Synthetic Cannabinoid activation of hTRPA1 and naturally occuring channel variants
thesisposted on 2022-03-28, 13:21 authored by Saarin Josh Pearson
THC, the primary psychoactive compound in cannabis, is a low efficacy agonist of the CB1 receptor. Synthetic cannabinoids (SC's) are compounds structurally unrelated to THC, which also function as agonists of the CB receptors. Recreational SC products have been monitored since the emergence of JWH-018 in 2008, with new compounds rapidly developed to evade legislation and detection. SC consumption, including mass intoxication events, is associated with a range of adverse effects uncharacteristic of plant derived cannabinoids, such as psychomotor agitation, aggression, cardiac arrhythmias, seizures and death. The mechanisms of SC toxicity are not established, however, some SCs are higher efficacy agonists of CB receptors than common research cannabinoids, and have the potential to act at non-CB receptor targets. Polymorphic variants of these targets may influence individual toxicity. Transient receptor potential ankyrin 1 (TRPA1) is a calcium-permeable ion channel highly expressed in the brain, sensory neurons and the epithelium of the lungs. TRPA1 is activated by THC and some synthetic cannabinoids, with several naturally occurring polymorphic variants in humans. HEK293 cells stably transfected with human TRPA1 and five select SNP variants were studied by measuring changes in intracellular [Ca2+] in response to selected high concern SCs and some natural ligands. The SC's MDMB-CHMICA, PB-22, 5F-PB-22, UR-144, XLR-11 and 5-OH-UR-144 activate hTRPA1 and each mutant, although they exhibited varying degrees of efficacy between the mutants. The R58T variant resulted in increased activation by PB-22 and 5F-PB-22 compared to the WT. R3C, E179K, H1018R and R3C+R58T resulted in decreased activated compared to the WT by UR-144 and XLR-11. The 5-hydroxypentyl metabolite common to both remained unaffected by hTRPA1 polymorphisms, as did MDMB-CHMICA and two prototypic ligands, cinnamaldehyde and allyl isothiocyanate. At hTRPA1, XLR-11 was relatively more potent than the structurally similar UR-144. The common 5-OH metabolite exhibited greater relative potency than both parents at some hTRPA1 variants. THC was shown to be a more potent agonist at hTRPA1 than all synthetic cannabinoids tested. These data show that the efficacy of SCs varies at naturally occurring hTRPA1 polymorphisms, but that different drugs are affected in distinct ways. If SC toxicity is related to actions at non-CB proteins such as TRPA1, mechanisms of drug toxicity may be highly individualized.