Basic Study
Copyright ©The Author(s) 2019. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Apr 21, 2019; 25(15): 1865-1878
Published online Apr 21, 2019. doi: 10.3748/wjg.v25.i15.1865
Unconjugated bilirubin alleviates experimental ulcerative colitis by regulating intestinal barrier function and immune inflammation
Jia-Dong Zheng, Yan He, Heng-Yuan Yu, Yuan-Li Liu, Yi-Xuan Ge, Xue-Ting Li, Xue Li, Yan Wang, Meng-Ru Guo, Yi-Lin Qu, Xiao-Fa Qin, Ming-Shan Jiang, Xiu-Hong Wang
Jia-Dong Zheng, Yan He, Heng-Yuan Yu, Yuan-Li Liu, Yi-Xuan Ge, Xue-Ting Li, Xue Li, Yan Wang, Meng-Ru Guo, Yi-Lin Qu, Xiu-Hong Wang, Department of Biochemistry and Molecular Biology, Heilongjiang Provincial Science and Technology Innovation Team in Higher Education Institutes for Infection and Immunity, Harbin Medical University, Harbin 150086, Heilongjiang Province, China
Xiao-Fa Qin, Founder, GI Biopharma Inc., Westfield, NJ 07090, United States
Ming-Shan Jiang, Department of General Surgery, the Second Affiliated Hospital of Harbin Medical University, Harbin 150001, Heilongjiang Province, China
Author contributions: Wang XH and Zheng JD contributed to study concept and design; He Y, Ge YX, Yu HY, Li X, Wang Y, Guo MR, Liu YL, Qu YL and Li XT contributed to acquisition of data; Zheng JD analyzed and interpreted the data; Zheng JD and He Y drafted the manuscript; Jiang MS and Qin XF contributed to critical revision of the manuscript for intellectual content; Wang XH contributed to study supervision.
Supported by grants from the National Natural Foundation of China, No. 81703232.
Institutional review board statement: The study was reviewed and approved by the Ethics Committee of Harbin Medical University, Harbin, China (HMUIRB20180015).
Institutional animal care and use committee statement: All procedures involving animals were reviewed and approved by the Institutional Animal Care and Use Committee of Harbin Medical University.
Conflict-of-interest statement: No conflict of interest exists in this study.
Data sharing statement: No additional data are available.
ARRIVE guidelines statement: The authors have read the ARRIVE guidelines, and the manuscript was prepared and revised according to the ARRIVE guidelines.
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:
Corresponding author: Xiu-Hong Wang, MSc, PhD, Academic Research, Professor, Department of Biochemistry and Molecular Biology, Heilongjiang Provincial Science and Technology Innovation Team in Higher Education Institutes for Infection and Immunity, Harbin Medical University, 157 Baojian Rd, Harbin 150086, Heilongjiang Province, China.
Telephone: +86-13836111380 Fax: +86-13836111380
Received: January 4, 2019
Peer-review started: January 4, 2019
First decision: January 30, 2019
Revised: March 5, 2019
Accepted: March 15, 2019
Article in press: March 16, 2019
Published online: April 21, 2019

Unconjugated bilirubin (UCB) is generally considered toxic but has gained recent prominence for its anti-inflammatory properties. However, the effects of it on the interaction between intestinal flora and organisms and how it influences immune responses remain unresolved.


To investigate the role of UCB in intestinal barrier function and immune inflammation in mice with dextran-sulfate-sodium-induced colitis.


Acute colitis was induced by 3% (w/v) dextran sulfate sodium salt in drinking water for 6 d followed by untreated water for 2 d. Concurrently, mice with colitis were administered 0.2 mL UCB (400 μmol/L) by intra-gastric gavage for 7 d. Disease activity index (DAI) was monitored daily. Mice were sacrificed at the end of the experiment. The length of the colon and weight of the spleen were recorded. Serum level of D-lactate, intestinal digestive proteases activity, and changes to the gut flora were analyzed. In addition, colonic specimens were analyzed by histology and for expression of inflammatory markers and proteins.


Mice treated with UCB had significantly relieved severity of colitis, including lower DAI, longer colon length, and lower spleen weight (colon length: 4.92 ± 0.09 cm vs 3.9 ± 0.15 cm; spleen weight: 0.33 ± 0.04 vs 0.74 ± 0.04, P < 0.001). UCB administration inactivated digestive proteases (chymotrypsin: 18.70 ± 0.69 U/g vs 44.81 ± 8.60 U/g; trypsin: 1.52 ± 0.23 U/g vs 9.05 ± 1.77 U/g, P < 0.01), increased expression of tight junction (0.99 ± 0.05 vs 0.57 ± 0.03, P < 0.001), decreased serum level of D-lactate (31.76 ± 3.37 μmol/L vs 54.25 ± 1.45 μmol/L, P < 0.001), and lowered histopathological score (4 ± 0.57 vs 7 ± 0.57, P < 0.001) and activity of myeloperoxidase (46.79 ± 2.57 U/g vs 110.32 ± 19.19 U/g, P < 0.001). UCB also regulated the intestinal microbiota, inhibited expression of tumor necrosis factor (TNF) α and interleukin 1β (TNF-α: 52.61 ± 7.81 pg/mg vs 105.04 ± 11.92 pg/mg, interleukin 1β: 13.43 ± 1.68 vs 32.41 ± 4.62 pg/mg, P < 0.001), decreased expression of Toll-like receptor 4 (0.61 ± 0.09 vs 1.07 ± 0.03, P < 0.001) and myeloid differentiation primary response gene 88 (0.73 ± 0.08 vs 1.01 ± 0.07, P < 0.05), and increased expression of TNF-receptor-associated factor 6 (0.79 ± 0.02 vs 0.43 ± 0.09 P < 0.05) and inhibitor of kappa B α (0.93 ± 0.07 vs 0.72 ± 0.07, P < 0.05) in the colon.


UCB can protect intestinal barrier function, regulate normal intestinal homeostasis, and suppress inflammation via the Toll-like receptor 4/ nuclear factor-κB signaling pathway.

Keywords: Ulcerative colitis, Unconjugated bilirubin, Intestinal barrier, Intestinal homeostasis, Digestive proteases, Inflammation

Core tip: Intestinal function and microbiota are desired therapeutic endpoints for treatment of inflammatory bowel disease. However, a major problem is the lack of powerful and safe drugs. Unconjugated bilirubin (UCB) has anti-inflammatory and antitoxin effects. We found that UCB significantly decreased intestinal permeability and improved intestinal barrier function; regulated composition of gut microbiota; and relieved intestinal inflammation through suppressing the Toll-like receptor 4/nuclear factor-κB pathway. This study demonstrated that UCB ameliorates ulcerative colitis via intestinal barrier function through inactivating the digestive proteases and inhibiting immune inflammation through the Toll-like receptor 4/nuclear factor-κB pathway.