Objective
Therapeutic hypothermia is being clinically employed to reduce neurological deficits after cardiac arrest (CA). Patients receiving hypothermia after CA receive a wide-array of medications. During hypothermia, drug metabolism is markedly reduced. Little, however, is known about the impact of hypothermia on drug metabolism after re-warming. The objective of this study was to examine the effect of CA and hypothermia on the functional regulation of two major drug metabolizing cytochrome P450 (CYP) isoforms.
Design
Laboratory investigation.
Setting
University pharmacy school and animal research facility.
Subjects
Thirty-six male Sprague-Dawley rats.
Interventions
Hypothermia was induced via surface cooling in a rat CA model and maintained for 3h. Animals were sacrificed at 5 or 24h and liver was analyzed for hepatic activity and mRNA expression of CYP3A2 and CYP2E1. Plasma interleukin-6 (IL-6) concentrations were determined. The effect of IL-6 on PXR mediated transcription of the rat CYP3A2 promoter was evaluated via luciferace reporter in HepG2 cells.
Measurements and Main Results
At 24h after CA a decrease in CYP3A2 and CYP2E1 activity was observed, 55.7±12.8% and 46.8±29.7% of control, respectively (p<0.01). CA decreased CYP3A2 mRNA(p<0.05), but not CYP2E1 mRNA. Expression of other PXR target enzymes and transporter genes were similarly down-regulated. CA also produced a ∼10-fold increase in plasma IL-6. CA mediated inhibition of CYP3A2 and CYP2E1 was attenuated by hypothermia, as was the increase in IL-6. Furthermore, IL-6 attenuated PXR-mediated transcription of the CYP3A2 promoter.
Conclusions
CA produces CYP3A2 down-regulation at 24h, potentially via IL-6 effects on PXR-mediated transcription. Also, hypothermia attenuates the CA mediated down-regulation, thereby normalizing drug metabolism after re-warming.