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Increased expression of the adipocytokine omentin in the epicardial adipose tissue of coronary artery disease patients
Atherosclerosis 251 (2016) 299e304
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Increased expression of the adipocytokine omentin in the epicardial adipose tissue of coronary artery disease patients Ken Harada a, *, Rei Shibata b, Noriyuki Ouchi b, Yoshiyuki Tokuda c, Hiroshi Funakubo a, Mayu Suzuki a, Takashi Kataoka a, Tomoyuki Nagao a, Satoshi Okumura a, Norihiro Shinoda a, Bunichi Kato a, Shinichi Sakai a, Masataka Kato a, Nobuyuki Marui a, Hideki Ishii d, Tetsuya Amano e, Tatsuaki Matsubara f, Toyoaki Murohara d a
Department of Cardiology, Chubu Rosai Hospital, Nagoya, Japan Department of Advanced Cardiovascular Therapeutics, Nagoya University Graduate School of Medicine, Nagoya, Japan c Department of Cardiac Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan d Department of Cardiology, Nagoya University Graduate School of Medicine, Nagoya, Japan e Department of Cardiology, Aichi Medical University Hospital, Aichi, Japan f Department of Internal Medicine, Aichi-Gakuin School of Dentistry, Nagoya, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 March 2016 Received in revised form 1 July 2016 Accepted 5 July 2016 Available online 6 July 2016
Background and aims: Omentin, an adipocytokine secreted by visceral adipose tissue, protects against obesity-linked cardiovascular complications. However, little is known about its role in epicardial adipose tissue (EAT) and coronary artery disease (CAD). We investigated the expression of omentin in EAT from CAD subjects. Methods: EAT, subcutaneous adipose tissue (SCAT), and plasma samples were collected from CAD (n ¼ 15; 23.3 ± 3.1 kg/m2) and non-CAD patients (n ¼ 10; 20.8 ± 3.9 kg/m2). Omentin mRNA expression was measured using real-time PCR, while plasma concentrations were measured using an ELISA. EAT volume was determined with 64-slice computed tomography. Results: Omentin expression in EAT and EAT volume were higher in CAD patients compared with controls (2.49 ± 2.6 vs. 0.85 ± 0.3, p ¼ 0.002 and 113 ± 58 ml vs. 92.4 ± 30 ml, p ¼ 0.045, respectively). Omentin expression in SCAT was similar between CAD and control patients (1.37 ± 0.84 vs. 1.07 ± 0.55, p ¼ 0.267). Plasma omentin levels were lower in CAD patients compared with controls (343 ± 158 ng/ml vs. 751 ± 579 ng/ml, p ¼ 0.025), and were negatively associated with the expression of omentin in EAT, in patients with CAD (b ¼ 0.78, p ¼ 0.049). On the other hand, there was no association between omentin in EAT and clinical variables in patients with non-CAD. Conclusions: Omentin expression increases in the EAT of non-obese CAD patients, despite a decrease in plasma levels, suggesting that omentin may play a role in the pathogenesis of CAD. © 2016 Elsevier Ireland Ltd. All rights reserved.
Keywords: Omentin Epicardial adipose tissue Subcutaneous adipose tissue Coronary artery disease Non-obese
1. Introduction Adipose tissue is recognized as an active endocrine organ system that secretes adipocytokines responsible for both local and systemic regulation of numerous metabolic and inflammatory processes [1]. The circulating concentrations of many adipocytokines have been found to be increased in overweight individuals
* Corresponding author. Department of Cardiology, Chubu Rosai Hospital, 10-6 1chome Komei, Minato-ku, Nagoya, 455-8530, Japan. E-mail address: [email protected] (K. Harada). http://dx.doi.org/10.1016/j.atherosclerosis.2016.07.003 0021-9150/© 2016 Elsevier Ireland Ltd. All rights reserved.
with higher amounts of visceral fat [2]. In fact, the dysregulated secretion of adipocytokines appears to trigger obesity-associated chronic inflammation and contributes to the development of cardiovascular atherosclerosis [3]. This link has been suggested to be related primarily to the adipose tissue surrounding arteries, including perivascular adipose tissue, periadventitial adipose tissue, and epicardial adipose tissue (EAT). For example, perivascular adipose tissue has been shown to play a direct role in the pathogenesis of vascular disease acceleration [4], while inflammation in periadventitial adipose tissue induces various cytokines to infiltrate atherosclerosis lesions, which enhances neointima formation and plaque vulnerability [5,6]. Furthermore, EAT, the adipose tissue
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surrounding the heart, is deposited under the visceral layer of the pericardium and is thought to serve as a source of adipocytokines [7]. Given its close proximity, it is not surprising that excessive EAT is thought to be directly responsible for the inflammation of adjacent coronary arteries and appears to contribute to the pathogenesis of atherosclerosis [8e11]. Omentin, also known as intelectin-1, is a recently identified adipocytokine, whose expression is abundantly detected in human visceral adipose tissue [12,13]. Omentin is also detectable in human plasma and appears to be downregulated in obese subjects and those with type 2 diabetes [14,15]. Moreover, low levels of plasma omentin have been associated with insulin resistance and endothelial dysfunction [16,17]. Thus, it is conceivable that circulating omentin may also be associated with obesity-linked coronary artery disease (CAD). Previous research indicates that omentin is predominantly found in EAT compared with internal mammary artery periadventitial and subcutaneous fat [18]. However, the functional significance of omentin expression in these tissues is not fully understood. Furthermore, the relationship between omentin expression in EAT and CAD is also largely unexplored. In the present study, we have investigated the expression of omentin in EAT and subcutaneous adipose tissue (SCAT) in CAD patients and compared them to non-CAD patients in order to determine any potential associations between omentin and CAD pathogenesis.
levels were determined with an omentin enzyme-linked immunosorbent assay (ELISA) kit (Bio Vendor, NC, USA). The intra-assay and inter-assay coefficients of variation of this kit were 4.1% and 4.8%, respectively.
2. Materials and methods
2.7. Statistical analysis
2.1. Study population
Categorical and continuous variables are presented as the number (percentage) of patients, means ± SD and median with interquartile. Differences between mean values for two groups (CAD and non-CAD) were evaluated with the Student’s unpaired ttest or the Mann-Whitney U test. Mann-Whitney test was performed in case of non-normal distribution, and Student’s t-test was performed in case of normal distribution according to the Shapiro test. The potential correlation of omentin expression in adipose tissue with other clinical parameters was examined with Spearman’s correlation coefficient by rank test. Multivariate regression analysis adjusted age and gender was performed to assess the relationship between omentin expression and clinical parameters. A p value less than 0.05 was considered statistically significant. All statistical analysis was performed with the use of StatView for Windows software (Abacus Concepts, Berkeley, CA).
Adipose samples and peripheral blood were obtained from 15 patients who underwent elective coronary artery bypass graft surgery (CAD group) and 10 patients who underwent elective surgery for aortic or mitral valve replacement (non-CAD group) at Chubu Rosai Hospital between November 2011 and January 2013. We excluded patients with acute coronary syndrome, acute decompensated heart failure, and hemodialysis. The protocol of this study was approved by the institutional review boards of the Chubu Rosai Hospital and written informed consent was obtained from each patient. 2.2. Adipose samples Adipose samples were obtained after the opening the thorax, prior to heparinization and cardiopulmonary bypass. EAT biopsy samples were taken near the proximal left coronary artery at the base of the heart, and SCAT samples were taken from the subcutaneous fat on the sternum. Adipose samples were isolated from any attached connective tissue and superficial blood vessels, bisected, and stored separately at 80 C. 2.3. Analysis of omentin gene expression in adipose tissue The total mRNA was extracted from the EAT and SCAT samples using an RNA isolation kit (Qiagen, Valencia, CA, USA) according to the manufacture’s protocol. We measured the expression of omentin mRNA using real-time PCR. Quantitative PCR analysis was performed with a BioRad real-time PCR detection system (TOYOBO, Osaka, Japan). Gene expression was normalized to that of glyceraldehyde 3-phosphate dehydrogenase. 2.4. Plasma analysis and measurement of plasma omentin levels Peripheral venous blood samples were collected from each patient for chemical analysis after an overnight fast. Plasma omentin
2.5. CT image analysis of epicardial fat The volume of EAT was determined on the basis of cardiac CT scanning by two experienced analysts. EAT volume was defined as the total amount of adipose tissue between the surface of the heart and the visceral layer of the pericardium. The methods of measurement of EAT volume have been described in our previous study [19]. Interobserver variability for the quantification of EAT volume was less than 5.0%. 2.6. SYNTAX score and Gensini scoring system The SYNTAX score reflects a comprehensive anatomical assessment, with higher scores indicating more complex coronary disease [20]. To assess the severity of cardiac ischemia, we used the Gensini scoring system [21]. In this system, the coronary artery score equals the sum of all segment scores (where each segment score equals the segment weighting factor multiplied by the severity score).
3. Results 3.1. Clinical characteristics The clinical characteristics of the patients included in this study are shown in Table 1. The mean age of CAD patients was significantly lower than that of non-CAD patients. 10 (66%) CAD patients and 7 (70%) non-CAD patients were male, but this difference was not significant. The average body mass index (BMI) was 23.3 ± 3.1 kg/m2 for the CAD group and 20.8 ± 3.9 kg/m2 for the non-CAD group. In terms of the number of coronary artery bypass grafts, 3 subjects received 4 bypass grafts, 5 received 3 bypass grafts, 6 received 2 bypass grafts, and 1 received 1 bypass graft. The clinical data of the study population are shown in Table 2. Patients with CAD were found to have a higher volume of EAT and increased plasma low-density lipoprotein (LDL) cholesterol levels, but decreased plasma omentin levels compared to non-CAD patients. Furthermore, the increased EAT volume appeared to be related to the decreased plasma omentin levels, but this relationship was not found to be significant (r ¼ 0.30, p ¼ 0.284) (Supplementary Table 1).
K. Harada et al. / Atherosclerosis 251 (2016) 299e304 Table 1 Baseline characteristics of the patients included in this study.
Age (years) Male, n (%) Body mass index (kg/m2) Current smoker, n (%) Blood pressure Systolic (mmHg) Diastolic (mmHg) Treatment Hypertension, n (%) Diabetes mellitus, n (%) Dyslipidemia, n (%) Medications Aspirin, n (%) ACE inhibitor or ARB, n (%) b-blocker, n (%) Ca2þ channel blocker, n (%) Statin, n (%) Procedure, n (%) CABG CABG þ AVR AVR MVR MVP þ TAP SYNTAX score Gentini score
CAD (n ¼ 15)
non-CAD (n ¼ 10)
p value
66 ± 8.2 10 (67) 23.3 ± 3.1 3 (20)
77 ± 8.1 7 (70) 20.8 ± 3.9 1 (10)
0.008 0.864 0.089 0.223
132 ± 22 73 ± 13
126 ± 21 66 ± 14
0.728 0.165
10 (67) 5 (33) 7 (47)
7 (70) 1 (10) 4 (40)
0.488 0.164 0.223
15 (100) 7 (47) 10 (67) 6 (40) 12 (80)
6 5 1 3 5
0.024 0.503 0.004 0.241 0.102
(60) (50) (10) (30) (50)
14 (93) 1 (7) 6 (60) 3 (30) 1 (10) 24.3 ± 9.7 56.0 ± 35
Data are presented as means ± SD or number (%) of patients as indicated. p values were determined by Mann-Whitney U test, with those less than 0.05 being highlighted in bold. CAD, coronary artery disease ; CABG, coronary artery bypass graft; AVR, aortic valve replacement; MVR, mitral valve replacement; MVP, mitral valvuloplasty; TAP, tricuspid annuloplasty. SYNTAX, Synergy between PCI with Taxus and Cardiac Surgery.
3.2. Omentin expression in EAT and SCAT The expression of omentin mRNA present in the EAT of CAD patients was found to be significantly higher than for the non-CAD patients (Fig. 1A). Moreover, there appears to be a negative correlation between level of omentin present in EAT versus level of omentin present in the plasma (r ¼ 0.63, p ¼ 0.027) in patients with CAD. On the other hand, omentin expression in SCAT did not differ between the CAD patients and non-CAD patients (Fig. 1B). 3.3. Relationship between clinical parameters and omentin Our data indicate that there is no correlation between omentin
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expression in EAT and EAT volume or abdominal visceral fat area. Omentin expression in SCAT also did not appear to be correlated with EAT volume or abdominal visceral fat area. However, it was observed that omentin in EAT was positively correlated with plasma calcium levels and inversely correlated with age. On the other hand, omentin in SCAT positively correlated with plasma LDL cholesterol and calcium and inversely with age (Table 3). Further, male patients showed a tendency for having decreased omentin levels in EAT, but this trend was not found to be significant. The average SYNTAX score of the CAD patients included in this study was 24.3 ± 9.7 (an intermediate score). Their SYNTAX scores were not correlated with omentin expression in EAT, but were positively correlated with omentin expression in SCAT (r ¼ 0.531, p ¼ 0.041). Furthermore, we did not observe a correlation between omentin expression in adipose tissue and the patient’s Gensini score. We performed multiple regression analysis in CAD and non-CAD patients, separately (Table 4). In the CAD group, the amount of omentin in EAT was inversely associated with plasma omentin levels (b ¼ 0.78, p ¼ 0.049). On the other hand, triglyceride and LDL cholesterol were positively associated the amount of omentin in SCAT (b ¼ 0.78, p ¼ 0.015 and b ¼ 0.79, p ¼ 0.009, respectively) in patients with non-CAD. Additionally, we performed re-evaluation using Bonferroni correction, since the data sample was small. We found no significant association between omentin in EAT or SCAT and clinical parameters after Bonferroni correction. 4. Discussion In this study, we found that the amount of omentin mRNA was enhanced in the EAT of patients with CAD compared to non-CAD patients. Our data also demonstrate that the expression of omentin mRNA in EAT was positively correlated with BMI, but not EAT volume, for our patients. On the other hand, there was no significant difference in the amount of omentin mRNA in SCAT between the CAD and non-CAD patients. We have shown that plasma omentin levels were associated with omentin expression in EAT in patients with CAD. However, there was no association between omentin in EAT and clinical variables in patients with non-CAD. These findings suggest that omentin could contribute to the pathogenesis of CAD. Nakamura et al. [22] reported that plasma adiponectin was inversely associated with visceral adipose tissue area and positively associated with subcutaneous adipose tissue area. Visceral adipose
Table 2 Clinical data of the study patients.
Biochemical markers Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) BNP (pg/mL) hs-CRP (mg/L) Adipocytokines Omentin in EAT Omentin in SCAT Plasma omentin (ng/mL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL)
CAD (n ¼ 15)
non-CAD (n ¼ 10)
p value
133 (97, 142) 47.0 (44, 52) 126 (108, 147) 5.8 (5.2, 6.6) 174 (20, 413) 1.10 (0.50, 2.20)
115 (75, 129) 46.5 (33, 56) 87 (74, 122) 5.7 (5.1, 6.6) 401 (43, 738) 0.55 (0.40, 0.75)
0.405 0.850 0.008 0.828 0.076 0.675
1.25 (1.10, 2.85) 1.03 (0.71, 2.14) 323 (225, 553) 81.8 (61, 125) 95.8 (78, 139)
0.76 (0.71, 0.89) 0.86 (0.64, 1.53) 630 (325, 954) 77.0 (62, 114) 81.6 (66, 117)
0.002 0.267 0.025 0.401 0.045
Data are presented as median with interquartile of patients as indicated. p values were determined by Student’s t test or Mann-Whitney U test, with those less than 0.05 being highlighted in bold. LDL, low density lipoprotein; HDL, high density lipoprotein; BNP, brain natriuretic peptide; CRP, C-reactive protein; EAT, epicardial adipose tissue; SCAT, subcutaneous adipose tissue.
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Fig. 1. Omentin expression in adipose tissue. The mRNA expression of omentin in epicardial adipose tissue (A) and subcutaneous adipose tissue (B). Expression was assessed by real-time polymerase chain reaction, followed by normalization for GAPDH expression. CAD, coronary artery disease; GAPDH, glyceraldehyde 3-phosphate dehydrogenase.
Table 3 Correlations between clinical parameters and omentin expression in EAT or SCAT. Parameter
Age (years) Gender (male) Body mass index (kg/m2) Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) Calcium (mg/dL) Plasma omentin (mg/dL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL) SYNTAX score Gensini score
Omentin in EAT
Omentin in SCAT
r
p value
r
p value
¡0.59 ¡0.10 0.41 0.11 0.10 0.25 ¡0.02 0.55 ¡0.63 0.11 0.18 0.10 ¡0.11
<0.01 0.629 0.051 0.604 0.650 0.221 0.924 <0.01 0.027 0.646 0.442 0.743 0.729
¡0.42 ¡0.25 0.24 0.18 ¡0.10 0.42 ¡0.36 0.53 ¡0.21 0.15 0.39 0.531 0.341
0.034 0.228 0.270 0.389 0.617 0.034 0.075 0.012 0.519 0.563 0.082 0.041 0.213
r, correlation coefficient. Other abbreviations as in Tables 1and 2. Correlation coefficients and p values for significant correlations are highlighted in bold.
tissue and subcutaneous adipose tissue have differential associations with serum adiponectin concentrations. Our previous report supports the notion that epicardial adipose tissue may promote coronary atherosclerosis directly through paracrine effects rather than through a systemic action [23]. Therefore, epicardial adipose tissue may have unique mechanisms affecting the development of
coronary atherosclerosis, which is different from subcutaneous adipose tissue. 4.1. Omentin in EAT and the severity of CAD The secretion of bioactive inflammatory molecules by EAT was previously implicated in the formation of atherosclerotic plaques and the onset of CAD [11,24,25]. Fain et al. [18] were the first to identify omentin in human EAT. They reported that omentin mRNA was predominantly found in EAT. Notably, their CAD study population had also undergone coronary artery bypass graft surgery. While their results confirm our findings, it is also important to note that their study population was obese, whereas our study population included non-obese patients. Previous studies show decreased levels of circulating omentin are also associated with the presence and severity of CAD in postmenopausal women [26]. We assessed the relationship between omentin in EAT and CAD severity using the SYNTAX and Gensini scoring systems and found no correlation between omentin in EAT and CAD severity using either system. However, we did observe that the top five patients with the highest amount of omentin expressed in their EAT had all received left anterior descending artery bypass surgery. We compared their clinical parameters to other ten CAD patients’. Triglyceride, LDL cholesterol, hemoglobin A1c and brain natriuretic peptide (BNP) were higher in these five patients than in the other ten CAD patients.
K. Harada et al. / Atherosclerosis 251 (2016) 299e304 Table 4 Multivariate regression analysis between omentin in EAT or SCAT and clinical parameters.
CAD (n ¼ 15) Body mass index (kg/m2) Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) Calcium (mg/dL) Plasma omentin (mg/dL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL) SYNTAX score Gensini score Non-CAD (n ¼ 10) Body mass index (kg/m2) Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) Calcium (mg/dL) Plasma omentin (mg/dL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL)
Omentin in EAT
Omenti in SCAT
b
p value
b
p value
0.32 0.19 0.23 0.22 0.13 0.51 0.78 0.09 0.29 0.14 0.30
0.325 0.508 0.430 0.462 0.651 0.083 0.049 0.812 0.476 0.662 0.333
0.06 0.22 0.07 0.06 0.37 0.44 0.63 0.28 0.39 0.53 0.04
0.856 0.456 0.805 0.838 0.190 0.155 0.094 0.467 0.337 0.085 0.899
0.17 0.54 0.06 0.44 0.56 0.07 0.42 0.10 0.18
0.792 0.140 0.892 0.240 0.086 0.894 0.214 0.855 0.676
0.36 0.78 0.33 0.79 0.08 0.65 0.68 0.38 0.57
0.528 0.015 0.453 0.009 0.827 0.054 0.109 0.393 0.207
Multivariate regression analysis was adjusted for age and gender.
b, standard partial regression coefficient. Other abbreviation as in Table 2. Regression coefficients and p values for significant associations are highlighted in bold.
However, there were no significant differences in age, gender, BMI, the frequency of smokers, plasma omentin, SYNTAX score, Gentini score, abdominal visceral fat area and epicardial fat volume between the two groups (Supplementary Table 2). It is therefore possible that lipid metabolism abnormality, impaired glucose tolerance or heart strain might also be factors that affect omentin expression in EAT. A larger sample size should be investigated in order to clarify these results.
4.2. Plasma omentin in non-obese CAD patients, gender disparities Recently, several studies demonstrated that plasma omentin levels were independently associated with CAD prevalence in obese patients [27,28]. Auguet et al. [29], for example, have reported that circulating levels of omentin as well as expression in adipose tissue were decreased in morbidly obese women. Furthermore, in obese subjects, it has been shown that omentin is highly expressed in human visceral fat, but not in subcutaneous fat, while expression in plasma and visceral fat deposits are reduced [14]. It also appears that circulating omentin may also have a protective effect. This phenomena was highlighted in a study that exposed cardiomyocytes to conditioned media derived from EAT from patients with diabetes [30]. These treated cells had induced contractile dysfunction and insulin resistance, which was subsequently prevented by the addition of omentin. Thus, it is possible that decreased omentin levels in a patient’s plasma could contribute to the induction of cardiovascular dysfunction. Our data also show that plasma omentin levels are decreased in non-obese patients with CAD. This data is supported by another report in which plasma omentin levels were decreased in nonobese patients with CAD, especially men [31]. However, we did not find any association between plasma omentin levels and gender. A study also suggest that increased EAT volume is associated with coronary atherosclerosis in men [32]. Further investigation will be required regarding gender difference.
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4.3. Omentin as a cardio protective agent Omentin production and expression mechanisms are poorly understood in relation to myocardial ischemia. Beyond its secretory capacities, it has been suggested that epicardial fat deposits have beneficial properties, such as protecting the coronary arteries [33]. Moreover, it has already been reported that omentin has beneficial anti-inflammatory properties and promotes insulin sensitivity in addition to being anti-atherogenic [34e36]. Omentin also ameliorates endothelial function and reperfusion after ischemia by increasing the production of nitric oxide by endothelial NO synthase [37]. Kataoka et al. [38] report that there was a significant decrease in cardiac infarction size in mice following treatment with omentin, demonstrating that omentin also has a protective effect against myocardial ischemia. It also appears that omentin can stimulate vasodilatation and suppress cytokine-stimulated inflammation [39,40], indicating that omentin may modulate adipocytokine-related coronary artery complications. Our present study demonstrates that the expression of omentin in the EAT of CAD patients increases, despite a decrease in plasma omentin levels. A possible explanation of this is that circulating omentin is sequestered in EAT in response to myocardial ischemia. Alternatively, this difference in expression may be due to changes in omentin production and secretion, with expression being upregulated in EAT while the secretion from these tissues into the blood could be reduced in patients with CAD. Furthermore, it is also possible that the increased expression of omentin in the EAT of CAD patients may play a cardio protective role. Additional studies concerning the cardiac ischemia evaluated by myocardial scintigraphy are warranted. Omentin mRNA expression appears to be enhanced in the EAT in non-obese CAD patients, despite a decrease in plasma omentin levels. On the other hand, there was no significant difference in omentin expression in SCAT between the CAD and non-CAD patients included in this study. Moreover, EAT volume was increased, but did not correlate with omentin expression in EAT in patients with CAD. Our findings suggest that EAT is not only altered in terms of amount, but that its properties may have also been affected in CAD patients. It is important to note that the number of subjects in the present study was small. Although we found significant differences in omentin levels in EAT between CAD and non-CAD patients, we cannot exclude the possibility that our findings might have been influenced by lipid metabolism, impaired glucose tolerance or heart stress. Thus, to confirm our results, a large-scale study is necessary. Taken together, our data demonstrate that omentin may in fact play an important function during CAD pathogenesis in non-obese patients. Conflict of interest The authors declared they do not have anything to disclose regarding conflict of interest with respect to this manuscript. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.atherosclerosis.2016.07.003. References [1] A.S. Greenberg, M.S. Obin, Obesity and the role of adipose tissue in inflammation and metabolism, Am. J. Clin. Nutr. 83 (2006) 461Se465S. [2] A.E. Malavazos, M.M. Corsi, F. Ermetici, C. Coman, F. Sardanelli, A. Rossi, L. Morricone, B. Ambrosi, Proinflammatory cytokines and cardiac abnormalities in uncomplicated obesity: relationship with abdominal fat deposition, Nutr. Metab. Cardiovasc. Dis. 17 (2007) 294e302.
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Ouchi, Association of a fat-derived plasma protein omentin with carotid artery intima-media thickness in apparently healthy men, Hypertens. Res. 34 (12) (2011) 1309e1312. [37] H. Yamawaki, Vascular effects of novel adipocytokines: focus on vascular contractility and inflammatory responses, Biol. Pharm. Bull. 34 (3) (2011) 307e310. [38] Y. Kataoka, R. Shibata, K. Ohashi, T. Kambara, T. Enomoto, Y. Uemura, Y. Ogura, D. Yuasa, K. Matsuo, T. Nagata, T. Oba, H. Yasukawa, Y. Numaguchi, T. Sone, T. Murohara, N. Ouchi, Omentin prevents myocardial ischemic injury through AMP-activated protein kinase- and Akt-dependent mechanisms, J. Am. Coll. Cardiol. 63 (24) (2014) 2722e2733. [39] H. Yamawaki, J. Kuramoto, S. Kameshima, T. Usui, M. Okada, Y. Hara, Omentin, a novel adipocytokine inhibits TNF-induced vascular inflammation in human endothelial cells, Biochem. Biophys. Res. Commun. 408 (2) (2011) 339e343. [40] H. Yamawaki, N. Tsubaki, M. Mukohda, M. Okada, Y. 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Increased expression of the adipocytokine omentin in the epicardial adipose tissue of coronary artery disease patients Ken Harada a, *, Rei Shibata b, Noriyuki Ouchi b, Yoshiyuki Tokuda c, Hiroshi Funakubo a, Mayu Suzuki a, Takashi Kataoka a, Tomoyuki Nagao a, Satoshi Okumura a, Norihiro Shinoda a, Bunichi Kato a, Shinichi Sakai a, Masataka Kato a, Nobuyuki Marui a, Hideki Ishii d, Tetsuya Amano e, Tatsuaki Matsubara f, Toyoaki Murohara d a
Department of Cardiology, Chubu Rosai Hospital, Nagoya, Japan Department of Advanced Cardiovascular Therapeutics, Nagoya University Graduate School of Medicine, Nagoya, Japan c Department of Cardiac Surgery, Nagoya University Graduate School of Medicine, Nagoya, Japan d Department of Cardiology, Nagoya University Graduate School of Medicine, Nagoya, Japan e Department of Cardiology, Aichi Medical University Hospital, Aichi, Japan f Department of Internal Medicine, Aichi-Gakuin School of Dentistry, Nagoya, Japan b
a r t i c l e i n f o
a b s t r a c t
Article history: Received 25 March 2016 Received in revised form 1 July 2016 Accepted 5 July 2016 Available online 6 July 2016
Background and aims: Omentin, an adipocytokine secreted by visceral adipose tissue, protects against obesity-linked cardiovascular complications. However, little is known about its role in epicardial adipose tissue (EAT) and coronary artery disease (CAD). We investigated the expression of omentin in EAT from CAD subjects. Methods: EAT, subcutaneous adipose tissue (SCAT), and plasma samples were collected from CAD (n ¼ 15; 23.3 ± 3.1 kg/m2) and non-CAD patients (n ¼ 10; 20.8 ± 3.9 kg/m2). Omentin mRNA expression was measured using real-time PCR, while plasma concentrations were measured using an ELISA. EAT volume was determined with 64-slice computed tomography. Results: Omentin expression in EAT and EAT volume were higher in CAD patients compared with controls (2.49 ± 2.6 vs. 0.85 ± 0.3, p ¼ 0.002 and 113 ± 58 ml vs. 92.4 ± 30 ml, p ¼ 0.045, respectively). Omentin expression in SCAT was similar between CAD and control patients (1.37 ± 0.84 vs. 1.07 ± 0.55, p ¼ 0.267). Plasma omentin levels were lower in CAD patients compared with controls (343 ± 158 ng/ml vs. 751 ± 579 ng/ml, p ¼ 0.025), and were negatively associated with the expression of omentin in EAT, in patients with CAD (b ¼ 0.78, p ¼ 0.049). On the other hand, there was no association between omentin in EAT and clinical variables in patients with non-CAD. Conclusions: Omentin expression increases in the EAT of non-obese CAD patients, despite a decrease in plasma levels, suggesting that omentin may play a role in the pathogenesis of CAD. © 2016 Elsevier Ireland Ltd. All rights reserved.
Keywords: Omentin Epicardial adipose tissue Subcutaneous adipose tissue Coronary artery disease Non-obese
1. Introduction Adipose tissue is recognized as an active endocrine organ system that secretes adipocytokines responsible for both local and systemic regulation of numerous metabolic and inflammatory processes [1]. The circulating concentrations of many adipocytokines have been found to be increased in overweight individuals
* Corresponding author. Department of Cardiology, Chubu Rosai Hospital, 10-6 1chome Komei, Minato-ku, Nagoya, 455-8530, Japan. E-mail address: [email protected] (K. Harada). http://dx.doi.org/10.1016/j.atherosclerosis.2016.07.003 0021-9150/© 2016 Elsevier Ireland Ltd. All rights reserved.
with higher amounts of visceral fat [2]. In fact, the dysregulated secretion of adipocytokines appears to trigger obesity-associated chronic inflammation and contributes to the development of cardiovascular atherosclerosis [3]. This link has been suggested to be related primarily to the adipose tissue surrounding arteries, including perivascular adipose tissue, periadventitial adipose tissue, and epicardial adipose tissue (EAT). For example, perivascular adipose tissue has been shown to play a direct role in the pathogenesis of vascular disease acceleration [4], while inflammation in periadventitial adipose tissue induces various cytokines to infiltrate atherosclerosis lesions, which enhances neointima formation and plaque vulnerability [5,6]. Furthermore, EAT, the adipose tissue
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surrounding the heart, is deposited under the visceral layer of the pericardium and is thought to serve as a source of adipocytokines [7]. Given its close proximity, it is not surprising that excessive EAT is thought to be directly responsible for the inflammation of adjacent coronary arteries and appears to contribute to the pathogenesis of atherosclerosis [8e11]. Omentin, also known as intelectin-1, is a recently identified adipocytokine, whose expression is abundantly detected in human visceral adipose tissue [12,13]. Omentin is also detectable in human plasma and appears to be downregulated in obese subjects and those with type 2 diabetes [14,15]. Moreover, low levels of plasma omentin have been associated with insulin resistance and endothelial dysfunction [16,17]. Thus, it is conceivable that circulating omentin may also be associated with obesity-linked coronary artery disease (CAD). Previous research indicates that omentin is predominantly found in EAT compared with internal mammary artery periadventitial and subcutaneous fat [18]. However, the functional significance of omentin expression in these tissues is not fully understood. Furthermore, the relationship between omentin expression in EAT and CAD is also largely unexplored. In the present study, we have investigated the expression of omentin in EAT and subcutaneous adipose tissue (SCAT) in CAD patients and compared them to non-CAD patients in order to determine any potential associations between omentin and CAD pathogenesis.
levels were determined with an omentin enzyme-linked immunosorbent assay (ELISA) kit (Bio Vendor, NC, USA). The intra-assay and inter-assay coefficients of variation of this kit were 4.1% and 4.8%, respectively.
2. Materials and methods
2.7. Statistical analysis
2.1. Study population
Categorical and continuous variables are presented as the number (percentage) of patients, means ± SD and median with interquartile. Differences between mean values for two groups (CAD and non-CAD) were evaluated with the Student’s unpaired ttest or the Mann-Whitney U test. Mann-Whitney test was performed in case of non-normal distribution, and Student’s t-test was performed in case of normal distribution according to the Shapiro test. The potential correlation of omentin expression in adipose tissue with other clinical parameters was examined with Spearman’s correlation coefficient by rank test. Multivariate regression analysis adjusted age and gender was performed to assess the relationship between omentin expression and clinical parameters. A p value less than 0.05 was considered statistically significant. All statistical analysis was performed with the use of StatView for Windows software (Abacus Concepts, Berkeley, CA).
Adipose samples and peripheral blood were obtained from 15 patients who underwent elective coronary artery bypass graft surgery (CAD group) and 10 patients who underwent elective surgery for aortic or mitral valve replacement (non-CAD group) at Chubu Rosai Hospital between November 2011 and January 2013. We excluded patients with acute coronary syndrome, acute decompensated heart failure, and hemodialysis. The protocol of this study was approved by the institutional review boards of the Chubu Rosai Hospital and written informed consent was obtained from each patient. 2.2. Adipose samples Adipose samples were obtained after the opening the thorax, prior to heparinization and cardiopulmonary bypass. EAT biopsy samples were taken near the proximal left coronary artery at the base of the heart, and SCAT samples were taken from the subcutaneous fat on the sternum. Adipose samples were isolated from any attached connective tissue and superficial blood vessels, bisected, and stored separately at 80 C. 2.3. Analysis of omentin gene expression in adipose tissue The total mRNA was extracted from the EAT and SCAT samples using an RNA isolation kit (Qiagen, Valencia, CA, USA) according to the manufacture’s protocol. We measured the expression of omentin mRNA using real-time PCR. Quantitative PCR analysis was performed with a BioRad real-time PCR detection system (TOYOBO, Osaka, Japan). Gene expression was normalized to that of glyceraldehyde 3-phosphate dehydrogenase. 2.4. Plasma analysis and measurement of plasma omentin levels Peripheral venous blood samples were collected from each patient for chemical analysis after an overnight fast. Plasma omentin
2.5. CT image analysis of epicardial fat The volume of EAT was determined on the basis of cardiac CT scanning by two experienced analysts. EAT volume was defined as the total amount of adipose tissue between the surface of the heart and the visceral layer of the pericardium. The methods of measurement of EAT volume have been described in our previous study [19]. Interobserver variability for the quantification of EAT volume was less than 5.0%. 2.6. SYNTAX score and Gensini scoring system The SYNTAX score reflects a comprehensive anatomical assessment, with higher scores indicating more complex coronary disease [20]. To assess the severity of cardiac ischemia, we used the Gensini scoring system [21]. In this system, the coronary artery score equals the sum of all segment scores (where each segment score equals the segment weighting factor multiplied by the severity score).
3. Results 3.1. Clinical characteristics The clinical characteristics of the patients included in this study are shown in Table 1. The mean age of CAD patients was significantly lower than that of non-CAD patients. 10 (66%) CAD patients and 7 (70%) non-CAD patients were male, but this difference was not significant. The average body mass index (BMI) was 23.3 ± 3.1 kg/m2 for the CAD group and 20.8 ± 3.9 kg/m2 for the non-CAD group. In terms of the number of coronary artery bypass grafts, 3 subjects received 4 bypass grafts, 5 received 3 bypass grafts, 6 received 2 bypass grafts, and 1 received 1 bypass graft. The clinical data of the study population are shown in Table 2. Patients with CAD were found to have a higher volume of EAT and increased plasma low-density lipoprotein (LDL) cholesterol levels, but decreased plasma omentin levels compared to non-CAD patients. Furthermore, the increased EAT volume appeared to be related to the decreased plasma omentin levels, but this relationship was not found to be significant (r ¼ 0.30, p ¼ 0.284) (Supplementary Table 1).
K. Harada et al. / Atherosclerosis 251 (2016) 299e304 Table 1 Baseline characteristics of the patients included in this study.
Age (years) Male, n (%) Body mass index (kg/m2) Current smoker, n (%) Blood pressure Systolic (mmHg) Diastolic (mmHg) Treatment Hypertension, n (%) Diabetes mellitus, n (%) Dyslipidemia, n (%) Medications Aspirin, n (%) ACE inhibitor or ARB, n (%) b-blocker, n (%) Ca2þ channel blocker, n (%) Statin, n (%) Procedure, n (%) CABG CABG þ AVR AVR MVR MVP þ TAP SYNTAX score Gentini score
CAD (n ¼ 15)
non-CAD (n ¼ 10)
p value
66 ± 8.2 10 (67) 23.3 ± 3.1 3 (20)
77 ± 8.1 7 (70) 20.8 ± 3.9 1 (10)
0.008 0.864 0.089 0.223
132 ± 22 73 ± 13
126 ± 21 66 ± 14
0.728 0.165
10 (67) 5 (33) 7 (47)
7 (70) 1 (10) 4 (40)
0.488 0.164 0.223
15 (100) 7 (47) 10 (67) 6 (40) 12 (80)
6 5 1 3 5
0.024 0.503 0.004 0.241 0.102
(60) (50) (10) (30) (50)
14 (93) 1 (7) 6 (60) 3 (30) 1 (10) 24.3 ± 9.7 56.0 ± 35
Data are presented as means ± SD or number (%) of patients as indicated. p values were determined by Mann-Whitney U test, with those less than 0.05 being highlighted in bold. CAD, coronary artery disease ; CABG, coronary artery bypass graft; AVR, aortic valve replacement; MVR, mitral valve replacement; MVP, mitral valvuloplasty; TAP, tricuspid annuloplasty. SYNTAX, Synergy between PCI with Taxus and Cardiac Surgery.
3.2. Omentin expression in EAT and SCAT The expression of omentin mRNA present in the EAT of CAD patients was found to be significantly higher than for the non-CAD patients (Fig. 1A). Moreover, there appears to be a negative correlation between level of omentin present in EAT versus level of omentin present in the plasma (r ¼ 0.63, p ¼ 0.027) in patients with CAD. On the other hand, omentin expression in SCAT did not differ between the CAD patients and non-CAD patients (Fig. 1B). 3.3. Relationship between clinical parameters and omentin Our data indicate that there is no correlation between omentin
301
expression in EAT and EAT volume or abdominal visceral fat area. Omentin expression in SCAT also did not appear to be correlated with EAT volume or abdominal visceral fat area. However, it was observed that omentin in EAT was positively correlated with plasma calcium levels and inversely correlated with age. On the other hand, omentin in SCAT positively correlated with plasma LDL cholesterol and calcium and inversely with age (Table 3). Further, male patients showed a tendency for having decreased omentin levels in EAT, but this trend was not found to be significant. The average SYNTAX score of the CAD patients included in this study was 24.3 ± 9.7 (an intermediate score). Their SYNTAX scores were not correlated with omentin expression in EAT, but were positively correlated with omentin expression in SCAT (r ¼ 0.531, p ¼ 0.041). Furthermore, we did not observe a correlation between omentin expression in adipose tissue and the patient’s Gensini score. We performed multiple regression analysis in CAD and non-CAD patients, separately (Table 4). In the CAD group, the amount of omentin in EAT was inversely associated with plasma omentin levels (b ¼ 0.78, p ¼ 0.049). On the other hand, triglyceride and LDL cholesterol were positively associated the amount of omentin in SCAT (b ¼ 0.78, p ¼ 0.015 and b ¼ 0.79, p ¼ 0.009, respectively) in patients with non-CAD. Additionally, we performed re-evaluation using Bonferroni correction, since the data sample was small. We found no significant association between omentin in EAT or SCAT and clinical parameters after Bonferroni correction. 4. Discussion In this study, we found that the amount of omentin mRNA was enhanced in the EAT of patients with CAD compared to non-CAD patients. Our data also demonstrate that the expression of omentin mRNA in EAT was positively correlated with BMI, but not EAT volume, for our patients. On the other hand, there was no significant difference in the amount of omentin mRNA in SCAT between the CAD and non-CAD patients. We have shown that plasma omentin levels were associated with omentin expression in EAT in patients with CAD. However, there was no association between omentin in EAT and clinical variables in patients with non-CAD. These findings suggest that omentin could contribute to the pathogenesis of CAD. Nakamura et al. [22] reported that plasma adiponectin was inversely associated with visceral adipose tissue area and positively associated with subcutaneous adipose tissue area. Visceral adipose
Table 2 Clinical data of the study patients.
Biochemical markers Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) BNP (pg/mL) hs-CRP (mg/L) Adipocytokines Omentin in EAT Omentin in SCAT Plasma omentin (ng/mL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL)
CAD (n ¼ 15)
non-CAD (n ¼ 10)
p value
133 (97, 142) 47.0 (44, 52) 126 (108, 147) 5.8 (5.2, 6.6) 174 (20, 413) 1.10 (0.50, 2.20)
115 (75, 129) 46.5 (33, 56) 87 (74, 122) 5.7 (5.1, 6.6) 401 (43, 738) 0.55 (0.40, 0.75)
0.405 0.850 0.008 0.828 0.076 0.675
1.25 (1.10, 2.85) 1.03 (0.71, 2.14) 323 (225, 553) 81.8 (61, 125) 95.8 (78, 139)
0.76 (0.71, 0.89) 0.86 (0.64, 1.53) 630 (325, 954) 77.0 (62, 114) 81.6 (66, 117)
0.002 0.267 0.025 0.401 0.045
Data are presented as median with interquartile of patients as indicated. p values were determined by Student’s t test or Mann-Whitney U test, with those less than 0.05 being highlighted in bold. LDL, low density lipoprotein; HDL, high density lipoprotein; BNP, brain natriuretic peptide; CRP, C-reactive protein; EAT, epicardial adipose tissue; SCAT, subcutaneous adipose tissue.
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Fig. 1. Omentin expression in adipose tissue. The mRNA expression of omentin in epicardial adipose tissue (A) and subcutaneous adipose tissue (B). Expression was assessed by real-time polymerase chain reaction, followed by normalization for GAPDH expression. CAD, coronary artery disease; GAPDH, glyceraldehyde 3-phosphate dehydrogenase.
Table 3 Correlations between clinical parameters and omentin expression in EAT or SCAT. Parameter
Age (years) Gender (male) Body mass index (kg/m2) Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) Calcium (mg/dL) Plasma omentin (mg/dL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL) SYNTAX score Gensini score
Omentin in EAT
Omentin in SCAT
r
p value
r
p value
¡0.59 ¡0.10 0.41 0.11 0.10 0.25 ¡0.02 0.55 ¡0.63 0.11 0.18 0.10 ¡0.11
<0.01 0.629 0.051 0.604 0.650 0.221 0.924 <0.01 0.027 0.646 0.442 0.743 0.729
¡0.42 ¡0.25 0.24 0.18 ¡0.10 0.42 ¡0.36 0.53 ¡0.21 0.15 0.39 0.531 0.341
0.034 0.228 0.270 0.389 0.617 0.034 0.075 0.012 0.519 0.563 0.082 0.041 0.213
r, correlation coefficient. Other abbreviations as in Tables 1and 2. Correlation coefficients and p values for significant correlations are highlighted in bold.
tissue and subcutaneous adipose tissue have differential associations with serum adiponectin concentrations. Our previous report supports the notion that epicardial adipose tissue may promote coronary atherosclerosis directly through paracrine effects rather than through a systemic action [23]. Therefore, epicardial adipose tissue may have unique mechanisms affecting the development of
coronary atherosclerosis, which is different from subcutaneous adipose tissue. 4.1. Omentin in EAT and the severity of CAD The secretion of bioactive inflammatory molecules by EAT was previously implicated in the formation of atherosclerotic plaques and the onset of CAD [11,24,25]. Fain et al. [18] were the first to identify omentin in human EAT. They reported that omentin mRNA was predominantly found in EAT. Notably, their CAD study population had also undergone coronary artery bypass graft surgery. While their results confirm our findings, it is also important to note that their study population was obese, whereas our study population included non-obese patients. Previous studies show decreased levels of circulating omentin are also associated with the presence and severity of CAD in postmenopausal women [26]. We assessed the relationship between omentin in EAT and CAD severity using the SYNTAX and Gensini scoring systems and found no correlation between omentin in EAT and CAD severity using either system. However, we did observe that the top five patients with the highest amount of omentin expressed in their EAT had all received left anterior descending artery bypass surgery. We compared their clinical parameters to other ten CAD patients’. Triglyceride, LDL cholesterol, hemoglobin A1c and brain natriuretic peptide (BNP) were higher in these five patients than in the other ten CAD patients.
K. Harada et al. / Atherosclerosis 251 (2016) 299e304 Table 4 Multivariate regression analysis between omentin in EAT or SCAT and clinical parameters.
CAD (n ¼ 15) Body mass index (kg/m2) Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) Calcium (mg/dL) Plasma omentin (mg/dL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL) SYNTAX score Gensini score Non-CAD (n ¼ 10) Body mass index (kg/m2) Triglyceride (mg/dL) HDL-cholesterol (mg/dL) LDL-cholesterol (mg/dL) Hemoglobin A1c (%) Calcium (mg/dL) Plasma omentin (mg/dL) Abdominal visceral fat area (cm2) Epicardial fat volume (mL)
Omentin in EAT
Omenti in SCAT
b
p value
b
p value
0.32 0.19 0.23 0.22 0.13 0.51 0.78 0.09 0.29 0.14 0.30
0.325 0.508 0.430 0.462 0.651 0.083 0.049 0.812 0.476 0.662 0.333
0.06 0.22 0.07 0.06 0.37 0.44 0.63 0.28 0.39 0.53 0.04
0.856 0.456 0.805 0.838 0.190 0.155 0.094 0.467 0.337 0.085 0.899
0.17 0.54 0.06 0.44 0.56 0.07 0.42 0.10 0.18
0.792 0.140 0.892 0.240 0.086 0.894 0.214 0.855 0.676
0.36 0.78 0.33 0.79 0.08 0.65 0.68 0.38 0.57
0.528 0.015 0.453 0.009 0.827 0.054 0.109 0.393 0.207
Multivariate regression analysis was adjusted for age and gender.
b, standard partial regression coefficient. Other abbreviation as in Table 2. Regression coefficients and p values for significant associations are highlighted in bold.
However, there were no significant differences in age, gender, BMI, the frequency of smokers, plasma omentin, SYNTAX score, Gentini score, abdominal visceral fat area and epicardial fat volume between the two groups (Supplementary Table 2). It is therefore possible that lipid metabolism abnormality, impaired glucose tolerance or heart strain might also be factors that affect omentin expression in EAT. A larger sample size should be investigated in order to clarify these results.
4.2. Plasma omentin in non-obese CAD patients, gender disparities Recently, several studies demonstrated that plasma omentin levels were independently associated with CAD prevalence in obese patients [27,28]. Auguet et al. [29], for example, have reported that circulating levels of omentin as well as expression in adipose tissue were decreased in morbidly obese women. Furthermore, in obese subjects, it has been shown that omentin is highly expressed in human visceral fat, but not in subcutaneous fat, while expression in plasma and visceral fat deposits are reduced [14]. It also appears that circulating omentin may also have a protective effect. This phenomena was highlighted in a study that exposed cardiomyocytes to conditioned media derived from EAT from patients with diabetes [30]. These treated cells had induced contractile dysfunction and insulin resistance, which was subsequently prevented by the addition of omentin. Thus, it is possible that decreased omentin levels in a patient’s plasma could contribute to the induction of cardiovascular dysfunction. Our data also show that plasma omentin levels are decreased in non-obese patients with CAD. This data is supported by another report in which plasma omentin levels were decreased in nonobese patients with CAD, especially men [31]. However, we did not find any association between plasma omentin levels and gender. A study also suggest that increased EAT volume is associated with coronary atherosclerosis in men [32]. Further investigation will be required regarding gender difference.
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4.3. Omentin as a cardio protective agent Omentin production and expression mechanisms are poorly understood in relation to myocardial ischemia. Beyond its secretory capacities, it has been suggested that epicardial fat deposits have beneficial properties, such as protecting the coronary arteries [33]. Moreover, it has already been reported that omentin has beneficial anti-inflammatory properties and promotes insulin sensitivity in addition to being anti-atherogenic [34e36]. Omentin also ameliorates endothelial function and reperfusion after ischemia by increasing the production of nitric oxide by endothelial NO synthase [37]. Kataoka et al. [38] report that there was a significant decrease in cardiac infarction size in mice following treatment with omentin, demonstrating that omentin also has a protective effect against myocardial ischemia. It also appears that omentin can stimulate vasodilatation and suppress cytokine-stimulated inflammation [39,40], indicating that omentin may modulate adipocytokine-related coronary artery complications. Our present study demonstrates that the expression of omentin in the EAT of CAD patients increases, despite a decrease in plasma omentin levels. A possible explanation of this is that circulating omentin is sequestered in EAT in response to myocardial ischemia. Alternatively, this difference in expression may be due to changes in omentin production and secretion, with expression being upregulated in EAT while the secretion from these tissues into the blood could be reduced in patients with CAD. Furthermore, it is also possible that the increased expression of omentin in the EAT of CAD patients may play a cardio protective role. Additional studies concerning the cardiac ischemia evaluated by myocardial scintigraphy are warranted. Omentin mRNA expression appears to be enhanced in the EAT in non-obese CAD patients, despite a decrease in plasma omentin levels. On the other hand, there was no significant difference in omentin expression in SCAT between the CAD and non-CAD patients included in this study. Moreover, EAT volume was increased, but did not correlate with omentin expression in EAT in patients with CAD. Our findings suggest that EAT is not only altered in terms of amount, but that its properties may have also been affected in CAD patients. It is important to note that the number of subjects in the present study was small. Although we found significant differences in omentin levels in EAT between CAD and non-CAD patients, we cannot exclude the possibility that our findings might have been influenced by lipid metabolism, impaired glucose tolerance or heart stress. Thus, to confirm our results, a large-scale study is necessary. Taken together, our data demonstrate that omentin may in fact play an important function during CAD pathogenesis in non-obese patients. Conflict of interest The authors declared they do not have anything to disclose regarding conflict of interest with respect to this manuscript. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.atherosclerosis.2016.07.003. References [1] A.S. Greenberg, M.S. Obin, Obesity and the role of adipose tissue in inflammation and metabolism, Am. J. Clin. Nutr. 83 (2006) 461Se465S. [2] A.E. Malavazos, M.M. Corsi, F. Ermetici, C. Coman, F. Sardanelli, A. Rossi, L. Morricone, B. Ambrosi, Proinflammatory cytokines and cardiac abnormalities in uncomplicated obesity: relationship with abdominal fat deposition, Nutr. Metab. Cardiovasc. Dis. 17 (2007) 294e302.
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