Gelidium elegans Regulates the AMPK-PRDM16-UCP-1 Pathway and Has a Synergistic Effect with Orlistat on Obesity-Associated Features in Mice Fed a High-Fat Diet

Abstract

The incidence of obesity is rising at an alarming rate throughout the world and is becoming a major public health concern with incalculable social and economic costs. Gelidium elegans (GENS), also previously known as Gelidium amansii, has been shown to exhibit anti-obesity effects. Nevertheless, the mechanism by which GENS is able to do this remains unclear. In the present study, our results showed that GENS prevents high-fat diet (HFD)-induced weight gain through modulation of the adenosine monophosphate-activated protein kinase (AMPK)-PR domain-containing16 (PRDM16)-uncoupling protein-1 (UCP-1) pathway in a mice model. We also found that GENS decreased hyperglycemia in mice that had been fed a HFD compared to corresponding controls. We also assessed the beneficial effect of the combined treatment with GENS and orlistat (a Food and Drug Administration-approved obesity drug) on obesity characteristics in HFD-fed mice. We found that in HFD-fed mice, the combination of GENS and orlistat is associated with more significant weight loss than orlistat treatment alone. Moreover, our results demonstrated a positive synergistic effect of GENS and orlistat on hyperglycemia and plasma triglyceride level in these animals. Thus, we suggest that a combination therapy of GENS and orlistat may positively influence obesity-related health outcomes in a diet-induced obese population.

Keywords: Gelidium amansii; Gelidium elegans; high-fat diet-induced obese mice; hyperglycemia; obesity.

Figure 1

Effect of GENS on body weight change (A); subcutaneous fat (B); abdominal fat (C); total food intake (D); serum levels of insulin (E); levels of serum triglycerides (TG) (F); and high-density lipoprotein (HDL)-cholesterol concentration (G) in high-fat diet (HFD)-fed mice. Five-week-old mice were maintained with or without GENS (50 and 200 mg/kg/day) under HFD for 7 weeks. Data are mean ± SD (n = 6).

Figure 2

Effect of GENS on key adipogenic factors in HFD-fed mice of white adipose tissue and glucose tolerance. Five-week-old mice were maintained with or without GENS (50 and 200 mg/kg/day) under HFD for 7 weeks. Each parameter was measured by western blot analysis with C/EBPα and PPARγ. The protein expression level was normalized against GAPDH. Protein level was quantified using Image J software (A). Five groups of male mice (5 weeks old) were fasted for 12 h (dark-period). After 12-h fasting, mice were administered 1.0 g/kg glucose by intraperitoneal injection. The first group received only Phosphate Buffered Saline (PBS), the second group received 1.0 g/kg glucose, the third group received 1.0 g/kg glucose + 140 mg/kg metformin and the fourth and fifth group received 1.0 g/kg glucose + GENS (50 and 200 mg/kg). Blood glucose levels were measured at the indicated times (0, 30, 60, and 90 min) (B). Data are mean ± SD (n = 6).

Figure 3

GENS represses hepatic lipogenesis and cholesterol factors in HFD-fed mice. Five-week-old mice were maintained with or without GENS (50 and 200 mg/kg/day) under HFD for 7 weeks. Each parameter was measured by western blot analysis with specific antibodies. The liver sections stained with Oil red O (A); Hepatic TG content (B); Expression levels of HMG-CoA reductase and LDLR genes were determined by quantitative RT-PCR in liver samples (C); p-AMPK, AMPK, SREBP-1, p-ACC, ACC, DGAT-1, and FAS (D); PRDM16 (E). The protein expression level was normalized against AMPK, ACC, and GAPDH. Protein level was quantified using Image J software. Data are mean ± SD (n = 6).

Figure 4

Effect of GENS on energy expenditure protein expression in brown adipose tissue of HFD-fed mice. Five-week-old mice were maintained with or without GENS (50 and 200 mg/kg/day) under HFD for 7 weeks. Each parameter was measured by western blot analysis with p-AMPK, PRDM16, and uncoupling protein-1 (UCP-1). The protein expression level was normalized against AMPK and GAPDH. Protein level was quantified using Image J software. Data are mean ± SD (n = 6).

Figure 5

Synergistic effect of GENS and orlistat on weight change (A); body weight gain (B); subcutaneous fat (C); abdominal fat (D); HDL-cholesterol concentration (E); total food intake (F); serum levels of insulin (G); and serum levels of TG (H) in HFD-fed mice. Five-week-old mice were maintained with or without GENS (50 and 200 mg/kg/day) under HFD for 7 weeks. Data are mean ± SD (n = 6).

Figure 6

Combination effect of GENS and orlistat on white adipose tissue and hepatic lipogenesis and cholesterol synthesis-associated genes in HFD-fed mice. Five-week-old mice were maintained with or without orlistat (20 mg/kg/day) and GENS (50 mg/kg/day) under HFD for 7 weeks. Each parameter was measured by western blot analysis with C/EBPα and PPARγ (A); The liver sections stained with Oil red O (B); Hepatic TG content (C); Expression levels of HMG-CoA reductase and LDLR genes were determined by quantitative RT-PCR in liver samples (D); p-AMPK, AMPK, SREBP-1, p-ACC, ACC, DGAT-1, FAS (E) and PRDM16 (F). The protein expression level was normalized against AMPK, ACC, and GAPDH. Protein level was quantified using Image J software. Data are mean ± SD (n = 6).

Figure 7

Combination effect of GENS and orlistat on energy expenditure-associated protein expression in brown adipose tissue of HFD-fed mice. Five-week-old mice were maintained with or without orlistat (20 mg/kg/day) and GENS (50 mg/kg/day) under HFD for 7 weeks. Protein extracts from brown adipose tissue were assayed for p-AMPK, PRDM16, and UCP-1 by western blot analysis with specific antibodies. The protein expression level was normalized against GAPDH (A). Protein level was quantified using Image J software. Five groups of male mice (5 weeks old) were fasted for 12 h (dark-period). After 12-h fasting, mice were administered 1.0 g/kg glucose by intraperitoneal injection. The first group received only PBS, the second group received 1.0 g/kg glucose, third groups received 1.0 g/kg glucose + 140 mg/kg metformin, the fourth group received 1.0 g/kg glucose + 20 mg/kg orlistat and the fifth group received 1.0 g/kg glucose + 20 mg/kg orlistat + 50 mg/kg GENS. Blood glucose levels were measured at the indicated times (0, 30, 60, and 90 min) (B). Data are mean ± SD (n = 6).