29th Annual Meeting of the American Society of Photobiology

Downtown Marriot

Chicago, Il.

Nitric Oxide as a Cellular Antioxidant

Abstract-
Nitric oxide is a two edged sword in that it can be a pro-oxidant or antioxidant. It is thought that the antioxidant effect is due to its radical scavenging abilities. We investigated the effectiveness of NO as antioxidant in cellular lipid peroxidation initiated by singlet oxygen or unsaturated fatty acids and ferrous iron. We hypothesized that NO would be a more effective antioxidant in lipid peroxidation if its primary reaction is with radicals formed during the initiation step. To test this hypothesis lipid peroxidation in HL-60 cells were initiated by a) system I: cells were exposed to a photosensitizer and light (no radicals during initiation) and radical chain reactions then started by addition of ferrous iron or b) system II cells were enriched with unsatturated fatty acids and lipid peroxidation initiated with ferrous iron (radical formation during initiation). To determine the influence of NO on lipid peroxidation we measured O2 consumption and radical formation. If NO is added after initiation of radical chain reactions by iron , inhibition of O2 consumption is comparable between system I and II. If NO is added before addition of iron O2 consumption is only decreased in system II. Initial reduction of O2 consumption by NO was a) dependent on [NO] (0.5 - 2 uM )in system I but not system II and b)only slightly dependent on [Fe(II)] (5 - 20 uM). Oxygen consumption after addition of iron correlated directly with [cell] (5 - 20 x 10^6 cells/3 mL). However when using 20 x 10^6 cells in system I less O2 was consumed compared to the other [cell]. The data suggest that the place of O2 consumption and the kind of radicals formed determine the effectiveness of NO as antioxidant in lipid peroxidation. (This work was supported by NIH Grant CA-66081and CA-81090.)

Keywords: nitric oxide, antioxidants, lipid peroxidation, singlet oxygen