Adiponectin and its potential in the treatment of obesity, diabetes and insulin resistance

Adiponectin is a protein hormone produced exclusively by adipocytes. Its circulating levels are decreased in individuals with obesity, atherosclerosis and insulin resistance, suggesting that its deficiency may have a causal role in the etiopathogenesis of these diseases. Studies have shown that adiponectin administration in rodents has insulin-sensitizing, anti-atherogenic and anti-inflammatory effects and under certain settings also decreases body weight. Therefore, adiponectin replacement in humans may represent a promising approach to prevent and/or treat obesity, insulin resistance and type 2 diabetes; however, clinical studies with adiponectin administration need to be conducted to confirm this hypothesis. Current experimental and clinical data regarding adiponectin physiology and pathophysiology are detailed in this review.     

Dual roles of adiponectin/Acrp30 in vivo as an anti-diabetic and anti-atherogenic adipokine

Genome-wide scanning is a powerful tool to identify susceptible chromosome loci, however, individual chromosomal regions still have many candidate genes. Although cDNA microarray analysis provides valuable information for identifying genes involved in pathogenesis, expression levels of many genes are changed. A novel approach for identification of therapeutic targets is the combination of genome-wide scanning and the use of DNA chips, as shown in Fig. (1). Using DNA chips, we screened for secreted molecules, the expressions of which were changed in adipose tissues from mice rendered insulin resistance. Decreased expression of one of these molecules, adiponectin/Acrp30, correlates strongly with insulin resistance. Interestingly, recent genome-wide scans have mapped a susceptibility locus for type 2 diabetes and metabolic syndrome to chromosome 3q27, where adiponectin gene is located. Decreasing serum adiponectin levels are associated with increased risk for type 2 diabetes. Interestingly, adiponectin was decreased in insulin resistant rodent models both of obesity and lipoatrophy, and replenishment of adiponectin ameliorated their insulin resistance. Moreover, adiponectin transgenic mice ameliorated insulin resistance and diabetes Adiponectin knockout mice showed insulin resistance and glucose intolerance. In muscle and liver, adiponectin activated AMP kinase and PPARalpha pathways thereby increasing beta-oxidation of lipids, leading to decreased TG content, which ameliorated insulin resistance under a high-fat diet. Despite similar plasma glucose and lipid levels on an apoE deficient background, adiponectin transgenic apoE deficient mice showed amelioration of atherosclerosis, which was associated with decreased expressions of class A scavenger receptor and tumor necrosis factor alpha. Finally, cDNA encoding adiponectin receptors (AdipoR1 and R2) have been identified by expression cloning, which facilitates the understanding of molecular mechanisms of adiponectin actions and obesity-linked diseases such as diabetes and atherosclerosis and the designing of novel antidiabetic and anti-atherogenic drugs with AdipoR1 and R2 as molecular targets.     

Adiponectin and its receptors: Partners contributing to the “vicious circle” leading to the metabolic syndrome?

Although already described five years ago, it is only from year 2000, following intensive research in the field of genetics that the adiponectin protein was related with insulin sensitivity, type 2 diabetes and the metabolic syndrome. The story began with a paradox as this protein exclusively secreted by fat tissue was dramatically decreased in patients presenting an excess of fat mass. Later this decrease was reported with insulin resistance and metabolic syndrome associated phenotypes. The search for genetic variants in the adiponectin encoding ACDC gene and epidemio genetic investigations allowed to associate genetic variations of the gene and phenotypic traits of the metabolic syndrome. One of the major points was the correlation of the levels of circulating adiponectin with insulin sensitivity, leading to a better knowledge of the role of adiponectin. Indeed it is now clearly admitted that adiponectin is an insulin sensitizing cytokine. Recently two adiponectin receptors were described and genetic variations in their genes were associated with features of the metabolic syndrome. Interactions of adiponectin with various partners are discussed in view of a better understanding of adiponectin resistance and insulin resistance.     

Adiponectin and its receptors: Partners contributing to the “vicious circle” leading to the metabolic syndrome?

Although already described five years ago, it is only from year 2000, following intensive research in the field of genetics that the adiponectin protein was related with insulin sensitivity, type 2 diabetes and the metabolic syndrome. The story began with a paradox as this protein exclusively secreted by fat tissue was dramatically decreased in patients presenting an excess of fat mass. Later this decrease was reported with insulin resistance and metabolic syndrome associated phenotypes. The search for genetic variants in the adiponectin encoding ACDC gene and epidemio genetic investigations allowed to associate genetic variations of the gene and phenotypic traits of the metabolic syndrome. One of the major points was the correlation of the levels of circulating adiponectin with insulin sensitivity, leading to a better knowledge of the role of adiponectin. Indeed it is now clearly admitted that adiponectin is an insulin sensitizing cytokine. Recently two adiponectin receptors were described and genetic variations in their genes were associated with features of the metabolic syndrome. Interactions of adiponectin with various partners are discussed in view of a better understanding of adiponectin resistance and insulin resistance.     

The insulin-sensitizing role of the fat derived hormone adiponectin

Adiponectin is an insulin-sensitizing hormone whose blood concentration is reduced in obesity and type 2 diabetes. Administration of recombinant adiponectin in rodents increases glucose uptake and increases fat oxidation in muscle, reduces fatty acid uptake and hepatic glucose production in liver, and improves whole body insulin resistance. The exact receptor and signaling systems are unknown, however, recent studies suggest adiponectin activates AMPK, a putative master metabolic regulator. Thus, excitement surrounds the potential for adiponectin, or a homologue of adiponectin, as pharamacotherapy agents for patients suffering from the metabolic syndrome and more particularly for individuals with insulin resistance and type 2 diabetes.     

The mechanisms by which PPARgamma and adiponectin regulate glucose and lipid metabolism

Obesity, a state of increased adipose tissue mass, is a major cause for type 2 diabetes, hyperlipidemia, and hypertension, resulting in clustering of risk factors for atherosclerosis. Heterozygous PPARgamma knockout mice and KKA(y) mice administered with a PPARgamma antagonist were protected from high-fat diet-induced adipocyte hypertrophy and insulin resistance. Moderate reduction of PPARgamma activity prevented adipocyte hypertrophy, thereby diminution of TNFalpha, resistin, and FFA and upregulation of adiponectin and leptin. These alterations led to reduction of tissue TG content in muscle/liver, thereby ameliorating insulin resistance. Insulin resistance in the lipoatrophic mice and KKA(y) mice were ameliorated by replenishment of adiponectin. Moreover, adiponectin transgenic mice ameliorated insulin resistance and diabetes, but not the obesity of ob/ob mice. Furthermore, targeted disruption of the adiponectin gene caused moderate insulin resistance and glucose intolerance. In muscle, adiponectin activated AMP kinase and PPARgamma pathways, thereby increasing beta-oxidation of lipids, leading to decreased TG content, which ameliorated muscle insulin resistance. In the liver, adiponectin also activated AMPK, thereby downregulating PEPCK and G6Pase, leading to decreased glucose output from the liver. In conclusion, PPARgamma plays a central role in the regulation of adipocyte hypertrophy and insulin sensitivity. The upregulation of the adiponectin pathway by PPARgamma may play a role in the increased insulin sensitivity of heterozygous PPARgamma knockout mice, and activation of adiponectin pathway may provide novel therapeutic strategies for obesity-linked disorders such as type 2 diabetes and metabolic syndrome.     

Treatment of insulin resistance in diabetes mellitus

Insulin resistance is a condition in which the glycemic response to insulin is less than normal. The change in insulin sensitivity leads to several sets of responses. One set effects the beta cell and leads to its accelerated destruction and the development of diabetes mellitus. The other set generates a series of nontraditional cardiovascular risk factors that result in accelerated atherosclerosis. Both of these sets of responses may have impacts on other tissues such as the nervous system. Insulin resistance is probably the result of increased visceral adiposity with increased release of free fatty acids and cytokines and a decreased release of adiponectin. Treatment of insulin resistance and its associated abnormalities can be achieved by lifestyle modification which results in weight loss, by drugs that reverse the abnormal adipocyte effects, by drugs that improve insulin sensitivity at the level of the liver and by anti-inflammatory agents that block activation of the nuclear factor kappa B cascade.     

固醇调节元件结合蛋白-1与阻塞性睡眠呼吸暂停代谢异常的研究进展

阻塞性睡眠呼吸暂停(OSA)是高脂血症、胰岛素抵抗、动脉粥样硬化、非酒精性脂肪性肝病的危险因素，其病理基础的核心是间歇性低氧(IH)。固醇调节元件结合蛋白(SREBP)是脂质生物合成的一类调控因子，主要在肝脏和脂肪细胞中表达，参与调节脂肪酸和胆固醇生物合成。近年来，SREBP-1在IH条件下表达上调对脂质合成的影响备受关注。现针对SREBP-1在IH下对OSA相关代谢性疾病的研究进展进行综述，为预防或延缓OSA相关代谢疾病的进展以及新的靶向治疗提供思路。     

The role of the adipocyte hormone adiponectin in cardiovascular disease

Adiponectin, a novel hormone made by fat tissue, regulates energy metabolism and endothelial activation. Serum levels of adiponectin are reduced in conditions that are associated with an increased risk of cardiovascular disease, such as diabetes and the metabolic syndrome. Adiponectin trimers assemble into higher-order oligomers, which have different signaling properties. Adiponectin trimers and a C-terminal globular domain activate AMP-activated protein kinase, whereas hexamer and high-molecular weight isoforms activate nuclear factor-kappa B signaling pathways. Exogenous adiponectin corrects metabolic defects that are associated with insulin resistance, and might protect the endothelium from the progression of cardiovascular disease. Receptors for adiponectin have been described and might provide future therapeutic targets for the treatment of cardiovascular disease.     

Adiponectin and cardiovascular disease: mechanisms and new therapeutic approaches

Adiponectin is an abundant plasma protein secreted from adipocytes. Its role in energy homeostasis is well-known, including the regulation of hydrocarbons and lipids metabolism as well as the improvement of insulin resistance. It has been thought to be a key molecule in the development of type 2 diabetes mellitus and metabolic syndrome, which are epidemiological targets for preventing cardiovascular disease. In addition to beneficial metabolic effects, adiponectin seems to have anti-inflammatory, anti-atherosclerotic and vasoprotective actions. Furthermore, adiponectin affects signalling in myocardial cells and exerts beneficial actions on the heart after pressure overload and ischemia-reperfusion injury. The ability of adiponectin to reduce insulin resistance in conjunction with its antiinflammatory and cardioprotective properties makes this adipocytokine a promising therapeutic target. On clinical interest, agents that enhance endogenous adiponectin production or action have potential for the treatment of cardiovascular disease. Management strategies that increase adiponectin levels include weight reduction, Mediterranean diet, thiazolidinediones, antihypertensive and lipid lowering drugs. Current knowledge on the main actions of adiponectin and therapeutic approaches for cardiovascular disease is summarized in this review.     

The role of resistin in obesity-induced insulin resistance

Resistin is a 12.5-kDa polypeptide hormone produced by adipocytes and immunocompetent cells. It was originally proposed as a link between obesity and insulin resistance/diabetes. Later, studies revealed that substantial inter-species differences exist between the major sites of resistin production in rodents (adipocytes) and humans (immunocompetent cells). While in rodents resistin appears to have an important role in the development of liver insulin resistance, its role in humans is less clear, and it is probably involved in the regulation of inflammatory processes rather than in insulin sensitivity. Current experimental and clinical data concerning resistin physiology and pathophysiology, and its possible role in the development of insulin resistance and atherosclerosis are detailed in this review.     

Insulin- and growth factor-resistance impairs vascular regeneration in diabetes mellitus

Diabetes and pre-diabetes are major contributors to cardiovascular mortality and morbidity. Insulin resistance is a key pathophysiological determinant of the metabolic and vascular abnormalities noted in these disorders. Ineffective vascular repair is likely to be an important contributor to the development of endothelial dysfunction, and subsequently atherosclerosis, in patients with diabetes. Beyond the systemic effects of the insulin resistant phenotype, including factors such as dysglycaemia and inflammation, cellular insulin resistance is emerging as an important factor in diabetic vascular disease. Disordered signal transduction via the PI3-kinase/Akt and MAP-kinase cascades is a hallmark of cellular insulin resistance, and such changes have been linked with both endothelial dysfunction and impaired angiogenesis. In this review we highlight the importance of insulin resistance to vascular repair and regeneration, discuss important cross-talk between the intracellular signalling of insulin and key pro-angiogenic molecules, and link these concepts to common patterns of vascular disease.     

Inflammation, adiponectin, obesity and cardiovascular risk

The development of atherosclerotic lesions leading to myocardial infarction (MI) or stroke encompasses a cascade of cellular and molecular events that can well be characterized as a chronic immune-mediated inflammation occurring preferentially in the biologic surrounding of the so called metabolic syndrome. Adipokines, chemokines, cytokines, and their receptors are critically involved in the initiation and perpetuation of atherosclerosis, and they play important roles at all levels in the pathogenesis of this disease. Metabolic risk profiles associated with sedentary lifestyle, obesity, especially intra-abdominal fat accumulation, insulin resistance, and dyslipidemia pave the way for a chronic, immune-mediated vascular inflammation around vascular lipid deposits. In the present article, the impact of adiponectin, monocyte and T-cell associated cytokines (with emphasis on Neopterin), individual adipose tissue - distribution and pleiotropic drug effects on the individual course of atherosclerosis and associated cardiovascular disease are reviewed.     

代谢综合征患者血清脂联素水平与胰岛素抵抗的相关性研究

目的:探讨代谢综合征患者血清脂联素水平与胰岛素抵抗的关系。方法:选取代谢综合征患者35例,另选健康对照组20例,所有实验对象空腹采血离心取血清测定脂联素、胰岛素、血糖、胰岛素敏感性指数、胰岛素抵抗指数。结果:与对照组相比,代谢综合征组血清脂联素水平、胰岛素敏感性指数显著降低(P<0.01),血清胰岛素、血糖显著升高(P<0.01)。在代谢综合征组中,血清脂联素与胰岛素、血糖、胰岛素抵抗指数呈负相关,与胰岛素敏感性指数呈正相关(P<0.05)。结论:低血清脂联素水平与胰岛素抵抗密切相关。     

A personalized approach to metabolic aspects of obesity

Metabolic syndrome, which is entwined in semantic controversy as to its actual existence as a distinct entity, links several important health conditions with obesity, and more specifically, excessive visceral adiposity. The most common linked disease states include type 2 diabetes mellitus, hypertension, dyslipidemia, obstructive sleep apnea, and cardiovascular and coronary heart disease. Much of the controversy surrounding the metabolic syndrome case definition is the purported centrality of insulin resistance as root cause, there being no universally agreed-upon standard for measurement of insulin resistance. Over the past decade, the visceral adipocyte itself has emerged as a key contributor rather than passive bystander in the genesis of the metabolic syndrome. Rather than being a simple storage bin for excess triglyceride, the visceral adipocyte is an active endocrine cell secreting a variety of signal hormones known in the aggregate as adipokines. In optimal health, the predominant recognized adipokine is adiponectin, with downstream insulin-sensitizing, anti-inflammatory, antithrombotic, provasodilatory effects systemically. By contrast, metabolic syndrome is characterized by reduced adiponectin and increased inflammatory adipokine secretion, with downstream effects of insulin resistance, heightened inflammation, prothrombosis, and vasoconstriction. These alternative metabolic states of the adipocyte are characterized in this review as metabolic "yin" and "yang." Lifestyle modifications and drug therapies that promote weight loss, increased physical exercise activity, and increased adiponectin production tend to modulate the system favorably toward metabolic "yin."     

非酒精性脂肪性肝病的治疗进展

目前全球非酒精性脂肪性肝病的发病率增加,并与代谢综合征,尤其是肥胖及糖尿病密切相关.越来越多的证据表明,胰岛素抵抗是代谢综合征患者发生脂肪性肝炎的关键病因,其可增加脂肪变性及肝脏游离脂肪酸聚集,刺激氧化应激反应,促进脂质过氧化及炎症细胞因子产生.非酒精性脂肪性肝病的治疗以改善代谢综合征为主,尚缺乏已验证的疗效理想的治疗药物.近年来随着对其发病机制的深入理解,一些尚处于动物试验及前期临床研究的新药值得关注.     

Adiponectin and its role in cardiovascular diseases

Studies performed during the last decade indicate that adipose tissue is not only a site of triglyceride storage but also an active endocrine organ which secretes many biologically active mediators referred to as "adipokines". In contrast to many adipokines which are overproduced in obese individuals and exert deleterious effects on insulin sensitivity, lipoprotein metabolism and cardiovascular system, such as leptin, tumor necrosis factor-alpha, plasminogen activator inhibitor-1, resistin, etc., adiponectin seems to be a unique adipokine which is produced in lower amounts in obese than in lean subjects and possesses predominantly beneficial activities, i.e. increases insulin sensitivity, stimulates fatty acid oxidation, inhibits inflammatory reaction and induces endothelium-dependent nitric oxide-mediated vasorelaxation. Adiponectin binds two receptors, AdipoR1 and AdipoR2. Adiponectin knockout mice exhibit various manifestations of the metabolic syndrome such as insulin resistance, glucose intolerance, hyperlipidemia, impaired endothelium-dependent vasorelaxation and hypertension, as well as augmented neointima formation after vascular injury. Clinical studies indicate that plasma adiponectin concentration is lower in patients with essential hypertension and ischemic heart disease. Raising endogenous adiponectin level or increasing the sensitivity to this hormone may be a promising therapeutic strategy for patients with metabolic and cardiovascular diseases. Among currently used drugs, thiazolidinediones (peroxisome proliferator activated receptor gamma agonists) are most effective in elevating adiponectin level.     

脂联素与代谢综合征

脂联素（APN）在＋276T/G、＋45T/G、164I/T、＋10211T/G、-11391G/A、-11377G/C等位点的基因多态性与代谢综合征（MS）及其相关性疾病有关。APN水平与三酰甘油（TG）、总胆固醇（TC）、低密度脂蛋白胆固醇（LDL-C）、高密度脂蛋白胆固醇（HDL-C）独立相关,血清APN水平降低是独立于体脂因素的胰岛素敏感性的因素之一,APN与2型糖尿病（T2DM）呈强负相关,APN水平与高血压发病呈独立负相关,低APN水平是MS的一个独立危险因素,血清APN水平降低是MS的特征性标志。APN水平与无粥样斑块的颈动脉内膜中层厚度呈负相关,是动脉粥样硬化早期的独立预测因子。APN与MS密切相关。     

Resistin: functional roles and therapeutic considerations for cardiovascular disease

Resistin, originally described as an adipocyte-specific hormone, has been suggested to be an important link between obesity, insulin resistance and diabetes. Although its expression was initially defined in adipocytes, significant levels of resistin expression in humans are mainly found in mononuclear leukocytes, macrophages, spleen and bone marrow cells. Increasing evidence indicates that resistin plays important regulatory roles apart from its role in insulin resistance and diabetes in a variety of biological processes: atherosclerosis and cardiovascular disease (CVD), non-alcoholic fatty liver disease, autoimmune disease, malignancy, asthma, inflammatory bowel disease and chronic kidney disease. As CVD accounts for a significant amount of morbidity and mortality in patients with diabetes and without diabetes, it is important to understand the role that adipokines such as resistin play in the cardiovascular system. Evidence suggests that resistin is involved in pathological processes leading to CVD including inflammation, endothelial dysfunction, thrombosis, angiogenesis and smooth muscle cell dysfunction. The modes of action and signalling pathways whereby resistin interacts with its target cells are beginning to be understood. In this review, the current knowledge about the functions and pathophysiological implications of resistin in CVD development is summarized; clinical translations, therapeutic considerations and future directions in the field of resistin research are discussed. LINKED ARTICLES: This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.