Serum level of IgG autoantibodies against oxidized low density lipoproteins and lag-phase of serum oxidation in coronary heart disease--inverse correlation.

High affinity IgG autoantibodies (ABs) against oxLDLs and lag-phase of serum oxidation were tested in patients with coronary heart disease (CHD). Fifty one (37 M/14 F) patients with CHD defined as Q-wave myocardial infarction and/or stenosis of more than 50% and 51 (34 M/17 F) healthy blood donors as controls participated in this study. LDLs were isolated by gradient ultracentrifugation and oxidized with CuSO4. The modified LDLs (oxLDLs) or native LDLs (nLDLs) were used as antigens in an enzyme immunoassay (ELISA) to detect IgG ABs in both groups. The serum was oxidized by CuSO4 and the oxidation was monitored spectrophotometrically at lambda = 234 nm to follow the formation of conjugated diens. The lag-phase (in minutes) is the interval between the addition of CuSO4 to the serum and the beginning of extensive oxidation (increasing absorbance at 234 nm). The concentrations of total cholesterol, triglycerides, HDL-cholesterol, apo-A and apo-B were measured as well. The mean level of ABs against oxLDLs (expressed as optical density units) was 0.590 +/- 0.330 in CHD-patients vs 0.244 +/- 0.200 in controls (p < 0.001). The lag-phase in minutes was 47.00 +/- 27.19 in CHD-patients and 80.23 +/- 26.30 in controls (p < 0.001). A negative correlation between ABs levels and lag-phase was established in CHD-patients (r = -0.69, p < 0.001) and controls (r = -0.62, p < 0.001). A poor correlation was established between ABs levels or lag-phase, on one hand, and other measured parameters. In conclusion, the lag-phase of serum oxidation by Cu2+ could be informative for LDL susceptibility to modification and the extent of consequent humoral immune response.