Abstract 1167: Hyper-Low-Density-Lipoproteinemia in Mice Lacking All Nitric Oxide Synthases
Background: Nitric oxide (NO) is synthesized by three different isoforms of NO synthase (NOS): 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 investigated the lipid metabolism in those mice.
Methods: Experiments were performed in 3-month-old male wild-type, singly nNOS−/−, iNOS−/−, eNOS−/−, and triply n/i/eNOS−/− mice. The mice were maintained on a regular diet. Plasma lipid profile was analyzed by the high-performance liquid chromatography.
Results: Plasma concentrations of total cholesterol (mg/dl) were significantly higher in nNOS−/− (121±2), iNOS−/− (154±8), eNOS−/− (154 ± 6) and triply n/i/eNOS−/− mice (152 ± 8) than in wild-type mice (104 ± 3) (all P < 0.05, n = 7–9). Plasma concentrations of high-density lipoprotein cholesterol (mg/dl) were also significantly more elevated in the nNOS−/− (98 ± 2), iNOS−/− (121 ± 9), eNOS−/− (146 ± 3) and triply n/i/eNOS−/− mice (105 ± 7) than in wild-type mice (65 ± 1) (all P < 0.05, n = 7–9). In contrast, plasma concentrations of low-density lipoprotein (LDL) cholesterol (mg/dl) and small dense LDL particle (mg/dl) were markedly increased only in the triply n/i/eNOS−/− mice (29.3 ± 2 and 17.5 ± 4, respectively, both P < 0.05), but not in any singly NOS−/− mice, as compared with the wild-type mice (9.9 ± 0.8 and 5.7 ± 0.5) (n = 7–9). Supplementation of NO by long-term treatment with isosorbide dinitrate (0.4 mg/day, 6 weeks, dermal application) significantly reversed the plasma levels of LDL (14.4 ± 1.8) and small dense LDL particle (7.8 ± 0.7) in the triply n/i/eNOS−/− mice (both P < 0.05, n = 8). Intriguingly, blockade of the angiotensin II type 1 (AT1) receptor by long-term treatment with olmesartan (5 mg/kg/day, 6 weeks, PO) also significantly reduced both plasma LDL (16.6 ± 3) and small dense LDL particle levels (8.8 ± 1.5) in the triply n/i/eNOS−/− mice (both P < 0.05, n = 8).
Conclusions: These results indicate for the first time that complete disruption of all NOSs results in marked increase in plasma LDL in mice in vivo, possibly via an AT1 receptor-dependent pathway, demonstrating a central role of the defective NOS system in the increase in plasma levels of LDL.