Antioxidants prevent amyloid peptide-induced apoptosis and alteration of calcium homeostasis in cultured cortical neurons

Inhibitory Activities of Sesame Seed Extract and its Constituents against β-Secretase

The need for a preventive agent against dementia led us to screen natural plant resources. Among the herbs and spices tested, sesame seed prepared from Sesamum indicum seeds showed potent β-secretase inhibitory activity. The active principles were determined to be sesamin and sesamolin, typical lignans in S. indicum. The IC50 values of sesamin and sesamolin were 257 and 140 μM, respectively. These compounds were investigated in a preliminary absorption experiment. After oral administration, these compounds were detected in an intact form in the brain and serum. These results suggest that consumption of sesame seeds may prevent dementia by sesamin and sesamolin, the constituents in sesame seeds.

Oxidative stress involving changes in Nrf2 and ER stress in early stages of Alzheimer's disease

Oxidative stress and endoplasmic reticulum (ER) stress have been associated with Alzheimer's disease (AD) progression. In this study we analyzed whether oxidative stress involving changes in Nrf2 and ER stress may constitute early events in AD pathogenesis by using human peripheral blood cells and an AD transgenic mouse model at different disease stages. Increased oxidative stress and increased phosphorylated Nrf2 (p(Ser40)Nrf2) were observed in human peripheral blood mononuclear cells (PBMCs) isolated from individuals with mild cognitive impairment (MCI). Moreover, we observed impaired ER Ca2+ homeostasis and increased ER stress markers in PBMCs from MCI individuals and mild AD patients. Evidence of early oxidative stress defense mechanisms in AD was substantiated by increased p(Ser40)Nrf2 in 3month-old 3xTg-AD male mice PBMCs, and also with increased nuclear Nrf2 levels in brain cortex. However, SOD1 protein levels were decreased in human MCI PBMCs and in 3xTg-AD mice brain cortex; the latter further correlated with reduced SOD1 mRNA levels. Increased ER stress was also detected in the brain cortex of young female and old male 3xTg-AD mice. We demonstrate oxidative stress and early Nrf2 activation in AD human and mouse models, which fails to regulate some of its targets, leading to repressed expression of antioxidant defenses (e.g., SOD-1), and extending to ER stress. Results suggest markers of prodromal AD linked to oxidative stress associated with Nrf2 activation and ER stress that may be followed in human peripheral blood mononuclear cells.

ITH12410/SC058: a new neuroprotective compound with potential in the treatment of Alzheimer's disease

The neuroprotective profile of the dibenzothiadiazepine ITH12410/SC058 (2-chloro-5,6-dihydro-5,6-diacetyldibenzo[b,f][1,4,5]thiadiazepine) against several neurotoxicity models related to neurodegenerative diseases is herein described. ITH12410/SC058 protected SH-SY5Y cells against the loss of cell viability elicited by amyloid beta peptide and okadaic acid, a selective inhibitor of phosphoprotein phosphatase 2A that induces neurofibrillary tangle formation. Furthermore, ITH12410/SC058 is neuroprotective against several in vitro models of oxidative stress, that is, H2O2 exposure or incubation with rotenone plus oligomycin A in SH-SY5Y cells, and oxygen and glucose deprivation followed by reoxygenation in rat hippocampal slices. By contrast, ITH12410/SC058 was unable to significantly protect SH-SY5Y neuroblastoma cells against the toxicity elicited by Ca(2+) overload. Our results confirm the hypothesis that the dibenzothiadiazepine ITH12410/SC058 features its neuroprotective actions in a multitarget fashion, and is a promising drug for the treatment of neurodegenerative diseases.

Protective effect of a sesamin derivative, 3-bis (3-methoxybenzyl) butane-1, 4-diol on Aβ-stressed PC12 cells

Amyloid beta-protein (Aβ) is involved in the pathogenesis of Alzheimer's disease (AD). Aβ induces free radical production in neuronal cells, leading to oxidative stress and up-regulation of c-Jun N-terminal kinases (JNK), extracellular-signal-regulated kinases (ERK), p38 mitogen-activated protein kinase (MAPK) pathways and pro-apoptotic Bax expression. Sesamin has been shown to have protection to several models of neurodegenerative diseases by its antioxidant and anti-inflammatory properties. In the present study, we examined the neuroprotective effect of a sesamin derivative, 3-bis (3-methoxybenzyl) butane-1,4-diol (BBD) on Aβ1-42 induced cytotoxicity of PC12 cells. Aβ1-42 induced lipid peroxidation, calcium, reactive oxygen species from the PC12 cells. The effect of BBD on these harmful factors and the related signaling pathways were examined by biochemical and western blot assays. The result showed that BBD protected PC12 cells from Aβ1-42 induced cytotoxicity with the increased cell viability and acetylcholine release, and the decreased lactate dehydrogenase, malondialdehyde and calcium release. BBD significantly reduced Aβ-induced JNK, ERK, p38 MAPK pathways and Bax expression in PC12 cells. Therefore the neuroprotective effect of BBD on Aβ-induced cytotoxicity was involved with antioxidant and anti-inflammatory effects. The result would help the development of new CNS drug for protection of AD.

Vitamin E modulates oxidative stress and protein kinase C activator (PMA)-induced TRPM2 channel gate in dorsal root ganglion of rats

It is well known that Ca(2+) influx through cation channels induces peripheral pain in dorsal root ganglion (DRG) neurons. Melastatin-like transient receptor potential 2 (TRPM2) channel is a oxidative redox sensitive Ca(2+)-permeable cation channel. There is scarce report on block of the channels. Since the mechanisms that lead to TRPM2 inhibition in response to oxidative stress and protein kinase C (PKC) activation are not understood, we investigated effects of the antioxidants on the inhibition of TRPM2 channel currents in the DRG neurons of rats. The DRG peripheral neurons were freshly isolated from rats and the neurons were incubated by phorbol 12-myristate 13-acetate (PMA) which leads to activation of PKC and cause oxidative stress. In whole-cell patch clamp experiments, TRPM2 currents in the DRG incubated with PMA were stimulated by H2O2. In addition, the PMA-induced activation of TRPM2 channels were blocked by nonspecific TRPM2 channels inhibitors [2-aminoethyl diphenylborinate (2-APB) and N-(p-amylcinnamoyl)anthranilic acid (ACA)]. The currents in the neurons are also totally blocked by vitamin E incubation. However, administration of catalase and vitamin C with/without the vitamin E incubation did not block the currents. In conclusion, we indicated that vitamin E modulated oxidative stress-induced TRPM2 channel activation in the DRG neurons. The results may be useful modulation of oxidative stress-induced peripheral pain in sensory neurons.

Amyloid β-induced ER stress is enhanced under mitochondrial dysfunction conditions

Previously we reported that endoplasmic reticulum (ER)-mitochondria crosstalk is involved in amyloid-β (Aβ)-induced apoptosis. Now we show that mitochondrial dysfunction affects the ER stress response triggered by Aβ using cybrids that recreate the defect in mitochondrial cytochrome c oxidase (COX) activity detected in platelets from Alzheimer's disease (AD) patients. AD and control cybrids were treated with Aβ or classical ER stressors and the ER stress-mediated apoptotic cell death pathway was accessed. Upon treatment, we found increased glucose-regulated protein 78 (GRP78) levels and caspase-4 activation (ER stress markers) which were more pronounced in AD cybrids. Treated AD cybrids also exhibited decreased cell survival as well as increased caspase-3-like activity, poli-ADP-ribose-polymerase (PARP) levels and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive apoptotic cells. Finally, we showed that Aβ-induced caspase-3 activation in both cybrid cell lines was prevented by dantrolene, thus implicating ER Ca(2+) release in ER stress-mediated apoptosis. Our results demonstrate that mitochondrial dysfunction occurring in AD patients due to COX inhibition potentiates cell susceptibility to Aβ-induced ER stress. This study further supports the close communication between ER and mitochondria during apoptosis in AD.

Ergothioneine protects against neuronal injury induced by cisplatin both in vitro and in vivo

The neuroprotective effects of ergothioneine (EGT) against cisplatin toxicity were investigated both in vitro and in vivo. For in vitro study, two types of neuronal cells, primary cortical neuron (PCN) cells and rat pheochromocytoma (PC12) cells, were incubated with EGT (0.1-10.0 μM) for 2 h followed by incubation with 0.5 μM cisplatin for 72 h. Results show that cisplatin markedly decreased the proliferation of PC12 cells and strongly inhibited the growth of axon and dendrite of PCN cells, but these effects were significantly prevented by EGT. For in vivo study, CBA mice were orally administered with 2 or 8 mg EGT/kg body weight for 58 consecutive days and were injected i.p. with 5mg cisplatin/kg body weight on days 7, 9 and 11. We found that EGT significantly restored the learning and memory deficits in mice treated with cisplatin evaluated by active and passive avoidance tests. EGT also significantly prevented brain lipid peroxidation, restored acetylcholinesterase (AChE) activity and maintained glutathione/glutathione disulfide ratio in brain tissues of mice treated with cisplatin. These results demonstrate that EGT protects against cisplatin-induced neuronal injury and enhances cognition, possibly through the inhibition of oxidative stress and restoration of AChE activity in neuronal cells.

The galanin receptor 2/3 agonist Gal2-11 protects the SN56 cells against beta-amyloid 25-35 toxicity

The neuropeptide galanin is a modulator of cholinergic function and may play a role in A beta peptide-induced degeneration of cholinergic forebrain neurons. We have studied the effect of galanin and its galanin receptor subtype 2/3 agonist Gal2-11on toxicity induced by freshly-prepared beta-amyloid(25-35) in the cholinergic cell line SN56. Both nuclear fragmentation and caspase-3 expression were analysed. beta-amyloid(25-35)-exposure induced a significant increase in caspase-3 mRNA expression after 30, 60, 90 or 150 min of beta-amyloid(25-35) exposure. These effects were abolished in the presence of Gal2-11 (10 nM). Similarly, beta-amyloid(25-35)-induced nuclear fragmentation was prevented by the galanin agonist at all time points studied. These findings indicate that the galanin 2/3 agonist Gal2-11 protects SN56 cholinergic cells from beta-amyloid(25-35)-induced cell death and that this action is mediated by an early reduction of caspase-3 expression.

H2O2 and PAF mediate Abeta1-42-induced Ca2+ dyshomeostasis that is blocked by EGb761

Calcium (Ca2+) dyshomeostasis may be of pivotal importance in mediating the neurotoxic action of amyloid beta peptide (Abeta), but the mechanism whereby Abeta disrupts Ca2+ homeostasis remains unclear. Using hippocampal neuronal cultures, the present study investigated possible mechanisms underlying Ca2+ dyshomeostasis induced by the oligomeric form of Abeta1-42 and two possible mediators of its toxicity, hydrogen peroxide (H2O2) and platelet-activating factor (PAF). It was found that, both H2O2 and PAF were able to reproduce each of the events induced by oligomeric Abeta1-42, including (a) Ca2+ influx via N-methyl-D-aspartic acid (NMDA) receptors, (b) enhancement of Ca2+ response to NMDA via activation of protein kinase C (PKC), (c) the increase of extracellular concentrations of glutamate and (d) the increase in cytosolic free Ca2+ ([Ca2+]i). Moreover, each of these events could be blocked by Ginkgo biloba extract EGb761, a free radical scavenger with PAF antagonism, and by quercetin, a constituent with well-established free radical scavenging property. In contrast, ginkgolide B, another constituent of EGb761 with well-established PAF-antagonizing activity protected the neurons against Ca2+ dyshomeostasis induced by Abeta1-42 and PAF, but not by H2O2. These results suggested the possibility that Abeta1-42-induced Ca2+ dyshomeostasis might be mediated by formation of toxic mediators such as H2O2 and PAF. Therefore, increased production of toxic mediators such as H2O2 and PAF in the brain may be critical in the pathological mechanism of neurodegenerative diseases, particularly Alzheimer's disease (AD), and may serve as major therapeutic targets for these diseases.

Crosstalk between calcium and redox signaling: from molecular mechanisms to health implications

Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

Novel squamosamide derivative (compound FLZ) attenuates Abeta25-35-induced toxicity in SH-SY5Y cells

AIM

The aim of the present study was to investigate the protective effect of compound N-[2-(4-hydroxy-phenyl)-ethyl]-2-(2,5-dimethoxy-phenyl)-3-(3-methoxy-4-hydroxy-phenyl)-acrylamide (compound FLZ), a novel synthetic analogue of nature squamosamide, on Abeta25-35-induced toxicity and its active mechanism in human neuroblastoma SH-SY5Y cells.

METHODS

SH-SY5Y cells were pre-incubated with various concentrations of compound FLZ for 30 min and then cultivated with Abeta25-35 (25 micromol/L) for 48 h to induce neurotoxicity. Cell viability, lactate dehydrogenase (LDH) release, and the glutathione (GSH) level were determined by a biochemical analysis. The cell apoptotic ratio and intracellular reactive oxygen species (ROS) level were measured by a flow cytometry analysis. The expression of apoptosis protein (Bcl-2 and Bax) and cytochrome c release were assayed by the Western blot method.

RESULTS

The pretreatment of SH-SY5Y cells with FLZ (1 and 10 micromol/L) markedly increased cell viability and decreased LDH release and morphological injury. Also, FLZ attenuated the Abeta25-35-induced apoptotic cell ratio, regulated the apoptosis protein (Bcl-2 and Bax) expression, and decreased the cytochrome c release from mitochondria. FLZ also significantly inhibited the generation of ROS and the depletion of GSH induced by Abeta25-35 in SH-SY5Y cells.

CONCLUSION

FLZ has protective action against Abeta25-35-induced toxicity in SH-SY5Y cells, which might be mediated through its antioxidant property.

Effect of the knockdown of amyloid precursor protein on intracellular calcium increases in a neuronal cell line derived from the cerebral cortex of a trisomy 16 mouse

Murine trisomy 16 (Ts16) is a useful model to study the deleterious effect of aneuploidy in neural pathophysiology. The CTb cell line derived from the cerebral cortex of a Ts16 mouse overexpresses the amyloid precursor protein (APP) and exhibits altered intracellular Ca(2+) homeostasis. In the present work, we induced knockdown of APP by transfecting specific mRNA antisense sequences into CTb cells. Forty-eight hours after transfection, the APP expression was knocked down by 40%, reaching levels comparable to those of the cortical line CNh, derived from a normal animal. Calcium measurements showed that the APP knockdown decreased intracellular Ca(2+) basal levels and accelerated the kinetics of the decay of Ca(2+) responses induced by glutamatergic agonists, nicotine, depolarization or ionomycin, to levels similar to those previously reported for CNh cells. The present results suggest that APP overexpression plays an important role on the altered intracellular Ca(2+) homeostasis in the trisomic cells.

Protective effects of compound FLZ on beta-amyloid peptide-(25-35)-induced mouse hippocampal injury and learning and memory impairment

AIM

To study the protective effects of compound FLZ, a novel synthetic analogue of natural squamosamide, on learning and memory impairment and lesions of the hippocampus caused by icv injection of beta-amyloid(25-35)(Abeta(25-35)) in mice.

METHODS

Mice were icv injected with the Abeta(25-35) (15 nmol/mouse), and then treated with oral administration of 75 mg/kg or 150 mg/kg of FLZ once daily for 16 consecutive days. The impairment of learning and memory in mice were tested using step-down test and Morris water maze test. The content of malondialdehyde (MDA) and the expressions of acetylcholinesterase (AChE), Bax, and Bcl-2 in the CA1 region of the mouse hippocampus were measured by biochemical and immunohistochemical analysis, respectively. The pathological damages of hippocampus were observed using a microscope.

RESULTS

FLZ (75 mg/kg, 150 mg/kg) significantly attenuated Abeta(25-35)-induced impairment of learning and memory in the step-down test and Morris water maze test. FLZ also reduced pathological damages to the hippocampus induced by Abeta(25-35). Furthermore, FLZ prevented the increase of AChE and Bax, and the decrease of Bcl-2 immunoreactive cells in the CA1 region of the hippocampus, and reduced the increase of MDA content in the hippocampus in mice injected with Abeta(25-35).

CONCLUSION

FLZ has protective action against the impairment of learning and memory and pathological damage to the hippocampus induced by icv injection of Abeta(25-35) in mice.

S100B protects LAN-5 neuroblastoma cells against Abeta amyloid-induced neurotoxicity via RAGE engagement at low doses but increases Abeta amyloid neurotoxicity at high doses

At the concentrations normally found in the brain extracellular space the glial-derived protein, S100B, protects neurons against neurotoxic agents by interacting with the receptor for advanced glycation end products (RAGE). It is known that at relatively high concentrations S100B is neurotoxic causing neuronal death via excessive stimulation of RAGE. S100B is detected within senile plaques in Alzheimer's disease, where its role is unknown. The present study was undertaken to evaluate a putative neuroprotective role of S100B against Abeta amyloid-induced neurotoxicity. We treated LAN-5 neuroblastoma cultures with toxic amounts of Abeta25-35 amyloid peptide. Our results show that at nanomolar concentrations S100B protects cells against Abeta-mediated cytotoxicity, as assessed by 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and terminal deoxynucleotidyl transferase-mediated dUTP-fluorescein isothiocyanate nick end-labeling (TUNEL) experiments, by countering the Abeta-mediated decrease in the expression of the anti-apoptotic factor Bcl-2. This effect depends on S100B binding to RAGE because S100B is unable to contrast Abeta-mediated neurotoxicity in neurons overexpressing a signaling-deficient RAGE mutant lacking the cytosolic and transducing domain. Our data suggest that at nanomolar doses S100B counteracts Abeta peptide neurotoxicity in a RAGE-mediated manner. However, at micromolar doses S100B is toxic to LAN-5 cells and its toxicity adds to that of the Abeta peptide, suggesting that additional molecular mechanisms may be involved in the neurotoxic process.

Mitochondria in health and disease: perspectives on a new mitochondrial biology

The integrity of mitochondrial function is fundamental to cell life. It follows that disturbances of mitochondrial function will lead to disruption of cell function, expressed as disease or even death. In this review, I consider recent developments in our knowledge of basic aspects of mitochondrial biology as an essential step in developing our understanding of the contributions of mitochondria to disease. The identification of novel mechanisms that govern mitochondrial biogenesis and replication, and the delicately poised signalling pathways that coordinate the mitochondrial and nuclear genomes are discussed. As fluorescence imaging has made the study of mitochondrial function within cells accessible, the application of that technology to the exploration of mitochondrial bioenergetics is reviewed. Mitochondrial calcium uptake plays a major role in influencing cell signalling and in the regulation of mitochondrial function, while excessive mitochondrial calcium accumulation has been extensively implicated in disease. Mitochondria are major producers of free radical species, possibly also of nitric oxide, and are also major targets of oxidative damage. Mechanisms of mitochondrial radical generation, targets of oxidative injury and the potential role of uncoupling proteins as regulators of radical generation are discussed. The role of mitochondria in apoptotic and necrotic cell death is seminal and is briefly reviewed. This background leads to a discussion of ways in which these processes combine to cause illness in the neurodegenerative diseases and in cardiac reperfusion injury. The demands of mitochondria and their complex integration into cell biology extends far beyond the provision of ATP, prompting a radical change in our perception of mitochondria and placing these organelles centre stage in many aspects of cell biology and medicine.

Alcohol intake in relation to brain magnetic resonance imaging findings in older persons without dementia

BACKGROUND

Consumers of light-to-moderate amounts of alcohol have a lower risk of dementia and, possibly, Alzheimer disease than do abstainers. Because vascular disease may contribute to symptoms of Alzheimer disease, reduction of cerebrovascular disease in consumers of light amounts of alcohol could account for that observation. However, a low concentration of alcohol may also have direct effects on the hippocampus, a brain structure highly affected by Alzheimer disease.

OBJECTIVE

We investigated alcohol intake in relation to brain magnetic resonance imaging (MRI) findings of presumed vascular origin (ie, white matter lesions and infarcts) and findings more specifically found in early Alzheimer disease (ie, hippocampal and amygdalar atrophy).

DESIGN

In a population-based sample of 1074 older persons without dementia (aged 60-90 y), we made brain MRIs from which we rated white matter lesions and brain infarcts. In a subset of 509 people, hippocampal and amygdalar volumes on MRI were measured. Alcohol intake was assessed by using a structured questionnaire. We categorized alcohol intake as lifetime abstention and very light (<1 drink/wk), light (>/=1 drink/wk to <1 drink/d), moderate (>/=1 drink/d to <4 drinks/d), and heavy (>/=4 drinks/d) intakes.

RESULTS

Persons whose alcohol consumption was light to moderate had less severe white matter lesions and brain infarcts on MRI than did abstainers or heavy drinkers. Abstainers and very light drinkers had smaller hippocampal and amygdalar volumes on MRI than did light-to-moderate drinkers, but only if the former carried an apolipoprotein (APOE) epsilon4 allele.

CONCLUSION

Light-to-moderate alcohol intake is associated with a lower prevalence of vascular brain findings and, in APOE epsilon4 carriers, hippocampal and amygdalar atrophy on MRI.

Protective effects of sesamin and sesamolin on murine BV-2 microglia cell line under hypoxia

Sesamin and sesamolin were tested for their ability to protect BV-2 microglia from hypoxia-induced cell death. These antioxidants dose-dependently reduced hypoxia-induced lactate dehydrogenase (LDH) release and dichlorofluorescein (DCF)-sensitive reactive oxygen species (ROS) production. Their effects on signaling pathway mitogen-activated protein kinases (MAPKs) and caspase-3 in hypoxia-induced cell death were further examined. Extracellular signal-regulated protein kinases (ERK1/2), c-jun NH(2)-terminal kinase (JNK), and p38 MAPKs were activated during hypoxia. The sesamin or sesamolin reduced caspase-3 and MAPK activation correlated well with diminished LDH release in BV-2 cells under hypoxia. Furthermore, they preserved superoxide dismutase (SOD) and catalase activities in BV-2 cells under hypoxia. Taken together, these results indicate that the mechanism of sesame antioxidants involves inhibition of MAPK pathways and apoptosis through scavenging of ROS in hypoxia-stressed BV-2 cells.

Involvement of endoplasmic reticulum Ca2+ release through ryanodine and inositol 1,4,5-triphosphate receptors in the neurotoxic effects induced by the amyloid-beta peptide

Studies with in-vitro-cultured neurons treated with amyloid-beta (A beta) peptides demonstrated neuronal loss by apoptosis that is due, at least in part, to the perturbation of intracellular Ca(2+) homeostasis. In addition, it was shown that an endoplasmic reticulum (ER)-specific apoptotic pathway mediated by caspase-12, which is activated upon the perturbation of ER Ca(2+) homeostasis, may contribute to A beta toxicity. To elucidate the involvement of deregulation of ER Ca(2+) homeostasis in neuronal death induced by A beta peptides, we have performed a comparative study using the synthetic peptides A beta(25-35) or A beta(1-40) and thapsigargin, a selective inhibitor of Ca(2+) uptake into the ER. Incubation of cortical neurons with thapsigargin (2.5 microM) increased the intracellular Ca(2+) levels and activated caspase-3, leading to a significant increase in the number of apoptotic cells. Similarly, upon incubation of cortical cultures with the A beta peptides (A beta(25-35), 25 microM; A beta(1-40), 0.5 microM), we observed a significant increase in [Ca(2+)](i), in caspase-3-like activity, and in number of neurons exhibiting apoptotic morphology. The role of ER Ca(2+) release through ryanodine receptors (RyR) or inositol 1,4,5-trisphosphate receptors (IP(3)R) in A beta neurotoxicity has been also investigated. Dantrolene and xestospongin C, inhibitors of ER Ca(2+) release through RyR or IP(3)R, were able to prevent the increase in [Ca(2+)](i) and the activation of caspase-3 and to protect partially against apoptosis induced by treatment with A beta(25-35) or A beta(1-40). In conclusion, our results demonstrate that the release of Ca(2+) from the ER, mediated by both RyR and IP(3)R, is involved in A beta toxicity and can contribute, together with the activation of other intracellular neurotoxic mechanisms, to A beta-induced neuronal death. This study suggests that A beta accumulation may have a key role in the pathogenesis of AD as a result of deregulation of ER Ca(2+) homeostasis.

Toxicity of amyloid beta peptide: tales of calcium, mitochondria, and oxidative stress

Alzheimer's disease (AD) is characterized by the accumulation of amyloid-beta (Abeta) peptides. Although the disease undoubtedly reflects the interaction of complex multifactorial processes, Abeta itself is toxic to neurons in vitro and the load of Abeta in vivo correlates well with the degree of cognitive impairment. There has therefore been considerable interest in the mechanism(s) of Abeta neurotoxicity. We here review the basic biology of Abeta processing and consider some of the major areas of focus of this research. It is clear that both AD and Abeta toxicity are characterized by oxidative stress, alterations in the activity of enzymes of intermediary metabolism, and mitochondrial dysfunction, especially impaired activity of cytochrome c oxidase. Studies in vitro also show alterations in cellular calcium signaling. We consider the mechanisms proposed to mediate cell injury and explore evidence to indicate which of these many changes in function are primary and which secondary.

Inhibition of alpha-ketoglutarate dehydrogenase complex promotes cytochrome c release from mitochondria, caspase-3 activation, and necrotic cell death

Mitochondrial dysfunction has been implicated in cell death in many neurodegenerative diseases. Diminished activity of the alpha-ketoglutarate dehydrogenase complex (KGDHC), a key and arguably rate-limiting enzyme of the Krebs cycle, occurs in these disorders and may underlie decreased brain metabolism. The present studies used alpha-keto-beta-methyl-n-valeric acid (KMV), a structural analogue of alpha-ketoglutarate, to inhibit KGDHC activity to test effects of reduced KGDHC on mitochondrial function and cell death cascades in PC12 cells. KMV decreased in situ KGDHC activity by 52 +/- 7% (1 hr) or 65 +/- 4% (2 hr). Under the same conditions, KMV did not alter the mitochondrial membrane potential (MMP), as assessed with a method that detects changes as small as 5%. KMV also did not alter production of reactive oxygen species (ROS). However, KMV increased lactate dehydrogenase (LDH) release from cells by 100 +/- 4.7%, promoted translocation of mitochondrial cytochrome c to the cytosol, and activated caspase-3. Inhibition of the mitochondrial permeability transition pore (MPTP) by cyclosporin A (CsA) partially blocked this KMV-induced change in cytochrome c (-40%) and LDH (-15%) release, and prevented necrotic cell death. Thus, impairment of this key mitochondrial enzyme in PC12 cells may lead to cytochrome c release and caspase-3 activation by partial opening of the MPTP before the loss of mitochondrial membrane potentials.

A neuron-specific EGF family protein, NELL2, promotes survival of neurons through mitogen-activated protein kinases

NELL2 is a neuron-specific thrombospondin-1-like extracellular protein containing six epidermal growth factor-like domains. NELL2 is highly expressed in the hippocampus and cerebral cortex. Although the involvement of NELL2 in neural functions has been inferred from its expression and biochemical profiles, biological roles of NELL2 remain uncertain. We evaluated the survival effect of NELL2 using primary cultured neurons from fetal rat brain following treatment with a recombinant NELL2 protein. NELL2 increased survival of neurons from the hippocampus and cerebral cortex. We further examined the protective effect of NELL2 from oxygen-glucose deprivation- and beta-amyloid-induced neuronal death, and found that NELL2 did not protect neurons from these insults. To understand signaling properties underlying the survival effect, we studied activation of mitogen-activated protein kinases (MAPKs) by NELL2. Treatment of primary cultured cells from the hippocampus with NELL2 enhanced phosphorylation of c-jun N-terminal kinase (JNK), whereas phosphorylation of extracellular signal-regulated kinase (ERK) was decreased by NELL2 treatment. NELL2-enhanced survival of hippocampal neurons was completely blocked by SP600125, an anthrapyrazolone inhibitor of JNK, while treatment of MEK (MAPK/ERK kinase) inhibitors per se enhanced survival of neurons similar to NELL2 treatment. These results suggest that NELL2 promotes survival of neurons by modulating MAPK activities.

A beta 25-35-induced depression of long-term potentiation in area CA1 in vivo and in vitro is attenuated by verapamil

The effect of intracerebroventricular (icv) injection of A beta 25-35 and/or intraperitoneal (ip) application of the L-type calcium channel (VDCC) blockers verapamil or diltiazem were examined in vivo. To by-pass possible systemic actions of these agents, their effects on long-term potentiation (LTP) in the CA1 region of the in vitro hippocampal slice preparation were also examined. Application of A beta 25-35 (10 nmol in 5 microl, i.c.v.) significantly impaired LTP in vivo, as did IP injection of verapamil (1 or 10 mg/kg) or diltiazem (1 or 10 mg/kg). In the in vitro slice preparation, LTP was also depressed by prior application of A beta 25-35 (500 nmol), verapamil (20 microM), or diltiazem (50 microM). Combined application of A beta 25-35 and verapamil in either the in vivo or in vitro preparation resulted in a significant reversal of the LTP depression observed in the presence of either agent alone. However, co-application of diltiazem and A beta 25-35 failed to attenuate the depression of LTP observed in the presence of either agent alone in vivo or in vitro. Since LTP is a cellular correlate of memory and A beta is known to be involved in Alzheimer's disease (AD), these results indicate that verapamil, a phenylalkylamine, may be useful in the treatment of cognitive deficits associated with AD.

Potential use of stem cells in neuroreplacement therapies for neurodegenerative diseases

The use of stem cells for neuroreplacement therapy is no longer science fiction--it is science fact. We have succeeded in the development of neural and mesenchymal stem cell transplantation to produce neural cells in the brain. We have also seen improvement in cognitive function following stem cell transplantation in a memory-impaired aged animal model. These results promise a bright future for stem cell therapies in neurodegenerative diseases. Before we begin to think about clinical applications beyond the present preclinical studies, we have to consider the pathophysiological environment of individual diseases and weigh the factors that affect stem cell biology. Here, I not only review potential therapeutic applications of stem cell strategies in neurodegenerative diseases, but also discuss stem cell biology regarding factors that are altered under disease conditions.

Divergent pathways account for two distinct effects of amyloid beta peptides on exocytosis and Ca(2+) currents: involvement of ROS and NF-kappaB

Amyloid peptides (AbetaPs) are implicated in neuronal death associated with Alzheimer's disease. Their toxicity involves disruption cellular Ca(2+) homeostasis, leading to activation of caspases and cell death. Antioxidants can prevent such cell death and show beneficial clinical effects in Alzheimer's disease patients. Using the model neurosecretory cell line, PC12, we have shown that AbetaPs cause enhancement of evoked exocytosis via formation of a Cd(2+) -resistant Ca(2+) influx pathway, and also cause selective, functional up-regulation of current through L-type Ca(2+) channels. The involvement of reactive oxygen species (ROS) in these effects were investigated by examining the ability of various antioxidants to interfere with these responses. Both melatonin and ascorbic acid fully blocked the enhancement of catecholamine secretion caused by application of AbetaP((1-40)), as monitored in real time amperometrically, but inhibition of the transcriptional regulator NF-kappaB with SN-50 did not affect secretion. Enhanced immunofluorescence, observed in AbetaP-treated cells using a monoclonal antibody raised against the N-terminus of AbetaP, was also suppressed by melatonin. Ascorbic acid, melatonin and ebselen also fully prevented augmentation of whole-cell Ca(2+) currents caused by application of AbetaP((1-40)). By contrast, inhibitors of NF-kappaB (sulfasalazine and SN-50) were able to prevent AbetaP induced Ca(2+) channel current enhancement, whilst inhibitors of mitogen-activated protein kinase and protein kinase C could not. Our results indicate that augmentation or induction by AbetaPs of two important, distinct factors regulating Ca(2+) homeostasis is mediated by increased ROS production, but only one of these (up-regulation of native Ca(2+) channels) requires activation of NF-kappaB.

Neuroprotective MK801 is associated with nitric oxide synthase during hypoxia/reoxygenation in rat cortical cell cultures

The neuroprotective effect of MK801 against hypoxia and/or reoxygenation-induced neuronal cell injury and its relationship to neuronal nitric oxide synthetase (nNOS) expression were examined in cultured rat cortical cells. Treatment of cortical neuronal cells with hypoxia (95% N(2)/5% CO(2)) for 2 h followed by reoxygenation for 24 h induced a release of lactate dehydrogenase (LDH) into the medium, and reduced the protein level of MAP-2 as well. MK801 attenuated the release of LDH and the reduction of the MAP-2 protein by hypoxia, suggesting a neuroprotective role of MK801. MK801 also diminished the number of nuclear condensation by hypoxia/reoxygenation. The NOS inhibitors 7-nitroindazole (7-NI) and N (G)-nitro-L-arginine methyl ester (L-NAME), as well as the Ca(2+) channel blocker nimodipine, reduced hypoxia-induced LDH, suggesting that nitric oxide (NO) and calcium homeostasis contribute to hypoxia and/or the reoxygenation-induced cell injury. The levels of nNOS immunoactivities and mRNA by RT-PCR were enhanced by hypoxia with time and, down regulated following 24 h reoxygenation after hypoxia, and were attenuated by MK801. In addition, the reduction of nNOS mRNA levels by hypoxia/reoxygenation was also diminished by MK801. Further delineation of the mechanisms of NO production and nNOS regulation are needed and may lead to additional strategies to protect neuronal cells against hypoxic/reoxygenation insults.

Alpha-lipoic acid protects rat cortical neurons against cell death induced by amyloid and hydrogen peroxide through the Akt signalling pathway

Substantial evidence suggests that the accumulation of beta-amyloid (Abeta)-derived peptides contributes to the aetiology of Alzheimer's disease (AD) by stimulating formation of free radicals. Thus, the antioxidant alpha-lipoate, which is able to cross the blood-brain barrier, would seem an ideal substance in the treatment of AD. We have investigated the potential effectiveness of alpha-lipoic acid (LA) against cytotoxicity induced by Abeta peptide (31-35) (30 microM) and hydrogen peroxide (H(2)O(2)) (100 microM) with the cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) reduction and fluorescence dye propidium iodide assays in primary neurons of rat cerebral cortex. We found that treatment with LA protected cortical neurons against cytotoxicity induced by Abeta or H(2)O(2). In addition, LA-induced increase in the level of Akt in the neurons was observed by Western blot. The LA-induced neuroprotection and Akt increase were attenuated by pre-treatment with the phosphatidylinositol 3-kinase inhibitor, LY294002 (50 microM). Our data suggest that the neuroprotective effects of the antioxidant LA are partly mediated through activation of the PKB/Akt signaling pathway.

The action of acetyl-L-carnitine on the neurotoxicity evoked by amyloid fragments and peroxide on primary rat cortical neurones

The amyloid beta-peptides have been implicated in the excitotoxic mechanism of neuronal injury in the pathogenesis of Alzheimer's disease. In this paper we examine the effect of different amyloid fragments (beta A1-40, A1-28, and A25-35), as well as potential neuroprotective compounds on rat cortical neuron viability. Exposure of neurones to beta A25-35 or A1-40 at concentrations as low as 1 microgram/ml inhibited, significantly, the MTT response and this level of inhibition was similar after 24-h or three-day exposure. Furthermore, the level of inhibition was not affected by the presence or absence of 5% horse serum in the medium. Preexposure (10 min) of neurones to ALC at concentrations of 0.1, 1, 5, and 10 mM attenuated the inhibition of the MTT response caused by beta A25-35 (50 micrograms/ml) in serum free medium for 24 h. The treatment of cells with vitamin E (100 microM), catalase (4 mg/ml), NGF (0.1 and 10 ng/ml), or cycloheximide (0.1 microgram/ml) significantly restored the MTT response that was inhibited by beta A25-35. The mechanism for the protective actions of these compounds against beta A25-35 toxicity is not clear but may involve free radical scavenger action and preservation of energy production, although other mechanisms, especially for ALC, such as a direct effect on A-beta interaction with charged anionic phospholipids and/or stabilizing action on membranes, are also possible.

Review of the next generation of Alzheimer's disease therapeutics: challenges for drug development

1. AD is believed to stem from dysfunctional cholinergic signaling in the regions of the brain associated with memory and cognition. 2. The occurrence of AD in afflicted individuals correlates with an increase in the accumulation of A beta-rich senile plaques and neurofibrillary tangles in the brain. 3. Currently, the only FDA-approved AD therapies are a group of acetylcholinesterase inhibitors which slow the turnover of the neurotransmitter acetylcholine in the synapse. 4. Many other compounds which target other aspects of the disease, such as reducing neuronal damage and limiting oxidation, are in clinical trials. These include monoamine oxidase (MAO-B) inhibitors, NSAIDs, antioxidants and estrogen, among others. 5. Recent research discoveries have more completely defined the molecular nature of AD, and are generating new approaches for treatment. One idea is to limit the ability of the protein tau to become phosphorylated in hopes that this will limit the formation of neurofibrillary tangles in the brain. 6. A separate approach that is being pursued is to prevent formation and accumulation of A beta plaques. This may be accomplished by either regulating gamma-secretase activity, or using anti-beta-amyloid antibodies to reduce the size of existing plaques. 7. Employing improved procedural and technological approaches during clinical trials, such as bridging studies, dynabridge studies and PET analysis, promises to streamline the drug development process. 8. The use of biomarkers and MRI analysis may be an effective means by which to identify the disease early. Consequently, early intervention treatment therapies may be an effective way of delaying onset of the disease. 9. Long term AD studies, particularly those focusing on the MCI population, are likely to provide statistically valid results using a smaller study population.

A nonfibrillar form of the fusogenic prion protein fragment [118-135] induces apoptotic cell death in rat cortical neurons

Neuronal loss is a salient feature of prion diseases. However, its cause and mechanism, particularly its relationship with the accumulation and precipitation of the pathogenic, protease-resistant isoform PrP(Sc) of the cellular prion protein PrP(C), are still an enigma. Several studies suggest that neuronal loss could occur through a process of programmed cell death, which is consistent with the lack of inflammation in these conditions. By analogy with the pathological events occurring during the development of Alzheimer's disease, controversies still exist regarding the relationship between amyloidogenesis, prion aggregation, and neuronal loss. We recently demonstrated that a prion protein fragment (118-135) displayed membrane-destabilizing properties and was able to induce, in a nonfibrillar form, the fusion of unilamellar liposomes. To unravel the mechanism of prion protein neurotoxicity, we characterize the effects of the human Pr[118-135] peptide on rat cortical neurons. We demonstrate that low concentrations of the Pr[118-135] peptide, in a nonfibrillar form, induce a time- and dose- dependent apoptotic cell death, including caspase activation, DNA condensation, and fragmentation. This toxicity might involve oxidative stress, because antioxidant molecules, such as probucol and propyl gallate, protect neurons against prion peptide toxicity. By contrast, a nonfusogenic variant Pr[118-135, 0 degrees ] peptide, which displays the same amino acid composition but several amino acid permutations, is not toxic to cortical neurons, which emphasizes the critical role of the fusogenic properties of the prion peptide in its neurotoxicity. Taken together, our results suggest that the interaction between the Pr[118-135] peptide and the plasma membrane of neurons might represent an early event in a cascade leading to neurodegeneration.