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

Adipose Tissue Remodeling: Its Role in Energy Metabolism and Metabolic Disorders

The adipose tissue is a central metabolic organ in the regulation of whole-body energy homeostasis. The white adipose tissue functions as a key energy reservoir for other organs, whereas the brown adipose tissue accumulates lipids for cold-induced adaptive thermogenesis. Adipose tissues secrete various hormones, cytokines, and metabolites (termed as adipokines) that control systemic energy balance by regulating appetitive signals from the central nerve system as well as metabolic activity in peripheral tissues. In response to changes in the nutritional status, the adipose tissue undergoes dynamic remodeling, including quantitative and qualitative alterations in adipose tissue-resident cells. A growing body of evidence indicates that adipose tissue remodeling in obesity is closely associated with adipose tissue function. Changes in the number and size of the adipocytes affect the microenvironment of expanded fat tissues, accompanied by alterations in adipokine secretion, adipocyte death, local hypoxia, and fatty acid fluxes. Concurrently, stromal vascular cells in the adipose tissue, including immune cells, are involved in numerous adaptive processes, such as dead adipocyte clearance, adipogenesis, and angiogenesis, all of which are dysregulated in obese adipose tissue remodeling. Chronic overnutrition triggers uncontrolled inflammatory responses, leading to systemic low-grade inflammation and metabolic disorders, such as insulin resistance. This review will discuss current mechanistic understandings of adipose tissue remodeling processes in adaptive energy homeostasis and pathological remodeling of adipose tissue in connection with immune response.

Bardoxolone Methyl Prevents Mesenteric Fat Deposition and Inflammation in High-Fat Diet Mice

Mesenteric fat belongs to visceral fat. An increased deposition of mesenteric fat contributes to obesity associated complications such as type 2 diabetes and cardiovascular diseases. We have investigated the therapeutic effects of bardoxolone methyl (BARD) on mesenteric adipose tissue of mice fed a high-fat diet (HFD). Male C57BL/6J mice were administered oral BARD during HFD feeding (HFD/BARD), only fed a high-fat diet (HFD), or fed low-fat diet (LFD) for 21 weeks. Histology and immunohistochemistry were used to analyse mesenteric morphology and macrophages, while Western blot was used to assess the expression of inflammatory, oxidative stress, and energy expenditure proteins. Supplementation of drinking water with BARD prevented mesenteric fat deposition, as determined by a reduction in large adipocytes. BARD prevented inflammation as there were fewer inflammatory macrophages and reduced proinflammatory cytokines (interleukin-1 beta and tumour necrosis factor alpha). BARD reduced the activation of extracellular signal-regulated kinase (ERK) and Akt, suggesting an antioxidative stress effect. BARD upregulates energy expenditure proteins, judged by the increased activity of tyrosine hydroxylase (TH) and AMP-activated protein kinase (AMPK) and increased peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), and uncoupling protein 2 (UCP2) proteins. Overall, BARD induces preventive effect in HFD mice through regulation of mesenteric adipose tissue.

McSkimming C, Harmon DB, Garmey JC, Oldham SN, Hallowell P, McNamara CA. Adipocyte progenitor cells initiate monocyte chemoattractant protein-1-mediated macrophage accumulation in visceral adipose tissue

OBJECTIVE

Macrophages are important producers of obesity-induced MCP-1; however, initial obesity-induced increases in MCP-1 production precede M1 macrophage accumulation in visceral adipose tissue (VAT). The initial cellular source of obesity-induced MCP-1 in vivo is currently unknown. Preliminary reports based on in vitro studies of preadipocyte cell lines and adherent stroma-vascular fraction cells suggest that resident stromal cells express MCP-1. In the past several years, elegant methods of identifying adipocyte progenitor cells (AdPCs) have become available, making it possible to study these cells in vivo. We have previously published that global deletion of transcription factor Inhibitor of Differentiation 3 (Id3) attenuates high fat diet-induced obesity, but it is unclear if Id3 plays a role in diet-induced MCP-1 production. We sought to determine the initial cellular source of MCP-1 and identify molecular regulators mediating MCP-1 production.

METHODS

Id3 (+/+) and Id3 (-/-) mice were fed either a standard chow or HFD for varying lengths of time. Flow cytometry, semi-quantitative real-time PCR, ELISAs and adoptive transfers were used to assess the importance of AdPCs during diet-induced obesity. Flow cytometry was also performed on a cohort of 14 patients undergoing bariatric surgery.

RESULTS

Flow cytometry identified committed CD45(-)CD31 (-) Ter119(-)CD29(+)CD34(+)Sca-1(+)CD24(-) adipocyte progenitor cells as producers of high levels of MCP-1 in VAT. High-fat diet increased AdPC numbers, an effect dependent on Id3. Loss of Id3 increased p21(Cip1) levels and attenuated AdPC proliferation, resulting in reduced MCP-1 and M1 macrophage accumulation in VAT, compared to Id3 (+/+) littermate controls. AdPC rescue by adoptive transfer of 50,000 Id3 (+/+) AdPCs into Id3 (-/-) recipient mice increased MCP-1 levels and M1 macrophage number in VAT. Additionally, flow cytometry identified MCP-1-producing CD45(-)CD31(-)CD34(+)CD44(+)CD90(+) AdPCs in human omental and subcutaneous adipose tissue, with a higher percentage in omental adipose. Furthermore, high surface expression of CD44 marked abundant MCP-1 producers, only in visceral adipose tissue.

CONCLUSIONS

This study provides the first in vivo evidence, to our knowledge, that committed AdPCs in VAT are the initial source of obesity-induced MCP-1 and identifies the helix-loop-helix transcription factor Id3 as a critical regulator of p21(Cip1) expression, AdPC proliferation, MCP-1 expression and M1 macrophage accumulation in VAT. Inhibition of Id3 and AdPC expansion, as well as CD44 expression in human AdPCs, may serve as unique therapeutic targets for the regulation of adipose tissue inflammation.

Tomato extract suppresses the production of proinflammatory mediators induced by interaction between adipocytes and macrophages

Obese adipose tissue is characterized by enhanced macrophage infiltration. A loop involving monocyte chemoattractant protein-1 (MCP-1) and tumor necrosis factor-α (TNFα) between adipocytes and macrophages establishes a vicious cycle that augments inflammatory changes and insulin resistance in obese adipose tissue. Tomatoes, one of the most popular crops worldwide, contain many beneficial phytochemicals that improve obesity-related diseases such as diabetes. Some of them have also been reported to have anti-inflammatory properties. In this study, we focused on the potential protective effects of phytochemicals in tomatoes on inflammation. We screened fractions of tomato extract using nitric oxide (NO) assay in lipopolysaccharide (LPS)-stimulated RAW264 macrophages. One fraction, RF52, significantly inhibited NO production in LPS-stimulated RAW264 macrophages. Furthermore, RF52 significantly decreased MCP-1 and TNFα productions. The coculture of 3T3-L1 adipocytes and RAW264 macrophages markedly enhanced MCP-1, TNFα, and NO productions compared with the control cultures; however, the treatment with RF52 inhibited the production of these proinflammatory mediators. These results suggest that RF52 from tomatoes may have the potential to suppress inflammation by inhibiting the production of NO or proinflammatory cytokines during the interaction between adipocytes and macrophages.

Novel phosphorylation of PPARγ ameliorates obesity-induced adipose tissue inflammation and improves insulin sensitivity

Chronic inflammation in adipose tissue is highly associated with insulin resistance. Herein, we demonstrate that a novel modification of PPARγ is strongly associated with inflammatory responses in adipose tissue. c-Src kinase directly phosphorylated PPARγ at Tyr78, and this process was reversed by protein tyrosine phosphatase-1B (PTP-1B). In adipocytes, phosphorylation of PPARγ suppressed the expression of pro-inflammatory genes as well as the secretion of chemokines and cytokines, thus reducing macrophage migration. Importantly, pharmacological inhibition of c-Src kinase aggravated insulin resistance in obese mice with a concomitant increase in the expression of pro-inflammatory genes in adipose tissue. These data strongly suggest that PPARγ phosphorylation is the key regulatory mechanism of the inflammatory response in adipose tissue, which is highly associated with glucose tolerance and insulin sensitivity. Furthermore, these data increase our understanding of the mechanical aspects of developing novel anti-diabetic drugs targeting PPARγ phosphorylation.

Inflammation, adiposity, and atherogenic dyslipidemia in rheumatoid arthritis: is there a paradoxical relationship?

Dyslipidemia is highly prevalent in rheumatoid arthritis (RA) and appears to be present very early in the RA disease process, in some studies even before a diagnosis of clinical RA has been made. The association between lipid measures and the risk of cardiovascular disease (CVD) in RA appears to be paradoxical, whereby lower levels of total cholesterol (TC), low-density lipoprotein (LDL-C), and atherogenic ratios are associated with higher CVD risk. This may be due to the lipid-lowering effects of RA-related systemic inflammation. Therefore, standard CVD risk calculators have been shown to underperform in RA. Data also suggest that lipoprotein particle sizes and the apolipoprotein cargo of lipoproteins skew toward atherogenic dyslipidemia in RA and may contribute to the initiation and progression of atherosclerosis. Inflammatory burden in RA may also alter the anti-inflammatory and atheroprotective roles associated with high-density lipoprotein cholesterol (HDL-C). Adipose tissue is quantitatively increased in RA patients compared with matched non-RA controls and may be more inflamed and metabolically dysfunctional compared with an otherwise similar non-RA patient. In vitro, animal, and a handful of non-RA human, studies suggest that inflamed, metabolically dysfunctional adipose tissue contributes directly to lower HDL-C levels. In turn, lower HDL-C that has been altered functionally by inflammation may lead to expanded adipose mass and further adipose dysfunction and inflammation. In the last part of this review, we speculate how the RA disease state may recapitulate these processes.

The pathophysiology of abdominal adipose tissue depots in health and disease

Obesity is currently the most important contributor to ill health and expenditure worldwide. More alarming is the fact that the pediatric population parallels adults, with obesity closely associated to type 2 diabetes mellitus (T2D), cardiovascular disease, hypertension, non-alcoholic fatty liver disease, vitamin D deficiency (VDD) and certain types of cancer. The observation in the early 1950s that android or truncal adipose tissue (AT) distribution compared to gynoid had a greater association with metabolic dysfunction, in particular T2D and cardiovascular disease risk, led to the hypothesis that obesity-associated complications are not associated with fat mass per se, but the pattern of fat distribution. This concept was further supported by groups of individuals with metabolic dysfunction despite a lean phenotype, and healthy obese people protected from metabolic dysfunction. It is now well recognized that an increase in visceral AT is an independent risk factor for the development of obesity-associated comorbidities with AT depot distribution, their anatomic, cellular and molecular features defining their role. The differences and the plasticity of subcutaneous, visceral and ectopic ATs to store and release fatty acids and to synthesize and secrete adipokines, defines the metabolic outcomes. The present review will examine the phenotypic and pathophysiological differences between the different AT depots, with a particular focus on the abdominal depots and their link to metabolic complications.

The gut-adipose-liver axis in the metabolic syndrome

Obesity is associated with altered gut microbiota composition and impaired gut barrier function. These changes, together with interrelated mesenteric adipose tissue inflammation, result in increased release of pro-inflammatory cytokines, bacteria-derived factors, and lipids into the portal circulation, promoting the development of (hepatic) insulin resistance. Herein, the potential impact of obesity-related changes in gut and visceral adipose tissue biology on the development of insulin resistance and Type 2 diabetes is reviewed.

Inflammatory and cardiometabolic risk on obesity: role of environmental xenoestrogens

CONTEXT

Some chemicals used in consumer products or manufacturing (eg, plastics, pesticides) have estrogenic activities; these xenoestrogens (XEs) may affect immune responses and have recently emerged as a new risk factors for obesity and cardiovascular disease. However, the extent and impact on health of chronic exposure of the general population to XEs are still unknown.

OBJECTIVE

The objective of the study was to investigate the levels of XEs in plasma and adipose tissue (AT) depots in a sample of pre- and postmenopausal obese women undergoing bariatric surgery and their cardiometabolic impact in an obese state.

DESIGN AND PARTICIPANTS

We evaluated XE levels in plasma and visceral and subcutaneous AT samples of Portuguese obese (body mass index ≥ 35 kg/m(2)) women undergoing bariatric surgery. Association with metabolic parameters and 10-year cardiovascular disease risk was assessed, according to menopausal status (73 pre- and 48 postmenopausal). Levels of XEs were determined by gas chromatography with electron-capture detection. Anthropometric and biochemical data were collected prior to surgery. Adipocyte size was determined on tissue sections obtained during surgery.

RESULTS

Our data show that XEs are pervasive in this obese population. Distribution of individual and concentration of total XEs differed between plasma, visceral AT, and subcutaneous AT, and the pattern of accumulation was different between pre- and postmenopausal women. Significant associations between XE levels and metabolic and inflammatory parameters were found. In premenopausal women, XEs in plasma seem to be a predictor of 10-year cardiovascular disease risk.

CONCLUSIONS

Our findings point toward a different distribution of XE between plasma and AT in pre- and postmenopausal women, and reveal the association between XEs on the development of metabolic abnormalities in obese premenopausal women.

Esculetin inhibits the inflammatory response by inducing heme oxygenase-1 in cocultured macrophages and adipocytes

Obesity is associated with chronic low-grade inflammation of adipose tissue. In this study, we investigated the anti-inflammatory effects of esculetin (ECT) through up-regulation of heme oxygenase-1 (HO-1) in cocultured macrophages and adipocytes. RAW264.7 macrophages and differentiated 3T3-L1 adipocytes were cocultured in serum-free Dulbecco's modified Eagle's medium with or without ECT for 24 h. Nitric oxide (NO), tumor necrosis factor-α (TNF-α), and monocyte chemoattractant protein-1 (MCP-1) production was measured in the coculture supernatant. ECT decreased the secretion of NO, TNF-α, and MCP-1. The expression of adipogenic proteins, including peroxisome proliferator-activated receptors γ (PPARγ) and CCAAT/enhancer binding protein α (C/EBPα) in cocultured adipocytes and inducible nitric oxide synthase (iNOS) in cocultured macrophages, was inhibited by ECT. Additionally, HO-1 expression was induced in cocultured macrophages and adipocytes. Silencing of HO-1 expression increased the production of NO, TNF-α, and MCP-1 in cocultured cells, in spite of the presence of ECT. This study demonstrated that ECT exhibited anti-inflammatory properties by inhibiting the production of proinflammatory cytokines in the interaction between adipocytes and macrophages through HO-1 expression. ECT may have the potential to improve chronic inflammation in obesity.

Higher plasma lipopolysaccharide concentrations are associated with less favorable phenotype in overweight/obese men

PURPOSE

Lipopolysaccharide (LPS) from the outer membrane of gram-negative bacteria might be an inflammation trigger in adipose tissue. It has recently been proposed that there is a link between adipose tissue distribution and blood LPS. However, the number of studies on this topic is scarce, and further investigation in humans is required. In this study, we explored the association between plasma LPS concentrations and body fat distribution, as well as the biochemical parameters that may indicate the presence of metabolic disorders.

METHODS

Sixty-seven young adult men with body mass index of 26-35 kg/m(2) were evaluated. Anthropometry, body composition and body fat distribution, blood pressure, energy expenditure, physical activity level, dietary intake, and biochemical parameters were assessed.

RESULTS

Men with median plasma LPS ≥ 0.9 EU/mL presented higher sagittal abdominal diameter, trunk fat percentage, and android fat percentage, and mass, insulin and alanine aminotransferase concentrations, homeostasis model assessment of insulin resistance (HOMA-IR), and beta cell dysfunction (HOMA-B) than those with lower plasma LPS. LPS correlated positively with the trunk fat percentage, and android fat percentage, and mass, insulin, aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase concentrations, as well as HOMA-IR and HOMA-B.

CONCLUSION

Our results suggest that a higher plasma LPS concentration is associated with a less favorable phenotype as characterized by higher central adiposity, higher values of HOMA-IR, and beta cell function impairment in overweight/obese men.

Adipose tissue immune response: novel triggers and consequences for chronic inflammatory conditions

Adipose tissue inflammation mediates the association between excessive body fat accumulation and several chronic inflammatory diseases. A high prevalence of obesity-associated adipose tissue inflammation was observed not only in patients with cardiovascular conditions but also in patients with inflammatory bowel diseases, abdominal aortic aneurysm, or cardiorenal syndrome. In addition to excessive caloric intake, other triggers promote visceral adipose tissue inflammation followed by chronic, low-grade systemic inflammation. The infiltration and accumulation of immune cells in the inflamed and hypertrophied adipose tissue promote the production of inflammatory cytokines, contributing to target organ damages. This comorbidity seems to delimit subgroups of individuals with systemic adipose tissue inflammation and more severe chronic inflammatory diseases that are refractory to conventional treatment. This review highlights the association between adipose tissue immune response and the pathophysiology of visceral adiposity-related chronic inflammatory diseases, while suggesting several new therapeutic strategies.

Effect of citrus flavonoids, naringin and naringenin, on metabolic syndrome and their mechanisms of action

Flavonoids are important natural compounds with diverse biologic activities. Citrus flavonoids constitute an important series of flavonoids. Naringin and its aglycone naringenin belong to this series of flavonoids and were found to display strong anti-inflammatory and antioxidant activities. Several lines of investigation suggest that naringin supplementation is beneficial for the treatment of obesity, diabetes, hypertension, and metabolic syndrome. A number of molecular mechanisms underlying its beneficial activities have been elucidated. However, their effect on obesity and metabolic disorder remains to be fully established. Moreover, the therapeutic uses of these flavonoids are significantly limited by the lack of adequate clinical evidence. This review aims to explore the biologic activities of these compounds, particularly on lipid metabolism in obesity, oxidative stress, and inflammation in context of metabolic syndrome.

Dietary trimethylamine N-oxide exacerbates impaired glucose tolerance in mice fed a high fat diet

Trimethylamine N-oxide (TMAO) is an oxidation product of trimethylamine (TMA) and is present in many aquatic foods. Here, we investigated the effects of TMAO on glucose tolerance in high fat diet (HFD)-fed mice. Male C57BL/6 mice were randomly assigned to the control, high fat (HF), and TMAO groups. The HF group was fed a diet containing 25% fat, and the TMAO group was fed the HFD plus 0.2% TMAO for 4 weeks. After 3 weeks of feeding, oral glucose tolerance tests were performed. Dietary TMAO increased fasting insulin levels and homeostasis model assessment-estimated insulin resistance (HOMA-IR) and exacerbated the impaired glucose tolerance in HFD-fed mice. These effects were associated with the expression of genes related to the insulin signal pathway, glycogen synthesis, gluconeogenesis and glucose transport in liver. mRNA levels of the pro-inflammatory cytokine MCP-1 increased significantly and of the anti-inflammatory cytokine IL-10 greatly decreased in adipose tissue. Our results suggest that dietary TMAO exacerbates impaired glucose tolerance, obstructs the hepatic insulin signaling pathway, and causes adipose tissue inflammation in mice fed a high fat diet.

Exercise, but not quercetin, ameliorates inflammation, mitochondrial biogenesis, and lipid metabolism in skeletal muscle after strenuous exercise by high-fat diet mice

[Purpose]

The purpose of this study was to investigate whether moderate exercise and quercetin intake with a low fat diet contribute to inflammatory cytokine production, mitochondrial biogenesis, and lipid metabolism in skeletal muscle after strenuous exercise by high-fat diet mice.

[Methods]

Male C57BL/6 mice were randomly divided into four groups: (1) High-fat for 12 weeks and low-fat diet control (C; n = 6); (2) high-fat diet for 12 weeks and low-fat diet with quercetin (Q; n = 4); (3) high-fat diet for 12 weeks and low-fat diet with exercise (E; n = 4); or (4) high-fat diet for 12 weeks and low-fat diet with exercise and quercetin (EQ; n = 5). Quercetin (10 mg/kg) was administered once per day, 5 day/week for 8 weeks. Exercise training was performed at moderate intensity for 8 weeks, 5 days/week for 30–60 min/day. Mice were subjected to a strenuous exercise bout of 60 min at a speed of 25 m/min (VO₂ max 85%) conducted as an exercise-induced fatigue just before sacrifice.

[Results]

As results, body weights were significantly different among the groups. Exercise training significantly reduced inflammatory cytokines after strenuous exercise in skeletal muscle of high-fat diet mice. Exercise training increased Tfam mRNA in the soleus muscle after strenuous exercise. Exercise training significantly decreased lipogenesis markers in skeletal muscle of obese mice after strenuous exercise. Moderate exercise significantly increased lipolysis markers in the tibialis anterior muscle.

[Conclusion]

These findings suggest that exercise training reduced inflammatory cytokine levels and improved mitochondrial biogenesis and lipid metabolism. However quercetin supplementation did not affect these parameters. Thus, long-term moderate exercise training has positive effects on obesity.

CB1 blockade potentiates down-regulation of lipogenic gene expression in perirenal adipose tissue in high carbohydrate diet-induced obesity

De novo lipogenesis and hypercaloric diets are thought to contribute to increased fat mass, particularly in abdominal fat depots. CB₁ is highly expressed in adipose tissue, and CB₁-mediated signalling is associated with stimulation of lipogenesis and diet-induced obesity, though its contribution to increasing fat deposition in adipose tissue is controversial. Lipogenesis is regulated by transcription factors such as liver X receptor (LXR), sterol-response element binding protein (SREBP) and carbohydrate-responsive-element-binding protein (ChREBP). We evaluated the role of CB₁ in the gene expression of these factors and their target genes in relation to lipogenesis in the perirenal adipose tissue (PrAT) of rats fed a high-carbohydrate diet (HCHD) or a high-fat diet (HFD). Both obesity models showed an up-regulated gene expression of CB₁ and Lxrα in this adipose pad. The Srebf-1 and ChREBP gene expressions were down-regulated in HFD but not in HCHD. The expression of their target genes encoding for lipogenic enzymes showed a decrease in diet-induced obesity and was particularly dramatic in HFD. In HCHD, CB₁ blockade by AM251 reduced the Srebf-1 and ChREBP expression and totally abrogated the remnant gene expression of their target lipogenic enzymes. The phosphorylated form of the extracellular signal-regulated kinase (ERK-p), which participates in the CB₁-mediated signalling pathway, was markedly present in the PrAT of obese rats. ERK-p was drastically repressed by AM251 indicating that CB₁ is actually functional in PrAT of obese animals, though its activation loses the ability to stimulate lipogenesis in PrAT of obese rats. Even so, the remnant expression levels of lipogenic transcription factors found in HCHD-fed rats are still dependent on CB₁ activity. Hence, in HCHD-induced obesity, CB₁ blockade may help to further potentiate the reduction of lipogenesis in PrAT by means of inducing down-regulation of the ChREBP and Srebf-1 gene expression, and consequently in the expression of lipogenic enzymes.

Anti-inflammatory effects of phenolic compounds isolated from the flowers of Nymphaea mexicana Zucc

Nymphaea mexicana Zucc. is an aquatic plant species which belongs to the family Nymphaea and is commonly known as the yellow water lily. The aim of this work was to study the in vitro antiinflammatory effects of phenolic compounds isolated from the flowers of Nymphaea mexicana Zucc. Seven phenolic compounds including vanillic acid, 4-methoxy-3,5-dihydroxybenzoic acid, (2R,3R)-3,7-dihydroxyflavanone, naringenin (4), kaempferol 3-O-(3-O-acetyl-a-L-rhamnopyranoside), kaempferol 3-O-(2-O-acetyl-a-L-rhamnopyranoside), and quercetin 3-(30 0-acetylrhamnoside) (7) were isolated from the flowers of Nymphaea mexicana Zucc. These results revealed that compound 4 has the most prominent inhibitory effect on the LPS-stimulated nitric oxide (NO), monocyte chemotactic protein-1 (MCP-1), and tumor necrosis factor-alpha (TNF-a) production in RAW 264.7 macrophages. In addition, compound 4 also inhibited LPS-mediated induction of protein expressions of inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and phospho-ERK in RAW 264.7 macrophages. Thus, compound 4 from the flowers of Nymphaea mexicana Zucc. may provide a potential therapeutic approach for inflammation-associated disorders.

Quercetin suppresses MIP-1α-induced adipose inflammation by downregulating its receptors CCR1/CCR5 and inhibiting inflammatory signaling

Obesity-induced inflammation is characterized by recruitment of adipose tissue macrophages that release inflammatory cytokines and chemokines. MIP-1α (macrophage inflammatory protein 1α)/CCL3, a CC chemokine, induces monocyte/macrophage infiltration and thus is implicated in obesity-induced adipose inflammation. Quercetin has been shown to modulate obesity-induced inflammation, but the mechanism of its action remains unclear. Here we demonstrate that quercetin decreases MIP-1α release from adipocytes and macrophages and from cocultured adipocytes/macrophages; it also opposes MIP-1α-induced macrophage infiltration and activation. The inhibitory action of quercetin on the MIP-1α-induced inflammatory responses of macrophages is mediated by downregulation of CCR1/CCR5, and inhibition of activation of JNK, p38 mitogen-activated-protein kinase (MAPK), and IKK as well as IκBα degradation. These findings suggest that quercetin may be a useful agent against obesity-induced adipose tissue inflammation.

Immunomodulatory Role of an Ayurvedic Formulation on Imbalanced Immunometabolics during Inflammatory Responses of Obesity and Prediabetic Disease

Kal-1 is a polyherbal decoction of seven different natural ingredients, traditionally used in controlling sugar levels, inflammatory conditions particularly regulating metabolic and immunoinflammatory balance which are the major factors involved in obesity and related diseases. In the present study, we aimed to investigate the effect of Kal-1 (an abbreviation derived from the procuring source) on diet-induced obesity and type II diabetes using C57BL/6J mice as a model. The present study was performed with two experimental groups involving obese and prediabetic mice as study animals. In one, the mice were fed on high-fat with increased sucrose diet, and different amounts (5, 20, and 75 μL) of Kal-1 were administered with monitoring of disease progression over a period of 21 weeks whereas in the second group the mice were first put on the same diet for 21 weeks and then treated with the same amounts of Kal-1. A significant reduction in body weight, fat pads, fasting blood glucose levels, insulin levels, biochemical parameters, immunological parameters, and an array of pro- and anticytokines was observed in obese and diabetic mice plus Kal-1 than control (lean) mice fed on normal diet. In conclusion, Kal-1 has immunomodulatory potential for diet-induced obesity and associated metabolic disorders.

Plasma lipopolysaccharide is closely associated with glycemic control and abdominal obesity: evidence from bariatric surgery

OBJECTIVE

It is of vital importance to elucidate the triggering factors of obesity and type 2 diabetes to improve patient care. Bariatric surgery has been shown to prevent and even cure diabetes, but the mechanism is unknown. Elevated levels of lipopolysaccharide (LPS) predict incident diabetes, but the sources of LPS are not clarified. The objective of the current study was to evaluate the potential impact of plasma LPS on abdominal obesity and glycemic control in subjects undergoing bariatric surgery.

RESEARCH DESIGN AND METHODS

This was a prospective observational study involving a consecutive sample of 49 obese subjects undergoing bariatric surgery and 17 controls. Main assessments were plasma LPS, HbA1c, adipose tissue volumes (computed tomography), and quantified bacterial DNA in adipose tissue compartments.

RESULTS

Plasma levels of LPS were elevated in obese individuals compared with controls (P < 0.001) and were reduced after bariatric surgery (P = 0.010). LPS levels were closely correlated with HbA1c (r = 0.56; P = 0.001) and intra-abdominal fat volumes (r = 0.61; P < 0.001), but only moderately correlated with subcutaneous fat volumes (r = 0.33; P = 0.038). Moreover, there was a decreasing gradient (twofold) in bacterial DNA levels going from mesenteric via omental to subcutaneous adipose tissue compartments (P = 0.041). Finally, reduced LPS levels after bariatric surgery were directly correlated with a reduction in HbA1c (r = 0.85; P < 0.001).

CONCLUSIONS

Our findings support a hypothesis of translocated gut bacteria as a potential trigger of obesity and diabetes, and suggest that the antidiabetic effects of bariatric surgery might be mechanistically linked to, and even the result of, a reduction in plasma levels of LPS.

Stop feeding cancer: pro-inflammatory role of visceral adiposity in liver cancer

Liver cancer is the fifth most common cancer in the world with an estimated over half a million new cases diagnosed every year. Due to the difficulty in early diagnosis and lack of treatment options, the prevalence of liver cancer continues to climb with a 5-year survival rate of between 6% and 11%. Coinciding with the rise of liver cancer, the prevalence of obesity has rapidly increased over the past two decades. Evidence from epidemiological studies demonstrates a higher risk of hepatocellular carcinoma (HCC) in obese individuals. Obesity is recognised as a low-grade inflammatory disease, this is of particular relevance as inflammation has been proposed as the seventh hallmark of cancer development with abdominal visceral adiposity considered as an important source of pro-inflammatory stimuli. Emerging evidence points towards the direct role of visceral adipose tissue rather than generalised body fat in carcinogenesis. Cytokines such as IL-6 and TNF-α secreted from visceral adipose tissue have been demonstrated to induce a chronic inflammatory condition predisposing the liver to a protumourigenic milieu. This review focuses on excess visceral adiposity rather than simple obesity; particularly adipokines and their implications for chronic inflammation, lipid accumulation, insulin resistance, Endoplasmic Reticulum (ER) stress and angiogenesis. Evidence of molecular signalling pathways that may give rise to the onset and progression of HCC in this context are depicted. Delineation of the pro-inflammatory role of visceral adiposity in liver cancer and its targeting will provide better rational and therapeutic approaches for HCC prevention and elimination. The concept of a central role for metabolism in cancer is the culmination of an effort that began with one of the 20th century's leading biochemists and Nobel laureate of 1931, Otto Warburg.

Loss of CCR5 results in glucose intolerance in diet-induced obese mice

Macrophage and T cell infiltration into metabolic tissues contributes to obesity-associated inflammation and insulin resistance (IR). C-C chemokine receptor 5 (CCR5), expressed on macrophages and T cells, plays a critical role in the recruitment and activation of proinflammatory M1 and TH1 immune cells to tissues and is elevated in adipose tissue (AT) and liver of obese humans and mice. Thus, we hypothesized that deficiency of CCR5 would protect against diet-induced inflammation and IR. CCR5-deficient (CCR5(-/-)) mice and C57BL/6 (WT) controls were fed 10% low-fat (LF) or 60% high-fat (HF) diets for 16 wk. HF feeding increased adiposity, blood glucose, and plasma insulin levels equally in both genotypes. Opposing our hypothesis, HF-fed CCR5(-/-) mice were significantly more glucose intolerant than WT mice. In AT, there was a significant reduction in the M1-associated gene CD11c, whereas M2 associated genes were not different between genotypes. In addition, HF feeding caused a twofold increase in CD4(+) T cells in the AT of CCR5(-/-) compared with WT mice. In liver and muscle, no differences in immune cell infiltration or inflammatory cytokine expression were detected. However, in AT and muscle, there was a mild reduction in insulin-induced phosphorylation of AKT and IRβ in CCR5(-/-) compared with WT mice. These findings suggest that whereas CCR5 plays a minor role in regulating immune cell infiltration and inflammation in metabolic tissues, deficiency of CCR5 impairs systemic glucose tolerance as well as AT and muscle insulin signaling.

Adipocyte fetuin-A contributes to macrophage migration into adipose tissue and polarization of macrophages

Macrophage infiltration into adipose tissue during obesity and their phenotypic conversion from anti-inflammatory M2 to proinflammatory M1 subtype significantly contributes to develop a link between inflammation and insulin resistance; signaling molecule(s) for these events, however, remains poorly understood. We demonstrate here that excess lipid in the adipose tissue environment may trigger one such signal. Adipose tissue from obese diabetic db/db mice, high fat diet-fed mice, and obese diabetic patients showed significantly elevated fetuin-A (FetA) levels in respect to their controls; partially hepatectomized high fat diet mice did not show noticeable alteration, indicating adipose tissue to be the source of this alteration. In adipocytes, fatty acid induces FetA gene and protein expressions, resulting in its copious release. We found that FetA could act as a chemoattractant for macrophages. To simulate lipid-induced inflammatory conditions when proinflammatory adipose tissue and macrophages create a niche of an altered microenvironment, we set up a transculture system of macrophages and adipocytes; the addition of fatty acid to adipocytes released FetA into the medium, which polarized M2 macrophages to M1. This was further confirmed by direct FetA addition to macrophages. Taken together, lipid-induced FetA from adipocytes is an efficient chemokine for macrophage migration and polarization. These findings open a new dimension for understanding obesity-induced inflammation.

The role of inflammatory pathways in cancer-associated cachexia and radiation resistance

Dysregulated inflammatory responses are key contributors to a multitude of chronic ailments, including cancer. Evidence indicates that disease progression in cancer is dependent on the complex interaction between the tumor and the host microenvironment. Most recently, the inflammatory response has been suggested to be critical, as both the tumor and microenvironment compartments produce cytokines that act on numerous target sites, where they foster a complex cascade of biologic outcomes. Patients with cancer-associated cachexia (CAC) suffer from a dramatic loss of skeletal muscle and adipose tissue, ultimately precluding them from many forms of therapeutic intervention, including radiotherapy. The cytokines that have been linked to the promotion of the cachectic response may also participate in radiation resistance. The major changes at the cytokine level are, in part, due to transcriptional regulatory alterations possibly due to epigenetic modifications. Herein we discuss the role of inflammatory pathways in CAC and examine the potential link between cachexia induction and radiation resistance.

Oral but not intravenous glucose acutely decreases circulating interleukin-6 concentrations in overweight individuals

BACKGROUND

Plasma interleukin-6 (IL-6) concentrations decrease acutely 1 h after ingestion of a glucose load or mixed meals and this may be mediated by an anti-inflammatory effect of insulin. The aim of the present study was to compare the effect of higher versus lower insulin levels on plasma IL-6 concentrations following oral compared with intravenous glucose administration in overweight/obese subjects.

METHODS AND FINDINGS

Fifteen subjects (12 women and 3 men) with BMI >28 kg/m(2) were given an oral glucose load (75 g) followed a week later by an intravenous infusion of glucose aimed at matching plasma glucose concentrations during the oral glucose load. A week later, they drank a volume of water equivalent to the volume consumed with the oral glucose load. Plasma glucose, insulin, nonesterified fatty acids, and IL-6 concentrations and blood hematocrit were measured at 30 minute intervals for 2 h following each intervention. Plasma IL-6 decreased (13-20%) significantly (P = 0.009) at 30 min to 90 min following the oral glucose load and did not change significantly following the other two interventions. The incremental area under the curve for plasma IL-6 concentrations following oral intake of glucose was significantly lower compared with concentrations following intravenous glucose (P = 0.005) and water control (P = 0.02). Circulating insulin concentrations were significantly (P<0.001) and 2.8 fold higher following oral compared with intravenous glucose administration.

CONCLUSIONS

These data show that plasma IL-6 concentrations did not decrease during isoglycemic, intravenous glucose administration suggesting that the markedly higher circulating insulin levels and/or gut-related factors may mediate the acute decrease in plasma IL-6 after oral glucose intake in overweight/obese subjects.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry ACTRN12612000491864.

Auraptene suppresses inflammatory responses in activated RAW264 macrophages by inhibiting p38 mitogen-activated protein kinase activation

SCOPE

Inflammation plays a key role in obesity-related pathologies such as insulin resistance and type 2 diabetes. Hypertrophied adipocytes trigger the enhancement of macrophage infiltration and the release of various proinflammatory factors in obese adipose tissue. In this study, we examined whether auraptene, a citrus-fruit-derived compound, could suppress the production of inflammatory factors that mediate the interaction between adipocytes and macrophages.

METHODS AND RESULTS

Experiments using a co-culture system of 3T3-L1 adipocytes and RAW264 macrophages showed that auraptene reduced the production of nitric oxide and tumor necrosis factor-α. In RAW264 macrophages, auraptene also suppressed the inflammation induced by either LPS or the conditioned medium derived from 3T3-L1 adipocytes. In addition, auraptene inhibited the phosphorylation of the p38 mitogen-activated protein kinase and suppressed the production of proinflammatory mediators in activated macrophages.

CONCLUSION

Our findings indicate that auraptene exhibits anti-inflammatory properties by suppressing the production of inflammatory factors that mediate the interaction between adipocytes and macrophages, suggesting that auraptene is a valuable food-derived compound with a potential to attenuate chronic inflammation in adipose tissue and to improve obesity-related insulin resistance.

Infiltration of M1 macrophages into adipose tissue of ddY-H mice preceding spontaneous appearances of insulin resistance

We have isolated insulin resistant mice (ddY-H mice) which are spontaneously induced at 12-weeks of age even if fed with the standard chow pellets. Since accumulated evidences have suggested that an appearance of insulin resistance is associated with obesity and a state of inflammation in adipose tissue, the present study investigated an appearance of macrophages in adipose tissue of ddY-H mice. Although ddY-H mice were fed the standard chow pellets ad libitam, increases in body weight, adipose tissue mass, and fat cell size were observed. In adipose tissues of ddY-H mice, gene expression of monocyte chemoattractant protein-1 (MCP-1) elevated slightly at 5-weeks of age and was maintained at higher levels at 9- and 12-weeks of age, and MCP-1 content in adipose tissue increased 2-fold at 12-weeks of age. Also, increased gene expressions of CD68 and F4/80, markers of macrophage, in adipose tissue were observed at 9-weeks of age. In addition, F4/80 positive cells were histologically found in adipose tissue at 15-weeks of age but not at 7-weeks of age, suggesting an increased infiltration of macrophage into adipose tissue. In adipose tissue of ddY-H mice, gene expressions of CD11c and toll-like receptor 4 (TLR4), markers of proinflammatory macrophages (M1), markedly increased although those of CD163 and mannose receptor (MR), markers of anti-inflammatory macrophages (M2), did not change. These results suggest that proinflammatory (M1) macrophages infiltrate into enlarged adipose tissues of ddY-H mice, which is preceding spontaneous appearance of insulin resistance.

Citrus flavonoid naringenin inhibits TLR2 expression in adipocytes

Toll-like receptors (TLRs) were recently shown to be involved in obesity-induced inflammation in adipose tissue, which contributes to the development of insulin resistance and type 2 diabetes. Thus, the appropriate regulation of TLR expression or activation is an important strategy for improving obesity-related diseases. In this report, we show that naringenin, a citrus flavonoid, inhibits TLR2 expression during adipocyte differentiation. This effect is mediated in part through peroxisome proliferator-activated receptor γ activation. In addition, naringenin suppresses TLR2 expression induced by the co-culture of differentiated adipocytes and macrophages and also inhibits tumor necrosis factor-α (TNF-α)-induced TLR2 expression by inhibiting the activation of nuclear factor-κB and c-Jun NH2-terminal kinase pathways in differentiated adipocytes. Furthermore, naringenin decreases TLR2 expression in adipose tissue of high-fat diet-fed mice. These results are correlated with the improvement of hyperglycemia and the suppression of inflammatory mediators, including TNF-α and monocyte chemotactic protein-1. Taken together, these data suggest that naringenin exhibits anti-inflammatory properties, presumably by inhibiting TLR2 expression in adipocytes. Our findings suggest a molecular mechanism by which naringenin exerts beneficial effects against obesity-related diseases.

Alternatively activated macrophages in types 1 and 2 diabetes

Macrophages are innate immune cells derived from monocytes, which, in turn, arise from myeloid precursor cells in the bone marrow. Macrophages have many important roles in the innate and adaptive immune response, as well as in tissue homeostasis. Two major populations have been defined: The classically activated macrophages that respond to intracellular pathogens by secreting proinflammatory cytokines and reactive oxygen species and alternatively activated macrophages which are induced during Th2 responses displaying anti-inflammatory activities. Both macrophage populations are central players in diabetes, the first one triggering inflammatory responses which initiates insulitis and pancreatic β cell death during type 1 diabetes, whereas the second population decreases hyperglycemia, insulitis, and inflammation in the pancreas, thereby negatively regulate type 1 diabetes. Obesity is an important factor in the development of type 2 diabetes; classically activated macrophages are a dominant cell population involved in the establishment of the inflammatory profile, insulin resistance, and activation of inflammatory signals during the development and progression of this disease. In contrast, alternatively activated macrophages regulate the release of proinflammatory cytokines, attenuating adipose tissue inflammation. Here, we review the advantages and disadvantages of these two macrophage populations with regard to their roles in types 1 and 2 diabetes.

Advanced glycation endproducts stimulate renal epithelial cells to release chemokines that recruit macrophages, leading to renal fibrosis

Diabetic nephropathy is a major complication of diabetes and tubulointerstitial fibrosis is one of its manifestations. This study aimed to clarify the pathogenicity of advanced glycation endproducts (AGEs) toward NRK-52E, a tubular epithelial cell line. The AGE-exposed cells significantly increased gene expression of transforming growth factor beta, plasminogen activator inhibitor-1, and tissue transglutaminase, and a medium conditioned by them showed strong potential to recruit macrophages, partly through a chemokine, monocyte chemoattractant protein-1. Albumin denatured by maintenance at 37 °C for 120 d exhibited similar activities, but they were lower than those of the AGEs. Thus, AGEs generated in diabetic patients might exacerbate fibrosis in the kidneys directly through renal epithelial cell stimulation, and indirectly by recruitment of macrophages.

Depot-specific differences in adipocyte insulin sensitivity in mice are diet- and function-dependent

Fat depots of different localization vary in their biological/metabolic function. We recently provided evidence for different regulation of lipolysis between perigonadal and mesenteric adipocytes; in particular insulin-induced suppression of lipolysis was significantly higher in perigonadal compared with mesenteric adipocytes in chow-fed mice. Moreover, insulin’s anti-lipolytic effect was maintained in mesenteric but lost in perigonadal adipocytes under high fat diet (HFD). Herein, we expanded our previous study and included inguinal (subcutaneous) adipocytes in our analysis. When compared with perigonadal adipocytes, inguinal adipocytes are equally sensitive to insulin’s anti-lipolytic effect under chow diet. However, they remain insulin-sensitive under HFD. Moreover, insulin-stimulated glucose incorporation was equally blunted in adipocytes of all three depots in HFD-fed mice. In conclusion, regulation of insulin sensitivity in murine adipocytes is diet-, depot- and function-dependent.

Obesity: considerations about etiology, metabolism, and the use of experimental models

Studies have been conducted in order to identify the main factors that contribute to the development of obesity. The role of genetics has also been extensively studied. However, the substantial augmentation of obesity prevalence in the last 20 years cannot be justified only by genetic alterations that, theoretically, would have occurred in such a short time. Thus, the difference in obesity prevalence in various population groups is also related to environmental factors, especially diet and the reduction of physical activity. These aspects, interacting or not with genetic factors, could explain the excess of body fat in large proportions worldwide. This article will focus on positive energy balance, high-fat diet, alteration in appetite control hormones, insulin resistance, amino acids metabolism, and the limitation of the experimental models to address this complex issue.

Relation of depot-specific adipose inflammation to insulin resistance in human obesity

BACKGROUND:

A low-grade state of adipose tissue inflammation associated with obesity has been linked to mechanisms of systemic metabolic dysfunction. However, the relation of clinical phenotypes to depot-specific inflammation has not been well examined in human obesity.

OBJECTIVE:

To characterize the inflammatory status of subcutaneous and visceral fat depots, as assessed by tissue presence of macrophage crown-like structures (CLS) as a hallmark of chronic inflammation, and determine the relation of systemic insulin resistance to inflammatory abnormalities in subcutaneous and visceral fat.

METHODS:

We collected adipose tissue simultaneously from subcutaneous and visceral (omental and mesenteric) depots in 92 obese participants (age 42±11 years; BMI⩾30 kg m⁻²) during planned bariatric surgery. Using immunohistochemistry, we categorized individuals as CLS⁺ or CLS⁻ based on the presence or absence, respectively, of macrophage CLS in subcutaneous (CLS_s), omental (CLS_o) and mesenteric (CLS_m) adipose depots.

RESULTS:

The majority of participants exhibited adipose tissue inflammation manifest by the presence of CLS (CLS⁺) in both subcutaneous and intra-abdominal visceral depots. CLS status in subcutaneous fat was highly sensitive and modestly specific for inflammation of visceral fat. In multivariable models, plasma insulin and homeostatis model assessment levels were positively associated with CLS⁺ status in all depots independent of age, waist circumference, BMI and type 2 diabetes, and worsened with the increasing number of adipose regions involved.

CONCLUSIONS:

In severely obese participants, systemic insulin resistance is linked to adipose inflammation in both subcutaneous and visceral depots. The findings suggest that examination of subcutaneous regions that are more easily accessible by transcutaneous biopsy may prove useful in clinical studies designed to investigate adipose phenotypes in relation to human disease.

Adipose tissue inflammation and cancer cachexia: possible role of nuclear transcription factors

Cancer cachexia is a multifaceted syndrome whose aetiology is extremely complex and is directly related to poor patient prognosis and survival. Changes in lipid metabolism in cancer cachexia result in marked reduction of total fat mass, increased lipolysis, total oxidation of fatty acids, hyperlipidaemia, hypertriglyceridaemia, and hypercholesterolaemia. These changes are believed to be induced by inflammatory mediators, such as tumour necrosis factor-α (TNF-α) and other factors. Attention has recently been drawn to the current theory that cachexia is a chronic inflammatory state, mainly caused by the host's reaction to the tumour. Changes in expression of numerous inflammatory mediators, notably in white adipose tissue (WAT), may trigger several changes in WAT homeostasis. The inhibition of adipocyte differentiation by PPARγ is paralleled by the appearance of smaller adipocytes, which may partially account for the inhibitory effect of PPARγ on inflammatory gene expression. Furthermore, inflammatory modulation and/or inhibition seems to be dependent on the IKK/NF-κB pathway, suggesting that a possible interaction between NF-κB and PPARγ is required to modulate WAT inflammation induced by cancer cachexia. In this article, current literature on the possible mechanisms of NF-κB and PPARγ regulation of WAT cells during cancer cachexia are discussed. This review aims to assess the role of a possible interaction between NF-κB and PPARγ in the setting of cancer cachexia as well as its significant role as a potential modulator of chronic inflammation that could be explored therapeutically.

A high-fat diet increases angiogenesis, solid tumor growth, and lung metastasis of CT26 colon cancer cells in obesity-resistant BALB/c mice

We evaluated whether high-fat diet (HFD), in the absence of increased calorie intake, increases colon cancer growth and metastasis. Four-week-old male BALB/c mice were fed on an HFD (60 kcal% fat) or control diet (10 kcal% fat) for 16 wk, after which CT26 colon cancer cells were subcutaneously injected into the right flank. Solid tumor growth and the number and volume of tumor nodules in the lung were increased markedly in the HFD group with only a slight increase in body weight (5.9%). HFD feeding increased tumor tissue levels of Ki67, cyclin A, cyclin D1, CDK2, Bcl-xL, and Bcl-2; reduced p53 levels and TUNEL-positive apoptotic cells; increased the levels of CD45, CD68, CD31, VEGF, P-VEGF receptor-2, iNOS, and COX-2 as well as hemoglobin content; and increased the levels of HIF-1α, P-STAT3-Y705, P-STAT3-S727, P-IκB-α, P-p65, p65, P-c-Jun, P-Akt, P-ERK1/2, P-p38, and P-SAPK/JNK. HFD feeding increased the serum levels of EGF, insulin, IGF-I, IFN-γ, leptin, RANTES, MCP-1, IL-1ra, and SDF-1α and media conditioned by epididymal fat tissue explants from HFD-fed mice caused an increase in microvessel outgrowth from the mouse aorta and tube formation of human umbilical vein endothelial cells. These results indicate that the chronic consumption of an HFD increases colon cancer cell proliferation, tumor angiogenesis, and lung metastasis in mice in the absence of discernible weight gain. HFD feeding increases the levels of growth factors which activate transcription factors, thereby inducing the expression of many genes involved in the stimulation of inflammation, angiogenesis, and cellular proliferation.

A black soybean seed coat extract prevents obesity and glucose intolerance by up-regulating uncoupling proteins and down-regulating inflammatory cytokines in high-fat diet-fed mice

Black soybean seed coat extract (BE) is a polyphenol-rich food material consisting of 9.2% cyanidin 3-glucoside, 6.2% catechins, 39.8% procyanidins, and others. This study demonstrated that BE ameliorated obesity and glucose intolerance by up-regulating uncoupling proteins (UCPs) and down-regulating inflammatory cytokines in C57BL/6 mice fed a control or high-fat diet containing BE for 14 weeks. BE suppressed fat accumulation in mesenteric adipose tissue, reduced the plasma glucose level, and enhanced insulin sensitivity in the high-fat diet-fed mice. The gene and protein expression levels of UCP-1 in brown adipose tissue and UCP-2 in white adipose tissue were up-regulated by BE. Moreover, the gene expression levels of major inflammatory cytokines, tumor necrosis factor-α and monocyte chemoattractant protein-1 were remarkably decreased by BE in white adipose tissue. BE is a beneficial food material for the prevention of obesity and diabetes by enhancing energy expenditure and suppressing inflammation.

Vitamin C modulates the interaction between adipocytes and macrophages

SCOPE

Increased adiposity is related with monocyte infiltration into the adipose tissue that accentuates inflammation. Antioxidant treatments emerge as approaches to counteract this phenomenon.

METHODS AND RESULTS

Cocultures of differentiated 3T3-L1 adipocytes and RAW264.7 macrophages were incubated for 24-72 h with/without 100 nM insulin and/or 200 μM vitamin C (VC). Nitric oxide (NO) secretion (24 h) was measured. Also, expression (24 h) and secretion (72 h) of MCP-1, leptin and apelin were analyzed. NO secretion was significantly inhibited by insulin and VC only in cocultures. MCP-1 expression/secretion was enhanced in cocultures. Insulin incubation reduced MCP-1 expression in both cultures and VC only in controls. Both treatments inhibited MCP-1 secretion in cocultures. Apelin gene expression was induced in cocultures. Insulin induced apelin mRNA expression, but VC inhibited its expression in cocultures under insulin treatment. Apelin secretion was notably induced by insulin and inhibited by VC in cocultures. Leptin expression was decreased in coculture, while presented no effects by VC.

CONCLUSION

VC importantly modulates the established pro-inflammatory state in the interaction between adipocytes and macrophages.

Removal of intra-abdominal visceral adipose tissue improves glucose tolerance in rats: role of hepatic triglyceride storage

Epidemiological studies have demonstrated a strong link between increased visceral fat and metabolic syndrome. In rodents, removal of intra-abdominal but non-visceral fat improves insulin sensitivity and glucose homeostasis, though previous studies make an imprecise comparison to human physiology because actual visceral fat was not removed. We hypothesize that nutrient release from visceral adipose tissue may have greater consequences on metabolic regulation than nutrient release from non-visceral adipose depots since the latter drains into systemic but not portal circulation. To assess this we surgically decreased visceral white adipose tissue (~0.5 g VWATx) and compared the effects to removal of non-visceral epididymal fat (~4 g; EWATx), combination removal of visceral and non-visceral fat (~4.5 g; EWATx/VWATx) and sham-operated controls, in chow-fed rats. At 8 weeks after surgery, only the groups with visceral fat removed had a significantly improved glucose tolerance, although 8 times more fat was removed in EWATx compared with VWATx. This suggests that mechanisms controlling glucose metabolism are relatively more sensitive to reductions in visceral adipose tissue mass. Groups with visceral fat removed also had significantly decreased hepatic lipoprotein lipase (LPL) and triglyceride content compared with controls, while carnitine palmitoyltransferase (CPT-1A) was decreased in all fat-removal groups. In a preliminary experiment, we assessed the opposite hypothesis; i.e., we transplanted excess visceral fat from a donor rat to the visceral cavity (omentum and mesentery), which drains into the hepatic portal vein, of a recipient rat but observed no major metabolic effect. Overall, our results indicate surgical removal of intra-abdominal fat improves glucose tolerance through mechanism that may be mediated by reductions in liver triglyceride.

Supplement of bamboo extract lowers serum monocyte chemoattractant protein-1 concentration in mice fed a diet containing a high level of saturated fat

Monocyte chemoattractant protein-1 (MCP-1) is an inflammatory chemokine up-regulated in obese subjects, contributing to the development of type 2 diabetes. The present study investigated the inhibitory effect of an ethanol-water extract from bamboo (BEX, Phyllostachys edulis) on the blood concentration of MCP-1. C57BL/6J mice were fed a standard diet or a high-fat diet with or without the BEX supplement (11 g dry mass/17 000 kJ) for 6 months. A total of ten mice were used in each group. Body weight and food consumption were measured weekly. After euthanisation, the weight of visceral fat and circulating MCP-1 concentration were measured. In comparison with the standard control group, the high-fat control group had increased body weight, abdominal fat storage and serum MCP-1 concentration by 60 % (P < 0·001), 266 % (P < 0·001) and 180 % (P < 0·01), respectively. In comparison with the high-fat control group, the high-fat BEX group showed a 3 % decrease in body weight (P < 0·01), 24 % decrease in mesenteric fat depot (P < 0·01) and 49 % decrease in serum MCP-1 concentration (P < 0·05). The present study suggests that the BEX supplement in the high-fat diet ameliorates elevated MCP-1 concentrations in the blood, and whether this is related to modulated endocrine properties of the visceral fat is to be studied.

Effects of polyphenolic compounds on tumor necrosis factor-α (TNF-α)-induced changes of adipokines and oxidative stress in 3T3-L1 adipocytes

Over the last few decades, obesity has become a global epidemic in both developed and developing countries. Recent studies have indicated that obesity is closely associated with chronic inflammation characterized by abnormal levels of adipocytokines and inflammatory cytokines in adipocytes. The aim of this work was to study the effects of 21 polyphenolic compounds on tumor necrosis factor-α (TNF-α)-induced changes of adipokines and oxidative stress in 3T3-L1 adipocytes. The results showed that p-coumaric acid, quercetin, and resveratrol have greater inhibition (p < 0.05) of a TNF-α-induced increase in the production of interleukin-6 (IL-6) among 21 tested polyphenolic compounds. p-Coumaric acid, quercetin, and resveratrol demonstrated inhibitions of TNF-α-induced changes in levels of monocyte chemoattractant protein-1 (MCP-1), plasminogen activator inhibitor-1 (PAI-1), and intracellular reactive oxygen species (ROS) in 3T3-L1 adipocytes. Furthermore, p-coumaric acid, quercetin, and resveratrol increased levels (p < 0.05) of secreted adiponectin, superoxide dismutase (SOD), glutathione (GSH), glutathione peroxidase (GPx), and glutathione S-transferase (GST) in TNF-α-treated 3T3-L1 adipocytes. These results indicate that the inhibition of TNF-α-induced changes of adipokines and oxidative stress by some polyphenolic compounds might have further implications in preventing obesity-related pathologies.

LIGHT/TNFSF14 enhances adipose tissue inflammatory responses through its interaction with HVEM

Obesity-induced adipose tissue inflammation is characterized by increased macrophage infiltration and cytokine production, and is associated with metabolic disorders. LIGHT/TNFSF14, a member of the TNF superfamily, plays a role in the development of various inflammatory diseases. The purpose of this study was to examine the involvement of soluble LIGHT (sLIGHT) in obesity-induced adipose tissue inflammatory responses. LIGHT gene expression on macrophages/adipocytes was upregulated by treatment with obesity-related factors. sLIGHT displayed chemotactic activity for macrophages and T cells, and enhanced inflammatory cytokine release from macrophages, adipocytes, and adipose tissue-derived SVF cells. The sLIGHT-induced inflammatory responses were blunted by neutralizing anti-HVEM antibody or knockout of HVEM, a receptor for sLIGHT. These findings indicate that sLIGHT enhances adipose tissue inflammatory responses through its interaction with HVEM.

The immune signaling molecule 4-1BB stimulation reduces adiposity, insulin resistance, and hepatosteatosis in obese mice

Immune cells (e.g. macrophages and T cells) in adipose tissue play a crucial role in the development of obesity-induced inflammation and metabolic disorders. Here we report findings suggesting that the immune signaling molecule 4-1BB/CD137 is a novel target for treatment of obesity and metabolic disorders. 4-1BB stimulation with agonistic antibody reduced body weight and adiposity and markedly improved glucose intolerance and hepatosteatosis in diet-induced obese mice and genetically obese/diabetic mice. Increases in lymphoid T cell expansion/activation and adipose/hepatic CD8+ T cell recruitment were evident in the anti-4-1BB antibody-treated obese mice. Glycolysis, β-oxidation, and oxygen consumption rates also increased in the treated mice. These findings suggest that 4-1BB-stimulation accompanied by CD8+ T cell expansion/activation enhances glucose/lipid metabolism, leading to increased energy expenditure. Manipulation of 4-1BB may provide a unique immunological strategy against obesity and metabolic disorders.

Absence of macrophage inflammatory protein-1{alpha} does not impact macrophage accumulation in adipose tissue of diet-induced obese mice

Macrophages and T-lymphocytes are known to accumulate in the white adipose tissue (WAT) of obese mice and humans, but the factors that cause this infiltration are not yet determined. Chemokines, which attract leukocytes to inflammatory sites, are candidates for this process. Macrophage inflammatory protein-1alpha (MIP-1alpha) expression is significantly elevated in WAT of obese mice and humans and positively correlates with fasting plasma insulin, but its potential role in leukocyte recruitment to WAT is unknown. MIP-1alpha-deficient, heterozygous, and wild-type mice were fed a Western diet (WD) for 16 wk. Plasma lipids, adipose tissue mass, energy expenditure, food intake, liver triglyceride content, and inflammatory cytokine expression were not different among genotypes. Gene expression of macrophage markers F4/80 and CD68, as well as T-lymphocyte marker CD3epsilon was increased in perigonadal WAT of obese WD-fed mice but was not influenced by MIP-1alpha expression level. Immunohistochemical analysis of WAT also showed no effect of MIP-1alpha on macrophage content. Two related chemokines, MIP-1beta and RANTES, had reduced expression in obese male MIP-1alpha-deficient mice compared with wild-type controls (P < or = 0.05). In mice fed the WD for 6 wk, WAT macrophage content was unchanged; however, CD8+ T-lymphocytes accumulated to a lesser extent in the MIP-1alpha-null mice. Therefore, expression of MIP-1alpha, as well as that of MIP-1beta and RANTES, increases as a consequence of weight gain, but these chemokines may not be required for the recruitment of monocytes to WAT during diet-induced obesity in mice and may impact T-lymphocyte recruitment only at early time points after WD feeding.

P-selectin glycoprotein ligand-1 regulates adhesive properties of the endothelium and leukocyte trafficking into adipose tissue

RATIONALE

Adhesive interactions between endothelial cells and leukocytes affect leukocyte trafficking in adipose tissue. The role of P-selectin glycoprotein ligand-1 (Psgl-1) in this process is unclear.

OBJECTIVE

The goal of this study was to determine the effect of Psgl-1 deficiency on adhesive properties of the endothelium and on leukocyte recruitment into obese adipose depots.

METHODS AND RESULTS

A genetic model of obesity was generated to study the effects of Psgl-1 deficiency on leukocyte trafficking. Leukocyte-endothelial interactions were increased in obese leptin receptor mutant mice (Lepr(db/db),Psgl-1(+/+)) but not obese Psgl-1-deficient mice (Lepr(db/db),Psgl-1(-/-)), when compared with lean mice (Lepr(+/+),Psgl-1(+/+)). This effect of Psgl-1 deficiency was due to indirect effects of Psgl-1, because Psgl-1(+/+) adoptively transferred leukocytes did not exhibit enhanced rolling in Lepr (db/db),Psgl-1(-/-) mice. Additionally, circulating levels of P-selectin, E-selectin, monocyte chemoattractant protein-1, and macrophage content of visceral adipose tissue were reduced in Lepr(db/db),Psgl-1(-/-) compared with Lepr(db/db),Psgl-1(+/+) mice. Reduced leukocyte-endothelial interactions and macrophage content of visceral adipose tissue due to Psgl-1 deficiency was also observed in a diet-induced obese mouse model. Psgl-1(-/-) mice were resistant to the endothelial effects of exogenous IL-1beta, suggesting that defective cytokine signaling contributes to the effect of Psgl-1 deficiency on leukocyte-endothelial interactions. Mice deficient in the IL-1 receptor also had reduced levels of circulating P-selectin, similar to those observed in Psgl-1(-/-) mice.

CONCLUSIONS

Deficiency of Psgl-1 is associated with reduced IL-1 receptor-mediated adhesive properties of the endothelium and is protective against visceral fat inflammation in obese mice.

Various Terpenoids Derived from Herbal and Dietary Plants Function as PPAR Modulators and Regulate Carbohydrate and Lipid Metabolism

Several herbal plants improve medical conditions. Such plants contain many bioactive phytochemicals. Terpenoids (also called “isoprenoids”) constitute one of the largest families of natural products accounting for more than 40,000 individual compounds of both primary and secondary metabolisms. In particular, terpenoids are contained in many herbal plants, and several terpenoids have been shown to be available for pharmaceutical applications, for example, artemisinin and taxol as malaria and cancer medicines, respectively. Various terpenoids are contained in many plants for not only herbal use but also dietary use. In this paper, we describe several bioactive terpenoids contained in herbal or dietary plants, which can modulate the activities of ligand-dependent transcription factors, namely, peroxisome proliferator-activated receptors (PPARs). Because PPARs are dietary lipid sensors that control energy homeostasis, daily eating of these terpenoids might be useful for the management for obesity-induced metabolic disorders, such as type 2 diabetes, hyperlipidemia, insulin resistance, and cardiovascular diseases.