The heat shock/oxidative stress connection. Relevance to Alzheimer disease

Mitochondria-Mediated Moderation of Apoptosis by EGCG in Cytotoxic Neuronal Cells Induced by Lead (Pb) and Amyloid Peptides

The developmental, epigenetic, and epidemiological studies on lead (Pb) toxicity have reported a strong connection between lead exposure and the progression of Alzheimer's disease (AD). The amyloid peptides were the main triggering elements, in the generation of extracellular plaques through which multiple cellular signaling events such as apoptosis and primarily oxidant-antioxidant balancing system will be affected, which leads to neuronal cell death. Our previous studies indicated that epigallocatechin gallate (EGCG), abundantly present in green tea, was found to be effective in alleviating the metal-induced neurotoxicity at the cellular level in terms of cell viability and apoptosis The aim of this study was to explore the protective mechanism of EGCG on the markers of oxidant-antioxidant system and mitochondria, which are involved in metal-induced neuronal cell death. Initially, the IC₅₀ values for lead(Pb-5 µM), amyloid peptides (AP(1-40)-60 µM; AP(1-40)-8 µM), and EC₅₀ value for EGCG(50 µM) were determined by both time- (12 h, 24 h, 48 h) and concentration-dependent manner and analyzed by MTT assay. The experimental groups were designed initially by treating with Pb and APs individually and in different combinations along with the presence of EGCG and are compared to the Pb and AP treated group without EGCG exposure. The cell lysates were used for analyzing oxidative stress markers by standardized laboratory protocol and the expression of mitochondrial markers such as VDAC and cytochrome C which were analyzed by both western blot and real-time PCR. Our results indicate that the EGCG-treated group has shown a significant increase in antioxidant marker expression levels (GSH, SOD, catalase, vitamin C) and a decrease in oxidative stress marker (NOS, MDA) levels when compared to the group without EGCG treatment (p < 0.05). Similarly, a significant decrease in expression levels of VDAC and cytochrome c were observed in the EGCG-treated group when compared to the group without EGCG treatment (p < 0.05). Our approach revealed that EGCG protects SH-SY5Y cells from Pb- and AP-induced cytotoxicity by regulating voltage-dependent anion channel (VDAC) expression and oxidant-antioxidant system and inhibits neuronal cell death.

Relationship between oxidative stress and lifespan in Daphnia pulex

Macromolecular damage leading to cell, tissue and ultimately organ dysfunction is a major contributor to aging. Intracellular reactive oxygen species (ROS) resulting from normal metabolism cause most damage to macromolecules and the mitochondria play a central role in this process as they are the principle source of ROS. The relationship between naturally occurring variations in the mitochondrial (MT) genomes leading to correspondingly less or more ROS and macromolecular damage that changes the rate of aging associated organismal decline remains relatively unexplored. MT complex I, a component of the electron transport chain (ETC), is a key source of ROS and the NADH dehydrogenase subunit 5 (ND5) is a highly conserved core protein of the subunits that constitute the backbone of complex I. Using Daphnia as a model organism, we explored if the naturally occurring sequence variations in ND5 correlate with a short or long lifespan. Our results indicate that the short-lived clones have ND5 variants that correlate with reduced complex I activity, increased oxidative damage, and heightened expression of ROS scavenger enzymes. Daphnia offers a unique opportunity to investigate the association between inherited variations in components of complex I and ROS generation which affects the rate of aging and lifespan.

Cytoskeletal remodeling via Rho GTPases during oxidative and thermal stress in Caenorhabditis elegans

Biological systems are highly sensitive to changes in their environment. Indeed, the molecular basis of the environmental stress response suggests that the specialized stress responses share more commonalities than previously believed. Here, we used the nematode C. elegans to gain insight into the role of Rho signaling during two common environmental challenges, oxidative and thermal stress. In response to heat shock (HS), wild type (N2) worms demonstrated reduced viability which was rescued by genetic suppression of CDC42 and RHO-1. Visualization of F-actin by phalloidin-rhodamine underscored a strict correlation between the levels of F-actin following GTPase suppression and survival. Additionally, genetic ablation of OSG-1, a Guanine Nucleotide Exchange Factor (GEF) previously implicated in oxidative stress, was associated with constitutively lower levels of F-actin and increased mortality. However, upon an oxidative insult F-actin stability decreased in N2 worms, a rescue of this affect was observed in OSG-1 null worms, consistent with the resistance exhibited by these worms to oxidative stress (OS). Together these data suggest that during conditions of thermal or oxidative stress Rho signaling promotes vulnerability by altering actin dynamics. Thus, the stability of the actin cytoskeleton, in part through a conserved mechanism mediated by Rho signaling, is a crucial factor for the cell's survival to environmental challenges.

Emerging roles of pathogens in Alzheimer disease

Chronic spirochetal infection can cause slowly progressive dementia, cortical atrophy and amyloid deposition in the atrophic form of general paresis. There is a significant association between Alzheimer disease (AD) and various types of spirochete (including the periodontal pathogen Treponemas and Borrelia burgdorferi), and other pathogens such as Chlamydophyla pneumoniae and herpes simplex virus type-1 (HSV-1). Exposure of mammalian neuronal and glial cells and organotypic cultures to spirochetes reproduces the biological and pathological hallmarks of AD. Senile-plaque-like beta amyloid (Aβ) deposits are also observed in mice following inhalation of C. pneumoniae in vivo, and Aβ accumulation and phosphorylation of tau is induced in neurons by HSV-1 in vitro and in vivo. Specific bacterial ligands, and bacterial and viral DNA and RNA all increase the expression of proinflammatory molecules, which activates the innate and adaptive immune systems. Evasion of pathogens from destruction by the host immune reactions leads to persistent infection, chronic inflammation, neuronal destruction and Aβ deposition. Aβ has been shown to be a pore-forming antimicrobial peptide, indicating that Aβ accumulation might be a response to infection. Global attention and action is needed to support this emerging field of research because dementia might be prevented by combined antibiotic, antiviral and anti-inflammatory therapy.

Brain damage after heat stroke

Cerebellar syndromes and radiologic cerebellar atrophy after hyperpyrexia have occasionally been reported, mostly in neuroleptic malignant syndromes, but neuropathologic studies are extremely rare. We studied 3 patients (a 74-year-old woman, a 63-year-old man, and an 80-year-old man) who had heat stroke during heat waves in France. One patient had generalized seizures and died 28 hours after admission. The other patients survived one month and 2 months after admission; both had palatal myoclonus, and in one case, magnetic resonance imaging showed high signal intensity in the cerebral peduncles. The main neuropathology in the 3 cases was severe diffuse loss of Purkinje cells associated with heat shock protein 70 expression by Bergmann glia. In situ end labeling was negative in surviving Purkinje cells, suggesting that the mechanism of neuronal death was not apoptosis. Degeneration of Purkinje cells axons resulted in myelin pallor of the white matter of the folia and of the hilum of the dentate nuclei. DNA internucleosomal breakages were identified by in situ end labeling in the dentate nuclei and centromedian nuclei of the thalamus and were associated with degeneration of the cerebellar efferent pathways: superior cerebellar peduncles, decussation of the superior cerebellar peduncles (Wernekinck commissure), and dentatothalamic tract. These findings suggest that the mechanisms of neuronal death in the dentate nuclei and centromedian nuclei of the thalamus was different from that in Purkinje cells and more likely resulted from deafferentation. Ammon's horn and other areas susceptible to hypoxia were spared. These observations confirm the selective vulnerability of Purkinje cells to heat-induced injury and involvement of the cerebellar efferent pathways in palatal myoclonus.

Low GSK-3beta in schizophrenia as a consequence of neurodevelopmental insult

Glycogen synthase kinase-3 (GSK-3) is a protein kinase highly abundant in brain and involved in signal transduction cascades, particularly neurodevelopment. Its activity and protein levels have been reported to be over 40% lower in postmortem frontal cortex of schizophrenic patients. GSK-3beta in occipital cortex of schizophrenic patients was not reduced, suggesting regional specificity. There was no reduction in GSK-3beta protein levels in fresh and immortalized lymphocytes and both GSK-3 activity and GSK-3beta mRNA levels in fresh lymphocytes from schizophrenic patients. In the schizophrenia-related neonatal ventral hippocampal lesion rat model, we measured GSK-3beta protein levels and GSK-3 activity in the frontal cortex. GSK-3beta protein levels in lesioned rats were significantly lower than in sham rats, favoring perinatal insult as a cause of low GSK-3beta in schizophrenia. Taken together, these studies suggest that low GSK-3 in postmortem brain of schizophrenic patients is a late consequence of perinatal neurodevelopmental insult in schizophrenia. In rats, acute or chronic cold restraint stress did not change GSK-3beta protein levels. Chronic treatment of rats with lithium, valproate, haloperidol or clozapine did not change rat cortical GSK-3beta protein levels ex vivo, supporting the concept that low GSK-3beta in schizophrenia is not secondary to stress or drug treatment. Our initial findings of low GSK-3beta protein levels in postmortem brain have been replicated by another group. Our own group has found additionally that GSK-3beta mRNA levels were 40% lower in postmortem dorsolateral prefrontal cortex (DLPFC) of schizophrenic patients, supporting our previous findings. Further studies will be aimed at determining whether nonspecific neonatal damage or only specific factors cause low GSK-3 as a late effect. We plan to study whether low GSK-3beta activity is associated with biochemical effects such as elevated beta-catenin levels.

Metal catalyzed oxidation of tyrosine residues by different oxidation systems of copper/hydrogen peroxide

Metal-catalysed oxidation (MCO) reactions result in the formation of reactive oxygen species (ROS) in biological systems. These ROS cause oxidative stress that contributes to a number of pathological processes leading to a variety of diseases. Tyrosine is one residue that is very susceptible to oxidative modification and the formation of dityrosine (DT) and 3,4-dihydroxyphenylalanine (DOPA) have been widely reported in a number of diseases. However, the mechanisms of MCO of tyrosine in biological systems are poorly understood and require further investigation. In this study we investigated the mechanism of DT and DOPA formation by MCO using N-acetyl tyrosine ethyl ester as a model for tyrosine in proteins and peptides. The results showed that DT formation could be observed upon Cu2+/H2O2 oxidation at pH 7.4. Our results indicate that it is unlikely to be via Fenton chemistry since Cu+/H2O2 oxidative conditions did not lead to the formation of DT.

HSP70-2 (HSPA1B) is associated with noncognitive symptoms in late-onset Alzheimer's disease

Neuropsychiatric manifestations are common in Alzheimer's disease (AD) and their phenotypic expression might be related to physiopathological and genetic causes. Multiple studies have implicated oxidative stress to the pathogenesis and possible etiology of AD. One of the mechanisms to protect cells from oxidative stress is the expression of heat-shock proteins (HSP). HSPA1B (alternatively known as HSP70-2) has been related to AD pathophysiology. In the present analysis, 77 AD patients were classified according to their cognitive status with the Neuropsychiatric Inventory and were genotyped for an insertion/deletion (A1/A2) polymorphism. The A2 allele conferred a significant increase of psychiatric morbidity in an allele-dose manner (P < .05). This pattern can be attributed to all AD stages and the severity of the behavioral disturbances was higher for those patients carrying one or two A2 alleles. These results indicate a possible association between the A2 allele and an overexpression of noncognitive symptoms in AD.

Lack of effect of acute, subchronic, or chronic stress on glycogen synthase kinase-3beta protein levels in rat frontal cortex

Glycogen synthase kinase (GSK)-3beta is a conserved serine/threonine protein kinase highly abundant in brain tissue. A dominant mechanism by which cells react to stress involves GSK-3beta. We studied the effect of stress on GSK-3beta levels ex vivo. We have previously found reduced GSK-3beta protein levels and GSK-3 activity in postmortem prefrontal cortex of schizophrenic patients. Since schizophrenic patients experience stress more severely than healthy people, we questioned whether their GSK-3beta reduction is stress-related using a rat model. Rats were exposed to acute, subchronic, or chronic stress using brief cold restraint. No effect was found on frontal cortex GSK-3beta protein levels. These results suggest that reduction in GSK-3beta levels in schizophrenic patients is not affected by cold restraint stress and supports the possibility that the changes observed in postmortem brains may be related to the disease.

DnaK dependence of mutant ethanol oxidoreductases evolved for aerobic function and protective role of the chaperone against protein oxidative damage in Escherichia coli

The adhE gene of Escherichia coli encodes a multifunctional ethanol oxidoreductase (AdhE) that catalyzes successive reductions of acetyl-CoA to acetaldehyde and then to ethanol reversibly at the expense of NADH. Mutant JE52, serially selected for acquired and improved ability to grow aerobically on ethanol, synthesized an AdhE(A267T/E568K) with two amino acid substitutions that sequentially conferred improved catalytic properties and stability. Here we show that the aerobic growth ability on ethanol depends also on protection of the mutant AdhE against metal-catalyzed oxidation by the chaperone DnaK (a member of the Hsp70 family). No DnaK protection of the enzyme is evident during anaerobic growth on glucose. Synthesis of DnaK also protected E. coli from H2O2 killing under conditions when functional AdhE is not required. Our results therefore suggest that, in addition to the known role of protecting cells against heat stress, DnaK also protects numerous kinds of proteins from oxidative damage.

The cerebrocortical areas in normal brain aging and in Alzheimer's disease: noticeable differences in the lipid peroxidation level and in antioxidant defense

The markers of oxidative stress were measured in four cerebrocortical regions of Alzheimer's disease (AD) and age-matched control brains. In controls the levels of diene conjugates (DC) and lipid peroxides (LOOH) were significantly higher in the sensory postcentral and occipital primary cortex than in the temporal inferior or frontal inferior cortex. The antioxidant capacity (AOC) was highest in the temporal, and GSH in the frontal inferior cortex. The highest activity of superoxide dismutase (SOD) and catalase (CAT) was found in the occipital primary cortex. Compared with controls, significantly higher level of DC and LOOH and attenuated AOC were evident in AD temporal inferior cortex. In AD frontal inferior cortex moderate increase in LOOH was associated with positive correlation between SOD activity and counts of senile plaques. Our data suggest that in AD cerebral cortex, the oxidative stress is expressed in the reducing sequence: temporal inferior cortex > frontal inferior cortex > sensory postcentral cortex approximately = occipital primary cortex, corresponding to the histopathological spreading of AD from the associative to primary cortical areas.

Identification of age-dependent changes in expression of senescence-accelerated mouse (SAMP8) hippocampal proteins by expression array analysis

Aging is associated with extensive cognitive impairments, although the biochemical and physiological basis of these deficits are unknown. As the hippocampus plays a vital role in cognitive functions, we have selected this tissue to analyze changes in gene expression at two different ages. Array technology is utilized to explore how gene expression in hippocampus is affected by accelerated cognitive impairment in Senescence-Accelerated Mouse (SAM P8) strain. We show that the expression of genes associated with stress response and xenobiotic metabolism are strongly affected at a time when cognitive impairment occurs. Affected genes include those involved both in signaling and chaperone function. The effector and regulator family of chaperones, which play an important role in protein folding, and also the xenobiotic metabolizing enzymes that play crucial role in antioxidant systems, show significant changes in gene expression between 4 and 12 months.

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

Beta-amyloid ((A)beta) is a peptide of 39-42 amino acids that is the primary component of plaques in Alzheimer's disease (AD). The mechanism by which (A)beta expresses its neurotoxic effects may involve induction of reactive oxygen species (ROS) and elevation of intracellular free calcium levels. Cultured cortical cells were utilized to study the alterations in calcium homeostasis underlying the neurotoxic effect of (A)beta. Serum supplement B27 and vitamin E were effective in preventing neuronal death as assessed by lactate dehydrogenase (LDH) release, (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and number of apoptotic nuclei. In addition, (A)beta-induced cytosolic free calcium ([Ca2+]i) was blocked by antioxidants vitamin E and U83836E, but not by N-methyl-D-aspartic acid (NMDA) receptor antagonist MK-801, or by voltage-gated calcium channel blocker nimodipine. Taken together, the results suggest that NMDA receptor and voltage-gated calcium channels are not involved in (A)beta-induced [Ca2+]i increase. This increase appeared to be the result of extracellular calcium influx by some unknown mechanisms. In addition, antioxidants such as B27 were effective in protecting cultured cortical neurons against (A)beta, and correlated with (A)beta attenuation of early calcium response.

Redox potential measurements of plasma in patients undergoing coronary artery bypass graft and its clinical significance

The apparent redox potentials (Em) of plasma as a marker of oxidant injury during coronary artery bypass graft (CABG) is determined, and their clinical significance is discussed. We measured plasma Em of normal volunteers (n = 20) and samples drawn at different time points from patients undergoing elective CABG (n = 60) directly and by adding 5 microl (20 mM) oxidants or reductants with known redox potential to plasma (95 microl), using a micro Pt/AgCl combination redox electrode. The Em value stays elevated up to 30 min during the surgery, after the administration of protamine it came down toward a more reduced state. Similar changes are seen with the lactate pyruvate ratio. Smaller changes of Em than normal are observed in plasma samples from patients treated with Aprotinin (antiprotease), Carmeda (heparin-coated) circuit and aspirin reflecting their protective effect. Redox potential (Em) measurements appear to be effective and useful in monitoring redox shifts wherever oxidative stress needs to be monitored.

Melatonin prevents death of neuroblastoma cells exposed to the Alzheimer amyloid peptide

Studies from several laboratories have generated evidence suggesting that oxidative stress is involved in the pathogenesis of Alzheimer's disease (AD). The finding that the amyloid beta protein (Abeta) has neurotoxic properties and that such effects are, in part, mediated by free radicals has provided insights into mechanisms of cell death in AD and an avenue to explore new therapeutic approaches. In this study we demonstrate that melatonin, a pineal hormone with recently established antioxidant properties, is remarkably effective in preventing death of cultured neuroblastoma cells as well as oxidative damage and intracellular Ca2+ increases induced by a cytotoxic fragment of Abeta. The effects of melatonin were extremely reproducible and corroborated by multiple quantitative methods, including cell viability studies by confocal laser microscopy, electron microscopy, and measurements of intracellular calcium levels. The importance of this finding is that, in contrast to conventional antioxidants, melatonin has a proposed physiological role in the aging process. Secretion levels of this hormone are decreased in aging and more severely reduced in AD. The reported phenomenon may be of therapeutic relevance in AD.