Evaluating the analgesic effect of metamizole in the mouse model for DSS-induced acute colitis.

A commonly used mouse model of ulcerative colitis is the Dextran Sodium Sulphate (DSS) colitis model, including symptoms of weight loss, softening of stool up to diarrhea, and abdominal pain. To address 3R-refinement, we aimed to reduce severity in this model through pain therapy with metamizole. In addition to the potential analgesic effect, we investigated whether metamizole had a modulatory effect on inflammatory processes. In the study, ten-week-old female C57BL/6J mice were used. For pharmacological analysis, mice were treated with 200 mg/kg/d metamizole over 2 days to calculate baseline plasma concentration of metamizole metabolites using LC-MS/MS. After 14 days, DSS was administered via drinking water for 5 days, followed by metamizole for 2 days to determine plasma concentration. To assess disease severity and pain therapy, mice received DSS via drinking water for 5 days, controls received water only. Mice were then treated with metamizole via the drinking water for an additional 5 days, while corresponding sub-cohorts were left untreated (water+water, water+metamizole, DSS+water, DSS+metamizole). For severity assessment, changes in bodyweight, posture, stool consistency, voluntary wheel running (VWR) and Mouse Grimace Scale (MGS) were analyzed. Furthermore, colon samples were used for histology and gene expression analyses. LC-MS/MS analysis revealed significantly higher plasma concentrations of 4-methylaminoantipyrine and increased concentrations of 4-aminoantipyrine following DSS and subsequent metamizole treatment when compared to baseline. Assessing disease severity in control mice (water+water or water+metamizole-treated) demonstrated no clinical signs or changes in VWR. DSS+water and DSS+metamizole treated mice showed similar loss of body weight and clinical signs. VWR performances were decreased in DSS+water-treated mice as well as in DSS+metamizole-treated mice. There were no statistically significant differences between untreated and metamizole-treated animals with DSS-colitis. Interestingly, none of the groups showed elevated MGS scores, nor did the gene expression analyses detect relevant differences. This study showed that administering metamizole via drinking water led to detectable levels of metamizole metabolites in the plasma of treated mice. However, metamizole did not reduce disease severity or pain in this mouse model. Therefore, other refinement strategies should be explored in future studies.