Nicotine induces proinflammatory responses in macrophages and the aorta leading to acceleration of atherosclerosis in low-density lipoprotein receptor-/- mice

Objective: We investigated the molecular mechanism of nicotine-accelerated atherosclerosis in a hyperlipidemic low-density lipoprotein receptor(-/-) mouse model. Methods and Results: Low-density lipoprotein receptor(-/-) mice received time-release nicotine or placebo pellets for 90 days. Aortic lesion size was 2.5 times larger in nicotine-treated than in placebo-treated mice (P < 0.001). A mild increase in lipids was seen in treated mice. We quantified 18 different serum cytokines and found a significant increase of tumor necrosis factor alpha, interleukin 1 beta, and keratinocyte-derived chemokine in nicotine- treated mice. Among 107 nuclear factor kappa B (NF-kappa B) target genes screened from the aorta, we found that nicotine treatment upregulated only 4 atherogenic genes including vascular adhesion molecule 1 and cyclooxygenase 2 on day 60 and platelet-derived growth factor B and platelet 12-lipoxygenase on day 90. At the cellular level, nicotine induced tumor necrosis factor alpha and inducible nitric oxide synthase expression in RAW264.7 cells via the nicotinic acetylcholine receptors. Induction was confirmed in peritoneal macrophages isolated from nicotine- treated mice. Finally, we showed that preconditioned medium from nicotine- treated RAW264.7 cells activated NF-kappa B in human smooth muscle cells and vascular endothelial cells as evidenced by nuclear localization and electromobility shift assay. Conclusions: Chronic nicotine exposure augments atherosclerosis by enhancing the production of proinflammatory cytokines by macrophages, which, in turn, activate atherogenic NF-kappa B target genes in the aortic lesions.