The Variability of Tryptophan Metabolism in Patients with Mixed Type of Irritable Bowel Syndrome

Abstract

Patients with a mixed type of irritable bowel syndrome (IBS-M) experience constipation and diarrhea, which alternate between weeks or months. The pathogenesis of this syndrome is still little understood. The aim of the study was mainly to evaluate the urinary excretion of selected tryptophan (TRP) metabolites during the constipation and diarrhea periods of this syndrome. In 36 patients with IBS-M and 36 healthy people, serum serotonin level was measured by ELISA and urinary levels of 5-hydroxyindoleacetic acid (5-HIAA), kynurenine (KYN) and indican (3-IS) were determined using the LC-MS/MS method. The levels of all above metabolites were higher in the patient group, and increased significantly during the diarrheal period of IBS-M. In particular, the changes concerned 5-HIAA (3.67 ± 0.86 vs. 4.59 ± 0.95 mg/gCr, p < 0.001) and 3-IS (80.2 ± 17.4 vs. 93.7 ± 25.1 mg/g/Cr, p < 0.001). These changes coexisted with gut microbiome changes, assessed using hydrogen-methane and ammonia breath tests. In conclusion, the variability of TRP metabolism and the gut microbiome may cause the alternation of IBS-M symptoms.

Keywords: gut microbiome; irritable bowel syndrome; tryptophan metabolism.

Figure 1

Comparison of serum serotonin (5-HT) levels (ng/mL) and urinary levels of 5-hydroxyindoleacetic acid (5-HIAA, mg/g/Cr) in healthy people and IBS-M patients during constipation and diarrhea; differences between controls and patients were evaluated using a Wilcoxon test; center line—mean value; box—SD; whiskers—min-max.

Figure 2

Comparison of urinary levels of kynurenine (KYN, mg/gCr) and indican (3-IS, mg/gCr) in healthy people and IBS-M patients during constipation and diarrhea period; differences between controls and patients were evaluated by Wilcoxon test; center line—mean value; box—SD; whiskers—min-max.