Selective microdetermination of lipid hydroperoxides.

A sensitive and selective assay for lipid hydroperoxides was developed based upon the activation by hydroperoxides of the cyclooxygenase activity of prostaglandin H synthase. The assay measures hydroperoxides directly by their stimulatory action on the cyclooxygenase and thus differs from the methods used currently which rely on the measurement of secondary products to estimate the amount of hydroperoxide. The present assay of enzymatic response was approximately linear in the range 10 to 150 pmol of added lipid hydroperoxide. This sensitivity for lipid peroxides is about 50-fold greater than that of the thiobarbiturate assay with fluorescence detection. When applied to samples of human plasma, the enzymatic assay indicated that the concentration of lipid hydroperoxides in normal subjects is 0.5 microM, more than 50-fold lower than estimated by the thiobarbiturate assay (30-50 microM). Nevertheless, the circulating concentration of 0.5 microM lipid hydroperoxide approaches that reported to have deleterious effects upon vascular prostacyclin synthase.