Calcitriol attenuates diethylnitrosamine-induced hepatic fibrosis in rats by reducing oxidative stress and fibrogenic mediators.

Vitamin D deficiency is associated with poor outcomes and increased mortality in cirrhosis. Calcitriol, the active form of vitamin D3, has antioxidant and hepatoprotective properties; however, its effects on diethylnitrosamine (DEN)-induced liver fibrosis remain unclear. This study investigated the effects of calcitriol on oxidative stress, inflammation, and fibrogenesis in DEN-induced liver fibrosis rat model. Male Sprague-Dawley rats (n = 6/group) were assigned to four groups: control (CON), DEN, DEN + low-dose calcitriol (DEN + LVD3: 5 µg/kg BW), and DEN + high-dose calcitriol (DEN + HVD3: 10 µg/kg BW). Liver fibrosis was induced by weekly DEN injections (70 mg/kg, i.p.) for 8 weeks. Calcitriol was administered twice weekly (i.p.) throughout the experiment. Oxidative stress (hepatic malondialdehyde; MDA), liver injury (serum ALT, AST), hepatic inflammation (NF-κB p65), antioxidant gene expression (SOD-1, GPX-1), and fibrosis markers (TGF-β1, MMP-12, TIMP-1, α-SMA, collagen) were evaluated by biochemical assays, immunohistochemistry, qRT-PCR, western blotting and H&E and Sirius Red staining. Calcitriol significantly attenuated DEN-induced oxidative stress by decreasing hepatic MDA levels in a dose-dependent manner, and lowered serum ALT and AST levels. It partially enhanced hepatic antioxidant defenses by increasing SOD-1 expression toward control levels and upregulating GPX-1 expression. Calcitriol also markedly suppressed NF-κB p65 activation and fibrotic markers (TGF-β1, MMP-12, α-SMA, collagen), which corresponded with improved histopathological fibrosis scores. TIMP1 expression remained unchanged across all groups. Therefore, calcitriol attenuates DEN-induced liver fibrosis by reducing oxidative stress, suppressing inflammatory and fibrogenic signaling, and enhancing antioxidant defenses.