Basic Study
Copyright ©The Author(s) 2015. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Diabetes. May 15, 2015; 6(4): 662-672
Published online May 15, 2015. doi: 10.4239/wjd.v6.i4.662
Advanced glycation end-product expression is upregulated in the gastrointestinal tract of type 2 diabetic rats
Peng-Min Chen, Hans Gregersen, Jing-Bo Zhao
Peng-Min Chen, Department of Molecular Biology, Institute of Clinical Medicine, China-Japan Friendship Hospital, Beijing 100029, China
Hans Gregersen, GIOME Center, College of Bioengineering, Chongqing University, Chongqing 400045, China
Jing-Bo Zhao, Institute of Clinical Medicine, Aarhus University, Aarhus N 8200, Denmark
Author contributions: Gregersen H and Zhao JB designed the research; Chen PM and Zhao JB performed the research and analyzed the data; Chen PM and Zhao JB wrote the paper; Gregersen H revised the paper.
Supported by Karen Elise Jensens Foundation.
Ethics approval: Ethics of the study was approved by the Danish Committee for Animal Experimentation. The license number is 2008/561-1530.
Institutional animal care and use committee: All procedures involving animals were reviewed and approved by the Danish Committee for Animal Experimentation. The license number is 2008/561-1530. Animals in poor clinical condition were euthanized and excluded from the study. The rats were euthanized with CO2 inspiration during the anesthesia. The animals were acclimatized to laboratory conditions (22 °C, 12 h/12 h light/dark, 50% humidity, ad libitum access to food and water) for 2 wk prior to experimentation. The animal protocol was designed to minimize pain or discomfort to the animals.
Conflict-of-interest: We declare that we have no proprietary, financial, professional or other personal interest of any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitle “Advanced Glycation End-Product expression is upregulated in the Gastrointestinal Tract of Type 2 Diabetic Rats”.
Data sharing: 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: Hans Gregersen, Professor, GIOME Center, College of Bioengineering, Chongqing University, 83 Shabei Road, Chongqing 400045, China. hag@giome.org
Telephone: +86-186-00556254
Received: August 6, 2014
Peer-review started: August 7, 2014
First decision: October 28, 2014
Revised: March 4, 2015
Accepted: March 16, 2015
Article in press: March 18, 2015
Published online: May 15, 2015
Processing time: 282 Days and 2.4 Hours
Abstract

AIM: To investigate changes in advanced glycation end products (AGEs) and their receptor (RAGE) expression in the gastrointestinal (GI) tract in type 2 diabetic rats.

METHODS: Eight inherited type 2 diabetic rats Goto-Kakizak (GK) and ten age-matched normal rats were used in the study. From 18 wk of age, the body weight and blood glucose were measured every week and 2 wk respectively. When the rats reached 32 wk, two-centimeter segments of esophagus, duodenum, jejunum, ileum, and colon were excised and the wet weight was measured. The segments were fixed in 10% formalin, embedded in paraffin and five micron sections were cut. The layer thickness was measured in Hematoxylin and Eosin-stained slides. AGE [N epsilon-(carboxymethyl) lysine and N epsilon-(carboxyethyl)lysine] and RAGE were detected by immunohistochemistry staining and image analysis was done using Sigmascan Pro 4.0 image analysis software.

RESULTS: The blood glucose concentration (mmol/L) at 18 wk age was highest in the GK group (8.88 ± 1.87 vs 6.90 ± 0.43, P < 0.001), a difference that continued to exist until the end of the experiment. The wet weight per unit length (mg/cm) increased in esophagus, jejunum and colon from the normal to the GK group (60.64 ± 9.96 vs 68.56 ± 11.69, P < 0.05 for esophagus; 87.01 ± 9.35 vs 105.29 ± 15.45, P < 0.01 for jejunum; 91.37 ± 7.25 vs 97.28 ± 10.90, P < 0.05 for colon). Histologically, the layer thickness of the GI tract was higher for esophagus, jejunum and colon in the GK group [full thickness (μm): 575.37 ± 69.22 vs 753.20 ± 150.41, P < 0.01 for esophagus; 813.51 ± 44.44 vs 884.81 ± 45.31, P < 0.05 for jejunum; 467.12 ± 65.92 vs 572.26 ± 93.60, P < 0.05 for colon]. In esophagus, the AGE and RAGE mainly distributed in striated muscle cells and squamous epithelial cells. The AGE distribution was much stronger in the GK group compared to the normal group both in the striated muscle layer and mucosa layer (immuno-positive area/ total measuring area %: 4.52 ± 0.89 vs 10.96 ± 1.34, P < 0.01 for muscle; 8.90 ± 2.62 vs 22.45 ± 1.26, P < 0.01 for mucosa). No visible difference was found for RAGE distribution between the two groups. In the intestine AGE and RAGE distributed in epithelial cells of villi and crypt. RAGE was also found in neurons in the myenteric and submucosal plexus. The intensity of AGE staining in mucosa of all segments and RAGE staining in neurons in all segments were strongest in the diabetes group. Significant difference for AGE was found in the epithelial cells of villi and crypt in duodenum (immuno-positive area/total measuring area %: 13.37 ± 3.51 vs 37.48 ± 8.43, P < 0.05 for villi; 0.38 ± 0.12 vs 1.87 ± 0.53, P < 0.05 for crypt) and for RAGE in neurons of all segments (e.g., for jejunum: no staining neurons% 0 vs 0, mild 36.0 ± 5.2 vs 28.7 ± 3.5, moderate 53.2 ± 4.8 vs 55.8 ± 5.4, strong 10.7 ± 1.1 vs 15.4 ± 2.0, P < 0.05). In the colon, RAGE was primarily found in neurons in the myenteric and submucosal plexus. It was stronger in the diabetes group than in the normal group (no staining neurons% 6.2 ± 0.2 vs 0.3 ± 0.04, mild 14.9 ± 2.1 vs 17.6 ± 1.5, moderate 53.1 ± 4.6 vs 44.7 ± 4.4, strong 25.6 ± 18 vs 43.6 ± 4.0, P < 0.05). In the rectum, RAGE was primarily found in the mucosa epithelial cells.

CONCLUSION: The AGE and RAGE expression was up-regulated in the GI tract of GK diabetic rats and may contribute to GI dysfunction in type 2 diabetic patients.

Keywords: Diabetes mellitus; Gastrointestinal complications; Advanced glycation end products; Receptor of advanced glycation end products

Core tip: Changes in advanced glycation end products (AGEs) and their receptor (RAGE) expression in the gastrointestinal (GI) tract in type 2 diabetic rats were studied. The AGE and RAGE were widely distributed in epithelial cells of all segments as well as in striated muscle cells in the esophagus. RAGE also distributed in neurons in all segments. Up-regulated AGE and RAGE expression was found in the GI tract of GK diabetic rats. The altered AGE and RAGE may be a contributing factor for GI dysfunction in type 2 diabetic patients.