Loureirin B Attenuates Methotrexate-Induced Liver Injury Associated with Oxidative Stress, SIRT1 Alterations, and TGF-β/SMAD3-Related Profibrotic Responses

Background: Methotrexate-induced oxidative stress is mechanistically linked not only to hepatocellular injury but also to DNA damage, indicating that oxidative stress, hepatotoxicity, and genotoxicity represent interconnected manifestations of the same antifolate-driven toxic cascade. Methotrexate (MTX)-induced hepatotoxicity is characterized not only by oxidative stress, but also by progressive fibrotic remodeling driven by activation of the TGF-β/SMAD signaling pathway. Objective: We aimed to examine the hepatoprotective effects of Loureirin B, with a particular focus on its anti-fibrotic potential and underlying molecular mechanisms in MTX-induced liver injury. Methods: Thirty female Wistar rats were assigned to normal control, MTX, and MTX + Loureirin B groups. Liver injury was induced with a single intraperitoneal MTX dose (20 mg/kg), followed by oral administration of Loureirin B (50 mg/kg/day) for 10 days. Biochemical, molecular, and histopathological analyses were performed, including ALT, AST, ALP, MDA, SIRT1, TGF-β, SMAD3, hydroxyproline, and VEGF levels, alongside the evaluation of necrosis, fibrosis, and inflammatory infiltration. Results: MTX induced significant hepatic injury characterized by elevated serum ALT, AST, and ALP levels, increased oxidative stress, suppression of SIRT1, and increased TGF-β and SMAD3 levels, accompanied by elevated collagen-associated markers. Loureirin B treatment significantly reduced the serum liver enzyme levels and oxidative stress, partially restored SIRT1 levels, and decreased fibrosis-associated markers, including hydroxyproline and VEGF. Although the TGF-β levels were significantly reduced following Loureirin B treatment, the reduction in SMAD3 levels did not remain statistically significant after correction for multiple comparisons. Histopathological findings further demonstrated attenuation of fibrosis-associated changes and partial improvement in hepatic architecture. Conclusions: Loureirin B may exert protective effects against methotrexate-associated liver injury through the modulation of oxidative stress, partial restoration of SIRT1 levels, attenuation of profibrotic alterations associated with the TGF-β/SMAD pathway, and modulation of VEGF-related responses.