Atherosclerotic lesion formation and triglyceride storage in obese apolipoprotein AI-deficient mice

Protective Effect of Edaravone Against Oxidative Stress in C2C12 Myoblast and Impairment of Skeletal Muscle Regeneration Exposed to Ischemic Injury in Ob/ob Mice

Background

The aims of this study were to analyze the effects of the administration of edaravone on C2C12 myoblasts exposed to oxidative stress; to evaluate the skeletal muscles in ob/ob mice; and to analyze the effect of the administration of edaravone in the regeneration of skeletal muscle after ischemic injury.

Methods

In C2C12 myoblasts, oxidative stress was induced by the exposure to 250 μM H₂O₂ for 4 h with or without pretreatment of 100 μM edaravone. Thereafter, the viability and expression of TNF-α were analyzed by MTS assay and PCR, respectively. Furthermore, an in vivo study was performed on male C57/BL6-ob/ob mice (10 weeks old) and the respective control mice. The skeletal muscles of tibialis anterior and gastrocnemius were excised for histological analysis and TBARS assay after the measurement of blood flow. In addition, the regeneration of the skeletal muscles was analyzed for the expression of MyoD 7 days after the ligation of the right femoral artery.

Results

Edaravone significantly inhibited the reduction of the viability as well as upregulation of TNF-α expression by treatment with H₂O₂. In ob/ob mice, wet weight of muscles was significantly lower than that in control mice. In histology, ob/ob mice had significantly less multi-angle shaped myofibers and a significantly high level of MDA. Furthermore, MyoD expression was lower in ob/ob mice than in control mice after the ischemic injury, while edaravone (3 mg/kg) increasingly enhanced MyoD expression.

Conclusion

Edaravone attenuated the oxidative stress on C2C12 myoblasts, and was effective to regeneration of skeletal muscles after ischemia in ob/ob mice.

Applications and Limitations of Mouse Models for Understanding Human Atherosclerosis

Most of the biological understanding of mechanisms underlying coronary artery disease (CAD) derives from studies of mouse models. The identification of multiple CAD loci and strong candidate genes in large human genome-wide association studies (GWASs) presented an opportunity to examine the relevance of mouse models for the human disease. We comprehensively reviewed the mouse literature, including 827 literature-derived genes, and compared it to human data. First, we observed striking concordance of risk factors for atherosclerosis in mice and humans. Second, there was highly significant overlap of mouse genes with human genes identified by GWASs. In particular, of the 46 genes with strong association signals in CAD GWASs that were studied in mouse models, all but one exhibited consistent effects on atherosclerosis-related phenotypes. Third, we compared 178 CAD-associated pathways derived from human GWASs with 263 from mouse studies and observed that the majority were consistent between the species.

Associations of ApoAI and ApoB-containing lipoproteins with AngII-induced abdominal aortic aneurysms in mice

OBJECTIVE

Dyslipidemia is implicated in abdominal aortic aneurysms (AAAs) in humans and angiotensin (Ang) II-infused mice. This study determined effects of major lipoprotein classes on AngII-induced AAAs using multiple mouse strains with dietary and pharmacological manipulations.

APPROACH AND RESULTS

Western diet had minor effects on plasma cholesterol concentrations and the low incidence of AngII-induced AAAs in C57BL/6J mice. Low incidence of AAAs in this strain was not attributed to protection from high-density lipoprotein, because apolipoprotein (apo) AI deficiency did not increase AngII-induced AAAs. ApoAI deletion also failed to alter AAA occurrence in hypercholesterolemic mice. Low-density lipoprotein receptor-/- mice fed normal diet had low incidence of AngII-induced AAAs. Western diet feeding of this strain provoked pronounced hypercholesterolemia because of increased apoB-containing lipoproteins with attendant increases of atherosclerosis in both sexes, but AAAs only in male mice. ApoE-deficient mice fed normal diet were modestly hypercholesterolemic, whereas this strain fed Western diet was severely hypercholesterolemic because of increased apoB-containing lipoprotein concentrations. The latter augmented atherosclerosis, but did not change the high incidence of AAAs in this strain. To determine whether reductions in apoB-containing lipoproteins influenced AngII-induced AAAs, ezetimibe was administered at a dose that partially reduced plasma cholesterol concentrations to ApoE-deficient mice fed Western diet. This decreased atherosclerosis, but not AAAs. This ezetimibe dose in ApoE-deficient mice fed normal diet significantly decreased plasma apoB-containing lipoprotein concentrations and reduced AngII-induced AAAs.

CONCLUSIONS

ApoB-containing lipoproteins contribute to augmentation of AngII-induced AAA in male mice. However, unlike atherosclerosis, AAA occurrence was not correlated with increases in plasma apoB-containing lipoprotein concentrations.

The Influence of an Obesogenic Diet on Oxysterol Metabolism in C57BL/6J Mice

Our current understanding of oxysterol metabolism during different disease states such as obesity and dyslipidemia is limited. Therefore, the aim of this study was to determine the effect of diet-induced obesity on the tissue distribution of various oxysterols and the mRNA expression of key enzymes involved in oxysterol metabolism. To induce obesity, male C57BL/6J mice were fed a high fat-cholesterol diet for 24 weeks. Following diet-induced obesity, plasma levels of 4β-hydroxycholesterol, 5,6α-epoxycholesterol, 5,6β-epoxycholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, and 27-hydroxycholesterol were significantly (P < 0.05) increased. In the liver and adipose tissue of the obese mice, 4β-hydroxycholesterol was significantly (P < 0.05) increased, whereas 27-hydroxycholesterol was increased only in the adipose tissue. No significant changes in either hepatic or adipose tissue mRNA expression were observed for oxysterol synthesizing enzymes 4β-hydroxylase, 27-hydroxylase, or 7α-hydroxylase. Hepatic mRNA expression of SULT2B1b, a key enzyme involved in oxysterol detoxification, was significantly (P < 0.05) elevated in the obese mice. Interestingly, the appearance of the large HDL₁ lipoprotein was observed with increased oxysterol synthesis during obesity. In diet-induced obese mice, dietary intake and endogenous enzymatic synthesis of oxysterols could not account for the increased oxysterol levels, suggesting that nonenzymatic cholesterol oxidation pathways may be responsible for the changes in oxysterol metabolism.

Hypercholesterolemia and reduced HDL-C promote hematopoietic stem cell proliferation and monocytosis: studies in mice and FH children

Previous studies have shown that mice with defects in cellular cholesterol efflux show hematopoietic stem cell (HSPC) and myeloid proliferation, contributing to atherogenesis. We hypothesized that the combination of hypercholesterolemia and defective cholesterol efflux would promote HSPC expansion and leukocytosis more prominently than either alone. We crossed Ldlr(-/-) with Apoa1(-/-) mice and found that compared to Ldlr(-/-) mice, Ldlr(-/-)/Apoa1(+/-) mice, with similar LDL-cholesterol levels but reduced HDL-cholesterol (HDL-C) levels, had expansion of HSPCs, monocytosis and neutrophilia. Ex vivo studies showed that HSPCs expressed high levels of Ldlr, Scarb1 (Srb1), and Lrp1 and were able to take up both native and oxidized LDL. Native LDL directly stimulated HSPC proliferation, while co-incubation with reconstituted HDL attenuated this effect. We also assessed the impact of HDL-C levels on monocytes in children with familial hypercholesterolemia (FH) (n = 49) and found that subjects with the lowest level of HDL-C, had increased monocyte counts compared to the mid and higher HDL-C levels. Overall, HDL-C was inversely correlated with the monocyte count. These data suggest that in mice, a balance of cholesterol uptake and efflux mechanisms may be one factor in driving HSPC proliferation and monocytosis. Higher monocyte counts in children with FH and low HDL-cholesterol suggest a similar pattern in humans.

Effect of a novel biphenyl compound, VMNS2e on ob/ob mice

VMNS2e is a novel biphenyl compound, which in previous studies had showed most favourable interactions with the active site of protein tyrosine phosphatase 1B (PTP1B). The effect of acute and chronic treatment of VMNS2e (30mg/kg) was investigated in ob/ob mice. Plasma glucose was measured after acute administration of VMNS2e (30mg/kg) in both lean and ob/ob mice. In the chronic study, VMNS2e (30mg/kg) was given orally, once daily for 60days. Metformin (300mg/kg) was taken as standard therapy. Body weight, food intake and blood glucose was measured weekly while glycosylated hemoglobin A(1c) (HbA(1c)), insulin, triglyceride, total cholesterol, low density lipoprotein (LDL), fructosamine, non esterified fatty acid and organ weight were estimated after the completion of treatment period. Oral glucose tolerance test was performed on the last day of treatment. Liver and epididymal fat weights were taken. Acute dose of VMNS2e elicited an anti hyperglycemic effect. It reduced blood glucose by 14% (0.5h) and 35.6% (6h). Chronic VMNS2e treatment improved glucose tolerance by 25.3%. It decreased blood glucose levels. Hyperinsulinemia was reduced (19.6%). VMNS2e treatment had no significant effect on body weight and food consumption. VMNS2e treatment exhibited significant reduction (28.2%) in HbA(1c), plasma triglyceride (49%), LDL (24%) and fructosamine (13%) levels. VMNS2e treatment did not alter total cholesterol and non esterified fatty acid levels. Epididymal fat/body weight ratio was reduced (26.3%). VMNS2e exhibited both acute and chronic anti hyperglycemic effect, insulin sensitivity along with improvement in various lipid parameters and glycemic control.

Mouse models of the metabolic syndrome

The metabolic syndrome (MetS) is characterized by obesity concomitant with other metabolic abnormalities such as hypertriglyceridemia, reduced high-density lipoprotein levels, elevated blood pressure and raised fasting glucose levels. The precise definition of MetS, the relationships of its metabolic features, and what initiates it, are debated. However, obesity is on the rise worldwide, and its association with these metabolic symptoms increases the risk for diabetes and cardiovascular disease (among many other diseases). Research needs to determine the mechanisms by which obesity and MetS increase the risk of disease. In light of this growing epidemic, it is imperative to develop animal models of MetS. These models will help determine the pathophysiological basis for MetS and how MetS increases the risk for other diseases. Among the various animal models available to study MetS, mice are the most commonly used for several reasons. First, there are several spontaneously occurring obese mouse strains that have been used for decades and that are very well characterized. Second, high-fat feeding studies require only months to induce MetS. Third, it is relatively easy to study the effects of single genes by developing transgenic or gene knockouts to determine the influence of a gene on MetS. For these reasons, this review will focus on the benefits and caveats of the most common mouse models of MetS. It is our hope that the reader will be able to use this review as a guide for the selection of mouse models for their own studies.