Gut microbiome-related tryptophan metabolites modulate drug transporters, with prominent effects on OAT1 and OAT3.

The gut microbiome plays a key role in tryptophan metabolism by directly generating indole derivatives and indirectly modulating the host-driven kynurenine pathway via microbial metabolites. In this study, we examined the effects of 12 gut microbiome-related tryptophan metabolites on major drug transporters. In vitro assays using transporter-overexpressing cell lines revealed that indole-3-acrylic acid (IA), indole-3-propionic acid (IPA), kynurenic acid (KA), xanthurenic acid (XA), and 3-hydroxyanthranilic acid (HAA) inhibited organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) activity by up to 83.7%, with half-maximal inhibitory concentration (IC50) values ranging from 5.41 to 121 μM for OAT1 and 0.31 to 9.50 μM for OAT3. Molecular docking analysis provided qualitative support for potential interactions with OAT1. In vivo pharmacokinetic studies in rats showed that the coadministration of these metabolites significantly increased systemic exposure of furosemide, a representative OAT1/OAT3 substrate, by 1.3- to 2.9-fold and was accompanied by changes in renal excretion. In contrast, most metabolites showed minimal effects on other transporters such as organic anion transporting polypeptide 1B1/1B3 (OATP1B1/OATP1B3), organic cation transporter 2 (OCT2), multidrug and toxin extrusion 1 (MATE1), multidrug resistance protein 1 (MDR1), and breast cancer resistance protein (BCRP). These findings provide mechanistic in vitro evidence that selected gut microbiome-related tryptophan metabolites interact with OAT1/OAT3 and proof-of-concept rat pharmacokinetic data showing altered furosemide disposition after metabolite coadministration. Further studies are required to determine whether these transporter-related effects are clinically relevant in humans.