Dyslipidaemia in type II diabetic mice does not aggravate contractile impairment but increases ventricular stiffness.

AIMS: Type II diabetes, often associated with abdominal obesity, frequently leads to heart failure. Clinical and epidemiological evidence suggests that supplemental dyslipidaemia and hypertension, as clustered in the metabolic syndrome, aggravate the cardiovascular outcome. The differential impact of type II diabetes and the metabolic syndrome on left ventricular function, however, remains incompletely defined. METHODS AND RESULTS: We studied left ventricular function in vivo using pressure-volume analysis in obese diabetic mice with leptin deficiency (ob/ob) and obese diabetic dyslipidemic mice with combined leptin and low-density lipoprotein-receptor deficiency (DKO). ob/ob and DKO mice developed a diabetic cardiomyopathy, characterized by impaired contractility and relaxation, from the age of 24 weeks onwards. This was-at least partially-explained by increased apoptosis and disturbed Ca(2+) reuptake in the sarcoplasmic reticulum (SR) in both mouse models. DKO, but not ob/ob, developed increased end-diastolic ventricular stiffness, paralleled by increased left ventricular myocardial fibrosis. Cardiac output was preserved in ob/ob mice by favourable loading conditions, whereas it decreased in DKO mice. CONCLUSIONS: Type II diabetes in mice leads to impaired contractility and relaxation due to disturbed Ca(2+) reuptake in the SR, but only when dyslipidaemia and hypertension are superimposed does vascular-ventricular stiffening increase and left ventricular myocardial fibrosis develop.

Rosuvastatin increases vascular endothelial PPARgamma expression and corrects blood pressure variability in obese dyslipidaemic mice.

AIMS: Statins improve atherosclerotic diseases through cholesterol-reducing effects. Whether the latter exclusively mediate similar benefits, e.g. on hypertension, in the metabolic syndrome is unclear. We examined the effects of rosuvastatin on the components of this syndrome, as reproduced in mice doubly deficient in LDL receptors and leptin (DKO). METHODS AND RESULTS: DKO received rosuvastatin (10 mg/kg/day or 20 mg/kg/day) or saline for 12 weeks. Saline-treated DKO mice had elevated blood pressure (BP) and nitric oxide-sensitive BP variability recorded by telemetry. Compared with saline, rosuvastatin (20 mg/kg/day) had no effect on weight gain and a minor effect on plasma cholesterol. Despite incomplete correction of insulin sensitivity, rosuvastatin fully corrected BP and its variability (P = 0.01), in conjunction with upregulation of PPARgamma (but not PPARalpha) in the aortic arch. Rosuvastatin similarly increased PPARgamma (P = 0.002) and SOD1 (P = 0.01) expression in isolated endothelial cells. Both GW9662, a PPARgamma-specific antagonist, and siRNA raised against PPARgamma abrogated rosuvastatin's effect, which was reproduced in PPARgamma- (but not PPARalpha-) dependent transactivation assays. CONCLUSION: Beyond partial improvement in insulin sensitivity, rosuvastatin normalized BP homeostasis in obese dyslipidaemic mice independently of changes in body weight or plasma cholesterol. Upregulation of PPARgamma and SOD1 in the endothelium may be involved as a unique vasculoprotective effect of statin treatment.

Defective leptin/leptin receptor signaling improves regulatory T cell immune response and protects mice from atherosclerosis.

OBJECTIVE: Obesity is a major risk factor for atherosclerosis and is associated with increased cardiovascular morbidity and mortality. However, the precise molecular pathways responsible for this close association remain poorly understood. METHODS AND RESULTS: In this study, we report that leptin-deficiency (ob/ob) in low-density lipoprotein receptor knockout (ldlr(-/-)) mice induces an unexpected 2.2- to 6-fold reduction in atherosclerotic lesion development, compared with ldlr(-/-) mice having similar total cholesterol levels. Ldlr(-/-)/ob/ob mice show reduced T cell helper type 1 (Th1) response, enhanced expression of Foxp3, the specification transcription factor of regulatory T (Treg) cells, and improved Treg cell function. Leptin receptor-deficient (db/db) mice display marked increase in the number and suppressive function of Treg cells. Supplementation of Treg-deficient lymphocytes with Treg cells from db/db mice in an experimental model of atherosclerosis induces a significant reduction of lesion size and a marked inhibition of interferon (INF)-gamma production, compared with supplementation by Treg cells from wild-type mice. CONCLUSIONS: These results identify a critical role for leptin/leptin receptor pathway in the modulation of the regulatory immune response in atherosclerosis, and suggest that alteration in regulatory immunity may predispose obese individuals to atherosclerosis.

Human paraoxonase-1 overexpression inhibits atherosclerosis in a mouse model of metabolic syndrome.

BACKGROUND: The metabolic syndrome is typified by obesity, dyslipidemia, diabetes, hypertension, increased oxidative stress, and accelerated atherosclerosis. Paraoxonase1 (PON1), a high-density lipoprotein (HDL)-associated antioxidant enzyme that prevents the oxidation of low-density lipoprotein (LDL), is low in the metabolic syndrome. METHODS AND RESULTS: We used adenovirus-mediated PON1 gene transfer (AdPON1) to overexpress human PON1 in mice with combined leptin and LDL receptor deficiency, a model of metabolic syndrome. PON1 activity, plasma lipids, the titer of autoantibodies against malondialdehyde (MDA)-modified LDL, and atherosclerosis in AdPON1 mice were compared with these in mice that received a control recombinant adenovirus (AdRR5). PON1 activity was increased 4.4-fold (P<0.001) in AdPON1 mice (N = 12), whereas in AdRR5 mice (N = 11) activity did not change. Expressing human PON1 significantly reduced the total plaque volume, the volume of plaque macrophages, and of plaque-associated oxidized LDL. It increased the percentage of smooth muscle cells in the plaques. Expressing human PON1 lowered the titer of autoantibodies against MDA-modified LDL, a proxy for oxidized LDL in mice. It had no overall effect on plasma total cholesterol and triglycerides, as evidenced by the similar area under the curves, and on the HDL distribution profile. CONCLUSIONS: Our data suggest that in this mouse model of metabolic syndrome, expressing human PON1 inhibited the development of atherosclerosis, probably by reducing the amount of oxidized LDL in plasma and in the plaque, thereby preventing its proatherogenic effects. Adenovirus-mediated gene transfer of human PON1 may be a potential and useful tool to prevent/retard atherosclerosis in humans.

Peroxisome proliferator-activated receptor-alpha,gamma-agonist improves insulin sensitivity and prevents loss of left ventricular function in obese dyslipidemic mice.

OBJECTIVE: We investigated the effect of a dual peroxisome proliferator-activated receptor (PPAR)alpha,gamma-agonist on atherosclerosis and cardiac function in mice with combined leptin and low-density lipoprotein receptor deficiency (DKO). In these mice, obesity, diabetes, and hyperlipidemia are associated with accelerated atherosclerosis and loss of cardiac function. METHODS AND RESULTS: We treated 12-week-old DKO mice with the PPARalpha,gamma-agonist (S)-3-(4-(2-carbazol-9-yl-ethoxy) phenyl-2-ethoxy-propionic-acid) for 12 weeks. The agonist lowered free fatty acids with 42% and increased insulin sensitivity with 76%. It had no effect on plasma cholesterol and triglycerides. RT-PCR analysis showed that the agonist increased the expression of fatty acid transport protein-4, fatty acid binding protein-4, glucose transporter-4, hormone-sensitive lipase, and adiponectin in white adipose tissue that was associated with the increase in insulin sensitivity. At 24 weeks, the shortening fraction (SF) of placebo DKO mice was 30% lower than that of C57BL6 mice. The PPAR agonist increased PPARgamma but not PPARalpha expression in the heart and prevented loss of left ventricular function. Adiponectin correlated positively with PPARgamma in the heart and with SF. The agonist had no effect on atherosclerosis in the aortic arch of DKO mice. CONCLUSIONS: The dual PPARalpha,gamma-agonist improved insulin sensitivity without affecting cholesterol and triglycerides. This was associated with induction of PPARgamma in the heart and prevention of loss of left ventricle function.

Weight-loss-associated induction of peroxisome proliferator-activated receptor-alpha and peroxisome proliferator-activated receptor-gamma correlate with reduced atherosclerosis and improved cardiovascular function in obese insulin-resistant mice.

BACKGROUND: Weight loss in obese insulin-resistant but not in insulin-sensitive persons reduces coronary heart disease risk. To what extent changes in gene expression are related to atherosclerosis and cardiovascular function is unknown. METHODS AND RESULTS: We studied the effect of diet restriction-induced weight loss on gene expression in the adipose tissue, the heart, and the aortic arch and on atherosclerosis and cardiovascular function in mice with combined leptin and LDL-receptor deficiency. Obesity, hypertriglyceridemia, and insulin resistance are associated with hypertension, impaired left ventricular function, and accelerated atherosclerosis in those mice. Compared with lean mice, peroxisome proliferator-activated receptors (PPAR)-alpha and PPAR-gamma expression was downregulated in obese double-knockout mice. Diet restriction caused a 45% weight loss, an upregulation of PPAR-alpha and PPAR-gamma, and a change in the expression of genes regulating glucose transport and insulin sensitivity, lipid metabolism, oxidative stress, and inflammation, most of which are under the transcriptional control of these PPARs. Changes in gene expression were associated with increased insulin sensitivity, decreased hypertriglyceridemia, reduced mean 24-hour blood pressure and heart rate, restored circadian variations of blood pressure and heart rate, increased ejection fraction, and reduced atherosclerosis. PPAR-alpha and PPAR-gamma expression was inversely related to plaque volume and to oxidized LDL content in the plaques. CONCLUSIONS: Induction of PPAR-alpha and PPAR-gamma in adipose tissue, heart, and aortic arch is a key mechanism for reducing atherosclerosis and improving cardiovascular function resulting from weight loss. Improved lipid metabolism and insulin signaling is associated with decreased tissue deposition of oxidized LDL that increases cardiovascular risk in persons with the metabolic syndrome.

Increased low-density lipoprotein oxidation and impaired high-density lipoprotein antioxidant defense are associated with increased macrophage homing and atherosclerosis in dyslipidemic obese mice: LCAT gene transfer decreases atherosclerosis.

BACKGROUND: Obesity-associated dyslipidemia in humans is associated with increased low-density lipoprotein (LDL) oxidation. Mice with combined leptin and LDL receptor deficiency are obese and show severe dyslipidemia and insulin resistance. We investigated the association between oxidation of apolipoprotein B-containing lipoproteins, high-density lipoprotein (HDL) antioxidant defense, and atherosclerosis in these mice. METHODS AND RESULTS: LDL receptor knockout (LDLR-/-), leptin-deficient (ob/ob), double-mutant (LDLR-/-;ob/ob), and C57BL6 mice were fed standard chow. Double-mutant mice had higher levels of non-HDL (P<0.001) and HDL (P<0.01) cholesterol and of triglycerides (P<0.001). They also had higher oxidative stress, evidenced by higher titers of autoantibodies against malondialdehyde-modified LDL (P<0.001). C57BL6 and ob/ob mice had no detectable lesions. Lesions covered 20% of total area of the thoracic abdominal aorta in double-mutant mice compared with 3.5% in LDLR-/- mice (P<0.01). Higher macrophage homing and accumulation of oxidized apolipoprotein B-100-containing lipoproteins were associated with larger plaque volumes in the aortic root of double-mutant mice (P<0.01). The activity of the HDL-associated antioxidant enzymes paraoxonase and lecithin:cholesterol acyltransferase (LCAT) (ANOVA; P<0.0001 for both) was lower in double-mutant mice. Adenovirus-mediated LCAT gene transfer in double-mutant mice increased plasma LCAT activity by 64% (P<0.01) and reduced the titer of autoantibodies by 40% (P<0.01) and plaque volume in the aortic root by 42% (P<0.05) at 6 weeks. CONCLUSIONS: Dyslipidemia and insulin resistance in obese LDL receptor-deficient mice are associated with increased oxidative stress and impaired HDL-associated antioxidant defense, evidenced by decreased paraoxonase and LCAT activity. Transient LCAT overexpression was associated with a reduction of oxidative stress and atherosclerosis.