Objective-Weight gain is associated with infiltration of fat by macrophages, suggesting that they are an important source of inflammation in obese adipose tissue. Here we developed an in vitro coculture system composed of adipocytes and macrophages and examined the molecular mechanism whereby these cells communicate. Methods and Results-Coculture of differentiated 3T3-L1 adipocytes and macrophage cell line RAW264 results in the marked upregulation of proinflammatory cytokines, such as tumor necrosis factor ␣ (TNF-␣), and the downregulation of the antiinflammatory cytokine adiponectin. Such inflammatory changes are induced by the coculture without direct contact, suggesting the role of soluble factors. A neutralizing antibody to TNF-␣, which occurs mostly in macrophages, inhibits the inflammatory changes in 3T3-L1, suggesting that TNF-␣ is a major macrophage-derived mediator of inflammation in adipocytes. Conversely, free fatty acids (FFAs) may be important adipocyte-derived mediators of inflammation in macrophages, because the production of TNF-␣ in RAW264 is markedly increased by palmitate, a major FFA released from 3T3-L1. The inflammatory changes in the coculture are augmented by use of either hypertrophied 3T3-L1 or adipose stromal vascular fraction obtained from obese ob/ob mice. Key Words: macrophage Ⅲ adipocyte Ⅲ fatty acids Ⅲ TNF-␣ Ⅲ obesity T he metabolic syndrome is a constellation of visceral fat obesity, impaired glucose metabolism, atherogenic dyslipidemia, and blood pressure elevation, which all independently increase a risk of atherosclerotic diseases, such as ischemic heart disease and cerebral stroke. 1,2 The molecular basis for the clustering of such independent risks of atherosclerosis has not fully been elucidated, with visceral fat obesity considered most important. 3,4 Systemic insulin resistance has been implicated as one possible factor that links visceral fat obesity and the adverse metabolic consequences. 4,5 Evidence has accumulated indicating that obesity is associated with a state of chronic, low-grade inflammation, suggesting that inflammation may be a potential mechanism whereby obesity leads to insulin resistance. 5,6 Indeed, obesity and insulin resistance are strongly associated with systemic markers of inflammation, and, clinically, inflammation has been recognized as a major predictor of atherosclerotic disease. [5][6][7] Conclusions-We See coverThe adipose tissue is an important endocrine organ that secretes many biologically active substances, such as leptin, adiponectin, tumor necrosis factor ␣ (TNF-␣), and monocyte chemoattractant protein 1 (MCP-1), which are collectively termed adipocytokines. 4,8 -10 Dysregulated production of proinflammatory and antiinflammatory adipocytokines seen in visceral fat obesity is associated with the metabolic syndrome, 4,6 suggesting that inflammatory changes within the adipose tissue may critically contribute to the development of many aspects of the metabolic syndrome and results in diabetes and atherosclerosis. For example, it has bee...

Neutrophil gelatinase-associated lipocalin (Ngal), also known as siderocalin, forms a complex with ironbinding siderophores (Ngal:siderophore:Fe). This complex converts renal progenitors into epithelial tubules.In this study, we tested the hypothesis that Ngal:siderophore:Fe protects adult kidney epithelial cells or accelerates their recovery from damage. Using a mouse model of severe renal failure, ischemia-reperfusion injury, we show that a single dose of Ngal (10 μg), introduced during the initial phase of the disease, dramatically protects the kidney and mitigates azotemia. Ngal activity depends on delivery of the protein and its siderophore to the proximal tubule. Iron must also be delivered, since blockade of the siderophore with gallium inhibits the rescue from ischemia. The Ngal:siderophore:Fe complex upregulates heme oxygenase-1, a protective enzyme, preserves proximal tubule N-cadherin, and inhibits cell death. Because mouse urine contains an Ngaldependent siderophore-like activity, endogenous Ngal might also play a protective role. Indeed, Ngal is highly accumulated in the human kidney cortical tubules and in the blood and urine after nephrotoxic and ischemic injury. We reveal what we believe to be a novel pathway of iron traffic that is activated in human and mouse renal diseases, and it provides a unique method for their treatment.

These findings suggest that saturated FAs, which are released in large quantities from hypertrophied adipocytes via the macrophage-induced adipocyte lipolysis, serve as a naturally occurring ligand for TLR4, thereby inducing the inflammatory changes in both adipocytes and macrophages through NF-kappaB activation.

The adipose tissue secretes a large number of bioactive substances, adipocytokines, which may be involved in a variety of physiologic and pathologic processes. Unbalanced production of pro- and anti-inflammatory adipocytokines seen in visceral fat obesity contributes critically to the development of the metabolic syndrome. Evidence has accumulated indicating that obesity is associated with a state of chronic, low-grade inflammation, suggesting that inflammation may be a potential mechanism, whereby obesity leads to insulin resistance. Indeed, obese adipose tissue is characterized by adipocyte hypertrophy, followed by increased angiogenesis, immune cell infiltration, extracellular matrix overproduction, and thus, increased production of proinflammatory adipocytokines during the progression of chronic inflammation. The dynamic change found in the adipose tissue can be referred to as "adipose tissue remodeling," in which stromal cells change dramatically in number and cell type during the course of obesity. Among stromal cells, infiltration of macrophages in the adipose tissue precedes the development of insulin resistance in animal models, suggesting that they are crucial for obesity-related adipose tissue inflammation. We have demonstrated that a paracrine loop involving saturated fatty acids and TNF-alpha derived from adipocytes and macrophages, respectively, aggravates obesity-induced adipose tissue inflammation. Notably, saturated fatty acids, which are released from hypertrophied adipocytes via the macrophage-induced lipolysis, serve as a naturally occurring ligand for TLR4 complex, thereby activating macrophages. Understanding the molecular mechanism underlying adipose tissue remodeling may lead to the identification of novel, therapeutic strategies to prevent or treat obesity-induced adipose tissue inflammation.

Objectives-Fish oil rich in n-3 polyunsaturated fatty acids (PUFAs) or n-3 PUFAs have been shown to reduce the incidence of coronary heart disease. Here we investigated the effect of highly purified eicosapentaenoic acid (EPA) on production of adiponectin, the only established antiatherogenic and antiinflammatory adipocytokine, in rodent models of obesity and human obese subjects. Methods and Results-We demonstrated that EPA increases adiponectin secretion in genetically obese ob/ob mice and high-fat diet-induced obese mice. In the in vitro coculture of adipocytes and macrophages, EPA reversed the coculture-induced decrease in adiponectin secretion at least in part through downregulation of tumor necrosis factor-␣ in macrophages. We also showed significant increase in plasma adiponectin concentrations in human obese subjects after a 3-month treatment with EPA (1.8 g daily). Multivariate regression analysis revealed that EPA treatment is the only independent determinant of plasma adiponectin concentrations. Conclusion-This study demonstrates that EPA increases adiponectin secretion in rodent models of obesity and human obese subjects, possibly through the improvement of the inflammatory changes in obese adipose tissue. Because EPA has reduced the risk of major coronary events in a large-scale, prospective, randomized clinical trial, this study provides important insight into its therapeutic implication in obesity-related metabolic sequelae. (Arterioscler Thromb Vasc Biol. 2007;27:1918-1925.)Key Words: adipocytes Ⅲ adiponectin Ⅲ EPA Ⅲ macrophages Ⅲ obesity T he adipose tissue has a high capacity to secrete many biologically active substances (or adipocytokines) such as leptin and tumor necrosis factor-␣ (TNF␣). 1 Dysregulation of pro-and antiinflammatory adipocytokine production is associated with the metabolic syndrome, suggesting that inflammatory changes within obese adipose tissue may critically contribute to the development of many aspects of the metabolic syndrome and results in diabetes and atherosclerosis. Among numerous adipocytokines, adiponectin is unique in that it is the only established adipocytokine with antiatherogenic and antiinflammatory properties. 2,3 It also increases tissue fat oxidation, leading to reduced levels of fatty acids (FAs) and tissue triglyceride content, thus enhancing insulin sensitivity in the liver and skeletal muscle. 2,4,5 Because plasma adiponectin concentrations are decreased in obese subjects, 1,2 extensive researches have been aimed at the upregulation of adiponectin and its cognate receptors (AdipoR1 and AdipoR2) for the treatment of obesityrelated metabolic sequelae. 2 Previous studies showed that the adipose tissue is markedly infiltrated by macrophages in several models of rodent obesities and human obese subjects, 6,7 suggesting that macrophages participate in the inflammatory pathways that are activated in obese adipose tissue. Using an in vitro coculture system composed of adipocytes and macrophages, we have demonstrated that a paracrine loop involving saturate...