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      A Mouse Model of Metabolic Syndrome: Insulin Resistance, Fatty Liver and Non-Alcoholic Fatty Pancreas Disease (NAFPD) in C57BL/6 Mice Fed a High Fat Diet

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          Abstract

          Diet-induced obesity in C57BL/6 mice triggers common features of human metabolic syndrome (MetS). The purpose is to assess the suitability of a diet-induced obesity model for investigating non-alcoholic fatty pancreatic disease (NAFPD), fatty liver and insulin resistance. Adult C57BL/6 mice were fed either high-fat chow (HFC, 60% fat) or standard chow (SC, 10% fat) during a 16-week period. We evaluated in both groups: hepatopancreatic injuries, pancreatic islets size, alpha and beta-cell immunodensities, intraperitoneal insulin tolerance test (IPITT) and oral glucose tolerance test (OGTT). The HFC mice displayed greater mass gain ( p<0.0001) and total visceral fat pads ( p<0.001). OGTT showed impairment of glucose clearance in HFC mice ( p<0.0001). IPITT revealed insulin resistance in HFC mice ( p<0.0001). The HFC mice showed larger pancreatic islet size and significantly greater alpha and beta-cell immunodensities than SC mice. Pancreas and liver from HFC were heavier and contained higher fat concentration. In conclusion, C57BL/6 mice fed a high-fat diet develop features of NAFPD. Insulin resistance and ectopic accumulation of hepatic fat are well known to occur in MetS. Additionally, the importance of fat accumulation in the pancreas has been recently highlighted. Therefore, this model could help to elucidate target organ alterations associated with metabolic syndrome.

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          Most cited references44

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          Adipocyte death, adipose tissue remodeling, and obesity complications.

          We sought to determine the role of adipocyte death in obesity-induced adipose tissue (AT) inflammation and obesity complications. Male C57BL/6 mice were fed a high-fat diet for 20 weeks to induce obesity. Every 4 weeks, insulin resistance was assessed by intraperitoneal insulin tolerance tests, and epididymal (eAT) and inguinal subcutaneous AT (iAT) and livers were harvested for histological, immunohistochemical, and gene expression analyses. Frequency of adipocyte death in eAT increased from <0.1% at baseline to 16% at week 12, coincident with increases in 1) depot weight; 2) AT macrophages (ATM Phi s) expressing F4/80 and CD11c; 3) mRNA for tumor necrosis factor (TNF)-alpha, monocyte chemotactic protein (MCP)-1, and interleukin (IL)-10; and 4) insulin resistance. ATM Phi s in crown-like structures surrounding dead adipocytes expressed TNF-alpha and IL-6 proteins. Adipocyte number began to decline at week 12. At week 16, adipocyte death reached approximately 80%, coincident with maximal expression of CD11c and inflammatory genes, loss (40%) of eAT mass, widespread collagen deposition, and accelerated hepatic macrosteatosis. By week 20, adipocyte number was restored with small adipocytes, coincident with reduced adipocyte death (fourfold), CD11c and MCP-1 gene expression (twofold), and insulin resistance (35%). eAT weight did not increase at week 20 and was inversely correlated with liver weight after week 12 (r = -0. 85, P < 0.001). In iAT, adipocyte death was first detected at week 12 and remained
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            Fatty liver: a novel component of the metabolic syndrome.

            Although the epidemic of obesity has been accompanied by an increase in the prevalence of the metabolic syndrome, not all obese develop the syndrome and even lean individuals can be insulin resistant. Both lean and obese insulin resistant individuals have an excess of fat in the liver which is not attributable to alcohol or other known causes of liver disease, a condition defined as nonalcoholic fatty liver disease (NAFLD) by gastroenterologists. The fatty liver is insulin resistant. Liver fat is highly significantly and linearly correlated with all components of the metabolic syndrome independent of obesity. Overproduction of glucose, VLDL, CRP, and coagulation factors by the fatty liver could contribute to the excess risk of cardiovascular disease associated with the metabolic syndrome and NAFLD. Both of the latter conditions also increase the risk of type 2 diabetes and advanced liver disease. The reason why some deposit fat in the liver whereas others do not is poorly understood. Individuals with a fatty liver are more likely to have excess intraabdominal fat and inflammatory changes in adipose tissue. Intervention studies have shown that liver fat can be decreased by weight loss, PPARgamma agonists, and insulin therapy.
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              NASH and insulin resistance: Insulin hypersecretion and specific association with the insulin resistance syndrome.

              Nonalcoholic steatohepatitis (NASH) is often linked with disorders that are clearly associated with insulin resistance (IR): obesity, type 2 diabetes mellitus, and hypertriglyceridemia. We tested the hypotheses that (1) IR is an essential requirement for the development of NASH and (2) a high association between IR and liver disease is relatively specific for NASH. We measured body mass index (BMI), waist/hip ratio, and fasting serum lipid, insulin, C-peptide, and glucose levels in 66 patients with NASH (21 with advanced fibrosis and 45 with mild fibrosis). IR was determined by the homeostasis model assessment (HOMA). We also determined the strength of the association of NASH with insulin resistance syndrome (IRS) as defined by World Health Organization criteria. To assess whether the finding of IR was relatively specific to NASH rather than simply to obesity or liver disease, we compared the results of a subset of 36 patients with less-severe NASH with 36 age- and sex-matched patients with chronic hepatitis C virus (HCV) of comparable fibrotic severity. IR was confirmed in 65 patients (98%) with NASH, and 55 (87%) fulfilled minimum criteria for IRS. IR was found in lean as well as in overweight and obese patients. The IR values and the prevalence of IRS (75% vs. 8.3%) were significantly higher in those with NASH than in comparable cases of HCV. Hyperinsulinemia was attributable to increased insulin secretion rather than decreased hepatic extraction. In conclusion, most patients with NASH have IRS, and there is a near-universal association between NASH and IR irrespective of obesity. IR is present in mild as well as advanced cases of NASH but is unusual in chronic HCV of similar fibrotic severity.
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                Author and article information

                Journal
                J Clin Biochem Nutr
                JCBN
                Journal of Clinical Biochemistry and Nutrition
                the Society for Free Radical Research Japan (Kyoto, Japan )
                0912-0009
                1880-5086
                May 2010
                10 April 2010
                : 46
                : 3
                : 212-223
                Affiliations
                [1]Laboratory of Morphometry and Cardiovascular Morphology, Biomedical Center, Institute of Biology, State University of Rio de Janeiro, Av 28 de Setembro, 87 (fds) – CEP 20551-030, Rio de Janeiro, Brazil
                Author notes
                *To whom correspondence should be addressed. Tel: (+55.21) 2587-6416 Fax: (+55.21) 2587-6133 E-mail: mandarim@ 123456uerj.br
                Article
                jcbn09-83
                10.3164/jcbn.09-83
                2872226
                20490316
                217c06d3-f58b-4ae7-ab6b-e46c9054cc5c
                Copyright © 2010 JCBN

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 20 August 2009
                : 23 December 2009
                Categories
                Original Article

                Biochemistry
                metabolic syndrome,fatty liver,high-fat diet,insulin resistance,non-alcoholic fatty pancreatic disease

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