Enhanced expression of glutathione peroxidase protects islet β cells from hypoxia‐reoxygenation

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Abstract
The survival of pancreatic islet beta-cell xenografts and allografts may be affected by damaging reactive oxygen and nitrogen species generated during hypoxia-reoxygenation. Peroxynitrite, which is formed from superoxide and nitric oxide, appears to be an important mediator of beta-cell destruction. The intracellular antioxidant enzymes glutathione peroxidase-1 (Gpx-1) and copper-zinc superoxide dismutase (CuZn SOD) detoxify peroxynitrite and superoxide, respectively. The aim of this study was to examine whether enhanced expression of Gpx-1 and/or CuZn SOD protected NIT-1 mouse insulinoma cells from hypoxia-reoxygenation injury. Stable transfectants expressing human Gpx-1 or CuZn SOD were isolated and tested for their resistance to hydrogen peroxide (H(2)O(2)) and menadione, which generates superoxide intracellularly. Clones expressing one or both enzymes were subjected to hypoxia in glucose-free medium for 18 h, followed by reoxygenation in complete medium for 1.5 h. Cell viability was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromide (MTT) reduction assay. Increases of up to two fold in Gpx or total SOD activity protected NIT-1 cells from H(2)O(2) and menadione. Expression of Gpx-1 significantly increased NIT-1 survival following hypoxia-reoxygenation (viability 65 +/- 9% vs. control 15 +/- 3%, P < 0.001) but CuZn SOD expression had no effect (15 +/- 1%). Expression of both enzymes was no more protective (60 +/- 6%) than expression of Gpx-1 alone. Genetic manipulation of islet beta cells to increase expression of Gpx-1 may protect them from oxidative injury associated with the transplantation procedure.