Discussion
The presence of THC in our THCA-A certified standard agrees with decarboxylation kinetics (literature reviewed herein), which indicate contamination with THC is nearly unavoidable. THCA-A binding at 10μM approximated THC binding at 200nM. We therefore suspect some of our THCA-A binding curve was artifact-from its inevitable decarboxylation into THC-and the binding affinity of THCA-A is even weaker than our estimated values. We conclude that THCA-A has little affinity or efficacy at CB1 or CB2.
Methods
Purity of certified reference standards were tested with high performance liquid chromatography (HPLC). Binding affinity of THCA-A and THC at human (h) CB1 and hCB2 was measured in competition binding assays, using transfected HEK cells and [3H]CP55,940. Efficacy at hCB1 and hCB2 was measured in a cyclic adenosine monophosphase (cAMP) assay, using a Bioluminescence Resonance Energy Transfer (BRET) biosensor.
Results
The THCA-A reagent contained 2% THC. THCA-A displayed small but measurable binding at both hCB1 and hCB2, equating to approximate Ki values of 3.1μM and 12.5μM, respectively. THC showed 62-fold greater affinity at hCB1 and 125-fold greater affinity at hCB2. In efficacy tests, THCA-A (10μM) slightly inhibited forskolin-stimulated cAMP at hCB1, suggestive of weak agonist activity, and no measurable efficacy at hCB2.