bluuebunny/crossref_metadata_2025 huggingface dataset:
Induction of glial glutamate transporters in adult mesenchymal stem cells
Authors: De Hemptinne Isabelle , Vermeiren Céline , Maloteaux Jean‐Marie , Hermans Emmanuel
Published: March 2006

Adult bone marrow mesenchymal stem cells are multipotent cells that can differentiate into a variety of mesodermal tissues. Recent studies have reported on their ability to also evolve into non‐mesodermal cells, especially neural cells. While most of these studies revealed that manipulating these cells triggers the expression of typical neurone markers, less is known about the induction of neuronal‐ or glial‐related physiological properties. The present study focused on the characterisation of glutamate transporters expression and activity in rat mesenchymal stem cells grown in culture conditions favouring their differentiation into astroglial cells. Ten days exposure of the cells to the culture supplement G5 was found to increase the expression of nestin (neuro‐epithelial stem cell intermediate filament), an intermediate filament protein expressed by neural stem cells. Simultaneously, a robust induction of the high‐affinity glutamate transporter GLT‐1 (and GLAST) expression was detected by RT‐PCR and immunocytochemistry. This expression was correlated with a highly significant increase in the Na+‐dependent [3H]d‐aspartate uptake. Finally, while glial fibrillary acidic protein immunoreactivity could not be detected, the induced expression of the astrocytic enzyme glutamine synthetase was demonstrated. These results indicate that in vitro differentiation of adult mesenchymal stem cells in neural precursors coincides with the induction of functional glutamate transport systems. Although the astrocytic nature of these cells remains to be confirmed, this observation gives support to the study of mesenchymal stem cells as a promising tool for the treatment of neurological diseases involving glutamate excitoxicity.
Nicastrin expression in mouse peripheral tissues is not co‐ordinated with presenilin and is high in muscle
Authors: Ilaya Nancy T. , Evin Geneviève , Masters Colin L. , Culvenor Janetta G.
Published: March 2006

Nicastrin was the first binding partner of presenilin (PS) shown to be a critical component of the presenilin/γ‐secretase complex essential in development and differentiation, and in generation of Alzheimer's disease Aβ amyloid peptide. To investigate the function of this glycoprotein, we compared nicastrin and presenilin protein expression in various mouse tissues. Western blot analysis of PS1, PS2 and nicastrin indicates their expression levels are not coordinated. In adult mouse, nicastrin is highly expressed in muscle membranes, whereas presenilin levels are very low. By Blue Native electrophoresis, a PS1 complex of 400 kDa was detected in lung, brain, thymus and heart; nicastrin was also detected as a 400‐kDa complex in brain but in muscle it was detected with a complex mobility of 240 and 290 kDa, suggesting association with alternate protein complexes. Immunocytochemistry confirms strong intracellular expression of nicastrin in skeletal muscle and blood vessel smooth muscle. These findings suggest a function for nicastrin in muscle other than participation in the γ‐secretase complex.
The mood stabilizer valproic acid stimulates GABA neurogenesis from rat forebrain stem cells
Authors: Laeng Pascal , Pitts Richard L. , Lemire Andrew L. , Drabik Christopher E. , Weiner Arin , Tang Haiping , Thyagarajan Rathi , Mallon Barbara S. , Altar C. Anthony
Published: March 2006

Valproate, an anticonvulsant drug used to treat bipolar disorder, was studied for its ability to promote neurogenesis from embryonic rat cortical or striatal primordial stem cells. Six days of valproate exposure increased by up to fivefold the number and percentage of tubulin β III‐immunopositive neurons, increased neurite outgrowth, and decreased by fivefold the number of astrocytes without changing the number of cells. Valproate also promoted neuronal differentiation in human fetal forebrain stem cell cultures. The neurogenic effects of valproate on rat stem cells exceeded those obtained with the neurotrophins brain‐derived growth factor (BDNF) or NT‐3, and slightly exceeded the effects obtained with another mood stabilizer, lithium. No effect was observed with carbamazepine. Most of the newly formed neurons were GABAergic, as shown by 10‐fold increases in neurons that immunostained for GABA and the GABA‐synthesizing enzyme GAD65/67. Double immunostaining for bromodeoxyuridine and tubulin β III showed that valproate increased by four‐ to fivefold the proliferation of neuronal progenitors derived from rat stem cells and increased cyclin D2 expression. Valproate also regulated the expression of survival genes, Bad and Bcl‐2, at different times of treatment. The expression of prostaglandin E synthase, analyzed by quantitative RT‐PCR, was increased by ninefold as early as 6 h into treatment by valproate. The enhancement of GABAergic neuron numbers, neurite outgrowth, and phenotypic expression via increases in the neuronal differentiation of neural stem cell may contribute to the therapeutic effects of valproate in the treatment of bipolar disorder.
Enhanced activation of Akt and extracellular‐regulated kinase pathways by simultaneous occupancy of Gq‐coupled 5‐HT2Areceptors and Gs‐coupled 5‐HT7Areceptors in PC12 cells
Authors: Johnson‐Farley Nadine N. , Kertesy Sylvia B. , Dubyak George R. , Cowen Daniel S.
Published: March 2006

The most commonly prescribed antidepressants, the serotonin (5‐HT) selective reuptake inhibitors, increase 5‐HT without targeting specific receptors. Yet, little is known about the interaction of multiple receptor subtypes expressed by individual neurons. Specifically, the effect of increases in cAMP induced by Gs‐coupled 5‐HT receptor subtypes on the signaling pathways modulated by other receptor subtypes has not been studied. We have, therefore, examined the activation of the extracellular‐regulated kinase (ERK) and Akt pathways by Gs‐coupled 5‐HT7Areceptors and Gq‐coupled 5‐HT2Areceptors, which are co‐expressed in discrete brain regions. Agonists for both receptors were found to activate ERK and Akt in transfected PC12 cells. 5‐HT2Areceptor‐mediated activation of the two pathways was found to be Ca2+‐dependent. In contrast, 5‐HT7Areceptor‐mediated activation of Akt required increases in both [cAMP] and intracellular [Ca2+], while activation of ERK was inhibited by Ca2+. The activation of ERK and Akt stimulated by simultaneous treatment of cells with 5‐HT2Aand 5‐HT7Areceptor agonists was found to be at least additive. Cell‐permeable cAMP analogs mimicked 5‐HT7Areceptor agonists in enhancing 5‐HT2Areceptor‐mediated activation of ERK and Akt. A role was identified for the cAMP–guanine exchange factor, Epac, in this augmentation of ERK, but not Akt, activation. Our finding of enhanced activation of neuroprotective Akt and ERK pathways by simultaneous occupancy of 5‐HT2Aand 5‐HT7Areceptors may also be relevant to the interaction of other neuronally expressed Gq‐ and Gs‐coupled receptors.
RNAi knockdown of Par‐4 inhibits neurosynaptic degeneration in ALS‐linked mice
Authors: Xie Jun , Awad Keytam S. , Guo Qing
Published: March 2006

Evidence from human amyotrophic lateral sclerosis (ALS) patients and ALS‐linked Cu/Zn superoxide dismutase (Cu/Zn‐SOD) transgenic mice bearing the mutation of glycine to alanine at position 93 (G93A) suggests that the pro‐apoptotic protein prostate apoptosis response‐4 (Par‐4) might be a critical link in the chain of events leading to motor neuron degeneration. We now report that Par‐4 is enriched in synaptosomes and post‐synaptic density from the ventral horn of the spinal cord. Levels of Par‐4 in synaptic compartments increased significantly during rapid and slow declining stages of muscle strength in hSOD1 G93A mutant mice. In the pre‐muscle weakness stage, hSOD1 G93A mutation sensitized synaptosomes from the ventral horn of the spinal cord to increased levels of Par‐4 expression following excitotoxic and apoptotic insults. In ventral spinal synaptosomes, Par‐4‐mediated production of pro‐apoptotic cytosolic factor(s) was significantly enhanced by the hSOD1 G93A mutation. RNA interference (RNAi) knockdown of Par‐4 inhibited mitochondrial dysfunction and caspase‐3 activation induced by G93A mutation in synaptosomes from the ventral horn of the spinal cord, and protected spinal motor neurons from apoptosis. These results identify the synapse as a crucial cellular site for the cell death promoting actions of Par‐4 in motor neurons, and suggest that targeted inhibition of Par‐4 by RNAi may prove to be a neuroprotective strategy for motor neuron degeneration.
Activation of NADPH oxidase and extracellular superoxide production in seizure‐induced hippocampal damage
Authors: Patel Manisha , Li Qing‐You , Chang Ling‐Yi , Crapo James , Liang Li‐Ping
Published: March 2006

We sought to determine whether the extracellular compartment contributed to seizure‐induced superoxide (O2.−) production and to determine the role of the NADPH oxidase complex as a source of this O2.− production. The translocation of NADPH oxidase subunits (p47phox, p67phox and rac1) was assessed by immunoblot analysis and NADPH‐driven O2.− production was measured using 2‐(4‐hydroxybenzyl)‐6‐(4‐hydroxyphenyl)‐8‐benzyl‐3,7‐dihydroimidazo [1,2‐α] pyrazin‐3‐one‐enhanced chemiluminescence. Kainate‐induced status epilepticus resulted in a time‐dependent translocation of NADPH oxidase subunits (p47phox, p67phox and rac‐1) from hippocampal cytosol to membrane fractions. Hippocampal membrane fractions from kainate‐injected rats showed increased NADPH‐driven and diphenylene iodonium‐sensitive O2.− production in comparison to vehicle‐treated rats. The time‐course of kainate‐induced NADPH oxidase activation coincided with microglial activation in the rat hippocampus. Finally, kainate‐induced neuronal damage and membrane oxygen consumption were inhibited in mice overexpressing extracellular superoxide dismutase. These results suggest that seizure activity activates the membrane NADPH oxidase complex resulting in increased formation of O2.−.
Chronic exposure to ammonia induces isoform‐selective alterations in the intracellular distribution and NMDA receptor‐mediated translocation of protein kinase C in cerebellar neurons in culture
Authors: Giordano Gennaro , Sanchez‐Perez Ana M. , Burgal Maria , Montoliu Carmina , Costa Lucio G , Felipo Vicente
Published: March 2006

Hyperammonemia is responsible for most neurological alterations in patients with hepatic encephalopathy by mechanisms that remain unclear. Hyperammonemia alters phosphorylation of neuronal protein kinase C (PKC) substrates and impairs NMDA receptor‐associated signal transduction. The aim of this work was to analyse the effects of hyperammonemia on the amount and intracellular distribution of PKC isoforms and on translocation of each isoform induced by NMDA receptor activation in cerebellar neurons. Chronic hyperammonemia alters differentially the intracellular distribution of PKC isoforms. The amount of all isoforms (except PKC ζ) was reduced (17–50%) in the particulate fraction. The contents of α, β1, and ε isoforms decreased similarly in cytosol (65–78%) and membranes (66–83%), whereas γ, δ, and θ isoforms increased in cytosol but decreased in membranes, and ζ isoform increased in membranes and decreased in cytosol. Chronic hyperammonemia also affects differentially NMDA‐induced translocation of PKC isoforms. NMDA‐induced translocation of PKC α and β is prevented by ammonia, whereas PKC γ, δ, ε, or θ translocation is not affected. Inhibition of phospholipase C did not affect PKC α translocation but reduced significantly PKC γ translocation, indicating that NMDA‐induced translocation of PKC α is mediated by Ca2+, whereas PKC γ translocation is mediated by diacylglycerol. Chronic hyperammonemia reduces Ca+2‐mediated but not diacylglycerol‐mediated translocation of PKC isoforms induced by NMDA.
Pathogenic mutations inactivate parkin by distinct mechanisms
Authors: Henn Iris H. , Gostner Johanna M. , Lackner Peter , Tatzelt Jörg , Winklhofer Konstanze F.
Published: March 2006

Loss of parkin function is the major cause of autosomal recessive Parkinson's disease (ARPD). A wide variety of parkin mutations have been identified in patients; however, the pathophysiological mechanisms leading to the inactivation of mutant parkin are poorly understood. In this study we characterized pathogenic C‐ and N‐terminal parkin mutants and found distinct pathways of parkin inactivation. Deletion of the C terminus abrogated the association of parkin with cellular membranes and induced rapid misfolding and aggregation. Four N‐terminal missense mutations, located within the ubiquitin‐like domain (UBL), decrease the stability of parkin; as a consequence, these mutants are rapidly degraded by the proteasome. Furthermore, we present evidence that a smaller parkin species of 42 kDa, which is present in extracts prepared from human brain and cultured cells, originates from an internal start site and lacks the N‐terminal UBL domain.
Activated JNK brings about accelerated apoptosis of Bcl‐2‐overexpressing C6 glioma cells on treatment with tamoxifen
Authors: Moodbidri Madhavi S. , Shirsat Neelam V.
Published: March 2006

Tamoxifen causes apoptosis of malignant glial cells at a concentration that does not kill normal astrocytes. C6 glioma cells were stably transfected with a vector expressing Bcl‐2 under the control of metallothionin promoter. Low leaky Bcl‐2 expression offered complete protection against tamoxifen‐induced apoptosis. High Bcl‐2 levels, on the other hand, accelerated the apoptosis, with Bcl‐2‐overexpressing clones dying within 48 h of tamoxifen treatment as compared to 6 days for parental C6 cells. Overexpressed Bcl‐2 is localized primarily in mitochondria and to a much lower extent in endoplasmic reticulum (ER). Only a minor fraction of the overexpressed Bcl‐2 gets phosphorylated in tamoxifen‐treated cells and the phosphorylation does not affect its binding to Bax. Tamoxifen treatment of Bcl‐2‐overexpressing clones was found to result in activation of c‐Jun N‐terminal kinase (JNK) and p38 kinase. Inhibition of JNK but not p38 kinase completely abrogated the accelerated apoptosis. Constitutively expressed endogenous c‐Jun was found to be phosphorylated, resulting in increased activator protein 1 (AP‐1) DNA‐binding activity. Expression of Fas ligand (FasL), an AP‐1 transcriptional target, increased during accelerated cell death. This presumably brought about activation of caspase 8, as inhibition of caspase 8 blocked the apoptosis. The JNK/c‐Jun/AP‐1/FasL pathway could be considered as a potential target for the therapy of gliomas.
Vlgr1 knockout mice show audiogenic seizure susceptibility
Authors: Yagi Hideshi , Takamura Yoshihiro , Yoneda Takunari , Konno Daijiro , Akagi Yoshio , Yoshida Kazunori , Sato Makoto
Published: March 2006

Susceptibility to audiogenic seizures, which are reflex seizures provoked by loud noise, can be induced in rodents by acoustic priming (exposing animals to strong auditory stimuli at an early developmental stage). Some strains of mice and rats are susceptible to audiogenic seizures without priming and these have been used as good experimental models with which to study epilepsies. Here we identified Vlgr1d and Vlgr1e, novel alternatively‐spliced variants of Vlgr1b/MGR1, which, upon sequence analysis, were shown to be transcripts from a locus previously characterized as mass1. Vlgr1 (Vlgr1b, Vlgr1d and Vlgr1e) mRNA is expressed predominantly in the neuroepithelium of the developing mouse brain. Our protein‐tagged experiment suggested that Vlgr1d and Vlgr1e are secretory molecules, while Vlgr1b is a receptor. Knockout mice lacking exons 2–4 of Vlgr1 were susceptible to audiogenic seizures without priming, although there were no apparent histological abnormalities in their brains. Ninety‐five percent of these knockout mice exhibited wild running, a feature typical of the preconvulsive phase of audiogenic seizures triggered by loud noise (11 kHz, 105 dB), and 68% exhibited tonic convulsions at 3 weeks after birth. Our monogenic mice, which have a unique genetic background, serve as a useful tool for further studies on seizures.
Decreased calcium/calmodulin‐dependent protein kinase II and protein kinase C activities mediate impairment of hippocampal long‐term potentiation in the olfactory bulbectomized mice
Authors: Moriguchi Shigeki , Han Feng , Nakagawasai Osamu , Tadano Takeshi , Fukunaga Kohji
Published: March 2006

Olfactory bulbectomized (OBX) mice showed significant impairment of learning and memory‐related behaviors 14 days after olfactory bulbectomy, as measured by passive avoidance and Y‐maze tasks. We here observed a large impairment of hippocampal long‐term potentiation (LTP) in the OBX mice. Concomitant with decreased acetylcholinesterase expression, protein kinase C (PKC)α autophosphorylation and NR1(Ser‐896) phosphorylation significantly decreased in the hippocampal CA1 region of OBX mice. Both PKCα and NR1(Ser‐896) phosphorylation significantly increased following LTP in the control mice, whereas increases were not observed in OBX mice. Like PKC activities, calcium/calmodulin‐dependent protein kinase II (CaMKII) autophosphorylation significantly decreased in the hippocampal CA1 region of OBX mice as compared with that of control mice. In addition, increased CaMKII autophosphorylation following LTP was not observed in OBX mice. Finally, the impairment of CaMKII autophosphorylation was closely associated with reduced pGluR1(Ser‐831) phosphorylation, without change in synapsin I (site 3) phosphorylation in the hippocampal CA1 region of OBX mice. Taken together, in OBX mice NMDA receptor hypofunction, possibly through decreased PKCα activity, underlies decreased CaMKII activity in the post‐synaptic regions, thereby impairing LTP induction in the hippocampal CA1 region. Both decreased PKC and CaMKII activities with concomitant LTP impairment account for the learning disability observed in OBX mice.
Simvastatin prevents oxygen and glucose deprivation/reoxygenation‐induced death of cortical neurons by reducing the production and toxicity of 4‐hydroxy‐2E‐nonenal
Authors: Lim Ji Hyae , Lee Jae‐Chul , Lee Yong Hyun , Choi In Young , Oh Yu‐Kyoung , Kim Hee‐Sun , Park Jin‐Sun , Kim Won‐Ki
Published: March 2006

Lipid membrane peroxidation is highly associated with neuronal death in various neurodegenerative diseases including cerebral stroke. Here, we report that simvastatin decreases oxygen and glucose deprivation (OGD)/reoxygenation‐evoked neuronal death by inhibiting the production and cytoxicity of 4‐hydroxy‐2E‐nonenal (HNE), the final product of lipid peroxidation. Simvastatin markedly decreased the OGD/reoxygenation‐evoked death of cortical neurons. OGD/reoxygenation increased the intracellular HNE level mostly in neuronal cells, not glial cells. Simvastatin decreased the intracellular level of HNE in neuronal cells exposed to OGD/reoxygenation. We further found that HNE induced the cytotoxicity in neuronal cells and synergistically increased the N‐methyl‐D‐aspartate (NMDA) receptor‐mediated excitotoxicity. Simvastatin largely blocked the NMDA neurotoxicity potentiated by HNE. However, simvastatin did not alter the NMDA‐evoked calcium influx in the absence or presence of HNE. HNE inhibited the activity of nuclear factor‐kappa B (NF‐κB), and the cytotoxicity of HNE was in good correlation with inactivation of NF‐κB. Simvastatin reversed the inhibition of NF‐κB activity induced by OGD/reoxygenation or HNE. The neuroprotection by simvastatin was significantly attenuated by various NF‐κB inhibitors, implying that simvastatin inhibits the cytotoxicity of HNE at least in part by maintaining the activity of NF‐κB. Further understanding of the neuroprotective mechanism of simvastatin may provide a therapeutic strategy for oxidative stress‐related neurodegenerative diseases.
Activation of ERK1/2 MAP kinases in Familial Amyloidotic Polyneuropathy
Authors: Monteiro F. A. , Sousa M. M. , Cardoso I. , do Amaral J. Barbas , Guimarães A. , Saraiva M. J.
Published: March 2006

Familial amyloidotic polyneuropathy (FAP) is a neurodegenerative disorder characterized by the extracellular deposition of transthyretin (TTR), especially in the PNS. Given the invasiveness of nerve biopsy, salivary glands (SG) from FAP patients were used previously in microarray analysis; mitogen‐activated protein (MAP) kinase phosphatase 1 (MKP‐1) was down‐regulated in FAP. Results were validated by RT‐PCR and immunohistochemistry both in SG and in nerve biopsies of different stages of disease progression. MKP‐3 was also down‐regulated in FAP SG biopsies. Given the relationship between MKPs and MAPKs, the latter were investigated. Only extracellular signal‐regulated kinases 1/2 (ERK1/2) displayed increased activation in FAP SG and nerves. ERK1/2 kinase (MEK1/2) activation was also up‐regulated in FAP nerves. In addition, an FAP transgenic mouse model revealed increased ERK1/2 activation in peripheral nerve affected with TTR deposition when compared to control animals. Cultured rat Schwannoma cell line treatment with TTR aggregates stimulated ERK1/2 activation, which was partially mediated by the receptor for advanced glycation end‐products (RAGE). Moreover, caspase‐3 activation triggered by TTR aggregates was abrogated by U0126, a MEK1/2 inhibitor, indicating that ERK1/2 activation is essential for TTR aggregates‐induced cytotoxicity. Taken together, these data suggest that abnormally sustained activation of ERK in FAP may represent an early signaling cascade leading to neurodegeneration.
Regulation of AMPA receptor trafficking by N‐cadherin
Authors: Nuriya Mutsuo , Huganir Richard L.
Published: March 2006

Dendritic spines are dynamically regulated, both morphologically and functionally, by neuronal activity. Morphological changes are mediated by a variety of synaptic proteins, whereas functional changes can be dramatically modulated by the regulation of α‐amino‐3‐hydroxy‐5‐methylisoxazole‐4‐propionate (AMPA) receptor trafficking. Although these two forms of plasticity appear to be highly coordinated, the connections between them are not fully understood. In this study the synaptic cell adhesion molecule N‐cadherin was found to associate with AMPA receptors and regulate AMPA receptor trafficking in neurons. N‐cadherin and β‐catenin formed a protein complex with AMPA receptors in vivo, and this association was regulated by extracellular Ca2+. In addition, these proteins co‐clustered at synapses in cultured neurons. In heterologous cells and in cultured neurons, overexpression of wild‐type N‐cadherin specifically increased the surface expression level of the AMPA receptor subunit glutamate receptor 1 (GluR1) and this effect was reversed by a dominant‐negative form of N‐cadherin. Finally, GluR1 increased the surface expression of N‐cadherin in heterologous cells. Importantly, recent studies suggest that N‐cadherin and β‐catenin play key roles in structural plasticity in neurons. Therefore, our data suggest that the association of N‐cadherin with AMPA receptors may serve as a biochemical link between structural and functional plasticity of synapses.
DOC2A and DOC2B are sensors for neuronal activity with unique calcium‐dependent and kinetic properties
Authors: Groffen Alexander J. A. , Friedrich Reut , Brian Elisabeth C. , Ashery Uri , Verhage Matthijs
Published: March 2006

Elevation of the intracellular calcium concentration ([Ca2+]i) to levels below 1 µm alters synaptic transmission and induces short‐term plasticity. To identify calcium sensors involved in this signalling, we investigated soluble C2 domain‐containing proteins and found that both DOC2A and DOC2B are modulated by submicromolar calcium levels. Fluorescent‐tagged DOC2A and DOC2B translocated to plasma membranes after [Ca2+]i elevation. DOC2B translocation preceded DOC2A translocation in cells co‐expressing both isoforms. Half‐maximal translocation occurred at 450 and 175 nm[Ca2+]i for DOC2A and DOC2B, respectively. This large difference in calcium sensitivity was accompanied by a modest kinetic difference (halftimes, respectively, 2.6 and 2.0 s). The calcium sensitivity of DOC2 isoforms can be explained by predicted topologies of their C2A domains. Consistently, neutralization of aspartates D218 and D220 in DOC2B changed its calcium affinity. In neurones, both DOC2 isoforms were reversibly recruited to the plasma membrane during trains of action potentials. Consistent with its higher calcium sensitivity, DOC2B translocated at lower depolarization frequencies. Styryl dye uptake experiments in hippocampal neurones suggest that the overexpression of mutated DOC2B alters the synaptic activity. We conclude that both DOC2A and DOC2B are regulated by neuronal activity, and hypothesize that their calcium‐dependent translocation may regulate synaptic activity.
The mechanism of 1,2,3,4‐tetrahydroisoquinolines neuroprotection: the importance of free radicals scavenging properties and inhibition of glutamate‐induced excitotoxicity
Authors: Antkiewicz‐Michaluk Lucyna , Lazarewicz Jerzy W. , Patsenka Antoni , Kajta Malgorzata , Zieminska Elzbieta , Salinska Elzbieta , Wasik Agnieszka , Golembiowska Krystyna , Vetulani Jerzy
Published: March 2006

1‐Methyl‐1,2,3,4‐tetrahydroisoquinoline (1MeTIQ), unlike several other tetrahydroisoquinolines, displays neuroprotective properties. To elucidate this action we compared the effects of 1MeTIQ with 1,2,3,4‐tetrahydroisoquinoline (TIQ), a compound sharing many activities with 1MeTIQ (among them reducing free radicals formed during dopamine catabolism), but offering no clear neuroprotection. We found that the compounds similarly inhibit free‐radical generation in an abiotic system, as well as indices of neurotoxicity (caspase‐3 activity and lactate dehydrogenase release) induced by glutamate in mouse embryonic primary cell cultures (a preparation resistant to NMDA toxicity). However, in granular cell cultures obtained from 7‐day‐old rats, 1MeTIQ prevented the glutamate‐induced cell death and45Ca2+influx, whereas TIQ did not. This suggested a specific action of 1MeTIQ on NMDA receptors, which was confirmed by the inhibition of [3H]MK‐801 binding by 1MeTIQ. Finally, we demonstrated in anin vivomicrodialysis experiment that 1MeTIQ prevents kainate‐induced release of excitatory amino acids from the rat frontal cortex. Our results indicate that 1MeTIQ, in contrast to TIQ, offers a unique and complex mechanism of neuroprotection in which antagonism to the glutamatergic system may play a very important role. The results suggest the potential of 1MeTIQ as a therapeutic agent in various neurodegenarative illnesses of the central nervous system.
Fe(III) mineral formation and cell encrustation by the nitrate‐dependent Fe(II)‐oxidizer strain BoFeN1
Authors: KAPPLER A. , SCHINK B. , NEWMAN D. K.
Published: March 2006

Understanding the mechanisms of anaerobic microbial iron cycling is necessary for a full appreciation of present‐day biogeochemical cycling of iron and carbon and for drawing conclusions about these cycles on the ancient Earth. Towards that end, we isolated and characterized an anaerobic nitrate‐dependent Fe(II)‐oxidizing bacterium from a freshwater sediment. The 16SrRNA gene sequence of the isolated bacterium (strain BoFeN1) places it within the β‐Proteobacteria, with Acidovorax sp. strain G8B1 as the closest known relative. During mixotrophic growth with acetate plus Fe(II) and nitrate as electron acceptor, strain BoFeN1 forms Fe(III) mineral crusts around the cells. The amount of the organic cosubstrate acetate present seems to control the rate and extent of Fe(II) oxidation and the viability of the cells. The crystallinity of the mineral products is influenced by nucleation by Fe minerals that are already present in the inoculum.
The coupling of biological iron cycling and mineral weathering during saprolite formation, Luquillo Mountains, Puerto Rico
Authors: BUSS H. L. , BRUNS M. A. , SCHULTZ M. J. , MOORE J. , MATHUR C. F. , BRANTLEY S. L.
Published: March 2006

Corestones of quartz diorite bedrock in the Rio Icacos watershed in Puerto Rico weather spheroidally to form concentric sets of partially weathered rock layers (referred to here as rindlets) that slowly transform to saprolite. The rindlet zone (0.2–2 m thick) is overlain by saprolite (2–8 m) topped by soil (0.5–1 m). With the objective of understanding interactions between weathering, substrate availability, and resident micro‐organisms, we made geochemical and microbiological measurements as a function of depth in 5 m of regolith (soil + saprolite). We employed direct microscopic counting of total cell densities; enumeration of culturable aerobic heterotrophs; extraction of microbial DNA for yield calculations; and biochemical tests for iron‐oxidizing bacteria. Total cell densities, which ranged from 2.5 × 106 to 1.6 × 1010 g−1 regolith, were higher than 108 g−1 at three depths: in the upper 1 m, at 2.1 m, and between 3.7 and 4.9 m, just above the rindlet zone. High proportions of inactive or unculturable cells were indicated throughout the profile by very low percentages of culturable heterotrophs (0.0004% to 0.02% of total cell densities). The observed increases in total and culturable cells and DNA yields at lower depths were not correlated with organic carbon or total iron but were correlated with moisture and HCl‐extractable iron. Biochemical tests for aerobic iron‐oxidizers were also positive at 0.15–0.6 m, at 2.1–2.4 m, and at 4.9 m depths. To interpret microbial populations within the context of weathering reactions, we developed a model for estimating growth rates of lithoautotrophs and heterotrophs based on measured substrate fluxes. The calculations and observations are consistent with a model wherein electron donor flux driving bacterial growth at the saprolite–bedrock interface is dominated by Fe(II) and where autotrophic iron‐oxidizing bacteria support the heterotrophic population and contribute to bedrock disaggregation and saprolite formation.
On the energetics of chemolithotrophy in nonequilibrium systems: case studies of geothermal springs in Yellowstone National Park
Authors: INSKEEP W. P. , ACKERMAN G. G. , TAYLOR W. P. , KOZUBAL M. , KORF S. , MACUR R. E.
Published: March 2006

Chemolithotrophic micro‐organisms are important primary producers in high‐temperature geothermal environments and may catalyse a number of different energetically favourable redox reactions as a primary energy source. Analysis of geochemical constituents followed by chemical speciation and subsequent calculation of reaction free energies (ΔGrxn) is a useful tool for evaluating the thermodynamic favourability and potential energy available for microbial metabolism. The primary goal of this study was to examine relationships among geochemical gradients and microbial population distribution, and to evaluate the utility of energetic approaches for predicting microbial metabolism from free‐energy calculations, utilizing as examples, several geothermal habitats in Yellowstone National Park where thorough geochemical and phylogenetic analyses have been performed. Acidic (pH ∼ 3) and near‐neutral (pH ∼ 6–7) geothermal springs were chosen for their range in geochemical properties. Aqueous and solid phase samples obtained from the source pools and the outflow channels of each spring were characterized for all major chemical constituents using laboratory and field methods to accurately measure the concentrations of predominant oxidized and reduced species. Reaction free energies (ΔGrxn) for 33 oxidation–reduction reactions potentially important to chemolithotrophic micro‐organisms were calculated at relevant spring temperatures after calculating ion activities using an aqueous equilibrium model. Free‐energy values exhibit significant variation among sites for reactions with pH dependence. For example, free‐energy values for reactions involving Fe3+ are especially variable across sites due in large part to the pH dependence of Fe3+ activity, and exhibit changes of up to 40 kJ mol−1 electron from acidic to near neutral geothermal springs. Many of the detected 16S rRNA gene sequences represent organisms whose metabolisms are consistent with exergonic processes. However, sensitivity analyses demonstrated that reaction free energies do not generally represent the steep gradients in local geochemical conditions resulting from air–water gas exchange and solid phase deposition that are important in defining microbial habitats and 16S rRNA gene sequence distribution within geothermal outflow channels.
Addition of U(VI) to a uranium mining waste sample and resulting changes in the indigenous bacterial community
Authors: GEISSLER A. , SELENSKA‐POBELL S.
Published: March 2006

Based on 16S rRNA gene sequence retrieval, changes in natural bacterial community structure induced by addition of uranyl or sodium nitrate to soil samples from a uranium mining waste pile were investigated. Our results demonstrate that both treatments cause drastic changes in the bacterial composition of the studied samples, resulting in strongly reducing the originally predominant Acidobacteria and Alphaproteobacteria. The addition of sodium nitrate induced a strong propagation of particular denitrifying and nitrate‐reducing populations belonging to Actinobacteria and Bacteroidetes. The treatment of the samples with uranyl nitrate demonstrated that most part of the mentioned Bacteroidetes and some of the actinobacterial populations do not tolerate high U(VI) concentrations. Instead, a strong propagation of Pseudomonas spp. from the Gammaproteobacteria occurred. At the initial stages of incubation (4 weeks after the addition of uranyl nitrate) U(VI)‐reducing Geobacter spp. appeared. However, at the later stages of incubation (14 weeks after the beginning of supplementation) no Geobacter populations were detected anymore. Interestingly, different U‐sensitive Bacteroidetes and alphaproteobacterial populations propagated in the U(VI)‐treated samples at these late stages of incubation. That indicated that the added U(VI) was no longer bioavailable.

The drastic changes in bacterial community structure of the soil samples from the depleted uranium mining waste caused by the addition of uranyl nitrate indicate that most of the established indigenous bacterial populations do not tolerate U(VI). By the treatment with uranyl nitrate they are replaced by particular uranium resistant nitrate‐reducing and denitrifying populations that potentially interact with the added radionuclide. On the other hand, the large number of dead uranium‐sensitive bacteria likely liberates phosphate‐rich and other biopolymers capable of binding U(VI). On the basis of our results, we propose that bacteria along with the abiotic soil components such as minerals and humic acids may influence the behaviour of U(VI) in nature.
Microbial stratification in deeply buried marine sediment reflects changes in sulfate/methane profiles
Authors: BIDDLE J. F. , HOUSE C. H. , BRENCHLEY J. E.
Published: March 2006

We examined sediments collected at Ocean Drilling Program (ODP) Leg 201 Site 1229 on the Peru Margin for microbial populations throughout the sediment column. Heterotrophic cultivation from these sediments yielded numerous colonies from various depths, including 49 bacterial isolates. At ODP Site 1229, there are significant interfaces of sulfate and methane, across which microbial cell numbers increase substantially. At these sulfate/methane transition zones (SMTZs), however, we observed a decrease in the success rate for the cultivation of bacterial colonies. Utilizing both direct plating and enrichment in different media, we cultivated isolates from the upper SMTZ around 30 m below seafloor (mbsf); however, similar attempts yielded no colonies from within the lower zone at 85 mbsf. The phylogenetic relationships of the 16S rRNA gene sequences for the isolates were determined and most were related to other organisms and sequences previously found in the subsurface belonging to the γ‐Proteobacteria, cytophaga–flavobacterium–bacteroides, high G + C Gram‐positives, and Firmicutes groups. The most diverse group of isolates from Site 1229 was found between the SMTZs at 50 mbsf. ODP Leg 201 Site 1228 was examined for comparison and yielded an additional 18 isolates from 16 to 179 mbsf that were similar to those found at Site 1229. Direct plating at Site 1228 also showed decreased colony formation in the area of sulfate/methane transition. Our results suggest that heterotrophic bacterial populations are affected by SMTZs in deeply buried sediment.
Economic Instruments to Improve UK Home Energy Efficiency without Negative Social Impacts*
Authors: Dresner Simon , Ekins Paul
Published: March 2006

The research examined how to use economic instruments to reduce carbon emissions from the UK housing sector without causing negative impacts on the poorest households. Carbon taxes would worsen the problem of fuel poverty. Compensation mechanisms involving the tax and benefit system were examined, but found not to be entirely effective because of the enormous range in the existing energy efficiency of homes. Exemptions for low‐income households were examined, but found impractical to target. It was concluded that the best way to use economic instruments was through a scheme involving energy audits and surcharges to council tax and stamp duty for homeowners who failed to make cost‐effective energy efficiency improvements within a specified time, with grants and loans to assist low‐income households. After the implementation of such a scheme for 10 years, it would be practical to introduce a targeted carbon tax.
The Analysis of Poverty Data with Endogenous Transitions*
Authors: Burgess Simon , Propper Carol , Dickson Matt
Published: March 2006

It is common to analyse poverty data broken down by household or economic status. Implicitly, it is assumed that people change state (for example, single, married, children, no children) for exogenous reasons. If we bring economic behaviour into the problem, then such transitions become endogenous. The data are then insufficient to identify the claims made from them. The distribution of the characteristics of the individuals in the states will be endogenous, and the state average poverty rate will depend on the composition of the individuals in the state as well as on the economic impact of being in that state per se. In this paper, we set out a simple model with endogenous transitions to make our point, and apply this to Family Expenditure Survey data for Britain. We show that our argument has empirical content for Britain.
Quantifying the Costs of Investment Limits for Chilean Pension Funds*
Authors: Berstein Solange M. , Chumacero Rómulo A.
Published: March 2006

Since the creation of the Chilean pension fund industry in 1981, pension fund administrators have not been free to choose their investment portfolios because of stringent regulation of investment limits. The diagnosis implicit with the imposition of limits was that the Chilean capital market was not deep, that there was an important demand for funds to finance the expansion of the productive sector and that, due to principal‐agent problems, protection for uninformed account holders was needed. As this regulation entails an inefficient combination of risk and return, this paper quantifies its costs.
UNRESOLVED ISSUES IN DIALYSIS: Ultrapure Dialysate: Facts and Myths
Authors: Bommer Juergen , Jaber Bertrand L.
Published: March 2006

During hemodialysis, blood comes in contact with a large volume of dialysate. Since the purity of dialysate has been linked to acute and long‐term complications in hemodialysis patients, the limit of bacterial and endotoxin contamination has been reduced in recent years. Questions have been raised as to whether ultrapure dialysate is required to prevent such complications; in particular, the chronic inflammatory status frequently found in chronically hemodialyzed patients. In vivo and in vitro data suggest that cytokine stimulation in the blood depends on the concentration of bacteria or endotoxin in the dialysate and on the endotoxin permeability of the dialysis membrane. It is not proven whether ultrapure dialysate reduces significantly proinflammatory cytokine generation compared with standard dialysate within the limits of recent recommendations, if rather impermeable dialysis membranes are used. Cuprophane membranes are more permeable to cytokine‐inducing substances compared with synthetic membranes such as polysulfone and polyamide. Clinical reports have also attempted to link several acute and chronic complications of hemodialysis to dialysate purity. To date, however, there is no large randomized clinical trial demonstrating that ultrapure dialysate significantly reduces biomarkers of inflammation and other consequential putative complications, including dialysis‐related amyloidosis, erythropoietin requirement, and cardiovascular morbidity and mortality. In conclusion, based on the existing clinical data, ultrapure dialysate is recommended in the setting of suboptimal bacteriologic quality of standard dialysate and the use of permeable dialysis membranes.
UNRESOLVED ISSUES IN DIALYSIS: Dialyzer Best Practice: Single Use or Reuse?
Authors: Lacson Eduardo , Lazarus J. Michael
Published: March 2006

Outcome studies have shown either no additional risk or a small additional risk for hospitalization and mortality associated with reprocessing dialyzers. Although the risks from reprocessing dialyzers have yet to be fully elucidated, reuse can be done safely if it is performed in full compliance with the standards of Association for the Advancement of Medical Instrumentation (AAMI). Like most industrial processes, however, complete control of the reuse process in a clinical environment and full compliance with regulations at all times is difficult. Potential errors and breakdowns in the reuse process are continuing concerns. The quality controls for reprocessing of dialyzers are not equal to the rigor of the manufacturing process under the purview of the U.S. Food and Drug Administration (FDA). Therefore, if one were to determine “best practice,” single use is preferable to reuse of dialyzers based on medical criteria and risk assessment. The long‐term and cumulative effects of exposure to reuse reagents are unknown and there is no compelling medical indication for reprocessing of dialyzers. The major impediment when deciding to convert from reuse to single use of dialyzers is economic. The experience in Fresenius Medical Care—North America (FMCNA) facilities demonstrates that converting from a practice of reuse to single use is achievable. However, the overall economic impact of conversion to single use is provider specific. The dominance of reuse has been negated of late by a major shift in practice toward single use. Physicians and patients should be well informed in making decisions regarding the practice of single use versus reuse of dialyzers.
UNRESOLVED ISSUES IN DIALYSIS: Adiposity in Dialysis: Good or Bad?
Authors: Friedman Allon N.
Published: March 2006

There exists in the general population a complex and mostly positive relationship between adiposity and mortality risk. Because the dialysis population has a high prevalence of excess adiposity, in addition to a strikingly elevated mortality rate, the effects of obesity are of potential clinical importance. In contrast to the general population, the preponderance of data in dialysis, particularly hemodialysis patients, suggest that adiposity has a neutral or even protective association with mortality. Although methodological concerns exist with regards to confounding and survival bias, among others, the major limitation of this body of literature is its inability to establish causality. Thus, although obese dialysis patients, with certain exceptions, appear to live longer, there is no evidence to suggest that intentional weight loss adversely affects patient outcomes. In light of these limitations and the substantial body of literature implicating obesity as a pathophysiological state, it is currently premature to advocate for excess adiposity as being beneficial or intentional weight loss as dangerous. Decisions regarding optimal weight should be made by clinicians on an individual basis and with close supervision and follow‐up. Efforts should be made to preserve lean mass during weight loss regimens by encouraging exercise and recommending sufficient protein consumption. Future research efforts in this area should focus on interventional trials designed to manipulate weight and measure outcomes, identifying potentially beneficial secretory products of adipose tissue, and documenting obesity's effects on quality of life and resource utilization in the dialysis setting.
UNRESOLVED ISSUES IN DIALYSIS: Managing Erythropoietin Hyporesponsiveness
Authors: Kwack Christina , Balakrishnan Vaidyanathapuram S.
Published: March 2006

The anemia of chronic kidney disease is associated with cardiovascular disease, decreased quality of life, and mortality. The introduction of recombinant human erythropoietin (rHuEPO) has transformed the management of this condition. However, a significant proportion of patients fail to respond to even high doses of rHuEPO. Several factors have been implicated in the hyporesponsiveness to rHuEPO. Iron deficiency, whether absolute or functional, is considered the most important, and maintenance of adequate iron stores reduces rHuEPO requirements among patients on hemodialysis. However, traditional indices of iron that are currently utilized may not reflect iron stores accurately, and there is also increasing concern regarding the potential long‐term toxicity of parenteral iron therapy. Infection and inflammation also influence the response to rHuEPO, both by disruption of iron metabolism and by eliciting the release of cytokines that inhibit erythropoiesis. Oxidative stress may contribute to rHuEPO hyporesponsiveness directly by promoting lipid peroxidation in cell membranes, leading to increased erythrocyte fragility and reduced life span and also through its strong association with inflammation. Severe hyperparathyroidism can lead to a reduced number of erythroid progenitor cells. Inadequate dialysis dose, aluminum overload, nutritional factors such as deficiencies of carnitine, vitamin B12, folic acid, and vitamin C can also reduce the efficacy of rHuEPO therapy. Hyporesponsiveness to rHuEPO presents a challenge to both diagnosis and management in an era where optimizing response to rHuEPO is critical both in limiting the burgeoning costs of anemia management and improving clinical outcomes in the dialysis population.