Diabetes and obesity are two metabolic diseases characterized by insulin resistance and a low-grade inflammation. Seeking an inflammatory factor causative of the onset of insulin resistance, obesity, and diabetes, we have identified bacterial lipopolysaccharide (LPS) as a triggering factor. We found that normal endotoxemia increased or decreased during the fed or fasted state, respectively, on a nutritional basis and that a 4-week high-fat diet chronically increased plasma LPS concentration two to three times, a threshold that we have defined as metabolic endotoxemia. Importantly, a high-fat diet increased the proportion of an LPScontaining microbiota in the gut. When metabolic endotoxemia was induced for 4 weeks in mice through continuous subcutaneous infusion of LPS, fasted glycemia and insulinemia and whole-body, liver, and adipose tissue weight gain were increased to a similar extent as in highfat-fed mice. In addition, adipose tissue F4/80-positive cells and markers of inflammation, and liver triglyceride content, were increased. Furthermore, liver, but not wholebody, insulin resistance was detected in LPS-infused mice. CD14 mutant mice resisted most of the LPS and high-fat diet-induced features of metabolic diseases. This new finding demonstrates that metabolic endotoxemia dysregulates the inflammatory tone and triggers body weight gain and diabetes. We conclude that the LPS/CD14 system sets the tone of insulin sensitivity and the onset of diabetes and obesity. Lowering plasma LPS concentration could be a potent strategy for the control of metabolic diseases. Diabetes 56: [1761][1762][1763][1764][1765][1766][1767][1768][1769][1770][1771][1772] 2007 T he outbreak of a fat-enriched diet in Western countries is becoming a problem of the utmost importance. Obesity is the result of a complex interaction between genetic and environmental factors. Among the latter, changes in eating habits to increase fat intake are involved in the increased occurrence of metabolic diseases, such as obesity and diabetes, which are bearing features of the metabolic syndrome. The major metabolic consequence of a high-fat diet is that insulin action and the regulatory mechanisms of body weight are impaired through a well-described lipotoxic effect (1). In addition, it has been recently determined that obesity and insulin resistance are associated with lowgrade chronic systemic inflammation (2). In models of diet-induced and genetic obesity, the adipose tissue presents increased expression and content of proinflammatory cytokines such as tumor necrosis factor (TNF)-␣ (3,4), interleukin (IL)-1 (3,4), and IL-6 (4). This cytokine production is then deleterious for muscle insulin action; for example, TNF-␣ has been shown to cause insulin resistance by increasing serine phosphorylation on insulin receptor substrate-1 (5), leading to its inactivation. The consequent insulin resistance will favor hyperinsulinemia and excessive hepatic and adipose tissue lipid storage. However, while extensive research is dedicated to the effects of an in...

Aims/hypothesis Inflammation is associated with obesity and has been implicated in the development of diabetes and atherosclerosis. During gram-negative bacterial infection, lipopolysaccharide causes an inflammatory reaction via toll-like receptor 4 (TLR4), which has an essential function in the induction of innate and adaptative immunity. Our aim was to determine what role TLR4 plays in the development of metabolic phenotypes during high-fat feeding. Materials and methods We evaluated metabolic consequences of a high-fat diet in TLR4 mutant mice (C3H/HeJ) and their respective controls. Results TLR4 inactivation reduced food intake without significant modification of body weight, but with higher epididymal adipose tissue mass and adipocyte hypertrophy. It also attenuated the inflammatory response and increased glucose transport and the expression levels of adiponectin and lipogenic markers in white adipose tissue. In addition, TLR4 inactivation blunted insulin resistance induced by lipopolysaccharide in differentiated adipocytes. Increased feeding efficiency in TLR4 mutant mice was associated with lower mass and lower expression of uncoupling protein 1 gene in brown adipose tissue. Finally, TLR4 inactivation slowed the development of hepatic steatosis, reducing the liver triacylglycerol content and also expression levels of lipogenic and fibrosis markers. Conclusions/interpretation TLR4 influences white adipose tissue inflammation and insulin sensitivity, as well as liver fat storage, and is important in the regulation of metabolic phenotype during a fat-enriched diet.

In adipose tissue from both obese mice and humans, plasminogen activator inhibitor 1 (PAI-1) expression has been reported to be upregulated to levels of increased plasma PAI-1. This elevated expression has been shown to be partly controlled by tumor necrosis factor (TNF)-␣ in mice. In humans, increased PAI-1 expression is associated with insulin resistance characterized by visceral fat accumulation. Therefore, the aim of this study was to investigate the expression pattern of PAI-1 and TNF-␣ (antigen and mRNA) in visceral human adipose fat in comparison with subcutaneous (SC) fat. Because transforming growth factor (TGF)-␤ 1 is a potent inducer of PAI-1 synthesis and has been shown to influence adipocyte metabolism, this work was extended to TGF-␤ 1 quantification. A total of 32 obese individuals (BMI 42 ± 6.8 kg/m 2 ) were investigated. Freshly collected visceral adipose tissue did not exhibit a higher content of PAI-1 or TGF-␤ 1 than did SC tissue. Although most of the TNF-␣ values were at the detection limit of the methods, TNF-␣ antigen was 3-fold higher and TNF-␣ mRNA was 1.2-fold higher in visceral fat. The levels of tissue TGF-␤ 1 antigen correlated well with those of PAI-1 antigen, regardless of the fat depot studied (SC tissue: n = 21, r = 0.72, P = 0.0006; visceral tissue: n = 20, r = 0.49, P < 0.03), and they were both significantly associated with BMI. Conversely, no relationship was observed between the levels of TNF-␣ and PAI-1 or TNF-␣ and BMI. Tissue PAI-1 levels were also significantly correlated with those of circulating PAI-1. These results describe, in severe obesity, a proportional increase in tissue PAI-1 and TGF-␤ 1 in visceral and SC tissues. This increased PAI-1 expression could be the result of tissue cytokine disturbances, such as elevated TGF-␤ 1 expression.

Objective-Because obesity and insulin resistance (IR) are strongly associated with liver steatosis (LS), we investigated the relation between the degree of LS and plasminogen activator inhibitor-1 (PAI-1) in ob/ob mice, in C57/BL6 mice with alcoholic LS, and in severely obese humans. Methods and Results-In both mouse models, plasma PAI-1 levels were associated with PAI-1 expression in the liver and with the degree of LS. Liver PAI-1 antigen was associated with the tumor necrosis factor receptor-II (TNFRII) antigen, whereas association with TNF antigen content was found in ob/ob mice only. No significant correlation between plasma PAI-1 and PAI-1 expression in adipose tissue of ob/ob mice was observed. Furthermore, the relation between plasma PAI-1 levels and body weight was positive in ob/ob mice but negative in C57/BL6 mice (both PϽ0.001). In humans, PAI-1 levels were correlated with the degree of LS, and 26% of plasma PAI-1 activity was independently explained by LS and serum insulin levels. Conclusions-Plasma PAI-1 levels are more closely related to fat accumulation and PAI-1 expression in the liver than in adipose tissue. In steatotic liver, PAI-1 antigen content is associated with those of TNF and TNFRII. Therefore, we suggest that TNF pathway dysregulation in LS could be involved in increased plasma PAI-1 in obesity with IR. Key Words: liver steatosis Ⅲ PAI-1 Ⅲ adipose tissue Ⅲ insulin resistance P lasminogen activator inhibitor type 1 (PAI-1) is the main inhibitor of fibrinolysis. PAI-1 modulates the development of atherosclerosis in mice, 1,2 and an elevated plasma PAI-1 concentration is predictive for myocardial infarction in humans. 3,4 Interestingly, the predictive value of circulating PAI-1 levels is highly dependent on the insulin resistance syndrome. 4,5 Despite several efforts in the last few years, the mechanism of increased plasma PAI-1 concentration in insulin resistance associated with android obesity is not completely understood. PAI-1 is expressed in murine as well as in human adipose tissue, 6 -9 and its expression in adipose tissue is correlated positively with body mass index (BMI). 9 -11 Human visceral adipose tissue expresses more PAI-1 than does subcutaneous abdominal adipose tissue. 7,12 Furthermore, PAI-1 expression in only abdominal, but not in femoral subcutaneous adipose tissue, is associated with the features of insulin resistance. 11 Therefore, it has been postulated that in the insulin resistance syndrome with central obesity, abdominal adipose tissue is an important source of plasma PAI-1. Of note, an increase in plasma PAI-1 is also observed in lipodystrophy associated with antiretroviral treatment in HIV patients. These patients typically have prominent, peripheral fat wasting and maintained or decreased visceral fat depots and are insulin resistant. Interestingly, the difference in plasma PAI-1 levels between HIV patients and healthy controls was independent of HIV infection status and was not affected after adjustment for visceral fat estimation but was rather explained by...