Atherogenic and pulmonary responses of ApoE- and LDL receptor-deficient mice to sidestream cigarette smoke

Plasma lipoproteins play important roles in the development and progression of atherosclerosis. Two widely used mouse models of experimental atherosclerosis, apolipoprotein E-deficient (ApoE −/−) and LDL receptor-deficient (LDLr −/−) mice, have major differences in lipoprotein characteristics. These include differences in lipoprotein cholesterol distribution, lipoprotein compositions, apoliporoteins distribution, and susceptibility to oxidation. In the present study, we compared pulmonary and cardiovascular responses of ApoE −/− and LDLr −/− mice to sidestream cigarette smoke (SSCS) exposure to determine if strain differences influence their predisposition to SSCS-mediated promotion of atherosclerosis. Female ApoE −/− and LDLr −/− mice were maintained on a saturated fat enriched diet and exposed to SSCS in whole body exposure chambers for 15 weeks (4 h/day, 5 days/week). At terminations, the levels of pulmonary injury markers in bronchoalveolar lavage (BAL) fluids from 6 mice per group and atherosclerotic lesion formation in 14 mice per group were analyzed. Total BAL cells and polymorphonuclear leukocytes were not significantly altered by SSCS exposure in both mouse models. Total protein, LDH, and cytokine concentrations in cell-free BAL fluids were also not significantly affected by chronic SSCS exposure in either mouse strain. SSCS significantly reduced surfactant protein D levels in both strains to a similar extent. However, SSCS exposure increased significantly the percent atherosclerotic lesion areas covering aortic intimal surfaces of ApoE −/− (control-25.3 ± 1.52 vs. SSCS-31.9 ± 2.02, p = 0.012) as well as in LDLr −/− (control-30.97 ± 1.1 vs. SSCS-36.61 ± 1.7, p = 0.028) mice. In contrast, the serum cholesterol concentrations of SSCS-exposed ApoE −/− mice were similar to that of controls (control-1255 ± 85 vs. SSCS-1190 ± 61 mg/dl, p = 0.552) but increased significantly in SSCS-exposed LDLr −/− mice (control-998 ± 114 vs. SSCS-1577 ± 142 mg/dl, p = 0.008). These results showing different effects of identical SSCS exposure on plasma cholesterol concentrations in these two mouse models suggest a role of multiple mechanisms in SSCS-induced atherosclerosis.