CYP and non-CYP drug metabolizing enzyme families exhibit differential sensitivities towards pro-inflammatory cytokine modulation.

Abstract

Compromised hepatic drug metabolism in response to pro-inflammatory cytokine release is primarily attributed to downregulation of cytochrome P450 (CYP) enzymes. However, whether inflammation also affects other phase I and phase II drug metabolizing enzymes (DMEs) like the flavin monooxygenases (FMOs), carboxylesterases (CESs) and UDP glucuronosyltransferases (UGTs) remains unclear. This study aimed to decipher the impact of physiologically relevant concentrations of pro-inflammatory cytokines on expression and activity of phase I and phase II enzymes, in order to establish a hierarchy of their sensitivity as compared to the CYPs. Hereto, HepaRG cells were exposed to interleukin-6 and interleukin-1β to measure alterations in DME gene expression (24h) and activity (72h). Sensitivity of DMEs towards pro-inflammatory cytokines was evaluated by determining IC50 (potency) and Imax (maximal inhibition) values from the concentration-response curves. Pro-inflammatory cytokine treatment led to nearly complete downregulation of CYP3A4 (~98%), but was generally less efficacious at reducing gene expression of the non-CYP DME families. Importantly, FMO, CES and UGT family members were less sensitive towards interleuking-6 induced inhibition in terms of potency, with IC50 values that were 4.3-7.4 fold higher than CYP3A4. Similarly, 18- to 31-fold more interleukin-1β was required to achieve 50% of the maximal downregulation of FMO3, FMO4, CES1, UGT2B4 and UGT2B7 expression. The differential sensitivity persisted at enzyme activity level, highlighting that alterations in DME gene expression during inflammation are predictive for subsequent alterations in enzyme activity. In conclusion, we have shown that FMOs, CES and UGTs enzymes are less impacted by inflammation as compared to CYP enzymes. Significance Statement While the impact of pro-inflammatory cytokines on CYP expression is well established, their effects on non-CYP phase I and phase II drug metabolism remains underexplored, particularly regarding alterations in drug metabolizing enzyme activity. This study provides a quantitative understanding of the sensitivity differences to inflammation between DME family members, suggesting that non-CYP DMEs may become more important for the metabolism of drugs during inflammatory conditions due to their lower sensitivity as compared to the CYPs.