Citrus unshiu peel extract ameliorates hyperglycemia and hepatic steatosis by altering inflammation and hepatic glucose- and lipid-regulating enzymes in db/db mice☆ Hae-Jin Park a,b,1 , Un Ju Jung a,b,1 , Su-Jung Cho a,b , Hee-Kyung Jung c , Sangphil Shim d , Myung-Sook Choi a,b, ⁎ a Department of Food Science and Nutrition, Kyungpook National University, Daegu, Republic of Korea b Center for Food and Nutritional Genomics Research, Kyungpook National University, Daegu, Republic of Korea c Bio Industry Center, Daegu Technopark, Daegu, Republic of Korea d Foodwell Corp., Daegu, Republic of Korea Received 23 September 2011; received in revised form 15 December 2011; accepted 22 December 2011 Abstract Insulin resistance in Type 2 diabetes leads to hepatic steatosis that can accompanied by progressive inflammation of the liver. Citrus unshiu peel is a rich source of citrus flavonoids that possess anti-inflammatory, anti-diabetic and lipid-lowering effects. However, the ability of citrus unshiu peel ethanol extract (CPE) to improve hyperglycemia, adiposity and hepatic steatosis in Type 2 diabetes is unknown. Thus, we evaluated the effects of CPE on markers for glucose, lipid metabolism and inflammation in Type 2 diabetic mice. Male C57BL/KsJ-db/db mice were fed a normal diet with CPE (2 g/100 g diet) or rosiglitazone (0.001 g/100 g diet) for 6 weeks. Mice supplemented with the CPE showed a significant decrease in body weight gain, body fat mass and blood glucose level. The antihyperglycemic effect of CPE appeared to be partially mediated through the inhibition of hepatic gluconeogenic phosphoenolpyruvate carboxykinase mRNA expression and its activity and through the induction of insulin/glucagon secretion. CPE also ameliorated hepatic steatosis and hypertriglyceridemia via the inhibition of gene expression and activities of the lipogenic enzymes and the activation of fatty acid oxidation in the liver. These beneficial effects of CPE may be related to increased levels of anti-inflammatory adiponectin and interleukin (IL)-10, and decreased levels of pro-inflammatory markers (IL-6, monocyte chemotactic protein-1, interferon-γ and tumor necrosis factor-α) in the plasma or liver. Taken together, we suggest that CPE has the potential to improve both hyperglycemia and hepatic steatosis in Type 2 diabetes. © 2013 Elsevier Inc. All rights reserved. Keywords: Citrus unshiu peel extract; Type 2 diabetic db/db mice; Anti-diabetic; Lipid metabolism; Inflammation 1. Introduction Diabetes is a global public health problem, and its prevalence is currently estimated to be about 6.4% worldwide [1]. In particular, there has been a dramatic increase in Type 2 diabetes in the past 2 decades [1]. Type 2 diabetes is characterized by hyperglycemia resulting from the combination of resistance to insulin action and inadequate insulin secretion. Insulin resistance is strongly associated with hepatic steatosis which is a relatively early condition of nonalcoholic fatty liver disease (NAFLD) and can lead to more severe NAFLD complications, such as steatohepatitis (steatosis plus inflammation and/or fibrosis) and cirrhosis [2]. Although it remains unclear whether hepatic steatosis is a consequence of insulin resistance or causes hepatic insulin resistance, patients with NAFLD are more prone to have insulin resistance and Type 2 diabetes [3], and the prevalence of the severe stage of NAFLD is high in Type 2 diabetes [4]. Most notably, insulin sensitizers such as thiazolidine- diones and antioxidants improve Type 2 diabetes [5,6]. However, thiazolidinediones like rosiglitazone (RGZ) have some unfavorable complications including weight gain [7], hepatotoxicity [8] and congestive heart failure [9]. In recent years, medicinal plants that act as potent anti-inflammatory and antioxidant agent have attracted a lot of attention globally [10]. Citrus unshiu (Citrus unshiu Marcorv., Family: Rutaceae) is a seedless and easy-peeling Korean citrus fruit and it accounts for 30% of the total fruits produced in Korea. Its peels have been widely used as a folk medicine to improve bronchial and asthmatic conditions or blood circulation in Korea, China and Japan [11]. Previous studies reported that citrus unshiu peels have many pharmacologic activities including anti-inflammatory, antioxidant, anti-allergic and anti-cancer properties [12-15]. No studies have so far been done on its anti-diabetic and lipid-lowering effects. Citrus unshiu peel contains many phytochemicals such as hesperidin, naringin and nobiletin [16]. We previously demonstrated that hesperidin and niringin ameliorated hyperglycemia, dyslipidemia Available online at www.sciencedirect.com Journal of Nutritional Biochemistry 24 (2013) 419 – 427 ☆ Funding Source: This work was supported by the Korea Ministry of Knowledge Economy and the National Research Foundation of Korea (NRF) grant funded by the Korean government (MEST) (No. 2011-0000920). ⁎ Corresponding author. Department of Food Science and Nutrition, Kyungpook National University, 1370 Sankyuk Dong Puk-ku, 702-701, Daegu, Republic of Korea. Tel.: +82 53 950 6232; fax: +82 53 950 6229. E-mail address: mschoi@knu.ac.kr (M.-S. Choi). 1 These authors contributed equally to this work. 0955-2863/$ - see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jnutbio.2011.12.009