Metabolomics-based predictive biomarker discovery for thiopurine response in Crohn disease: Plasma histidine as a promising biomarker.

Thiopurine drugs are cornerstone immunosuppressive agents for treating Crohn disease (CD), yet their clinical utility is limited by significant interindividual variability in efficacy and a lack of reliable predictive biomarkers. This study aimed to identify and validate plasma metabolites that can predict therapeutic response to thiopurine drugs in patients with CD. A total of 270 patients with CD receiving azathioprine or mercaptopurine monotherapy were retrospectively enrolled. Untargeted metabolomics was performed to discover candidate predictive metabolites associated with treatment outcomes, followed by targeted quantification of histidine levels using liquid chromatography-mass spectrometry. Treatment efficacy was evaluated by biochemical remission, clinical remission, and mucosal healing. In vitro experiments using lipopolysaccharide-stimulated a human monocytic leukemia cell line macrophages were conducted to assess the anti-inflammatory role of histidine. Untargeted metabolomics identified l-histidine as a metabolite positively correlated with therapeutic response across biochemical remission, clinical remission, and mucosal healing. Targeted analysis confirmed significantly higher histidine levels in responders versus nonresponders (P < .0001). Histidine levels were negatively correlated with disease activity indices (Crohn's Disease Activity Index, C-reactive protein, and Simple Endoscopic Score for Crohn's Disease) and tumor necrosis factor-α levels. Receiver operating characteristic analysis identified 9.39 μg/mL histidine as the cutoff predicting mucosal healing (area under the curve = 0.690). Kaplan-Meier analysis showed improved remission maintenance in patients with higher histidine levels. In vitro, histidine suppressed tumor necrosis factor-α production in a human monocytic leukemia cell line cells and enhanced azathioprine's anti-inflammatory effects. Plasma histidine is a promising biomarker for predicting thiopurine efficacy in CD and may support early therapeutic stratification. These findings warrant prospective studies to verify the potential benefit of histidine supplementation in enhancing therapeutic outcomes. SIGNIFICANCE STATEMENT: This study identifies plasma histidine as a pharmacometabolic biomarker of thiopurine response in Crohn disease. By linking baseline amino acid metabolism to variability in therapeutic efficacy, these findings highlight metabolic status as a determinant of drug response and support metabolomics in precision pharmacotherapy.