Adiponectin and insulin cross talk: the microvascular connection

Differences in metabolic characteristics between Metabolically Healthy Obesity (MHO) and Metabolically Unhealthy Obesity (MUO) in weight reduction therapy

Metabolically Healthy Obesity (MHO) is generally recognized as the absence of any metabolic disorders and cardiovascular diseases, including type 2 diabetes, dyslipidemia, and hypertension, in obese individuals; however, it is not clearly defined. Therefore, the present study investigated differences in metabolic characteristics between individuals with MHO and Metabolically Unhealthy Obesity (MUO) during weight reduction therapy. The key factors defining MHO and the importance of weight reduction therapy for MHO were also examined. Cohort data from the Japan Obesity and Metabolic Syndrome (JOMS) study were analyzed. Subjects were divided into the MHO (n = 25) and MUO (n = 120) groups. Prior to weight reduction therapy, serum adiponectin levels were significantly higher in the MHO group than in the MUO group. Serum adiponectin levels also negatively correlated with the area of subcutaneous adipose tissue (SAT) and Homeostasis model assessment (HOMA)-R in the MHO group, but not in the MUO group. Collectively, the present results suggest the importance of adiponectin for maintaining metabolic homeostasis in the MHO group. On the other hand, no significant differences were observed in inflammatory markers between the MHO and MUO groups, suggesting the presence of chronic inflammation in both groups. Furthermore, a positive correlation was noted between changes in serum cystatin C levels and waist circumference in the MHO group, which indicated that despite the absence of metabolic disorders, the MHO group exhibited anti-inflammatory responses during weight reduction therapy. These results underscore the significance of weight reduction even for individuals with MHO.

The Role of Perivascular Adipose Tissue in the Pathogenesis of Endothelial Dysfunction in Cardiovascular Diseases and Type 2 Diabetes Mellitus

Cardiovascular diseases (CVDs) and type 2 diabetes mellitus (T2DM) are two of the four major chronic non-communicable diseases (NCDs) representing the leading cause of death worldwide. Several studies demonstrate that endothelial dysfunction (ED) plays a central role in the pathogenesis of these chronic diseases. Although it is well known that systemic chronic inflammation and oxidative stress are primarily involved in the development of ED, recent studies have shown that perivascular adipose tissue (PVAT) is implicated in its pathogenesis, also contributing to the progression of atherosclerosis and to insulin resistance (IR). In this review, we describe the relationship between PVAT and ED, and we also analyse the role of PVAT in the pathogenesis of CVDs and T2DM, further assessing its potential therapeutic target with the aim of restoring normal ED and reducing global cardiovascular risk.

Role of adipokines in sarcopenia

ABSTRACT

Sarcopenia is an age-related disease that mainly involves decreases in muscle mass, muscle strength and muscle function. At the same time, the body fat content increases with aging, especially the visceral fat content. Adipose tissue is an endocrine organ that secretes biologically active factors called adipokines, which act on local and distant tissues. Studies have revealed that some adipokines exert regulatory effects on muscle, such as higher serum leptin levels causing a decrease in muscle function and adiponectin inhibits the transcriptional activity of Forkhead box O3 (FoxO3) by activating peroxisome proliferators-activated receptor-γ coactivator -1α (PGC-1α) and sensitizing cells to insulin, thereby repressing atrophy-related genes (atrogin-1 and muscle RING finger 1 [MuRF1]) to prevent the loss of muscle mass. Here, we describe the effects on muscle of adipokines produced by adipose tissue, such as leptin, adiponectin, resistin, mucin and lipocalin-2, and discuss the importance of these adipokines for understanding the development of sarcopenia.

Liraglutide and Exercise Synergistically Attenuate Vascular Inflammation and Enhance Metabolic Insulin Action in Early Diet-Induced Obesity

Inflammation-induced vascular insulin resistance is an early event in diet-induced obesity and contributes to metabolic insulin resistance. To examine whether exercise and glucagon-like peptide 1 (GLP-1) receptor agonism, alone or in combination, modulate vascular and metabolic insulin actions during obesity development, we performed a euglycemic insulin clamp in adult male rats after 2 weeks of high-fat diet feeding with either access to a running wheel (exercise), liraglutide, or both. Rats exhibited increased visceral adiposity and blunted microvascular and metabolic insulin responses. Exercise and liraglutide alone each improved muscle insulin sensitivity, but their combination fully restored insulin-mediated glucose disposal rates. The combined exercise and liraglutide intervention enhanced insulin-mediated muscle microvascular perfusion, reduced perivascular macrophage accumulation and superoxide production in the muscle, attenuated blood vessel inflammation, and improved endothelial function, along with increasing endothelial nucleus translocation of NRF2 and increasing endothelial AMPK phosphorylation. We conclude that exercise and liraglutide synergistically enhance the metabolic actions of insulin and reduce vascular oxidative stress and inflammation in the early stage of obesity development. Our data suggest that early combination use of exercise and GLP-1 receptor agonism might be an effective strategy in preventing vascular and metabolic insulin resistance and associated complications during the development of obesity.

ARTICLE HIGHLIGHTS

Inflammation-induced vascular insulin resistance occurs early in diet-induced obesity and contributes to metabolic insulin resistance. We examined whether exercise and GLP-1 receptor agonism, alone or in combination, modulate vascular and metabolic insulin actions during obesity development. We found that exercise and liraglutide synergistically enhanced the metabolic actions of insulin and reduced perimicrovascular macrophage accumulation, vascular oxidative stress, and inflammation in the early stage of obesity development. Our data suggest that early combination use of exercise and a GLP-1 receptor agonist might be an effective strategy in preventing vascular and metabolic insulin resistance and associated complications during the development of obesity.

Bones and Hormones: Interaction between Hormones of the Hypothalamus, Pituitary, Adipose Tissue and Bone

The bony skeleton, as a structural foundation for the human body, is essential in providing mechanical function and movement. The human skeleton is a highly specialized and dynamic organ that undergoes continuous remodeling as it adapts to the demands of its environment. Advances in research over the last decade have shone light on the various hormones that influence this process, modulating the metabolism and structural integrity of bone. More recently, novel and non-traditional functions of hypothalamic, pituitary, and adipose hormones and their effects on bone homeostasis have been proposed. This review highlights recent work on physiological bone remodeling and discusses our knowledge, as it currently stands, on the systemic interplay of factors regulating this interaction. In this review, we provide a summary of the literature on the relationship between bone physiology and hormones including kisspeptin, neuropeptide Y, follicle-stimulating hormone (FSH), prolactin (PRL), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), growth hormone (GH), leptin, and adiponectin. The discovery and understanding of this new functionality unveils an entirely new layer of physiologic circuitry.

Prospects of potential adipokines as therapeutic agents in obesity-linked atherogenic dyslipidemia and insulin resistance

BACKGROUND

In normal circumstances, AT secretes anti-inflammatory adipokines (AAKs) which regulates lipid metabolism, insulin sensitivity, vascular hemostasis, and angiogenesis. However, during obesity AT dysfunction occurs and leads to microvascular imbalance and secretes several pro-inflammatory adipokines (PAKs), thereby favoring atherogenic dyslipidemia and insulin resistance. Literature suggests decreased levels of circulating AAKs and increased levels of PAKs in obesity-linked disorders. Importantly, AAKs have been reported to play a vital role in obesity-linked metabolic disorders mainly insulin resistance, type-2 diabetes mellitus and coronary heart diseases. Interestingly, AAKs counteract the microvascular imbalance in AT and exert cardioprotection via several signaling pathways such as PI3-AKT/PKB pathway. Although literature reviews have presented a number of investigations detailing specific pathways involved in obesity-linked disorders, literature concerning AT dysfunction and AAKs remains sketchy. In view of the above, in the present contribution an effort has been made to provide an insight on the AT dysfunction and role of AAKs in modulating the obesity and obesity-linked atherogenesis and insulin resistance.

MAIN BODY

"Obesity-linked insulin resistance", "obesity-linked cardiometabolic disease", "anti-inflammatory adipokines", "pro-inflammatory adipokines", "adipose tissue dysfunction" and "obesity-linked microvascular dysfunction" are the keywords used for searching article. Google scholar, Google, Pubmed and Scopus were used as search engines for the articles.

CONCLUSIONS

This review offers an overview on the pathophysiology of obesity, management of obesity-linked disorders, and areas in need of attention such as novel therapeutic adipokines and their possible future perspectives as therapeutic agents.

Space Flight-Promoted Insulin Resistance as a Possible Disruptor of Wound Healing

During space flight, especially when prolonged, exposure to microgravity results in a number of pathophysiological changes such as bone loss, muscle atrophy, cardiovascular and metabolic changes and impaired wound healing, among others. Interestingly, chronic low-grade inflammation and insulin resistance appear to be pivotal events linking many of them. Interestingly, real and experimental microgravity is also associated to altered wound repair, a process that is becoming increasingly important in view of prolonged space flights. The association of insulin resistance and wound healing impairment may be hypothesized from some dysmetabolic conditions, like the metabolic syndrome, type 2 diabetes mellitus and abdominal/visceral obesity, where derangement of glucose and lipid metabolism, greater low-grade inflammation, altered adipokine secretion and adipocyte dysfunction converge to produce systemic effects that also negatively involve wound healing. Indeed, wound healing impairment after traumatic events and surgery in space remains a relevant concern for space agencies. Further studies are required to clarify the molecular connection between insulin resistance and wound healing during space flight, addressing the ability of physical, endocrine/metabolic, and pharmacological countermeasures, as well as nutritional strategies to prevent long-term detrimental effects on tissue repair linked to insulin resistance. Based on these considerations, this paper discusses the pathophysiological links between microgravity-associated insulin resistance and impaired wound healing.

Correlation between adiponectin level and the degree of fibrosis in patients with non-alcoholic fatty liver disease

Background

Non-alcoholic fatty liver disease (NAFLD) is one of the most prevalent chronic liver diseases, particularly in Egypt. It is defined as the accumulation of lipids inside the hepatocytes, in the absence of other etiologies of hepatic damage. It is frequently associated with obesity, diabetes mellitus, and metabolic syndrome. Adiponectin is an abundant adipocyte-derived protein with well-established anti-atherogenic, insulin-sensitizing, and anti-inflammatory properties. The liver is a major target organ for adiponectin especially in fatty liver diseases, and this adipocytokine has the ability to control many liver functions including metabolism, inflammation, and fibrosis. In this study, we aimed to find out the correlation between the degree of liver fibrosis in NAFLD patients and their serum adiponectin level as a future non-invasive method for the assessment of liver fibrosis to substitute liver biopsy to avoid its hazardous complication and also to study the correlation between diabetes mellitus as well as obesity and serum adiponectin level.

Results

Fifty patients were selected to participate in our study based on our inclusion criteria. They were recruited from the Internal Medicine Department, Gastroenterology Clinic in Al-Demerdash Hospital using a convenient sampling method. Diagnosis of NAFLD was confirmed by laboratory markers: aspartate aminotransferase (AST), alanine aminotransferase (ALT), lipid profile, ultrasound, and FibroScan examination. Analyzing the adiponectin levels showed that besides its significant correlation with body mass index (BMI), hypertension, diabetes mellitus, and dyslipidemia, it was significantly lower in the high-grade fibrosis group compared to the low-grade fibrosis group with a P-value of (0.000) and a cutoff value for stage 3/4 fibrosis of about 2.31 μg/ml which marked a promising hope of adiponectin being of protective value against liver fibrosis.

Conclusion

Both serum levels and hepatic adiponectin receptor expression are decreased in NAFLD. Therefore, either adiponectin itself or adiponectin-inducing agents might be of key therapeutic interest in the near future in the treatment of NAFLD.

Adiponectin: Structure, Physiological Functions, Role in Diseases, and Effects of Nutrition

Adiponectin (a protein consisting of 244 amino acids and characterized by a molecular weight of 28 kDa) is a cytokine that is secreted from adipose tissues (adipokine). Available evidence suggests that adiponectin is involved in a variety of physiological functions, molecular and cellular events, including lipid metabolism, energy regulation, immune response and inflammation, and insulin sensitivity. It has a protective effect on neurons and neural stem cells. Adiponectin levels have been reported to be negatively correlated with cancer, cardiovascular disease, and diabetes, and shown to be affected (i.e., significantly increased) by proper healthy nutrition. The present review comprehensively overviews the role of adiponectin in a range of diseases, showing that it can be used as a biomarker for diagnosing these disorders as well as a target for monitoring the effectiveness of preventive and treatment interventions.

Insulin Resistance across the Spectrum of Nonalcoholic Fatty Liver Disease

Insulin resistance (IR) is defined as a lower-than-expected response to insulin action from target tissues, leading to the development of type 2 diabetes through the impairment of both glucose and lipid metabolism. IR is a common condition in subjects with nonalcoholic fatty liver disease (NAFLD) and is considered one of the main factors involved in the pathogenesis of nonalcoholic steatohepatitis (NASH) and in the progression of liver disease. The liver, the adipose tissue and the skeletal muscle are major contributors for the development and worsening of IR. In this review, we discuss the sites and mechanisms of insulin action and the IR-related impairment along the spectrum of NAFLD, from simple steatosis to progressive NASH and cirrhosis.

Impact of weight reduction on insulin resistance, adhesive molecules and adipokines dysregulation among obese type 2 diabetic patients

BACKGROUND

Type 2 diabetes mellitus is usually related to vascular problems and is associated with impairment in endothelial function characterized by impaired endothelial-dependent vasodilation and increased platelet adhesion. There is limitation in clinical studies that have addressed the beneficial effects of weight reduction in modulating biomarkers of endothelial dysfunction and adipokines dysregulation for obesity associated with type 2 diabetes mellitus.

OBJECTIVE

This study was designed to detect the effects of weight loss on insulin resistance, adhesive molecules and adipokines dysregulation in obese type 2 diabetic patients.

METHODS

Eighty obese patients with type 2 diabetes mellitus, their age ranged from 35-55 years and their body mass index ranged from 31-37 kg/m² were equally assigned into 2 groups: the weight reduction group received aerobic exercises in addition to diet regimen, where the control group received medical treatment only for 12 weeks.

RESULTS

There was a 24.04%, 19.33%, 22.78% ,12.28%, 9.35%, 22.53% & 10.12 % reduction in mean values of Homeostasis Model Assessment-Insulin Resistance Index (HOMA-IR), Leptin, Adiponectin, Resistin, intercellular cell adhesion molecule -1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and E-selectin & body mass index (BMI) respectively in addition to 26.20% & 24.58% increase in the mean values of adiponectin & the quantitative insulin-sensitivity check index (QUICKI) respectively in group (A) at the end of the study. The mean values of leptin, resistin, insulin, HOMA-IR, ICAM-1, VCAM-1, E-selectin & BMI were significantly decreased in addition to significant increase in the mean values of adiponectin & QUICKI in group (A) those that received aerobic exercise training in addition to diet regimen. While the results of group (B) those that received no treatment intervention were not significant. In addition, there were significant differences between mean levels of the investigated parameters in group (A) and group (B) after treatment (P<0.05).

CONCLUSION

Within the limit of this study, 10% reduction in body mass index modulates insulin resistance, adhesive molecules and adipokines dysregulation among obese type 2 diabetic patients.

Adiponectin as a novel biomarker for liver fibrosis

Adiponectin is known to play primary roles in the regulation of systemic glucose homeostasis and lipid metabolism. Interestingly, emerging evidence indicates beneficial effects of adiponectin on liver fibrosis; however, the exact mechanisms of this action remain unclear. Herein, we aimed to summarize the recent findings regarding the role of adiponectin in liver fibrogenesis and update the current comprehensive knowledge regarding usefulness of adiponectin-based treatments in liver fibrosis. Adiponectin has been demonstrated to have an anti-fibrotic action in the liver by blocking the activation of hepatic stellate cell-mediated adenosine monophosphate-activated protein kinase and peroxisome proliferator-activated receptor-alpha pathways, which in turn diminish the expression of pro-fibrotic genes. In addition, hyperadiponectinemia was noted in patients with various chronic liver diseases (CLDs)-related liver fibrosis. An increase in circulating adiponectin levels was also found to be associated with the development of liver fibrosis, indicating a role of adiponectin as a non-invasive biomarker for predicting the progression of liver fibrosis. It is therefore reasonable to speculate that adiponectin may be developed as a new therapeutic candidate for the treatment of liver fibrosis. Nonetheless, future observations are still necessary to fully elucidate the extent of the effects of adiponectin on liver fibrotic outcomes, in order to modify adiponectin as an anti-fibrotic therapy that would speed up fibrosis reversal in patients with CLD.

Effect of Serum Adiponectin Levels on the Association Between Childhood Body Mass Index and Adulthood Carotid Intima-Media Thickness

Childhood obesity predicts adult cardiovascular risk. We hypothesized that the association between childhood body mass index (BMI) and adult carotid intima-media thickness (CIMT) may be modified by levels of adiponectin, an adipocytokine that connects body fatness with cardiovascular risk. The study sample included 1,052 adults (71% white and 29% black, 57% female) aged 23.8 to 43.5 years who were previously examined as children in the Bogalusa Heart Study cohort, with an average follow-up period of 26.5 (range 14.1 to 29.6) years. Childhood BMI, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, triglycerides, and systolic blood pressure were standardized to age-specific z-scores. General linear models were used for data analyses. Childhood BMI (p = 0.034), low-density lipoprotein cholesterol (p <0.001), and systolic blood pressure (p = 0.005), along with adult adiponectin levels (p = 0.002) were associated with adult CIMT, adjusted for race, sex, adult age, and cigarette smoking. Further, adult adiponectin levels significantly modified the association between childhood BMI and adult CIMT (P for interaction = 0.0003) such that a significant association between childhood BMI and adult CIMT (p <0.0001) was only observed in those with adiponectin levels below the median. In conclusion, these results suggest that serum adiponectin levels modify the association between childhood obesity and adult atherosclerosis, which has implications for risk stratification and targeted intervention for obese children with low levels of adiponectin.

A Comprehensive Survey of the Roles of Highly Disordered Proteins in Type 2 Diabetes

Type 2 diabetes mellitus (T2DM) is a chronic and progressive disease that is strongly associated with hyperglycemia (high blood sugar) related to either insulin resistance or insufficient insulin production. Among the various molecular events and players implicated in the manifestation and development of diabetes mellitus, proteins play several important roles. The Kyoto Encyclopedia of Genes and Genomes (KEGG) database has information on 34 human proteins experimentally shown to be related to the T2DM pathogenesis. It is known that many proteins associated with different human maladies are intrinsically disordered as a whole, or contain intrinsically disordered regions. The presented study shows that T2DM is not an exception to this rule, and many proteins known to be associated with pathogenesis of this malady are intrinsically disordered. The multiparametric bioinformatics analysis utilizing several computational tools for the intrinsic disorder characterization revealed that IRS1, IRS2, IRS4, MAFA, PDX1, ADIPO, PIK3R2, PIK3R5, SoCS1, and SoCS3 are expected to be highly disordered, whereas VDCC, SoCS2, SoCS4, JNK9, PRKCZ, PRKCE, insulin, GCK, JNK8, JNK10, PYK, INSR, TNF-α, MAPK3, and Kir6.2 are classified as moderately disordered proteins, and GLUT2, GLUT4, mTOR, SUR1, MAPK1, IKKA, PRKCD, PIK3CB, and PIK3CA are predicted as mostly ordered. More focused computational analyses and intensive literature mining were conducted for a set of highly disordered proteins related to T2DM. The resulting work represents a comprehensive survey describing the major biological functions of these proteins and functional roles of their intrinsically disordered regions, which are frequently engaged in protein–protein interactions, and contain sites of various posttranslational modifications (PTMs). It is also shown that intrinsic disorder-associated PTMs may play important roles in controlling the functions of these proteins. Consideration of the T2DM proteins from the perspective of intrinsic disorder provides useful information that can potentially lead to future experimental studies that may uncover latent and novel pathways associated with the disease.

Targeting endothelial metaflammation to counteract diabesity cardiovascular risk: Current and perspective therapeutic options

The association of obesity and diabetes, termed "diabesity", defines a combination of primarily metabolic disorders with insulin resistance as the underlying common pathophysiology. Cardiovascular disorders associated with diabesity represent the leading cause of morbidity and mortality in the Western world. This makes diabesity, with its rising impacts on both health and economics, one of the most challenging biomedical and social threats of present century. The emerging comprehension of the genes whose alteration confers inter-individual differences on risk factors for diabetes or obesity, together with the potential role of genetically determined variants on mechanisms controlling responsiveness, effectiveness and safety of anti-diabetic therapy underlines the need of additional knowledge on molecular mechanisms involved in the pathophysiology of diabesity. Endothelial cell dysfunction, resulting from the unbalanced production of endothelial-derived vascular mediators, is known to be present at the earliest stages of insulin resistance and obesity, and may precede the clinical diagnosis of diabetes by several years. Once considered as a mere consequence of metabolic abnormalities, it is now clear that endothelial dysfunctional activity may play a pivotal role in the progression of diabesity. In the vicious circle where vascular defects and metabolic disturbances worsen and reinforce each other, a low-grade, chronic, and 'cold' inflammation (metaflammation) has been suggested to serve as the pathophysiological link that binds endothelial and metabolic dysfunctions. In this paradigm, it is important to consider how traditional antidiabetic treatments (specifically addressing metabolic dysregulation) may directly impact on inflammatory processes or cardiovascular function. Indeed, not all drugs currently available to treat diabetes possess the same anti-inflammatory potential, or target endothelial cell function equally. Perspective strategies pointing at reducing metaflammation or directly addressing endothelial dysfunction may disclose beneficial consequences on metabolic regulation. This review focuses on existing and potential new approaches ameliorating endothelial dysfunction and vascular inflammation in the context of diabesity.

Intrinsic disorder in biomarkers of insulin resistance, hypoadiponectinemia, and endothelial dysfunction among the type 2 diabetic patients

Type 2 diabetes mellitus (T2DM) is a chronic and progressive disease that is strongly associated with various complications including cardiovascular diseases and related mortality. The present study aimed to analyze the abundance and functionality of intrinsically disordered regions in several biomarkers of insulin resistance, adiponectin, and endothelial dysfunction found in the T2DM patients. In fact, in comparison to controls, obese T2DM patients are known to have significantly higher levels of inter-cellular adhesion molecule (iCAM-1), vascular cell adhesion molecule (vCAM-1), and E-selectin, whereas their adiponectin levels are relatively low. Bioinformatics analysis revealed that these selected biomarkers (iCAM-1, vCAM-1, E-selectin, and adiponectin) are characterized by the noticeable levels of intrinsic disorder propensity and high binding promiscuity, which are important features expected for proteins serving as biomarkers. Within the limit of studied groups, there is an association between insulin resistance and both hypoadiponectinemia and endothelial dysfunction.

Vascular function, insulin action, and exercise: an intricate interplay

Insulin enhances the compliance of conduit arteries, relaxes resistance arterioles to increase tissue blood flow, and dilates precapillary arterioles to expand muscle microvascular blood volume. These actions are impaired in the insulin resistant states. Exercise ameliorates endothelial dysfunction and improves insulin responses in insulin resistant patients, but the precise underlying mechanisms remain unclear. The microvasculature critically regulates insulin action in muscle by modulating insulin delivery to the capillaries nurturing the myocytes and trans-endothelial insulin transport. Recent data suggest that exercise may exert its insulin-sensitizing effect via recruiting muscle microvasculature to increase insulin delivery to and action in muscle. The current review focuses on how the interplay among exercise, insulin action, and the vasculature contributes to exercise-mediated insulin sensitization in muscle.

Adipocytokines and hepatic fibrosis

Obesity and metabolic syndrome pose significant risk for the progression of many types of chronic illness, including liver disease. Hormones released from adipocytes, adipocytokines, associated with obesity and metabolic syndrome, have been shown to control hepatic inflammation and fibrosis. Hepatic fibrosis is the final common pathway that can result in cirrhosis, and can ultimately require liver transplantation. Initially, two key adipocytokines, leptin and adiponectin, appeared to control many fundamental aspects of the cell and molecular biology related to hepatic fibrosis and its resolution. Leptin appears to act as a profibrogenic molecule, while adiponectin has strong-antifibrotic properties. In this review, we emphasize pertinent data associated with these and other recently discovered adipocytokines that may drive or halt the fibrogenic response in the liver.