Milan Obradovic

Regulation of Inducible Nitric Oxide Synthase (iNOS) and its Potential Role in Insulin Resistance, Diabetes and Heart Failure.

Nitric oxide synthases (NOS) are the enzymes responsible for nitric oxide (NO) generation. NO is a reactive oxygen species as well as a reactive nitrogen species. It is a free radical which mediates several biological effects. It is clear that the generation and actions of NO under physiological and pathophysiological conditions are regulated and extend to almost every cell type and function within the circulation. In mammals 3 distinct isoforms of NOS have been identified: neuronal NOS (nNOS), inducible NOS (iNOS) and endothelial NOS (eNOS). The important isoform in the regulation of insulin resistance (IR) is iNOS. Understanding the molecular mechanisms regulating the iNOS pathway in normal and hyperglycemic conditions would help to explain some of vascular abnormalities observed in type 2 diabetes mellitus (T2DM). Previous studies have reported increased myocardial iNOS activity and expression in heart failure (HF). This review considers the recent animal studies which focus on the understanding of regulation of iNOS activity/expression and the role of iNOS agonists as potential therapeutic agents in treatment of IR, T2DM and HF.

PCSK9 Inhibition - A Novel Mechanism to Treat Lipid Disorders?

Plasma low-density lipoprotein cholesterol (LDL-C) is one of the biomarkers of cardiovascular disease (CVD) risk. LDL is cleared from the circulation preferentially through the LDL receptor (LDLR) pathway. Proprotein convertase subtilisin/kexin 9 (PCSK9) promotes the degradation of the LDLR. PCSK9 inhibition is attractive as a new strategy for lowering LDL-C levels, especially in combination with lipid lowering drugs such as statins. We review data from the available studies which focus on PCSK9 as a potential target in the treatment of hyperlipidemia. Further studies are still necessary to investigate the potential underlying mechanisms involved.

Resistin: An Inflammatory Cytokine. Role in Cardiovascular Diseases, Diabetes and the Metabolic Syndrome

Resistin is an adipocyte- and monocyte-derived cytokine which has been implicated in the modulation of insulin action, energy, glucose and lipid homeostasis. Resistin has been associated with insulin resistance and many of its known complications. As a molecular link between metabolic signals, inflammation, and vascular dysfunction, resistin can be proposed as playing a significant role in the heightened inflammatory state induced by metabolic stress linked to excessive caloric intake, thus contributing to the risk for metabolic syndrome (MetS), type 2 diabetes (T2DM), and cardiovascular diseases (CVD). In this review, we highlighted the role of resistin, as an inflammatory cytokine, in the development of CVD, T2DM and the MetS.

Peroxisome Proliferator-Activated Receptors and Atherosclerosis

The peroxisome proliferator-activated receptors (PPARs) represent the family of 3 nuclear receptor isoforms-PPARα, -γ, and -δ/β, which are encoded by different genes. As lipid sensors, they are primarily involved in regulation of lipid metabolism and subsequently in inflammation and atherosclerosis. Atherosclerosis considers accumulation of the cells and extracellular matrix in the vessel wall leading to the formation of atherosclerotic plaque, atherothrombosis, and other vascular complications. Besides existence of natural ligands for PPARs, their more potent synthetic ligands are fibrates and thiazolidindiones. Future investigations should now focus on the mechanisms of PPARs activation, which might present new approaches involved in the antiatherosclerotic effects revealed in this review. In addition, in this review we are presenting latest data from recent performed clinical studies which have focus on novel approach to PPARs agonists as potential therapeutic agents in the treatment of complex disease such as atherosclerosis.

In vivo effects of 17β-estradiol on cardiac Na(+)/K(+)-ATPase expression and activity in rat heart.

In this study the in vivo effects of estradiol in regulating Na(+)/K(+)-ATPase function in rat heart was studied. Adult male Wistar rats were treated with estradiol (40μg/kg, i.p.) and after 24h the animals were sacrificed and the heart excised. Following estradiol administration, cardiac Na(+)/K(+)-ATPase activity, expression of the α1 subunit, and phosphorylation of the α1 subunit were significantly increased. These animals also had significantly decreased levels of digoxin-like immunoreactive factor(s). Na(+) levels were also significantly reduced but to a level that was still within the normal physiological range, highlighting the ability of the Na(+)/K(+)-ATPase to balance the ionic composition following treatment with estradiol. Estradiol treated rats also showed increased phosphorylation of protein kinase B (Akt), and extracellular-signal-regulated kinase 1/2 (ERK1/2). We therefore suggest a role for Akt and/or ERK1/2 in estradiol-mediated regulation of cardiac Na(+)/K(+)-ATPase expression and activity in rat heart.

Effects of obesity and estradiol on Na+/K+-ATPase and their relevance to cardiovascular diseases

Obesity is associated with aberrant sodium/potassium-ATPase (Na(+)/K(+)-ATPase) activity, apparently linked to hyperglycemic hyperinsulinemia, which may repress or inactivate the enzyme. The reduction of Na(+)/K(+)-ATPase activity in cardiac tissue induces myocyte death and cardiac dysfunction, leading to the development of myocardial dilation in animal models; this has also been documented in patients with heart failure (HF). During several pathological situations (cardiac insufficiency and HF) and in experimental models (obesity), the heart becomes more sensitive to the effect of cardiac glycosides, due to a decrease in Na(+)/K(+)-ATPase levels. The primary female sex steroid estradiol has long been recognized to be important in a wide variety of physiological processes. Numerous studies, including ours, have shown that estradiol is one of the major factors controlling the activity and expression of Na(+)/K(+)-ATPase in the cardiovascular (CV) system. However, the effects of estradiol on Na(+)/K(+)-ATPase in both normal and pathological conditions, such as obesity, remain unclear. Increasing our understanding of the molecular mechanisms by which estradiol mediates its effects on Na(+)/K(+)-ATPase function may help to develop new strategies for the treatment of CV diseases. Herein, we discuss the latest data from animal and clinical studies that have examined how pathophysiological conditions such as obesity and the action of estradiol regulate Na(+)/K(+)-ATPase activity.

Estradiol In Vivo Induces Changes in Cardiomyocytes Size in Obese Rats

We studied the in vivo effects of estradiol on size and biochemical parameters of cardiomyocytes in pathophysiological conditions such as obesity and insulin resistance. Male Wistar rats were normally fed (controls, n = 7) or fed with high-fat diet (obese, n = 14). Half of the obese rats (obese + estradiol, n = 7) were treated with a single dose of estradiol (40 μg/kg, intraperitoneally) and 24 hours after treatment all the rats were killed. Estradiol in vivo in obese rats resulted in a significant increase in protein kinase B (Akt) activation (P < .05) and decrease in heart mass (P < .05), ratio of the heart mass/body mass (P < .05), transverse diameters of cardiomyocytes (P < .001), concentration of serum high-sensitivity C-reactive protein (P < .001), and total cholesterol (P < .01) compared with obese nontreated rats. Our results suggest that estradiol in obese/IR rats affects the size of cardiomyocytes and its actions lead in vivo to a reduction in obesity-induced cardiac hypertrophy, via Akt.

A review of the cardiovascular and anti-atherogenic effects of ghrelin.

Ghrelin is a peptide hormone produced mainly in the stomach that has widespread tissue distribution and diverse hormonal, metabolic and cardiovascular activities. The circulating ghrelin concentration increases during fasting and decreases after food intake. Ghrelin secretion may thus be initiated by food intake and is possibly controlled by nutritional factors. Lean subjects have increased levels of circulating ghrelin compared with obese subjects. Recent reports show that low plasma ghrelin is associated with elevated fasting insulin levels, insulin resistance and type 2 diabetes mellitus. Factors involved in the regulation of ghrelin secretion have not yet been defined; however, it is assumed that blood glucose levels represent a significant regulator. Recent evidence indicates that ghrelin can increase myocardial contractility, enhance vasodilatation, and has protective effect from myocardial damage. It has been shown that ghrelin may improve cardiac function through growth hormone (GH)-dependent mechanisms but there is also evidence to suggest that ghrelins cardioprotective activity is independent of GH. Recent data demonstrate that ghrelin can influence key events in atherogenesis. Thus, ghrelin may be a new target for the treatment of some cardiovascular diseases. In this review, we consider the current literature focusing on ghrelin as a potential antiatherogenic agent in the treatment of various pathophysiological conditions.

A high fat diet induces sex-specific differences in hepatic lipid metabolism and nitrite/nitrate in rats

Men and women differ substantially with regard to the severity of insulin resistance (IR) but the underlying mechanism(s) of how this occurs is poorly characterized. We investigated whether a high fat (HF) diet resulted in sex-specific differences in nitrite/nitrate production and lipid metabolism and whether these variances may contribute to altered obesity-induced IR. Male and female Wistar rats were fed a standard laboratory diet or a HF diet for 10 weeks. The level of plasma nitrite/nitrate, as well as free fatty acid (FFA), in both plasma and liver lysates were assessed. The levels of inducible nitric oxide (NO) synthase (iNOS), p65 subunit of NFκB, total and phosphorylated forms of Akt, mTOR and PDK-1 in lysates, and the levels of glucose transporter 2 (Glut-2) and fatty acid translocase/cluster of differentiation 36 (FAT/CD36) in plasma membrane fractions of liver were assessed. HF-fed male rats exhibited a significant increase in plasma nitrite/nitrate, and hepatic FFA and FAT/CD36 levels compared with controls. They also displayed a relative decrease in iNOS and Glut-2 levels in the liver. Phosphorylation of Akt (at Ser(473) and Thr(308)), mTOR and PDK-1 was also reduced. HF-fed female rats exhibited increased levels of NFκB-p65 in liver compared with controls, while levels of Glut-2, FAT/CD36 and Akt phosphorylation at Thr(308) and PDK-1 were decreased. Our results reveal that altered lipid and glucose metabolism in obesity, lead to altered iNOS expression and nitrite/nitrate production. It is likely that this mechanism contributes to sex-specific differences in the development of IR.

Interrelatedness between C-reactive protein and oxidized low-density lipoprotein

Abstract C-reactive protein (CRP) is a marker of inflammation. Atherosclerosis is now recognized as inflammatory disease, and it seems that CRP directly contributes to atherogenesis. Oxidation of low-density lipoprotein (LDL) molecule increases the uptake of lipid products by macrophages leading to cholesterol accumulation and subsequent foam cell formation. The elevated levels of high sensitivity CRP (hsCRP) and oxidized LDL (OxLDL) in the blood were found to be associated with cardiovascular diseases (CVD). In this review, we highlighted the evidence that CRP and OxLDL are involved in interrelated (patho) physiological pathways. The findings on association between hsCRP and OxLDL in the clinical setting will be also summarized.