Involvement of Aldehyde Dehydrogenase 1 in the Oxidation of 4-hydroxynonenal in Rat Lens and Human Lens Epithelial Cells

Abstract

Abstract: : Purpose: : The Lens epithelium is rich in polyunsaturated fatty acids(PUFAs) and the oxidation-induced toxicity is mediated by the lipid derived aldehydes (LDAs) such as 4-hydroxynonenal (HNE). HNE must be detoxified to maintain lens clarity. We have reported that HNE is metabolized to hydroxynonenoic acid (HNA) by aldehyde dehydrogenase (ALDH). Since inhibitors of ALDH decreased the formation of HNA in the rat lens and in the human lens epithelial cells (HLEC), we therefore investigated the preventive role of ALDH isozymes in oxidation-/HNE-induced toxicity in rat lens and HLEC. Methods: 1) Metabolism of ³H-HNE was studied in ALDH3 knockout mouse lens and in HLEC transfected with antisense or SiRNA specific to either ALDH1 or 3. Appropriate controls such as wild type mouse lens, scrambled oligonucleotides or the transfection reagent were used. 2) Transfected HLEC were exposed to oxidative stress (Fenton reaction) or HNE (30µM) for three hours. Toxicity parameters such as cell viability , apoptosis and protein-HNE adducts were correlated with the oxidation of exogenously added ³H-HNE. Rat lenses were transfected with the SiRNA specific to ALDH1 and oxidation of ³H-HNE was correlated with the increase in the susceptibility of the transfected lenses to oxidation-induced opacification. Results: No difference in the oxidation of ³H-HNE was observed in the lenses of the wild type and ALDH3 knock out mice. Similarly, transfection of HLEC with ALDH3 antisense or SiRNA did not affect the oxidation of ³H-HNE. Ablation of ALDH1 however, resulted in a decrease in the oxidation of ³H-HNE by the transfected HLEC with a proportionate increase in the toxicity (cell death, protein-HNE and apoptosis) when exposed to oxidative stress or HNE. Similarly, rat lenses transfected with ALDH1-SiRNA displayed a decrease in the oxidation of ³H-HNE and increased susceptibility of oxidation-induced opacification. Conclusions: Our results suggest that under oxidative stress, HNE produced in the epithelium can cause its degeneration and thus contribute to oxidation-induced cataractogenesis. Furthermore, our results demonstrate that the isozyme ALDH1 is crucial for the detoxification of HNE and thereby in the maintenance of lens clarity under oxidative stress.

Keywords: oxidation/oxidative or free radical damage • cataract • apoptosis/cell death