Reduced vascular nitric oxide-cGMP signaling contributes to adipose tissue inflammation during high-fat feeding

Endothelial Dysfunction in Obesity and Therapeutic Targets

Parallel to the increasing prevalence of obesity in the world, the mortality from cardiovascular disease has also increased. Low-grade chronic inflammation in obesity disrupts vascular homeostasis, and the dysregulation of adipocyte-derived endocrine and paracrine effects contributes to endothelial dysfunction. Besides the adipose tissue inflammation, decreased nitric oxide (NO)-bioavailability, insulin resistance (IR), and oxidized low-density lipoproteins (oxLDLs) are the main factors contributing to endothelial dysfunction in obesity and the development of cardiorenal metabolic syndrome. While normal healthy perivascular adipose tissue (PVAT) ensures the dilation of blood vessels, obesity-associated PVAT leads to a change in the profile of the released adipo-cytokines, resulting in a decreased vasorelaxing effect. Higher stiffness parameter β, increased oxidative stress, upregulation of pro-inflammatory cytokines, and nicotinamide adenine dinucleotide phosphate (NADP) oxidase in PVAT turn the macrophages into pro-atherogenic phenotypes by oxLDL-induced adipocyte-derived exosome-macrophage crosstalk and contribute to the endothelial dysfunction. In clinical practice, carotid ultrasound, higher leptin levels correlate with irisin over-secretion by human visceral and subcutaneous adipose tissues, and remnant cholesterol (RC) levels predict atherosclerotic disease in obesity. As a novel therapeutic strategy for cardiovascular protection, liraglutide improves vascular dysfunction by modulating a cyclic adenosine monophosphate (cAMP)-independent protein kinase A (PKA)-AMP-activated protein kinase (AMPK) pathway in PVAT in obese individuals. Because the renin-angiotensin-aldosterone system (RAAS) activity, hyperinsulinemia, and the resultant IR play key roles in the progression of cardiovascular disease in obesity, RAAS-targeted therapies contribute to improving endothelial dysfunction. By contrast, arginase reciprocally inhibits NO formation and promotes oxidative stress. Thus, targeting arginase activity as a key mediator in endothelial dysfunction has therapeutic potential in obesity-related vascular comorbidities. Obesity-related endothelial dysfunction plays a pivotal role in the progression of type 2 diabetes (T2D). The peroxisome proliferator-activated receptor gamma (PPARγ) agonist, rosiglitazone (thiazolidinedione), is a popular drug for treating diabetes; however, it leads to increased cardiovascular risk. Selective sodium-glucose co-transporter-2 (SGLT-2) inhibitor empagliflozin (EMPA) significantly improves endothelial dysfunction and mortality occurring through redox-dependent mechanisms. Although endothelial dysfunction and oxidative stress are alleviated by either metformin or EMPA, currently used drugs to treat obesity-related diabetes neither possess the same anti-inflammatory potential nor simultaneously target endothelial cell dysfunction and obesity equally. While therapeutic interventions with glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide or bariatric surgery reverse regenerative cell exhaustion, support vascular repair mechanisms, and improve cardiometabolic risk in individuals with T2D and obesity, the GLP-1 analog exendin-4 attenuates endothelial endoplasmic reticulum stress.

Combined systematic pharmacology and urine metabonomics to study the therapeutic mechanism of type 2 diabetic treated with the herbal pair of Salvia miltiorrhiza Bunge and Pueraria montana var. lobata (Willd.) Sanjappa & Pradeep

BACKGROUND

The herbal pair of Salvia miltiorrhiza Bunge and Pueraria montana var. lobata (Willd.) Sanjappa & Pradeep (DG) is commonly used in the treatment of type 2 diabetes (T2DM) in traditional Chinese medicine (TCM). The drug pair DG was designed by Dr. Zhu chenyu to improve the treatment of T2DM.

AIM

This study combined with systematic pharmacology and urine metabonomics to explore the mechanism of DG in the treatment of T2DM.

METHODS

The therapeutic effect of DG on T2DM was evaluated by fasting blood glucose (FBG) and biochemical indexes. Systematic pharmacology was used to screen the active components and targets that may be related to DG. Metabonomics was established to find urinary metabolites and pathways that may be induced by DG. Finally, integrate the results of these two parts for mutual verification.

RESULTS

FBG and biochemical indexes showed that DG could reduce FBG and adjust the related biochemical indexes. Metabolomics analysis indicated that 39 metabolites were related to DG for T2DM treatment. In addition, systematic pharmacology showed compounds and potential targets which were associated with DG. Finally, 12 promising targets were selected as targets for T2DM therapy by integrating the results.

CONCLUSION

The combination of metabonomics and systematic pharmacology based on LC-MS is feasible and effective, which provides strong support for exploring the effective components and pharmacological mechanism of TCM.

Paracrine Regulation of Adipose Tissue Macrophages by Their Neighbors in the Microenvironment of Obese Adipose Tissue

Obesity has recently been defined as a chronic low-grade inflammatory disease. Obesity-induced inflammation of adipose tissue (AT) is an essential trigger for insulin resistance (IR) and related metabolic diseases. Although the underlying molecular basis of this inflammation has not been fully identified, there is consensus that the recruited and activated macrophages in AT are the most important culprits of AT chronic inflammation. Adipose tissue macrophages (ATMs) are highly plastic and could be polarized from an anti-inflammatory M2 to proinflammatory M1 phenotypes on stimulation by microenvironmental signals from obese AT. Many efforts have been made to elucidate the molecular signaling pathways of macrophage polarization; however, the upstream drivers governing and activating macrophage polarization have rarely been summarized, particularly regulatory messages from the AT microenvironment. In addition to adipocytes, the AT bed also contains a variety of immune cells, stem cells, as well as vascular, neural, and lymphatic tissues throughout, which together orchestrate the AT microenvironment. Here, we summarize how the aforesaid neighbors of ATMs in the AT microenvironment send messages to ATMs and thus regulate its phenotype during obesity. Deciphering the biology and polarization of ATMs in the obese environment is expected to provide a precise immunotherapy for adipose inflammation and obesity-related metabolic diseases.

Demonstration of Ameliorating Effect of Vardenafil Through Its Anti-Inflammatory and Neuroprotective Properties in Autism Spectrum Disorder Induced by Propionic Acid on Rat Model

Introduction: Autism spectrum disorder (ASD) is a neurodevelopmental disorder with complex etiology. In this study, we aimed to determine the ameliorating effects of vardenafil in the ASD rat model induced by propionic acid (PPA) in terms of neurobehavioral changes and also support these effects with histopathological changes, brain biochemical analysis and magnetic resonance spectroscopy (MRS) findings.Materials and Methods: Twenty-one male rats were randomly assigned into 3 groups. Group 1 (control, 7 rats) did not receive treatment. Rats in groups 2 and 3 were given PPA at the dose of 250 mg/kg/day intraperitoneally for 5 days. After PPA administration, animals in group 2 (PPAS, 7 rats) were given saline and animals in group 3 (PPAV, 7 rats) were given vardenafil. Behavioral tests were performed between the 20th and 24th days of the study. The rats were taken for MRS on the 25^th day. At the end of the study, brain levels of interleukin-2 (IL-2), IL-17, tumor necrosis factor-α, nerve growth factor, cGMP and lactate levels were measured. In the cerebellum and the CA1 and CA3 regions of the hippocampus, counts of neurons and Purkinje cells and glial fibrillary acidic protein (associated with gliosis) were evaluated histologically.Results: Three chamber sociability and passive avoiding test, histopathological results, lactate levels derived from MRS, and biochemical biomarkers revealed significant differences among the PPAV and PPAS groups.Conclusion: We concluded that vardenafil improves memory and social behaviors and prevent loss of neuronal and Purkinje cell through its anti-inflammatory and neuroprotective effect.

SGLT2 inhibition potentiates the cardiovascular, renal and metabolic effects of sGC stimulation in hypertensive rats with prolonged exposure to high fat diet

Prolonged high-fat diet (HFD) accelerates the cardiovascular, renal, and metabolic dysfunction in hypertensive rats with altered renal development (ARDev). Soluble guanylate cyclase (sGC) stimulation or sodium-glucose cotransporter 2 (SGLT2) inhibition may improve cardiovascular, renal, and metabolic function in settings of hypertension and obesity. This study examined whether 6 wk treatment with an SGLT2 inhibitor (empagliflozin, 7 mg/kg/day) enhances the cardiovascular, renal, and metabolic effects of a sGC stimulator (praliciguat, 10 mg/kg/day) in hypertensive rats with ARDev and prolonged exposure to HFD. Arterial pressure (AP), renal vascular resistance (RVR), fat abdominal volume (FAV), insulin resistance, leptin and triglycerides levels, and intrarenal infiltration of inflammatory cells were higher, but cardiac output and creatinine clearance were lower in hypertensive rats (n = 15) than in normotensive rats (n = 7). Praliciguat administration (n = 10) to hypertensive rats reduced (P < 0.05) AP, FAV, plasma concentrations of leptin and triglycerides, and increased (P < 0.05) cardiac output and creatinine clearance. Empagliflozin administration (n = 8) only increased (P < 0.05) glucosuria and creatinine clearance and decreased (P < 0.05) plasma leptin and triglycerides concentrations in hypertensive rats. Simultaneous administration of praliciguat and empagliflozin (n = 10) accelerated the decrease in AP, improved glucose tolerance, reduced (P < 0.05) incremental body weight gain, and decreased (P < 0.05) insulin resistance index, RVR, and the infiltration of T-CD3 lymphocytes in renal cortex and renal medulla. In summary, the combined administration of praliciguat and empagliflozin leads to a greater improvement of the cardiovascular, renal, and metabolic dysfunction secondary to prolonged exposure to HFD in hypertensive rats with ARDev than the treatment with either praliciguat or empagliflozin alone.

NEW & NOTEWORTHY This is the first study, to our knowledge, showing that SGLT2 inhibition potentiates the beneficial cardiovascular, renal, and metabolic effects elicited by sGC stimulation in hypertensive rats with prolonged high-fat diet. The effects of the simultaneous administration of praliciguat and empagliflozin are greater than those elicited by either one alone. The effects of the simultaneous treatment may be related to a greater reduction in the inflammatory status.

Paracrine Role of the Endothelium in Metabolic Homeostasis in Health and Nutrient Excess

The vascular endothelium traditionally viewed as a simple physical barrier between the circulation and tissue is now well-established as a key organ mediating whole organism homeostasis by release of a portfolio of anti-inflammatory and pro-inflammatory vasoactive molecules. Healthy endothelium releases anti-inflammatory signaling molecules such as nitric oxide and prostacyclin; in contrast, diseased endothelium secretes pro-inflammatory signals such as reactive oxygen species, endothelin-1 and tumor necrosis factor-alpha (TNFα). Endothelial dysfunction, which has now been identified as a hallmark of different components of the cardiometabolic syndrome including obesity, type 2 diabetes and hypertension, initiates and drives the progression of tissue damage in these disorders. Recently it has become apparent that, in addition to vasoactive molecules, the vascular endothelium has the potential to secrete a diverse range of small molecules and proteins mediating metabolic processes in adipose tissue (AT), liver, skeletal muscle and the pancreas. AT plays a pivotal role in orchestrating whole-body energy homeostasis and AT dysfunction, characterized by local and systemic inflammation, is central to the metabolic complications of obesity. Thus, understanding and targeting the crosstalk between the endothelium and AT may generate novel therapeutic opportunities for the cardiometabolic syndrome. Here, we provide an overview of the role of the endothelial secretome in controlling the function of AT. The endothelial-derived metabolic regulatory factors are grouped and discussed based on their physical properties and their downstream signaling effects. In addition, we focus on the therapeutic potential of these regulatory factors in treating cardiometabolic syndrome, and discuss areas of future study of potential translatable and clinical significance. The vascular endothelium is emerging as an important paracrine/endocrine organ that secretes regulatory factors in response to nutritional and environmental cues. Endothelial dysfunction may result in imbalanced secretion of these regulatory factors and contribute to the progression of AT and whole body metabolic dysfunction. As the vascular endothelium is the first responder to local nutritional changes and adipocyte-derived signals, future work elucidating the changes in the endothelial secretome is crucial to improve our understanding of the pathophysiology of cardiometabolic disease, and in aiding our development of new therapeutic strategies to treat and prevent cardiometabolic syndrome.

Small-molecule Akt-activation in airway cells induces NO production and reduces IL-8 transcription through Nrf-2

BACKGROUND

The non-cancerous functions of Akt in the airway are understudied. In some tissues, Akt phosphorylates and activates endothelial nitric oxide synthase (eNOS) to produce nitric oxide (NO) that has anti-inflammatory effects. NO production has antibacterial and antiviral effects in the airway, and increasing NO may be a useful anti-pathogen strategy. Akt also stimulates the nuclear factor erythroid 2-related factor 2 (Nrf-2) transcription factor, which transcribes antioxidant genes. Therefore, we hypothesized that activation of the Akt/eNOS pathway, which also activates Nrf-2, may have protective effects in human airway cells against injury.

METHODS

To directly test the effects of Akt signaling in the airway, we treated A549 and 16HBE cells as well as primary bronchial, nasal, and type II alveolar epithelial cells with small molecule Akt activator SC79. We examined the effects of SC79 on eNOS activation, NO production, Nrf-2 target levels, and interleukin-8 (IL-8) transcription during exposure to TNF-α or Pseudomonas flagellin (TLR5 agonist). Additionally, air-liquid interface bronchial cultures were treated with cadmium, an oxidative stressor that causes airway barrier breakdown.

RESULTS

SC79 induced a ~ twofold induction of p-eNOS and Nrf-2 protein levels blocked by PI3K inhibitor LY294002. Live cell imaging revealed SC79 increased acute NO production. Quantitative RT-PCR showed a ~ twofold increase in Nrf-2 target gene transcription. TNF-α or flagellin-induced IL-8 levels were also significantly reduced with SC79 treatment. Moreover, the transepithelial electrical resistance decrease observed with cadmium was ameliorated by SC79, likely by an acute increase in tight junction protein ZO-1 levels.

CONCLUSIONS

Together, the data presented here demonstrate SC79 activation of Akt induces potentially anti-pathogenic NO production, antioxidant gene transcription, reduces IL-8 transcription, and may protect against oxidative barrier dysfunction in a wide range of airway epithelial cells.

Pink pressure: beetroot (Beta vulgaris rubra) as a possible novel medical therapy for chronic kidney disease

Chronic kidney disease (CKD) manifests with systemic inflammation, oxidative stress, and gut dysbiosis, resulting in metabolic disorders and elevated rates of cardiovascular disease-associated death. These all correlate with a high economic cost to healthcare systems. Growing evidence indicates that diet is an indispensable ally in the prevention and management of CKD and its complications. In this context, the root vegetable beetroot (Beta vulgaris rubra) deserves special attention because it is a source of several bioactive compounds, such as nitrate, betaine, and betalain, and has shown beneficial effects in CKD, including reduction of blood pressure, anti-inflammatory effects, and antioxidant actions by scavenging radical oxidative species, as observed in preclinical studies. Beetroot consumption as a possible therapeutic strategy to improve the clinical treatment of patients with CKD and future directions for clinical studies are addressed in this narrative review.

MRI-based in vivo detection of coronary microvascular dysfunction before alterations in cardiac function induced by short-term high-fat diet in mice

Endothelial dysfunction is one of the hallmarks of vascular abnormalities in metabolic diseases and has been repeatedly demonstrated in coronary and peripheral circulation in mice fed high-fat diet (HFD), particularly after long-term HFD. However, the temporal relationship between development of coronary microvascular endothelial dysfunction and deterioration in diastolic and systolic cardiac function after short-term feeding with HFD has not yet been studied. This study aimed to correlate the changes in coronary microvascular endothelial function and global cardiac performance indices in vivo after short-term feeding with HFD in mice. Short-term feeding with a HFD (60% fat + 1% cholesterol) resulted in severely impaired coronary microvascular function, as evidenced by the diminished effect of nitric oxide synthase inhibition (by L-NAME) assessed using T1 mapping via in vivo MRI. Deterioration of coronary microvascular function was detected as early as after 7 days of HFD and further declined after 8 weeks on a HFD. HFD-induced coronary microvascular dysfunction was not associated with impaired myocardial capillary density and was present before systemic insulin resistance assessed by a glucose tolerance test. Basal coronary flow and coronary reserve, as assessed using the A2A adenosine receptor agonist regadenoson, were also not altered in HFD-fed mice. Histological analysis did not reveal cardiomyocyte hypertrophy or fibrosis. Increased lipid accumulation in cardiomyocytes was detected as early as after 7 days of HFD and remained at a similar level at 8 weeks on a HFD. Multiparametric cardiac MRI revealed a reduction in systolic heart function, including decreased ejection rate, increased end-systolic volume and decreased myocardial strain in diastole with impaired ejection fraction, but not until 4 weeks of HFD. Short-term feeding with HFD resulted in early endothelial dysfunction in coronary microcirculation that preceded alteration in cardiac function and systemic insulin resistance.

CD47 differentially regulates white and brown fat function

Mechanisms that enhance energy expenditure are attractive therapeutic targets for obesity. Previously we have demonstrated that mice lacking cd47 are leaner, exhibit increased energy expenditure, and are protected against diet-induced obesity. In this study, we further defined the physiological role of cd47 deficiency in regulating mitochondrial function and energy expenditure in both white and brown adipose tissue. We observed that cd47 deficient mice (under normal chow diet) had comparable amount of white fat mass but reduced white adipocyte size as compared to wild-type mice. Subsequent ex vivo and in vitro studies suggest enhanced lipolysis, and not impaired lipogenesis or energy utilization, contributes to this phenotype. In contrast to white adipose tissue, there were no obvious morphological differences in brown adipose tissue between wild-type and knockout mice. However, mitochondria isolated from brown fat of cd47 deficient mice had significantly higher rates of free fatty acid-mediated uncoupling. This suggests that enhanced fuel availability via white adipose tissue lipolysis may perpetuate elevated brown adipose tissue energy expenditure and contributes to the lean phenotype observed in cd47 deficient mice.

P2Y Purinergic Receptors, Endothelial Dysfunction, and Cardiovascular Diseases

Purinergic G-protein-coupled receptors are ancient and the most abundant group of G-protein-coupled receptors (GPCRs). The wide distribution of purinergic receptors in the cardiovascular system, together with the expression of multiple receptor subtypes in endothelial cells (ECs) and other vascular cells demonstrates the physiological importance of the purinergic signaling system in the regulation of the cardiovascular system. This review discusses the contribution of purinergic P2Y receptors to endothelial dysfunction (ED) in numerous cardiovascular diseases (CVDs). Endothelial dysfunction can be defined as a shift from a “calm” or non-activated state, characterized by low permeability, anti-thrombotic, and anti-inflammatory properties, to a “activated” state, characterized by vasoconstriction and increased permeability, pro-thrombotic, and pro-inflammatory properties. This state of ED is observed in many diseases, including atherosclerosis, diabetes, hypertension, metabolic syndrome, sepsis, and pulmonary hypertension. Herein, we review the recent advances in P2Y receptor physiology and emphasize some of their unique signaling features in pulmonary endothelial cells.

Endothelial Dysfunction in Diabetes

Diabetes is a worldwide health issue closely associated with cardiovascular events. Given the pandemic of obesity, the identification of the basic underpinnings of vascular disease is strongly needed. Emerging evidence has suggested that endothelial dysfunction is a critical step in the progression of atherosclerosis. However, how diabetes affects the endothelium is poorly understood. Experimental and clinical studies have illuminated the tight link between insulin resistance and endothelial dysfunction. In addition, macrophage polarization from M2 towards M1 contributes to the process of endothelial damage. The possibility that novel classes of anti-hyperglycemic agents exert beneficial effects on the endothelial function and macrophage polarization has been raised. In this review, we discuss the current status of knowledge regarding the pathological significance of insulin signaling in endothelium. Finally, we summarize recent therapeutic strategies against endothelial dysfunction with an emphasis on macrophage polarity.

Assessment of Inflammation in Pulmonary Artery Hypertension by 68Ga-Mannosylated Human Serum Albumin

Rationale: Diagnosis and monitoring of patients with pulmonary artery hypertension (PAH) is currently difficult.Objectives: We aimed to develop a noninvasive imaging modality for PAH that tracks the infiltration of macrophages into the pulmonary vasculature, using a positron emission tomography (PET) agent, ⁶⁸Ga-2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) mannosylated human serum albumin (MSA), that targets the mannose receptor (MR).Methods: We induced PAH in rats by monocrotaline injection. Tissue analysis, echocardiography, and ⁶⁸Ga-NOTA-MSA PET were performed weekly in rats after monocrotaline injection and in those treated with either sildenafil or macitentan. The translational potential of ⁶⁸Ga-NOTA-MSA PET was explored in patients with PAH.Measurements and Main Results: Gene sets related to macrophages were significantly enriched on whole transcriptome sequencing of the lung tissue in PAH rats. Serial PET images of PAH rats demonstrated increasing uptake of ⁶⁸Ga-NOTA-MSA in the lung by time that corresponded with the MR-positive macrophage recruitment observed in immunohistochemistry. In sildenafil- or macitentan-treated PAH rats, the infiltration of MR-positive macrophages by histology and the uptake of ⁶⁸Ga-NOTA-MSA on PET was significantly lower than that of the PAH-only group. The pulmonary uptake of ⁶⁸Ga-NOTA-MSA was significantly higher in patients with PAH than normal subjects (P = 0.009) or than those with pulmonary hypertension by left heart disease (P = 0.019) (n = 5 per group).Conclusions: ⁶⁸Ga-NOTA-MSA PET can help diagnose PAH and monitor the inflammatory status by imaging the degree of macrophage infiltration into the lung. These observations suggest that ⁶⁸Ga-NOTA-MSA PET has the potential to be used as a novel noninvasive diagnostic and monitoring tool of PAH.

Mutational landscape of receptor guanylyl cyclase C: Functional analysis and disease-related mutations

Guanylyl cyclase C (GC-C) is the receptor for the heat-stable enterotoxin, which causes diarrhea, and the endogenous ligands, guanylin and uroguanylin. GC-C is predominantly expressed in the intestinal epithelium and regulates fluid and ion secretion in the gut. The receptor has a complex domain organization, and in the absence of structural information, mutational analysis provides clues to mechanisms of regulation of this protein. Here, we review the mutational landscape of this receptor that reveals regulatory features critical for its activity. We also summarize the available information on mutations in GC-C that have been reported in humans and contribute to severe gastrointestinal abnormalities. Since GC-C is also expressed in extra-intestinal tissues, it is likely that mutations thus far reported in humans may also affect other organ systems, warranting a close observation of these patients in future.

Bitter taste receptors stimulate phagocytosis in human macrophages through calcium, nitric oxide, and cyclic-GMP signaling

Bitter taste receptors (T2Rs) are GPCRs involved in detection of bitter compounds by type 2 taste cells of the tongue, but are also expressed in other tissues throughout the body, including the airways, gastrointestinal tract, and brain. These T2Rs can be activated by several bacterial products and regulate innate immune responses in several cell types. Expression of T2Rs has been demonstrated in immune cells like neutrophils; however, the molecular details of their signaling are unknown. We examined mechanisms of T2R signaling in primary human monocyte-derived unprimed (M0) macrophages (M[Formula: see text]s) using live cell imaging techniques. Known bitter compounds and bacterial T2R agonists activated low-level calcium signals through a pertussis toxin (PTX)-sensitive, phospholipase C-dependent, and inositol trisphosphate receptor-dependent calcium release pathway. These calcium signals activated low-level nitric oxide (NO) production via endothelial and neuronal NO synthase (NOS) isoforms. NO production increased cellular cGMP and enhanced acute phagocytosis ~ threefold over 30-60 min via protein kinase G. In parallel with calcium elevation, T2R activation lowered cAMP, also through a PTX-sensitive pathway. The cAMP decrease also contributed to enhanced phagocytosis. Moreover, a co-culture model with airway epithelial cells demonstrated that NO produced by epithelial cells can also acutely enhance M[Formula: see text] phagocytosis. Together, these data define M[Formula: see text] T2R signal transduction and support an immune recognition role for T2Rs in M[Formula: see text] cell physiology.

Hematopoietic Cell-Expressed Endothelial Nitric Oxide Protects the Liver From Insulin Resistance

OBJECTIVE

Mice genetically deficient in endothelial nitric oxide synthase (Nos3^-/-) have fasting hyperinsulinemia and hepatic insulin resistance, indicating the importance of Nos3 (nitric oxide synthase) in maintaining metabolic homeostasis. Although the current paradigm holds that these metabolic effects are derived specifically from the expression of Nos3 in the endothelium, it has been established that bone marrow-derived cells also express Nos3. The aim of this study was to investigate whether bone marrow-derived cell Nos3 is important in maintaining metabolic homeostasis. Approach and Results: To test the hypothesis that bone marrow-derived cell Nos3 contributes to metabolic homeostasis, we generated chimeric male mice deficient or competent for Nos3 expression in circulating blood cells. These mice were placed on a low-fat diet for 5 weeks, a time period which is known to induce hepatic insulin resistance in global Nos3-deficient mice but not in wild-type C57Bl/6 mice. Surprisingly, we found that the absence of Nos3 in the bone marrow-derived component is associated with hepatic insulin resistance and that restoration of Nos3 in the bone marrow-derived component in global Nos3-deficient mice is sufficient to restore hepatic insulin sensitivity. Furthermore, we found that overexpression of Nos3 in bone marrow-derived component in wild-type mice attenuates the development of hepatic insulin resistance during high-fat feeding. Finally, compared with wild-type macrophages, the loss of macrophage Nos3 is associated with increased inflammatory responses to lipopolysaccharides and reduced anti-inflammatory responses to IL-4, a macrophage phenotype associated with the development of hepatic and systemic insulin resistance.

CONCLUSIONS

These results would suggest that the metabolic and hepatic consequences of high-fat feeding are mediated by loss of Nos3/nitric oxide actions in bone marrow-derived cells, not in endothelial cells.

Endothelial adenosine kinase deficiency ameliorates diet-induced insulin resistance

Insulin resistance-related disorders are associated with endothelial dysfunction. Accumulating evidence has suggested a role for adenosine signaling in the regulation of endothelial function. Here, we identified a crucial role of endothelial adenosine kinase (ADK) in the regulation of insulin resistance. Feeding mice with a high-fat diet (HFD) markedly enhanced the expression of endothelial Adk. Ablation of endothelial Adk in HFD-fed mice improved glucose tolerance and insulin sensitivity and decreased hepatic steatosis, adipose inflammation and adiposity, which were associated with improved arteriole vasodilation, decreased inflammation and increased adipose angiogenesis. Mechanistically, ADK inhibition or knockdown in human umbilical vein endothelial cells (HUVECs) elevated intracellular adenosine level and increased endothelial nitric oxide synthase (NOS3) activity, resulting in an increase in nitric oxide (NO) production. Antagonism of adenosine receptor A2b abolished ADK-knockdown-enhanced NOS3 expression in HUVECs. Additionally, increased phosphorylation of NOS3 in ADK-knockdown HUVECs was regulated by an adenosine receptor-independent mechanism. These data suggest that Adk-deficiency-elevated intracellular adenosine in endothelial cells ameliorates diet-induced insulin resistance and metabolic disorders, and this is associated with an enhancement of NO production caused by increased NOS3 expression and activation. Therefore, ADK is a potential target for the prevention and treatment of metabolic disorders associated with insulin resistance.

Role of cAMP and cGMP Signaling in Brown Fat

Cold-induced activation of brown adipose tissue (BAT) is mediated by norepinephrine and adenosine that are released during sympathetic nerve activation. Both signaling molecules induce an increase in intracellular levels of 3',5'-cyclic adenosine monophosphate (cAMP) in murine and human BAT. In brown adipocytes, cAMP plays a central role, because it activates lipolysis, glucose uptake, and thermogenesis. Another well-studied intracellular second messenger is 3',5'-cyclic guanosine monophosphate (cGMP), which closely resembles cAMP. Several studies have shown that intact cGMP signaling is essential for normal adipogenic differentiation and BAT-mediated thermogenesis in mice. This chapter highlights recent observations, demonstrating the physiological significance of cyclic nucleotide signaling in BAT as well as their potential to induce browning of white adipose tissue (WAT) in mice and humans.

Vascular and metabolic profiles in offspring born to pregnant mice with metabolic syndrome treated with inositols

BACKGROUND

Inositols (INOs) supplementation during pregnancy, specifically the combination of myo-inositol (MI) and D-chiro-inositol (DCI), has been reported to improve vascular parameters in women with gestational diabetes mellitus. We demonstrated previously that offspring born to pregnant mice lacking the endothelial nitric oxide synthase (eNOS+/-) gene have hypertension (HTN) as adults and, when fed a high-fat diet (HFD), develop a metabolic syndrome (MS) phenotype.

OBJECTIVE

Our aim was to evaluate whether INOs treatment in pregnancy complicated by MS improves the vascular and metabolic profile in mice offspring programmed in utero to develop HTN and MS.

MATERIALS AND METHODS

Heterozygous eNOS+/- mice fed an HFD manifest a MS phenotype. Female eNOS+/- mice with MS were bred with a wild-type (WT) male. On gestational day 1, pregnant females were randomly allocated to receive either a mixture of INOs (MI/DCI: 7.2/0.18 mg/mL) or water as placebo until delivery. The female offspring obtained were genotyped and categorized as: WT (genetically normal, with eNOS gene) and eNOS+/- offspring (genetically modified, heterozygous for eNOS gene). Both offspring developed in an abnormal uterine environment due to maternal MS. At 9-10 weeks of age, the offspring underwent a glucose tolerance test (GTT) and systolic blood pressure (SBP) measurement. The mice were then sacrificed, and the carotid arteries were isolated for evaluation of vascular responses. Responses to phenylephrine (PE), in the presence and absence of a nonspecific nitric oxide inhibitor (N-nitro-L-arginine methyl ester [L-NAME]), the vasodilator acetylcholine (ACh), and sodium nitroprusside (SNP) were assessed.

RESULTS

The GTT showed lower glucose levels in both eNOS+/-INOs (P = .03) and WT-INOs (P = .05) offspring born to MS dams on INOs supplementation compared to offspring born to untreated dams. SBP was higher in eNOS+/- offspring compared to WT (169 ± 7 vs 142 ± 9 mm Hg, respectively, P = .04) and INOs treatment decreased SBP in WT-INOs (110 ± 10 mm Hg, P = .01) but not in eNOS+/-INOs offspring. Maximal (%Max) contractile response to PE was higher in eNOS+/- offspring born to MS dams and was decreased in those born to MS dams treated with INOs (%Max, eNOS+/-, 123 ± 7 vs eNOS+/-INOs, 82 ± 11 mm Hg, P = .007). No differences were seen in PE contractile responses in WT offspring born to MS dams treated or not treated with INOs (WT, 92 ± 4 vs WT-INOs, 75 ± 7). The L-NAME response was decreased in eNOS+/-INOs and WT-INOs offspring compared to untreated ones. The ACh vasorelaxation was impaired in eNOS+/- and WT offspring born to MS dams, and maternal INOs treatment improved offspring vascular relaxation in both offspring (P = .01 and P = .03, respectively). No differences were seen in response to SNP.

CONCLUSION

Inositols supplementation improved glucose tolerance, SBP, and vascular responses in adult eNOS+/- and WT offspring born to dams with MS. Interestingly, WT born to MS dams show an altered vascular profile similar to eNOS+/- offspring and exhibit an improved response to INOs treatment. Our findings suggest that the benefits of INOs treatment are more pronounced in offspring exposed to environmental factors in utero, and less likely in those due to genetic factors.

Mechanisms of obesity-induced metabolic and vascular dysfunctions

Obesity has reached epidemic proportions and its prevalence is climbing. Obesity is characterized by hypertrophied adipocytes with a dysregulated adipokine secretion profile, increased recruitment of inflammatory cells, and impaired metabolic homeostasis that eventually results in the development of systemic insulin resistance, a phenotype of type 2 diabetes. Nitric oxide synthase (NOS) is an enzyme that converts L-arginine to nitric oxide (NO), which functions to maintain vascular and adipocyte homeostasis. Arginase is a ureohydrolase enzyme that competes with NOS for L-arginine. Arginase activity/expression is upregulated in obesity, which results in diminished bioavailability of NO, impairing both adipocyte and vascular endothelial cell function. Given the emerging role of NO in the regulation of adipocyte physiology and metabolic capacity, this review explores the interplay between arginase and NO, and their effect on the development of metabolic disorders, cardiovascular diseases, and mitochondrial dysfunction in obesity. A comprehensive understanding of the mechanisms involved in the development of obesity-induced metabolic and vascular dysfunction is necessary for the identification of more effective and tailored therapeutic avenues for their prevention and treatment.

Class II transactivator (CIITA) mediates IFN-γ induced eNOS repression by enlisting SUV39H1

Endothelial nitric oxide synthase (eNOS), selectively expressed in vascular endothelial cells, plays important roles in a range of biological and pathological processes. eNOS levels can be altered by extrinsic and intrinsic cues at the transcriptional level. Here we examined the epigenetic mechanism whereby the pro-inflammatory cytokine interferon gamma (IFN-γ) represses eNOS transcription. In response to IFN-γ treatment, there was a simultaneous down-regulation of eNOS expression and up-regulation of class II trans-activator (CIITA). Over-expression of CIITA directly repressed eNOS promoter while CIITA knockdown attenuated IFN-γ induced eNOS repression. Chromatin immunoprecipitation (ChIP) assay revealed that IFN-γ stimulation promoted CIITA occupancy on the proximal eNOS (-430/-168). Coincidently, CIITA recruitment to the eNOS promoter was paralleled by the disappearance of trimethylated histone H3K4 (H3K4Me3) and the enrichment of trimethylated H3K9 (H3K9Me3) with no significant changes in the levels of trimethylated H3K27 (H3K27Me3) or trimethylated H4K20 (H4K20Me3). In accordance, CIITA depletion was associated with the normalization of H3K4Me3 and H3K9Me3 on the eNOS promoter. Mechanistically, CIITA interacted with and enlisted the histone H3K9 trimethyltransferase SUV39H1 to the eNOS promoter to repress transcription. IFN-γ treatment augmented SUV39H1 expression and promoted SUV39H1 recruitment to the eNOS promoter in endothelial cells. Silencing of SUV39H1 abrogated eNOS repression by IFN-γ by erasing H3K9Me3 from the eNOS promoter. In conclusion, our data reveal a novel role for CIITA in endothelial cells and present SUV39H1 as a druggable target in the intervention of endothelial dysfunction.

Vasodilator-Stimulated Phosphoprotein: Regulators of Adipokines Resistin and Phenotype Conversion of Epicardial Adipocytes

Background

Endothelial dysfunction plays a central part in the pathogenesis of coronary atherosclerosis. The adipokine resistin is one of the key players in endothelial cell dysfunction. In addition, the role of epicardial fat in coronary artery endothelial dysfunction is also emphasized.

We investigated whether vasodilator-stimulated phosphoprotein (VASP) is involved in resistin-related endothelial dysfunction and the phenotype conversion of epicardial adipocytes.

Material/Methods

Cell proliferation and migration were evaluated by MTT and Transwell chamber assay, respectively. Next, we took epicardial fat samples from patients with valvular heart disease and non-coronary artery disease. Gene expression was determined by reverse transcription-quantitative polymerase chain reaction and relative abundance of the protein by Western blotting.

Results

Resistin induced endothelial proliferation and migration in a dose-dependent manner. Both resistin-induced cell proliferation and migration were effectively blocked by ablation of VASP. The brown adipose tissue-specific genes for uncoupling protein 1 (UCP-1) and PR-domain-missing16 (PRDM16) decreased, but the white adipose tissue-specific genes for resistin and RIP140 increased in VASP-deficient adipocytes compared with the LV-sicntr group. However, disruption of the Ras homolog gene family member A (RhoA) /Rho-associated kinase (ROCK) in VASP-deficient adipocytes with specific inhibitors inverted the adipocyte phenotype existing in VASP-deficient adipocytes. Furthermore, the expressions of proinflammatory cytokines interleukin-6 (IL-6), interleukin-8 (IL-8), and monocyte chemoattractantprotein-1 (MCP-1) in VASP-deficient adipocytes were markedly upregulated compared with the LV-sicntr group.

Conclusions

These results suggest a physiological role for VASP in coronary atherosclerosis through regulating adipokine resistin and phenotype conversion of epicardial adipose tissue.

The interplay between adipose tissue and the cardiovascular system: is fat always bad?

Obesity is a risk factor for cardiovascular disease (CVD). However, clinical research has revealed a paradoxically protective role for obesity in patients with chronic diseases including CVD, suggesting that the biological 'quality' of adipose tissue (AT) may be more important than overall AT mass or body weight. Importantly, AT is recognised as a dynamic organ secreting a wide range of biologically active adipokines, microRNAs, gaseous messengers, and other metabolites that affect the cardiovascular system in both endocrine and paracrine ways. Despite being able to mediate normal cardiovascular function under physiological conditions, AT undergoes a phenotypic shift characterised by acquisition of pro-oxidant and pro-inflammatory properties in cases of CVD. Crucially, recent evidence suggests that AT depots such as perivascular AT and epicardial AT are able to modify their phenotype in response to local signals of vascular and myocardial origin, respectively. Utilisation of this unique property of certain AT depots to dynamically track cardiovascular biology may reveal novel diagnostic and prognostic tools against CVD. Better understanding of the mechanisms controlling the 'quality' of AT secretome, as well as the communication links between AT and the cardiovascular system, is required for the efficient management of CVD.

Pharmacological Characterization of IW-1973, a Novel Soluble Guanylate Cyclase Stimulator with Extensive Tissue Distribution, Antihypertensive, Anti-Inflammatory, and Antifibrotic Effects in Preclinical Models of Disease

Soluble guanylate cyclase (sGC), a key signal-transduction enzyme, increases the conversion of guanosine-5'-triphosphate to cGMP upon binding of nitric oxide (NO). Endothelial dysfunction and/or reduced NO signaling have been implicated in cardiovascular disease pathogenesis and complications of diabetes and have been associated with other disease states and aging. Soluble guanylate cyclase (sGC) stimulators are small-molecule drugs that bind sGC and enhance NO-mediated cGMP signaling. The pharmacological characterization of IW-1973 [1,1,1,3,3,3-hexafluoro-2-(((5-fluoro-2-(1-(2-fluorobenzyl)-5-(isoxazol-3-yl)-1H-pyrazol-3-yl) pyrimidin-4-yl)amino)methyl)propan-2-ol], a novel clinical-stage sGC stimulator under clinical investigation for treatment of heart failure with preserved ejection fraction and diabetic nephropathy, is described. In the presence of NO, IW-1973 stimulated sGC in a human purified enzyme assay and a HEK-293 whole cell assay. sGC stimulation by IW-1973 in cells was associated with increased phosphorylation of vasodilator-stimulated phosphoprotein. IW-1973, at doses of 1-10 mg/kg, significantly lowered blood pressure in normotensive and spontaneously hypertensive rats. In a Dahl salt-sensitive hypertension model, IW-1973 significantly reduced blood pressure, inflammatory cytokine levels, and renal disease markers, including proteinuria and renal fibrotic gene expression. The results were affirmed in mouse lipopolysaccharide-induced inflammation and rat unilateral ureteral obstruction renal fibrosis models. A quantitative whole-body autoradiography study of IW-1973 revealed extensive tissue distribution and pharmacokinetic studies showed a large volume of distribution and a profile consistent with predicted once-a-day dosing in humans. In summary, IW-1973 is a potent, orally available sGC stimulator that exhibits renoprotective, anti-inflammatory, and antifibrotic effects in nonclinical models.

Adipocyte-specific expression of C-type natriuretic peptide suppresses lipid metabolism and adipocyte hypertrophy in adipose tissues in mice fed high-fat diet

C-type natriuretic peptide (CNP) is expressed in diverse tissues, including adipose and endothelium, and exerts its effects by binding to and activating its receptor, guanylyl cyclase B. Natriuretic peptides regulate intracellular cGMP and phosphorylated vasodilator-stimulated phosphoprotein (VASP). We recently revealed that overexpression of CNP in endothelial cells protects against high-fat diet (HFD)-induced obesity in mice. Given that endothelial CNP affects adipose tissue during obesity, CNP in adipocytes might directly regulate adipocyte function during obesity. Therefore, to elucidate the effect of CNP in adipocytes, we assessed 3T3-L1 adipocytes and transgenic (Tg) mice that overexpressed CNP specifically in adipocytes (A-CNP). We found that CNP activates the cGMP–VASP pathway in 3T3-L1 adipocytes. Compared with Wt mice, A-CNP Tg mice showed decreases in fat weight and adipocyte hypertrophy and increases in fatty acid β-oxidation, lipolysis-related gene expression, and energy expenditure during HFD-induced obesity. These effects led to decreased levels of the macrophage marker F4/80 in the mesenteric fat pad and reduced inflammation. Furthermore, A-CNP Tg mice showed improved glucose tolerance and insulin sensitivity, which were associated with enhanced insulin-stimulated Akt phosphorylation. Our results suggest that CNP overexpression in adipocytes protects against adipocyte hypertrophy, excess lipid metabolism, inflammation, and decreased insulin sensitivity during HFD-induced obesity.

The soluble guanylate cyclase stimulator IW-1973 prevents inflammation and fibrosis in experimental non-alcoholic steatohepatitis

BACKGROUND AND PURPOSE

Non-alcoholic steatohepatitis (NASH) is the hepatic manifestation of metabolic syndrome and is characterized by steatosis, inflammation and fibrosis. Soluble guanylate cyclase (sGC) stimulation reduces inflammation and fibrosis in experimental models of lung, kidney and heart disease. Here, we tested whether sGC stimulation is also effective in experimental NASH.

EXPERIMENTAL APPROACH

NASH was induced in mice by feeding a choline-deficient, l-amino acid-defined, high-fat diet. These mice received either placebo or the sGC stimulator IW-1973 at two different doses (1 and 3 mg·kg^-1 ·day^-1 ) for 9 weeks. IW-1973 was also tested in high-fat diet (HFD)-induced obese mice. Steatosis, inflammation and fibrosis were assessed by Oil Red O, haematoxylin-eosin, Masson's trichrome, Sirius Red, F4/80 and α-smooth muscle actin staining. mRNA expression was assessed by quantitative PCR. Levels of IW-1973, cytokines and cGMP were determined by LC-MS/MS, Luminex and enzyme immunoassay respectively.

KEY RESULTS

Mice with NASH showed reduced cGMP levels and sGC expression, increased steatosis, inflammation, fibrosis, TNF-α and MCP-1 levels and up-regulated collagen types I α1 and α2, MMP2, TGF-β1 and tissue metallopeptidase inhibitor 1 expression. IW-1973 restored hepatic cGMP levels and sGC expression resulting in a dose-dependent reduction of hepatic inflammation and fibrosis. IW-1973 levels were ≈40-fold higher in liver tissue than in plasma. IW-1973 also reduced hepatic steatosis and adipocyte hypertrophy secondary to enhanced autophagy in HFD-induced obese mice.

CONCLUSIONS AND IMPLICATIONS

Our data indicate that sGC stimulation prevents hepatic steatosis, inflammation and fibrosis in experimental NASH. These findings warrant further evaluation of IW-1973 in the clinical setting.

Interplay between Obesity-Induced Inflammation and cGMP Signaling in White Adipose Tissue

Current worldwide figures suggest that obesity is pandemic. Understanding the underlying molecular mechanisms would help develop viable anti-obesity therapies. Here, we assess the influence of obesity-induced inflammation on white adipocyte cyclic guanosine monophosphate (cGMP) signaling, which is beneficial for adipocyte differentiation and thermogenesis. We find that murine gonadal and not inguinal fat is prone to obesity-induced inflammation. Correspondingly, the cGMP cascade is dysregulated in gonadal but not in inguinal fat of obese mice. Analysis of two independent human cohorts reveals a defective cGMP pathway only in visceral fat of obese subjects. Congruently, cGMP signaling is dysregulated in tumor necrosis factor α (TNF-α)-treated primary white adipocytes. TNF-α-mediated suppression of sGCβ₁ is mediated via NF-κB, whereas PKG is repressed by JNK signaling. Additionally, TNF-α-activated JNK signaling suppresses PPARγ and aP2. Taken together, the intensity of obesity-induced inflammation dictates the amplitude of cGMP signaling dysregulation in white adipocytes through distinct pathways.

Udenafil, a Phosphodiesterase 5 Inhibitor, Reduces Body Weight in High-Fat-Fed Mice

Purpose

High-fat (HF) feeding induces hypothalamic leptin resistance via the activation of toll-like receptor 4 (TLR4). TLR4 deficiency confers resistance to diet-induced obesity. Udenafil, an anti-impotence drug, inhibits TLR4 in airway epithelial cells in vitro. In this study, we evaluated whether udenafil suppressed the hypothalamic expression of TLR4 and reduced body weight.

Materials and Methods

The hypothalamic expression of TLR4, phosphodiesterase 5 (PDE5), nuclear factor-κB (NF-κB), and myeloid differentiation primary response gene 88 (Myd88) was analyzed by real-time polymerase chain reaction after treating mice for 2 days with udenafil (0, 12, 120, or 600 µg/d). Furthermore, the hypothalamic expression of TLR4, pro-opiomelanocortin (POMC), and neuropeptide Y (NPY) was analyzed after 9 days' treatment with udenafil and/or leptin. We also measured body weight and food intake following 9 days of udenafil and/or leptin treatment in control- and HF-fed mice.

Results

Udenafil suppressed hypothalamic TLR4 mRNA expression dose-dependently. The changes were associated with decreased PDE5, NF-κB, and Myd88 expression. Udenafil treatment for 9 days reduced body weight and caloric intake in HF-fed mice. This may have been associated with the suppression of NPY expression that was elevated by HF feeding. POMC expression was not affected by udenafil. However, udenafil did not augment the effects of leptin on the reduction of body weight and caloric intake in HF-fed mice.

Conclusions

These results suggested that udenafil reduced body weight by suppressing hypothalamic TLR4 mRNA expression in HF-fed mice and the combination effect of udenafil and leptin was additive rather than synergistic.

Effect of tadalafil administration on insulin secretion and insulin sensitivity in obese men

AIM

To evaluate the effect of tadalafil administration on insulin secretion and insulin sensitivity in obese men without diabetes.

METHODS

A randomized, double-blind, placebo-controlled clinical trial was carried out in obese male patients between 30 and 50 years of age. Eighteen subjects were randomly assigned to two groups of nine patients each. During a 28-day period, subjects received 5 mg orally of tadalafil or placebo each night. Patients were evaluated before and after the intervention. Total insulin secretion and first phase of insulin secretion were calculated by insulinogenic index and Stumvoll index, respectively, and insulin sensitivity was calculated using the Matsuda index. Tolerability and compliance were evaluated permanently throughout the study.

RESULTS

There were no significant differences after administration of tadalafil in total insulin secretion (0.82 ± 0.45 vs. 0.61 ± 0.27, p = 0.594), first phase of insulin secretion (1332 ± 487 vs. 1602 ± 800, p = 0.779) and insulin sensitivity (4.6 ± 1.2 vs. 4.9 ± 2.5, p = 0.779). No significant differences were shown in other measurements.

CONCLUSION

Tadalafil administration for 28 days did not modify insulin secretion or insulin sensitivity in obese men.

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.

Endothelial Dysfunction in Obesity

Chronic inflammatory state in obesity causes dysregulation of the endocrine and paracrine actions of adipocyte-derived factors, which disrupt vascular homeostasis and contribute to endothelial vasodilator dysfunction and subsequent hypertension. While normal healthy perivascular adipose tissue (PVAT) ensures the dilation of blood vessels, obesity-associated PVAT leads to a change in profile of the released adipo-cytokines, resulting in a decreased vasorelaxing effect. Adipose tissue inflammation, nitric oxide (NO)-bioavailability, insulin resistance and oxidized low-density lipoprotein (oxLDL) are main participating factors in endothelial dysfunction of obesity. In this chapter, disruption of inter-endothelial junctions between endothelial cells, significant increase in the production of reactive oxygen species (ROS), inflammation mediators, which are originated from inflamed endothelial cells, the balance between NO synthesis and ROS , insulin signaling and NO production, and decrease in L-arginine/endogenous asymmetric dimethyl-L-arginine (ADMA) ratio are discussed in connection with endothelial dysfunction in obesity.

Effect of phosphodiesterase-5 inhibitors on glycemic control in person with type 2 diabetes mellitus: A systematic review and meta-analysis

Chronic use of phosphodiesterase-5 inhibitors (PDE-5i) has been shown to improve insulin action on muscle glucose uptake by the prolongation of nitric oxide (NO)/cyclic guanosine monophosphate (cGMP)/protein kinase (PKG) signalling.

Aims

As the effects of PDE-5i on glycemic control in person with type 2 diabetes mellitus (T2DM) have not been systematically explored, we conducted a meta-analysis of available randomized controlled trials (RCTs).

Methods

A literature search was performed through electronic databases including MEDLINE (Pubmed), The Cochrane Library, SCOPUS, Web of Science, CINAHL, www.clinicaltrials.gov and www.clinicaltrialresults.org until April 2016 without language restriction. Studies were included if they met the following criteria: (i) RCTs of the chronic use of PDE-5i compared with placebo or no active treatment in T2DM patients (ii) reporting of HbA1c or glycated haemoglobin or fasting plasma glucose (FPG).

Results

Four studies involving a total of 198 patients fit into the inclusion criteria. All included studies used the same PDE-5i, sildenafil. Reports of HbA1c were analysed as only one study reported FPG. PDE-5i had no beneficial effect on HbA1c with weighted mean difference (WMD) of 0.17% (95% CI, −0.64 to 0.97).

Conclusion

This meta-analysis suggests that large and well-controlled studies are warranted to shed light on the effect of PDE-5i on glycemic control in people with type 2 diabetes mellitus.

Dietary olive oil induces cannabinoid CB2 receptor expression in adipose tissue of ApcMin/+ transgenic mice

BACKGROUND: Cannabinoid- 2 (CB2) receptor is known for its anti-obesity effects silencing the activated immune cells that are key drivers of metabolic syndrome and inflammation. Nutritional interventions in experimental models of carcinogenesis have been demonstrated to modulate tissue inflammation state and proliferation.

OBJECTIVE: Aim of this study was to test, in Apc^Min/+ mice, whether a diet enriched with olive oil, omega- 3 and omega-6- PUFAs affects the adipose tissue inflammation status.

METHODS: Four groups of animal were studied: ST group, receiving a standard diet; OO group, receiving the standard diet in which soybean oil (source of fats) was replaced with olive oil; OM-3 group, receiving the standard diet in which soybean oil was replaced with salmon oil; OM-6 group, receiving the standard diet in which soybean oil was replaced with oenothera oil. Gene and protein expression, in adipose tissue, were evaluated by RT-PCR and Western Blotting, respectively. Enzymatic activities were assayed by fluorescent and radiometric method, where appropriated.

RESULTS: The diet enriched with olive oil significantly induced CB2 receptor expression and it was able to control inflammatory and proliferative activity of mice adipose tissue.

CONCLUSIONS: The present findings open opportunities for developing novel nutritional strategies considering olive oil a key ingredient of a healthy dietary pattern.

Cardiovascular magnetic resonance detects the progression of impaired myocardial perfusion reserve and increased left-ventricular mass in mice fed a high-fat diet

BACKGROUND

Impaired myocardial perfusion reserve (MPR) is prevalent in obesity and diabetes, even in the absence of obstructive coronary artery disease (CAD), and is prognostic of adverse events. We sought to establish the time course of reduced MPR and to investigate associated vascular and tissue properties in mice fed a high-fat diet (HFD), as they are an emerging model of human obesity, diabetes, and reduced MPR without obstructive CAD.

METHODS

C57Bl/6 mice fed a HFD or a low-fat diet (control) were imaged at 6, 12, 18 and 24 weeks post-diet. The cardiovascular magnetic resonance (CMR) protocol included multi-slice cine imaging to assess ejection fraction (EF), left-ventricular (LV) mass, LV wall thickness (LVWT), and LV volumes, and first-pass perfusion CMR to quantify MPR. Coronary vascular reactivity, aortic atherosclerosis, myocardial capillary density and tissue fibrosis were also assessed.

RESULTS

Body weight was increased in HFD mice at 6-24 weeks post-diet (p < 0.05 vs. control). MPR in HFD mice was reduced and LV mass and LVWT were increased in HFD mice at 18 and 24 weeks post-diet (p < 0.05 vs. control). Coronary arteriolar vascular reactivity to adenosine and acetylcholine were reduced in HFD mice (p < 0.05 vs. control). There were no significant differences in cardiac volumes, EF, or capillary density measurements between the two groups. Histology showed interstitial fibrosis in HFD and no aortic atherosclerosis in either group.

CONCLUSIONS

C57Bl/6 mice fed a HFD for 18-24 weeks have progressively increased LV mass and impaired MPR with fibrosis, normal capillary density and no aortic plaque. These results establish C57Bl/6 mice fed a HFD for 18-24 weeks as a model of impaired MPR without obstructive CAD due to obesity and diabetes.

Nitric oxide synthase-mediated blood pressure regulation in obese melanocortin-4 receptor-deficient pregnant rats

Although obesity increases the risk for hypertension in pregnancy, the mechanisms responsible are unknown. Increased nitric oxide (NO) production results in vasodilation and reduced blood pressure during normal pregnancy in lean rats; however, the role of NO is less clear during obese pregnancies. We examined the impact of obesity on NO synthase (NOS)-mediated regulation of blood pressure during pregnancy by testing the hypothesis that NOS activity, expression, and regulation of vascular tone and blood pressure are reduced in obese pregnant rats. At gestational day 19, melanocortin-4 receptor (MC4R)-deficient obese rats (MC4R) had greater body weight and fat mass with elevated blood pressure and circulating sFlt-1 levels compared with MC4R pregnant rats. MC4R pregnant rats also had less circulating cGMP levels and reduced total NOS enzymatic activity and expression in mesenteric arteries. Despite decreased biochemical measures of NO/NOS in MC4R rats, NOS inhibition enhanced vasoconstriction only in mesenteric arteries from MC4R rats, suggesting greater NOS-mediated tone. To examine the role of NOS on blood pressure regulation in obese pregnant rats, MC4R and MC4R pregnant rats were administered the nonselective NOS inhibitor N^G-nitro-l-arginine methyl ester (l-NAME, 100 mg/l) from gestational day 14 to 19 in drinking water. The degree by which l-NAME raised blood pressure was similar between obese and lean pregnant rats. Although MC4R obese pregnant rats had elevated blood pressure associated with reduced total NOS activity and expression, they had enhanced NOS-mediated attenuation of vasoconstriction, with no evidence of alterations in NOS-mediated regulation of blood pressure.

Vascular Smooth Muscle Sirtuin-1 Protects Against Diet-Induced Aortic Stiffness

Arterial stiffness, a major cardiovascular risk factor, develops within 2 months in mice fed a high-fat, high-sucrose (HFHS) diet, serving as a model of human metabolic syndrome, and it is associated with activation of proinflammatory and oxidant pathways in vascular smooth muscle (VSM) cells. Sirtuin-1 (SirT1) is an NAD(+)-dependent deacetylase regulated by the cellular metabolic status. Our goal was to study the effects of VSM SirT1 on arterial stiffness in the context of diet-induced metabolic syndrome. Overnight fasting acutely decreased arterial stiffness, measured in vivo by pulse wave velocity, in mice fed HFHS for 2 or 8 months, but not in mice lacking SirT1 in VSM (SMKO). Similarly, VSM-specific genetic SirT1 overexpression (SMTG) prevented pulse wave velocity increases induced by HFHS feeding, during 8 months. Administration of resveratrol or S17834, 2 polyphenolic compounds known to activate SirT1, prevented HFHS-induced arterial stiffness and were mimicked by global SirT1 overexpression (SirT1 bacterial artificial chromosome overexpressor), without evident metabolic improvements. In addition, HFHS-induced pulse wave velocity increases were reversed by 1-week treatment with a specific, small molecule SirT1 activator (SRT1720). These beneficial effects of pharmacological or genetic SirT1 activation, against HFHS-induced arterial stiffness, were associated with a decrease in nuclear factor kappa light chain enhancer of activated B cells (NFκB) activation and vascular cell adhesion molecule (VCAM-1) and p47phox protein expressions, in aorta and VSM cells. In conclusion, VSM SirT1 activation decreases arterial stiffness in the setting of obesity by stimulating anti-inflammatory and antioxidant pathways in the aorta. SirT1 activators may represent a novel therapeutic approach to prevent arterial stiffness and associated cardiovascular complications in overweight/obese individuals with metabolic syndrome.

Ablation of eNOS does not promote adipose tissue inflammation

Adipose tissue (AT) inflammation is a hallmark characteristic of obesity and an important determinant of insulin resistance and cardiovascular disease; therefore, a better understanding of factors regulating AT inflammation is critical. It is well established that reduced vascular endothelial nitric oxide (NO) bioavailability promotes arterial inflammation; however, the role of NO in modulating inflammation in AT remains disputed. In the present study, 10-wk-old C57BL6 wild-type and endothelial nitric oxide synthase (eNOS) knockout male mice were randomized to either a control diet (10% kcal from fat) or a Western diet (44.9% kcal from fat, 17% sucrose, and 1% cholesterol) for 18 wk (n= 7 or 8/group). In wild-type mice, Western diet-induced obesity led to increased visceral white AT expression of inflammatory genes (e.g., MCP1, TNF-α, and CCL5 mRNAs) and markers of macrophage infiltration (e.g., CD68, ITGAM, EMR1, CD11C mRNAs, and Mac-2 protein), as well as reduced markers of mitochondrial content (e.g., OXPHOS complex I and IV protein). Unexpectedly, these effects of Western diet on visceral white AT were not accompanied by decreases in eNOS phosphorylation at Ser-1177 or increases in eNOS phosphorylation at Thr-495. Also counter to expectations, eNOS knockout mice, independent of the diet, were leaner and did not exhibit greater white or brown AT inflammation compared with wild-type mice. Collectively, these findings do not support the hypothesis that reduced NO production from eNOS contributes to obesity-related AT inflammation.

MicroRNA-181b Improves Glucose Homeostasis and Insulin Sensitivity by Regulating Endothelial Function in White Adipose Tissue

RATIONALE

The pathogenesis of insulin resistance involves dysregulated gene expression and function in multiple cell types, including endothelial cells (ECs). Post-transcriptional mechanisms such as microRNA-mediated regulation of gene expression could affect insulin action by modulating EC function.

OBJECTIVE

To determine whether microRNA-181b (miR-181b) affects the pathogenesis of insulin resistance by regulating EC function in white adipose tissue during obesity.

METHODS AND RESULTS

MiR-181b expression was reduced in adipose tissue ECs of obese mice, and rescue of miR-181b expression improved glucose homeostasis and insulin sensitivity. Systemic intravenous delivery of miR-181b robustly accumulated in adipose tissue ECs, enhanced insulin-mediated Akt phosphorylation at Ser473, and reduced endothelial dysfunction, an effect that shifted macrophage polarization toward an M2 anti-inflammatory phenotype in epididymal white adipose tissue. These effects were associated with increased endothelial nitric oxide synthase and FoxO1 phosphorylation as well as nitric oxide activity in epididymal white adipose tissue. In contrast, miR-181b did not affect insulin-stimulated Akt phosphorylation in liver and skeletal muscle. Bioinformatics and gene profiling approaches revealed that Pleckstrin homology domain leucine-rich repeat protein phosphatase, a phosphatase that dephosphorylates Akt at Ser473, is a novel target of miR-181b. Knockdown of Pleckstrin homology domain leucine-rich repeat protein phosphatase increased Akt phosphorylation at Ser473 in ECs, and phenocopied miR-181b's effects on glucose homeostasis, insulin sensitivity, and inflammation of epididymal white adipose tissue in vivo. Finally, ECs from diabetic subjects exhibited increased Pleckstrin homology domain leucine-rich repeat protein phosphatase expression.

CONCLUSIONS

Our data underscore the importance of adipose tissue EC function in controlling the development of insulin resistance. Delivery of miR-181b or Pleckstrin homology domain leucine-rich repeat protein phosphatase inhibitors may represent a new therapeutic approach to ameliorate insulin resistance by improving adipose tissue endothelial Akt-endothelial nitric oxide synthase-nitric oxide signaling.

M2 Macrophage Polarization Mediates Anti-inflammatory Effects of Endothelial Nitric Oxide Signaling

Endothelial nitric oxide (NO) signaling plays a physiological role in limiting obesity-associated insulin resistance and inflammation. This study was undertaken to investigate whether this NO effect involves polarization of macrophages toward an anti-inflammatory M2 phenotype. Mice with transgenic endothelial NO synthase overexpression were protected against high-fat diet (HFD)-induced hepatic inflammation and insulin resistance, and this effect was associated with reduced proinflammatory M1 and increased anti-inflammatory M2 activation of Kupffer cells. In cell culture studies, exposure of macrophages to endothelial NO similarly reduced inflammatory (M1) and increased anti-inflammatory (M2) gene expression. Similar effects were induced by macrophage overexpression of vasodilator-stimulated phosphoprotein (VASP), a key downstream mediator of intracellular NO signaling. Conversely, VASP deficiency induced proinflammatory M1 macrophage activation, and the transplantation of bone marrow from VASP-deficient donor mice into normal recipients caused hepatic inflammation and insulin resistance resembling that induced in normal mice by consumption of an HFD. These data suggest that proinflammatory macrophage M1 activation and macrophage-mediated inflammation are tonically inhibited by NO → VASP signal transduction, and that reduced NO → VASP signaling is involved in the effect of HFD feeding to induce M1 activation of Kupffer cells and associated hepatic inflammation. Our data implicate endothelial NO → VASP signaling as a physiological determinant of macrophage polarization and show that signaling via this pathway is required to prevent hepatic inflammation and insulin resistance.

Tongxinluo inhibits vascular inflammation and neointimal hyperplasia through blockade of the positive feedback loop between miR-155 and TNF-α

Tongxinluo (TXL), a traditional Chinese medicine, has multiple vasoprotective effects, including anti-inflammation. MicroRNA-155 (miR-155) is involved in vascular inflammation and atherosclerosis. However, a direct relationship between TXL and miR-155 in the development of vascular inflammation and remodeling had not yet been shown. The objective of the present study was to investigate whether TXL exerts an inhibitory effect on the vascular inflammatory response and neointimal hyperplasia by regulating miR-155 expression. Using the carotid artery ligation model in mice, we have shown that TXL dose dependently inhibited neointimal formation and reduced the vascular inflammatory response by inhibiting inflammatory cytokine production and macrophage infiltration. miR-155 was induced by carotid artery ligation, and neointimal hyperplasia was strongly reduced in miR-155(−/−) mice. In contrast, miR-155 overexpression partly reversed the inhibitory effect of TXL on neointimal hyperplasia. In bone marrow-derived macrophages, miR-155 and TNF-α formed a positive feedback loop to promote the inflammatory response, which could be blocked by TXL. Furthermore, TXL increased Akt1 protein expression and phosphorylation in TNF-α-stimulated marrow-derived macrophages, and knockdown of Akt1 abrogated the TXL-induced suppression of miR-155. In conclusion, TXL inhibits the vascular inflammatory response and neointimal hyperplasia induced by carotid artery ligation in mice. Suppression of miR-155 expression mediated by Akt1 and blockade of the feedback loop between miR-155 and TNF-α are important pathways whereby TXL exerts its vasoprotective effects.

Interaction between leucine and phosphodiesterase 5 inhibition in modulating insulin sensitivity and lipid metabolism

PURPOSE

Leucine activates SIRT1/AMP-activated protein kinase (AMPK) signaling and markedly potentiates the effects of other sirtuin and AMPK activators on insulin signaling and lipid metabolism. Phosphodiesterase 5 inhibition increases nitric oxide-cGMP signaling, which in turn exhibits a positive feedback loop with both SIRT1 and AMPK, thus amplifying peroxisome proliferator-activated receptor γ co-activator α (PGC1α)-mediated effects.

METHODS

We evaluated potential synergy between leucine and PDE5i on insulin sensitivity and lipid metabolism in vitro and in diet-induced obese (DIO) mice.

RESULTS

Leucine (0.5 mM) exhibited significant synergy with subtherapeutic doses (0.1-10 nM) of PDE5-inhibitors (sildenafil and icariin) on fat oxidation, nitric oxide production, and mitochondrial biogenesis in hepatocytes, adipocytes, and myotubes. Effects on insulin sensitivity, glycemic control, and lipid metabolism were then assessed in DIO-mice. DIO-mice exhibited fasting and postprandial hyperglycemia, insulin resistance, and hepatic steatosis, which were not affected by the addition of leucine (24 g/kg diet). However, the combination of leucine and a subtherapeutic dose of icariin (25 mg/kg diet) for 6 weeks reduced fasting glucose (38%, P<0.002), insulin (37%, P<0.05), area under the glucose tolerance curve (20%, P<0.01), and fully restored glucose response to exogenous insulin challenge. The combination also inhibited hepatic lipogenesis, stimulated hepatic and muscle fatty acid oxidation, suppressed hepatic inflammation, and reversed high-fat diet-induced steatosis.

CONCLUSION

These robust improvements in insulin sensitivity, glycemic control, and lipid metabolism indicate therapeutic potential for leucine-PDE5 inhibitor combinations.

CD47 deficiency protects mice from diet-induced obesity and improves whole body glucose tolerance and insulin sensitivity

CD47 is a transmembrane protein with several functions including self-recognition, immune cell communication, and cell signaling. Although it has been extensively studied in cancer and ischemia, CD47 function in obesity has never been explored. In this study, we utilized CD47 deficient mice in a high-fat diet induced obesity model to study for the first time whether CD47 plays a role in the development of obesity and metabolic complications. Male CD47 deficient and wild type (WT) control mice were fed with either low fat (LF) or high fat (HF) diets for 16 weeks. Interestingly, we found that CD47 deficient mice were protected from HF diet-induced obesity displaying decreased weight gain and reduced adiposity. This led to decreased MCP1/CCR2 dependent macrophage infiltration into adipose tissue and reduced inflammation, resulting in improved glucose tolerance and insulin sensitivity. In addition, CD47 deficiency stimulated the expression of UCP1 and carnitine palmitoyltransferase 1b (CPT1b) levels in brown adipose tissue, leading to increased lipid utilization and heat production. This contributes to the increased energy utilization and reduced adiposity observed in these mice. Taken together, these data revealed a novel role for CD47 in the development of obesity and its related metabolic complications.

Influence of habitual high dietary fat intake on endothelium-dependent vasodilation

High-fat diets are associated with an increased risk of cardiovascular disease. A potential underlying mechanism for the increased cardiovascular risk is endothelial dysfunction. Nitric oxide (NO)-mediated endothelium-dependent vasodilation is critical in the regulation of vascular tone and overall vascular health. The aim of this study was to determine the influence of dietary fat intake on endothelium-dependent vasodilation. Forty-four middle-aged and older sedentary, healthy adults were studied: 24 consumed a lower fat diet (LFD; 29% ± 1% calories from fat) and 20 consumed a high-fat diet (HFD; 41% ± 1% calories from fat). Four-day diet records were used to assess fat intake, and classifications were based on American Heart Association guidelines (<35% of total calories from fat). Forearm blood flow (FBF) responses to acetylcholine, in the absence and presence of the endothelial NO synthase inhibitor N(G)-monomethyl-l-arginine (L-NMMA), as well as responses to sodium nitroprusside were determined by plethysmography. The FBF response to acetylcholine was lower (∼15%; P < 0.05) in the HFD group (4.5 ± 0.2 to 12.1 ± 0.8 mL/100 mL tissue/min) than in the LFD group (4.6 ± 0.2 to 14.4 ± 0.6 mL/100 mL tissue/min). L-NMMA significantly reduced the FBF response to acetylcholine in the LFD group (∼25%) but not in the HFD group. There were no differences between groups in the vasodilator response to sodium nitroprusside. These data indicate that a high-fat diet is associated with endothelium-dependent vasodilator dysfunction due, in part, to diminished NO bioavailability. Impaired NO-mediated endothelium-dependent vasodilation may contribute to the increased cardiovascular risk with high dietary fat intake.

Guanylin-Guanylyl cyclase-C signaling in macrophages regulates mesenteric fat inflammation induced by high-fat diet

Guanylin (Gn), a bioactive peptide, and its receptor, guanylyl cyclase-C (GC-C), are primarily present in the intestine and maintain homeostasis in body fluids. Recently, rats whose macrophages overexpress Gn and GC-C were found to be resistant to diet-induced obesity. Considering that obesity is strongly related to a chronic inflammatory state in white adipose tissues, it is possible that Gn-GC-C macrophages contribute to the regulation of inflammation. In the present study, we investigated the inflammatory state of mesenteric fat in rats transgenic for both Gn and GC-C (double-transgenic [dTg] rats) by evaluating the levels of cyclic guanosine monophosphate (cGMP), a second messenger of Gn-GC-C, cGMP-dependent protein kinase (PKG), and phosphorylated vasodilator-stimulated phosphoprotein (VASP), a target protein of PKG. The levels of cGMP in dTg rats was higher than in WT rats fed the same diet. Although there were no significant differences in levels of PKG and phosphorylated VASP between WT and dTg rats fed a standard diet (STD), these levels in dTg rats fed a high fat diet (HFD) were markedly increased compared with levels in HFD WT rats. Furthermore, mRNA levels of proinflammatory factors in mesenteric fat were lower in HFD dTg rats than in HFD WT rats and were similar to levels in STD WT and dTg rats. These results indicate that the Gn-GC-C system in macrophages regulates the cGMP-PKG-VASP pathway and controls obesity through the downregulation of proinflammatory factors.

Specific activation of insulin-like growth factor-1 receptor by ginsenoside Rg5 promotes angiogenesis and vasorelaxation

Ginsenoside Rg5 is a compound newly synthesized during the steaming process of ginseng; however, its biological activity has not been elucidated with regard to endothelial function. We found that Rg5 stimulated in vitro angiogenesis of human endothelial cells, consistent with increased neovascularization and blood perfusion in a mouse hind limb ischemia model. Rg5 also evoked vasorelaxation in aortic rings isolated from wild type and high cholesterol-fed ApoE(-/-) mice but not from endothelial nitric-oxide synthase (eNOS) knock-out mice. Angiogenic activity of Rg5 was highly associated with a specific increase in insulin-like growth factor-1 receptor (IGF-1R) phosphorylation and subsequent activation of multiple angiogenic signals, including ERK, FAK, Akt/eNOS/NO, and Gi-mediated phospholipase C/Ca(2+)/eNOS dimerization pathways. The vasodilative activity of Rg5 was mediated by the eNOS/NO/cGMP axis. IGF-1R knockdown suppressed Rg5-induced angiogenesis and vasorelaxation by inhibiting key angiogenic signaling and NO/cGMP pathways. In silico docking analysis showed that Rg5 bound with high affinity to IGF-1R at the same binding site of IGF. Rg5 blocked binding of IGF-1 to its receptor with an IC50 of ∼90 nmol/liter. However, Rg5 did not induce vascular inflammation and permeability. These data suggest that Rg5 plays a novel role as an IGF-1R agonist, promoting therapeutic angiogenesis and improving hypertension without adverse effects in the vasculature.

Vasodilator-stimulated phosphoprotein protects against vascular inflammation and insulin resistance

Among the pleotropic effects of endothelial nitric oxide (NO) is protection against vascular inflammation during high-fat diet (HFD) feeding. The current work investigated the role of the enzyme vasodilatory-stimulated phosphoprotein (VASP) as a downstream mediator of the anti-inflammatory effect of NO signaling in vascular tissue. Relative to mice fed a low-fat diet (LFD), levels of VASP Ser(239) phosphorylation, a marker of VASP activation, were dramatically reduced in aortic tissue of mice with obesity induced by consuming a HFD. As reported previously, the effect of the HFD was associated with increased aortic inflammation, as measured by increased NF-κB-dependent gene expression, and reduced vascular insulin sensitivity (including insulin-stimulated phosphorylation of eNOS and Akt). These effects of the HFD were recapitulated by VASP knockout, implying a physiological role for VASP to constrain inflammatory signaling and thereby maintain vascular insulin sensitivity. Conversely, overexpression of VASP in endothelial cells blocked inflammation and insulin resistance induced by palmitate. The finding that transplantation of bone marrow from VASP-deficient donors into normal recipients does not recapitulate the vascular effects of whole body VASP deficiency suggests that the protective effects of this enzyme are not mediated in immune or other bone marrow-derived cells. These studies implicate VASP as a downstream mediator of the NO/cGMP pathway that is both necessary and sufficient to protect against vascular inflammation and insulin resistance. As such, this work identifies VASP as a potential therapeutic target in the treatment of obesity-related vascular dysfunction.

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.