Cigatette smoking is ranked among the leading risk factors in the etiology of atherosclerotic vascular disease. The mechanisms, however, that link cigarette smoking to increased incidence of atherosclerosis are not understood. The adherence of circulating monocytes to the endothelium, migration into the subendothelium, and subsequent formation of foam cells are principal initial events in the development of atherosclerosis. We therefore determined whether cigarette smoke caused increased adherence of monocytes to endothelial cells and the cellular mechanism of this increased adherence. Cigarette smoke condensate (CSC), the particulate fraction of cigarette smoke derived from 2R1 standard research cigarettes, at a concentration of 25-30 pg/ml (average yield of CSC is 26.1 mgcigarette), augmented (70-90%) basal adherence of human peripheral blood monocytes to a cultured monolayer of endothelial cells derived from bovine aorta (BAEC) and human umbilical vein (HUVEC). There was a concomitant increase in the expression of C D l l b ligand on the surface of monocytes as determined by flow cytometry, utilizing FlTC conjugated Mab MO-1 (CD11 b).
However, nicotine (1-1 5 @nl) and cadmium sulfate (10 pgml), constituents of CSC, individually or in combination had no effect either on C D l l b expression or adherence of monocytes to endothelial cells. Treatment of HUVEC with CSC for 60 min also resulted in an increased expression of ICAM-1 and ELAM-1 as determined by mean fluorescence intensity of ICAM-1 and ELAM-1 labeled cells in flow cytometric analysis. The CSC induced expression of CDI 1 b in monocytes was optimal at 25-30 min and was inhibited by protein kinase C inhibitors, staurosporine and H-7, and also by baicalein, a Iipoxygenase inhibitor. Similarly, CSC induced ICAM-1 and ELAM-1 expression in HUVEC was inhibited by protein kinase C inhibitors. CSC stimulated the adherence of human monocytes but not the monocytic cell lines HL-60, U937, and THP-1 to endothelial cells. The CSC stimulated adherence of human monocytes was inhibited (80%) by MAb to CD11 b and 50% by Mab to ICAM-1 and ELAM-1. These results suggest that cigarettee smoke particulate constituents activate protein kinase C, leading to increased surface expression of adhesive ligand C D l l b on peripheral blood monocytes and counter receptor(s) ICAM-1 and ELAM-1 in endothelial cells. The expression of ligand and counter receptor leads to potentiated adherence of monocytes to endothelial cells, an initial event in the pathogenesis of cigarette smoke induced inflammatory response in the vessel wall. o 1994 Wiiey-Liss, Inc Epidemiological studies have established a strong correlation between cigarette smoking and the development and progression of atherosclerosis (U.S. Office on Smoking and Health, 1989; McGill, 1990). However, there is a paucity of information concerning the cellular mechanisms whereby cigarette smoking influences the process of atherosclerosis. The characterization of the cellular mechanism by which cigarette smoking ini- tiates or contributes to the development of atherosclerosis is compounded by the fact that cigarette smoke contains approximately 4,000 constituents (Hoffmann and Wynder, 1986) which could act individually or in combination as potential stimuli for atherogenesis. The 0 1994 WILEY-LISS, INC.
mainstream smoke coming from a burning cigarette comprises 92% of gaseous components and 8% of partic-