Microvascular Endothelial Dysfunction in Obesity Is Driven by Macrophage-Dependent Hydrogen Sulfide Depletion

Exosomal miR-27b-3p secreted by visceral adipocytes contributes to endothelial inflammation and atherogenesis

Obesity, particularly increased visceral fat, positively correlates with various metabolic challenges, including atherosclerosis, but the mechanism is not fully understood. The aim of this study is to determine the role of visceral-fat-derived exosomes (Exo) in endothelial cells and atherosclerosis. We show that obesity changes the miRNA profile of visceral adipose exosomes in mice. Importantly, exosomal miR-27b-3p efficiently enters into the vascular endothelial cells and activates the NF-κB pathway by downregulating PPARα. Mechanistically, miR-27b-3p binds directly to the CDS region of PPARα mRNA, thereby promoting mRNA degradation and suppressing translation. In ApoE-deficient mice, administration of miR-27b-3p mimic increases inflammation and atherogenesis, while overexpression of PPARα protects against atherosclerosis. Thus, obesity-induced exosomal miR-27b-3p promotes endothelial inflammation and facilitates atherogenesis by PPARα suppression. We reveal an exosomal pathway by which obesity aggravates atherosclerosis and proposed therapeutic strategies for atherosclerosis in people with obesity.

Hydrogen Sulfide Regulates Macrophage Function in Cardiovascular Diseases

Significance: Hydrogen sulfide (H₂S) is an endogenous gasotransmitter that plays a vital role in immune system regulation. Recently, the regulation of macrophage function by H₂S has been extensively and actively recognized. Recent Advances: The mechanisms by which endogenous H₂S controls macrophage function have attracted increasing attention. The generation of endogenous H₂S from macrophages is mainly catalyzed by cystathionine-γ-lyase. H₂S is involved in the macrophage activation and inflammasome formation, which contributes to macrophage apoptosis, adhesion, chemotaxis, and polarization. In addition, H₂S has redox ability and interacts with reactive oxygen species to prevent oxidative stress. Moreover, H₂S epigenetically regulates gene expression. Critical Issues: In this article, the generation of endogenous H₂S in macrophages and its regulatory effect on macrophage function are reviewed. In addition, the signal transduction targeting macrophages by H₂S is also addressed. Finally, the potential therapeutic effect of H₂S on macrophages is discussed. Future Directions: Further experiments are required to explore the involvement of endogenous H₂S in the regulation of macrophage function in various physiological and pathophysiological processes and elucidate the mechanisms involved. Regarding the clinical translation of H₂S, further exploration of the application of H₂S in inflammation-related diseases is needed. Antioxid. Redox Signal. 38, 45-56.

Targeting hydrogen sulfide and nitric oxide to repair cardiovascular injury after trauma

The systemic cardiovascular effects of major trauma, especially neurotrauma, contribute to death and permanent disability in trauma patients and treatments are needed to improve outcomes. In some trauma patients, dysfunction of the autonomic nervous system produces a state of adrenergic overstimulation, causing either a sustained elevation in catecholamines (sympathetic storm) or oscillating bursts of paroxysmal sympathetic hyperactivity. Trauma can also activate innate immune responses that release cytokines and damage-associated molecular patterns into the circulation. This combination of altered autonomic nervous system function and widespread systemic inflammation produces secondary cardiovascular injury, including hypertension, damage to cardiac tissue, vascular endothelial dysfunction, coagulopathy and multiorgan failure. The gasotransmitters nitric oxide (NO) and hydrogen sulfide (H2S) are small gaseous molecules with potent effects on vascular tone regulation. Exogenous NO (inhaled) has potential therapeutic benefit in cardio-cerebrovascular diseases, but limited data suggests potential efficacy in traumatic brain injury (TBI). H2S is a modulator of NO signaling and autonomic nervous system function that has also been used as a drug for cardio-cerebrovascular diseases. The inhaled gases NO and H2S are potential treatments to restore cardio-cerebrovascular function in the post-trauma period.

Endothelium-Derived Relaxing Factors and Endothelial Function: A Systematic Review

BACKGROUND

The endothelium plays a pivotal role in homeostatic mechanisms. It specifically modulates vascular tone by releasing vasodilatory mediators, which act on the vascular smooth muscle. Large amounts of work have been dedicated towards identifying mediators of vasodilation and vasoconstriction alongside the deleterious effects of reactive oxygen species on the endothelium. We conducted a systematic review to study the role of the factors released by the endothelium and the effects on the vessels alongside its role in atherosclerosis.

METHODS

A search was conducted with appropriate search terms. Specific attention was offered to the effects of emerging modulators of endothelial functions focusing the analysis on studies that investigated the role of reactive oxygen species (ROS), perivascular adipose tissue, shear stress, AMP-activated protein kinase, potassium channels, bone morphogenic protein 4, and P2Y2 receptor.

RESULTS

530 citations were reviewed, with 35 studies included in the final systematic review. The endpoints were evaluated in these studies which offered an extensive discussion on emerging modulators of endothelial functions. Specific factors such as reactive oxygen species had deleterious effects, especially in the obese and elderly. Another important finding included the shear stress-induced endothelial nitric oxide (NO), which may delay development of atherosclerosis. Perivascular Adipose Tissue (PVAT) also contributes to reparative measures against atherosclerosis, although this may turn pathological in obese subjects. Some of these factors may be targets for pharmaceutical agents in the near future.

CONCLUSION

The complex role and function of the endothelium is vital for regular homeostasis. Dysregulation may drive atherogenesis; thus, efforts should be placed at considering therapeutic options by targeting some of the factors noted.

The Efficacy of Exercise Training for Cutaneous Microvascular Reactivity in the Foot in People with Diabetes and Obesity: Secondary Analyses from a Randomized Controlled Trial

It is unclear if cutaneous microvascular dysfunction associated with diabetes and obesity can be ameliorated with exercise. We investigated the effect of 12-weeks of exercise training on cutaneous microvascular reactivity in the foot. Thirty-three inactive adults with type 2 diabetes and obesity (55% male, 56.1 ± 7.9 years, BMI: 35.8 ± 5, diabetes duration: 7.9 ± 6.3 years) were randomly allocated to 12-weeks of either (i) moderate-intensity continuous training [50−60% peak oxygen consumption (VO2peak), 30−45 min, 3 d/week], (ii) low-volume high-intensity interval training (90% VO2peak, 1−4 min, 3 d/week) or (iii) sham exercise placebo. Post-occlusive reactive hyperaemia at the hallux was determined by laser-Doppler fluxmetry. Though time to peak flux post-occlusion almost halved following moderate intensity exercise, no outcome measure reached statistical significance (p > 0.05). These secondary findings from a randomised controlled trial are the first data reporting the effect of exercise interventions on cutaneous microvascular reactivity in the foot in people with diabetes. A period of 12 weeks of moderate-intensity or low-volume high-intensity exercise may not be enough to elicit functional improvements in foot microvascular reactivity in adults with type 2 diabetes and obesity. Larger, sufficiently powered, prospective studies are necessary to determine if additional weight loss and/or higher exercise volume is required.

The role of adipose tissue-derived hydrogen sulfide in inhibiting atherosclerosis

Hydrogen sulfide (H₂S) is the third gaseous signaling molecule discovered in the body after NO and CO and plays an important organismal protective role in various diseases. Within adipose tissue, related catalytic enzymes (cystathionine-β-synthetase, cystathionine-γ-lyase, and 3-mercaptopyruvate transsulfuration enzyme) can produce and release endogenous H₂S. Atherosclerosis (As) is a pathological change in arterial vessels that is closely related to abnormal glucose and lipid metabolism and a chronic inflammatory response. Previous studies have shown that H₂S can act on the cardiovascular system, exerting effects such as improving disorders of glycolipid metabolism, alleviating insulin resistance, protecting the function of vascular endothelial cells, inhibiting vascular smooth muscle cell proliferation and migration, regulating vascular tone, inhibiting the inflammatory response, and antagonizing the occurrence and development of As.

Physiological roles of hydrogen sulfide in mammalian cells, tissues and organs

H2S belongs to the class of molecules known as gasotransmitters, which also includes nitric oxide (NO) and carbon monoxide (CO). Three enzymes are recognized as endogenous sources of H2S in various cells and tissues: cystathionine g-lyase (CSE), cystathionine β-synthase (CBS) and 3-mercaptopyruvate sulfurtransferase (3-MST). The current article reviews the regulation of these enzymes as well as the pathways of their enzymatic and non-enzymatic degradation and elimination. The multiple interactions of H2S with other labile endogenous molecules (e.g. NO) and reactive oxygen species are also outlined. The various biological targets and signaling pathways are discussed, with special reference to H2S and oxidative posttranscriptional modification of proteins, the effect of H2S on channels and intracellular second messenger pathways, the regulation of gene transcription and translation and the regulation of cellular bioenergetics and metabolism. The pharmacological and molecular tools currently available to study H2S physiology are also reviewed, including their utility and limitations. In subsequent sections, the role of H2S in the regulation of various physiological and cellular functions is reviewed. The physiological role of H2S in various cell types and organ systems are overviewed. Finally, the role of H2S in the regulation of various organ functions is discussed as well as the characteristic bell-shaped biphasic effects of H2S. In addition, key pathophysiological aspects, debated areas, and future research and translational areas are identified A wide array of significant roles of H2S in the physiological regulation of all organ functions emerges from this review.

Plasma Hydrogen Sulfide Is Positively Associated With Post-operative Survival in Patients Undergoing Surgical Revascularization

Objective: Hydrogen sulfide (H₂S) is a gaseous signaling molecule and redox factor important for cardiovascular function. Deficiencies in its production or bioavailability are implicated in atherosclerotic disease. However, it is unknown if circulating H₂S levels differ between vasculopaths and healthy individuals, and if so, whether H₂S measurements can be used to predict surgical outcomes. Here, we examined: (1) Plasma H₂S levels in patients undergoing vascular surgery and compared these to healthy controls, and (2) the association between H₂S levels and mortality in a cohort of patients undergoing surgical revascularization.

Methods: One hundred and fifteen patients undergoing carotid endarterectomy, open lower extremity revascularization or lower leg amputation were enrolled at a single institution. Peripheral blood was also collected from a matched control cohort of 20 patients without peripheral or coronary artery disease. Plasma H₂S production capacity and sulfide concentration were measured using the lead acetate and monobromobimane methods, respectively.

Results: Plasma H₂S production capacity and plasma sulfide concentrations were reduced in patients with PAD (p < 0.001, p = 0.013, respectively). Patients that underwent surgical revascularization were divided into high vs. low H₂S production capacity groups by median split. Patients in the low H₂S production group had increased probability of mortality (p = 0.003). This association was robust to correction for potentially confounding variables using Cox proportional hazard models.

Conclusion: Circulating H₂S levels were lower in patients with atherosclerotic disease. Patients undergoing surgical revascularization with lower H₂S production capacity, but not sulfide concentrations, had increased probability of mortality within 36 months post-surgery. This work provides insight on the role H₂S plays as a diagnostic and potential therapeutic for cardiovascular disease.

Heart Failure Syndrome With Preserved Ejection Fraction Is a Metabolic Cluster of Non-resolving Inflammation in Obesity

Heart failure with preserved ejection fraction (HFpEF) is an emerging disease with signs of nonresolving inflammation, endothelial dysfunction, and multiorgan defects. Moreover, based on the clinical signs and symptoms and the rise of the obesity epidemic, the number of patients developing HFpEF is increasing. From recent molecular and cellular studies, it becomes evident that HFpEF is not a single and homogenous disease but a cluster of heterogeneous pathophysiology with aging at the base of the pyramid. Obesity superimposed on aging drives the number of inflammatory pathways that intersect with metabolic dysfunction and suboptimal inflammation. Here, we compiled information on obesity-directed macrophage dysfunction that coincide with metabolic defects. Obesity-associated proinflammatory stimuli facilitates heart and interorgan inflammation in HFpEF. Furthermore, diversified mechanisms that drive heart failure urge the need of studying pervasive and unresolved inflammation in animal models to understand HFpEF. A broad and system-based approach will help to study major translational aspects of HFpEF, since no single animal model recapitulates all signs of differential HFpEF stages in the clinical setting. Here, we covered experimental models that target HFpEF and emphasized the advances observed with formyl peptide 2 (FPR2) receptor, a prime sensor that is important in inflammation-resolution signaling. Dysfunction of FPR2 led to the development of spontaneous obesity, impaired macrophage function, and triggered kidney fibrosis, providing evidence of multiorgan defects in HFpEF in an obesogenic aging experimental model.

Adipose tissue macrophages as a therapeutic target in obesity-associated diseases

Obesity is an increasing problem in developed and developing countries. Individuals with obesity have a higher risk of several diseases, such as cardiovascular disease, increased risk of insulin resistance, type 2 diabetes, infertility, degenerative disorders, and also certain types of cancer. Adipose tissue (AT) is considered an extremely active endocrine organ, and the expansion of AT is accompanied by the infiltration of different types of immune cells, which induces a state of low-grade, chronic inflammation and metabolic dysregulation. Even though the exact mechanism of this low-grade inflammation is not fully understood, there is clear evidence that AT-infiltrating macrophages (ATMs) play a significant role in the pro-inflammatory state and dysregulated metabolism. ATMs represent the most abundant class of leukocytes in AT, constituting 5% of the cells in AT in individuals with normal weight. However, this percentage dramatically increases up to 50% in individuals with obesity, suggesting an important role of ATMs in obesity and its associated complications. In this review, we discuss current knowledge of the function of ATMs during steady-state and obesity and analyze its contribution to different obesity-associated diseases, highlighting the potential therapeutic target of ATMs in these pathological conditions.

Recent Update on the Molecular Mechanisms of Gonadal Steroids Action in Adipose Tissue

The gonadal steroids, including androgens, estrogens and progestogens, are involved in the control of body fat distribution in humans. Nevertheless, not only the size and localization of the fat depots depend on the sex steroids levels, but they can also highly affect the functioning of adipose tissue. Namely, the gonadocorticoids can directly influence insulin signaling, lipid metabolism, fatty acid uptake and adipokine production. They may also alter energy balance and glucose homeostasis in adipocytes in an indirect way, e.g., by changing the expression level of aquaglyceroporins. This work presents the recent advances in understanding the molecular mechanism of how the gonadal steroids influence the functioning of adipose tissue leading to a set of detrimental metabolic consequences. Special attention is given here to highlighting the sexual dimorphism of adipocyte functioning in terms of health and disease. Particularly, we discuss the molecular background of metabolic disturbances occurring in consequence of hormonal imbalance which is characteristic of some common endocrinopathies such as the polycystic ovary syndrome. From this perspective, we highlight the potential drug targets and the active substances which can be used in personalized sex-specific management of metabolic diseases, in accord with the patient's hormonal status.

Role of Inflammation in Coronary Epicardial and Microvascular Dysfunction

There is accumulating evidence highlighting a close relationship between inflammation and coronary microvascular dysfunction (CMD) in various experimental and clinical settings, with major clinical implications. Chronic low-grade vascular inflammation plays important roles in the underlying mechanisms behind CMD, especially in patients with coronary artery disease, obesity, heart failure with preserved ejection fraction and chronic inflammatory rheumatoid diseases. The central mechanisms of coronary vasomotion abnormalities comprise enhanced coronary vasoconstrictor reactivity, reduced endothelium-dependent and -independent coronary vasodilator capacity and increased coronary microvascular resistance, where inflammatory mediators and responses are substantially involved. How to modulate CMD to improve clinical outcomes of patients with the disorder and whether CMD management by targeting inflammatory responses can benefit patients remain challenging questions in need of further research. This review provides a concise overview of the current knowledge of the involvement of inflammation in the pathophysiology and molecular mechanisms of CMD from bench to bedside.

Degree of adiposity and obesity severity is associated with cutaneous microvascular dysfunction in type 2 diabetes

BACKGROUNDS AND AIMS

Obesity and diabetes independently contribute to cutaneous microvascular dysfunction via pathological processes that are not fully understood. We sought to determine if obesity severity is associated with cutaneous microvascular dysfunction and measures of peripheral arterial disease in adults with type 2 diabetes in cross-sectional observational study design.

METHODS AND RESULTS

Primary outcomes were post-occlusive reactive hyperaemia as determined by laser-Doppler fluxmetry (peak flux post-occlusion, time to peak flux post-occlusion, peak as a percentage of baseline, and area under the curve [AuC] index post-occlusion to pre-occlusion). Secondary outcomes were ankle- and toe-brachial indices (ABI and TBI) and systolic toe pressure. Thirty-six participants (20 men, 16 women) with mean age 55 ± 8 years, BMI of 36 ± 5 kg/m² and duration of diabetes 8 ± 6 years underwent measurements. After adjusting for age and duration of diabetes, SAT and total percentage body fat were able to explain 29% (p = 0.001) and 20% (p = 0.01) of variance of AuC index models, as well as 29% (p = 0.02) and 18% (p = 0.02) of peak as a percentage of baseline models, respectively. Though TBI demonstrated moderate, significant correlations with SAT (r:0.37, p = 0.04) and total percentage body fat (r:0.39, p = 0.03), these were not upheld by regression analyses. Neither ABI nor systolic toe pressure significantly correlated with any measure of adiposity or obesity.

CONCLUSION

These findings demonstrate impairment in cutaneous microvascular function related to adiposity and obesity severity in adults with type 2 diabetes, suggesting that obesity may pathologically effect cutaneous microvascular function in the absence of overt macrovascular disease, warranting further investigation.

Impact of sex on microvascular reactivity in a murine model of diet-induced obesity and insulin resistance

The association of obesity with cardiovascular disease is well established. However, the interplay of obesity and vascular dysfunction in peripheral tissues such as skeletal muscle, which plays a key in role metabolic homeostasis, requires further study. In particular, there is a paucity of data with regard to sex-differences. Therefore, using a murine model (C57BL/6) of high-fat diet-induced obesity and insulin resistance, we investigated changes in vascular function in gluteus maximus muscle of female and male mice. Diet-induced obesity resulted in alterations in microvascular function. Obese male mice displayed impaired vasoconstriction in second order arterioles compared to lean, male mice, whereas arterioles of obese, female mice displayed significant impairments of both vasodilation and vasoconstrictor responses compared to lean, female mice. Overall, this study identifies distinct differences in how obesity impacts the female and male murine response to skeletal muscle vascular function. This work advances our understanding of sex-specific risk of metabolic complications of obesity and indicates the need for expansion of this study as well as detailed investigation of sex-specific differences in obesity pathology in the future.

Role of Hydrogen Sulfide in the Endocrine System

Hydrogen sulfide (H₂S), as one of the three known gaseous signal transduction molecules in organisms, has attracted a surging amount of attention. H₂S is involved in a variety of physiological and pathological processes in the body, such as dilating blood vessels (regulating blood pressure), protecting tissue from ischemia-reperfusion injury, anti-inflammation, carcinogenesis, or inhibition of cancer, as well as acting on the hypothalamus and pancreas to regulate hormonal metabolism. The change of H₂S concentration is related to a variety of endocrine disorders, and the change of hormone concentration also affects the synthesis of H₂S. Understanding the effect of biosynthesis and the concentration of H₂S on the endocrine system is useful to develop drugs for the treatment of hypertension, diabetes, and other diseases.

The Role of H2S in the Metabolism of Glucose and Lipids

Glucose and lipids are essential elements for maintaining the body's homeostasis, and their dysfunction may participate in the pathologies of various diseases, particularly diabetes, obesity, metabolic syndrome, cardiovascular ailments, and cancers. Among numerous endogenous mediators, the gasotransmitter hydrogen sulfide (H₂S) plays a central role in the maintenance of glucose and lipid homeostasis. Current evidence from both pharmacological studies and transgenic animal models suggest a complex relationship between H₂S and metabolic dysregulation, especially in diabetes and obesity. This notion is achieved through tissue-specific expressions and actions of H₂S on target metabolic and hormone organs including the pancreas, skeletal muscle, livers, and adipose. In this chapter, we will summarize the roles and mechanisms of H₂S in several metabolic organs/tissues that are necessary for glucose and lipid metabolic homeostasis. In addition, future research directions and valuable therapeutic avenues around the pharmacological regulation of H₂S in glycolipid metabolism disorder will be also discussed.

The role of host defences in Covid 19 and treatments thereof

Hydrogen sulfide (H₂S) is a natural defence against the infections from enveloped RNA viruses and is likely involved also in Covid 19. It was already shown to inhibit growth and pathogenic mechanisms of a variety of enveloped RNA viruses and it was now found that circulating H₂S is higher in Covid 19 survivors compared to fatal cases. H₂S release is triggered by carbon monoxide (CO) from the catabolism of heme by inducible heme oxygenase (HO-1) and heme proteins possess catalytic activity necessary for the H₂S signalling by protein persulfidation. Subjects with a long promoter for the HMOX1 gene, coding for HO-1, are predicted for lower efficiency of this mechanism. SARS-cov-2 exerts ability to attack the heme of hemoglobin and other heme-proteins thus hampering both release and signalling of H₂S. Lack of H₂S-induced persulfidation of the K_ATP channels of leucocytes causes adhesion and release of the inflammatory cytokines, lung infiltration and systemic endothelial damage with hyper-coagulability. These events largely explain the sex and age distribution, clinical manifestations and co-morbidities of Covid-19. The understanding of this mechanism may be of guidance in re-evaluating the ongoing therapeutic strategies, with special attention to the interaction with mechanical ventilation, paracetamol and chloroquine use, and in the individuation of genetic traits causing increased susceptibility to the disruption of these physiologic processes and to a critical Covid 19. Finally, an array of therapeutic interventions with the potential to clinically modulate the HO-1/CO/H₂S axis is already available or under development. These include CO donors and H₂S donors and a boost to the endogenous production of H₂S is also possible.

Hydrogen sulfide: An endogenous regulator of the immune system

Hydrogen sulfide (H₂S) is now recognized as an endogenous signaling gasotransmitter in mammals. It is produced by mammalian cells and tissues by various enzymes - predominantly cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfurtransferase (3-MST) - but part of the H₂S is produced by the intestinal microbiota (colonic H₂S-producing bacteria). Here we summarize the available information on the production and functional role of H₂S in the various cell types typically associated with innate immunity (neutrophils, macrophages, dendritic cells, natural killer cells, mast cells, basophils, eosinophils) and adaptive immunity (T and B lymphocytes) under normal conditions and as it relates to the development of various inflammatory and immune diseases. Special attention is paid to the physiological and the pathophysiological aspects of the oral cavity and the colon, where the immune cells and the parenchymal cells are exposed to a special "H₂S environment" due to bacterial H₂S production. H₂S has many cellular and molecular targets. Immune cells are "surrounded" by a "cloud" of H₂S, as a result of endogenous H₂S production and exogenous production from the surrounding parenchymal cells, which, in turn, importantly regulates their viability and function. Downregulation of endogenous H₂S producing enzymes in various diseases, or genetic defects in H₂S biosynthetic enzyme systems either lead to the development of spontaneous autoimmune disease or accelerate the onset and worsen the severity of various immune-mediated diseases (e.g. autoimmune rheumatoid arthritis or asthma). Low, regulated amounts of H₂S, when therapeutically delivered by small molecule donors, improve the function of various immune cells, and protect them against dysfunction induced by various noxious stimuli (e.g. reactive oxygen species or oxidized LDL). These effects of H₂S contribute to the maintenance of immune functions, can stimulate antimicrobial defenses and can exert anti-inflammatory therapeutic effects in various diseases.

Local Peroxynitrite Impairs Endothelial Transient Receptor Potential Vanilloid 4 Channels and Elevates Blood Pressure in Obesity

BACKGROUND

Impaired endothelium-dependent vasodilation is a hallmark of obesity-induced hypertension. The recognition that Ca2+ signaling in endothelial cells promotes vasodilation has led to the hypothesis that endothelial Ca2+ signaling is compromised during obesity, but the underlying abnormality is unknown. In this regard, transient receptor potential vanilloid 4 (TRPV4) ion channels are a major Ca2+ influx pathway in endothelial cells, and regulatory protein AKAP150 (A-kinase anchoring protein 150) enhances the activity of TRPV4 channels.

METHODS

We used endothelium-specific knockout mice and high-fat diet-fed mice to assess the role of endothelial AKAP150-TRPV4 signaling in blood pressure regulation under normal and obese conditions. We further determined the role of peroxynitrite, an oxidant molecule generated from the reaction between nitric oxide and superoxide radicals, in impairing endothelial AKAP150-TRPV4 signaling in obesity and assessed the effectiveness of peroxynitrite inhibition in rescuing endothelial AKAP150-TRPV4 signaling in obesity. The clinical relevance of our findings was evaluated in arteries from nonobese and obese individuals.

RESULTS

We show that Ca2+ influx through TRPV4 channels at myoendothelial projections to smooth muscle cells decreases resting blood pressure in nonobese mice, a response that is diminished in obese mice. Counterintuitively, release of the vasodilator molecule nitric oxide attenuated endothelial TRPV4 channel activity and vasodilation in obese animals. Increased activities of inducible nitric oxide synthase and NADPH oxidase 1 enzymes at myoendothelial projections in obese mice generated higher levels of nitric oxide and superoxide radicals, resulting in increased local peroxynitrite formation and subsequent oxidation of the regulatory protein AKAP150 at cysteine 36, to impair AKAP150-TRPV4 channel signaling at myoendothelial projections. Strategies that lowered peroxynitrite levels prevented cysteine 36 oxidation of AKAP150 and rescued endothelial AKAP150-TRPV4 signaling, vasodilation, and blood pressure in obesity. Peroxynitrite-dependent impairment of endothelial TRPV4 channel activity and vasodilation was also observed in the arteries from obese patients.

CONCLUSIONS

These data suggest that a spatially restricted impairment of endothelial TRPV4 channels contributes to obesity-induced hypertension and imply that inhibiting peroxynitrite might represent a strategy for normalizing endothelial TRPV4 channel activity, vasodilation, and blood pressure in obesity.

Hydrogen sulfide and hepatic lipid metabolism - a critical pairing for liver health

Hydrogen sulfide (H2 S) is the most recently recognized gasotransmitter, influencing a wide range of physiological processes. As a critical regulator of metabolism, H2 S has been suggested to be involved in the pathology of many diseases, particularly obesity, diabetes and cardiovascular disorders. Its involvement in liver health has been brought to light more recently, particularly through knockout animal models, which show severe hepatic lipid accumulation upon ablation of H2 S metabolic pathways. A complex relationship between H2 S and lipid metabolism in the liver is emerging, which has significant implications for liver disease establishment and/or progression, regardless of the disease-causing agent. In this review, we discuss the critical importance of H2 S in hepatic lipid metabolism. We then describe the animal models so far related with H2 S and lipid-associated liver disease, as well as H2 S-based treatments available. Finally, we highlight important considerations for future studies and identify areas in which much still remains to be determined. LINKED ARTICLES: This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc.

Role of Endothelial Dysfunction in Cardiovascular Diseases: The Link Between Inflammation and Hydrogen Sulfide

Endothelial cells are important constituents of blood vessels that play critical roles in cardiovascular homeostasis by regulating blood fluidity and fibrinolysis, vascular tone, angiogenesis, monocyte/leukocyte adhesion, and platelet aggregation. The normal vascular endothelium is taken as a gatekeeper of cardiovascular health, whereas abnormality of vascular endothelium is a major contributor to a plethora of cardiovascular ailments, such as atherosclerosis, aging, hypertension, obesity, and diabetes. Endothelial dysfunction is characterized by imbalanced vasodilation and vasoconstriction, elevated reactive oxygen species (ROS), and proinflammatory factors, as well as deficiency of nitric oxide (NO) bioavailability. The occurrence of endothelial dysfunction disrupts the endothelial barrier permeability that is a part of inflammatory response in the development of cardiovascular diseases. As such, abrogation of endothelial cell activation/inflammation is of clinical relevance. Recently, hydrogen sulfide (H₂S), an entry as a gasotransmitter, exerts diverse biological effects through acting on various targeted signaling pathways. Within the cardiovascular system, the formation of H₂S is detected in smooth muscle cells, vascular endothelial cells, and cardiomyocytes. Disrupted H₂S bioavailability is postulated to be a new indicator for endothelial cell inflammation and its associated endothelial dysfunction. In this review, we will summarize recent advances about the roles of H₂S in endothelial cell homeostasis, especially under pathological conditions, and discuss its putative therapeutic applications in endothelial inflammation-associated cardiovascular disorders.

The role of adipose tissue in cardiovascular health and disease

Accumulating knowledge on the biology and function of the adipose tissue has led to a major shift in our understanding of its role in health and disease. The adipose tissue is now recognized as a crucial regulator of cardiovascular health, mediated by the secretion of several bioactive products, including adipocytokines, microvesicles and gaseous messengers, with a wide range of endocrine and paracrine effects on the cardiovascular system. The adipose tissue function and secretome are tightly controlled by complex homeostatic mechanisms and local cell-cell interactions, which can become dysregulated in obesity. Systemic or local inflammation and insulin resistance lead to a shift in the adipose tissue secretome from anti-inflammatory and anti-atherogenic towards a pro-inflammatory and pro-atherogenic profile. Moreover, the interplay between the adipose tissue and the cardiovascular system is bidirectional, with vascular-derived and heart-derived signals directly affecting adipose tissue biology. In this Review, we summarize the current knowledge of the biology and regional variability of adipose tissue in humans, deciphering the complex molecular mechanisms controlling the crosstalk between the adipose tissue and the cardiovascular system, and their possible clinical translation. In addition, we highlight the latest developments in adipose tissue imaging for cardiovascular risk stratification and discuss how therapeutic targeting of the adipose tissue can improve prevention and treatment of cardiovascular disease.

Obesity: a neuroimmunometabolic perspective

Neuroimmunology and immunometabolism are burgeoning topics of study, but the intersection of these two fields is scarcely considered. This interplay is particularly prevalent within adipose tissue, where immune cells and the sympathetic nervous system (SNS) have an important role in metabolic homeostasis and pathology, namely in obesity. In the present Review, we first outline the established reciprocal adipose-SNS relationship comprising the neuroendocrine loop facilitated primarily by adipose tissue-derived leptin and SNS-derived noradrenaline. Next, we review the extensive crosstalk between adipocytes and resident innate immune cells as well as the changes that occur in these secretory and signalling pathways in obesity. Finally, we discuss the effect of SNS adrenergic signalling in immune cells and conclude with exciting new research demonstrating an immutable role for SNS-resident macrophages in modulating SNS-adipose crosstalk. We posit that the latter point constitutes the existence of a new field - neuroimmunometabolism.

Mechanistic Links Between Obesity, Diabetes, and Blood Pressure: Role of Perivascular Adipose Tissue

Obesity is increasingly prevalent and is associated with substantial cardiovascular risk. Adipose tissue distribution and morphology play a key role in determining the degree of adverse effects, and a key factor in the disease process appears to be the inflammatory cell population in adipose tissue. Healthy adipose tissue secretes a number of vasoactive adipokines and anti-inflammatory cytokines, and changes to this secretory profile will contribute to pathogenesis in obesity. In this review, we discuss the links between adipokine dysregulation and the development of hypertension and diabetes and explore the potential for manipulating adipose tissue morphology and its immune cell population to improve cardiovascular health in obesity.

The Role of NADPH Oxidases in the Etiology of Obesity and Metabolic Syndrome: Contribution of Individual Isoforms and Cell Biology

Significance: Highly prevalent in Western cultures, obesity, metabolic syndrome, and diabetes increase the risk of cardiovascular morbidity and mortality and cost health care systems billions of dollars annually. At the cellular level, obesity, metabolic syndrome, and diabetes are associated with increased production of reactive oxygen species (ROS). Increased levels of ROS production in key organ systems such as adipose tissue, skeletal muscle, and the vasculature cause disruption of tissue homeostasis, leading to increased morbidity and risk of mortality. More specifically, growing evidence implicates the nicotinamide adenine dinucleotide phosphate oxidase (NOX) enzymes in these pathologies through impairment of insulin signaling, inflammation, and vascular dysfunction. The NOX family of enzymes is a major driver of redox signaling through its production of superoxide anion, hydrogen peroxide, and attendant downstream metabolites acting on redox-sensitive signaling molecules. Recent Advances: The primary goal of this review is to highlight recent advances and survey our present understanding of cell-specific NOX enzyme contributions to metabolic diseases. Critical Issues: However, due to the short half-lives of individual ROS and/or cellular defense systems, radii of ROS diffusion are commonly short, often restricting redox signaling and oxidant stress to localized events. Thus, special emphasis should be placed on cell type and subcellular location of NOX enzymes to better understand their role in the pathophysiology of metabolic diseases. Future Directions: We discuss the targeting of NOX enzymes as potential therapy and bring to light potential emerging areas of NOX research, microparticles and epigenetics, in the context of metabolic disease.

Metabolism, Obesity, and Diabetes Mellitus

Obesity and diabetes remain leading causes of reduced health span and life span throughout the world. Hence, it is not surprising that these areas are at the center of highly active areas of research. The identification of novel mechanisms underlying these metabolic disorders sets the stage for uncovering new potential therapeutic strategies. In this issue of Highlights in Arteriosclerosis, Thrombosis and Vascular Biology, we review recently published papers in the journal that add to our understanding of causes and consequences of obesity and diabetes and how these disorders impact metabolic function. Collectively, these studies in cultured cells to in vivo animal models to human subjects add to the growing body of evidence that both cell-intrinsic and cell-cell communication mechanisms collaborate in metabolic disorders to cause obesity, insulin resistance and diabetes and its complications.

Emerging Roles of Sympathetic Nerves and Inflammation in Perivascular Adipose Tissue

Perivascular adipose tissue (PVAT) is no longer recognised as simply a structural support for the vasculature, and we now know that PVAT releases vasoactive factors which modulate vascular function. Since the discovery of this function in 1991, PVAT research is rapidly growing and the importance of PVAT function in disease is becoming increasingly clear. Obesity is associated with a plethora of vascular conditions; therefore, the study of adipocytes and their effects on the vasculature is vital. PVAT contains an adrenergic system including nerves, adrenoceptors and transporters. In obesity, the autonomic nervous system is dysfunctional; therefore, sympathetic innervation of PVAT may be the key mechanistic link between increased adiposity and vascular disease. In addition, not all obese people develop vascular disease, but a common feature amongst those that do appears to be the inflammatory cell population in PVAT. This review will discuss what is known about sympathetic innervation of PVAT, and the links between nerve activation and inflammation in obesity. In addition, we will examine the therapeutic potential of exercise in sympathetic stimulation of adipose tissue.

Hyperlipidemias and Obesity

The organs require oxygen and other types of nutrients (amino acids, sugars, and lipids) to function, the heart consuming large amounts of fatty acids for oxidation and adenosine triphosphate (ATP) generation.

Immunomodulatory Effects of Glutathione, Garlic Derivatives, and Hydrogen Sulfide

Glutathione and aged garlic extract are sulfur-containing products that play important protective and regulatory roles within the immune system and in oxidative processes. Hydrogen sulfide (H₂S), an endogenous, gaseous, signaling transmitter, has also been shown to be involved in the regulation of inflammation. Recent studies have shown that sulfur-containing compounds from garlic have beneficial effects in attenuating outcomes associated with cardiovascular disease and inflammation by a mechanism that may be related to the H₂S signaling pathway. In this review, we summarize the main functions of glutathione (GSH), garlic derivatives and H₂S and their role in the immune response and impact on health and disease.

Dietary methionine restriction ameliorates the impairment of learning and memory function induced by obesity in mice

Dietary methionine restriction improves impairment of learning and memory function induced by obesity, likely by increasing H₂S production.

Cellular mechanisms underlying obesity-induced arterial stiffness

Obesity is an emerging pandemic driven by consumption of a diet rich in fat and highly refined carbohydrates (a Western diet) and a sedentary lifestyle in both children and adults. There is mounting evidence that arterial stiffness in obesity is an independent and strong predictor of cardiovascular disease (CVD), cognitive functional decline, and chronic kidney disease. Cardiovascular stiffness is a precursor to atherosclerosis, systolic hypertension, cardiac diastolic dysfunction, and impairment of coronary and cerebral flow. Moreover, premenopausal women lose the CVD protection normally afforded to them in the setting of obesity, insulin resistance, and diabetes, and this loss of CVD protection is inextricably linked to an increased propensity for arterial stiffness. Stiffness of endothelial and vascular smooth muscle cells, extracellular matrix remodeling, perivascular adipose tissue inflammation, and immune cell dysfunction contribute to the development of arterial stiffness in obesity. Enhanced endothelial cortical stiffness decreases endothelial generation of nitric oxide, and increased oxidative stress promotes destruction of nitric oxide. Our research over the past 5 years has underscored an important role of increased aldosterone and vascular mineralocorticoid receptor activation in driving development of cardiovascular stiffness, especially in females consuming a Western diet. In this review the cellular mechanisms of obesity-associated arterial stiffness are highlighted.

Endothelial Functions

The endothelium plays important roles in modulating vascular tone by synthesizing and releasing a variety of endothelium-derived relaxing factors, including vasodilator prostaglandins, NO, and endothelium-dependent hyperpolarization factors, as well as endothelium-derived contracting factors. Endothelial dysfunction is mainly caused by reduced production or action of these relaxing mediators. Accumulating evidence has demonstrated that endothelial functions are essential to ensure proper maintenance of vascular homeostasis and that endothelial dysfunction is the hallmark of a wide range of cardiovascular diseases associated with pathological conditions toward vasoconstriction, thrombosis, and inflammatory state. In the clinical settings, evaluation of endothelial functions has gained increasing attention in view of its emerging relevance for cardiovascular disease. Recent experimental and clinical studies in the vascular biology field have demonstrated a close relationship between endothelial functions and cardiovascular disease and the highlighted emerging modulators of endothelial functions, new insight into cardiovascular disease associated with endothelial dysfunction, and potential therapeutic and diagnostic targets with major clinical implications. We herein will summarize the current knowledge on endothelial functions from bench to bedside with particular focus on recent publications in Arteriosclerosis, Thrombosis, and Vascular Biology.

Role of cystathionine-γ-lyase in hypoxia-induced changes in TASK activity, intracellular [Ca2+] and ventilation in mice

Cystathionine-γ-lyase (CSE) is a multifunctional enzyme, and hydrogen sulfide (H₂S) is one of its products. CSE and H₂S have recently been proposed to be critical signaling molecules in hypoxia-induced excitation of carotid body (CB) glomus cells and the chemosensory response. Because the role of H₂S in arterial chemoreception is still debated, we further examined the role of CSE by studying the effects of hypoxia on TASK K⁺ channel activity, cell depolarization, [Ca²⁺]_i and ventilation using CSE^+/+ and CSE^-/- mice. As predicted, hypoxia reduced TASK activity and depolarized glomus cells isolated from CSE^+/+ mice. These effects of hypoxia were not significantly altered in glomus cells from CSE^-/- mice. Basal [Ca²⁺]_i and hypoxia-induced elevation of [Ca²⁺] were also not significantly different in glomus cells from CSE^+/+ and CSE^-/- mice. In whole-body plethysmography, hypoxia (10%O₂) increased minute ventilation in both CSE^+/+ and CSE^-/- mice equally well, and no significant differences were found in either males or females when adjusted by body weight. Together, these results show that deletion of the CSE gene has no effects on hypoxia-induced changes in TASK, cell depolarization, [Ca²⁺]_i and ventilation, and therefore do not support the idea that CSE/H₂S signaling is important for CB chemoreceptor activity in mice.