Purine, kynurenine, neopterin and lipid peroxidation levels in inflammatory bowel disease.

The kynurenine metabolites of tryptophan may be involved in the regulation of neuronal activity and thus gut motility and secretion. We have now performed a pilot study to measure serum concentrations of purines and kynurenines in patients with mild inflammatory bowel disease, as well as in sex- and age-matched control subjects. For some analyses, the patients were subdivided into subgroups of those with Crohn's disease and those with ulcerative colitis. The analyses indicated an increased activity in one branch of the kynurenine pathway. While there was no demonstrable difference in neopterin levels in either of the patient groups compared with controls, indicating that the disorders were in an inactive quiescent phase, both groups showed significantly higher levels of lipid peroxidation products. This suggests the presence of increased oxidative stress even during relative disease inactivity. The increased level of kynurenic acid may represent either a compensatory response to elevated activation of enteric neurones or a primary abnormality which induces a compensatory increase in gut activity. In either case, the data may indicate a role for kynurenine modulation of glutamate receptors in the symptoms of inflammatory bowel disease.