PGF2-isoprostanes formed during copper-induced oxidation of low-density lipoproteins are the prostaglandins that cross-react with PGE2 antibodies.

ABSTRACT

It has been previously shown that LDL oxidation can produce a prostaglandin artifact(s) which cross-reacts with PGE2 antibodies. The nature of this cross-reacting material had not been identified. In this study we have examined the products of LDL oxidation and found substances cross-reacting with both PGE2 and LTB4 antibodies. Lipid extracts of copper oxidised LDL were separated by reverse-phase HPLC and fractions cross-reacting with PGE2 antibody identified. Fractions were collected and examined by GC-MS as methyl ester TMS ether derivatives. 8-epi PGF2 alpha (8-isoprostane) was identified as one of the major metabolites eluting in fractions cross-reacting with PGE2. 8-epi-PGF2 alpha showed 4% cross-reactivity with a PGE2 antibody but very little with LTB4 or thromboxane B2 antibodies. Treatment of oxidised LDL with a specific 8-isoprostane antibody removed any detectable PGE2 levels in subsequent PGE2 RIA. The generation of cross-reacting material during LDL oxidation was not influenced by indomethacin. The generation of 8-isoprostanes by free radical oxidation of arachidonic acid in LDL may explain much of the cross-reactivity seen with PGE2 antibodies. The identity of substances cross-reacting with LTB4 have yet to be identified.