Biliverdin/Bilirubin Redox Pair Protects Lens Epithelial Cells against Oxidative Stress in Age-Related Cataract by Regulating NF-κB/iNOS and Nrf2/HO-1 Pathways

Age-related cataract (ARC) is the leading cause of vision impairment globally. It has been widely accepted that excessive reactive oxygen species (ROS) accumulation in lens epithelial cells (LECs) is a critical risk factor for ARC formation. Biliverdin (BV)/bilirubin (BR) redox pair is the active by-product of heme degradation with robust antioxidative stress and antiapoptotic effects. Thus, we purpose that BV and BR may have a therapeutic effect on ARC. In the present study, we determine the expression levels of enzymes regulating BV and BR generation in human lens anterior capsule samples. The therapeutic effect of BV/BR redox pair on ARC was assessed in hydrogen peroxide (H(2)O(2))-damaged mouse LECs in vitro. The NF-κB/inducible nitric oxide synthase (iNOS) and nuclear factor erythroid 2-related factor 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling pathways were evaluated to illustrate the molecular mechanism. The results revealed that the mRNA expressions of Nrf2, HO-1, and biliverdin reductase A (BVRA) were all decreased in human samples of age-related nuclear cataract. BV/BR redox pair pretreatment protected LECs against H(2)O(2) damage by prohibiting NF-κB p65 nuclear trafficking, ameliorating iNOS expression, reducing intracellular and mitochondrial ROS levels, and restoring glutathione (GSH) and superoxide dismutase (SOD) levels. BV and BR pretreatment also regulated the expression of apoptotic molecules (Bax, Bcl-2, and cleaved caspase-3), thus decreasing the apoptosis of LECs. In addition, BV/BR pair promoted Nrf2 nuclear accumulation and HO-1 induction, whereas the knockdown of BVRA counteracted the effect of BV on activating Nrf2/HO-1 pathway and antiapoptosis. These findings implicated that BV/BR redox pair protects LECs against H(2)O(2)-induced apoptosis by regulating NF-κB/iNOS and Nrf2/HO-1 pathways. Moreover, BVRA is responsible for BV-mediated cytoprotection by reductive conversion of BV to BR. This trial is registered with ChiCTR2000036059