Bilirubin exerts pro-angiogenic property through Akt-eNOS-dependent pathway

Low serum bilirubin levels are associated with the risk of cardiovascular diseases including peripheral artery disease. Bilirubin is known to exert its property such as anti-oxidant effect or the enhancement of flow-mediated vasodilation, however, bilirubin action on angiogenesis remains unclear. To investigate the molecular mechanism of bilirubin on angiogenic effect, we first employed C57BL/6J mice with unilateral hindlimb ischemia surgery and divided the mice into two groups (vehicle-treated group and bilirubin treated group). The analysis of laser speckle blood flow demonstrated the enhancement of blood flow recovery in response to ischemia of mice with bilirubin treatment. The density of capillaries was significantly higher in ischemic adductor muscles of bilirubin-treated mice. The phosphorylated levels of endothelial nitric oxide synthesis (eNOS) and Akt were increased in ischemic skeletal muscles of mice with bilirubin treatment compared vehicle treatment. In in vitro experiments by using human aortic endothelial cells, bilirubin augmented eNOS and Akt phosphorylation, cell proliferation, cell migration and tube formation. These bilirubin actions on endothelial cell activation were inhibited by LY294002, a phosphatidylinositol 3-kinase inhibitor. In conclusion, bilirubin promotes angiogenesis through endothelial cells activation via Akt-eNOS-dependent manner.

This is the Author's Accepted Manuscript of the following article: Bilirubin exerts pro-angiogenic property through Akt-eNOS-dependent pathway, Yasumasa Ikeda, Hirofumi Hamano, Akiho Satoh, Yuya Horinouchi, Yuki Izawa-Ishizawa, Yoshitaka Kihira, Keisuke Ishizawa, Ken-ichi Aihara, Koichiro Tsuchiya & Toshiaki Tamaki, Hypertension Research 38, 733-740 (2015), which has been published in final form at https://doi.org/10.1038/hr.2015.74.