Galanin in the trinitrobenzene sulfonic acid rat model of experimental colitis
Introduction
Inflammatory bowel diseases (IBD), including ulcerative colitis and Crohn's disease, are chronic inflammatory disorders of the gastrointestinal tract of unknown aetiology. Much of our understanding of this pathology comes from studies in animal models of intestinal inflammation providing the opportunity to evaluate novel therapeutic approaches [1], [2]. The intrarectal instillation of trinitrobenzene sulphonic acid (TNBS) causes inflammation as demonstrated by many inflammatory markers. One of the earliest inflammatory factors involved includes the development of an abnormal immune response, which is mediated predominantly by activated mast cells and leukocytes, specially neutrophils, and characterized by an enhanced formation of reactive oxygen and nitrogen species [3], [4]. Many other inflammatory mediators have been also related; tumour necrosis factor-α (TNF-α) plays a prominent role and the neutralization of this cytokine is accompanied by a remarkable clinical response in patients with IBD. In the same line, the expression of inducible nitric oxide synthase (iNOS), and the subsequent increased generation of nitric oxide (NO), has been demonstrated in biopsies of patients with inflammatory colitis injury and both related to the progression of the disease [5]. Its inhibition has shown to have a beneficial action on colonic injury and inflammation in different models of colitis including the TNBS model [6], [7].
Some studies published in the past years have analyzed the role of a variety of soluble peptides and other mediators that once secreted in a coordinated fashion in the injured area are able to restore mucosal integrity [8]. Neuropeptides are small molecules produced by a variety of cells, including neurons and immune cells, that in the intestine modulate several biological processes and modify the activity of cells responsible either to trigger tissue damage or to promote healing [9], [10].
In humans, Galanin is a 30-aa-long neuroendocrine peptide, whose physiological functions are regulated by G protein-coupled receptors. Galanin is found throughout the central and peripheral nervous systems and the gastrointestinal tract and, its effects include control of neurotransmitters involved in regulation and memory acquisition, modulation of appetite or sexual conduct, gastrointestinal motion as well as effects on controlling nociception or in the pathogenesis of certain neurodegenerative disorders [11], [12]. Peripheral anti-inflammatory effects of Galanin were observed previously; A report on the immunoregulatory properties of Galanin in rats showed that Galanin mRNA was expressed in immunocytes/macrophages in the epidermis of normal skin as in the skin of inflamed joint [13]. Similarly, in a model of adjuvant arthritis, Galanin demonstrated to be involved in the response observed [14]. Given that Galanin could emerge as an interesting alternative for the treatment of immunological disorders, we were interested in investigating its potential therapeutic use in other inflammatory disorder, such as IBD, and to study its effect in the TNBS-induced model of colitis. In the present study, we show that treatment with Galanin has a significant preventive effect in the TNBS-induced acute model of colitis.
Section snippets
Experimental animals
Male and female Wistar rats supplied by Animal Services of the University of Seville, Spain, weighing 180–200 g, were placed singly in cages with wire-net floors in a controlled room (temperature 24–25 °C, humidity 70–75%, lighting regimen of 12L/12D) and were fed a normal laboratory diet (Panlab, Barcelona, Spain). Rats were deprived of food for 12 h prior to the induction of colitis, but were allowed free access to tap water throughout. They were randomly assigned to groups of 12 animals.
Results
48 h after intracolonic administration of TNBS, the control animals showed prostration, piloerection and hypomotility. Body weight loss was significantly elevated compared with the control animals (p < 0.001). A significant increase of weight/length of the rat colon (p < 0.001), as indicator of inflammation, and presence of adhesions to adjacent organs and of diarrhoea (p < 0.001 and p < 0.05 respectively) were frequently observed in TNBS-treated rats (Table 1). Macroscopic inspection of the caecum,
Discussion
Galanin is a biologically active neuropeptide, widely distributed in the central and peripheral nervous as well as in the endocrine systems, and with multiple biological effects such as nociception, gastrointestinal motion or immunoregulation [19], [13]. In this study, we aimed to assess the role of Galanin in a model of colitis using TNBS, a well-accepted model for IBD because the inflammatory response provoked by the hapten is considered to reproduce many of the macroscopic, histological and
Acknowledgment
This research was supported by Grant BFI2002-03544 from the Spanish General Direction of Research Government (MCYT).
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