Diet-induced obesity and diabetes reduce coronary responses to nitric oxide due to reduced bioavailability in isolated mouse hearts

Impact of different hormones on the regulation of nitric oxide in diabetes

Polymetabolic syndrome achieved pandemic proportions and dramatically influenced public health systems functioning worldwide. Chronic vascular complications are the major contributors to increased morbidity, disability, and mortality rates in diabetes patients. Nitric oxide (NO) is among the most important vascular bed function regulators. However, NO homeostasis is significantly deranged in pathological conditions. Additionally, different hormones directly or indirectly affect NO production and activity and subsequently act on vascular physiology. In this paper, we summarize the recent literature data related to the effects of insulin, estradiol, insulin-like growth factor-1, ghrelin, angiotensin II and irisin on the NO regulation in physiological and diabetes circumstances.

Expanding landscape of coronary microvascular disease in co-morbid conditions: Metabolic disease and beyond

Coronary microvascular disease (CMD) and impaired coronary blood flow control are defects that occur early in the pathogenesis of heart failure in cardiometabolic conditions, prior to the onset of atherosclerosis. In fact, recent studies have shown that CMD is an independent predictor of cardiac morbidity and mortality in patients with obesity and metabolic disease. CMD is comprised of functional, structural, and mechanical impairments that synergize and ultimately reduce coronary blood flow in metabolic disease and in other co-morbid conditions, including transplant, autoimmune disorders, chemotherapy-induced cardiotoxicity, and remote injury-induced CMD. This review summarizes the contemporary state-of-the-field related to CMD in metabolic and these other co-morbid conditions based on mechanistic data derived mostly from preclinical small- and large-animal models in light of available clinical evidence and given the limitations of studying these mechanisms in humans. In addition, we also discuss gaps in current understanding, emerging areas of interest, and opportunities for future investigations in this field.

Anti-obesity and anti-diabetic effects of L-citrulline are sex-dependent

AIMS

Anti-diabetic and anti-obesity effects of L-citrulline (Cit) have been reported in male rats. This study determined sex differences in response to Cit in Wistar rats.

MAIN METHODS

Type 2 diabetes (T2D) was induced using a high-fat diet followed by low-dose of streptozotocin (30 mg/kg) injection. Male and female Wistar rats were divided into 4 groups (n = 6/group): Control, control+Cit, T2D, and T2D + Cit. Cit (4 g/L in drinking water) was administered for 8 weeks. Obesity indices were recorded, serum fasting glucose and lipid profile were measured, and glucose and pyruvate tolerance tests were performed during the Cit intervention. White (WAT) and brown (BAT) adipose tissues were weighted, and the adiposity index was calculated at the end of the study.

KEY FINDINGS

Cit was more effective in decreasing fasting glucose (18 % vs. 11 %, P = 0.0100), triglyceride (20 % vs. 14 %, P = 0.0173), and total cholesterol (16 % vs. 11 %, P = 0.0200) as well as decreasing gluconeogenesis and improving glucose tolerance, in females compared to male rats with T2D. Following Cit administration, decreases in WAT weight (16 % vs. 14 % for gonadal, 21 % vs. 16 % for inguinal, and 18 % vs. 13 % for retroperitoneal weight, all P < 0.0001) and increases in BAT weight (58 % vs. 19 %, for interscapular and 10 % vs. 7 % for axillary, all P < 0.0001) were higher in females than male rats with T2D. The decrease in adiposity index was also higher (11 % vs. 9 %, P = 0.0007) in females.

SIGNIFICANCE

The anti-obesity and anti-diabetic effects of Cit in rats are sex-dependent, with Cit being more effective in female than male rats.

Combination of Gold Nanoparticles with Carnitine Attenuates Brain Damage in an Obesity Animal Model

Obesity causes inflammation in the adipose tissue and can affect the central nervous system, leading to oxidative stress and mitochondrial dysfunction. Therefore, it becomes necessary to seek new therapeutic alternatives. Gold nanoparticles (GNPs) could take carnitine to the adipose tissue, thus increasing fatty acid oxidation, reducing inflammation, and, consequently, restoring brain homeostasis. The objective of this study was to investigate the effects of GNPs associated with carnitine on the neurochemical parameters of obesity-induced mice. Eighty male Swiss mice that received a normal lipid diet (control group) or a high-fat diet (obese group) for 10 weeks were used. At the end of the sixth week, the groups were divided for daily treatment with saline, GNPs (70 µg/kg), carnitine (500 mg/kg), or GNPs associated with carnitine, respectively. Body weight was monitored weekly. At the end of the tenth week, the animals were euthanized and the mesenteric fat removed and weighed; the brain structures were separated for biochemical analysis. It was found that obesity caused oxidative damage and mitochondrial dysfunction in brain structures. Treatment with GNPs isolated reduced oxidative stress in the hippocampus. Carnitine isolated decreased the accumulation of mesenteric fat and oxidative stress in the hippocampus. The combination of treatments reduced the accumulation of mesenteric fat and mitochondrial dysfunction in the striatum. Therefore, these treatments in isolation, become a promising option for the treatment of obesity.

Diabetic Nephropathy and Gaseous Modulators

Diabetic nephropathy (DN) remains the leading cause of vascular morbidity and mortality in diabetes patients. Despite the progress in understanding the diabetic disease process and advanced management of nephropathy, a number of patients still progress to end-stage renal disease (ESRD). The underlying mechanism still needs to be clarified. Gaseous signaling molecules, so-called gasotransmitters, such as nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), have been shown to play an essential role in the development, progression, and ramification of DN depending on their availability and physiological actions. Although the studies on gasotransmitter regulations of DN are still emerging, the evidence revealed an aberrant level of gasotransmitters in patients with diabetes. In studies, different gasotransmitter donors have been implicated in ameliorating diabetic renal dysfunction. In this perspective, we summarized an overview of the recent advances in the physiological relevance of the gaseous molecules and their multifaceted interaction with other potential factors, such as extracellular matrix (ECM), in the severity modulation of DN. Moreover, the perspective of the present review highlights the possible therapeutic interventions of gasotransmitters in ameliorating this dreaded disease.

Effects of Combined Inorganic Nitrate and Nitrite Supplementation on Cardiorespiratory Fitness and Skeletal Muscle Oxidative Capacity in Type 2 Diabetes: A Pilot Randomized Controlled Trial

Nitric oxide (NO) stimulates mitochondrial biogenesis in skeletal muscle. However, NO metabolism is disrupted in individuals with type 2 diabetes mellitus (T2DM) potentially contributing to their decreased cardiorespiratory fitness (i.e., VO2max) and skeletal muscle oxidative capacity. We used a randomized, double-blind, placebo-controlled, 8-week trial with beetroot juice containing nitrate (NO3−) and nitrite (NO2−) (250 mg and 20 mg/day) to test potential benefits on VO2max and skeletal muscle oxidative capacity in T2DM. T2DM (N = 36, Age = 59 ± 9 years; BMI = 31.9 ± 5.0 kg/m2) and age- and BMI-matched non-diabetic controls (N = 15, Age = 60 ± 9 years; BMI = 29.5 ± 4.6 kg/m2) were studied. Mitochondrial respiratory capacity was assessed in muscle biopsies from a subgroup of T2DM and controls (N = 19 and N = 10, respectively). At baseline, T2DM had higher plasma NO3− (100%; p < 0.001) and lower plasma NO2− levels (−46.8%; p < 0.0001) than controls. VO2max was lower in T2DM (−26.4%; p < 0.001), as was maximal carbohydrate- and fatty acid-supported oxygen consumption in permeabilized muscle fibers (−26.1% and −25.5%, respectively; p < 0.05). NO3−/NO2− supplementation increased VO2max (5.3%; p < 0.01). Further, circulating NO2−, but not NO3−, positively correlated with VO2max after supplementation (R2= 0.40; p < 0.05). Within the NO3−/NO2− group, 42% of subjects presented improvements in both carbohydrate- and fatty acid-supported oxygen consumption in skeletal muscle (vs. 0% in placebo; p < 0.05). VO2max improvements in these individuals tended to be larger than in the rest of the NO3−/NO2− group (1.21 ± 0.51 mL/(kg*min) vs. 0.31 ± 0.10 mL/(kg*min); p = 0.09). NO3−/NO2− supplementation increases VO2max in T2DM individuals and improvements in skeletal muscle oxidative capacity appear to occur in those with more pronounced increases in VO2max.

Chronic nitrate administration increases the expression the genes involved in the browning of white adipose tissue in female rats

Nitrate, a nitric oxide (NO) donor, has antiobesity effect in female rats. This study hypothesized that the antiobesity effect of nitrate in female rats is due to the browning of white adipose tissue (WAT). Female Wistar rats (aged 8 months) were divided into two groups (n = 10/group): the control group received tap water and the nitrate group received water containing 100 mg/L of sodium nitrate for 9 months. At months 0, 3, 6, and 9, obesity indices were measured. At month 9, gonadal adipose tissue was used to measure messenger RNA (mRNA) and protein levels of peroxisome proliferator-activated receptor-γ (PPAR-γ), PPAR-γ coactivator 1-α (PGC1-α), uncoupling protein 1 (UCP1), and adipocyte density and area. After the 9-month intervention, nitrate-treated rats had lower body weight, body mass index, thoracic circumference, and abdominal circumference by 6.4% (p = .012), 9.1% (p = .029), 6.0% (p = .056), and 5.7% (p = .098), respectively. In addition, nitrate-treated rats had higher PPAR-γ (mRNA: 1.78-fold, p = .016 and protein: 19%, p = .076), PGC1-α (mRNA: 1.69-fold, p = .012 and protein: 68%, p = .001), and UCP1 (mRNA: 2.50-fold, p = .001 and protein: 81%, p = .001) in gonadal adipose tissue. Nitrate also reduced adipocyte area by 35% (p = .054) and increased adipocyte density by 31% (p = .086). In conclusion, antiobesity effect of nitrate in female rats is associated with increased browning of gonadal adipose tissue as indicated by higher expression of PPAR-γ, PGC1-α, and UCP1 and reduced adipocyte area and increased adipocyte density.

Impact of Vitamin D Supplementation on Inflammatory Markers' Levels in Obese Patients

In view of research suggesting a possible beneficial impact of vitamin D on systemic inflammatory response, the authors decided to investigate an influence of vitamin D supplementation on serum levels of certain inflammatory markers in obese patients. The current study included such biomarkers as interleukin-6 (IL-6), pituitary adenylate cyclase-activating peptide (PACAP), advanced oxidation protein products (AOPP), C-X3-C Motif Chemokine Ligand 1 (CX3CL1), monocyte chemoattractant protein-1 (MCP-1), and nitric oxide (NO). The measurements were performed with the ELISA method before and after 3-month-long supplementation of 2000 IU of vitamin D orally. The results showed that the therapy did not induce any statistically significant changes in serum levels of MCP-1, IL-6, CX3CL1, and PACAP. The supplementation was related to a significant increase in measurements of NO and AOPP levels, although the correlation analysis between vitamin D concentration after its supplementation and the concentration of the molecular parameters did not show significant relation. In conclusion, our study seems to contradict certain aspects of findings available in the literature regarding the vitamin D’s impact.

TGF-β: The missing link in obesity-associated airway diseases?

Obesity is emerging as a global public health epidemic. The co-morbidities associated with obesity significantly contribute to reduced quality of life, mortality, and global healthcare burden. Compared to other asthma comorbidities, obesity prominently engenders susceptibility to inflammatory airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), contributes to greater disease severity and evokes insensitivity to current therapies. Unlike in other metabolic diseases associated with obesity, the mechanistic link between obesity and airway diseases is only poorly defined. Transforming growth factor-β (TGF-β) is a pleiotropic inflammatory cytokine belonging to a family of growth factors with pivotal roles in asthma. In this review, we summarize the role of TGF-β in major obesity-associated co-morbidities to shed light on mechanisms of the diseases. Literature evidence shows that TGF-β mechanistically links many co-morbidities with obesity through its profibrotic, remodeling, and proinflammatory functions. We posit that TGF-β plays a similar mechanistic role in obesity-associated inflammatory airway diseases such as asthma and COPD. Concerning the role of TGF-β on metabolic effects of obesity, we posit that TGF-β has a similar mechanistic role in obesity-associated inflammatory airway diseases in interplay with different comorbidities such as hypertension, metabolic diseases like type 2 diabetes, and cardiomyopathies. Future studies in TGF-β-dependent mechanisms in obesity-associated inflammatory airway diseases will advance our understanding of obesity-induced asthma and help find novel therapeutic targets for prevention and treatment.

Bariatric Surgery Normalizes Protein Glycoxidation and Nitrosative Stress in Morbidly Obese Patients

The results of recent studies indicate the key role of nitrosative stress and protein oxidative damage in the development of morbid obesity. Nevertheless, the effect of bariatric surgery on protein oxidation/glycation and nitrosative/nitrative stress is not yet known. This is the first study evaluating protein glycoxidation and protein nitrosative damage in morbidly obese patients before and after (one, three, six and twelve months) laparoscopic sleeve gastrectomy. The study included 50 women with morbid obesity as well as 50 age- and gender-matched healthy controls. We demonstrated significant increases in serum myeloperoxidase, plasma glycooxidative products (dityrosine, kynurenine, N-formyl-kynurenine, amyloid, Amadori products, glycophore), protein oxidative damage (ischemia modified albumin) and nitrosative/nitrative stress (nitric oxide, peroxy-nitrite, S-nitrosothiols and nitro-tyrosine) in morbidly obese subjects as compared to lean controls, whereas plasma tryptophan and total thiols were statistically decreased. Bariatric surgery generally reduces the abnormalities in the glycoxidation of proteins and nitrosative/nitrative stress. Noteworthily, in the patients with metabolic syndrome (MS+), we showed no differences in most redox biomarkers, as compared to morbidly obese patients without MS (MS−). However, two markers: were able to differentiate MS+ and MS− with high specificity and sensitivity: peroxy-nitrite (>70%) and S-nitrosothiols (>60%). Further studies are required to confirm the diagnostic usefulness of such biomarkers.

Experimental animal models of coronary microvascular dysfunction

Coronary microvascular dysfunction (CMD) is commonly present in patients with metabolic derangements and is increasingly recognized as an important contributor to myocardial ischaemia, both in the presence and absence of epicardial coronary atherosclerosis. The latter condition is termed 'ischaemia and no obstructive coronary artery disease' (INOCA). Notwithstanding the high prevalence of INOCA, effective treatment remains elusive. Although to date there is no animal model for INOCA, animal models of CMD, one of the hallmarks of INOCA, offer excellent test models for enhancing our understanding of the pathophysiology of CMD and for investigating novel therapies. This article presents an overview of currently available experimental models of CMD-with an emphasis on metabolic derangements as risk factors-in dogs, swine, rabbits, rats, and mice. In all available animal models, metabolic derangements are most often induced by a high-fat diet (HFD) and/or diabetes mellitus via injection of alloxan or streptozotocin, but there is also a wide variety of spontaneous as well as transgenic animal models which develop metabolic derangements. Depending on the number, severity, and duration of exposure to risk factors-all these animal models show perturbations in coronary microvascular (endothelial) function and structure, similar to what has been observed in patients with INOCA and comorbid conditions. The use of these animal models will be instrumental in identifying novel therapeutic targets and for the subsequent development and testing of novel therapeutic interventions to combat ischaemic heart disease, the number one cause of death worldwide.

Nuclear factor-kB and nitric oxide synthases in red blood cells: good or bad in obesity? A preliminary study

Emerging evidence suggests that red blood cells (RBCs) are involved in many functions essential for life. Nuclear factor-kB (NF-kB), nitric oxide synthases (inducible nitric oxide synthase -iNOS-, endothelial nitric oxide synthase -eNOS-) and interleukin-1β (-IL-1β-) are all proteins that have been identified in RBCs. In nucleated cells, such as white blood cells (WBCs), these proteins have well investigated roles, linked to stress and inflammation. It is not the same in erythrocytes, for this reason, we considered obese patients for studying the morphology of RBCs. We studied a possible correlation between their morphological changes and several protein expressions. Moreover, we compared the results about the aforementioned proteins and antioxidant markers with those obtained in WBCs from healthy and obese patients before and after omega-3 polyunsaturated fatty acid supplementation. This latter scientific point is important in order to determine whether there are differences in the expression of nucleated and anucleated cells. The morphology of RBCs changed in obese patients, but it is significantly restored after six weeks of supplementation. The expression of antioxidant enzymes changed in RBCs and WBCs in obesity but all proteins restore their positivity after supplementation. We found that: the presence of NF-kB, antioxidant enzymes and eNOS in healthy RBCs could indicate a role of these proteins as regulators of cellular metabolism; obese WBCs showed a higher NF-kB, iNOS and IL-1β positivity, whereas eNOS presence did not significantly change in these cells. We tried to explain the different positivity of NF-kB, proposing a dual role for this protein, as prolifespan and as proinflammatory processes, depending on examined cells. In conclusion, we have considered the literature that focuses on the omega-6/omega-3 ratio. The ratio changed from the past, especially in people whose diet is strongly westernized worsening the state of health of the patient and leading to an higher incidence of obesity. Our study hypothesizes that the supplementation could help to restore the correct ratio.

Obesity-related cognitive impairment: The role of endothelial dysfunction

Obesity is a global pandemic associated with macro- and microvascular endothelial dysfunction. Microvascular endothelial dysfunction has recently emerged as a significant risk factor for the development of cognitive impairment. In this review, we present evidence from clinical and preclinical studies supporting a role for obesity in cognitive impairment. Next, we discuss how obesity-related hyperinsulinemia/insulin resistance, systemic inflammation, and gut dysbiosis lead to cognitive impairment through induction of endothelial dysfunction and disruption of the blood brain barrier. Finally, we outline the potential clinical utility of dietary interventions, exercise, and bariatric surgery in circumventing the impacts of obesity on cognitive function.

Emerging Roles of Vascular Endothelium in Metabolic Homeostasis

Our understanding of the role of the vascular endothelium has evolved over the past 2 decades, with the recognition that it is a dynamically regulated organ and that it plays a nodal role in a variety of physiological and pathological processes. Endothelial cells (ECs) are not only a barrier between the circulation and peripheral tissues, but also actively regulate vascular tone, blood flow, and platelet function. Dysregulation of ECs contributes to pathological conditions such as vascular inflammation, atherosclerosis, hypertension, cardiomyopathy, retinopathy, neuropathy, and cancer. The close anatomic relationship between vascular endothelium and highly vascularized metabolic organs/tissues suggests that the crosstalk between ECs and these organs is vital for both vascular and metabolic homeostasis. Numerous reports support that hyperlipidemia, hyperglycemia, and other metabolic stresses result in endothelial dysfunction and vascular complications. However, how ECs may regulate metabolic homeostasis remains poorly understood. Emerging data suggest that the vascular endothelium plays an unexpected role in the regulation of metabolic homeostasis and that endothelial dysregulation directly contributes to the development of metabolic disorders. Here, we review recent studies about the pivotal role of ECs in glucose and lipid homeostasis. In particular, we introduce the concept that the endothelium adjusts its barrier function to control the transendothelial transport of fatty acids, lipoproteins, LPLs (lipoprotein lipases), glucose, and insulin. In addition, we summarize reports that ECs communicate with metabolic cells through EC-secreted factors and we discuss how endothelial dysregulation contributes directly to the development of obesity, insulin resistance, dyslipidemia, diabetes mellitus, cognitive defects, and fatty liver disease.

Hemostasis, endothelial stress, inflammation, and the metabolic syndrome

Obesity and the metabolic syndrome (MS) are two of the pressing healthcare problems of our time. The MS is defined as increased abdominal obesity in concert with elevated fasting glucose levels, insulin resistance, elevated blood pressure, and plasma lipids. It is a key risk factor for type 2 diabetes mellitus (T2DM) and for cardiovascular complications and mortality. Here, we review work demonstrating that various aspects of coagulation and hemostasis, as well as vascular reactivity and function, become impaired progressively during chronic ingestion of a western diet, but also acutely after meals. We outline that both T2DM and cardiovascular disease should be viewed as inflammatory diseases and describe that chronic overload of free fatty acids and glucose can trigger inflammatory pathways directly or via increased production of ROS. We propose that since endothelial stress and increases in platelet activity precede inflammation and overt symptoms of the MS, they are likely the first hit. This suggests that endothelial activation and insulin resistance are probably causative in the observed chronic low-level metabolic inflammation, and thus both metabolic and cardiovascular complications linked to consumption of a western diet.

Metformin influences on respiratory system in obese mice induced by postnatal overnutrition

Many studies have confirmed the merits of metformin to treat type 2 diabetes, but few studies have addressed its effect on the respiratory system. Moreover, vascular endothelial growth factor (VEGF) is critical to many lung functions. In this way, we evaluated the metformin impact on the lung in treated obese Swiss mice, induced by postnatal overnutrition. Glucose and insulin were detected and the insulin resistance index (HOMA) was calculated; inflammatory cells and nitrite/nitrate concentration (NOx) was quantified from bronchoalveolar lavage, collagen and lung VEGF-a was analysed in the lung tissue and lung mechanics were evaluated by methacholine-induced bronchoconstriction. Values of glucose, insulin, HOMA; VEGF-a and collagen demonstrate the partial ability of metformin to improve the effects of obesity. However, metformin is ineffective in re-establishing the inflammation, shows no effects on NOx and does not restore bronchoconstriction in obese mice. In conclusion, metformińs beneficial effects on lung are questionable in the postnatal overnutrition model of obesity.

Alterations in Circulating Amino Acid Metabolite Ratio Associated with Arginase Activity Are Potential Indicators of Metabolic Syndrome: The Korean Genome and Epidemiology Study

Upregulated arginase activity, which competes with nitric oxide synthase (NOS), impairs nitric oxide production and has been implicated in various metabolic disorders. This study examined whether circulating amino acid metabolite ratios are associated with arginase and NOS activities and whether arginine bioavailability is associated with metabolic syndrome (MetS). Data related to arginase and NOS activities were collected from non-diabetic Koreans without cardiovascular disease (n = 1998) in the Ansan-Ansung cohorts (2005-2006). Subsequently, correlation and multivariate logistic regression analyses were performed. With the increase in the number of MetS risk factors, ratios of circulating amino acid metabolites, such as those of ornithine/citrulline, proline/citrulline, and ornithine/arginine, also significantly increased, whereas arginine bioavailability significantly decreased. These metabolite ratios and arginase bioavailability were also significantly correlated with MetS risk-related parameters, which remained significant after adjusting for covariates. In addition, logistic regression analysis revealed that high ratios of circulating metabolites and low arginine bioavailability, which indicated increased arginase activity, were significantly associated with a high MetS risk. This study demonstrated that altered ratios of circulating amino acid metabolites indicates increased arginase activity and decreased arginine bioavailability, both of which can be potential markers for MetS risk.

Role of NO/VASP Signaling Pathway against Obesity-Related Inflammation and Insulin Resistance

Obesity has quickly become a worldwide pandemic, causing major adverse health outcomes such as dyslipidemia, type 2 diabetes mellitus, cardiovascular disease and cancers. Obesity-induced insulin resistance is the key for developing these metabolic disorders, and investigation to understand the molecular mechanisms involved has been vibrant for the past few decades. Of these, low-grade chronic inflammation is suggested as a critical concept in the development of obesity-induced insulin resistance, and the anti-inflammatory effect of nitric oxide (NO) signaling has been reported to be linked to improvement of insulin resistance in multiple organs involved in glucose metabolism. Recently, a body of evidence suggested that vasodilatory-stimulated phosphoprotein (VASP), a downstream mediator of NO signaling plays a crucial role in the anti-inflammatory effect and improvement of peripheral insulin resistance. These preclinical studies suggest that NO/VASP signaling could be an ideal therapeutic target in the treatment of obesity-related metabolic dysfunction. In this review, we introduce studies that investigated the protective role of NO/VASP signaling against obesity-related inflammation and insulin resistance in various tissues.

Nitrite increases glucose-stimulated insulin secretion and islet insulin content in obese type 2 diabetic male rats

PURPOSE

Reduced bioavailability of nitric oxide (NO) is associated with pathogenesis of type 2 diabetes. Nitrite can act as a substrate for generation of systemic NO. The aim of this study was to examine the effects of nitrite administration on glucose-stimulated insulin secretion (GSIS) and islet insulin content in obese type 2 diabetic rats.

METHODS

Male rats were divided into 4 groups: Control, control + nitrite, diabetes, and diabetes + nitrite. Sodium nitrite (50 mg/L in drinking water) was administered for 8 weeks. Diabetes was induced using high-fat diet and low-dose of streptozotocine. Serum levels of fasting glucose, insulin, and lipid profile were measured and the insulin resistance/sensitivity indices were calculated every 2 weeks. Glycated hemoglobin (HbA_1C) was measured every month. At the end of the study, tissue levels of glucose transporter 4 (GLUT4) protein and serum interleukin-1 beta (IL-1β) were measured as well as glucose and insulin tolerance test were done. GSIS from isolated pancreatic islets and islet insulin content were also determined.

RESULTS

Nitrite administration significantly increased insulin secretion in both control and diabetic rats in presence of 16.7 mM glucose. Nitrite also significantly increased islet insulin content by 27% and 39% in both control and diabetic rats, respectively. Nitrite decreased elevated serum IL-1β in diabetic rats (4.0 ± 0.2 vs. 2.9 ± 0.2 pg/mL, P = 0.001). In diabetic rats, nitrite also significantly increased tissue levels of GLUT4 by 22% and 26% in soleus muscle and epididymal adipose tissue, respectively. In addition, nitrite significantly improved glucose and insulin tolerance, insulin sensitivity, lipid profile, and decreased fasting glucose and insulin, but had no effect on HbA_1C.

CONCLUSIONS

Long-term nitrite administration increased both insulin secretion and insulin content in obese type 2 diabetic rats. In addition, nitrite therapy had favorable effects on glucose tolerance, insulin resistance, inflammation, and dyslipidemia in type 2 diabetic rats.

Nitric oxide levels in patients with diabetes mellitus: A systematic review and meta-analysis

BACKGROUND

Altered serum nitric oxide (NO) levels in patients with diabetes mellitus (DM) have been reported by different studies; however, results are still controversial. Until this date, no meta-analysis evaluated the association of NO levels with DM. Thus, this paper describes a meta-analysis conducted to evaluate if there is a relationship between NO levels and type 1 DM (T1DM) or type 2 DM (T2DM).

METHODS

A literature search was done to identify all studies that investigated NO levels between T1DM or T2DM patients (cases) and non-diabetic subjects (controls). Measurement of nitrate and nitrite (NOx - the stable NO products) were used to estimate NO concentrations because they closely reflect NO bioavailability. Weighted mean differences (WMD) of NOx levels between case and control samples were calculated for T1DM and T2DM groups.

RESULTS

Thirty studies were eligible for inclusion in the meta-analysis (8 in T1DM samples and 22 in T2DM samples). NOx levels were increased in European T1DM patients compared with controls [random effect model (REM) WMD = 8.55, 95% CI 2.88 - 14.21]. No other ethnicity was evaluated in T1DM studies. NOx levels were also increased in both European (REM WMD = 18.76, 95% CI 1.67 - 35.85) and Asian (REM WMD = 18.41, 95% CI 8.01 - 28.81) T2DM patients, but not in Latin American patients compared with controls.

CONCLUSIONS

This meta-analysis detected a significant increase in NOx levels in European T1DM patients as well as European and Asian T2DM patients. Further studies in other ethnicities are necessary to confirm these data.

Mitochondrial involvement in skeletal muscle insulin resistance: A case of imbalanced bioenergetics

Skeletal muscle insulin resistance in obesity associates with mitochondrial dysfunction, but the causality of this association is controversial. This review evaluates mitochondrial models of nutrient-induced muscle insulin resistance. It transpires that all models predict that insulin resistance arises as a result of imbalanced cellular bioenergetics. The nature and precise origin of the proposed insulin-numbing molecules differ between models but all species only accumulate when metabolic fuel supply outweighs energy demand. This observation suggests that mitochondrial deficiency in muscle insulin resistance is not merely owing to intrinsic functional defects, but could instead be an adaptation to nutrient-induced changes in energy expenditure. Such adaptive effects are likely because muscle ATP supply is fully driven by energy demand. This market-economic control of myocellular bioenergetics offers a mechanism by which insulin-signalling deficiency can cause apparent mitochondrial dysfunction, as insulin resistance lowers skeletal muscle anabolism and thus dampens ATP demand and, consequently, oxidative ATP synthesis.

Nitric Oxide Exerts Basal and Insulin-Dependent Anorexigenic Actions in POMC Hypothalamic Neurons

The arcuate nucleus of the hypothalamus represents a key center for the control of appetite and feeding through the regulation of 2 key neuronal populations, notably agouti-related peptide/neuropeptide Y and proopimelanocortin (POMC)/cocaine- and amphetamine-regulated transcript neurons. Altered regulation of these neuronal networks, in particular the dysfunction of POMC neurons upon high-fat consumption, is a major pathogenic mechanism involved in the development of obesity and type 2 diabetes mellitus. Efforts are underway to preserve the integrity or enhance the functionality of POMC neurons in order to prevent or treat these metabolic diseases. Here, we report for the first time that the nitric oxide (NO(-)) donor, sodium nitroprusside (SNP) mediates anorexigenic actions in both hypothalamic tissue and hypothalamic-derived cell models by mediating the up-regulation of POMC levels. SNP increased POMC mRNA in a dose-dependent manner and enhanced α-melanocortin-secreting hormone production and secretion in mHypoA-POMC/GFP-2 cells. SNP also enhanced insulin-driven POMC expression likely by inhibiting the deacetylase activity of sirtuin 1. Furthermore, SNP enhanced insulin-dependent POMC expression, likely by reducing the transcriptional repression of Foxo1 on the POMC gene. Prolonged SNP exposure prevented the development of insulin resistance. Taken together, the NO(-) donor SNP enhances the anorexigenic potential of POMC neurons by promoting its transcriptional expression independent and in cooperation with insulin. Thus, increasing cellular NO(-) levels represents a hormone-independent method of promoting anorexigenic output from the existing POMC neuronal populations and may be advantageous in the fight against these prevalent disorders.

Gasotransmitters in Vascular Complications of Diabetes

In the past decades three gaseous signaling molecules-so-called gasotransmitters-have been identified: nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S). These gasotransmitters are endogenously produced by different enzymes in various cell types and play an important role in physiology and disease. Despite their specific functions, all gasotransmitters share the capacity to reduce oxidative stress, induce angiogenesis, and promote vasorelaxation. In patients with diabetes, a lower bioavailability of the different gasotransmitters is observed when compared with healthy individuals. As yet, it is unknown whether this reduction precedes or results from diabetes. The increased risk for vascular disease in patients with diabetes, in combination with the extensive clinical, financial, and societal burden, calls for action to either prevent or improve the treatment of vascular complications. In this Perspective, we present a concise overview of the current data on the bioavailability of gasotransmitters in diabetes and their potential role in the development and progression of diabetes-associated microvascular (retinopathy, neuropathy, and nephropathy) and macrovascular (cerebrovascular, coronary artery, and peripheral arterial diseases) complications. Gasotransmitters appear to have both inhibitory and stimulatory effects in the course of vascular disease development. This Perspective concludes with a discussion on gasotransmitter-based interventions as a therapeutic option.

Oxidative Stress-Dependent Coronary Endothelial Dysfunction in Obese Mice

Obesity is involved in several cardiovascular diseases including coronary artery disease and endothelial dysfunction. Endothelial Endothelium vasodilator and vasoconstrictor agonists play a key role in regulation of vascular tone. In this study, we evaluated coronary vascular response in an 8 weeks diet-induced obese C57BL/6 mice model. Coronary perfusion pressure in response to acetylcholine in isolated hearts from obese mice showed increased vasoconstriction and reduced vasodilation responses compared with control mice. Vascular nitric oxide assessed in situ with DAF-2 DA showed diminished levels in coronary arteries from obese mice in both basal and acetylcholine-stimulated conditions. Also, released prostacyclin was decreased in heart perfusates from obese mice, along with plasma tetrahydrobiopterin level and endothelium nitric oxide synthase dimer/monomer ratio. Obesity increased thromboxane A2 synthesis and oxidative stress evaluated by superoxide and peroxynitrite levels, compared with control mice. Obese mice treated with apocynin, a NADPH oxidase inhibitor, reversed all parameters to normal levels. These results suggest that after 8 weeks on a high-fat diet, the increase in oxidative stress lead to imbalance in vasoactive substances and consequently to endothelial dysfunction in coronary arteries.

Regional variation in arterial stiffening and dysfunction in Western diet-induced obesity

Increased central vascular stiffening, assessed in vivo by determination of pulse wave velocity (PWV), is an independent predictor of cardiovascular event risk. Recent evidence demonstrates that accelerated aortic stiffening occurs in obesity; however, little is known regarding stiffening of other disease-relevant arteries or whether regional variation in arterial stiffening occurs in this setting. We addressed this gap in knowledge by assessing femoral PWV in vivo in conjunction with ex vivo analyses of femoral and coronary structure and function in a mouse model of Western diet (WD; high-fat/high-sugar)-induced obesity and insulin resistance. WD feeding resulted in increased femoral PWV in vivo. Ex vivo analysis of femoral arteries revealed a leftward shift in the strain-stress relationship, increased modulus of elasticity, and decreased compliance indicative of increased stiffness following WD feeding. Confocal and multiphoton fluorescence microscopy revealed increased femoral stiffness involving decreased elastin/collagen ratio in conjunction with increased femoral transforming growth factor-β (TGF-β) content in WD-fed mice. Further analysis of the femoral internal elastic lamina (IEL) revealed a significant reduction in the number and size of fenestrae with WD feeding. Coronary artery stiffness and structure was unchanged by WD feeding. Functionally, femoral, but not coronary, arteries exhibited endothelial dysfunction, whereas coronary arteries exhibited increased vasoconstrictor responsiveness not present in femoral arteries. Taken together, our data highlight important regional variations in the development of arterial stiffness and dysfunction associated with WD feeding. Furthermore, our results suggest TGF-β signaling and IEL fenestrae remodeling as potential contributors to femoral artery stiffening in obesity.

Impact of nutrient excess and endothelial nitric oxide synthase on the plasma metabolite profile in mice

An increase in calorie consumption is associated with the recent rise in obesity prevalence. However, our current understanding of the effects of nutrient excess on major metabolic pathways appears insufficient to develop safe and effective metabolic interventions to prevent obesity. Hence, we sought to identify systemic metabolic changes caused by nutrient excess and to determine how endothelial nitric oxide synthase (eNOS)—which has anti-obesogenic properties—affects systemic metabolism by measuring plasma metabolites. Wild-type (WT) and eNOS transgenic (eNOS-TG) mice were placed on low fat or high fat diets for 6 weeks, and plasma metabolites were measured using an unbiased metabolomic approach. High fat feeding in WT mice led to significant increases in fat mass, which was associated with significantly lower plasma levels of 1,5-anhydroglucitol, lysophospholipids, 3-dehydrocarnitine, and bile acids, as well as branched chain amino acids (BCAAs) and their metabolites. Plasma levels of several lipids including sphingomyelins, stearoylcarnitine, dihomo-linoleate and metabolites associated with oxidative stress were increased by high fat diet. In comparison with low fat-fed WT mice, eNOS-TG mice showed lower levels of several free fatty acids, but in contrast, the levels of bile acids, amino acids, and BCAA catabolites were increased. When placed on a high fat diet, eNOS overexpressing mice showed remarkably higher levels of plasma bile acids and elevated levels of plasma BCAAs and their catabolites compared with WT mice. Treatment with GW4064, an inhibitor of bile acid synthesis, decreased plasma bile acid levels but was not sufficient to reverse the anti-obesogenic effects of eNOS overexpression. These findings reveal unique metabolic changes in response to high fat diet and eNOS overexpression and suggest that the anti-obesity effects of eNOS are likely independent of changes in the bile acid pool.

Regulation of obesity and insulin resistance by nitric oxide

Obesity is a risk factor for developing type 2 diabetes and cardiovascular disease and has quickly become a worldwide pandemic with few tangible and safe treatment options. Although it is generally accepted that the primary cause of obesity is energy imbalance, i.e., the calories consumed are greater than are utilized, understanding how caloric balance is regulated has proven a challenge. Many "distal" causes of obesity, such as the structural environment, occupation, and social influences, are exceedingly difficult to change or manipulate. Hence, molecular processes and pathways more proximal to the origins of obesity-those that directly regulate energy metabolism or caloric intake-seem to be more feasible targets for therapy. In particular, nitric oxide (NO) is emerging as a central regulator of energy metabolism and body composition. NO bioavailability is decreased in animal models of diet-induced obesity and in obese and insulin-resistant patients, and increasing NO output has remarkable effects on obesity and insulin resistance. This review discusses the role of NO in regulating adiposity and insulin sensitivity and places its modes of action into context with the known causes and consequences of metabolic disease.

Antiobesogenic role of endothelial nitric oxide synthase

The prevalence of obesity has increased remarkably in the past four decades. Because obesity can promote the development of type 2 diabetes and cardiovascular disease, understanding the mechanisms that engender weight gain and discovering safe antiobesity therapies are of critical importance. In particular, the gaseous signaling molecule, nitric oxide (NO), appears to be a central factor regulating adiposity and systemic metabolism. Obese and diabetic states are characterized by a deficit in bioavailable NO, with such decreases commonly attributed to downregulation of endothelial NO synthase (eNOS), loss of eNOS activity, or quenching of NO by its reaction with oxygen radicals. Gain-of-function studies, in which vascular-derived NO has been increased pharmacologically or genetically, reveal remarkable actions of NO on body composition and systemic metabolism. This review addresses the metabolic actions of eNOS and the potential therapeutic utility of harnessing its antiobesogenic effects.

Co-administration of Grape Seed Extract and Exercise Training Improves Endothelial Dysfunction of Coronary Vascular Bed of STZ-Induced Diabetic Rats

Background

One of the known complications of diabetes mellitus is vascular dysfunction. Inability of the coronary vascular response to cardiac hyperactivity might cause a higher incidence of ischemic heart disease in diabetic subjects. It has been indicated that regular exercise training and antioxidants could prevent diabetic cardiovascular problems enhanced by vascular damage.

Objectives

The aim of this study was to determine the effects of grape seed extract (as antioxidant), with and without exercise training on coronary vascular function in streptozotocin induced diabetic rats.

Materials and Methods

Fifty male Wistar rats weighing 200 – 232 grams were randomly divided into five groups of 10 rats each: sedentary control, sedentary diabetic, trained diabetic, grape seed extract (200 mg/kg) treated sedentary diabetic and, grape seed extract treated trained diabetic. Diabetes was induced by one intraperitoneal injection of streptozotocin. After eight weeks, coronary vascular responses to vasoactive agents were determined.

Results

The endothelium dependent vasorelaxation to acetylcholine was reduced significantly in diabetic animals; exercise training or grape seed extract administration partially improves this response. However, exercise training in combination with grape seed extract restores endothelial function completely. The endothelium independent vasorelaxation to sodium nitroprusside was improved by combination of exercise training and grape seed extract. On the other hand, the basal perfusion pressure and vasoconstrictive response to phenylephrine did not change significantly.

Conclusions

The data indicated that co-administration of grape seed extract and exercise training had more significant effects than exercise training or grape seed extract alone; this may constitute a convenient and inexpensive therapeutic approach to diabetic vascular complications.

Regulation of adipose tissue energy availability through blood flow control in the metabolic syndrome

Maintenance of blood flow rate is a critical factor for tissue oxygen and substrate supply. The potentially large mass of adipose tissue deeply influences the body distribution of blood flow. This is due to increased peripheral resistance in obesity and the role of this tissue as the ultimate destination of unused excess of dietary energy. However, adipose tissue cannot grow indefinitely, and the tissue must defend itself against the avalanche of nutrients provoking inordinate growth and inflammation. In the obese, large adipose tissue masses show lower blood flow, limiting the access of excess circulating substrates. Blood flow restriction is achieved by vasoconstriction, despite increased production of nitric oxide, the vasodilatation effects of which are overridden by catecholamines (and probably also by angiotensin II and endothelin). Decreased blood flow reduces the availability of oxygen, provoking massive glycolysis (hyperglycemic conditions), which results in the production of lactate, exported to the liver for processing. However, this produces local acidosis, which elicits the rapid dissociation of oxyhemoglobin, freeing bursts of oxygen in localized zones of the tissue. The excess of oxygen (and of nitric oxide) induces the production of reactive oxygen species, which deeply affect the endothelial, blood, and adipose cells, inducing oxidative and nitrosative damage and eliciting an increased immune response, which translates into inflammation. The result of the defense mechanism for adipose tissue, localized vasoconstriction, may thus help develop a more generalized pathologic response within the metabolic syndrome parameters, extending its effects to the whole body.

Obesity and risk of vascular disease: importance of endothelium-dependent vasoconstriction

Obesity has become a serious global health issue affecting both adults and children. Recent devolopments in world demographics and declining health status of the world's population indicate that the prevalence of obesity will continue to increase in the next decades. As a disease, obesity has deleterious effects on metabolic homeostasis, and affects numerous organ systems including heart, kidney and the vascular system. Thus, obesity is now regarded as an independent risk factor for atherosclerosis-related diseases such as coronary artery disease, myocardial infarction and stroke. In the arterial system, endothelial cells are both the source and target of factors contributing to atherosclerosis. Endothelial vasoactive factors regulate vascular homeostasis under physiological conditions and maintain basal vascular tone. Obesity results in an imbalance between endothelium-derived vasoactive factors favouring vasoconstriction, cell growth and inflammatory activation. Abnormal regulation of these factors due to endothelial cell dysfunction is both a consequence and a cause of vascular disease processes. Finally, because of the similarities of the vascular pathomechanisms activated, obesity can be considered to cause accelerated, 'premature' vascular aging. Here, we will review some of the pathomechanisms involved in obesity-related activation of endothelium-dependent vasoconstriction, the clinical relevance of obesity-associated vascular risk, and therapeutic interventions using 'endothelial therapy' aiming at maintaining or restoring vascular endothelial health.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Altered role of smooth muscle endothelin receptors in coronary endothelin-1 and α1-adrenoceptor-mediated vasoconstriction in Type 2 diabetes

Regulation of vascular tone and blood flow involves interactions between numerous local and systemic vascular control signals, many of which are altered by Type 2 diabetes (T2D). Vascular responses to endothelin-1 (ET-1) are mediated by endothelin type A (ETA) and type B (ETB) receptors that have been implicated in cross talk with α1-adrenoceptors (α1-AR). ETAand ETBreceptor expression and plasma ET-1 levels are elevated in T2D; however, whether this influences coronary α1-AR function has not been examined. Therefore, we examined the effect of ETAand ETBreceptor inhibition on coronary vasoconstriction to ET-1 and α1-AR activation in a mouse model of T2D. Coronary vascular responses were examined in isolated mouse hearts from control and diet-induced T2D C57BL/6J mice. Responses to ET-1 and the selective α1-AR agonist phenylephrine (PE) were examined alone and in the presence of the nitric oxide synthase inhibitor Nω-nitro-l-arginine methyl ester (l-NAME) alone or in combination with selective ETAor ETBreceptor inhibitors BQ-123 and BQ-788, respectively. Vasoconstriction to ET-1 was enhanced, whereas ETB, but not ETA, receptor blockade reduced basal coronary tone in T2D hearts. In the presence of l-NAME, ETAreceptor inhibition attenuated ET-1 vasoconstriction in both groups, whereas ETBinhibition abolished this response only in control hearts. In addition, ETAinhibition enhanced α1-AR-mediated vasoconstriction in T2D, but not control, hearts following l-NAME treatment. Therefore, in this model, enhanced coronary ET-1 responsiveness is mediated primarily through smooth muscle ETBreceptors, whereas the interaction with α1-ARs is mediated solely through the ETAreceptor subtype.