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

Different methionine to cysteine supplementation ratios altered bone quality of broilers with or without Eimeria challenge assessed by dual energy X-ray absorptiometry and microtomography

Despite the acknowledged significance of nutrition in bone development, effects of methionine (Met) and cysteine (Cys) on bone quality remain under-researched, particularly during Eimeria challenge. We investigated the effects of different supplemental Met to Cys ratios (MCR) on bone quality of broilers under Eimeria challenge. A total of 720 fourteen-day old Cobb500 broilers were allocated into a 5 × 2 factorial arrangement. Five diets with Met and Cys supplemented at MCR of 100:0, 75:25, 50:50, 25:75, and 0:100 were fed to the birds with or without Eimeria challenge. Body composition was measured by dual energy x-ray absorptiometry, and the femur bone characteristics were assessed by microtomography. Data were analyzed by two-way ANOVA and orthogonal polynomial contrast. The results reaffirmed the detrimental effects of Eimeria challenge on bone quality. On 9 d post inoculation (DPI), significant interaction effects were found for whole body bone mineral content (BMC), lean tissue weight, and body weight (P < 0.05); in the nonchallenged group (NCG), these parameters linearly decreased as MCR decreased (P < 0.05). In the challenged group (CG), body weight and lean tissue weight were unaffected by MCR, and BMC linearly increased as MCR decreased (P < 0.05). For the cortical bone of femoral metaphysis on 6 DPI, bone mineral density (BMD) linearly increased as MCR decreased (P < 0.05). Bone volume to tissue volume ratio (BV/TV) in the CG linearly increased as MCR decreased (P < 0.05). On 9 DPI, BMC and TV linearly increased as MCR decreased (P < 0.05) in the NCG. BMD and BV/TV changed quadratically as MCR decreased (P < 0.05). For the trabecular bone of femoral metaphysis on 9 DPI, BV/TV, and trabecular number linearly increased as MCR decreased (P < 0.05) in the NCG. For the femoral diaphysis, BV, TV, BMC on 6 DPI, and BMD on 9 DPI linearly increased as MCR decreased (P < 0.05). In conclusion, this study showed that both Eimeria challenge and varying supplemental MCR could influence bone quality of broilers.

Transsulfuration and folate pathways in rheumatoid arthritis: A systematic review and meta-analysis

BACKGROUND

Metabolomic assessment of the transsulfuration and folic acid biochemical pathways could lead to the identification of promising biomarkers of nitric oxide dysregulation and oxidative stress in rheumatoid arthritis (RA).

METHODS

We conducted a systematic review and meta-analysis of transsulfuration (methionine, homocysteine, and cysteine) and folic acid (folic acid, vitamin B6 , and vitamin B12 ) metabolites in RA patients in remission and healthy controls. Electronic databases were searched from inception to 15 July 2023 for relevant articles. We assessed the risk of bias using the JBI checklist and the certainty of evidence using GRADE.

RESULTS

In 28 eligible studies, compared to controls, RA patients had significantly higher concentrations of homocysteine (standardized mean difference, SMD = 0.74, 95% CI 0.54-0.93, p < 0.001; low certainty of evidence) and methionine (SMD = 1.00, 95% CI 0.57-1.44, p < 0.001; low certainty) and lower concentrations of vitamin B6 (SMD = -6.62, 95% CI -9.65 to -3.60, p < 0.001; low certainty). By contrast, there were non-significant between-group differences in vitamin B12 and folic acid. In meta-regression and subgroup analysis, there were no associations between the effect size and several study and patient characteristics except for homocysteine (year of publication, C-reactive protein, triglycerides, and analytical method) and folic acid (biological matrix).

CONCLUSIONS

The results of our study suggest that homocysteine, methionine, and vitamin B6 are promising biomarkers to assess nitric oxide dysregulation and oxidative stress in RA. (PROSPERO registration number: CRD42023461081).

Impacts of varying methionine to cysteine supplementation ratios on growth performance, oxidative status, intestinal health, and gene expression of immune response and methionine metabolism in broilers under Eimeria spp. challenge

A study was conducted to investigate effects of different methionine (Met) to cysteine (Cys) supplementation ratios (MCR) on growth performance, oxidative status, intestinal health, immune responses, and methionine metabolism in broilers under Eimeria challenge. A total of 720 male Cobb500 broilers (14-day-old) were allocated in a 2 × 5 factorial arrangement (5 diets, with or without challenge) with 6 replicates per treatment. The total sulfur amino acid concentrations were consistent across treatments meeting the breeder's recommendation, only MCR varied. The diets were labeled as MET100; MET75; MET50; MET25; and MET0, representing MCR of 100:0; 75:25; 50:50; 25:75; and 0:100, respectively. Data were analyzed by 2-way ANOVA and orthogonal polynomial contrast. Growth performance declined linearly or quadratically as MCR decreased (P < 0.01). On 6-day postinoculation (DPI), interaction effects (P < 0.01) were found; BW and body weight gain were lower in MET0 compared to the other treatments in the nonchallenged groups, whereas not in the challenged groups. On 6 and 9 DPI, serum total antioxidant capacity linearly decreased as MCR decreased (P < 0.05). Hepatic activities of glutathione peroxidase on 6 DPI and superoxide dismutase on 9 DPI changed quadratically as MCR decreased (P < 0.05). The digestibility of Met linearly decreased whereas the digestibility of Cys linearly increased as MCR decreased. The ileal crypt depth linearly decreased as MCR decreased (P < 0.01) on 6 DPI. The expression of transforming growth factor beta on 6 and 9 DPI, tumor necrotic factor alpha and interleukin 10 on 9 DPI changed quadratically as MCR decreased (P < 0.05). Eimeria challenge increased expression of Met adenosyltransferase and cystathionine gamma-lyase, whereas decreasing the expression of other Met metabolism genes (P < 0.01) on 6 DPI. Expression of Met metabolism genes linearly increased as MCR decreased (P < 0.05). In conclusion, different Met to Cys supplementation ratios exerted linearly or quadratically effects on the growth performance, oxidative status, intestinal health, and metabolism of Met in broiler chickens under Eimeria infection.

Shenkang Injection for Treating Renal Fibrosis-Metabonomics and Regulation of E3 Ubiquitin Ligase Smurfs on TGF-β/Smads Signal Transduction

At present, TGF-β is the most critical fibrogenic factor known. Smad ubiquitin ligase Smurfs play an important role in the regulation of the TGF-/Smads signaling pathway, which is linked to metabolite changes in renal fibrosis. Previous studies have shown that Shenkang injection can prevent and treat chronic kidney disease through multiple channels of action. However, the precise relationship between Shenkang injection and the regulation of the TGF-/Smads signaling pathway in the treatment of chronic kidney disease is unknown. Here, we evaluated the pharmacological effects of Shenkang injection on ubiquitination and metabolic changes of the TGF-β/Smads signaling pathway in UUO mice using pathology-related indicators, immunoprecipitation, subcellular co-location, and metabonomics analysis. Our findings indicate that Shenkang injection can promote nuclear translocation of Smurf1 and Smurf2 to TGF- membrane receptors TR-I and Smad2 and ubiquitinated degradation of these proteins. Furthermore, the formation of TβR-I/TβR-II, TβR-I/Smad2, and TβR-I/Smad3 complexes was inhibited to negatively regulate the TGF-β/Smad signaling pathway induced renal tubular epithelial transdifferentiation (EMT). The EMT process is not very relevant in vivo, although it is clear that TGF-β induces EMT in cultured cells, which has been demonstrated by numerous teams around the world. However, this is not the case with the in vivo models of kidney fibrosis, especially UUO. In addition, Shenkang injection can improve amino acid metabolism, purine metabolism, and fatty acid metabolism disorders.

Tocotrienol Supplementation Led to Higher Serum Levels of Lysophospholipids but Lower Acylcarnitines in Postmenopausal Women: A Randomized Double-Blinded Placebo-Controlled Clinical Trial

Osteoporosis is a major health problem in postmenopausal women. Herein we evaluated the effects of 12-week tocotrienols (TT) supplementation on serum metabolites in postmenopausal, osteopenic women. Eighty-nine participants (59.7 ± 6.8 yr, BMI 28.7 ± 5.7 kg/m²) were assigned to 3 treatments: placebo (860 mg olive oil/day), 300mg TT (300 mg TT/day), and 600mg TT (600 mg TT/day) for 12 weeks. TT consisted of 90% δ-TT and 10% γ-TT. In this metabolomic study, we evaluated the placebo and 600mgTT at baseline and 12 weeks. As expected, TT and its metabolite levels were higher in the supplemented group after 12 weeks. At baseline, there were no differences in demographic parameters or comprehensive metabolic panels (CMP). Metabolomics analysis of serum samples revealed that 48 biochemicals were higher and 65 were lower in the 600mg TT group at 12 weeks, compared to baseline. The results confirmed higher serum levels of tocotrienols and lysophospholipids, but lower acylcarnitines and catabolites of tryptophan and steroids in subjects given 600mg TT. In summary, 12-week TT supplementation altered many serum metabolite levels in postmenopausal women. The present study supports our previous findings that TT supplementation helps reduce bone loss in postmenopausal osteopenic women by suppressing inflammation and oxidative stress. Furthermore, the body incorporates TT which restructures biomembranes and modifies phospholipid metabolism, a response potentially linked to reduced inflammation and oxidative stress.

The impact of glutathione metabolism in autism spectrum disorder

This paper reviews the potential role of glutathione (GSH) in autism spectrum disorder (ASD). GSH plays a key role in the detoxification of xenobiotics and maintenance of balance in intracellular redox pathways. Recent data showed that imbalances in the GSH redox system are an important factor in the pathophysiology of ASD. Furthermore, ASD is accompanied by decreased concentrations of reduced GSH in part caused by oxidation of GSH into glutathione disulfide (GSSG). GSSG can react with protein sulfhydryl (SH) groups, thereby causing proteotoxic stress and other abnormalities in SH-containing enzymes in the brain and blood. Moreover, alterations in the GSH metabolism via its effects on redox-independent mechanisms are other processes associated with the pathophysiology of ASD. GSH-related regulation of glutamate receptors such as the N-methyl-D-aspartate receptor can contribute to glutamate excitotoxicity. Synergistic and antagonistic interactions between glutamate and GSH can result in neuronal dysfunction. These interactions can involve transcription factors of the immune pathway, such as activator protein 1 and nuclear factor (NF)-κB, thereby interacting with neuroinflammatory mechanisms, ultimately leading to neuronal damage. Neuronal apoptosis and mitochondrial dysfunction are recently outlined as significant factors linking GSH impairments with the pathophysiology of ASD. Moreover, GSH regulates the methylation of DNA and modulates epigenetics. Existing data support a protective role of the GSH system in ASD development. Future research should focus on the effects of GSH redox signaling in ASD and should explore new therapeutic approaches by targeting the GSH system.

Impact of Glutathione and Vitamin B-6 in Cirrhosis Patients: A Randomized Controlled Trial and Follow-Up Study

Vitamin B-6 and glutathione (GSH) are antioxidant nutrients, and inadequate vitamin B-6 may indirectly limit glutathione synthesis and further affect the antioxidant capacities. Since liver cirrhosis is often associated with increased oxidative stress and decreased antioxidant capacities, we conducted a double-blind randomized controlled trial to assess the antioxidative effect of vitamin B-6, GSH, or vitamin B-6/GSH combined supplementation in cirrhotic patients. We followed patients after the end of supplementation to evaluate the association of vitamin B-6 and GSH with disease severity. In total, 61 liver cirrhosis patients were randomly assigned to placebo, vitamin B-6 (50 mg pyridoxine/d), GSH (500 mg/d), or B-6 + GSH groups for 12 weeks. After the end of supplementation, the condition of patient’s disease severity was followed until the end of the study. Neither vitamin B-6 nor GSH supplementation had significant effects on indicators of oxidative stress and antioxidant capacities. The median follow-up time was 984 d, and 21 patients were lost to follow-up. High levels of GSH, a high GSH/oxidized GSH ratio, and high GSH-St activity at baseline (Week 0) had a significant effect on low Child–Turcotte–Pugh scores at Week 0, the end of supplementation (Week 12), and the end of follow-up in all patients after adjusting for potential confounders. Although the decreased GSH and its related enzyme activity were associated with the severity of liver cirrhosis, vitamin B-6 and GSH supplementation had no significant effect on reducing oxidative stress and increasing antioxidant capacities.

Possible Synergistic Effects of Glutathione and C-Reactive Protein in the Progression of Liver Cirrhosis

Liver cirrhosis is often associated with increased inflammatory responses and changes of glutathione (GSH) status. The possible interactions between these two factors in mediating damages of liver function remain unclear. Here, we measured the inflammatory responses and GSH status in liver cirrhotic patients and compared them with healthy subjects. In addition, we assessed the relationship of the GSH status and levels of inflammatory markers with the severity of the disease. This was a cross-sectional study. In total, we recruited 63 liver cirrhotic patients with Child⁻Turcotte⁻Pugh class A scores, and 12 patients with class B⁻C scores, together with 110 healthy subjects. Patients with class B⁻C scores showed the highest level of high-sensitivity C-reactive protein (hs-CRP) when compared with class A patients or healthy subjects. Patients in class A group had significantly higher GSH levels when compared with class B⁻C group or healthy subjects. After adjusting for potential confounders and each other, serum hs-CRP levels showed positive association with the Child⁻Turcotte⁻Pugh scores, while GSH levels showed negative association with Child⁻Turcotte⁻Pugh scores. Interactions were found between levels of plasma GSH and serum hs-CRP (β = 0.004, p = 0.016). CRP and GSH levels, which had showed interactions, were associated with the severity of liver cirrhosis.

Changes of Oxidative Stress, Glutathione, and Its Dependent Antioxidant Enzyme Activities in Patients with Hepatocellular Carcinoma before and after Tumor Resection

The changes in and relationship between oxidative stress and the glutathione (GSH) antioxidant system in the plasma and tissues of patients with hepatocellular carcinoma (HCC) before and after tumor resection have not been clearly determined. We investigated the changes in oxidative stress, GSH status and its dependent antioxidant enzyme activities in HCC patients before and after tumor resection, and to determine the association of oxidative stress with GSH and its dependent antioxidant enzyme activities in plasma and tissues. This study employed a cross-sectional design. Forty-four men and 16 women with HCC were recruited. Fasting blood was drawn on the day before the tumor resection and one month after the tumor resection. HCC tissue and adjacent normal liver tissue were obtained at the time of surgical resection. Patients had significantly increased plasma malondialdehyde (MDA) and oxidized-low density lipoprotein levels but decreased GSH and oxidized GSH levels before tumor resection compared with the corresponding post-resection values. GSH and trolox equivalent antioxidant capacity (TEAC) levels and activities of GSH peroxidase were significantly increased while MDA level was significantly lower in HCC tissue when compared with the adjacent normal tissue. The pre-resection plasma MDA level was significantly correlated with pre-resection plasma GSH concentration, and MDA level in HCC and adjacent normal tissues. Pre-resection plasma GSH concentration was significantly correlated with GSH and TEAC level in HCC tissue. HCC patients had increased oxidative stress, decreased GSH, and lower dependent antioxidant capacities before tumor resection. However, hepatocellular tumor had increased GSH and TEAC levels as well as GSH peroxidase activities which might protect itself against increased oxidative stress.

Reactive oxygen species and fibrosis: further evidence of a significant liaison

Age-related diseases such as obesity, diabetes, non-alcoholic fatty liver disease, chronic kidney disease and cardiomyopathy are frequently associated with fibrosis. Work within the last decade has improved our understanding of the pathophysiological mechanisms contributing to fibrosis development. In particular, oxidative stress and the antioxidant system appear to be crucial modulators of processes such as transforming growth factor-β1 (TGF-β1) signalling, metabolic homeostasis and chronic low-grade inflammation, all of which play important roles in fibrosis development and persistence. In the current review, we discuss the connections between reactive oxygen species, antioxidant enzymes and TGF-β1 signalling, together with functional consequences, reflecting a concept of redox-fibrosis that can be targeted in future therapies.

Graphical abstract

Redox-fibrosis: Impact of TGFβ1 on ROS generators, mediators and functional consequences

Fibrosis is one of the most prevalent features of age-related diseases like obesity, diabetes, non-alcoholic fatty liver disease, chronic kidney disease, or cardiomyopathy and affects millions of people in all countries. Although the understanding about the pathophysiology of fibrosis has improved a lot during the recent years, a number of mechanisms still remain unknown. Although TGF-β1 signaling, loss of metabolic homeostasis and chronic low-grade inflammation appear to play important roles in the pathogenesis of fibrosis, recent evidence indicates that oxidative stress and the antioxidant system may also be crucial for fibrosis development and persistence. These findings point to a concept of a redox-fibrosis where the cellular oxidant and antioxidant system could be potential therapeutic targets. The current review aims to summarize the existing links between TGF-β1 signaling, generation and action of reactive oxygen species, expression of antioxidative enzymes, and functional consequences including epigenetic redox-mediated responses during fibrosis.

Branched-chain amino acids inhibit the TGF-beta-induced down-regulation of taurine biosynthetic enzyme cysteine dioxygenase in HepG2 cells

Taurine deficiency has been suggested to contribute to the pathogenesis and complications of advanced hepatic diseases. The molecular basis for a low level of taurine associated with hepatic failure is largely unknown. Using carbon tetrachloride (CCl₄)-induced cirrhotic rat model, we found that the activity and expression of cysteine dioxygenase (CDO), a rate-limiting enzyme in taurine synthesis, were significantly decreased in the liver of these rats. To investigate the underlying mechanisms for the suppression, we examined the effects of pathological cytokines on CDO expression in human hepatoma HepG2 cells. Among the several cytokines, transforming growth factor-β (TGF-β), one of the key mediators of fibrogenesis, suppressed Cdo1 gene transcription through the MEK/ERK pathway. Finally, we further examined potential effects of branched-chain amino acids (BCAA) on CDO expression, as it has been reported that oral BCAA supplementation increased plasma taurine level in the patients with liver cirrhosis. BCAA, especially leucine, promoted Cdo1 gene transcription, and attenuated TGF-β-mediated suppression of Cdo1 gene expression. These results indicate that the low plasma level of taurine in advanced hepatic disease is due to decreased hepatic CDO expression, which can be partly attributed to suppressive effect of TGF-β on Cdo1 gene transcription. Furthermore, our observation that BCAA promotes Cdo1 expression suggests that BCAA may be therapeutically useful to improve hepatic taurine metabolism and further suppress dysfunctions associated with low level of taurine in hepatic diseases.

Transsulfuration Is a Significant Source of Sulfur for Glutathione Production in Human Mammary Epithelial Cells

The transsulfuration pathway, through which homocysteine from the methionine cycle provides sulfur for cystathionine formation, which may subsequently be used for glutathione synthesis, has not heretofore been identified as active in mammary cells. Primary human mammary epithelial cells (HMEC's) were labeled with S35-methionine for 24 hours following pretreatment with a vehicle control, the cysteine biosynthesis inhibitor propargylglycine or the gamma-glutamylcysteine synthesis inhibitor buthionine sulfoximine. Cell lysates were prepared and reacted with glutathione-S-transferase and the fluorescent labeling compound monochlorobimane to form a fluorescent glutathione-bimane conjugate. Comparison of fluorographic and autoradiographic images indicated that glutathione had incorporated S35-methionine demonstrating that functional transsulfuration occurs in mammary cells. Pathway inhibitors reduced incorporation by roughly 80%. Measurement of glutathione production in HMEC's treated with and without hydrogen peroxide and/or pathway inhibitors indicates that the transsulfuration pathway plays a significant role in providing cysteine for glutathione production both normally and under conditions of oxidant stress.

Molecular mechanisms involved in NAFLD progression

Non-alcoholic fatty liver disease (NAFLD) is an emerging metabolic-related disorder characterized by fatty infiltration of the liver in the absence of alcohol consumption. NAFLD ranges from simple steatosis to non-alcoholic steatohepatitis (NASH), which might progress to end-stage liver disease. This progression is related to the insulin resistance, which is strongly linked to the metabolic syndrome consisting of central obesity, diabetes mellitus, and hypertension. Earlier, the increased concentration of intracellular fatty acids within hepatocytes leads to steatosis. Subsequently, multifactorial complex interactions between nutritional factors, lifestyle, and genetic determinants promote necrosis, inflammation, fibrosis, and hepatocellular damage. Up to now, many studies have revealed the mechanism associated with insulin resistance, whereas the mechanisms related to the molecular components have been incompletely characterized. This review aims to assess the potential molecular mediators initiating and supporting the progression of NASH to establish precocious diagnosis and to plan more specific treatment for this disease.

Nutritional treatment of chronic liver failure

The liver plays a central role in the regulation of nutrition by trafficking the metabolism of nutrients, their distribution and appropriate use. Accordingly, protein-energy malnutrition is common in patients with advanced liver disease, and it is a significant prognostic factor, affecting survival, the success of liver transplantation and quality of life. Clinical guidelines for the assessment and treatment of malnutrition have been issued by International societies, suggesting that nutritional therapy should be instituted in all patients where requirements are not adequately met by diet. The supplementation of the diet with amino acids (mainly branched-chain amino acids) and trace elements may improve nutritional status, liver function and hepatic encephalopathy. Nutritional issues should be carefully considered in Liver Units treating patients with advanced cirrhosis, and long-term, carefully controlled studies are needed to better define the type of nutritional support and the amount and timing of administration.

Mathematical models of folate-mediated one-carbon metabolism

Folate-mediated one-carbon metabolism is an unusually complex metabolic network, consisting of several interlocking cycles, and compartmentation between cytosol and mitochondria. The cycles have diverse functions, the primary being thymidylate synthesis (the rate limiting step in DNA synthesis), the initial steps in purine synthesis, glutathione synthesis, and a host of methyl transfer reactions that include DNA and histone methylation. Regulation within the network is accomplished by numerous allosteric interactions in which metabolites in one part of the network affect the activity of enzymes elsewhere in the network. Although a large body of experimental work has elucidated the details of the mechanisms in every part of the network, the multitude of complex and non-linear interactions within the network makes it difficult to deduce how the network as a whole operates. Understanding the operation of this network is further complicated by the fact that human populations maintain functional polymorphisms for several enzymes in the network, and that the network is subject to continual short and long-term fluctuations in its inputs as well as in demands on its various outputs. Understanding how such a complex system operates is possible only by means of mathematical models that take account of all the reactions and interactions. Simulations with such models can be used as an adjunct to laboratory experimentation to test ideas and alternative hypotheses and interpretations quickly and inexpensively. A number of mathematical models have been developed over the years, largely motivated by the need to understand the complex mechanisms by which anticancer drugs like methotrexate inhibit nucleotide synthesis and thus limit the ability of cells to divide. More recently, mathematical models have been used to investigate the regulatory and homeostatic mechanisms that allow the system to accommodate large fluctuations in one part of the network without affecting critical functions elsewhere in the network.

Survival of atherosclerotic patients as related to oxidative stress and gene polymorphisms

A prospective molecular epidemiology study was implemented in a cohort of 98 subjects suffering from severe atherosclerotic lesions requiring removal of an abdominal aorta fragment. We previously published the results relative to detection, in the aorta medium layer, of bulky DNA adducts and fluorescent polycyclic aromatic hydrocarbon-related DNA adducts, oxidative DNA damage, and mitochondrial DNA 4977 common deletion, as well as GSTM1 and GSTT1 gene polymorphisms. We report herein new data, relative to oxidative stress biomarkers, including oxidative DNA damage in both inner and medium aorta layers, malondialdehyde in the medium layer, homocysteine and reduced glutathione in plasma, and those relative to additional gene polymorphisms, including NAT1, NAT2, OGG1, MTHFR, Leiden factor V, and prothrombin. The results of biochemical and molecular analyses were related to survival of the patients, whose average age was 70 at the start of the follow up. During the following 14 years, 71.4% of them died. The results obtained provide evidence for the crucial impact of oxidative stress and certain gene polymorphisms on clinical and biochemical patterns as well as on survival of patients. Survival was significantly affected not only by traditional risk factors for atherosclerosis but also by molecular end-points and adverse gene polymorphisms, and by their combinations.

Total Parenteral Nutrition: Challenges and Practice in the Cirrhotic Patient

Patients with cirrhosis develop metabolic derangements of protein, carbohydrate, and lipid metabolism. Malnutrition is commonplace and is associated with morbidity and mortality. Specific nutrient deficiencies may occur and enteral or parenteral nutritional support may improve outcome in appropriately selected patients. Parenteral nutrition itself has been associated with hepatic dysfunction, although the preponderance of evidence suggests that hepatic dysfunction is more a function of the underlying disorder and malabsorption. Intravenously infused organic nutrients may be metabolized differently than the same nutrient consumed enterally. The pathophysiology of total parenteral nutrition-associated liver disease is discussed as well as potential management options.

The effects of sulfur amino acid intake on immune function in humans

No direct data exist on the influence of supranormal intakes of sulfur amino acids on immune function in humans. However 3 major products of sulfur amino acids, glutathione (GSH), homocysteine (Hcy), and taurine (Tau), influence, mainly, inflammatory aspects of the immune response in vitro and in vivo. Methionine intakes above approximately 1 g/d transiently raise plasma Tau, Hcy, and GSH. Tau and GSH ameliorate inflammation. Hcy has the opposite effect. A biphasic relation, between cellular GSH and CD4+ and CD8+ numbers occurs in healthy men. How changes in sulfur amino acid intake influence this phenomenon is unknown. In animals, high Tau intakes are antiinflammatory. How immune function in humans is affected is unknown. A positive relation between plasma neopterin (a marker of a Th-1-type immune response) and Hcy indicates that Hcy may play a part in inflammatory aspects of Parkinson's disease and aging. In vitro, Hcy, at concentrations seen following consumption of approximately 6 g L-methionine/d in adults, increases the interactions among T lymphocytes, monocytes, and endothelium. Whether a similar phenomenon occurs in vivo is unknown. Polymorphisms in the methylenetetrahydrofolate reductase gene are associated with raised plasma Hcy in young but not old subjects. The relation of this observation to immune function is unknown. The relationships among Hcy, inflammatory aspects of disease, and in vitro alterations in immune cell behavior create a cautionary note about supplementation of diets with l-methionine to raise intake above approximately 1 g/d. Studies directly linking methionine intake, genetics, plasma Hcy, Tau, and GSH and immune function are needed.

The in vivo sparing of methionine by cysteine in sulfur amino acid requirements in animal models and adult humans

Sulfur amino acid metabolism has been receiving increased attention because of the link to chronic diseases such as cardiovascular disease, Alzheimer's disease, and diabetes. In addition, the role of cysteine and optimal intakes for physiological substrates such as glutathione are currently of considerable interest in human health. Although the dietary indispensability of methionine is not in question, the ability of cysteine to substitute for a portion of its requirement has been the topic of much debate. Methionine is often the most limiting amino acid in the diets of the developing world's population because of its low concentration in cereal grains. Therefore, the ability of cysteine to substitute for methionine requirement is not just biologically interesting; it is also of considerable economic and social importance. The primary goal of this review is to discuss the available evidence on the effect of cysteine substitution for methionine to meet the total sulfur amino acid requirement in adult humans, including an assessment of the methodological features of experiments with conflicting results. Assessment of the requirement experiments for amino acids with complex metabolism such as methionine and cysteine must begin with a careful definition of requirements and what substitution means. As a result of these definitions, a set of criteria for the intakes of methionine that will allow demonstration of the substitution effect have been developed. Some recent publications are assessed using these definitions and criteria, and a possible reason for the conflicting results in the literature is proposed. An approach to estimating tolerable upper intakes is also proposed. Research on in vivo sulfur amino acid metabolism in humans is tremendously difficult, and therefore, we do not wish to be overly critical of the high-quality work of the ambitious and highly intelligent men and women who have conducted various studies. Our goal is to objectively review the data for the reader in a logical and comprehensive manner and propose methods that may avoid difficulties in future studies.

Antioxidant levels in peripheral blood, disease activity and fibrotic stage in chronic hepatitis C

BACKGROUND

This study addressed the suggested association between levels of the antioxidants glutathione (GSH), vitamin C and vitamin E in peripheral blood and the histological activity and fibrosis stage in chronic hepatitis C (CHC). We then determined whether regular antioxidant supplementation influenced these antioxidant levels or disease severity.

METHODS

Clinical, biochemical, histological and demographic data were collected from 247 CHC patients at the time of liver biopsy. Whole blood total GSH, plasma vitamin C and E were assessed by high-performance liquid chromatography. Statistical analyses were performed to test for associations between the variables and to identify independent predictors for hepatic necroinflammatory and fibrosis scores.

RESULTS

GSH and vitamin C, but not vitamin E correlated with both portal/periportal activity (r = -0.19, P = 0.004; r = -0.19, P = 0.009 respectively) and fibrosis stage (r = -0.18, P = 0.007; r = -0.18, P = 0.009 respectively). GSH was an independent negative predictor of portal/periportal inflammation (P = 0.02) and fibrosis (P = 0.01). Vitamin C was an independent negative predictor of fibrosis stage (P = 0.02). Antioxidant intake was associated with higher vitamin C (P < 0.0001) and vitamin E (P = 0.005) levels, but not GSH.

CONCLUSIONS

Whole blood GSH and plasma vitamin C are negatively associated with hepatic portal/periportal inflammation and fibrosis stage in CHC. Controlled intervention studies with vitamin C and agents that boost endogenous GSH levels are warranted.

Effect of protein restriction on sulfur amino acid catabolism in insulin-dependent diabetes mellitus

Persons with conventionally treated insulin-dependent diabetes mellitus (IDDM) appear to be impaired in their ability to reduce fed-state urea production appropriately in response to dietary protein restriction (Hoffer LJ, Taveroff A, and Schiffrin A. Am J Physiol 272: E59-E67, 1997). To determine whether these conclusions apply to whole body sulfur amino acid (SAA) catabolism, we used samples from this protocol to measure daily urinary sulfate excretion and fed-state sulfate production after a high-protein test meal before and after dietary protein restriction. Eight normal subjects and six IDDM subjects treated with twice-daily intermediate- and short-acting insulin consumed a mixed test meal containing 0.50 g protein/kg after adaptation to 4 days of high protein intake (1.28 g protein/kg body wt) and again after 5 days of dietary protein restriction (0.044 g/kg). Adaptation to protein restriction decreased daily urinary sulfate and urea-N excretion by approximately 80%. Over the first 24 h of protein restriction, urinary sulfate excretion decreased more than urea-N excretion for both the normal and IDDM subjects. Under conditions of a high prior protein intake, fed-state sulfate production was normal for the IDDM subjects; protein restriction reduced fed-state sulfate production by 51% (normal subjects) and 59% (IDDM subjects; not significant). We conclude that whole body SAA metabolism is normal in conventionally treated IDDM before and after dietary protein restriction. SAA catabolism, as measured by fed-state sulfate production, may be a convenient and useful method to determine the extent of whole body protein dysregulation in IDDM.

Methods for measuring sulfur amino acid metabolism

PURPOSE OF REVIEW

The importance of sulfur amino acid metabolism has become increasingly apparent in recent years. Methionine and cysteine are precursors of glutathione, which plays an important role in intracellular antioxidant/free radical defenses. Homocysteine is a non-protein-bound sulfur amino acid strongly implicated in the pathogenesis of several diseases. Both glutathione and homocysteine are affected by abnormalities in sulfur amino acid metabolism that occur in the clinical setting.

RECENT FINDINGS

The Storch-Young model, which determines methionine turnover and homocysteine remethylation by means of a tracer methionine infusion, has been improved by using plasma homocysteine (rather than methionine) enrichment in the model. A complex new tracer method involving the use of tracer serine, methionine, and leucine has been described to determine the effects of folate or pyridoxine deficiency on sulfur amino acid-methyl transfer reactions in humans. The etiology of hyperhomocysteinemia in chronic renal failure is controversial; new concepts in this area are described. There is new interest in the subspecies of homocysteine in the circulation. A new method is described for measuring the extremely low plasma concentrations of reduced homocysteine, using gas chromatography-mass spectrometry. Plasma S-adenosylhomocysteine, measured by fluorescence high-performance liquid chromatography, has been suggested as being superior to homocysteine as a predictor of the risk of vascular disease.

SUMMARY

This review highlights and critiques the above recent developments, and points out some of the complexities and pitfalls in designing and interpreting human metabolic studies involving the sulfur amino acids.

Evidence of oxidative imbalance in long-term liver transplant patients

BACKGROUND

Oxidative stress in patients undergoing liver transplantation results both from the pre-existing cirrhosis and ischaemia-reperfusion injury related to surgery. Previous studies have provided information limited to the immediate post-operative period. It remains to be established whether this oxidative imbalance is reversed in a longer time.

AIM, METHODS AND PATIENTS

This study aimed to compare plasma concentrations of thiobarbituric acid-reactant substances and alpha-tocopherol in 20 cirrhotic patients before liver transplantation and 22 patients in whom transplant had been carried out at least 6 months previously. Thirty healthy age and sex-matched volunteers served as controls (cross-sectional study). Five patients were evaluated before and after liver transplantation (longitudinal study).

RESULTS AND CONCLUSIONS

Pre-transplant patients showed greater thiobarbituric acid-reactant substances and lower alpha-tocopherol levels than controls. Transplanted patients presented lower thiobarbituric acid-reactant substances and greater alpha-tocopherol levels than cirrhotic patients without reaching, however, the levels observed in controls. No correlations were found between oxidative parameters and liver tests. Hypertransaminasaemia, liver disease recurrence, and rejection episodes did not significantly influence the oxidative parameters. In the longitudinal study, transplantation induced a significant decrease in plasma thiobarbituric acid-reactant substances and a rise in alpha-tocopherol. Although a long-term improvement in the oxidative injury observed in cirrhotic patients occurs after liver transplantation, mild oxidative stress persists even in successfully transplanted patients.