Mice Fed Western Diet Research Articles

γ-Secretase inhibitor reduces diet-induced atherosclerosis in apolipoprotein E-deficient mice

Atherosclerosis is a chronic inflammatory disease resulting from interactions between lipids, macrophages and arterial wall cells. The Notch signaling pathway is involved in the activation of macrophages in atherosclerotic lesions. This study examined whether pharmacological inhibition of Notch signaling using a γ-secretase inhibitor (GSI) can reduce atherosclerotic lesion formation. Notch-related molecules were significantly increased in aortas from apolipoprotein E-deficient (ApoE −/−) mice. In particular, macrophages in the plaques showed strong expression of Notch1 and a downstream transcriptional factor, Hes-1. A GSI (LY411,575, 0.2, and 1.0 mg/kg/day) or vehicle control was then administered to ApoE −/− mice fed Western diet for 8 weeks before measuring the expression of Notch-related molecules. Systemic administration of GSI suppressed Notch signaling in vivo and reduced total plaque areas and fatty streak content in the aortic sinus in a dose-dependent manner without serious adverse effects. The GSI also suppressed the migratory activity of macrophages and reduced the expression of intercellular adhesion molecule-1, resulting in significantly decreased macrophage infiltration in the atherosclerotic plaques. These results provided new insight into the anti-atherogenic properties of GSI in Apo E −/− mice fed Western diet.

Hepatic steatosis and inflammation: Role of western diet and lipoproteins

Background: We have shown in our previous study in ApoE−/− mice that leukocyte recruitment within the liver precedes the development of steatosis. Our objective was to examine the role of fat and lipoproteins in the development of non-alcoholic steatohepatitis. Methods: Wild type C57Bl/6 mice fed normal diet (WTND) or a western diet (WTWD), P-selectin deficient mice fed western diet and LDLr deficient mice fed normal diet (LDLND) were studied. After 8 weeks, leukocyte endothelial cell interactions we determined by intra-vital microscopy of the hepatic microcirculation. Results: Mice on the western diet had a significantly greater weight gain (217% vs. 154%). Only WTWD mice had leukocyte recruitment in the hepatic microcirculation with significantly greater number of rolling (7.0±0.4) and firmly adherent leukocytes (5.6±0.4) within the post-sinusoidal venules. There was no sinusoidal leukocyte recruitment in any of the groups. Mice on the western diet also had a significant reduction in the number of flowing sinusoids compared to those fed normal diet (6.6±0.4 vs. 12.8±0.7). The microcirculation of LDLND mice was not different from WTND mice. Conclusion: Mice fed a western diet develop a LDL receptor dependent hepatic steatosis with a resultant decrease in sinusoidal density. Western diet-induced hepatic leukocyte recruitment is P-selectin dependent in the post-sinusoidal venules.

Accelerated atherosclerosis in apolipoprotein E-deficient mice fed Western diets containing palm oil compared with extra virgin olive oils: A role for small, dense high-density lipoproteins

To test the hypothesis that extra virgin olive oils from different cultivars added to Western diets might behave differently than palm oil in the development of atherosclerosis, apoE-deficient mice were fed diets containing different cultivars of olive oil for 10 weeks. Female mice were assigned randomly to one of the following five groups: (1–4) fed chow diets supplemented with 0.15% (w/w) cholesterol and 20% (w/w) extra virgin olive oil from the Arbequina, Picual, Cornicabra, or Empeltre cultivars, and (5) fed a chow diet supplemented with 0.15% cholesterol and 20% palm oil. Compared to diets containing palm oil, a Western diet supplemented with one of several varieties of extra virgin olive oil decreased atherosclerosis lesions, reduced plaque size, and decreased macrophage recruitment. Unexpectedly, total plasma paraoxonase activity, apoA-I, plasma triglycerides, and cholesterol played minor roles in the regulation of differential aortic lesion development. Extra virgin olive oil induced a cholesterol-poor, apoA-IV-enriched lipoparticle that has enhanced arylesterase and antioxidant activities, which is closely associated with reductions in atherosclerotic lesions. Given the anti-atherogenic properties of extra virgin olive oil evident in animal models fed a Western diet, clinical trials are needed to establish whether these oils are a safe and effective means of treating atherosclerosis.

Quantification and 3D reconstruction of atherosclerotic plaque components in apolipoprotein E knockout mice using ex vivo high-resolution MRI.

To investigate the ability of high-resolution MRI to determine composition and microanatomy of atherosclerosis in mouse aortic root and brachiocephalic artery. Aortic root and brachiocephalic arteries of apolipoprotein E knockout (apoE-/-) mice fed Western diet for 10, 20, or 30 weeks were imaged ex vivo (11.7 T; 3D multiecho sequence; resolution 47x47x62.5 microm). Using semiautomated histogram-based methods, MRI accurately quantified lipid-rich/necrotic areas in the aortic root (r2=0.84; P<0.001) and brachiocephalic artery (r2=0.90; P<0.001) compared with histology. Similarly, cell-rich caps in aortic roots, quantified by MRI and histology, correlated closely (r2=0.74; P<0.001). Reconstruction of segmented brachiocephalic arteries in 3D provided unique insights into plaque microanatomy and enabled volumetric quantification of plaque and lipid-rich/necrotic core. Between 10 and 30 weeks, 3D measurement identified an 11.6-fold increase in plaque volume (versus 4.1-fold for 2D) and a 21.3-fold increase in plaque lipid-rich/necrotic core volume (versus 6.4-fold for 2D), indicating superior power of 3D quantification. Ex-vivo high-resolution 3D MRI accurately quantified lipid-rich/necrotic core and cell-rich cap areas in atherosclerotic lesions in apoE-/- mice. Reconstruction and volumetric quantification of segmented brachiocephalic arteries demonstrated greater sensitivity in detecting changes in plaque size and lipid composition over time than 2D analysis.

Aberrant antibody responses to oxidized LDL and increased intimal thickening in apoE−/− mice exposed to cigarette smoke

Cigarette smoking is associated with increased atherosclerosis and intimal thickening, and has immune-suppressive effects. The immune system modulates atherosclerosis and intimal thickening. We hypothesized that detrimental effects of cigarette smoke (CS) involves modulation of the immune response to oxidized low-density lipoprotein (oxLDL). ApoE−/− mice fed Western diet were exposed to CS starting at 20 weeks of age. Control mice were exposed to air. After 5 weeks of CS, mice were subjected to carotid arterial cuffing for 21 days. Intimal thickening was significantly increased in CS mice compared to control (0.050±0.034 mm 2 versus 0.023±0.021 mm 2; P<0.05). Spleen lymphocyte population, cytokine mRNA expression, and total IgM and IgG levels were similar. Anti-MDA oxLDL IgG was reduced by 40% ( P<0.05) in CS mice compared to control. Copper-oxidized LDL IgG antibodies remained unchanged but IgM increased in CS mice, associated with increased intimal thickening. Anti-phosphorylcholine (PC) IgM was also increased in the CS mice, associated with increased intimal thickening. Lymphocyte signaling molecule lymphotoxin β (LTβ) expression was significantly decreased in spleens of CS exposed mice. Our results suggest that immune modulation by CS characterized by aberrant antibody responses to oxLDL and reduced LTβ mRNA expression is associated with increased intimal thickening after arterial cuffing.

L-4F, an apolipoprotein A-1 mimetic, dramatically improves vasodilation in hypercholesterolemia and sickle cell disease.

Hypercholesterolemia and sickle cell disease (SCD) impair endothelium-dependent vasodilation by dissimilar mechanisms. Hypercholesterolemia impairs vasodilation by a low-density lipoprotein (LDL)-dependent mechanism. SCD has been characterized as a chronic state of inflammation in which xanthine oxidase (XO) from ischemic tissues increases vascular superoxide anion (O2*-) generation. Recent reports indicate that apolipoprotein (apo) A-1 mimetics inhibit atherosclerosis in LDL receptor-null (Ldlr-/-) mice fed Western diets. Here we hypothesize that L-4F, an apoA-1 mimetic, preserves vasodilation in hypercholesterolemia and SCD by decreasing mechanisms that increase O2*- generation. Arterioles were isolated from hypercholesterolemic Ldlr-/- mice and from SCD mice that were treated with either saline or L-4F (1 mg/kg per day). Vasodilation in response to acetylcholine was determined by videomicroscopy. Effects of L-4F on LDL-induced increases in endothelium-dependent O2*- generation were determined on arterial segments via the hydroethidine assay and on stimulated endothelial cell cultures via superoxide dismutase-inhibitable ferricytochrome c reduction. Effects of L-4F on XO bound to pulmonary arterioles and content in livers of SCD mice were determined by immunofluorescence. Hypercholesterolemia impaired vasodilation in Ldlr-/- mice, which L-4F dramatically improved. L-4F inhibited LDL-induced increases in O2*- in arterial segments and in stimulated cultures. SCD impaired vasodilation, increased XO bound to pulmonary endothelium, and decreased liver XO content. L-4F dramatically improved vasodilation, decreased XO bound to pulmonary endothelium, and increased liver XO content compared with levels in untreated SCD mice. These data show that L-4F protects endothelium-dependent vasodilation in hypercholesterolemia and SCD. Our findings suggest that L-4F restores vascular endothelial function in diverse models of disease and may be applicable to treating a variety of vascular diseases.

Decreased sensitivity to nitric oxide in the aorta of severely hypercholesterolemic apolipoprotein E-deficient mice.

A normal response to nitric oxide donors has been cited as evidence that impaired endothelium-dependent vasodilation during hypercholesterolemia is due to decreased synthesis of nitric oxide. This tenet was examined by determining responses to nitric oxide gas as well as to acetylcholine and sodium nitroprusside in the isolated aorta of apolipoprotein E-deficient mice fed normal or Western-type cholesterol-rich diet until 21 or 35 weeks of age. In mice fed normal chow, relaxation to all agents remained comparable to that obtained in wild-type mice. In mice fed Western diet, the relaxation to acetylcholine as well as to nitric oxide was decreased at 35 weeks of age. At 21 weeks of age, decreased sensitivity to nitric oxide was observed despite a normal response to acetylcholine. The response to sodium nitroprusside was normal in all groups. A decrease in aortic superoxide dismutase activity as well as an increase in aortic superoxide anion generated in the presence of NADH as measured by lucigenin chemiluminescence was observed in the group fed Western diet at 35 weeks. This provides evidence that altered superoxide anion could contribute to the deterioration in nitric oxide sensitivity that underlies the impaired endothelium-dependent relaxation. These data indicate that decreased sensitivity to nitric oxide may contribute to the development of impaired endothelium-dependent relaxation in hypercholesterolemia. The response to sodium nitroprusside appears not to reflect the decreased sensitivity of vascular smooth muscle to authentic nitric oxide.

Comparison of human apoA-I expression in mouse models of atherosclerosis after gene transfer using a second generation adenovirus

Gene transfer and expression of apolipoprotein A-I (apoA-I), the major protein component of high density lipoproteins (HDL), is a potentially attractive method for investigating the effects of apoA-I on atherosclerosis. We constructed a second generation recombinant adenovirus encoding the human apoA-I cDNA. This adenoviral vector or a control vector was injected intravenously into apoE-deficient mice fed a chow diet and low density lipoprotein (LDL) receptor (LDLR)-deficient mice fed Western diet, as well as control wild-type C57BL/6 mice. The mean peak plasma human apoA-I concentrations were 235, 324, and 276 mg/dL in apoE-deficient, LDLR-deficient, and wild-type mice, respectively. Human apoA-I concentrations decreased rapidly in apoE-deficient mice and were barely detectable 6 weeks after injection. In contrast, substantially higher levels of human apoA-I were sustained in LDLR-deficient mice. In wild-type mice, human apoA-I levels decreased more rapidly than in LDLR-deficient mice, but could still be detected in plasma for up to 8 months after virus injection. In apoE-deficient mice a substantial fraction of human apoA-I was found associated with triglyceride (TG)-rich lipoproteins; in contrast, in LDLR-deficient and wild-type mice the majority of human apoA-I was found in the HDL fraction. Finally, expression of human apoA-I caused a transient but significant increase in triglyceride levels in all three mouse models. In summary: 1) a second generation recombinant adenovirus resulted in high-level expression of human apoA-I in mice; 2) significantly higher levels of human apoA-I persisted for a longer time in LDLR-deficient mice compared with apoE-deficient mice; and 3) substantial human apoA-I was found associated with TG-rich lipoproteins in apoE-deficient but not LDLR-deficient mice.