Effect of Citrus Unshiu Peel Extract Fermented by Aspergillus niger on Obesity and Hyperglycemia in High­Fat Diet Fed C57BL/6J Mice

Abstract

Citrus unshiu peel is a Korean citrus fruit that has abundant bioactive compounds including flavonoids like naringin, hesperidin, and narirutin. In this study, we examined the anti­obesity and anti­hyperglycemia effects of citrus unshiu peel extract fermented by mycotoxin non­producing Aspergillus niger FMB S46494 using high­fat diet induced obese mice. The total flavonoid contents of citrus unshiu peel extract (CPE) and fermented citrus unshiu peel extract (FCPE) were 55.6 mg/g NE (naringin equivalents) and 173.5 mg/g NE respectively. The contents of flavonoid were determined by HPLC. Narirutin and hesperidin were the major flavonoids in citrus peel extract. Naringenin level reached 14.1 mg/g after fermentation. Four­week­old male C75BL/6J mice were divided into five groups (n = 8) and fed the respective experimental diets for 13 weeks

LFD (low­fat diet), HFD (high­fat diet), CPE (HFD + 1% (w/w) CPE), FCPE 0.3% (HFD + 0.3% (w/w) FCPE) and FCPE 1% (HFD + 1% (w/w) FCPE). FCPE 0.3% group and FCPE 1% group had significantly lower body weight gains (14.1% and 13.2% less respectively, p＜0.05) and epididymal fat weight (28.8% and 23.5% less respectively, p＜0.05). The fasting blood glucose levels were significantly lower in the FCPE groups in comparison to the HFD group (p＜0.05). In intraperitoneal glucose tolerance test, AUC level was significantly lower in the FCPE 0.3% group compared to the HFD group (p＜0.05). In morphology of liver, lipid droplet accumulation was less pronounced in the FCPE 0.3% group and FCPE 1% group. Adipocyte size of epididymal fat was lower in the FCPE groups. Furthermore, the levels of total cholesterol and LDL cholesterol in plasma were significantly lower in the FCPE groups (p＜0.05). Expression of genes related to hepatic glucose homeostasis (Gk, G6pase, Pepck), hepatic glucose transporter (Glut2), hepatic lipogenesis and fatty acid oxidation (Srebp1c, Acc, Fas, Cpt1) as well as hepatic cholesterol homeostasis (Srebp2, Hmgr, Pcsk9, Acat2, Cyp7a1, Ldlr) were determined by real­time PCR. The mRNA levels of Gk, Glut2 and CPT1 were significantly higher in the FCPE groups compared with the HFD group (p＜0.05). In addition, FCPE groups had significantly lower Srebp1c, Srebp2, Fas, Acc, Hmgr and Pcsk9 mRNA expression (p＜0.05). In conclusion, FCPE supplementation may function to improve hepatic lipid and cholesterol metabolism as well as hepatic glucose metabolism in high­fat fed mice. These results suggest that FCPE, which contains naringenin, is a fermented food material that has promising effect in amelioration of obesity and obesity-­induced hyperglycemia.