Inhibition of Bilirubin Generation Exacerbates Oxidative Stress and Liver Injury in Early‐to‐Intermediate Obstructive Cholestasis

OBJECTIVE: We have previously shown that hemeoxygenase-1 (HO1) induction and resulting elevation of bilirubin (BR) protects the liver from oxidative stress (OS)-induced acute cholestasis in vivo. AIM: To characterise the protective role of BR at the early-to-intermediate stages of obstructive cholestasis by investigating the consequences of inhibiting BR generation in vivo. METHODS: Zinc protoporphyrin IX (ZnPP), a HO1 inhibitor, was administered 24 h before BDL to male Wistar rats. After confirming establishment of obstructive cholestasis and successful impairment in BR generation, we studied the impact of these interventions on redox status and histopathological features in liver tissue. RESULTS: OS biomarkers were significantly elevated in ZnPP-pretreated BDL animals versus BDL-only controls, showing that under cholestatic conditions, oxidative damage is increased when BR production is impaired. Levels of antioxidant defences were lower in animals lacking BR generation, indicating that hepatic oxidative damage is more severe and antioxidant defences are weaker when BR production is inhibited. Histopathological analysis revealed significantly more severe obstructive injury in HO1-inhibited animals than in those subjected to BDL alone, indicating that BR generation impairment worsens the outcome of obstructive injury. CONCLUSIONS: The inhibition of HO1 and consequent decrease in the endogenous levels of BR negatively impacts the outcome of obstructive cholestasis due to the loss of BR's antioxidant and cytoprotective effects. BR accumulation during cholestasis serves as a critical defence against oxidative damage induced by retained bile salts.