Emodin, a natural product, selectively inhibits 11beta-hydroxysteroid dehydrogenase type 1 and ameliorates metabolic disorder in diet-induced obese mice

Abstract

Background and purpose: 11beta-Hydroxysteroid dehydrogenase type 1 (11beta-HSD1) is an attractive therapeutic target of type 2 diabetes and metabolic syndrome. Emodin, a natural product and active ingredient of various Chinese herbs, has been demonstrated to possess multiple biological activities. Here, we investigated the effects of emodin on 11beta-HSD1 and its ability to ameliorate metabolic disorders in diet-induced obese (DIO) mice.

Experimental approach: Scintillation proximity assay was performed to evaluate inhibition of emodin against recombinant human and mouse 11beta-HSDs. The ability of emodin to inhibit prednisone- or dexamethasone-induced insulin resistance was investigated in C57BL/6J mice and its effect on metabolic abnormalities was observed in DIO mice.

Key results: Emodin is a potent and selective 11beta-HSD1 inhibitor with the IC(50) of 186 and 86 nM for human and mouse 11beta-HSD1, respectively. Single oral administration of emodin inhibited 11beta-HSD1 activity of liver and fat significantly in mice. Emodin reversed prednisone-induced insulin resistance in mice, whereas it did not affect dexamethasone-induced insulin resistance, which confirmed its inhibitory effect on 11beta-HSD1 in vivo. In DIO mice, oral administration of emodin improved insulin sensitivity and lipid metabolism, and lowered blood glucose and hepatic PEPCK, and glucose-6-phosphatase mRNA.

Conclusions and implications: This study demonstrated a new role for emodin as a potent and selective inhibitor of 11beta-HSD1 and its beneficial effects on metabolic disorders in DIO mice. This highlights the potential value of analogues of emodin as a new class of compounds for the treatment of metabolic syndrome or type 2 diabetes.

Figure 1

Molecular modelling of emodin and 11β-HSD1. Molecular docking simulation was performed employing the program DOCK4.0, based on the X-ray crystal structure of 11β-HSD1 complex (PDB entry 2IRW). The complex structure (A), hydrophobic contacts among 11β-HSD1, emodin and NADP (B).

Figure 2

Oral administration of emodin inhibited hepatic 11β-HSD1 activity in C57BL/6J mice. Emodin was orally administered to male C57BL/6J mice, and analysis of 11β-HSD1 activity in 10 µg liver homogenates (Figure 2A) and 30 µg mesenteric fat homogenates (Figure 2B) was conducted with SPA at 2 h post-dose. Data are expressed as mean ± SEM for n= 10 mice. *P < 0.05; **P < 0.01 versus control mice.

Figure 3

Emodin antagonized insulin resistance induced by glucocorticoids. Mice were treated as described in Methods. The insulin tolerance test was conducted in mice deprived of food overnight (0.5 U·kg⁻¹ insulin administered by an i.p. injection) at day 14 of treatment. Values are expressed as mean ± SEM for n= 8 mice. #P < 0.05; ##P < 0.01 versus control mice. *P < 0.05; **P < 0.01 versus prednisone-treated mice.

Figure 4

Emodin lowered blood glucose and increased insulin sensitivity of DIO mice. DIO mice were treated as described in Methods. Fasting blood glucose concentrations (A) were measured regularly during the treatment period. Glucose tolerance (B) and the corresponding insulin levels (C) were determined at day 24 of the treatment. Insulin tolerance (D) was determined at day 28 of the treatment. Serum insulin concentration (E) was measured in mice deprived of food for 5 h (5 h fasted mice) at the end of the treatment period. Values are expressed as mean ± SEM for n= 8 mice. *P < 0.05; **P < 0.01 versus control mice.

Figure 5

Emodin decreased serum lipids of DIO mice. DIO mice were treated as described in Methods. Serum triacylglycerol (A), cholesterols (B) and NEFA (C) concentrations were evaluated at the end of the treatment period. Data are mean ± SEM for n= 8 mice. *P < 0.05 versus control mice.

Figure 6

Emodin decreased body weight, food intake and fat pad weight of DIO mice. DIO mice were treated as described in Methods. Body weight (A) and food intake (B) were recorded regularly during the treatment period. Different fat pads (C) were also weighed at the end of the experiment. Values are mean ± SEM for n= 8 mice. *P < 0.05; **P < 0.01; ***P < 0.001 versus control mice.

Figure 7

Emodin suppressed 11β-HSD1 activity and reduced the mRNA levels of gluconeogenic genes in DIO mice. DIO mice were treated as described in Methods. 11β-HSD1 activity (A) in liver and mesenteric adipose tissues was measured by SPA at the end of the treatment period. The expression of 11β-HSD1 mRNA (B), PEPCK and G6Pase mRNA (C) were also determined by real-time PCR at the end of the treatment period. Values are mean ± SEM for n= 4–8 mice. *P < 0.05; **P < 0.01 versus control mice.