Oxidation of lipoproteins, particularly low-density lipoprotein, is thought to play a major role in the development of atherosclerosis, We set out to identify and quantitate the major fatty acid oxidation products in human atherosclerotic plaque obtained from individuals undergoing carotid endarterectomy. Oxidized lipids were extracted from plaque homogenate under conditions to prevent artifactual oxidation, Identification and quantitation was performed using HPLC and GC-MS, High levels of hydroxyoctadecanoic acids (0.51 +/- 0.17 ng/mug of linoleic acid), 15-hydroxyeicosatetranoic acid (HETE) (0.66 +/- 0.24 ng/mug of arachidonic acid), and 11-HETE (0.84 +/- 0.24 ng/mug of arachidonic acid) were detected in all atherosclerotic plaques (n = 10), Low levels of 9-oxo-octadecanoic acid (oxoODE) (0.04 +/- 0.01 ng/mug of linoleic acid), were present in all samples, while 13-oxoODE (0.01 +/- 0.008 ng/mug of linoleic acid) was present in only 4 of the 10 plaque samples. Of interest was the identification of two previously unidentified compounds in atherosclerotic plaque, 11-oxo-eicosatetranoic acid in 9 of the 10 samples and 5,6-dihydroxyeicosatetranoic acid in 3 samples. Chiral analysis revealed that all the major compounds identified in this study are of a nonenzymatic origin. This study is the first to provide a convenient HPLC method to quantify all the products of both linoleic acid and arachidonic acid oxidation in human atherosclerotic plaque. The quantitation of lipid peroxidation products in plaque may be important given the potential biological activity of these compounds and their possible relationship to plaque pathogenesis and instability. (C) 2001 Academic Press.