Brodifacoum does not modulate human cannabinoid receptor-mediated hyperpolarization of AtT20 cells or inhibition of adenylyl cyclase in HEK 293 cells

Background: Synthetic cannabinoids are a commonly used class of recreational drugs that can have significant adverse effects. There have been sporadic reports of co-consumption of illicit drugs with rodenticides such as warfarin and brodifacoum (BFC) over the past 20 years but recently, hundreds of people have been reported to have been poisoned with a mixture of synthetic cannabinoids and BFC. We have sought to establish whether BFC directly affects cannabinoid receptors, or their activation by the synthetic cannabinoid CP55940 or the phytocannabinoid Δ⁹-tetrahydrocannabinol (Δ⁹-THC).

Methods: The effects of BFC on the hyperpolarization of wild type AtT20 cells, or AtT20 cells stably expressing human CB₁- or CB₂- receptors, were studied using a fluorescent assay of membrane potential. The effect of BFC on CB₁- and CB₂-mediated inhibition of forskolin-stimulated adenylyl cyclase (AC) activation was measured using a BRET assay of cAMP levels in HEK 293 cells stably expressing human CB₁ or CB₂.

Results: BFC did not activate CB₁ or CB₂ receptors, or affect the hyperpolarization of wild type AtT20 cells produced by somatostatin. BFC (1 µM) did not affect the hyperpolarization of AtT20-CB₁ or AtT20-CB₂ cells produced by CP55940 or Δ⁹-THC. BFC (1 µM) did not affect the inhibition of forskolin-stimulated AC activity by CP55940 in HEK 293 cells expressing CB₁ or CB₂. BFC (1 µM) also failed to affect the desensitization of CB₁ and CB₂ signaling produced by prolonged (30 min) application of CP55940 or Δ⁹-THC to AtT20 cells.

Discussion: BFC is not a cannabinoid receptor agonist, and appeared not to affect cannabinoid receptor activation. Our data suggests there is no pharmacodynamic rationale for mixing BFC with synthetic cannabinoids; however, it does not speak to whether BFC may affect synthetic cannabinoid metabolism or biodistribution. The reasons underlying the mixing of BFC with synthetic cannabinoids are unknown, and it remains to be established whether the "contamination" was deliberate or accidental. However, the consequences for people who ingested the mixture were often serious, and sometimes fatal, but this seems unlikely to be due to BFC action at cannabinoid receptors.