N-Acetylcysteine delays age-associated memory impairment in mice: role in synaptic mitochondria

Targeting the Cysteine Redox Proteome in Parkinson's Disease: The Role of Glutathione Precursors and Beyond

Encouraging recent data on the molecular pathways underlying aging have identified variants and expansions of genes associated with DNA replication and repair, telomere and stem cell maintenance, regulation of the redox microenvironment, and intercellular communication. In addition, cell rejuvenation requires silencing some transcription factors and the activation of pluripotency, indicating that hidden molecular networks must integrate and synchronize all these cellular mechanisms. Therefore, in addition to gene sequence expansions and variations associated with senescence, the optimization of transcriptional regulation and protein crosstalk is essential. The protein cysteinome is crucial in cellular regulation and plays unexpected roles in the aging of complex organisms, which show cumulative somatic mutations, telomere attrition, epigenetic modifications, and oxidative dysregulation, culminating in cellular senescence. The cysteine thiol groups are highly redox-active, allowing high functional versatility as structural disulfides, redox-active disulfides, active-site nucleophiles, proton donors, and metal ligands to participate in multiple regulatory sites in proteins. Also, antioxidant systems control diverse cellular functions, including the transcription machinery, which partially depends on the catalytically active cysteines that can reduce disulfide bonds in numerous target proteins, driving their biological integration. Since we have previously proposed a fundamental role of cysteine-mediated redox deregulation in neurodegeneration, we suggest that cellular rejuvenation of the cysteine redox proteome using GSH precursors, like N-acetyl-cysteine, is an underestimated multitarget therapeutic approach that would be particularly beneficial in Parkinson's disease.

Geroscience-guided repurposing of FDA-approved drugs to target aging: A proposed process and prioritization

Common chronic diseases represent the greatest driver of rising healthcare costs, as well as declining function, independence, and quality of life. Geroscience-guided approaches seek to delay the onset and progression of multiple chronic conditions by targeting fundamental biological pathways of aging. This approach is more likely to improve overall health and function in old age than treating individual diseases, by addressing aging the largest and mostly ignored risk factor for the leading causes of morbidity in older adults. Nevertheless, challenges in repurposing existing and moving newly discovered interventions from the bench to clinical care have impeded the progress of this potentially transformational paradigm shift. In this article, we propose the creation of a standardized process for evaluating FDA-approved medications for their geroscience potential. Criteria for systematically evaluating the existing literature that spans from animal models to human studies will permit the prioritization of efforts and financial investments for translating geroscience and allow immediate progress on the design of the next Targeting Aging with MEtformin (TAME)-like study involving such candidate gerotherapeutics.

N-Acetyl-Cysteine: Modulating the Cysteine Redox Proteome in Neurodegenerative Diseases

In the last twenty years, significant progress in understanding the pathophysiology of age-associated neurodegenerative diseases has been made. However, the prevention and treatment of these diseases remain without clinically significant therapeutic advancement. While we still hope for some potential genetic therapeutic approaches, the current reality is far from substantial progress. With this state of the issue, emphasis should be placed on early diagnosis and prompt intervention in patients with increased risk of neurodegenerative diseases to slow down their progression, poor prognosis, and decreasing quality of life. Accordingly, it is urgent to implement interventions addressing the psychosocial and biochemical disturbances we know are central in managing the evolution of these disorders. Genomic and proteomic studies have shown the high molecular intricacy in neurodegenerative diseases, involving a broad spectrum of cellular pathways underlying disease progression. Recent investigations indicate that the dysregulation of the sensitive-cysteine proteome may be a concurrent pathogenic mechanism contributing to the pathophysiology of major neurodegenerative diseases, opening new therapeutic opportunities. Considering the incidence and prevalence of these disorders and their already significant burden in Western societies, they will become a real pandemic in the following decades. Therefore, we propose large-scale investigations, in selected groups of people over 40 years of age with decreased blood glutathione levels, comorbidities, and/or mild cognitive impairment, to evaluate supplementation of the diet with low doses of N-acetyl-cysteine, a promising and well-tolerated therapeutic agent suitable for long-term use.

N-acetyl-cysteine in Schizophrenia: Potential Role on the Sensitive Cysteine Proteome

BACKGROUND

N-acetyl-cysteine (NAC) has shown widespread utility in different psychiatric disorders, including a beneficial role in schizophrenic patients. Although the replenishment of glutathione and the antioxidant activity of NAC have been suggested as the mechanisms that improve such a wide range of disorders, none seems to be sufficiently specific to explain these intriguing effects. A sensitive cysteine proteome is emerging as a functional and structural network of interconnected Sensitive Cysteine-containing Proteins (SCCPs) that together with reactive species and the cysteine/ glutathione cycles can regulate the bioenergetic metabolism, the redox homeostasis and the cellular growth, differentiation and survival, acting through different pathways that are regulated by the same thiol radical in cysteine residues.

OBJECTIVE

Since this sensitive cysteine network has been implicated in the pathogenesis of Parkinson's and Alzheimer's diseases, I have reviewed if the proteins that play a role in schizophrenia can be classified as SCCPs.

RESULTS

The results show that the principal proteins playing a role in schizophrenia can be classified as SCCPs, suggesting that the sensitive cysteine proteome (cysteinet) is defective in this type of psychosis.

CONCLUSION

The present review proposes that there is a deregulation of the sensitive cysteine proteome in schizophrenia as the consequence of a functional imbalance among different SCCPs, which play different functions in neurons and glial cells. In this context, the role of NAC to restore and prevent schizophrenic disorders is discussed.

Redox modifications in synaptic components as biomarkers of cognitive status, in brain aging and disease

Aging is a natural process that includes several changes that gradually make organisms degenerate and die. Harman's theory proposes that aging is a consequence of the progressive accumulation of oxidative modifications mediated by reactive oxygen/nitrogen species, which plays an essential role in the development and progression of many neurodegenerative diseases. This review will focus on how abnormal redox modifications induced by age impair the functionality of neuronal redox-sensitive proteins involved in axonal elongation and guidance, synaptic plasticity, and intercellular communication. We will discuss post-transcriptional regulation of gene expression by microRNAs as a mechanism that controls the neuronal redox state. Finally, we will discuss how some brain-permeant antioxidants from the diet have a beneficial effect on cognition. Taken together, the evidence revised here indicates that oxidative-driven modifications of specific proteins and changes in microRNA expression may be useful biomarkers for aging and neurodegenerative diseases. Also, some specific antioxidant therapies have undoubtedly beneficial neuroprotective effects when administered in the correct doses, in the ideal formulation combination, and during the appropriate therapeutic window. The use of some antioxidants is, therefore, still poorly explored for the treatment of neurodegenerative diseases such as Alzheimer's disease.

Medical and Dietary Uses of N-Acetylcysteine

N-acetylcysteine (NAC), a plant antioxidant naturally found in onion, is a precursor to glutathione. It has been used as a drug since the 1960s and is listed on the World Health Organization (WHO) Model List of Essential Medicines as an antidote in poisonings. There are numerous other uses or proposed uses in medicine that are still in preclinical and clinical investigations. NAC is also used in food supplements and cosmetics. Despite its abundant use, there are projections that the NAC global market will grow in the next five years; therefore, the purpose of this work is to provide a balanced view of further uses of NAC as a dietary supplement. Although NAC is considered a safe substance, the results among clinical trials are sometimes controversial or incomplete, like for many other antioxidants. More clinical trials are underway that will improve our understanding of NAC applicability.

Supplementation with N-Acetyl Cysteine Affects Motor and Cognitive Function in Young but Not Old Mice

BACKGROUND

N-acetyl cysteine (NAC) is a thiolic antioxidant that is thought to increase cellular glutathione (GSH) by augmenting the concentration of available cysteine, an essential precursor to GSH production. Manipulating redox status can affect brain function, and NAC intake has been associated with improving brain function in models of neurodegenerative diseases.

OBJECTIVES

The objective of the study was to determine if short-term dietary supplementation with NAC could ameliorate functional impairment associated with aging.

METHODS

C57BL/6J male mice aged 6, 12, or 24 mo were fed a control diet or the control diet supplemented with 0.3% NAC for a total of 12 wk. After 4 wk of dietary supplementation, mice began a series of behavioral tests to measure spontaneous activity (locomotor activity test), psychomotor performance (bridge-walking and coordinated running), and cognitive capacity (Morris water maze and discriminated active avoidance). The performance of the mice on these tests was analyzed through the use of analyses of variance with Age and Diet as factors.

RESULTS

Supplementation of NAC improved peak motor performance in a coordinated running task by 14% (P < 0.05), and increased the time spent around the platform by 24% in a Morris water maze at age 6 mo. However, the supplementation had no to minimal effect on the motor and cognitive functions of 12- and 24-mo-old mice.

CONCLUSIONS

The findings of this preclinical study support the claim that NAC has nootropic properties in 6-mo-old mice, but suggest that it may not be useful for improving motor and cognitive impairments in older mice.

Overview on the Effects of N-Acetylcysteine in Neurodegenerative Diseases

N-acetylcysteine (NAC), which is an acetylated cysteine compound, has aroused scientific interest for decades due to its important medical applications. It also represents a nutritional supplement in the human diet. NAC is a glutathione precursor and shows antioxidant and anti-inflammatory activities. In addition to the uses quoted in the literature, NAC may be considered helpful in therapies to counteract neurodegenerative and mental health diseases. Furthermore, this compound has been evaluated for its neuroprotective potential in the prevention of cognitive aging dementia. NAC is inexpensive, commercially available and no relevant side effects were observed after its administration. The purpose of this paper is to give an overview on the effects and applications of NAC in Parkinson's and Alzheimer's disorders and in neuropathic pain and stroke.

Mitochondria in Developmental and Adult Neurogenesis

Generation of new neurons is a tightly regulated process that involves several intrinsic and extrinsic factors. Among them, a metabolic switch from glycolysis to oxidative phosphorylation, together with mitochondrial remodeling, has emerged as crucial actors of neurogenesis. However, although accumulating data raise the importance of mitochondrial morphology and function in neural stem cell proliferation and differentiation during development, information regarding the contribution of mitochondria to adult neurogenesis processes remains limited. In the present review, we discuss recent evidence covering the importance of mitochondrial morphology, function, and energy metabolism in the regulation of neuronal development and adult neurogenesis, and their impact on memory processes.

Nicotine Modulates Cognitive Function in D-Galactose-Induced Senescence in Mice

Here, we tested the claim that nicotine attenuates the signs of brain dysfunction in the model of brain aging induced by D-galactose (DGal) in mice. We administered nicotine at doses of 0.1, 0.5 and 1 mg/kg by the subcutaneous (s.c.) or at 0.1 mg/kg by the intranasal (i.n.) routes in mice that had received DGal at the dose of 500 mg/kg subcutaneous (s.c.) for 6 weeks. We assessed animal withdrawal signs as the number of presented somatic signs, thermal hyperalgesia, elevated plus maze (EPM) and open field tests. We evaluated spatial memory and recognition with Barnes maze and novel object recognition (NOR) tests. We tested brain tissue for reactive oxygen species (ROS), mitochondrial membrane potential, caspase-3, Bax, Bcl-2, cytochrome C, brain-derived neurotrophic factor and nerve growth factor levels. Nicotine administration in model groups (0.5 mg/kg s.c. and 0.1 mg/kg i.n. doses) significantly attenuated impairment of spatial and episodic memories in comparison to normal saline-received model group. These doses also reduced mito-oxidative damage as well as apoptosis and raised neurotrophic factors level in model groups in comparison to normal saline-received model group. The 1 mg/kg s.c. dose nicotine revealed withdrawal signs compared with the other nicotine-received groups. Nicotine at specific doses and routes has the potential to attenuate age-related cognitive impairment, mito-oxidative damage, and apoptosis. The doses raise neurotrophic factors without producing withdrawal signs.

Antioxidants Reverse the Changes in the Cholinergic System Caused by L-Tyrosine Administration in Rats

Tyrosinemia type II is an inborn error of metabolism caused by a deficiency in the activity of the enzyme tyrosine aminotransferase, leading to tyrosine accumulation in the body. Although the mechanisms involved are still poorly understood, several studies have showed that higher levels of tyrosine are related to oxidative stress and therefore may affect the cholinergic system. Thus, the aim of this study was to investigate the effects of chronic administration of L-tyrosine on choline acetyltransferase activity (ChAT) and acetylcholinesterase (AChE) in the brain of rats. Moreover, we also examined the effects of one antioxidant treatment (N-acetylcysteine (NAC) + deferoxamine (DFX)) on cholinergic system. Our results showed that the chronic administration of L-tyrosine decreases the ChAT activity in the cerebral cortex, while the AChE activity was increased in the hippocampus, striatum, and cerebral cortex. Moreover, we found that the antioxidant treatment was able to prevent the decrease in the ChAT activity in the cerebral cortex. However, the increase in AChE activity induced by L-tyrosine was partially prevented the in the hippocampus and striatum, but not in the cerebral cortex. Our results also showed no differences in the aversive and spatial memory after chronic administration of L-tyrosine. In conclusion, the results of this study demonstrated an increase in AChE activity in the hippocampus, striatum, and cerebral cortex and an increase of ChAT in the cerebral cortex, without cognitive impairment. Furthermore, the alterations in the cholinergic system were partially prevented by the co-administration of NAC and DFX. Thus, the restored central cholinergic system by antioxidant treatment further supports the view that oxidative stress may be involved in the pathophysiology of tyrosinemia type II.

Chronic N-acetylcysteine treatment alleviates acute lipopolysaccharide-induced working memory deficit through upregulating caveolin-1 and synaptophysin in mice

RATIONALE

Working memory (WM) is a dynamic encoding process and an active representation of information over a short time. The ability to guide forthcoming behavior would be disrupted if WM was impaired by various factors including inflammation, stress, free radicals, and disease states such as schizophrenia. However, the mechanism underlying acute working memory impairment remains to be defined.

OBJECTIVES

In this study, we tested the hypothesis that decreased caveolin-1 (Cav-1) and synaptophysin (SYP) accounted for the WM impairment challenged with acute intraperitoneally lipopolysaccharide (LPS), which mimicked neuroinflammation. Delayed alternation T-maze task (DAT) was used to assess working memory of adult male C57BL/6 mice, and western blot and immunostaining were used to detect protein expression and distribution in medial prefrontal cortex (mPFC) and hippocampus.

RESULTS

Our results showed that LPS dose-dependently induced working memory deficit accompanied by the decrease of Cav-1 and SYP in mPFC but not hippocampus. In addition, LPS significantly decreased protein level of Cav-1 and SYP in neurons by activating microglia cells. More important, 2-week N-acetylcysteine (NAC) treatment dose-dependently inhibited LPS-induced working memory deficit by improving the ability to use Lose-shift but not Win-shift strategy and significantly inhibited LPS-induced downregulation of Cav-1 and SYP in mPFC.

CONCLUSIONS

Taken together, our findings demonstrate that chronic NAC treatment alleviates acute LPS-induced working memory deficit through upregulating Cav-1 and SYP in mice.

Mitochondrial dysfunction in bipolar disorder: Evidence, pathophysiology and translational implications

Bipolar disorder (BD) is a chronic psychiatric illness characterized by severe and biphasic changes in mood. Several pathophysiological mechanisms have been hypothesized to underpin the neurobiology of BD, including the presence of mitochondrial dysfunction. A confluence of evidence points to an underlying dysfunction of mitochondria, including decreases in mitochondrial respiration, high-energy phosphates and pH; changes in mitochondrial morphology; increases in mitochondrial DNA polymorphisms; and downregulation of nuclear mRNA molecules and proteins involved in mitochondrial respiration. Mitochondria play a pivotal role in neuronal cell survival or death as regulators of both energy metabolism and cell survival and death pathways. Thus, in this review, we discuss the genetic and physiological components of mitochondria and the evidence for mitochondrial abnormalities in BD. The final part of this review discusses mitochondria as a potential target of therapeutic interventions in BD.

The protective effects of different treatments on rat salivary glands after radiotherapy

This study was aimed to evaluate the efficacy of treatment modalities for minimizing salivary gland damage caused by radiotherapy. Forty rats were divided into five groups. Group 1 had no irradiation or any treatment. Group 2 underwent only 15 Gy single dose radiotherapy. N-acetylcysteine, dexamethasone, hyperbaric oxygen treatment were given, respectively to the group 3, 4 and 5 for 5 days. 15 Gy single dose radiotherapy was applied to the group 3, 4 and 5 on the second day. Pyknosis, lysis, and vacuolization were examined in ductal cells and pyknosis, lysis, vacuolization, inflammation and collective duct damage in acinar cells. Dexamethasone and hyperbaric oxygen did not prove to have a positive effect on acinar and ductal cell. N-acetylcysteine-applied group had statistically significantly lower amount of damage. We determined that the decrease of ductal and acinar cell damage in parotid glands of N-acetylcysteine-applied rats was more distinct and statistically.

NMDA Receptor Function During Senescence: Implication on Cognitive Performance

N-methyl-D-aspartate (NMDA) receptors, a family of L-glutamate receptors, play an important role in learning and memory, and are critical for spatial memory. These receptors are tetrameric ion channels composed of a family of related subunits. One of the hallmarks of the aging human population is a decline in cognitive function; studies in the past couple of years have demonstrated deterioration in NMDA receptor subunit expression and function with advancing age. However, a direct relationship between impaired memory function and a decline in NMDA receptors is still ambiguous. Recent studies indicate a link between an age-associated NMDA receptor hypofunction and memory impairment and provide evidence that age-associated enhanced oxidative stress might be contributing to the alterations associated with senescence. However, clear evidence is still deficient in demonstrating the underlying mechanisms and a relationship between age-associated impaired cognitive faculties and NMDA receptor hypofunction. The current review intends to present an overview of the research findings regarding changes in expression of various NMDA receptor subunits and deficits in NMDA receptor function during senescence and its implication in age-associated impaired hippocampal-dependent memory function.

Impairments in hippocampal synaptic plasticity following prenatal ethanol exposure are dependent on glutathione levels

Previous studies from our laboratory have shown that prenatal ethanol exposure (PNEE) causes a significant deficit in synaptic plasticity, namely long-term potentiation (LTP), in the dentate gyrus (DG) region of the hippocampus of male rats. PNEE has also been shown to induce an increase in oxidative stress and a reduction in antioxidant capacity in the brains of both male and female animals. In this study the interaction between LTP and the major antioxidant in the brain, glutathione (GSH), is examined. We show that depletion of the intracellular reserves of GSH with diethyl maleate (DEM) reduces LTP in control male, but not female animals, mirroring the effects of PNEE. Furthermore, treatment of PNEE animals with N-acetyl cysteine (NAC), a cysteine donor for the synthesis of GSH, increases GSH levels in the hippocampus and completely restores the deficits in LTP in PNEE males. These results indicate that in males GSH plays a major role in regulating LTP, and that PNEE may cause reductions in LTP by reducing the intracellular pool of this endogenous antioxidant.

Attention deficit and hyperactivity disorder scores are elevated and respond to N-acetylcysteine treatment in patients with systemic lupus erythematosus

OBJECTIVE

To investigate whether attention deficit hyperactivity disorder (ADHD) may serve as a marker of neuropsychiatric disease and as a target for N-acetylcysteine (NAC) treatment in patients with systemic lupus erythematosus (SLE).

METHODS

The ADHD Self-Report Scale (ASRS) was used to assess 49 patients with SLE and 46 matched healthy control subjects. Twenty-four of the patients with SLE were randomized to receive either placebo, NAC at a dosage of 2.4 gm/day, or NAC at a dosage of 4.8 gm/day. Disease activity was evaluated monthly using the British Isles Lupus Assessment Group (BILAG) index, the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI), the Fatigue Assessment Scale (FAS), and the ASRS, before and during the 3-month treatment period and after a 1-month washout period.

RESULTS

The cognitive/inattentive (ASRS part A), hyperactivity/impulsive (ASRS part B), and combined (total) ASRS scores were increased in patients with SLE compared with control subjects (mean ± SEM 17.37 ± 1.03 [P = 3 × 10(-7) ], 14.51 ± 0.89 [P = 2 × 10(-4) ], and 31.92 ± 1.74 [P = 8 × 10(-7) ], respectively, versus 10.41 ± 1.02, 9.61 ± 1.21, and 20.02 ± 1.98, respectively. ASRS part A scores correlated with SLEDAI (r = 0.53, P < 0.0001) and BILAG scores (r = 0.36, P = 0.011). ASRS total scores also correlated with SLEDAI (r = 0.45, P = 0.0009) and BILAG scores (r = 0.31, P = 0.025). ASRS part A (r = 0.73, P < 0.0001), ASRS part B (r = 0.47, P = 0.0006), and ASRS total scores (r = 0.67, P < 0.0001) correlated with the FAS score. Relative to the scores in placebo-treated patients, ASRS total scores were reduced in SLE patients treated with NAC dosages of 2.4 gm/day and 4.8 gm/day combined (P = 0.037). ASRS part A scores were reduced by NAC dosages of 2.4 gm/day (P = 0.001) and 4.8 gm/day (P < 0.0001) as well as by NAC at dosages of 2.4 gm/day and 4.8 gm/day combined (P = 0.001).

CONCLUSION

In patients with SLE, elevated ASRS scores reveal previously unrecognized and clinically significant symptoms of ADHD that respond to NAC treatment.

The potential role of ozone in ameliorating the age-related biochemical changes in male rat cerebral cortex

Controlled ozone (O(3)) administration is known to promote oxidative preconditioning and, thus, may reverse chronic oxidative stress that accompanies aging. Therefore, the present work was undertaken to study the potential role of O(3) in ameliorating certain age-related biochemical changes represented by impaired activities of inner mitochondrial membrane enzymes, compromised energy production and increased oxidative burden in male rat cerebral cortex. Prophylactic administration of O(3)-O(2) mixture to 3 month-old rats, at an intrarectal dose of 0.6 mg O(3) kg(-1) body weight twice/week for 3 months then once/week until the age of 15 months, normalized reduced glutathione content, adenosine triphosphate/adenosine diphosphate ratio, mitochondrial superoxide dismutase (SOD) and complex IV (cytochrome-c oxidase) activities, improved glutathione redox index (GSHRI), complex I (NADH-ubiquinone oxidoreductase) and mitochondrial nitric oxide synthase (mtNOS) activities, and attenuated the rise in malondialdehyde (MDA) and mitochondrial protein carbonyl levels. On the other hand, therapeutic administration of the same dose of O(3)-O(2) mixture to 14 month-old rats three times/week for 1 month, reduced mitochondrial protein carbonyl level only. Other favorable effects, including normalization of Na,K-adenosine triphosphatase (Na,K-ATPase) activity and reduction in lipofuscin level in the prophylactic group, as well as improvement in mitochondrial SOD and complex I activities with a decrease in total MDA level in the therapeutic group, were comparable to the effects observed in the corresponding O(2)-treated control groups. In conclusion, the present study revealed that prophylactic administration of O(3)-O(2) mixture provided better amelioration of age-related cerebrocortical alterations by combining the advantages of both O(3) and O(2) therapies.

N-acetyl-cysteine in the treatment of Parkinson's disease. What are we waiting for?

Parkinson's disease is an age-related neurodegenerative disorder that is ameliorated with levodopa. However, long-term use of this drug is limited by motor complications, postural instability and dementia resulting in the progression of the disease. Insights into the organization of the basal ganglia and knowledge of the mechanisms responsible for cell death in Parkinson's disease has permitted the development of putative neuro-protective drugs that might slow the disease progression. Although no drug has yet been established to alter the rate of disease progression, recent publications have confirmed previous results and hypotheses about the probable role of thiolic antioxidants on Parkinson's disease, demonstrating a significant reduction of dopaminergic neuronal degeneration in α-synuclein over expressing mice treated with oral N-acetyl-cysteine. This thiolic antioxidant is a modified form of the natural amino acid cysteine, which is the precursor of the most potent intracellular antioxidant glutathione. Besides, increasing evidence has been accumulated in the last 10years about the beneficial effects of this thiolic antioxidant in experimental and pathologic states of the nervous system, including against neurotoxic substances. The present paper put forward the existing rationale evidence for the use of N-acetyl-cysteine alone or in combination with levodopa in the clinical management of this neurodegenerative disorder.

Reversal of age-related oxidative stress prevents hippocampal synaptic plasticity deficits by protecting D-serine-dependent NMDA receptor activation

Oxidative stress (OS) resulting from an imbalance between antioxidant defenses and the intracellular accumulation of reactive oxygen species (ROS) contributes to age-related memory deficits. While impaired synaptic plasticity in neuronal networks is thought to underlie cognitive deficits during aging, whether this process is targeted by OS and what the mechanisms involved are still remain open questions. In this study, we investigated the age-related effects of the reducing agent N-acetyl-L-cysteine (L-NAC) on the activation of the N-methyl-D-aspartate receptor (NMDA-R) by its co-agonist D-serine, because alterations in this mechanism contribute greatly to synaptic plasticity deficits in aged animals. Long-term dietary supplementation with L-NAC prevented oxidative damage in the hippocampus of aged rats. Electrophysiological recordings in the CA1 of hippocampal slices indicated that NMDA-R-mediated synaptic potentials and theta-burst-induced long-term potentiation (LTP) were depressed in aged animals, deficits that could be reversed by exogenous D-serine. Chronic treatment with L-NAC, but not acute application of the reducing agent, restored potent D-serine-dependent NMDA-R activation and LTP induction in aged rats. In addition, it is also revealed that the age-related decrease in D-serine levels and in the expression of the synthesizing enzyme serine racemase, which underlies the decrease in NMDA-R activation by the amino acid, was rescued by long-term dietary treatment with L-NAC. Our results indicate that protecting redox status in aged animals could prevent injury to the cellular mechanisms underlying cognitive aging, in part by maintaining potent NMDA-R activation through the D-serine-dependent pathway.

Drugs, nutrients, and phytoactive principles improving the health span of rodent models of human age-related diseases

Rodents are often the species of choice to examine the effect of drugs on survival and on the progression of specific diseased tissues. This statement is also true for research laboratories working in the field of nutrition and aging. In addition to diets that can reduce the life expectancy of rodents, such as diabetogenic or high-fat diets, genetically modified rodents exhibiting different accelerated age-associated diseases also provide important biologic tools to decipher the impact of drugs, nutrients, or phytoactive compounds on their health and life span. This review covers some of the chemicals believed to decelerate the appearance of age-related diseases in different rodent models. Such chemicals include antioxidants, anti-inflammatory molecules, modulators of metabolic sensors, calorie restriction mimetics, and vegetal polyphenolic compounds that affect mitochondrial functions, cellular proliferation or differentiation as well as cell functionality.

The energy-redox axis in aging and age-related neurodegeneration

Decrease in mitochondrial energy-transducing capacity is a feature of the aging process that accompanies redox alterations, such as increased generation of mitochondrial oxidants, altered GSH status, and increased protein oxidation. The decrease in mitochondrial energy-transducing capacity and altered redox status should be viewed as a concerted process that embodies the mitochondrial energy-redox axis and is linked through various mechanisms including: (a) an inter-convertible reducing equivalents pool (i.e., NAD(P)(+)/NAD(P)H) and (b) redox-mediated protein post-translational modifications involved in energy metabolism. The energy-redox axis provides the rationale for therapeutic approaches targeted to each or both component(s) of the axis that effectively preserves or improve mitochondrial function and that have implications for aging and age-related neurodegenerative disorders.

Neurochemistry, neuropathology, and heredity in SAMP8: a mouse model of senescence

The SAMP8 strain spontaneously develops learning and memory deficits with characteristics of aging, and is a good model for studying the mechanism of cognitive dysfunction with age. Oxidative stress occurs systemically in SAMP8 from early on in life and increases with aging. Neuropathological changes such as the deposition of A beta, hyperphosphorylation of tau, impaired development of dendritic spines, and sponge formation, and neurochemical changes were found in the SAMP8 brain. These changes may be partially mediated by oxidative stress. Oxidative damage is a major factor in neurodegenerative disorders and aging. A decline in the respiratory control ratio suggesting mitochondrial dysfunction was found in the brain of SAMP8. The rise in oxidative stress following mitochondrial dysfunction may trigger neuropathological and neurochemical changes, disrupting the development of neural networks in the brain in SAMP8.

Effect of N-acetylcysteine on radiation-induced genotoxicity and cytotoxicity in rat bone marrow

The aim of this study is to evaluate the potential radioprotective effects of N-acetylcysteine (NAC) against genotoxicity and cytotoxicity. The effect of WR-2721, as a representative of clinically used radioprotector, was compared with that of NAC, using the chromosomal aberration (CA) and micronucleus (MN) test systems in the irradiated rat's femoral bone marrow cells. We also investigated the mitotic index (MI), and the ratio of polychromatic erythrocytes (PCEs) to normochromatic erythrocytes (NCEs). The rats (n = 16) were divided randomly and equally into four groups: Control (C), Radiation (R), R+NAC (received irradiation and 1000 mg/kg NAC) and R+WR-2721 (received irradiation and 200 mg/kg WR-2721) rats. All the irradiated groups received whole-body gamma irradiation as a single dose of 6 Gy. Group R showed higher CA and MN formation when compared to C. Group R showed higher frequency of MN formation when compared to both R+NAC and R+WR-2721. The mean MI and PCE/NCE ratios were lower in Group R when compared to those of Group C. The mean MI and PCE/NCE ratios of both R+NAC and R+WR-2721 groups were lower when compared to those of Group C. The MI in Group R was lower when compared to that of both R+NAC and R+WR-2721 groups. In this study, the results give clues about the beneficial effects of NAC against radiation-induced genotoxicity and cytotoxicity in rat bone marrow and its effect may be comparable to that observed for WR-2721.

Neuroprotective effect of N-acetylcysteine in the development of diabetic encephalopathy in streptozotocin-induced diabetes

Diabetic encephalopathy is characterized by impaired cognitive functions that involve neuronal damage triggered by glucose driven oxidative stress. The objective of the present study was to determine whether N-acetylcysteine (NAC) supplementation ameliorates learning and memory deficits caused by hyperglycemia-induced oxidative stress in experimental diabetes. Male Wistar rats (200-250 g) were rendered diabetic by a single intraperitoneal injection of streptozotocin (50 mg/kg). Cognitive deficits were observed in diabetic animals assessed using elevated plus maze test after 8 weeks of induction of diabetes. Acetylcholinesterase activity, a marker of cholinergic function, was decreased by 15.6% in the cerebral cortex, 20.9% in cerebellum and 14.9% in brain stem of diabetic rats compared to control rats. There was an increase in lipid peroxidation in cerebral cortex (21.97%), cerebellum (20.4%) and brain stem (25.5%) of diabetic rats. This was accompanied by decrease in glutathione and total thiol content along with decrease in the activities of superoxide dismutase, catalase and glutathione reductase. However, glutathione peroxidase activity increased by 11.2%, 13.6% and 23.1% in cerebral cortex, cerebellum and brain stem respectively, while the activity of glutathione-s-transferase decreased only in cerebral cortex (21.7%). Supplementation with NAC (1.4 g/kg/day in drinking water) significantly attenuated cognitive deficits and oxidative stress in diabetic rats. Our results emphasize the involvement of increased oxidative stress in cognitive impairment in diabetic animals and point towards the potential beneficial role of NAC as an adjuvant therapy to conventional anti-hyperglycemic regimens for the prevention and treatment of diabetic encephalopathy.

Reversion of age-related recognition memory impairment by iron chelation in rats

It is now generally accepted that iron accumulates in the brain during the ageing process. Increasing evidence demonstrate that iron accumulation in selective regions of the brain may generate free radicals, thereby possessing implications for the etiology of neurodegenerative disorders. In a previous study we have reported that aged rats present recognition memory deficits. The aim of the present study was to evaluate the effect of desferoxamine (DFO), an iron chelator agent, on age-induced memory impairment. Aged Wistar rats received intraperitoneal injections of saline or DFO (300mg/kg) for 2 weeks. The animals were submitted to a novel object recognition task 24h after the last injection. DFO-treated rats showed normal recognition memory while the saline group showed long-term recognition memory deficits. The results show that DFO is able to reverse age-induced recognition memory deficits. We also demonstrated that DFO reduced the oxidative damage to proteins in cortex and hippocampus. Thus, the present findings provide the first evidence that iron chelators might prevent age-related memory dysfunction.

Alzheimer's disease pathogenesis and therapeutic interventions

Alzheimer's disease (AD) is a neurodegenerative disorder of the central nervous system associated with progressive cognitive and memory loss. Molecular hallmarks of the disease are characterized by extracellular deposition of the amyloid beta peptide (Abeta) in senile plaques, the appearance of intracellular neurofibrillary tangles (NFT), cholinergic deficit, extensive neuronal loss and synaptic changes in the cerebral cortex and hippocampus and other areas of brain essential for cognitive and memory functions. Abeta deposition causes neuronal death via a number of possible mechanisms including oxidative stress, excitotoxicity, energy depletion, inflammation and apoptosis. Despite their multifactorial etiopathogenesis, genetics plays a primary role in progression of disease. To date genetic studies have revealed four genes that may be linked to autosomal dominant or familial early onset AD (FAD). These four genes include: amyloid precursor protein (APP), presenilin 1 (PS1), presenilin 2 (PS2) and apolipoprotein E (ApoE). Plaques are formed mostly from the deposition of Abeta, a peptide derived from APP. The main factors responsible for Abeta formation are mutation of APP or PS1 and PS2 genes or ApoE gene. All mutations associated with APP and PS proteins can lead to an increase in the production of Abeta peptides, specifically the more amyloidogenic form, Abeta42. In addition to genetic influences on amyloid plaque and intracellular tangle formation, environmental factors (e.g., cytokines, neurotoxins, etc.) may also play important role in the development and progression of AD. A direct understanding of the molecular mechanism of protein aggregation and its effects on neuronal cell death could open new therapeutic approaches. Some of the therapeutic approaches that have progressed to the clinical arena are the use of acetylcholinesterase inhibitors, nerve growth factors, nonsteroidal inflammatory drugs, estrogen and the compounds such as antioxidants, neuronal calcium channel blockers or antiapoptotic agents. Inhibition of secretase activity and blocking the formation of beta-amyloid oligomers and fibrils which may inhibit fibrilization and fibrilization-dependent neurotoxicity are the most promising therapeutic strategy against the accumulation of beta-amyloid fibrils associated with AD. Furthermore, development of immunotherapy could be an evolving promising therapeutic approach for the treatment of AD.

Oxidative stress and aberrant signaling in aging and cognitive decline

Brain aging is associated with a progressive imbalance between antioxidant defenses and intracellular concentrations of reactive oxygen species (ROS) as exemplified by increases in products of lipid peroxidation, protein oxidation, and DNA oxidation. Oxidative conditions cause not only structural damage but also changes in the set points of redox-sensitive signaling processes including the insulin receptor signaling pathway. In the absence of insulin, the otherwise low insulin receptor signaling is strongly enhanced by oxidative conditions. Autophagic proteolysis and sirtuin activity, in turn, are downregulated by the insulin signaling pathway, and impaired autophagic activity has been associated with neurodegeneration. In genetic studies, impairment of insulin receptor signaling causes spectacular lifespan extension in nematodes, fruit flies, and mice. The predicted effects of age-related oxidative stress on sirtuins and autophagic activity and the corresponding effects of antioxidants remain to be tested experimentally. However, several correlates of aging have been shown to be ameliorated by antioxidants. Oxidative damage to mitochondrial DNA and the electron transport chain, perturbations in brain iron and calcium homeostasis, and changes in plasma cysteine homeostasis may altogether represent causes and consequences of increased oxidative stress. Aging and cognitive decline thus appear to involve changes at multiple nodes within a complex regulatory network.

Memantine reduces oxidative damage and enhances long-term recognition memory in aged rats

Many neurodegenerative diseases, including Alzheimer's (AD), Parkinson's (PD) and Huntington's diseases (HD), are caused by different mechanisms but may share a common pathway to neuronal injury as a result of the overstimulation of glutamate receptors. It has been suggested that this pathway can be involved in generation of cognitive deficits associated with normal aging. Previous studies performed in our laboratory have demonstrated that aged rats presented recognition memory deficits. The aim of the present study was to evaluate the effect of memantine, a low-affinity N-methyl-D-aspartate (NMDA) receptor antagonist, on age-induced recognition memory deficits. Additionally, parameters of oxidative damage in cerebral regions related to memory formation were evaluated. In order to do that, male Wistar rats (24 months old) received daily injections of saline solution or memantine (20 mg/kg i.p.) during 21 days. The animals were submitted to a novel object recognition task 1 week after the last injection. Memantine-treated rats showed normal recognition memory while the saline group showed long-term recognition memory deficits. The results show that memantine is able to reverse age-induced recognition memory deficits. We also demonstrated that memantine reduced the oxidative damage to proteins in cortex and hippocampus, two important brain regions involved in memory formation. Thus, the present findings suggest that, at least in part, age-induced cognitive deficits are related to oxidative damage promoted by NMDA receptor overactivation.

Impairment in consolidation of learned place preference following dopaminergic neurotoxicity in mice is ameliorated by N-acetylcysteine but not D1 and D2 dopamine receptor agonists

Some of the major concerns related to methamphetamine (METH) abuse are the neuronal damage inflicted at dopamine (DA) nerve terminals and the cognitive deficits observed in human METH abusers. We have shown that a high dose of METH selectively depleted dopaminergic markers in striatum, frontal cortex and amygdala of Swiss Webster mice, and impaired learned place preference. In this study, we investigated whether deficits in consolidation of place learning, as a consequence of METH neurotoxicity, underlie the underperformance of cocaine conditioned place preference (CPP). Administration of METH (5 mg/kg x 3) to Swiss Webster mice decreased striatal tyrosine hydroxylase (TH) immunoreactive neurons and significantly increased glial fibrillary acidic protein (GFAP) expression, confirming the neurotoxic potential of METH in mice. This treatment significantly attenuated the establishment of cocaine (15 mg/kg) CPP compared to control. To investigate whether manipulation of the consolidation phase improves learned place preference, mice were trained by cocaine and received daily post-training injections of DA receptor agonists or N-acetylcysteine (NAC). As memory consolidation occurs shortly after training, drugs were administered either immediately or 2 h post-training. Immediate post-training administration of the D1 DA receptor agonist SKF38393 (5, 10, and 20 mg/kg) or the D2 DA receptor agonist quinpirole (0.25, 0.5, and 1.0 mg/kg) did not improve the establishment of CPP following METH neurotoxicity. However, immediate but not delayed NAC administration (50 and 100 mg/kg) enhanced cocaine CPP following METH neurotoxicity and had no effect on control CPP. The levels of the reduced form of glutathione (GSH) in striatum, amygdala, hippocampus and frontal cortex were significantly lower in METH-treated mice compared to control during the period of CPP training. Acute and repeated administration of NAC to METH-treated mice restored the decreased brain GSH but had no effect on controls. Results suggest that METH-induced dopaminergic neurotoxicity is associated with impairment of consolidation of learned place preference, and that this impairment is improved by immediate post-training administration of the glutathione precursor NAC and not by D1 or D2 DA receptor agonists. Restoration of brain glutathione levels immediately post-training may facilitate the consolidation process.

Perturbed Synaptosomal Calcium Homeostasis and Behavioral Deficits Following Carbofuran Exposure: Neuroprotection by N-Acetylcysteine

The protective effects of N-acetylcysteine (NAC) on carbofuran-induced alterations in calcium homeostasis and neurobehavioral functions were investigated in rats. Rats were exposed to carbofuran at a dose of 1 mg/kg body weight, orally for a period of 28 days. A significant decrease in Ca2+ATPase activity was observed following carbofuran exposure with a concomitant increase in K+ -induced (45)Ca2+ uptake through voltage operated calcium channels. This was accompanied with a marked accumulation of intracellular free calcium in synaptosomes. The increase in intracellular calcium levels were associated with an increased lipid peroxidation and decreased glutathione content in carbofuran exposed animals. NAC administration (200 mg/kg body weight, orally) to the carbofuran exposed animals had a beneficial effect on carbofuran-induced alterations in calcium homeostasis and resulted in repletion in glutathione levels and resulted in lowering the extent of lipid peroxidation. Marked impairment in the motor functions were seen following carbofuran exposure, which were evident by the significant decrease in the locomotor activity and reduction in the retention time of the rats on rotating rods. Cognitive deficits were also seen as indicated by the significant decrease in active and passive avoidance response. NAC treatment, on the other hand, protected the animals against carbofuran-induced neurobehavioral deficits. The results support the hypothesis that carbofuran exerts its toxic effects by disrupting calcium homeostasis, which may have serious consequences on neuronal functioning, and clearly show the potential beneficial effects of N-acetylcysteine on carbofuran induced alterations in synaptosomal calcium homeostasis.

Long-term treatment with N-acetylcysteine, but not caloric restriction, protects mesenchymal stem cells of aged rats against tumor necrosis factor-induced death

The survival of mesenchymal stem cells (MSCs) to tumor necrosis factor alpha (TNFalpha) stimulation was evaluated after a long-term antioxidant treatment, or caloric restriction, in aged rats. MSCs were isolated from bone marrow of 30-month-old rats which orally received N-acetylcysteine in the last 18 months. The necrotic cell death-induced in vitro by TNFalpha, determined by trypan blue exclusion, was markedly attenuated in MSCs obtained from treated vs. control aged rats (percent mean+/-SEM: 10.9+/-2.17 vs. 17.8+/-0.53; p<0.05). Also, the proliferation rate of MSCs from control, but not N-acetylcysteine-treated, aged rats evaluated up to 2 weeks was significantly higher than that of MSCs from younger (4-month-old) rats. No significant effect was observed relative to the parameters investigated when the aged rats were previously subjected to a hypocaloric diet for 18 months. In conclusion, a prolonged supplementation with N-acetylcysteine in rats can increase resistance to necrotic death of MSCs and may also counteract an excessive rate of MSC proliferation.

Antioxidative activity and ameliorative effects of memory impairment of sulfur-containing compounds in Allium species

The antioxidative activity and ameliorative effects on memory impairment by sulfur-containing compounds which occur in Allium vegetables such as onion and garlic were investigated. The antioxidative activities of S-alk(en)yl-L-cysteines and their sulfoxides, volatile alk(en)yl disulfides and trisulfides, and vinyldithiins were examined by using human low-density lipoprotein. It was elucidated that the alk(en)yl substituents and the number of sulfur atoms in the compounds were important for the antioxidative activities. To demonstrate the ameliorative effects on memory impairment, onion extract and synthesized di-n-propyl trisulfide were administered to senescence-accelerated mouse P8. The behavioral experiments showed that onion extract and di-n-propyl trisulfide had highly ameliorative effect of memory impairment. Furthermore, it was found that the hippocampus lipid hydroperoxide in senescence-accelerated mouse P8 was decreased by the administration of di-n-propyl trisulfide. These results suggest that di-n-propyl trisulfide contained in onion ameliorates memory impairment in SAMP8 mouse by its antioxidant effect.

Carbofuran-induced neurochemical and neurobehavioral alterations in rats: attenuation by N-acetylcysteine

Carbofuran, a widely used carbamate pesticide, has been reported to cause neurotoxicity. However, the underlying mechanisms involved in carbofuran neurotoxicity are not well understood. The present study was envisaged to investigate the possible role of oxidative stress in carbofuran neurotoxicity and to evaluate the protective effects of N-acetylcysteine (NAC). Acetylcholinesterase activity was significantly inhibited in all the regions of brain after carbofuran exposure (1 mg/kg body weight, orally, for 28 days). NAC, on the other hand, was found to partially restore the activity of acetylcholinesterase in carbofuran treated animals. Carbofuran exposure resulted in increased lipid peroxidation (LPO) in brain regions accompanied by decreased levels of glutathione. NAC administration to the carbofuran exposed animals lowered LPO along with partial repletion in glutathione levels. Concomitantly, the activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase were significantly decreased after carbofuran exposure, while no significant change in the activity of glutathione-S-transferase was observed. NAC treatment to carbofuran treated rats resulted in protective effect on the activities of these enzymes. Marked impairment in the motor function was seen following carbofuran exposure, which is evident by significant decrease in the retention time of the rats on rotating rods. Cognitive deficits were also seen after carbofuran exposure as indicated by the significant decrease in active avoidance response. NAC treatment significantly improved the carbofuran-induced neurobehavioral deficits. The results clearly demonstrate that carbofuran exerts its neurotoxic effects by accentuating oxidative stress and suggest neuroprotective role of NAC in carbofuran neurotoxicity.

Tissue-specific changes of mitochondrial functions in aged rats: effect of a long-term dietary treatment with N-acetylcysteine

The understanding of the involvement of mitochondrial oxidative phosphorylation (OXPHOS) in the aging process has often been biased by the different methodological approaches as well as the choice of the biological material utilized by the various groups. In the present paper, we have carried out a detailed analysis of several bioenergetic parameters and oxidative markers in brain and heart mitochondria from young (2 months) and old (28 months) rats. This analysis has revealed an age-related decrease in respiratory fluxes in brain but not in heart mitochondria. The age-related decrease in respiratory rate (-43%) by NAD-dependent substrates was associated with a consistent decline (-40%) of complex I activity in brain mitochondria. On the other hand, heart mitochondria showed an age-related decline of complex II activity. Both tissues showed, however, an age-associated accumulation of oxidative damage. We have then performed the same analysis on old (28 months) rats subjected to a long-term (16 months) diet containing the antioxidant N-acetylcysteine (NAC). The treated old rats showed a slight brain-specific improvement of mitochondrial energy production efficiency, mostly with NAD-dependent substrates, together with a decrease in carbonyl protein content and an increase in the amount of protein thiols of brain cytosolic fraction. A full recovery of complex II activity was detected in heart mitochondria from NAC-treated old rats. The present work documents the marked tissue specificity of the decline of bioenergetic functions in isolated mitochondria from aged rats and provides the first data on the effects of a long-term treatment with N-acetylcysteine.

Effect of dietary restriction and N-acetylcysteine supplementation on intestinal mucosa and liver mitochondrial redox status and function in aged rats

The age-related changes of glutathione (GSH) levels and the effect of hypocaloric regimen and N-acetylcysteine (NAC) supplementation were investigated in intestinal mucosa and liver mitochondria of 28 months rats. Old rats exhibited lower proteins, GSH and protein sulphydrils (PSH) concentrations, higher GSH-peroxidase (GSH-Px) activity and protein carbonyl deposit, partial inhibition of succinate stimulated mitochondrial state III respiration and decreased mitochondrial nitrosothiols (RSNO) concentration. Lower electric potential and current intensity were found in the colonic mucosa. Old rats undergone hypocaloric regimen showed higher intestinal concentrations of GSH, lower oxidized protein accumulation and GSH-Px activity and higher mitochondrial RSNO levels. Mitochondrial state III respiration and intestinal transport were improved. NAC supplementation enhanced GSH and PSH levels in the ileal but not in the colonic mucosa, GSH and RSNO in liver mitochondria, while GSH-Px and protein carbonyls were decreased everywhere. Mitochondrial respiration ameliorated. In conclusion, ageing is characterized by a spread decrease of GSH concentrations, increased protein oxidation and decreased mitochondrial NO content. Hypocaloric diet ameliorated intestinal transport and, as well as NAC, was effective in enhancing GSH levels but at different extent according to the investigated districts. Both interventions reduced the age-associated increase of GSH-Px and protein carbonyls and improved mitochondrial respiration.

Alterations of markers related to synaptic function in aging rat brain, in normal conditions or under conditions of long-term dietary manipulation

Neurochemical alterations of markers related to synaptic function are potential candidates for age-related impairment of brain function and cognition. The process of aging, including brain aging, can be counteracted to some degree by maintaining animals in long-term conditions of caloric restriction, or supplementing their diet with antioxidant substances. We report here that the age-related decline of the cholinergic and GABAergic systems, that takes place in some CNS regions of aged rats, is not affected by maintaining them under conditions of dietary restriction and, therefore, of reduced calorie intake, from the 12th to the 30th month of age. We also notice the same lack of effect by adding, during the same period, the aging rat diet with the potential antioxidant substance, N-acetylcysteine (NAC). The same dietary manipulations are also unable to counteract the derangement of the first step of the main biosynthetic pathway for polyamines, putative neuromodulators in the CNS, that occurs in the aged spinal cord. Some age-related alterations in the expression of different subunits of the NMDA-type glutamate receptors in some CNS regions of aged rats were instead, at least in some cases, counteracted by long-term dietary manipulation.

The antioxidants alpha-lipoic acid and N-acetylcysteine reverse memory impairment and brain oxidative stress in aged SAMP8 mice

Oxidative stress may play a crucial role in age-related neurodegenerative disorders. Here, we examined the ability of two antioxidants, alpha-lipoic acid (LA) and N-acetylcysteine (NAC), to reverse the cognitive deficits found in the SAMP8 mouse. By 12 months of age, this strain develops elevated levels of Abeta and severe deficits in learning and memory. We found that 12-month-old SAMP8 mice, in comparison with 4-month-old mice, had increased levels of protein carbonyls (an index of protein oxidation), increased TBARS (an index of lipid peroxidation) and a decrease in the weakly immobilized/strongly immobilized (W/S) ratio of the protein-specific spin label MAL-6 (an index of oxidation-induced conformational changes in synaptosomal membrane proteins). Chronic administration of either LA or NAC improved cognition of 12-month-old SAMP8 mice in both the T-maze footshock avoidance paradigm and the lever press appetitive task without inducing non-specific effects on motor activity, motivation to avoid shock, or body weight. These effects probably occurred directly within the brain, as NAC crossed the blood-brain barrier and accumulated in the brain. Furthermore, treatment of 12-month-old SAMP8 mice with LA reversed all three indexes of oxidative stress. These results support the hypothesis that oxidative stress can lead to cognitive dysfunction and provide evidence for a therapeutic role for antioxidants.

Homocysteine-induced brain lipid peroxidation: effects of NMDA receptor blockade, antioxidant treatment, and nitric oxide synthase inhibition

The effect of homocysteine (HCY) on lipid peroxidation (LP), a current mechanism of oxidative neurotoxicity, was investigated in rat brain synaptosomes. LP was assessed by measuring the amount of thiobarbituric acid-reactive substances (TBARS) formed from synaptosomal fractions following HCY treatment. Increasing HCY concentrations (5-1000 micro M) enhanced the TBARS formation in brain synaptosomes in a concentration-dependent manner. When compared at equimolar concentrations (100 micro M), the oxidative potency of HCY was lower than that of the oxidant ferrous sulfate, similar to that produced by glutamate (Glu) and the mitochondrial toxin 3-nitropropionic acid, and higher than that of the Glu agonists, kainate and quinolinate. The N-methyl-D-aspartate receptor (NMDAr) antagonist dizocilpine (MK-801) completely blocked the HCY-induced LP at concentrations between 5 to 1000 micro M, whereas the well-known antioxidant N-acetylcysteine (NAC) was less effective, but still protective against the HCY oxidative toxicity at higher concentrations (400 and 1000 micro M). Three nitric oxide synthase (NOS) inhibitors, 7-nitroindazole (7-NI), Nomega-nitro-L-arginine (L-NARG) and Nomega-nitro-L-arginine methyl ester (L-NAME), were also tested on HCY-induced LP at increasing concentrations. Both nonspecific NOS inhibitors (L-NARG and L-NAME) decreased more effectively the HCY-induced LP than did the selective neuronal NOS inhibitor, 7-NI. These results show that submillimolar concentrations of HCY can induce oxidative injury to nerve terminals, and this effect involves NMDAr stimulation, NOS activation, and associated free radicals formation.

Aging-related changes in the thiol/disulfide redox state: implications for the use of thiol antioxidants

Genetic and biochemical studies suggest that free radical-derived reactive oxygen species play a key role in a common mechanism of aging in many or all animal species. This led to the hypothesis that the quality of life in old age may be improved by pharmacological or dietary thiol antioxidants. This review describes important details about how the organism deals with its own thiol antioxidants. Aging was found to be associated with an oxidative shift in the thiol/disulfide redox state (REDST) of the intracellular glutathione pool and of the plasma cyst(e)ine and albumin pools. There is also a decrease in plasma thiol (mainly cysteine) concentration. The oxidative shift in intracellular REDST was found to be typically associated with cellular dysfunctions. Studies in humans related to plasma REDST revealed correlations with aging-related pathophysiological processes, suggesting that oxidative changes in REDST play a key role in processes and diseases which limit the human life span. The age-related shift in plasma REDST is mediated, at least partly, by the decreasing capacity to remove dietary cysteine from the oxidative environment of the blood. Thiol antioxidants were found to ameliorate various aging-related processes but obviously ought to be used with caution in consideration of the oxidative environment of the blood.

N-acetylcysteine and celecoxib lessen cadmium cytotoxicity which is associated with cyclooxygenase-2 up-regulation in mouse neuronal cells

In many neurodegenerative disorders, aggregates of ubiquitinated proteins are detected in neuronal inclusions, but their role in neurodegeneration remains to be defined. To identify intracellular mechanisms associated with the appearance of ubiquitin-protein aggregates, mouse neuronal HT4 cells were treated with cadmium. This heavy metal is a potent cell poison that mediates oxidative stress and disrupts the ubiquitin/proteasome pathway. In the current studies, the following intracellular events were found to be also induced by cadmium: (i) a specific rise in cyclooxygenase-2 (COX-2) gene expression but not COX-1; (ii) an increase in the extracellular levels of the proinflammatory prostaglandin E2, a product of COX-2; and (iii) production of 4-hydroxy-2-nonenal-protein adducts, which result from lipid peroxidation. In addition, cadmium treatment led to the accumulation of high molecular weight ubiquitin-COX-2 conjugates and perturbed COX-2 glycosylation. The thiol-reducing antioxidant N-acetylcysteine, and, to a lesser extent, the COX-2 inhibitor celecoxib, attenuated the loss of cell viability induced by cadmium demonstrating that oxidative stress and COX-2 activation contribute to cadmium cytotoxicity. These findings establish that disruption of the ubiquitin/proteasome pathway is not the only event triggered by cadmium. This oxidative stressor also activates COX-2 function. Both events could be triggered by formation of 4-hydroxy-2-nonenal as a result of cadmium-induced lipid peroxidation. Proinflammatory responses stimulated by oxidative stressors that mimic the cadmium effects may, therefore, be important initiators of the neurodegenerative process and exacerbate its progress.

Modification of brain aging and neurodegenerative disorders by genes, diet, and behavior

Multiple molecular, cellular, structural, and functional changes occur in the brain during aging. Neural cells may respond to these changes adaptively, or they may succumb to neurodegenerative cascades that result in disorders such as Alzheimer's and Parkinson's diseases. Multiple mechanisms are employed to maintain the integrity of nerve cell circuits and to facilitate responses to environmental demands and promote recovery of function after injury. The mechanisms include production of neurotrophic factors and cytokines, expression of various cell survival-promoting proteins (e.g., protein chaperones, antioxidant enzymes, Bcl-2 and inhibitor of apoptosis proteins), preservation of genomic integrity by telomerase and DNA repair proteins, and mobilization of neural stem cells to replace damaged neurons and glia. The aging process challenges such neuroprotective and neurorestorative mechanisms. Genetic and environmental factors superimposed upon the aging process can determine whether brain aging is successful or unsuccessful. Mutations in genes that cause inherited forms of Alzheimer's disease (amyloid precursor protein and presenilins), Parkinson's disease (alpha-synuclein and Parkin), and trinucleotide repeat disorders (huntingtin, androgen receptor, ataxin, and others) overwhelm endogenous neuroprotective mechanisms; other genes, such as those encoding apolipoprotein E(4), have more subtle effects on brain aging. On the other hand, neuroprotective mechanisms can be bolstered by dietary (caloric restriction and folate and antioxidant supplementation) and behavioral (intellectual and physical activities) modifications. At the cellular and molecular levels, successful brain aging can be facilitated by activating a hormesis response in which neurons increase production of neurotrophic factors and stress proteins. Neural stem cells that reside in the adult brain are also responsive to environmental demands and appear capable of replacing lost or dysfunctional neurons and glial cells, perhaps even in the aging brain. The recent application of modern methods of molecular and cellular biology to the problem of brain aging is revealing a remarkable capacity within brain cells for adaptation to aging and resistance to disease.

Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment

Free radicals and other so-called 'reactive species' are constantly produced in the brain in vivo. Some arise by 'accidents of chemistry', an example of which may be the leakage of electrons from the mitochondrial electron transport chain to generate superoxide radical (O2*-). Others are generated for useful purposes, such as the role of nitric oxide in neurotransmission and the production of O2*- by activated microglia. Because of its high ATP demand, the brain consumes O2 rapidly, and is thus susceptible to interference with mitochondrial function, which can in turn lead to increased O2*- formation. The brain contains multiple antioxidant defences, of which the mitochondrial manganese-containing superoxide dismutase and reduced glutathione seem especially important. Iron is a powerful promoter of free radical damage, able to catalyse generation of highly reactive hydroxyl, alkoxyl and peroxyl radicals from hydrogen peroxide and lipid peroxides, respectively. Although most iron in the brain is stored in ferritin, 'catalytic' iron is readily mobilised from injured brain tissue. Increased levels of oxidative damage to DNA, lipids and proteins have been detected by a range of assays in post-mortem tissues from patients with Parkinson's disease, Alzheimer's disease and amyotrophic lateral sclerosis, and at least some of these changes may occur early in disease progression. The accumulation and precipitation of proteins that occur in these diseases may be aggravated by oxidative damage, and may in turn cause more oxidative damage by interfering with the function of the proteasome. Indeed, it has been shown that proteasomal inhibition increases levels of oxidative damage not only to proteins but also to other biomolecules. Hence, there are many attempts to develop antioxidants that can cross the blood-brain barrier and decrease oxidative damage. Natural antioxidants such as vitamin E (tocopherol), carotenoids and flavonoids do not readily enter the brain in the adult, and the lazaroid antioxidant tirilazad (U-74006F) appears to localise in the blood-brain barrier. Other antioxidants under development include modified spin traps and low molecular mass scavengers of O2*-. One possible source of lead compounds is the use of traditional remedies claimed to improve brain function. Little is known about the impact of dietary antioxidants upon the development and progression of neurodegenerative diseases, especially Alzheimer's disease. Several agents already in therapeutic use might exert some of their effects by antioxidant action, including selegiline (deprenyl), apomorphine and nitecapone.