Toxicity of methionine in humans

Methionine deficiency inhibited pyroptosis in primary hepatocytes of grass carp (Ctenopharyngodon idella): possibly via activating the ROS-AMPK-autophagy axis

BACKGROUND

Methionine (Met) is the only sulfur-containing amino acid among animal essential amino acids, and methionine deficiency (MD) causes tissue damage and cell death in animals. The common modes of cell death include apoptosis, autophagy, pyroptosis, necroptosis. However, the studies about the major modes of cell death caused by MD have not been reported, which worth further study.

METHODS

Primary hepatocytes from grass carp were isolated and treated with different doses of Met (0, 0.5, 1, 1.5, 2, 2.5 mmol/L) to examine the expression of apoptosis, pyroptosis, autophagy and necroptosis-related proteins. Based on this, we subsequently modeled pyroptosis using lipopolysaccharides and nigericin sodium salt, then autophagy inhibitors chloroquine (CQ), AMP-activated protein kinase (AMPK) inhibitors compound C (CC) and reactive oxygen species (ROS) scavengers N-acetyl-L-cysteine (NAC) were further used to examine the expression of proteins related to pyroptosis, autophagy and AMPK pathway in MD-treated cells respectively.

RESULTS

MD up-regulated B-cell lymphoma protein 2 (Bax), microtubule-associated protein 1 light chain 3 II (LC3 II), and down-regulated the protein expression levels of B-cell lymphoma-2 (Bcl-2), sequestosome 1 (p62), cleaved-caspase-1, cleaved-interleukin (IL)-1β, and receptor-interacting protein kinase (RIP) 1 in hepatocytes, while it did not significantly affect RIP3. In addition, MD significantly increased the protein expression of liver kinase B1 (LKB1), p-AMPK, and Unc-51-like kinase 1 (ULK1) without significant effect on p-target of rapamycin. Subsequently, the use of CQ increased the protein expression of NOD-like receptor thermal protein domain associated protein 3 (NLRP3), cleaved-caspase-1, and cleaved-IL-1β inhibited by MD; the use of CC significantly decreased the protein expression of MD-induced LC3 II and increased the protein expression of MD-suppressed p62; then the use of NAC decreased the MD-induced p-AMPK protein expression.

CONCLUSION

MD promoted autophagy and apoptosis, but inhibited pyroptosis and necroptosis. MD inhibited pyroptosis may be related regarding the promotion of autophagy. MD activated AMPK by inducing ROS production which in turn promoted autophagy. These results could provide partial theoretical basis for the possible mechanisms of Met in ensuring the normal structure and function of animal organs. Furthermore, ferroptosis is closely related to redox states, it is worth investigating whether MD affects ferroptosis in hepatocytes.

The Association of the Essential Amino Acids Lysine, Methionine, and Threonine with Clinical Outcomes in Patients at Nutritional Risk: Secondary Analysis of a Randomized Clinical Trial

Lysine, methionine, and threonine are essential amino acids with vital functions for muscle and connective tissue health, metabolic balance, and the immune system. During illness, the demand for these amino acids typically increases, which puts patients at risk for deficiencies with harmful clinical consequences. In a secondary analysis of the Effect of Early Nutritional Support on Frailty, Functional Outcomes, and Recovery of Malnourished Medical Inpatients Trial (EFFORT), which compared individualized nutritional support to usual care nutrition in patients at nutritional risk, we investigated the prognostic impact of the lysine, methionine, and threonine metabolism. We had complete clinical and amino acid data in 237 patients, 58 of whom reached the primary endpoint of death at 30 days. In a model adjusted for comorbidities, sex, nutritional risk, and trial intervention, low plasma methionine levels were associated with 30-day mortality (adjusted HR 1.98 [95% CI 1.16 to 3.36], p = 0.01) and with a decline in functional status (adjusted OR 2.06 [95% CI 1.06 to 4.01], p = 0.03). The results for lysine and threonine did not show statistically significant differences regarding clinical outcomes. These findings suggest that low levels of methionine may be critical during hospitalization among patients at nutritional risk. Further studies should investigate the effect of supplementation of methionine in this patient group to improve outcomes.

Methionine as a regulator of bone remodeling with fasting

Caloric restriction improves metabolic health but is often complicated by bone loss. We studied bone parameters in humans during a 10-day fast and identified candidate metabolic regulators of bone turnover. Pro-collagen 1 intact N-terminal pro-peptide (P1NP), a bone formation marker, decreased within 3 days of fasting. Whereas dual-energy x-ray absorptiometry measures of bone mineral density were unchanged after 10 days of fasting, high-resolution peripheral quantitative CT demonstrated remodeling of bone microarchitecture. Pathway analysis of longitudinal metabolomics data identified one-carbon metabolism as fasting dependent. In cultured osteoblasts, we tested the functional significance of one-carbon metabolites modulated by fasting, finding that methionine - which surged after 3 days of fasting - affected markers of osteoblast cell state in a concentration-dependent manner, in some instances exhibiting a U-shaped response with both low and high concentrations driving putative antibone responses. Administration of methionine to mice for 5 days recapitulated some fasting effects on bone, including a reduction in serum P1NP. In conclusion, a 10-day fast in humans led to remodeling of bone microarchitecture, potentially mediated by a surge in circulating methionine. These data support an emerging model that points to a window of optimal methionine exposure for bone health.

Role of folate receptor α in the partial rejuvenation of dentate gyrus cells: Improvement of cognitive function in 21-month-old aged mice

Neuronal aging may be, in part, related to a change in DNA methylation. Thus, methyl donors, like folate and methionine, may play a role in cognitive changes associated to neuronal aging. To test the role of these metabolites, we performed stereotaxic microinjection of these molecules into the dentate gyrus (DG) of aged mice (an average age of 21 month). Folate, but not S-Adenosyl-Methionine (SAM), enhances cognition in aged mice. In the presence of folate, we observed partial rejuvenation of DG cells, characterized by the expression of juvenile genes or reorganization of extracellular matrix. Here, we have also tried to identify the mechanism independent of DNA methylation, that involve folate effects on cognition. Our analyses indicated that folate binds to folate receptor α (FRα) and, upon folate binding, FRα is transported to cell nucleus, where it is acting as transcription factor for expressing genes like SOX2 or GluN2B. In this work, we report that a FRα binding peptide also replicates the folate effect on cognition, in aged mice. Our data suggest that such effect is not sex-dependent. Thus, we propose the use of this peptide to improve cognition since it lacks of folate-mediated side effects. The use of synthetic FRα binding peptides emerge as a future strategy for the study of brain rejuvenation.

The live biotherapeutic SYNB1353 decreases plasma methionine via directed degradation in animal models and healthy volunteers

Methionine is an essential proteinogenic amino acid, but its excess can lead to deleterious effects. Inborn errors of methionine metabolism resulting from loss of function in cystathionine β-synthase (CBS) cause classic homocystinuria (HCU), which is managed by a methionine-restricted diet. Synthetic biotics are gastrointestinal tract-targeted live biotherapeutics that can be engineered to replicate the benefits of dietary restriction. In this study, we assess whether SYNB1353, an E. coli Nissle 1917 derivative, impacts circulating methionine and homocysteine levels in animals and healthy volunteers. In both mice and nonhuman primates (NHPs), SYNB1353 blunts the appearance of plasma methionine and plasma homocysteine in response to an oral methionine load. A phase 1 clinical study conducted in healthy volunteers subjected to an oral methionine challenge demonstrates that SYNB1353 is well tolerated and blunts plasma methionine by 26%. Overall, SYNB1353 represents a promising approach for methionine reduction with potential utility for the treatment of HCU.

Mutations in the promoter region of methionine transporter gene metM (Rv3253c) confer para-aminosalicylic acid (PAS) resistance in Mycobacterium tuberculosis

Tuberculosis (TB) is a significant global public health threat. Despite the long-standing use of para-aminosalicylic acid (PAS) as a second-line anti-TB drug, its resistance mechanism remains unclear. In this study, we isolated 90 mutants of PAS-resistant Mycobacterium tuberculosis (MTB) H37Ra in 7H11 solid medium and performed whole-genome sequencing, gene overexpression, transcription level comparison and amino acid level determination in MTB, and promoter activity by β-galactosidase assays in Mycobacterium smegmatis to elucidate the mechanism of PAS resistance. Herein, we found that 47 of 90 (52.2%) PAS-resistant mutants had nine different mutations in the intergenic region of metM (Rv3253c) and Rv3254. Beta-galactosidase assays confirmed that mutations increased promoter activity only for metM but not Rv3254. Interestingly, overexpression of MetM or its M. smegmatis homolog (MSMEI_1796) either by its promoter in metM's direction or by exogenous expression in MTB induced PAS resistance in a methionine-dependent manner. Therefore, drug susceptibility results for the metM promoter mutants can be misleading when using standard 7H10 or 7H9 medium, which lacks methionine. At the metabolism level, PAS treatment led to higher intracellular methionine levels in the mutants than the wild type, antagonizing PAS and conferring resistance. Furthermore, 12 different mutations in the metM promoter were identified in clinical MTB strains. In summary, we found a novel mechanism of PAS resistance in MTB. Mutations in the metM (Rv3253c) promoter upregulate metM transcription and elevate intracellular methionine, which antagonize PAS. Our findings shed new light on the mechanism of PAS resistance in MTB and highlight issues with the current PAS susceptibility culture medium.IMPORTANCEAlthough para-aminosalicylic acid (PAS) has been used to treat TB for more than 70 years, the understanding of PAS resistance mechanisms is still vague, living gaps in our ability to predict resistance and apply PAS effectively in clinical practice. This study aimed to address this knowledge gap by inducing in vitro PAS resistance in Mycobacterium tuberculosis (MTB) using 7H11 medium and discovering a new PAS resistance mechanism. Our research revealed that spontaneous mutations occurring in the promoter region of the methionine transporting gene, metM, can upregulate the expression of metM, resulting in increased intracellular transport of methionine and consequently high-level resistance of Mycobacterium tuberculosis to PAS. Notably, this resistance phenotype cannot be observed when using the commonly recommended 7H10 medium, possibly due to the lack of additional methionine supply compared with that when using the 7H11 medium. Mutations on the regulatory region of metM were also found in some clinical MTB strains. These findings may have important implications for the unexplained PAS resistance observed in clinical settings and provide insight into the failures of PAS treatment. Additionally, they underscore the importance of considering the choice of culture media when conducting drug susceptibility testing for MTB.

[Diet as a source of hydrogen sulfide and its effects on health and disease]

Introduction

Initially known for its deleterious health effects, hydrogen sulfide (H2S) has recently been recognized as a biologically important gas carrier, like nitric oxide and carbon monoxide. H2S is produced endogenously in mammalian cells by enzymatic and non-enzymatic pathways. When it is produced by the enzymatic pathway, its synthesis is carried out from the amino acid L-cysteine through the transsulfuration pathway. It can also be produced endogenously from exogenous compounds that function as H2S donors as, for example, the naturally occurring organic donors found in some plants. Currently, the role of S2H is well known as brain and cardiac protector, and its research as a therapeutic adjuvant in metabolic diseases such as obesity and type-2 diabetes is becoming increasingly important. The objective of this review is to examine how the contribution of donors and precursors of hydrogen sulfide by the diet impacts health and disease.

Genetic and molecular understanding for the development of methionine-rich maize: a holistic approach

Maize (Zea mays) is the most important coarse cereal utilized as a major energy source for animal feed and humans. However, maize grains are deficient in methionine, an essential amino acid required for proper growth and development. Synthetic methionine has been used in animal feed, which is costlier and leads to adverse health effects on end-users. Bio-fortification of maize for methionine is, therefore, the most sustainable and environmental friendly approach. The zein proteins are responsible for methionine deposition in the form of δ-zein, which are major seed storage proteins of maize kernel. The present review summarizes various aspects of methionine including its importance and requirement for different subjects, its role in animal growth and performance, regulation of methionine content in maize and its utilization in human food. This review gives insight into improvement strategies including the selection of natural high-methionine mutants, molecular modulation of maize seed storage proteins and target key enzymes for sulphur metabolism and its flux towards the methionine synthesis, expression of synthetic genes, modifying gene codon and promoters employing genetic engineering approaches to enhance its expression. The compiled information on methionine and essential amino acids linked Quantitative Trait Loci in maize and orthologs cereals will give insight into the hotspot-linked genomic regions across the diverse range of maize germplasm through meta-QTL studies. The detailed information about candidate genes will provide the opportunity to target specific regions for gene editing to enhance methionine content in maize. Overall, this review will be helpful for researchers to design appropriate strategies to develop high-methionine maize.

Markers of arterial stiffness and urinary metabolomics in young adults with early cardiovascular risk: the African-PREDICT study

INTRODUCTION

Increased exposure to risk factors in the young and healthy contributes to arterial changes, which may be accompanied by an altered metabolism.

OBJECTIVES

To increase our understanding of early metabolic alterations and how they associate with markers of arterial stiffness, we profiled urinary metabolites in young adults with cardiovascular disease (CVD) risk factor(s) and in a control group without CVD risk factors.

METHODS

We included healthy black and white women and men (N = 1202), aged 20-30 years with a detailed CVD risk factor profile, reflecting obesity, physical inactivity, smoking, excessive alcohol intake, masked hypertension, hyperglycemia, dyslipidemia and low socio-economic status, forming the CVD risk group (N = 1036) and the control group (N = 166). Markers of arterial stiffness, central systolic blood pressure (BP) and pulse wave velocity were measured. A targeted metabolomics approach was followed by measuring amino acids and acylcarnitines using a liquid chromatography-tandem mass spectrometry method.

RESULTS

In the CVD risk group, central systolic BP (adjusted for age, sex, ethnicity) was negatively associated with histidine, arginine, asparagine, serine, glutamine, dimethylglycine, threonine, GABA, proline, methionine, pyroglutamic acid, aspartic acid, glutamic acid, branched chain amino acids (BCAAs) and butyrylcarnitine (all P ≤ 0.048). In the same group, pulse wave velocity (adjusted for age, sex, ethnicity, mean arterial pressure) was negatively associated with histidine, lysine, threonine, 2-aminoadipic acid, BCAAs and aromatic amino acids (AAAs) (all P ≤ 0.044). In the control group, central systolic BP was negatively associated with pyroglutamic acid, glutamic acid and dodecanoylcarnitine (all P ≤ 0.033).

CONCLUSION

In a group with increased CVD risk, markers of arterial stiffness were negatively associated with metabolites related to AAA and BCAA as well as energy metabolism and oxidative stress. Our findings may suggest that metabolic adaptations may be at play in response to increased CVD risk to maintain cardiovascular integrity.

Methionine Sources Differently Affect Production of Reactive Oxygen Species, Mitochondrial Bioenergetics, and Growth of Murine and Quail Myoblasts In Vitro

An optimal supply of L-methionine (L-Met) improves muscle growth, whereas over-supplementation exerts adverse effects. To understand the underlying mechanisms, this study aims at exploring effects on the growth, viability, ROS production, and mitochondrial bioenergetics of C2C12 (mouse) and QM7 (quail) myoblasts additionally supplemented (100 or 1000 µM) with L-Met, DL-methionine (DL-Met), or DL-2-hydroxy-4-(methylthio)butanoic acid (DL-HMTBA). In both cell lines, all the supplements stimulated cell growth. However, in contrast to DL-Met, 1000 µM of L-Met (C2C12 cells only) or DL-HMTBA started to retard growth. This negative effect was stronger with DL-HMTBA and was accompanied by significantly elevated levels of extracellular H₂O₂, an indicator for OS, in both cell types. In addition, oversupplementation with DL-HMTBA (1000 µM) induced adaptive responses in mitochondrial bioenergetics, including reductions in basal (C2C12 and QM7) and ATP-synthase-linked (C2C12) oxygen consumption, maximal respiration rate, and reserve capacity (QM7). Only QM7 cells switched to nonmitochondrial aerobic glycolysis to reduce ROS production. In conclusion, we found a general negative effect of methionine oversupplementation on cell proliferation. However, only DL-HMTBA-induced growth retardation was associated with OS and adaptive, species-specific alterations in mitochondrial functionality. OS could be better compensated by quail cells, highlighting the role of species differences in the ability to cope with methionine oversupplementation.

Pharmaceutical Oral Formulation of Methionine as a Pediatric Treatment in Inherited Metabolic Disease

L-Methionine (Met) is an essential alpha-amino acid playing a key role in several metabolic pathways. Rare inherited metabolic diseases such as mutations affecting the MARS1 gene encoding methionine tRNA synthetase (MetRS) can cause severe lung and liver disease before the age of two years. Oral Met therapy has been shown to restore MetRS activity and improve clinical health in children. As a sulfur-containing compound, Met has a strongly unpleasant odor and taste. The objective of this study was to develop an optimized pediatric pharmaceutical formulation of Met powder, to be reconstituted with water, to obtain a stable oral suspension. Organoleptic characteristics and physicochemical stability of the powdered Met formulation and suspension were evaluated at three storage temperatures. Met quantification was assessed by a stability-indicating chromatographic method as well as microbial stability. The use of a specific fruit flavor (e.g., strawberry) with sweeteners (e.g., sucralose) was considered acceptable. No drug loss, pH changes, microbiological growth, or visual changes were observed at 23 ± 2 °C and 4 ± 2 °C with the powder formulation for 92 days, and the reconstituted suspension for at least 45 days. The developed formulation facilitates the preparation, administration, the dose adjustment and palatability of Met treatment in children.

Metoclopramide as a Potential Antipsychotic Against Long-Term Methionine Exposure in Zebrafish

Methionine (MET) contributes to brain function and is required for proper functioning of the central nervous system. However, exceptionally high levels of MET and its metabolites in plasma have been found to be toxic and can lead to cell alterations. Long-term exposure to MET has been shown to mimic psychotic symptoms in schizophrenic patients and rodents. The present study evaluated behavioral and neurochemical effects of long-term exposure to MET in zebrafish. Five groups of zebrafish were exposed to MET at a concentration of 4.5 mM for 7 days, along with acute exposure to 25 μM of clozapine and 750, 1000, and 1250 μM of metoclopramide. In contrast, the normal group was exposed to only water and dimethyl sulfoxide. After the treatment, social interaction, anxiety, memory, and locomotion of zebrafish and serotonin levels in zebrafish brains were evaluated. Our results showed that metoclopramide was not only beneficial in improving MET-induced cognitive impairment but it also prevented social withdrawal in zebrafish exposed to MET. In addition, metoclopramide reversed anxiety-like behavior, as indicated by significant changes in locomotion activity. Despite slight changes in serotonin levels in the zebrafish brain, an in vitro serotonin assay failed to demonstrate significant differences between the disease control, normal, and two treatment groups. Finally, results from the study showed that repeated administration of MET induced schizophrenia-like symptoms, although metoclopramide ameliorated the MET-mediated negative symptoms and cognitive deficits in zebrafish. Overall, our findings suggest a new perspective to further explore the antipsychotic properties of metoclopramide.

Effects of low-energy diet supplemented with betaine on growth performance, nutrient digestibility, and serum metabolomic profiles in growing pigs

Two experiments were carried out to evaluate the effects of betaine (BET) supplementation in diets with reduced net energy (NE) levels on growth performance, nutrient digestibility, and serum metabolomic profiles in growing pigs. In experiment 1, 24 growing pigs (initial body weight, BW, 30.83 ± 2.50 kg) were allotted to one of the four treatments (six replications with 1 pig per pen) in a 2 × 2 factorial arrangement, including two dietary NE levels (2475 [N-NE] or 2395 [R80-NE] kcal/kg) and two BET doses (0 or 1500 mg/kg). In experiment 2, 72 growing pigs were used in a 2 × 3 factorial arrangement, including three dietary NE levels (2475 [N-NE], 2415 [R60-NE], or 2355 [R120-NE] kcal/kg) and two BET doses (0 or 1500 mg/kg). Pigs with initial BW of 31.44 ± 1.65 kg were divided to one of the six treatments (six replications with 2 pigs per pen). In experiment 1, lowing NE concentrations increased average daily feed intake (ADFI) by 10.69% in pigs fed the diet without BET (P > 0.05). BET significantly increased ADFI in N-NE diet (P < 0.05) but had no influence on ADFI in R80-NE diet (P > 0.05). BET enhanced the apparent digestibility of crude protein (CP), dry matter (DM), organic matter (OM), gross energy (GE), and ether extract (EE) in R80-NE diet (P < 0.05). In experiment 2, lowing NE concentrations enhanced ADFI (P > 0.05) and decreased average daily gain (ADG; P < 0.05). The reduction in feed intake by BET was further enhanced as NE concentrations decreased from 2415 to 2355 kcal/kg (P < 0.10). BET reversed the elevation of serum triglyceride, alkaline phosphatase, aspartate aminotransferase, and alanine aminotransferase levels caused by R120-NE diet (P < 0.05). The concentrations of cholecystokinin and glucagon-like peptide 1 were increased by BET in pigs fed the R120-NE diet (P < 0.05). Serum metabolomics reveals that lowing dietary NE concentrations affected mainly amino acid biosynthetic pathways (P < 0.05). BET supplementation in R120-NE diet up-regulated serum BET levels and down-regulated homocysteine, DL-carnitine, and four amino acid secondary metabolites (P < 0.05). In conclusion, lowing dietary NE contents reduced the growth performance and caused metabolic abnormalities in growing pigs. However, BET decreased feed intake to a certain extent and improved the metabolic health of pigs fed the low-NE diets, which may be related to the dual regulation of amino acid metabolism and the secretion of appetite related hormones by BET.

Plasma Amino Acid Concentration in Obese Horses with/without Insulin Dysregulation and Laminitis

Laminitic horses commonly suffer from an endocrine disease such as equine metabolic syndrome. Hyperinsulinemia is considered a key factor in the pathogenesis of laminitis. Since insulin also affects protein turnover in the body, the resting plasma amino acid concentrations of obese horses that were presented for a combined glucose insulin test (CGIT) were determined. In total, 25 obese horses and two lean horses with recurrent laminitis underwent a CGIT. Of these, five were not insulin dysregulated (obese), 14 were insulin dysregulated (ID), and eight were insulin-dysregulated and laminitic (IDL). Significant differences in the resting concentrations between obese and insulin dysregulated and laminitic (citrulline p = 0.038, obese: 73.001 ± 12.661 nmol/mL, IDL: 49.194 ± 15.486 nmol/mL; GABA p = 0.02, obese: 28.234 ± 3.885 nmol/mL, IDL: 16.697 ± 1.679 nmol/mL; methionine p = 0.018, obese: 28.691 ± 5.913 nmol/mL, IDL: 20.143 ± 3.09 nmol/mL) as well as between insulin dysregulated individuals with and without laminitis (GABA p < 0.001, ID: 28.169 ± 6.739 nmol/mL) regarding three amino acids were determined. This may be an interesting approach, especially for diagnostic testing and possibly also for the feed supplements of horses at risk of developing laminitis. However, further research, including a higher number of cases, is required.

Interactions between dopamine transporter and N-methyl-d-aspartate receptor-related amino acids on cognitive impairments in schizophrenia

BACKGROUND

Cognitive impairments, the main determinants of functional outcomes in schizophrenia, had limited treatment responses and need a better understanding of the mechanisms. Dysfunctions of the dopamine system and N-methyl-d-aspartate receptor (NMDAR), the primary pathophysiologies of schizophrenia, may impair cognition. This study explored the effects and interactions of striatal dopamine transporter (DAT) and plasma NMDAR-related amino acids on cognitive impairments in schizophrenia.

METHODS

We recruited 36 schizophrenia patients and 36 age- and sex-matched healthy controls (HC). All participants underwent cognitive assessments of attention, memory, and executive function. Single-photon emission computed tomography with 99mTc-TRODAT and ultra-performance liquid chromatography were applied to determine DAT availability and plasma concentrations of eight amino acids, respectively.

RESULTS

Compared with HC, schizophrenia patients had lower cognitive performance, higher methionine concentrations, decreased concentrations of glutamic acid, cysteine, aspartic acid, arginine, the ratio of glutamic acid to gamma-aminobutyric acid (Glu/GABA), and DAT availability in the left caudate nucleus (CN) and putamen. Regarding memory scores, Glu/GABA and the DAT availability in left CN and putamen exhibited positive relationships, while methionine concentrations showed negative associations in all participants. The DAT availability in left CN mediated the methionine-memory relationship. An exploratory backward stepwise regression analysis for the four biological markers associated with memory indicated that DAT availability in left CN and Glu/GABA remained in the final model.

CONCLUSIONS

This study demonstrated the interactions of striatal DAT and NMDAR-related amino acids on cognitive impairments in schizophrenia. Future studies to comprehensively evaluate their complex interactions and treatment implications are warranted.

Hyperhomocysteinemia in acute hepatic porphyria (AHP) and implications for treatment with givosiran

INTRODUCTION

Homocysteine is a sulfur-containing amino acid formed in the intermediary metabolism of methionine. Amino acid metabolism and heme biosynthesis pathways are complexly intertwined. Plasma homocysteine elevation, hyperhomocysteinemia (HHcy), has been reported in patients with acute hepatic porphyria (AHP), a family of rare genetic disorders caused by defects in hepatic heme biosynthesis.

AREAS COVERED

This article summarizes published case series in which givosiran, a subcutaneously administered small interfering RNA approved for AHP treatment, appeared to exacerbate dysregulated homocysteine metabolism in patients with AHP. A comprehensive exploratory analysis of ENVISION trial data demonstrated that on a population level, givosiran increased homocysteine but with wide interpatient variations, and there is no proof of correlations between HHcy and changes in efficacy or safety of givosiran.

EXPERT OPINION

The strong correlation and co-increase of homocysteine and methionine suggest that HHcy associated with givosiran is likely attributable to the impaired trans-sulfuration pathway catalyzed by cystathionine β-synthase, which uses vitamin B6 as a cofactor. Data-based consensus supports monitoring total plasma homocysteine and vitamin B6, B12, and folate levels before and during givosiran treatment; supplementing with pyridoxine/vitamin B6 in patients with homocysteine levels >100 μmol/L; and involving patients with homocysteine levels >30 μmol/L in decisions to supplement.

Implications of trimethylamine N-oxide (TMAO) and Betaine in Human Health: Beyond Being Osmoprotective Compounds

Osmolytes are naturally occurring small molecular weight organic molecules, which are accumulated in large amounts in all life forms to maintain the stability of cellular proteins and hence preserve their functions during adverse environmental conditions. Trimethylamine N-oxide (TMAO) and N,N,N-trimethylglycine (betaine) are methylamine osmolytes that have been extensively studied for their diverse roles in humans and have demonstrated opposing relations with human health. These osmolytes are obtained from food and synthesized endogenously using dietary constituents like choline and carnitine. Especially, gut microbiota plays a vital role in TMAO synthesis and contributes significantly to plasma TMAO levels. The elevated plasma TMAO has been reported to be correlated with the pathogenesis of numerous human diseases, including cardiovascular disease, heart failure, kidney diseases, metabolic syndrome, etc.; Hence, TMAO has been recognized as a novel biomarker for the detection/prediction of several human diseases. In contrast, betaine acts as a methyl donor in one-carbon metabolism, maintains cellular S-adenosylmethionine levels, and protects the cells from the harmful effects of increased plasma homocysteine. Betaine also demonstrates antioxidant and anti-inflammatory activities and has a promising therapeutic value in several human diseases, including homocystinuria and fatty liver disease. The present review examines the multifarious functions of TMAO and betaine with possible molecular mechanisms towards a better understanding of their emerging and diverging functions with probable implications in the prevention, diagnosis, and treatment of human diseases.

Urinary metabolomics profiling by cardiovascular risk factors in young adults: the African Prospective study on Early Detection and Identification of Cardiovascular disease and Hypertension study

AIM

Risk factors contributes to a dysregulated metabolism and may ultimately increase the predisposition for cardiovascular disease (CVD) development. To increase our understanding of mechanistic pathways associated with CVD risk, we profiled the urinary metabolome according to individual and clusters of CVD risk factors in comparison with a control group without any risk factors.

METHODS AND RESULTS

Healthy black and white women and men ( N  = 1202), aged 20-30 years with a detailed CVD risk factor profile were included. CVD risk groups: obese, physical inactive, smoking, excessive alcohol intake, masked hypertensive, hyperglycaemic, dyslipidemic and low socioeconomic status. CVD risk clusters were based on the presence of 1, 2 and 3 or more risk factors. Liquid chromatography-tandem mass spectrometry was used to obtain urinary metabolomics data (amino acids and acylcarnities). Compared with the control group, higher levels of metabolites associated with aromatic and branched chain amino acid metabolism including phenylalanine, tyrosine and leucine/isoleucine were found in the obese, masked hypertensive, hyperglycaemic, low socioeconomic groups (all q  ≤ 0.032) and 3+ CVD risk cluster (all P  ≤ 0.034). Metabolites associated with the y-glutamyl cycle including glycine, histidine, serine, glutamine, methionine, cystine and pyroglutamic acid were found in the hyperglycaemic, low socioeconomic groups (all q  ≤ 0.050), 2 and 3+ CVD risk clusters (all P  ≤ 0.041). Metabolites associated with energetics including acetylcarnitine (lower levels), hexanoylcarnitine and decanoylcarnitine were found in the low socioeconomic group, 1 and 3+ CVD risk clusters ( q / P  ≤ 0.050) ( β -oxidation). In addition to the above-mentioned amino acids, alanine and threonine were found in the hyperglycaemic, low socioeconomic groups, 2 and 3+ CVD risk clusters (all q / P  ≤ 0.047) (glycolysis). Creatine in the obese, hyperglycaemic groups (all q  ≤ 0.049) and 3+ CVD risk cluster (all P  ≤ 0.041) (creatine pathway).

CONCLUSION

Exposure to CVD risk factors is associated with a dysregulated metabolism in the above-mentioned pathways that may precede the development of CVD.

Low-Molecular-Weight Synthetic Antioxidants: Classification, Pharmacological Profile, Effectiveness and Trends

Mounting research has been performed and published on natural antioxidants, more so than on synthetic ones, as key molecules that control oxidative damage and its pathway to disease. Since the discovery of vitamins, various fully synthetic or natural-identical compounds have been developed as stable small molecules translated into constantly active and completely controlled products which are widely exploited in the food and pharmaceutical industries. There is currently a debate within the literature about their mechanism of action, bioavailability, safety and real benefit for human health. Using a semiquantitative method and eligible criteria of selection, this review aimed to provide a very useful classification of antioxidants and a comprehensive cross-disciplinary description of 32 approved synthetic/natural-identical antioxidants, in terms of regulatory, antioxidant mechanism of action, safety issues, pharmacological properties, effectiveness in human health, timeline and future trends. Enriched interpretation of the data was obtained from summary bibliometrics, useful to portray the “good antioxidant” within the period 1966–2021 and, hopefully, to encourage further research.

A High-Methionine Diet for One-Week Induces a High Accumulation of Methionine in the Cerebrospinal Fluid and Confers Bipolar Disorder-like Behavior in Mice

Methionine (Met) is considered the most toxic amino acid in mammals. Here, we investigated biochemical and behavioral impacts of ad libitum one-week feeding of high-Met diets on mice. Adult male mice were fed the standard rodent diet that contained 0.44% Met (1×) or a diet containing 16 graded Met doses (1.2×–13×). High-Met diets for one-week induced a dose-dependent decrease in body weight and an increase in serum Met levels with a 2.55 mM peak (versus basal 53 µM) on the 12×Met diet. Total homocysteine (Hcy) levels were also upregulated while concentrations of other amino acids were almost maintained in serum. Similarly, levels of Met and Hcy (but not the other amino acids) were highly elevated in the cerebrospinal fluids of mice on the 10×Met diet; the Met levels were much higher than Hcy and the others. In a series of behavioral tests, mice on the 10×Met diet displayed increased anxiety and decreased traveled distances in an open-field test, increased activity to escape from water soaking and tail hanging, and normal learning/memory activity in a Y-maze test, which were reflections of negative/positive symptoms and normal cognitive function, respectively. These results indicate that high-Met ad libitum feeding even for a week can induce bipolar disorder-like disease models in mice.

Targeted metabolomics analysis of serum amino acid profiles in patients with Moyamoya disease

Amino acids are one of the main metabolites in the body, and provide energy for the body and brain. The purpose of this study is to provide a profile of amino acid changes in the serum of patients with Moyamoya disease (MMD) and identify potential disease biomarkers. In this paper, we quantitatively determined the serum amino acid metabolic profiles of 43 MMD patients and 42 healthy controls (HCs). T test, multivariate statistical analysis, and receiver operating characteristic (ROC) curve analysis were used to identify candidate markers. Thirty-nine amino acids were quantified, and 12 amino acid levels differed significantly between the MMD patients and HCs. Moreover, based on ROC curve analysis, four amino acid (L-methionine, L-glutamic acid, β-alanine and o-phosphoserine) biomarkers showed high sensitivity and specificity (AUC > 0.90), and showed the best sensitivity and specificity in MetaboAnalyst 5.0 using binary logistic regression analysis. We have provided serum amino acid metabolic profiles of MMD patients, and identified four potential biomarkers which may both provide clinicians with an objective diagnostic method for early detection of MMD and further our understanding of MMD pathogenesis.

Methionine supplementation for multi-organ dysfunction in MetRS-related pulmonary alveolar proteinosis

INTRODUCTION

Pulmonary alveolar proteinosis related to mutations in the methionine tRNA synthetase (MARS1) gene is a severe, early-onset disease that results in death before the age of 2 years in one-third of patients. It is associated with a liver disease, growth failure and systemic inflammation. As methionine supplementation in yeast models restored normal enzymatic activity of the synthetase, we studied the tolerance, safety and efficacy of daily oral methionine supplementation in patients with severe and early disease.

METHODS

Four patients received methionine supplementation and were followed for respiratory, hepatic, growth, and inflammation-related outcomes. Their course was compared to those of historical controls. Reactive oxygen species (ROS) production by patient monocytes before and after methionine supplementation was also studied.

RESULTS

Methionine supplementation was associated with respiratory improvement, clearance of the extracellular lipoproteinaceous material, and discontinuation of whole-lung lavage in all patients. The three patients who required oxygen or non-invasive ventilation could be weaned off within 60 days. Liver dysfunction, inflammation, and growth delay also improved or resolved. At a cellular level, methionine supplementation normalised the production of reactive oxygen species by peripheral monocytes.

CONCLUSION

Methionine supplementation was associated with important improvements in children with pulmonary alveolar proteinosis related to mutations in the MARS1 gene. This study paves the way for similar strategies for other tRNA synthetase deficiencies.

A planetary health perspective on synthetic methionine

Methionine is an amino acid that humans and farm animals must derive from food. This metabolite, a tightly regulated resource in ecosystems, has become a mass commodity in the global economy, with well over 1 million tons being produced annually from petroleum to fortify livestock feed. Viewed from the standpoint of planetary health, anthropogenic methionine synthesis is an important enabler of low-cost animal protein production, with interdependent but unexamined effects on human health and ecosystems. At a time when agrochemical engineering is shifting the way sulphur is assimilated and moves up our food chain, research suggests that dietary methionine restriction alone captures many healthspan benefits noted with calorie restriction. As such, methionine synthesis is an excellent exemplar of planetary scale anthropogenic activity that manifests at the molecular scale of cellular metabolism, with potential systemic effects on human health. In this Personal View we establish the scale and historical trajectory of the methionine industry and provide a preliminary model for tracing this amino acid through the food supply into the human body. We draw together insights across disparate publications of applied animal agriculture, human nutrition, and biomedical research to call for cross-disciplinary dialogue on responsible use of methionine-augmentation technologies.

Association of dietary sulfur amino acid intake with mortality from diabetes and other causes

PURPOSE

Sulfur amino acid (SAA) consumption in Western countries is far greater than recommended levels. In preclinical studies, reduced SAA intake enhanced longevity and reduced risk for numerous chronic diseases. The current objective was to examine for associations between the intake of total SAA, including methionine (Met) and cysteine (Cys), and all-cause and disease-specific mortality US adults.

METHODS

This prospective analysis included 15,083 US adult participants (mean age = 46.7 years) from the Third National Examination and Nutritional Health Survey (NHANES III, 1988-1994) with available mortality status (National Death Registry, 1988-2011). Dietary SAA intake was obtained from 24-h recall data. Associations between quintile (Q) of SAA intake (expressed as absolute intake or protein density) and mortality were assessed using Cox proportional hazard models and expressed as hazard ratio (HR).

RESULTS

During follow-up (mean = 16.9 years), 4636 deaths occurred. After multivariable adjustment (including demographics and traditional risk factors, such as fat and other micronutrients intake), diabetes-caused mortality rates were nearly threefold higher in the highest compared to lowest SAA intake quintiles [HR_Q5-Q1 total SAA_, 2.68 (1.46-4.90); HR_Q5-Q1 methionine, 2.45 (1.37-4.38); HR_Q5-Q1 cysteine, 2.91 (1.57-5.37)] (P < 0.01)]. Higher total SAA protein density was also associated with diabetes-caused mortality [HR_Q5-Q1 1.75 (1.31-2.35)]. Associations between SAA intake and all-cause mortality, and mortality caused by other major diseases were not detected.

CONCLUSION

Results suggest that high-SAA diets are associated with increased risk for diabetes mortality and that lowering intake towards to Recommended Dietary Allowance levels could lead to reductions in lifetime risk.

Epigenetic Mechanisms Mediate Nicotine-Induced Reward and Behaviour in Zebrafish

Nicotine induces long-term changes in the neural activity of the mesocorticolimbic reward pathway structures. The mechanisms involved in this process have not been fully characterized. The hypothesis discussed here proposed that epigenetic regulation participates in the installation of persistent adaptations and long-lasting synaptic plasticity generated by nicotine action on the mesolimbic dopamine neurons of zebrafish. The epigenetic mechanisms induced by nicotine entail histone and DNA chemical modifications, which have been described to lead to changes in gene expression. Among the enzymes that catalyze epigenetic chemical modifications, histone deacetylases (HDACs) remove acetyl groups from histones, thereby facilitating DNA relaxation and making DNA more accessible to gene transcription. DNA methylation, which is dependent on DNA methyltransferase (DNMTs) activity, inhibits gene expression by recruiting several methyl binding proteins that prevent RNA polymerase binding to DNA. In zebrafish, phenylbutyrate (PhB), an HDAC inhibitor, abolishes nicotine rewarding properties together with a series of typical reward-associated behaviors. Furthermore, PhB and nicotine alter long- and short-term object recognition memory in zebrafish, respectively. Regarding DNA methylation effects, a methyl group donor L-methionine (L-met) was found to dramatically reduce nicotine-induced conditioned place preference (CPP) in zebrafish. Simultaneous treatment with DNMT inhibitor 5-aza-2’-deoxycytidine (AZA) was found to reverse the L-met effect on nicotine-induced CPP as well as nicotine reward-specific effects on genetic expression in zebrafish. Therefore, pharmacological interventions that modulate epigenetic regulation of gene expression should be considered as a potential therapeutic method to treat nicotine addiction.

Methionine Diet Evoked Hyperhomocysteinemia Causes Hippocampal Alterations, Metabolomics Plasma Changes and Behavioral Pattern in Wild Type Rats

L-methionine, an essential amino acid, plays a critical role in cell physiology. High intake and/or dysregulation in methionine (Met) metabolism results in accumulation of its intermediate(s) or breakdown products in plasma, including homocysteine (Hcy). High level of Hcy in plasma, hyperhomocysteinemia (hHcy), is considered to be an independent risk factor for cerebrovascular diseases, stroke and dementias. To evoke a mild hHcy in adult male Wistar rats we used an enriched Met diet at a dose of 2 g/kg of animal weight/day in duration of 4 weeks. The study contributes to the exploration of the impact of Met enriched diet inducing mild hHcy on nervous tissue by detecting the histo-morphological, metabolomic and behavioural alterations. We found an altered plasma metabolomic profile, modified spatial and learning memory acquisition as well as remarkable histo-morphological changes such as a decrease in neurons' vitality, alterations in the morphology of neurons in the selective vulnerable hippocampal CA 1 area of animals treated with Met enriched diet. Results of these approaches suggest that the mild hHcy alters plasma metabolome and behavioural and histo-morphological patterns in rats, likely due to the potential Met induced changes in "methylation index" of hippocampal brain area, which eventually aggravates the noxious effect of high methionine intake.

Methionine Supplementation Abolishes Nicotine-Induced Place Preference in Zebrafish: a Behavioral and Molecular Analysis

In zebrafish, nicotine is known to regulate sensitivity to psychostimulants via epigenetic mechanisms. Little however is known about the regulation of addictive-like behavior by DNA methylation processes. To evaluate the influence of DNA methylation on nicotine-induced conditioned place preference (CPP), zebrafish were exposed to methyl supplementation through oral L-methionine (Met) administration. Met was found to reduce dramatically nicotine-induced CPP as well as behaviors associated with drug reward. The reduction was associated with the upregulation of DNA methyltransferases (DNMT1 and 3) as well as with the downregulation of methyl-cytosine dioxygenase-1 (TET1) and of nicotinic receptor subunits. Met also increased the expression of histone methyltransferases in nicotine-induced CPP groups. It reversed the nicotine-induced reduction in the methylation at α7 and NMDAR1 gene promoters. Treatment with the DNMT inhibitor 5-aza-2'-deoxycytidine (AZA) was found to reverse the effects of Met in structures of the reward pathway. Interestingly, Met did not modify the amount of the phospho-form of CREB (pCREB), a key factor establishing nicotine conditioning, whereas AZA increased pCREB levels. Our data suggest that nicotine-seeking behavior is partially dependent on DNA methylation occurring probably at specific gene loci, such as α7 and NMDAR1 receptor gene promoters. Overall, they suggest that Met should be considered as a potential therapeutic drug to treat nicotine addiction.

Plasma Sulfur Amino Acids and Risk of Cerebrovascular Diseases: A Nested Case-Control Study in the EPIC-Norfolk Cohort

BACKGROUND AND PURPOSE

B-vitamin supplements lower circulating concentrations of homocysteine and may reduce stroke incidence. Homocysteine concentrations are associated with the incidence of stroke but other sulfur-containing compounds in the related metabolic pathway have not yet been investigated for an association with incident cerebrovascular diseases.

METHODS

Nested within the EPIC (European Prospective Investigation Into Cancer and Nutrition)-Norfolk cohort, we established a case-control study with 480 incident cases of cerebrovascular diseases and 480 controls matched by age, sex, and year of baseline examination (1993-1997). Using baseline plasma samples, we assayed sulfur-containing compounds including methionine, homocysteine, cystathionine, cysteine, glutathione, and taurine with liquid chromatography-tandem mass spectrometry. We examined the association of concentrations of each of the compounds and the ratio of methionine to homocysteine (representing activity of one-carbon metabolism) with risk of incident cerebrovascular diseases, adjusted for potential confounders.

RESULTS

Plasma methionine and the methionine/homocysteine ratio were inversely associated with risk of cerebrovascular diseases, with odds ratios per 1 SD of 0.83 (95% CI, 0.72-0.96) and 0.82 (95% CI, 0.71-0.95), respectively. The association of methionine remained significant after adjustment for homocysteine. None of the other examined compounds was significantly associated with incident cerebrovascular diseases.

CONCLUSIONS

These findings suggest that greater availability of methionine, an essential amino acid, may play a role in the prevention of cerebrovascular diseases and explain the previously recognized link between elevated homocysteine and stroke. Further research is needed to determine causation and the potential of circulating methionine as a target in cerebrovascular disease prevention.

Lessons Learned from Inherited Metabolic Disorders of Sulfur-Containing Amino Acids Metabolism

The metabolism of sulfur-containing amino acids (SAAs) requires an orchestrated interplay among several dozen enzymes and transporters, and an adequate dietary intake of methionine (Met), cysteine (Cys), and B vitamins. Known human genetic disorders are due to defects in Met demethylation, homocysteine (Hcy) remethylation, or cobalamin and folate metabolism, in Hcy transsulfuration, and Cys and hydrogen sulfide (H2S) catabolism. These disorders may manifest between the newborn period and late adulthood by a combination of neuropsychiatric abnormalities, thromboembolism, megaloblastic anemia, hepatopathy, myopathy, and bone and connective tissue abnormalities. Biochemical features include metabolite deficiencies (e.g. Met, S-adenosylmethionine (AdoMet), intermediates in 1-carbon metabolism, Cys, or glutathione) and/or their accumulation (e.g. S-adenosylhomocysteine, Hcy, H2S, or sulfite). Treatment should be started as early as possible and may include a low-protein/low-Met diet with Cys-enriched amino acid supplements, pharmacological doses of B vitamins, betaine to stimulate Hcy remethylation, the provision of N-acetylcysteine or AdoMet, or experimental approaches such as liver transplantation or enzyme replacement therapy. In several disorders, patients are exposed to long-term markedly elevated Met concentrations. Although these conditions may inform on Met toxicity, interpretation is difficult due to the presence of additional metabolic changes. Two disorders seem to exhibit Met-associated toxicity in the brain. An increased risk of demyelination in patients with Met adenosyltransferase I/III (MATI/III) deficiency due to biallelic mutations in the MATIA gene has been attributed to very high blood Met concentrations (typically >800 μmol/L) and possibly also to decreased liver AdoMet synthesis. An excessively high Met concentration in some patients with cystathionine β-synthase deficiency has been associated with encephalopathy and brain edema, and direct toxicity of Met has been postulated. In summary, studies in patients with various disorders of SAA metabolism showed complex metabolic changes with distant cellular consequences, most of which are not attributable to direct Met toxicity.

Metabolism of Sulfur-Containing Amino Acids: How the Body Copes with Excess Methionine, Cysteine, and Sulfide

Metabolism of excess methionine (Met) to homocysteine (Hcy) by transmethylation is facilitated by the expression of methionine adenosyltransferase (MAT) I/III and glycine N-methyltransferase (GNMT) in liver, and a lack of either enzyme results in hypermethioninemia despite normal concentrations of MATII and methyltransferases other than GNMT. The further metabolism of Hcy by the transsulfuration pathway is facilitated by activation of cystathionine β-synthase (CBS) by S-adenosylmethionine (SAM) as well as the relatively high KM of CBS for Hcy. Transmethylation plus transsulfuration effects catabolism of the Met molecule along with transfer of the sulfur atom of Met to serine to synthesize cysteine (Cys). Oxidation and excretion of Met sulfur depend upon Cys catabolism and sulfur oxidation pathways. Excess Cys is oxidized by cysteine dioxygenase 1 (CDO1) and further metabolized to taurine or sulfate. Some Cys is normally metabolized by desulfhydration pathways, and the hydrogen sulfide (H2S) produced is further oxidized to sulfate. If Cys or Hcy concentrations are elevated, Cys or Hcy desulfhydration can result in excess H2S and thiosulfate production. Excess Cys or Met may also promote their limited metabolism by transamination pathways.

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.

Chemistry and Biochemistry of Sulfur Natural Compounds: Key Intermediates of Metabolism and Redox Biology

Sulfur contributes significantly to nature chemical diversity and thanks to its particular features allows fundamental biological reactions that no other element allows. Sulfur natural compounds are utilized by all living beings and depending on the function are distributed in the different kingdoms. It is no coincidence that marine organisms are one of the most important sources of sulfur natural products since most of the inorganic sulfur is metabolized in ocean environments where this element is abundant. Terrestrial organisms such as plants and microorganisms are also able to incorporate sulfur in organic molecules to produce primary metabolites (e.g., methionine, cysteine) and more complex unique chemical structures with diverse biological roles. Animals are not able to fix inorganic sulfur into biomolecules and are completely dependent on preformed organic sulfurous compounds to satisfy their sulfur needs. However, some higher species such as humans are able to build new sulfur-containing chemical entities starting especially from plants' organosulfur precursors. Sulfur metabolism in humans is very complicated and plays a central role in redox biochemistry. The chemical properties, the large number of oxidation states, and the versatile reactivity of the oxygen family chalcogens make sulfur ideal for redox biological reactions and electron transfer processes. This review will explore sulfur metabolism related to redox biochemistry and will describe the various classes of sulfur-containing compounds spread all over the natural kingdoms. We will describe the chemistry and the biochemistry of well-known metabolites and also of the unknown and poorly studied sulfur natural products which are still in search for a biological role.

Withdrawal Effects Following Methionine Exposure in Adult Zebrafish

Methionine (Met) has important functions for homeostasis of various species, including zebrafish. However, the increased levels of this amino acid in plasma, a condition known as hypermethioninemia, can lead to cell alterations. Met is crucial for the methylation process and its excesses interfere with the cell cycle, an effect that persists even after the removal of this amino acid. Some conditions may lead to a transient increase of this amino acid with unexplored persistent effects of Met exposure. In the present study, we investigated the behavioral and neurochemical effects after the withdrawal of Met exposure. Zebrafish were divided into two groups: control and Met-treated group (3 mM) for 7 days and after maintained for 8 days in tanks containing only water. In the eighth day post-exposure, we evaluated locomotion, anxiety, aggression, social interaction, and memory, as well as oxidative stress parameters, amino acid, and neurotransmitter levels in the zebrafish brain. Our results showed that 8 days after Met exposure, the treated group showed decreased locomotion and aggressive responses, as well as impaired aversive memory. The Met withdrawal did not change thiobarbituric acid reactive substances, reactive oxygen species, and nitrite levels; however, we observed a decrease in antioxidant enzymes superoxide dismutase, catalase, and total thiols. Epinephrine and cysteine levels were decreased after the Met withdrawal whereas carnitine and creatine levels were elevated. Our findings indicate that a transient increase in Met causes persistent neurotoxicity, observed by behavioral and cognitive changes after Met withdrawal and that the mechanisms underlying these effects are related to changes in antioxidant system, amino acid, and neurotransmitter levels.

Methionine dietary supplementation potentiates ionizing radiation-induced gastrointestinal syndrome

Methionine is an essential amino acid needed for a variety of processes in living organisms. Ionizing radiation depletes tissue methionine concentrations and leads to the loss of DNA methylation and decreased synthesis of glutathione. In this study, we aimed to investigate the effects of methionine dietary supplementation in CBA/CaJ mice after exposure to doses ranging from 3 to 8.5 Gy of ¹³⁷Cs of total body irradiation. We report that mice fed a methionine-supplemented diet (MSD; 19.5 vs. 6.5 mg/kg in a methionine-adequate diet, MAD) developed acute radiation toxicity at doses as low as 3 Gy. Partial body irradiation performed with hindlimb shielding resulted in a 50% mortality rate in MSD-fed mice exposed to 8.5 Gy, suggesting prevalence of radiation-induced gastrointestinal syndrome in the development of acute radiation toxicity. Analysis of the intestinal microbiome demonstrated shifts in the gut ecology, observed along with the development of leaky gut syndrome and bacterial translocation into the liver. Normal gut physiology impairment was facilitated by alterations in the one-carbon metabolism pathway and was exhibited as decreases in circulating citrulline levels mirrored by decreased intestinal mucosal surface area and the number of surviving crypts. In conclusion, we demonstrate that a relevant excess of methionine dietary intake exacerbates the detrimental effects of exposure to ionizing radiation in the small intestine.NEW & NOTEWORTHY Methionine supplementation, instead of an anticipated health-promoting effect, sensitizes mice to gastrointestinal radiation syndrome. Mechanistically, excess of methionine negatively affects intestinal ecology, leading to a cascade of physiological, biochemical, and molecular alterations that impair normal gut response to a clinically relevant genotoxic stressor. These findings speak toward increasing the role of registered dietitians during cancer therapy and the necessity of a solid scientific background behind the sales of dietary supplements and claims regarding their benefits.

NMR-based plasma metabolic profiling in patients with unstable angina

OBJECTIVES

Unstable angina (UA) is a form of the acute coronary syndrome (ACS) that affects more than a third of the population before age 70. Due to the limitations of diagnostic tests, appropriate identification of UA is difficult. In this study, we proceeded to investigate metabolite profiling in UA patients compared with controls to determine potential candidate biomarkers.

MATERIALS AND METHODS

Ninety-four plasma samples from UA and 32 samples from controls were analyzed based on 1H NMR spectroscopy. The raw data were processed, analyzed, and subjected to partial least squares-discrimination analysis (PLS-DA), a supervised classification method with a good separation of control and UA patients was observed. The most important variables (VIP) ≥1 were selected and submitted to MetaboAnalyst pathway enrichment to identify the most important ones.

RESULTS

We identified 17 disturbed metabolites in UA patients in comparison with the controls. These metabolites are involved in various biochemical pathways such as steroid hormone biosynthesis, aminoacyl-tRNA biosynthesis, and lysine degradation. Some of the metabolites were deoxycorticosterone, 17-hydroxyprogesterone, androstenedione, androstanedione, etiocholanolone, estradiol, 2-hydroxyestradiol, 2-hydroxyestrone, 2-methoxyestradiol, and 2-methoxyestrone. In order to determine test applicability in diagnosing UA, a diagnostic model was further created using the receiver operator characteristic (ROC) curve. The areas under the curve (AUC), sensitivity, specificity, and precision were 0.87, 90%, 65%, and 91%, respectively, for diagnosing of UA.

CONCLUSION

These metabolites could not only be useful for the diagnosis of UA patients but also provide more information for further deciphering of the biological processes of UA.

Association of sulfur amino acid consumption with cardiometabolic risk factors: Cross-sectional findings from NHANES III

BACKGROUND

An average adult American consumes sulfur amino acids (SAA) at levels far above the Estimated Average Requirement (EAR) and recent preclinical data suggest that higher levels of SAA intake may be associated with a variety of aging-related chronic diseases. However, there are little data regarding the relationship between SAA intake and chronic disease risk in humans. The aim of this study was to examine the associations between consumption of SAA and risk factors for cardiometabolic diseases.

METHODS

The sample included 11,576 adult participants of the Third National Examination and Nutritional Health Survey (NHANES III) Study (1988-1994). The primary outcome was cardiometabolic disease risk score (composite risk factor based on blood cholesterol, triglycerides, HDL, C-reactive protein (CRP), uric acid, glucose, blood urea nitrogen (BUN), glycated hemoglobin, insulin, and eGFR). Group differences in risk score by quintiles of energy-adjusted total SAA, methionine (Met), and cysteine (Cys) intake were determined by multiple linear regression after adjusting for age, sex, BMI, smoking, alcohol intake, and dietary factors. We further examined for associations between SAA intake and individual risk factors.

FINDINGS

Mean SAA consumption was > 2.5-fold higher than the EAR. After multivariable adjustment, higher intake of SAA, Met, and Cys were associated with significant increases in composite cardiometabolic disease risk scores, independent of protein intake, and with several individual risk factors including serum cholesterol, glucose, uric acid, BUN, and insulin and glycated hemoglobin (p < 0.01).

INTERPRETATION

Overall, our findings suggest that diets lower in SAA (close to the EAR) are associated with reduced risk for cardiometabolic diseases. Low SAA dietary patterns rely on plant-derived protein sources over meat derived foods. Given the high intake of SAA among most adults, our findings may have important public health implications for chronic disease prevention.

FUNDING

This study does not have any funding.

Cystathionine beta synthase deficiency and brain edema associated with methionine excess under betaine supplementation: Four new cases and a review of the evidence

CBS deficient individuals undergoing betaine supplementation without sufficient dietary methionine restriction can develop severe hypermethioninemia and brain edema. Brain edema has also been observed in individuals with severe hypermethioninemia without concomitant betaine supplementation. We systematically evaluated reports from 11 published and 4 unpublished patients with CBS deficiency and from additional four cases of encephalopathy in association with elevated methionine. We conclude that, while betaine supplementation does greatly exacerbate methionine accumulation, the primary agent causing brain edema is methionine rather than betaine. Clinical signs of increased intracranial pressure have not been seen in patients with plasma methionine levels below 559 μmol/L but occurred in one patient whose levels did not knowingly exceed 972 μmol/L at the time of manifestation. While levels below 500 μmol/L can be deemed safe it appears that brain edema can develop with plasma methionine levels close to 1000 μmol/L. Patients with CBS deficiency on betaine supplementation need to be regularly monitored for concordance with their dietary plan and for plasma methionine concentrations. Recurrent methionine levels above 500 μmol/L should alert clinicians to check for clinical signs and symptoms of brain edema and review dietary methionine intake. Levels approaching 1000 μmol/L do increase the risk of complications and levels exceeding 1000 μmol/L, despite best dietetic efforts, should be acutely addressed by reducing the prescribed betaine dose.

Sulfur-containing amino acid supplementation to gilts from late pregnancy to lactation altered offspring's intestinal microbiota and plasma metabolites

Maternal nutrition during late pregnancy and lactation is highly involved with the offspring's health status. The study was carried out to evaluate the effects of different ratios of methionine and cysteine (Met/Cys: 46% Met, 51% Met, 56% Met, and 62% Met; maintained with 0.78% of total sulfur-containing amino acids; details in "Materials and methods") supplements in the sows' diet from late pregnancy to lactation on offspring's plasma metabolomics and intestinal microbiota. The results revealed that the level of serum albumin, calcium, iron, and magnesium was increased in the 51% Met group compared with the 46% Met, 56% Met, and 62% Met groups. Plasma metabolomics results indicated that the higher ratios of methionine and cysteine (0.51% Met, 0.56% Met, and 0.62% Met)-supplemented groups enriched the level of hippuric acid, retinoic acid, riboflavin, and δ-tocopherol than in the 46% Met group. Furthermore, the 51% Met-supplemented group had a higher relative abundance of Firmicutes compared with the other three groups (P < 0.05), while the 62% Met-supplemented group increased the abundance of Proteobacteria compared with the other three groups (P < 0.05) in piglets' intestine. These results indicated that a diet consisting with 51% Met is the optimum Met/Cys ratio from late pregnancy to lactation can maintain the offspring's health by improving the serum biochemical indicators and altering the plasma metabolomics profile and intestinal gut microbiota composition, but higher proportion of Met/Cys may increase the possible risk to offspring's health.

[Homoarginine level and methionine-homocysteine balance in patients with ischemic heart disease.]

The level of homoarginine (hArg) in terms of prognostic significance may exceed the natriuretic peptides and other well-known markers according to the latest data about the progression of cardiovascular diseases. The lack of data on the association of hArg levels with levels of other metabolites makes it difficult to understand its role in the pathogenesis of cardiovascular diseases. Relationships of hArg and other amino acids, including methionine (Met) and total homocysteine (tHcy), and their ratio in patients with ischemic heart disease were evaluated. The study included 74 patients with coronary heart disease (57 men and 17 women) aged 62 (57 - 67) years before coronary artery bypass surgery and 27 healthy people of similar age. In patients, the level of hArg was almost 2 times lower (p < 0.05) than in healthy individuals and rates lower than 1.4 μM were in half of them. The statistically significant decrease (p = 0.0025) of the Met/tHcy ratio corresponded to a decrease in the level of hArg. This ratio did not correlate with glucose level or body mass index. Less statistical significance of hArg correlation with levels of Met or tHcy separately was observed. In the subgroup of patients with hAarg level above 2.1 μM, a lower incidence of myocardial infarction was noted. Thus, a low hArg level is associated with impaired metabolism of sulfur-containing amino acids involved in transmethylation reactions, in patients with ischemic heart disease. The Met/tHcy ratio, closely correlating with the level of hArg, apparently reveals a link between the reactions of creatine formation and transmethylation, highlighting a cohort of patients with the most profound and dangerous changes in tissue metabolism.

Ncl1-mediated metabolic rewiring critical during metabolic stress

Accumulation of cysteine induces translational defects and metabolic rewiring that are abrogated by leucine in a transfer RNA (tRNA) methyltransferase NCL1-dependent manner in yeast.

Nutritional limitation has been vastly studied; however, there is limited knowledge of how cells maintain homeostasis in excess nutrients. In this study, using yeast as a model system, we show that some amino acids are toxic at higher concentrations. With cysteine as a physiologically relevant example, we delineated the pathways/processes that are altered and those that are involved in survival in the presence of elevated levels of this amino acid. Using proteomics and metabolomics approach, we found that cysteine up-regulates proteins involved in amino acid metabolism, alters amino acid levels, and inhibits protein translation—events that are rescued by leucine supplementation. Through a comprehensive genetic screen, we show that leucine-mediated effect depends on a transfer RNA methyltransferase (NCL1), absence of which decouples transcription and translation in the cell, inhibits the conversion of leucine to ketoisocaproate, and leads to tricarboxylic acid cycle block. We therefore propose a role of NCL1 in regulating metabolic homeostasis through translational control.

The Chemistry of Protein Oxidation in Food

Oxidation is one of the deterioration reactions of proteins in food, the importance of which is comparable to others such as Maillard, lipation, or protein-phenol reactions. While research on protein oxidation has led to a precise understanding of the processes and consequences in physiological systems, knowledge about the specific effects of protein oxidation in food or the role of "oxidized" dietary protein for the human body is comparatively scarce. Food protein oxidation can occur during the whole processing axis, from primary production to intestinal digestion. The present review summarizes the current knowledge and mechanisms of food protein oxidation from a chemical, technological, and nutritional-physiological viewpoint and gives a comprehensive classification of the individual reactions. Different analytical approaches are compared, and the relationship between oxidation of food proteins and oxidative stress in vivo is critically evaluated.

A critical review of zebrafish schizophrenia models: Time for validation?

Schizophrenia is a mental disorder that affects 1% of the population worldwide and is manifested as a broad spectrum of symptoms, from hallucinations to memory impairment. It is believed that genetic and/or environmental factors may contribute to the occurrence of this disease. Recently, the zebrafish has emerged as a valuable and attractive model for various neurological disorders including schizophrenia. In this review, we describe current pharmacological models of schizophrenia with special emphasis on providing insights into the pros and cons of using zebrafish as a behavioural model of this disease. Moreover, we highlight the advantages and utility of using zebrafish for elucidating the genetic mechanisms underlying this psychiatric disorder. We believe that the zebrafish has high potential also in the area of precision medicine and may complement the development of therapeutics, especially for pharmacoresistant patients.

Neonatal methionine adenosyltransferase I/III deficiency with abnormal signal intensity in the central tegmental tract

Methionine adenosyltransferase I/III (MAT I/III) deficiency is characterized by persistent hypermethioninemia. The clinical manifestations in cases with MAT I/III deficiency vary from a complete lack of symptoms to neurological problems associated with brain demyelination. We experienced a neonatal case with MAT I/III deficiency, in which severe hypermethioninemia was detected during the newborn screening test. The patient gradually showed hyperreflexia, foot clonus, and irritability from the age of 1 month onwards, and his brain magnetic resonance imaging scans showed abnormal signal intensity in the bilateral central tegmental tracts. His neurological manifestations improved after the S-adenosylmethionine (SAMe) treatment, deteriorated after discontinuation of SAMe, and re-improved owing to re-administration of SAMe. He achieved normal neurodevelopment through SAMe and methionine restriction therapy. Lack of SAMe as well as severe hypermethioninemia were thought to contribute towards the clinical psychophysical state. Moreover, impaired MAT I/III activity contributed to the development of neurological disorder from the early neonatal period.

Diet Composition Differentially Affects Insulin Pathway Compromised and Control Flies

The insulin pathway is an anabolic pathway that controls, amongst other things, glucose homeostasis. It is an evolutionarily conserved pathway. Disruptions in insulin pathway functions can lead to diabetic states. Diabetes, a very common occurrence in modern life, afflicts a significant portion of the population of developed and developing countries worldwide. Yet, few studies have addressed the evolution of diabetic states on a long-term basis. Here, we cultured three different insulin pathway signaling compromised flies (heteroallelic mutant combinations, akin to diabetes mellitus type II) and wild type control flies, for the extent of one generation in different isocaloric diets fed at libitum, with or without extra methionine added. All fly stocks have a homogenized genetic background. We measured weight, total lipid, and carbohydrate content of adults at two different time points, and survival of adults reared in some of the different diets. Results show that, despite the fact that all diet regimes allow survival of at least a fraction of flies to adulthood, life histories are significantly different. Higher protein content diets promote better survival compared to higher percentage lipid and carbohydrate diets, and added methionine promotes survival in moderately reduced protein content diets. In mutants, survival is significantly reduced, and added methionine generally has an effect, albeit a more modest one. Our results highlight the value of higher percentage protein diets, and differences in effects in “healthy” versus “diabetic” states. They also show that added methionine, proposed as a “sensor” for protein content in food for flies, leads to differential effects depending on the adequacy of the diet regime.

Impact of sulfur-containing amino acids on the plasma metabolomics and intestinal microflora of the sow in late pregnancy

Which optimum ratio of Met/Cys is better to maintain the health status of the sow during late pregnancy?