Exenatide improves hepatic steatosis by enhancing lipid use in adipose tissue in nondiabetic rats

Figure 1 Changes in body weight and energy intake. A: Time-course of body weight. Four-week-old rats were fed a control diet (control group; n = 8) or a high-fat diet (HFD) (n = 16). After 4 wk of feeding, HFD-fed rats were subdivided into two groups (n = 8 per group) and intraperitoneally injected with either 10 μg/kg body weight exenatide [HFD-Ex(+) group] or saline [HFD-Ex(-) group] every day for 12 wk. Rats in the control group were injected with saline. At week 16 of feeding, the body weight was significantly lower in the HFD-Ex(+) group than in the control and HFD-Ex(-) groups. n = 8. ^aP < 0.05 vs other groups; B: Daily energy intake during the treatment period. Energy intake was lower in the HFD-Ex(+) group than in the control or HFD-Ex(-) group.

Figure 2 Oxygen consumption and respiratory exchange ratio evaluated by indirect calorimetry in the high-fat diet-Ex(+) and high-fat diet-Ex(-) groups at week 12 of feeding. A: Oxygen consumption was significantly greater in the high-fat diet (HFD)-Ex(+) group than in the HFD-Ex(-) group, particularly during the dark cycle; B: Respiratory exchange ratio (RER) was significantly lower in the HFD-Ex(+) group than in the HFD-Ex(-) group. n = 4. ^aP < 0.05 between groups.

Figure 3 Histological evaluation of lipid accumulation in the liver and adipose tissue. A: Numerous hepatocytes containing lipid droplets were observed in the high-fat diet (HFD)-Ex(-) group, whereas scant lipid-containing hepatocytes were found in the HFD-Ex(+) group; B: In epididymal white adipose tissue, there were abundant enlarged adipocytes in the HFD-Ex(-) group but not in the HFD-Ex(+) group; C: The number of hepatic lipid droplets was significantly decreased in the HFD-Ex(+) group compared with the HFD-Ex(-) group; D: The mean diameter of adipocytes in the HFD-Ex(+) group was significantly smaller than that in the HFD-Ex(-) group and was similar to that in the control group. The fold changes were calculated as the ratio of the average size of adipocytes in the HFD-Ex(+) or HFD-Ex(-) group to that in the control group. n = 5, ^aP < 0.05 between groups. Scale bar = 100 μm. ND: Not detected.

Figure 4 Effects of glucagon-like peptide-1 on the expression levels of genes associated with lipid metabolism in the liver and skeletal muscle. A: In the liver, there were no significant differences in the expression levels of sterol regulatory element-binding protein-1c (SREBP1c), fatty acid synthase (FAS), acetyl-CoA carboxylase-1 (ACC1), hormone-sensitive lipase (HSL), and apolipoprotein B (ApoB), carnitine palmitoyltransferase-1 (CPT1), long-chain acyl-CoA dehydrogenase (LCAD), or acyl-CoA oxidase 1 (ACOX1) among the three groups; B: In skeletal muscle, the expression of LPL was significantly greater in the high-fat diet (HFD)-Ex(+) group than in the control group. There were no significant differences in the expression levels of HSL, LPL, CPT1, LCAD, or ACOX1 between the HFD-Ex(-) and HFD-Ex(+) group. The fold changes were calculated as the ratio of the expression level in the HFD-Ex(+) or HFD-Ex(-) group to that in the control group. n = 8, ^aP < 0.05 between groups.

Figure 5 Effects of exenatide on the expression levels of genes associated with lipid metabolism, reactive oxygen species elimination, and macrophage activation in adipose tissue. A: The expression levels of hormone-sensitive lipase (HSL), carnitine palmitoyltransferase-1 (CPT1), long-chain acyl-CoA dehydrogenase (LCAD), and acyl-CoA oxidase 1 (ACOX1) were significantly greater in the high-fat diet (HFD)-Ex(+) group than in the control and HFD-Ex(-) groups; B: The expression levels of catalase and superoxide dismutase (SOD)2 were significantly greater in the HFD-Ex(+) group than in the control and HFD-Ex(-) groups. There were no significant differences in tumor necrosis factor (TNF) or monocyte chemotactic protein 1 (MCP1) expression levels among the three groups. The fold changes were calculated as the ratio of the expression level in the HFD-Ex(+) or HFD-Ex(-) group to that in the control group. n = 8, ^aP < 0.05 between groups.

Figure 6 Effects of exenatide on the expression levels of mitochondrial morphologic regulators in adipose tissue. Genes involved in mitochondrial fusion [mitofusin-1 (Mfn1) and mitofusin-2 (Mfn2) and optic atrophy-1 (Opa1)] were significantly greater in the high-fat diet (HFD)-Ex(+) group than in the control and HFD-Ex(-) groups. The expression of dynamin-1 (Dnm1), which is involved in mitochondrial fission, was not significantly different between the HFD-Ex(+) and HFD-Ex(-) groups. The fold changes were calculated as the ratio of the expression level in the HFD-Ex(+) or HFD-Ex(-) group to that in the control group. n = 8, ^aP < 0.05 between groups.

Figure 7 Effect of exenatide on glucose tolerance. Intraperitoneal glucose tolerance tests (IPGTTs) were performed in the high-fat diet (HFD)-Ex(+) and HFD-Ex(-) groups at week 12 of feeding. Fasting plasma glucose levels were slightly lower in the HFD-Ex(+) group than in the HFD-Ex(-) group, but no significant differences were observed at the other times during the IPGTTs.

Figure 8 Effects of exenatide on AMP-activated protein kinase activation in adipose tissue. Immunoblotting for total AMP-activated protein kinase (AMPK), phosphorylated AMPK (P-AMPK), and β-actin were performed. The protein levels of total AMPK and P-AMPK were not significantly different among the three groups. HFD: High-fat diet.