Search

Cigarette smoking is a major risk factor for atherosclerosis and cardiovascular disease. CD36 mediates oxidized LDL (oxLDL) uptake and contributes to macrophage foam cell formation. We investigated a role for the CD36 pathway in nicotine-induced activation of macrophages and foam cell formation in vitro and in vivo. Nicotine in the same plasma concentration range found in smokers increased the CD36+/CD14+ cell population in human peripheral blood mononuclear cells, increased CD36 expression of human THP1 macrophages, and increased macrophage production of reactive oxygen species, PKCd phosphorylation, and peroxisome proliferator-activated receptor-? (PPAR?) expression. Nicotine-induced CD36 expression was suppressed by antioxidants and by specific PKCd and PPAR? inhibitors, implicating mechanistic roles for these intermediates. Nicotine synergized with oxLDL to increase macrophage expression of CD36 and cytokines TNF-a, monocyte chemoattractant protein-1, IL-6, and CXCL9, all of which were prevented by CD36 small interfering (si)RNA. Incubation with oxLDL (50 µg/ml) for 72 h resulted in lipid deposition in macrophages and foam cell formation. Preincubation with nicotine further increased oxLDL-induced lipid accumulation and foam cell formation, which was also prevented by CD36 siRNA. Treatment of apoE-/- mice with nicotine markedly exacerbated inflammatory monocyte levels and atherosclerotic plaque accumulation, effects that were not seen in CD36-/- apoE-/- mice. Our results show that physiological levels of nicotine increase CD36 expression in macrophages, a pathway that may account at least in part for the known proinflammatory and proatherogenic properties of nicotine. These results identify such enhanced CD36 expression as a novel nicotine-mediated pathway that may constitute an independent risk factor for atherosclerosis in smokers. The results also suggest that exacerbated atherogenesis by this pathway may be an adverse side effect of extended use of high concentrations of nicotine independent of their mode of administration. [ABSTRACT FROM AUTHOR]

Cigarette smoke (CS) is the most important source of preventable morbidity and mortality in the United States. Recent clinical studies have suggested that, in addition to being a major cardiovascular risk factor, CS promotes the progression of kidney disease. The mechanisms by which CS promotes the progression of chronic kidney disease have not been elucidated. Here we demonstrate for the first time that human mesangial cells (MCs) are endowed with the nicotinic ACh receptors (nAChRs) α4, α5, α7, α2, α3, and α4. Studies performed in other cell types have shown that these nAChRs are ionotropic receptors that function as agonist-regulated Ca2+ channels. Nicotine induced MC proliferation in a dose-dependent manner. At 10-7 M, a concentration found in the plasma of active smokers, nicotine induced MC proliferation (control, 1,328 ± 50 vs. nicotine, 2,761 ± 90 counts/minute (cpm); P < 0.05) and increased the synthesis of fibronectin (50%), a critical matrix component involved in the progression of chronic kidney disease. We and others have shown that, in response to PKC activation, MC synthesize reactive oxygen species (ROS) via NADPH oxidase. In the current studies we demonstrate that PKC inhibition as well as diphenyleneiodonium and apocynin, two inhibitors of NADPH oxidase, prevented the effects of nicotine on MC proliferation and fibronectin production, hence establishing ROS as second messengers of the actions of nicotine. Furthermore, nicotine increased the production of ROS as assessed by 2′,7′-dichlorofluorescein diacetate fluorescence (control, 184.4 ± 26 vs. nicotine, 281.5 ± 26 arbitrary fluorescence units (AFU); n = 5 experiments, P < 0.05). These studies unveil previously unrecognized mechanisms that indict nicotine, a component of CS, as an agent that may accelerate and promote the progression of kidney disease. [ABSTRACT FROM AUTHOR]