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Journal of Clinical Endocrinology & Metabolism , doi:10.1210/jc.2007-2630
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The Journal of Clinical Endocrinology & Metabolism Vol. 93, No. 8 3215-3221
Copyright © 2008 by The Endocrine Society

CC Chemokine and CC Chemokine Receptor Profiles in Visceral and Subcutaneous Adipose Tissue Are Altered in Human Obesity

Joakim Huber, Florian W. Kiefer, Maximilian Zeyda, Bernhard Ludvik, Gerd R. Silberhumer, Gerhard Prager, Gerhard J. Zlabinger and Thomas M. Stulnig

Clinical Division of Endocrinology and Metabolism, Department of Internal Medicine, III (J.H., F.W.K., M.Z., B.L., T.M.S.), Department of Surgery (G.R.S., G.P.), and Institute of Immunology (G.J.Z.), Medical University of Vienna, 1090 Vienna, Austria

Address all correspondence and requests for reprints to: Thomas M. Stulnig, M.D., Clinical Division of Endocrinology and Metabolism, Department of Internal Medicine III, Medical University Vienna, Währinger Gürtel 18-20, 1090 Vienna, Austria. E-mail: thomas.stulnig{at}meduniwien.ac.at.


   Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Background/Aims: Obesity is associated with a low-grade inflammation, insulin resistance, and macrophage infiltration of adipose tissue. The role of CC chemokines and their respective receptors in human adipose tissue inflammation remains to be determined.

Methods: sc and visceral adipose tissue of obese patients (body mass index 53.1 ± 11.3 kg/m2) compared with lean controls (body mass index 25.9 ± 3.8 kg/m2) was analyzed for alterations in inflammatory gene expression.

Results: Macrophage infiltration was increased in sc and visceral adipose tissue of obese patients as determined by increased mRNA expression of a macrophage-specific marker (CD68) and by elevated macrophage infiltration. Gene expression of CC chemokines involved in monocyte chemotaxis (CCL2, CCL3, CCL5, CCL7, CCL8, and CCL11) and their receptors (CCR1, CCR2, CCR3, and CCR5) was higher in sc and visceral adipose tissue of obese patients. Serum concentrations of the inflammatory marker IL-6 and C-reactive protein were elevated in obese patients compared with lean controls. Obese patients revealed increased insulin resistance as assessed by the homeostasis model assessment of insulin resistance index and reduced plasma adiponectin concentrations. Adipose tissue expression of many CC chemokines and their receptors in the obese group positively correlated with CD68 expression.

Conclusion: Up-regulation of the CC chemokines and their respective receptors in adipose tissue occurs in human obesity and is associated with increased systemic inflammation.


   Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Obesity is considered a low-grade chronic inflammatory disease (1, 2) that is associated with an increased risk of cardiovascular disease and type 2 diabetes (3). The obesity associated systemic inflammation originates primarily from adipose tissue itself, which secretes a panel of inflammatory cytokines, i.e. adipokines (3). A causal relationship of obesity associated inflammation with metabolic deterioration is indicated by epidemiological data showing association of systemic markers of inflammation such as C-reactive protein (CRP) and IL-6 with insulin resistance and risk for developing type 2 diabetes (4).

Chemokines are small proteins that have originally been shown to direct the movement of circulating leukocytes to sites of inflammation or injury by chemotaxis. In addition, chemokines activate the production and secretion of inflammatory mediators (5). Chemokines are categorized into families according to the position of critical cysteine residues. The largest family is the CC chemokines in which two cysteine residues are adjacent to each other. CC chemokines attract mononuclear cells to sites of chronic inflammation (5). CCL2 seems to play a role in obesity associated infiltration of macrophages into adipose tissue in mouse models and in humans (6, 7), but functional data are not clear (8, 9, 10). Within the CC chemokine family, different ligands can bind to different receptors with overlapping specificities (5, 11). This redundancy for CC chemokines and their respective receptors that are most important for monocyte/macrophage attraction is illustrated in the supplemental Table, which is published as supplemental data on The Endocrine Society’s Journals Online web site at http://jcem.endojournals.org. Thus, different CC chemokines could provoke similar effects, and antagonizing a single chemokine will not neutralize effects of molecules with overlapping receptor specificities. Therefore, chemokines and receptors responsible for monocyte infiltration have to be analyzed in a comprehensive manner to understand better the regulation of the inflammatory process in adipose tissue of obese patients.

Several CC chemokines have been up-regulated in sc adipose tissue of obese patients compared with a lean cohort (12). However, the metabolically important visceral adipose tissue has not been analyzed in that study. Moreover, little is known about human adipose tissue expression of CC chemokine receptors. CCR1, CCR2, and CCR5 are expressed in human cultured adipocytes and are present on the cell surface of adipocytes in sc adipose tissue (13).

Therefore, the role of CC chemokines and their receptors, especially in human visceral adipose tissue, and the metabolic consequences in obesity remain to be determined. A systematic analysis of the expression pattern of CC chemokines and their respective receptors in adipose tissue is crucial for our understanding of the mechanisms driving adipose tissue inflammation, and for the development of chemokine-related strategies to prevent and treat type 2 diabetes. To provide a comprehensive picture of CC chemokines in obesity, we analyzed gene expression of a panel of CC chemokines and their respective receptors related to monocyte chemotaxis in visceral and sc adipose tissue of obese patients and lean controls.


   Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Paired samples of visceral (omental) and sc adipose tissue were obtained from 40 Caucasian men (n = 12) and women (n = 28). Morbidly obese patients [body mass index (BMI) >40 kg/m2] who underwent laparoscopic surgery for gastric banding (n = 20) were matched for age and sex to lean control subjects (BMI <30 kg/m2) undergoing laparoscopic cholecystectomy (n = 15), fundoplication (n = 3), resection of liver cysts (n = 1), or partial colon resection (n = 1). Adipose tissue samples were taken from similar locations in all patients. After explantation tissue specimens were washed in saline buffer. Blood and visible blood vessels were removed and specimens immediately snap frozen in liquid nitrogen. Criteria for exclusion were the presence of any infectious, inflammatory, neoplastic, or systemic disease, diabetes (excluded by fasting plasma glucose or the use of antidiabetic drugs) or other uncontrolled endocrine disease, and the current use of antibiotics, antiinflammatory, or antiobesity drugs. The study was approved by the ethics committee of the Medical University of Vienna. All subjects gave written informed consent before taking part in the study.

Bioelectrical impedance analysis and laboratory measurements

Bioelectrical impedance analysis was conducted to estimate total fat-free mass and body fat using the BIA-2000 Analyzer (Data Input, Hofheim, Germany). Percent body fat was estimated according to Gray et al. (14). Waist circumference was measured with a nonelastic tape, placed on the skin, directly above the iliac crest.

Blood samples were obtained after a 12-h overnight fast and were stored at –80 C. Fasting serum concentrations of cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) cholesterol, triglyceride, glucose, glycosylated hemoglobin (HbA1c), and TSH were determined by routine laboratory methods. High-sensitivity CRP was measured by a commercially available ELISA (R&D Systems, Inc., Minneapolis, MN). Plasma free fatty acid concentration was measured with a microfluorometric method (Wako Chemicals USA, Inc., Richmond, VA). Leptin, adiponectin (Human Leptin and Human Adiponectin RIA; LINCO Research, Inc., St. Charles, MO), and insulin (Serono Diagnostics, Freiburg, Germany) were determined in duplicates by commercial RIAs. The homeostasis model assessment (HOMA) of insulin resistance (HOMA-IR) was calculated to estimate insulin sensitivity using fasting insulin and glucose as described before (15). Serum CCL2 [monocyte chemotactic protein (MCP)-1], CCL3 [macrophage inflammatory protein (MIP)-1{alpha}], CCL5 [regulated on activation, normal T cell expressed and secreted (RANTES)], IL-6, and TNF{alpha} were determined by the Human Fluorokine Multi Analyte Profiling Kits (R&D Systems) and the Luminex 100 IS system (Luminex Corp., Austin, TX) according to the manufacturer’s instructions.

Immunofluorescence analysis

Frozen tissue sections from omental and sc adipose tissue were stained for macrophages as described in Ref. 16 using biotin-conjugated CD206 (mannose receptor) monoclonal antibody (Abcam, Inc., Cambridge, UK) and Alexa Fluor 488-labeled avidin (Molecular Probes, Inc., Eugene, OR), followed by counterstaining of nuclei with 4',6-diamidino-2-phenylindole (Sigma-Aldrich, St. Louis, MO). CD206 surface expression was used for detection of adipose tissue macrophages (16), and this marker was coexpressed with CD68 on human adipose tissue macrophages (data not shown). For quantification the number of macrophages infiltrating adipose tissue were counted as percentage of the total number of nuclei.

Analysis of gene expression

Total RNA was prepared by disrupting adipose tissue in TRIZOL reagent (Invitrogen Corp., Carlsbad, CA) with a tissue homogenizer, followed by RNA isolation according the manufacturer’s instructions. One microgram of total RNA was treated with DNase I and reverse transcribed into cDNA by Superscript II using random hexamer priming (all Invitrogen). Quantitative real-time PCR was performed using gene-specific FAM-TAMRA-labeled commercial Assays-on-Demand (Applied Biosystems, Foster City, CA) normalized to 18S VIC-TAMRA as endogenous control (Applied Biosystems). Expression of specific mRNAs in each sample was quantitated in duplicates on an ABI PRISM 7000 Cycler (Applied Biosystems) using the {Delta}{Delta}Ct method with a tolerated coefficient of variation of less than or equal to 10%. To determine whether 18S was a good housekeeping gene for adipose tissue, the glyceraldehyde-3-phosphate dehydrogenase gene was also evaluated in all samples revealing no expression differences for either housekeeping gene between groups (data not shown).

Statistical analysis

All data are presented as mean ± SEM. Gene expression data, glucose, CRP, and IL-6 were log transformed to obtain normal distributions for statistical analysis. Differences of clinical, metabolic, or inflammatory characteristics between matched obese and lean patients were compared by the two-tailed paired Student’s t test. Repeated measures ANOVA was used in a factorial design to compare gene expression between matched subjects of different groups and between omental and sc adipose tissue, respectively. Post hoc analysis was calculated by the paired Student’s t test and is indicated in the figures. Pearson’s coefficient was used for correlation analysis. P < 0.05 was considered to indicate statistically significant differences. Calculations were performed using the statistical package SPSS version 14.0 (Statistical Package for the Social Sciences, SPSS, Inc., Chicago, IL).


   Results
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Clinical and metabolic characteristics of the study population

The study population is described in Table 1Go. Obese individuals showed significantly elevated waist circumference, percentage of body fat, HbA1c, and leptin compared with lean controls. HDL cholesterol concentrations tended to be lower in obese patients but just failed to reach statistical significance (P = 0.058). The two groups did not differ regarding serum concentrations of triglycerides, total cholesterol, LDL cholesterol, free fatty acids, or TSH (Table 1Go). Obese patients exhibited significantly higher concentrations of fasting plasma glucose, and fasting plasma insulin. Accordingly, the HOMA-IR index was elevated in obese compared with lean subjects (Table 1Go). Plasma adiponectin concentrations were reduced in obese subjects compared with the lean control group.


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  		TABLE 1. Characteristics of the study population

 
Serum concentrations of inflammatory markers and chemokines

Serum concentrations of IL-6 and CRP, but not of TNF{alpha}, were significantly higher in obese patients compared with lean controls (Fig. 1AGo). Serum concentrations of CCL5 RANTES, but not of CCL2 (MCP-1) and CCL3 (MIP-1{alpha}), were significantly elevated in obese vs. lean subjects (Fig. 1BGo).


Figure 1
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  		FIG. 1. Systemic concentrations of inflammatory markers (A) and CC chemokines (B) in obese patients compared with lean controls. Serum IL-6, CRP, TNF{alpha} (A), CCL2, CCL3, and CCL5 (B) were measured as described in Subjects and Methods. Data are expressed as mean ± SEM. *, P < 0.05; #, P < 0.001 obese compared with lean.

 
Adipose tissue expression of macrophage markers and macrophage infiltration

Adipose tissue in obese subjects is characterized by macrophage infiltration and the production of inflammatory mediators (6, 7). Gene expression in omental (visceral) and sc adipose tissue of obese patients and lean controls was determined by quantitative real-time PCR. Expression of the macrophage marker CD68 and TNF{alpha} was higher in both adipose tissues of obese patients compared with lean controls (Fig. 2AGo), as shown previously (7, 17).


Figure 2
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  		FIG. 2. Increased macrophage infiltration into adipose tissue with obesity. A, Adipose tissue expression of the macrophage markers CD68 and TNF{alpha} of obese patients (black bars) compared with lean controls. Mean gene expression in omental (visceral) adipose tissue of lean controls was set to 100%. Data are shown as mean ± SEM. For statistical analysis repeated measures ANOVA was calculated in a full factorial design by defining the factors weight (obese/lean) and location [omental (om)/sc adipose tissue]. Obese compared with lean within the same location showed P < 0.001. Comparison of omental with sc adipose tissue was not significant for CD68 (P = 0.476) and TNF{alpha} (P = 0.277). Post hoc tests between obese and lean were calculated separately for omental and sc adipose tissue and P values indicated as *, P < 0.05; #, P < 0.001, if significant. B, Representative histological sections showing immunofluorescence detection of macrophages performed with an antibody to CD206 (mannose receptor) (green) counterstaining of nuclei with 4',6-diamidino-2-phenylindole (blue). Bar, 50 µm. C, Number of macrophages infiltrating omental (om) and sc adipose tissue of obese patients (black bars) compared with lean controls counted as percentage of the total number of nuclei. Means ± SEM (n = 7 for each group). #, P < 0.001 obese compared with lean.

 
Immunofluorescence analysis of macrophage infiltration by staining for the macrophage mannose receptor (CD206) revealed considerable infiltration in omental and sc adipose tissue of obese patients compared with lean controls (Fig. 2BGo). The number of macrophages was about 3-fold higher in both adipose tissues of obese patients compared with lean controls (Fig. 2CGo). There was no significant difference in macrophage infiltration between omental and sc adipose tissue in obese patients.

Adipose tissue expression of CC chemokines and chemokine receptors

Gene expression of CC chemokines CCL2, CCL3, CCL5, CCL7, CCL8, and CCL11 was increased in omental and sc adipose tissue of obese patients compared with lean controls (Fig. 3Go). CCL5 and CCL11 expression was higher in omental compared with sc adipose tissue, whereas CCL8 expression was lower. Gene expression of CC chemokine receptors CCR1, CCR2, CCR3, and CCR5 was significantly elevated in omental and sc adipose tissue of obese patients compared with lean controls (Fig. 4Go). In addition, expression of CCR2 and CCR5 in omental adipose tissue was higher than in sc adipose tissue. The expression of most of the CC chemokines and their respective receptors positively correlated with the expression of the macrophage marker CD68 in both adipose tissues (Table 2Go).


Figure 3
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  		FIG. 3. Adipose tissue expression of CC chemokines of obese patients (black bars) compared with lean controls (white bars). Mean gene expression in omental (visceral) adipose tissue of lean controls was set to 100%. Data are shown as mean ± SEM. For statistical analysis repeated measures ANOVA was calculated in a full factorial design by defining the factors weight (obese/lean) and location [omental (om)/sc adipose tissue]. Obese compared with lean showed P < 0.001 for all genes except CCL11 (P = 0.023). Comparison of omental with sc adipose tissue was significant for CCL2 (P = 0.014), CCL5 (P = 0.015), CCL8 (P = 0.024), and CCL11 (P = 0.002), but not for CD68 (P = 0.476), TNF{alpha} (P = 0.277), CCL3 (P = 0.284), CCL3 (P = 0.284), and CCL7 (P = 0.472). Post hoc tests between obese and lean were calculated separately for omental and sc adipose tissue, and P values are indicated as *, P < 0.05; #, P < 0.001, if significant.

 

Figure 4
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  		FIG. 4. Adipose tissue expression of CC chemokine receptors in obese patients (black bars) compared with lean controls (white bars). Comparison and statistical analysis are indicated as detailed in the legend to Fig. 3Go. Obese compared with lean were significantly different at P < 0.001 for all genes. Comparison of omental with sc adipose tissue was significant for CCR2 (P < 0.001) and CCR5 (P = 0.015), but not for CCR1 (P = 0.603) or CCR3 (P = 0.271). Post hoc tests between obese and lean were calculated separately for omental and sc adipose tissue, and P values are indicated as *, P < 0.05; #, P < 0.001, if significant.

 

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  		TABLE 2. Correlation of CC chemokines and their receptors with CD68 expression in omental and sc adipose tissue within the obese group

 
Correlation analysis of gene expression with metabolic parameters within the obese study population

In sc adipose tissue, we found a positive correlation of CD68 expression with LDL (r = 0.49; P = 0.03), plasma free fatty acids (r = 0.62; P = 0.008), and a negative correlation with HDL (r = 0.46; P = 0.04) concentrations. In contrast, correlation analysis of CD68 expression with metabolic parameters showed no association for omental fat (data not shown).

Correlation analysis of CC chemokine and chemokine receptor expression in sc adipose tissue revealed that plasma free fatty acid concentrations positively correlated with CCL3 (r = 0.52; P = 0.034), CCL5 (r = 0.58; P = 0.015), CCR1 (r = 0.68; P = 0.003), and CCR2 (r = 0.62; P = 0.009). However, no correlation was found for CC chemokine and receptor expression with metabolic parameters in omental adipose tissue. Insulin concentration, HOMA-IR index, and fasting glucose concentration did not correlate with CD68, CC chemokine or receptor expression in either adipose tissues (data not shown).

Waist circumference is a well-established marker of abdominal fat mass (sc and intra-abdominal) (18), is associated with cardiometabolic risk, including insulin resistance and type 2 diabetes (19, 20), and is an important parameter of the metabolic syndrome according to the National Cholesterol Education Program-Third Adult Treatment Panel and, particularly, International Diabetes Federation criteria (21). To study a possible independent association of CC chemokine and chemokine receptor expression with measures of insulin resistance, we applied multiple regression analysis adjusting for waist circumference. CCL3, CCL5, and their receptor CCR1 in sc adipose tissue positively correlated with serum fasting insulin concentration (P = 0.046, P = 0.028, and P = 0.015, respectively), independent of waist circumference. In addition, CCL3 and CCL5 positively correlated with HOMA-IR at borderline significance (P = 0.088 and P = 0.059), independent of waist circumference.

To elucidate further the association of CC chemokine and chemokine receptor expression with cardiometabolic risk, we analyzed possible expression differences according to the presence of the metabolic syndrome in our obese population. Nearly half of our obese patients (45%) fulfilled the National Cholesterol Education Program-Third Adult Treatment Panel criteria for metabolic syndrome. However, no differences were found when comparing obese patients with or without the metabolic syndrome with respect to systemic inflammatory or gene expression data (data not shown). Similar was found when dividing obese patients into two groups of identical size by HOMA-IR (data not shown).


   Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
Obesity is associated with a state of chronic low-grade inflammation and increased adipose tissue inflammation (22, 23). Adipose tissue in obese subjects is characterized by macrophage infiltration and the production of inflammatory mediators (6, 7). In our study, gene expression of the macrophage marker CD68 was increased in obese patients compared with lean controls, which is in accordance with previous studies. Consistently, macrophage infiltration was elevated in obese patients compared with lean controls in omental and sc adipose tissue (Fig. 2CGo). Interestingly, there was no difference in macrophage numbers between both tissue locations. Recently, it was demonstrated that the number of infiltrated macrophages was twice as high in omental fat compared with sc fat in subjects with a mean BMI of 48 kg/m2 without giving data on visceral obesity (24). However, in obese patients with a mean BMI of 43 kg/m2 and a mean waist circumference of 120 cm, macrophage counts relative to adipocytes were only 1.2-fold higher in omental vs. sc fat (25). Our obese cohort had a substantially higher mean BMI of 53 kg/m2 with a more pronounced central obesity (mean waist circumference 142 cm). Data that were previously published (25) and data from our group indicate that the difference in macrophage infiltration between visceral and sc adipose tissue depots is blunted in severe obesity.

CC chemokines are crucial for the attraction of mononuclear cells from the circulation into tissues (26). In this study we analyzed gene expression of CC chemokines involved in macrophage attraction in human adipose tissue of obese patients and lean controls. Gene expression of multiple CC chemokines in sc adipose tissue was associated with obesity (Fig. 3Go). Increased expression of CCL7 (MCP-3) has not been reported before. As a ligand of CCR2, CCL7 could also contribute to macrophage attraction (27). Accordingly, CC chemokines such as CCL2, CCL3, and CCL8 have been up-regulated in human sc adipose tissue with obesity (12). Obese humans with metabolic syndrome have higher mRNA expression of CCL5 (RANTES) in sc adipose tissue compared with lean controls (28). Gene expression of CCL11 (eotaxin) has been found higher in visceral than in sc adipose tissue (29), in accordance with our results (Fig. 3Go). However, possible alterations of adipose tissue CCL11 expression of obese vs. lean subjects have not been shown previously (29).

Little is known about CC chemokine expression in visceral adipose tissue in humans. Expression of CCL2, CCL3, and CCL5 is enhanced in obese subjects (30, 31). In addition to previous studies, we show for the first time that gene expression of CCL5, CCL7, CCL8, and CCL11 is increased in visceral adipose tissue of obese patients compared with lean controls. Within the obese cohort, expression of the macrophage marker CD68 correlated with CC chemokine expression (Table 2Go).

Together, CC chemokines expressed in visceral and sc adipose tissue could play a role in promoting adipose tissue inflammation in obesity. Adipose tissue macrophages but also adipocytes produce chemokines, e.g. CCL2 and CCL3, to attract and activate inflammatory cells (26, 32, 33). Since we studied whole adipose tissue, the cellular source of chemokine expression remains to be determined.

Most chemokines bind to several G protein-coupled receptors, and, vice versa, chemokine receptors show overlapping ligand specificities (supplemental Table) (5). Currently, 10 CC chemokine receptors (CCR1–10) are assigned (11) whose expression in adipose tissue could mediate leukocyte infiltration and the inflammatory response. Obese mice with a genetic deficiency in CCR2 had fewer macrophages in their sc and visceral adipose tissue depots compared with wild-type mice (34). However, CCR2 deficiency did not normalize macrophage content to that observed by lean animals, indicating that macrophage accumulation is modulated by CCR2-independent factors as well.

In a mouse model of obesity, we found that CCR1, CCR2, and CCR5 were expressed in adipose tissue macrophages but essentially not in adipocytes (unpublished observation). Little is known about chemokine receptor expression in human adipose tissue. Chemokine receptors CCR1, CCR2, and CCR5 were also expressed in human adipocytes in vitro, and these proteins could be detected in sections of human sc abdominal adipose tissue (13). Increased gene expression of CCR5 in sc adipose tissue was found in obese humans compared with lean controls (28). CCR5 was expressed on macrophages and T cells. Here, we demonstrate highly increased gene expression of CC chemokine receptors (CCR1, CCR2, CCR3, and CCR5) in sc and also in visceral adipose tissue in obese patients compared with lean controls (Fig. 3Go). Our data suggest that in addition to CCR2, other CC chemokine receptors could be involved in adipose tissue inflammation.

The function of chemokine receptors in adipose tissue is closely linked to insulin sensitivity. In obese mice CCR2 deficiency or short-term treatment with a pharmacological antagonist of CCR2 reduced adipose tissue macrophage content and attenuated insulin resistance (34). Because adipose tissue inflammatory gene expression was not as consistently reduced, additional chemokine receptors such as CCR1, CCR3, and CCR5 according to our study, could contribute to adipose tissue inflammation and insulin resistance. Because expression of CCR1 positively correlated with fasting insulin concentrations independent of abdominal obesity, it could be an interesting candidate linking obesity to deterioration of insulin sensitivity. Clinical trials of chemokine receptor antagonists for diabetes prevention in obese patients are eagerly awaited. Because CC chemokines bind to various receptors, simultaneous antagonism of multiple receptors, e.g. CCR1 and CCR2, could be required for clinically significant effects in terms of improved insulin sensitivity and diabetes prevention.

Obesity is a major risk factor for insulin resistance and type 2 diabetes (35, 36). Obese patients showed higher fasting insulin concentrations, HOMA index, and fasting glucose concentrations, indicating reduced insulin sensitivity (Table 1Go). There is increasing evidence that CC chemokines produced by adipose tissue cause insulin resistance (13, 37, 38), e.g. in a paracrine and/or autocrine mode. For example, CCL2 impairs adipocyte glucose uptake in vitro (39). In our study increased expression of CC chemokines CCL3 and CCL5 in sc adipose tissue correlated with insulin resistance (HOMA-IR) in obese patients independent of waist circumference.

Correlation of CC chemokine and chemokine receptor expression with metabolic parameters among obese patients differed in sc compared with omental adipose tissue. CCL3, CCL5, and CCR1 positively correlated with plasma free fatty acid concentrations independent of waist circumference only in sc adipose tissue. Subcutaneous fat was quantitatively more important than visceral fat in supplying circulating free fatty acids in obese subjects (40, 41). Thus, lipolysis enhanced via CCR1-mediated inflammatory alterations in sc adipose tissue could play an important role for fatty acid release and generation of insulin resistance.

One limitation of our study is that we evaluated chemokine gene expression and do not provide data on protein concentrations. Previous studies showed that gene and protein expression of distinct chemokines and chemokine receptors was increased in parallel (12, 13, 28). Due to its cross-sectional design, our study cannot ascertain that the given alterations are directly linked by cause and effect. Further prospective studies are needed to establish the pathophysiological role of chemokines and receptors in human obesity associated inflammatory and metabolic alterations.

Epidemiological studies predict a substantial increase in the incidence of obesity and the development of diabetes (36). Preventing diabetes will increasingly become a major task for the health system in the future. Obesity and adipose tissue inflammation seem to contribute to insulin resistance and diabetes development. Reduction of adipose tissue inflammation by CC chemokine receptor antagonists could turn out to be a valuable tool for the prevention and treatment of type 2 diabetes.


   Acknowledgments
 
We thank Margarethe Merio and Peter Nowotny for excellent technical assistance.


   Footnotes
 
This work was supported by the Austrian Science Fund (project no. P18776-B11 and part of the Cell Communication in Health and Disease doctoral program [W1205-B09]), the European Community’s 7th Framework Programe (FP7/2007-2013) under grant agreement no. 201608, and the Joseph-Skoda-Award of the Austrian Society of Internal Medicine (all to T.M.S.).

Disclosure Information: The authors have nothing to declare.

First Published Online May 20, 2008

Abbreviations: BMI, Body mass index; CRP, C-reactive protein; HbA1c, glycosylated hemoglobin; HDL, high-density lipoprotein; HOMA, homeostasis model assessment; HOMA-IR, homeostasis model assessment of insulin resistance; LDL, low-density lipoprotein; MCP, monocyte chemotactic protein; MIP, macrophage inflammatory protein; RANTES, regulated on activation, normal T cell expressed and secreted.

Received November 28, 2007.

Accepted May 9, 2008.


   References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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