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Microbiome dysbiosis resulting in altered metabolite profiles may be associated with certain diseases, including inflammatory bowel diseases (IBD), which are characterized by active intestinal inflammation. Several studies have indicated the beneficial anti-inflammatory effect of metabolites from gut microbiota, such as short-chain fatty acids (SCFAs) and/or D-amino acids in IBD therapy, through orally administered dietary supplements. In the present study, the potential gut protective effects of d-methionine (D-Met) and/or butyric acid (BA) have been investigated in an IBD mouse model. We have also built an IBD mouse model, which was cost-effectively induced with low molecular weight DSS and kappa-carrageenan. Our findings revealed that D-Met and/or BA supplementation resulted in the attenuation of the disease condition as well as the suppression of several inflammation-related gene expressions in the IBD mouse model. The data shown here may suggest a promising therapeutic potential for improving symptoms of gut inflammation with an impact on IBD therapy. However, molecular metabolisms need to be further explored.

Htoo et al discuss the effects of D-methionine compared with L-methionine on N retention, gut morphology and antioxidant status of weaned pigs. A N-balance study was conducted to compare the effect of D-methionine (D-Met) or L-methionine (L-Met) supplementation on N balance, gut morphology and antioxidant status of weaned pigs. These data indicate that D-Met and L-Met are equally efficient to support N retention, intestinal morphology and oxidative status in weaned pigs.

Background: There are close links between chemotherapy-induced intestinal mucositis and microbiota dysbiosis. Previous studies indicated that D-methionine was an excellent candidate for a chemopreventive agent. Here, we investigated the effects of D-methionine on cisplatin-induced mucositis. Materials and methods: Male Wistar rats (176–200 g, 6 weeks old) were given cisplatin (5 mg/kg) and treated with D-methionine (300 mg/kg). Histopathological, digestive enzymes activity, oxidative/antioxidant status, proinflammatory/anti-inflammatory cytokines in intestinal tissues were measured. Next-generation sequencing technologies were also performed to investigate the gut microbial ecology. Results: D-methionine administration increased villus length and crypt depth and improved digestive enzyme (leucine aminopeptidase, sucrose and alkaline phosphatase) activities in the brush-border membrane of cisplatin-treated rats (p < 0.05). Furthermore, D-methionine significantly attenuated oxidative stress and inflammatory reaction and increased interleukin-10 levels in cisplatin-induced intestinal mucositis (p < 0.05). Cisplatin administration resulted in high relative abundances of Deferribacteres and Proteobacteria and a low diversity of the microbiota when compared with control groups, D-methionine only and cisplatin plus D-methionine. Cisplatin markedly increased comparative abundances of Bacteroides caccae, Escherichia coli, Mucispirillum schaedleri, Bacteroides uniformis and Desulfovibrio C21-c20, while Lactobacillus was almost completely depleted, compared with the control group. There were higher abundances of Lactobacillus, Lachnospiraceae, and Clostridium butyrium in cisplatin plus D-methionine rats than in cisplatin rats. D-methionine treatment alone significantly increased the number of Lactobacillus reuteri. Conclusion: D-methionine protects against cisplatin-induced intestinal damage through antioxidative and anti-inflammatory effects. By enhancing growth of beneficial bacteria (Lachnospiraceae and Lactobacillus), D-methionine attenuates gut microbiome imbalance caused by cisplatin and maintains gut homeostasis.

A validated liquid chromatography–tandem mass spectrometry method was developed for the simultaneous determination of d- and l-amino acids in human serum. Under the optimum conditions, except for dl-proline, l-glutamine, and d-lysine, the enantioseparation of the other 19 enantiomeric pairs of proteinogenic amino acids and nonchiral glycine was achieved with a CROWNPAK CR-I(+) chiral column within 13 min. The lower limits of quantitation for l-amino acids (including glycine) and d-amino acids were 5–56.25 μM and 0.625–500 nM, respectively, in human serum. The intraday precision and interday precision for all the analytes were less than 15%, and the accuracy ranged from −12.84% to 12.37% at three quality control levels. The proposed method, exhibiting high rapidity, enantioresolution, and sensitivity, was successfully applied to the quantification of d- and l-amino acid levels in serum from hepatocellular carcinoma patients and healthy individuals. The serum concentrations of l-arginine, l-isoleucine, l-aspartate, l-tryptophan, l-alanine, l-methionine, l-serine, glycine, l-valine, l-leucine, l-phenylalanine, l-threonine, d-isoleucine, d-alanine, d-glutamate, d-glutamine, d-methionine, and d-threonine were significantly reduced in the hepatocellular carcinoma patients compared with the healthy individuals (P < 0.01). d-Glutamate and d-glutamine were identified as the most downregulated serum markers (fold change greater than 1.5), which deserves further attention in hepatocellular carcinoma research.

Occult bacterial infections represent a worldwide health problem. Differentiating active bacterial infection from sterile inflammation can be difficult using current imaging tools. Present clinically viable methodologies either detect morphologic changes (CT/ MR), recruitment of immune cells ( 111 In-WBC SPECT), or enhanced glycolytic flux seen in inflammatory cells ( 18 F-FDG PET). However, these strategies are often inadequate to detect bacterial infection and are not specific for living bacteria. Recent approaches have taken advantage of key metabolic differences between prokaryotic and eukaryotic organisms, allowing easier distinction between bacteria and their host. In this report, we exploited one key difference, bacterial cell wall biosynthesis, to detect living bacteria using a positron-labeled D-amino acid. After screening several 14 C D-amino acids for their incorporation into E. coli in culture, we identified D-methionine as a probe with outstanding radiopharmaceutical potential. Based on an analogous procedure to that used for L-[methyl- 11 C]methionine ([ 11 C] L-Met), we developed an enhanced asymmetric synthesis of D-[methyl- 11 C]methionine ([ 11 C] D-Met), and showed that it can rapidly and selectively differentiate both E. coli and S. aureus infections from sterile inflammation in vivo . We believe that the ease of [ 11 C] D-Met radiosynthesis, coupled with its rapid and specific in vivo bacterial accumulation, make it an attractive radiotracer for infection imaging in clinical practice.

Purpose This study examined whether combining antioxidants could enhance protection and permit lower dosing for treating noise-induced hearing loss (NIHL). The therapeutic effects of D-methionine (DMET) and N-acetylcysteine (NAC) were evaluated in a guinea pig model. Methods Ninety-six guinea pigs were randomly assigned to eight groups: control, saline, three NAC-only groups (100, 150, 200 mg/kg), and three NAC + DMET groups (100, 200, 400 mg/kg). One hour after six hours of broadband noise exposure, treatments were administered intraperitoneally every 12 h for seven days. Auditory brainstem responses (ABR) were measured before exposure and on day 14. Cochlear tissues were analyzed for Na⁺/K⁺-ATPase and Ca²⁺-ATPase activities and lipid peroxidation (LPO) levels. Results No significant body weight differences were observed between saline and treated groups. NAC alone and in combination with DMET improved ABR thresholds in a dose-dependent manner. The combined NAC (200 mg/kg) + DMET (400 mg/kg) group achieved complete ABR recovery. Noise-induced reductions in ATPase activities were dose-dependently reversed by both treatments. The highest-dose combination restored 87.3% of Na⁺/K⁺-ATPase and 94.7% of Ca²⁺-ATPase activity compared to controls. LPO levels declined with increasing NAC doses, with NAC 200 mg/kg alone showing the greatest reduction. Conclusions Combined NAC (200 mg/kg) and DMET (400 mg/kg) yielded the most substantial functional protection against NIHL. This combination was accompanied by lower LPO levels and higher Na⁺/K⁺-ATPase and Ca²⁺-ATPase activities in the cochlear lateral wall, indicating a potential role in maintaining cochlear homeostasis following acoustic injury.

The Escherichia coli methionine ABC transporter MetNI exhibits both high-affinity transport toward L-methionine and broad specificity toward methionine derivatives, including D-methionine. In this work, we characterize the transport of D-methionine derivatives by the MetNI transporter. Unexpectedly, the N229A substrate-binding deficient variant of the cognate binding protein MetQ was found to support high MetNI transport activity toward D-selenomethionine. We determined the crystal structure at 2.95 Å resolution of the ATPγS-bound MetNIQ complex in the outward-facing conformation with the N229A apo MetQ variant. This structure revealed conformational changes in MetQ providing substrate access through the binding protein to the transmembrane translocation pathway. MetQ likely mediates uptake of methionine derivatives through two mechanisms: in the methionine-bound form delivering substrate from the periplasm to the transporter (the canonical mechanism) and in the apo form by facilitating ligand binding when complexed to the transporter (the noncanonical mechanism). This dual role for substrate-binding proteins is proposed to provide a kinetic strategy for ABC transporters to transport both high- and low-affinity substrates present in a physiological concentration range.

The objective of this study was to compare the effects of supplementation with two methionine isoforms, L-methionine (L-Met) or D-methionine (D-Met), on transcriptome expression in broiler chickens under acute heat stress. A total of 240 one-day-old chicks were randomly assigned to one of four treatments in a 2 × 2 factorial arrangement: thermo-neutral vs. acute heat-stress and L-Met vs. D-Met supplementation. On day 14, the heat-stressed group was exposed to 32°C for 5 h, while the others remained at 25°C. Six chicks were randomly selected per treatment and total RNA was isolated from whole blood, ileum, and liver tissues. Two RNA samples from each tissue of each treatment group were randomly selected and pooled in equal amounts. A total of 1.87 billion raw reads obtained from 36 samples (four treatments × three tissues × three composited replicates) were mapped to the reference genome build (Gallus_gallus-5.0) and used to identify differentially expressed genes (DEGs) using DESeq2. Functional enrichment of DEGs was tested using DAVID. Comparing the two isoforms of supplemented methionine, two, three, and ten genes were differentially expressed (> 1 or < -1 log 2 fold change) in whole blood, ileum, and liver, respectively. A total of 38, 71, and 16 genes were differentially expressed in response to the interaction between heat stress and Met isoforms in the blood, ileum, and liver, respectively. Three-tissue-specific DEGs were functionally enriched for regulation of cholesterol homeostasis and metabolism, glucose metabolism, and vascular patterning. Chicks fed with L-Met had lower immune (e.g., IL4I1 and SERPINI1 ) and intestinal angiogenic responses (e.g., FLT1 and FGD5 ), and stable glucose and lipid metabolism (e.g., PCK1 and LDLR ) under heat stress conditions. In conclusion, unlike D-Met, L-Met supplementation seems to help maintain physiological homeostasis and enhances cellular defense systems against external stresses like high environmental temperature.

A novel class of chiral sulfonium salts, derived from L- and D-methionine, was designed and successfully employed for the diastereoselective synthesis of epoxy amides. This new methodology of asymmetric epoxidation was exploited for the stereoselective construction of fused polycyclic ethers, which are structural motifs present in a great variety of natural products of marine origin. This methodology proved to be useful for the synthesis of the tricyclic A–C system contained in yessotoxin and adriatoxin, and also in many other related natural products of marine origin belonging to the fused polycyclic ether toxins.

Enterococcus faecalis is the most frequent species present in post-treatment disease and plays a significant role in persistent periapical infections following root canal treatment. Its ability to persist in stressful environments is inter alia, due to its ability to form biofilms. The presence of certain D-amino acids (DAAs) has previously been shown to reduce formation of Bacillus subtilis biofilms. The aims of this investigation were to determine if DAAs disrupt biofilms in early and late growth stages for clinical E. faecalis strains and to test their efficacy in disrupting E. faecalis biofilms grown in sub-minimum inhibitory concentrations of commonly used endodontic biocides. From thirty-seven E. faecalis strains, the ten \"best\" biofilm producers were used to test the ability of a mixture containing D-leucine, D-methionine, D-tyrosine and D-tryptophan to reduce biofilm growth over a period of 24, 72 and 144 hours and when compared to their cognate L-Amino Acids (LAAs). We have previously shown that sub-MIC levels of tetracycline and sodium hypochlorite promotes biofilm growth in clinical strains of E. faecalis. DAAs were therefore tested for their effectiveness to reduce biofilm growth in the presence of sub-minimal concentrations of sodium hypochlorite (NaOCl-0.031%) and Odontocide™ (0.25% w/v), and in the presence of Odontopaste™ (0.25% w/v). DAAs significantly reduced biofilm formation for all strains tested in vitro, while DAAs significantly reduced biofilm formation compared to LAAs. The inhibitory effect of DAAs on biofilm formation was concentration dependent. DAAs were also shown to be effective in reducing E. faecalis biofilms in the presence of Odontopaste™ and sub-MIC levels of NaOCl and Odontocide™. The results suggest that the inclusion of DAAs into current endodontic procedures may reduce E. faecalis biofilms.