Sensing of nutrients and microbes in the gut

The importance of the gut microbiome and its signals for a healthy nervous system and the multifaceted mechanisms of neuropsychiatric disorders

Increasing evidence links the gut microbiome and the nervous system in health and disease. This narrative review discusses current views on the interaction between the gut microbiota, the intestinal epithelium, and the brain, and provides an overview of the communication routes and signals of the bidirectional interactions between gut microbiota and the brain, including circulatory, immunological, neuroanatomical, and neuroendocrine pathways. Similarities and differences in healthy gut microbiota in humans and mice exist that are relevant for the translational gap between non-human model systems and patients. There is an increasing spectrum of metabolites and neurotransmitters that are released and/or modulated by the gut microbiota in both homeostatic and pathological conditions. Dysbiotic disruptions occur as consequences of critical illnesses such as cancer, cardiovascular and chronic kidney disease but also neurological, mental, and pain disorders, as well as ischemic and traumatic brain injury. Changes in the gut microbiota (dysbiosis) and a concomitant imbalance in the release of mediators may be cause or consequence of diseases of the central nervous system and are increasingly emerging as critical links to the disruption of healthy physiological function, alterations in nutrition intake, exposure to hypoxic conditions and others, observed in brain disorders. Despite the generally accepted importance of the gut microbiome, the bidirectional communication routes between brain and gut are not fully understood. Elucidating these routes and signaling pathways in more detail offers novel mechanistic insight into the pathophysiology and multifaceted aspects of brain disorders.

Effects of Low Protein Diet on Production Performance and Intestinal Microbial Composition in Pigs

In order to study the effects of a low protein diet on the production performance and intestinal microbiota composition of Hexi pigs, twenty-seven Hexi pigs with an initial body weight of 60.50 ± 2.50 kg were randomly divided into three groups (control group (CG), group 1 (G1), and group 2 (G2)) and participated in a 60-day finishing trial. The CG was fed a normal protein level diet with a protein level of 16.0%, and G1 and G2 were fed a low protein level diet with protein levels of 14.0% and 12.0%, respectively. The results showed that the low protein level diet had no significant effect on the production performance of Hexi pigs, compared with the CG, the slaughter rate of G1 and G2 increased by 2.49% (p > 0.05) and 6.18% (p > 0.05), the shear force decreased by 2.43% (p > 0.05) and 15.57% (p > 0.05), the cooking loss decreased by 24.02% (p < 0.05) and 21.09% (p > 0.05), and the cooking percentage increased by 13.20% (p > 0.05) and 11.59% (p > 0.05). From 45 min to 24 h and 48 h after slaughter, each group of pH decreased by 1.02, 0.66, and 0.42. For muscle flesh color, the lightness (L) increased by 13.31% (p > 0.05) and 18.01% (p > 0.05) in G1 and G2 and the yellowness (b) increased by 7.72% (p > 0.05) and 13.06% (p > 0.05). A low protein level diet can improve the intestinal flora richness and diversity of growing and finishing pigs. In the jejunum, the ACE index (899.95), Simpson index (0.90), and Shannon (4.75) index were higher in G1 than in the other groups, but the Chao1 index (949.92) was higher in G2 than in the remaining two groups. Proteobacteria, Actinobacteria, Euryarchaeota, and Verrucomicrobia were significantly higher in G1 than in the CG. The relative abundances of Lactobacillus, Terrisporobacter, and Megasphaera in G1 was significantly higher than in the CG (p < 0.05). In the cecum, the ACE index (900.93), Chao1 index (879.10), Simpson index (0.94), and Shannon (5.70) index were higher in G1 than in the remaining groups. The Spirochaetes in G2 were significantly higher than in the other groups, but the Verrucomicrobia was significantly lower than in the other groups. The relative abundances of Lactobacillus were higher in G1 and G2 than in the CG (p > 0.05). The relative abundances of unidentified_Clostridiales and Terrisporobacter in G2 were significantly lower than in the CG (p < 0.05). The relative abundance of Turicibacter in G1 was significantly lower than in the CG (p < 0.05). The relative abundances of other bacterial genera in G1 and G2 were increased by 30.81% (p > 0.05) and 17.98% (p > 0.05).

Lactobacillus rhamnosus GG ATCC53103 and Lactobacillus plantarum JL01 improved nitrogen metabolism in weaned piglets by regulating the intestinal flora structure and portal vein metabolites

At present, most studies have shown that probiotics have a positive regulatory effect on the nutritional metabolism of the body, but the mechanism is still unclear. Here, 48 piglets were divided into four groups. The control group was not fed probiotics, the Lac group was fed L. Rhamnosus GG ATCC53103, the Rha group was fed L. Plantarum JL01, and the mix group was fed two types of probiotics. Nitrogen metabolism and mRNA levels of mTOR and S6K in skeletal muscle were observed in each group. Then, metagenome and non-targeted metabonomics were used to observe the changes of intestinal microorganisms and plasma metabolites in portal channels after probiotics feeding. Finally, we combined the results of omics analysis to reveal the mechanism of probiotics on nitrogen metabolism in weaned piglets. The results showed that L. Rhmnosus GG ATCC53103 and L. Plantarum JL01 increased nitrogen apparent digestibility, nitrogen deposition rate, and nitrogen utilization rate of weaned piglets (P < 0.05); the relative expression of mTOR and SK6 mRNA in skeletal muscle increased significantly (P < 0.05). When L. rhamnosus GG ATCC53103 and L. plantarum JL01 were combined, we found that Clostridium and Prevotella significantly increased in the jejunum (P < 0.05). The relative abundance of Lactobacillus, Ruminococcus, Streptococcus, and Prevotella in the ileum increased significantly (P < 0.05). Compared with the control group, L-Tryptophan, 3-Phosphonyloxypyruvate, cis-Aconitate, and Carbamoyl phosphate were significantly increased in the mixed group portal vein. The result of the combinatorial analysis showed that the significantly increased microorganisms could encode the enzyme genes for the synthesis of L-Tryptophan, 3-Phosphonooxypyruvate, cis-Aconitate, and Carbamoyl phosphate. In summary, our results demonstrated that L. Rhamnosus GG ATCC53103 and L. Plantarum JL01 could stimulate the expression of skeletal muscle protein synthesis genes of weaned piglets by modulating the structure of the gut microbiota and its metabolites, thereby improving nitrogen metabolism in weaned piglets.

Interactions between gut microbiota and Parkinson's disease: The role of microbiota-derived amino acid metabolism

Non-motor symptoms (NMS) of Parkinson's disease (PD), such as constipation, sleep disorders, and olfactory deficits, may emerge up to 20 years earlier than motor symptoms. A series of evidence indicates that the pathology of PD may occur from the gastrointestinal tract to the brain. Numerous studies support that the gut microbiota communicates with the brain through the immune system, special amino acid metabolism, and the nervous system in PD. Recently, there is growing recognition that the gut microbiota plays a vital role in the modulation of multiple neurochemical pathways via the “gut microbiota-brain axis” (GMBA). Many gut microbiota metabolites, such as fatty acids, amino acids, and bile acids, convey signaling functions as they mediate the crosstalk between gut microbiota and host physiology. Amino acids' abundance and species alteration, including glutamate and tryptophan, may disturb the signaling transmission between nerve cells and disrupt the normal basal ganglia function in PD. Specific amino acids and their receptors are considered new potential targets for ameliorating PD. The present study aimed to systematically summarize all available evidence on the gut microbiota-derived amino acid metabolism alterations associated with PD.

Chemical Metabolism of Xenobiotics by Gut Microbiota

Among the gut microbiota's newly explored roles in human biology is the ability to modify the chemical structures of foreign compounds (xenobiotics). A growing body of evidence has now provided sufficient acumen on the role of the gut microbiota on xenobiotic metabolism, which could have an intense impact on the therapy for various diseases in the future. Gut microbial xenobiotic metabolites have altered bioavailability, bioactivity and toxicity and can intervene with the actions of human xenobiotic-metabolizing enzymes to affect the destiny of other ingested molecules. These modifications are diverse and could lead to physiologically important consequences. In the current manuscript we aim to review the data currently available on how the gut microbiota directly modifies drugs, dietary compounds, chemicals, pollutants, pesticides and herbal supplements.