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

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.

Keywords: fatty liver; high-fat diet; insulin resistance; metabolic syndrome; non-alcoholic fatty pancreatic disease.

Fig. 1

Body mass. Body mass evolution and respective areas under the curve (AUC) show significant differences between the body mass gain in the standard chow (SC) group and in the very high-fat chow (HFC) group. Values are mean ± SEM, n = 10/group. *p<0.05, differnts from HFC Group.

Fig. 2

Fat pads. Abdominal ventral view of dissected mice showing the fat pads (bar = 2.5 mm): Retroperitoneal fat pads: (a) SC group, the kidneys (white open arrows) are surrounded by small fat pads extending until the urinary bladder (black open arrow); (b) HFC group, the fat pads (asterisks) are greater than in SC group, covering partially the kidneys. Epididymal fat pads: (c) SC group—they cover up the inferior abdominal cavity but are much more developed in HFC group (d) (arrows). Photomicrographs of adipocytes (hematoxylin and eosin stain—bar = 60 µm). (e) shows typical epididymal fat adipocytes from lean mice fed SC and (f) shows adipocytes for the HFC group, with greater diameter.

Fig. 3

Feed efficiency. Feed efficiency (values are means) measured in standard chow (SC) group and in very high-fat chow (HFC) group. The areas under the curve (AUC) show the differences between the groups. Values are mean ± SEM, n = 10/group.

Fig. 4

Oral glucose tolerance test. Oral glucose tolerance test curve at 14th week. The areas under the curve show significant differences between the standard chow (SC) group and the very high-fat chow (HFC) group. Values are mean ± SEM, n = 5/group. *p<0.05, differnts from HFC Group.

Fig. 5

Intraperitoneal insulin tolerance test. Intraperitoneal insulin tolerance test curve at 15th week. The areas under the curve show significant differences between the standard chow (SC) group and the very high-fat chow (HFC) group. Values are mean ± SEM, n = 5/group. *p<0.05, differnts from HFC Group.

Fig. 6

Photomicrographs of liver and pancreas. Photomicrographs of liver and pancreas (hematoxylin and eosin stain): (a) typical liver of a lean mice fed SC and (b) liver of high-fat fed mice with macro- and microvesicular steatosis (arrows); (c) typical pancreas of a lean mice fed SC and (d) pancreas of high-fat fed mice showing intracellular lipid vesicles in acinar cells (arrows); (e) adipose infiltration in pancreas of high-fat fed mice (black arrow) and (f) ectopic deposition of the interlobular fat of high-fat fed mice (black arrow).

Fig. 7

Pancreatic islet alpha-cell. The pancreatic islet alpha-cell volume densities in the standard chow (SC) group and in the very high-fat chow (HFC) group were measured by image analysis. It was significantly greater in the HFC group. Photomicrographs under de column bars show typical islets of the two groups with positive stain for glucagon (same magnification, bar = 40 µm). Values are mean ± SEM, n = 10/group.

Fig. 8

Pancreatic islet beta-cell. The pancreatic islet beta-cell volume densities in the standard chow (SC) group and in the very high-fat chow (HFC) group were measured by image analysis. It was significantly greater in the HFC group. Photomicrographs under de column bars show typical islets of the two groups with positive stain for insulin (same magnification, bar = 40 µm). Values are mean ± SEM, n = 10/group.