D-amino Acids Ameliorate Experimental Colitis and Cholangitis by Inhibiting Growth of Proteobacteria: Potential Therapeutic Role in Inflammatory Bowel Disease.

BACKGROUND & AIMS: D-amino acids, the chiral counterparts of protein L-amino acids, were primarily produced and utilized by microbes, including those in the human gut. However, little was known about how orally administered or microbe-derived D-amino acids affected the gut microbial community or gut disease progression. METHODS: The ratio of D- to L-amino acids was analyzed in feces and blood from patients with ulcerative colitis (UC) and healthy controls. Also, composition of microbe was analyzed from patients with UC. Mice were treated with D-amino acid in dextran sulfate sodium colitis model and liver cholangitis model. RESULTS: The ratio of D- to L-amino acids was lower in the feces of patients with UC than that of healthy controls. Supplementation of D-amino acids ameliorated UC-related experimental colitis and liver cholangitis by inhibiting growth of Proteobacteria. Addition of D-alanine, a major building block for bacterial cell wall formation, to culture medium inhibited expression of the ftsZ gene required for cell fission in the Proteobacteria Escherichia coli and Klebsiella pneumoniae, thereby inhibiting growth. Overexpression of ftsZ restored growth of E. coli even when D-alanine was present. We found that D-alanine not only inhibited invasion of pathological K. pneumoniae into the host via pore formation in intestinal epithelial cells but also inhibited growth of E. coli and generation of antibiotic-resistant strains. CONCLUSIONS: D-amino acids might have potential for use in novel therapeutic approaches targeting Proteobacteria-associated dysbiosis and antibiotic-resistant bacterial diseases by means of their effects on the intestinal microbiota community.

Hepatic Adenosine Triphosphate Reduction Through the Short-Chain Fatty Acids-Peroxisome Proliferator-Activated Receptor γ-Uncoupling Protein 2 Axis Alleviates Immune-Mediated Acute Hepatitis in Inulin-Supplemented Mice.

How liver tolerance is disrupted in immune-mediated liver injury is currently unclear. There is also insufficient information available regarding susceptibility, precipitation, escalation, and perpetuation of autoimmune hepatitis. To explore how dietary fiber influences hepatic damage, we applied the concanavalin A (ConA)-induced acute immune-mediated liver injury model in mice fed a diet supplemented with 6.8% inulin, a water-soluble fermentable fiber. Twelve hours after ConA administration, inulin-supplemented diet-fed mice demonstrated significantly alleviated hepatic damage histologically and serologically, with down-regulation of hepatic interferon-γ and tumor necrosis factor and reduced myeloperoxidase (MPO)-producing neutrophil infiltration. Preconditioning with an inulin-supplemented diet for 2 weeks significantly reduced hepatic adenosine triphosphate (ATP) content; suramin, a purinergic P2 receptor antagonist, abolished the protective effect. Of note, the portal plasma derived from mice fed the inulin-supplemented diet significantly alleviated ConA-induced immune-mediated liver injury. Mechanistically, increased portal short-chain fatty acid (SCFA) levels, such as those of acetate and butyrate, by inulin supplementation leads to up-regulation of hepatic γ-type peroxisome proliferator-activated receptor (Pparg) and uncoupling protein 2 (Ucp2), which uncouples mitochondrial ATP synthesis downstream of PPARγ. Pparg down-regulating small interfering RNA cancelled the protective effect of inulin supplementation against MPO-producing neutrophil infiltration and the subsequent immune-mediated liver injury, suggesting that the SCFA-PPARγ-UCP2 axis plays a key role in the protective effect by inulin supplementation. Moreover, significant changes in the gut microbiota, including increased operational taxonomic units in genera Akkermansia and Allobaculum, also characterized the protective effect of the inulin-supplemented diet. Conclusion: There is a possible unraveled etiopathophysiological link between the maintenance of liver tolerance and dietary fiber. The SCFA-PPARγ-UCP2 axis may provide therapeutic targets for immune-mediated liver injury in the future.

Intestinal Dysbiosis and Biotin Deprivation Induce Alopecia through Overgrowth of Lactobacillus murinus in Mice.

Metabolism by the gut microbiota affects host physiology beyond the gastrointestinal tract. Here, we find that antibiotic-induced dysbiosis, in particular, overgrowth of Lactobacillus murinus (L. murinus), impaired gut metabolic function and led to the development of alopecia. While deprivation of dietary biotin per se did not affect skin physiology, its simultaneous treatment with vancomycin resulted in hair loss in specific pathogen-free (SPF) mice. Vancomycin treatment induced the accumulation of L. murinus in the gut, which consumes residual biotin and depletes available biotin in the gut. Consistently, L. murinus induced alopecia when monocolonized in germ-free mice fed a biotin-deficient diet. Supplementation of biotin can reverse established alopecia symptoms in the SPF condition, indicating that L. murinus plays a central role in the induction of hair loss via a biotin-dependent manner. Collectively, our results indicate that luminal metabolic alterations associated with gut dysbiosis and dietary modifications can compromise skin physiology.

Direct effects of corticosterone on ATP production by mitochondria from immortalized hypothalamic GT1-7 neurons.

Glucocorticoids are known to decrease intracellular ATP levels in the brain. This study was performed to investigate whether corticosterone at physiological levels depresses mitochondrial ATP production by directly acting on mitochondria. Mitochondria were isolated from immortalized hypothalamic GT1-7 neurons. ATP levels were determined using a luciferase-luciferin assay. When malate, alpha-ketoglutarate or pyruvate was used as a respiration substrate, corticosterone at > or =100 nM decreased ATP production by 10%. In contrast, corticosterone did not affect ATP production when succinate or N,N,N',N'-tetramethyl-p-phenylenediamine+ascorbate were used. To investigate the specificity of corticosterone inhibition, we examined several steroids. All steroids tested suppressed mitochondrial ATP production by 10% at a concentration of 100 nM, in a manner similar to that of corticosterone. To examine the effects of corticosterone on GT1-7 cell physiology, we incubated GT1-7 cells with t-butyl hydroperoxide (t-BuOOH) with corticosterone. Corticosterone largely enhanced t-BuOOH-induced cell death. These results indicate that corticosterone non-specifically inhibits mitochondrial ATP production by suppressing electron transfer from NADH to the electron transfer chain through complex I. Partial inhibition of mitochondrial ATP production by corticosterone may contribute to oxidative stress-induced cell death.