Role of Substance P in the Pathophysiology of Inflammatory Bowel Disease and Its Correlation With the Degree of Inflammation

Inflammatory bowel disease (IBD) is a multi-factorial, chronic inflammation of the gastrointestinal tract, containing ulcerative colitis (UC) and Crohn's disease (CD). In UC, inflammation and sores are confined morphologically and microscopically to the mucosa, the innermost surface of the colon and the rectum. Although, in CD, the infection is granulomatous and transmural, affecting the entire gastrointestinal tract from the mouth to the anus, with the skip area in-between. A Neuropeptide, substance P (SP), which acts as a neurotransmitter and as a neuromodulator, plays a vital role in the brain-gut axis under stress. Owing to the pro-inflammatory effects of SP, neuropeptide dysregulation induces inflammation in the intestine. There are variations in the distribution of substance P immunoreactive fibres in the various intestinal layers. The highest concentration of SP is in the mucosa and the lowest concentration in the lamina propria of the intestinal muscular membrane. Reduced vasoactive intestinal peptide (VIP) levels and elevated SP levels observed in the colonic mucosa of IBD by using immunohistochemistry and immunoassay. This literature review aims to find out the correlations between the level of substance P (SP) and disease activity. We conducted a literature review on IBD, SP, and we searched PubMed and Google Scholar for relevant articles in English. The result of the study supports a positive relationship between the level of substance P (SP) and disease activity, with increased concentration of substance p in the colon and rectum of CD and UC patients. It is concluded that patients with active CD, along with inflammatory changes, had elevated plasma SP levels and immunoreactivity of SP in the colon than those seen in control and inactive cases. These alterations are more prevalent in ulcerative colitis than Crohn's disease and are more prevalent in the moderately infected area than the least affected area of the intestine.