Unraveling the cellular mechanisms of thiopurine-induced pancreatitis in pediatric inflammatory bowel disease: Insights from induced pluripotent stem cell models

Thiopurines are effective drugs for inflammatory bowel disease, but their use is limited by side effects such as pancreatitis, whose mechanism remains unknown and may be more severe in children. This study investigated in a personalized way thiopurine-induced pancreatitis mechanism using induced pluripotent stem cells from pediatric inflammatory bowel disease patients. Ten pediatric patients, five developing pancreatitis (cases) and five without it (controls), were enrolled. Patient-specific stem cells and their pancreatic differentiated counterparts were used to evaluate thiopurine cytotoxicity, to quantify metabolites levels by liquid chromatography-tandem mass spectrometry, and to assess thiopurine pharmacodynamics by western-blot assay. Statistical analyses were performed applying Student's t-test or two-way ANOVA followed by Bonferroni's post-hoc test for multiple comparisons. Cytotoxicity assays revealed higher thioguanine cytotoxicity in stem and pancreatic cells from cases; pancreatic cells from cases were also more sensitive to mercaptopurine. Moreover, thioguanine treatment on stem cells produced thioguanosine monophosphate and its methylated form, but their concentration did not differ significantly between the groups. In addition, higher TPMT gene expression was observed in stem cells from cases, but no differences were observed in pancreatic cells. No significant differences were detected in HPRT, NUDT15, ITPA, or PACSIN2 expression. Lastly, Rac1 protein concentration was similar in stem cells from cases and controls, but pancreatic cells from cases exhibited significantly higher Rac1 expression. These findings suggest that thiopurine cytotoxicity differences might be linked to pharmacokinetics in stem cells, while altered Rac1 expression in pancreatic cells might contribute to pancreatitis, implicating distinct mechanisms between stem and differentiated cells.