Human cardiac microvascular and macrovascular endothelial cells respond differently to oxidatively modified LDL

Oxidation of low density lipoproteins (LDL) is considered a key event in the pathogenesis of atherosclerotic lesions. Disturbed generation of coagulatory and anticoagulatory factors by endothelial cells contributes to thrombosis and the progression of atherosclerosis in coronary arteries. In this study, the effects of native LDL (n-LDL) and oxidized LDL (ox-LDL) on human coronary endothelial cells were measured. The reaction of coronary endothelial cells to LDL were compared with those of cardiac microvascular endothelial cells grown under comparable conditions. LDL was isolated by ultracentrifugation and copper oxidized. The degree of oxidation was expressed as malondialdehyde (MDA) equivalents and was 0.78 ± 0.14 nM MDA/mg LDL for native LDL and 13.63 ± 1.18 nmol MDA/mg LDL for ox-LDL. Basal secretion of t-PA and PAI-1 activity were higher in macrovascular endothelial cells. Incubation of n-LDL in concentrations ranging from 3 to 100 μM/ml LDL-protein did not change t-PA-secretion, PAI-1 activity or procoagulant activity in both cell types. Ox-LDL (3 to 100 μM/ml LDL protein) decreased t-PA secretion in a concentration dependent manner from 30.9 ± 1.7 to 13.7 ± 30 ng/ml per 24 h per 10⁶ cells (P < 0.01), increased PAI-1 antigen from 2772 ± 587 to 4441 ± 766 ng/ml per 24 h per 10⁶ cells (P < 0.05) as well as PAI-1 activity from 34 ± 6 to 55 ± 9 AU/ml per 24 h per 10⁶ cells (P < 0.05) in macrovascular endothelial cells but had only minor effects on microvascular endothelial cells. Procoagulant activity measured as coagulation time, similarly increased only in macrovascular endothelial cells from 197 ± 6 to 76 ± 6 s/24 h per 10⁶ cells (P < 0.05). The effect on PAI- 1 secretion showed a dependency to the degree of oxidation and could be completely blocked by the antioxidant probucol. The angiotensin converting enzyme (ACE), which represents an endothelial enzyme not related to coagulation, remained unchanged during incubation with ox-LDL. Basal ACE activity was higher in microvascular endothelial cells. The higher susceptibility of macrovascular endothelial cells to ox-LDL may partially determine the localization of thrombus formation and the development of atherosclerotic plaques in hyperlipidemic patients.