Eicosapentaenoic acid ameliorates hyperglycemia in high-fat diet-sensitive diabetes mice in conjunction with restoration of hypoadiponectinemia

Abstract

Background/objective: Eicosapentaenoic acid (EPA) exerts pleiotropic effects on metabolic disorders such as atherosclerosis and dyslipidemia, but its effectiveness in the treatment of type 2 diabetes mellitus remains controversial.

Methods: We examined the antidiabetic effect of EPA in insulin receptor mutant (Insr(P1195L/+)) mice that exhibit high-fat diet (HFD)-dependent hyperglycemia.

Results: EPA supplementation was found to alleviate hyperglycemia of Insr(P1195L/+) mice fed HFD (Insr(P1195L/+)/HFD mice), which was accompanied by amelioration of increased gluconeogenesis and impaired insulin signaling, as assessed by glucose-6-phosphatase (G6pc) expression on refeeding and insulin-induced phosphorylation of Akt in the liver, respectively. We found that serum levels of adiponectin, the antidiabetic adipokine, were decreased by HFD along with the body weight gain in Insr(P1195L/+) mice but not in wild-type mice, suggesting that Insr(P1195L/+) mice are prone to hypoadiponectinemia in response to obesity. Interestingly, the blood glucose levels of Insr(P1195L/+) mice were in reverse proportion to their serum adiponectin levels and EPA supplementation ameliorated their hyperglycemia in conjunction with the restoration of hypoadiponectinemia.

Conclusions: EPA exerts an antidiabetic effect in Insr(P1195L/+)/HFD mice, an HFD-sensitive, insulin-resistant animal model, possibly through its action against hypoadiponectinemia.

Figure 1

Amelioration of glucose metabolism by EPA supplementation. (a) Changes in blood glucose levels fed ad libitum. (b) Changes in body weight. (c) Blood glucose levels after oral glucose loading (1 g kg⁻¹). (d) Blood glucose levels after intraperitoneal insulin administration (0.75 U kg⁻¹). (e, f) mRNA expression levels of Pck1 (e) and G6pc (f) in the liver at fasted (after 16 h fasting) and refed (after 3 h refeeding) state. *P<0.05, **P<0.01, ***P<0.001. (g) Changes in blood glucose levels after intraperitoneal glycerol administration (0.5 g kg⁻¹). Data are mean±s.e.m. (a–d, g) ^¶P<0.05 (Insr^P1195L/+/HFD vs WT/HFD); ^§P<0.05 (Insr^P1195L/+/HFD vs Insr^P1195L/+/HFD+EPA); ^†P<0.05 (WT/HFD vs WT/HFD+EPA); ^‡P<0.05 (Insr^P1195L/+/HFD+EPA vs WT/HFD+EPA). The number in the parenthesis (a–d, g) and in the bottom of the columns (e, f) denotes sample size.

Figure 2

Phosphorylation of Akt in the liver and primary hepatocytes. (a, b) Akt phosphorylation after insulin administration (0.1 U kg⁻¹, intravenous) in vivo. (c–f) Akt phosphorylation in primary hepatocytes. (a, c, e) A representative result of p-Akt. (b) Quantified result of p-Akt levels. The number in the bottom of the columns denotes sample size. (d, f) Quantified result of p-Akt levels (n=3 per each group). Data are mean±s.e.m. *P<0.05.

Figure 3

Chronic inflammation in WAT of Insr^P1195L/+/HFD mice. (a, b) HE staining of epididymal fat. (a) A representative result. Scale bar: 200 μm. (b) CLS number. (c) Serum FFA levels. (d, e) mRNA expression levels of Tnfa (d) and Emr1 (e). Data are mean±s.e.m. *P<0.05, **P<0.01, ***P<0.001. (b–e) The number in the bottom of the columns denotes sample size.

Figure 4

Effect of EPA supplementation on adiposity and steatosis in Insr^P1195L/+/HFD mice at 18–20 weeks of age. (a) Computed tomographic images at the level of lower end of right kidney. Visceral and subcutaneous fat are indicated in pink and yellow, respectively. (b) Weight of epididymal WAT. (c) Immunostaining of caveolin in epididymal fat. (d) Mean adipocyte size. Scale bar: 200 μm. (e) Histogram of the cell area of four mouse groups. (f) HE staining of the liver. (g) TG content in the liver. (b, d, e, g) Data are mean±s.e.m. *P<0.05, **P<0.01, ***P<0.001. The number in the bottom of the columns (b, d, g) and in the parenthesis (e) denotes sample size.

Figure 5

Serum adiponectin levels and their correlation with body weight or blood glucose levels. (a) Serum adiponectin levels fed ad libitum (16–18 weeks of age). (b) Relationship between body weight and adiponectin levels. Most of the data of Insr^P1195L/+ mice and WT mice are plotted inside the solid- and dotted-circle, respectively. (c) Relationship between blood glucose levels and adiponectin levels. (b, c) r=Pearson's correlation coefficient. (d, e) mRNA expression levels of Acrp30 (d) and Pparg2 (e) in WAT under refed condition. Data are mean±s.e.m. *P<0.05, ***P<0.001. The number in the bottom of the columns (a, d, e) and in the parenthesis (b, c) denotes sample size.