Background: Biliverdin reductase (BVR) plays a central role in bile pigment metabolism by reducing biliverdin (BV) to bilirubin (BR), a potent antioxidant that scavenges reactive oxygen species (ROS) under normal and pathological conditions. Elevated oxidative stress activates extracellular signal-regulated protein kinases 1/2 (ERK1/2) signaling, which strongly interacts with BVR’s C and D motifs, forming the BVR/ERK1/2 axis. In pathological states, increased ERK1/2 activity inhibits BVR’s ability to convert BV to BR, exacerbating oxidative damage and contributing to cardiovascular disease. Therefore, the interaction between BVR and ERK1/2 is critical in modulating oxidative stress. Objectives: This study aimed to evaluate the effects of BR and the ERK1/2 inhibitor PD-98059, both individually and in combination, on ROS levels, ERK1/2 activity, and vascular responses under normoxic and hypoxia-reoxygenation (H-R) injury conditions. Methods: Aortic rings from rats were subjected to equal distending pressure after oxidative stress induction using 22'-Azobis (2-amidinopropane) dihydrochloride (ABAP) in an organ bath. Different doses of BR were administered in combination with the ERK1/2 inhibitor PD-98059 to assess their impact on ROS depletion, vascular relaxation, and maximal effect (Emax). Results: The combination of BR and PD-98059 significantly enhanced aortic relaxation and Emax under both normoxic and H/R conditions compared to either treatment alone. Inhibiting ERK1/2 with PD-98059 appeared to upregulate BVR activity, increasing BR synthesis and reducing oxidative damage in aortic rings. Conclusions: Biliverdin reductase plays a vital role in defending against oxidative stress and endothelial dysfunction through its dual-specificity kinase activity and interaction with ERK1/2. ERK1/2 inhibition further enhances BR’s ROS-scavenging ability and vascular protective effects. Targeting the interaction between BVR and ERK1/2 holds potential as an effective therapeutic strategy for conditions characterized by excessive ROS levels, such as cardiovascular diseases.

Endothelial dysfunction is an important risk factor for the development of cardiovascular diseases, and its condition is further aggravated by oxidative stress. Biliverdin (BV) and bilirubin (BR) are potent antioxidants that protect endothelial cells, with biliverdin reductase (BVR) converting BV to BR to maintain redox balance. This study explored BVR’s role in mediating these protective effects under normoxic and hypoxia-reoxygenation conditions. Pharmacological inhibition of BVR reduced the protective effects of BV and BR, as evidenced by the decreased cell viability, cellular antioxidant activity, and intracellular bilirubin levels. Activation of ERK1/2 reduced BVR’s protective function, while its inhibition enhanced it. Additionally, disruption of the BVR-ERK interaction further modulated these effects, highlighting BVR-ERK1/2 interaction sites as potential therapeutic targets for oxidative stress-induced endothelial dysfunction.