Basic Study
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Feb 28, 2016; 22(8): 2512-2523
Published online Feb 28, 2016. doi: 10.3748/wjg.v22.i8.2512
Glucagon-like peptide-1 analogue prevents nonalcoholic steatohepatitis in non-obese mice
Takaya Yamamoto, Yukiomi Nakade, Taeko Yamauchi, Yuji Kobayashi, Norimitsu Ishii, Tomohiko Ohashi, Kiyoaki Ito, Ken Sato, Yoshitaka Fukuzawa, Masashi Yoneda
Takaya Yamamoto, Yukiomi Nakade, Taeko Yamauchi, Yuji Kobayashi, Norimitsu Ishii, Tomohiko Ohashi, Kiyoaki Ito, Ken Sato, Yoshitaka Fukuzawa, Masashi Yoneda, Division of Hepatology and Pancreatology, Department of Internal Medicine, Aichi Medical University, Nagakute, Aichi 480-1195, Japan
Author contributions: Yamamoto T and Nakade Y designed the experiments; Yamamoto T, Nakade Y, Yamauchi T, Kobayashi Y and Ishii N prepared the materials and carried out the animal experiments; Histological examinations were performed by Ito K, Sato K, Ohashi T and Fukuzawa Y; Western blot analysis and real-time PCR were performed by Yamauchi T and Nakade Y; data analysis was performed by Nakade Y and Yoneda M; and the manuscript was prepared by Yamamoto T, Nakade Y and Yoneda M.
Supported by Grant-in-Aid from the Ministry of Education, Culture, Sport, Science and Technology of Japan to Nakade Y and Yoneda M and a grant from the Aikeikai Foundation.
Institutional review board statement: All procedures involving animals were reviewed and approved by the Institutional Animal Care and Use Committee of Aichi Medical University.
Institutional animal care and use committee statement: All procedures involving animals were reviewed and approved by the Institutional Animal Care and Use Committee of Aichi Medical University (AMU protocol number 2008-55).
Conflict-of-interest statement: There are no conflicts of interest concerning this study.
Data sharing statement: No additional data are available
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Yukiomi Nakade, MD, PhD, Division of Hepatology and Pancreatology, Department of Internal Medicine Aichi Medical University, 1-1 Karimata Yazako Nagakute Aichi 480-1195, Japan. ynakade@aichi-med-u.ac.jp
Telephone: +81-561-623311 Fax: +81-561-621508
Received: October 27, 2015
Peer-review started: October 27, 2015
First decision: November 27, 2015
Revised: December 8, 2015
Accepted: December 19, 2015
Article in press: December 21, 2015
Published online: February 28, 2016
Processing time: 122 Days and 0.3 Hours
Abstract

AIM: To investigate whether a glucagon-like peptide-1 (GLP-1) analogue inhibits nonalcoholic steatohepatitis (NASH), which is being increasingly recognized in Asia, in non-obese mice.

METHODS: A methionine-choline-deficient diet (MCD) along with exendin-4 (20 μg/kg per day, ip), a GLP-1 analogue, or saline was administered to male db/db mice (non-obese NASH model). Four or eight weeks after commencement of the diet, the mice were sacrificed and their livers were excised. The excised livers were examined by histochemistry for evidence of hepatic steatosis and inflammation. Hepatic triglyceride (TG) and free fatty acid (FFA) content was measured, and the expression of hepatic fat metabolism- and inflammation-related genes was evaluated. Oxidative stress-related parameters and macrophage recruitment were also examined using immunohistochemistry.

RESULTS: Four weeks of MCD feeding induced hepatic steatosis and inflammation and increased the hepatic TG and FFA content. The expression of fatty acid transport protein 4 (FATP4), a hepatic FFA influx-related gene; macrophage recruitment; and the level of malondialdehyde (MDA), an oxidative stress marker, were significantly augmented by a 4-wk MCD. The levels of hepatic sterol regulatory element-binding protein-1c (SREBP-1c) mRNA (lipogenesis-related gene) and acyl-coenzyme A oxidase 1 (ACOX1) mRNA (β-oxidation-related gene) had decreased at 4 wk and further decreased at 8 wk. However, the level of microsomal triglyceride transfer protein mRNA (a lipid excretion-related gene) remained unchanged. The administration of exendin-4 significantly attenuated the MCD-induced increase in hepatic steatosis, hepatic TG and FFA content, and FATP4 expression as well as the MCD-induced augmentation of hepatic inflammation, macrophage recruitment, and MDA levels. Additionally, it further decreased the hepatic SREBP-1c level and alleviated the MCD-mediated inhibition of the ACOX1 mRNA level.

CONCLUSION: These results suggest that GLP-1 inhibits hepatic steatosis and inflammation through the inhibition of hepatic FFA influx and oxidative stress in a non-obese NASH model.

Keywords: Glucagon like peptide-1; Nonalcoholic steatohepatitis; Kupffer cells; Free fatty acid; Oxidative stress

Core tip: Herein, we suggest that a glucagon-like peptide-1 (GLP-1) analogue inhibits nonalcoholic steatohepatitis (NASH), which is being increasingly recognized in Asia, in non-obese mice. A methionine-choline-deficient diet (MCD) was reported to induce steatohepatitis, which is morphologically similar to NASH. Additionally, it increases serum free fatty acid levels and hepatic free fatty acid and triglyceride content in mice. In our study, we showed for the first time that exendin-4, a novel GLP-1 analogue, improved steatohepatitis through the inhibition of hepatic free fatty acid influx and by suppression of macrophage recruitment and oxidative stress in our MCD-fed NASH model.