Adiponectin is an adipose tissue-specific protein that is abundantly present in the circulation and suggested to be involved in insulin sensitivity and development of atherosclerosis. Because cytokines are suggested to regulate adiponectin, the aim of the present study was to investigate the interaction between adiponectin and three adipose tissue-derived cytokines (IL-6, IL-8, and TNF-α). The study was divided into three substudies as follows: 1) plasma adiponectin and mRNA levels in adipose tissue biopsies from obese subjects [mean body mass index (BMI): 39.7 kg/m², n = 6] before and after weight loss; 2) plasma adiponectin in obese men (mean BMI: 38.7 kg/m², n = 19) compared with lean men (mean BMI: 23.4 kg/m², n = 10) before and after weight loss; and 3) in vitro direct effects of IL-6, IL-8, and TNF-α on adiponectin mRNA levels in adipose tissue cultures. The results were that 1) weight loss resulted in a 51% ( P < 0.05) increase in plasma adiponectin and a 45% ( P < 0.05) increase in adipose tissue mRNA levels; 2) plasma adiponectin was 53% ( P < 0.01) higher in lean compared with obese men, and plasma adiponectin was inversely correlated with adiposity, insulin sensitivity, and IL-6; and 3) TNF-α ( P < 0.01) and IL-6 plus its soluble receptor ( P < 0.05) decreased adiponectin mRNA levels in vitro. The inverse relationship between plasma adiponectin and cytokines in vivo and the cytokine-induced reduction in adiponectin mRNA in vitro suggests that endogenous cytokines may inhibit adiponectin. This could be of importance for the association between cytokines (e.g., IL-6) and insulin resistance and atherosclerosis.

Human adipose tissue (AT) produces several adipokines including monocyte chemoattractant protein (MCP)-1, involved in the pathogenesis of atherosclerosis. Objective: Human AT cultures, isolated adipocytes, and stromal-vascular cells were used to investigate the relationship among AT-resident macrophages, MCP-1, and adiposity and the regulation of MCP-1. Results: mRNA levels of specific macrophage markers (CD68 and CD14) are correlated with adiposity in sc AT and visceral AT (P < 0.05). MCP-1 production is higher in stromal-vascular cells vs. adipocytes (P < 0.01) and correlates with macrophage markers in both AT compartments (P < 0.05). MCP-1 release is higher in obese subjects (P < 0.05) and in VAT (P < 0.01), but after adjusting for AT-resident macrophages, the differences disappear. MCP-1 is stimulated by IL-1β, TNF-α, IL-8, IL-4, and IL-6 + IL-6-soluble receptor and is decreased by dexamethasone, IL-10, metformin, and thiazolidinediones. Discussion: MCP-1 is correlated with specific macrophage markers, adiposity, and AT localization, but the relationship seems to be related to the number of AT-resident macrophages. Despite this, MCP-1 may be involved in obesity-related health complications, and the decrease of MCP-1 by metformin and thiazolidinediones suggests that these antidiabetic compounds have antiinflammatory properties improving the low-grade inflammatory state observed in obesity.

Obesity is associated with low-grade inflammation, insulin resistance, type 2 diabetes, and cardiovascular disease. This study investigated the effect of a 15-wk lifestyle intervention (hypocaloric diet and daily exercise) on inflammatory markers in plasma, adipose tissue (AT), and skeletal muscle (SM) in 27 severely obese subjects (mean body mass index: 45.8 kg/m²). Plasma samples, subcutaneous abdominal AT biopsies, and vastus lateralis SM biopsies were obtained before and after the intervention and analyzed by ELISA and RT-PCR. The intervention reduced body weight ( P < 0.001) and increased insulin sensitivity (homeostasis model assessment; P < 0.05). Plasma adiponectin ( P < 0.001) increased, and C-reactive protein ( P < 0.05), IL-6 ( P < 0.01), IL-8 ( P < 0.05), and monocyte chemoattractant protein-1 ( P < 0.01) decreased. AT inflammation was reduced, determined from an increased mRNA expression of adiponectin ( P < 0.001) and a decreased expression of macrophage-specific markers (CD14, CD68), IL-6, IL-8, and tumor necrosis factor-α ( P < 0.01). After adjusting for macrophage infiltration in AT, only IL-6 mRNA was decreased ( P < 0.05). Only very low levels of inflammatory markers were found in SM. The intervention had no effect on adiponectin receptor 1 and 2 mRNA in AT or SM. Thus hypocaloric diet and increased physical activity improved insulin sensitivity and reduced low-grade inflammation. Markers of inflammation were particularly reduced in AT, whereas SM does not contribute to this attenuation of whole body inflammation.

The purpose of this study was to investigate the effect of exercise training and diet-induced weight loss alone or in combination on inflammatory markers in circulation, in adipose tissue (AT) and in skeletal muscle (SM) in obese subjects. Seventy-nine obese subjects were randomized into a 12-wk intervention: 1) exercise only (EXO), 2) diet-induced weight loss using a very low energy diet (DIO), and 3) exercise and diet-induced weight-loss combined (DEX). Blood samples (metabolic and inflammatory markers) and AT and SM biopsies (mRNA expression) were collected at baseline and after 12 wk. In the EXO group the weight loss was 3.5 kg and in the DIO and DEX groups it was 12 kg in both. V̇o_2max was increased by 14–18% in the EXO and DEX groups with no changes in the DIO group. In the DIO and DEX groups, circulating levels of MCP-1, MIP-1α, IL-15, and IL-18 were decreased, and adiponectin was increased ( P < 0.05 for all). In the EXO group, MCP-1 was decreased with 10% ( P = 0.06). By combining the weight loss in all three groups, we found a correlation between the degree of weight loss and improvement in several of the inflammatory markers ( P < 0.05). In AT biopsies, subjects in the DIO and DEX groups achieved a general beneficial but nonsignificant effect on the gene expression of inflammatory markers. In the EXO group, no changes in AT adipokine mRNA were found except for an increment of adiponectin ( P < 0.05). In SM, the only observed change was that the gene expression of IL-6 was increased in all three groups ( P < 0.05). In conclusion, rather large weight losses (>5–7%) were found to have beneficial effects on circulating inflammatory markers in these obese subjects. Aerobic exercise for 12 wk, which increased V̇o_2max, was found to have no effects on circulating inflammatory markers in these obese patients. It is suggested that more intensive exercise may be necessary to affect systemic inflammation.

IL-8 is released from human adipose tissue. Circulating IL-8 is increased in obese compared with lean subjects and is associated with measures of insulin resistance, development of atherosclerosis, and cardiovascular disease. We studied 1) the production and release of IL-8 in vitro from paired samples of subcutaneous (SAT) and visceral (VAT) adipose tissue and 2) the production of IL-8 from whole adipose tissue, isolated adipocytes, and nonfat cells of adipose tissue. IL-8 release from VAT was fourfold higher than from SAT ( P < 0.05), and IL-8 mRNA was twofold higher in VAT compared with SAT ( P < 0.01). Dexamethasone (50 nM) attenuated IL-8 production by 50% ( P < 0.05), and IL-1β (2 μg/l) increased IL-8 production up to 15-fold ( P < 0.001). IL-8 release from whole SAT explants correlated with body mass index (BMI; r = 0.78; P < 0.001), as did IL-8 release from nonfat cells ( r = 0.79; P < 0.001). However, no correlation was found between IL-8 release from the fraction of isolated adipocytes and BMI ( r = 0.01). In conclusion, we demonstrated an increased release of IL-8 from VAT compared with SAT. Furthermore, our data suggest that the observed elevation in circulating levels of IL-8 in obese subjects is due primarily to the release of IL-8 from nonfat cells from adipose tissue. The high levels of IL-8 release from human adipose tissue and accumulation of this tissue in obese subjects may account for some of the increase in circulating IL-8 observed in obesity.