Troglitazone-binding to Ldl and its glycated modifications - Its role in cell-catalysed and Cu-mediated Ldl-oxidation

Troglitazone (T), an anti-diabetic drug improving insulin resistance, was s tudied as to its inhibition of copper ion-catalysed oxidation of native, gl ycated and glycoxidated low-density lipoprotein (LDL). A dose-dependent inh ibition was noted in the concentration range 40-160 mu g/ml. An almost comp lete inhibition of oxidation (2-8 h), as monitored by the formation of thio barbituric acid-reactive substances, was observed for both native and glyca ted LDL at a concentration of 160 mu g/ml T, while the maximal inhibition f or glycoxidated LDL amounted only to 60% at this concentration of the drug. This is reflected by differences in the affinity of the drug for the diffe rent types of LDL modification: While the binding of T both to native or gl ycated LDL increased linearly with increasing T concentration and was not s aturable in the concentration range rested (0-160 mu g/ml), binding of the drug to glycoxidated LDL was already nearly saturated at 10 mu g/ml. The ne arly complete inhibitory action of T towards oxidation of native and glycat ed LDL was lost, however, upon increasing the total oxidation time to 24 h. In human umbilical vein endothelial cell-mediated oxidation of LDL, T at a concentration of 20 mu g/ml significantly reduced formation of oxidation-d ependent fluorescent chromophores and liberation of 8-epi-PGF(2 alpha). In contrast, generation of thiobarbituric acid-reactive substances was not sig nificantly inhibited. As opposed to copper-mediated LDL-oxidation, differen t binding of T to LDL-modifications does not govern inhibition of human umb ilical vein endothelial cell-mediated LDL-oxidation. (C) 2000 Elsevier Scie nce Inc. All rights reserved.