Effect of PAR2 in regulating TNF-α and NAD(P)H oxidase in coronary arterioles in type 2 diabetic mice

Exercise Training Prevents Coronary Endothelial Dysfunction in Type 2 Diabetic Mice

Type 2 diabetes (T2D) is a leading risk factor for cardiovascular diseases including atherosclerosis and coronary heart disease. Exercise training (ET) is thought to have a beneficial effect on these disorders, but the basis for this effect is not fully understood. Because endothelial dysfunction plays a key role in the pathological events leading to cardiovascular complications in T2D, we hypothesized that the effects of ET will be evidenced by improvements in coronary endothelial function. To test this hypothesis, we assessed the effects of ET on vascular function of diabetic (db/db, Lepr(db)) mice by evaluating endothelial function of isolated coronary arterioles of wild-type (WT) and db/db mice with/without ET. Although dilation of vessels to the endothelial-independent vasodilator, sodium nitroprusside was not different between db/db and WT, dilation to the endothelial-dependent agonist, acetylcholine (ACh), was impaired in db/db compared to WT mice. Vasodilation to ACh was restored in db/db with ET and insulin sensitivity was improved in the db/db after ET. Exercise did not change body weight of db/db, but superoxide dismutase (SOD1 and SOD2) and phosphorylated- eNOS protein (Ser1177) expression in heart tissue was up-regulated whereas tumor necrosis factor-alpha (TNF-α) protein level was decreased by ET. Serum level of interleukin-6 (IL-6) was higher in db/db mice but ET decreased IL-6. This suggests that ET may improve endothelial function by increasing nitric oxide bioavailability as well as decreasing chronic inflammation. We suggest this connection may be the basis for the benefit of ET in T2D.

The potential effects of anti-diabetic medications on myocardial ischemia-reperfusion injury

Heart disease and stroke account for 65% of the deaths in people with diabetes mellitus (DM). DM and hyperglycemia cause systemic inflammation, endothelial dysfunction, a hypercoagulable state with impaired fibrinolysis and increased platelet degranulation, and reduced coronary collateral blood flow. DM also interferes with myocardial protection afforded by preconditioning and postconditioning. Newer anti-diabetic agents should not only reduce serum glucose and HbA1c levels, but also improve cardiovascular outcomes. The older sulfonylurea agent, glyburide, abolishes the benefits of ischemic and pharmacologic preconditioning, but newer sulfonylurea agents, such as glimepiride, may not interfere with preconditioning. GLP-1 analogs and sitagliptin, an oral dipeptidyl peptidase IV inhibitor, limit myocardial infarct size in animal models by increasing intracellular cAMP levels and activating protein kinase A, whereas metformin protects the heart by activating AMP-activated protein kinase. Both thiazolidinediones (rosiglitazone and pioglitazone) limit infarct size in animal models. The protective effect of pioglitazone is dependent on downstream activation of cytosolic phospholipase A(2) and cyclooxygenase-2 with subsequent increased production of 15-epi-lipoxin A(4), prostacyclin and 15-d-PGJ(2). We conclude that agents used to treat DM have additional actions that have been shown to affect the ability of the heart to protect itself against ischemia-reperfusion injury in preclinical models. However, the effects of these agents in doses used in the clinical setting to minimize ischemia-reperfusion injury and to affect clinical outcomes in patients with DM have yet to be shown. The clinical implications as well as the mechanisms of protection should be further studied.

Interferon-gamma induced adipose tissue inflammation is linked to endothelial dysfunction in type 2 diabetic mice

Interferon-gamma (IFNγ) has previously been associated with immuno-mediated inflammation in diet-induced obesity and type 1 diabetes. This study sought to define the role of IFNγ-induced adipose tissue inflammation in endothelial dysfunction in type 2 diabetes. We examined mesenteric adipose tissue (MAT) inflammation, and endothelial function of small mesenteric artery (SMA) in control mice (m Lepr(db)), diabetic mice (Lepr(db)), m Lepr(db) treated with IFNγ, and Lepr(db) treated with anti-IFNγ or anti-monocyte chemoattractant protein-1 (anti-MCP-1). mRNA and protein expression of IFNγ and MCP-1 were increased in MAT of Lepr(db), accompanied by increased T-lymphocyte and macrophage infiltration. Anti-IFNγ reduced MAT inflammatory cell infiltration and inflammatory cytokine expression in Lepr(db), while IFNγ treatment showed the opposite effects in m Lepr(db). Acetylcholine (ACh)-induced vasorelaxation of SMA was impaired in Lepr(db) versus m Lepr(db), but sodium nitroprusside (SNP)-induced vasorelaxation was comparable. Both anti-IFNγ and anti-MCP-1 improved endothelial function of Lepr(db), while IFNγ treatment impaired endothelial function of m Lepr(db). Superoxide production was higher in both MAT and SMA of Lepr(db) mice, and anti-IFNγ reduced MAT and SMA superoxide production. Macrophage accumulation in the adventitia of SMA, and mRNA expression of MCP-1 in SMA were increased in Lepr(db) and IFNγ-treated m Lepr(db), but reduced in anti-IFNγ treated Lepr(db). These findings suggest IFNγ has a key role in the regulation of visceral adipose tissue inflammatory response and endothelial dysfunction in type 2 diabetes.

Coronary arterioles in type 2 diabetic (db/db) mice undergo a distinct pattern of remodeling associated with decreased vessel stiffness

Little is known about the impact of type 2 diabetes mellitus (DM) on coronary arteriole remodeling. The aim of this study was to determine the mechanisms that underlie coronary arteriole structural remodeling in type 2 diabetic (db/db) mice. Passive structural properties of septal coronary arterioles isolated from 12- to 16-week-old diabetic db/db and control mice were assessed by pressure myography. Coronary arterioles from 12-week-old db/db mice were structurally similar to age-matched controls. By 16 weeks of age, coronary wall thickness was increased in db/db arterioles (p < 0.01), while luminal diameter was reduced (control: 118 ± 5 μm; db/db: 102 ± 4 μm, p < 0.05), augmenting the wall-to-lumen ratio by 58% (control: 5.9 ± 0.6; db/db: 9.5 ± 0.4, p < 0.001). Inward hypertrophic remodeling was accompanied by a 56% decrease in incremental elastic modulus (p < 0.05, indicating decreased vessel coronary wall stiffness) and a ~30% reduction in coronary flow reserve (CFR) in diabetic mice. Interestingly, aortic pulse wave velocity and femoral artery incremental elastic modulus were increased (p < 0.05) in db/db mice, indicating macrovascular stiffness. Molecular tissue analysis revealed increased elastin-to-collagen ratio in diabetic coronaries when compared to control and a decrease in the same ratio in the diabetic aortas. These data show that coronary arterioles isolated from type 2 diabetic mice undergo inward hypertrophic remodeling associated with decreased stiffness and increased elastin-to-collagen ratio which results in a decreased CFR. This study suggests that coronary microvessels undergo a different pattern of remodeling from macrovessels in type 2 DM.

Bariatric surgery reduces visceral adipose inflammation and improves endothelial function in type 2 diabetic mice

OBJECTIVE

Bariatric surgery is emerging as an effective method to alleviate a multitude of medical conditions associated with morbid obesity and type 2 diabetes. However, little is known about the effects and mechanisms of bariatric surgery on visceral fat inflammation and endothelial dysfunction in type 2 diabetes. We hypothesize that bariatric surgery ameliorates interferon-γ-mediated adipose tissue inflammation/oxidative stress and improves endothelial function in type 2 diabetic mice.

METHODS AND RESULTS

Control mice (m Lepr(db)) and diabetic mice (Lepr(db)) were treated with either sham surgery or improved gastric bypass surgery and then were evaluated at 5, 10, 20, and 30 days to assess postsurgical effects. Surgery reduced body weight, abdominal adiposity, blood glucose level, and food intake in Lepr(db). The surgery-induced decrease in visceral adiposity was accompanied by amelioration of T-lymphocytes and macrophage infiltration, as well as reduction in the expression of interferon-γ and other inflammatory cytokines in the mesenteric adipose tissue (MAT) of Lepr(db) mice. Furthermore, surgery improved endothelium-dependent, but not endothelium-independent, vasorelaxation in small mesenteric arteries (SMA) of Lepr(db) mice. The improvement in endothelial function was largely attenuated by nitric oxide synthase inhibitor (L-NAME) incubation. Interferon-γ treatment increased the mRNA expression of tumor necrosis factor-α in the MAT of control mice and incubation of SMA of control mice with tumor necrosis factor-α caused impairment of endothelial function. Superoxide production in MAT/SMA and nitrotyrosine protein level in SMA were elevated in diabetic mice. Surgery reduced MAT/SMA oxidative stress in Lepr(db) mice.

CONCLUSIONS

The amelioration of adipose tissue inflammation and the improvement of endothelial function may represent important mechanisms that result in cardiovascular benefits after bariatric surgery.

NADPH oxidases in cardiovascular disease: insights from in vivo models and clinical studies

NADPH oxidase family enzymes (or NOXs) are the major sources of reactive oxygen species (ROS) that are implicated in the pathophysiology of many cardiovascular diseases. These enzymes appear to be especially important in the modulation of redox-sensitive signalling pathways that underlie key cellular functions such as growth, differentiation, migration and proliferation. Seven distinct members of the family have been identified of which four (namely NOX1, 2, 4 and 5) may have cardiovascular functions. In this article, we review our current understanding of the roles of NOX enzymes in several common cardiovascular disease states, with a focus on data from genetic studies and clinical data where available.

The role of mitochondrial K(ATP) channels in cardioprotection

Pro-coagulant and pro-inflammatory intramyocardial (micro)vasculature plays an important role in acute myocardial infarction (AMI). Currently, inhibition of serine protease dipeptidyl peptidase 4 (DPP4) receives a lot of interest as an anti-hyperglycemic therapy in type 2 diabetes patients. However, DPP4 also possesses anti-thrombotic properties and may behave as an immobilized anti-coagulant on endothelial cells. Here, we studied the expression and activity of endothelial DPP4 in human myocardial infarction in relation to a prothrombogenic endothelial phenotype. Using (immuno)histochemistry, DPP4 expression and activity were found on the endothelium of intramyocardial blood vessels in autopsied control hearts (n = 9). Within the infarction area of AMI patients (n = 73), this DPP4 expression and activity were significantly decreased, coinciding with an increase in Tissue Factor expression. In primary human umbilical vein endothelial cells (HUVECs), Western blot analysis and digital imaging fluorescence microscopy revealed that DPP4 expression was strongly decreased after metabolic inhibition, also coinciding with Tissue Factor upregulation. Interestingly, inhibition of DPP4 activity with diprotin A also enhanced the amount of Tissue Factor encountered and induced the adherence of platelets under flow conditions. Ischemia induces loss of coronary microvascular endothelial DPP4 expression and increased Tissue Factor expression in AMI as well as in vitro in HUVECs. Our data suggest that the loss of DPP4 activity affects the anti-thrombogenic nature of the endothelium.