bluuebunny/crossref_metadata_2025_split huggingface dataset:
Preparation of interconnected highly porous polymeric structures by a replication and freeze‐drying process
Authors: Hou Qingpu , Grijpma Dirk W. , Feijen Jan 
Published: October 2003

AbstractThree‐dimensional degradable porous polymeric structures with high porosities (93–98%) and well‐interconnected pore networks have been prepared by freeze‐drying polymer solutions in the presence of a leachable template followed by leaching of the template. Templates of the pore network were prepared by fusing sugar or salt particles to form a well‐connected structure. The interstices of the template were then filled with a polymer solution (5–15% w/v) in 1,4‐dioxane, followed by freeze‐drying of the solvent. Subsequent leaching of the sugar template ensures the connectivity of the pore network. The scaffold architecture consists of relatively large interconnected pores modeled after the template and smaller pores resulting from the freeze‐drying process. The total porosity of the resultant porous structures is determined by the interstitial space of the leachable template and by the polymer concentration in the freeze‐drying solution. The freezing temperature also has an effect on the final morphology of the porous structures. Compared with freeze‐drying and combination of freeze‐drying /particulate leaching techniques, this method facilitates higher interconnectivity of the scaffolds. Porous structures have been prepared from several relevant polymers in the biomedical and tissue‐engineering field: poly(D,L‐lactide) (PDLLA), 1000PEOT70PBT30, a segmented poly(ether ester) based on polyethylene oxide and polybutylene terephthalate, and poly(ϵ‐caprolactone) (PCL). The mechanical properties of the porous structures prepared by this technique depend on the nature of the polymer, porosity, and the freezing temperature. With porosities in the range of 95–97%, the compression moduli of scaffolds prepared from the different polymers could be varied between 13.0 and 301.5 kPa. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 67B: 732–740, 2003
Biological response to wear debris generated in carbon based composites as potential bearing surfaces for artificial hip joints
Authors: Howling G. I. , Sakoda H. , Antonarulrajah A. , Marrs H. , Stewart T. D. , Appleyard S. , Rand B. , Fisher J. , Ingham E. 
Published: October 2003

AbstractUHMWPE wear particles have been implicated in osteolysis, implant loosening, and long‐term failure of total hip arthroplasties in vivo. This study examined four carbon‐based composite materials as alternatives for UHMWPE in joint bearings. These materials were HMU‐CVD, SMS‐CVD, P25‐CVD, and CFR‐PEEK. New bearing materials should satisfy certain criteria: they should have good wear properties that at least match UHMWPE, and produce wear particles with low levels of biological activity. Of the four materials tested in multidirectional pin‐on‐plate tribological tests, SMS‐CVD, P25‐CVD, and CFR‐PEEK showed lower volumetric wear factors than UHMWPE. P25‐CVD had the lowest wear factor of 0.54 ± 0.34 × 10−7 mm3/Nm. Analysis of P25‐CVD wear particles by transmission electron microscopy showed that the debris was very small, with the vast majority of particles being under 100 nm in size, which was similar in size to metal wear particles. The P25‐CVD particles were isolated and cultured with L929 fibroblasts and U937 monocytic cells to assess their effect on cell viability. P25‐CVD particles were significantly less cytotoxic (p < 0.01, ANOVA) to both cell types than CoCr metal wear particles. This work suggests that carbon–carbon composite materials may have potential for use in total hip replacement bearings. Of the materials tested P25‐CVD had the lowest wear factor, and produced very small wear debris that had minimal cytotoxic effect on L929 and U937 cells in vitro. Therefore carbon–carbon composites, such as P25‐CVD, may be important in the development of next‐generation implants with lower wear rates and reduced cytotoxic potential. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 67B: 758–764, 2003
In vitro cytotoxicity testing of AB‐polymer networks based on oligo(ϵ‐caprolactone) segments after different sterilization techniques
Authors: Rickert Dorothee , Lendlein A. , Schmidt A. M. , Kelch S. , Roehlke W. , Fuhrmann R. , Franke R. P. 
Published: October 2003

AbstractRecently developed versatile biodegradable polymeric biomaterial offer new therapeutic options in numerous medical fields. Biocompatibility is a crucial requirement for the biomedical application of biomaterials, including the sterilization of these materials with the use of accepted protocols. Ethylene‐oxide (EO) and low‐temperature plasma (LTP) sterilization are frequently used low‐temperature sterilization technologies for heat‐sensitive materials. The agarose diffusion assay is a recommended cell‐screening test to assess the cytotoxicity of biomaterials in vitro. The sensitivity of the agarose assay can be increased by using a modified computer‐based image‐analysis system. The influence of EO and LTP sterilization on the cytotoxicity of a versatile polymer system of shape‐memory polymer networks based on oligo (ϵ‐caprolactone) dimethacrylate and n‐butyl acrylate was investigated. Statistically significant differences in the rate of cell lysis after EO and LTP sterilization of the polymer samples were detected by using this modified quantification system. The influence of the different sterilization techniques on the cytotoxicity of the polymeric material, as well as the clinical relevance of the described differences, are discussed. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 67B: 722–731, 2003
The fall and rise of active chloride transport: Implications for regulation of intraocular pressure
Authors: Civan Mortimer M. 
Published: October 2003

AbstractEarly study of transepithelial salt transfer focused on Cl− and not Na+, partly because Cl− was readily measureable. The advent of flame photometry and tracer techniques brought Na+ to the fore, especially since short‐circuited frog skin (Rana temporaria) produces baseline net movement of Na+ and not of Cl−. Zadunaisky was among the first to describe what is currently termed secondary active Cl− transport, helping stimulate interest in Cl− handling by other tissues, notably the thick ascending limb of the loop of Henle important in renal counter‐current multiplication. More recently, molecules responsible for electroneutral and electrogenic Cl− transfer have been cloned, and specific diseases resulting from their faulty expression have been identified. The clinical importance of transepithelial Cl− transfer is illustrated by studies of aqueous humor formation by the eye's bilayered ciliary epithelium. NaCl is taken up from the stroma by the pigmented ciliary epithelial (PE) layer, diffuses through gap junctions into the nonpigmented ciliary epithelial (NPE) layer, and is released into the aqueous humor largely through Na+ pumps and Cl− channels. ATP released by NPE cells can be ecto‐enzymatically metabolized to adenosine. Adenosine can mediate paracrine/autocrine stimulation of Cl− channels and aqueous humor secretion by occupying A3 adenosine receptors (ARs). A3AR agonists indeed elevate, and A3AR antagonists lower, intraocular pressure (IOP) in wild‐type mice. A3AR knockout mice have low IOP and their responses to A3AR agonists and antagonists are blunted; this suggests that reducing Cl−‐channel activity with A3AR antagonists may provide a novel approach for treating glaucoma. J. Exp. Zool. 300A:5–13, 2003. © 2003 Wiley‐Liss, Inc.
Purinergic signaling in the rabbit ciliary body epithelium
Authors: Farahbakhsh Nasser A. 
Published: October 2003

AbstractIn the past forty years, a wealth of information has accumulated that points to the presence of adenosine and adenine nucleotides in the anterior segment of the eye and a number of hypotheses have been introduced to describe the possible role of these agents in the regulation of aqueous humor flow. However, in the absence of a generally accepted model for the cellular and molecular mechanisms of aqueous humor formation by the ciliary body epithelium, efforts to identify the signal transduction pathway(s) responsible for regulation of the ion and water transport have not been successful. This article briefly reviews the evidence for (i), the presence in aqueous humor of adenine nucleotides, cyclic adenosine monophosphate and adenosine, their metabolic product, (ii), the possible role of these agents in the regulation of aqueous humor dynamics, and (iii), the expression of ecto‐nucleotidases, receptors, and second messengers that may mediate such regulation. Finally, a model for the regulation of aqueous humor formation by adenosine and ATP is proposed. J. Exp. Zool. 300A:14–24, 2003. © 2003 Wiley‐Liss, Inc.
Cl− absorption in European eel intestine and its regulation
Authors: Schettino T. , Lionetto M.G. 
Published: October 2003

AbstractThe intestinal epithelium of the euryhaline teleost fish, Anguilla anguilla, absorbs Cl− transepithelially. This gives rise to a negative transepithelial potential at the basolateral side of the epithelium and to a measured short circuit current. Cl− absorption occurs via bumetanide‐sensitive Na+‐K+‐2Cl− cotransport, localized on the luminal membrane. The cotransport operates in parallel with a luminal K+ conductance that recycles the ion into the lumen. Cl− leaves the cell across the basolateral membrane by way of Cl− conductance and presumably via a KCl cotransport. The driving force for this process is provided by the electrochemical sodium gradient across the plasma membrane, generated and maintained by the basolateral Na+‐K+‐ATPase. The resulting NaCl absorption process is active and enables marine fish to take up water, thereby compensating for water that was lost passively from the body. Fresh water acclimatized eel also absorb Cl− actively, although in smaller quantities, utilizing the same ion transport mechanisms as marine eels. This mechanism is basically the same as the model proposed for the thick ascending limb (cTAL). Cl− absorption is regulated by a number of cellular factors, such as HCO3−, pH, Ca2+, cyclic nucleotides, and cytoskeletal elements. It is sensitive to osmotic stress, and therefore is a good physiological model to study ion transport mechanisms that are activated when osmotic stress induces cell volume regulation. The activation of these various ion transport pathways is dependent on cellular transduction mechanisms in which phosphorylation events (mainly by PKC and MLCK for the hypertonic response) and cytoskeletal elements, either microfilaments or microtubules, seem to play key roles. J. Exp. Zool. 300A:63–68, 2003 © 2003 Wiley‐Liss, Inc.
The xenobiotic transporter, MRP2, in epithelia from insects, sharks, and the human breast: Implications for health and disease
Authors: Karnaky Karl John , Hazen‐Martin Debra , Miller David S. 
Published: October 2003

AbstractA large number of mechanisms, including special excretory transporters, have evolved to help organisms excrete deleterious xenobiotics and endogenous molecules. We have examined the xenobiotic transport function of a putative multidrug resistance associated protein, MRP2, in three different epithelia: the insect renal (Malpighian) tubules, the secretory tubule of the shark rectal gland, and in ductules of the human breast. In the case of the insect and shark, transporter activity occurs in epithelia capable of great fluid transport. In the case of the insect Malpighian tubule, understanding the underlying mechanisms of this transporter may help with efforts to control populations of disease‐carrying agriculturally important insects. In striking contrast, ductule architecture in nonlactating human breast ductules is that of an epithelium with a closed lumen. Immunocytochemical studies show that MRP2 is localized in the apical region of the ductule epithelial cells. In this unique case, MRP2 substrates transported into the lumen could possibly be concentrated. Transport substrates of MRP2 include carcinogens as well as antioxidants and other salutary molecules. Thus, in the breast ductule, MRP2 may play a significant role in breast epithelial cell health and cancer carcinogenesis. J. Exp. Zool. 300A:91–97, 2003. © 2003 Wiley‐Liss, Inc.
Proteasome‐mediated degradation of the C‐terminus of the Alzheimer's disease β‐amyloid protein precursor: Effect of C‐terminal truncation on production of β‐amyloid protein
Authors: Nunan Janelle , Williamson Nicholas A. , Hill Andrew F. , Sernee M. Fleur , Masters Colin L. , Small David H. 
Published: October 2003

AbstractThe β‐amyloid protein (Aβ) is derived by proteolytic processing of the amyloid protein precursor (APP). Cleavage of APP by β‐secretase generates a C‐terminal fragment (APP‐CTFβ), which is subsequently cleaved by γ‐secretase to produce Aβ. Our previous studies have shown that the proteasome can cleave the C‐terminal cytoplasmic domain of APP. To identify proteasome cleavage sites in APP, two peptides homologous to the C‐terminus of APP were incubated with recombinant 20S proteasome. Cleavage of the peptides was monitored by reversed phase high‐performance liquid chromatography and mass spectrometry. Proteasome cleaved the APP C‐terminal peptides at several sites, including a region around the sequence YENPTY that interacts with several APP‐binding proteins. To examine the effect of this cleavage on Aβ production, APP‐CTFβ and mutant forms of APP‐CTFβ terminating on either side of the YENPTY sequence were expressed in CHO cells. Truncation of APP‐CTFβ on the N‐terminal side of the YENPTY sequence at residue 677 significantly decreased the amount of Aβ produced, whereas truncation on the C‐terminal side of residue 690 had little effect. The results suggest that proteasomal cleavage of the cytosolic domain of APP at the YENPTY sequence decreases γ‐secretase processing, and consequently inhibits Aβ production. Therefore, the proteasome‐dependent trafficking pathway of APP may be a valid therapeutic target for altering Aβ production in the Alzheimer's disease brain. © 2003 Wiley‐Liss, Inc.
Regulators of the neuropeptide‐degrading enzyme, EC 3.4.24.15 (thimet oligopeptidase), in cerebrospinal fluid
Authors: Shrimpton Corie N. , Wolfson Adele J. , Smith A. Ian , Lew Rebecca A. 
Published: October 2003

AbstractEndopeptidase EC 3.4.24.15 (EP 24.15; thimet oligopeptidase) is a soluble metalloendopeptidase implicated in the metabolism of a number of neuropeptides, including neurotensin, gonadotropin‐releasing hormone, and opioid peptides. We have shown previously that thiol reducing agents, such as dithiothreitol, activate EP 24.15 by mediating the conversion of inactive multimeric forms to active monomers and that this conversion involves the disruption of intermolecular disulfide bonds involving cysteine residues 246, 248, and 253. We have identified two components of cerebrospinal fluid that activate recombinant EP 24.15, but have no effect on a thiol‐independent cysteine mutant form of the enzyme. The low molecular weight (<10 kDa) component co‐elutes with glutathione by reversed‐phase HPLC, whereas the high molecular weight component (>50 kDa) is sensitive to digestion with trypsin, suggesting it is proteinaceous in nature. These results suggest that EP 24.15 activity in the brain may be modulated by factors released into cerebrospinal fluid. © 2003 Wiley‐Liss, Inc.
ADAMs family members as amyloid precursor protein α‐secretases
Authors: Allinson Tobias M.J. , Parkin Edward T. , Turner Anthony J. , Hooper Nigel M. 
Published: October 2003

AbstractIn the non‐amyloidogenic pathway, the Alzheimer's amyloid precursor protein (APP) is cleaved within the amyloid‐β domain by α‐secretase precluding deposition of intact amyloid‐β peptide. The large ectodomain released from the cell surface by the action of α‐secretase has several neuroprotective properties. Studies with protease inhibitors have shown that α‐secretase is a zinc metalloproteinase, and several members of the adamalysin family of proteins, tumour necrosis factor‐α convertase (TACE, ADAM17), ADAM10, and ADAM9, all fulfil some of the criteria required of α‐secretase. We review the evidence for each of these ADAMs acting as the α‐secretase. What seems to be emerging from numerous studies, including those with mice in which each of the ADAMs has been knocked out, is that there is a team of zinc metalloproteinases able to cleave APP at the α‐secretase site. We also discuss how upregulation of α‐secretase activity by muscarinic agonists, cholesterol‐lowering drugs, steroid hormones, non‐steroidal anti‐inflammatory drugs, and metal ions may explain some of the therapeutic actions of these agents in Alzheimer's disease. © 2003 Wiley‐Liss, Inc.
Caspase regulation of genotoxin‐induced neural precursor cell death
Authors: D'Sa Cleta , Klocke Barbara J. , Cecconi Francesco , Lindsten Tulia , Thompson Craig B. , Korsmeyer Stanley J. , Flavell Richard A. , Roth Kevin A. 
Published: October 2003

AbstractNeural precursor cells (NPCs) critically regulate brain morphogenesis and recent studies have revealed an unexpectedly high frequency of NPC chromosomal abnormalities and apoptosis in the developing brain. We have shown previously that the apoptotic response of NPCs to genotoxic agents is dependent on p53 and caspase‐9, but not Bax or caspase‐3 expression. In this study, we found that NPCs deficient in Apaf‐1, or both the pro‐apoptotic multidomain Bcl‐2 family members Bax and Bak, were resistant to cytosine arabinoside and γ‐irradiation‐induced apoptosis. Inhibitors of gene transcription, protein translation, and caspase activity also blocked genotoxin‐induced NPC apoptosis. Although caspase‐3 and caspase‐6 were both cleaved in response to DNA damage, neither of these effector caspases was critical for apoptosis. Genotoxin‐induced NPC death was accompanied by the generation of reactive oxygen species and could be inhibited by several known antioxidants. Conversely, DNA damage‐induced reactive oxygen species generation was inhibited significantly by gene disruption of p53, Apaf‐1, or caspase‐9, and combined deficiency of Bax and Bak, but not by caspase‐3 or caspase‐6 deficiency. These studies suggest that caspase‐9 activation is both necessary and sufficient for genotoxin‐induced neural precursor cell reactive oxygen species generation and death. © 2003 Wiley‐Liss, Inc.
Role of proteolysis in polyglutamine disorders
Authors: Tarlac V. , Storey E. 
Published: October 2003

AbstractTo date, nine polyglutamine disorders have been characterised, including Huntington's disease (HD), spinobulbar muscular atrophy (SBMA), dentatorubral‐pallidoluysian atrophy (DRPLA), and spinocerebellar ataxias 1, 2, 3, 6, 7 and 17 (SCAs). Although knockout and transgenic mouse experiments suggest that a toxic gain of function is central to neuronal death in these diseases (with the probable exception of SCA6), the exact mechanisms of neurotoxicity remain contentious. A further conundrum is the characteristic distribution of neuronal damage in each disease, despite ubiquitous expression of the abnormal proteins. One mechanism that could possibly underlie the specific distribution of neuronal toxicity is proteolytic cleavage of the full‐length expanded polyglutamine tract‐containing proteins. There is evidence found in vitro or in vivo (or both) of proteolytic cleavage in HD, SBMA, DRPLA, and SCAs 2, 3, and 7. In HD, cleavage has been demonstrated to be regionally specific, occurring as a result of caspase activation. These diseases are also characterised by development of intraneuronal aggregates of the abnormal protein that co‐localise with components of the ubiquitin‐proteasome pathway. It remains unclear whether these aggregates are pathogenic or merely disease markers; however, at least in the case of ataxin‐3, cleavage promotes aggregation. Inhibition of specific proteases constitutes a potential therapeutic approach in these diseases. © 2003 Wiley‐Liss, Inc.
JLK isocoumarin inhibitors: Selective γ‐secretase inhibitors that do not interfere with notch pathway in vitro or in vivo
Authors: Petit A. , Pasini A. , Alves da Costa C. , Ayral E. , Hernandez J.F. , Dumanchin‐Njock C. , Phiel C.J. , Marambaud P. , Wilk S. , Farzan M. , Fulcrand P. , Martinez J. , Andrau D. , Checler F. 
Published: October 2003

Abstractγ‐Secretase activity is involved in the generation of Aβ and therefore likely contributes to the pathology of Alzheimer's disease. Blocking this activity was seen as a major therapeutic target to slow down or arrest Aβ‐related AD progression. This strategy seemed more doubtful when it was established that γ‐secretase also targets other substrates including Notch, a particularly important transmembrane protein involved in vital functions, at both embryonic and adulthood stages. We have described previously new non‐peptidic inhibitors able to selectively inhibit Aβ cellular production in vitro without altering Notch pathway. We show here that in vivo, these inhibitors do not alter the Notch pathway responsible for somitogenesis in the zebrafish embryo. In addition, we document further the selectivity of JLK inhibitors by showing that, unlike other described γ‐secretase inhibitors, these agents do not affect E‐cadherin processing. Finally, we establish that JLKs do not inhibit β‐site APP cleaving enzymes (BACE) 1 and BACE2, α‐secretase, the proteasome, and GSK3β kinase. Altogether, JLK inhibitors are the sole agents to date that are able to prevent Aβ production without triggering unwanted cleavages of other proteins. © 2003 Wiley‐Liss, Inc.
Consolidation of memory for odour‐reward association requires transient polysialylation of the neural cell adhesion molecule in the rat hippocampal dentate gyrus
Authors: Foley Andrew G. , Hedigan Kate , Roullet Pascal , Moricard Yves , Murphy Keith J. , Sara Susan J. , Regan Ciaran M. 
Published: October 2003

AbstractCell adhesion molecule function is involved in hippocampal synaptic plasticity and is associated with memory consolidation. At the infragranular zone of the dentate gyrus, neurons expressing the polysialylated form of the neural cell adhesion molecule (NCAM PSA) transiently increase their frequency at the 12‐hr posttraining time in behaviours elicited by stressful stimuli, such as those associated with conditioned avoidance, water maze, and fear conditioning paradigms. To determine whether learning‐induced modulation of NCAM polysialylation is limited to stressful paradigms, we employed a reward‐based odour discrimination task. Animals show a rapid acquisition and recall of this task in terms of latency to identify the food‐associated odour and the number of choice errors. Immunohistochemical procedures were employed to determine the change in NCAM PSA expression following task acquisition. NCAM PSA immunoreactivity in the hippocampal formation was most intense on the granule‐like neurons in the infragranular zone of the dentate gyrus, and their frequency transiently increased in the 12‐hr posttraining period. The nature of the transient increase in NCAM PSA‐immunoreactive neurons was indistinguishable from that observed following avoidance conditioning or spatial learning, in that it occurred at the same time. The transient increase in NCAM PSA expression is suggested to facilitate dendritic elaboration in response to the acquisition of novel behavioural repertoires. © 2003 Wiley‐Liss, Inc.