NADPH dependent Alkenal/one oxidoreductase (AOR) was discovered as a highly inducible gene in rat liver by treatment of a cancer chemopreventive agent 1,2-dithiol-3-thione (D3T). AOR was further characterized as an Nrf2-regulated antioxidative enzyme that reduces carbon-carbon double bonds in a variety of α, β-unsaturated aldehydes and ketones. Such reduction processes can serve as the detoxification step in metabolism of these reactive species. Previous studies on rat AOR had shown its protective properties in cultured cells against the cytotoxicity of 4-hydroxynonenal, a prominent product of lipid peroxidation. This current study examines the properties of human AOR and its role in influencing the metabolism of α, β-unsaturated aldehydes and ketones. Our data suggested that human AOR catalytic rate is nearly one order of magnitude lower compared to its rat counterpart. However, human AOR was equivalent to rat AOR in protecting cultured cells against 4-hydroxynonenal. The lethal concentration 50 of 4-hydroxynonenal increased from 4.5μM to 12.1μM in 293 cells transfected with human AOR, compared to 14.6μM with rat AOR. 15-deoxy Δ12,14-PGJ2(prostaglandin J2), the final metabolic product of prostaglandin D2, is a potent endogenous inducer of Phase 2 enzymes and acts through multiple signaling processes including the Nrf2-Keap1 pathway. 15-Deoxy Δ12,14-PGJ2 contains two α, β-unsaturated carbon-carbon double bonds, one of which is located on a cyclopentanone ring. Due to its electrophilic nature, this double bond is postulated to be critical for inducer activity by interacting with transcriptional factor machineries. 15-DeoxyΔ12,14-PGJ2 is a substrate for rat AOR in vitro, suggested that AOR is an inducible negative regulator of 15-deoxy Δ12,14-PGJ2 mediated signaling pathways. Mouse embryonic fibroblast (MEF) cells derived from transgenic animals overexpressing rat AOR showed an attenuated induction of NOQ1 in response to PGJ2, compared to the NQO1 induction response observed in MEF cells from wildtype mice. Taken together, these data suggest that while induction of human AOR could facilitate detoxification of reactive aldehyde/one species, sustained expression might impede induction of other cytoprotective enzymes by 15-deoxy Δ12,14-PGJ2 through the Keap1-Nrf2 signaling pathway.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]