Silibinin Alleviates Liver Oxidative Stress in D-Galactose-Treated Kunming Mice via Microbiota Homeostasis in a Microbiota-Dependent Manner

Hepatic oxidative stress is a key driver in liver injury pathogenesis, with D-galactose (D-gal) modeling serving as an established inducer of accelerated oxidative damage. Silibinin (SLB), a flavonolignan from milk thistle, shows therapeutic promise through potent antioxidant activity and gut-liver axis modulation. This study investigated whether the hepatoprotective effect of SLB against oxidative stress depends on gut microbiota regulation. Using mouse models with gut microbiota ablation by oral antibiotics or direct oxidative stress induction by D-gal (150 mg/kg), SLB treatment (200 mg/kg) was administered. The protective mechanisms were evaluated through the Nrf2/ARE pathway, target gene expression, gut microbiota profiling, and cecal metabolomics. Results demonstrated that SLB significantly alleviated D-gal-induced hepatic oxidative stress (e.g., reduced MDA by 33.3%), but this protection was markedly weakened after antibiotic-induced microbiota depletion (e.g., a loss of efficacy exceeding 50%). Integrated omics revealed that antibiotics caused a severe reduction in unclassified_Muribaculaceae (a butyrate producer, decreased by 80%), impairing butyrate-mediated Nrf2/Keap1 activation. Simultaneously, the absence of Parabacteroides led to accumulated primary bile acids and inhibited secondary bile acid production (e.g., taurochenodeoxycholate reduced by 75%), further disrupting redox homeostasis. Conclusion: Silibinin's mitigation of hepatic oxidative stress is gut microbiota-dependent, highlighting the therapeutic potential of microbiota-targeted antioxidant strategies for oxidative stress-related pathologies.