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

The Possible Mechanism of Physiological Adaptation to the Low-Se Diet and Its Health Risk in the Traditional Endemic Areas of Keshan Diseases

Selenium is an essential trace element for humans and animals. As with oxygen and sulfur, etc., it belongs to the sixth main group of the periodic table of elements. Therefore, the corresponding amino acids, such as selenocysteine (Sec), serine (Ser), and cysteine (Cys), have similar spatial structure, physical, and chemical properties. In this review, we focus on the neglected but key role of serine in a possible mechanism of the physiological adaptation to Se-deficiency in human beings with an adequate intake of dietary protein: the insertion of Cys in place of Sec during the translation of selenoproteins dependent on the Sec insertion sequence element in the 3'UTR of mRNA at the UGA codon through a novel serine-dependent pathway for the de novo synthesis of the Cys-tRNA^[Ser]Sec, similar to Sec-tRNA^[Ser]Sec. We also discuss the important roles of serine in the metabolism of selenium directly or indirectly via GSH, and the maintenance of selenium homostasis regulated through the methylation modification of Sec-tRNA^[Ser]Sec at the position 34U by SAM. Finally, we propose a hypothesis to explain why Keshan disease has gradually disappeared in China and predict the potential health risk of the human body in the physiological adaptation state of low selenium based on the results of animal experiments.

Amino acid-enriched plant-based RUTF treatment was not inferior to peanut-milk RUTF treatment in restoring plasma amino acid levels among patients with oedematous or non-oedematous malnutrition

Ready-to-use therapeutic food (RUTF) with adequate quality protein is used to treat children with oedematous and non-oedematous severe acute malnutrition (SAM). The plasma amino acid (AA) profile reflects the protein nutritional status; hence, its assessment during SAM treatment is useful in evaluating AA delivery from RUTFs. The objective was to evaluate the plasma AAs during the treatment of oedematous and non-oedematous SAM in community-based management of acute malnutrition (CMAM) using amino acid-enriched plant-based RUTFs with 10% milk (MSMS-RUTF) or without milk (FSMS-RUTF) compared to peanut milk RUTF (PM-RUTF). Plasma AA was measured in a non-blinded, 3-arm, parallel-group, simple randomized controlled trial conducted in Malawi. The RUTFs used for SAM were FSMS-RUTF, MSMS-RUTF or PM-RUTF. A non-inferiority hypothesis was tested to compare plasma AA levels from patients treated with FSMS-RUTF or MSMS-RUTF with those from patients treated with PM-RUTF at discharge. For both types of SAM, FSMS-RUTF and MSMS-RUTF treatments were non-inferior to the PM-RUTF treatment in restoration of the EAA and cystine except that for FSMS-RUTF, methionine and tryptophan partially satisfied the non-inferiority criteria in the oedematous group. Amino-acid-enriched milk-free plant-source-protein RUTF has the potential to restore all the EAA, but it is possible that enrichment with amino acids may require more methionine and tryptophan for oedematous children.

Association of Plasma Total Cysteine and Anthropometric Status in 6-30 Months Old Indian Children

High-quality protein has been associated with child growth; however, the role of the amino acid cysteine remains unclear. The aim was to measure the extent to which plasma total cysteine (tCys) concentration is associated with anthropometric status in children aged 6–30 months living in New Delhi, India. The study was a prospective cohort study including 2102 children. We calculated Z-scores for height-for-age (HAZ), weight-for-height (WHZ), or weight-for-age (WAZ) according to the WHO Child Growth Standards. We used multiple regression models to estimate the association between tCys and the anthropometric indices. A high proportion of the children were categorized as malnourished at enrolment; 41% were stunted (HAZ ≤ −2), 19% were wasted (WHZ ≤ −2) and 42% underweight (WAZ ≤ −2). Plasma total cysteine (tCys) was significantly associated with HAZ, WHZ and WAZ after adjusting for relevant confounders (p < 0.001). Low tCys (≤25th percentile) was associated with a decrease of 0.28 Z-scores for HAZ, 0.10 Z-scores for WHZ, and 0.21 Z-scores for WAZ compared to being >25th percentile. In young Indian children from low-to-middle socioeconomic neighborhoods, a low plasma total cysteine concentration was associated with an increased risk of poor anthropometric status.

Methionine Nutrition and Metabolism: Insights from Animal Studies to Inform Human Nutrition

Methionine is a nutritionally indispensable amino acid, and is unique among indispensable amino acids due to its sulfur atom. Methionine is involved in cysteine synthesis via the transsulfuration pathway, which is rate limiting for the key antioxidant molecule, glutathione. Methionine is also the primary methyl donor in the body through S-adenosylmethionine via the transmethylation pathway, which is involved in the synthesis of several key metabolites including creatine and phosphatidylcholine. Methionine can also be remethylated from homocysteine, in the presence of betaine via choline and/or folate. Thus methionine demands from a dietary perspective are regulated not only by the presence of cysteine in the body, but also by the demands in vivo for the various metabolites formed from it, and also by the presence of these compounds in foods. Indeed, methionine, cysteine, and the various methyl donors/acceptors vary in human foods, and thus regulate methionine availability, especially under conditions of growth and development. Much of our understanding of methionine nutrition and metabolism arises from experiments in animal models. This is because most animal feed formulations are plant-based and plant sources are relatively low in methionine and cysteine amounts. Thus, this brief review will touch on some broad aspects of human methionine nutrition, including requirements in different life stages, disease, and bioavailability, with some examples from the insights/lessons learned from experiments initially conducted in animals.

Metabolic Consequences of Supplemented Methionine in a Clinical Context

The central position of methionine (Met) in protein metabolism indicates the importance of this essential amino acid for growth and maintenance of lean body mass. Therefore, Met might be a tempting candidate for supplementation. However, because Met is also the precursor of homocysteine (Hcy), a deficient intake of B vitamins or excessive intake of Met may result in hyperhomocysteinemia (HHcy), which is a risk factor for cardiovascular disease. This review discusses the evidence generated in preclinical and clinical studies on the importance and potentially harmful effects of Met supplementation and elaborates on potential clinical applications of supplemental Met with reference to clinical studies performed over the past 20 y. Recently acquired knowledge about the NOAEL (no observed adverse effect level) of 46.3 mg · kg-1 · d-1 and the LOAEL (lowest observed adverse effect level) of 91 mg · kg-1 · d-1 of supplemented Met will guide the design of future studies to further establish the role of Met as a potential (safe) candidate for nutritional supplementation in clinical applications.

Substitution of Dietary Sulfur Amino Acids by dl-2-Hydroxy-4-Methylthiobutyric Acid Reduces Fractional Glutathione Synthesis in Weaned Piglets

BACKGROUND

Cys is limiting for reduced glutathione (GSH) synthesis and can be synthesized from Met. We hypothesized that the dietary Met hydroxyl analogue dl-2-hydroxy-4-methylthiobutyric acid (dl-HMTBA) affects Cys and GSH metabolism and oxidative stress defense differently than Met.

OBJECTIVE

The objective was to elucidate whether dl-HMTBA supplementation of a Met-deficient diet affects Cys flux, GSH fractional synthetic rate (FSR), and the basal oxidative stress level relative to Met supplementation in pigs.

METHODS

Twenty-nine male German Landrace piglets aged 28 d were allocated to 3 dietary groups: a basal diet limiting in Met (69% of Met plus Cys requirement) supplemented with either 0.15% l-Met (LMET; n = 9), 0.15% dl-Met (DLMET; n = 11), or 0.17% dl-HMTBA (DLHMTBA; n = 9) on an equimolar basis. At age 54 d the pigs received a continuous infusion of [1-13C]-Cys to calculate Cys flux and Cys oxidation. After 3 d, GSH FSR was determined by [2,2-2H2]-glycine infusion, and RBC GSH and oxidized GSH concentrations were measured. At age 62 d the animals were killed to determine hepatic mRNA abundances of enzymes involved in GSH metabolism, GSH concentrations, and plasma oxidative stress defense markers.

RESULTS

The Cys oxidation was 21-39% and Cys flux 5-15% higher in the fed relative to the feed-deprived state (P < 0.001). On average, GSH FSR was 49% lower (P < 0.01), and RBC GSH and total GSH concentrations were 12% and 9% lower, respectively, in DLHMTBA and DLMET relative to LMET pigs (P < 0.05). In the feed-deprived state, Gly flux, the GSH:oxidized glutathione (GSSG) ratio, RBC GSSG concentrations, plasma oxidative stress markers, and the hepatic GSH content did not differ between groups.

CONCLUSIONS

Although GSH FSR was higher in LMET compared with DLMET or DLHMTBA feed-deprived pigs, these differences were not reflected by lower oxidative stress markers and antioxidant defense enzymes in LMET pigs.

Edematous severe acute malnutrition is characterized by hypomethylation of DNA

Edematous severe acute childhood malnutrition (edematous SAM or ESAM), which includes kwashiorkor, presents with more overt multi-organ dysfunction than non-edematous SAM (NESAM). Reduced concentrations and methyl-flux of methionine in 1-carbon metabolism have been reported in acute, but not recovered, ESAM, suggesting downstream DNA methylation changes could be relevant to differences in SAM pathogenesis. Here, we assess genome-wide DNA methylation in buccal cells of 309 SAM children using the 450 K microarray. Relative to NESAM, ESAM is characterized by multiple significantly hypomethylated loci, which is not observed among SAM-recovered adults. Gene expression and methylation show both positive and negative correlation, suggesting a complex transcriptional response to SAM. Hypomethylated loci link to disorders of nutrition and metabolism, including fatty liver and diabetes, and appear to be influenced by genetic variation. Our epigenetic findings provide a potential molecular link to reported aberrant 1-carbon metabolism in ESAM and support consideration of methyl-group supplementation in ESAM.

Ligustrazine modulates renal cysteine biosynthesis in rats exposed to cadmium

The objective of this study was to determine the effect of ligustrazine (TMP) on cadmium (Cd)-induced nephrotoxicity and its relevant mechanism. TMP (50mg/kg) was injected intraperitoneally (i.p.) into rats 1h prior to CdCl₂ exposure (at a Cd dose of 0.6mg/kg). TMP reversed Cd-induced nephrotoxicity, evidenced by the relatively normal architecture of the renal cortex. Additionally, TMP alleviated renal oxidative stress of rats that were exposed to Cd, evidenced by the decreased levels of malondialdehyde (MDA), 4-hydroxynonenal (4-HNE), elevated levels of glutathione (GSH) and GSH/GSSG (glutathione disulfide) ratios. Furthermore, TMP also raised the decreased levels of S-adenosylmethionine (SAM) and cystathionine involved in cysteine biosynthesis in rats exposed to Cd. Further analysis revealed that TMP treatment upregulated expression of several proteins involved in cysteine biosynthesis including methionine adenosyltransferases (MATs) and cystathionine-beta-synthase (CBS). Taken together, these results suggest that TMP remodeled metabolomics of cysteine biosynthesis in rat kidneys and attenuated Cd-induced nephrotoxicity.

L-Cysteine metabolism and its nutritional implications

L-Cysteine is a nutritionally semiessential amino acid and is present mainly in the form of L-cystine in the extracellular space. With the help of a transport system, extracellular L-cystine crosses the plasma membrane and is reduced to L-cysteine within cells by thioredoxin and reduced glutathione (GSH). Intracellular L-cysteine plays an important role in cellular homeostasis as a precursor for protein synthesis, and for production of GSH, hydrogen sulfide (H(2)S), and taurine. L-Cysteine-dependent synthesis of GSH has been investigated in many pathological conditions, while the pathway for L-cysteine metabolism to form H(2)S has received little attention with regard to prevention and treatment of disease in humans. The main objective of this review is to highlight the metabolic pathways of L-cysteine catabolism to GSH, H(2)S, and taurine, with special emphasis on therapeutic and nutritional use of L-cysteine to improve the health and well-being of animals and humans.