An In Vitro Investigation of Cannabidiol Metabolism, Pharmacokinetics, and Hepatotoxicity

Cannabidiol (CBD) is a pharmacologically active metabolite of cannabis that is FDA-approved to treat seizures associated with Lennox-Gastaut syndrome, Dravet syndrome, and tuberous sclerosis complex in children aged one year and older. During clinical trials, CBD caused dose-dependent hepatocellular toxicity at therapeutic doses, resulting in dose reduction or interruption of therapy in two-thirds of affected patients. The risk for toxicity was increased in patients taking valproate (VPA), another hepatotoxic antiepileptic drug, through an unknown mechanism. CBD liver toxicity has been observed both in epileptic patients and healthy volunteers. With the growing popularity of CBD in the consumer market, an improved understanding of safety risks associated with CBD is needed to ensure public health. The goal of this dissertation was to determine how CBD metabolism may influence the adverse effect profile and risk of liver injury for those taking CBD. This dissertation provides an overview of the current knowledge on the pharmacology, pharmacokinetics, and safety profile of CBD in Chapter 1. In Chapters 2-3, the hepatic metabolism of CBD was characterized using reaction phenotyping experiments with human liver microsomes, cytosol, and S9. Formation of the active metabolite 7-hydroxy-CBD was mediated by CYP2C9 and CYP2C19, and formation of the major circulating metabolite 7-carboxy-CBD was found to occur through a multi-step reaction catalyzed by cytosolic dehydrogenase enzymes. To understand the hepatotoxic interaction between CBD and VPA in the liver, three-dimensional human hepatocyte spheroids were developed as a model for CBD-induced liver injury (Chapter 4). A delayed onset, dose-dependent toxicity was observed in spheroids following exposure to CBD ± VPA. This study was the first to examine the toxic relationship between CBD and VPA in an in vitro culture model. In Chapter 5, a summary of findings is provided followed by a discussion of the limitations and future directions for the dissertation. Future work will focus on intracellular mechanisms of the CBD-induced hepatotoxicity by using in vitro assays for bile acid-mediated liver injury, measuring mitochondrial respiration in hepatocytes following CBD and VPA treatment, and using a multi-omics approach to identify mechanisms of toxicity in hepatocyte spheroids.