Adiponectin and cardiovascular health: an update

Adipose tissue in control of metabolism

Adipose tissue plays a central role in regulating whole-body energy and glucose homeostasis through its subtle functions at both organ and systemic levels. On one hand, adipose tissue stores energy in the form of lipid and controls the lipid mobilization and distribution in the body. On the other hand, adipose tissue acts as an endocrine organ and produces numerous bioactive factors such as adipokines that communicate with other organs and modulate a range of metabolic pathways. Moreover, brown and beige adipose tissue burn lipid by dissipating energy in the form of heat to maintain euthermia, and have been considered as a new way to counteract obesity. Therefore, adipose tissue dysfunction plays a prominent role in the development of obesity and its related disorders such as insulin resistance, cardiovascular disease, diabetes, depression and cancer. In this review, we will summarize the recent findings of adipose tissue in the control of metabolism, focusing on its endocrine and thermogenic function.

From obesity to cancer: a review on proposed mechanisms

Nowadays, obesity is considered as a serious and growing global health problem. It is documented that the overweight and obesity are major risk factors for a series of noncommunicable diseases, and in recent years, the obesity-cancer link has received much attention. Numerous epidemiological studies have shown that obesity is associated with increased risk of several cancer types, including colon, breast, endometrium, liver, kidney, esophagus, gastric, pancreatic, gallbladder, and leukemia, and can also lead to poorer treatment. We review here the epidemiological and experimental evidences for the association between obesity and cancer. Specifically, we discuss potential mechanisms focusing how dysfunctional angiogenesis, chronic inflammation, interaction of proinflammatory cytokines, endocrine hormones, and adipokines including leptin, adiponectin insulin, growth factors, estrogen, and progesterone and strikingly, cell metabolism alteration in obesity participate in tumor development and progression, resistance to chemotherapy, and targeted therapies such as antiangiogenic and immune therapies.

Pioglitazone Ameliorates Smooth Muscle Cell Proliferation in Cuff-Induced Neointimal Formation by Both Adiponectin-Dependent and -Independent Pathways

The aim of this study is to elucidate to what degree adiponectin is involved in TZD-mediated amelioration of neointimal formation. We investigated the effect of 3- or 8-weeks' pioglitazone on cuff-induced neointimal formation in adiponectin-deficient (APN-KO) and wild-type (WT) mice. Pioglitazone for 3 weeks reduced neointimal formation in the WT mice with upregulation of the plasma adiponectin levels, but failed to reduce neointimal formation in the APN-KO mice, suggesting that pioglitazone suppressed neointimal formation by adiponectin-dependent mechanisms. Pioglitazone for 3 weeks suppressed vascular smooth muscle cell (VSMC) proliferation and increased AdipoR2 expression in the WT mice. In vitro, globular adiponectin activated AMPK through both AdipoR1 and AdipoR2, resulting in the inhibition of VSMC proliferation. Interestingly, 8-weeks' pioglitazone was reduced neointimal formation in APN-KO mice to degree similar to that seen in the WT mice, suggesting that pioglitazone can also suppress neointimal formation via a mechanism independent of adiponectin. Pioglitazone for 8 weeks completely abrogated the increased VSMC proliferation, along with a reduction of cyclin B1 and cyclin D1 expressions and cardiovascular risk profile in the APN-KO mice. In vitro, pioglitazone suppressed these expressions, leading to inhibition of VSMC proliferation. Pioglitazone suppresses neointimal formation via both adiponectin-dependent and adiponectin-independent mechanisms.

Association between carotid intima-media thickness and adiponectin in participants without diabetes or cardiovascular disease of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil)

Objective The study assessed the association of adiponectin concentration with carotid intima-media thickness (CIMT) in middle-aged participants of the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil) without diabetes or cardiovascular disease. Design Cross-sectional analyses. Methods A sample of 687 individuals (35-54 years old) without diabetes or cardiovascular disease was stratified into two categories according to CIMT (< or ≥ 75th percentile). Traditional risk factors, C-reactive protein and adiponectin values were compared between categories by Student's t-test and frequencies by chi-square test. In linear regression models, associations of CIMT with adiponectin, adjusted for adiposity, blood pressure, C-reactive protein and homeostasis model assessment-insulin resistance were tested. Mean CIMT values were compared across quartiles of adiponectin concentrations using analysis of variance. Results Three hundred and forty-one individuals (49.6%) were women and 130 (19.0%) had three traditional cardiovascular risk factors. Those with elevated CIMT (21.8%) had greater mean values of body mass index (26.2(3.8) vs. 27.7(4.0)kg/m², p < 0.001), waist circumference (86.9(10.1) vs. 90.1(10.8) cm, p = 0.001), systolic blood pressure (116.2(13.6) vs.121.2(16.1) mmHg, p < 0.001), homeostasis model assessment index (1.4(0.9-2.4) vs. 1.8(1.1-2.9), p = 0.011), C-reactive protein (1.2 (0.6-2.6) vs. 1.4(0.8-3.2) mg/l, p = 0.054) and adiponectin (9.9 (6.0-14.7) vs. 8.9 (5.3-13.8) µg/ml, p = 0.002) levels than the counterpart, while plasma glucose and lipids were not different between groups. In the adjusted model, blood pressure (directly) and adiponectin (inversely) persisted associated with high CIMT. Mean CIMT was greater in the first quartile of adiponectin when compared with the other three quartiles ( p = 0.019). Conclusions Lower adiponectin levels together with higher blood pressure were independently associated with elevated CIMT. Adiponectin concentration may be an independent marker of early structural damage in individuals at low-to-moderate cardiovascular risk.

Long-chain monounsaturated fatty acid-rich fish oil attenuates the development of atherosclerosis in mouse models

SCOPE

Fish oil-derived long-chain monounsaturated fatty acids (LCMUFA) containing chain lengths longer than 18 were previously shown to improve cardiovascular disease risk factors in mice. However, it is not known if LCMUFA also exerts anti-atherogenic effects. The main objective of the present study was to investigate the effect of LCMUFA on the development of atherosclerosis in mouse models.

METHODS AND RESULTS

LDLR-KO mice were fed Western diet supplemented with 2% (w/w) of either LCMUFA concentrate, olive oil, or not (control) for 12 wk. LCMUFA, but not olive oil, significantly suppressed the development of atherosclerotic lesions and several plasma inflammatory cytokine levels, although there were no major differences in plasma lipids between the three groups. At higher doses 5% (w/w) LCMUFA supplementation was observed to reduce pro-atherogenic plasma lipoproteins and to also reduce atherosclerosis in ApoE-KO mice fed a Western diet. RNA sequencing and subsequent qPCR analyses revealed that LCMUFA upregulated PPAR signaling pathways in liver. In cell culture studies, apoB-depleted plasma from LDLR-K mice fed LCMUFA showed greater cholesterol efflux from macrophage-like THP-1 cells and ABCA1-overexpressing BHK cells.

CONCLUSION

Our research showed for the first time that LCMUFA consumption protects against diet-induced atherosclerosis, possibly by upregulating the PPAR signaling pathway.

Sertraline inhibits increases in body fat and carbohydrate dysregulation in adult female cynomolgus monkeys

Selective serotonin reuptake inhibitor (SSRI) antidepressants are widely prescribed for depression and other disorders. SSRIs have become one of the most commonly used drugs in the United States, particularly by women. Acute effects on body composition and carbohydrate metabolism have been reported, but little is known regarding the effects of chronic SSRI use. We evaluated the effects of chronic administration of a commonly prescribed SSRI, sertraline HCl, on body weight and composition, fat distribution, carbohydrate metabolism, as well as activity, in adult female depressed and nondepressed cynomolgus monkeys (Macaca fascicularis; n=42) using a placebo-controlled, longitudinal, randomized study design. Phenotypes were evaluated prior to and after 18 months of oral sertraline (20mg/kg) or placebo. Over the 18 month treatment period, the placebo group experienced increases in body weight, body fat (visceral and subcutaneous) fasting insulin concentrations, and homeostasis model assessment of insulin resistance scores (HOMA-IR). Sertraline treatment prevented increases in body weight, fat, insulin, and HOMA-IR (all p<0.05), without significantly altering activity levels. Sertraline treatment altered adiponectin in an unusual way - reducing circulating adiponectin in depressed monkeys without affecting fat mass or body weight. Deleterious effects on adiponectin, a potentially insulin-sensitizing and atheroprotective protein, may result in adverse effects on cardiovascular health despite otherwise beneficial effects on body composition and carbohydrate metabolism.

Weight-Loss Diets, Adiponectin, and Changes in Cardiometabolic Risk in the 2-Year POUNDS Lost Trial

CONTEXT

Compelling evidence suggests that the beneficial effects of weight-loss diet interventions on improvement of cardiometabolic risk factors may be partly through modulating secretion of adiponectin from adipose tissue.

OBJECTIVE

To investigate the effects of long-term weight-loss diets with different compositions of macronutrients on longitudinal changes in circulating adiponectin concentrations and how such changes, if they exist, affect cardiometabolic risk.

DESIGN, SETTING, AND PARTICIPANTS

In the 2-year Preventing Overweight Using Novel Dietary Strategies trial, 811 overweight or obese adults were randomly assigned to 1 of 4 diets varying in macronutrient intakes. The current analysis was restricted to participants who had baseline adiponectin measurement (n = 768). Circulating concentrations of adiponectin and cardiometabolic outcomes were repeatedly measured at baseline, 6 months, and 2 years.

MAIN OUTCOME MEASURES

Circulating concentrations of adiponectin and cardiometabolic risk factors.

RESULTS

Weight-loss diet interventions significantly increased circulating adiponectin concentrations over 2 years, similarly in 4 diet groups (P value for difference >.05). We found that the increase of adiponectin was significantly associated with reduction of waist circumference and low-density lipoprotein cholesterol, but associated with increase of high-density lipoprotein cholesterol (P < .001 for each), after adjusting for age, sex, ethnicity, follow-up time, diet group, baseline body mass index, baseline level of respective outcome trait, and concurrent weight change.

CONCLUSIONS

Our findings indicate that long-term interventions by weight-loss diets varying in macronutrients similarly increase circulating adiponectin, which may particularly improve abdominal fat distribution and lipid metabolism independently of weight change.

Adipokine Imbalance in the Pericardial Cavity of Cardiac and Vascular Disease Patients

Aim

Obesity and especially hypertrophy of epicardial adipose tissue accelerate coronary atherogenesis. We aimed at comparing levels of inflammatory and atherogenic hormones from adipose tissue in the pericardial fluid and circulation of cardiovascular disease patients.

Methods and Results

Venous plasma (P) and pericardial fluid (PF) were obtained from elective cardiothoracic surgery patients (n = 37). Concentrations of leptin, adipocyte fatty acid-binding protein (A-FABP) and adiponectin (APN) were determined by enzyme-linked immunosorbent assays (ELISA). The median concentration of leptin in PF (4.3 (interquartile range: 2.8–9.1) μg/L) was comparable to that in P (5.9 (2.2–11) μg/L) and these were significantly correlated to most of the same patient characteristics. The concentration of A-FABP was markedly higher (73 (28–124) versus 8.4 (5.2–14) μg/L) and that of APN was markedly lower (2.8 (1.7–4.2) versus 13 (7.2–19) mg/L) in PF compared to P. APN in PF was unlike in P not significantly related to age, body mass index, plasma triglycerides or coronary artery disease. PF levels of APN, but not A-FABP, were related to the size of paracardial adipocytes. PF levels of APN and A-FABP were not related to the immunoreactivity of paracardial adipocytes for these proteins.

Conclusion

In cardiac and vascular disease patients, PF is enriched in A-FABP and poor in APN. This adipokine microenvironment is more likely determined by the heart than by the circulation or paracardial adipose tissue.

Preventive and chronic mineralocorticoid receptor antagonism is highly beneficial in obese SHHF rats

BACKGROUND AND PURPOSE

Mineralocorticoid receptor (MR) activation contributes to heart failure (HF) progression. Its overactivity in obesity is thought to accelerate cardiac remodelling and HF development. Given that MR antagonists (MRA) are beneficial in chronic HF patients, we hypothesized that early MRA treatment may target obesity-related disorders and consequently delay the development of HF.

EXPERIMENTAL APPROACH

Twenty spontaneously hypertensive HF dyslipidaemic obese SHHF(cp/cp) rats and 18 non-dyslipidaemic lean SHHF(+/+) controls underwent regular monitoring for their metabolic and cardiovascular phenotypes with or without MRA treatment [eplerenone (eple), 100 mg∙kg(-1) ∙day(-1) ] from 1.5 to 12.5 months of age.

KEY RESULTS

Eleven months of eple treatment in obese rats (SHHF(cp/cp) eple) reduced the obesity-related metabolic disorders observed in untreated SHHF(cp/cp) rats by reducing weight gain, triglycerides and total cholesterol levels and by preserving adiponectinaemia. The MRA treatment predominantly preserved diastolic and systolic functions in obese rats by alleviating the eccentric cardiac hypertrophy observed in untreated SHHF(cp/cp) animals and preserving ejection fraction (70 ± 1 vs. 59 ± 1%). The MRA also improved survival independently of these pressure effects.

CONCLUSION AND IMPLICATIONS

Early chronic eple treatment resulted in a delay in cardiac remodelling and HF onset in both SHHF(+/+) and SHHF(cp/cp) rats, whereas SHHF(cp/cp) rats further benefited from the MRA treatment through a reduction in their obesity and dyslipidaemia. These findings suggest that preventive MRA therapy may provide greater benefits in obese patients with additional risk factors of developing cardiovascular complications.

Sodium Intake Regulates Glucose Homeostasis through the PPARδ/Adiponectin-Mediated SGLT2 Pathway

High sodium intake is a major risk factor for developing hypertension in diabetes. Promotion of sodium excretion reduces cardiometabolic lesions in diabetes. However, the interaction between sodium intake and glucose homeostasis remains elusive. Here, we report that high sodium intake remarkably increased natriuresis in wild-type mice, but this effect was blunted in adipose-specific PPARδ knockout mice and diabetic mice. PPARδ activation in perirenal fat by agonist or high sodium intake inhibited renal sodium-glucose cotransporter 2 (SGLT2) function, which is mediated by increased production of adipose adiponectin. In addition, high salt intake-induced natriuresis was impaired in diabetic states because of renal SGLT2 dysfunction. Type 2 diabetic patients with uncontrolled hyperglycemia had less natriuresis that was correlated to their plasma adiponectin levels. Our findings provide insights into the distinctive role of the PPARδ/adiponectin/SGLT2 pathway in the regulation of sodium and glucose homeostasis.

Elevated Adiponectin Antibody Levels in Sera of Patients with Atherosclerosis-Related Coronary Artery Disease, Cerebral Infarction and Diabetes Mellitus

Adiponectin secreted from the adipocytes plays pleiotropic, anti-atherosclerotic roles, such as enhancement of insulin secretion and an increase in energy expenditure. The measurement of levels of circulating adiponectin is useful to evaluate the progression of atherosclerosis-related diseases, such as coronary artery disease (CAD), cerebral infarction (CI) and diabetes mellitus (DM). We examined the serum antibody levels against recombinant adiponectin protein via the amplified luminescent proximity homogeneous assay-linked immunosorbent assay (AlphaLISA) method. The results revealed that the antibody levels were significantly higher in patients with CAD, CI and type 2 DM, than in healthy donors. Receiver operating curve analysis showed that the sensitivity was in a range of 41–48% for CAD, CI and DM. Thus, the serum anti-adiponectin antibody levels could be a common marker for atherosclerosis-related diseases.

The FGF21-adiponectin axis in controlling energy and vascular homeostasis

Whole-body energy metabolism and cardiovascular homeostasis are tightly controlled processes that involve highly coordinated crosstalk among distal organs. This is mainly achieved by a large number of hormones released from each organ. Among them, fibroblast growth factor 21 (FGF21) and adiponectin have recently gained considerable attention, since both of them possess multiple profound protective effects against a myriad of cardio-metabolic disorders. Despite their distinct structures and production sites, these two hormones share striking functional similarity. This dichotomy is recently reconciled by the demonstration of the FGF21-adiponectin axis. In adipocytes, both transcription and secretion of adiponectin are strongly induced by FGF21, which is partially dependent on PPARγ activity. Furthermore, the glucose-lowering, lipid-clearing, and anti-atherosclerotic functions of FGF21 are diminished in adiponectin-null mice, suggesting that adiponectin serves as an obligatory mediator of FGF21-elicited metabolic and vascular benefits. However, in both animals and human subjects with obesity, circulating FGF21 levels are increased whereas plasma adiponectin concentrations are reduced, perhaps due to FGF21 resistance, suggesting that dysfunctional FGF21-adiponectin axis is an important contributor to the pathogenesis of obesity-related cardio-metabolic syndrome. The FGF21-adiponectin axis protects against a cluster of cardio-metabolic disorders via mediating multi-organ communications, and is a promising target for therapeutic interventions of these chronic diseases.

The role of adipokines in ischemic stroke risk stratification

Background

Adiponectin, leptin, and resistin are the most well-studied adipokines and play important roles in the regulation of glucose metabolism, subclinical inflammation, and cardiovascular homeostasis. Accordingly, measurement of adipokine levels might be useful in cardiovascular risk stratification. Moreover, the study of single-nucleotide polymorphisms of genes that encode these adipokines might also represent a valuable predictive tool in cardiovascular disease prevention strategies.

Aims

To summarize the biologic role of the adipokines adiponectin, leptin, and resistin and the prognostic value of their serum levels regarding the occurrence and outcome of ischemic stroke. We also discuss the relationship of single-nucleotide polymorphisms of the adiponectin, leptin genes, and the −420C > G polymorphism of resistin gene with stroke risk.

Summary of review

Several studies in the general population evaluated the association between these adipokines and stroke risk, yielding conflicting results. There are more limited data regarding the effect of these adipokines on stroke severity and outcome. A small number of studies also assessed the predictive role of single-nucleotide polymorphisms of the adiponectin, leptin, and resistin genes regarding stroke risk, but the findings were also controversial.

Conclusions

It is unclear whether adiponectin, leptin, and resistin levels or the single-nucleotide polymorphisms of their encoding genes are independently associated with stroke risk. However, given the role of these adipokines in the pathogenesis of atherosclerosis, larger prospective studies, both in the general population and in patients with a history of stroke, are needed to determine whether the measurement of serum levels of these adipokines or the evaluation of single-nucleotide polymorphisms in their encoding genes could improve stroke risk prediction. If this relationship is proven, therapeutic interventions targeting adipokine levels might represent a novel approach to reduce stroke-related mortality and disability.

Swimming training attenuates the morphological reorganization of the myocardium and local inflammation in the left ventricle of growing rats with untreated experimental diabetes

Diabetic cardiomyopathy is associated with cardiac remodeling, myocardial dysfunction, low-grade inflammation, and reduced cardiac adiponectin in patients with type 1 diabetes mellitus (T1DM). Alternatively, physical exercise is an important strategy for the management of diabetes. This study aimed to investigate the influence of low-intensity swimming training in cardiac cytokines, structural remodeling, and cardiomyocyte contractile dysfunction in growing rats with untreated experimental DM. Thirty-day-old male Wistar rats were divided into four groups (n=14, per group): sedentary control (SC), exercised control (EC), sedentary diabetic (SD), and exercised diabetic (ED). Diabetes was induced by streptozotocin (60 mg kg(-1), i.p.). Animals from exercised groups swam (5 days/week, 90 min/day, loading up to 5% body weight around the animal's chest) for 8 weeks. The left ventricle (LV) was removed for molecular, morphological, and cardiomyocyte mechanical analysis. Diabetic animals presented cardiac remodeling with myocardial histoarchitectural disorganization, fibrosis, and necrosis. The capillary density was lower in diabetic animals. LV cardiomyocytes from diabetic animals exhibited more prolonged time to the peak of contraction and time to half relaxation than those from control animals. The cardiac levels of interleukin 10, nitric oxide, and total and high molecular weight (HMW) adiponectin were significantly decreased in diabetic animals. Exercise training reduced the level of TNF-α, increased capillary density, and attenuated the histopathological parameters assessed in diabetic rats. In conclusion, the cardiac structural remodeling coexists with reduced levels of total and HMW adiponectin, inflammation, and cardiomyocyte contractility dysfunction in experimental DM. More important, low-intensity swimming training attenuates part of these pathological changes, indicating the beneficial role for exercise in untreated T1DM.

Fibroblast Growth Factor 21 Protects against Atherosclerosis via Fine-Tuning the Multiorgan Crosstalk

Fibroblast growth factor 21 (FGF21) is a metabolic hormone with pleiotropic effects on energy metabolism and insulin sensitivity. Besides its antiobese and antidiabetic activity, FGF21 also possesses the protective effects against atherosclerosis. Circulating levels of FGF21 are elevated in patients with atherosclerosis, macrovascular and microvascular complications of diabetes, possibly due to a compensatory upregulation. In apolipoprotein E-deficient mice, formation of atherosclerotic plaques is exacerbated by genetic depletion of FGF21, but is attenuated upon replenishment with recombinant FGF21. However, the blood vessel is not the direct target of FGF21, and the antiatherosclerotic activity of FGF21 is attributed to its actions in adipose tissues and liver. In adipocytes, FGF21 promotes secretion of adiponectin, which in turn acts directly on blood vessels to reduce endothelial dysfunction, inhibit proliferation of smooth muscle cells and block conversion of macrophages to foam cells. Furthermore, FGF21 suppresses cholesterol biosynthesis and attenuates hypercholesterolemia by inhibiting the transcription factor sterol regulatory element-binding protein-2 in hepatocytes. The effects of FGF21 on elevation of adiponectin and reduction of hypercholesterolemia are also observed in a phase-1b clinical trial in patients with obesity and diabetes. Therefore, FGF21 exerts its protection against atherosclerosis by fine-tuning the interorgan crosstalk between liver, brain, adipose tissue, and blood vessels.

Serum adiponectin is independently associated with the metabolic syndrome in Hong Kong, Chinese women with polycystic ovary syndrome

OBJECTIVE

To evaluate the association of serum adiponectin level with the metabolic syndrome in Chinese women with polycystic ovary syndrome (PCOS).

METHODS

This was a cross-sectional study carried out in Hong Kong Chinese women with PCOS at a university-affiliated tertiary hospital between January 2010 and January 2011. Clinical and biochemical parameters of the women were analysed. Prediction of the metabolic syndrome was determined by receiver-operator characteristic (ROC) curves, univariate and multivariate logistic regression analyses.

RESULTS

A total of 116 women diagnosed to have PCOS were analysed. The area under the ROC curve of adiponectin for the prediction of metabolic syndrome was 0.820, 95% confidence interval (CI) 0.737-0.886. Univariate binary logistic regression showed that testosterone, sex hormone-binding globulin (SHBG), free androgen index (FAI), waist circumference, body mass index (BMI), quantitative insulin-sensitivity check index (QUICKI), homeostasis model assessment of insulin resistance (HOMA-IR) and adiponectin were significantly associated with the metabolic syndrome. On multivariate logistic regression analysis, adiponectin (p =  0.020), HOMA-IR, age (p =  0.011) and BMI (p =  0.019) were independently associated with the metabolic syndrome, but not FAI (p =  0.256).

CONCLUSIONS

Serum adiponectin is independently associated with the metabolic syndrome in Chinese women with PCOS. Further longitudinal follow-up studies are needed to determine whether serum adiponectin adds to the prediction of long-term cardiometabolic morbidity conferred by age, BMI and measures of insulin resistance.

Exercise Modulates Oxidative Stress and Inflammation in Aging and Cardiovascular Diseases

Despite the wealth of epidemiological and experimental studies indicating the protective role of regular physical activity/exercise training against the sequels of aging and cardiovascular diseases, the molecular transducers of exercise/physical activity benefits are not fully identified but should be further investigated in more integrative and innovative approaches, as they bear the potential for transformative discoveries of novel therapeutic targets. As aging and cardiovascular diseases are associated with a chronic state of oxidative stress and inflammation mediated via complex and interconnected pathways, we will focus in this review on the antioxidant and anti-inflammatory actions of exercise, mainly exerted on adipose tissue, skeletal muscles, immune system, and cardiovascular system by modulating anti-inflammatory/proinflammatory cytokines profile, redox-sensitive transcription factors such as nuclear factor kappa B, activator protein-1, and peroxisome proliferator-activated receptor gamma coactivator 1-alpha, antioxidant and prooxidant enzymes, and repair proteins such as heat shock proteins, proteasome complex, oxoguanine DNA glycosylase, uracil DNA glycosylase, and telomerase. It is important to note that the effects of exercise vary depending on the type, intensity, frequency, and duration of exercise as well as on the individual's characteristics; therefore, the development of personalized exercise programs is essential.

Cell Systems to Investigate the Impact of Polyphenols on Cardiovascular Health

Polyphenols are a diverse group of micronutrients from plant origin that may serve as antioxidants and that contribute to human health in general. More specifically, many research groups have investigated their protective effect against cardiovascular diseases in several animal studies and human trials. Yet, because of the excessive processing of the polyphenol structure by human cells and the residing intestinal microbial community, which results in a large variability between the test subjects, the exact mechanisms of their protective effects are still under investigation. To this end, simplified cell culture systems have been used to decrease the inter-individual variability in mechanistic studies. In this review, we will discuss the different cell culture models that have been used so far for polyphenol research in the context of cardiovascular diseases. We will also review the current trends in cell culture research, including co-culture methodologies. Finally, we will discuss the potential of these advanced models to screen for cardiovascular effects of the large pool of bioactive polyphenols present in foods and their metabolites.

Leptin dose-dependently decreases atherosclerosis by attenuation of hypercholesterolemia and induction of adiponectin

OBJECTIVES

Conflicting evidence concerning leptin in atherosclerosis has been published. Furthermore, dose-dependent effects of leptin on atherogenesis have not been studied.

METHODS

Leptin-deficient low-density lipoprotein receptor (LDLR) knockout (LDLR(-/-);ob/ob) mice were treated with saline, 0.1, 0.5, or 3.0mg/kg body weight (BW)/d recombinant leptin over 12weeks starting at 8weeks of age. Aortic root and brachiocephalic artery (BCA) atherosclerotic lesions were analyzed by oil red O staining. Furthermore, glucose homeostasis, lipid metabolism, and liver function including tissue studies were assessed in all animals.

RESULTS

Leptin treatment dose-dependently decreased BW in LDLR(-/-);ob/ob mice as compared to saline. Mice in the 0.1 and 0.5mg/kgBW/d groups remained heavier (i.e. subphysiological leptin dose) and in the 3.0mg/kgBW/d group had similar weight (i.e. physiological leptin dose) as compared to non-leptin-deficient LDLR(-/-) animals. Recombinant leptin dose-dependently reduced plaque area in the aortic root and the BCA by 36% and 58%, respectively. Leptin-mediated reductions of plasma total and LDL-cholesterol (Chol) remained independent predictors for aortic root plaque area. Chol content in liver, as well as hepatic expression of key lipid and proinflammatory genes, were dose-dependently regulated by leptin. Furthermore, leptin treatment increased circulating levels and adipose tissue mRNA expression of the adipokine adiponectin.

CONCLUSIONS

Leptin administration within the subphysiological to physiological range diminishes atherosclerotic lesions. Leptin appears to mediate its antiatherogenic effects indirectly through reduction of hypercholesterolemia and liver steatosis, as well as upregulation of insulin-sensitizing and atheroprotective adiponectin.

Adipokines and endothelial dysfunction in acute myocardial infarction and the risk of recurrent cardiovascular events

AIMS

The aim of the study was to evaluate the prognostic role of adipokines (adiponectin, apelin, resistin, and visfatin) in patients with acute myocardial infarction (AMI) in relation to the extent of glucose metabolism impairment and intensity of systemic low-grade inflammation.

METHODS

This case-control study covered 131 patients with coronary artery disease: 104 consecutive patients with AMI (74% men, mean age of 62 ± 11 years) treated with primary percutaneous coronary intervention with stent implantation, and 27 patients with stable angina (70% men, mean age of 63 ± 11 years), who were initially assessed in terms of adipokine levels, C-reactive protein and various echocardiographic and vascular parameters. Major adverse cardiovascular events were recorded in the AMI group during 3-year follow-up.

RESULTS

Resistin and visfatin serum levels were significantly higher (P < 0.001), and adiponectin and apelin were lower (P < 0.001) in AMI patients as compared to patients with stable angina. In AMI patients, adipokine levels were not related to glucose metabolism disturbances, yet adiponectin (P = 0.03) and resistin (P = 0.001) concentrations were related to the number of affected coronary vessels. Serum adiponectin level correlated negatively (r = -0.608, P < 0.05), whereas resistin and visfatin correlated positively (r = 0.526, P < 0.05 and r = 0.352, P < 0.05, respectively) with C-reactive protein levels. All of the analyzed adipokines significantly accounted for the flow-mediated dilation variability (Radjusted 32%) in the AMI group. The Cox survival analysis indicated that resistin and visfatin were independent risk factors of recurrent AMI/unstable angina, with the diagnostic threshold above 12.2 ng/ml for resistin and above 11.8 ng/ml for visfatin concentrations.

CONCLUSION

An abnormal profile in serum adipokines observed in AMI is related to systemic inflammation and the degree of atherosclerosis independently of glucose metabolism disturbances and heralds major adverse cardiovascular event occurrence in long-term observation.

Association of Adiponectin with Adolescent Cardiovascular Health in a Dietary Intervention Study

OBJECTIVE

To investigate whether an infancy-onset, low saturated fat-oriented dietary intervention influences serum adiponectin concentration in adolescents, and to study the association of adiponectin with subclinical markers of vascular health, and cardio-metabolic risk factors.

STUDY DESIGN

The longitudinal, randomized Special Turku Coronary Risk Factor Intervention Project aimed to modify child's dietary fat quality replacing saturated fat with unsaturated fat. Serum adiponectin (n = 521) along with weight, height, high-density lipoprotein cholesterol, C-reactive protein (CRP), triglycerides, and insulin were measured at age 15 years. Adiposity was assessed using body mass index, waist circumference, and abdominal fat thickness measured with ultrasound. Metabolic syndrome was defined according to International Diabetes Foundation criteria. Vascular ultrasound measures including carotid intima-media thickness (IMT) were assessed.

RESULTS

Adiponectin concentrations were similar in the intervention and control groups (P = .16). Adiponectin associated with carotid IMT (r = -0.13, P = .005), high-density lipoprotein cholesterol (r = 0.18, P < .0001), triglycerides (r = -0.16, P = .0004), CRP (r = -0.10, P = .02), insulin (r = -0.14, P = .002), and adiposity (r = -0.18-0.24, P ≤ .0001). When adjusted for adiposity indices, the association with carotid IMT was only marginally diluted (P = .03-.06), but the associations with insulin and CRP became nonsignificant. Adolescents with adiponectin ≤median had 4-fold risk of metabolic syndrome than peers with adiponectin >median (CI 1.8-10.2, P = .0001).

CONCLUSIONS

In healthy adolescents, low serum adiponectin is related with carotid IMT and metabolic syndrome. We found no evidence that repeated low saturated fat-oriented dietary counseling would influence serum adiponectin in adolescence.

TRIAL REGISTRATION

Registered with ClinicalTrials.gov: NCT00223600.

Obesity, adipokines and cancer: an update

Obesity causes dysfunction of adipose tissue, with resultant chronic inflammation and adverse interplay of various adipokines, sex steroids and endocrine hormones. All these drive tumourigenesis and explain the epidemiological link between obesity and cancer. Over the past decade, the associations among obesity, adipokines and cancer have been increasingly recognized. Adipokines and their respective signalling pathways have drawn much research attention in the field of oncology and cancer therapeutics. This review will discuss the recent advances in the understanding of the association of several adipokines with common obesity-related cancers and the clinical therapeutic implications.

Imidazoline-like drugs improve insulin sensitivity through peripheral stimulation of adiponectin and AMPK pathways in a rat model of glucose intolerance

Altered adiponectin signaling and chronic sympathetic hyperactivity have both been proposed as key factors in the pathogenesis of metabolic syndrome. We recently reported that activation of I1 imidazoline receptors (I1R) improves several symptoms of the metabolic syndrome through sympathoinhibition and increases adiponectin plasma levels in a rat model of metabolic syndrome (Fellmann L, Regnault V, Greney H, et al. J Pharmacol Exp Ther 346: 370-380, 2013). The present study was designed to explore the peripheral component of the beneficial actions of I1R ligands (i.e., sympathoinhibitory independent effects). Aged rats displaying insulin resistance and glucose intolerance were treated with LNP509, a peripherally acting I1R agonist. Glucose tolerance, insulin sensitivity, and adiponectin signaling were assessed at the end of the treatment. Direct actions of the ligand on hepatocyte and adipocyte signaling were also studied. LNP509 reduced the area under the curve of the intravenous glucose tolerance test and enhanced insulin hypoglycemic action and intracellular signaling (Akt phosphorylation), indicating improved glucose tolerance and insulin sensitivity. LNP509 stimulated adiponectin secretion acting at I1R on adipocytes, resulting in increased plasma levels of adiponectin; it also enhanced AMPK phosphorylation in hepatic tissues. Additionally, I1R activation on hepatocytes directly enhanced AMPK phosphorylation. To conclude, I1R ligands can improve insulin sensitivity acting peripherally, independently of sympathoinhibition; stimulation of adiponectin and AMPK pathways at insulin target tissues may account for this effect. This may open a promising new way for the treatment of the metabolic syndrome.

Gender-Specific Associations between Circulating T-Cadherin and High Molecular Weight-Adiponectin in Patients with Stable Coronary Artery Disease

Close relationships exist between presence of adiponectin (APN) within vascular tissue and expression of T-cadherin (T-cad) on vascular cells. APN and T-cad are also present in the circulation but here their relationships are unknown. This study investigates associations between circulating levels of high molecular weight APN (HMW-APN) and T-cad in a population comprising 66 women and 181 men with angiographically proven stable coronary artery disease (CAD). Plasma HMW-APN and T-cad were measured by ELISA and analysed for associations with baseline clinical characteristics and with each other. In multivariable analysis BMI and HDL were independently associated with HMW-APN in both genders, while diabetes and extent of coronary stenosis were independently associated with T-cad in males only. Regression analysis showed no significant association between HMW-APN and T-cad in the overall study population. However, there was a negative association between HMW-APN and T-cad (P=0.037) in a subgroup of young men (age <60 years, had no diabetes and no or 1-vessel CAD) which persisted after multivariable analysis with adjustment for all potentially influential variables (P=0.021). In the corresponding subgroup of women there was a positive association between HMW-APN and T-cad (P=0.013) which disappeared after adjustment for HDL. After exclusion of the young men, a positive association (P=0.008) between HMW-APN and T-cad was found for the remaining participants of the overall population which disappeared after adjustment for HDL and BMI. The existence of opposing correlations between circulating HMW-APN and T-cad in male and female patient populations underscores the necessity to consider gender as a confounding variable when evaluating biomarker potentials of APN and T-cad.

Adiponectin predicts cardiovascular events in diabetes dialysis patients

OBJECTIVES

Adiponectin is an insulin-sensitizing, anti-inflammatory adipokine with anti-atherogenic actions in the general population. In dialysis patients it is unclear whether adiponectin conserves its protective value or is, on the contrary, associated to worse prognosis. We assessed the predictive value of adiponectin for atherosclerosis related cardiovascular events in type 2 diabetic dialysis patients.

DESIGN AND METHODS

Prevalent diabetic dialysis patients from three dialysis units (n=77) were enrolled in a 3years' prospective observational study. Serum adiponectin, clinical and laboratory parameters were determined at baseline; new occurrence of atherosclerosis related events (coronary events, atherosclerosis obliterans, and stroke) was recorded.

RESULTS

Baseline adiponectin was 17.25(9.53-31.97) μg/mL and significantly correlated to HDL cholesterol (r=0.29, p=0.01), triglycerides (r=-0.40, p=0.0004), ferritin (r=-0.29, p=0.02), transferrin (r=-0.28, p=0.02), and uric acid (r=-0.24, p=0.04). In multivariate analysis association to triglycerides (p=0.001), HDL cholesterol (p=0.01) and ferritin (p=0.04) remained significant. 36 new fatal and non-fatal new cardiovascular events occurred, 29 patient died. Cox proportional regression analysis showed that adiponectin below or above a ROC-derived cut-off of 27.33μg/mL significantly influenced event-free survival: hazard ratio (HR) 2.48, 95% confidence interval (CI) (1.09-5.66), p=0.031 along with fasting glucose HR 1.01, 95%CI(1.00-1.02), p=0.01 and history of cardiovascular events at inclusion HR 3.16, 95%CI(1.36-7.32), p=0.007. In multivariate analysis baseline adiponectin HR 5.02, 95%CI(0.98-25.06), p=0.05 and glycemia HR 1.01, 95%CI(1.00-1.02), p=0.01 influenced event-free survival. Adiponectin also predicted cardiovascular events in patients without cardiovascular disease at inclusion but was not associated to overall mortality.

CONCLUSIONS

In diabetes dialysis patients low adiponectin favors occurrence of atherosclerosis related cardiovascular events.

Fibroblast growth factor 21 prevents atherosclerosis by suppression of hepatic sterol regulatory element-binding protein-2 and induction of adiponectin in mice

Supplemental Digital Content is available in the text.

Background—

Fibroblast growth factor 21 (FGF21) is a metabolic hormone with pleiotropic effects on glucose and lipid metabolism and insulin sensitivity. It acts as a key downstream target of both peroxisome proliferator-activated receptor α and γ, the agonists of which have been used for lipid lowering and insulin sensitization, respectively. However, the role of FGF21 in the cardiovascular system remains elusive.

Methods and Results—

The roles of FGF21 in atherosclerosis were investigated by evaluating the impact of FGF21 deficiency and replenishment with recombinant FGF21 in apolipoprotein E^−/− mice. FGF21 deficiency causes a marked exacerbation of atherosclerotic plaque formation and premature death in apolipoprotein E^−/− mice, which is accompanied by hypoadiponectinemia and severe hypercholesterolemia. Replenishment of FGF21 protects against atherosclerosis in apolipoprotein E^−/−mice via 2 independent mechanisms, inducing the adipocyte production of adiponectin, which in turn acts on the blood vessels to inhibit neointima formation and macrophage inflammation, and suppressing the hepatic expression of the transcription factor sterol regulatory element-binding protein-2, thereby leading to reduced cholesterol synthesis and attenuation of hypercholesterolemia. Chronic treatment with adiponectin partially reverses atherosclerosis without obvious effects on hypercholesterolemia in FGF21-deficient apolipoprotein E^−/− mice. By contrast, the cholesterol-lowering effects of FGF21 are abrogated by hepatic expression of sterol regulatory element-binding protein-2.

Conclusions—

FGF21 protects against atherosclerosis via fine tuning the multiorgan crosstalk among liver, adipose tissue, and blood vessels.

Overexpression of the adiponectin gene mimics the metabolic and stress resistance effects of calorie restriction, but not the anti-tumor effect

Adiponectin (Adipoq), a peptide hormone secreted from the white adipose tissue, may play a role in the anti-aging and/or anti-tumor effects of calorie restriction (CR). We analyzed metabolic traits in Adipoq gene-overexpressing mice fed ad libitum with a regular diet (RD) or a high-fat diet (HFD), or fed 30% CR of RD initiated at 12 weeks of age. Adipoq-RD and -HFD mice at 6 months of age showed reduced blood glucose and insulin concentrations, and thus increased insulin sensitivity, compared with WT mice fed a RD or a HFD. In the epididymal white adipose tissue in Adipoq mice, senescence-like changes such as upregulation of p53 protein and of biomarkers of inflammation, Cd68 and Ccl2 mRNA, were ameliorated compared with WT-RD and WT-HFD mouse tissues. Resistance to stress induced by lipopolysaccharide was also strengthened in Adipoq mice compared with WT mice. These metabolic changes and stress resistance were also noted in the WT-CR mice, suggesting that Adipoq plays a part in the effect of CR. In contrast, in an allograft tumor growth model, tumor growth was not inhibited in Adipoq mice. The present findings suggest that Adipoq plays a part in the anti-aging, but not in the anti-tumor, effects of CR.

Differential Role of Leptin and Adiponectin in Cardiovascular System

Leptin and adiponectin are differentially expressed adipokines in obesity and cardiovascular diseases. Leptin levels are directly associated with adipose tissue mass, while adiponectin levels are downregulated in obesity. Although significantly produced by adipocytes, leptin is also produced by vascular smooth muscle cells and cardiomyocytes. Plasma leptin concentrations are elevated in cases of cardiovascular diseases, such as hypertension, congestive heart failure, and myocardial infarction. As for the event of left ventricular hypertrophy, researchers have been stirring controversy about the role of leptin in this form of cardiac remodeling. In this review, we discuss how leptin has been shown to play an antihypertrophic role in the development of left ventricular hypertrophy through in vitro experiments, population-based cross-sectional studies, and longitudinal cohort studies. Conversely, we also examine how leptin may actually promote left ventricular hypertrophy using in vitro analysis and human-based univariate and multiple linear stepwise regression analysis. On the other hand, as opposed to leptin's generally detrimental effects on the cardiovascular system, adiponectin is a cardioprotective hormone that reduces left ventricular and vascular hypertrophy, oxidative stress, and inflammation. In this review, we also highlight adiponectin signaling and its protective actions on the cardiovascular system.

Role of adiponectin system in insulin resistance

The knowledge of the pathogenesis of obesity and its metabolic sequelae has significantly advanced over the last few decades and adipose tissue is now considered a link between obesity and insulin resistance. Adiponectin, one of the major adipocyte-secreted proteins, has attracted scientific interest in recent years and has been extensively studied both in human and animal models. Adiponectin exerts insulin-sensitizing effects through binding to its receptors, leading to activation of AMPK, PPAR-α, and potentially other unknown molecular pathways. In obesity-linked insulin resistance, both adiponectin and adiponectin receptors are downregulated, leading to activation of signaling pathways involved in metabolism regulation. Up-regulation of adiponectin/adiponectin receptors or enhancing adiponectin receptor function may be an interesting therapeutic strategy for obesity-linked insulin resistance. In this review we will focus on the recent research related to the relationship between the adiponectin system and insulin resistance. The potential use of adiponectin or its receptor for therapeutic intervention will be also discussed.

Challenging oneself intermittently to improve health

Humans and their predecessors evolved in environments where they were challenged intermittently with: 1) food scarcity; 2) the need for aerobic fitness to catch/kill prey and avoid or repel attackers; and 3) exposure to biological toxins present in foodstuffs. Accordingly, cells and organ systems acquired and retained molecular signaling and metabolic pathways through which the environmental challenges enhanced the functionality and resilience of the cells and organisms. Within the past 60 years there has been a precipitous diminution of such challenges in modern societies because of the development of technologies that provide a continuous supply of energy-dense processed foods and that largely eliminate the need for physical exertion. As a consequence of the modern 'couch potato' lifestyle, signaling pathways that mediate beneficial effects of environmental challenges on health and disease resistance are disengaged, thereby rendering people vulnerable to obesity, diabetes, cardiovascular disease, cancers and neurodegenerative disorders. Reversal of the epidemic of diseases caused by unchallenging lifestyles will require a society-wide effort to re-introduce intermittent fasting, exercise and consumption of plants containing hormetic phytochemicals into daily and weekly routines.

Physical exercise-induced hippocampal neurogenesis and antidepressant effects are mediated by the adipocyte hormone adiponectin

Adiponectin (ADN) is an adipocyte-secreted protein with insulin-sensitizing, antidiabetic, antiinflammatory, and antiatherogenic properties. Evidence is also accumulating that ADN has neuroprotective activities, yet the underlying mechanism remains elusive. Here we show that ADN could pass through the blood-brain barrier, and elevating its levels in the brain increased cell proliferation and decreased depression-like behaviors. ADN deficiency did not reduce the basal hippocampal neurogenesis or neuronal differentiation but diminished the effectiveness of exercise in increasing hippocampal neurogenesis. Furthermore, exercise-induced reduction in depression-like behaviors was abrogated in ADN-deficient mice, and this impairment in ADN-deficient mice was accompanied by defective running-induced phosphorylation of AMP-activated protein kinase (AMPK) in the hippocampal tissue. In vitro analyses indicated that ADN itself could increase cell proliferation of both hippocampal progenitor cells and Neuro2a neuroblastoma cells. The neurogenic effects of ADN were mediated by the ADN receptor 1 (ADNR1), because siRNA targeting ADNR1, but not ADNR2, inhibited the capacity of ADN to enhance cell proliferation. These data suggest that adiponectin may play a significant role in mediating the effects of exercise on hippocampal neurogenesis and depression, possibly by activation of the ADNR1/AMPK signaling pathways, and also raise the possibility that adiponectin and its agonists may represent a promising therapeutic treatment for depression.

Adiponectin protects against acetaminophen-induced mitochondrial dysfunction and acute liver injury by promoting autophagy in mice

BACKGROUND & AIMS

Acetaminophen (APAP) overdose causes hepatic necrosis and acute liver injury by inducing mitochondrial dysfunction and damage. Although the biochemical pathways that mediate APAP-induced hepatotoxicity have been well studied, the body's defense mechanism to attenuate this disease remains elusive. This study investigated the roles of adiponectin, an adipocyte-secreted adipokine with pleiotropic protective effects against obesity-related metabolic dysfunction, in the pathogenesis of APAP-induced liver injury in mice.

METHODS

Adiponectin knockout (ADN KO) and C57 wild type mice were treated with an overdose of APAP, followed by histological and biochemical evaluation of liver injury and activation of autophagy. The mechanism of adiponectin in APAP-induced hepatocytic toxicity was also explored in primary cultured hepatocytes.

RESULTS

APAP overdose triggers a marked accumulation of adiponectin in injured liver tissues. ADN KO mice exhibit severely exacerbated mitochondrial dysfunction and damage, oxidative stress and necrosis and much higher mortality in response to APAP overdose, whereas these changes are reversed by a single injection of adiponectin. Mechanistically, adiponectin induces autophagosome formation by AMP-activated protein kinase (AMPK)-dependent activation of the Unc-51-like kinase 1, consequently leading to the removal of damaged mitochondria from hepatocytes. The protective effects of adiponectin against APAP-induced mitochondrial damage, oxidative stress and necrosis are abrogated by blockage of AMPK or pharmacological inhibition of autophagy.

CONCLUSIONS

Our findings suggest that the APAP-induced accumulation of adiponectin in liver tissues serves as an adaptive mechanism to ameliorate hepatotoxicity by promoting autophagy-mediated clearance of damaged mitochondria. Adiponectin agonists may represent a promising therapy for the drug-induced acute liver failure.

Short-term melatonin consumption protects the heart of obese rats independent of body weight change and visceral adiposity

Chronic melatonin treatment has been shown to prevent the harmful effects of diet-induced obesity and reduce myocardial susceptibility to ischaemia-reperfusion injury (IRI). However, the exact mechanism whereby it exerts its beneficial actions on the heart in obesity/insulin resistance remains unknown. Herein, we investigated the effects of relatively short-term melatonin treatment on the heart in a rat model of diet-induced obesity. Control and diet-induced obese Wistar rats (fed a high calorie diet for 20 wk) were each subdivided into three groups receiving drinking water with or without melatonin (4 mg/kg/day) for the last 6 or 3 wk of experimentation. A number of isolated hearts were perfused in the working mode, subjected to regional or global ischaemia-reperfusion; others were nonperfused. Metabolic parameters, myocardial infarct sizes (IFS), baseline and postischaemic activation of PKB/Akt, ERK42/44, GSK-3β and STAT-3 were determined. Diet-induced obesity caused increases in body weight gain, visceral adiposity, fasting blood glucose, serum insulin and triglyceride (TG) levels with a concomitant cardiac hypertrophy, large postischaemic myocardial IFSs and a reduced cardiac output. Melatonin treatment (3 and 6 wk) decreased serum insulin levels and the HOMA index (P < 0.05) with no effect on weight gain (after 3 wk), visceral adiposity, serum TG and glucose levels. It increased serum adiponectin levels, reduced myocardial IFSs in both groups and activated baseline myocardial STAT-3 and PKB/Akt, ERK42/44 and GSK-3β during reperfusion. Overall, short-term melatonin administration to obese/insulin resistant rats reduced insulin resistance and protected the heart against ex vivo myocardial IRI independently of body weight change and visceral adiposity.

Adiponectin mediated APPL1-AMPK signaling induces cell migration, MMP activation, and collagen remodeling in cardiac fibroblasts

Defects in adiponectin action have been implicated in the development of cardiac dysfunction in obesity and diabetes. Cardiac fibroblasts play an important role in regulating extracellular matrix remodeling yet little is known regarding the direct effects of adiponectin on cardiac fibroblasts. In this study, we first demonstrated temporal relocalization of cellular APPL1 in response to adiponectin in primary cardiac fibroblasts and that siRNA-mediated knockdown of APPL1 attenuated stimulation of AMPK by adiponectin. The cell surface content of MT1-MMP and activation of MMP2 were induced by adiponectin and these responses were dependent on AMPK signaling. Enhanced MMP activity facilitated increased fibroblast migration in response to adiponectin which was also prevented by inhibition of AMPK, with no change in cell proliferation observed. Collagen and elastin immunofluorescence demonstrated reorganization of the extracellular matrix in accordance with increased MMP activity, whereas quantitative mRNA analysis, (3) H-proline incorporation and picrosirius red assays showed no change in intracellular or extracellular total collagen levels in response to adiponectin. In summary, these data are the first to report the adiponectin stimulated APPL1-AMPK signaling axis in cardiac fibroblasts and characterize MT1-MMP translocation, MMP2 activity and cell migration as functional outcomes. These effects may be of significance in heart failure associated with obesity and diabetes.

Peroxisome proliferator-activated receptors for hypertension

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors belonging to the nuclear receptor superfamily, which is composed of four members encoded by distinct genes (α, β, γ, and δ). The genes undergo transactivation or transrepression under specific mechanisms that lead to the induction or repression of target gene expression. As is the case with other nuclear receptors, all four PPAR isoforms contain five or six structural regions in four functional domains; namely, A/B, C, D, and E/F. PPARs have many functions, particularly functions involving control of vascular tone, inflammation, and energy homeostasis, and are, therefore, important targets for hypertension, obesity, obesity-induced inflammation, and metabolic syndrome in general. Hence, PPARs also represent drug targets, and PPARα and PPARγ agonists are used clinically in the treatment of dyslipidemia and type 2 diabetes mellitus, respectively. Because of their pleiotropic effects, they have been identified as active in a number of diseases and are targets for the development of a broad range of therapies for a variety of diseases. It is likely that the range of PPARγ agonist therapeutic actions will result in novel approaches to lifestyle and other diseases. The combination of PPARs with reagents or with other cardiovascular drugs, such as diuretics and angiotensin II receptor blockers, should be studied. This article provides a review of PPAR isoform characteristics, a discussion of progress in our understanding of the biological actions of PPARs, and a summary of PPAR agonist development for patient management. We also include a summary of the experimental and clinical evidence obtained from animal studies and clinical trials conducted to evaluate the usefulness and effectiveness of PPAR agonists in the treatment of lifestyle-related diseases.

Adiponectin gene variants and the risk of coronary heart disease: a 16-year longitudinal study

OBJECTIVE

Circulating adiponectin levels have been shown to be associated with a risk of coronary heart disease (CHD). However, its primary role in protecting against the development of CHD remains controversial due to conflicting observations in prospective studies. To gain further insight into the primary role of adiponectin, our major objective was to investigate the relationship between single nucleotide polymorphisms (SNPs) of the adiponectin gene (ADIPOQ) and incident CHD in a population-based cohort with no CHD at baseline.

DESIGN AND METHODS

We conducted a 16-year longitudinal study in 2196 subjects from the Hong Kong Cardiovascular Risk Factor Prevalence Study (CRISPS). During 33 862 person-years of follow-up, 184 subjects developed CHD (cumulative incidence rate=5.4 per 1000 person-years). Nine ADIPOQ SNPs with potential functional relevance or shown to be associated with adiponectin levels and/or CHD were genotyped.

RESULTS

Among the nine ADIPOQ SNPs, +276G>T (rs1501299) was independently associated with incident CHD in men but not in women, even after adjustments for traditional cardiovascular risk factors (Padjusted=5.5×10(-3) to 0.023; hazard ratio=1.39-1.54). Furthermore, there was a significant association of the T allele of +276G>T with a lower adiponectin level (P=0.027; β (95% CI)=-0.05 (-0.10, -0.01).

CONCLUSIONS

This study demonstrated that +276G>T may be an independent predictor of CHD development. Our findings suggest that low adiponectin levels, as may be influenced by +276G>T, confer a higher risk of CHD, in keeping with a role of hypoadiponectinaemia in the development of CHD in the general population.

Effect of monomeric adiponectin on cardiac function and perfusion in anesthetized pig

Adiponectin, the most abundant adipokine released by adipose tissue, appears to play an important role in the regulation of vascular endothelial and cardiac function. To date, however, the physiological effects of human monomeric adiponectin on the coronary vasculature and myocardial systo-diastolic function, as well as on parasympathetic/sympathetic involvement and nitric oxide (NO) release, have not yet been investigated. Thus, we planned to determine the primary in vivo effects of human monomeric adiponectin on coronary blood flow and cardiac contractility/relaxation and the related role of autonomic nervous system, adiponectin receptors, and NO. In 30 anesthetized pigs, human monomeric adiponectin was infused into the left anterior descending coronary artery at constant heart rate and arterial blood pressure, and the effects on coronary blood flow, left ventricular systo-diastolic function, myocardial oxygen metabolism, and NO release were examined. The mechanisms of the observed hemodynamic responses were also analyzed by repeating the highest dose of human monomeric adiponectin infusion after autonomic nervous system and NO blockade, and after specific adiponectin 1 receptor antagonist administration. Intracoronary human monomeric adiponectin caused dose-related increases of coronary blood flow and cardiac function. Those effects were accompanied by increased coronary NO release and coronary adiponectin levels. Moreover, the vascular effects of the peptide were prevented by blockade of β2-adrenoceptors and NO synthase, whereas all effects of human monomeric adiponectin were prevented by adiponectin 1 receptor inhibitor. In conclusion, human monomeric adiponectin primarily increased coronary blood flow and cardiac systo-diastolic function through the involvement of specific receptors, β2-adrenoceptors, and NO release.

Adiponectin: a manifold therapeutic target for metabolic syndrome, diabetes, and coronary disease?

Adiponectin is the most abundant peptide secreted by adipocytes, being a key component in the interrelationship between adiposity, insulin resistance and inflammation. Central obesity accompanied by insulin resistance is a key factor in the development of metabolic syndrome (MS) and future macrovascular complications. Moreover, the remarkable correlation between coronary artery disease (CAD) and alterations in glucose metabolism has raised the likelihood that atherosclerosis and type 2 diabetes mellitus (T2DM) may share a common biological background. We summarize here the current knowledge about the influence of adiponectin on insulin sensitivity and endothelial function, discussing its forthcoming prospects and potential role as a therapeutic target for MS, T2DM, and cardiovascular disease. Adiponectin is present in the circulation as a dimer, trimer or protein complex of high molecular weight hexamers, >400 kDa. AdipoR1 and AdipoR2 are its major receptors in vivo mediating the metabolic actions. Adiponectin stimulates phosphorylation and AMP (adenosin mono phosphate) kinase activation, exerting direct effects on vascular endothelium, diminishing the inflammatory response to mechanical injury and enhancing endothelium protection in cases of apolipoprotein E deficiency. Hypoadiponectinemia is consistently associated with obesity, MS, atherosclerosis, CAD, T2DM. Lifestyle correction helps to favorably modify plasma adiponectin levels. Low adiponectinemia in obese patients is raised via continued weight loss programs in both diabetic and nondiabetic individuals and is also accompanied by reductions in pro-inflammatory factors. Diet modifications, like intake of fish, omega-3 supplementation, adherence to a Mediterranean dietary pattern and coffee consumption also increase adiponectin levels. Antidiabetic and cardiovascular pharmacological agents, like glitazones, glimepiride, angiotensin converting enzyme inhibitors and angiotensin receptor blockers are also able to improve adiponectin concentration. Fibric acid derivatives, like bezafibrate and fenofibrate, have been reported to enhance adiponectin levels as well. T-cadherin, a membrane-associated adiponectin-binding protein lacking intracellular domain seems to be a main mediator of the antiatherogenic adiponectin actions. The finding of novel pharmacologic agents proficient to improve adiponectin plasma levels should be target of exhaustive research. Interesting future approaches could be the development of adiponectin-targeted drugs chemically designed to induce the activaton of its receptors and/or postreceptor signaling pathways, or the development of specific adiponectin agonists.

The role of adiponectin signaling in metabolic syndrome and cancer

The increased prevalence of obesity has mandated extensive research focused on mechanisms responsible for associated clinical complications. Emerging from the focus on adipose tissue biology as a vitally important adipokine is adiponectin which is now believed to mediate anti-diabetic, anti-atherosclerotic, anti-inflammatory, cardioprotective and cancer modifying actions. Adiponectin mediates these primarily beneficial effects via direct signaling effects and via enhancing insulin sensitivity via crosstalk with insulin signaling pathways. Reduced adiponectin action is detrimental and occurs in obesity via decreased circulating levels of adiponectin action or development of adiponectin resistance. This review will focus on cellular mechanisms of adiponectin action, their crosstalk with insulin signaling and the resultant role of adiponectin in cardiovascular disease, diabetes and cancer and reviews data from in vitro cell based studies through animal models to clinical observations.

Adiponectin: key role and potential target to reverse energy wasting in chronic heart failure

The concept of skeletal muscle myopathy as a main determinant of exercise intolerance in chronic heart failure (HF) is gaining acceptance. Symptoms that typify HF patients, including shortness of breath and fatigue, are often directly related to the abnormalities of the skeletal muscle in HF. Besides muscular wasting, alterations in skeletal muscle energy metabolism, including insulin resistance, have been implicated in HF. Adiponectin, an adipocytokine with insulin-sensitizing properties, receives increasing interest in HF. Circulating adiponectin levels are elevated in HF patients, but high levels are paradoxically associated with poor outcome. Previous analysis of m. vastus lateralis biopsies in HF patients highlighted a striking functional adiponectin resistance. Together with increased circulating adiponectin levels, adiponectin expression within the skeletal muscle is elevated in HF patients, whereas the expression of the main adiponectin receptor and genes involved in the downstream pathway of lipid and glucose metabolism is downregulated. In addition, the adiponectin-related metabolic disturbances strongly correlate with aerobic capacity (VO2 peak), sub-maximal exercise performance and muscle strength. These observations strengthen our hypothesis that adiponectin and its receptors play a key role in the development and progression of the "heart failure myopathy". The question whether adiponectin exerts beneficial rather than detrimental effects in HF is still left unanswered. This current research overview will elucidate the emerging role of adiponectin in HF and suggests potential therapeutic targets to tackle energy wasting in these patients.

Direct effects of adipokines on the heart: focus on adiponectin

Cardiovascular disease, including heart failure, is a principal cause of death in individuals with obesity and diabetes. However, the mechanisms of obesity- and diabetes-induced heart disease are multifaceted and remain to be clearly defined. Of relevance to this review, there is currently great research and clinical interest in the endocrine effects of adipokines on the myocardium and their role in heart failure. We will discuss the potential significance of adipokines in the pathogenesis of heart failure via their ability to regulate remodeling events including metabolism, hypertrophy, fibrosis, and cell death. As an excellent example, we will first focus on adiponectin which is best known to confer numerous cardioprotective effects. However, we comprehensively discuss the existing literature that highlights it would be naive to assume that this was always the case. We also focus on lipocalin-2 which mediates pro-inflammatory and pro-apoptotic effects. It is important when studying actions of adipokines to integrate cellular and mechanistic analyses and translate these to physiologically relevant in vivo models and clinical studies. However, assimilating studies on numerous cardiac remodeling events which ultimately dictate cardiac dysfunction into a unifying conclusion is challenging. Nevertheless, there is undoubted potential for the use of adipokines as robust biomarkers and appropriate therapeutic targets in heart failure.

Effects of interventions on adiponectin and adiponectin receptors

Adiponectin secreted from adipose tissue binds to two distinct adiponectin receptors (AdipoR1 and AdipoR2) identified and exerts its anti-diabetic effects in insulin-sensitive organs including liver, skeletal muscle and adipose tissue as well as amelioration of vascular dysfunction in the various vasculatures. A number of experimental and clinical observations have demonstrated that circulating levels of adiponectin are markedly reduced in obesity, type 2 diabetes, hypertension, and coronary artery disease. Therapeutic interventions which can improve the action of adiponectin including elevation of circulating adiponectin concentration or up-regulation and/or activation of its receptors, could provide better understanding of strategies to ameliorate metabolic disorders and vascular disease. The focus of the present review is to summarize accumulating evidence showing the role of interventions such as pharmacological agents, exercise, and calorie restriction in the expression of adiponectin and adiponectin receptors.

Serum levels of the myokine irisin in relation to metabolic and renal function

OBJECTIVE

Irisin has recently been introduced as a novel myokine which reverses visceral obesity and improves glucose metabolism in mice. However, regulation of irisin in humans in relation to renal and metabolic disease has not been comprehensively studied.

DESIGN AND METHODS

Serum irisin levels were quantified by ELISA and correlated with anthropometric and biochemical parameters of renal function, glucose and lipid metabolism, as well as inflammation, in 532 patients with stages 1-5 of chronic kidney disease (CKD).

RESULTS

Median serum irisin levels adjusted for age, gender, and BMI significantly decreased with increasing CKD stage and lowest concentrations were seen in patients with CKD stage 5. Furthermore, irisin concentrations were associated with facets of the metabolic syndrome including diastolic blood pressure, markers of impaired glucose tolerance, and dyslipidemia in univariate analysis. Moreover, markers of renal function, e.g. glomerular filtration rate, and insulin resistance, e.g. homeostasis model assessment of insulin resistance, remained independently associated with circulating irisin levels in robust multivariate analysis.

CONCLUSIONS

We show that irisin serum concentrations decrease with increasing CKD stage and are independently and positively predicted by renal function and insulin resistance. The physiological relevance of our findings, as well as the factors contributing to irisin regulation in humans, needs to be further defined in future experiments.