect susceptibility and age of onset for Alzheimer's disease. Spontaneous Alzheimer's disease is hypothesized to be under the control of other genes and environmental factors that have yet to be identified. Additionally, inhibition of amyloid β aggregation, and hence toxicity, is believed to be beneficial therapeutically in the treatment of Alzheimer's disease. Sev eral reports have appeared providing evidence that small, diffusable aggregates 9 (Lambert et al , Pi oc Nail Acad Sci , 95, 6448-6453 ( 1998) PCT International Application WO 98/33815), and protofibnls (Hai pei ct al C hun Biol , 4, 1 1 9-125 ( 1997 ), Harpei et al , Chem Biol , 4, 951 -959 ( 1997), Walsh et al , J Biol Chem , 272, 22364-22374 ( 1997)), and not the completely fibi illai peptide, might be the Aβ species toxic to living cells The physical differences in the alleged toxic species identi fied by these different research groups "supports the concept that different Aβ assemblies have distinct neurobiological activities, which may be manifested differently using an electrophysiological l eadout" (Hartley et al , J Neui oscienc e, 19 8876-8884 ( 1999)) Thus, the etiology of Alzheimer's disease mav be quite complex, and may warrant a variety of different avenues of diagnosis and ti eatment Along these lines, U S Patent 5,876,948 descπbes screening methods to identi fy inhibitors of the neurotoxic effect of amyloid β In particular, the '948 patent purportedly provides a method of screening candidate compounds, wherein the method comprises obtaining a cell such as a primary neuron, a neuronal cell, or a cell developmentally derived from neuronal tissue The cell is contacted with a candidate compound in the presence of a neurotoxin selected from the group consisting of amyloid β l -38, β l -40, β l -43, and β29-35, and it is determined whether the compound reduces the effect of the neurotoxin (e g , reduces cell death), or reduces accumulation of amyloid β on the cell surface Accordingly, this patent piovides no information on how to screen for compounds that target cell events that precede cell death, apart from accumulation of the peptide on the cell surface A need thus remains for useful assays to screen for compounds that exert protective effects at a stage prior to cell death mediated by amyloid β, and for compounds that exert their effect apart from interference with amyloid β deposition on the cell surface Furthermore, the '948 patent does not appear to consider any effect of the aggregation state of amyloid β on neurotoxicity A related patent, U S Patent 5, 137,873, claims a method for treating a disease that is characterized by accumulation of amvloid β which compnses administration of a therapeutically effective amount of a tachykinin agonist such as substance P U S Patent 5,892,018 pertains to DNA sequences encoding a novel subfamily of amiloπde-sensitive sodium channel pi otems from the human centi al nervous system PCT Internatioi al Application WO 98/54316 descπbes a new class of sodium channel piotein that m ιy function as a l eceptoi for endogenous ti ansmitters Both the '01 8 patent and the '316 application suggest that ion channels may play some role in the pathogenesis or treatment of Alzheimei 's disease (see, '3 16 application, pages 1 and 15, see, '018 patent, column 1 , lines 50-54) However, neithei document presents any assay for diagnosis of Alzheimer's disease, much less any methods for its tieatment Thus, there remains a need for further understanding of the functioning of amyloid β or its aggregates, and means to diagnose, predict, prevent and treat diseases, disorders, and conditions that result from amyloid β or its aggregates These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein BRIEF SUMMARY OF THE I VENTION The present invention relates to a surprising observation of an interaction between amyloid β or its aggregates with sodium channels Based on this novel and unexpected interaction, the present invention provides a method for identifying compounds that modulate the interaction of amyloid β or its aggregates with a sodium channel, wherein the method preferably comprises contacting a cell which comprises a sodium channel with amyloid β or its aggregates in the presence and in the absence of a test compound, and then determining whether there is any impact on the sodium channel in the presence of the test compound as compared with in the absence, with a compound that exhibits an impact being considered a modulator of the interaction of amyloid β or its aggregates with said sodium channel In preferred embodiments, the impact on the sodium channel is assessed by either examining resting membrane potential, action potential, or measuring the fast inward sodium current Preferably as employed in the invention, the cell is a neuronal cell, or is a non-neuional cell, as described herein The method of identifying compounds that modulate the interaction of amyloid β oi its aggregates with a sodium channel also can be carried out according to the invention w herein the method compi iscs obtaining a fii st cell that pi oduces amyloid β or its aggi egates, obtaining a second cell compnsing a sodium channel, contacting the second cell with the first cell in the pi esence and absence of a test compound, and detei mining the activ ity of the sodium channel in the presence of said test compound as compai ed with in the absence, wherein a test compound that impacts activity is considered a modulatoi of the mtei action of amyloid β or its aggi egates ith said sodium channel Preferably one of the first and second cells is a neuronal cell and the othei is a non-ncuronal cell or both of the first and second cells ai e either a neuronal cell or a non-neuronal cell Also, preferably the method of identifying compounds that modulate the mteiaction of amyloid β or its aggiegates w ith a sodium channel can be carried out according to the invention wherein the method comprises the steps of obtaining a composition comprising a purified sodium channel, contacting the sodium channel with amyloid β or its aggregates in the presence and absence of a test compound, and determining the activity of the sodium channel in the presence of the test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggregates with the sodium channel The invention also provides a method for diagnosing Alzheimer's disease (or prion disease) in a mammal suspected of having Alzheimer's disease (or prion disease), the method comprising the step of measuring the activity of a sodium channel in a cell of the mammal, wheiein reduced activity of the sodium channel is correlated with the existence of an Alzheimer's disease state (oi a prion disease state) The invention furthei provides a method of screening a mammal for susceptibility to Alzheimer's disease, comprising the steps of (a) isolating a cell fiom the mammal, the cell comprising a sodium channel, and (b) measuring activity of the sodium channel in the absence and in the presence of amyloid β protein, wherein reduced activity of the sodium channel in the presence of amyloid β as compared to in the absence is con elated with a susceptibility to developing Alzheimer's disease Additionally, the invention provides a method for preventing, treating, oi reversing diseases such as Alzheimer's disease and prion disease in a mammal, wherein the method preferably comprises contacting a sodium channel of the mammal with a compound that protects the sodium channel from a negative impact of amyloid β or its aggregates This method optionally is carried out with use of a compound that opens the sodium channel. Furthermore, the invention provides for the use of a compound that modulates the interaction of amyloid β or its aggregates with cellular sodium channels for the manufacture of a medicament for the treatment of a neurological disorder (e.g , Alzheimer's disease). Additional features and variations of the invention will be apparent to those skilled in the art from the entirety of this application, including the detailed description, and all such features are intended as aspects of the invention. Likewise, features of the invention described herein can be recombined into additional embodiments that also are intended as aspects of the invention, irrespective of whether the combination of features is specifically mentioned above as an aspect or embodiment of the invention. Also, only such limitations which are described herein as critical to the invention should be viewed as such; variations of the invention lacking limitations which have not been described herein as critical are intended as aspects of the invention. In addition to the foregoing, the invention includes, as an additional aspect, all embodiments of the invention narrower in scope in any way than the variations specifically mentioned above. Although the apphcant(s) invented the full scope of the claims appended hereto, the claims appended hereto are not intended to encompass within their scope the prior art work of others Therefore, in the event that statutory prior art within the scope of a claim is brought to the attention of the applicants by a Patent Office or other entity or individual, the applιcant(s) reserve the right to exercise amendment rights under applicable patent laws to redefine the subject matter of such a claim to specifically exclude such statutory prior art or obvious variations of prior ait fiom the scope of such a claim Vanations of the invention defined by such amended claims also are intended as aspects of the invention BRIEF DESCRI PTION OF THE DRAWINGS Figures 1 A-C are recoi dings taken from an Axopatch 200 Amphfici which show changes of an action potential recoi ded fi om a single cortical neuron (A) in the absence of amyloid β 1 -40 peptide, (B) in the pi esence of 1 1 5 μM amyloid β 1 -40 peptide, or (C) following washing of the ncuion with peptide-fi ee solution Figures 2A-C are recordings taken from an Axopatch 200 Amphfici which show changes of an action potential l ecoi ded from a single hippocampal neuron (A) in the absence of amyloid β 1 -40 peptide, (B) in the presence of 1 1 5 μM amyloid β 1 - 40 peptide, or (C) following washing of the neuron with peptide-free solution Figures 3A-C are recordings taken from an Axopatch 200 Amplifier which show the progressive reduction in a fast inward sodium current of a hippocampal neuron elicited by step potential change from -80 mV (millivolt) to -30 mV in the absence of amyloid β 1-40 (Figure 3A), in the presence of 50 μM amyloid β 1 -40 following about 90 minutes shake-induced amyloid β aggregation (Figure 3B), and in the piesence of 50 μM amyloid β 1 -40 following about 120 minutes shake-induced amyloid β aggregation (Figure 3C) The effect of the peptide cannot wash out The arrow indicates the direction of progressive current depression by the peptide Figure 4 is a graph which shows the progressive change of peak amplitude of inward sodium current (I πa ) measured in pico ampere (pA) (Y-axis) with time (second) (X-axis), in the absence of amyloid β 1 -40 (open cucles), in the presence of 50 μM amyloid β 1 -40 following about 90 minutes of shake-induced amyloid β aggregation (solid circles), and in the presence of 50 μM amyloid β 1 -40 following about 120 minutes shake-induced amyloid β aggregation (solid squares) The readings were from the same experiment as in Figure 3A-C. Figures 5A-D are recordings taken from an Axopatch 200 Amplifier which show the effect of amyloid β 1 -40 on the fast inward sodium current of a hippocampal neuion over a broad range of membrane potentials ranging from about -50 to +20 m, with each panel showing eight fast inward sodium cuπent traces supei imposed on the same time n ame elicited b step potential changes li om a holding potential of 80 mV to - ) mV then 1 0 m\ inci . nents, to +20 m\ in the absence of amvloid β 1 -40 (Figure 5A) in the presenc of 50 uM amvloid β 1 40 f ollow ing about 90 minutes shake induced amyloid β aggregation (Figure 5B) in the presence of 50μM amvloid R 1 -40 following about 120 minutes shake-induced amyloid β aggi egation (Figure 5C) and following wash out of the peptide (Figui e 5D) The effect of amyloid β 1 -40 cannot wash out Figure 6 is a graph which shows peak amplitude of fast inwaid sodium cuπ ent in pA (Y-axis) over a bioad range of membi ane potential in mV (X-axis) in the absence of amyloid β 1 -40 (open circles), in the presence of 50 uM amyloid β 1 - 40 follow ing about 90 minutes shake induced amyloid β aggregation (solid cucles), in the presence of 50 «M amyloid β 1 -40 following about 120 minutes shake induced amyloid β aggregation (open squares), and following wash out of the peptide (solid squares) The readings were from the same experiment as in Figures 5A-D Figures 7A-C are recordings taken from an Axopatch 200 Amplifier which show superimposed sodium current traces of a hippocampal neuron elicited from a holding potential of -80 V to -70 mV, and then at 10 mV increments to + 10 mV, and obtained in the absence of the specific fast mward sodium channel blocker tetrodotoxin (TTX) (Figure 7A), in the presence of 1 μM TTX (Figure 7B), and in washing out of TTX (Figure 7C) Figure 8 is a graph which shows peak amplitude of fast inward sodium current in pA (Y-axis) over a broad range of membrane potential in mV (X-axis) in the absence of TTX (open circles), in the presence of 1 μM TTX (solid circles), and following wash out of TTX (solid squares) The readings were from the same expenment as in Figures 7A-C Figures 9A-B are recordings taken from an Axopatch 200 Amplifier which show a single calcium current elicited in isolated hippocampal neurons from a holding potential of -40 mV to +10 mV, m the absence of amyloid β 1 -40 (Figure 9A), and in the pi esence of 50 μM amyloid β 1 -40 peptide following about 70 minutes shake- induced amyloid β aggi egation (Figure 9B) Figure 10 is a graph which shows peak calcium current ( I CJ ) amplitude in pA (Y-axis) over time seconds (sec) (X-axis) in the absence of amyloid β (open circles), and in the pi esence of 50 μM amyloid β 1 -40 follow ing about 70 minutes shake-induced amyloid β aggregation (solid circles) The readings were from the same experiment as in Figures 9A-B Figures 1 1 A-D are recordings taken from an Axopatch 200 Ampli fier which show potassium currents elicited by a step potential from a holding potential of -40 mV to + 10 mV, in 10 mV increments in the absence of amyloid β 1 -40 (Figure 1 1 A), in the presence of 50 μM amyloid 13 1 -40 following about 90 minutes shake-induced amyloid β aggregation (Figure 11 B), in the presence of 50 μM amyloid β 1 -40 following about 120 minutes shake-induced amyloid β aggregation (Figure 1 1 C), and following wash out of the peptide (Figure 1 I D). Figure 12 is a graph which shows peak amplitude of potassium currents in nanoampere (nA) (Y-axis) over a broad range of membrane potential in mV (X-axis) in the absence of amyloid β 1 -40 (solid line), in the presence of 50 μM amyloid β 1 - 40 following about 90 minutes shake-induced amyloid β aggregation (cross-hatched line), and in the presence of 50 μM amyloid β 1 -40 following about 120 minutes shake-induced amyloid β aggregation (dotted line). The readings were from the same experiments as in Figure 1 1 A-D. Figure 13 is a graph which shows the impact of amyloid β on the sodium channel (Y-axis, % decrease in I Na ) at different time points (X-axis, in minutes) of aggregation The peak impact on activity appears at about 60-80 minutes of shake- induced aggregation of the 50 μM amyloid β 1 -40. For each datapoint, the number of independent measurements from independent neurons is indicated, and error bars are provided where multiple measurements have been averaged. The detailed description and examples are provided to enhance the understanding of the invention, but are not intended to limit the scope of the invention. DETAILED DESCRIPTION OF THE INVENTION It is well established that, in cultuied cells oi neonatal neuions, certain forms of amyloid β (Aβ) ai e neurotoxic by interfering with noimal neuronal functions Howevei , the precise target channel(s) and subsequent changes in action potential firing patterns of native neurons in adult mammals have not been established This important issue was examined using a highly sensitive, well-defined neuional preparation freshly dissociated from adult rat biams and the suction pipette recording technique It surpi isingly was discovered that amyloid β depressed or eliminated neuronal action potentials by specifically blocking fast inward sodium channels, thereby shutting off neuronal impulses Furthermore, it was determined that low molecular weight amyloid β aggregates had greater ability to deleteπously impact cell functions (/ e , including sodium channel activity) than either monomers or polymers Based on the foregoing, and as further described herein, the present invention provides, among other things, a method for identifying compounds that modulate the interaction of amyloid β or its aggregates with a sodium channel Such compounds are useful in diagnosing, preventing, treating, or reversing various disorders (e g , Alzheimer's disease and prion disease) that are characterized by disruption of sodium channels Amyloid β or its Aggregates According to the invention, "amyloid β" (Aβ) is any of the sequences 1 -43,1 - 42,1-41 , 1 -40, 1 -39, and 1 -38, and truncated sequences of any of the previous, resulting from β-secretase and γ-secretase cleavage of the amyloid precursor protein (see, e g , Yan et al , Natui e, 402, 533-537 (1999), Kang et al , Natwe, 325, 733 (1987), Selkoe, In Annual Review ofNeuroscience, Cowan (Ed ), 17, IX + 623, 489- 517 ( 1994)) Aβ can be that of any species, particularly a mammalian species, and especially human Furthermore, "amyloid β" includes any amino acid substitutions in the foregoing sequences that result in a modified peptide/protem having aggregation properties similar to the native peptide/protem In particular, amyloid β is a piotein (oi peptide) comprising lesidues 1 -38, 1 -40 1 -43 oi 29-35 of APP, as set forth in U S Patent 5,876,948, and which can be pi oduced bv recombinant oi svnthetic means Amyloid β can be pui chased from a v anetv of commercial supphci s including but not limited to Polypeptide Laboi atones ( roπ ance, CA, Catalog numbei P-0036) and Bachem Biochemica (Heidelberg, Germanv ) Aβ also can be pi oduced by a cell natui ally, produced by a cell using recombinant means, produced by one cell (e g , neuronal ) while its impact is assayed on anothci (e g , non-neuional ), employed in its polypeptide form (/ e , either pre-aggregated or not) to contact a sodium channel, or employed as part of a composition (e g , including micelles) to contact a sodium channel All these various permutations, as w ell as additional v ariations that would be obvious to one skilled in the art, are encompassed bv the subject invention "Aggregates" of amyloid β include any higher ol der structure formed by an association of more than one Aβ monomer with an ability to inhibit the fast ward sodium current (I NJ ), and especially include a tetramer of amyloid β (/ e , a higher order structure formed by the association of four amvloid β monomers) Aggregation of amyloid β preferably is done in an appropriate buffer If the aggregated amyloid β subsequently is not to be used with cells, then the buffer desirably comprises about 10 mM phosphate, 1 00 mM Na l, pH 7 4, or another similar buffer If the amyloid β subsequently is to be used with cells (e g , whole cells, isolated cells, or othei ), then the buffer employed for aggregation desirably comprises the same tissue culture medium in which the cells are aggregated (c g , Hank's balanced salt solution) Aggregation desirably is carried out by shaking the mixture of amyloid β in buffer (e g , desirably at a rate of from about 700 to 800 rpm) Optimally, aggregation is carried out for v arious times, particularly as described in the Examples Desirably, aggregation is monitored, e % , by measuring light scattering at 405 nm More detailed information on aggregation can be obtained from the Examples, as well as the reference of Findcis et al , Biochemist! i , 38, 6791 -6800 ( 1999) Furthermore, preferably prior to dissolution the appiopnate buffer, the amyloid β fust preferably is treated in an appropnate fashion to obtain random coil monomei This can be done, foi instance, by tieatment w ith hexafluoroisopiopyl alcohol (HFIPA)(as describ ed in the Examples which follow), oi by acid ti eatment (as described in the Examples which follow, and in Findeis et al , supr a) Sodium Channels and Cells Comprising Same The sodium channels for use in the invention include but ai e not limited to all native sodium channels in all tissues, especially in the nervous system, and most particulai ly in cells from the brain and spinal cord tissues, which are targets for Aβ of v arious forms and at various stages of aggregation (/ c , which are sensitive at some level to the deleterious effects of Aβ or its aggregates) Thus, accoiding to the invention, a "cell" preferably is a primary neuron, a neuronal cell, or a cell that is developmentally derived from neuronal tissue The invention also desirably can be carried out with the use of sodium channels in cells from non-neuronal tissue (t e , non-neuronal cells). A "non-neuronal cell" is a cell that is not a primary neuron, a neuronal cell, or a cell that is developmentally derived from neuronal tissue Preferred non-neui onal cells for use in the invention include but are not limited to primary cells that have a cell geometry, cell number, and degree of homogeneity that allows relatively easy harvesting of the cells for single-cell electrophysiology assays Especially preferred non-neuronal cells are muscle cells, especially muscle cells confirmed to have a sodium channel similar in function to that of neuronal cells (e g , skeletal muscle cells, and cardiac muscle cells such as pacemaker cells, atπal cells, atπal-ventπcular nodal cells, left ventricular cells, right ventricular cells, papillary muscle cells, and Purkinje fiber cells), although other muscle cells that have not been so charactenzed also can be employed (e.g , smooth muscle cells, particularly cardiac smooth muscle cells) Cells that are less than optimal for electrophysiology studies (e g , those having a smaller size oi a flat versus lounded morphology, those having a low cell number, and/or those which are located as part of a nonhomogeneous tissue) also can be used, with appropriate optimization of the assays according to the invention Such cells include blood cells, kidney cells, and epithelial cells (i e , those lining the intestines) None of these cells aie developmentally derived from neuronal cells Additionally, cultured cells including non-neuronal cancer cell lines also optionally can be employed, so long as the cells can be maintained under conditions that de-differentiation is infrequent and unlikely Such established cell lines differ from primary cells m that the cell lines have undergone a genetic change that renders them effectiv ely immortal Prefei ably the cell is an avian cell, or a mammalian cell including but not limited to that of a t odent, primate (e g , monkey, ape, gorilla, chimpanzee, gibbon, orangutan, and the like), feline, canine, ungulate ( g , ruminant or swine), and particularly that of a human Desirably the cell is of a mammalian (especially a human) species. A cell can be present as a single entity, or can be part of a larger collection of cells, such as, for instance, a cell culture, a tissue (e g , neui al tissue), an organ (e , brain or spinal cord), an organ system (e.g , cential nervous system), or an organism (e g , mammal) Preferably a "sodium channel" is a fast inward sodium channel. A "fast inwai d sodium channel" is a large trans-membrane, voltage-sensitive protein that opens (/ e , provides a passage through the cell membrane, from a cell's exterior to its interior) in response to membrane depolarization. Once opened, the channel allows massive influx of sodium ion into the cell, for a few milliseconds only, and in a neuronal cell, allows the generation of the action potential that is critical for conducting nerve impulses. Without opening of fast inward sodium channels, a neuronal network stays silent and becomes non-functional. The sodium channels that are contemplated for use in the invention include those known in the art as "voltage- gated", "non-voltage-gated", and "exchangers". The current measured at a fast mward sodium channel is the fast inward sodium current. All tetrodotoxin (TTX)-sensιtιve and TTX- sensitive sodium channels from tissue/cell sources stated above are the key targets for amyloid β of various forms and at various stages of aggregation. However, in preferred embodiments, the invention is practiced using sodium channels that are TTX-sensitive. The sodium channels useful for practice of the invention further include non- native sodium channels (e g , those obtained by recombinant means, such as molecularly cloned sodium channels, including those cloned fi om cells of any tissues, particularly from the cential nervous system, and especially from brain) as targets for amyloid β of various forms and at various stages of aggregation. Non-native sodium channels useful for conducting assays of the invention are sensitive at some level to the deleterious effects of amyloid β or its aggregates. However, non-nativ e sodium channels that are not sensitive to the deleterious effects of amyloid β or its aggregates are useful for determining those regions at which amyloid β interacts with the channel (e.g. , by comparing the structure of the non-native channel with that of the native channel). Such non-nativ e sodium channels include but are not limited to those described in U.S. Patent 5,892,018, and PCT International Application WO 98/543 16. Thus, the deleterious activity of amyloid β or its aggregates can be studied and modulated by introducing into cells expression vectors that result in production of high levels of a sodium channel. Along these lines, the invention further provides methods of using purified sodium channels (or portions thereof) and genetically engineered host cells that express recombinant sodium channels to evaluate and screen for modulators of the interaction between amyloid β peptide and the sodium channel. Assay for Modulators of the Interaction of Amyloid β or its Aggregates with the Sodium Channel The present invention provides methods of screening for putative modulators using any of a variety of drug screening techniques. Such modulators will provide the basis for pharmaceutical compositions for the treatment and amelioration of symptoms associated with the activity of amyloid β or its aggregates. Modulators of the interaction of amyloid β or its aggregates with the sodium channel include modulators that facilitate (i.e., increase the effectiveness of, or make happen more readily) the interaction of amyloid β or its aggregates with the sodium channel, and compounds that impair (i.e. , decrease the effectiveness of, or make happen less readily) the interaction of amyloid β or its aggregates with the sodium channel. In the context of the present invention, compounds that impair the interaction of amyloid β or its aggregates with the sodium channel may find particular use in the prevention and/or treatment of Alzheimer's disease and prion disease, as well as other disorders, as further described herein. According to the invention, modulators that impair the interaction of amyloid β or its aggregates with the sodium channel allow a reduction of no more than from 0% to about 20% in the fast inward sodium current when a sodium channel is contacted with amyloid β or its aggregates and the modulator (i.e. , as compared to when a sodium channel is contacted with amyloid β or its aggregates in the absence of the modulator), or cause the reduction that occurs following such contacting to have a delayed onset and/or less prolonged duration (i.e. , as compared to when a sodium channel is contacted with amyloid β or its aggregates in the absence of the modulator). By comparison, modulators that facilitate the interaction of amyloid β or its aggregates with the sodium channel increase the reduction in the fast inward sodium current when a sodium channel is exposed to amyloid β or its aggregates by at least from about 10% to about 20% (i.e., as compared to when a sodium channel is exposed to amyloid β or its aggregates in the absence of the modulator), or cause the reduction that occurs following such exposure to have a more rapid onset and/or more prolonged duration (i.e., as compared to when a sodium channel is contacted with amyloid β or its aggregates in the absence of the modulator). In one embodiment, the invention provides a method for identifying compounds that modulate the interaction of amyloid β or its aggregates with a sodium channel preferably comprising: (a) obtaining a cell that comprises a sodium channel; (b) contacting the sodium channel with amyloid β or its aggregates in the presence and absence of a test compound; and (c) determining the activity of the sodium channel in the presence of the test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggregates with the sodium channel. The sodium channels employed in the assay methods of the invention may be free in solution, affixed to a solid support, present on a cell surface, or located in micelles or other structures. Additionally, as discussed above, the sodium channel (and/or amyloid β or its aggregates) can be provided to a cell by recombinant means (e g , pi oduced within the cell by virtue of recombinant DNA modifications of the cell, or produced by a neighboring cell such as a neuionai cell and employed to impact a non neui onai cell being studied) The amyloid β as applied foi contacting the sodium channel optionally is in polypeptide foi m, and, as so supplied, can be eithei pi e-aggi egated for vanous lengths of time (e g as pi eviously desci ibcd and as set out in the Examples which follow), oi can be employed foi contacting in its monomer form In one variation, the method pi eferably can be cai πed out by (a) obtaining a fii st cell that produces amyloid β or its aggi egates, (b) obtaining a second cell compi ising a sodium channel, (c) contacting the second cell with the fu st cell in the presence and absence of a test compound, and (d) determining the activity of the sodium channel in the piesence of the test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggregates with the sodium channel The method preferably can be carried out wherein the first and second cell are of the same type cells, thus both the first and second cells are either a neuronal cell or a non-neuronal cell (e g , both are either neuronal or non- neuronal cells, or both are of the same type of either neuronal oi non-neuronal cells) The method also preferably can be carried out w hei ein the first and the second cells are different types of cells, for instance, one of the first and second cells is a neuronal cell and the other is a non-neuronal cell, or one is of one type of a neuronal or non- neuional cell and the other is of another type of neuronal or non-neuronal cell) The method also optionally can be carried out by (a) obtaining a composition comprising a purified sodium channel, (b) contacting the sodium channel with amyloid β oi its aggregates in the presence and absence of a test compound, and (c) determining the activity of the sodium channel in the presence of the test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggiegates with the sodium channel The assay methods described herein preferably ai e earned out wherein the activity of the sodium channel (and hence the impact on the sodium channel) in the pi esence of the test compound as compared with in the absence is determined oi assessed by a method selected from the group consisting of examining l estmg membrane potential, examining action potential, or measui g the fast inward sodium current. In comparison to the fast inward sodium current, there ai e slow inward sodium currents, but these play a minimal role in the generation of action potentials In particular, reduction and/or abrogration of action potential can be assessed, as well as the relief of such reduction or blockage (e g , by so-called "sodium channel opcnci s", as described below). Likewise, reduction oi blockage of the fast inward sodium current can be assessed, as well as the relief of such reduction or blockage (e g , by so-called sodium channel "openers"). Such measurements can be done using methods known in the art, and described in the Examples that follow . The modulation of the effects of amyloid β or its aggregates on a sodium channel by an agent being tested (i.e. , a "test compound") may be measured by means described herein, or other means known in the art, which are amenable to biochemical or cell-based high throughput screening (HTS) assays (e g , melanophore assay systems to investigate receptor-hgand interactions, yeast-based assay systems, and potentially mammalian cell expression systems, and the like). For a review, see .layawickreme and Kost, Curr 0pm. Biolechnol ,8, 629-634 ( 1997). Automated and miniaturized HTS assays are also comprehended as described, for example, in Houston and Banks, Curr Opin. Biolechnol, 8, 734-740 ( 1997). Such HTS assays are used to screen libraries of compounds to identi fy particular compounds that exhibit a desired ability to modulate the interaction of amyloid β or its aggregates with the sodium channel Any library of compounds may be used, including chemical libraries, natural product libraries, combinatorial libraries comprising random or designed ohgopeptides, ohgonucleotides, or other organic compounds. Chemical libraries may contain known compounds, piopπetary structural analogs of known compounds, or compounds that are identified from natural product Natui al product libraries are collections of materials isolated from natui al sources, typically, micioorgamsms, animals, plants, oi marine organisms Natui al pioducts ai e isolated fi om then sources by fermentation of microorganisms followed by isolation and extraction of the fermentation broths or by direct extraction fi om the microoi ganisms or tissues (plants or animal) themselves Natural pioduct libranes include polyketides, non- πbosomal peptides, and vanants (including non-natui ally occurring variants) thei eof For a review, see Cane et al , Science, 282, 63-68 ( 1998) Combinatorial hbiaues ai e composed of large numbers of related compounds, such as peptides. ohgonucleotides, or other organic compounds as a mixtuie Such compounds ai e relatively straightforward to design and prepare by traditional automated synthesis protocols, PCR, cloning or proprietary synthetic methods Of particular interest are peptide and ohgonucleotide combinatorial libraries Still other libraries of interest include peptide, protein, peptidomimetic, multiparallel synthetic collection, recombinatoπal, and polypeptide libraries For a review of combinatorial chemistry and libraries created thereby, see Myers, Curr Opin Biolechnol , 5, 701 -707 ( 1997). Once compounds have been identified that show activity as modulators of the interaction of amyloid β or its aggregates with the sodium channel, a program of optimization can be undertaken in an effort to improve the potency and or selectivity of the activity, if so desired This analysis of structure-activity relationships (SAR) typically involves an iterative series of selective modifications of compound structures and their correlation to biochemical or biological activity Families of related compounds can be designed that all exhibit the desired activity, with certain members of the family potentially qualifying as therapeutic candidates Accordingly, the invention provides for the use of a compound that modulates the interaction of amyloid β or its aggregates with sodium channels for the manufacture of a medicament for the treatment of a neurological disorder (e g , Alzheimefs disease) In particular, the present provides compounds that protect sodium channels from the inhibitory action of amyloid β of various forms and at various stages of aggregation The present invention further piovides compounds that open sodium channels in the presence of amyloid β of various forms and at v anous stages of aggi egation Such compounds ("sodium channel openers") can be employed to impact all action potentials generated by sodium channels, as viable targets foi amyloid β of v anous forms and at various stages of aggi egation Desn ably accoiding to the invention, a sodium channel opener also can be a compound that opens sodium channels in the absence of amyloid β of various forms and at v arious stages of aggregation Examples of sodium channel openers include but ai e not limited to vei atπdine and DP 1201 Veratπdine and DP 1201 , howev ei , change the gating mechanism of the channel allowing too much sodium in the cell, and thus while useful in a t esearch context, may not prove as useful in the treatment of disease Similarly, these and other compounds according to the invention can be employed to impact all calcium and/or potassium channels as viable targets for amyloid β of various forms and at various stages of aggregation In particulai , preferably according to the invention, a modulator identified according to the methods described herein can be employed to treat Alzheimer's disease (or prion disease) as part of a composition comprising the modulator The present invention desirably provides a compound identified as a modulator according to the scieening methods described herein The invention further preferably provides a composition comprising such a compound so identified in a pharmaceutically acceptable earner Furthermore, the invention preferably provides a method of using a compound so identified in the manufacture of a medicament for the prevention, treatment, or reversal of Alzheimer's disease (or prior disease) in a mammal Host Cell Expression Systems As previously indicated, both the sodium channel (or constituent components thereof) and/or amyloid β can be provided to cells in the form of their encoding nucleic acids, and thus produced by the neuronal cell, or can be intioduced into a host cell in their polypeptide form The term "polypeptide" as used herein shall include all peptides (e g , portions of proteins) and proteins (/ e , having an ammo and caiboxyl terminus) whether recombinant, synthetic, or punfied fi om natuial sources Accordinglv , host c "11s are provided, including prokai yotic or eukaryotic cells, eithei stably or transiently modified by mtioduction of a polynucleotide to pennit expi ession of the encoded sodium channel (or constituent components theieof) and/or amyloid β, or stably or transiently modified by introduction of the sodium channel itself (or constituent components thereof) and/or amyloid β While eukaiyotic cells such as neuronal cells can be applied du ectly in the assays of the invention, other eukaryotic cells or prokaryotic cells may prove useful in other ways (e g , foi in vitro piotein production, or foi construction of other expression vectois appropriate for use in neuronal cells) The fonn in which polynucleotides that encode the sodium channel (or constituent components thereof) and/or amyloid β, and the sodium channel itself (or constituent components thereof) and/or amyloid β, aie introduced into cells can be further described as a "construct" A "construct" is any form of molecule in which a polypeptide sequence (e g , sodium channel or constituent components thereof and/or amyloid β) or its encoding polynucleotide sequence is joined to or forms part of a larger molecule The connection between the polynucleotide and/or polypeptide sequence and its site of attachment in the molecule preferably can be by a noncovalent bond (e g , as in antibody/antigen binding), or by a covalent bond Along these lines, a "construct" includes, but is not limited to a vector (e g , having genetic incorporation of a polypeptide coding sequence into a polynucleotide vector), or a conjugate-type vector (e g , wherein a coding sequence, polypeptide sequence, or other moiety is noncovalently associated with a vector), or other appropriate moiety that can be employed for effecting cell entry As used herein a "vector" is a vehicle capable of effecting entry into a cell, e g , particularly for gene transfei, and has the general meaning of that term as understood by those of skill in the art The invention accordingly contemplates expiession constructs comprising polynucleotides that encode the sodium channel (or constituent components thereof) and/or amyloid β operatively linked to an endogenous or exogenous expression control DNA sequence and a transcription terminator Expression control DNA sequences include piomoters, enhancers, and operatois, and are generally selected based on the expression systems in which the expression construct is to be used. Preferred promoter and enhancer sequences are generally selected for the ability to lnci ease gene expression, while operator sequences ai e generally selected foi the ability to regulate gene expression. Preferred constructs of the invention also include sequences necessary for replication in a host cell Expi ession constructs ai e preferably used for production of an encoded sodium channel (or constituent components thereof) and/or amyloid β. Thus, polynucleotides of the invention may be introduced into the host cell desirably as part of a circular plasmid, or as hneai DNA comprising an isolated protein coding region, contained on a viral vector, or by any other appropriate means. Methods for introducing DNA in to a host cell include ti ansfoπnation, transfection, electroporation, nuclear injection, or fusion with carπci s such as hposomes, micelles, ghost cells, and protoplasts, to name but a few. Any appropriate expression vector (e.g , as described in Pouwels et al., Cloning Vectors. A Laboratory Manual (Elsevior, NY.. 1985)) and corresponding suitable host can be employed for production of polypeptides/proteins for practice of the invention. Expression hosts include, but are not limited to, bacteria, yeast, fungal, mammalian, plant, and insect host cell systems including baculovirus systems (e g , as described by Luckow et al., Bio/Technology , 6, 47 ( 1988)) to name but a few, and established cell lines such as the COS-7, C127, 3T3, CHO, HeLa, BHK cell line, and the like. For introduction into cells, use of a construct that is capable of entering that particular type of cell is preferred (e g., a herpes virus vector for entry into a neuronal cell). Other viral vectors include, but are not limited to, expression vectors derived from retroviruses, adenovirus, or vaccinia virus. Alternately, the proteins can be delivered to target cells in hposomes. Similarly, in the different hosts, the nature of the non-coding DNA upstream of the coding region of the sodium channel (or constituent components thereof) and/oi amyloid β polynucleotide sequences should be composed of transcription/translation signals appropriate for the host. Host cells of the inv ention ai e useful methods foi lai ge-scale pi oduction oi use of sodium channel (oi constituent components thei eof) and/oi amyloid β polypeptides For example, recombinant sodium channel (or constituent components thereof) and/oi amyloid β pi oducts can be produced and isolated fi om host cells foi use in /// \ ιtι o assays such as di ug sci ec ng assays In such methods, the host cells are gi ovv n in a suitable culture medium and the desu ed polypeptide product is isolated from the cells or fiom the medium in which the cells are grown The polypeptide pi oduct (e g , sodium channel or Aβ) optionally can be isolated by purification methods known the art, such as conv entional chi omatographic methods including lmmunoaffinity chromatography, receptoi affinity chromatography, hydrophobic intei action chromatogi aphy, lectin affinity chiomatography, size exclusion filtration, cation or anion exchange chromatography, high performance liquid chromatography (HPLC), reverse-phase HPLC, and the like Still other methods of purification include those in which the desired protein is expressed and purified as a fusion protein in which the sodium channel (or constituent components thereof) and/or amyloid β is hgated to a heterologous amino acid sequence Suitable heterologous sequences can include a specific tag, label, or chelat g moiety that is recognized by a specific binding partner or agent For example, for screening of peptide libraries for modulators of the interaction between the sodium channel and amyloid β, it is possible to produce either component fused to a selected heterologous protein selected to be specifically identifiable, e g , using a probe antibody A fusion protein also may be engineered to contain a cleavage site (e g , a factor XA or enteiokinase sensitive sequence) located between the sodium channel (or constituent components thereof) and/or amyloid β sequence and the heterologous protein sequence, to permit the sodium channel (or constituent components thei eof) and/or amyloid β to be cleaved from the heterologous protein and subsequently punfied Cleavage of the fusion component may produce a form of the desired protein having additional ammo acid residues resulting from the cleavage process In a preferred embodiment of the present invention, a sodium channel (oi constituent components thereof) and/or amyloid β, or a host cell that expiesses coding ?? sequences for a sodium channel (or constituent components thereof) and/or amyloid β may be used to screen for peptides, oi other molecules, such as organic oi lnoi ganic molecules, that act as modulators of the intei action between the sodium channel (oi constituent components thereof) and amyloid β For example, screening of peptide libraries or organic libraries made by combinatorial chemistry with the aforementioned polypeptides or cell lines may be useful for identi fication of therapeutic molecules that function by modulating the interaction between a sodium channel and amyloid β Synthetic compounds, natui al products, and other sources of potentially biologically active materials can be screened in a number of ways deemed routine by those of skill in the art Contacting The "contacting" described above between amyloid β or its aggregates with a sodium channel, and optionally, with a modulator according to the invention can be done by any means known to those skilled in the art, and described herein, by which the apparent touching or mutual tangency of amyloid β or its aggregates with a sodium channel, and optionally, with a modulator according to the invention, can be effected For instance, contacting can be done by mixing these components in a small volume of the same solution. Alternately, the components need not necessarily be brought into contact in a small volume, as, for instance, in cases where the one or more of the components is present in, and/or is administered to, a host, and travels within the host by the bloodstream, cerebrospinal fluid, or other bodily fluid Also, the components need not always be added all at the same time; it suffices that all the components necessary for the assay just are present together at some time during the assay (or treatment, as described further below) The method of the present invention can be employed for means of contact either //; vitro or in vivo, for instance for research, diagnosis, or therapy. According to the invention "contacting" comprises any means of contact, the method is not dependent on any particular means and is not to be so construed Such means are well known to those skilled in the art. and also are exemplified herein Howevei , for con ponents piovided in the foim of a constiuct (e g , polynucleotide forms of so dium channel piote s and amvloid β), contacting can be effected foi instance, either in vitr o (e σ , m tissue culture studies) or m \ ιvo by electi opoi ation, transformation, transduction, conjugation oi tπpaiental mating, (co)tι ansfectιon, (co-)ιnfectιon, membrane fusion with cationic hpids, high velocity bombaidment with DNA-coated micropiojectiles, incubation with calcium phosphate- DNA pi ecipitate, direct microinjection into single cells, and the like Snuilai ly, the consti ucts can be introduced by means of cationic hpids, e g , hposomes Such hposomes are commercially available (e « • , Lipofectin , Lipofectamine™, and the like, supplied by Life Technologies, Gibco BRL, Gaitheisburg, Md , and othei commcicial vendors) Othei methods also ai e available and ai e known to those skilled in the art Diagnostic and Therapeutic Methods The compounds uncovered according to the invention that modulate the interaction of amyloid β or its aggregates with the sodium channel potentially can be employed in the diagnosis, prevention, treatment, oi reversal of disorders that are due to deleterious effects of amyloid β within the centi al nervous system, i e , mediated by the effect of Aβ on the sodium channel "Prevention" as used herein lefers to preventing a disorder from occurring in a mammal (especially a human) that may be pi edisposed to the disorder, but has not yet been diagnosed as having it "Treating" means inhibiting the disordei , / c , arresting its development, relieving the disorder, / e , causing its regression, or ameliorating the disorder, i e , reducing the severity of symptoms associated with the disorder "Disorder" is intended to encompass medical disordei s, diseases, conditions, syndromes, and the like, without limitation In particular, the method of the invention may be employed to treat mammals (i e , especially humans) therapeutically or piophylactically, foi instance, mammals that are or may be subject to disorders that include but are not limited to Alzheimer's disease, adult Down's syndiome (/ c , over the age of 40 years), hereditary cerebral hemon hage with amyloidosis, non-inhented congophihc angiopathy with cei ebi al hemon hage and senile dementia These ai e all disoi dei s that ai e characterized by the pi esence of Aβ, for instance, deposited in aggi egales/plaques It is demonstrated fot the fii st time heiein that Aβ deleteπously impacts sodium channel functioning Such an impact on sodium channel functioning could pi oduce the neui al and cognitiv e defects and othei symptoms that aie observed with these disoi ders Thus, it is reasonable to expect that modulators that uupaii the ability of Aβ to deleteπously impact sodium channel functioning can be employed to 1 educe, i f not entu ely prevent the ncut al and cognitive defects and other symptoms that ai e obsei ved with these disoi dei s Accoi dingly the present invention pi ovides a method for diagnosing Alzheimei 's disease in a mammal (e g , a human) suspected of having Alzheimer's disease, the method comprising the step of measunng the activity of a sodium channel in a neuronal cell of the mammal, wherein reduced activity of the sodium channel is coirelatcd with the existence of an Alzheimer's disease state Desirably the activity is determined by a method selected from the gioup consisting of examining resting membrane potential, examining action potential, and measunng the fast inward sodium current It is expected that the methods of the invention w ill prove useful in such diagnosis or prediction since it is anticipated that an impact on the sodium ion channel can occur prior to manifestation of all the symptoms of the disorder (e g , prior to all the symptoms of Alzheimer's disease) If the functionality of the sodium channel appears to be reduced, optionally furthei tests can be carried out to confinn that the reduced functioning is due to an impact of amyloid β oi its aggregates on the sodium channel For instance, the method further optionally can comprise a step of measuring the amount of amyloid β or its aggregates in the cell (e g , wherein the cell is a neuionai cell that has been isolated from the mammal), on the surface of the cell, or in exti acellular fluid fiom the mammal that contacts the cell, wherein the presence of amyloid β or its aggregates in the cell or fluid (e s: , along with the presence of reduced sodium channel activity) is correlated with the existence of an Alzheimer's disease state Pi eferably according to the invention, the fluid tested is cei ebrospmal fluid The invention furthei pi ovides a method of sci eening a mammal for susceptibi lity to Alzheimer's disease, compnsing the steps of ( a) isolating a cell fiom the mammal, the cell compnsing a sodium channel, and (b) measuring activity of the sodium channel in the absence and in the presence of amyloid β piotein or its aggiegates, w herein l educed activity of the sodium channel in the presence of amyloid β or its aggi egates as compared to in the absence is correlated with a susceptibility to dev eloping Alzheimer's disease The pi esent invention also provides a method foi prev enting, ti eating, or rev ersing Alzheimer's disease in a mammal, the method prelei ably comprising contacting a sodium channel of the mammal with a compound that protects the sodium channel from a reduction in sodium channel activity due to amyloid β or its aggregates Treatment with compounds identified according to the screening methods of the invention is explicitly contemplated Also, like Alzheimer's disease, prion disease is a neurodegenerative disease in which prion protein causes neurotoxicity Those knowledgeable in the art would understand that prion protein, like amyloid β or its aggregates, can affect neural sodium channel function as part of the pathology of prion disease In like manner, the sodium channel impact of prion proteins can be useful in finding new therapies for prion disease For instance, certain of the modulators identified as useful for Alzheimei 's disease may be expected to have beneficial effects in prion disease by virtue of restoring or alleviating a block on sodium channel functioning Analysis of sodium channel proteins and sodium channel regulatory pioteins will provide the basis foi diagnostic tests of Alzheimer's disease and clinical markers for following progression and the efficacy of prion therapy The invention accordingly further provides method for diagnosing prion disease in a mammal suspected of having prion disease, the method comprising the step of measunng the activity of a sodium channel in a cell of the mammal, wherein reduced activity of the sodium channel is correlated with the existence of a prion disease state Similarly, the piesent invention pro ides a method for preventing, treating, oi reversing prion disease in a mammal, the method desnably compnsing contacting a sodium channel of the mammal w ith a compound that piotects the sodium channel from a 1 eduction in sodium channel activity due to amyloid β or its aggiegates In a preferred embodiment, the present invention piovides compounds that aie capable of opening the sodium channel, / e , "sodium channel openers" Accoidingly, the present invention piovides a method for preventing, treating, oi leversing Alzheimer's disease in a mammal, wherein the method desirably comprises contacting a sodium channel of the mammal with a compound that opens the sodium channel Also, the invention piovides a method for preventing, treating, or leversing prion disease in a mammal, wherein the method preferably comprises contacting a sodium channel of the mammal with a compound that opens the sodium channel In terms of therapeutic uses, various assays will be employed to evaluate the efficacy of a particular therapeutic treatment regimen, and to determine a nonnal or standard profile. Such assays include the specific sodium ion channel studies set out in the Examples that follow Such assays may be tailored to suit a particular application, and may be used in animal studies, in clinical trials, or in monitoring the treatment of an individual patient To provide a basis for the diagnosis and treatment of disease, a normal or standard profile must be established This is accomplished by combining a biological sample taken from a normal subject. Standard values obtained from noπnal samples may be compared with values obtained from samples from subjects potentially affected by a disorder or disease related to the deleterious effects of Aβ or its aggregates. Deviation between standard and subject values establishes the presence of the disease state. If disease is established, a therapeutic agent is administered, if so desired, and treatment profile or values may be generated The assay may be repeated on a regular basis to evaluate whether the values progress toward oi leturn to the normal or standard pattern Successive tieatment profiles may be used to show the efficacy of treatment over a period of several days or several months Othei Uses Apart from the diagnostic and thei apeutic uses descnbed abov e thei c ai e manv additional uses and dist ov enes that stem fi om the pi esent inv ention Foi instance, the discovery descnbed hei ein of sodium channels as a novel mechanism of negativ e impact foi Aβ indicates that sodium channels are one of pi ev iouslv unknown elements linked to Alzheimef s susceptibility Thus sodium channel genes or genes for iegulatoi s of the sodium channel impacted by Aβ activity may be associated with susceptibility foi Alzheimer s disease Analysis of genetic v anants of both the stiuctural genes sodium channel and sodium channel l egulatoi y piotems can be used for linkage of speci fic mutants or v anants of these genes with susceptibility to Alzheimer's disease T ests foi these mutant or v ariant genes will be diagnostic foi Alzheimer's disease and susceptibility to this disease Thus, the discov ery as described herein of the link between sodium channels and the deleterious actions of Aβ and its aggregates will provide the basis for both diagnostic tests for Alzheimer's disease and clinical markers for following the piogression and efficacy of treatments for Alzheimer's disease Additionally, the present invention also provides for the use of kinetic measurements of Aβ peptide effects (as described in Example 5) in conjunction with measurements of the inward sodium current Such a kinetic approach similarly can be employed to discover drugs used to treat Alzheimer's disease Phannaceutical Compositions The present invention thus further pi ovides pharmaceutical compositions Pharmaceutical compositions optionally comprise as an active agent modulators (as previously described), or polynucleotides that encode a sodium channel (or a peptide thereof) and/or amyloid β, along with a biocompatible pharmaceutical carrier, adjuv ant, or vehicle Preferably the activ e agent is active in treating a medical condition that is due to the negative effects of amyloid β or its aggregates The composition can include the agent as the only active moiety or in combination with other active agents, optionally mixed with excιpιent(s) or other phamiaceutically acceptable earners Phamiaceutically acceptable excipients to be added to pharmaceutical compositions ai e well-known to those who ai e skilled the art. and arc i cadily av ailable The choice of excipient will be determined in part by the pai ticulai method used to administer the composition according to the invention Accoi dingly, thei e is a wide va ety of suitable formulations for use the context of the pi esent invention The following methods and excipients ai e merely exemplai y and are in no way limiting Techniques for formulation and administration of phaimaceutical compositions may be found in Remington 's Phai maceutical S ienc es, 1 8th Ed , Mack Publishing Co, Easton PA, 1990, and ai e w ell known to those skilled in the ait The pharmaceutical compositions of the present inv ention may be manufactured using any conventional method, e g , mixing, dissolving, gianulatmg, dragee-making, levigating, emulsifying, encapsulating, entiapping, melt-spinning, spray-di ying, oi lyophihzing piocesses However, the optimal pharmaceutical formulation wi ll be determined by one of skill in the art depending on the route of administration and the desu ed dosage. Such formulations may influence the physical state, stability, rale of in vivo release, and rate oϊ in vivo clearance of the administered agent. Depending on the condition being treated, these pharmaceutical compositions may be formulated and administered systemically or locally. The pharmaceutical compositions may be administered to the subject by any conventional method, including parenteral and enteral techniques Parenteral administration modalities include those in which the composition is administered by a route other than through the gastrointestinal tract, foi example, intravenous, mtraartenal, intraperitoneal, intramedullary, intramuscular, lntiaaiticular, intrathecal, and intraventricular injections Enteral administration modalities include, for example, oial (including buccal and subhngual) and rectal administration. Transepithehal administration modalities include, for example, transmucosal administration and transdermal administration Transmucosal administration includes, foi example, enteral administration as well as nasal, inhalation, and deep lung administration; vaginal administration, and rectal administi ation Transdennal administration includes passive or active ti ansdeimal oi tianscutaneous modalities, including, for example, patches and iontophoresis devices, as well as topical application of pastes, salves, or ointments Suigical techniques include implantation of depot (leservon ) compositions, osmotic pumps, and the like The pharmaceutical compositions are formulated to contain suitable phamiaceutically acceptable carriers, and may optionally comprise excipients and auxihanes that facilitate processing of the active compounds into preparations that can be used phamiaceutically The administration modality will geneially determine the natui e of the caniei For example, formulations foi pai enteral administration may compnse aqueous solutions of the active compounds in water-soluble fonn Carriers suitable foi paienteral administration can be selected from among saline, buffered saline, dextiose, water, and other physiologically compatible solutions Pieferred canieis for paienteral administration aie physiologically compatible buffers such as Hank's solution, Ringer's solutions, oi physiologically buffered saline For tissue or cellular administration, penetrants appropriate to the particular ban ier to be penneated are used in the formulation Such penetrants are generally known in the art For prepaiations comprising proteins, the formulation may include stabilizing materials, such as polyols (e g , sucrose) and/or surfactants (e g , nonio c surfactants), and the like Alternatively, formulations for parenteral use may comprise suspensions of the active compounds prepared as appropriate oily injection suspensions Suitable lipophihc solvents or vehicles include fatty oils, such as sesame oil, and synthetic fatty acid esteis, such as ethyl oleate or tπglyceπdes, or hposomes Aqueous injection suspensions may contain substances that increase the viscosity of the suspension, such as sodium carboxymethyl cellulose, sorbitol, or dextran Optionally, the suspension may also contain suitable stabilizers or agents that increase the solubility of the compounds to allow for the preparation of highly concentrated solutions Emulsions, e g , oil-in-water and water-in- oil dispersions, can also be used, optionally stabilized by an emulsifying agent or dispersant (surface-active materials, suifactants) Liposomes containing the active agent may also be employed for parenteial administration Alternatively the phamiaceutical compositions comprising the agent in dosages suitable for oi al administi ation can be formulated using phai maceutical ly acceptable earners well known in the art The pi epai ations foi mutated foi oi al administi ation may be in the fonn of tablets, pills, capsules, cachets, di agees, lozenges, liquids, gels, syi ups, slurries, suspensions, or powders To illusti ate, phamiaceutical preparations for oi al use can be obtained by combining the active compounds with a solid excipient, optionally grinding the l esulting mixtui c, and processing the mixtuie of granules, after adding suitable auxiliaries i f desired, to obtain tablets oi dragee cores Note that oral formulations may employ liquid carriers similai in type to those described for parentei al use, e g , buffered aqueous solutions, suspensions, and the like Pieferred oral foπnulations include tablets, dragees, and gelatin capsules These preparations may contain one or excipients, which include, without limitation a) diluents such as sugars, including lactose, dextrose, suciose, mannitol, or soibitol, b) binders such as magnesium aluminum silicate, starch fiom corn, wheat, rice, potato, etc , c) cellulose materials such as methyl cellulose, hydroxypropylmethyl cellulose, and sodium carboxymethyl cellulose, polyvinyl pyrrohdone, gums such as gum arable and gum tragacanth, and proteins such as gelatin and collagen, d) disintegrating or solubihzing agents such as cross-linked polyvinyl pyrrohdone, starches, agar, alginic acid or a salt thereof such as sodium alginate, or effervescent compositions, e) lubricants such as silica, talc, steaπc acid or its magnesium oi calcium salt, and polyethylene glycol, f) flavorants, and sweeteners, g) colorants or pigments, e g , to identify the product oi to characterize the quantity (dosage) of active compound, and h) other ingredients such as pieservatives, stabihzei s, swelling agents, emulsifying agents, solution promoters, salts for regulating osmotic pi essure, and buffei s Gelatin capsules include push-fit capsules made of gelatin, as well as soft, sealed capsules made of gelatin and a coating such as glycerol or sorbitol. Push-fit capsules can contain the active ingredient(s) mixed with fillers, binders, lubricants, and/or stabilizers, etc. In soft capsules, the active compounds may be dissolved or suspended in suitable fluids, such as fatty oils, liquid paraffin, or liquid polyethylene glycol with or without stabilizers. Dragee cores can be provided with suitable coatings such as concentrated sugar solutions, which may also contain gum arabic, talc, polyvinyl pyrrohdone, carbopol gel, polyethylene glycol, and/or titanium dioxide, lacquer solutions, and suitable organic solvents or solvent mixtures. The phamiaceutical composition may be provided as a salt of the active agent, which can be formed with many acids, including but not limited to hydrochloric, sulfuric, acetic, lactic, tartaric, malic, succinic, etc. Salts tend to be more soluble in aqueous or other protonic solvents that are the corresponding free base forms. As noted above, the characteristics of the agent itself and the formulation of the agent can influence the physical state, stability, rate of in vivo release, and rate of in vivo clearance of the administered agent. Such phannacokinetic and pharmacodynamic information can be collected through pre-clinical in vitro and in vivo studies, later confirmed in humans during the course of clinical trials. Thus, for any compound used in the method of the invention, a therapeutically effective dose in mammals, particularly humans, can be estimated initially from biochemical and/or cell-based assays. Then, dosage can be formulated in animal models to achieve a desirable circulating concentration range (e.g., of the modulator). As human studies are conducted, further information will emerge regarding the appropriate dosage levels and duration of treatment for various diseases and conditions. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for detennining the LD 50 (the dose lethal to 50% of the population) and the ED o (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the "therapeutic index, " which is typically expressed as the ratio LDso/ED^o- Compounds that exhibit large therapeutic indices are preferred. The data obtained from such cell culture assays and additional animal studies can be used formulating a range of dosage foi human use The dosage of such compounds lies prefci ably within a range of en dilating concenti ations that include the ED-,o with little or no toxicity For the method of the invention, any effective administration regimen regulating the timing and sequence of doses may be used Doses of the agent pi eferably include phamiaceutical dosage units compnsing an effective amount of the agent As used herein, "effective amount " refci s to an amount sufficient to provide or modulate interaction of amyloid β or its aggi egates with the sodium channel through administration of one or more of the pharmaceutical dosage units Exemplary dosage levels for a human subject are of the order of from about 0 001 milligram of active agent per kilogram body weight (mg/kg) to about 100 mg/kg Typically, dosage units of the activ e agent comprise from about 0.01 mg to about 10,000 mg, preferably from about 0 1 mg to about 1 ,000 mg, depending upon the indication, route of administration, etc Depending on the route of administration, a suitable dose may be calculated according to body weight, body surface area, or organ size. The final dosage regimen will be deteπnined by the attending physician in view of good medical practice, considering various factors that modify the action of drugs, e g , the agent's specific activity, the severity of the disease state, the responsiveness of the patient, the age, condition, body weight, sex, and diet of the patient, the severity of any infection, and the like Additional factors that may be taken into account include time and frequency of administration, drug combιnatιon(s), reaction sensitivities, and tolerance/response to therapy Further refinement of the dosage appropriate for treatment involving any of the formulations mentioned herein is done routinely by the skilled practitioner without undue experimentation, especially in light of the dosage information and assays disclosed, as well as the phannacokinetic data observed in yeast clinical trials Appropriate dosages may be ascertained through use of established assays for determining concentration of the agent in a body fluid or other sample together with dose response data The frequency of dosing will depend on the pharmacokinetic parameters of the agent and the route of administration Dosage and administration are adjusted to pi ov ide sufficient levels of the active moiety or to maintain the desired effect Accordingly, the pharmaceutical compositions can be administered in a single dose, multiple discrete doses, continuous infusion, sustained l elease depots, oi combinations thereof, as required to maintain desued minimum lev el of the agent Short-acting phaimaceutical compositions (i e , short half-li fe) can be administered once a day oi moie than once a day (e g , two, three, or foui times a day) Long acting pharmaceutical compositions might be administered every 3 to 4 days, every week, or once every two weeks Pumps, such as subcutaneous, intraperitoneal, or subduial pumps, may be preferred for continuous infusion. Compositions comprising an active agent of the invention formulated in a phaimaceutical acceptable carrier may be prepared, placed in an appropriate containei , and labeled for treatment of an indicated condition Conditions indicated on the label may include, but are not limited to, tieatmcnt and diagnosis of Alzheimer's disease and prion disease. Kits are also contemplated, wherein the kit comprises a dosage form of a phamiaceutical composition and a package insert containing instructions for use of the composition in treatment of a medical condition. Examples The following examples further illustrate the present invention but should not be construed as in any way limiting its scope. The examples presuppose an understanding of conventional methods well- known to those persons having ordinary skill in the art to which the examples pertain, e g , the techniques for isolation and electrophysiological assessment of cells (e g , neuronal cells) Such methods are described in detail in numerous publications including, for example, in Hille, In, Io ic Channels of Excitable Membranes Sinauer Associates, Inc. (1992) The contents of this publication and other publications cited in the Examples are incorporated by reference, in their entirety For all studies as described herein, single neurons freshly dissociated from adult tats (Chad et al, In, Cellular Neurobiologγ, Ed. J. Chad and H Wheal, Oxford University Press (1991)) were examined using the suction pipette method (Lee et al., J Neitrosc Methods, 2; 51-78 (1980)) under current- or voltage-clamp, with use of an Axopatch 200 Amplifier (Axon Instruments, Foster City, CA). Amyloid β 1 -40 was obtained from Polypeptide Laboratories, Torrance, CA, or from Bachem Biochcmica, Heidelberg, Germany. Shaken aggregation assays (i.e., as in Examples 1-4) were performed as described previously (e.g. , Findeis et al., Biocheinistiy, 38, 6791 -6800 ( 1999)). This aggregation perfoπned prior to use of the aggregated amyloid for contacting cells was done in the same media as the cells were contained, i.e. , Hank's Balanced Salt Solution. Aggregation of amyloid for kinetic studies (i.e., as in Example 5), was done in a buffer composed of 10 mM phosphate, 100 mM NaCl, pFI 7.4. In each case, aggregation was carried out in 96 well plates containing 25-50 μM amyloid β 1 -40 in a final volume of 250 μl. The plates were rotary shaken using a titer plate shaker (Lab-Line Model 4623, Lab-Line Inst., Melrose Park, IL) at a rate of from about 700 to 800 rpm (monitored by a tachometer) to induce aggregation. At given times, the turbidities of the reaction mixture were read by measuring light scattering at 405 n in a Molecular Devices (Menlo Park, CA) Vmax Microplate Reader. For all the Examples, the aggregating material was removed at timed intervals and added to isolated neurons to examine its effect. Prior to aggregation, to prepare amyloid β in monomeric form, amyloid β 1 -40 (e.g., to be used as an HPLC standard) was treated with hexafluoroisopropyl alcohol (HFIPA), which had been dried over Molecular Sieve, Type 4A, at 4°C and centrifuged at 15,000 X g for 10 minutes to remove molecular sieve dust. For aggregation assays, the peptide was dissolved in the HFIPA at 8 mg/ml and held in the solvent for 18 to 24 hours to disaggregate any preformed particles. Following this monomerization step, 20 μl aliquots of this solution were flash frozen in liquid nitrogen and stored at -195°C until use. Without thawing, the HFIPA in the peptide was removed by lyophilization under dry ice. Complete removal of the HFIPA without thawing was essential to achieve non-aggregated starting material, e.g., if the frozen pellets melt prior complete lyophilization. there is a high probability that multimers will refonn. The lyophilized Aβ 1 -40 was dissolved in anhydrous DMSO (usually 20 μl) and sonicated in a bath sonicator for 15 minutes. Since the above procedure is lengthy and cumbersome, for some experiments, the acid treatment procedure wherein the Aβ -40 is dissolved in 0.1 % acetic acid prior to aggregation (Findeis et. al., supra) was employed, and w as found to be acceptable for peptide randomization. Example 1 In this experiment, the firing patterns of isolated adult rat cortical and hippocampal neurons were examined using an Axopatch 200 Amplifier in the presence or absence of amyloid β 1 -40 peptide. In current-clamp, the resting membrane potential and action potentials of single neurons were continuously monitored for at least 10-20 minutes until the neuronal activity became stable. Then, 10-50 μM amyloid β 1 -40 preaggregated for different times was added to the neuron slowly without causing any flow artifact, in 5-10 minutes, resting potentials started to move to either a depolarized or hyperpolarized direction, depending on the neuronal type examined. However, the common effect was the slow disappearance of spontaneous or evoked action potentials. After about 20-30 minutes of peptide exposure, the action potentials in most of the neurons examined disappeared altogether. These amyloid β treated neurons became silent, non-functional, and in a vegetative state after prolonged exposure (i.e., about 30 to 60 minutes) to amyloid β . These results are depicted in Figures 1A-C for cortical neurons, and Figures 2A-C for hippocampal neurons. These results confirm an abrogation of action potentials in cortical and hippocampal neurons with addition to the neuron of 1 1.5 «M amyloid β 1-40. These results thus confirm that amyloid β 1 -40 peptide alters the firing patterns of adult rat cortical and hippocampal neurons. Example 2 In this experiment, the effect of amyloid β 1-40 on the fast inward sodium current (I Na ) of isolated rat hippocampal neurons was studied using an Axopatch 200 Amplifier. These studies were done by voltage-clamping the neurons at a holding potential of -50 to -80 mV where the sodium channels were fully activated. Again, a stable control was obtained. Then, 10-50 μM amyloid β 1 -40 aggregated for various times at room temperature (23°C) in 10 mM phosphate, 1 0 mM NaCI at pFl 7.4 was applied to the neurons. In about 5-30 minutes, approximately the same time frame for the action potentials to disappear, the fast inward sodium current was blocked by amyloid β 1 -40 by as much as 90%, as can be seen by comparing results in Figures 3A (control) with those in Figure 3B (90 minute aggregated amyloid β) and Figure 3C ( 120 minute aggregated amyloid β). The progressive change of peak amplitude of inward sodium current for the same experiments with hippocampal neurons is graphed in Figure 4 for 90 minute aggregated amyloid β (solid circles), and 120 minute aggregated amyloid β (solid squares). Also, at this time, switching back to current-clamp, the neuron failed to fire action potentials (as can be seen in Figures 1 B and Figures 2B), thus confirming that the mechanism of action potential elimination by amyloid β 1 -40 is through blockade of the fast inward sodium channels. This further can be seen for rat hippocampal neurons, by comparing readings obtained for resting potential in Figure 5A (control) and Figure 5D (wash condition) with those obtained in Figure 5B (90 minute aggregated amyloid β) and Figure 5C (120 minute aggregated amyloid β). For the same experiment, switching back to current-clamp, the neuron failed to fire action potentials, as can be seen in Figure 6 for 90 minute aggregated amyloid β (solid circles), and 120 minute aggregated amyloid β (open squares). Additionally, it was shown that this fast inward sodium current is sensitive to tetrodotoxin (TTX). This can be seen by comparing sodium current traces obtained from hippocampal neurons in Figures 7A (control, having no TTX exposure) and Figure 7C (wash) with those obtained in Figure 7B ( 1 0 " ' M TTX). For the same experiment, changes of peak amplitude of inward sodium current over a broad potential range from -80 mV to +10 mV are shown in Figure 8 for the control (open circles) and wash condition (closed squares) as compared to the neurons exposed to TTX (closed circles). These results confirm that amyloid β 1 -40 inhibits the fast inward sodium cm lent ( I N I ) This is a novel and unexpected finding, since pnor results focused on the impact of amyloid β on calcium and/oi potassium channels Furthei moi e, the lesults con fiim that the amyloid β 1 -40-targeted a fast ln aid sodium channel and is sensitiv e to tetiodotoxin However, other types of sodium channels may also be involv ed, and/or may be sensitive to the negative effects of amyloid β Example 3 In this experiment, the effect of amyloid β 1 -40 on the calcium ion channel was studied using the methods described in Experiment 2 for the sodium channel The amyloid β 1 -40 peptide also was found to depress neuronal inward calcium currents (see, Figures 9A-B and Figure 10) However, the calcium channel may be more resistant to the inhibitory action of amyloid β 1 -40 These results confirm that amyloid β 1 -40 affects neuronal calcium currents Example 4 In this experiment, the effect of amyloid β 1 -40 on the potassium ion channel was studied using the methods described in Experiment 2 for the sodium channel In voltage-clamp, within the first 2-5 minutes, in some cells the peptide induced an outward holding current measuring about 10-50 pA, but this small current was enough to hyperpolaπze the resting membrane potential from -50 mV to -90 mV In other cells, the peptide instead caused a gradual depolarization to about 40m V due to a slight inhibition of the outward holding current In all cells, amyloid β 1 -40 blocked the delayed outward potassium current by about 30-40% at all step potentials The corresponding action potential measurement show ed that this effect resulted in bioadening of normal action potential duration (shown in Figure I B) These lesults are presented in Figures 11A-B and Figure 12 These results thus confirm that amyloid β 1 -40 affects major neuronal potassium currents Example 5 In this experiment, the relationship between amyloid β 1 -40 aggregation and its ability to impact a variety of parameters as descnbed herein, including sodium channel activity, was studied By way of background, the kinetics of amyloid I) pcptide's spontaneous aggregation are characterized by a long lag phase in which at least a small quantity of the aggi egate can be detected by thioflavine T fluorescence The lag phase is follow ed by a log phase which is rapid and results in the deposition of peptide until the solution is totally depleted of amyloid β monomei s The i apid accelei ation (propagation) of fibril growth occurs from a prefomied nucleus The most important step in the whole piocess is nucleation from which fibnl formation proceeds l apidly Inhibition of nucleation halts the entne process and an assay capable of measunng this early event would be highly desirable The sharp, exponential rise dunng the propagation phase is indicative of the presence of higher order aggi egation and growth of the aggregate The kinetics of spontaneous aggregation were studied f rom experiments done herein, as well as making use of hteratuie reported data (e g , Lansbury et al., Arzn For Drug Research, 45, 432-434 ( 1995), Pillot et al , Eui J Biochem , 243, 650-659 ( 1997)). For these studies, in order to leam more about the form of the amyloid β peptide having the greatest ability to deleteπously impact various cell parameters, kinetic experiments were first performed to establish the time course of the formation of the β-tum form of Aβ 1 -40 (activated monomer), and of the tetramei T hen, ahquots of the peptide were taken at select time points from the actively aggregating solution of Aβ 1 -40, and were added to isolated rat hippocampal neurons The impact of various aggregated forms of Aβ were studied using a variety of tests including: ( 1 ) resting membrane potentials; (2) action potentials, (3) fast inward sodium channels (TTX-sensitive); (4) calcium channels; and (5) outward potassium channels The data obtained from the kinetic studies was assessed using several multiple order kinetic models for spontaneous aggregation It was found that the simplest scheme (as set out in Equations 1 -3 below) consistent with these data is one in which the nonnucleating, random c )il structure, monomeric peptide (inactive A) is converted to an active, nucleatable forri (B) according to the equation: A → B k] (Equation 1 ) B then oligomerizes to a tetrameric inteπnediate (C): 4B -→ C k n (Equation 2) that binds species A rapidly to form the insoluble fibrillar structure (P): Fast C + A - C + P k p (Equation 3) The system of differential equations describing this model is: dA = - k,A - k p C * A dt (Equation 4) dB = k,A - k n B 4 dt (Equation 5) dC = k,,B 4 - k p C * A dt (Equation 6) dP k p C * A dt (Equation 7) Because the solution to the differential equations 4-7 is nonintegrable, the data had to be fit using a proper nonlinear least squares fitting algorithm chained to a fifth-order Runge-Kutta numerical integration algorithm. The nonlinear least squares fitting program used in this case was one written by Dr. Ferenc Kezdy (Phannacia & Upjohn, Kalmazoo, Michigan). The data are consistent with a model of a slow change of the peptide in solution from an inactive, non-nucleating fomi to an active form that can initiate amyloid β aggregation. The analysis showed that a tetramer form of the peptide is responsible for nucleation. After nucleation, the determining factor in the steep portion of the kinetics is piopagation and the compound that forms the tcti amei t eaches a steady state at this point f he kinetics of all spontaneous aggregation expenments pei formed hei ein, and by othei s (Lansbui y ct al , Aizn I oi ϋi ιι ξ Res , 432-434 ( 1991 ), Pillot ct al , Tin 1 Biυc hem , 241, 650-659 ( 1997)) w ei e consistent only with tins model The l esults may suggest that the deleterious impact (e g , cell killing) of the amyloid peptide is due to the amyloid tctramer fonning a poi e in biological membranes, similar to the toxic teti amenc fomi of mehttin Following the kinetic studies, ahquots of amyloid β wei e taken at select time points fiom the actively aggregating solution of Aβ 1 -40, and were added to it hippocampal cortical neurons The inwaid sodium cui rent was then measured continuously The percentage decrease in the inw ard sodium current was determined foi each test point as the rate at which the sodium current was generated Additionally, the various aggregated forms of Aβ were assessed for any impact on resting membrane potential, action potential, calcium channel, and outwaid potassium channel Monomers of amyloid β 1 -40 did not show significant impact on the parameters assessed But as the monomeis aggi egate, to fonn dimers, tetramers and then polymers, the ability of amyloid β 1 -40 to negatively impact channel activity then appeared, and increased exponentially, approximately following the time course of peptide aggregation The fraction having the greatest negative impact on channel activity appeared just before the monomers' complete disappearance and saturation of peptide aggregation After reaching the satui ation, the peak impact decreased, but was still above the 50% inhibition level of the fast inward sodium channels (shown in Figure 13, which is the mean values of foui experiments with 29 cells each) The negative impact of amyloid β was seen on five levels of neuronal activities (1 ) resting membrane potentials, (2) action potentials, (3) fast inward sodium channels (TTX-sensitive), (4) calcium channels, and (5) outward potassium channels However, the ma ion channel target foi amyloid β 1 -40 is the TTX- sensitiv e fast inward sodium channel This confirms that the deleterious eftects of an amyloid β aggiegate are upon the fast inwaid sodium channel, which disables the neurons in terms of generating electrical impulses that are critical for brain and nerve functions These results further confirm that low molecular weight peptide aggregates of amyloid β 1-40 monomer have higher potency foi inhibiting the fast inwaid sodium channels All of the references cited herein are hereby incorporated in their entireties by refeicnce While this invention has been described with an emphasis upon a preferred embodiment, it will be obvious to those of ordinary skill in the art that variations in the preferred composition and method may be used and that it is intended that the invention may be practiced otherwise than as specifically described herein Accordingly, this invention includes all modifications encompassed within the spirit and scope of the invention as defined by the following claims.

Claims: WHAT IS CLAIMED IS 1 A method for identifying compounds that modulate the mtci action of amyloid β oi its aggregates with a sodium channel, said method comprising (a) obtaining a cell that compnses a sodium channel, (b) contacting said sodium channel with amyloid β or its aggi egates in the presence and absence of a test compound, and (c) determining the activity of said sodium channel in the presence of said test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggregates with said sodium channel 2 A method for identifying compounds that modulate the interaction of amyloid β or its aggregates with a sodium channel, said method comprising (a) obtaining a composition comprising a purified sodium channel, (b) contacting said sodium channel with amyloid β or its aggregates in the presence and absence of a test compound, and (c) determining the activity of said sodium channel in the pi esence of said test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggregates with said sodium channel 3 The method of claims 1 oi 2, further comprising a step of nianufactui ing a composition comprising a modulator identified accoiding to step (c) in a pharmaceutically acceptable carrier 4 The method of claims 1 or 2, further comprising a step of ti eating Alzheimer's disease with a composition compnsing a modulator identified accoiding to step (c) 5 A method foi st reening for compounds that modulate the interaction of amyloid β or its aggi egates .vith i sodium channel, said method compnsing (a) obtaining a fu st cell that pi oduces amyloid β oi its aggi egates, (b) obtaining a second cell comprising a sodium channel, (c) contacting said second cell with said first cell in the pi esence and absence of a test compound, and (d) detennining the activity of said sodium channel in the presence of said test compound as compared with in the absence, wherein a test compound that impacts activity is considered a modulator of the interaction of amyloid β or its aggregates with said sodium channel 6 The method of claim 5, wherein one of said first and second cells is a neuronal cell and the other is a non-neuronal cell 7. The method of claim 5, wherein both said first and second cells are either a neuronal cell or a non-neuronal cell 8 The method of any of claims 5 through 7, further comprising a step of manufacturing a composition comprising a modulator identified according to step (d) in a pharmaceutically acceptable carrier. 9 The method of any of claims 5 through 7, further comprising a step of treating Alzheimer's disease with a composition comprising a modulator identified according to step (d). 10. A compound identified as a modulator according to any of the preceding claims 1 1 . A composition comprising a compound according to claim 10 in a pharmaceutically acceptable carrier 12 A method of using a compound accoiding to claim 10 in the manufacture of a medicament for the prevention, ti eatment, oi t evei sal of Alzheimer ' s disease in a mammal 1 3 A method for diagnosing Alzheimer's disease in a mammal suspected of having Alzheimer's disease, said method compnsing the step of measuring the activity of a sodium channel a cell of said mammal, wherein reduced activity of said sodium channel is coirelatcd with the existence of an Alzheimer's disease state 14. The method of claim 13, furthei comprising a step of measuring the amount of amyloid β or its aggi egates in said cell or extracellular fluid from said mammal that contacts the cell, wherein the presence of amyloid β or its aggregates in said cell or fluid is correlated with the existence of an Alzheimer's disease state 15 A method of screening a mammal for susceptibility to Alzheimer's disease, comprising the steps of. (a) isolating a cell from said mammal, said cell comprising a sodium channel, and (b) measuring activity of said sodium channel in the absence and in the presence of amyloid β or its aggregates, wherein reduced activity of said sodium channel in the presence of amyloid β or its aggregates as compared to in the absence is correlated with a susceptibility to developing Alzheimer's disease 16 A method for diagnosing prion disease in a mammal suspected of having prion disease, said method comprising the step of measuring the activity of a sodium channel in a cell of said mammal, wherein reduced activity of said sodium channel is correlated with the existence of a prion disease state. 17 Use of a compound that protects a sodium channel from a i eduction m sodium channel activity due to amyloid β oi its aggiegates foi the manufacture of a medicament for pi eventing, ti eating or lev eising Alzhcimci s disease in a mammal 18 Use of a compound that protects a sodium channel fiom a reduction in sodium channel activity due to amyloid β or its aggregates for the manufactuie of a medicament for preventing, treating, or reversing prion disease in a mammal 19 Use of a compound that opens a sodium channel for the manufacture of a medicament for preventing, treating, or reversing Alzheimer's disease in a mammal 20 Use of a compound that opens a sodium channel for the manufacture of a medicament for preventing, treating, or reversing prion disease in a mammal 21 The method of any of claims 1 through 4, and 13 thiough 16, wherein said cell is a neuronal cell 22 The method of any of claims 1 through 4, and 13 through 16, wherein said cell is a non-neuronal cell 23 The method of any of the preceding claims, wherein said activity is detemnned by a method selected from the group consisting of examining resting membrane potential, examining action potential, and measuring the fast inward sodium current

Inventors: BUHL ALLEN E, EPPS DENNIS E, LEE KAI S, SUN XIAO-DONG, TAYLOR BRUCE M, BUHL, ALLEN, E., EPPS, DENNIS, E., LEE, KAI, S., SUN, XIAO-DONG, TAYLOR, BRUCE, M.
Applicants: BUHL ALLEN E, EPPS DENNIS E, LEE KAI S, SUN XIAO DONG, TAYLOR BRUCE M, UPJOHN CO, BUHL, ALLEN, E., EPPS, DENNIS, E., LEE, KAI, S., PHARMACIA & UPJOHN COMPANY, SUN, XIAO-DONG, TAYLOR, BRUCE, M.
Application year: 2000
Main classification: G01N33
IPC codes: A61K45, A61P25, A61P43, G01N27, G01N33