Gut microbial disturbance affects allergic diseases including asthma, atopic dermatitis (AD) via the aberrant immune response. Some Bifidobacterial species and strains have been reported to improve AD via modulating immune-microbe interactions in patients. However, the effective metabolites and mechanism of alleviating AD in bifidobacteria remain to be elucidated. This study aimed to explore the microbial metabolite and mechanism of Bifidobacterium longum to improve AD. Based on shotgun metagenomic sequencing and UHPLC Q-Exactive-MS targeted metabolic experiments in vitro and in vivo, we focused on tryptophan metabolism and indole derivatives, which are endogenous ligands for aryl hydrocarbon receptor (AHR). Indole-3-carbaldehyde (I3C), a tryptophan metabolite of B. longum CCFM1029 activated AHR-mediated immune signaling pathway to improve AD symptoms in animal and clinical experiments. B. longum CCFM1029 upregulated tryptophan metabolism and increased I3C to suppress aberrant T helper 2 type immune responses, but these benefits were eliminated by AHR antagonist CH223191. Furthermore, B. longum CCFM1029 reshaped gut microbial composition in AD patients, increased fecal and serum I3C, and maintained the abundance of Lachnospiraceae related to tryptophan metabolism of gut microbiota. The results suggested that based on the interactions of the gut-skin axis, B. longum CCFM1029 upregulated tryptophan metabolism and produced I3C to activate AHR-mediated immune response, alleviating AD symptoms. Indole derivates, microbial metabolites of tryptophan, may be the potential metabolites of bifidobacteria to alleviate AD via the AHR signaling pathway.

Atopic dermatitis (AD) is a public health concern and is increasing in prevalence in urban areas. Recent advances in sequencing technology have demonstrated that the development of AD not only associate with the skin microbiome but gut microbiota. Gut microbiota plays an important role in allergic diseases including AD. The hypothesis of the “gut-skin” axis has been proposed and the cross-talk mechanism between them has been gradually demonstrated in the research. Probiotics contribute to the improvement of the intestinal environment, the balance of immune responses, regulation of metabolic activity. Most studies suggest that probiotic supplements may be an alternative for the prevention and treatment of AD. This study aimed to discuss the effects of probiotics on the clinical manifestation of AD based on gut microbial alterations. Here we reviewed the gut microbial alteration in patients with AD, the association between gut microbiota, epidermal barrier, and toll-like receptors, and the interaction of probiotics and gut microbiota. The potential mechanisms of probiotics on alleviating AD via upregulation of epidermal barrier and regulation of immune signaling had been discussed, and their possible effective substances on AD had been explored. This provides the supports for targeting gut microbiota to attenuate AD.

The gut microbiota could affect human health and disease. Although disease-associated microbiota alteration has been extensively investigated in the Chinese population, a nationwide Chinese gut microbiota baseline is still lacking. Here we performed 16 S rRNA gene sequencing on fecal samples from 2678 healthy Chinese individuals, who belonged to eight ethnic groups and resided in 63 counties/cities of 28 provinces. We identified four enterotypes, three of which were enriched forPrevotella,Bacteroides,andEscherichia, respectively, whereas the fourth one had no dominant genus. By assessing the association between the gut microbiota and 20 variables belonging to six categories, geography, demography, diet, urbanization, lifestyle, and sampling month, we revealed that geography explained the largest microbiota variation, and clarified the distinct patterns in the associations with staple food type, ethnicity, and urban/rural residence. Specifically, the gut microbiota of Han Chinese and ethnic minority groups from the same sites was more alike than that of the same ethnic minority groups from different sites. Individuals consuming wheat as staple food were predicted to have more microbial genes involving in glucan 1,3-beta-glucosidase andS-adenosyl-l-methionine biosynthesis than those who consumed rice, based on functional prediction. Besides, an appreciable effect of urbanization on decreased intra-individual diversity, increased inter-individual diversity, and increased proportion of theBacteroidesenterotype was observed. Collectively, our study provided a nationwide gut microbiota baseline of the Chinese population and knowledge on important covariates, which are fundamental to translational microbiota research.

Lactobacilli are inherent microorganisms in the human gut and are widely used in the food processing industries due to their probiotic properties. Prophages were reportedly hidden in numerous Lactobacillus genomes and can potentially contaminate entire batches of fermentation or modulate the intestinal microecology once they are released.

Evidence linking Faecalibacterium prausnitzii abundance to nonalcoholic fatty liver disease (NAFLD) is accumulating; however, the causal relationship remains obscure. In this study, 12 F. prausnitzii strains were orally administered to high fat diet fed C57BL/6J mice for 12 weeks to evaluate the protective effects of F. prausnitzii on NAFLD. We found that five F. prausnitzii strains, A2-165, LB8, ZF21, PL45, and LC49, significantly restored serum lipid profiles and ameliorated glucose intolerance, adipose tissue dysfunction, hepatic steatosis, inflammation, and oxidative stress in a mouse model of NAFLD. Moreover, two strains, LC49 and LB8, significantly enhanced short-chain fatty acid (SCFA) production and modulated the gut microbiota. Based on the combined analysis of linear discriminant analysis effect size and microbial communities, the core microbiome related to NAFLD comprised Odoribacter, Roseburia, Erysipelatoclostridium, Tyzzerella, Faecalibaculum, Blautia, and Acetatifactor, and the last five genera can be reversed by treatment with the LC49 and LB8 strains. Additionally, the LC49 and LB8 strains enriched Lactobacillus, Ileibacterium, Faecalibacterium, Dubosiella, and Bifidobacterium and downregulated pathways involving carbohydrate metabolism, amino acid metabolism, and fatty acid biosynthesis. Interestingly, LC49 supplementation also upregulated tryptophan metabolism, glutathione metabolism, and valine, leucine, and isoleucine degradation, which might be related to NAFLD prevention. Collectively, F. prausnitzii LC49 and LB8 exerted considerable anti-NAFLD and microbiota-regulating effects, indicating their potential as probiotic agents for NAFLD treatment.