Oxidative stress and ageing: is ageing a cysteine deficiency syndrome?

Plasma biomarkers of oxidative and AGE-mediated damage of proteins and glycosaminoglycans during healthy ageing: a possible association with ECM metabolism

The aim of this study was to examine whether oxidative and AGE-mediated processes correlates with the metabolic changes of proteoglycans (PGs) and proteins during physiological ageing. The age and gender-associated changes of PGs metabolism were evaluated by plasma chondroitin sulfates (CS), dermatan sulfates (DS) and heparan sulfates and heparin (HS/H). We found a linear age-related decline in CS, DS and HS/H, the first one being the predominant plasma GAG during ageing. The possible deleterious effect of oxidative phenomenon on proteins' and proteoglycans' metabolism during ageing process was analyzed by plasma carbonyls (PCO) and thiols (PSH) as well as by total antioxidant capacity (TAS). An age-dependent increase in PCO and decrease in PSH concentrations were found, both strongly correlated with decreasing with age plasma TAS. Intensity of glycation was assessed by circulating N(ε)-(carboxymethyl)lysine (CML) and endogenous secretory receptor for AGE (esRAGE), both of them founding associated with ageing. Moreover, all markers of oxidative and AGE-mediated damage correlated with CS and DS level and could be contributing factors to age-related changes of these GAG types. Thus, plasma CS and DS could become promising biomarkers of human ageing to date, owning to its close association with oxidative status and glycation processes.

L-cysteine supplementation as an adjuvant therapy for type-2 diabetes

Diabetes remains a major public health issue. According to the American Diabetes Association, 23.5 million, or 10.7% of people in the USA aged 20 years and older, have diabetes. Type-2 diabetes is treated both by controlling the diet and with oral hypoglycemic drugs. However, for many patients, achieving a tight control of glucose is difficult with current regimens. This chapter discusses a relatively low-cost dietary supplement that could be used as an adjuvant therapy for type-2 diabetes. A review of the literature indicates that cysteine-rich whey protein improves glucose metabolism in diabetic animals and type-2 diabetic patients. Similarly, in animal studies, improvement in glucose metabolism is observed after supplementation with L-cysteine, or molecules containing a cysteine moiety. This chapter discusses the biochemical mechanisms by which L-cysteine can upregulate the insulin-dependent signaling cascades of glucose metabolism. Further studies are needed to examine whether clinical interventions using L-cysteine as an adjuvant therapy indeed help to control glycemia and vascular inflammation in the diabetic patient population.

Hydrogen sulfide in biochemistry and medicine

SIGNIFICANCE

An abundance of experimental evidence suggests that hydrogen sulfide (H(2)S) plays a prominent role in physiology and pathophysiology. Many targets exist for H(2)S therapy. The molecular targets of H(2)S include proteins, enzymes, transcription factors, and membrane ion channels.

RECENT ADVANCES

Novel H(2)S precursors are being synthesized and discovered that are capable of releasing H(2)S in a slow and sustained manner. This presents a novel and advantageous approach to H(2)S therapy for treatment of chronic conditions associated with a decline in endogenous H(2)S, such as diabetes and cardiovascular disease.

CRITICAL ISSUES

While H(2)S is cytoprotective at physiological concentrations, it is not universally cytoprotective, as it appears to have pro-apoptotic actions in cancer cells and is well known to be toxic at supraphysiological concentrations. Many of the pleiotropic effects of H(2)S on health are associated with the inhibition of inflammation and upregulation of prosurvival pathways. The powerful anti-inflammatory, cytoprotective, immunomodulating, and trophic effects of H(2)S on the vast majority of normal cells seem to be mediated mainly by its actions as an extremely versatile direct and indirect antioxidant and free radical scavenger. While the overall effects of H(2)S on transformed (i.e., malignant) cells can be characterized as pro-oxidant and pro-apoptotic, they contrast sharply with the cytoprotective effects on most normal cells.

FUTURE DIRECTIONS

H(2)S has become a molecule of great interest, and several slow-releasing H(2)S prodrugs are currently under development. We believe that additional agents regulating H(2)S bioavailability will be developed during the next 10 years.

Effect of chromium dinicocysteinate supplementation on circulating levels of insulin, TNF-α, oxidative stress, and insulin resistance in type 2 diabetic subjects: randomized, double-blind, placebo-controlled study

SCOPE

Chromium and cysteine supplementation have been shown to improve glucose metabolism in animal studies. This study examined the hypothesis that chromium dinicocysteinate (CDNC), a complex of chromium and l-cysteine, is beneficial in lowering oxidative stress, vascular inflammation, and glycemia in type 2 diabetic subjects.

METHODS AND RESULTS

Type 2 diabetic subjects enrolled in this study were given placebo for 1 month for stabilization and then randomized into one of three groups: placebo (P), chromium picolinate (CP), or CDNC, after which they received daily oral supplementation for 3 months. Of the 100 patients enrolled in the study, 74 patients completed it. There were 25 patients in the P supplemented group, 25 in the CP supplemented and 24 in the CDNC supplemented group who completed the study. Blood markers of glycemia, vascular inflammation, HOMA insulin resistance, and oxidative stress were determined at randomization and after 3 months of supplementation with P, CP, or CDNC. There was a significant decrease at 3 months in insulin resistance (p = 0.02) and in the levels of protein oxidation (p = 0.02) and TNF-α (p = 0.01) in the CDNC supplemented cohort compared to baseline. However, there was no statistically significant change in these markers in the CP supplemented group compared to baseline. Insulin levels significantly decreased (p = 0.01) for subjects receiving CDNC but not CP. There was no significant impact of supplementation on HbA(1c) or glucose levels in either of the groups.

CONCLUSION

CDNC supplementation lowers insulin resistance by reducing blood levels of TNF-α, insulin, and oxidative stress in type 2 diabetic subjects. Therefore, CDNC supplementation has potential as an adjunct therapy for individuals with type 2 diabetes.

Polysaccharides from the Medicinal Mushroom Cordyceps taii Show Antioxidant and Immunoenhancing Activities in a D-Galactose-Induced Aging Mouse Model

Cordyceps taii, an edible medicinal mushroom native to south China, is recognized as an unparalleled resource of healthy foods and drug discovery. In the present study, the antioxidant pharmacological properties of C. taii were systematically investigated. In vitro assays revealed the scavenging activities of the aqueous extract and polysaccharides of C. taii against various free radicals, that is, 1,1-diphenyl-2-picrylhydrazyl radical, hydroxyl radical, and superoxide anion radical. The EC₅₀ values for superoxide anion-free radical ranged from 2.04 mg/mL to 2.49 mg/mL, which was at least 2.6-fold stronger than that of antioxidant thiourea. The polysaccharides also significantly enhanced the antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) and markedly decreased the malondialdehyde production of lipid peroxidation in a D-galactose-induced aging mouse model. Interestingly, the immune function of the administration group was significantly boosted compared with the D-galactose-induced aging model group. Therefore, the C. taii polysaccharides possessed potent antioxidant activity closely associated with immune function enhancement and free radical scavenging. These findings suggest that the polysaccharides are a promising source of natural antioxidants and antiaging drugs. Consequently, a preliminary chemical investigation was performed using gas chromatography-mass spectroscopy and revealed that the polysaccharides studied were mainly composed of glucose, mannose, and galactose. Fourier-transform infrared spectra also showed characteristic polysaccharide absorption bands.

Identification of a redox-sensitive switch within the JAK2 catalytic domain

Four cysteine residues (Cys866, Cys917, Cys1094, and Cys1105) have direct roles in cooperatively regulating Janus kinase 2 (JAK2) catalytic activity. Additional site-directed mutagenesis experiments now provide evidence that two of these residues (Cys866 and Cys917) act together as a redox-sensitive switch, allowing JAK2's catalytic activity to be directly regulated by the redox state of the cell. We created several variants of the truncated JAK2 (GST/(NΔ661)rJAK2), which incorporated cysteine-to-serine or cysteine-to-alanine mutations. The catalytic activities of these mutant enzymes were evaluated by in vitro autokinase assays and by in situ autophosphorylation and transphosphorylation assays. Cysteine-to-alanine mutagenesis revealed that the mechanistic role of Cys866 and Cys917 is functionally distinct from that of Cys1094 and Cys1105. Most notable is the observation that the robust activity of the CC866,917AA mutant is unaltered by pretreatment with dithiothreitol or o-iodosobenzoate, unlike all other JAK2 variants previously examined. This work provides the first direct evidence for a cysteine-based redox-sensitive switch that regulates JAK2 catalytic activity. The presence of this redox-sensitive switch predicts that reactive oxygen species can impair the cell's response to JAK-coupled cytokines under conditions of oxidative stress, which we confirm in a murine pancreatic β-islet cell line.

Mate tea prevents oxidative stress in the blood and hippocampus of rats with acute or chronic ethanol administration

OBJECTIVE

The aim of this study was to evaluate the influence of acute and chronic intake of mate tea on the effects elicited by acute and chronic administration of ethanol.

METHODS

Oxidative stress was evaluated by measuring thiobarbituric acid-reactive substances (TBARS), as well as the activities of the antioxidant enzymes, catalase (CAT), glutathione peroxidase (GSH-Px), and superoxide dismutase (SOD) in the hippocampus and blood of rats. Male Wistar rats were randomly assigned to four groups, for both acute and chronic treatment: (1) control group, (2) treated group, (3) intoxicated group, (4) and intoxicated group treated with mate tea.

RESULTS

Both ethanol administrations significantly increased TBARS in plasma and hippocampus of rats and altered antioxidant enzyme activities, changes which were reverted by mate tea administration.

CONCLUSIONS

Data indicate that acute and chronic ethanol administration induced oxidative stress in hippocampus and blood and that mate tea treatment was able to prevent this situation.

Exploring real-time in vivo redox biology of developing and aging Caenorhabditis elegans

Reactive oxygen species (ROS) are no longer considered merely toxic by-products of the oxidative metabolism. Tightly controlled concentrations of ROS and fluctuations in redox potential may be important mediators of signaling processes. Understanding the role of ROS and redox status in physiology, stress response, development, and aging requires their nondisruptive, spatiotemporal, real-time quantification in a living organism. We established Caenorhabditis elegans strains bearing the genetically encoded fluorescent biosensors HyPer and Grx1-roGFP2 for the detection of hydrogen peroxide (H(2)O(2)) and the glutathione redox potential, respectively. Although, given its transparency and genetic tractability, C. elegans is perfectly suitable as a model organism for such approaches, they have never been tried before in this nematode. We found that H(2)O(2) treatment clearly induces a dose-dependent, reversible response of both biosensors in the living worms. The ratio of oxidized to reduced glutathione decreases during postembryonic development. H(2)O(2) levels increase with age and this effect is delayed when life span is extended by dietary restriction. In young adults, we detected several regions with distinct redox properties that may be linked to their biological function. Our findings demonstrate that genetically encoded biosensors can reveal previously unknown details of in vivo redox biology in multicellular organisms.

Therapeutic paracetamol treatment in older persons induces dietary and metabolic modifications related to sulfur amino acids

Sulfur amino acids are determinant for the detoxification of paracetamol (N-acetyl-p-aminophenol) through sulfate and glutathione conjugations. Long-term paracetamol treatment is common in the elderly, despite a potential cysteine/glutathione deficiency. Detoxification could occur at the expense of anti-oxidative defenses and whole body protein stores in elderly. We tested how older persons satisfy the extra demand in sulfur amino acids induced by long-term paracetamol treatment, focusing on metabolic and nutritional aspects. Effects of 3 g/day paracetamol for 14 days on fasting blood glutathione, plasma amino acids and sulfate, urinary paracetamol metabolites, and urinary metabolomic were studied in independently living older persons (five women, five men, mean (±SEM) age 74 ± 1 years). Dietary intakes were recorded before and at the end of the treatment and ingested sulfur amino acids were evaluated. Fasting blood glutathione, plasma amino acids, and sulfate were unchanged. Urinary nitrogen excretion supported a preservation of whole body proteins, but large-scale urinary metabolomic analysis revealed an oxidation of some sulfur-containing compounds. Dietary protein intake was 13% higher at the end than before paracetamol treatment. Final sulfur amino acid intake reached 37 mg/kg/day. The increase in sulfur amino acid intake corresponded to half of the sulfur excreted in urinary paracetamol conjugates. In conclusion, older persons accommodated to long-term paracetamol treatment by increasing dietary protein intake without any mobilization of body proteins, but with decreased anti-oxidative defenses. The extra demand in sulfur amino acids led to a consumption far above the corresponding population-safe recommendation.

Acetaminophen metabolism after major surgery: a greater challenge with increasing age

Patients undergoing major surgery represent a good model for the study of the hepatic metabolism of acetaminophen (APAP) after surgery and for the evaluation of how the detoxification process is influenced by aging. Thirty patients received intravenous APAP (1 g/6 h) for 4 days (D1-D4). Daily 24-h urinary metabolites-cysteine-APAP, mercapturate-APAP, APAP, and glucuronide and sulfate conjugates-as well as blood glutathione levels were compared with repeated-measures analysis of variance (significance, P<0.05). Between D1 and D4, cysteine-APAP increased (308±308 mg vs. 570±512 mg, P=0.005), and sulfate and glucuronide conjugates decreased (1,365±1,084 mg vs. 694±600 mg, P<0.0001 and 2,418±817 mg vs. 1,513±1,076 mg, P=0.011, respectively). Blood glutathione decreased (790±125 vs. 623±132 µmol/l, P<0.0001. These changes increased with aging. APAP disposition after major surgery shifts toward the oxidative pathways of metabolism, and this is enhanced with aging. Supplementation with sulfur-containing amino acids should be investigated further as it might minimize the effect on antioxidant defenses, especially in older persons undergoing more extensive surgical procedures.

Hydrogen sulfide and L-cysteine increase phosphatidylinositol 3,4,5-trisphosphate (PIP3) and glucose utilization by inhibiting phosphatase and tensin homolog (PTEN) protein and activating phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase (AKT)/protein kinase Cζ/λ (PKCζ/λ) in 3T3l1 adipocytes

This work examined the novel hypothesis that reduced levels of H(2)S or L-cysteine (LC) play a role in the impaired glucose metabolism seen in diabetes. 3T3L1 adipocytes were treated with high glucose (HG, 25 mM) in the presence or absence of LC or H(2)S. Both LC and H(2)S treatments caused an increase in phosphatidylinositol-3,4,5 trisphosphate (PIP3), AKT phosphorylation, and glucose utilization in HG-treated cells. The effect of LC on PIP3 and glucose utilization was prevented by propargylglycine, an inhibitor of cystathionine γ-lyase that catalyzes H(2)S formation from LC. This demonstrates that H(2)S mediates the effect of LC on increased PIP3 and glucose utilization. H(2)S and LC caused phosphatidylinositol 3-kinase activation and PTEN inhibition. Treatment with LC, H(2)S, or PIP3 increased the phosphorylation of IRS1, AKT, and PKCζ/λ as well as GLUT4 activation and glucose utilization in HG-treated cells. This provides evidence that PIP3 is involved in the increased glucose utilization observed in cells supplemented with LC or H(2)S. Comparative signal silencing studies with siAKT2 or siPKCζ revealed that PKCζ phosphorylation is more effective for the GLUT4 activation and glucose utilization in LC-, H(2)S-, or PIP3-treated cells exposed to HG. This is the first report to demonstrate that H(2)S or LC can increase cellular levels of PIP3, a positive regulator of glucose metabolism. The PIP3 increase is mediated by PI3K activation and inhibition of PTEN but not of SHIP2. This study provides evidence for a molecular mechanism by which H(2)S or LC can up-regulate the insulin-signaling pathways essential for maintenance of glucose metabolism.

Free radicals and redox signalling in T-cells during chronic inflammation and ageing

During chronic inflammation and ageing, the increase in oxidative stress in both intracellular and extracellular compartments is likely to influence local cell functions. Redox changes alter the T-cell proteome in a quantitative and qualitative manner, and post-translational modifications to surface and cytoplasmic proteins by increased reactive species can influence T-cell function. Previously, we have shown that RA (rheumatoid arthritis) T-cells exhibit reduced ROS (reactive oxygen species) production in response to extracellular stimulation compared with age-matched controls, and basal ROS levels [measured as DCF (2′,7′-dichlorofluorescein) fluorescence] are lower in RA T-cells. In contrast, exposing T-cells in vitro to different extracellular redox environments modulates intracellular signalling and enhances cytokine secretion. Together, these data suggest that a complex relationship exists between intra- and extra-cellular redox compartments which contribute to the T-cell phenotype.

p53, oxidative stress, and aging

Mammalian aging is associated with elevated levels of oxidative damage of DNA, proteins, and lipids as a result of unbalanced prooxidant and antioxidant activities. Accumulating evidence indicates that oxidative stress is a major physiological inducer of aging. p53, the guardian of the genome that is important for cellular responses to oxidative stresses, might be a key coordinator of oxidative stress and aging. In response to low levels of oxidative stresses, p53 exhibits antioxidant activities to eliminate oxidative stress and ensure cell survival; in response to high levels of oxidative stresses, p53 exhibits pro-oxidative activities that further increase the levels of stresses, leading to cell death. p53 accomplishes these context-dependent roles by regulating the expression of a panel of genes involved in cellular responses to oxidative stresses and by modulating other pathways important for oxidative stress responses. The mechanism that switches p53 function from antioxidant to prooxidant remains unclear, but could account for the findings that increased p53 activities have been linked to both accelerated aging and increased life span in mice. Therefore, a balance of p53 antioxidant and prooxidant activities in response to oxidative stresses could be important for longevity by suppressing the accumulation of oxidative stresses and DNA damage.

Protein and DNA oxidation in different anatomic regions of rat brain in a mimetic ageing model

It has been reported that d-galactose administration causes an increase in oxidative and osmotic stresses in several tissues of rodents. In this study, we established a brain ageing model by using d-galactose and investigated the concentrations of oxidative stress markers on the hippocampus, parietal and frontal lobes of male Sprague-Dawley rats. A mimetic ageing model was established by injecting d-galactose (60 mg/kg/day/i.p.) in the experimental group for 42 days. At the end of this period, we tested spatial memory using the Morris water maze test. To investigate the magnitude of oxidative damage in proteins, lipids and DNA, we studied the concentrations of various oxidative stress parameters in the hippocampus, parietal and frontal lobes of the brain. Glial and neuronal cell oxidative damage was observed in each of the three anatomic regions. It was found that protein carbonyl groups and advanced oxidation product concentrations in the d-galactose applied group were significantly high in each of the three brain lobes compared with the control group. Thiol concentration was found to be decreased in the parietal lobe. A concurrent increase in lipid hydroperoxides was also observed in this lobe. On the other hand, 8-hydroxy-2'-deoxyguanosine concentration was significantly increased in the hippocampal lobe of rats in the experimental group when compared with the controls. The results obtained from the mimetic ageing model rats showed that various anatomical regions of brain have different susceptibility to oxidative damage of proteins, lipids and DNA.

Oxidative stress accumulates in adipose tissue during aging and inhibits adipogenesis

Aging constitutes a major independent risk factor for the development of type 2 diabetes and is accompanied by insulin resistance and adipose tissue dysfunction. One of the most important factors implicitly linked to aging and age-related chronic diseases is the accumulation of oxidative stress. However, the effect of increased oxidative stress on adipose tissue biology remains elusive. In this study, we demonstrate that aging in mice results in a loss of fat mass and the accumulation of oxidative stress in adipose tissue. In vitro, increased oxidative stress through glutathione depletion inhibits preadipocyte differentiation. This inhibition of adipogenesis is at least in part the result of reduced cell proliferation and an inhibition of G₁→S-phase transition during the initial mitotic clonal expansion of the adipocyte differentiation process. While phosphorylation of the retinoblastoma protein (Rb) by cyclin/cdk complexes remains unaffected, oxidative stress decreases the expression of S-phase genes downstream of Rb. This silencing of S phase gene expression by increased oxidative stress is mediated through a transcriptional mechanism involving the inhibition of E2F recruitment and transactivation of its target promoters. Collectively, these data demonstrate a previously unrecognized role of oxidative stress in the regulation of adipogenesis which may contribute to age-associated adipose tissue dysfunction.

Cysteine/cystine redox signaling in cardiovascular disease

Extracellular thiol/disulfide redox environments are highly regulated in healthy individuals. The major thiol/disulfide redox couple in human plasma is cysteine (Cys) and its disulfide form, cystine (CySS). Oxidation of this redox couple, measured as a more positive steady-state redox potential (E(h)), is associated with risk factors for cardiovascular disease (CVD), including aging, smoking, obesity, and alcohol abuse. Rodent and vascular cell studies show that the extracellular redox state of Cys/CySS (E(h)CySS) can play a vital role in controlling CVD through proinflammatory signaling. This inflammatory signaling is regulated by cell-surface protein redox state and involves mitochondrial oxidation, nuclear factor-κB activation, and elevated expression of genes for monocyte recruitment to endothelial cells. Gene array and proteomics studies reveal the global nature of redox effects, and different cell types, e.g., endothelial cells, monocytes, fibroblasts, and epithelial cells, show cell-specific redox responses with different phenotypic traits, e.g., proliferation and apoptosis, which can contribute to CVD. The critical nature of the proinflammatory redox signaling and cell biology associated with E(h)CySS supports the use of plasma levels of Cys, CySS, and E(h)CySS as key indicators of vascular health. Plasma redox-state-based pharmacologic interventions to control or improve E(h)CySS may be effective in preventing CVD onset or progression.

Chromium dinicocysteinate supplementation can lower blood glucose, CRP, MCP-1, ICAM-1, creatinine, apparently mediated by elevated blood vitamin C and adiponectin and inhibition of NFkappaB, Akt, and Glut-2 in livers of zucker diabetic fatty rats

Chromium and cysteine supplementation can improve glucose metabolism in animal studies. This study examined the hypothesis that a cysteinate complex of chromium is significantly beneficial than either of them in lowering blood glucose and vascular inflammation markers in Zucker diabetic fatty (ZDF) rats. Starting at the age of 6 wk, ZDF rats were supplemented orally (daily gavages for 8 more weeks) with saline-placebo (D) or chromium (400 microg Cr/Kg body weight) as chromium dinicocysteinate (CDNC), chromium dinicotinate (CDN) or chromium picolinate (CP) or equimolar L-cysteine (LC, img/Kg body weight), and fed Purina 5008 diet for 8 wk. ZDF rats of 6 wk age before any supplementations and onset of diabetes were considered as baseline. D rats showed elevated levels of fasting blood glucose, HbA(1), CRP, MCP-1, ICAM-1 and oxidative stress (lipid peroxidation) and lower adiponectin and vitamin C, when compared with baseline rats. In comparison to D group, CDNC group had significantly lower blood glucose, HbA(1), CRP, MCP-1, ICAM-1 and lipid peroxidation and increased vitamin C and adiponectin levels. CDN, CP or LC showed significantly less or no effect on these biomarkers. Only CDNC lowered blood creatinine levels in comparison to D. While CDN and CP had no effect, activation of NFkappaB, Akt and glucose transporter-2 levels were decreased, insulin receptor substrate 1 (IRS-1) activation increased in livers of CDNC-rats. CDNC effect on glycemia, NFkappaB, Akt and IRS-1 in liver was significantly greater compared with LC. Blood chromium levels did not differ between Cr-groups. Exogenous vitamin C supplementation significantly inhibited MCP-1 secretion in U937 monocytes cultured in high-glucose-medium. CDNC is a potent hypoglycemic compound with anti-inflammatory activity apparently mediated by elevated blood vitamin C and adiponectin and inhibition of NFkappaB, Akt, and Glut-2 and increased IRS-1 activation in livers of type 2 diabetic rats.

Reducing carcinogenic acetaldehyde exposure in the achlorhydric stomach with cysteine

BACKGROUND

Acetaldehyde, associated with alcohol consumption, has recently been classified as a group 1 carcinogen in humans. Achlorhydric atrophic gastritis is a well-known risk factor for gastric cancer. Achlorhydria leads to microbial colonization of the stomach. Several of these microbes are able to produce significant amounts of acetaldehyde by oxidation from alcohol. Acetaldehyde can be eliminated from saliva after alcohol intake and during smoking with a semi-essential amino acid, L-cysteine. The aim of this study was to determine whether cysteine can be used to bind acetaldehyde in the achlorhydric stomach after ethanol ingestion.

METHODS

Seven volunteers with achlorhydric atrophic gastritis were given either slow-release L-cysteine or placebo capsules in a double-blinded randomized trial. Volunteers served as their own controls. A naso-gastric tube was inserted to each volunteer. The volunteers ingested placebo or 200 mg of L-cysteine capsules, and ethanol 0.3 g/kg body weight (15 vol%) was infused intragastrically through a naso-gastric tube. Five-milliliter samples of gastric contents were aspirated at 5-minute intervals.

RESULTS

During the follow-up period, the mean acetaldehyde level of gastric juice was 2.6 times higher with placebo than with L-cysteine (13 vs. 4.7 μM, p < 0.05, n = 7).

CONCLUSIONS

L-cysteine can be used to decrease acetaldehyde concentration in the achlorhydric stomach during alcohol exposure. Intervention studies with L-cysteine are needed on reducing acetaldehyde exposure in this important risk group for gastric cancer.

Strategies for the discovery of anti-aging compounds

IMPORTANCE OF THE FIELD

Life expectancy has increased across the globe and the number of aged people is increasing rapidly. With the rise in the average age of people, the prevalence of age related pathologies has also increased and thus the strategies to find anti-aging molecules assume significance. Anti-aging basically concerns the prevention or delaying the alterations taking place as a function of age which are manifested as age-associated illnesses.

AREAS COVERED IN THIS REVIEW

This review covers anti-aging strategies involving supplementation of dietary antioxidants such as polyphenols, vitamins E and C, lipoic acid, acetyl carnitine, carnosine and cysteine along with the application of mammalian target of rapamycin inhibitors and plasma membrane redox system activators. It also presents the use of different hormone supplementation, for example, melatonin, dehydroepiandrosterone, growth hormone and sex hormones as a tool against aging. The use of caloric restriction and calorie restriction mimetics as an anti-aging intervention is also reviewed.

WHAT THE READER WILL GAIN

The concept, use and efficacy of different anti-aging approaches.

TAKE HOME MESSAGE

Despite a lot of research and sustained ongoing efforts, finding a viable anti-aging therapy which can extend the maximum human lifespan remains elusive. However, several interventions aimed towards a longer healthy life seem promising.

Acetylation of H4K12 in porcine oocytes during in vitro aging: potential role of ooplasmic reactive oxygen species

Deterioration in the quality of mammalian mature oocytes during metaphase-II (M-II) arrest is called "oocyte aging". Although histone acetylation may affect the progression of aging in murine oocytes, the mechanism is unknown. The objective was to determine the role of ooplasmic reactive oxygen species (ROS) in acetylation of histone H4 at lysine 12 (acH4K12) in porcine aged oocytes in vitro. Based on immunostaining with a specific antibody, acetylation of H4K12 in porcine oocytes increased during in vitro aging, which coincided with changing patterns of ooplasmic ROS content. Furthermore, both hydrogen peroxide (H(2)O(2)), and the mitochondrial membrane potential disrupter, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), which can moderately elevate oocyte ROS content, significantly increased acetylation levels of H4K12 in porcine oocytes. It was noteworthy that acetylation in the CCCP group was decreased when ROS was counteracted by cysteine, a common antioxidant. In addition, the intracellular mRNA abundance of acetyltransferase gene HAT1 in aged and H(2)O(2) treated oocytes was higher than in M-II phase oocytes, suggesting that HAT1 was involved in this reaction. After parthenogenetic activation, a lower proportion of oocytes developed to the blastocyst stage after CCCP or H(2)O(2) treatment when compared with M-II phase oocytes (20 and 0% for CCCP and H(2)O(2) groups, respectively, versus 42% for the M-II group, P < 0.05). In conclusion, elevated levels of H4K12 acetylation were attributed to increased ooplasmic ROS content during porcine oocyte aging in vitro.

Murine models of premature ageing for the study of diet-induced immune changes: improvement of leucocyte functions in two strains of old prematurely ageing mice by dietary supplementation with sulphur-containing antioxidants

Several immune functions are markers of health, biological age and predictors of longevity. A chronic oxidative and inflammatory state is the main cause of ageing and the immune system is involved in the rate of ageing. Thus, several murine models of premature ageing have been proposed owing to their early immunosenescence and oxidative stress, such as ovariectomised rats and mice, obese rats and anxious mice. In the last model, the most extensively studied by us, mice showing anxiety have an aged immune function and redox status as well as a shorter longevity in comparison with animals without anxiety of the same chronological age, being denominated prematurely ageing mice. A confirmation of the above is that the administration of diets supplemented with antioxidants improves the redox status and immune functions and increases the longevity of prematurely ageing mice. Antioxidant precursors of glutathione such as thioproline or N-acetylcysteine, which have a relevant role in ageing, have been the most widely investigated in adult prematurely ageing mice in our laboratory. In the present work, we have studied the effects of the ingestion for 5 weeks of a diet supplemented with 0·1% (w/w) thioproline+N-acetylcysteine on several functions of leucocytes from chronological old (69-73 weeks of age) prematurely ageing mice of two strains (Swiss and BALB/c). The results show an improvement of the immune functions, with their values becoming closer to those in adult animals (24±2 weeks). Thus, an adequate nutrition with antioxidants, even in aged subjects, could be a good strategy to retard ageing.

Serum albumin and biomolecular oxidative damage of human atherosclerotic plaques

OBJECTIVES

To investigate the association of serum albumin (SA) with oxidative damage of human atherosclerotic plaques and the severity of atherosclerosis.

DESIGN AND METHODS

Correlation of the levels of SA with those of lipid and protein oxidation of endarterectomy-removed carotid atherosclerotic plaques; SA and plaque oxidative biomarkers comparison between 2 groups of patients with different severity of atherosclerotic carotid stenosis, i.e. <90% (group I) or ≥90% (group II).

RESULTS

SA was strongly inversely correlated with plaque oxidative damage; SA was lower and plaque oxidative damage higher in group II than group I.

CONCLUSIONS

Lowered SA is associated with oxidative damage of atherosclerotic plaques and the severity of atherosclerosis.

Low levels of hydrogen sulfide in the blood of diabetes patients and streptozotocin-treated rats causes vascular inflammation?

Hydrogen sulfide (H(2)S) is emerging as a physiological neuromodulator as well as a smooth muscle relaxant. We submit the first evidence that blood H(2)S levels are significantly lower in fasting blood obtained from type 2 diabetes patients compared with age-matched healthy subjects, and in streptozotocin-treated diabetic rats compared with control Sprague-Dawley rats. We further observed that supplementation with H(2)S or an endogenous precursor of H(2)S (l-cysteine) in culture medium prevents IL-8 and MCP-1 secretion in high-glucose-treated human U937 monocytes. These first observations led to the hypothesis that lower blood H(2)S levels may contribute to the vascular inflammation seen in diabetes.

"Old" hearts and arteries: the role of oxidative stress

Despite decades of investigation, the roles of reactive oxygen species (ROS) in atherosclerosis and aging have yet to be defined. We have developed mouse models that allow this question to be addressed experimentally. Given the increase in risk factors for atherosclerosis--particularly related to marked increases in obesity and diabetes in industrialized countries--a better understanding of the molecular mechanisms that define both atherosclerosis and aging is needed.

Reactive oxygen and nitrogen species in normal physiological processes

Abstract Reactive oxygen species (ROS) and reactive nitrogen species have generally been considered as being highly reactive and cytotoxic molecules. Besides their noxious effects, ROS participate in physiological processes in a carefully regulated manner. By way of example, microbicidal ROS are produced in professional phagocytes, ROS function as short-lived messengers having a role in signal transduction and, among other processes, participate in the synthesis of the iodothyronine hormones, reproduction, apoptosis and necrosis. Because of their ability to mediate a crosstalk between key molecules, their role might be dual (at least in some cases). The levels of ROS increase from a certain age, being associated with various diseases typical of senescence. The aim of this review is to summarize the recent findings on the physiological role of ROS. Other issues addressed are an increase in ROS levels during ageing, and the possibility of the physiological nature of this process.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.

L-cysteine supplementation lowers blood glucose, glycated hemoglobin, CRP, MCP-1, and oxidative stress and inhibits NF-kappaB activation in the livers of Zucker diabetic rats

This study examined the hypothesis that l-cysteine supplementation can lower insulin resistance, glycemia, oxidative stress, and markers of vascular inflammation in type 2 diabetes using Zucker diabetic fatty (ZDF) rats as a model. Starting at the age of 6 weeks, ZDF rats were supplemented orally (daily gavage, 8 weeks) with saline placebo (D) or l-cysteine (LC; 1 mg/kg bw) and fed a high-calorie diet. Six-week-old rats without any supplementation were considered baseline (BL) rats. D rats showed elevated fasting blood glucose, glycated Hb, CRP, and MCP-1 compared with BL rats in which there was no onset of diabetes. LC supplementation significantly lowered blood levels of glucose (18%, p= 0.05), glycated Hb (8%, p= 0.02), CRP (23%, p= 0.02), MCP-1 (32%, p= 0.01), and insulin resistance (25%) compared with levels seen in saline-supplemented D rats. There was a decrease in plasma protein oxidation levels (p< 0.01); however, GSH levels were similar in LC and D groups. Although LC did not change blood hematocrit or levels of transaminases, it did lower alkaline phosphatase (29%, p= 0.01) levels in comparison to D. Western blotting analyses of liver showed increased activation of NF-kappaB and Akt (50% pNF-kappaB and 20% pAkt) in D compared with BL rats. LC supplementation inhibited these effects (17% pAkt, 18% pNF-kappaB). This is the first report showing that l-cysteine supplementation can lower glycemia and markers of vascular inflammation in diabetes apparently by preventing NF-kappaB activation in a diabetic animal model.

Homocysteine, cysteine, and body composition in the Hordaland Homocysteine Study: does cysteine link amino acid and lipid metabolism?

BACKGROUND

The lean phenotype of cystathionine beta-synthase-deficient homocystinuria and the positive association of plasma total cysteine (tCys) with body mass index (BMI) suggest that total homocysteine (tHcy) and tCys are associated with body composition.

OBJECTIVES

We aimed to study associations of tCys and tHcy with body composition in the general population.

DESIGN

Using data from 7038 Hordaland Homocysteine Study participants, we fitted regression models and dose-response curves of tCys and tHcy with BMI. In 5179 participants, we investigated associations of tCys and tHcy with fat mass and lean mass and examined whether changes in these aminothiols predicted body composition 6 y later.

RESULTS

tCys showed positive associations with BMI (partial r = 0.28, P < 0.001), and fat mass (partial r = 0.25, P < 0.001), independent of diet, exercise, and plasma lipids. Women in the highest tCys quintile had fat mass 9 kg (95% CI: 8, 10 kg; P < 0.001) greater than that of women in the lowest quintile. The corresponding values for men were 6 kg (95% CI: 5, 7 kg; P < 0.001; P < 0.001 in both sexes, ANOVA across quintiles). The rise in tCys over 6 y was associated with greater fat mass at follow-up (P < 0.001), but there was no effect on lean mass. tHcy was not associated with lean mass, and it became significantly inversely associated with BMI and fat mass only after adjustment for tCys. The association between tHcy and lean mass was not significant.

CONCLUSIONS

tCys concentrations show a strong positive association with BMI, mediated through fat mass. The link between cysteine and lipid metabolism deserves further investigation.

L-cysteine influx in erythrocytes as a function of human age

In erythrocytes, although three amino acids are required for the synthesis of reduced glutathione (GSH), the rate of GSH synthesis is determined only by the availability of L-cysteine. Cysteine supplementation has been shown to ameliorate several parameters that are known to degenerate during human aging; this has led to an interesting hypothesis that aging could be a cysteine deficiency syndrome. In the present study, we measured L-cysteine influx in human erythrocytes by suspending cells in solution containing 10 mM L-cysteine. We show a significant decline in the influx of L-cysteine in erythrocytes during aging in humans. The decrease in cysteine influx correlates with the decrease in antioxidant potential of plasma measured in terms of FRAP (ferric-reducing ability of plasma) during aging. We conclude that a decreased influx of L-cysteine may be an important factor contributing to the development of oxidative stress in human erythrocytes during aging.

Muscle disuse: adaptation of antioxidant systems is age dependent

This study investigated the age effect on antioxidant adaptation to muscle disuse. Adult and old rats were randomized into 4 groups: weight bearing (control), 3 days of hind-limb unloading (HU), 7 days of HU, and 14 days of HU. Activities of Cu-Zn superoxide dismutase (SOD), catalase, and glutathione (GSH), as well as GSH peroxidase levels were measured in the soleus. Neither disuse nor aging changed the activity of Cu-Zn SOD. The old rats had greater GSH peroxidase activity, whereas the activity of catalase had a compensatory increase with disuse, independent of age. Reduced GSH level and total glutathione (tGSH) level had age-related change with disuse. In old rats, the GSH and tGSH levels were lower with disuse, whereas the levels remained stable with disuse in adult rats. The depletion of intracellular GSH and tGSH levels of muscles from aged animals with disuse may make aged muscles more susceptible to oxidative damage.

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

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

Antithrombin activity is inhibited by acrolein and homocysteine thiolactone: Protection by cysteine

Conditions in which serum or tissue acrolein levels are high (e.g.: renal failure, heavy smoking, oxidative stress) are also associated with increased thrombogenicity. Another emerging cardiovascular risk factor is homocysteine, and its derivative, homocysteine thiolactone. Antithrombin is one of the most important inhibitors of blood coagulation Since its activation by heparin binding requires critical interactions involving 3 Lys residues; we hypothesized that acrolein or homocysteine thiolactone impair antithrombin activity. When we incubated human antithrombin with increasing concentrations of acrolein (0-2 mmol/L) over a short period of time (0-4 h), a time and concentration dependent loss of activity was apparent (IC(50)=0.25 mmol/L). At 2 mmol/L, maximum inhibition (60%) is achieved at 1 h. This loss of activity was mirrored by changes in the electrophoretic pattern (homogeneity of the native antithrombin band as well as polymerization). In the same conditions, homocysteine thiolactone produces a significant, yet far less pronounced effect; acrolein being 3 times more potent than homocysteine thiolactone. When antithrombin was co-incubated with acrolein and cysteine, only less than 10% of antithrombin activity was lost. Aminoguanidine or carnosine displayed a significant yet, minor protective effect. The results suggest that in conditions where circulating or local acrolein concentrations are increased (atheroma plaque, thrombosis, sites of lipoperoxidation, smokers), acrolein-mediated loss of antithrombin activity could be a plausible phenomenon. This could contribute to explain increased thrombogenicity in smokers and in other conditions, as well as pointing at dietary intervention or the use of thiol-conserving reducing compounds as putative coadjuvant therapeutic measures.

Aberrant insulin receptor signaling and amino acid homeostasis as a major cause of oxidative stress in aging

The mechanisms leading to the increase in free radical-derived oxidative stress in "normal aging" remains obscure. Here we present our perspective on studies from different fields that reveal a previously unnoticed vicious cycle of oxidative stress. The plasma cysteine concentrations during starvation in the night and early morning hours (the postabsorptive state) decreases with age. This decrease is associated with a decrease in tissue concentrations of the cysteine derivative and quantitatively important antioxidant glutathione. The decrease in cysteine reflects changes in the autophagic protein catabolism that normally ensures free amino acid homeostasis during starvation. Autophagy is negatively regulated by the insulin receptor signaling cascade that is enhanced by oxidative stress in the absence of insulin. This synopsis of seemingly unrelated processes reveals a novel mechanism of progressive oxidative stress in which decreasing antioxidant concentrations and increasing basal (postabsorptive) insulin receptor signaling activity compromise not only the autophagic protein catabolism but also the activity of FOXO transcription factors (i.e., two functions that were found to have an impact on lifespan in several animal models of aging). In addition, the aging-related decrease in glutathione levels is likely to facilitate certain "secondary" disease-related mechanisms of oxidative stress. Studies on cysteine supplementation show therapeutic promise.

Life and death: metabolic rate, membrane composition, and life span of animals

Maximum life span differences among animal species exceed life span variation achieved by experimental manipulation by orders of magnitude. The differences in the characteristic maximum life span of species was initially proposed to be due to variation in mass-specific rate of metabolism. This is called the rate-of-living theory of aging and lies at the base of the oxidative-stress theory of aging, currently the most generally accepted explanation of aging. However, the rate-of-living theory of aging while helpful is not completely adequate in explaining the maximum life span. Recently, it has been discovered that the fatty acid composition of cell membranes varies systematically between species, and this underlies the variation in their metabolic rate. When combined with the fact that 1) the products of lipid peroxidation are powerful reactive molecular species, and 2) that fatty acids differ dramatically in their susceptibility to peroxidation, membrane fatty acid composition provides a mechanistic explanation of the variation in maximum life span among animal species. When the connection between metabolic rate and life span was first proposed a century ago, it was not known that membrane composition varies between species. Many of the exceptions to the rate-of-living theory appear explicable when the particular membrane fatty acid composition is considered for each case. Here we review the links between metabolic rate and maximum life span of mammals and birds as well as the linking role of membrane fatty acid composition in determining the maximum life span. The more limited information for ectothermic animals and treatments that extend life span (e.g., caloric restriction) are also reviewed.

Are we getting enough sulfur in our diet?

Sulfur, after calcium and phosphorus, is the most abundant mineral element found in our body. It is available to us in our diets, derived almost exclusively from proteins, and yet only 2 of the 20 amino acids normally present in proteins contains sulfur. One of these amino acids, methionine, cannot be synthesized by our bodies and therefore has to be supplied by the diet. Cysteine, another sulfur containing amino acid, and a large number of key metabolic intermediates essential for life, are synthesized by us, but the process requires a steady supply of sulfur.

Proteins contain between 3 and 6% of sulfur amino acids. A very small percentage of sulfur comes in the form of inorganic sulfates and other forms of organic sulfur present in foods such as garlic, onion, broccoli, etc.

The minimal requirements (RDA) for all the essential amino acids have always been estimated in terms of their ability to maintain a nitrogen balance. This method asses amino acid requirements for protein synthesis, only one of the pathways that methionine follows after ingestion. To adequately evaluate the RDA for methionine, one should perform, together with a nitrogen balance a sulfur balance, something never done, neither in humans nor animals.

With this in mind we decided to evaluate the dietary intake of sulfur (as sulfur amino acids) in a random population and perform sulfur balance studies in a limited number of human volunteers. Initially this was done to try and gain some information on the possible mode of action of a variety of sulfur containing compounds (chondroitin sulfate, glucosamine sulfate, and others, ) used as dietary supplements to treat diseases of the joints. Out of this study came information that suggested that a significant proportion of the population that included disproportionally the aged, may not be receiving sufficient sulfur and that these dietary supplements, were very likely exhibiting their pharmacological actions by supplying inorganic sulfur.

Postprandial oxidative stress is exacerbated in cigarette smokers

Both cigarette smoking and high fat meals induce oxidative stress, which is associated with the pathogenesis of numerous diseases. We compared blood antioxidant status, oxidative stress biomarkers and TAG in twenty smokers and twenty non-smokers, matched for age and physical activity, in response to a high fat test meal standardized to body mass. Blood samples were collected before feeding (resting and fasted) and at 1, 2, 4 and 6 h post feeding and analysed for antioxidant capacity (trolox equivalent antioxidant capacity; TEAC), xanthine oxidase activity (XO), hydrogen peroxide (H2O2), malondialdehyde (MDA) and TAG. Smoking status (P < 0.001) and time (P < or = 0.01) effects were noted for all variables, with smokers demonstrating higher values compared with non-smokers for all variables except for TEAC, for which values were lower for smokers. XO, H2O2, MDA and TAG increased following feeding with a peak response at the 4 h post feeding time point, with the opposite response occurring for TEAC. Although no interaction effects were noted (P>0.05), contrasts revealed greater values in smokers compared with non-smokers for XO, H2O2, MDA and TAG, and lower values for TEAC at times from 1-6 h post feeding (P < or = 0.05). Our findings indicate that young cigarette smokers experience an exaggerated oxidative stress response to feeding, as well as hypertriacylglycerolaemia, as compared with non-smokers. These data provide insight into another possible mechanism associating cigarette smoking with ill health and disease.

Age-associated perturbations in glutathione synthesis in mouse liver

The nature of the mechanisms underlying the age-related decline in glutathione (GSH) synthetic capacity is at present unclear. Steady-state kinetic parameters of mouse liver GCL (glutamate-cysteine ligase), the rate-limiting enzyme in GSH synthesis, and levels of hepatic GSH synthesis precursors from the trans-sulfuration pathway, such as homocysteine, cystathionine and cysteine, were compared between young and old C57BL/6 mice (6- and 24-month-old respectively). There were no agerelated differences in GCL V(max), but the apparent K(m) for its substrates, cysteine and glutamate, was higher in the old mice compared with the young mice (approximately 800 compared with approximately 300 microM, and approximately 710 compared with 450 microM, P<0.05 for cysteine and glutamate in young and old mice respectively). Amounts of cysteine, cystathionine and Cys-Gly increased with age by 91, 24 and 28% respectively. Glutathione (GSH) levels remained unchanged with age, whereas GSSG content showed an 84% increase, suggesting a significant pro-oxidizing shift in the 2GSH/GSSG ratio. The amount of the toxic trans-sulfuration/glutathione biosynthetic pathway intermediate, homocysteine, was 154% higher (P<0.005) in the liver of old mice compared with young mice. The conversion of homocysteine into cystathionine, a rate-limiting step in trans-sulfuration catalysed by cystathionine beta-synthase, was comparatively less efficient in the old mice, as indicated by cystathionine/homocysteine ratios. Incubation of tissue homogenates with physiological concentrations of homocysteine caused an up to 4.4-fold increase in the apparent K(m) of GCL for its glutamate substrate, but had no effect on V(max). The results suggest that perturbation of the catalytic efficiency of GCL and accumulation of homocysteine from the trans-sulfuration pathway may adversely affect de novo GSH synthesis during aging.

Hypoxic remodelling of Ca2+signalling in SH-SY5Y cells: influence of glutathione

Prolonged hypoxia alters various cellular processes, including Ca2+ signalling. As these effects can be prevented by antioxidants, we examined the role of glutathione, the major intracellular redox buffer, in modulation of Ca2+ signalling in the human neuroblastoma SH-SY5Y by hypoxia. Rises of [Ca2+]i evoked by bradykinin, and subsequent capacitative Ca2+ entry, were enhanced by prior hypoxia (1% O2, 24 h) without effect on reduced glutathione levels. Glutathione depletion reversed the effects of chronic hypoxia, but did not affect normoxically cultured cells. Elevation of glutathione levels also prevented the effects of hypoxia, but restored such effects in glutathione-depleted cells. Glutathione is therefore required for hypoxia to modify Ca2+ signalling, but its role is more complex than simple buffering of reactive oxygen species.

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.