Inflammatory biomarkers associated with obesity and insulin resistance: a focus on lipocalin-2 and adipocyte fatty acid-binding protein

Ruminant Trans Fatty Acid Intake Modulates Inflammation Pathways in the Adipose Tissue Transcriptome of C57BL/6 Mice

SCOPE

The study aims to analyze transcriptomic profiles in adipose tissues postconsumption of elaidic acid (EA; trans-18:1n-9) and trans-palmitoleic acid (TPA; trans-16:1n-7), elucidating their different effects on inflammation and glucose metabolism.

METHODS AND RESULTS

Twenty C57BL/6 mice are divided into four groups. Each group receives one of the following formulations in drinking water: lecithin nanovesicles, nanovesicles containing either lecithin with EA or TPA (86:14 w/w), or water (control) for 28 days with a regular fat diet (18% calories from fat). Total RNA is extracted, and paired-end sequencing is performed. TPA intake alters the expression of 351 genes compared to EA intake, including 11 downregulated and 340 upregulated genes (fold change [FC] >1.5, p < 0.05). TPA compares to EA upregulated: Slc5a8, Lcn2, Csf3, Scube1, Mapk13, Bdkrb2, Ctla2a, Slc2a1, Oas3, Cx3cl1, Oas2, Nlrp6, Pycard, Cyba, Ddr1, and Prkab1 and downregulated Fas gene. These genes are related to the NOD-like receptor, lipid and atherosclerosis, IL-17 signaling, TNF, nonalcoholic fatty liver disease, cytokine-cytokine receptor interaction, adipocytokine, glucagon, insulin resistance, and inflammatory mediator regulation of TRP channels signaling.

CONCLUSION

TPA intake has a distinct impact on the regulation of inflammation and diabetes-related pathways in adipose tissue compared to EA.

Physiological Changes and Pathological Pain Associated with Sedentary Lifestyle-Induced Body Systems Fat Accumulation and Their Modulation by Physical Exercise

A sedentary lifestyle is associated with overweight/obesity, which involves excessive fat body accumulation, triggering structural and functional changes in tissues, organs, and body systems. Research shows that this fat accumulation is responsible for several comorbidities, including cardiovascular, gastrointestinal, and metabolic dysfunctions, as well as pathological pain behaviors. These health concerns are related to the crosstalk between adipose tissue and body systems, leading to pathophysiological changes to the latter. To deal with these health issues, it has been suggested that physical exercise may reverse part of these obesity-related pathologies by modulating the cross talk between the adipose tissue and body systems. In this context, this review was carried out to provide knowledge about (i) the structural and functional changes in tissues, organs, and body systems from accumulation of fat in obesity, emphasizing the crosstalk between fat and body tissues; (ii) the crosstalk between fat and body tissues triggering pain; and (iii) the effects of physical exercise on body tissues and organs in obese and non-obese subjects, and their impact on pathological pain. This information may help one to better understand this crosstalk and the factors involved, and it could be useful in designing more specific training interventions (according to the nature of the comorbidity).

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.

Adipose Tissue-Derived Signatures for Obesity and Type 2 Diabetes: Adipokines, Batokines and MicroRNAs

: Obesity is one of the main risk factors for type 2 diabetes mellitus (T2DM). It is closely related to metabolic disturbances in the adipose tissue that primarily functions as a fat reservoir. For this reason, adipose tissue is considered as the primary site for initiation and aggravation of obesity and T2DM. As a key endocrine organ, the adipose tissue communicates with other organs, such as the brain, liver, muscle, and pancreas, for the maintenance of energy homeostasis. Two different types of adipose tissues-the white adipose tissue (WAT) and brown adipose tissue (BAT)-secrete bioactive peptides and proteins, known as "adipokines" and "batokines," respectively. Some of them have beneficial anti-inflammatory effects, while others have harmful inflammatory effects. Recently, "exosomal microRNAs (miRNAs)" were identified as novel adipokines, as adipose tissue-derived exosomal miRNAs can affect other organs. In the present review, we discuss the role of adipose-derived secretory factors-adipokines, batokines, and exosomal miRNA-in obesity and T2DM. It will provide new insights into the pathophysiological mechanisms involved in disturbances of adipose-derived factors and will support the development of adipose-derived factors as potential therapeutic targets for obesity and T2DM.

Circulating adipocyte fatty acid-binding protein levels predict the development of subclinical atherosclerosis in type 2 diabetes

OBJECTIVE

The aim of this study was to investigate the prospective association of circulating adipocyte fatty acid-binding protein (A-FABP) levels with the development of subclinical atherosclerosis in patients with type 2 diabetes in an 8-year prospective study.

METHODS

A total of 170 patients with newly diagnosed type 2 diabetes were recruited in the study and 133 patients completed the follow-up of 8 years. Baseline plasma A-FABP levels were measured with enzyme-linked immunosorbent assays. The role of A-FABP in predicting the development of subclinical atherosclerosis over 8 years was analyzed using multiple logistic regression.

RESULTS

Of the 133 patients without subclinical atherosclerosis at baseline, a total of 100 had progressed to subclinical atherosclerosis over 8 years. Baseline A-FABP level was significantly higher in patients who had progressed to subclinical atherosclerosis at year 8 compared with ones who had not developed subclinical atherosclerosis after adjustment for sex (15.3 [12.1-23.2] versus 13.3 [10.0-18.9] ng/ml, P = 0.021). High baseline A-FABP level was an independent predictor for the development of subclinical atherosclerosis in patients with type 2 diabetes (odds ratio: 16.24, P = 0.022).

CONCLUSIONS

Circulating A-FABP levels predict the development of subclinical atherosclerosis in type 2 diabetes patients.

Peroxisome proliferator-activated receptors as therapeutic targets for heart failure

Heart failure (HF) is a common clinical syndrome that affects more than 23 million individuals worldwide. Despite the marked advances in its management, the mortality rates in HF patients have remained unacceptably high. Peroxisome proliferator-activated receptors (PPARs) are nuclear transcription regulators, involved in the regulation of fatty acid and glucose metabolism. PPAR agonists are currently used for the treatment of type II diabetes mellitus and hyperlipidemia; however, their role as therapeutic agents for HF remains under investigation. Preclinical studies have shown that pharmacological modulation of PPARs can upregulate the expression of fatty acid oxidation genes in cardiomyocytes. Moreover, PPAR agonists were proven able to improve ventricular contractility and reduce cardiac remodelling in animal models through their anti-inflammatory, anti-oxidant, anti-fibrotic, and anti-apoptotic activities. Whether these effects can be replicated in humans is yet to be proven. This article reviews the interactions of PPARs with the pathophysiological mechanisms of HF and how the pharmacological modulation of these receptors can be of benefit for HF patients.

Adipokines: Potential Therapeutic Targets for Vascular Dysfunction in Type II Diabetes Mellitus and Obesity

Adipokines are bioactive molecules that regulate several physiological functions such as energy balance, insulin sensitization, appetite regulation, inflammatory response, and vascular homeostasis. They include proinflammatory cytokines such as adipocyte fatty acid binding protein (A-FABP) and anti-inflammatory cytokines such as adiponectin, as well as vasodilator and vasoconstrictor molecules. In obesity and type II diabetes mellitus (DM), insulin resistance causes impairment of the endocrine function of the perivascular adipose tissue, an imbalance in the secretion of vasoconstrictor and vasodilator molecules, and an increased production of reactive oxygen species. Recent studies have shown that targeting plasma levels of adipokines or the expression of their receptors can increase insulin sensitivity, improve vascular function, and reduce the risk of cardiovascular morbidity and mortality. Several reviews have discussed the potential of adipokines as therapeutic targets for type II DM and obesity; however, this review is the first to focus on their therapeutic potential for vascular dysfunction in type II DM and obesity.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Adipose inflammation at the heart of vascular disease

Visceral adipose tissue is a primary site of chronic inflammation in obesity and may contribute to systemic inflammation and development of atherosclerotic vascular disease. Few studies identify molecular mechanisms and secretory pathways which mediate this process. In this edition of Clinical Science, Kwok et al. utilize a transgenic mouse in which dominant-negative c-Jun NH2 terminal kinase (dnJNK) expression is restricted to adipose tissue to implicate JNK-driven expression of adipocyte fatty acid binding protein (A-FABP) in visceral adipose tissue as a key secretory pathway to exacerbate development of atherosclerosis in ApoE-/- mice. They further demonstrate that ApoE-/- mice transplanted with visceral adipose tissue in which JNK has been inactivated display less systemic inflammation and develop significantly less atherosclerosis compared with control mice. Together, the findings of the present study reinforce our understanding of visceral adipose tissue as a secretory organ and the importance of the JNK/A-FABP pathway in mediating adipose vascular cross-talk and exacerbation of atherosclerosis.

Mechanism and clinical evidence of lipocalin-2 and adipocyte fatty acid-binding protein linking obesity and atherosclerosis

Obesity is considered to be a chronic inflammatory state in which the dysfunction of adipose tissue plays a central role. The adipokines, which are cytokines secreted by adipose tissue, are key links between obesity and related diseases such as metabolic syndrome and atherosclerosis. LCN2 and A-FABP, both of which are major adipokines predominantly produced in adipose tissue, have recently been shown to be pivotal modulators of vascular function. However, different adipokines modulate the development of atherosclerosis in distinctive manners, which are partly attributable to their unique regulatory mechanisms and functions. This review highlights recent advances in the understanding of the role of two adipokines in mediating chronic inflammation and the pathogenesis of atherosclerosis.

Evaluation of Total Adiponectin, Adipocyte Fatty Acid Binding Protein and Fibroblast Growth Factor 21 Levels in Individuals With Metabolic Syndrome

Although many studies have investigated the relationships of several adipokines to metabolic syndrome (MetS), the interrelationships of adiponectin (ADP), adipocyte fatty acid binding protein (A-FABP) and fibroblast growth factor 21 (FGF 21) have not been described in detail. We examined 209 asymptomatic dyslipidemic patients divided into MetS+ (n=73) and MetS- (n=136) groups. The aim of study was to evaluate the relationships between observed adipokines, to compare the levels of total ADP, A-FABP and FGF 21 in individuals with and without MetS, and to elucidate the relationships of individual adipokines to lipid parameters, markers of insulin resistance and endothelial hemostatic markers in these groups. In MetS+ group, we found the independent positive association ADP with A-FABP (beta=0.4888, p=0.0382), A-FABP with FGF 21 (beta=0.3811, p=0.0002) and von Willebrand factor (beta=0.4502, p=0.0013), and FGF 21 with A-FABP (beta=0.4422, p=0.0002). Our study has confirmed the well-established risk profile of subjects with MetS, although clinically asymptomatic. MetS+ patients had also lower levels of ADP and higher levels of A-FABP and FGF 21. Our study evaluated the interrelationships of ADP, A-FABP and FGF 21 in asymptomatic dyslipidemic subjects with diagnosis of MetS. Especially strong association between A-FABP and FGF 21 needs to be clarified in further studies.

Adiposity and insulin resistance in humans: the role of the different tissue and cellular lipid depots

Human adiposity has long been associated with insulin resistance and increased cardiovascular risk, and abdominal adiposity is considered particularly adverse. Intra-abdominal fat is associated with insulin resistance, possibly mediated by greater lipolytic activity, lower adiponectin levels, resistance to leptin, and increased inflammatory cytokines, although the latter contribution is less clear. Liver lipid is also closely associated with, and likely to be an important contributor to, insulin resistance, but it may also be in part the consequence of the lipogenic pathway of insulin action being up-regulated by hyperinsulinemia and unimpaired signaling. Again, intramyocellular triglyceride is associated with muscle insulin resistance, but anomalies include higher intramyocellular triglyceride in insulin-sensitive athletes and women (vs men). Such issues could be explained if the "culprits" were active lipid moieties such as diacylglycerol and ceramide species, dependent more on lipid metabolism and partitioning than triglyceride amount. Subcutaneous fat, especially gluteofemoral, appears metabolically protective, illustrated by insulin resistance and dyslipidemia in patients with lipodystrophy. However, some studies suggest that deep sc abdominal fat may have adverse properties. Pericardial and perivascular fat relate to atheromatous disease, but not clearly to insulin resistance. There has been recent interest in recognizable brown adipose tissue in adult humans and its possible augmentation by a hormone, irisin, from exercising muscle. Brown adipose tissue is metabolically active, oxidizes fatty acids, and generates heat but, because of its small and variable quantities, its metabolic importance in humans under usual living conditions is still unclear. Further understanding of specific roles of different lipid depots may help new approaches to control obesity and its metabolic sequelae.

Small lipid-binding proteins in regulating endothelial and vascular functions: focusing on adipocyte fatty acid binding protein and lipocalin-2

Dysregulated production of adipokines from adipose tissue plays a critical role in the development of obesity-associated cardiovascular abnormalities. A group of adipokines, including adipocyte fatty acid binding protein (A-FABP) and lipocalin-2, possess specific lipid-binding activity and are up-regulated in obese human subjects and animal models. They act as lipid chaperones to promote lipotoxicity in endothelial cells and cause endothelial dysfunction under obese conditions. However, different small lipid-binding proteins modulate the development of vascular complications in distinctive manners, which are partly attributed to their specialized structural features and functionalities. By focusing on A-FABP and lipocalin-2, this review summarizes recent advances demonstrating the causative roles of these newly identified adipose tissue-derived lipid chaperones in obesity-related endothelial dysfunction and cardiovascular complications. The specific lipid-signalling mechanisms mediated by these two proteins are highlighted to support their specialized functions. In summary, A-FABP and lipocalin-2 represent potential therapeutic targets to design drugs for preventing vascular diseases associated with obesity.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Lipocalin-2 deficiency prevents endothelial dysfunction associated with dietary obesity: role of cytochrome P450 2C inhibition

BACKGROUND AND PURPOSE

Lipocalin-2 is a pro-inflammatory adipokine up-regulated in obese human subjects and animal models. Its circulating levels are positively correlated with the unfavourable lipid profiles, elevated blood pressure and insulin resistance index. Augmented lipocalin-2 has been found in patients with cardiovascular abnormalities.The present study was designed to investigate the role of lipocalin-2 in regulating endothelial function and vascular reactivity.

EXPERIMENTAL APPROACH

Wild-type and lipocalin-2 knockout (Lcn2-KO) mice were fed with either a standard chow or a high-fat diet. Blood pressures and endothelium-dependent relaxations/contractions were monitored at 2 week intervals.

RESULTS

Systolic blood pressure was elevated by high-fat diet in wild-type mice but not in Lcn2-KO mice. Endothelial dysfunction, reflected by the impaired endothelium-dependent relaxations to insulin and augmented endothelium-dependent contractions to ACh, was induced by high-fat diet in wild-type mice. In contrast, Lcn2-KO mice were largely protected from the deterioration of endothelial function caused by dietary challenges. The eNOS dimer/monomer ratio, NO bioavailability, basal and insulin-stimulated PKB/eNOS phosphorylation responses were higher in aortae of Lcn2-KO mice. Administration of lipocalin-2 attenuated endothelium-dependent relaxations to insulin and promoted endothelium-dependent contractions to ACh. It induced eNOS uncoupling and elevated COX expression in the arteries. Treatment with sulphaphenazole, a selective inhibitor of cytochrome P450 2C9, improved endothelial function in wild-type mice and blocked the effects of lipocalin-2 on both endothelium-dependent relaxations to insulin and endothelium-dependent contractions to ACh, as well as eNOS uncoupling.

CONCLUSIONS

Lipocalin-2, by modulating cytochrome P450 2C9 activity, is critically involved in diet-induced endothelial dysfunction.

Adiponectin and adipocyte fatty acid binding protein in the pathogenesis of cardiovascular disease

The heart and blood vessels are surrounded by epicardial and perivascular adipose tissues, respectively, which play important roles in maintaining cardiovascular homeostasis by secreting a number of biologically active molecules, termed "adipokines." Many of these adipokines function as an important component of the 'adipo-cardiovascular axis' mediating the cross talk between adipose tissues, the heart, and the vasculature. On the one hand, most adipokines [including tumor necrosis factor-α, resistin, adipocyte fatty acid binding protein (A-FABP), and lipocalin-2] are proinflammatory and causally associated with endothelial and cardiac dysfunction by their endocrine/paracrine actions. On the other hand, adiponectin is one of the few adipokines that possesses multiple salutary effects on the prevention of cardiovascular disease, because of its pleiotropic actions on the heart and the blood vessels. The discordant production of adipokines in dysfunctional adipose tissue is a key contributor to obesity-related cardiovascular disease. This review provides an update in understanding the roles of adipokines in the pathogenesis of cardiovascular disorders associated with obesity and diabetes and focuses on the two most abundant adipokines, adiponectin and A-FABP. Indeed, data from both animal studies and clinical investigations imply that these two adipokines are prognostic biomarkers for cardiovascular disease and even promising therapeutic targets for its treatment.

Cross-talk between adipose tissue and vasculature: role of adiponectin

Adipose tissue is a highly dynamic endocrine organ, secreting a number of bioactive substances (adipokines) regulating insulin sensitivity, energy metabolism and vascular homeostasis. Dysfunctional adipose tissue is a key mediator that links obesity with insulin resistance, hypertension and cardiovascular disease. Obese adipose tissue is characterized by adipocyte hypertrophy and infiltration of inflammatory macrophages and lymphocytes, leading to the augmented production of pro-inflammatory adipokines and vasoconstrictors that induce endothelial dysfunction and vascular inflammation through their paracrine and endocrine actions. By contrast, the secretion of adiponectin, an adipokine with insulin sensitizing and anti-inflammatory activities, is decreased in obesity and its related pathologies. Emerging evidence suggests that adiponectin is protective against vascular dysfunction induced by obesity and diabetes, through its multiple favourable effects on glucose and lipid metabolism as well as on vascular function. Adiponectin improves insulin sensitivity and metabolic profiles, thus reducing the classical risk factors for cardiovascular disease. Furthermore, adiponectin protects the vasculature through its pleiotropic actions on endothelial cells, endothelial progenitor cells, smooth muscle cells and macrophages. Data from both animal and human investigations demonstrate that adiponectin is an important component of the adipo-vascular axis that mediates the cross-talk between adipose tissue and vasculature. This review highlights recent work on the vascular protective activities of adiponectin and discusses the molecular pathways underlying the vascular actions of this adipokine.

Chronic hepatitis C is associated with peripheral rather than hepatic insulin resistance

BACKGROUND & AIMS

Chronic hepatitis C (CHC) is associated with insulin resistance (IR), liver steatosis (genotype 3), and increased diabetes risk. The site and mechanisms of IR are unclear.

METHODS

We compared cross-sectionally 29 nonobese, normoglycemic males with CHC (genotypes 1 and 3) to 15 adiposity and age-matched controls using a 2-step hyperinsulinemic-euglycemic clamp with [6,6-(2)H(2)] glucose to assess insulin sensitivity in liver and peripheral tissues and (1)H-magnetic resonance spectroscopy to evaluate liver and intramyocellular lipid. Insulin secretion was assessed after intravenous glucose.

RESULTS

Insulin secretion was not impaired in CHC. Peripheral insulin sensitivity was 35% higher in controls vs CHC (P < .001) during high-dose (264.3 +/- 25 [standard error] mU/L) insulin (P < .001); this was negatively associated with viral load (R(2) = .12; P = .05) and subcutaneous fat (R(2) = .41; P < .001). IR was similar in both genotypes despite 3-fold increased hepatic fat in genotype 3 (P < .001). Hepatic glucose production (P = .25) and nonesterified free fatty acid (P = .84) suppression with insulin were not different between CHC and controls inferring no adipocyte IR, and suggesting IR is mainly in muscle. In CHC, intramyocellular lipid was nonsignificantly increased but levels of glucagon (73.8 +/- 3.6 vs 52.8 +/- 3.1 ng/mL; P < .001), soluble tumor necrosis factor receptor 2 (3.1 +/- 0.1 vs 2.3 +/- 0.1 ng/mL; P < .001), and Lipocalin-2 (36.4 +/- 2.9 vs 19.6 +/- 1.6 ng/mL; P < .001) were elevated.

CONCLUSIONS

CHC represents a unique infective/inflammatory model of IR, which is predominantly in muscle, correlates with subcutaneous, not visceral, adiposity, and is independent of liver fat.

Serum zinc-alpha2-glycoprotein correlates with adiposity, triglycerides, and the key components of the metabolic syndrome in Chinese subjects

CONTEXT

Zinc-alpha2-glycoprotein (ZAG) is a 40-kDa circulating glycoprotein secreted from the liver and adipose tissues. Animal studies have demonstrated the role of ZAG as a lipid-mobilizing factor involved in regulating lipid metabolism and adiposity. However, the clinical relevance of these findings remains to be established.

OBJECTIVE

This study aimed to address the relationship of serum ZAG levels with adiposity and cardiometabolic risk factors in humans.

DESIGN AND SETTING

A total of 258 Chinese subjects [aged 55.1 +/- 12.5 yr; 120 males, 138 females; body mass index (BMI), 25.4 +/- 4.1 kg/m(2)] were randomly selected from the population-based Hong Kong Cardiovascular Risk Factor Prevalence Study, based on their BMI. Serum ZAG levels were determined with ELISA. The relationship between serum ZAG levels and cardiometabolic parameters was assessed.

RESULTS

Serum ZAG levels were higher in men (P < 0.001 vs. women). Serum ZAG correlated positively with age, parameters of adiposity (waist circumference and BMI), fasting insulin, insulin resistance indices, serum triglycerides, adipocyte-fatty acid-binding protein, and C-reactive protein, and diastolic blood pressure (all P < 0.005, age- and sex-adjusted), and inversely with high-density lipoprotein-cholesterol levels (P = 0.008, age- and sex-adjusted). It was also elevated progressively with an increasing number of components of the metabolic syndrome (P for trend < 0.001). On multivariate analysis, serum ZAG was independently associated with male sex, the metabolic syndrome (or type 2 diabetes and serum triglycerides), and C-reactive protein (all P <or= 0.002).

CONCLUSIONS

ZAG might be involved in the pathogenesis of obesity-related metabolic disorders in humans and thus warrants further investigation.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, exercise and dietary factors) and down-regulated (e.g. oxidative stress, smoking and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g. diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Major urinary protein-1 increases energy expenditure and improves glucose intolerance through enhancing mitochondrial function in skeletal muscle of diabetic mice

Major urinary protein-1 (MUP-1) is a low molecular weight secreted protein produced predominantly from the liver. Structurally it belongs to the lipocalin family, which carries small hydrophobic ligands such as pheromones. However, the physiological functions of MUP-1 remain poorly understood. Here we provide evidence demonstrating that MUP-1 is an important player in regulating energy expenditure and metabolism in mice. Both microarray and real-time PCR analysis demonstrated that the MUP-1 mRNA abundance in the liver of db/db obese mice was reduced by approximately 30-fold compared with their lean littermates, whereas this change was partially reversed by treatment with the insulin-sensitizing drug rosiglitazone. In both dietary and genetic obese mice, the circulating concentrations of MUP-1 were markedly decreased compared with the lean controls. Chronic elevation of circulating MUP-1 in db/db mice, using an osmotic pump-based protein delivery system, increased energy expenditure and locomotor activity, raised core body temperature, and decreased glucose intolerance as well as insulin resistance. At the molecular level, MUP-1-mediated improvement in metabolic profiles was accompanied by increased expression of genes involved in mitochondrial biogenesis, elevated mitochondrial oxidative capacity, decreased triglyceride accumulation, and enhanced insulin-evoked Akt signaling in skeletal muscle but not in liver. Altogether, these findings raise the possibility that MUP-1 deficiency might contribute to the metabolic dysregulation in obese/diabetic mice, and suggest that the beneficial metabolic effects of MUP-1 are attributed in part to its ability in increasing mitochondrial function in skeletal muscle.