FRACTIONAL CONTRIBUTION OF CYP AND UGT ENZYMES TO THE DISPOSITION OF CANNABINOIDS

AIMS: Use of marijuana during pregnancy has been associated with negative fetal outcomes. These outcomes are likely mediated by the psychotropic and most abundant cannabinoid in marijuana, Δ⁹-tetrahydrocannabinol (THC) and its active metabolite, 11-hydroxy- Δ⁹-THC (11-OH-THC). Determining fetal exposure to THC/11-OH-THC to assess fetal/neonatal risks from maternal consumption of marijuana is ethically and logistically challenging. Alternatively, physiologically-based pharmacokinetic (PBPK) modeling and simulation can be used to predict maternal and fetal THC/11-OH-THC exposure throughout pregnancy. To do so, we determined the fraction metabolized by previously identified cytochrome P450 (CYP) and UGT enzymes involved in the depletion of THC and depletion/formation of 11-OH-THC.

METHODS: Depletion studies using physiologically relevant concentrations of THC (500 nM) and 11-OH-THC (50 nM) were conducted in pooled (n=50) human liver microsomes (HLMs) in the presence of co-factors NADPH (CYPs), UDPGA (UGTs) and selective competitive inhibitors of CYP2C9 (10 μM sulfaphenazole), CYP3A4 (2 μM itraconazole), CYP2C19 (30 μM omeprazole), CYP2D6 (1 μM quinidine), and time-dependent inhibitor of CYP1A1 (10 μM furafylline). 11-OH-THC depletion by recombinant UGT1A4 and UGT1A9 was also determined. THC/11-OH-THC depletion and 11-OH-THC formation was monitored via LC-MS/MS.

RESULTS: CYP2C9 was the largest contributor to the depletion of THC (fm ~0.78) followed by CYP3A4 (fm ~0.22). Slight inhibition of THC depletion was observed with omeprazole and quinidine but not furafylline. UGTs did not deplete THC. UGT contribution to 11-OH-THC depletion (0.402 ml/min/mg) was slightly greater than that by CYPs (0.305 ml/min/mg). CYP2C9 and CYP3A4 were the major contributors to the formation and depletion of 11-OH-THC, respectively (fm ~0.88 and fm ~0.73). UGT1A9, but not UGT1A4, metabolized 11-OH-THC.

CONCLUSIONS: Since CYP2C9 is modestly induced (1.6-fold) during pregnancy¹, THC clearance will only modestly be affected during pregnancy. Although hepatic CYP3A4 activity increases 2-fold during pregnancy¹, the effect on 11-OH-THC exposure is likely to be dampened because UGTs also significantly contribute to the depletion of 11-OH-THC. UGT1A4, which is induced during pregnancy¹, does not metabolize 11-OH-THC, while UGT1A9, which is present in the placenta, does. The mechanistic information presented here will be incorporated into a maternal-fetal PBPK model previously developed in our laboratory² to predict maternal, placental, and fetal THC/11-OH-THC exposure throughout pregnancy and will be verified using existing or collected clinical data.

References:

[1] Ke AB, Rostami-Hodjegan A, Zhao P, and Unadkat JD (2014) Pharmacometrics in pregnancy: An unmet need. Annu Rev Pharmacol Toxicol 54:53-69.

[2] Zhang Z, Imperial MZ, Patilea-Vrana GI, Wedagedera J, Gaohua L, and Unadkat JD (2017) Development of a Novel Maternal-Fetal Physiologically Based Pharmacokinetic Model I: Insights into Factors that Determine Fetal Drug Exposure through Simulations and Sensitivity Analyses. Drug Metab Dispos. [Epub ahead of print]

Supported by NCATS Grant TL1 TR000422 and NIDA Grant P01DA032507.