Lack of Adrenomedullin Aggravates Acute TNBS-Induced Colitis Symptoms in Mice, Especially in Females

Abstract

Adrenomedullin (AM) is a biologically active peptide which has been tested as a new therapy for inflammatory bowel disease (IBD) in animal models and in patients with severe ulcerative colitis. We used an inducible knockout (KO) mouse model for AM to evaluate the effects of endogenous levels of this peptide on the development and degree of pathogenesis of IBD. Acute colitis was induced in mice of both sexes by rectal instillation of 3 mg 2,4,6-trinitrobenzenesulfonic acid (TNBS) in 100 μL of 50% ethanol. Control mice received the same volume of saline in 50% ethanol. During the following 5 days, the weight and the disease severity index of all animals were recorded. After sacrifice, the inflammatory response was macroscopically assessed by analyzing the weight of the colon; by histomorphometrical analysis on histological sections; and by qRT-PCR determination of different inflammatory, adhesion, and regeneration molecules. TNBS administration caused a significantly more severe colitis in KO mice, and especially in females, when compared to wild type (WT) animals. Abrogation of the AM gene caused more severe diarrhea, accompanied by rectal bleeding, anorexia, and a significant increase of colon weight. Histological analysis of TNBS-treated KO mice showed large areas of lymphocyte infiltrates in the mucosa and submucosa, with loss of tissue architecture. No alterations were observed in the expression levels of inflammatory cytokines at the time of sacrifice; meanwhile lack of AM resulted in lower levels of some adhesion molecules and regeneration markers. Taken together, these results support the protective role of endogenous AM against the development of acute colitis, and that its effects are particularly beneficial on females.

Adrenomedullin: Not Just Another Gastrointestinal Peptide

“…Results from the inducible total KO model for Adm also demonstrated that endogenous AM is necessary to maintain a proper immune response against colonic damage [ 14 , 15 ]. Lack of AM/PAMP results in an abnormal immune response in the two principal chemical-induced models of colitis (i.e., DSS and TNBS) with an overexpression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α) and a downregulation of anti-inflammatory cytokines (IL-10) [ 14 , 15 ].…”

“…These two peptides coexist in GI cells, where they regulate many physiological functions including vasodilation, angiogenesis, anti-inflammation, organ protection, and tissue repair. AM suppresses inflammatory cytokine production in the intestinal mucosa, improves vascular and lymphatic function, mucosal epithelial repair, and intestinal barrier function in animal models with intestinal inflammation [ 10 , 13 , 14 , 15 ]. Different research groups have demonstrated that AM has a protective role in many GI diseases, and its administration in rodents and humans ameliorates the severity of different gut pathologies such as gastric ulcer [ 16 ] or inflammatory bowel disease (IBD) [ 17 , 18 ].…”

Adrenomedullin: A Novel Therapeutic for the Treatment of Inflammatory Bowel Disease

“…Further, TNBS enteritis is more severe in AM knockout mice than in control mice [30]. Administering AM antagonists to indomethacin-induced small intestinal ulcer rat models increased the severity of enteritis [31], suggesting that endogenous, physiological AM may also relieve enteritis.…”

“…Several research groups in Europe and Japan have reported that AM ameliorates nitrobenzene sulfonic acid (TNBS) and DSS-induced colitis in various animal mod [28,29]. Further, TNBS enteritis is more severe in AM knockout mice than in control m [30]. Administering AM antagonists to indomethacin-induced small intestinal ulcer models increased the severity of enteritis [31], suggesting that endogenous, physiologi AM may also relieve enteritis.…”

“…Animal enteritis models have shown that AM administration decreases the production of the pro-inflammatory cytokines; TNF-α, IL-6, and IFN-γ, and increases the production of the immunosuppressive cytokines; IL-10 and TGF-β in intestinal mucosa and mesenteric lymph node mononuclear cells [27][28][29][30][31].…”