Effects of in vitro addition of captopril on copper-induced low density lipoprotein oxidation

Low density lipoprotein (LDL) was incubated with 20 microM of the angiotensin converting enzyme (ACE) inhibitors captopril, fosinopril and quinapril or ethanol. Oxidation of LDL was initiated by addition of CuSO4 and monitored for production of conjugated dienes, thiobarbituric acid reactive substances (TBARS) and lipid peroxides. The inhibition of production of conjugated dienes was expressed as the lag phase in minutes. The lag phase for control samples was 55.2 +/- 6.1 (mean +/- s.e. mean) min and for captopril 86.4 +/- 7.0 min (P = 0.0058). Quinapril had a small but nonsignificant effect, fosinopril and ethanol had no effect. LDL incubated with captopril showed only 13.8% of TBARS and 22.7% of lipid peroxides produced by control (100%) after 1 h. Increasing concentrations of captopril showed a linear increase in the lag phase. We conclude that captopril increases the resistance of LDL to copper-induced oxidation.