Honokiol Improves Insulin Resistance, Hepatic Steatosis, and Inflammation in Type 2 Diabetic db/ db Mice

Abstract

This study focuses on the effect of honokiol (HON) on glucose homeostasis, insulin resistance, dyslipidemia, hepatic steatosis, and inflammation in type 2 diabetic db/db mice. Male C57BL/KsJ-db/db mice were fed a normal diet with or without HON (0.02%, w/w) or pioglitazone (PIO, anti-diabetic agent, 0.01%, w/w) for 5 weeks. Blood biomarker, tissue morphology and enzymatic and genetic parameters were determined. PIO significantly decreased food intake, fasting blood glucose, and glycosylated hemoglobin (HbA1c) levels, but markedly increased body weight, adipose tissue weight, and plasma leptin levels. HON did not significantly affect food intake, body weight, or levels of plasma leptin and blood glucose. However, HON led to significant decreases in adipose tissue weight, plasma insulin, blood HbA1c and HOMA-IR levels and improved glucose tolerance. The anti-diabetic and anti-adiposity effects of HON were partially related to the inhibition of gluconeogenic enzymes and their mRNA expression in the liver; and the inhibition of lipogenic enzymes in adipose tissue, respectively. Unlike PIO, HON did not affect dyslipidemia, but ameliorated hepatic steatosis by inhibiting hepatic lipogenic enzymes activity. Moreover, HON exhibited anti-inflammatory effects similar to PIO. These results suggest that HON can protect against type 2 diabetes by improving insulin resistance, glucose and lipid metabolism, and inflammation.

Keywords: anti-inflammatory effect; anti-insulin resistance effect; anti-steatotic effect; honokiol; type 2 diabetic db/db mice.

Figure 1

Effect of dietary HON on daily food intake (A), initial and final body weight (B), adipose tissue weight (C), plasma leptin levels (D), and the activity of lipid-regulating enzymes in adipose tissue (E) in db/db mice. Male C57BL/KsJ-db/db mice were fed a normal diet with or without HON (0.02%, w/w), or PIO (0.01%, w/w) for 5 weeks (n = 10 per group). Data are presented as mean ± SE. ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001. CON; control group, PIO; pioglitazone, HON; honokiol.

Figure 2

Effect of dietary HON on fasting blood glucose levels (A), blood HbA1c levels (B), IPGTT (C), HOMA-IR (D), plasma insulin levels (E), immunohistochemistry with anti-insulin (F), the activity and mRNA expression of hepatic glucose-regulating enzymes (G,H), and hepatic glycogen content (I) in db/db mice. Male C57BL/KsJ-db/db mice were fed a normal diet with or without HON (0.02%, w/w) or PIO (0.01%, w/w) for 5 weeks (n = 10 per group). (A,C): Data are presented as mean ± SE. CON vs. PIO ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001; PIO vs. HON ^# p < 0.05, ^## p < 0.01, ^### p < 0.001; CON vs. HON ^§ p < 0.05. (B,D,E,G–I): Data are presented as mean ± SE. ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001. (F): Immunohistochemistry with antibodies against insulin. Original magnification ×200. CON; control group, PIO; pioglitazone, HON; honokiol, HbA1c; blood glycosylated hemoglobin, IPGTT; intraperitoneal glucose tolerance test, HOMA-IR; homeostatic index of insulin resistance, PEPCK; phosphoenolpyruvate carboxykinase, G6Pase; glucose-6-phosphatase.

Figure 3

Effect of dietary HON on plasma lipid levels (A), hepatic lipid content (B), hepatic morphology (C), and hepatic lipid-regulating enzyme activity (D) in db/db mice. Male C57BL/KsJ-db/db mice were fed a normal diet with or without HON (0.02%, w/w) or PIO (0.01%, w/w) for 5 weeks (n = 10 per group). (A,B,D): Data are presented as mean ± SE. ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001. (C): Hepatic lipid droplet accumulation in fixed transverse liver sections stained with H&E. Original magnification ×200. CON; control group, PIO; pioglitazone, HON; honokiol. Atherogenic index = [(total cholesterol) − (HDL-cholesterol)]/(HDL-cholesterol).

Figure 4

Effect of dietary HON on plasma pro-inflammatory cytokine levels (A), and the mRNA expression of pro-inflammatory cytokines in adipose tissue and livers (B,C) of db/db mice. Male C57BL/KsJ-db/db mice were fed a normal diet with or without HON (0.02%, w/w) or PIO (0.01%, w/w) for 5 weeks (n = 10 per group). Data are presented as mean ± SE. ^* p < 0.05, ^** p < 0.01, ^*** p < 0.001. CON; control group, PIO; pioglitazone, HON; honokiol, TNF-α; tumor necrosis factor- α, IL-6; interleukin-6, IL-12p70; interleukin-12p70; IFN-γ; interferon-γ.