Lipoprotein susceptibility to oxidation in the macromolecular fraction of plasma: relation to plasma lipids and oleate/linoleate ratio in comparison with whole plasma in hypertriglyceridemia.

Background: Susceptibility of lipoprotein to oxidation is usually studied using purified lipoproteins. However, for large clinical studies or routine clinical assessment, a rapid less time-consuming method is desirable. Therefore, we studied copper-mediated oxidation of the macromolecule fraction of plasma in comparison with oxidation directly in whole unfractionated plasma in a group of hyperlipidemic individuals.

Methods: Lag phase rate (LR), propagation phase rate (PR), lag time (LT), and maximal extent of oxidation were determined for copper-mediated oxidation in plasma from 16 hyperlipidemic individuals. Oxidation parameters obtained for whole plasma (WP) and macromolecules were subjected to correlation analysis with plasma lipid concentrations and with the oleic acid/linoleic acid ratio (18:1/18:2) in phospholipids (PL), triglycerides (TG), and cholesterol esters (CE).

Results: Total cholesterol (TC) concentration was significantly correlated with lag rate (negative, p<0.05), lag time (positive, p<0.01), and with maximal extent of oxidation (positive, p<0.05) for plasma macromolecules (PM). Triglyceride concentration was not significantly correlated with lag rate, lag time, or propagation rate for plasma macromolecules. Triglyceride concentration was positively correlated with the maximal extent of oxidation (p<0.01) for plasma macromolecules. In the cholesterol ester fraction, the 18:1/18:2 ratio was significantly correlated (positive, p<0.05) with lag time. Phospholipid 18:1/18:2 ratio did not correlate with oxidative parameters. This ratio in triglycerides correlated better, but statistical significance was not obtained. Parameters obtained with whole plasma did not significantly correlate with lipid values.

Conclusions: Oxidation parameters obtained for plasma macromolecules correlated with lipid parameters known to be associated with oxidative susceptibility of lipoproteins and were unaffected by soluble antioxidants found in whole plasma or serum. Therefore, plasma macromolecules were superior to whole plasma for assessing lipoprotein susceptibility to oxidation. This approach will facilitate larger clinical trials by saving the time and labor involved in lipoprotein isolation.