Abstract 1173: Severe Dyslipidemia, Lipid-Rich Atherosclerotic Lesion Formation, and Sudden Death in Mice Lacking All Nitric Oxide Synthases Fed a High Cholesterol Diet
Background: Nitric oxide (NO) is synthesized by three different isoforms of NO synthase (NOS), including neuronal (nNOS), inducible (iNOS), and endothelial NOSs (eNOS). We have recently succeeded in developing mice in which all three NOS genes are completely disrupted (triply n/i/eNOS−/− mice) (PNAS 2005). In this study, we examined the effects of a high-cholesterol diet on lipid metabolism and vascular lesion formation in those mice.
Methods: One-month-old male wild-type (WT) and triply n/i/eNOS−/− [KO] mice were maintained on either a regular diet (0.1% cholesterol) or a high cholesterol diet (1.3% cholesterol). Three months later, plasma lipid profile was evaluated by the colorimetric method. Vascular lesion formation was assessed by hematoxylineosin and oil-red staining.
Results: High-cholesterol feeding for 3 months did not significantly change plasma levels of high-density lipoprotein cholesterol or triglyceride in either wild-type or triply-KO mice as compared with a regular diet (n = 4 – 8). In contrast, the high-cholesterol diet significantly increased plasma levels of total cholesterol (TC) (92 ± 18 to 326 ± 43 mg/dl in WT; 334 ± 144 to 2306 ± 1999 in triply-KO) and low-density-lipoprotein cholesterol (LDL) (0 ± 0 to 244 ± 54 mg/dl in WT; 96 ± 150 to 1948 ± 2089 in triply-KO) in both strains, compared with the regular diet (all P < 0.05, n = 4 – 8). Notably, these plasma TC and LDL levels induced by the high-cholesterol diet were markedly higher in the triply-KO than in the WT mice (7.1- and 7.9-fold increases in TC and LDL, respectively, both P < 0.05). Lipid accumulation in the aorta (lipid area, %) and atherosclerotic lesion formation in the aortic sinus (lesion area, mm2) by the high-cholesterol diet were also markedly greater in the triply-KO (21 ± 1 and 0.9 ± 0.2, respectively) than in the WT mice (4 ± 1 and 0 ± 0) (both P < 0.05). Moreover, the high-cholesterol diet caused sudden death in the triply-KO mice (5/13 [38%]) but not in the WT mice (0/8 [0%]) (P < 0.05).
Conclusions: These results indicate that a high-cholesterol diet causes severe dyslipidemia, lipid-rich atherosclerotic lesion formation, and sudden death in the presence of defective NO production in mice in vivo, suggesting the critical role of the NOS system to maintain cardiovascular homeostasis.