Plasma Cysteine Concentrations Research Articles

Potential mechanism for hyperhomocysteinemia in Greyhound dogs.

Greyhounds have been reported to have hyperhomocysteinemia (HHC), but the underlying mechanisms and clinical implications are unclear. Our primary aim was to assess serum concentrations of homocysteine (HCy) and related analytes in Greyhounds and to identify a likely metabolic pathway for HHC. A secondary aim was to determine whether HHC is associated with evidence of oxidative stress. Healthy pet Greyhounds (n = 31) and non-sighthound control dogs (n = 15). Analysis of serum HCy, cobalamin, folate, and methionine, and plasma cysteine, glutathione, and total 8-isoprostane concentrations. Homocysteine concentrations were higher in Greyhounds (median, 25.0 μmol/L) compared to controls (13.9 μmol/L; P < .0001). Cobalamin concentrations were lower in Greyhounds (median, 416 ng/L) compared to controls (644 ng/L; P = .004) and were inversely correlated with HCy (r = -0.40, P = .004). Serum concentrations of folate, which is regenerated when HCy is converted to methionine, also were inversely correlated with HCy (r = -0.47, P = .002). Serum methionine concentrations were more than 4-fold lower in Greyhounds (median, 3.2 μmol/L) compared to controls (median, 15.0 μmol/L), but this difference was not significant (P = .3). Plasma cysteine, glutathione, and 8-isoprostane concentrations did not differ significantly between groups. Our findings suggest a primary defect in conversion of HCy to methionine in Greyhounds, with related impaired folate generation. Ineffective cycling by methionine synthase could lead to secondary cobalamin depletion. Notably, low serum folate and cobalamin concentrations can be observed in Greyhounds without signs of intestinal disease.

52 Weaning Elicits a Distinct Increase in Plasma Cysteine Concentration in Pigs

Abstract Weaning is a stressful event in pigs that is associated with low and variable feed intake, poor nutrient utilization, and high feed costs. The sulfur amino acids (SAA) methionine and cysteine have key roles in pig production, but how SAA metabolism, and thus SAA requirements, is affected by weaning is poorly understood. The objective of this study was to determine weaning-induced changes in SAA metabolism. Pigs (initial BW = 7,233 ± 683 g) were either weaned at 21 d age and euthanized at 23 d age (n = 4) or remained with the sow and euthanized at 23 d age (n = 4). Weaned pigs were fasted but had free access to water. At euthanasia, blood and liver tissue were collected. Plasma amino acids and amino thiols were analyzed by HPLC following pre-column derivatization with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate and 4-fluoro-7-aminosulfonylbenzofurazan, respectively. The protein abundance of cystathionine β-synthase (CBS) and cystathionine γ-lyase (CTH), enzymes needed for methionine transsulfuration to cysteine, in liver were determined by Western blot. Total plasma non-essential amino acid (NEAA) concentrations declined in weaned compared with unweaned pigs (2,664 versus 4,290 ± 211 µmol/L, P &amp;lt; 0.01). Among NEAA, however, only plasma cysteine concentration increased in weaned compared with unweaned pigs (total cysteine, 253 versus 173 ± 16 µmol/L, P &amp;lt; 0.05; cystine, 43 versus 23 ± 5 µmol/L, P &amp;lt; 0.05). Plasma methionine tended to be less in weaned pigs (53 versus 65 ± 4 µmol/L, P = 0.075), whereas plasma taurine was less in weaned pigs (64 versus 128 ± 10 µmol/L, P &amp;lt; 0.01). The abundance of CBS and CTH protein in liver was not different between groups. Elevated plasma cysteine concentrations after weaning in pigs is likely due to decreased cysteine oxidation to taurine rather than greater methionine transsulfuration to cysteine.

The Effect of Oral L-cysteine on Breast Milk and Plasma Cysteine Concentrations.

PurposeGreater oxidative signaling is implicated in major depressive disorder; hence, there is considerable interest in developing oral supplements with anti-oxidant properties to prevent or treat mood disorders, such as postpartum depression. L-cysteine is a precursor for glutathione, an important antioxidant in the brain. So, developing L-cysteine as a dietary supplement may be useful, provided oral supplementation substantially raises its concentration in blood plasma yet does not affect its total concentration in breast milk. This study assessed the effect of oral L-cysteine on its concentration in breast milk and blood plasma of breastfeeding mothers.Participants and MethodsTwenty-four health breastfeeding women were randomly assigned to 0, 1.5, or 3 g of oral L-cysteine. Free and total cysteine in breast milk; and free cysteine in plasma were measured. While breast milk is the gold standard, measurement of infant formulas provides indices of nutritional intake considered safe. Therefore, free cysteine was also measured in six different formulas.ResultsTotal cysteine in breast milk was not affected by oral L-cysteine (Repeated Measures of ANOVA (rANOVA), intervention effect: p=0.75). Free cysteine levels in breast milk did rise (rANOVA, intervention effect: p=0.017), but were within the range of common infant formulas. There was no significant effect of L-cysteine supplementation on free cysteine levels in plasma (rANOVA, intervention effect: p=0.25), although a post hoc analysis found a trend towards greater plasma cysteine 30 minutes after oral supplementation (t(14)=−1.69, p=0.11, 3g versus no-dose).ConclusionThe negligible effect of oral cysteine administration on its total concentration in breast milk was favorable, but the minimal effect on its blood plasma concentration more strongly argues against further development of oral L-cysteine in postpartum, as well as other conditions.

Resistance exercise prevents impaired homocysteine metabolism and hepatic redox capacity in Walker-256 tumor-bearing male Wistar rats

ObjectiveThe aim of this study was to investigate changes in homocysteine (Hcy) metabolism and redox balance in response to exercise treatment in a tumor-bearing rat model. MethodsMale Wistar rats were exposed, or not, to a resistance exercise program 6 wk before inoculation with Walker-256 tumor cells or vehicle. After application, rats maintained their routine for 12 d and were then sacrificed for plasma and liver analyses. ResultsImpaired Hcy metabolism was evident after 12 d of tumor cell inoculation as demonstrated by significantly increased (P < 0.05) plasma total homocysteine (tHcy) concentration (53%) and decreased plasma cysteine, methionine, and vitamin B12 concentrations. Decreased hepatic cystathionine β-synthase (CBS) and betaine-homocysteine S-methyltransferase mRNA levels were found in tumor-bearing rats but not in controls. Tumor inoculation also decreased levels of liver reduced glutathione (GSH) and increased hepatic oxidative stress compared with non-tumor controls. However, resistance exercise prevented the tumor-impaired transsulfuration pathway as demonstrated by the decreased plasma tHcy, hepatic CBS expression, and increased GSH in tumor-exercised versus tumor-sedentary rats. Remarkably, all measures of liver oxidative stress were suppressed by exercise training. Tumor weight was unchanged between groups. ConclusionResistance exercise prevented tHcy accumulation and liver oxidative damage caused by Walker-256 tumor cell inoculation; the modulatory effects of resistance exercise on Hcy metabolism appear to be at the level of transsulfuration pathway.

Effects of randomized supplementation of methionine or alanine on cysteine and glutathione production during the early phase of treatment of children with edematous malnutrition

We have shown that a low glutathione concentration and synthesis rate in erythrocytes are associated with a shortage of protein-derived cysteine in children with edematous severe acute malnutrition (SAM). We tested the hypothesis that methionine supplementation may increase protein-derived cysteine and upregulate cysteine synthesis, thereby improving glutathione synthesis during the early treatment of edematous SAM. The cysteine flux, its de novo synthesis and release from protein breakdown, and erythrocyte glutathione synthesis rate were measured in 12 children with edematous SAM in the fed state by using stable isotope tracers at 3 clinical phases as follows: 3 ± 1 d (±SE) [clinical phase 1 (CP1)], 8 ± 1 d [clinical phase 2 (CP2)], and 14 ± 2 d (clinical phase 3) after admission. Subjects were randomly assigned to receive equimolar supplements (0.5 mmol ⋅ kg(-1) ⋅ d(-1)) of methionine or alanine (control) immediately after CP1. In the methionine compared with the alanine group, cysteine flux derived from protein breakdown was faster at CP2 than CP1 (P < 0.05), and the change in plasma cysteine concentration from CP1 to CP2 was greater (P < 0.05). However, there was no evidence of a difference in cysteine de novo synthesis and its total flux or erythrocyte glutathione synthesis rate and concentration between groups. Methionine supplementation increased cysteine flux from body protein but had no significant effect on glutathione synthesis rates. Although cysteine is made from methionine, increased dietary cysteine may be necessary to partially fulfill its demand in edematous SAM because glutathione synthesis rates and concentrations were less than previous values shown at full recovery. This study was registered at clinicaltrials.gov as NCT00473031.

Thiol/Redox Metabolomic Profiling Implicates GSH Dysregulation in Early Experimental Graft versus Host Disease (GVHD)

Graft-versus-host disease (GVHD) is a common complication of allogeneic bone marrow transplantation (BMT). Upregulation of inflammatory cytokines precedes the clinical presentation of GVHD and predicts its severity. In this report, thiol/redox metabolomics was used to identify metabolic perturbations associated with early preclinical (Day+4) and clinical (Day+10) stages of GVHD by comparing effects in Syngeneic (Syn; major histocompatibility complex- identical) and allogeneic transplant recipients (Allo BMT) in experimental models. While most metabolic changes were similar in both groups, plasma glutathione (GSH) was significantly decreased, and GSH disulfide (GSSG) was increased after allogeneic compared to syngeneic recipient and non-transplant controls. The early oxidation of the plasma GSH/GSSG redox couple was also observed irrespective of radiation conditioning treatment and was accompanied by significant rise in hepatic protein oxidative damage and ROS generation. Despite a significant rise in oxidative stress, compensatory increase in hepatic GSH synthesis was absent following Allo BMT. Early shifts in hepatic oxidative stress and plasma GSH loss preceded a statistically significant rise in TNF-α. To identify metabolomic biomarkers of hepatic GVHD injury, plasma metabolite concentrations analyzed at Day+10 were correlated with hepatic organ injury. GSSG (oxidized GSH) and β-alanine, were positively correlated, and plasma GSH cysteinylglycine, and branched chain amino acids were inversely correlated with hepatic injury. Although changes in plasma concentrations of cysteine, cystathionine (GSH precursors) and cysteinylglycine (a GSH catabolite) were not significant by univariate analysis, principal component analysis (PCA) indicated that accumulation of these metabolites after Allo BMT contributed significantly to early GVHD in contrast to Syn BMT. In conclusion, thiol/redox metabolomic profiling implicates that early dysregulation of host hepatic GSH metabolism and oxidative stress in sub-clinical GVHD before elevated TNF-α levels is associated with GVHD pathogenesis. Future studies will probe the mechanisms for these changes and examine the potential of antioxidant intervention strategies to modulate GVHD.

The Short-term Effects of Antioxidant and Zinc Supplements on Oxidative Stress Biomarker Levels in Plasma: A Pilot Investigation

To determine if short-term Age-Related Eye Disease Study (AREDS) antioxidant and zinc supplementation affects biomarkers of oxidative stress, possibly serving as a predictor of their efficacy. Prospective interventional case series. Nineteen subjects, 12 with intermediate or advanced age-related macular degeneration (AMD) (AREDS categories 3 or 4) and 7 non-AMD controls, were admitted to the Vanderbilt General Clinical Research Center and placed on a controlled diet for 7 days. Antioxidant and zinc supplements were stopped 2 weeks prior to study enrollment. Dietary supplementation with 500 mg vitamin C, 400 IU vitamin E, 15 mg β-carotene, 80 mg zinc oxide, and 2 mg cupric oxide per day was instituted on study day 2. Blood was drawn on study days 2 and 7, and plasma concentrations of cysteine (Cys), cystine (CySS), glutathione (GSH), isoprostane (IsoP), and isofuran (IsoF) were determined. Short-term AREDS supplementation significantly lowered mean plasma levels of CySS in participants on a regulated diet (P = .034). No significant differences were observed for Cys, GSH, IsoP, or IsoF. There were no significant differences between AMD patients and controls. This pilot interventional study shows that a 5-day course of antioxidant and zinc supplements can modify plasma levels of CySS, suggesting that this oxidative stress biomarker could help predict how likely an individual is to benefit from AREDS supplementation. Further, CySS may be useful for the evaluation of new AMD therapies, particularly those hypothesized to affect redox status.

Effects of betaine and sulfate supplementation on milk and wool production of Naeini ewes

Twenty lactating Naeini coarse wool ewes (45±3.2kg BW, approximately 35 months of age), were studied in a completely randomized design during a three-month experimental period in order to investigate the effect of betaine and sulfate supplementation on milk and wool characteristics. Treatments included, betaine supplementation, sulfate supplementation and betaine plus sulfate supplementation, along with control group. Ewes were randomly distributed in individual pens with five replications for each treatment. Isonitrogenous and isocaloric diets were twice offered to the ewes on a daily basis according to the NRC recommendation. The level of betaine used on the TMR was 5gkg−1 betaine, and basal diet contained 0.17% DM organic sulfur. Dry matter intake (DMI) was altered by betaine and sulfate supplementation (P<0.05). No significant effect of betaine and sulfate supplement was detected on body weight (P>0.05). Milk yield and milk fat percentage were increased by betaine and sulfate supplementation (P<0.05), whereas percentages of milk protein, lactose, ash and SNF were not significant by supplements (P>0.05). Betaine and sulfate supplementation significantly increased the daily growth rate of the wool, and the wool yield was compared with that of the control group (P<0.01). Mean fiber diameter was not affected by betaine and sulfate supplementation (P>0.05). Staple length was affected by the type of supplements (P<0.001). For the staple strength, a higher value was observed in the betaine plus sulfate treatment (P<0.05). Betaine plus sulfate supplementation significantly increased the concentration of wool sulfur (P<0.01). In contrast, wool wax and wool yellowness significantly decreased by the betaine and sulfate supplementation (P<0.05). Although there was an increase in the plasma cysteine concentration, it was not a significant one (P>0.05). In addition, no effects of betaine and sulfate supplementation were observed on plasma copper concentration. In conclusion, these data indicated that betaine plus sulfate supplementation had positive effects on milk and wool production of Naeini ewes.

Cysteine aggravates palmitate-induced cell death in hepatocytes

Aims Lipotoxicity, defined as cell death induced by excessive fatty acids, especially saturated fatty acids, is critically involved in the development of non-alcoholic steatohepatitis (NASH). Recent studies report that plasma cysteine concentrations is elevated in the subjects with either alcoholic steatohepatitis (ASH) or NASH than normal subjects. The present study was conducted to determine if elevation of cysteine could be a deleterious factor in palmitate-induced hepatocyte cell death. Main methods HepG2 and Hep3B cells were treated with palmitate with/without the inclusion of cysteine in the media for 24 h. The effects of cysteine inclusion on palmitate induced cell death were determined by lactate dehydrogenase (LDH) release and MTT assay. Oxidative stress was evaluated by intracellular glutathione (GSH) level, malondialdehyde (MDA) formation, and DCFH-DA assay. Western blotting was performed to detect the changes of endoplasmic reticulum(ER) stress markers: C/EBP homologous transcription factor (CHOP), GRP-78, and phosphorylated c-jun N-terminal kinase (p-JNK). Key findings Elevated intracellular cysteine aggravates hepatocytes to palmitate-induced cell death. Enhancement of ER stress, specifically increased activation of JNK pathway, contributed to this cell death process. Significance Increase of plasma cysteine levels, as observed in both ASH and NASH patients, may play a pathological role in the development of the liver diseases. Manipulation of dietary amino acid supplementation could be a therapeutic choice.

Deletion of Betaine-Homocysteine S-Methyltransferase in Mice Perturbs Choline and 1-Carbon Metabolism, Resulting in Fatty Liver and Hepatocellular Carcinomas

Betaine-homocysteine S-methyltransferase (BHMT) uses betaine to catalyze the conversion of homocysteine (Hcy) to methionine. There are common genetic polymorphisms in the BHMT gene in humans that can alter its enzymatic activity. We generated the first Bhmt(-/-) mouse to model the functional effects of mutations that result in reduced BHMT activity. Deletion of Bhmt resulted in a 6-fold increase (p < 0.01) in hepatic and an 8-fold increase (p < 0.01) in plasma total Hcy concentrations. Deletion of Bhmt resulted in a 43% reduction in hepatic S-adenosylmethionine (AdoMet) (p < 0.01) and a 3-fold increase in hepatic S-adenosylhomocysteine (AdoHcy) (p < 0.01) concentrations, resulting in a 75% reduction in methylation potential (AdoMet:AdoHcy) (p < 0.01). Bhmt(-/-) mice accumulated betaine in most tissues, including a 21-fold increase in the liver concentration compared with wild type (WT) (p < 0.01). These mice had lower concentrations of choline, phosphocholine, glycerophosphocholine, phosphatidylcholine, and sphingomyelin in several tissues. At 5 weeks of age, Bhmt(-/-) mice had 36% lower total hepatic phospholipid concentrations and a 6-fold increase in hepatic triacyglycerol concentrations compared with WT (p < 0.01), which was due to a decrease in the secretion of very low density lipoproteins. At 1 year of age, 64% of Bhmt(-/-) mice had visible hepatic tumors. Histopathological analysis revealed that Bhmt(-/-) mice developed hepatocellular carcinoma or carcinoma precursors. These results indicate that BHMT has an important role in Hcy, choline, and one-carbon homeostasis. A lack of Bhmt also affects susceptibility to fatty liver and hepatocellular carcinoma. We suggest that functional polymorphisms in BHMT that significantly reduce activity may have similar effects in humans.

A Sulfur Amino Acid–Free Meal Increases Plasma Lipids in Humans

The content of sulfur amino acid (SAA) in a meal affects postprandial plasma cysteine concentrations and the redox potential of cysteine/cystine. Because such changes can affect enzyme, transporter, and receptor activities, meal content of SAA could have unrecognized effects on metabolism during the postprandial period. This pilot study used proton NMR (1H-NMR) spectroscopy of human plasma to test the hypothesis that dietary SAA content changes macronutrient metabolism. Healthy participants (18–36 y, 5 males and 3 females) were equilibrated for 3 d to adequate SAA, fed chemically defined meals without SAA for 5 d (depletion), and then fed isoenergetic, isonitrogenous meals containing 56 mg·kg-1·d-1SAA for 4.5 d (repletion). On the first and last day of consuming the chemically defined meals, a morning meal containing 60% of the daily food intake was given and plasma samples were collected over an 8-h postprandial time course for characterization of metabolic changes by1H-NMR spectroscopy. SAA-free food increased peak intensity in the plasma1H-NMR spectra in the postprandial period. Orthogonal signal correction/partial least squares-discriminant analysis showed changes in signals associated with lipids, some amino acids, and lactate, with notable increases in plasma lipid signals (TG, unsaturated lipid, cholesterol). Conventional lipid analyses confirmed higher plasma TG and showed an increase in plasma concentration of the lipoprotein lipase inhibitor, apoC-III. The results show that plasma1H-NMR spectra can provide useful macronutrient profiling following a meal challenge protocol and that a single meal with imbalanced SAA content alters postprandial lipid metabolism.

N-Acetylcysteine in Handgrip Exercise: Plasma Thiols and Adverse Reactions

N-acetylcysteine (NAC) is a thiol donor with antioxidant properties that has potential use as an ergogenic aid. However, NAC is associated with adverse reactions that limit its use in humans. The authors evaluated NAC efficacy as a thiol donor before handgrip exercise, measuring changes in serum cysteine and glutathione status and recording adverse reactions in adult subjects across a range of doses. Healthy individuals ingested NAC capsules (9 ± 2 or 18 ± 4 mg/kg) or solution (0, 35, 70, or 140 mg/kg). Venous blood samples were collected and subjects answered a questionnaire about adverse reactions. Low doses of NAC (capsules) did not affect plasma cysteine or glutathione or cause adverse reactions. Adverse reactions to NAC solution were predominantly mild and gastrointestinal (GI). Intensity of GI reactions to 140 mg/kg NAC was significantly higher than placebo (in a.u., 0.67 ± 0.16 vs. 0.07 ± 0.04; p < .05). Plasma cysteine concentration increased with NAC dose from 9.3 ± 0.7 μM (placebo) to 65.3 ± 6.7 μM (140 mg/kg); however, there was no difference (p > .05) in plasma cysteine for 70 mg/kg vs. 140 mg/kg. Similar increases were observed for the ratio of cysteine to total cysteine, which was directly related to handgrip exercise performance. Plasma glutathione was elevated and oxidized glutathione diminished (p < .05) with NAC 140 mg/kg vs. placebo. NAC effects on plasma thiols are maximized by oral administration of 70 mg/kg, a dose that does not cause significant adverse reactions.

Serum Folate Is Significantly Correlated with Plasma Cysteine Concentrations in Healthy Industry Workers

Background: A low concentration of serum folate is associated with an increased risk of cardiovascular disease. Extracellular cysteine is involved in aging, cancer and cardiovascular disease. The relationship between serum folate and plasma cysteine is poorly understood. Therefore, we investigated this relationship in industry workers, whose health has economic implications. Methods: The concentration of serum folate was determined by the Access ImmunoAssay System Sanofi Pasteur. Plasma cysteine and homocysteine were measured by an ion-pair HPLC method. The concentrations of serum triglycerides were determined by an enzymatic colorimetric method. Results: We detected a positive correlation between the concentration of serum folate and plasma cysteine, whereas the concentration of serum folate was negatively correlated with plasma homocysteine and serum triglycerides. In a multiple regression analysis with adjustment for age, BMI and smoking, serum folate as the dependent variable exhibited a strong relationship with plasma cysteine, and a negative relationship with plasma homocysteine and serum triglycerides. Conclusion: We observed significant correlations between serum folate, plasma cysteine and serum triglyceride concentrations in industry workers, implying that folate may modulate key aspects of the body’s cysteine and lipid metabolism.

Redox Pioneer: Professor Wulf Dröge

Dr. Wulf Dröge is recognized here as a redox pioneer because he has published as first author an article on antioxidant/redox biology that has been cited more than 2000 times and over 10 articles that have been cited more than 100 times. One of the key discoveries (1987) was the stimulatory effect of superoxide radicals and hydrogen peroxide on lymphocyte functions, which triggered a series of studies on the role of reactive oxygen species, glutathione, and its precursor cysteine in physiological and pathological processes. He discovered abnormally low cysteine and glutathione levels in human immunodeficiency virus-infected patients and the age-related decline in the postabsorptive plasma cysteine concentration, which is believed to cause age-related oxidative stress. He developed a theoretical concept of the mechanism of aging and death, which is outlined in his books Avoiding the First Cause of Death and Challenging the Limits of the Human Lifespan.

The Addition of Choline to Parenteral Nutrition

Choline is a quaternary amine endogenously synthesized from the amino acid methionine or absorbed via the portal circulation. It is ubiquitous in the diet, although it has a greater presence in organ meats. Choline is an essential component of all cell membranes, and has been considered a required dietary nutrient since 1998 by the US Institute of Medicine's Food and Nutrition Board. Choline is necessary for DNA repair, mediated by its role as a methyl donor. It also serves as the precursor for the neurotransmitter acetylcholine. Evidence has accumulated that hepatic steatosis, which occurs during parenteral nutrition therapy, develops as a result of choline deficiency because endogenous production of choline from parenterally infused methionine is deficient. In addition, memory deficits and skeletal muscle abnormalities have been described, and choline deficiency appears to activate cellular apoptosis. Provision of intravenous choline ameliorates hepatic steatosis associated with parenteral nutrition infusion.

Homocysteine and cysteine concentrations are modified by recent exposure to environmental air pollution in São Paulo, Brazil

Millions of people worldwide are affected by anthropogenic air pollution derived from the combustion of fossil fuels. In this work, we tested the effects of fetal, lactation and post-weaning ambient air pollution exposure on total homocysteine (tHcy) concentrations and on a downstream pathway element, the plasma cysteine (Cys) concentration. Two similar exposure chambers (polluted and filtered chamber) were located near an area with heavy traffic in São Paulo, Brazil, and male Swiss mice were housed there from the pre-natal period until 3 months of age. Groups during fetal, lactation and adult periods of exposure were apportioned, and tHcy and Cys plasma concentrations were assessed when the animals were 3 months old. In our study, both the tHcy and Cys concentrations were decreased in groups that spent their final stage of life in polluted chambers, suggesting recent alterations in tHcy and Cys concentrations due to air pollution exposure. The possible relationship of these data with cardiovascular dysfunction is still a matter of controversy in animals; nevertheless, epigenetic mechanisms emerge as a possible issue to consider in the investigation of the link between air pollution and Hcy measurement.

Hypohomocysteinemic Effect of Cysteine Is Associated with Increased Plasma Cysteine Concentration in Rats Fed Diets Low in Protein and Methionine Levels

Rats were fed diets with and without 0.5% L-cysteine supplement for 14 d or shorter periods to clarify the mechanism by which dietary cysteine elicits its hypohomocysteinemic effect. Cysteine supplementation significantly decreased plasma homocysteine concentration with an increase in plasma cysteine concentration in rats fed 10% casein diet (10C) or 15% soybean protein diet (15S) but not in rats fed 25% casein diet (25C) or 25% soybean protein diet. Cysteine supplementation also significantly suppressed hyperhomocysteinemia induced by choline-deprived 10C with an increase in plasma cysteine concentration but not that induced by 25C+0.65% methionine or 25C+0.4% guanidinoacetic acid. Hepatic S-adenosylmethionine (SAM) and homocysteine concentrations were significantly decreased by cysteine supplementation of 15S. These decreases in plasma homocysteine concentration and hepatic SAM and homocysteine concentrations due to cysteine supplementation disappeared when 15S was fortified with 0.3% methionine. The plasma homocysteine concentration significantly decreased with an increase in plasma cysteine concentration only 1 d after diet change from 15S to cysteine-supplemented 15S, while hepatic cystathionine beta-synthase and betaine-homocysteine S-methyltransferase activities were not altered. Unlike cysteine, cysteic acid and 2-mercaptoethylamine did not decrease plasma homocysteine concentration. These results indicate that cysteine markedly decreases plasma homocysteine concentration only when added to diets low in both protein and methionine levels and suggest that increased plasma cysteine concentration and decreased flow of methionine toward homocysteine formation, but not alteration of homocysteine-metabolizing enzyme activities, are associated with the hypohomocysteinemic effect of cysteine.

Erythrocyte glutathione and plasma cysteine concentrations in young versus old dogs

To determine whether older, otherwise healthy, client-owned dogs were deficient in glutathione or cysteine, compared with young healthy pet dogs. Cross-sectional study. 35 healthy dogs between 7 and 14 years old (older dogs) and 26 healthy dogs between 1 and 3 years old (young dogs). In all dogs, erythrocyte reduced glutathione concentration and plasma cysteine concentration were determined by means of high-performance liquid chromatography. Median erythrocyte reduced glutathione and plasma cysteine concentrations were not significantly different between young (1.7 mM and 8.3 microM, respectively) and older (1.7 mM and 7.6 microM, respectively) dogs. Significant differences were also not identified when values for young dogs were compared with values for only those dogs>or=11 years old. Similarly, no differences were found between males and females overall or between males and females within age groups, although most dogs were neutered. Results suggested that otherwise healthy older pet dogs fed a variety of commercial diets do not have deficiencies in glutathione or cysteine, compared with younger dogs. Findings do not support the routine empirical use of antioxidant supplements, such as precursors of glutathione, to treat presumed circulating antioxidant deficiencies in older healthy dogs.

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.

Plasma Cysteine Concentrations in Uncomplicated Pregnancies

Objective: To measure levels of total plasma cysteine, homocysteine, cysteinylglycine and glutathione of normotensive primiparous pregnant women in the second and the third trimester. Methods: Two consecutive blood samples were taken from 65 healthy primiparous women in the 19th to 21st weeks of pregnancy and then in the 30th to 32nd weeks. Plasma total cysteine, homocysteine, cysteinylglycine and glutathione were determined by HPLC method. Women were followed until delivery. Sixty-two pregnant women were normotensive throughout the pregnancy and 3 developed pre-eclampsia. Median levels of thiols in the second and the third trimesters were compared using paired t test. Results: Levels (median [range], µmol/l) of plasma total cysteine in normotensive pregnant women were significantly lower in the third than in the mid-trimester (176.1 [163.0, 189.4] vs. 187.4 [178.7, 205.2], p < 0.001). Concentrations of total homocysteine, cysteinylglycine and glutathione were not different. Conclusion: Plasma total cysteine (t-Cys) is significantly lower in the third compared to the second trimester. Urinary excretion of t-Cys does not differ in the second compared to the third trimester. The decrease of t-Cys might indicate that cysteine is essential for the fetus.