GLYC-OXIDIZED LDL IMPAIR ENDOTHELIAL FUNCTION MORE POTENTLY THAN OXIDIZED LDL - ROLE OF ENHANCED OXIDATIVE STRESS

Hypercholesterolemia is associated with impairment of endothelial func tion due to increased levels of LDL. In diabetic patients, however, at tenuation of endothelial function occurs even under normocholesterolem ic conditions. Here we assessed whether glycation of LDL potentiates t heir influence on endothelial function, with particular emphasis on th e oxidizability of LDL and the role of O-2(-). Human LDL was glycated by dialyzation for 7 days against buffer containing 200 mmol/l glucose , or sham-treated without glucose, and oxidized by incubation with Cu2 +. Glycation significantly enhanced the oxidizability of LDL, as detec ted by diene formation and by electrophoretic mobility (27.5 mm for ox idized LDL vs. 34 mm for oxidized glycated LDL at 20 h of oxidation). Isolated rings of rabbit aorta were superfused with physiological salt solution, and isometric tension was recorded. Incubation of the aorti c rings with sham-treated or with glycated LDL, not oxidized, had no i nfluence on acetylcholine-induced, endothelium-dependent relaxation. E xposure of the aortic rings to oxidized non-glycated LDL caused a sign ificant inhibition (30% at 1 mu M acetylcholine) of the endothelium-de pendent relaxation only in the presence of diethyl-dithiocarbamate (DD C), an inhibitor of the endogenous superoxide dismutase (SOD). Incubat ion of aortic rings with oxidized glycated LDL attenuated endothelium- dependent relaxation even in the absence of DDC (by 31% at 1 mu M acet ylcholine). The presence of DDC potentiated the inhibition of relaxati on (65% inhibition at 1 mu M acetylcholine), and co-incubation with ex ogenous SOD and catalase prevented the inhibition of relaxation, indic ating a mediator role of O-2(-). Endothelium-independent relaxation in duced by forskolin was unaffected by any of the lipoproteins. Using a chemiluminescence assay, significantly increased O-2(-) production of aortic rings pretreated with oxidized glycated LDL (4101 +/- 360 count s/s) in comparison to control rings (753 +/- 81 counts/s) or arteries pretreated with oxidized non-glycated LDL (2358 +/- 169 counts/s) coul d be detected, suggesting that enhanced NO-inactivation by O-2(-) coul d be the underlying mechanism for the stronger impairment of endotheli um-dependent dilations by oxidized glycated LDL. Glycation increases t he oxidizability of LDL and potentiates its endothelium-damaging influ ence. The likely mechanism for attenuation of endothelium-dependent di lations is increased formation of O-2(-), resulting in inactivation of nitric oxide. This mechanism may play an important role in diabetic p atients and may contribute to disturbed organ perfusion. (C) 1998 Else vier Science Ireland Ltd. All rights reserved.