A role for the myoglobin redox cycle in the induction of endothelial cell apoptosis

This study investigates the potential role of the ferric/ferryl redox cycle of myoglobin (Mb) in the development of endothelial cell injury. Bovine aortic endothelial cells were incubated with ferric Mb (0.5–100 μM) in the presence or absence of low steady states of H2O2 (3–4 μM) generated by glucose oxidase (GOX). The reaction of ferric Mb with H2O2 generated ferryl Mb as monitored spectrophotometrically. Ferryl Mb formation correlated with the induction of apoptosis as indicated by morphological criteria, caspase 3 activation, phosphatidylserine (PS) externalization, and nuclear condensation by Hoechst 33342 staining. The addition of ascorbate or catalase inhibited the formation of ferryl Mb and the onset of apoptosis, whereas apoptosis was enhanced in cells depleted of intracellular glutathione by pretreatment with buthionine sulfoximine. Mb and Mb/GOX suppressed cell cycle progression, but only Mb/GOX produced significant cell loss revealed by the accumulation of sub G1 events. These results suggest a role for the Mb redox cycle in the induction of endothelial cell apoptosis, which may be relevant in the pathophysiology of diseases characterized by the release of Mb from damaged muscle.