LOW-DENSITY-LIPOPROTEIN COMPOSITION AND OXIDABILITY IN ATHEROSCLEROTIC CARDIOVASCULAR-DISEASE

Objectives: To characterize low-density lipoprotein (LDL) chemical com position and oxidability in normolipidemic and dyslipidemic patients w ith atherosclerotic cardiovascular disease, as compared with matched c ontrol subjects. To evaluate LDL susceptibility to oxidation, we deter mined the cutoff points of thiobarbituric reactive substances (TBARS) in LDL after oxidative stress, as well as its resistance to oxidation. Design and methods: LDL (density 1.019-1.063 g/mL) of 24 men with ath erosclerotic cardiovascular disease (12 normolipidemic and 12 dyslipid emic patients) and 18 age-matched healthy control men. LDL chemical co mposition was determined and apo B/cholesterol ratio was calculated. T BARS in native LDL and after 60 and 120 min of LDL oxidation with copp er were measured. The conjugated diene production kinetics during LDL incubation with copper were also studied, lag time being an oxidation resistance marker. Cutoff points for the positivity criterion of apoB/ cholesterol ratio in LDL and TBARS in native and oxidized LDL were eva luated using the receiver operator characteristic (ROC) graphic method . Results: LDL were triglyceride-enriched, the apoB/cholesterol ratio being higher in patients than in controls, without differences between normolipidemic and dyslipidemic subgroups. We have established the fo llowing cutoff values to differentiate between patients and controls: 0.43 mg/mg for the apo B/cholesterol ratio in LDL; 3.0 nmol malondiald ehyde/mg protein for TBARS in native LDL; 22 and 80 nmol malondialdehy de/mg protein after 60- and 120-min postoxidative stress, respectively . We did not find differences in the conjugated diene production kinet ics between patients and controls. Conclusions: The enrichment in trig lycerides and the high apoB/cholesterol ratio suggest the presence of an abnormal LDL particle in normolipidemic and dyslipidemic patients. This LDL particle was more susceptible to oxidation. In the ROC analys is, the TBARS plot at 120 min exhibited greater accuracy and better pe rformance than the other LDL oxidability markers.