Cannabielsoin (CBE), a CBD Oxidation Product, Is a Biased CB₁ Agonist

Cannabielsoin (CBE) is primarily recognized as an oxidation byproduct of cannabidiol (CBD) and a minor mammalian metabolite of CBD. The pharmacological interactions between CBE and cannabinoid receptors remain largely unexplored, particularly with respect to cannabinoid receptor type 1 (CB₁). The present study aimed to elucidate the interaction dynamics of CBE in relation to CB₁ by employing cyclic adenosine monophosphate (cAMP) and β-arrestin assays to assess its role as an agonist, antagonist, and positive allosteric modulator (PAM). To our knowledge, this is the first publication to investigate CBE's receptor activity in vitro. Our findings reveal that S-CBE acts as an agonist to CB₁ with EC₅₀ = 1.23 µg/mL (3.7 µM) in the cAMP assay. No agonist activity was observed in the β-arrestin assay in concentrations up to 12 µM, suggesting a noteworthy affinity towards G-protein activation and the cAMP signaling pathway. Furthermore, in silico molecular docking simulations were conducted to provide a structural basis for the interaction between CBE and CB₁, offering insights into the molecular determinants of its receptor affinity and functional selectivity.