Irritable bowel syndrome (IBS) is one of several
functional gastrointestinal disorders commonly encountered in both the clinical setting and the general population. The biopsychosocial model is currently believed to be a more complete explanatory mechanism of IBS symptom genesis and propagation. Gut
inflammation and immune activation is one of the
biological mechanisms for which evidence is emerging. Experimental
parasitic infection of mice bowel resulted in elevated
substance P levels and increased expression of
cyclooxygenase 2 (COX 2)
enzyme,
prostaglandin E2,
IL-4,
IL-5, and
IL-13. In IBS patients, increased cellularity and proximity of the inflammatory or immune cells to the nerve trunks of the bowel, elevated
interleukin-1beta mRNA expression in mucosal biopsies, and increased
inducible nitric oxide synthase and
nitrotyrosine elaboration (indicative of lymphocyte activation) were observed.
Corticosteroids given after the elimination of an experimentally applied parasite from the bowel of mice resulted in the reversal of persistent gut muscle dysfunction. Selective
COX-2 inhibitors attenuated the increased bowel smooth muscle contractility resulting from
parasite infection of mice gut. In humans, it has been observed that the relative risk of developing IBS in
asthma patients was reduced by 60% by the use of oral
steroids. Despite such preclinical and human evidence for the role of
inflammation and immune activation in IBS, the efficacy of anti-inflammatory and
immunomodulatory agents has not been adequately investigated.
Budesonide, a
corticosteroid with a high mucosal activity and a low bioavailability, is an
anti-inflammatory agent that may be worth investigating for its utility in
diarrhea-predominant IBS.