Elucidating The Role Of ?9-Tetrahydrocannabinol (Thc) And Cannabidiol (Cbd) In Developmental Toxicity

Increased availability of cannabis and cannabinoid-containing products necessitates the need for understanding how exposure to these compounds can affect development. Using cannabinoid receptor-null zebrafish (cnr1-/- and cnr2-/-), we conducted experiments to assess the roles of these receptors in ?9-tetrahydrocannabinol (THC) and cannabidiol (CBD) developmental and behavioral toxicity. THC increased mortality and deformities (pericardial and yolk sac edemas, a reduction in size) in cnr1-/- and cnr2-/- fish. Conversely, CBD-induced malformations and mortality were significantly reduced in the cnr1-/- and cnr2-/- larvae. THC and CBD exposure caused significantly decreased larval behavior (96 hpf), however, decreased distance travelled was protected in the cnr1-/- and cnr2-/- fish, suggesting these receptors are responsible for mediating behavioral toxicity. Transcriptomic profiling in cnr+/+ embryos developmentally exposed to 4 µM THC or 0.5 µM CBD revealed that a significant portion of differentially expressed genes were targets of PPAR?, a predicted upstream regulator. In Cnr-positive embryos, co-exposure to the PPAR? inhibitor GW9662 and THC or CBD, there was increased toxicity compared to exposure with THC or CBD alone. Co-treatment in the cnr2-/- fish with GW9662 did not alter the CBD-induced decrease in activity. However, co-treatment with GW9662 did remove the protective effect observed in cnr1-/- fish treated to CBD alone. Collectively, these results indicate that PPAR?, Cnr1, and Cnr2 all play crucial roles in the developmental toxicity of THC and CBD. Overall design: Tg(fli1:egfp) strain of zebrafish embryos was exposed to either DMSO, THC or CBD. We sequenced 4 biological replicates per treatment condition.