Lactobacillus Rhamnosus Reshapes Gut Microbes and Modulates L- kynurenine Metabolism to Decrease Susceptibility to Heroin Addiction in Mice

Abstract Heroin addiction is a public health problem that currently poses a serious threat to human health and a global concern. Lactobacillus rhamnosus is one of the most widely researched probiotics and has been applied to the treatment of multiple psychiatric disorders. We aimed to explore the mechanisms by which Lactobacillus rhamnosus alleviated heroin addiction based on the gut microbiome and metabolism. Firstly, we assessed the effect of a Lactobacillus rhamnosus intervention on the heroin addiction process using a conditioned positional preference experiment (CPP) and results showed that Lactobacillus rhamnosus significantly reduced and delayed the heroin addiction susceptibility and extent. We further assessed the impact of gut microbiota on heroin-addicted mice treated with Lactobacillus rhamnosus. We found that the gut microbiota of heroin-addicted mice was disturbed, characterized by an increase in α-diversity and a decrease in β-diversity, a disproportionate level of Firmicutes and Bacteroidetes, with a higher abundance of Actinomycetes. Lactobacillus rhamnosus significantly restored gut microbiota diversity in mice, increasing the abundance of Firmicutes, and decreasing the abundance of Bacteroidetes and Actinobacteria. At the genus level, Lactobacillus rhamnosus reduced the numbers of harmful bacteria such as Helicobacter and Enterorhabdus and expanded the relative abundance of helpful bacteria such as Akkermansia muciniphila and Bifidobacterium. Furthermore, we examined the metabolic alterations in the intestine, serum and the cortex of heroin-addicted mice separately and found out biomarkers. Notably, our study found that L-kynurenine, a key marker, showed similar trends in the gut, serum, and cerebral cortex. L-kynurenine was decreased in heroin-addicted mice, and intervention by Lactobacillus rhamnosus reversed this shift, leading to speculation that L-kynurenine may play as a key mediator of the brain-gut axis. In conclusion, our study indicated that Lactobacillus rhamnosus potentially alleviated heroin addiction by altering gut flora and metabolic disturbances.