Apoptosis and oxidative stress in the aging brain

The role of astrocytes response triggered by hyperglycaemia during spinal cord injury

Objective: This manuscript aimed to provide a comprehensive overview of the physiological, molecular, and cellular mechanisms triggered by reactive astrocytes (RA) in the context of spinal cord injury (SCI), with a particular focus on cases involving hyperglycaemia.Methods: The compilation of articles related to astrocyte responses in neuropathological conditions, with a specific emphasis on those related to SCI and hyperglycaemia, was conducted by searching through databases including Science Direct, Web of Science, and PubMed.Results and Conclusions: This article explores the dual role of astrocytes in both neurophysiological and neurodegenerative conditions within the central nervous system (CNS). In the aftermath of SCI and hyperglycaemia, astrocytes undergo a transformation into RA, adopting a distinct phenotype. While there are currently no approved therapies for SCI, various therapeutic strategies have been proposed to alleviate the detrimental effects of RAs following SCI and hyperglycemia. These strategies show promising potential in the treatment of SCI and its likely comorbidities.

BaZiBuShen alleviates cognitive deficits and regulates Sirt6/NRF2/HO-1 and Sirt6/P53-PGC-1α-TERT signaling pathways in aging mice

ETHNOPHARMACOLOGICAL RELEVANCE

BaZiBuShen formula (BZBS) is clinically used to counteract mental fatigue and to retard the aging process. Brain aging echoes in major risks of human sufferings and has become one of the main challenges to our societies and the health-care systems.

AIM OF THE STUDY

To investigate the effect and mode of action of BZBS on aging-associated cognitive impairments.

MATERIALS AND METHODS

BZBS was orally administered to D-galactose and NaNO2-induced aging mice. Premature senescence was assessed using the Morris water maze, step-down type passive avoidance, and pole-climbing tests. Telomere length was examined by qPCR analysis. Telomerase activity was assessed using PCR ELISA assay. Mitochondrial complex IV activity was examined by biochemical test. The levels of redox and immune status were determined by ELISA or biochemical assay. The expressions of sirtuin 6 (Sirt6), peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α), P53, telomerase reverse transcriptase (TERT), heme oxygenase-1 (HO-1), phospho(p)-nuclear factor erythroid-2 related factor 2 (NRF2), caspase-3, Bcl-2 associated x (Bax), and B-cell lymphoma-2 (Bcl-2) in the cerebral cortex were examined by Western blot and/or immunohistochemical staining.

RESULTS

BZBS intervention ameliorated reduced brain performances in aging mice, including memory, cognitive, and motor functions. In addition, BZBS administration to aging mice preserved redox homeostasis, attenuated immunosenescence, and maintained telomerase activity and telomere length. Moreover, BZBS treatment were associated with a declines in P53, caspase-3, Bax expressions and an increase in Sirt6, p-HO-1, p-NRF2, PGC-1α, and Bcl-2 expressions in the brains of this rapid aging mouse.

CONCLUSIONS

BZBS attenuates premature senescence possibly via the preservation of redox homeostasis and telomere integrity, and inhibition of apoptosis in rapid aging mouse. The mechanism governing the alterations may be associated with through the activation of Sirt6/NRF2/HO-1 and Sirt6/P53-PGC-1α-TERT signaling pathways. The results suggest that BZBS may provide a novel strategy for confronting aging and age-associated diseases.

Docosahexanoic acid signals through the Nrf2-Nqo1 pathway to maintain redox balance and promote neurite outgrowth

Evidence suggests that n-3 polyunsaturated fatty acids may act as activators of the Nrf2 antioxidant pathway. The antioxidant response, in turn, promotes neuronal differentiation and neurite outgrowth. Nrf2 has recently been suggested to be a cell intrinsic mediator of docosohexanoic acid (DHA) signaling. In the current study, we assessed whether DHA-mediated axodendritic development was dependent on activation of the Nrf2 pathway and whether Nrf2 protected from agrochemical-induced neuritic retraction. Expression profiling of the DHA-enriched Fat-1 mouse brain relative to wild type showed a significant enrichment of genes associated with neuronal development and neuronal projection and genes associated with the Nrf2-transcriptional pathway. Moreover, we found that primary cortical neurons treated with DHA showed a dose-dependent increase in Nrf2 transcriptional activity and Nrf2-target gene expression. DHA-mediated activation of Nrf2 promoted neurite outgrowth and inhibited oxidative stress-induced neuritic retraction evoked by exposure to agrochemicals. Finally, we provide evidence that this effect is largely dependent on induction of the Nrf2-target gene NAD(P)H: (quinone acceptor) oxidoreductase 1 (NQO1), and that silencing of either Nrf2 or Nqo1 blocks the effects of DHA on the axodendritic compartment. Collectively, these data support a role for the Nrf2-NQO1 pathway in DHA-mediated axodendritic development and protection from agrochemical exposure.

Astrocytic Oxidative/Nitrosative Stress Contributes to Parkinson's Disease Pathogenesis: The Dual Role of Reactive Astrocytes

Parkinson’s disease (PD) is the second most common neurodegenerative disease worldwide; it is characterized by dopaminergic neurodegeneration in the substantia nigra pars compacta, but its etiology is not fully understood. Astrocytes, a class of glial cells in the central nervous system (CNS), provide critical structural and metabolic support to neurons, but growing evidence reveals that astrocytic oxidative and nitrosative stress contributes to PD pathogenesis. As astrocytes play a critical role in the production of antioxidants and the detoxification of reactive oxygen and nitrogen species (ROS/RNS), astrocytic oxidative/nitrosative stress has emerged as a critical mediator of the etiology of PD. Cellular stress and inflammation induce reactive astrogliosis, which initiates the production of astrocytic ROS/RNS and may lead to oxidative/nitrosative stress and PD pathogenesis. Although the cause of aberrant reactive astrogliosis is unknown, gene mutations and environmental toxicants may also contribute to astrocytic oxidative/nitrosative stress. In this review, we briefly discuss the physiological functions of astrocytes and the role of astrocytic oxidative/nitrosative stress in PD pathogenesis. Additionally, we examine the impact of PD-related genes such as α-synuclein, protein deglycase DJ-1( DJ-1), Parkin, and PTEN-induced kinase 1 (PINK1) on astrocytic function, and highlight the impact of environmental toxicants, such as 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), rotenone, manganese, and paraquat, on astrocytic oxidative/nitrosative stress in experimental models.

Revisiting nicotine’s role in the ageing brain and cognitive impairment

Brain ageing is a complex process which in its pathologic form is associated with learning and memory dysfunction or cognitive impairment. During ageing, changes in cholinergic innervations and reduced acetylcholinergic tonus may trigger a series of molecular pathways participating in oxidative stress, excitotoxicity, amyloid-β toxicity, apoptosis, neuroinflammation, and perturb neurotrophic factors in the brain. Nicotine is an exogenous agonist of nicotinic acetylcholine receptors (nAChRs) and acts as a pharmacological chaperone in the regulation of nAChR expression, potentially intervening in age-related changes in diverse molecular pathways leading to pathology. Although nicotine has therapeutic potential, paradoxical effects have been reported, possibly due to its inverted U-shape dose-response effects or pharmacokinetic factors. Additionally, nicotine administration should result in optimum therapeutic effects without imparting abuse potential or toxicity. Overall, this review aims to compile the previous and most recent data on nicotine and its effects on cognition-related mechanisms and age-related cognitive impairment.

Phosphoinositide and Erk signaling pathways mediate activity-driven rodent olfactory sensory neuronal survival and stress mitigation

Olfactory sensory neurons (OSNs) are the initial site for olfactory signal transduction. Therefore, their survival is essential to olfactory function. In the current study, we demonstrated that while odorant stimulation promoted rodent OSN survival, it induced generation of reactive oxygen species in a dose- and time-dependent manner as well as loss of membrane potential and fragmentation of mitochondria. The MEK-Erk pathway played a critical role in mediating these events, as its inhibition decreased odorant stimulation-dependent OSN survival and exacerbated intracellular stress measured by reactive oxygen species generation and heat-shock protein 70 expression. The phosphoinositide pathway, rather than the cyclic AMP pathway, mediated the odorant-induced activation of the MEK-Erk pathway. These findings provide important insights into the mechanisms of activity-driven OSN survival, the role of the phosphoinositide pathway in odorant signaling, and demonstrate that odorant detection and odorant stimulation-mediated survival proceed via independent signaling pathways. This mechanism, which permits independent regulation of odorant detection from survival signaling, may be advantageous if not diminished by repeated or prolonged odor exposure. We investigated the role of odorant stimulation in generating cellular stress and the molecular mechanisms mitigating such stress and promoting neuronal survival. Odorant stimulation promoted olfactory sensory neuron (OSN) survival and also induced intracellular oxidative stress, which was exacerbated when MEK/Erks pathway was inhibited. Sensory stimulation simultaneously activated at least two parallel pathways, the AC/cAMP cascade responsible for odorant detection, and phosphoinositide hydrolysis to promote odorant stimulation-dependent neuronal survival odorants may activate parallel signaling cascades to mediate sensory detection and sensory stimulation-dependent survival. AC, adenylyl cyclase; cAMP, cyclic adenosine monophosphate; Erk, extracellular signal-regulated kinase; MEK, MAPK/ERK kinase.

Ototoxic Model of Oxaliplatin and Protection from Nicotinamide Adenine Dinucleotide

Oxaliplatin, an anticancer drug commonly used to treat colorectal cancer and other tumors, has a number of serious side effects, most notably neuropathy and ototoxicity. To gain insights into its ototoxic profile, oxaliplatin was applied to rat cochlear organ cultures. Consistent with it neurotoxic propensity, oxaliplatin selectively damaged nerve fibers at a very low dose 1 μM. In contrast, the dose required to damage hair cells and spiral ganglion neurons was 50 fold higher (50 μM). Oxailiplatin-induced cochlear lesions initially increased with dose, but unexpectedly decreased at very high doses. This non-linear dose response could be related to depressed oxaliplatin uptake via active transport mechanisms. Previous studies have demonstrated that axonal degeneration involves biologically active processes which can be greatly attenuated by nicotinamide adenine dinucleotide (NAD+). To determine if NAD+ would protect spiral ganglion axons and the hair cells from oxaliplatin damage, cochlear cultures were treated with oxaliplatin alone at doses of 10 μM or 50 μM respectively as controls or combined with 20 mM NAD+. Treatment with 10 μM oxaliplatin for 48 hours resulted in minor damage to auditory nerve fibers, but spared cochlear hair cells. However, when cochlear cultures were treated with 10 μM oxaliplatin plus 20 mM NAD+, most auditory nerve fibers were intact. 50 μM oxaliplatin destroyed most of spiral ganglion neurons and cochlear hair cells with apoptotic characteristics of cell fragmentations. However, 50 μM oxaliplatin plus 20 mM NAD+ treatment greatly reduced neuronal degenerations and hair cell missing. The results suggested that NAD+ provides significant protection against oxaliplatin-induced neurotoxicity and ototoxicity, which may be due to its actions of antioxidant, antiapoptosis, and energy supply.

Peroxynitrite induces neuronal cell death in aging and age-associated disorders: A review

Peroxynitrite produced from nitric oxide and superoxide has been proposed to cause neuronal dysfunction and cell death in aging and age-related degenerative diseases. 3-Nitrotyosine, an oxidation product of tyrosine by peroxynitrite, was reported to increase in degenerating brains. In this paper, involvement of peroxynitrite in neuronal cell death was studied by analyses of human brains and in vitro experiments on cell death induced by a peroxynitrite-generating agent, SIN-1. 3-Nitrotyrosine-containing proteins were detected in lipofuscin, a typical aging-related pigment in human brains. The cytotoxicity of peroxynitrite was examined in human dopaminergic SH-SY5Y cells by use of SIN-1. SIN-1 induced apoptotic cell death in the cells, and increased the level of 3-nitrotyrosine-containing proteins. The intracellular transduction of death signal was studied in apoptosis induced by peroxynitrite. Apoptosis was induced by sequential death cascade, collapse of mitochondrial membrane potential, activation of caspases and fragmentation of nuclear DNA. In addition, phosphorylation of p38 mitogen activated phosphokinase (MAPK) was found to be associated with apoptosis by SIN-1, as shown by inhibition of apoptotic process by SB202190, a p38 inhibitor. Involvement of peroxynitrite in the cell death is discussed in relation to neuronal degeneration in aging and age-associated diseases.

New and old mechanisms associated with hypertension in the elderly

Hypertension is a widely prevalent and important risk factor for cardiovascular diseases that increase with aging. The hallmark of hypertension in the elderly is increased vascular dysfunction. However, the molecular mechanisms by which increased blood pressure leads to vascular injury and impaired endothelial function are not well defined. In the present paper, we will analyze several mechanisms described in the scientific literature involved in hypertension in the elderly as endothelial dysfunction, increased oxygen delivery to tissues, inflammation, cellular apoptosis, and increased concentration of active metabolites. Also, we will focus on new molecular mechanisms involved in hypertension such as telomeres shortening, progenitor cells, circulating microparticles, and epigenetic factors that have appeared as possible causes of hypertension in the elderly. These molecular mechanisms may elucidate different origin for hypertension in the elderly and provide us with new targets for hypertension treatment.

The biology of aging and frailty

In developing and validating the concept of frailty as a geriatric syndrome, it has been necessary to distinguish the clinical expression of frailty from normal age-related changes and other age-related disease pathologies. A framework for excluding potentially confounding disease and a working clinical tool to diagnose frailty have been provided. The associations between frailty and other pathophysiologies has also been shown. However, investigating the underlying biologic basis for the geriatric syndrome of frailty by studying basic homeostatic pathways and mechanisms has not proceeded at the same rate. The following article provides an overview of the homeostatic pathways emphasized in research on aging and explains how this science may help to stimulate frailty research.

Protective effect of nicotinamide against poly(ADP-ribose) polymerase-1-mediated astrocyte death depends on its transporter-mediated uptake

AIM

Poly(ADP-ribose) polymerase-1 (PARP-1) is a DNA repair enzyme, and its excessive activation, following ischemia, trauma, etc., depletes cellular nicotinamide adenine dinucleotide (NAD(+)) as a substrate and eventually leads to brain cell death. Nicotinamide, an NAD(+) precursor and a PARP-1 inhibitor, is known to prevent PARP-1-triggered cell death, but there is no available information on the mechanisms involved in its transport. Here we clarified the transport characteristics of nicotinamide in primary cultured mouse astrocytes.

MAIN METHODS

Uptake characteristics of [(14)C]nicotinamide were assessed by a conventional method with primary cultured mouse astrocytes. Cell viability and PARP-1 activity were determined with intracellular LDH activity and immunocytochemical detection of PAR accumulation, respectively.

KEY FINDINGS

PARP-1 activation was induced by treatment of astrocytes with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), an alkylating agent. MNNG-triggered astrocyte death and PAR accumulation were completely inhibited by treatment with nicotinamide as with DPQ (3,4-dihydro-5-(4-(1-piperidinyl)butoxy)-1(2H)-isoquinolinone), a second generation PARP inhibitor. The uptake of [(14)C]nicotinamide was time-, temperature-, concentration- and pH-dependent, and was inhibited and stimulated by co- and pre-treatment with N-methylnicotinamide, a representative substrate of an organic cation transport system, respectively. Co-treatment of astrocytes with nicotinamide and N-methylnicotinamide resulted in a decrease in PAR accumulation and absolute prevention of cell death.

SIGNIFICANCE

These findings suggest that nicotinamide has a protective effect against PARP-1-induced astrocyte death and that its transporter-mediated uptake, which is extracellular pH-sensitive and common to N-methylnicotinamide, is critical for prevention of PARP-1-triggered cell death.

Serum markers of apoptosis decrease with age and cancer stage

The physical manifestations of aging reflect a loss of homeostasis that effects molecular, cellular and organ system functional capacity. As a sentinel homeostatic pathway, changes in apoptosis can have pathophysiological consequences in both aging and disease. To assess baseline global apoptosis balance, sera from 204 clinically normal subjects had levels of sFas (inhibitor of apoptosis), sFasL (stimulator of apoptosis), and total cytochrome c (released from cells during apoptosis) measured. Serum levels of sFas were significantly higher while sFasL and cytochrome c levels were lower in men compared to women. With increasing age there was a decrease in apoptotic markers (cytochrome c) and pro-apoptotic factors (sFasL) and an increase in anti-apoptotic factors (sFas) in circulation. The observed gender differences are consistent with the known differences between genders in mortality and morbidity. In a separate cohort, subjects with either breast (n = 66) or prostate cancer (n = 38) exhibited significantly elevated sFas with reduced sFasL and total cytochrome c regardless of age. These markers correlated with disease severity consistent with tumor subversion of apoptosis. The shift toward less global apoptosis with increasing age in normal subjects is consistent with increased incidence of diseases whose pathophysiology involves apoptosis dysregulation.

Cytoprotection of vascular endotheliocytes by phosphorylated ascorbate through suppression of oxidative stress that is generated immediately after post-anoxic reoxygenation or with alkylhydroperoxides

Vascular endotheliocytes BAE-2 underwent the gradually proceeding cell death until 48 h after reoxygenation (Reox) following 3 h anoxia (Anox), but protected by pre-Anox administration with L-ascorbic acid (Asc)-2-O-phosphate (Asc2P), an autooxidation-resistant Asc derivative, but not by Asc itself. This cytoprotection with Asc2P was achieved in a glucose (Glc)-lacking buffer more advantageously than in a Glc-containing buffer where less efficiency had been demonstrated for Asc entry into BAE-2 cells than in a Glc-lacking buffer. Superoxide anion radicals were detected explosively in the extracellular space at 2-5 min after Reox following the Anox treatment of HUVE endotheliocytes, and were thereafter retained at levels as high as approximately one-half of the maximum level until 60 min after Reox, as shown by cytochrome c reduction assay. Superoxide anions at 3 and 60 min after Reox were suppressed by pre-Anox administration with Asc2P, but not with Asc or dehydro-Asc, and were not suppressed by post-Anox administration with Asc2P; the cytoprotection may need the intracellular accumulation of the ROS-scavenging effector Asc that is converted from Asc2P until 3 min after Reox. The ROS-generator tert-butylhydroperoxide (t-BuOOH) also induced both the diminished cell viability and nuclear DNA strand cleavages of BAE-2 endotheliocytes, which were also protected dose-dependently with Asc2P. The cytoprotection was attributed to reduction of intracellular ROS including hydroperoxide and hydrogen peroxide with Asc2P as shown by fluorometry with the redox indicator CDCFH-DA. Thus Anox/Reox-induced cell death can be prevented by Asc2P that suppresses ROS-generation immediately after Reox following Anox more efficiently in the intracellular sphere rather than in the extracellular space.

Differential regulation of apoptotic cell death in senescent human cells

Aging of human cells can be reproduced in monolayer cultures, revealing the phenotype of replicative senescence. It was shown that diploid human fibroblasts enter a stable growth arrest phenotype at the end of their lifespan and, in particular, these cells are resistant to various apoptotic stimuli. In contrast, human endothelial cells from the umbilical vein (HUVEC) acquire a proapoptotic phenotype when reaching senescence and this probably results from reactive oxygen species (ROS) induced damage and associated signaling. Ceramides were shown to accumulate in senescent fibroblasts and are also known as potent regulators of apoptotic cell death. To further study age-associated changes in proneness to apoptosis between fibroblasts and endothelial cells, both cell types were challenged by administration of exogenous ceramide and apoptotic cell death was determined. While ceramide can efficiently induce apoptosis in both young and senescent cells of either histotype, quantitative evaluation of the data show that senescent fibroblasts are more resistant to apoptosis induction when compared to their young counterparts, whereas in the case of endothelial cells proneness for apoptosis is increased in senescent cells. Together, these data suggest significant differences in the regulation of apoptosis associated with senescence in fibroblasts and endothelial cells.

The soy isoflavone, genistein, protects human cortical neuronal cells from oxidative stress

Genistein, a soy isoflavone, has been shown to mimic the pharmacological actions of the endogenous steroid estrogen with which it has structural similarities. There is now evidence that the genistein can prevent disorders-like heart diseases, cancer and diabetes as well. However, very few studies have looked at the effect of genistein on the central nervous system. Published studies also show conflicting conclusions regarding the effects of genistein in the brain. The current study was conducted in the human cortical cell lines HCN1-A and HCN2 in order to determine the neuroprotective efficacy of genistein. It was observed that pre-treatment with 50 or 10 microM genistein was able to protect HCN1-A and HCN2 cells from the cell death induced by 100 microM or 1 mM tertiary butylhydroperoxide (t-BuOOH; a free radical generating toxin). The morphological disruption caused by t-BuOOH was also prevented by genistein in HCN2 cells. Moreover, genistein was able to prevent the down-regulation of the anti-apoptotic protein bcl-2 that was caused by t-BuOOH treatment. These results indicate that genistein may have neuroprotective effect in cortical cells, which may be mediated by its regulation of the anti-apoptotic protein bcl-2.

A comparative study of the effect of oxidative stress on the cytoskeleton in human cortical neurons

Cytoskeleton disruption is a process by which oxidative stress disrupts cellular function. This study compares and contrasts the effect of oxidative stress on the three major cytoskeleton filaments, microfilaments (MFs), microtubule (MT), and vimentin in human cortical neuronal cell line (HCN2). HCN2 cells were treated with 100 microM tertiary butylhydroperoxide (t-BuOOH), a free radical generating neurotoxin for 1, 3, or 6 h. Cell viability studies demonstrated significant cell death although the morphology studies showed that there was a substantial loss in neurites of neurons treated with t-BuOOH for 6 h. Because the cytoskeleton plays a role in neurite outgrowth, the effect of oxidative stress on the cytoskeletal was studied. In neurons subjected to oxidative stress for 30 min or 1 h, there were no major changes in microfilament distribution though there was altered distribution of microtubule and vimentin filaments as compared to controls. However, loss and disruption of all the three cytoskeletal filaments was observed at later times (3 and 6 h), which was confirmed by Western Blot analysis. Further studies were done to measure the gene expression levels of actin, tubulin, and vimentin. Results indicated that the overall loss of the cytoskeletal proteins in neurons treated with free radical generating toxin might not be a direct result of the downregulation of the cytoskeletal genes. This study shows that free radical generation in human neurons leads to the disruption of the cytoskeleton, though there may be a difference in the susceptibility to oxidative stress among the individual components of the cytoskeletal filaments.

Zinc- or cadmium-pre-induced metallothionein protects human central nervous system cells and astrocytes from radiation-induced apoptosis

We have shown the protection of human central nervous system (CNS) cultures by zinc (Zn) or cadmium (Cd)-pre-induced metallothionein (MT) synthesis from radiation-induced cytotoxicity (lactate dehydrogenase (LDH) release and neuronal dendritic injury). The present study is to further define the types of cell death induced by different dose levels of radiation and investigate the effect of MT induction (by Zn or Cd) on radiation-induced apoptosis in primary human CNS and astrocyte cultures. Apoptosis was detected by fragmented DNA electrophoresis, TUNEL technique, and propidium iodide staining. Expression of MT protein was examined by immunofluorescent staining. Results showed that exposure of primary human CNS cultures to 15 and 30 Gy gamma-radiation predominantly induced apoptotic cell death, while exposure to 60 Gy gamma-radiation predominantly induced necrotic cell death. Normal primary human CNS cultures showed weak MT staining, while primary human CNS cultures exposed to Zn or Cd showed intense MT staining. The induced apoptotic cell death by exposure to 30 Gy gamma-radiation increased to a maximum level at 12 and 24 h, and was reduced significantly by Zn or Cd pre-induced MT. Using primary human astrocytes, the induction of MT protein by Zn or Cd was further confirmed. The enhanced MT expression also afforded a significant protection from 30 Gy gamma-ray-induced apoptosis in the primary human astrocytes. These results suggest that MT protected human CNS cells from apoptosis following ionizing radiation, probably through its antioxidant property.

Preventive effects of a water-soluble derivative of chroman moiety of vitamin E on lipid hydroperoxide-induced cell injuries and DNA cleavages through repressions of oxidative stress in the cytoplasm of human keratinocytes

ChrCrx (6-hydroxy-2, 5, 7, 8-tetramethyl-chroman-2-carboxylic acid) is a water-soluble analog in which 4', 8', 12'-trimethyltridecyl chain is deleted from an alpha-tocopherol molecule known as a hydrophobic antioxidant. Cell viability of human skin epidermal keratinocytes HaCaT was lowered by treatment with tert-butylhydroperoxide (t-BuOOH) of 50 microM for 48 h, designated as a subacute cytotoxicity, which was prevented by previous administration with ChrCrx in a dose-dependent manner as estimated by mitochondrial function-based WST-1 assay and cell morphological microscopy. In contrast an acute cytotoxicity due to treatment with t-BuOOH as dense as 200 microM for a period as short as 2 h could be also prevented with ChrCrx that was administered before and after, but was eliminated during, treatment with t-BuOOH. In contrast alpha-tocopherol was not cytoprotective against t-BuOOH. DNA strand cleavages were induced with t-BuOOH in the keratinocytes, and could be prevented by ChrCrx more effectively than alpha-tocopherol as assayed by TUNEL stain. The intracellular reactive oxygen species (ROS) was accumulated in a manner dependent on periods of t-BuOOH treatment in the cytoplasm more abundantly rather than the nucleus of keratinocytes, and was markedly diminished by ChrCrx as shown by fluorography using the redox indicator dye. Thus t-BuOOH-induced cell injuries and DNA cleavages of the keratinocytes can be prevented at least in part through efficient diminishment of ROS generated in the cytoplasm, to which the preferred distribution of ChrCrx may be advantageous over to the nucleus or membrane owing to its molecular hydrophilicity relative to alpha-tocopherol.

The effect of tertiary butylhydroperoxide and nicotinamide on human cortical neurons

It is well known that the generation of oxygen radicals can cause neuronal death by both apoptosis and necrosis, which may lead to the onset of neurodegenerative diseases. In previous in vivo studies, nicotinamide was found to prevent both DNA fragmentation and apoptosis that were induced by free radical generating toxins like tertiary butylhydroperoxide (t-BuOOH). Nicotinamide is a precursor for NAD and is an inhibitor of the enzyme poly(ADP-ribose) polymerase (PARP). However, the effect of nicotinamide on the regulation of pro- and anti-apoptotic proteins in neurons is not clear. In our study, the human cortical neuronal cell line HCN1-A has been used to determine the mechanism of action of nicotinamide at the cellular level. Cell viability studies showed that t-BuOOH treatment (both 100 microM and 1mM) caused significant cell death at 24 and 48h compared to control cells. Pretreatment with 1mM nicotinamide before t-BuOOH administration caused significant reduction in cell death. Moreover, the morphology of HCN1-A cells that were treated with both nicotinamide and t-BuOOH appeared to be closer to control cells when compared to HCN1-A cells treated with only t-BuOOH. Also, t-BuOOH treatment caused an elevation in the levels of the pro-apoptotic proteins p53 and p21/WAF-1 and a reduction in the levels of the anti-apoptotic protein bcl-2 compared to their levels in control HCN1-A cells, while pretreatment with nicotinamide reduced p53 and p21/WAF-1 levels even in the presence of t-BuOOH. However nicotinamide did not seem to alter bcl-2 levels. These results indicate that nicotinamide treatment can protect human neuronal cells from the toxic effects of t-BuOOH.

Anti-apoptotic defense of bcl-2 gene against hydroperoxide-induced cytotoxicity together with suppressed lipid peroxidation, enhanced ascorbate uptake, and upregulated Bcl-2 protein

Although it is well known that Bcl-2 can prevent apoptosis, the Bcl-2's anti-apoptotic mechanism is not fully understood. Here, we investigate the mechanism of oxidant-induced cell death and to investigate the role of Bcl-2 in the tert-butyl hydroperoxide (t-BuOOH)-induced oxidant injury in Rat-1 fibroblasts and their bcl-2 transfected counterparts, b5 cells. Treatment with t-BuOOH causes mitochondrial disfunction and induced morphological features consistent with apoptosis more markedly in Rat-1 cells than in b5 cells. The hydroperoxide t-BuOOH at concentrations less than 100 nM for as long as 48 h or with higher concentrations (up to 100 microM) for only 3 h induces death in Rat-1 cells, whereas their bcl-2 transfectants were significantly resistant to cytotoxicity by both time and all concentration other than 100 microM. The similar results were obtained also for DNA strand cleavages as detected by TUNEL stain. The bcl-2 transfectants significantly suppressed t-BuOOH-induced increases in both lipid peroxidation and caspase-3 activation 3 and 1 h after t-BuOOH exposure, respectively, but failed to suppress either caspase-1 activation or an enhanced production of the intracellular reactive oxygen species (ROS). Intracellular uptake of [1-(14)C] ascorbic acid (Asc) into the bcl-2 transfectants was superior to that into the non-transfectants always under examined conditions regardless of serum addition to culture medium and cell density. Upregulation of Bcl-2 proteins was rapidly induced after t-BuOOH exposure in the transfectants, but not in non-transfectants, and restored till 24 h to the normal Bcl-2 level. Thus suppressions of both lipid peroxidation and the subsequent cell death events such as caspase-3 activation and DNA cleavage were concerned with the inhibitory effects of Bcl-2 on the t-BuOOH-induced cytotoxicity. And some of these events may correlate with Bcl-2 expression-induced partial enhanced anti-oxidant cellular ability including enrichment of intracellular Asc and oxidative stress-induced upregulation of Bcl-2 protein. On the other hand, ROS production and caspase-1 activation were not related to cytoprotection by Bcl-2.

Nicotinamide therapy protects against both necrosis and apoptosis in a stroke model

BACKGROUND AND PURPOSE

Nicotinamide protects against brain damage in ischemia-reperfusion. However, the dosage and time of treatment require clarification. It is also not clear if nicotinamide can protect against both necrosis and apoptosis.

METHODS

Dose-response and time-effect studies were designed. Transient focal cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) for 90 min. Different doses of nicotinamide were injected upon reperfusion. In time-effect studies, 500 mg/kg nicotinamide was administered at different times after the onset of reperfusion. Neurological finding scores were recorded. Infarct volumes were measured.

RESULTS

In contrast to controls, neurological deficit scores and infarct volumes were greatly reduced by treatment with nicotinamide. The ED(50) of nicotinamide was 239+/-79 mg/kg (P=.95). It was found that nicotinamide injected during the first 6 h of reperfusion could effectively inhibit the development of brain damage. The optimal dose of nicotinamide was 500 mg/kg and gave a maximal response.

CONCLUSIONS

Poly(ADP-ribose) polymerase (PARP) plays a key role in DNA repair in stroke. Excessive PARP activity consumes NAD leading to energy depletion and neuronal damage. As an inhibitor of PARP, nicotinamide promotes the supply of energy. The results suggest that early application of nicotinamide at a suitable dosage significantly ameliorates necrotic and apoptotic brain injury after focal ischemia-reperfusion.

Differences between hippocampus and cerebral cortex in aged rats in an oxidative stress model

Ozone exposure increases the production of free radicals that causes oxidative stress (OS), a state that also occurs during aging and in neurodegenerative diseases. This study identified ultrastructural alterations produced by OS induced by acute ozone exposure in hippocampus and prefrontal cortex in aged compared with young rats. Animals were exposed to 0.70 ppm ozone for 4 h, and controls to flowing air. After the exposure, the tissues were processed for ultrastructural analysis. Results showed increased ultrastructural alterations in the hippocampus and prefrontal cortex in the aged exposed animals compared with controls. OS enhanced the modifications induced by the aging process in those areas related with learning and memory functions, which are the first where degenerative aging changes are observed.

Replicative senescence of human endothelial cells in vitro involves G1 arrest, polyploidization and senescence-associated apoptosis

Human ageing is characterized by a progressive loss of physiological functions, increased tissue damage and defects in various tissue renewal systems. Age-related decreases of the cellular replicative capacity can be reproduced by in vitro assays of cellular ageing. When diploid human fibroblasts reach their finite lifespan, they enter an irreversible G1 growth arrest status referred to as replicative senescence. While deregulation of programmed cell death (apoptosis) is a key feature of age-related pathology in several tissues, this is not reflected in the standard in vitro senescence model of human fibroblasts, and the role of apoptosis during cellular ageing remains unclear. We have analyzed replicative senescence of human umbilical vein endothelial cells (HUVEC) in vitro and found that senescent HUVEC also arrest in the G1 phase of the cell cycle but, unlike fibroblasts, accumulate with a 4N DNA content, indicative of polyploidization. In contrast to human fibroblasts, senescent endothelial cells display a considerable increase in spontaneous apoptosis. The data imply that age-dependent apoptosis is a regular feature of human endothelial cells and suggest cell type specific differences in human ageing.

Nicotinic receptors in human brain: topography and pathology

Brain nicotinic acetylcholine receptors (nAChR) are a class of ligand-gated channels composed of alpha and beta subunits with specific structural, functional and pharmacological properties. They participate in the physiological and behavioural effects of acetylcholine and mediate responses to nicotine. They are associated with numerous transmitter systems and their expression is altered during development and ageing as well as in diseases such as autism, schizophrenia, Alzheimer's disease, Parkinson's disease and Lewy body dementia. Nicotinic receptors containing a number of different subunits are highly expressed during early human development. Disorders believed to be associated with abnormal brain maturation involve deficits in both alpha4beta2, in the case of autism, and alpha7 possibly in addition to alpha4beta2 nAChRs in the case of schizophrenia. In ageing and age-related neurodegenerative disorders nAChR deficits are predominantly associated with alpha4-containing receptors, although some studies also indicate the involvement of alpha3 and alpha7 subunits. Whilst ageing appears to be associated with reductions in subunit mRNA as well as protein expression, in Alzheimer's disease only protein loss is apparent. Nicotinic therapy may be of benefit in a number of neurological conditions, however studies evaluating further both the distribution of specific subunit involvement and the correlation of nAChR deficits with clinical symptoms are required to inform therapeutic strategy.

The NAD+ precursors, nicotinic acid and nicotinamide protect cells against apoptosis induced by a multiple stress inducer, deoxycholate

The bile salt, sodium deoxycholate (NaDOC), is a natural detergent that promotes digestion of fats. At high physiologic levels, NaDOC activates many stress-response pathways and induces apoptosis in various cell types. NaDOC induces DNA damage and activates poly(ADP-ribose) polymerase (PARP), an enzyme that utilizes NAD+ as a substrate to repair DNA. NaDOC also induces oxidative stress, endoplasmic reticulum (ER) stress and contributes to protein malfolding. The NAD+ precursors, nicotinic acid (NA) and nicotinamide (NAM) were found to protect cells against NaDOC-induced apoptosis. NA and NAM also decreased constitutive levels of both activated NF-kappaB and GRP78, two proteins that respond to oxidative stress. However, the mechanism by which NA and NAM protects cells against apoptosis does not involve a reduction in constitutive levels of oxidative stress. NA or NAM treatment increased the protein levels of glyceraldehyde-3-phosphate dehydrogense (GAPDH), a multi-functional enzyme, in the nucleus and cytoplasm, respectively. NAM did not activate the promoter/response elements of 13 stress response genes nor reduce intracellular non-protein thiols, suggesting that it is non-toxic to cells. NAM thus has promise as a dietary supplement to help prevent disorders involving excessive apoptosis.

The growth hormone axis and cognition: empirical results and integrated theory derived from giant transgenic mice

Sleep is required for the consolidation of memory for complex tasks, and elements of the growth-hormone (GH) axis may regulate sleep. The GH axis also up-regulates protein synthesis, which is required for memory consolidation. Transgenic rat GH mice (TRGHM) express plasma GH at levels 100-300 times normal and sleep 3.4 h longer (30%) than their normal siblings. Consequently, we hypothesized that they might show superior ability to learn a complex task (8-choice radial maze); 47% of the TRGHM learned the task before any normal mice. All 17 TRGHM learned the task, but 33% of the 18 normal mice learned little. TRGHM learned the task significantly faster than normal mice (p < 0.05) and made half as many errors in doing so, even when the normal nonlearners were excluded from the analysis. Whereas normal mice expressed a linear learning curve, TRGHM showed exponentially declining error rates. The contribution of the GH axis to cognition is conspicuously sparse in literature syntheses of knowledge concerning neuroendocrine mechanisms of learning and memory. This paper synthesizes the crucial role of major components of the GH axis in brain functioning into a holistic framework, integrating learning, sleep, free radicals, aging, and neurodegenerative diseases. TRGHM show both enhanced learning in youth and accelerated aging. Thus, they may provide a powerful new probe for use in gaining an understanding of aspects of central nervous system functioning, which is highly relevant to human health.

Changes in caspase expression in Alzheimer's disease: comparison with development and aging

Changes in caspase-2 and -3 protein levels in Alzheimer's disease (AD) brains were assessed in comparison with their expression in development and aging. The protein levels of caspase-2 and -3 were significantly increased in AD brains, caspase-2 in the particulate fraction and caspase-3 in both the cytosolic and particulate fractions, compared with controls. Immunoblot analysis of brain extracts from embryonic day 19 (E19) to postnatal 96-week-old rats indicated that caspase-3 levels were high from E19 to 2 weeks, while caspase-2 remained high from 4 to 96 weeks, indicating that the expression of caspase-2 and -3 is differentially regulated during development and aging. These results suggest that caspase-2 and -3 are upregulated in AD and that the changes in AD are different from those observed in senescent brains.

The influence of neonatal nutrition on behavioral development: a critical appraisal

Specific nutrients appear to modify the metabolism of neurotransmitters, which are endogenous regulators of neurogenesis, neural migration, and synaptogenesis during both embryonic and early postnatal life. This has led to the question of whether, by affecting neurotransmission, malnutrition during the early neonatal period affects behavioral development. The literature based on animal models suggests that nutrient deficiencies during early life influence neurotransmission and, in some instances, also affect behavioral outcomes. A clear answer to the question, however, remains elusive. This can be attributed to the complexity of the process of brain development, where changes at a cellular level may not necessarily translate into changes at a behavioral level. Future investigations in this important area of research should work toward refinement of the design of behavioral experiments so that these studies can contribute to the understanding of the putative mechanisms involved.

Age-dependent sensitization to oxidative stress by dietary fatty acids

Experiments were designed to test the hypothesis that short-term feeding of a high polyunsaturated fatty acid (PUFA) diet would increase susceptibility to lipid peroxidation in an age-dependent manner. Young (6 month) and old (24 month) male B6C3F1 mice were fed modified AIN-76 diets containing either 5% corn oil (CO, N = 5 per age group) or 19% fish oil plus 1% corn oil (FO, N = 20 per age group) for two weeks. Five CO and five FO diet mice per age received an intraperitoneal injection of normal saline and were sacrificed one hour later; the remaining FO diet mice (N = 15 per age) were challenged with an acute systemic oxidative stress by intraperitoneal injection of 125 mg iron/kg body weight as iron dextran, and were sacrificed 1, 5, and 24 hours post-injection. Microsomal membrane fatty acid analysis revealed that increased age and a FO diet significantly increased membrane PUFA content. Serum iron levels increased significantly following iron treatment, peaking at 5 hours in both age groups. Formation of microsomal malondialdehyde (MDA), a product of lipid peroxidation, was significantly greater in the livers of the young mice. The temporal patterns of serum iron and microsomal MDA concentrations were significantly correlated in young mice, but not in old mice. Histochemical examination showed that liver iron accumulation following iron injection was similar in both age groups, but was associated with a significant temporal increase in liver apoptotic cells in young mice, but not in old mice. Thus, both age groups had similar iron exposure and iron accumulation, and the liver microsomal membranes of old mice were more unsaturated, yet there was significantly greater peroxidative damage (MDA formation) and cell death (apoptosis) in the young mouse livers. These findings suggest that the older animals have upregulated antioxidant defenses.

Differential expression of rat brain bcl-2 family proteins in development and aging

We have previously examined the involvement of the B cell leukemia-2 gene product (Bcl-2) family proteins (Bcl-2, Bcl-x, Bax, Bak, and Bad) in Alzheimer's disease (AD) and found that Bcl-2, Bcl-x, Bak, and Bad were upregulated. As AD is an aging-associated disease, in the present study we examined the developmental and aging-related changes in Bcl-2 family proteins in the rat brain. Immunoblot analyses of brain extracts from embryonic day 19 (E19) to postnatal 96-week-old rats indicated that the Bcl-2 protein level was highest at E19 and decreased after birth. Bcl-x levels remained high from E19 to 96 weeks. Bax levels were high from E19 to 2 weeks and decreased from 4 weeks onward. Bak levels were highest at E19 and decreased abruptly after birth. Bad levels were high from E19 to 2 weeks and decreased abruptly at 4 weeks. The present results suggest that the expression of each Bcl-2 family protein is differentially regulated during development and aging and that the changes in the senescent brains are different from those observed in AD.

Age-related neurodegeneration and oxidative stress: putative nutritional intervention

This review describes age-related changes that occur in neuronal function and cites evidence to show that these alterations may be the result of increased sensitivity to oxidative stress (OS). Evidence is presented to show that the abilities to mitigate the OS effects and to repair the damage from OS show decline as a function of age. Results from age- and OS-sensitive tests are given; these results indicate that one of the major sites of action of OS is the membranes, especially if compromised by high amounts of sphingomyelin, and one of the major effects of OS is to further alter the calcium disregulation in aging. It is suggested that attempts to increase antioxidant protection through diets comprised of fruits and vegetables identified as being high in total antioxidant activity might prevent or reverse the deleterious OS effects on neuronal aging.

Synaptic numbers across cortical laminae and cognitive performance of the rat during ageing

In this study, we have investigated the changes in the number of individual presynaptic boutons in the neocortex of rats and correlated them with cognitive performance. Brown Norway x Fischer 344 F1 hybrid rats, aged from one to 24 months, were used. Using synaptophysin as a marker for presynaptic boutons, we found that in the parietal II region of the neocortex an age-related decrease in the density of immunostained punctae representing presynaptic boutons occurred. Regression analysis showed that this decline in the number of presynaptic boutons correlates with ageing (r=0.495, P<0.05). Interestingly, we found that this age-related depletion of presynaptic boutons was more intense in the deeper cortical lamina, such as laminae V and VI (mean decrease of 18%), than in the superficial laminae (mean decrease of 8% in laminae I-IV). Using the Morris water maze test, we observed that young rats acquired the task at twice the speed of aged animals (48.9 +/- 9.0 s and 91.0 +/- 4.9 s for young and aged animals, respectively). Furthermore, at the end of the training period, the aged cohort still showed significantly higher escape latencies in the Morris water maze. The present findings support the concept that the decline in cognitive performances in ageing is related to the loss of synapses in the cerebral cortex.

Indomethacin inhibits delayed DNA fragmentation of hippocampal CA1 pyramidal neurons after transient forebrain ischemia in gerbils

Recent studies have shown a close association between reactive oxygen species and DNA fragmentation and that delayed neuronal death after transient forebrain ischemia manifests as DNA fragmentation-like apoptosis. We examined the effect of indomethacin on ischemic-induced delayed hippocampal neuronal death in gerbils using the TUNEL staining method, since indomethacin is neuroprotective in a variety of degenerative processes, such as Alzheimer's disease. Indomethacin (5 mg/kg, i.p.), administered 5 min before the ischemic insult, significantly decreased the number of TUNEL-positive hippocampal CA1 pyramidal neurons and delayed the appearance of TUNEL-positive neurons. Our results indicate that indomethacin is effective in inhibiting DNA fragmentation after transient forebrain ischemia.

Pharmacological intervention in age-associated brain disorders by Flupirtine: Alzheimer's and prion diseases

Alzheimer's disease, a major form of dementia in the elderly has become an increasingly important health problem in developed countries. In vitro studies on primary neurons demonstrate that Flupirtine (Katadolon) at a concentration of 1 microg/ml, significantly reduces the neurotoxic (apoptotic) effect displayed by A beta25-35, a segment of the amyloid beta-protein precursor the etiologic agent of Alzheimer's disease. Flupirtine, which has been in clinical use since 10 years ago, prevents the toxic effect of PrP, the presumed etiologic agent of the Creutzfeldt-Jakob disease as well as the excitatory amino acid glutamate on cortical neurons. Flupirtine displays a bimodal activity. Its strongest cytoprotective effect against glutamate-induced neurotoxicity was measured if administered at least 120 min prior to the addition of the glutamate. A likewise potent anti-apoptotic activity was measured if cells were simultaneously incubated with Flupirtine and the apoptotic inducers. Administration of Flupirtine during postincubation time in the experiments with glutamate did not result in neuroprotection. In parallel with the determination of the effect of Flupirtine on the toxin (A beta, PrP or glutamate)-induced neuronal death the effect of the drug on the intracellular Ca2+ level [Ca2+]i, was measured. It is well established that incubation of neurons with glutamate causes an increase in [Ca2+]i. It was found that a simultaneous administration of Flupirtine and glutamate did not reduce the glutamate-induced high Ca2+ level. Only if the cells had been preincubated for approximately 30 min with the drug the intracellular Ca2+ level was significantly lower. Experimental evidence given here shows that the molecular basis for the antiapoptotic effect of Flupirtine against glutamate, triggered during pre-incubation, is an increased expression of the protooncogene bcl-2. The neuroprotective effect determined during coincubation with the inducer is attributed to a normalization of the glutathione level which dropped in the presence of the inducers. It is concluded that Flupirtine is a promising drug to treat neurodegenerative disorders occurring with age, e.g. Alzheimer's disease and prion based diseases, like Creutzfeldt-Jakob disease. This conclusion is corroborated by the favourable pharmacokinetic profile of Flupirtine.

Contrasting effects of vitamins as modulators of apoptosis in cancer cells and normal cells: a review

Individual vitamins can induce direct apoptosis or indirect apoptosis via cell differentiation in cancer cells; however, they can also stimulate antiapoptotic events in certain cancer cells. These effects depend on the dose, type, and form of vitamins and the type of tumor cells. A mixture of antioxidant vitamins is more effective than individual vitamins, and there is no evidence that such a mixture ever stimulates antiapoptotic events in cancer cells. Vitamins in combination with nonvitamin, direct-acting, apoptotic agents (X-rays, chemotherapeutic agents, and hyperthermia) or in combination with nonvitamin, indirect-acting, apoptotic agents (adenosine 3',5'-cyclic monophosphate, butyric acid, and interferon) produce a greater extent of apoptotic death in cancer cells in culture. Certain antioxidant vitamins may reduce the efficacy of some chemotherapeutic agents on rodent fibrosarcoma cells. In contrast to vitamin-induced apoptosis in cancer cells, normal cells never undergo apoptotic death after treatment with vitamins (not including retinoids). On the contrary, vitamins protect normal cells against apoptosis induced by a certain group of chemicals. The reasons for this differential effect of vitamins on cancer and normal cells are unknown. The genetic regulation of apoptosis in cancer cells has not been adequately defined. Such studies would help in identifying molecular targets that can be used to develop effective doses of vitamins or new drugs to induce apoptosis selectively in cancer cells.

The effects of aging and neurodegeneration on apoptosis-associated DNA fragmentation and the benefits of nicotinamide

In this work, the tertiary butylhydroperoxide- (t-BuOOH) treated mouse was used as a model to study the oxidative stress that is associated with various neurodegenerative diseases. DNA was found to be an early target of t-BuOOH attack. Necrosis was associated with extensive DNA fragmentation that occurred in almost all regions of the brain within 20 min following intracerebroventricular (icv) injection of 109.7 mg/kg t-BuOOH. Apoptosis was associated with high levels of DNA fragmentation that was observed at 48 h after icv administration of 21.9 mg/kg t-BuOOH. Susceptibility to DNA damage was found to be age-dependent, since 24-mo-old mice exhibited consistently higher and more pervasive DNA damage than 8 mo-old-mice. Extensive DNA damage was seen in various brain regions in patients with Alzheimer disease (AD) and with both Alzheimer and Parkinson disease (AD-PD). These results directly implicate DNA damage in neurodegeneration. The DNA fragmentation ob-served can lead to both apoptosis and necrosis, as suggested by gel electrophoresis. Nicotinamide, a precursor of NAD in the brain, was able to prevent DNA fragmentation induced by low-dose t-BuOOH, when coadministered with the toxin.

Pharmacokinetics of intracerebroventricular tBuOOH in young adult and mature mice

This in vivo study compared the pharmacokinetics of intracerebroventricularly administered tertiary butylhydroperoxide (tBuOOH) (109.7 mg/kg) among six different brain regions in two age groups of mice (2- and 8-mo-old mice). Brains were dissected at 11 time-points ranging from 0.5-60 min. Pharmacokinetics parameters did not differ between the two age groups. This demonstrates that previously reported age-related differences in tBuOOH toxicity may not be owing to pharmacokinetic differences between the two age groups. Differences were found when comparing the pharmacokinetics of tBuOOH among the various brain regions. Area under the curve (AUC) values were highest in the striatum and thalamus, and lowest in the cerebellum. The half-life of tBuOOH varied widely among the regions with the longest half-lives in the cortex and hippocampus, and the shortest in the striatum and cerebellum. The oxidation of glutathione and the induction of DNA damage are critical aspects of tBuOOH toxicity. These data show that region-dependent differences in toxicity reported previously may result from factors, such as tBuOOH-induced glutathione oxidation and DNA damage.