Tryptophan (Trp) is an essential amino acid that can be metabolized via endogenous and exogenous pathways, including the Kynurenine Pathway, the 5-Hydroxyindole Pathway (also the Serotonin pathway), and the Microbial pathway. Of these, the Microbial Trp metabolic pathways in the gut have recently been extensively studied for their production of bioactive molecules. The gut microbiota plays an important role in host metabolism and immunity, and microbial Trp metabolites can influence the development and progression of various diseases, including inflammatory, cardiovascular diseases, neurological diseases, metabolic diseases, and cancer, by mediating the body’s immunity. This review briefly outlines the crosstalk between gut microorganisms and Trp metabolism in the body, starting from the three metabolic pathways of Trp. The mechanisms by which microbial Trp metabolites act on organism immunity are summarized, and the potential implications for disease prevention and treatment are highlighted.

Type 2 diabetes (T2D) is a commonly diagnosed condition that has been extensively studied. The composition and activity of gut microbes, as well as the metabolites they produce (such as short-chain fatty acids, lipopolysaccharides, trimethylamine N-oxide, and bile acids) can significantly impact diabetes development. Treatment options, including medication, can enhance the gut microbiome and its metabolites, and even reverse intestinal epithelial dysfunction. Both animal and human studies have demonstrated the role of microbiota metabolites in influencing diabetes, as well as their complex chemical interactions with signaling molecules. This article focuses on the importance of microbiota metabolites in type 2 diabetes and provides an overview of various pharmacological and dietary components that can serve as therapeutic tools for reducing the risk of developing diabetes. A deeper understanding of the link between gut microbial metabolites and T2D will enhance our knowledge of the disease and may offer new treatment approaches. Although many animal studies have investigated the palliative and attenuating effects of gut microbial metabolites on T2D, few have established a complete cure. Therefore, conducting more systematic studies in the future is necessary.

The objective of this study was to examine longitudinal trends in the prevalence of dogs that are successfully immunized against rabies virus (as measured by sufficient serum antibodies) in Changsha, an urban center of China. The secondary objective was to investigate the factors affecting the seroprevalence of rabies virus antibodies in dogs. In this study, 4515 canine serum samples were collected from 57 pet hospitals (immunization points) during the period of 2015–2021 in five major urban areas of Kaifu, Furong, Tianxin, Yuhua, and Yuelu in Changsha, China. The enzyme-linked immunosorbent assay (ELISA) method was used to analyze the level and trend of rabies virus antibodies in serum and further evaluate the potential factors affecting the immunization effect from five factors: sex, age, time interval after most recent vaccination and sample collection, number of vaccinations, and vaccine manufacturer. The results showed that the seroconversion from the urban dog in Changsha steadily increased from 46.13% to 73.38% during 2015–2017. The seropositivity prevalence remained above the international standard (70%) from 2018 to 2020 and up to 90.99% in 2021. Further analysis showed that the seroconversion of rabies virus among dogs was significantly affected by the age, the number of vaccinations, time interval after the most recent vaccination and sample collection, and vaccine manufacturer, while sex had less influence. The overall rabies vaccination situation in urban areas of Changsha generally meets international standards, with only a few areas showing low levels of antibodies in dogs after vaccination and risk of infectiousness. Therefore, it is recommended that the first vaccination should be given when the dog is about three months old and regularly repeated every year after that. At the same time, antibody concentrations in dogs, especially in newborn puppies and older dogs, need to be tested promptly after vaccination at the required time to ensure that they are at a high level of immune protection, which can strengthen the supervision of rabies.

Inflammatory bowel disease (IBD) is a chronic disease of unknown etiology with a progressive and destructive course and an increasing incidence worldwide. Dietary peptides have a variety of biological functions and are effective anti-inflammatories and antioxidants, making them a prospective class of material for treating intestinal inflammation. Our study investigated the association between Ile–Arg–Trp (IRW), a dietary oligopeptide, and intestinal microbial changes during the relief of colitis using different concentrations of IRW. We found that IRW can significantly alleviate mouse colonic barrier damage caused by dextran sulphate sodium salt (DSS) and promote intestinal health. The results of microbial community composition showed that the relative abundance of Bacillota and Lactobacillus in the gut microbiota at different concentrations of IRW was significantly increased and that the abundance of Bacteroides was suppressed. Surprisingly, the relative abundance of Odoribacter also received regulation by IRW concentration and had a positive correlation with acetic acid. IRW at 0.02 mg/mL and 0.04 mg/mL significantly altered the abundance of Bacillota, Odoribacter, and Lactobacillus.