Nrf2-mediated induction of cytoprotective enzymes by 15-deoxy- Δ^12,14-prostaglandin J₂ is attenuated by alkenal/one oxidoreductase

NADPH-dependent alkenal/one oxidoreductase (Aor) was discovered to be highly inducible in rat liver following treatment with the cancer chemopreventive agent 3H-1, 2-dithiole-3-thione. 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. 15-Deoxy-Δ^12,14-prostaglandin J₂ (15d-PGJ ₂) is a reactive membrane lipid metabolite that activates multiple pathways, including Nrf2-mediated induction of cytoprotective enzymes. Physiologically, it is postulated that 15d-PGJ₂ alkylates key regulatory proteins via the electrophilic carbon centers found in two α, β-unsaturated ketone moieties. This current study addresses the metabolism of 15d-PGJ₂ by rat Aor (rAor) and subsequent deactivation of the Nrf2 signaling pathway by both rat and human AOR. We demonstrate that induction of NADPH-dependent quinone oxidoreductase activity by 15d-PGJ₂ is markedly attenuated in mouse embryonic fibroblasts that overexpress rAor. Luciferase reporter assay and quantitative real-time PCR confirmed these findings. Concentrations required for doubling the NADPH-dependent quinone oxidoreductase response are increased from 1.8 μM in wild-type to >10 μM in rat Aor transgenic fibroblasts. 15d-PGJ₂ is metabolized by recombinant rAor with a K_m of 9.6 μM and k_cat of 18.5 min^-1. The major product is 12,13-dihydro-15-deoxy-Δ ^12,14-prostaglandin J₂ (dihydro-15d-PGJ₂). The reduction of C=C by Aor yielding dihydro-15d-PGJ₂ abolishes the inducibility in an antioxidant response element-driven luciferase assay. Collectively, these results demonstrate that 15d-PGJ₂ can be catabolized by Aor, thereby attenuating subsequent Nrf2 signaling and possibly inflammatory and apoptotic processes also influenced by 15d-PGJ₂.