Fig. 1

Metabolism of gut microbiota products from dietary substrates. Dietary subtrates enter the gastrointestinal tract and are further processed by gut microbes to various metabolites, including SCFAs (acetate, propionate, butyrate), H₂S and TMA. The majority of butyrate is oxidized to acetyl-CoA in the mitochondria of colonic epithelial cells. Propionate and acetate are partially metabolized in the gut. Though, the majority of propionate is oxidized to succinyl-CoA in the liver. From SCFAs, acetate reaches the highest concentrations in peripheral blood, thus contributing mostly to the systemic production of energy in the peripheral tissues. Additionally, colonic mucosa oxidizes H₂S by the action of mitochondrial SQR to thiosulfate. Thiosulfate may be either recycled to H₂S by the action of microbial TR in the lumen of the gut or reach liver for further oxidation to sulfite and sulfate by mitochondrial TST and SO respectively. Likewise, the fraction of TMA that reaches the liver is oxidized to TMAO by cytosolic FMO3. CoA; coenzyme A, SQR; sulfide quinone reductase, TR; thiosulfate reductase, TST; thiosulfate sulfurtransferase, SO; sulfite oxidase, TMA; trimethylamine, TMAO; trimethylamine N-oxide, FMO3; flavin-containing monooxygenase 3