¹Universitätsklinik für Innere Medizin, Universität Innsbruck, Innsbruck, Austria

²Universitätsklinik für Chirurgie, Universität Innsbruck, Innsbruck, Austria

Correspondence to: C F Ebenbichler, Universitätsklinik für Innere Medizin, Universität Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria. E-mail: Christoph.Ebenbichler@uibk.ac.at

Background: Human adipose tissue expresses and releases proinflammatory cytokines and these measures of chronic inflammation have recently been associated with obesity.

Hypothesis: To test whether the proinflammatory state is reversible in subjects undergoing weight loss by surgical measures.

Subjects and Methods: Twenty morbidly obese women participated in this prospective study. Subjects were examined for fat mass, high-sensitive C-reactive protein (hs-CRP), interleukin 6 (IL-6) and tumor necrosis factor-alpha (TNF-) before and 1 y after Swedish adjustable gastric banding.

Results: Anthropometric measures displayed a significant reduction of the body mass index (BMI) from 41.6±5.4 to 30.8±6.1 kg/m² and the fat mass from 53.9±10.3 to 29.8±12.1 kg (mean±s.d.). Hs-CRP levels decreased significantly from 1.33±1.21 mg/dl in pre-gastric banding subjects to 0.40±0.61 mg/dl in post-gastric banding subjects, respectively. IL-6 and TNF- levels did not differ significantly between pre- and post-gastric banding subjects.

Conclusions: We speculate that in these patients the marked reduction in C-reactive protein might be beneficial in reducing their cardiovascular risk and is not solely mediated by IL-6 and TNF-.

International Journal of Obesity (2002) 26, 659-662. DOI:10.1038/sj/ijo/0801970

obesity; inflammation; CRP; IL-6; gastric banding

Introduction

Obesity is associated with a variety of metabolic and hormonal dysfunctions such as the development of insulin resistance and dyslipidemia leading to increased morbidity and mortality in these subjects.^1,2

Adipose tissue plays an active role in metabolism. Interestingly, cytokines such as tumor necrosis factor-alpha (TNF-) and interleukin 6 (IL-6) are secreted by adipose tissue.^3,4 TNF- has been shown to be an important mediator of insulin resistance during the state of obesity.⁵ mRNA for both TNF- and IL-6 have been detected in human adipose tissue, and both cytokines were present in homogenates of adipose tissue and in supernatants of cell cultures. IL-6 is the main stimulator of acute phase protein production in the liver.

C-reactive protein (CRP), the main acute phase protein in humans, is a sensitive marker for systemic inflammation. Recent studies linked obesity with the presence of a low-grade systemic inflammation in these subjects. Visser et al⁶ investigated the National Health and Nutrition Examination Survey III (NHANES III) participants and observed elevated CRP levels in obese women and men. Several studies showed that low-grade inflammation is associated with an increased risk for the development of cardiovascular disease. Thus, CRP as a marker of inflammation seems to be an independent predictor for future cardiovascular complications.^7,8

Bariatric surgery is an efficient method to reduce body weight. Some beneficial metabolic effects such as the reversibility of the atherogenic lipoprotein profile by lowering triglycerides, by improving the insulin to glucose ratio and by an increase of HDL cholesterol have been described.^9,10,11 On the other hand, metabolic effects such as the induction of hyper-homocysteinemia¹² that have been linked to atherothrombosis have been observed after weight loss induced by bariatric surgery.

To investigate the reversibility of the association between markers of chronic inflammation and obesity we performed a prospective study in middle-aged women undergoing weight loss by surgical intervention.

Subjects and methods

Subjects

Twenty middle-aged women undergoing weight loss by surgical means were included in this prospective study. The study population were investigated before and 1 y after gastric banding. In addition 10 lean female subjects were examined as a control group.

In the current study group one patient has been shown to have impaired fasting glucose levels. All other study subjects were non diabetics. None of the participants received hormone replacement therapy.

Informed consent was obtained from the subjects. Procedures were performed in accordance with institutional guidelines at the Internal and Surgical Departments.¹³

Surgical procedure

The surgical procedure was performed as described by Forsell^14,15 at the General Surgical Department of the University Hospital in Innsbruck.^13,14,15 The Swedish adjustable gastric band was used in all of the study patients (SAGB Obtech Medical AG, Zug, Switzerland).

Analysis of body composition

Body composition was determined by impedance analysis using a multifrequency BIA 2000-M Impedance analyser (Data Input, Hofheim, Germany). Fat-free mass and fat mass were determined using Nutri 4 software (Data Input).

Laboratory measurements

Blood was drawn after an overnight fast from an antecubital vein into EDTA tubes (1.6 mg/ml). Plasma was separated from erythrocytes by centrifugation at 3000 rpm for 10 min at 4°C immediately after collection. Plasma samples were stored frozen at -80°C until assayed. CRP concentration was measured using the CRP (Latex) ultrasensitive assay (Roche Diagnostic Systems, Basel, Switzerland). IL-6 and TNF- were determined using the IL-6 and TNF- EASIA kit (Biosource, Nivelles, Belgium).

Plasma triglyceride (TG) and cholesterol concentrations were determined using enzymatic methods (Roche Diagnostic Systems, Basel, Switzerland). HDL cholesterol (HDL-C) concentrations were determined using a precipitation procedure with dextran sulfate and magnesium chloride.¹⁶ LDL cholesterol (LDL-C) was calculated according to the formula of Friedewald et al.¹⁷ Plasma glucose concentrations were measured using a standard enzymatic method (Roche Diagnostic Systems, Basel, Switzerland). Plasma insulin concentrations were measured using a microparticle enzyme immunoassay (Abbott, Vienna, Austria).

Leptin was measured using an enzyme-linked immunosorbent assay kit (R&D Systems, Wiesbaden, Germany).

Statistical analysis

Descriptive data are expressed as mean value±s.d. The data from the pre- and post-gastric banding group were compared using a paired-samples t-test. The data from the control group and the study groups were compared using an independent-samples t-test. Statistical significance was inferred at a two-tailed P-value of less than 0.05. Statistical analyses were calculated using SPSS release 8.0 for Windows (SPSS, Chicago, IL, USA).

Results

Anthropometric measures are displayed in Table 1. In the pre-gastric banding group body weight was 115.1±16.8 kg and body mass index (BMI) was 41.6±5.4 kg/m². Fat mass was 53.9±10.3 kg in the subjects undergoing surgical intervention. Body weight decreased to 84.4±16.0 kg and BMI to 30.8±6.1 kg/m². Fat mass as determined by BIA decreased to 29.8±12.1 kg, corresponding to a loss of fat mass of 24.1 kg. In the non-obese control group BMI (23.1±2.3 kg/m²) and fat mass (15.6±4.9 kg) were on significant lower levels compared to the two study groups.

In the study population CRP levels decreased from 1.33±1.21 mg/dl before gastric banding to 0.40±0.61 mg/dl after the procedure (P<0.001, Table 2). Lean control subjects had compared to the pre-gastric banding group significant lower CRP levels (0.15±0.19 mg/dl, P=0.005). No significant changes were found in the pre- and post-interventional IL-6 and TNF- levels. TNF- decreased from 34.5±10.7 to 27.6±13.7 pg/ml, IL-6 increased from 7.8±4.0 to 10.2±17.4 pg/ml after massive weight loss. Lean control subjects had significant lower TNF- levels (8.3±6.2 pg/ml) compared to the pre- (P<0.001) and post-gastric banding subjects (P=0.005). Circulating IL-6 levels were in the control group beyond the lower limit of the used assay.

Plasma TG concentrations decreased from 139±39 to 100±28 mg/dl (P<0.001). As shown in Table 2, total cholesterol, HDL-C and LDL-C did not change on significant levels after weight reduction.

Fasting plasma insulin concentration fell from 17.8±10.5 µU/ml before to 10.1±4.9 µU/ml after the surgical intervention (P<0.001). Fasting plasma glucose concentration decreased from 102±16 to 94±19 mg/dl.

Plasma leptin levels showed a considerable decrease from 45.5±20.8 ng/ml before to 18.1±12.0 ng/ml after SAGB. Compared to the pre- and post-gastric banding study group the control group showed significant lower plasma leptin levels (5.8±3.5 ng/ml, P<0.001 and P=0.009, respectively).

Discussion

CRP synthesis in the liver is mainly induced by IL-6.¹⁸ IL-6 production itself is markedly induced by TNF-.¹⁹ CRP, IL-6 and TNF- are related to the status of obesity¹⁹ and these cytokines inhibit the activity of the lipoprotein lipase.¹⁹ CRP levels have been observed to decrease proportional to weight loss induced by a very-low-fat, energy-restricted diet.²⁰ Another study showed a significant decrease in TNF- levels in obese female patients after diet and aerobic exercise induced weight loss.²¹

The present study showed that CRP levels decreased significantly after massive weight reduction following gastric banding. No significant differences were found for IL-6 and TNF- levels after weight loss. The decrease of CRP levels indicates that fat mass plays an important role in the production of CRP.

IL-6 has been shown to correlate positively with BMI in female^22,23 and male subjects.^23,24,25 In the absence of acute inflammation about 25% of circulating IL-6 might be produced by adipose tissue.²⁶ Adipose tissue IL-6 content expressed as picogram per total fat mass has been significantly correlated with plasma CRP levels indicating that elevated IL-6 levels in obesity are a consequence of the larger amount of fat mass and not the result of IL-6 overexpression in adipose tissue.²⁷ Fat mass reduction of about 3 kg induced by a very low-energy diet led to a decrease of IL-6 in obese women.²⁸

Our data suggest that IL-6 might not be the major determinant for elevated CRP levels in obesity, because CRP levels decrease despite of a moderate IL-6 increase. It is conceivable that a decrease of IL-6 caused by fat mass reduction is balanced through an irritational process in the area of the surgical band insertion in this specific clinical situation. Thus, we speculate that an additional mediator could have a role in the stimulation of CRP synthesis by the liver.

In conclusion, elevated CRP levels in morbidly obese subjects are reduced markedly after weight loss induced by surgical intervention suggesting a risk reduction for morbidity and mortality in these subjects. Despite the marked reduction in CRP, the main mediators of acute phase protein production, IL-6 and TNF-, were not changed. We speculate that under these conditions the reduction of additional, currently not known mediators of acute phase protein production leads to the observed low levels of CRP in subjects undergoing weight loss by surgical intervention.

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Table 1 Baseline characteristics

Table 2 C-reactive protein, IL-6, TNF-