Antioxidant Protective Mechanisms against Reactive Oxygen Species (ROS) Generated by Mitochondrial P450 Systems in Steroidogenic Cells
Drug metabolism reviews (Softcover ed.)
Mitochondrial P450 type enzymes catalyze central steps in steroid biosynthesis, including cholesterol conversion to pregnenolone, 11β and 18 hydroxylation in glucocorticoid and mineralocorticoid synthesis, C-27 hydroxylation of bile acids, and 1α and 24 hydroxylation of 25-OH-vitamin D. These monooxygenase reactions depend on electron transfer from NADPH via FAD adrenodoxin reductase and 2Fe-2S adrenodoxin. These systems can function as a futile NADPH oxidase, oxidizing NADPH in absence of
... in absence of substrate, and leak electrons via adrenodoxin and P450 to O 2 , producing superoxide and other reactive oxygen species (ROS). The degree of uncoupling depends on the P450 and steroid substrate. Studies with purified proteins and overexpression in cultured cells show consistently that adrenodoxin, but not reductase, is responsible for ROS production that can lead to apoptosis. In the ovary and corpus luteum, antioxidant enzyme activities superoxide dismutase, catalase, and glutathione peroxidase parallel steroidogenesis. Antioxidant β-carotene, α-tocopherol, and ascorbate can protect against oxidative damages of P450 systems. In testis Leydig cells, steroidogenesis is associated with aging of the steroidogenic capacity. I. HANUKOGLU ABBREVIATIONS AdR adrenodoxin reductase ROS reactive oxygen species SOD superoxide dismutase Subscript "red" reduced DEDICATION This review is dedicated to the memory of my dear friend and colleague Dr. David Kupfer (Z.L) whose research career was devoted to the study of the role of cytochrome P450 type enzymes in drug metabolism (Schenkman, 2005; Stresser, 2006) .