Antioxidative function and substrate specificity of NAD(P)H-dependent alkenal/one oxidoreductase -: A new role for leukotriene B4 12-hydroxydehydrogenase/15-oxoprostaglandin 13-reductase

There are several known routes for the metabolic detoxication of alpha,beta -unsaturated aldehydes and ketones, including conjugation to glutathione and reduction and oxidation of the aldehyde to an alcohol and a carboxylic acid, respectively. In this study, we describe a fourth class of detoxication that involves the reduction of the alpha,beta -carbon = carbon double bond to a single bond. This reaction is catalyzed by NAD(P)H-dependent alkenal/one oxidoreductase (AO), an enzyme heretofore known as leukotriene B-4 12-hydroxydehydrogenase, 15-oxoprostagiandin 13-reductase, and dithiolethione-inducible gene-1. AO is shown to effectively reduce cytotoxic lipid peroxidation products such as 4-hydroxy-2-nonenal (HNE) (k(cat) = 4.0 x 10(3) min(-1); k(cat)/K-m = 3.3 x 10(7) min(-1) M-1) and acrolein (k(cat) = 2.2 x 10(2) min(-1); k(cat)/K-m = 1.5 x 10(6) min(-1) m(-1)) and common industrial compounds such as ethyl vinyl ketone (k(cat) = 9.6 x 10(3) min(-1); k(cat)/K-m = 8.8 x 10(7) min(-1) M-1) and 15-oxoprostaglandin E-1 (k(cat) = 2.4 x 10(3) min(-1); k(cat)/K-m = 2.4 x 10(9) min(-1) M-1). Furthermore, transfection of human embryonic kidney cells with a rat liver AO expression vector protected these cells from challenge with HNE. The concentration of HNE at which 50% of the cells were killed after 24 h increased from similar to 15 mum in control cells to similar to 70 muM in AO-transfected cells. Overexpression of AO also completely abolished protein alkylation by HNE at all concentrations tested (up to 30 muM). Thus, we describe a novel antioxidative activity of a previously characterized bioactive lipid-metabolizing enzyme that could prove to be therapeutically or prophylactically useful due to its high catalytic rate and inducibility.