Cysteine and glutathione in catabolic conditions and immunological dysfunction

Appetite control and gastrointestinal hormonal behavior (CCK, GLP-1, PYY 1-36) following low doses of a whey protein-rich nutraceutic

Whey proteins represent the most satiating nutrients. In particular, their effects are due to enterohormonal changes (CCK, GLP-1 and PYY 1–36) observed after their exclusive ingestion. Glucomannan has important satiety property due to volume increase following gelification. The aim of the study is the evaluation of subjective rate of hunger and enterohormone concentrations (CCK, GLP-1, PYY 1–36) following oral loading of a mixture containing WP (8 g) or casein (8 g) plus glucomannan (1 g) (Colordiet^®, Inpha DUEMILA Srl Lecco, Italy). The study was conducted as a double-blind crossover with five healthy volunteers (BMI 22–26 kg/m² aging 18–65 years) in acute and a wash-out period of 1 week between the first and the second evaluation. From the analysis of the data, we observe that the load with WP induces a significant decrease in the desire to eat after 90 min (P < 0.0446) when compared with casein. As far as plasma hormones are concerned, there was a significant increase only in GLP-1 at 90 min after WP (P < 0.00166) and 180 min after casein (T0 vs. T180 P = 0.000129). There is a significant correlation between the increase in GLP-1 and decrease of desire to eat (R = −0.93). There is a tendency to the increasing of CCK after 90 min, which is not significant (P = 0.091). These results could be due to (a) the low number of cases or (b) the low dose of protein used. The present study suggests that a mixture of WP plus glucomannan exerts a decrease in the desire to eat which is correlated to enterohormonal modification (GLP-1 increase) despite the low content of protein (8 g) and the presence of glucomannan, which could reduce the fast absorption of WP in relation to the net forming during the gelification of the gastric environment.

Whey proteins influence hepatic glutathione after CCl4 intoxication

Whey proteins (WP) are known to contain more cysteine than casein (CAS), so it is suggested that they should ameliorate the oxidative equilibrium in the organisms. To evaluate the influence of a WP-based diet on liver glutathione (GSH) content, male Sprague-Dawley rats were fed for 3 weeks a balanced liquid diet containing either WP or CAS as main source of protein. Liver GSH content was evaluated at the end of the treatment by high performance liquid chromatography (HPLC), both in basal conditions and after oxidative stress induced by CCl4 acute intoxication. In basal conditions, WP diet significantly increased hepatic GSH in comparison to CAS diet. After CCl4 intoxication, hepatic GSH was negligibly increased in CAS group, while its increase was much more marked in WP group, so that the difference between the two diets was significant; this suggests that WP provided rats with better ability to increase their GSH synthesis in case of need.

Dangers, and benefits of the cytokine mediated response to injury and infection

The inflammatory response is essential for survival in an environment where continuous exposure to noxious events threaten the integrity of the organism. However, the beneficial effects of the response are influenced by factors, which disadvantage individuals within a population. These factors include malnutrition, infection, genotype, gender, pre-existing inflammation, and chronic intoxication. Although the inflammatory response is generally successful in dealing with noxious events, life-long exposure to these events takes its toll on the integrity of the body and becomes apparent as chronic disease, atherosclerosis, organ failure, and frailty. Progress in ameliorating the consequences of lifetime exposure to inflammatory events can only occur if a fuller understanding can be obtained of the factors, which influence the persistence and outcome of the inflammatory response at an individual level. A multitude of studies has shown that specific nutrients, diets, and dietary restriction are able to modulate the inflammatory response in the population as a whole. To advance in this area, precise knowledge is needed of how the disadvantageous factors, mentioned above, affect the individual's response to anti-inflammatory nutrients.

Red blood cells as a physiological source of glutathione for extracellular fluids

Plasma low molecular mass thiols are represented by glutathione, cysteine, cysteinylglycine and homocysteine. The physiological mechanisms responsible for maintaining the homeostasis of these compounds in the intracellular and extracellular spaces have not been fully clarified. Erythrocytes possess the enzymatic machinery to synthesize glutathione and an efflux of glutathione disulfide and glutathione conjugates from erythrocytes under various conditions occurs. In this study, the property of red blood cells (RBCs) to export low molecular mass thiols has been assessed. Plasma concentration of low molecular mass thiols has been measured in healthy volunteers by HPLC and a significant correlation with RBC number has been observed for glutathione and cysteinylglycine. A sustained export of reduced glutathione has been observed (about 21 nmol/h/ml RBCs) together with a lower, though significant, efflux of both cysteine and homocysteine. These results suggest that erythrocytes can contribute significantly to the extracellular pool of glutathione (GSH), thus cooperating with liver and other tissues to the dynamics of inter-organ GSH metabolism.

Plasma cystine concentration and redox state in aging and physical exercise

Because redox-regulated signalling pathways are often modulated by the thiol/disulfide redox state (REDST), changes in plasma REDST may possibly account for pathological processes. We, therefore, investigated the mechanisms that account for changes in the plasma REDST as derived in first approximation from the cystine and acid soluble thiol (mainly cysteine) concentrations. Elderly subjects (studies A) and younger subjects after intensive physical exercise (IPE) (study B) i.e. subjects in conditions typically associated with decreased insulin responsiveness, showed, on the average, an increase in the plasma total free amino acid (TAA) concentration to approximately 3000 microM, including an increase in cystine but no increase in the thiol concentration if compared with controls. The REDST was decreased accordingly. A study on the postabsorptive amino acid exchange rates across the lower extremities (study C) indicated that a TAA level > or =2800 microM supports a balanced net protein synthesis even under conditions of weak insulin stimulation, suggesting that high TAA levels may prevent the release of cysteine into the blood in the postabsorptive state. Collectively, these studies indicate that the age-related oxidative shift in plasma REDST may result from the decrease in amino acid clearance capacity and may be aggravated by excessive physical exercise.

Rethinking cystic fibrosis pathology: the critical role of abnormal reduced glutathione (GSH) transport caused by CFTR mutation

Though the cause of cystic fibrosis (CF) pathology is understood to be the mutation of the CFTR protein, it has been difficult to trace the exact mechanisms by which the pathology arises and progresses from the mutation. Recent research findings have noted that the CFTR channel is not only permeant to chloride anions, but other, larger organic anions, including reduced glutathione (GSH). This explains the longstanding finding of extracellular GSH deficit and dramatically reduced extracellular GSH:GSSG (glutathione disulfide) ratio found to be chronic and progressive in CF patients. Given the vital role of GSH as an antioxidant, a mucolytic, and a regulator of inflammation, immune response, and cell viability via its redox status in the human body, it is reasonable to hypothesize that this condition plays some role in the pathogenesis of CF. This hypothesis is advanced by comparing the literature on pathological phenomena associated with GSH deficiency to the literature documenting CF pathology, with striking similarities noted. Several puzzling hallmarks of CF pathology, including reduced exhaled NO, exaggerated inflammation with decreased immunocompetence, increased mucus viscoelasticity, and lack of appropriate apoptosis by infected epithelial cells, are better understood when abnormal GSH transport from epithelia (those without anion channels redundant to the CFTR at the apical surface) is added as an additional explanatory factor. Such epithelia should have normal levels of total glutathione (though perhaps with diminished GSH:GSSG ratio in the cytosol), but impaired GSH transport due to CFTR mutation should lead to progressive extracellular deficit of both total glutathione and GSH, and, hypothetically, GSH:GSSG ratio alteration or even total glutathione deficit in cells with redundant anion channels, such as leukocytes, lymphocytes, erythrocytes, and hepatocytes. Therapeutic implications, including alternative methods of GSH augmentation, are discussed.

Cysteine metabolism and whole blood glutathione synthesis in septic pediatric patients

OBJECTIVE

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.

DESIGN

Prospective cohort study.

SETTING

Multidisciplinary intensive care unit and pediatric inpatient units at a children's hospital.

PATIENTS

Ten septic pediatric patients and ten controls (children admitted to the hospital for elective surgery).

INTERVENTIONS

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.

MEASUREMENTS AND MAIN RESULTS

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)

CONCLUSIONS

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.

Metabolism 2000: the emperor needs new clothes

Metabolism is one of the corner stones of nutritional science. As biology enters the post-genomic era and with functional genomics beginning to takeoff, we anticipate that the study of metabolism will play an increasingly important role in helping to link advances made via the reductionist paradigm, that has been so successful in molecular and cellular biology, with those emerging from observational studies in animals and human subjects. A reconstructive metabolically-focused approach offers a timely paradigm for enhancing the elegance of nutritional science. Here we give particular attention to the use of tracers as phenotyping tools and discuss the application of our metaprobe concepts with respect to some novel features of metabolism, including 'underground metabolism', 'metabolic hijacking', 'catalytic promiscuity' and 'moonlighting proteins'. The opportunities for enhancing the study of metabolism by new and emerging technologies, and the importance of the interdisciplinary research enterprise are also touched upon. We conclude that: (1) the metaprobe concepts and approach, discussed herein, potentially yield a quantitative physiological (metabolic) phenotype against which to elaborate partial or focused genotypes; (2) physiological (metabolic) phenotypes which have a whole-body or kinetically-discernible inter-organ tissue-directed metabolic signature are an ideal target for this directed tracer-based definition of the 'functional' genotype; (3) metabolism, probed with tracer tool kits suitable for measuring rates of turnover, change and conversion, becomes in the current sociology of the 'Net', like AOL, Yahoo. Alta Vista, Lycos or Ask Jeeves, the portal for an exploration of the metabolic characteristics of the 'Genomics Internet'.