Identification of omentin mRNA in human epicardial adipose tissue: comparison to omentin in subcutaneous, internal mammary artery periadventitial and visceral abdominal depots. Int J Obes (Lond). 2008;32:810-815. [PMID: 18180782 DOI: 10.1038/sj.ijo.0803790]

Release of inflammatory mediators by human adipose tissue is enhanced in obesity and primarily by the nonfat cells: a review

This paper considers the role of putative adipokines that might be involved in the enhanced inflammatory response of human adipose tissue seen in obesity. Inflammatory adipokines [IL-6, IL-10, ACE, TGFbeta1, TNFalpha, IL-1beta, PAI-1, and IL-8] plus one anti-inflammatory [IL-10] adipokine were identified whose circulating levels as well as in vitro release by fat are enhanced in obesity and are primarily released by the nonfat cells of human adipose tissue. In contrast, the circulating levels of leptin and FABP-4 are also enhanced in obesity and they are primarily released by fat cells of human adipose tissue. The relative expression of adipokines and other proteins in human omental as compared to subcutaneous adipose tissue as well as their expression in the nonfat as compared to the fat cells of human omental adipose tissue is also reviewed. The conclusion is that the release of many inflammatory adipokines by adipose tissue is enhanced in obese humans.

Circulating omentin concentration increases after weight loss

Background

Omentin-1 is a novel adipokine expressed in visceral adipose tissue and negatively associated with insulin resistance and obesity. We aimed to study the effects of weight loss-induced improved insulin sensitivity on circulating omentin concentrations.

Methods

Circulating omentin-1 (ELISA) concentration in association with metabolic variables was measured in 35 obese subjects (18 men, 17 women) before and after hypocaloric weight loss.

Results

Baseline circulating omentin-1 concentrations correlated negatively with BMI (r = -0.58, p < 0.001), body weight (r = -0.35, p = 0.045), fat mass (r = -0.67, p < 0.001), circulating leptin (r = -0.7, p < 0.001) and fasting insulin (r = -0.37, p = 0.03). Circulating omentin-1 concentration increased significantly after weight loss (from 44.9 ± 9.02 to 53.41 ± 8.8 ng/ml, p < 0.001). This increase in circulating omentin after weight loss was associated with improved insulin sensitivity (negatively associated with HOMA value and fasting insulin, r = -0.42, p = 0.02 and r = -0.45, p = 0.01, respectively) and decreased BMI (r = -0.54, p = 0.001).

Conclusion

As previously described with adiponectin, circulating omentin-1 concentrations increase after weight loss-induced improvement of insulin sensitivity.

Adipokines in periaortic and epicardial adipose tissue: differential expression and relation to atherosclerosis

AIM

Adipokines are protein products of adipose tissue with paracrine and endocrine actions, which have been implicated in the pathogenesis of cardiovascular disease. Locally produced adipokines, especially by periadventitial adipose tissue, may affect vascular physiology and pathology. We investigated the expression of adiponectin, visfatin, leptin and novel adipokines chemerin and vaspin in human periaortic and epicardial adipose tissue, as well as their correlation to aortic and coronary atherosclerosis.

METHODS

Standard immunohistochemical staining for the adipokines was performed on samples of human periaortic, pericoronary and apical epicardial adipose tissue. Atherosclerotic lesions of the adjacent vascular wall were assessed using the AHA classification.

RESULTS

Adipokines were expressed in periadventitial and apical epicardial adipose tissue and - except for adiponectin - in vascular smooth muscle cells and foam cells in atherosclerotic lesions. Aortic atherosclerosis was positively correlated with chemerin, vaspin, visfatin and leptin periaortic fat expression. Coronary atherosclerosis was positively correlated with chemerin and visfatin pericoronary fat expression. Adipose tissue adiponectin expression was negatively correlated to atherosclerosis in both locations. Expression of adipokines in apical epicardial fat was not associated with atherosclerosis.

CONCLUSIONS

Our results show: a) a different expression pattern of adiponectin, visfatin, leptin, chemerin and vaspin in periaortic, pericoronary and apical epicardial adipose tissue, b) a correlation of these adipokines with either aortic or coronary atherosclerosis or both in a pattern characteristic for each adipokine and suggest that locally produced adipokines might differently affect the atherosclerotic process in different locations.

Echocardiographic epicardial fat: a review of research and clinical applications

Epicardial fat plays a role in cardiovascular diseases. Because of its anatomic and functional proximity to the myocardium and its intense metabolic activity, some interactions between the heart and its visceral fat depot have been suggested. Epicardial fat can be visualized and measured using standard two-dimensional echocardiography. Standard parasternal long-axis and short-axis views permit the most accurate measurement of epicardial fat thickness overlying the right ventricle. Epicardial fat thickness is generally identified as the echo-free space between the outer wall of the myocardium and the visceral layer of pericardium and is measured perpendicularly on the free wall of the right ventricle at end-systole. Echocardiographic epicardial fat thickness ranges from a minimum of 1 mm to a maximum of almost 23 mm. Echocardiographic epicardial fat thickness clearly reflects visceral adiposity rather than general obesity. It correlates with metabolic syndrome, insulin resistance, coronary artery disease, and subclinical atherosclerosis, and therefore it might serve as a simple tool for cardiometabolic risk prediction. Substantial changes in echocardiographic epicardial fat thickness during weight-loss strategies may also suggest its use as a marker of therapeutic effect. Echocardiographic epicardial fat measurement in both clinical and research scenarios has several advantages, including its low cost, easy accessibility, rapid applicability, and good reproducibility. However, more evidence is necessary to evaluate whether echocardiographic epicardial fat thickness may become a routine way of assessing cardiovascular risk in a clinical setting.

Omentin, a novel adipokine, induces vasodilation in rat isolated blood vessels

Omentin is a recently identified adipose tissue-derived cytokine and is implicated in obesity-related cardiovascular disorders. In the present study, we tested the hypothesis that omentin could directly affect vascular reactivity of isolated blood vessels. In endothelium-intact rat isolated aorta, pretreatment with omentin (300 ng/ml, 30 min) inhibited noradrenaline (NA; 1 nM-1 microM)-induced concentration-dependent contraction. In NA (100 nM)-pre-contracted aorta, omentin (1-300 ng/ml) directly induced an endothelium-dependent relaxation. While a nitric oxide (NO) synthase (NOS) inhibitor, N(G)-nitro-l-arginine methyl ester (100 microM, 30 min) inhibited the relaxation, a PI3K/Akt inhibitor, LY294002 (10 microM, 30 min) or a tyrosine kinase inhibitor, genistein (30 microM, 30 min) was ineffective. Omentin (300 ng/ml, 5 min) induced a phosphorylation of endothelial NOS at serine 1177 but not a phosphorylation of Akt at serine 473. Omentin (1-300 ng/ml) also relaxed NA pre-contracted mesenteric artery. Present study for the first time demonstrated that omentin has a vasodilating effect on isolated blood vessels, which is mediated through endothelium-derived NO.

Identification of cardiovascular genes in omentum from morbidly obese patients with type 2 diabetes

BACKGROUND

The metabolic syndrome describes the association between obesity and co-morbidities including insulin resistance, hypertension, dyslipidemia, and cardiovascular (CV) disease. Adipokines produced from omentum contribute to the risk of CV disease and increase the inflammatory state. This study examines the gene expression differences in the omental tissue of morbidly obese diabetic and non-diabetic patients.

METHODS

Twenty morbidly obese patients undergoing bariatric surgery were included. Ten patients were diabetic and 10 were non-diabetic. Omental samples were collected intraoperatively and snap frozen. Total RNA was extracted using the Trizol reagent and purified with the RNeasy kit (Qiagen). Microarray experiments were performed using the Affymetrix Gene 1.0 ST array and data was analyzed with the Partek 6.3 program using an unpaired t-test (P<0.05). The gene expression profiles of the diabetic group were compared with the non-diabetic group. Using the Ingenuity program, the gene list generated from the microarray analysis was evaluated and real-time quantitative PCR (qPCR) was used to validate the array data.

RESULTS

Compared with the non-diabetic group, the diabetic obese patients showed 79 upregulated genes and 4 downregulated genes with >1.4-fold difference in expression. Ingenuity analysis showed numerous dysregulated genes associated with CV disease including leptin, Von Willebrand factor, P-selectin, angiopoietin-1 (ANGPT1), phospholipase A2 (group VII), and periostin osteoblast specific factor. Microarray results for the earlier mentioned genes were confirmed with qPCR. The results were analyzed with respect to the presence or absence of hyperlipidemia, hypertension, and coronary artery disease. In patients with hyperlipidemia, ANGPT1 and P-selectin were upregulated 1.9- and 2.9-fold, respectively.

CONCLUSIONS

This microarray analysis of omental tissue from morbidly obese diabetic patients documents a host of upregulated genes related to CV disease. This study provides further evidence that diabetic status predisposes obese patients to a higher risk of developing CV disease.

Dexamethasone and the inflammatory response in explants of human omental adipose tissue

Dexamethasone is a synthetic glucocorticoid that is a potent anti-inflammatory agent. The present studies examined the changes in gene expression of 64 proteins in human omental adipose tissue explants incubated for 48h both in the absence and presence of dexamethasone as well as the release of 8 of these proteins that are putative adipokines. The proteins were chosen because they are inflammatory response proteins in other cells, are key regulatory proteins or are proteins with known functions. About 50% were significantly up-regulated while about 10% were unchanged and the remaining 40% were down-regulated. Dexamethasone significantly up-regulated the expression of about 33% of the proteins but down-regulated the expression of about 12% of the proteins. We conclude that dexamethasone is a selective anti-inflammatory agent since it inhibits only about one-fourth of the proteins up-regulated during in vitro incubation of human omental adipose tissue.

The inflammatory response seen when human omental adipose tissue explants are incubated in primary culture is not dependent upon albumin and is primarily in the nonfat cells

Background

The present studies were designed to investigate the changes in gene expression during in vitro incubation of human visceral omental adipose tissue explants as well as fat cells and nonfat cells derived from omental fat.

Methods

Adipose tissue was obtained from extremely obese women undergoing bariatric surgery. Explants of the tissue as well as fat cells and the nonfat cells derived by digestion with collagenase were incubated for 20 minutes to 48 h. The expression of interleukin 1β [IL-1β], tumor necrosis factor α [TNFα], interleukin 8 [IL-8], NFκB₁p50 subunit, hypoxia-inducible factor 1α [HIF1α], omentin/intelectin, and 11β-hydroxysteroid dehydrogenase 1 [11β-HSD1] mRNA were measured by qPCR as well as the release of IL-8 and TNFα.

Results

There was an inflammatory response at 2 h in explants of omental adipose tissue that was reduced but not abolished in the absence of albumin from the incubation buffer for IL-8, IL-1β and TNFα. There was also an inflammatory response with regard to upregulation of HIF1α and NFκB1 gene expression that was unaffected whether albumin was present or absent from the medium. In the nonfat cells derived by a 2 h collagenase digestion of omental fat there was an inflammatory response comparable but not greater than that seen in tissue. The exception was HIF1α where the marked increase in gene expression was primarily seen in intact tissue. The inflammatory response was not seen with respect to omentin/intelectin. Over a subsequent 48 h incubation there was a marked increase in IL-8 mRNA expression and IL-8 release in adipose tissue explants that was also seen to the same extent in the nonfat cells incubated in the absence of fat cells.

Conclusion

The marked inflammatory response seen when human omental adipose tissue is incubated in vitro is reduced but not abolished in the presence of albumin with respect to IL-1β, TNFα, IL-8, and is primarily in the nonfat cells of adipose tissue.

The relationship of visfatin/pre-B-cell colony-enhancing factor/nicotinamide phosphoribosyltransferase in adipose tissue with inflammation, insulin resistance, and plasma lipids

Visfatin/pre-B-cell colony-enhancing factor (PBEF)/nicotinamide phosphoribosyltransferase (Nampt) has been proposed as an insulin-mimicking adipocytokine predominantly secreted from visceral adipose tissue (VAT) and correlated with obesity. However, recent evidence challenged this proposal and instead suggested visfatin/PBEF/Nampt as a proinflammatory cytokine. The study aimed to examine whether visfatin/PBEF/Nampt was predominantly expressed in VAT and was correlated with obesity. The relationship of visfatin/PBEF/Nampt gene expression in adipose tissues with proinflammatory gene expression and metabolic phenotypes was also examined. The relative messenger RNA (mRNA) levels of visfatin/PBEF/Nampt, macrophage-specific marker CD68, and proinflammatory genes were measured in paired abdominal VAT and subcutaneous adipose tissues (SAT) and from 53 nondiabetic adults using quantitative real-time polymerase chain reaction. Fasting glucose, insulin, triglyceride, cholesterol, and uric acid levels were measured; and systemic insulin sensitivity was quantified with modified insulin suppression tests. There was no difference in visfatin/PBEF/Nampt mRNA levels between VAT and SAT, and neither was associated with measures of obesity. Visfatin/PBEF/Nampt mRNA levels were strongly correlated with proinflammatory gene expression including CD68 and tumor necrosis factor-alpha gene in both VAT and SAT. The VAT and SAT visfatin/PBEF/Nampt mRNA expressions were positively correlated with steady-state plasma glucose concentrations measured with modified insulin suppression tests, a direct measurement of systemic insulin resistance (r = 0.42, P = .03 and r = 0.44, P = .03, respectively). The VAT visfatin/PBEF/Nampt mRNA expression was also positively correlated with fasting triglyceride (r = 0.42, P = .002) and total cholesterol levels (r = 0.37, P = .009). Visfatin/PBEF/Nampt is not predominantly secreted from VAT and is not correlated with obesity. Our findings suggest that visfatin/PBEF/Nampt is a proinflammatory marker of adipose tissue associated with systemic insulin resistance and hyperlipidemia.

Uncoupling protein-1 and related messenger ribonucleic acids in human epicardial and other adipose tissues: epicardial fat functioning as brown fat

CONTEXT

Uncoupling protein-1 (UCP-1) is the inner mitochondrial membrane protein that is a specific marker for and mediator of nonshivering thermogenesis in brown adipocytes.

OBJECTIVE

This study was performed to better understand the putative thermogenic function of human epicardial fat.

DESIGN

We measured the expression of UCP-1 and brown adipocyte differentiation transcription factors PR-domain-missing 16 (PRDM16) and peroxisome-proliferator-activated receptor gamma co-activator-1 alpha (PGC-1 alpha) in epicardial, substernal, and sc thoracic, abdominal, and leg fat.

SETTING

The study was conducted at a tertiary care hospital cardiac center.

PATIENTS

Forty-four patients had coronary artery bypass surgery, and six had heart valve replacement.

INTERVENTIONS

Fat samples were taken at open heart surgery.

RESULTS

UCP-1 expression was 5-fold higher in epicardial fat than substernal fat and barely detectable in sc fat. Epicardial fat UCP-1 expression decreased with age, increased with body mass index, was similar in women and men and patients on and not on statin therapy, and showed no relationship to epicardial fat volume or waist circumference. UCP-1 expression was similar in patients without and with severe coronary atherosclerosis and metabolic syndrome or type 2 diabetes. PRDM16 and PGC-1 alpha expression was 2-fold greater in epicardial than sc fat. Epicardial fat UCP-1, PRDM16, and PGC1-alpha mRNAs were similar in diabetics treated with thiazolidinediones compared to diabetics not treated with thiazolidinediones.

CONCLUSION

Because UCP-1 is expressed at high levels in epicardial fat as compared to other fat depots, the possibility should be considered that epicardial fat functions like brown fat to defend the myocardium and coronary vessels against hypothermia. This process could be blunted in the elderly.

A rare variant in the visfatin gene (NAMPT/PBEF1) is associated with protection from obesity

Visfatin was recently reported as a novel adipokine encoded by the NAMPT (PBEF1) gene. This study was aimed at investigation of the possibility that single-nucleotide polymorphisms (SNPs) in the visfatin gene are associated with either obesity or type 2 diabetes (T2D). A set of eight "tag-SNPs" were selected and ABI SNPlex assays designed for genotyping purposes. A total of 1,709 severely obese subjects were typed (896 class III obese adults and 813 children) together with 2,367 T2D individuals and 2,850 controls. For quantitative trait analysis, an additional 2,362 subjects were typed for rs10487818 from a general population sample. One rare SNP, rs10487818, located in intron 4 of NAMPT was associated with severe obesity, with a minor allele frequency of 1.6% in controls, 0.4% in the class III obese adults and, remarkably, 0% in the severely obese children. A highly significant association was observed for the presence or absence of the rare allele, i.e., (A,A) vs. (A,T + T,T) genotypes, in children (P = 6 x 10(-9)) and in adults (P = 8 x 10(-5)). No other significant (P < 0.05) association was observed with obesity or T2D for this or any other SNP. No association with BMI or waist-to-hip ratio was observed in a general population sample (n = 5,212). This is one of the first rare SNPs shown to be protective against a common polygenic disease and provides further evidence that rare alleles of strong effect can contribute to complex diseases such as severe obesity.

Proinflammatory phenotype of perivascular adipocytes: influence of high-fat feeding

Adipose tissue depots originate from distinct precursor cells, are functionally diverse, and modulate disease processes in a depot-specific manner. However, the functional properties of perivascular adipocytes, and their influence on disease of the blood vessel wall, remain to be determined. We show that human coronary perivascular adipocytes exhibit a reduced state of adipocytic differentiation as compared with adipocytes derived from subcutaneous and visceral (perirenal) adipose depots. Secretion of antiinflammatory adiponectin is markedly reduced, whereas that of proinflammatory cytokines interleukin-6, interleukin-8, and monocyte chemoattractant protein-1, is markedly increased in perivascular adipocytes. These depot-specific differences in adipocyte function are demonstrable in both freshly isolated adipose tissues and in vitro-differentiated adipocytes. Murine aortic arch perivascular adipose tissues likewise express lower levels of adipocyte-associated genes as compared with subcutaneous and visceral adipose tissues. Moreover, 2 weeks of high-fat feeding caused further reductions in adipocyte-associated gene expression, while upregulating proinflammatory gene expression, in perivascular adipose tissues. These changes were observed in the absence of macrophage recruitment to the perivascular adipose depot. We conclude that perivascular adipocytes exhibit reduced differentiation and a heightened proinflammatory state, properties that are intrinsic to the adipocytes residing in this depot. Dysfunction of perivascular adipose tissue induced by fat feeding suggests that this unique adipose depot is capable of linking metabolic signals to inflammation in the blood vessel wall.

Stimulation of human omental adipose tissue lipolysis by growth hormone plus dexamethasone

Growth hormone [GH] administration results in a reduction in adiposity of humans that is attributed to stimulation of lipolysis. We examined the effect of direct addition of human GH, in both the absence and presence of dexamethasone [Dex], as well as that of interferon beta on lipolysis by omental adipose tissue explants from obese women incubated for 48h in primary culture. There was a significant stimulation of lipolysis by GH in the presence of Dex but not by Dex or GH alone. There was also a significant further stimulation by GH in the presence of Dex of hormone-sensitive lipase, perilipin, lipoprotein lipase and beta1 adrenergic receptor mRNA. We conclude that the direct lipolytic effect of GH is accompanied by an increase in HSL mRNA in the presence of DEX, but GH also increased the mRNAs for other proteins that could explain all or part of its lipolytic action.

Visfatin in pregnancy: proposed mechanism of peptide delivery

Visfatin is a newly identified 52 kD adipocytokine that appears to have insulinomimetic properties. We examined visfatin expression in visceral fat from lean and pregnant women. Visfatin gene expression was seven times higher in omental fat of pregnant women than in lean women. Both immunohistochemistry and immunoblot confirmed that visfatin protein was much higher in pregnant women than in nonpregnant women. However, serum visfatin was 20.8 +/- 7.7 ng/ml (n = 7) in lean women as compared to only a slight increase to 40.3 ng/ml in pregnant women (n = 4). We measured visfatin mRNA content of human placenta and found that placenta expresses high levels of visfatin mRNA and protein. At a concentration of 2 nM, visfatin and insulin produced nearly identical increase in glucose transport. The discrepancy between the elevated visfatin expression and tissue visfatin compared to only a small increase in serum visfatin is a matter of controversy. The data on serum visfatin concentrations are replete with contradictory data. Taken together, we suggest that visfatin is not a hormone. Instead, we propose that visfatin acts in either a paracrine or autocrine mode. This hypothesis would explain what various laboratories have found widely discrepant values for serum visfatin. Since visfatin potently and efficaciously induced glucose transport in a cell culture model, any hypothetical role for visfatin in pregnancy should include the possibility that it may play a role in maternal/fetal glucose metabolism or distribution and that it may do so by acting locally.

Perivascular adipose tissue-derived visfatin is a vascular smooth muscle cell growth factor: role of nicotinamide mononucleotide

AIMS

Perivascular adipose tissue (PVAT) inhibits vascular smooth muscle cell (VSMC) contraction and stimulates VSMC proliferation by releasing protein factors. The present study was to determine whether visfatin is involved in these paracrine actions of PVAT, and if so, to explore the underlying mechanisms.

METHODS AND RESULTS

Visfatin was preferentially expressed in Sprague-Dawley rat and monkey aortic PVAT, compared with subcutaneous and visceral adipose tissues. The PVAT-derived visfatin was found to be a VSMC growth factor rather than a VSMC relaxing factor, which was proved by visfatin-specific antibody/inhibitor and direct observation of recombinant visfatin. Exogenous visfatin stimulated VSMC proliferation in a dose- and time-dependent manner via extracellular signal-regulated kinase (ERK 1/2) and p38 signalling pathways. This proliferative effect was further confirmed by enhancement of DNA synthesis and upregulation of proliferative marker Ki-67. Visfatin had no anti-apoptotic effect on normal cultured VSMCs, and it exerted an anti-apoptotic effect only during cell apoptosis induced by H2O2, excluding a role of anti-apoptosis in the visfatin-induced VSMC proliferation. Insulin receptor knockdown did not show any action on the visfatin effect. However, visfatin acted as a nicotinamide phosphoribosyltransferase to biosynthesize nicotinamide mononucleotide (NMN), which mediated proliferative signalling pathways and cell proliferation similar to the visfatin effect.

CONCLUSION

Visfatin stimulates VSMC proliferation via NMN-mediated ERK1/2 and p38 signalling. The present study provides a molecular link of visfatin to the paracrine action of PVAT, demonstrates a novel function of visfatin in promoting VSMC proliferation, and reveals NMN as a novel signalling molecule that triggers the proliferative process.

Extension of coronary artery disease is associated with increased IL-6 and decreased adiponectin gene expression in epicardial adipose tissue

Epicardial adipose tissue (EAT) expresses lower levels of adiponectin in patients with CAD and higher levels of inflammatory mediators such as IL-6 and leptin than subcutaneous adipose tissue. This showed one important role of EAT in coronary artery disease. However, the relationship of EAT adiponectin and IL-6 levels to the extension of coronary artery disease has not hitherto been determined. We sought to determine whether the levels of adiponectin and interleukin-6 (IL-6) mRNA in epicardial adipose tissue are associated with the extension of coronary artery disease (CAD).

METHODS

Angiographic and hormones expression were evaluated from epicardial and subcutaneous adipose tissue. 92 patients (58 CAD, 34 non-CAD) who underwent cardiac surgery. Adiponectin and IL-6 mRNA levels were measured by real time RT-PCR in epicardial and subcutaneous adipose tissue (SAT) following angiographic evaluation of their coronary arteries.

RESULTS

We found that epicardial adipose tissue of CAD expressed lower levels of adiponectin mRNA and higher levels of IL-6 mRNA than that of non-CAD patients. As the number of injured arteries rose, adiponectin mRNA levels decreased (r=-0.402, p<0.001) and IL-6 mRNA increased (r=0.514, p<0.001) in epicardial adipose tissue.

CONCLUSIONS

The extension of CAD is significantly associated with the expression of adiponectin and IL-6 mRNA in EAT. These findings suggest that low adiponectin and high IL-6 expression by EAT may contribute to CAD extension.