Inflammation-Induced Mucosal KYNU Expression Identifies Human Ileal Crohn's Disease

Area of Science:

• Gastroenterology
• Immunology
• Metabolomics

Background:

• Inflammatory bowel disease (IBD) presents significant heterogeneity in pathological mechanisms and therapeutic responses.
• Current biomarkers primarily differentiate Crohn's disease (CD) from ulcerative colitis (UC), with limited options for subclassification within CD phenotypes.
• Altered tryptophan metabolism is linked to chronic inflammatory conditions, suggesting its potential role in IBD pathogenesis.

Purpose of the Study:

• To investigate the role of kynurenine metabolism in differentiating ileal CD from colonic CD.
• To identify potential mucosal biomarkers for classifying CD subtypes based on disease location.
• To compare immune cell infiltration and tryptophan metabolism profiles across different IBD phenotypes and healthy controls.

Main Methods:

• Immunohistochemical staining of mucosal biopsies from patients with UC, CD, and healthy controls.
• Localization-specific quantification of immune cell infiltration, including regulatory T cells and neutrophil granulocytes.
• Analysis of tryptophan-metabolizing enzyme expression (specifically kynureninase - KYNU) and downstream metabolite levels.

Main Results:

• Increased immune cell infiltrates were observed in all IBD patients compared to controls.
• Significant differences in immune cell infiltration patterns were noted between ileal and colonic CD.
• Decreased kynurenine levels and elevated kynureninase (KYNU) expression were specifically found in ileal CD patients, alongside increased 3-hydroxyanthranilic acid levels.

Conclusions:

• Kynureninase (KYNU) emerges as a potential mucosal biomarker for distinguishing ileal CD from colonic CD.
• These findings highlight the heterogeneity within CD and offer a novel approach for phenotype-specific diagnosis.
• Understanding localized tryptophan metabolism alterations can improve diagnostic strategies for IBD subtypes.