Calcium antagonists as inhibitors of in vitro low density lipoprotein oxidation and glycation

The peroxidation step in lipid transformation is considered to be essential in the pathogenesis of atherosclerosis. Calcium antagonists (CA) appear to have antioxidant effects in addition to their potent vasorelaxant properti es. In the present study, we compared the antioxidative efficacy of CA (aml odipine, lacidipine, nifedipine, isradipine. diltiazem, and semotiadil) in the copper-catalysed oxidation of low-density lipoprotein (LDL) with that o f glycated(g)/glycoxidated(go) LDL. This issue is of great importance when considering the potential therapeutic use of antioxidant drugs in diabetes- associated vasculopathy. Oxidation of native LDL was inhibited most efficie ntly (>90%) by lacidipine and semotiadil in the concentration range 10(-4)- 10(-3) M. We found, however, a dramatic decrease in antioxidant activity to wards g/goLDL as compared to native LDL in all the CA tested. Only lacidipi ne significantly inhibited copper-mediated oxidation of g/goLDL in the whol e concentration range tested (10(-5) M-10(-3) M). This probably resulted fr om the increased auto-oxidative potential introduced by early and advanced glycation end products (AGE) into the g/goLDL. We noted that coincubation o f LDL with 10(-3) M CA and 0.5 M glucose under oxidative/non-oxidative cond itions partially or fully restored the antioxidant capacity of the differen t CA to inhibit the subsequent copper-catalysed oxidation of the modified L DL. This is a clear indication that CA inhibit glycative or glycoxidative L DL changes during the preceding long-term glycation period. The notion that both oxidative: changes and long-term glycation effects were reduced by CA was corroborated by fluorescence analysis, AGE-ELISA, quantitation of lipi d peroxidation, and thiobarbituric acid reactive substance (TBARS) measurem ent of long-term g/goLDL. The strongest antioxidative effects during long-t erm glycation of LDL were seen with isradipine, lacidipine, nifedipine, and semotiadil. Diltiazem was the only CA that could not prevent TEARS formati on in LDL during the long-term glycation period. In contrast, Amadori produ ct formation. as measured by the generation of fructosamines, was not signi ficantly reduced by any CA tested. Thus CA, like other antioxidants, signif icantly retard AGE formation, while initial glycation reactions, such as Am adori product Formation, are only weakly inhibited. (C) 2001 Elsevier Scien ce Inc. All rights reserved.