Mechanisms of Regulation of Cannabinoid Disposition

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Cannabis is the most commonly used illicit substance in the world, and the use of cannabis by pregnant women is increasing. Approximately 4% of all pregnant women use cannabis despite studies suggesting that cannabis exposure during pregnancy has negative consequences to the developing fetus. This is a significant public health concern. However, delineating the impact of cannabis use on pregnancy outcomes has suffered from lack of understanding of how the pharmacokinetics of the active component of cannabis, ∆9- tetrahydrocannabinol (THC) is altered during pregnancy, and from lack of a reliable biomarker to quantify cannabis usage and exposure levels. In fact, at present the knowledge of processes that drive inter-individual variability in THC disposition are largely unknown. Existing data suggests that THC is mainly cleared by CYP2C9 with a minor contribution from CYP3A4. Several studies have shown that the elimination of the major metabolites of THC, 11-OH-THC and 11-nor-carboxy-THC is mediated by UGT1A enzymes. This is important in the context of THC disposition in pregnant women as CYP2C9 and UGT1A enzymes have been shown to be regulated by estradiol and glucocorticoids, major female hormones that are increased during pregnancy. Based on this data, we hypothesize that the clearance of THC and its metabolites is significantly increased with increasing estradiol and glucocorticoid concentrations. We propose that this increase can be mechanistically predicted from in vitro human hepatocyte and primary intestinal mucosal culture experiments with hormone treatments and innovative THC metabolism experiments. In the first part of this project we will test these hypotheses by determining the magnitude of changes in THC metabolism and in CYP2C9, CYP3A4 and UGT1A isoform expression following treatment of human hepatocytes and cryopreserved intestinal mucosa with estradiol and glucocorticoids. We will also establish how hepatic and intestinal fatty acid binding proteins (FABPs) affect the metabolism and distribution of THC and its metabolites in vitro. THC has been shown to bind to brain FABPs, but whether THC and its metabolites bind to liver and intestinal FABPs is unknown. We hypothesize that FABP binding directs THC metabolism, and contributes to cannabinoid clearance and delivery to metabolic enzymes. We will test this innovative hypothesis in vitro using biochemical methods. In the second part of this proposal, we will test in a clinical study whether estrogens and cortisol induce THC metabolism and exposure. We expect that these studies will form the foundation for overall prediction and modeling of THC disposition during human pregnancy. When completed, our studies will provide critical information of the processes that contribute to inter-individual variability of THC pharmacokinetics. These studies will also provide seminal data to allow modeling of THC metabolome in human plasma and urine as a function of THC consumption and time after consumption, making a significant impact on development of reliable biomarkers of THC exposures in humans.