Liver injury is a life-threatening condition, and the hepatoprotective potential of cyanidin-3-glucoside (C3G) has been previously demonstrated. However, due to the low bioavailability, it has been doubtful that relatively low concentrations of intact C3G in vivo could account for these bioactivities. In this study, the hepatoprotective effects of intragastric and intravenous administration of C3G were investigated in a CCl4 induced liver injury model. Intragastric C3G administration was more effective than intravenous C3G injection in reducing serum damage biomarkers, oxidative stress, and inflammatory responses, indicating that absorption of C3G into the bloodstream does not fully account for its observed benefits in vivo. Furthermore, intragastric C3G administration modulated the gut microbiota structure and increased the contents of five metabolites in the feces and serum with high inter-individual variation, indicating the key role of the interaction between C3G and the gut microbiota. At equivalent doses, the metabolites cyanidin and protocatechuic acid exhibited greater efficacy than C3G in reducing apoptosis and ROS production by activating the Nrf2 pathway in an AAPH-induced oxidative stress model. To achieve the desired health effects via C3G-rich food intake, more attention should be paid to microbially derived catabolites. Screening of specific metabolite-producing strains will help overcome individual differences and enhance the health-promoting effects of C3G.
