Plasma Cysteine Concentrations Research Articles

Cysteine Supplementation Decreases Plasma Homocysteine Concentration in Rats Fed on a Low-Casein Diet in Rats

The effect of dietary supplementation with cysteine on the plasma homocysteine concentration was investigated in rats fed on 10% casein (10C) and 30% casein (30C) diets. The 10C diet significantly increased the plasma homocysteine concentration as compared with the 30C diet. The hyperhomocysteinemia induced by the 10C diet was significantly suppressed by cysteine supplementation even at a 0.3% level, whereas cysteine did not decrease the plasma homocysteine concentration when added to the 30C diet. In contrast, 0.3% methionine supplementation of the 10C diet tended to increase the plasma homocysteine concentration. Cysteine supplementation to rats fed on the 10C diet did not alter the plasma cysteine concentration and the hepatic activities of cystathionine beta-synthase and betaine:homocysteine S-methyltransferase, whereas it significantly decreased the hepatic concentrations of S-adenosylmethionine and betaine. These results suggest that cysteine supplementation might be effective for suppressing the hyperhomocysteinemia induced by a low-protein diet.

Redox Imbalance in Cystine/Glutamate Transporter-deficient Mice

Cystine/glutamate transporter, designated as system x(-)(c), mediates cystine entry in exchange for intracellular glutamate in mammalian cells. This transporter consists of two protein components, xCT and 4F2 heavy chain, and the former is predicted to mediate the transport activity. This transporter plays a pivotal role for maintaining the intracellular GSH levels and extracellular cystine/cysteine redox balance in cultured cells. To clarify the physiological roles of this transporter in vivo, we generated and characterized mice lacking xCT. The xCT(-/-) mice were healthy in appearance and fertile. However, cystine concentration in plasma was significantly higher in these mice, compared with that in the littermate xCT(-/-) mice, while there was no significant difference in plasma cysteine concentration. Plasma GSH level in xCT(-/-) mice was lower than that in the xCT(-/-) mice. The embryonic fibroblasts derived from xCT(-/-) mice failed to survive in routine culture medium, and 2-mercaptoethanol was required for survival and growth. When 2-mercaptoethanol was removed from the culture medium, cysteine and GSH in these cells dramatically decreased, and cells started to die within 24 h. N-Acetyl cysteine also rescued xCT(-/-)-derived cells and permitted growth. These results demonstrate that system x(-)(c) contributes to maintaining the plasma redox balance in vivo but is dispensable in mammalian development, although it is vitally important to cells in vitro.

Nitric Oxide Inhibition of Homocysteine-induced Human Endothelial Cell Apoptosis by Down-regulation of p53-dependent Noxa Expression through the Formation of S-Nitrosohomocysteine

Hyperhomocysteinemia is believed to induce endothelial dysfunction and promote atherosclerosis; however, the pathogenic mechanism has not been clearly elucidated. In this study, we examined the molecular mechanism by which homocysteine (HCy) causes endothelial cell apoptosis and by which nitric oxide (NO) affects HCy-induced apoptosis. Our data demonstrated that HCy caused caspase-dependent apoptosis in cultured human umbilical vein endothelial cells, as determined by cell viability, nuclear condensation, and caspase-3 activation and activity. These apoptotic characteristics were correlated with reactive oxygen species (ROS) production, lipid peroxidation, p53 and Noxa expression, and mitochondrial cytochrome c release following HCy treatment. HCy also induced p53 and Noxa expression and apoptosis in endothelial cells from wild type mice but not in the p53-deficient cells. The NO donor S-nitroso-N-acetylpenicillamine, adenoviral transfer of inducible NO synthase gene, and antioxidants (alpha-tocopherol and superoxide dismutase plus catalase) but not oxidized SNAP, 8-Br-cGMP, nitrite, and nitrate, suppressed ROS production, p53-dependent Noxa expression, and apoptosis induced by HCy. The cytotoxic effect of HCy was decreased by small interfering RNA-mediated suppression of Noxa expression, indicating that Noxa up-regulation plays an important role in HCy-induced endothelial cell apoptosis. Overexpression of inducible NO synthase increased the formation of S-nitroso-HCy, which was inhibited by the NO synthase inhibitor N-monomethyl-l-arginine. Moreover, S-nitroso-HCy did not increase ROS generation, p53-dependent Noxa expression, and apoptosis. These results suggest that up-regulation of p53-dependent Noxa expression may play an important role in the pathogenesis of atherosclerosis induced by HCy and that an increase in vascular NO production may prevent HCy-induced endothelial dysfunction by S-nitrosylation.

Garlic extract attenuates hyperhomocysteinemia caused by folic acid deficiency in the rat

This study investigated the homocysteine lowering potential of garlic in rats rendered folic acid (FA) deficient. Rats fed AIN-93G diet devoid of FA exhibited mild folate deficiency and had a plasma level of total homocysteine higher than that for those fed AIN-93G diet containing FA (9 vs 5 μmol/L). Supplementation with aged garlic extract (AGE, 4%) to either diet did not alter plasma homocysteine levels. Subsequently, rats were made severely deficient in folate by feeding a folate-deficient l-amino acid diet containing succinyl sulfathiazole. Although folate concentrations in plasma, erythrocytes, liver, and kidneys were markedly depressed, plasma total homocysteine was increased to 32 μmol/L by the severe deficiency. Supplementation of AGE to the deficient diet reduced plasma protein-bound, free, and total homocysteine by 28% to 33%. The supplementation did not change plasma cysteine, cysteinylglycine, or glutathione concentrations. Liver concentration of S-adenosylmethionine was elevated by 26%, and S-adenosylhomocysteine was lowered by 15% in the AGE-supplemented group. It is speculated that the reduction of plasma homocysteine level by AGE stems, in part, from stimulation of transsulfuration via cystathionine β-synthase and inhibition of remethylation of homocysteine resulting from inactivated N 5, N 10-methylenehydrofolate reductase.

Plasma ascorbate deficiency is associated with impaired reduction of sulfamethoxazole-nitroso in HIV infection.

The objective of these studies was to determine the role of ascorbate deficiency in HIV infection in the defective detoxification of sulfamethoxazole-nitroso, the metabolite thought to mediate sulfonamide hypersensitivity reactions. Fifty-one HIV-infected patients and 26 healthy volunteers were evaluated. Vitamin supplementation histories were obtained, and blood samples were collected for determination of plasma ascorbate, dehydroascorbate, and cysteine concentrations, erythrocyte glutathione concentrations, and plasma reduction of sulfamethoxazole-nitroso in vitro. Plasma ascorbate concentrations were significantly lower in HIV-positive patients not taking vitamin supplements (29.5 +/- 22.3 microM) than in healthy subjects (54.8 +/- 22.3 microM; P = 0.0005) and patients taking 500-1000 mg of ascorbate daily (82.5 +/- 26.3 microM; P < 0.0001). Plasma ascorbate deficiency was strongly correlated with impaired reduction of sulfamethoxazole-nitroso to its hydroxylamine (r = 0.60, P < 0.0001), and during in vitro reduction, the loss of plasma ascorbate was strongly associated with the amount of nitroso reduced (r = 0.70, P < 0.0001). Ascorbate added ex vivo normalized this reduction pathway. Erythrocyte glutathione concentrations were significantly lower in HIV-positive patients (0.98+/-0.32 mM) than in healthy subjects (1.45+/-0.49 mM; P = 0.001), but this finding was unrelated to ascorbate supplementation. There was trend toward lower plasma cysteine concentrations in patients (8.4+/-3.9 microM) than in controls (10.3+/-4.3 microM), but this trend was similarly unrelated to ascorbate supplementation. Dehydroascorbate concentrations were not significantly higher in HIV-positive patients (7.4+/-10.5%) than in healthy controls (4.0+/-6.2%), even in the subset of patients taking ascorbate (8.4+/-9.4%). Ascorbate deficiency is common in HIV-positive patients and is associated with impaired detoxification of sulfamethoxazole-nitroso, the suspected proximate toxin in sulfonamide hypersensitivity. Patients taking daily ascorbate supplements (500-1000 mg) achieved high plasma ascorbate concentrations and did not show this detoxification defect. Ascorbate deficiency (or supplementation) was not associated with changes in glutathione or cysteine concentrations. These data suggest that ascorbate deficiency, independent of thiol status, may be an important determinant of impaired drug detoxification in HIV infection.

Effect of a methionine-supplemented diet on the blood pressure of Sprague-Dawley and deoxycorticosterone acetate-salt hypertensive rats.

The objectives of the present study were to evaluate the effects of a methionine-supplemented diet on systolic blood pressure (BP) and vasomotor functions in Sprague-Dawley (SD) and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. SD and DOCA rats were fed a normal or a methionine (8 g/kg)-supplemented diet for 10 weeks. Systolic BP was monitored and plasma homocysteine, methionine and cysteine levels were determined at the end of the experiment. Vasoconstriction and vasodilatation of aortic rings were measured. The methionine-supplemented diet induced a greater increase in homocysteinaemia concentration in DOCA rats than in SD rats and an increase in plasma cysteine concentration in DOCA rats. This diet was associated with an increase in systolic BP in SD rats and with a lesser development of DOCA-salt hypertension. An enhanced aortic constriction and a decreased responsiveness to acetylcholine, bradykinin and sodium nitroprusside in the SD rats fed the methionine-rich diet were consistent with the elevated systolic BP. In DOCA rats the increased responsiveness to bradykinin was in accordance with the systolic BP-lowering effect. In conclusion, the methionine-enriched diet cannot simply be considered as model of hyperhomocysteinaemia, since other metabolites and mechanisms seemed to be implicated in these complex interactions. The differential vasopressive effect of the methionine supplementation in SD and DOCA rats, and in particular the lowering of systolic BP obtained with a greater degree of hyperhomocysteinaemia in DOCA rats, suggest that more complex interactions exist between hyperhomocysteinaemia and BP than the simple positive association described previously.

Thiol metabolism in preterm infants during the first week of life

Background: Oxidative stress is implicated in the pathogenesis of several complications of prematurity. The glutathione cycle is one of the most important intracellular antioxidant systems. The synthesis of glutathione may not be adequate in preterm neonates because of the low levels of cysteine available. The aim of this study was to evaluate cysteine and glutathione metabolism during the first week of life in preterm infants. Methods: Plasma and erythrocyte thiol concentrations were measured in 78 preterm infants with a birthweight of 500-1500 g, and erythrocyte glutamate-cysteine ligase (GCL), glutathione peroxidase (GPx), glutathione reductase (GR), glutathione S-transferases (GST) and glucose 6-phosphatedehydrogenase (G6PDH) in 26 infants with a birthweight of 1000-1500 g. Results: The mean (SD) plasma glutathione concentration increased from day 0 to day 1 (14.9 (7.1) vs. 27.7 (11.9) μmol/L, p<0.001), and then decreased. The plasma cysteine concentration changed in the opposite direction (172 (59) vs. 129 (42) μmol/L, p<0.01). In infants with respiratory distress syndrome (RDS) the mean plasma glutathione concentration, but not cysteine, was lower on day 0 compared with infants without RDS (11.7 (5.2) vs. 21.4 (5.6) μmol/L, p<0.01). Erythrocyte glutathione concentration decreased during the first week of life, whereas erythrocyte cysteine concentration increased significantly from day 3 to day 7 (p<0.01). Erythrocyte cysteine and glutathione concentrations had a positive correlation. The GCL and GR activities did not change, but GST and G6PDH activities decreased during the first week (p<0.01). GPx activity decreased until day 3 (p<0.01) and was higher on day 0 and day 1 in infants with RDS. Conclusions: Very low birthweight infants have an initial increase in plasma glutathione and initial decrease in plasma cysteine level during the first week of life, and also a positive correlation between erythrocyte cysteine and glutathione levels.

Homocysteine is the only plasma thiol associated with carotid artery remodeling

Several authors have reported that moderate hyperhomocysteinemia is related to asymptomatic carotid arterial wall remodeling, but few data are available on other thiol compounds with potential vascular toxicity. We, therefore, investigated the relationships between major plasma thiol compounds (homocysteine, cysteine and glutathione) and the structural phenotype of the common carotid artery in a cohort of 123 subjects with no evidence of cardiovascular disease. Fasting levels of thiol compounds were measured by high-performance liquid chromatography, and arterial geometry was evaluated using high-resolution echotracking devices. In univariate regression analysis, plasma homocysteine and plasma cysteine concentrations were positively associated with carotid artery internal diameter ( P=0.0001 and 0.002, respectively) and intima media thickness ( P=0.003 and 0.004), but the plasma glutathione concentration was not. In multivariate analysis, plasma homocysteine was independently and positively associated with carotid artery internal diameter ( P<0.005) and intima media thickness ( P<0.05), but plasma cysteine was not. These data suggest that homocysteine is the only plasma thiol compound that may be considered as a risk factor for preclinical cardiovascular disease.

Umbilical Cord and Maternal Plasma Thiol Concentrations in Normal Pregnancy

Cysteine is the only sulfhydryl-containing amino acid in proteins and is the thiol residue in glutathione (1). In addition to its importance in the storage and transport of cysteine, glutathione plays a pivotal role in detoxification by the action of glutathione S -transferases and in scavenging free (oxygen) radicals by the action of glutathione peroxidases (1). Thiol metabolism may be altered during pregnancy. In healthy pregnant women, plasma concentrations of cysteine, glutathione, and homocysteine are decreased, whereas increased homocysteine and cysteine concentrations are seen in pathologic conditions, such as preeclampsia, in which oxidative stress may play an important role (2)(3)(4). Thiols may have important physiological functions in fetal metabolism. Although protein and amino acid turnover in the human placenta has been studied extensively (5)(6)(7), few data concerning fetal concentrations of thiols and placental maternal-fetal thiol interactions are currently available (8). During normal pregnancy, fetal growth depends on the supply of nutrients from the mother, and a clear correlation between maternal and fetal amino acid and homocysteine concentrations has been shown (6)(7)(8). Decreased concentrations of amino acids in the umbilical artery, as compared with the umbilical vein, have been interpreted as an uptake of amino acids into fetal tissues where they may be used in protein biosynthesis or as sources of energy (5). We studied fetal and maternal thiol plasma concentrations in normal pregnancies to determine reference concentrations for cysteine, homocysteine, and cysteinylglycine in arterial and venous umbilical cord plasma to gain insight into maternal-fetal thiol interactions. Arterial and venous umbilical cord blood samples from 320 consecutive neonates were drawn in preheparinized tubes …

Cysteine metabolism and whole blood glutathione synthesis in septic pediatric patients.

To investigate whole body in vivo cysteine kinetics and its relationship to whole blood glutathione (GSH) synthesis rates in septic, critically ill pediatric patients and controls. Prospective cohort study. Multidisciplinary intensive care unit and pediatric inpatient units at a children's hospital. Ten septic pediatric patients and ten controls (children admitted to the hospital for elective surgery). Septic patients (age, 31 months to 17 yrs) and controls (age, 24 months to 21 yrs) received a 6-hr primed, constant, intravenous tracer infusion of l-[1-13C]cysteine. Blood samples were obtained to determine isotopic enrichment of plasma cysteine and whole blood [1-13C]cysteinyl-glutathione by gas-chromatography mass spectrometric techniques. The plasma flux and oxidation rate of cysteine and the fractional and absolute synthesis rates of GSH were determined. Septic patients received variable protein and energy intake, as per routine clinical management, and controls were studied in the early postabsorptive state. Plasma cysteine fluxes were increased in the septic patients when compared with the controls (68.2 +/- 17.5 [sd] vs. 48.7 +/- 8.8 micromol x kg(-1) x hr(-1); p <.01), and the fraction of plasma cysteine flux associated with oxidative disposal was similar among the groups. The absolute rates of GSH synthesis in whole blood were decreased (p <.01) in the septic patients (368 +/- 156 vs. 909 +/- 272 micromol x L(-1) x day(-1)). The concentration of whole blood GSH also was decreased in the septic group (665.4 +/- 194 vs. 1059 +/- 334 microM; p <.01) Whole blood glutathione synthesis rates are decreased, by about 60%, in critically ill septic children receiving limited nutritional support. Plasma cysteine fluxes and concentration of cysteine were increased in the septic patients, suggesting a hypermetabolic state with increased protein breakdown. The mechanisms whereby GSH synthesis rates are decreased in these patients are probably multifactorial, presumably involving an inflammatory response in the presence of limited nutritional support. The role of nutritional modulation and the use of cysteine prodrugs in maintaining GSH concentration and synthesis remain to be established.

Intake and long-term cysteine supplementation change wool characteristics of Romney sheep

Sulfur amino acid supplementation increases wool production in sheep at low planes of nutrition but it is unclear whether there is any benefit of supplementation at planes of nutrition above maintenance and what implications this might have for wool quality characteristics. This experiment directly investigated the interaction between sulfur supplementation and plane of nutrition in terms of wool growth and fibre characteristics. Twenty-four Romney ewes, acclimatised in individual metabolism units over a 7-week pre-treatment period, were allocated to 1 of 4 treatment groups based on a 22 factorial arrangement. Groups were low (L) or high (H) intake (0.8 or 1.3 maintenance, respectively) with continuous intravenous infusion of either saline (–Cys) or cysteine (+Cys, 2 g/day). During the 3-month treatment period, measurements were obtained for liveweight, plasma cysteine concentration, wool sulfur concentration and output, clean wool growth, mean fibre diameter (MFD), length growth rate (LGR), colour, loose wool bulk, handle, and crimp frequency and character. Clean wool growth response (P &lt; 0.05) to cysteine supplementation was greater for the L sheep (6.06 v. 4.31 g/100 cm2) than the H sheep (7.20 v. 6.13 g/100 cm2). The response to supplementation in LGR (P &lt; 0.01) was similar in both H (14%) and L (20%) sheep. There was no response in MFD due to sulfur supplementation, although fibre diameter measurements made along the fibres suggest that there was a response in L but not H sheep (P &lt; 0.1). Wool sulfur concentration and output increased as a result of cysteine supplementation but concentration increased more in L (30.6 v. 24.5 mg S/g; P &lt; 0.01) than in H sheep (28.4 v. 26.2 mg S/g). Qualitative electrophoresis analyses suggested that the increase in wool sulfur was achieved primarily by an increase in ultra-high-sulfur proteins. Crimp frequency and character were both significantly (P &lt; 0.01) enhanced by cysteine supplementation. It is concluded that cysteine supplementation, at feed intakes that commonly occur in the commercial situation, can produce a useful increase in wool growth. This growth increase is primarily accomplished by increasing length growth rate rather than fibre diameter, which should also improve the value of the wool fibre produced.

Effects of parenteral cysteine and glutathione feeding in a baboon model of severe prematurity

The availability of cysteine for glutathione synthesis is low in premature infants with respiratory distress. The effects of gestational age, oxygen delivery, and cysteine infusion or glutathione infusion, or both, on plasma total cysteine and other methionine metabolites were studied in a baboon model of severe premature birth with respiratory distress. Premature baboons were studied as part of the multiinvestigator National Institutes of Health Collaborative Project on Bronchopulmonary Dysplasia. Premature baboons, 125 d (69% of term) or 140 d (78% of term) of gestational age, were maintained in neonatal intensive care units for </=14 d. Parenteral feeding with or without supplemental cysteine and glutathione infusions was given. Plasma total cysteine, methionine, N:-methylglycine, cystathionine, and the other methionine metabolites were monitored by capillary gas chromatography-mass spectrometry. Cord blood plasma total cysteine was the lowest in the 125-d-old premature baboons. Plasma total cysteine decreased in the first 3 d after delivery in the 125-d-old (but not in the 140-d-old) premature baboons even when cysteine was infused. Supplementation with glutathione from the first day of life raised plasma total cysteine markedly. Plasma cystathionine increased in all animals after birth but increased 4-fold in 125-d-old animals with glutathione infusion. At 6 and 10 d postdelivery, the arterial-alveolar oxygen gradient was significantly higher in the 125-d-old animals that received glutathione infusions. Glutathione, but not supplemental cysteine, infusions prevented the postdelivery decline in plasma cysteine concentrations in premature baboons. Glutathione infusions resulted in marked elevations of plasma cystathionine concentration.

Synthesis of glutathione in response to methionine load in control subjects and in patients with cirrhosis

The fasting plasma level of reduced glutathione (GSH), a methionine-derived tripeptide, is reduced in cirrhosis. There is evidence that a reduced activity of S-adenosyl-L-methionine synthetase limiting the flux of methionine along the transmethylation/transsulfuration pathway may contribute to decrease GSH levels. No studies have analyzed plasma GSH in response to a methionine load. In 6 control subjects and in 10 patients with cirrhosis, plasma sulfur amino acid and plasma and erythrocyte GSH levels were measured in response to a L-methionine load (0.1 g/kg). Blood samples were obtained throughout the day after the oral load. Urine was collected for measurement of sulfur excretion. During the study period, all subjects consumed a standard diet of 1,683 kcal containing 2% protein and virtually no methionine. Plasma methionine increased in both groups to a peak level exceeding 20 times the basal value 90 minutes after the load, and declined thereafter. Methionine clearance, calculated on the descending part of the methionine-time curve, was reduced by 50% in cirrhosis (P = .0001). Fasting GSH was higher in controls (mean ± SD, 3.9 ± 1.3 v 1.6 ± 0.7 μmol/L, P = .0004). In response to a methionine load, it peaked at 10.2 ± 7.2 and 3.2 ± 1.3 μmol/L, respectively (P = .009). Thereafter, plasma GSH progressively declined, and after 24 hours, it returned to the fasting preinfusion values in both groups. Plasma cysteine and taurine concentrations, as well as the erythrocyte GSH time course, paralleled plasma GSH levels, with less significant differences between groups. Sulfate excretion was delayed. GSH synthesis is stimulated by a methionine load. The reduced flux of methionine along the transmethylation/transsulfuration pathway reduces GSH synthesis in cirrhosis. Defective methionine metabolism also may be responsible for reduced fasting GSH. Copyright © 2000 by W.B. Saunders Company

Redox status of plasma homocysteine and other plasma thiols in stroke patients

Despite the growing evidence that plasma homocysteine is a cardiovascular risk factor, the mechanism behind the vascular injuries is still unknown. Studies are difficult as a result of the fact that little is known about the formation of different homocysteine species in vivo. Since extracellular glutathione and cysteine may influence the formation of different homocysteine species, we have in the present study investigated the different fractions of homocysteine and their relation to the different fractions of glutathione and cysteine in stroke patients and control subjects. We found a ratio of about 32–33% between reduced and total plasma glutathione concentrations and 2.6–3.0% between reduced and total plasma cysteine concentrations both in patients and in healthy control subjects. We noted an elevated concentration of total plasma homocysteine in stroke patients, but no difference in the ratio between reduced and total plasma homocysteine concentrations in patients and control subjects (mean value 1.20 and 1.10%, respectively). However, in a subgroup of patients with higher concentrations of total plasma homocysteine, we observed a significantly lower ratio of reduced to total plasma homocysteine compared to a subgroup of patients with lower concentration of total plasma homocysteine. A low reduced/total ratio of plasma homocysteine in combination with elevated plasma homocysteine concentrations might reflect an increased pro-oxidant activity in plasma from these patients. Thus, increased pro-oxidant activity in plasma might be one factor, besides genetic and nutritional factors, that could explain hyperhomocysteinemia. Since substantial evidence indicates that progression of atherosclerosis is related to enhanced pro-oxidant activity, the premature vascular disease associated with increased plasma homocysteine concentration might be as a result of increased pro-oxidant activity and the elevated plasma homocysteine concentration may only reflect the increased oxidative stress.

Case-control study of plasma folate, homocysteine, vitamin B(12), and cysteine as markers of cervical dysplasia.

An association between B-complex vitamins and related compounds with the development of cervical neoplasia is biologically plausible, yet to the authors' knowledge epidemiologic investigations of these potential biomarkers are limited. A case-control study was designed to examine the relation between plasma folate, homocysteine, vitamin B(12), and cysteine and early, premalignant changes in cervical epithelial cells among women identified from several clinics on Oahu, Hawaii, between 1992 and 1996. Fasting blood samples for plasma nutrient analysis, cervical smears for cytologic diagnosis, exfoliated cervical cells for human papillomavirus DNA testing by polymerase chain reaction, and a personal interview were obtained from 185 women with atypical squamous cells of undetermined significance (ASCUS) of the cervix, 147 women with squamous intraepithelial lesions (SIL), and 191 women with cytologically normal (Papanicolaou) smears. Age-adjusted and ethnicity-adjusted mean plasma concentrations of cysteine, but not other nutrients, were significantly lower among ASCUS cases (P = 0.006) and SIL cases (P = 0.01) than controls. A positive trend in the odds ratio for SIL but not ASCUS was found for increased plasma homocysteine concentrations, but this finding was not statistically significant. High plasma levels of cysteine were associated with a reduced risk of ASCUS (P value for trend = 0.006), with an odds ratio of 0.3 (95% confidence interval, 0.2-0.7) for the highest compared with the lowest quartile of cysteine concentration. A weak, negative relation between cysteine and the development of low grade SIL (LSIL) but not high grade SIL (HSIL) also was found. The results of the current study do not support the hypothesis that folate, homocysteine, or B(12) are markers of cervical dysplasia risk. A possible inverse association between plasma cysteine concentrations and the risk of cervical dysplasia needs further study.

Plasma antioxidant status after high-dose chemotherapy: a randomized trial of parenteral nutrition in bone marrow transplantation patients

Chemotherapy and radiation therapy result in increased free radical formation and depletion of tissue antioxidants. It is not known whether parenteral nutrition (PN) administered during bone marrow transplantation (BMT) supports systemic antioxidant status. The aims of the study were to determine 1) whether high-dose chemotherapy decreases concentrations of major circulating antioxidants in patients undergoing BMT and 2) whether administration of standard PN maintains systemic antioxidant concentrations compared with PN containing micronutrients and minimal lipids alone. Twenty-four BMT patients were randomly assigned to receive either standard PN containing conventional amounts of dextrose, amino acids, micronutrients, and lipid (120 kJ/d) or a solution containing only micronutrients (identical to those in standard PN) and a small amount of lipid (12 kJ/d). Plasma antioxidant status was measured before conditioning therapy and serially at days 1, 3, 7, 10, and 14 after BMT. Plasma glutathione (GSH) and alpha- and gamma-tocopherol concentrations decreased and the GSH redox state became more oxidized after conditioning chemotherapy. Plasma cysteine concentrations were unchanged, whereas cystine concentrations increased. Plasma vitamin C and zinc concentrations and GSH peroxidase activity increased over time. Plasma alpha-tocopherol concentrations were lower in patients given standard PN. There were no differences in other plasma antioxidants between groups. A significant decline in GSH-glutathione disulfide, cysteine-cystine, and vitamin E status occurs after chemotherapy and BMT. Standard PN does not improve antioxidant status compared with administration of micronutrients alone. Further evaluation of PN formulations to support patients undergoing high-dose chemotherapy and BMT are needed.

Cysteine may play a role in the immune response to internal parasites in sheep

To investigate the potential role of cysteine in the increased parasite susceptibility of sheep selected for increased wool production, ten 2-year-old rams from both fleece-weight-selected (FW) and randomly selected (C) Romney lines received either 2 g of supplemental cysteine per day (+CYS) or saline (+SAL), via abomasal infusion. Following drenching to remove any pre-existing parasites, all sheep were dosed with Haemonchus contortus and Trichostrongylus colubriformis infective larvae. Sheep were also subjected to non-parasitic immune challenges: inoculation with ovalbumin and a commercial clostridial vaccine containing the tetanus toxin. Cysteine infusion elevated plasma cysteine concentrations by an average of 65% (P &lt; 0.0001), but no difference in cysteine levels was observed between selection lines. Off-pasture faecal egg counts (FEC) were higher in FW sheep (645 v. 200 eggs/g, P &lt; 0.01). FEC were unaffected by selection line or infusion treatment following experimental infection, although FEC of +SAL sheep were at least double those of +CYS sheep. Total parasite numbers in the abomasum and small intestine at slaughter were unaffected by selection line or infusion treatment. Cysteine infusion tended to result in greater peripheral eosinophilia over the experimental period (P &lt; 0.10), and higher counts of globular leukocytes in the abomasum at slaughter (P &lt; 0.05). Anti-parasite antibody responses showed no response to experimental infection, tending to drop over time; previous parasitic infection may have confounded results. There were no effects of selection line or infusion treatment on IgG responses to tetanus toxin, although data suggested that a swifter response occurred in +CYS sheep. Anti-ovalbumin IgG responses tended to be greater in +CYS sheep (Day 52, P &lt; 0.10). This study supports the greater susceptibility of FW sheep in natural parasitic challenge, as indicated by off-pasture FEC. Cysteine appears to influence certain aspects of immunocompetency in sheep, although the exact role of cysteine in the relationship between wool production and parasite susceptibility requires further elucidation.

Effect of condensed tannins on the production of wool and on its processing characteristics in sheep grazing Lotus corniculatus

The effect of condensed tannins (CT) in Lotus corniculatus upon voluntary feed intake (VFI), concentration of rumen and plasma metabolites, production of wool, and wool processing characteristics was measured in grazing ewes restricted to maintenance feeding for 125 days during summer. A rotational grazing system with restricted feed allowance with 40 mixed aged dry ewes (54±1·0 kg) was used. Half of the ewes were selected randomly for twice-daily oral polyethylene glycol (PEG; MW 3500) supplementation (CT-inactivated), with the remainder being CT-acting animals. Measurements of the diet selected, VFI, wool production, and wool processing characteristics were made. The concentration of ammonia in rumen fluid and the concentrations of methionine, cysteine, and urea in blood plasma were also measured. The diet selected contained 32 g total nitrogen (N) and 28 g total CT/kg dry matter (DM) and had an in vitro organic matter digestibility of 0·70. Action of CT reduced rumen ammonia concentration (256 v. 302 mg N/L), reduced blood plasma urea concentration (7·3 v. 8·9 µM), and increased blood plasma cysteine concentration (30 v. 27 µM) compared with sheep receiving PEG supplementation. CT had no effect on VFI but increased clean fleece weight (2·53 v. 2·28 kg/ewe) and staple length (7·7 v. 6·9 cm), but did not affect liveweight gain (54 v 67 g/day). The CT reduced dag weight and tended to reduce wool yellowness relative to sheep receiving PEG. There were no signifiant effects of CT on fibre diameter, staple strength, bulk density, and wool resilience. It was concluded that action of CT in sheep fed L. corniculatus reduced the degradation of forage protein in the rumen and the principal effect of this was to increase the efficiency of wool production, with more wool being produced at the same feed intake and the wool being of reduced yellowness.

Susceptibility of plasma low- and high-density lipoproteins to oxidation in patients with severe hyperhomocysteinemia

A moderate increase in plasma homocysteine is increasingly considered an important risk factor of atherosclerosis and thrombosis. However, the mechanisms by which hyperhomocysteinemia induces vascular disease are not well defined. In vitro studies suggest that cysteine and homocysteine can induce oxidative modification of low-density lipoproteins (LDL). This suggestion is relevant because lipoprotein oxidation is thought to play a key role in the development of atherosclerosis and in the triggering of thrombotic events. An attractive model to study this topic is provided by patients with classical homocystinuria, an inherited disease characterized by severe hyperhomocysteinemia and a high incidence of thromboembolisms. We investigated the existence of oxidized LDL and the susceptibility to oxidation of the plasma cholesterol-rich lipoproteins in six patients with severe hyperhomocysteinemia, most likely due to classical homocystinuria, and compared the results with matched controls. The proportion of electronegative LDL and the concentration of thiobarbituric acid reactive substances in native LDL and high-density lipoproteins (HDL) did not differ between patients and controls, suggesting that the proportion of modified lipoproteins is not increased in patients with severe hyperhomocysteinemia. The susceptibility to oxidative modification of plasma LDL and HDL was also similar in the two groups, although the patients had homocysteine levels 18.3-fold higher than controls. Thus, increased oxidative modification is not likely to be a relevant mechanism in explaining their high incidence of vascular disease. A possible explanation for the lack of increased susceptibility to oxidation, as would be expected for the metabolic blockade that cause classical homocystinuria, is the 4.1-fold decrease in the concentration of cysteine in the plasma of patients. As a result the total concentration of homocysteine plus cysteine was slightly lower in patients than in controls. This interpretation implies that more studies are needed on lipoprotein susceptibility to oxidation in patients in which both plasma homocysteine and cysteine concentrations are increased. This metabolic situation may be frequent in the population with moderate hyperhomocysteinemia and vascular disease.

L-cysteine and glutathione metabolism are impaired in premature infants due to cystathionase deficiency

There are conflicting reports in the literature as to whether L-cysteine is an essential amino acid in premature infants as the result of the absence of hepatic cystathionase activity. To analyze the physiological importance of the cystathionase deficiency, we studied sulfur amino acid metabolism in human neonates of different gestational ages. Plasma cystathionine concentrations are higher in premature infants < or = 32 wk gestation (group 1) than in premature infants of 33-36 wk gestational age (group 2) or in full-term infants (group 3), whereas plasma cysteine concentrations are much lower in group 1 and 2 premature infants than in mature infants. Furthermore, erythrocytes from group 1 premature infants synthetize glutathione from L-methionine (a process dependent on the cystathionase pathway) at a much lower rate than do erythrocytes from group 2 premature or full-term infants. Thus, the metabolic flow through the transsulfuration pathway may be insufficient to meet the glutathione and cysteine requirements of very premature infants.