Metformin alleviates choline diet-induced TMAO elevation in C57BL/6J mice by influencing gut-microbiota composition and functionality

Trimethylamine-N-oxide (TMAO), a gut-microbiota-dependent metabolite generated from its dietary precursors such as choline, has been identified as an independent risk factor for atherosclerosis. Metformin is the most widely used drug for the treatment of type 2 diabetes (T2D), which has therapeutic effects on hyperglycemia accelerated atherosclerosis. A growing body of evidence suggest that metformin plays a therapeutic role by regulating the structure and metabolic function of gut microbiota. However, whether metformin has an impact on gut-microbiota-mediated TMAO production from choline remains obscure. In this study, the oral administration of metformin significantly reduced choline diet-increased serum TMAO in choline diet-fed C57BL/6J mice. The diversity analysis based on 16S rRNA gene sequencing of C57BL/6J mice fecal samples indicated that metformin markedly changed the gut-microbiota composition. Metformin was positively correlated with the enrichment of different intestinal bacteria such as Bifidobacterium and Akkermansia and a lower cutC (a choline utilization gene) abundance. Furthermore, the ex vivo and in vitro inhibitory effects of metformin on choline metabolism of TMA-producing bacteria were confirmed under anaerobic condition. The results suggested that metformin suppresses serum TMAO level by remodeling gut microbiota involved in TMA generation from choline.