C18 hydroxy fatty acids as markers of lipid peroxidation ex vivo and in vivo.

Different C18 monohydroxy fatty acids (OHFAs) were evaluated for their usefulness as markers of plasma lipid peroxidation (unsaturated fatty acid oxidation) ex vivo and in vivo. First, plasma samples (n = 5) were exposed for 3 h to different radical fluxes ex vivo. The formation of OHFAs was assessed by using varying concentrations of Cu2+ ions and AAPH (2,2'-azobis(2-amidinopropane) hydrochloride) as radical flux initiators. Secondly, a cross-sectional study was carried out in 47 middle-aged men. In this study, plasma concentrations of different in vivo OHFAs were compared with other indices of lipid peroxidation. Under mild oxidation conditions (heparin plasma containing 4.2 or 8.3 mM AAPH), concentrations of all the measured OHFAs (8, 9, 10, 11, 12, 13, 15 and 16-OH acids) increased in an identical manner, but under highly oxidative conditions (heparin plasma containing 83 mM AAPH or 4.2 to 8.3 mM CuSO4) mainly 9 and 13-OHFAs were formed. In the cross-sectional study, plasma 11 and 13-OHFA levels were associated statistically significantly with plasma free F2alpha-isoprostanes, recognized index of in vivo lipid peroxidation (r = 0.305, p = 0.037 and r = 0.308, p = 0.035, respectively). In addition, 16-OHFA levels correlated with the ratio of electronegatively charged LDL to total LDL (r = 0.335, p = 0.021). With respect to the other OHFAs, 15-OHFA had no correlation with either other OHFAs or the reference substances used. In addition, occasionally there were contamination problems in the assessment of 12-OHFA. It is concluded that all of the measured C18 OHFAs can be used as indicators of plasma lipid peroxidation under mild oxidation conditions, though the 12 and 15-OHFAs may need to be used with some caution. Under high oxidation conditions, 9-and 13-OHFAs seem to be the most useful indices because of their high formation capacity.