Adiponectin Mediates the Suppressive Effect of Rosiglitazone on Plasminogen Activator Inhibitor-1 Production

Orchestra of ligand-activated transcription factors in the molecular symphony of SERPINE 1 / PAI-1 gene regulation

Plasminogen activator inhibitor 1 (PAI-1) is a crucial serine protease inhibitor that prevents plasminogen activation by inhibiting tissue- and urokinase-type plasminogen activators (tPA, uPA). PAI-1 is well-known for its role in modulating hemocoagulation or extracellular matrix formation by inhibiting plasmin or matrix metalloproteinases, respectively. PAI-1 is induced by pro-inflammatory cytokines across various tissues, yet its regulation by ligand-activated transcription factors is partly disregarded. Therefore, we have attempted to summarize the current knowledge on the transcriptional regulation of PAI-1 expression by the most relevant xenobiotic and endocrine receptors implicated in modulating PAI-1 levels. This review aims to contribute to the understanding of the specific, often tissue-dependent regulation of PAI-1 and provide insights into the modulation of PAI-1 levels beyond its direct inhibition.

Amber Extract Reduces Lipid Content in Mature 3T3-L1 Adipocytes by Activating the Lipolysis Pathway

Amber-the fossilized resin of trees-is rich in terpenoids and rosin acids. The physiological effects, such as antipyretic, sedative, and anti-inflammatory, were used in traditional medicine. This study aims to clarify the physiological effects of amber extract on lipid metabolism in mouse 3T3-L1 cells. Mature adipocytes are used to evaluate the effect of amber extract on lipolysis by measuring the triglyceride content, glucose uptake, glycerol release, and lipolysis-related gene expression. Our results show that the amount of triacylglycerol, which is stored in lipid droplets in mature adipocytes, decreases following 96 h of treatment with different concentrations of amber extract. Amber extract treatment also decreases glucose uptake and increases the release of glycerol from the cells. Moreover, amber extract increases the expression of lipolysis-related genes encoding perilipin and hormone-sensitive lipase (HSL) and promotes the activity of HSL (by increasing HSL phosphorylation). Amber extract treatment also regulates the expression of other adipocytokines in mature adipocytes, such as adiponectin and leptin. Overall, our results indicate that amber extract increases the expression of lipolysis-related genes to induce lipolysis in 3T3-L1 cells, highlighting its potential for treating various obesity-related diseases.

Age-Biomarkers-Clinical Risk Factors for Prediction of Cardiovascular Events in Patients With Coronary Artery Disease

Objective- In patients with stable coronary artery disease, conventional risk factors provide limited incremental predictive value for cardiovascular events. We sought to investigate whether a panel of cardiometabolic biomarkers alone or combined with conventional risk factors would exhibit incremental value in the prediction of cardiovascular events. Approach and Results- In the discovery cohort, we measured serum adiponectin, A-FABP (adipocyte fatty acid-binding protein), lipocalin-2, FGF (fibroblast growth factor)-19 and 21, plasminogen activator inhibitor-1, and retinol-binding protein-4 in 1166 Chinese coronary artery disease patients. After a median follow-up of 35 months, 170 patients developed new-onset major adverse cardiovascular events (MACE). In the model with age ≥65 years and conventional risk factors, area under the curve for predicting MACE was 0.68. Addition of lipocalin-2 to the age-clinical risk factor model improved predictive accuracy (area under the curve=0.73). Area under the curve further increased to 0.75 when a combination of lipocalin-2, A-FABP, and FGF-19 was added to yield age-biomarkers-clinical risk factor model. The adjusted hazard ratio on MACEs for lipocalin-2, A-FABP, and FGF-19 levels above optimal cutoffs were 2.23 (95% CI, 1.62-3.08), 1.99 (95% CI, 1.43-2.76), and 1.65 (95% CI, 1.15-2.35), respectively. In the validation cohort of 1262 coronary artery disease patients with type 2 diabetes mellitus, the age-biomarkers-clinical risk factor model was confirmed to provide good discrimination and calibration over the conventional risk factor alone for prediction of MACE. Conclusions- A combination of the 3 biomarkers, lipocalin-2, A-FABP, and FGF-19, with clinical risk factors to yield the age-biomarkers-clinical risk factor model provides an optimal and validated prediction of new-onset MACE in patients with stable coronary artery disease.

Non-linear association of plasma level of high-density lipoprotein cholesterol with endobronchial biopsy bleeding in patients with lung cancer

Background

Despite a large body of studies have demonstrated the multifaceted behavior of high-density lipoproteins (HDLs) in several physiological and pathological processes, the levels of plasma HDL-cholesterol (HDL-C) that may be associated with endobronchial biopsy (EBB)-related bleeding have never been examined.

Methods

We conducted a single-center retrospective cohort study of 628 consecutive patients with primary lung cancer who had undergone EBB at a large tertiary hospital between January 2014 and February 2018. Patients were divided into the bleeding group and the non-bleeding group according to the bronchoscopy report. The association between HDL-C levels and EBB-induced bleeding was evaluated using the LASSO regression analysis, multiple regression analysis and smooth curve fitting adjusted for potential confounders.

Results

There was an inverse association of plasma HDL-C concentration with the incidence of EBB-induced bleeding as assessed by univariate analysis (P < 0.05). However, in piecewise linear regression analysis, a non-linear relationship with threshold saturation effects was observed between plasma HDL-C concentrations and EBB-induced bleeding. The incidence of EBB-induced bleeding decreased with HDL-C concentrations from 1.5 mmol/L up to 2.0 mmol/L (adjusted OR, 0.39; 95% CI, 0.20–0.74), but increased with HDL-C levels above the inflection point (HDL-C = 2.0 mmol/L).

Conclusions

There was a non-linear association between plasma HDL-C concentrations and the risk of EBB-induced bleeding in patients with lung cancer. The plasma level of HDL-C above 2.0 mmol/L or below 1.5 mmol/L may increase the risk of EBB-induced bleeding.

Adiponectin fine-tuning of liver regeneration dynamics revealed through cellular network modelling

Following partial hepatectomy, the liver initiates a regenerative programme involving hepatocyte priming and replication driven by the coordinated actions of cytokine and growth factors. We investigated the mechanisms underlying adiponectin's (Adn) regulation of liver regeneration through modulation of these mediators. Adn(-/-) mice showed delayed onset of hepatocyte replication, but accelerated cell cycle progression relative to wild-type mice, suggesting Adn has multiple effects fine-tuning the kinetics of liver regeneration. We developed a computational model describing the molecular and physiological kinetics of liver regeneration in Adn(-/-) mice. We employed this computational model to evaluate the underlying regulatory mechanisms. Our analysis predicted that Adn is required for an efficient early cytokine response to partial hepatectomy, but is inhibitory to later growth factor actions. Consistent with this prediction, Adn knockout reduced hepatocyte responses to interleukin-6 during the priming phase, but enhanced growth factor levels through peak hepatocyte replication. By contrast, supraphysiological concentrations of Adn resulting from rosiglitazone treatment suppressed regeneration by reducing growth factor levels during S phase, consistent with computational predictions. Together, these results revealed that Adn fine-tunes the progression of liver regeneration through dynamically modulating molecular mediator networks and cellular interactions within the liver.

Adiponectin Enhances Cold-Induced Browning of Subcutaneous Adipose Tissue via Promoting M2 Macrophage Proliferation

Adiponectin is an abundant adipokine with pleiotropic protective effects against a cluster of obesity-related cardiometabolic disorders. However, its role in adaptive thermogenesis has scarcely been explored. Here we showed that chronic cold exposure led to a markedly elevated production of adiponectin in adipocytes of subcutaneous white adipose tissue (scWAT), which in turn bound to M2 macrophages in the stromal vascular fraction. Chronic cold exposure-induced accumulation of M2 macrophages, activation of beige cells, and thermogenic program were markedly impaired in scWAT of adiponectin knockout (ADN KO) mice, whereas these impairments were reversed by replenishment with adiponectin. Mechanistically, adiponectin was recruited to the cell surface of M2 macrophages via its binding partner T-cadherin and promoted the cell proliferation by activation of Akt, consequently leading to beige cell activation. These findings uncover adiponectin as a key efferent signal for cold-induced adaptive thermogenesis by mediating the crosstalk between adipocytes and M2 macrophages in scWAT.

Metformin promotes irisin release from murine skeletal muscle independently of AMP-activated protein kinase activation

AIM

Irisin, a novel myocyte-secreted hormone mediating beneficial effects of exercise on metabolism, is supposed to be an ideal therapeutic target for metabolic disorders such as obesity and diabetes. Here, we investigated the potential effects of metformin and glibenclamide, two antidiabetic medicines, on irisin release in mouse.

METHODS

Wild-type and diabetic obese db/db mice were administrated with metformin and glibenclamide for 2 weeks, and cultured C2C12 myotubes were treated by metformin. Expression of irisin precursor FNDC5 was measured and blood irisin concentration was detected. AMP-activated protein kinase (AMPK) was blocked by chemical inhibitor compound C or knocking down with specific siRNA.

RESULTS

The mRNA and protein expression of FNDC5 in skeletal muscle and blood irisin concentrations were lower in diabetic db/db mice than those in wild-type mice. Metformin and glibenclamide decreased blood glucose in db/db mice. Metformin, but not glibenclamide, increased intramuscular FNDC5 mRNA/protein expression and blood irisin levels. Additionally, the reductions of blood glucose and body weight in metformin-treated db/db mice were positively associated with blood irisin concentrations. In C2C12 myotubes, metformin upregulated intracellular FDNC5 mRNA/protein expression and promoted irisin release. Although metformin activated AMPK signalling in skeletal muscle cells, disrupting of AMPK signalling by chemical inhibitor or siRNA-mediated knockdown did not abolish the promoting effect of metformin on irisin release.

CONCLUSION

Metformin promotes irisin release from murine skeletal muscle into blood, independently of AMPK pathway activation. Our results suggest that stimulation of irisin may be a novel molecular mechanism of metformin which is widely used for treatment of metabolic disorders.

Cardiovascular safety of sulfonylureas: a meta-analysis of randomized clinical trials

AIM

Cardiovascular safety of sulfonylurea has been questioned by some authors. This article aims at collecting all available data on this issue from randomized trials.

METHODS

A meta-analysis was performed including all trials with a duration of at least 6 months, comparing a sulfonylurea with a non-sulfonylurea agent in type 2 diabetes. Major cardiovascular events (MACE) and mortality were retrieved and combined to calculate Mantel-Haenzel odds ratio (MH-OR).

RESULTS

Of the 115 selected trials, 62 reported information on MACE, and 30 reported at least one event. MH-OR for sulfonylurea was 1.08 [0.86-1.36], p = 0.52 (1.85 [1.20-2.87], p = 0.005, in the five trials vs. DPP4 inhibitors, no significant differences vs. other comparators). The MH-OR for myocardial infarction and stroke was 0.88 [0.75-1.04], p = 0.13 and 1.28 [1.03-1.60], p = 0.026, respectively. Mortality was significantly increased with sulfonylureas (MH-OR: 1.22 [1.01-1.49], p = 0.047).

CONCLUSIONS

In type 2 diabetes, the use of sulfonylureas is associated with increased mortality and a higher risk of stroke, whereas the overall incidence of MACE appears to be unaffected. Significant differences in cardiovascular risk could be present in direct comparisons with specific classes of glucose-lowering agents, such as DPP4 inhibitors, but this hypothesis needs to be confirmed in long-term cardiovascular outcomes trials. The results of this meta-analysis need to be interpreted with caution, mainly because of limitations in trial quality and under-reporting of information on cardiovascular events and mortality. However, the cardiovascular safety of sulfonylureas cannot be considered established unless it is evaluated in long-term cardiovascular outcomes trials.

Obesity as the common soil of non-alcoholic fatty liver disease and diabetes: Role of adipokines

Non‐alcoholic fatty liver disease (NAFLD) describes a spectrum of liver conditions from simple steatosis, steatohepatitis to end‐stage liver disease. The prevalence of NAFLD has been on the rise in many parts of the world, including Asia, and NAFLD is now the liver disease associated with the highest mortality, consequent to the increased risk of cardiovascular diseases and hepatocellular carcinoma. Whereas NAFLD is an independent risk factor for type 2 diabetes, increased hepatic and peripheral insulin resistance contribute to the pathogenesis of both NAFLD and diabetes, which are associated with enhanced cardiovascular risk. Studies in humans and animal models have suggested obesity as the common link of these two diseases, likely mediated by adipose tissue inflammation and dysregulated adipokine production in obesity. In the present review, we discuss recent advances in our understanding of the role of several novel adipokines (adiponectin, adipocyte fatty acid binding protein and fibroblast growth factor‐21) in the pathophysiology of NAFLD and diabetes, as well as their use as potential biomarkers and therapeutic targets for dysglycemia in NAFLD patients.

Peroxisome Proliferator-Activated Receptor-γ Ligands Alter Breast Cancer Cell Motility through Modulation of the Plasminogen Activator System

We investigated peroxisome proliferator-activated receptor-γ (PPAR-γ) ligands effect on cell motility and the plasminogen activator system using normal MCF-10A and malignant MCF-10CA1 cell lines. Ciglitazone reduced both wound-induced migration and chemotaxis. However, the effect was not reversed with pretreatment of cells with the PPAR-γ-specific antagonist GW9662. Immunoblot analysis of conditioned media showed ciglitazone decreased plasminogen activator inhibitor-1 (PAI-1) in both cell lines; this effect was also unaltered by PPAR-γ antagonism. Alternatively, treatment with the ω-6 fatty acid arachidonic acid (ArA), but not the ω-3 fatty acid docosahexanoic acid, increased both MCF-10A cell migration and cell surface uPA activity. Pretreatment with a PPAR-γ antagonist reversed these effects, suggesting that ArA mediates its effect on cell motility and uPA activity through PPAR-γ activation. Collectively, the data suggest PPAR-γ ligands have a differential effect on normal and malignant cell migration and the plasminogen activation system, resulting from PPAR-γ-dependent and PPAR-γ-independent effects.

N-acetylcysteine and allopurinol synergistically enhance cardiac adiponectin content and reduce myocardial reperfusion injury in diabetic rats

Background

Hyperglycemia-induced oxidative stress plays a central role in the development of diabetic myocardial complications. Adiponectin (APN), an adipokine with anti-diabetic and anti-ischemic effects, is decreased in diabetes. It is unknown whether or not antioxidant treatment with N-acetylcysteine (NAC) and/or allopurinol (ALP) can attenuate APN deficiency and myocardial ischemia reperfusion (MI/R) injury in the early stage of diabetes.

Methodology/Principal Findings

Control or streptozotocin (STZ)-induced diabetic rats were either untreated (C, D) or treated with NAC (1.5 g/kg/day) or ALP (100 mg/kg/day) or their combination for four weeks starting one week after STZ injection. Plasma and cardiac biochemical parameters were measured after the completion of treatment, and the rats were subjected to MI/R by occluding the left anterior descending artery for 30 min followed by 2 h reperfusion. Plasma and cardiac APN levels were decreased in diabetic rats accompanied by decreased cardiac APN receptor 2 (AdipoR2), reduced phosphorylation of Akt, signal transducer and activator of transcription 3 (STAT3) and endothelial nitric oxide synthase (eNOS) but increased IL-6 and TNF-α (all P<0.05 vs. C). NAC but not ALP increased cardiac APN concentrations and AdipoR2 expression in diabetic rats. ALP enhanced the effects of NAC in restoring cardiac AdipoR2 and phosphorylation of Akt, STAT3 and eNOS in diabetic rats. Further, NAC and ALP, respectively, decreased postischemic myocardial infarct size and creatinine kinase-MB (CK-MB) release in diabetic rats, while their combination conferred synergistic protective effects. In addition, exposure of cultured rat cardiomyocytes to high glucose resulted in significant reduction of cardiomyocyte APN concentration and AdipoR2 protein expression. APN supplementation restored high glucose induced AdipoR2 reduction in cardiomyocytes.

Conclusions/Significance

NAC and ALP synergistically restore myocardial APN and AdipoR2 mediated eNOS activation. This may represent the mechanism through which NAC and ALP combination greatly reduces MI/R injury in early diabetic rats.

Metabolic nuclear receptor signaling and the inflammatory acute phase response

The acute phase response (APR) classically refers to the rapid reprogramming of gene expression and metabolism in response to inflammatory cytokine signaling. As components of the innate immune system, hepatocyte-derived acute phase proteins (APPs) play a central role in restoring tissue homeostasis. Recently, an intriguing 'metaflammatory' facet of the APR became evident with chronically elevated APP levels being connected to metabolic syndrome disorders. The causality of these connections is unclear but could relate to adverse metabolic and inflammatory disturbances, particularly those affecting lipoprotein properties, cholesterol metabolism and atherogenesis. Here we review these aspects with an emphasis on the emerging importance of lipid-sensing nuclear receptors (LXRs, LRH-1, PPARs), in conjunction with anti-inflammatory transrepression pathways, as physiological and pharmacological relevant modulators of the APR.

Adiponectin is required for PPARγ-mediated improvement of endothelial function in diabetic mice

Rosiglitazone is a PPARγ agonist commonly used to treat diabetes. In addition to improving insulin sensitivity, rosiglitazone restores normal vascular function by a mechanism that remains poorly understood. Here we show that adiponectin is required to mediate the PPARγ effect on vascular endothelium of diabetic mice. In db/db and diet-induced obese mice, PPARγ activation by rosiglitazone restores endothelium-dependent relaxation of aortae, whereas diabetic mice lacking adiponectin or treated with an anti-adiponectin antibody do not respond. Rosiglitazone stimulates adiponectin release from fat explants, and subcutaneous fat transplantation from rosiglitazone-treated mice recapitulates vasodilatation in untreated db/db recipients. Mechanistically, adiponectin activates AMPK/eNOS and cAMP/PKA signaling pathways in aortae, which increase NO bioavailability and reduce oxidative stress. Taken together, these results demonstrate that adipocyte-derived adiponectin is required for PPARγ-mediated improvement of endothelial function in diabetes. Thus, the adipose tissue represents a promising target for treating diabetic vasculopathy.

Pharmacological and non-pharmacological interventions to influence adipose tissue function

Obesity is associated with metabolic derangements such as insulin resistance, inflammation and hypercoagulobility which can all be understood as consequences of adipose tissue dysfunction. The potential role for adipose tissue derived cytokines and adipokines in the development of vascular disease and diabetes may produce a clinical need to influence adipose tissue function. Various pharmacological and non-pharmacological interventions affect plasma cytokine and adipokine levels. The effects of these interventions depend on weight loss per se, changes in fat distribution without weight loss and/or direct effects on adipose tissue inflammation.

Weight loss, as a result of diet, pharmacology and surgery, positively influences plasma adipokines and systemic inflammation. Several classes of drugs influence systemic inflammation directly through their anti-inflammatory actions. PPAR-γ agonism positively influences adipose tissue inflammation in several classes of intervention such as the thiazolidinediones and perhaps salicylates, CB1-antagonists and angiotensin II receptor blockers. Furthermore, within drug classes there are differential effects of individual pharmacologic agents on adipose tissue function.

It can be concluded that several commonly used pharmacological and non-pharmacological interventions have unintended influences on adipose tissue function. Improving adipose tissue function may contribute to reducing the risk of vascular diseases and the development of type 2 diabetes.

eNOS plays a major role in adiponectin synthesis in adipocytes

Nitric oxide (NO) stimulates mitochondrial biogenesis. We recently reported that adiponectin synthesis is regulated by mitochondrial function in adipocytes. This study was undertaken to test the hypothesis that endothelial NO synthase (eNOS) plays an important role in adiponectin synthesis by producing NO and enhancing mitochondrial function in adipocytes. We examined the effects of eNOS knockdown on adiponectin synthesis in 3T3-L1 adipocytes and also examined plasma adiponectin levels and the mitochondria in adipose tissue of eNOS knockout (eNOS(-/-)) mice with and without chronic administration of a NO donor. In cultured 3T3-L1 adipocytes, eNOS siRNA decreased rosiglitazone-induced adiponectin secretion, which was associated with decreases in mitochondrial proteins and biogenesis factors. Plasma adiponectin concentrations were reduced in adult eNOS(-/-) mice compared with age-matched wild-type mice. Mitochondrial contents in adipose tissue were reduced in eNOS(-/-) mice, and this was associated with decreased expression of mitochondrial biogenesis factors, increased levels of 8-hydroxyguanosine, a biomarker of oxidative stress, and morphological abnormalities in mitochondria. Rosiglitazone-induced increases in adiponectin expression and mitochondrial content were also reduced significantly in eNOS(-/-) mice. Chronic administration of a NO donor reversed mitochondrial abnormalities and increased adiponectin expression in adipose tissue of eNOS(-/-) mice. eNOS plays an important role in adiponectin synthesis in adipocytes by increasing mitochondrial biogenesis and enhancing mitochondrial function.

Adiponectin: an indispensable molecule in rosiglitazone cardioprotection following myocardial infarction

RATIONALE

Patients treated with peroxisome proliferator-activated receptor (PPAR)-gamma agonist manifest favorable metabolic profiles associated with increased plasma adiponectin (APN). However, whether increased APN production as a result of PPAR-gamma agonist treatment is an epiphenomenon or is causatively related to the cardioprotective actions of PPAR-gamma remains unknown.

OBJECTIVE

To determine the role of APN in rosiglitazone (RSG) cardioprotection against ischemic heart injury.

METHODS AND RESULTS

Adult male wild-type (WT) and APN knockdown/knockout (APN(+ or -) and APN(- or -)) mice were treated with vehicle or RSG (20 mg/kg per day), and subjected to coronary artery ligation 3 days after beginning treatment. In WT mice, RSG (7 days) significantly increased adipocyte APN expression, elevated plasma APN levels (2.6-fold), reduced infarct size (17% reduction), decreased apoptosis (0.23 + or - 0.02% versus 0.47 + or - 0.04% TUNEL-positive in remote nonischemic area), attenuated oxidative stress (48.5% reduction), and improved cardiac function (P<0.01). RSG-induced APN production and cardioprotection were significantly blunted (P<0.05 versus WT) in APN(+ or -), and completely lost in APN(- or -) (P>0.05 versus vehicle-treated APN(- or -) mice). Moreover, treatment with RSG for up to 14 days significantly improved the postischemic survival rate of WT mice (P<0.05 versus vehicle group) but not APN knockdown/knockout mice.

CONCLUSIONS

The cardioprotective effects of PPAR-gamma agonists are critically dependent on its APN stimulatory action, suggesting that under pathological conditions where APN expression is impaired (such as advanced type 2 diabetes), the harmful cardiovascular effects of PPAR-gamma agonists may outweigh its cardioprotective benefits.

Cytokine and cytokine-like inflammation markers, endothelial dysfunction, and imbalanced coagulation in development of diabetes and its complications

CONTEXT

Recent developments indicate that pathophysiological mechanisms leading to beta-cell damage, insulin resistance, and the vascular complications of diabetes include an activation of the inflammation cascade, endothelial dysfunction, and procoagulant imbalance. Their circulating biomarkers may therefore provide opportunities for early diagnosis and targets for novel treatments.

EVIDENCE

Circulating biomarkers of these pathways such as TNFalpha, IL-6, C-reactive protein (CRP) (inflammation), vascular cellular adhesion molecule-1, interstitial cellular adhesion molecule-1, E-selectin, von Willebrand factor (endothelial dysfunction), plasminogen activator inhibitor-1, fibrinogen, P-selectin (procoagulant state), and adiponectin (antiinflammation) may be associated with development of both type 1 and type 2 diabetes and some studies, particularly in type 2 diabetes, have demonstrated that certain biomarkers may have independent predictive value. Similarly studies have shown that these biomarkers may be associated with development of diabetic nephropathy and retinopathy, and again, particularly in type 2 diabetes, with cardiovascular events as well. Finally, the comorbidities of diabetes, namely obesity, insulin resistance, hyperglycemia, hypertension and dyslipidemia collectively aggravate these processes while antihyperglycemic interventions tend to ameliorate them.

CONCLUSIONS

Increased CRP, IL-6, and TNFalpha, and especially interstitial cellular adhesion molecule-1, vascular cellular adhesion molecule-1, and E-selectin are associated with nephropathy, retinopathy, and cardiovascular disease in both type 1 and type 2 diabetes. Whereas further work is needed, it seems clear that these biomarkers are predictors of increasing morbidity in prediabetic and diabetic subjects and should be the focus of work testing their clinical utility to identify high-risk individuals as well as perhaps to target interventions.

Obesity and breast cancer: the roles of peroxisome proliferator-activated receptor-γ and plasminogen activator inhibitor-1

Breast cancer is the most prominent cancer among females in the United States. There are a number of risk factors associated with development of breast cancer, including consumption of a high-fat diet and obesity. Plasminogen activator inhibitor-1 (PAI-1) is a cytokine upregulated in obesity whose expression is correlated with a poor prognosis in breast cancer. As a key mediator of adipogenesis and regulator of adipokine production, peroxisome proliferator-activated receptor-γ (PPAR-γ) is involved in PAI-1 expression from adipose tissue. We summarize the current knowledge linking PPAR-γ and PAI-1 expression to high-fat diet and obesity in the risk of breast cancer.

The role of plasminogen activator inhibitor 1 in renal and cardiovascular diseases

The 50 kDa glycoprotein plasminogen activator inhibitor 1 (PAI-1) is the major physiological inhibitor of tissue-type and urokinase-type plasminogen activator. These two molecules convert inactive plasminogen into its fibrin-degrading form, plasmin. Plasma and tissue concentrations of PAI-1 are extremely low under normal circumstances but increase under pathologic conditions. This increase is mediated by many factors, including reactive oxygen species. Increased PAI-1 activity is associated with an increased risk of ischemic cardiovascular events and tissue fibrosis. Whereas the antifibrinolytic property of PAI-1 derives mainly from its inhibition of serine proteases, its profibrotic actions seem to derive from a capacity to stimulate interstitial macrophage recruitment and increase transcription of profibrotic genes, as well as from inhibition of serine proteases. Despite studies in mice that lack or overexpress PAI-1, the biological effects of this molecule in humans remain incompletely understood because of the complexity of the PAI-1-plasminogen-activator-plasmin system. The cardioprotective and renoprotective properties of some currently available drugs might be attributable in part to inhibition of PAI-1. The development of an orally active, high-affinity PAI-1 inhibitor will provide a potentially important pharmacological tool for further investigation of the role of PAI-1 and might offer a novel therapeutic strategy in renal and cardiovascular diseases.

PPARgamma and its ligands: therapeutic implications in cardiovascular disease

The relevance of PPARgamma (peroxisome-proliferator-activated receptor gamma) as an important therapeutic target for the treatment of diabetes arises from its hypoglycaemic effects in diabetic patients and also from the critical role in the regulation of cardiovascular functions. From a clinical perspective, differences between current FDA (Food and Drug Administration)-approved PPARgamma drugs have been observed in terms of atherosclerosis and cardiac and stroke events. The adverse effects of PPARgamma-specific treatments that hamper their cardiovascular protective roles, affirm the strong need to evaluate the efficacy of the current drugs. Therefore active research is directed towards high-throughput screening and pharmacological testing of a plethora of newly identified natural or synthetic compounds. In the present review we describe the rationale behind drug design strategies targeting PPARgamma, based on current knowledge regarding the effects of such drugs in experimental animal models, as well as in clinical practice. Regarding endogenous PPARgamma ligands, several fatty acid derivatives bind PPARgamma with different affinities, although the physiological relevance of these interactions is not always evident. Recently, NO-derived unsaturated fatty acids were found to be potent agonists of PPARs, with preferential affinity for PPARgamma, compared with oxidized fatty acid derivatives. Nitroalkenes exert important bioactivities of relevance for the cardiovascular system including anti-inflammatory and antiplatelet actions, and are important mediators of vascular tone. A new generation of insulin sensitizers with PPARgamma function for the treatment of diabetes may serve to limit patients from the increased cardiovascular burden of this disease.

Circulating levels of adipocyte and epidermal fatty acid-binding proteins in relation to nephropathy staging and macrovascular complications in type 2 diabetic patients

OBJECTIVE

To investigate the relationships of serum adipocyte fatty acid-binding protein (A-FABP) and epidermal fatty acid-binding protein (E-FABP) with renal dysfunction and macrovascular complications in type 2 diabetic patients.

RESEARCH DESIGN AND METHODS

The associations of serum A-FABP and E-FABP with markers of renal function, nephropathy staging, and macrovascular complications were examined in 237 type 2 diabetic patients.

RESULTS

Serum A-FABP and E-FABP correlated significantly with serum creatinine, mean albumin excretion rate, and glomerular filtration rate (all P < 0.001) and were independently associated with diabetic nephropathy staging (P = 0.001 and P < 0.05, respectively). Circulating levels of both types of FABP were increased (P < 0.01) in subjects with macrovascular complications. Serum A-FABP was independently associated with macrovascular complications (odds ratio 2.92 [95% CI 1.42-6.01]; P = 0.004).

CONCLUSIONS

Serum A-FABP and E-FABP might be novel serum biomarkers for evaluating the progression of nephropathy and its cardiovascular risk in type 2 diabetic patients.

Mitochondrial dysfunction contributes to the increased vulnerabilities of adiponectin knockout mice to liver injury

Adiponectin is an adipocyte-derived hormone with a wide range of beneficial effects on obesity-related medical complications. Numerous epidemiological investigations in diverse ethnic groups have identified a lower adiponectin level as an independent risk factor for nonalcoholic fatty liver diseases and liver dysfunctions. Animal studies have demonstrated that replenishment of adiponectin protects against various forms of hepatic injuries, suggesting it to be a potential drug candidate for the treatment of liver diseases. This study was designed to investigate the cellular and molecular mechanisms underlying the hepatoprotective effects of adiponectin. Our results demonstrated that in adiponectin knockout (ADN-KO) mice, there was a preexisting condition of hepatic steatosis and mitochondrial dysfunction that might contribute to the increased vulnerabilities of these mice to secondary liver injuries induced by obesity and other conditions. Adenovirus-mediated replenishment of adiponectin depleted lipid accumulation, restored the oxidative activities of mitochondrial respiratory chain (MRC) complexes, and prevented the accumulation of lipid peroxidation products in ADN-KO mice but had no obvious effects on mitochondrial biogenesis. The gene and protein levels of uncoupling protein 2 (UCP2), a mitochondrial membrane transporter, were decreased in ADN-KO mice and could be significantly up-regulated by adiponectin treatment. Moreover, the effects of adiponectin on mitochondrial activities and on protection against endotoxin-induced liver injuries were significantly attenuated in UCP2 knockout mice.

CONCLUSION

These results suggest that the hepatoprotective properties of adiponectin are mediated at least in part by an enhancement of the activities of MRC complexes through a mechanism involving UCP2.

Adipose tissue and the metabolic syndrome: focusing on adiponectin and several novel adipokines

The metabolic syndrome represents a cluster of metabolic risk factors that predispose an individual to an increased risk for Type 2 diabetes, cardiovascular diseases and their associated morbidity and mortality. Visceral obesity is thought to be a major culprit. Adipokines secreted from the adipose tissue are now believed to be key factors mediating the metabolic and inflammatory effects of obesity. In this review, we shall examine the evidence suggesting that several novel adipokines, adiponectin, adipocyte fatty acid-binding protein, retinol-binding protein-4 and lipocalin-2, may hold promise as important clinical biomarkers to identify individuals at risk for the metabolic syndrome and related comorbidities.

Effects of peroxisome proliferator-activated receptor-gamma activation with pioglitazone on plasma adipokines in nondiabetic patients with either hypercholesterolemia or hypertension

Adipokines are substances produced by the adipose tissue that may play significant roles in the mechanisms contributing to the development of atherosclerosis. Thiazolidinediones have been shown to improve endothelium-dependent vasodilation and to exert multiple antiatherosclerotic effects. This study tested the hypotheses that nondiabetic patients with cardiovascular risk factors have altered levels of adipokines that can be modified by pioglitazone treatment. Eighty patients with hypertension or hypercholesterolemia were in a double-blinded, placebo-controlled, crossover study. In each treatment phase, patients received pioglitazone 45 mg/day or placebo for 8 weeks. Endothelial function studies and biochemical assays were performed at the end of each 8-week treatment period. Twenty-two normal volunteers, matched with patients for age, gender, and body mass index, were recruited as a control group. Compared with controls, placebo-treated patients had lower adiponectin levels (11,160 +/- 763 vs 6,078 +/- 385 ng/ml, p <0.001) and similar plasma leptin levels (21.5 +/- 3.8 vs 16.2 +/- 1.5 ng/ml, p = 0.128) and resistin levels (5.1 +/- 0.4 vs 4.4 +/- 0.2 ng/ml, p = 0.250). In patients, pioglitazone treatment markedly increased adiponectin (+121%, p <0.001) and decreased resistin (-10.5%, p = 0.03). Leptin was not significantly decreased (-7.1%, p = 0.10). In multivariate analysis, pioglitazone-induced changes in endothelial reactivity to acetylcholine were the only significant predictor of increases in adiponectin. In conclusion, in nondiabetic patients with major cardiovascular risk factors, pioglitazone treatment beneficially influences circulating adipokine levels. The relation between the increase in adiponectin levels and the improvement in endothelial vasodilator activity suggests a mechanistic link between vascular effects and adiponectinemia.

Post-translational modifications of adiponectin: mechanisms and functional implications

Adiponectin is an insulin-sensitizing adipokine with anti-diabetic, anti-atherogenic, anti-inflammatory and cardioprotective properties. This adipokine is secreted from adipocytes into the circulation as three oligomeric isoforms, including trimeric, hexameric and the HMW (high-molecular-mass) oligomeric complex consisting of at least 18 protomers. Each oligomeric isoform of adiponectin exerts distinct biological properties in its various target tissues. The HMW oligomer is the major active form mediating the insulin-sensitizing effects of adiponectin, whereas the central actions of this adipokine are attributed primarily to the hexameric and trimeric oligomers. In patients with Type 2 diabetes and coronary heart disease, circulating levels of HMW adiponectin are selectively decreased due to an impaired secretion of this oligomer from adipocytes. The biosynthesis of the adiponectin oligomers is a complex process involving extensive post-translational modifications. Hydroxylation and glycosylation of several conserved lysine residues in the collagenous domain of adiponectin are necessary for the intracellular assembly and stabilization of its high-order oligomeric structures. Secretion of the adiponectin oligomers is tightly controlled by a pair of molecular chaperones in the ER (endoplasmic reticulum), including ERp44 (ER protein of 44 kDa) and Ero1-Lalpha (ER oxidoreductase 1-Lalpha). ERp44 inhibits the secretion of adiponectin oligomers through a thiol-mediated retention. In contrast, Ero1-Lalpha releases HMW adiponectin trapped by ERp44. The PPARgamma (peroxisome-proliferator-activated receptor gamma) agonists thiazolidinediones selectively enhance the secretion of HMW adiponectin through up-regulation of Ero1-Lalpha. In the present review, we discuss the recent advances in our understanding of the structural and biological properties of the adiponectin oligomeric isoforms and highlight the role of post-translational modifications in regulating the biosynthesis of HMW adiponectin.

Interleukin-18 suppresses adiponectin expression in 3T3-L1 adipocytes via a novel signal transduction pathway involving ERK1/2-dependent NFATc4 phosphorylation

An inverse correlation between the pro-inflammatory cytokine interleukin-18 and the anti-atherogenic adipokine adiponectin has been reported in the chronic pathological conditions obesity, insulin resistance, coronary artery disease, and metabolic syndrome. We investigated whether this relationship is coincidental or has a causal basis. Here we show that interleukin-18 (IL-18) suppresses adiponectin transcription, mRNA expression, and secretion by 3T3-L1 adipocytes. IL-18 suppresses adiponectin promoter-reporter activity, an effect reversed by deletion or mutation of the NFATc4 core DNA-binding site. IL-18 induces NFATc4 phosphorylation (Ser(676)), nuclear translocation, and in vivo DNA binding. IL-18 induces ERK1/2 phosphorylation and enzyme activity, and pretreatment with the MEK inhibitor U0126, ERK1/2 inhibitor PD98059, or small interference RNA targeted to ERK1/2 attenuates ERK1/2 activation and NFATc4 phosphorylation. Finally, inhibition of ERK1/2 or NFATc4 knockdown reverses IL-18-mediated adiponectin suppression. In contrast to its inhibitory effects on adiponectin expression, IL-18 potently stimulates PAI-1 secretion. These data demonstrate for the first time that IL-18 selectively suppresses adiponectin expression via ERK1/2-dependent NFATc4 activation and suggest that the inverse relationship observed between IL-18 and adiponectin in various chronic pathological conditions is causally related. Thus, targeting IL-18 expression may enhance adiponectin expression and mitigate disease progression.