P354 Tryptophan metabolites as predictive biomarkers for dietary therapy outcomes in paediatric Crohn's disease

Background Crohn's disease (CD) exclusion diet combined with partial enteral nutrition (CDED+PEN) and exclusive enteral nutrition (EEN) are effective in inducing remission in mild-to-moderate paediatric CD. While tolerance is higher with CDED+PEN than with EEN, a subset of patients still does not achieve remission. Diet-induced remission at week 6 was associated with changes in tryptophan (Trp) metabolism.1 Our aim was to investigate whether baseline Trp metabolites could predict dietary therapy outcomes in paediatric CD. Methods In total, 26 mild-to-moderate treatment-naive paediatric CD patients from a prior randomized controlled trial 2, were classified as having remission 6 (R, n =19 (CDED+PEN=10 and EEN=9)) and No-Remission (NR, n=7 (CDED+PEN=3 and EEN=4)) following 6 weeks of CDED+PEN or EEN therapy, based on the Paediatric Crohn’s Disease Activity Index (PDCAI) score (≤10 remission, >10 no remission). We performed targeted quantitative analysis of 21 tryptophan metabolites in baseline faecal samples from both groups, utilizing liquid chromatography coupled with quadrupole mass spectrometry. Receiving Operator Characteristic Curve (ROC) and Random Forest Analysis were used to assess the predictive power of Trp metabolites for dietary outcomes. Results Baseline clinical characteristics were comparable between R and NR. Baseline fecal kynurenine was significantly higher in NR compared to R for CDED+PEN (p=0.02) (Fig 1A) and EEN (p=0.04) (Fig 2A). ROC analysis highlighted the robust predictive power of kynurenine for CDED+PEN (area under the curve (AUC)=0.97) (Fig 1B) and EEN (AUC=0.88) (Fig 2B) induced remission. Random Forest analysis corroborated these observations. Ratios of Trp metabolites were compared to investigate different downstream Trp pathways. The ratio serotonin/kynurenine was the strongest predictor of CDED+PEN-induced remission (AUC=1) (Fig 1C). The ratio 5-OH-Tryptophan/kynurenine (AUC=0.88) (Fig 2C) predicted EEN-induced remission. When data from CDED+PEN and EEN were combined, kynurenine (AUC=0.91) and the ratios of quinolinic acid/kynurenine (AUC=0.93) and kynurenine/indole-3-acetic acid (AUC=0.88) demonstrated strong predictive performance for dietary therapy in general (Fig 3A,B and C). Conclusion Baseline faecal kynurenine has potential as a prognostic biomarker for dietary therapies. Trp metabolite ratios, notably serotonin/kynurenine for CDED+PEN and 5-OH-tryptophan/kynurenine for EEN, showed promising predictive capabilities. If confirmed in validation studies, baseline faecal Trp markers may be able to provide much needed guidance to personalize dietary intervention within the management of paediatric CD. References 1. Gastroenterology. 2022 Oct;163(4):922-936. 2. Gastroenterology. 2019 Aug;157(2):440-450.