Related Experiment Video
Updated: Mar 17, 2026

Mechanistic Insight into the Development of TNBS-Mediated Intestinal Fibrosis and Evaluating the Inhibitory Effects of Rapamycin
Published on: September 12, 2019
Rac1 as a Potential Pharmacodynamic Biomarker for Thiopurine Therapy in Inflammatory Bowel Disease
Margien L Seinen1, Geerten P van Nieuw Amerongen, Nanne K H de Boer
1Departments of *Gastroenterology and Hepatology and †Physiology, VU University Medical Center, Amsterdam; and ‡Department of Gastroenterology, Geriatrics, Internal and Intensive Care Medicine (Co-MIK), Zuyderland Medical Center, Heerlen-Sittard-Geleen, the Netherlands.
Background:
Azathioprine and mercaptopurine (MP) are effective in treating patients with inflammatory bowel disease (IBD). Immunosuppressive effects of thiopurines involve T-cell apoptosis after inhibition of GTPase Ras-related C3 botulinum toxin substrate 1 (Rac1). This study aimed to assess whether expression and activity of Rac1 or phosphorylated ezrin-radixin-moesin (pERM) in patients with IBD could provide a useful biomarker for the pharmacodynamic thiopurine effect and might be related to clinical effectiveness.
Methods:
This was a 2-stage study: stage 1 concerned a cross-sectional cohort of patients with IBD clinically in remission and treated with (n = 10) or without stable weight-based thiopurine therapy (n = 11) and healthy controls (n = 6); stage 2 concerned a prospective study regarding IBD patients with clinically active disease who initiated MP therapy (n = 11) compared with healthy controls (n = 11). Expression and activity of Rac1 and ERM and pERM were determined.
Results:
The median Rac1 expression was statistically significantly reduced by thiopurine maintenance therapy {0.54 [interquartile range (IQR) 0.47-0.88] versus 0.80 arbitrary units [IQR 0.64-1.46]} compared with patients without immunosuppressive therapy (P = 0.042), but not Rac1 activity and pERM. In responders to MP therapy (n = 6), both median active Rac1 [93 (IQR 81-151) to 76 ng Rac1/mg protein (IQR 62-98)] and Rac1 expression [16.2 (8.8-29.4) to 1.5 arbitrary units (0.9-5.3)] decreased (P = 0.028). In nonresponders (n = 3), Rac1 expression and activity increased.
Conclusions:
IBD patients treated with thiopurines had a lower expression of Rac1 compared with those not treated with thiopurine. Effective MP therapy led to decreasing concentrations of Rac1-GTP and Rac1 expression. Therefore, Rac1-GTP and expression of Rac1, but not phosphorylation of ERM, form potentially pharmacodynamic markers of therapeutic thiopurine effectiveness in patients with IBD.
More Related Videos
07:34Induction of Intestinal Inflammation by Adoptive Transfer of CBir1 TCR Transgenic CD4+ T Cells to Immunodeficient Mice
Published on: December 16, 2021
09:44Evaluating Therapeutic Interventions in the SHIP-deficient Mouse Model of Crohn Disease-like Ileitis and Fibrosis
Published on: October 14, 2025
Related Concept Videos
Drugs for Treatment of Crohn's Disease in IBD Using Biologic Agents: Anti-TNF
Drugs for Treatment of Crohn's Disease in IBD Using Immunomodulatory Agents
Pharmacogenetics of Drug Targets: β₂-Adrenergic Receptors, Apo E, Thymidylate Synthase
Pharmacogenetics of Phase II Enzymes: N-acetyltransferase, Thiopurine S-methyltransferase, UDP-glucuronosyltransferase
Pharmacogenomics: Identification of New Drug Targets