The role of metabolism in Diclofenac-induced intestinal toxicity in human ex vivo

The use of Diclofenac (DCF: 2-(2,6-dichloranilino) phenyl acetic acid ), a non-steroidal anti-inflammatory drug is associated with severe gastro-intestinal side-effects. In vivo rat studies suggest that reactive metabolites of DCF, produced by the liver, play an important role in the intestinal toxicity; whether DCF itself induces direct toxicity is not clear. In this study, human precision-cut intestinal slices (PCIS), prepared from human jejunum were used as an ex vivo model to investigate the mechanism of DCF-induced intestinal toxicity. PCIS from 12 human individuals were incubated with a concentration range of DCF (0-600µM). After 5 h of incubation, DCF (≥400 μM) caused a significant decrease in ATP content and morphological damage. 4’and 5-Hydroxyl DCF and DCF acylglucuronide were detected as major metabolites in human PCIS, but with a large variation among individuals. Toxicity of 400μM DCF already became apparent after one hour of incubation and the metabolite formation rate was also strongly decreased at this time-point compared with that at the non-toxic doses, indicating enterocyte injury. Drug-protein adducts were detected by immunohistochemical staining. To investigate the role of metabolism in the toxicity, the PCIS were incubated with DCF in the presence of a non-toxic concentration of the CYP inhibitor cimetidine (5mM) or the UGT inhibitor borneol (0.5mM). Both inhibitors effectively decreased the metabolites formation but did not reduce the toxicity of DCF. In conclusion, using PCIS as an ex vivo model we show that DCF induces toxicity to the human intestine directly, but the detected hydroxyl or acylglucuronide metabolites are not responsible for the toxicity.