Mesenteric adipose tissue-derived monocyte chemoattractant protein-1 plays a crucial role in adipose tissue macrophage migration and activation in obese mice

Functional food targeting the regulation of obesity-induced inflammatory responses and pathologies

Obesity is associated with a low-grade systemic chronic inflammatory state, characterized by the abnormal production of pro- and anti-inflammatory adipocytokines. It has been found that immune cells such as macrophages can infiltrate adipose tissue and are responsible for the majority of inflammatory cytokine production. Obesity-induced inflammation is considered a potential mechanism linking obesity to its related pathologies, such as insulin resistance, cardiovascular diseases, type-2 diabetes, and some immune disorders. Therefore, targeting obesity-related inflammatory components may be a useful strategy to prevent or ameliorate the development of such obesity-related diseases. It has been shown that several food components can modulate inflammatory responses in adipose tissue via various mechanisms, some of which are dependent on peroxisome proliferator-activated receptor γ (PPARγ), whereas others are independent on PPARγ, by attenuating signals of nuclear factor-κB (NF-κB) and/or c-Jun amino-terminal kinase (JNK). In this review, we introduce the beneficial effects of anti-inflammatory phytochemicals that can help prevent obesity-induced inflammatory responses and pathologies.

Suppressive effect of insulin infusion on chemokines and chemokine receptors

OBJECTIVE

In view of the previously described anti-inflammatory effects of insulin, we investigated the potential suppressive effect of insulin on plasma concentrations and expression of the chemokines, monocyte chemoattractant protein-1 (MCP-1) and regulated on activation normal T-cell expressed and secreted (RANTES) and their receptors, chemokine receptor (CCR)-2 and CCR-5, in mononuclear cells (MNCs). We also investigated the effect of insulin on other chemokines.

RESEARCH DESIGN AND METHODS

Ten obese type 2 diabetic patients were infused with insulin (2 units/h with 100 ml of 5% dextrose/h) for 4 h. Another 8 and 6 type 2 diabetic patients were infused with 100 ml of 5% dextrose/h or saline for 4 h, respectively, and served as control subjects. Blood samples were obtained at 0, 2, 4, and 6 h.

RESULTS

Insulin infusion significantly suppressed the plasma concentrations of MCP-1, eotaxin, and RANTES and the expression of RANTES, macrophage inflammatory protein (MIP)-1beta, CCR-2, and CCR-5 in MNCs at 2 and 4 h. Dextrose and saline infusions did not alter these indexes.

CONCLUSIONS

A low-dose infusion of insulin suppresses the plasma concentration of key chemokines, MCP-1, and RANTES, and the expression of their respective receptors, CCR-2 and CCR-5, in MNCs. Insulin also suppresses the expression of RANTES and MIP-1beta in MNCs. These actions probably contribute to the comprehensive anti-inflammatory effect of insulin.

In vitro study of the effect of diesterified alkoxyglycerols with conjugated linoleic acid on adipocyte inflammatory mediators

Background

Adipocytes contribute to inflammation and the innate immune response through expression of inflammatory mediators. High levels of these mediators have been related to chronic inflammation state and insulin resistance, cardiovascular diseases and diabetes type 2, among other disorders. 3-octadecylglycerol (batyl alcohol) has been described as an inflammatory agent, whereas Conjugated Linoleic Acid (CLA) is considered effective against obesity. In this study we examined the anti-inflammatory activity and mechanisms of modified alkoxyglycerols. Tumor necrosis factor (TNF-α) activated mature adipocytes were used as cellular model of inflammation. Secreted levels and gene expressions of some inflammatory mediators, such as the adipokines, interleukin (IL)-1β, IL-6 and IL-10; and the levels of leptin and adiponectin hormones were quantified in presence and absence of alkoxyglycerols and when human adipocyte cells were or not activated by TNF-α. The aim of this study is to describe the effects of nonesterified alkoxyglycerols, CLA and diesterified alkoxyglycerols with CLA (DEA-CLA) and check if they present beneficial properties using an in vitro model of some chronic diseases related to the inflammatory process, such as obesity, using human mature adipocytes activated with TNF-α.

Results

Our data suggest that DEA-CLA, product of the esterification between the CLA and batyl alcohol, present beneficial effects on adipocytes close to observed and described for CLA (i.e. decrease of IL-1β) and no adverse effects as observed for batyl alcohol (i.e. decrease of IL-10). In addition, DEA-CLA presented similar activity to CLA showing a trend to increase the secreted levels of adiponectin and decreasing the secreted levels of leptin.

Conclusions

CLA and DEA-CLA modify adipocyte inflammatory mediators and also could play a role on energy homeostasis through depletion of leptin levels.

Dietary capsaicin reduces obesity-induced insulin resistance and hepatic steatosis in obese mice fed a high-fat diet

Obesity-induced inflammation contributes to the development of obesity-related metabolic disorders such as insulin resistance, type 2 diabetes, fatty liver disease, and cardiovascular disease. In this study, we investigated whether dietary capsaicin can reduce obesity-induced inflammation and metabolic disorders such as insulin resistance and hepatic steatosis. Male C57BL/6 obese mice fed a high-fat diet for 10 weeks received a supplement of 0.015% capsaicin for a further 10 weeks and were compared with unsupplemented controls. Glucose intolerance was estimated by glucose tolerance tests. Transcripts of adipocytokine genes and the corresponding proteins were measured by reverse transcription-PCR and enzyme-linked immunosorbent assay, and macrophage numbers were determined by flow cytometric analysis. Transient receptor potential vanilloid type-1 (TRPV-1), peroxisome proliferator-activated receptor (PPAR)-alpha, and PPARgamma coactivator-1alpha (PGC-1alpha) mRNAs were also measured by RT-PCR, and PPARalpha luciferase assays were performed. Dietary capsaicin lowered fasting glucose, insulin, leptin levels, and markedly reduced the impairment of glucose tolerance in obese mice. Levels of tumor necrosis factor-alpha (TNFalpha), monocyte chemoattractant protein-1 (MCP-1), and interleukin (IL)-6 mRNAs and proteins in adipose tissue and liver decreased markedly, as did macrophage infiltration, hepatic triglycerides, and TRPV-1 expression in adipose tissue. At the same time, the mRNA/protein of adiponectin in the adipose tissue and PPARalpha/PGC-1alpha mRNA in the liver increased. Moreover, luciferase assays revealed that capsaicin is capable of binding PPARalpha. Our data suggest that dietary capsaicin may reduce obesity-induced glucose intolerance by not only suppressing inflammatory responses but also enhancing fatty acid oxidation in adipose tissue and/or liver, both of which are important peripheral tissues affecting insulin resistance. The effects of capsaicin in adipose tissue and liver are related to its dual action on PPARalpha and TRPV-1 expression/activation.

Moderate doses of conjugated linoleic acid reduce fat gain, maintain insulin sensitivity without impairing inflammatory adipose tissue status in mice fed a high-fat diet

BACKGROUND

The enrichment of diet with nutrients with potential benefits on body composition is a strategy to combat obesity. Conjugated linoleic acid (CLA) due its beneficial effects on body composition and inflammatory processes becomes an interesting candidate, since the promotion and impairment of obesity is closely linked to a low-grade inflammation state of adipose tissue. Previously we reported the favourable effects of moderate doses of CLA mixture on body composition and inflammatory status of adipose tissue in mice fed a standard-fat diet. In the present study we assessed the potential beneficial effects of CLA mixture (cis-9, trans-11 and trans-10, cis-12, 50:50) in mice fed a high-fat diet.

METHODS

Two doses were assayed: 0.15 g (CLA1) and 0.5 g CLA/kg body weight (CLA2) for the first 30 days of the study and then animals received a double amount for another 35 days.

RESULTS

The lowest dose (CLA1) had minor effects on body composition, plasma parameters and gene expression. However, a clear reduction in fat accumulation was achieved by CLA2, accompanied by a reduction in leptin, adiponectin and non-esterified fatty acids (NEFA) plasma concentrations. Insulin sensitivity was maintained despite a slight increase in fasting glucose and insulin plasma concentrations. The study of gene expression both in adipocytes and in the stromal vascular fraction (SVF) suggested that CLA may reduce either the infiltration of macrophages in adipose tissue or the induction of expression of pro-inflammatory cytokines.

CONCLUSION

In conclusion, the use of moderate doses of an equimolar mix of the two main CLA isomers reduces body fat content, improves plasma lipid profile, maintains insulin sensitivity (despite a moderate degree of hyperinsulinaemia) without the promotion of inflammatory markers in adipose tissue of mice fed a high-fat diet.

Regulation of nutrient metabolism and inflammation

Metabolic and immune-related pathways intersect at numerous levels. Their common regulation is effectuated by several hormonal signaling routes that involve specific nuclear hormone receptors and adipokines. Glucocorticoids and leptin are hormones that play a key role in coordinating energy metabolism and food-seeking behavior during energy deficiency as does the nuclear hormone receptor Peroxisome Proliferator Activated Receptor α (PPARalpha). Importantly, the glucocorticoid, leptin, and PPARalpha signaling routes share a profound role in governing inflammation and other immune-related processes. Using specific examples, this chapter aims at illustrating the interplay between metabolism and immunity/inflammation by discussing common endocrine and transcriptional regulators of metabolism and inflammation and by highlighting the interaction between macrophages and metabolically active cells in liver and adipose tissue. Convergence of metabolic and immune signaling is likely at least partially driven by the evolutionary need during times of food insufficiency to minimize loss of energy to processes that are temporarily nonessential to the survival of the species.

A fraction of unripe kiwi fruit extract regulates adipocyte differentiation and function in 3T3-L1 cells

Adipocyte dysfunction is strongly associated with the development of insulin resistance and diabetes, and regulation of adipogenesis is important in prevention of diabetes. We prepared a 100% methanol fraction of methanolic extract from unripe kiwi fruit (Actinidia deliciosa), designated KMF (kiwi fruit methanol fraction). When applied to 3T3-L1 preadipocyte cells, KMF promoted adipocyte differentiation, increased glycerol-3-phosphate dehydrogenase (GPDH) activity, and increased triglyceride (TG) content. KMF markedly increased mRNA expression of peroxisome proliferator-activated receptor gamma (PPARgamma)-the master adipogenic transcription factor-and its target genes. Moreover, KMF increased mRNA expression and protein secretion of adiponectin, whereas mRNA expression and secretion of monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6) were decreased. Compared with troglitazone, KMF decreased the production of reactive oxygen species (ROS) and nuclear factor-kappaB (NFkappaB) activation. Glucose uptake was stimulated by KMF in differentiated 3T3-L1 adipocytes. Taken together, these results indicate that KMF may exert beneficial effects against diabetes via its ability to regulate adipocyte differentiation and function.

The role of chemokines in recruitment of immune cells to the artery wall and adipose tissue

The role of the immune system is to recognize pathogens, tumor cells or dead cells and to react with a very specific and localized response. By taking advantage of a highly sophisticated system of chemokines and chemokine receptors, leukocytes such as neutrophils, macrophages, and T-lymphocytes are targeted to the precise location of inflammation. While this is a beneficial process for acute infection and inflammation, recruitment of immune cells to sites of chronic inflammation can be detrimental. It is becoming clear that these inflammatory cells play a significant role in the initiation and progression of metabolic disorders such as atherosclerosis and insulin resistance by infiltrating the artery wall and adipose tissue (AT), respectively. Data from human studies indicate that elevated plasma levels of chemokines are correlated with these metabolic diseases. Recruitment of macrophages to the artery wall is well known to be one of the first steps in early atherosclerotic lesion formation. Likewise, recruitment of macrophages to AT is thought to contribute to insulin resistance associated with obesity. Based on this knowledge, much recent work in these areas has focused on the role of chemokines in attracting immune cells (monocytes/macrophages in particular) to these 2 sites. Thus, understanding the potential for chemokines to contribute to metabolic disease can help direct studies of chemokines as therapeutic targets. In this article, we will review current literature regarding the role of chemokines in atherosclerosis and obesity-related insulin resistance. We will focus on novel work showing that chemokine secretion from endothelial cells, platelets, and adipocytes can contribute to immune cell recruitment, with a diagram showing the time course of chemokine expression and leukocyte recruitment to AT. We will also highlight a few of the less-commonly known chemokine-chemokine receptor pairs. Finally, we will discuss the potential for chemokines as therapeutic targets for treatment of atherosclerosis and insulin resistance.

Direct and macrophage-mediated actions of fatty acids causing insulin resistance in muscle cells

Obesity is associated with insulin resistance and increased risk for developing type 2 diabetes. Enlarged adipocytes develop resistance to the anti-lipolytic action of insulin. Elevated levels of fatty acids in the plasma and interstitial fluids lead to whole-body insulin resistance by disrupting normal insulin-regulated glucose uptake and glycogen storage in skeletal muscle. A new understanding has been cultivated in the past 5 to 10 years that adipocytes and macrophages (resident or bone marrow-derived) in adipose tissue of obese animals and humans are activated in a pro-inflammatory capacity and secrete insulin resistance-inducing factors. However, only recently have fatty acids themselves been identified as agents that engage toll-like receptors of the innate immunity systems of macrophages, adipocytes and muscle cells to trigger pro-inflammatory responses. This review summarizes our observations that fatty acids evoke the release of pro-inflammatory factors from macrophages that consequently induce insulin resistance in muscle cells.

Glucocorticoids and thiazolidinediones interfere with adipocyte-mediated macrophage chemotaxis and recruitment

The link between intra-abdominal adiposity and type II diabetes has been known for decades, and adipose tissue macrophage (ATM)-associated inflammation has recently been linked to insulin resistance. However, the mechanisms associated with ATM recruitment remain ill defined. Herein, we describe in vitro chemotaxis studies, in which adipocyte conditioned medium was used to stimulate macrophage migration. We demonstrate that tumor necrosis factor alpha and free fatty acids, key inflammatory stimuli involved in obesity-associated autocrine/paracrine inflammatory signaling, stimulate adipocyte expression and secretion of macrophage chemoattractants. Pharmacological studies showed that peroxisome proliferator-activated receptor gamma agonists and glucocorticoids potently inhibit adipocyte- induced recruitment of macrophages. This latter effect was mediated by the glucocorticoid receptor, which led to decreased chemokine secretion and expression. In vivo results were quite comparable; treatment of high fat diet-fed mice with dexamethasone prevented ATM accumulation in epididymal fat. This decrease in ATM was most pronounced for the proinflammatory F4/80(+), CD11b(+), CD11c(+) M-1-like ATM subset. Overall, our results elucidate a beneficial function of peroxisome proliferator-activated receptor gamma activation and glucocorticoid receptor/glucocorticoids in adipose tissue and indicate that pharmacologic prevention of ATM accumulation could be beneficial.

Xanthohumol from hop (Humulus lupulus L.) is an efficient inhibitor of monocyte chemoattractant protein-1 and tumor necrosis factor-alpha release in LPS-stimulated RAW 264.7 mouse macrophages and U937 human monocytes

Activated macrophages in adipose tissue play a major role in the chronic inflammatory process that has been linked to the complications of overweight and obesity. The hop plant (Humulus lupulus L.) has been described to possess both anti-inflammatory and antidiabetic effects. In the present study, the chemical composition of a hop crude extract (HCE) was investigated by ultrahigh-performance liquid chromatography (UHPLC). Next, HCE and various fractions obtained by preparative HPLC were tested for their ability to inhibit production of two pro-inflammatory cytokines, monocyte chemoattractant protein-1 (MCP-1, CCL2) and tumor necrosis factor-alpha (TNF-alpha), which play crucial roles in the complications of obesity. The hop chalcone xanthohumol was found to be the most potent inhibitor of both cytokines in LPS-activated RAW 264.7 mouse macrophages and U937 human monocytes. Moreover, other constituents, namely, iso-alpha-acids, in combination with the beta-acid hulupone, showed a moderate but selective inhibitory activity only on MCP-1 release. These findings underscore the potential health effects of hop and support further optimization, selection, and use of this plant.

Effects of diet and exercise on metabolic disturbances in high-fat diet-fed mice

Consumption of a high-fat diet (HFD) is associated with white adipose tissue (WAT) inflammation, which contributes to key components of the metabolic syndrome, including insulin resistance (IR) and hepatic steatosis (HS). To determine the differential effects of exercise training (EX), low-fat diet (LFD), and their combination on WAT inflammation, Balb/cByJ male mice (n=34) were fed an HFD for 12 wks before they were randomized into one of four intervention groups: HFD-EX, LFD-EX, HFD-sedentary (SED), or LFD-SED. EX mice performed 12 wks of exercise training on a motorized treadmill (1h/d, 5d/wk, 12 m/min, 5% grade, approximately 65% VO(2) max), while SED mice remained sedentary in their home cages. WAT gene expression of adipokines was assessed using rt-PCR. IR was measured using HOMA-IR, and HS via hepatic triglyceride content. EX significantly reduced (53%) WAT gene expression of MCP-1, and LFD significantly reduced (50%) WAT gene expression of the macrophage specific marker, F4/80 as well as the adipocytokine IL-1 ra (25%). EX independently improved IR, while both EX and LFD improved HS. These findings suggest that both diet and exercise have unique beneficial effects on WAT inflammatory markers and the mechanism by which each treatment improves metabolic complications associated with chronic consumption of an HFD may be different.

Loss of total and visceral adipose tissue mass predicts decreases in oxidative stress after weight-loss surgery

It is not known whether there are mechanisms linking adipose tissue mass and increased oxidative stress in obesity. This study investigated associations between decreasing general and abdominal fat depots and oxidative stress during weight loss. Subjects were severely obese women who were measured serially at baseline and at 1, 6 (n = 30), and 24 months (n = 18) after bariatric surgery. Total fat mass (FAT) and volumes of visceral (VAT) and subcutaneous abdominal adipose tissue (SAT) were related to plasma concentrations of derivatives of reactive oxidative metabolites (dROMS), a measure of lipid peroxides and oxidative stress. After intervention, BMI significantly decreased, from 47.7 +/- 0.8 kg/m(2) to 43.3 +/- 0.8 kg/m(2) (1 month), 35.2 +/- 0.8 kg/m(2) (6 months), and 30.2 +/- 1.2 kg/m(2) (24 months). Plasma dROMS also significantly deceased over time. At baseline, VAT (r = 0.46), FAT (r = 0.42), and BMI (r = 0.37) correlated with 6-month decreases in dROMS. Similarly, at 1 month, VAT (r = 0.43) and FAT (r = 0.41) correlated with 6-month decreases in dROMS. Multiple regression analysis showed that relationships between VAT and dROMS were significant after adjusting for FAT mass. Increased plasma dROMS at baseline were correlated with decreased concentrations of high-density lipoprotein (HDL) at 1 and 6 months after surgery (r = -0.38 and -0.42). This study found longitudinal associations between general, and more specifically intra-abdominal adiposity, and systemic lipid peroxides, suggesting that adipose tissue mass contributes to oxidative stress.

Intestinal, adipose, and liver inflammation in diet-induced obese mice

Chronic inflammation and increased visceral adipose tissue (VAT) are key elements of the metabolic syndrome. Both are considered to play a pathogenic role in the development of liver steatosis and insulin resistance. The aim of the present study was to investigate the hypothesis that an inflamed intestine, induced both by diet and chemical irritation, could induce persistent inflammation in VAT. Female C57BL/6JOlaHsd mice were used. In study I, groups of mice (n = 6 per group) were given an obesity-inducing cafeteria diet (diet-induced obesity) or regular chow only (control) for 14 weeks. In study II, colitis in mice (n = 8) was induced by 3% dextran sulfate sodium in tap water for 5 days followed by 21 days of tap water alone. Healthy control mice (n = 8) had tap water only. At the end of the studies, all mice were killed; and blood and tissues were sampled and processed for analysis. Body weight of diet-induced obese mice was greatly increased, with evidence of systemic inflammation, insulin resistance, and liver steatosis. Tissue inflammation indexed by proinflammatory cytokine expression was recorded in liver, mesenteric fat, and proximal colon/distal ileum, but not in subcutaneous or perigonadal fat. In dextran sulfate sodium-induced colitis mice, mesenteric fat was even more inflamed than the colon, whereas a much milder inflammation was seen in liver and subcutaneous fat. The studies showed both diet- and colitis-initiated inflammation in mesenteric fat. Fat depots contiguous with intestine and their capacity for exaggerated inflammatory responses to conditions of impaired gut barrier function may account for the particularly pathogenic role of VAT in obesity-induced metabolic disorders.

Inflamed adipose tissue, insulin resistance and vascular injury

Type 2 diabetes is the most common metabolic disorder today and has reached epidemic proportions in many countries. Insulin resistance and inflammation play a central role in the pathogenesis of type 2 diabetes and are present long before the onset of the disease. During this time, many of the complications associated with type 2 diabetes are initiated. Of major concern is the two- to fourfold increase in cardiovascular morbidity and mortality in this group compared to a nondiabetic population. Obesity, characterized by enlarged fat cells, and insulin resistance are, like type 2 diabetes, associated with impaired adipogenesis and a low-grade chronic inflammation that to a large extent emanates from the adipose tissue. Both these processes contribute to unfavourable alterations of the circulating levels of several bioactive molecules (adipokines) that are secreted from the adipose tissue, many of which have documented inhibitory effects on insulin sensitivity in the liver and peripheral tissues and, in addition, have negative effects on the cardiovascular system.Here we review current knowledge of the adipose tissue as an endocrine organ, the local and systemic effects of a chronic state of low-grade inflammation residing in the adipose tissue, and, in particular, the effects of inflammation and circulating adipokines on the vascular wall.

Macrophage infiltration into adipose tissue: initiation, propagation and remodeling

It has long been known that adipose tissue in obesity is in a heightened state of inflammation. Recently, our understanding of this has been transformed by the knowledge that immune cells such as macrophages and T cells can infiltrate adipose tissue and are responsible for the majority of inflammatory cytokine production. These seminal findings have opened up a new area in biology that is garnering the interest of scientists involved in research relating to cell motility, inflammation, obesity, physiology, diabetes and cardiovascular disease. Some important general questions relevant to this field are: how are macrophages recruited to adipose tissue in obesity? What are the physiological consequences of macrophage-adipocyte interactions? Do these inflammatory macrophages contribute to pathophysiological conditions associated with obesity, such as insulin resistance, dyslipidemia, diabetes and cardiovascular disease? This review focuses on the first of these important questions.

The major green tea polyphenol, (-)-epigallocatechin-3-gallate, inhibits obesity, metabolic syndrome, and fatty liver disease in high-fat-fed mice

In this study, we investigated the effects of the major green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), on high-fat-induced obesity, symptoms of the metabolic syndrome, and fatty liver in mice. In mice fed a high-fat diet (60% energy as fat), supplementation with dietary EGCG treatment (3.2 g/kg diet) for 16 wk reduced body weight (BW) gain, percent body fat, and visceral fat weight (P < 0.05) compared with mice without EGCG treatment. The BW decrease was associated with increased fecal lipids in the high-fat-fed groups (r(2) = 0.521; P < 0.05). EGCG treatment attenuated insulin resistance, plasma cholesterol, and monocyte chemoattractant protein concentrations in high-fat-fed mice (P < 0.05). EGCG treatment also decreased liver weight, liver triglycerides, and plasma alanine aminotransferase concentrations in high-fat-fed mice (P < 0.05). Histological analyses of liver samples revealed decreased lipid accumulation in hepatocytes in mice treated with EGCG compared with high-fat diet-fed mice without EGCG treatment. In another experiment, 3-mo-old high-fat-induced obese mice receiving short-term EGCG treatment (3.2 g/kg diet, 4 wk) had decreased mesenteric fat weight and blood glucose compared with high-fat-fed control mice (P < 0.05). Our results indicate that long-term EGCG treatment attenuated the development of obesity, symptoms associated with the metabolic syndrome, and fatty liver. Short-term EGCG treatment appeared to reverse preexisting high-fat-induced metabolic pathologies in obese mice. These effects may be mediated by decreased lipid absorption, decreased inflammation, and other mechanisms.

Grape-seed procyanidins prevent low-grade inflammation by modulating cytokine expression in rats fed a high-fat diet

OBJECTIVE

The main objective of this study was to evaluate the effect of procyanidin intake on the level of inflammatory mediators in rats fed a hyperlipidic diet, which are a model of low-grade inflammation as they show an altered cytokine production.

DESIGN

Male Zucker Fa/fa rats were randomly grouped to receive a low-fat (LF) diet, a high-fat (HF) diet or a high-fat diet supplemented with procyanidins from grape seed (HFPE) (3.45 mg/kg feed) for 19 weeks and were then euthanized. We determined biochemical parameters, C-reactive protein (CRP) and IL-6 levels in plasma. Adipose tissue depots and body weight were also determined. We assessed CRP, IL-6, TNF-alpha and adiponectin gene expression in liver and white adipose tissue (WAT).

RESULTS

As expected, rats fed the HF diet show an enhanced production of CRP. Our results demonstrate that the HFPE diet decreases rat plasma CRP levels but not IL-6 levels. The decrease in plasma CRP in HFPE rats is related to a down-regulation of CRP mRNA expression in the liver and mesenteric WAT. We have also shown a decrease in the expression of the proinflammatory cytokines TNF-alpha and IL-6 in the mesenteric WAT. In contrast, adiponectin mRNA is increased in this tissue due to the procyanidin treatment. As previously reported, CRP plasma levels correlate positively with its expression in the mesenteric WAT, suggesting that procyanidin extract (PE) modulates CRP at the synthesis level. CRP plasma levels also correlate positively with body weight. As expected, body weight is associated with the adiposity index. Also, TNF-alpha expression and IL-6 expression have a strong positive correlation. In contrast, the expression of the anti-inflammatory cytokine adiponectin correlates negatively with the expression of TNF-alpha and IL-6 in the mesenteric WAT.

CONCLUSION

These results suggest a beneficial effect of PE on low-grade inflammatory diseases, which may be associated with the inhibition of the proinflammatory molecules CRP, IL-6 and TNF-alpha and the enhanced production of the anti-inflammatory cytokine adiponectin. These findings provide a strong impetus to explore the effects of dietary polyphenols in reducing obesity-related adipokine dysregulation to manage cardiovascular and metabolic risk factors.

Effects of the new C1q/TNF-related protein (CTRP-3) "cartonectin" on the adipocytic secretion of adipokines

BACKGROUND

Cartonectin (collagenous repeat-containing sequence of 26-kDa protein; CORS-26) was described as a new adipokine of the C1q/TNF molecular superfamily C1q/TNF-related protein-3 (CTRP-3), secreted by the adipocytes of mice and humans. The receptor and function of cartonectin are unknown and the recombinant protein is not commercially available.

OBJECTIVE

To investigate the effects of recombinant cartonectin on the secretion of adipokines such as adiponectin, leptin, and resistin from adipocytes of human and murine origin. The effect of the BMI of the adipocyte donor was also investigated.

METHODS AND PROCEDURES

Human adipocytes from pooled lean and preobese healthy individuals and murine 3T3-L1 adipocytes were used for stimulation experiments. Recombinant cartonectin was expressed in insect H5 cells. Adipokine secretion was measured using enzyme-linked immunosorbent assay. In addition, western blot analysis and luciferase reporter gene assays were employed.

RESULTS

Cartonectin (1, 10, 50, and 250 ng/ml) in higher doses stimulates the secretion of adiponectin and resistin from murine adipocytes. This effect is not caused by an induction of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) protein expression, as confirmed by western blot analysis. Also, luciferase reporter gene assay revealed that cartonectin failed to induce luciferase activity at the peroxisome proliferator-activated receptor responsive element site containing the adiponectin/luciferase promoter fragment. Human adipocytes from lean individuals secrete higher amounts of adiponectin and leptin when compared with adipocytes of individuals with a preobesity BMI (25-30 kg/m(2)). Cartonectin failed to stimulate adiponectin or leptin secretion from human adipocytes, irrespective of the BMI value.

DISCUSSION

Cartonectin is a new adipokine that differentially regulates the secretion of classical adipokines, with marked differences between the human and the murine systems. These effects are species-dependent, while basal adipokine secretion is influenced by the BMI.

Visceral fat accumulation induced by a high-fat diet causes the atrophy of mesenteric lymph nodes in obese mice

OBJECTIVE

A high intake of fat in the diet plays a crucial role in promoting obesity and obesity-related pathologies, and especially visceral obesity is closely associated with obesity-related complications. Because adipose tissue is anatomically associated with lymph nodes, the secondary lymphoid organ, we hypothesized that fat tissue-derived factors may influence the cellularity of lymphoid tissue embedded in fat.

METHODS AND PROCEDURES

Mesenteric and inguinal lymph nodes were isolated from obese mice fed a high-fat diet and control mice fed a regular diet. T-cell population, activation state, and the extent of apoptosis were determined by flow cytometric analysis or terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) assay.

RESULTS

The weight of mesenteric lymph nodes and the total number of lymphoid cells in the obese mice significantly decreased compared with those in the control mice; however, no change was observed in the weight of inguinal lymph nodes. The numbers of CD4(+) and CD8(+) T cells in the mesenteric lymph nodes of obese mice significantly decreased compared with those of the control. Enhanced T-cell activation and apoptosis were observed in the mesenteric lymph node cells of the obese mice. The treatment of lymph node cells with free fatty acids, oxidative stress, and chylomicrons, which are obesity-related factors, resulted in lymph node T-cell activation and apoptosis.

DISCUSSION

These results suggest that visceral fat accumulation with a high-fat diet can cause the atrophy of mesenteric lymph nodes by enhancing activation-induced lymphoid cell apoptosis. Dietary fat-induced visceral obesity may be crucial for obesity-related immune dysfunction.

Dead adipocytes, detected as crown-like structures, are prevalent in visceral fat depots of genetically obese mice

Accumulation of visceral fat is a key phenomenon in the onset of obesity-associated metabolic disorders. Macrophage infiltration induces chronic mild inflammation widely considered as a causative factor for insulin resistance and eventually diabetes. We previously showed that >90% of macrophages infiltrating the adipose tissue of obese animals and humans are arranged around dead adipocytes, forming characteristic crown-like structures (CLS). In this study we quantified CLS in visceral and subcutaneous depots from two strains of genetically obese mice, db/db and ob/ob. In both strains, CLS were prevalent in visceral compared with subcutaneous fat. Adipocyte size and CLS density exhibited a positive correlation both in visceral and in subcutaneous depots; however, the finding that adipocyte size was smallest and CLS density highest in visceral fat suggests a different susceptibility of visceral and subcutaneous adipocytes to death. Visceral fat CLS density was 3.4-fold greater in db/db than in ob/ob animals, which at the age at which our experimental strain was used are more prone to glucose metabolic disorders.

Visceral adipose tissue inflammation accelerates atherosclerosis in apolipoprotein E-deficient mice

BACKGROUND

Fat inflammation may play an important role in comorbidities associated with obesity such as atherosclerosis.

METHODS AND RESULTS

To first establish feasibility of fat transplantation, epididymal fat pads were harvested from wild-type C57BL/6J mice and transplanted into leptin-deficient (Lep(ob/ob)) mice. Fat transplantation produced physiological leptin levels and prevented obesity and infertility in Lep(ob/ob) mice. However, the transplanted fat depots were associated with chronically increased macrophage infiltration with characteristics identical to those observed in fat harvested from obese animals. The inflammation in transplanted adipose depots was regulated by the same factors that have been implicated in endogenous fat inflammation such as monocyte chemoattractant protein-1. To determine whether this inflamed adipose depot could affect vascular disease in mice, epididymal fat depots were transplanted into atherosclerosis-prone apolipoprotein E-deficient ApoE(-/-) mice. Plasma from ApoE(-/-) mice receiving fat transplants contained increased leptin, resistin, and monocyte chemoattractant protein-1 compared with plasma from sham-operated ApoE(-/-) mice. Furthermore, mice transplanted with visceral fat developed significantly more atherosclerosis compared with sham-operated animals, whereas transplants with subcutaneous fat did not affect atherosclerosis despite a similar degree of fat inflammation. Treatment of transplanted ApoE(-/-) mice with pioglitazone decreased macrophage content of the transplanted visceral fat pad and reduced plasma monocyte chemoattractant protein-1. Importantly, pioglitazone also reduced atherosclerosis triggered by inflammatory visceral fat but had no protective effect on atherosclerosis in the absence of the visceral fat transplantation.

CONCLUSIONS

Our results indicate that visceral adipose-related inflammation accelerates atherosclerosis in mice. Drugs such as thiazolidinediones might be a useful strategy to specifically attenuate the vascular disease induced by visceral inflammatory fat.

Citrus auraptene acts as an agonist for PPARs and enhances adiponectin production and MCP-1 reduction in 3T3-L1 adipocytes

Citrus fruit compounds have many health-enhancing effects. In this study, using a luciferase ligand assay system, we showed that citrus auraptene activates peroxisome proliferator-activated receptor (PPAR)-alpha and PPARgamma. Auraptene induced up-regulation of adiponectin expression and increased the ratio of the amount of high-molecular-weight multimers of adiponectin to the total adiponectin. In contrast, auraptene suppressed monocyte chemoattractant protein (MCP)-1 expression in 3T3-L1 adipocytes. Experiments using PPARgamma antagonist demonstrated that these effects on regulation of adiponectin and MCP-1 expression were caused by PPARgamma activations. The results indicate that auraptene activates PPARgamma in adipocytes to control adipocytekines such as adiponectin and MCP-1 and suggest that the consumption of citrus fruits, which contain auraptene can lead to a partial prevention of lipid and glucose metabolism abnormalities.

Adipocyte death, adipose tissue remodeling, and obesity complications

OBJECTIVE

We sought to determine the role of adipocyte death in obesity-induced adipose tissue (AT) inflammation and obesity complications.

RESEARCH DESIGN AND METHODS

Male C57BL/6 mice were fed a high-fat diet for 20 weeks to induce obesity. Every 4 weeks, insulin resistance was assessed by intraperitoneal insulin tolerance tests, and epididymal (eAT) and inguinal subcutaneous AT (iAT) and livers were harvested for histological, immunohistochemical, and gene expression analyses.

RESULTS

Frequency of adipocyte death in eAT increased from <0.1% at baseline to 16% at week 12, coincident with increases in 1) depot weight; 2) AT macrophages (ATM Phi s) expressing F4/80 and CD11c; 3) mRNA for tumor necrosis factor (TNF)-alpha, monocyte chemotactic protein (MCP)-1, and interleukin (IL)-10; and 4) insulin resistance. ATM Phi s in crown-like structures surrounding dead adipocytes expressed TNF-alpha and IL-6 proteins. Adipocyte number began to decline at week 12. At week 16, adipocyte death reached approximately 80%, coincident with maximal expression of CD11c and inflammatory genes, loss (40%) of eAT mass, widespread collagen deposition, and accelerated hepatic macrosteatosis. By week 20, adipocyte number was restored with small adipocytes, coincident with reduced adipocyte death (fourfold), CD11c and MCP-1 gene expression (twofold), and insulin resistance (35%). eAT weight did not increase at week 20 and was inversely correlated with liver weight after week 12 (r = -0. 85, P < 0.001). In iAT, adipocyte death was first detected at week 12 and remained <or=3%.

CONCLUSIONS

These results implicate depot-selective adipocyte death and M Phi-mediated AT remodeling in inflammatory and metabolic complications of murine obesity.

Changes in adiponectin and inflammatory genes in response to hormonal imbalances in female mice and exacerbation of depot selective visceral adiposity by high-fat diet: implications for insulin resistance

Early obesity and late onset of insulin resistance associated with hormonal imbalances occur in FSH receptor-deficient follitropin receptor knockout female mice. This study tests the hypothesis that chronic high-fat diet aggravates obesogenic changes in a depot-specific manner and explores some molecular links of hormone imbalances with insulin resistance. In SV 129 mice, hormonal imbalances seem obligatory for exacerbation of diet-induced obesity. Visceral adiposity, glucose intolerance, and lipid disturbances in 9-month follitropin receptor knockout females were associated with decrease in adiponectin signaling. High-molecular-weight plasma adiponectin and adipose tissue adiponectin mRNA were decreased. Adiponectin receptors R1 and R2 mRNA was selectively altered in mesenteric fat but not periuterine fat. R2 decreased in the liver and R1 was higher in muscle. Whereas hepatic adenosine monophosphate T-activated protein kinase activity was down-regulated, both phosphoenolpyruvate carboxykinase and glucose-6-phosphatase enzymes were up-regulated. Longitudinally, diminishing sex hormone signaling in adipose tissue was associated with progressive down-regulation of adiponectin activity and gradual impaired glucose tolerance. Chronic high-fat diet in SV129 wild-type mice did not produce overt obesity but induced visceral fat depot changes accompanied by liver lipid accumulation, high cholesterol, and up-regulation of inflammation gene mRNAs. Thus, TNF-alpha, C-C motif chemokine receptor-2, and C-C motif chemokine ligand-2 were selectively elevated in mesenteric fat without altering glucose tolerance and adiponectin signaling. Our study highlights adiponectin signaling and regulation to be involved in hormone imbalance-induced insulin resistance and demonstrates selective visceral adipose depot alterations by chronic high-fat diet and induction of inflammatory genes.

Obesity-induced inflammation in white adipose tissue is attenuated by loss of melanocortin-3 receptor signaling

Metabolic syndrome, a complex of highly debilitating disorders that includes insulin resistance, hypertension, and dyslipidemia, is associated with the development of obesity in humans as well as rodent models. White adipose tissue (WAT) inflammation, caused in part by macrophage infiltration, and fat accumulation in the liver are both linked to development of the metabolic syndrome. Despite large increases in body fat, melanocortin 3-receptor (MC3-R)-deficient mice do not get fatty liver disease or severe insulin resistance. This is in contrast to obese melanocortin 4-receptor (MC4-R)-deficient mice and diet-induced obese (DIO) mice, which show increased adiposity, fatty liver disease, and insulin resistance. We hypothesized that defects in the inflammatory response to obesity may underlie the protection from metabolic syndrome seen in MC3-R null mice. MC4-R mice fed a chow diet show increased proinflammatory gene expression and macrophage infiltration in WAT, as do wild-type (WT) DIO mice. In contrast, MC3-R-deficient mice fed a normal chow diet show neither of these inflammatory changes, despite their elevated adiposity and a comparable degree of adipocyte hypertrophy to the MC4-R null and DIO mice. Furthermore, even when challenged with high-fat chow for 4 wk, a period of time shown to induce an inflammatory response in WAT of WT animals, MC3-R nulls showed an attenuated up-regulation in both monocyte chemoattractant protein-1 (MCP-1) and TNFalpha mRNA in WAT compared with WT high-fat-fed animals.

Inhibitory effect of naringenin chalcone on inflammatory changes in the interaction between adipocytes and macrophages

Obese adipose tissue is characterized by an enhanced infiltration of macrophages. It is considered that the paracrine loop involving monocyte chemoattractant protein (MCP)-1 and tumor necrosis factor (TNF)-alpha between adipocytes and macrophages establishes a vicious cycle that augments the inflammatory changes and insulin resistance in obese adipose tissue. Polyphenols, which are widely distributed in fruit and vegetables, can act as antioxidants and some of them are also reported to have anti-inflammatory properties. Tomato is one of the most popular and extensively consumed vegetable crops worldwide, which also contains many flavonoids, mainly naringenin chalcone. We investigated the effect of flavonoids, including naringenin chalcone, on the production of proinflammatory mediators in lipopolysaccharide (LPS)-stimulated macrophages and in the interaction between adipocytes and macrophages. Naringenin chalcone inhibited the production of TNF-alpha, MCP-1, and nitric oxide (NO) by LPS-stimulated RAW 264 macrophages in a dose-dependent manner. Coculture of 3T3-L1 adipocytes and RAW 264 macrophages markedly enhanced the production of TNF-alpha, MCP-1, and NO compared with the control cultures; however, treatment with naringenin chalcone dose-dependently inhibited the production of these proinflammatory mediators. These results indicate that naringenin chalcone exhibits anti-inflammatory properties by inhibiting the production of proinflammatory cytokines in the interaction between adipocytes and macrophages. Naringenin chalcone may be useful for ameliorating the inflammatory changes in obese adipose tissue.

Capsaicin, a spicy component of hot peppers, modulates adipokine gene expression and protein release from obese-mouse adipose tissues and isolated adipocytes, and suppresses the inflammatory responses of adipose tissue macrophages

Adipokines are involved in the obesity-induced chronic inflammatory response that plays a crucial role in the development of obesity-related pathologies such as type II diabetes and atherosclerosis. We here demonstrate that capsaicin, a naturally occurring phytochemical, can suppress obesity-induced inflammation by modulating adipokine release from and macrophage behavior in obese mice adipose tissues. Capsaicin inhibited the expressions of IL-6 and MCP-1 mRNAs and protein release from the adipose tissues and adipocytes of obese mice, whereas it enhanced the expression of the adiponectin gene and protein. The action of capsaicin is associated with NF-kappaB inactivation and/or PPARgamma activation. Moreover, capsaicin suppressed not only macrophage migration induced by the adipose tissue-conditioned medium, but also macrophage activation to release proinflammatory mediators. Capsaicin may be a useful phytochemical for attenuating obesity-induced inflammation and obesity-related complications.

Macrophage-colony stimulating factor in obese adipose tissue: studies with heterozygous op/+ mice

OBJECTIVE

We examined the gene expression of macrophage-colony stimulating factor (M-CSF) in mice with diet-induced obesity and in genetically obese mice. We also examined the effect of decreased M-CSF signaling on the susceptibility to obesity and macrophage recruitment into the adipose tissue of mice.

RESEARCH METHODS AND PROCEDURES

The adipose tissue from mice with diet-induced obesity, obese KKA(y) mice, and ob/ob obese mice was used for RNA preparation. Production of M-CSF and monocyte chemoattractant protein-1 (MCP-1) was examined by quantitative real-time polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay. The op/+ heterozygous mice, with decreased functional M-CSF expression, were placed on a high-fat diet or crossed with KKA(y) mice to study the susceptibility to obesity. The gene expression of macrophage markers in adipose tissue was examined.

RESULTS

The expression of M-CSF was not significantly changed in mice on a high-fat diet or in either type of genetic obesity (KKA(y) or ob/ob mice). No change in the degree of obesity or macrophage-related gene expression (F4/80, CD68, and MCP-1) in the adipose tissue was observed in op/+ mice compared with +/+ control mice, which were either treated with a high-fat diet or crossed with KKA(y) mice.

DISCUSSION

This study demonstrated that there was no significant change in the expression of M-CSF in the adipose tissue from obese mice and only a minor phenotypic change, such as macrophage infiltration, in the adipose tissue from op/+ mice, suggesting that M-CSF does not play a major role in macrophage recruitment in the adipose tissue of obese mice.

Monocyte chemotactic protein-1 and its role in insulin resistance

PURPOSE OF REVIEW

In obesity, there is a strong link between increased adipose tissue mass and development of insulin resistance in tissues such as liver and muscle. Under these conditions, adipose tissue synthesizes various pro-inflammatory chemokines such as monocyte chemotactic protein-1. This review provides a summary of recent knowledge on the role of monocyte chemotactic protein-1 in adipose tissue inflammation and insulin resistance.

RECENT FINDINGS

Monocyte chemotactic protein-1 is a proinflammatory adipokine that is believed to play a role in the pathogenesis of obesity and diabetes. New in-vitro data demonstrate that monocyte chemotactic protein-1 has the ability to induce insulin resistance in adipocytes and skeletal muscle cells. By using mice that either overexpress monocyte chemotactic protein-1 or are deficient in monocyte chemotactic protein-1 or its receptor, exciting new insights have been obtained into the role of monocyte chemotactic protein-1 in adipose tissue inflammation and insulin resistance.

SUMMARY

Monocyte chemotactic protein-1 is an adipokine with insulin-resistance-inducing capacity that is related to increased adipose tissue mass in obesity and insulin resistance. It plays an important role in adipose tissue inflammation by recruiting macrophages into fat. Monocyte chemotactic protein-1 is thus a therapeutic target, and may represent an important factor linking adipose tissue inflammation, obesity and type 2 diabetes.

Active spice-derived components can inhibit inflammatory responses of adipose tissue in obesity by suppressing inflammatory actions of macrophages and release of monocyte chemoattractant protein-1 from adipocytes

Inflammation plays a key role in obesity-related pathologies such as cardiovascular disease, type II diabetes, and several types of cancer. Obesity-induced inflammation entails the enhancement of the recruitment of macrophages into adipose tissue and the release of various proinflammatory proteins from fat tissue. Therefore, the modulation of inflammatory responses in obesity may be useful for preventing or ameliorating obesity-related pathologies. Some spice-derived components, which are naturally occurring phytochemicals, elicit antiobesity and antiinflammatory properties. In this study, we investigated whether active spice-derived components can be applied to the suppression of obesity-induced inflammatory responses. Mesenteric adipose tissue was isolated from obese mice fed a high-fat diet and cultured to prepare an adipose tissue-conditioned medium. Raw 264.7 macrophages were treated with the adipose tissue-conditioned medium with or without active spice-derived components (i.e., diallyl disulfide, allyl isothiocyanate, piperine, zingerone and curcumin). Chemotaxis assay was performed to measure the degree of macrophage migration. Macrophage activation was estimated by measuring tumor necrosis factor-alpha (TNF-alpha), nitric oxide, and monocyte chemoattractant protein-1 (MCP-1) concentrations. The active spice-derived components markedly suppressed the migration of macrophages induced by the mesenteric adipose tissue-conditioned medium in a dose-dependent manner. Among the active spice-derived components studied, allyl isothiocyanate, zingerone, and curcumin significantly inhibited the cellular production of proinflammatory mediators such as TNF-alpha and nitric oxide, and significantly inhibited the release of MCP-1 from 3T3-L1 adipocytes. Our findings suggest that the spice-derived components can suppress obesity-induced inflammatory responses by suppressing adipose tissue macrophage accumulation or activation and inhibiting MCP-1 release from adipocytes. These spice-derived components may have a potential to improve chronic inflammatory conditions in obesity.