PREDOMINANCE OF ESTERIFIED HYDROPEROXY-LINOLEIC ACID IN HUMAN MONOCYTE-OXIDIZED LDL

Low density lipoprotein that was oxidized by activated human monocytes was analyzed to determine the identity of oxidized fatty acids presen t and the conditions required for their formation. The oxidized lipids were also analyzed under conditions allowing preservation of their ox idation state. Using reversed-phase high performance liquid chromatogr aphy (HPLC) analysis of native and saponified lipid extracts of oxidiz ed low density lipoprotein (LDL), we found that the major fatty acid o xidation product was esterified hydroperoxyoctadecadienoic acid (HPODE ), the oxidized product of the most abundant polyunsaturated fatty aci d in human LDL, linoleic acid. Although some esterified hydroxyoctadec adienoic acid (HODE) was also detected, the reduction of HPODE to HODE did not appear to be monocyte-dependent, Essentially all of the HPODE was found to be esterified with the majority being esterified to chol esterol followed by phospholipids and generally following the abundanc e of esterified linoleic acid within the lipid classes. The percent of cholesteryl linoleate converted to cholesteryl HPODE and cholesteryl HODE at the end of the 24-h incubation was determined to be approximat ely 13.5%. The formation of oxidized esterified linoleic acid in the L DL was shown to require immunological activation of the human monocyte s, a previously observed requirement for general LDL oxidation in this culture system. The oxidized esterified linoleic acid was present in the supernatant with the LDL and was not cell-associated. HPODE format ion on LDL was prevented by including superoxide dismutase (SOD) or ei cosatetraynoic acid (ETYA) during the 24-h coincubation of activated m onocytes with LDL whereas indomethacin was without effect. The analysi s of the lipid oxidation products in oxidized LDL can provide insight into the mechanisms involved in oxidation of LDL by activated human mo nocytes.