Inhibitory effects of flavonoids on organic cation transporter 1: Implications for food/herb-drug interactions and hepatoprotective effects.

Organic cation transporter 1 (OCT1, gene symbol: SLC22A1) is mainly responsible for the hepatic uptake of various cationic drugs, closely associated with drug-induced liver injury (DILI). Screening and identifying potent OCT1 inhibitors with little toxicity in natural products is of great value in alleviating OCT1-mediated liver injury. Flavonoids, a group of polyphenols commonly found in foodstuffs and herbal products, have been reported to cause transporter-mediated food/herb-drug interactions (FDIs). Our objective was to investigate potential inhibitors of OCT1 from 96 flavonoids, evaluate the hepatoprotective effects on retrorsine-induced liver injury, and clarify the structure-activity relationships of flavonoids with OCT1. Thirteen flavonoids exhibited significant inhibition (>50%) on OCT1 in OCT1-HEK293 cells. Among them, the five strongest flavonoid inhibitors (IC50 < 10 μM), including α-naphthoflavone, apigenin, 6-hydroxyflavone, luteolin, and isosilybin markedly decreased oxaliplatin-induced cytotoxicity. In retrorsine-induced liver injury models, they also reduced alanine aminotransferase (ALT) and aspartate aminotransferase (AST) to different levels, the best of which was 6-hydroxyflavone. The pharmacophore model clarified that hydrogen bond acceptors at the 4,8,5' position might play a vital role in the inhibitory effect of flavonoids on OCT1. Taken together, our findings would pave the way to predicting the potential risks of flavonoid-related FDIs in humans and optimizing flavonoid structure to alleviate OCT1-mediated liver injury.