Lashuel, H. A., D. Hartley, et al. (2002). "Neurodegenerative disease: amyloid pores from pathogenic mutations." Nature 418(6895): 291. Alzheimer's and Parkinson's diseases are associated with the formation in the brain of amyloid fibrils from beta-amyloid and alpha-synuclein proteins, respectively. It is likely that oligomeric fibrillization intermediates (protofibrils), rather than the fibrils themselves, are pathogenic, but the mechanism by which they cause neuronal death remains a mystery. We show here that mutant amyloid proteins associated with familial Alzheimer's and Parkinson's diseases form morphologically indistinguishable annular protofibrils that resemble a class of pore-forming bacterial toxins, suggesting that inappropriate membrane permeabilization might be the cause of cell dysfunction and even cell death in amyloid diseases. Albers, D. S. and M. F. Beal (2002). "Mitochondrial dysfunction in progressive supranuclear palsy." Neurochem Int 40(6): 559-64. A progressive impairment of mitochondrial function has been suggested to play a critical role in the pathogenesis of several neurodegenerative diseases, including Parkinson's disease, Alzheimer's disease and Huntington's disease. Mitochondrial dysfunction can lead to number of deleterious consequences including impaired calcium buffering, generation of free radicals, activation of the mitochondrial permeability transition pore and secondary excitotoxicity. Progressive supranuclear palsy (PSP) is a rare neurological disorder characterized by the appearance of supranuclear gaze palsy and extrapyramidal symptoms [Arch. Neurol. 10 (1964) 333]. Although the etiological basis of PSP is unknown, compelling evidence from spectroscopy studies in PSP patients, biochemical studies in post-mortem PSP brain tissue and PSP cybrids has emerged that supports a contributory role of bio-energetic defects in the pathogenesis of PSP. Abramova, N. A., D. S. Cassarino, et al. (2002). "Inhibition by R(+) or S(-) pramipexole of caspase activation and cell death induced by methylpyridinium ion or beta amyloid peptide in SH-SY5Y neuroblastoma." J Neurosci Res 67(4): 494-500. Cell models of neurodegenerative diseases (NDD) can involve expression of mutant nuclear genes associated with Mendelian forms of the diseases or effects of toxins believed to replicate essential disease features. Death produced by exposing neural cells to methylpyridinium ion (MPP(+)) or neurotoxic beta amyloid (BA) peptides is frequently used to study features of the sporadic, most prevalent forms of Parkinson's disease (PD) and Alzheimer's disease (AD), respectively. We examined in replicating SH-SY5Y human neuroblastoma cells the release of cytochrome C into cytoplasm, activation of caspases 9 and 3, and loss of calcein retention as markers of the "mitochondrial" pathway of cell death. Exposure to 5 mM MPP(+), which induces apoptotic cell death within 18-24 hr, released cytochrome C within 4 hr, activated caspases 9 and 3, and reduced calcein accumulation. BA 25-35 peptide produced more rapid and greater elevations of caspase 3 activity; no effects were observed with the nontoxic BA 35-25 reverse sequence. The dependence on mitochondrial transition pore (MTP) activity of MPP(+)-induced caspase activations was demonstrated by preincubation with bongkreckic acid, which blocked elevations of caspases 9 and 3. Stereoisomers of pramipexole (PPX), a free radical scavenger and inhibitor of MTP opening, inhibited caspase activation (MPP(+) and BA) and restored calcein accumulation (MPP(+)). Our results demonstrate that MPP(+) and BA can induce cell death through MTP-dependent activation of caspase cascades. PPX stereoisomers interfere with activation of these cell death pathways and may be useful clinically as neuroprotectants in PD and AD and related diseases. Youdim, M. B. and M. Weinstock (2001). "Molecular basis of neuroprotective activities of rasagiline and the anti-Alzheimer drug TV3326 [(N-propargyl-(3R)aminoindan-5-YL)-ethyl methyl carbamate]." Cell Mol Neurobiol 21(6): 555-73. Rasagiline (N-propargyl-1-(R)-aminoindan) is a selective, irreversible monoamine oxidase B (MAO B) inhibitor which has been developed as an anti-Parkinson drug. In controlled monotherapy and as adjunct to L-dopa it has shown anti-Parkinson activity. In cell culture (PC-12 and neuroblastoma SH-SY5Y cells) it exhibits neuroprotective and anti-apoptotic activity against several neurotoxins (SIN-1, MPTP, 6-hydroxydopamine and N-methyl-(R)-salsolinol) and ischemia. In vivo, it reduces the sequelae of traumatic brain injury in mice and speeds their recovery. The neuroprotective activity of rasagaline does not result from MAO B inhibition, since its S-enantiomer, TVP1022, which has 1000-fold weaker MAO inhibitory activity, exhibits similar neuroprotective properties. Introduction of a carbamate moiety into the rasagiline molecule to confer cholinesterase inhibitory activity for the treatment of Alzheimer's disease, resulted in compounds TV3326 [(N-Propargyl-(3R)Aminoindan-5-YL)-Ethyl Methyl Carbamate] and its S-enantiomer TV3279 [(N-Propargyl-(3S)Aminoindan-5-YL)-Ethyl Methyl Carbamate], which retain the neuroprotective activities of rasagiline and TVP1022. They also antagonize scopolamine-induced impairments in spatial memory. In addition, TV3326 exhibits brain-selective MAO A and B inhibitory activity after chronic administration and has antidepressant-like activity in the forced swim test. This is associated with an increase in brain levels of serotonin. The anti-apoptotic activity of these propargylamine-containing derivatives may be related to their ability to delay the opening of voltage-dependent anion channels (VDAC), which are part of the mitochondrial permeability transition pore. The propargylamine moiety is responsible for the increase in the mitochondrial family of Bcl-2 proteins, prevention in the fall in mitochondrial membrane potential, prevention of the activation of caspase 3, and of translocation of glyceraldehyde-3-phosphate dehydrogenase from the cytoplasm to the nucleus. The latter processes are closely associated with neurotoxin-induced apoptosis. Rasagiline interacts with and prevents the binding of PKI 1195 to the pro-apoptotic peripheral benzodiazepine receptor, which together with Bcl-2, hexokinase, porin, and adenine nucleotide translocator constitutes part of the VDAC. Furthermore, rasagiline, TV3326 and TV3279 are able to influence the processing of amyloid precursor protein by activation of alpha-secretase and increasing the release of soluble alpha APP in rat PC-12 and human neuroblastoma SH-SY5Y cells and in rat and mice cortex and hippocampus. This process has been shown to involve the upregulation of PKC and MAP kinase. It is quite likely that the induction of Bcl-2 and activation of PKC by rasagiline and TV3326 is closely linked to the anti-apoptotic action of these drugs and their ability to process APP by activation of alpha-secretase. Yoo, B. C., M. Fountoulakis, et al. (2001). "Changes of voltage-dependent anion-selective channel proteins VDAC1 and VDAC2 brain levels in patients with Alzheimer's disease and Down syndrome." Electrophoresis 22(1): 172-9. Voltage-dependent anion-selective channel proteins (VDACs) are pore-forming proteins found in the other mitochondrial membrane of all eukaryotes and in brain postsynaptic membranes. VDACs regulate anion fluxes of a series of metabolites including ATP, thus regulating mitochondrial metabolic functions. We determined protein levels of VDACs in individual post-mortem brain regions of patients with Down Syndrome (DS) and Alzheimer's disease (AD) using two-dimensional electrophoresis (2-DE) and matrix-assisted laser desorption/ionization-mass spectroscopy (MALDI-MS). VDAC1 (SWISS-PROT accession number P21796) and VDAC2 (P45880) were unambiguously identified and quantified, but VDAC3 was not found. The spots representing VDAC1 were separated with different p/s (p/7.5, 8.5, and 10.0) probably caused by post-translational modifications as, e.g., phosphorylation. In DS cerebellum, total VDAC1 protein was elevated significantly whereas VDAC2 did not show any significant alterations. In AD brains, VDAC1 p/10.0 was significantly reduced in temporal, frontal, and occipital cortex with the p/7.5 form elevated in occipital cortex. Total VDAC1 was significantly decreased in frontal cortex and thalamus. VDAC2 was significantly elevated in temporal cortex only. The biological meaning of our results may be derangement of voltage-dependent anion-selective channel function and reflecting impaired glucose, energy, and intermediary metabolism as well as apoptotic mechanisms. Tang, X. D., H. Daggett, et al. (2001). "Oxidative regulation of large conductance calcium-activated potassium channels." J Gen Physiol 117(3): 253-74. Reactive oxygen/nitrogen species are readily generated in vivo, playing roles in many physiological and pathological conditions, such as Alzheimer's disease and Parkinson's disease, by oxidatively modifying various proteins. Previous studies indicate that large conductance Ca(2+)-activated K(+) channels (BK(Ca) or Slo) are subject to redox regulation. However, conflicting results exist whether oxidation increases or decreases the channel activity. We used chloramine-T, which preferentially oxidizes methionine, to examine the functional consequences of methionine oxidation in the cloned human Slo (hSlo) channel expressed in mammalian cells. In the virtual absence of Ca(2+), the oxidant shifted the steady-state macroscopic conductance to a more negative direction and slowed deactivation. The results obtained suggest that oxidation enhances specific voltage-dependent opening transitions and slows the rate-limiting closing transition. Enhancement of the hSlo activity was partially reversed by the enzyme peptide methionine sulfoxide reductase, suggesting that the upregulation is mediated by methionine oxidation. In contrast, hydrogen peroxide and cysteine-specific reagents, DTNB, MTSEA, and PCMB, decreased the channel activity. Chloramine-T was much less effective when concurrently applied with the K(+) channel blocker TEA, which is consistent with the possibility that the target methionine lies within the channel pore. Regulation of the Slo channel by methionine oxidation may represent an important link between cellular electrical excitability and metabolism. Stolz, M., D. Stoffler, et al. (2000). "Monitoring biomolecular interactions by time-lapse atomic force microscopy." J Struct Biol 131(3): 171-80. The atomic force microscope (AFM) is a unique imaging tool that enables the tracking of single macromolecule events in response to physiological effectors and pharmacological stimuli. Direct correlation can therefore be made between structural and functional states of individual biomolecules in an aqueous environment. This review explores how time-lapse AFM has been used to learn more about normal and disease-associated biological processes. Three specific examples have been chosen to illustrate the capabilities of this technique. In the cell, actin polymerizes into filaments, depolymerizes, and undergoes interactions with numerous effector molecules (i.e., severing, capping, depolymerizing, bundling, and cross-linking proteins) in response to many different stimuli. Such events are critical for the function and maintenance of the molecular machinery of muscle contraction and the dynamic organization of the cytoskeleton. One goal is to use time-lapse AFM to examine and manipulate some of these events in vitro, in order to learn more about how these processes occur in the cell. Aberrant protein polymerization into amyloid fibrils occurs in a multitude of diseases, including Alzheimer's and type 2 diabetes. Local amyloid deposits may cause organ dysfunction and cell death; hence, it is of interest to learn how to interfere with fibril formation. One application of time-lapse AFM in this area has been the direct visualization of amyloid fibril growth in vitro. This experimental approach holds promise for the future testing of potential therapeutic drugs, for example, by directly visualizing at which level of fibril assembly (i.e., nucleation, elongation, branching, or lateral association of protofibrils) a given active compound will interfere. Nuclear pore complexes (NPCs) are large supramolecular assemblies embedded in the nuclear envelope. Transport of ions, small molecules, proteins, RNAs, and RNP particles in and out of the nucleus occurs via NPCs. Time-lapse AFM has been used to structurally visualize the response of individual NPC particles to various chemical and physical effectors known to interfere with nucleocytoplasmic transport. Taken together, such time-lapse AFM studies could provide novel insights into the molecular mechanisms of fundamental biological processes under both normal and pathological conditions at the single molecule level. Rodrigues, C. M., S. Sola, et al. (2000). "Bilirubin and amyloid-beta peptide induce cytochrome c release through mitochondrial membrane permeabilization." Mol Med 6(11): 936-46. BACKGROUND: The pathogenesis of bilirubin encephalopathy and Alzheimer's disease appears to result from accumulation of unconjugated bilirubin (UCB) and amyloid-beta (Abeta) peptide, respectively, which may cause apoptosis. Permeabilization of the mitochondrial membrane, with release of intermembrane proteins, has been strongly implicated in cell death. Inhibition of the mitochondrial permeability is one pathway by which ursodeoxycholate (UDC) and tauroursodeoxycholate (TUDC) protect against apoptosis in hepatic and nonhepatic cells. In this study, we further characterize UCB- and Abeta-induced cytotoxicty in isolated neural cells, and investigate membrane perturbation during incubation of isolated mitochondria with both agents. In addition, we evaluate whether the anti-apoptotic drugs UDC and TUDC prevent any changes from occurring. MATERIALS AND METHODS: Primary rat neuron and astrocyte cultures were incubated with UCB or Abeta peptide, either alone or in the presence of UDC. Apoptosis was assessed by DNA fragmentation and nuclear morphological changes. Isolated mitochondria were treated with each toxic, either alone or in combination with UDC, TUDC, or cyclosporine A. Mitochondrial swelling was measured spectrophotometrically and cytochrome c protein levels determined by Western blot. RESULTS: Incubation of neural cells with both UCB and Abeta induced apoptosis (p < 0.01). Coincubation with UDC reduced apoptosis by > 50% (p < 0.05). Both toxins caused membrane permeabilization in isolated mitochondria (p < 0.001); whereas, pretreatment with UDC was protective (p < 0.05). TUDC was even more effective at preventing matrix swelling mediated by Abeta (p < 0.01). UDC and TUDC markedly reduced cytochrome c release associated with mitochondrial permeabilization induced by UCB and Abeta, respectively (p < 0.05). Moreover, cyclosporine A significantly inhibited mitochondrial swelling and cytochrome c efflux mediated by UCB (p < 0.05). CONCLUSION: UCB and Abeta peptide activate the apoptotic machinery in neural cells. Toxicity occurs through a mitochondrial-dependent pathway, which in part involves opening of the permeability transition pore. Furthermore, membrane permeabilization is required for cytochrome c release from mitochondria and can be prevented by UDC or TUDC. These data suggest that the mitochondria is a pharmacological target for cytoprotection during unconjugated hyperbilirubinemia and neurodegenerative disorders, and that UDC or TUDC may be potential therapeutic agents. Ham, D. and H. M. Schipper (2000). "Heme oxygenase-1 induction and mitochondrial iron sequestration in astroglia exposed to amyloid peptides." Cell Mol Biol (Noisy-le-grand) 46(3): 587-96. The mechanisms responsible for pathological iron deposition and mitochondrial insufficiency that have been documented in the brains of Alzheimer (AD) patients remain poorly understood. In the present study, we demonstrate that low-micromolar concentrations of amyloid1-40 (A40) and amyloid 1-42 (A42), peptides implicated in the pathogenesis of AD, increase levels of heme oxygenase-1 (HO-1) mRNA and protein in cultured rat astroglia. Furthermore, 6 days of exposure to amyloid augments the sequestration of 55FeCl3-derived iron by astroglial mitochondria without affecting the disposition of this metal in whole-cell and lysosomal compartments. Mitochondrial iron deposition was not observed in the amyloid-treated glia when diferric-transferrin served as the metal donor. We had previously shown that inhibitors of HO-1 and the mitochondrial permeability transition pore (MTP) block the uptake of mitochondrial iron in astrocytes exposed to the pro-oxidant effects of dopamine and several pro-inflammatory cytokines. Similarly, in the current study, amyloid-induced mitochondrial iron trapping was significantly attenuated by co-administration of the HO-1 transcriptional suppressor, dexamethasone (DEX) or the MTP blocker, cyclosporin A (CSA). Thus, the marked enhancement of HO-1 expression previously demonstrated in AD-affected neurons and astroglia may transduce amyloid (oxidative) stress into the abnormal patterns of iron deposition and mitochondrial insufficiency characteristic of this disease. Finally, in experiments employing cytotoxic concentrations of A40, we provide evidence that inhibition of HO-1 transcription and related mitochondrial iron deposition may be an important mechanism by which DEX protects tissues subjected to amyloid stress. Deigner, H. P., U. Haberkorn, et al. (2000). "Apoptosis modulators in the therapy of neurodegenerative diseases." Expert Opin Investig Drugs 9(4): 747-64. Apoptosis is a prerequisite to model the developing nervous system. However, an increased rate of cell death in the adult nervous system underlies neurodegenerative disease and is a hallmark of multiple sclerosis (MS) Alzheimer's- (AD), Parkinson- (PD), or Huntington's disease (HD). Cell surface receptors (e.g., CD95/APO-1/Fas; TNF receptor) and their ligands (CD95-L; TNF) as well as evolutionarily conserved mechanisms involving proteases, mitochondrial factors (e.g. , Bcl-2-related proteins, reactive oxygen species, mitochondrial membrane potential, opening of the permeability transition pore) or p53 participate in the modulation and execution of cell death. Effectors comprise oxidative stress, inflammatory processes, calcium toxicity and survival factor deficiency. Therapeutic agents are being developed to interfere with these events, thus conferring the potential to be neuroprotective. In this context, drugs with anti-oxidative properties, e.g., flupirtine, N-acetylcysteine, idebenone, melatonin, but also novel dopamine agonists (ropinirole and pramipexole) have been shown to protect neuronal cells from apoptosis and thus have been suggested for treating neurodegenerative disorders like AD or PD. Other agents like non-steroidal anti-inflammatory drugs (NSAIDs) partly inhibit cyclooxygenase (COX) expression, as well as having a positive influence on the clinical expression of AD. Distinct cytokines, growth factors and related drug candidates, e.g., nerve growth factor (NGF), or members of the transforming growth factor-beta (TGF-beta ) superfamily, like growth and differentiation factor 5 (GDF-5), are shown to protect tyrosine hydroxylase or dopaminergic neurones from apoptosis. Furthermore, peptidergic cerebrolysin has been found to support the survival of neurones in vitro and in vivo. Treatment with protease inhibitors are suggested as potential targets to prevent DNA fragmentation in dopaminergic neurones of PD patients. Finally, CRIB (cellular replacement by immunoisolatory biocapsule) is an auspicious gene therapeutical approach for human NGF secretion, which has been shown to protect cholinergic neurones from cell death when implanted in the brain. This review summarises and evaluates novel aspects of anti-apoptotic concepts and pharmacological intervention including gene therapeutical approaches currently being proposed or utilised to treat neurodegenerative diseases. Cassarino, D. S. and J. P. Bennett, Jr. (1999). "An evaluation of the role of mitochondria in neurodegenerative diseases: mitochondrial mutations and oxidative pathology, protective nuclear responses, and cell death in neurodegeneration." Brain Res Brain Res Rev 29(1): 1-25. There is mounting evidence for mitochondrial involvement in neurodegenerative diseases including Alzheimer's and Parkinson's disease and amyotrophic lateral sclerosis. Mitochondrial DNA mutations, whether inherited or acquired, lead to impaired electron transport chain (ETC) functioning. Impaired electron transport, in turn, leads to decreased ATP production, formation of damaging free-radicals, and altered calcium handling. These toxic consequences of ETC dysfunction lead to further mitochondrial damage including oxidation of mitochondrial DNA, proteins, and lipids, and opening of the mitochondrial permeability transition pore, an event linked to cell death in numerous model systems. Although protective nuclear responses such as antioxidant enzymes and bcl-2 may be induced to combat these pathological changes, such a vicious cycle of increasing oxidative damage may insidiously damage neurons over a period of years, eventually leading to neuronal cell death. This hypothesis, a synthesis of the mitochondrial mutations and oxidative stress hypotheses of neurodegeneration, is readily tested experimentally, and clearly points out many potential therapeutic targets for preventing or ameliorating these diseases. Tatton, W. G. and R. M. Chalmers-Redman (1998). "Mitochondria in neurodegenerative apoptosis: an opportunity for therapy?" Ann Neurol 44(3 Suppl 1): S134-41. Apoptotic cell death has been shown to constitute the terminal process in some neurodegenerative diseases, notably Alzheimer's disease and Parkinson's disease (PD). A decrease in mitochondrial membrane potential (delta psiM) causing opening of the permeability transition pore (PTP) in mitochondrial membranes has been implicated as a critical effector of apoptosis in a variety of non-neural cells. Opening of the PTP leads to the release of so-called apoptosis initiation factors that induce the degradative events of apoptosis, such as nuclear chromatin condensation and DNA fragmentation. We have extended those findings to a neuronal model of apoptosis caused by trophic withdrawal, by showing that a decrease in delta psiM is an early event occurring 2 to 6 hours before the degradative events of apoptosis. A deficiency in mitochondrial complex I activity has been demonstrated in the substantia nigra of postmortem brains and several peripheral tissues obtained from PD patients. Because delta psiM is generated by the pumping of protons out across the inner mitochondrial membrane at the mitochondrial complexes, particularly complex I, we hypothesized that the decrease in complex activity could result in a decrease in delta psiM that would render PD substantia nigra neurons vulnerable to apoptosis. In preliminary studies, we have found a decrease in delta psiM in fibroblasts obtained from some PD patients. If a decrease in delta psiM consequent on decreased complex activity is an intrinsic defect in some PD patients, it would open a number of new avenues for the reduction of neuronal apoptosis in PD. The oncoprotein BCL-2 and the scavenger protein SOD-1 have been shown to reduce apoptosis by facilitating closure of the PTP. A number of agents have been shown to maintain BCL-2 and/or SOD-1 synthesis in damaged nerve cells and thereby reduce apoptosis. Other agents, such as cyclosporin A and some benzodiazepine receptor-binding agents, have been found to act directly on the PTP to reduce apoptosis. Accordingly, agents that maintain delta psiM and PTP closure may offer new and effective means of treating neurodegenerative apoptosis. Malin, S. A., W. X. Guo, et al. (1998). "Presenilins upregulate functional K+ channel currents in mammalian cells." Neurobiol Dis 4(6): 398-409. Mutations in presenilin 1 (PS-1) and presenilin 2 (PS-2) have been linked to early onset, autosomal dominant Alzheimer's disease. Neither the normal function(s) of the presenilins nor their role(s) in mediating the devastating neurological and pathological changes associated with Alzheimer's Disease, however, are well understood. The results of the experiments described here demonstrate that expression of wild-type PS-1 or PS-2 increases outward K+ current densities in HEK-293 cells relative to untransfected or mock-transfected cells. Western blot analysis reveals that there is a marked increase in full-length, rather than processed, presenilins in transiently transfected HEK-293 cells, suggesting that full-length PS-1 (or PS-2) underlies the observed increases in outward K+ current densities. Consistent with this hypothesis, EXpression of an N-terminal proteolytic fragment of PS-1 is without effects on the membrane properties of HEK-293 cells. Mean outward K+ current densities are also shown to be increased in HEK-293 cells expressing the exon 9 splice site PS-1 mutation (deltaex9/PS-1), a mutant that does not undergo proteolytic processing.In HEK- 293 cells transiently transfected with a missense (G209V) PS-1 mutant, however, mean K+ current densities were not significantly different from controls. Expression of wild-type PS-1 in neonatal rat ventricular myocytes also results in increased outward K+ currents, whereas no detectable effects on membrane currents were seen in PS-1-transfected COS-7 cells. These results suggest that the presenilins do not actually form K+ channels, but rather that these proteins upregulate functional K+ channel expression either directly by associating with K+ channel pore-forming subunits or indirectly by increasing the synthesis, assembly, and/or transport of these subunits. The observation that PS-1 and PS-2 are highly expressed in neurons, localized to the endoplasmic reticulum, suggests that the presenilins could regulate neuronal K+ channel expression; mutations in PS-1/PS-2 would then be expected to result in profound changes in neuronal excitability and contribute to the cognitive decline commonly associated with Alzheimer's Disease. Cassarino, D. S., R. H. Swerdlow, et al. (1998). "Cyclosporin A increases resting mitochondrial membrane potential in SY5Y cells and reverses the depressed mitochondrial membrane potential of Alzheimer's disease cybrids." Biochem Biophys Res Commun 248(1): 168-73. Alzheimer's disease (AD) brains exhibit oxidative stress and a biochemical defect of complex IV (cytochrome oxidase, COX) of the mitochondrial electron transport chain (ETC). This defect can be transferred through mitochondrial DNA (mtDNA) into clonal SY5Y cells depleted of their mtDNA. The resulting cytoplasmic hybrids or "cybrids" retain the complex IV defect and exhibit oxidative stress. We measured the mitochondrial membrane potential (delta psi m) in AD and control cybrids via H3-tetraphenylphosphonium ion (H3-TPP+) accumulation. AD cybrids exhibited a significant (about 30%) decrease in H3-TPP+ accumulation relative to controls. Acute treatment of normal SY5Ys with azide, a COX inhibitor, moderately decreased H3-TPP+ retention and strongly inhibited COX activity in a dose-dependent manner. As the mitochondrial transition pore (MTP) can be activated by reactive oxygen species and ETC inhibitors, and its opening causes delta psi m dissipation, we tested the effects of the MTP inhibitor cyclosporin A (CsA) on TPP+ accumulation. 5mM CsA increased basal H3-TPP+ accumulation in SY5Y cells about 10-fold, corresponding to about a 2-fold increase in delta psi m. In the AD cybrids, CsA increased the apparent delta psi m to the same final levels as it did in controls. These results indicate that low-conductance MTP activity contributes significantly to resting delta psi m in SY5Y cells. We propose the novel hypothesis that the COX defect and resulting oxidative stress in AD may pathologically activate the MTP, resulting in lower delta psi m and the release of mitochondrial factors involved in apoptosis.