FORMATION OF NON-CYCLOOXYGENASE-DERIVED PROSTANOIDS (F-2-ISOPROSTANES) IN PLASMA AND LOW-DENSITY-LIPOPROTEIN EXPOSED TO OXIDATIVE STRESS IN-VITRO

F-2-isoprostanes are prostaglandin F-2-like compounds that are known to be formed in vivo by free radical oxidation of arachidonyl-containing lipids, and their plasma levels have been suggested as indicators of in vivo oxidative stress. As oxidation of LDL, a likely causal factor in atherosclerosis, involves lipid peroxidation, we investigated whether F-2-isoprostanes are formed in plasma and LDL exposed to oxidative stress, and how F-2-isoprostane formation is related to endogenous antioxidant status. In plasma exposed to aqueous peroxyl radicals, lipid hydroperoxides and esterified F-2-isoprostanes were formed simultaneously after endogenous ascorbate and ubiquinol-10 had been exhausted, despite the continued presence of urate, alpha-tocopherol, beta-carotene, and lycopene. In isolated LDL exposed to aqueous peroxyl radicals or Cu2+, consumption of endogenous ubiquinol-10 and alpha-tocopherol was followed by rapid formation and subsequent breakdown of lipid hydroperoxides and esterified F-2-isoprostanes, and a continuous increase in LDL's electronegativity, indicative of atherogenic modification. In Cu2+-exposed LDL, the decrease in esterified F-2-isoprostane levels was paralleled by the appearance of free F-2-isoprostanes, suggesting that hydrolysis by an LDL-associated activity had occurred. Our data suggest that F-2-isoprostanes are useful markers of LDL oxidation in vivo. As F-2-isoprostanes are potent vasoconstrictors and can modulate platelet aggregation, their formation in LDL demonstrated here may also have important implications for the etiology of cardiovascular disease.