Naringenin suppresses macrophage infiltration into adipose tissue in an early phase of high-fat diet-induced obesity

Obese adipose tissue is characterized by increased macrophage infiltration, which results in chronic inflammation in adipose tissue and leads to obesity-related diseases such as type 2 diabetes mellitus and atherosclerosis. The regulation of macrophage infiltration into adipose tissue is an important strategy for preventing and treating obesity-related diseases. In this study, we report that naringenin, a citrus flavonoid, suppressed macrophage infiltration into adipose tissue induced by short-term (14 days) feeding of a high-fat diet in mice; although naringenin did not show any differences in high-fat diet-induced changes of serum biochemical parameters in this short administration period. Naringenin suppressed monocyte chemoattractant protein-1 (MCP-1) in adipose tissue, and this effect was mediated in part through inhibition of c-Jun NH₂-terminal kinase pathway. Naringenin also inhibited MCP-1 expression in adipocytes, macrophages, and a co-culture of adipocytes and macrophages. Our results suggest a mechanism by which daily consumption of naringenin may exhibit preventive effects on obesity-related diseases.     

FFAs and adipokine-mediated regulation of hsa-miR-143 expression in human adipocytes

Accumulating evidence suggests that microRNAs (miRNAs) play an important role in regulating the pathways in adipose tissue that control processes such as adipogenesis, insulin resistance, and inflammation. MiR-143 is a well-characterized miRNA involved in adipogenesis and may be involved in regulating insulin resistance. Free fatty acids (FFAs) and adipokines, such as tumor necrosis factor-α (TNF-α), leptin, resistin, and interleukin-6 (IL-6), have already been identified as main regulators of obesity and insulin sensitivity. Therefore, we studied the effects of these inflammatory cytokines on the expression of miR-143. FFAs, resistin, and leptin downregulated miR-143 expression in human adipocytes, whereas TNF-α and IL-6 had little effect on miR-143 expression. These results suggest that the expression of miR-143 is affected by a variety of factors that are related to insulin sensitivity. Therefore, miR-143 may be an important mediator in the development of obesity-related insulin resistance.     

Low-dose GH supplementation reduces the TLR2 and TNF-alpha expressions in visceral fat

The increased population of TLR2/TNF-α co-expressing adipocytes is associated with the development of insulin resistance. We have herein shown the significance of low-dose growth hormone (GH) supplementation for the regulation of TLR2 and TNF-α expressions in visceral fat using different kinds of mouse models fed with a high-fat diet. Low-dose GH supplementation reduced the increased population of TLR2/TNF-α co-expressing adipocytes in high-fat fed mice. The neutralization of IGF-1 abolished the effect of GH supplementation on the TLR2 expression using GH-overexpressing mice. IGF-1, but not GH, inhibited the FFA-induced TLR2 and TNF-α expression in 3T3-L1 cells. Finally, low-dose GH supplementation reduced the TLR2 expression without an obvious change in the visceral fat volume in ob/ob mice. These results indicate that low-dose GH supplementation possibly inhibits the high-fat induced change of the adipocytes to TLR2/TNF-α co-expressing cells through the action of IGF-1.     

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.     

Inflammation inhibits the expression of phosphoenolpyruvate carboxykinase in liver and adipose tissue

Inhibition of adipocyte triglyceride biosynthesis is required for fatty acid mobilization during inflammation. Triglyceride biosynthesis requires glycerol 3-phosphate and phosphoenolpyruvate carboxykinase (PEPCK) plays a key role. We demonstrate that LPS, zymosan, and TNF-α decrease PEPCK in liver and fat. Turpentine decreases PEPCK in liver, but not in fat. The LPS-induced decrease in PEPCK does not occur in TLR4 deficient animals, indicating that this receptor is required. The LPS-induced decrease in hepatic PEPCK does not occur in TNF receptor/IL-1 receptor knockout mice, but occurs in fat, indicating that TNF-α/IL-1 is essential for the decrease in liver but not fat. In 3T3-L1 adipocytes TNF-α, IL-1, IL-6, and IFNγ inhibit PEPCK indicating that there are multiple pathways by which PEPCK is decreased in adipocytes. The binding of PPARγ and RXRα to the PPARγ response element in the PEPCK promoter is markedly decreased in adipose tissue nuclear extracts from LPS treated animals. Lipopolysaccharide and zymosan reduce PPARγ and RXRα expression in fat, suggesting that a decrease in PPARγ and RXRα accounts for the decrease in PEPCK. Thus, there are multiple cytokine pathways by which inflammation inhibits PEPCK expression in adipose tissue which could contribute to the increased mobilization of fatty acids during inflammation.     

Eicosapentaenoic acid inhibits tumour necrosis factor-α-induced lipolysis in murine cultured adipocytes

Eicosapentaenoic acid (EPA) is an omega-3 polyunsaturated fatty acid with beneficial effects in obesity and insulin resistance. High levels of proinflammatory cytokine tumour necrosis factor-α (TNF-α) in obesity promote lipolysis in adipocytes, leading to the development of insulin resistance. Thus, the aims of the present study were to analyze the potential antilipolytic properties of EPA on cytokine-induced lipolysis and to investigate the possible mechanisms involved. The EPA effects on basal and TNF-α-induced lipolysis were determined in both primary rat and 3T3-L1 adipocytes. Treatment of primary rat adipocytes with EPA (100 and 200 μM) significantly decreased basal glycerol release (P<.01) and prevented cytokine-induced lipolysis in a dose-dependent manner (P<.001). Moreover, EPA decreased TNF-α-induced activation of nuclear factor-κB and extracellular-related kinase 1/2 phosphorylation. In addition, the antilipolytic action of EPA was stimulated by the AMP-kinase (AMPK) activator 5-aminoimidazole-4-carboxamide-1-b-d-ribofuranoside and blocked by the AMPK-inhibitor compound C. Moreover, we found that EPA stimulated hormone-sensitive lipase (HSL) phosphorylation on serine-565, which further supports the involvement of AMPK in EPA's antilipolytic actions. Eicosapentaenoic acid treatment (24 h), alone and in the presence of TNF-α,? also decreased adipose triglyceride lipase (ATGL) protein content in cultured adipocytes. However, oral supplementation with EPA for 35 days was able to partially reverse the down-regulation of HSL and ATGL messenger RNA observed in retroperitoneal adipose tissue of high-fat-diet-fed rats. These findings suggest that EPA inhibits proinflammatory cytokine-induced lipolysis in adipocytes. This effect might contribute to explain the insulin-sensitizing properties of EPA.     

Adipokine gene expression in dog adipose tissues and dog white adipocytes differentiated in primary culture.

Obesity and its associated disorders are increasing in companion animals, particularly in dogs. We have investigated whether genes encoding key adipokines, some of which are implicated in the pathologies linked to obesity, are expressed in canine adipose tissues. Using RT-PCR, mRNAs encoding the following adipokines were detected in dog white adipose tissue: adiponectin, leptin, angiotensinogen, plasminogen activator inhibitor-1, IL-6, haptoglobin, metallothionein-1 and 2, and nerve growth factor. The adipokine mRNAs were present in all fat depots examined. Fractionation of adipose tissue by collagenase digestion showed that each gene was expressed in mature adipocytes. The mRNA for TNFalpha was not evident in adipose tissue, but was detected in isolated adipocytes. Fibroblastic preadipocytes from gonadal white fat were differentiated into adipocytes in primary culture and adipokine expression examined before and after differentiation (days 0 and 11, respectively). Each adipokine gene expressed in dog white adipocytes was also expressed in the differentiated cells. These results demonstrate that dog white adipose tissue expresses major adipokine genes, expression being in the adipocytes. Investigation of adipokine production and function will provide insight into the mechanisms involved in obesity-related pathologies in dogs and serve as a model for the related human diseases.     

Haematopoietic TLR4 deletion attenuates perivascular brown adipose tissue inflammation in atherosclerotic mice

AimsTo investigate whether haematopoietic TLR4 deletion attenuates perivascular brown adipose tissue inflammation in atherosclerotic mice.Methods and ResultsExperiments were performed using irradiated LDL receptor-deficient (LDLR^−/−) mice with marrow from either TLR4-deficient (TLR4^−/−) or age-matched wild-type (WT) mice. After 12 weeks of being fed a high-cholesterol diet, TLR4^−/− → LDLR^−/− mice developed fewer atherosclerotic lesions in the aorta compared to WT → LDLR^−/− mice. This effect was associated with an increase in multilocular lipid droplets and mitochondria in perivascular adipose tissue (PVAT). Immunofluorescence analysis confirmed that there was an increase in capillary density and M2 macrophage infiltration, accompanied by a decrease in tumour necrosis factor (TNF)-α expression in the localized PVAT of TLR4^−/− → LDLR^−/− mice. In vitro studies indicated that bone marrow-derived macrophages (BMDMs) from WT mice demonstrated an M1-like phenotype and expression of inflammatory cytokines induced by palmitate. These effects were attenuated in BMDMs isolated from TLR4^−/− mice. Furthermore, brown adipocytes incubated with conditioned medium (CM) derived from palmitate-treated BMDMs, exhibited larger and more unilocular lipid droplets, and reduced expression of brown adipocyte-specific markers and perilipin-1 compared to those observed in brown adipocytes exposed to CM from palmitate-treated BMDMs of TLR4^−/− mice. This decreased potency was primarily due to TNF-α, as demonstrated by the capacity of the TNF-α neutralizing antibody to reverse these effects.ConclusionsThese results suggest that haematopoietic-specific deletion of TLR4 promotes PVAT homeostasis, which is involved in reducing macrophage-induced TNF-α secretion and increasing mitochondrial biogenesis in brown adipocytes.     

Lycopene attenuates body weight gain through induction of browning via regulation of peroxisome proliferator-activated receptor γ in high-fat diet-induced obese mice

Lycopene (LYC), one of the major carotenoids in tomatoes, has been preclinically and clinically used to obesity and type 2 diabetes management. However, whether its ability of countering body weight gain is related to induction of brown-like adipocyte phenotype in white adipose tissues (WAT) remains largely unknown. Activation of peroxisome proliferator-activated receptor γ (PPARγ) serves the brown-like phenotype conversion and energy expenditure. Here, we show that LYC treatment promotes glucose consumption and improves insulin sensitivity, as well as fosters white adipocytes browning through up-regulating mRNA and protein expression levels of PPARγ, uncoupling protein 1, PPARγ coactivator-1α and PR domain-containing 16 in the differentiated 3T3-L1 adipocytes and primary adipocytes, as well as in the WAT of HFD-exposed obese mice. In addition, LYC treatment attenuates body weight gain and improves serum lipid profiles as well as promotes brown adipose tissue activation in obese mice. Moreover, PPARγ is induced with LYC intervention in mitochondria respiration and browning in white adipocytes and tissues. Taken together, these results suggest that LYC counteracts obesity and improves glucose and lipid metabolism through induction of the browning via up-regulation of PPARγ, which offers a new perspective of this compound to combat obesity and obesity-related disorders.     

Secretory leukocyte protease inhibitor reduces inflammation and alveolar bone resorption in LPS-induced periodontitis in rats and in MC3T3-E1 preosteoblasts

In periodontitis, alveolar bone resorption is induced by excessive host immune and inflammatory response against bacterial infection. Secretory leukocyte protease inhibitor (SLPI) has anti-bacterial and anti-inflammatory activity in inflammatory responses. SLPI inhibits joint inflammation and bone destruction, but the function of SLPI in periodontitis is unclear. Therefore, this study investigated whether SLPI inhibits the inflammatory response and alveolar bone resorption in LPS-induced periodontitis of rats. Micro-computed tomography and histological analysis showed that SLPI inhibited alveolar bone resorption by LPS-induced periodontitis. Immunohistochemistry revealed that SLPI decreased tumor necrosis factor-α (TNF-α) and interleukine-1β (IL-1β) expression in periodontitis tissue, and decreased mRNA and protein expression of TNF-α and IL-1β in LPS-stimulated MC3T3-E1 cells. The results indicated that SLPI reduced alveolar bone resorption in LPS-induced periodontitis and inhibited inflammatory cytokine, such as TNF-α and IL-1β, expression in LPS-stimulated MC3T3-E1 preosteoblasts. Therefore, SLPI could be a regulatory molecule by inhibiting alveolar bone resorption through the reduction of inflammatory cytokines, and inducing osteoblast activation for bone formation.     

Weak Functional Coupling of the Melanocortin-1 Receptor Expressed in Human Adipocytes

The melanocortin (MC) receptor type-1 (MC1-R) is the only one of the five MC receptor subtypes expressed in human adipose tissue explants, human mesenchymal stem cells (MSCs), and MSC-derived adipocytes. Following our recent expression studies (Obesity 2007, 15, 40–49), we now investigated the functional role of MC1-R in these tissues and cells to deduce the coupling state of MC1-R to intracellular output signals in human fat cells and tissue. Expression of MC1-R by undifferentiated and differentiated MSCs was quantified by real-time TaqMan PCR. Intracellular output signals (cAMP, lipolysis, secretion of IL-6, IL-10, and TNF-α), as well as effects on the metabolic rate and proliferation of human MSCs were analyzed by standard assays, exposing undifferentiated and differentiated MSCs and, in part, human adipose tissue explants to the potent MC1-R agonist, [Nle⁴, D-Phe⁷]-α -MSH (NDP-MSH). This agonist induced a weak cAMP signal in MSC-derived adipocytes. However, it did not affect lipolysis in these cells or in adipose tissue explants, nor did it modulate cytokine release and mRNA expression of IL-6, IL-8, and TNF-α upon LPS stimulation. In undifferentiated MSCs, NDP-MSH did not alter the metabolic rate, but it showed a significant antiproliferative effect. Therefore, it appears that MC1-R–effector coupling in (differentiated) human adipocytes is too weak to induce a regulatory effect on lipolysis or inflammation; by contrast, MC1-R stimulation in undifferentiated MSCs induces an inhibitory signal on cell proliferation.     

Toll-like receptor 4 contributes to uterine activation by upregulating pro-inflammatory cytokine and CAP expression via the NF-κB/P38MAPK signaling pathway during pregnancy

Evidence indicates that inflammatory response is significant during the physiological process of human parturition; however, the specific signaling pathway that triggers inflammation is undefined. Toll-like receptors (TLRs) are key upstream gatekeepers that control inflammatory activation before preterm delivery. Our previous study showed that TLR4 expression was significantly increased in human pregnancy tissue during preterm and term labor. Therefore, we explore whether TLR4 plays a role in term labor by initiating inflammatory responses, therefore promoting uterine activation. The results showed that expression of TLR4, interleukin-1β (IL-1β), IL-6, tumor necrosis factor-α (TNF-α), CC chemokine ligand 2 (CCL-2), and uterine contraction-associated proteins (CAPs) was upregulated in the human and mice term labor (TL) group compared with the not-in-labor (TNL) group, and the TLR4 level positively correlated with CAP expression. In pregnant TLR4-knockout (TLR4^−/−) mice, gestation length was extended by 8 hr compared with the wild-type group, and the expression of IL-1β, IL-6, TNF-α, CCL-2, and CAPs was decreased in TLR4^−/− mice. Furthermore, nuclear factor-κB (NF-κB) and P38MAPK activation is involved in the initiation of labor but was inhibited in TLR4^−/− mice. In uterine smooth muscle cells, the expression of inflammatory cytokines and CAPs decreased when the NF-κB and P38MAPK pathway was inhibited. Our data suggest that TLR4 is a key factor in regulating the inflammatory response that drives uterine activation and delivery initiation via activating the NF-κB/P38MAPK pathway.