Ambient Air Particulate Matter Exposure and Tissue Factor Expression in Atherosclerosis

Abstract

Recent studies have suggested a link between inhaled particulate matter (PM) exposure and atherogenesis. We investigated tissue factor (TF) expression with ambient fine particulate matter (diameter < 2.5 μ m, PM2.5) exposure and in response to in vitro exposure to fine and ultrafine PM in cultured human bronchial epithelial cells, vascular smooth muscle cells (hSMCs), and monocytes. ApoE−/− mice, fed with normal chow (NC) or high-fat chow (HFC), were exposed to concentrated PM2.5 or filtered air (FA) for 6 mo (6 h/day, 5 day/wk, n = 28). Following in vivo ultrasound bio-microscopy (UBM) assessment of plaque area, macrophage infiltration (CD68) and TF expression in the aorta were quantified. Cultured cells were incubated with size-fractionated PM from cascade impactors, or with standard reference PM material (SRM, number 1649a) and assayed for TF protein, mRNA, and activity. UBM-derived plaque areas were 7 ± 1% larger in the PM2.5-HFC than the FA-HFC group (p = .04), but not significantly different between the PM2.5-NC and FA-NC groups (p = .07). Immunohistochemistry revealed increased TF (15 ± 3% vs. 8 ± 2%, p < .01) and macrophage infiltration (19 ± 2% vs. 14 ± 3%, p < .01) in the plaques of PM2.5-HFC compared with FA-HFC groups. Impactor-collected PM2.5 and ultrafine particles consistently increased TF protein in bronchial epithelial cells, monocytes, and hSMCs. TF mRNA expression increased rapidly (within 1 h) in response to SRM PM. We conclude that in vivo and in vitro exposure to ambient air PM2.5 induces TF expression.