Oxidized Low-Density Lipoproteins Facilitate Leukocyte Adhesion to Aortic Intima Without Affecting Endothelium-Dependent Relaxation

Abstract

Abstract Inflammatory cell deposition in atherosclerotic blood vessels has been thought to relate to loss of endothelium-derived nitric oxide (NO). To examine whether cell deposition correlates temporally with the loss of NO activity, rat aortic rings were incubated with buffer, native LDL (n-LDL), oxidized LDL (ox-LDL), or the endothelium-derived relaxing factor synthase inhibitor N ^ω -nitro- l -arginine methyl ester ( l- NAME) for 2 hours, and vascular contractile response to norepinephrine and relaxant response to acetylcholine, thrombin, and calcium ionophore A23,187 were examined. Thereafter, the rings were exposed to biotin-fluorescein isothiocyanate-labeled fluorescent or unlabeled leukocytes for 30 minutes. Cell adhesion was quantitated by fluorescent microscopy as well as by scanning electron microscopy. Incubation with n-LDL or ox-LDL did not affect either the contractile or the relaxant response of rings. However, leukocyte adhesion increased markedly in all ox-LDL–treated rings but not in those treated with n-LDL. Thus, leukocyte adhesion occurred independent of NO activity. In keeping with this concept, pretreatment of rings with the NO precursor l -arginine failed to influence leukocyte adhesion to rings incubated with ox-LDL. Treatment of rings with l- NAME also resulted in adhesion of a large number of leukocytes. Furthermore, all rings treated with ox-LDL or l- NAME demonstrated marked expression of P-selectin leukocyte adhesion molecules, determined by immunohistochemistry. Pretreatment of rings with the P-selectin blocking antibody PB1.3 markedly decreased deposition of leukocytes in rings exposed to ox-LDL. These data show that cell adhesion to vascular intima exposed to ox-LDL shows no temporal relation with attenuation of NO activity, although inhibition of NO synthesis leads to leukocyte deposition. P-selectin expression on vascular rings exposed to ox-LDL appears to be the basis of leukocyte deposition.