Evaluation of cannabimimetic effects of selected minor cannabinoids and Terpenoids in mice

Abstract

Background: The cannabis plant contains several cannabinoids, and many terpenoids that give cannabis its distinctive flavoring and aroma. Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) is the plant's primary psychoactive constituent. Given the abuse liability of Δ⁹-THC, assessment of the psychoactive effects of minor cannabinoids and other plant constituents is important, especially for compounds that may be used medicinally. This study sought to evaluate select minor cannabinoids and terpenes for Δ⁹-THC-like psychoactivity in mouse Δ⁹-THC drug discrimination and determine their binding affinities at CB₁ and CB₂ receptors.

Methods: Δ⁹-THC, cannabidiol (CBD), cannabinol (CBN), cannabichromene (CBC), cannabichromenevarin (CBCV), Δ⁸-tetrahydrocannabinol (Δ⁸-THC), (6aR,9R)-Δ¹⁰-tetrahydrocannabinol [(6aR,9R)-Δ¹⁰-THC], Δ⁹-tetrahydrocannabinol varin (THCV), β-caryophyllene (BC), and β-caryophyllene oxide (BCO) were examined.

Results: All minor cannabinoids showed measurable cannabinoid 1 (CB₁) and cannabinoid 2 (CB₂) receptor binding, with CBC, CBCV, and CBD, showing the weakest CB₁ receptor binding affinity. BC and BCO exhibited negligible affinity for both CB₁ and CB₂ receptors. In drug discrimination, only Δ⁸-THC fully substituted for Δ⁹-THC, while CBN and (6aR,9R)-Δ¹⁰-THC partially substituted for Δ⁹-THC. THCV and BCO did not alter the discriminative stimulus effects of Δ⁹-THC.

Conclusion: In summary, only some of myriad cannabinoids and other chemicals found in the cannabis plant bind potently to the identified cannabinoid receptors. Further, only four of the compounds tested herein [Δ⁹-THC, Δ⁸-THC, (6aR,9R)-Δ¹⁰-THC, and CBN] produced Δ⁹-THC-like discriminative stimulus effects, suggesting they may possess cannabimimetic subjective effects. Given that the medicinal properties of phytocannabinoids and terpenoids are being investigated scientifically, delineation of their potential adverse effects, including their ability to produce Δ⁹-THC-like intoxication, is crucial.

Keywords: Cannabidiol; Cannabinol; Drug discrimination; THCV; Tetrahydrocannabinol; β-Caryophyllene.

Figure 1.

Chemical structures of test compounds.

Figure 2.

[³H]CP55,940 displacement curves by phytocannabinoids and terpenes in hCB₁ expressing (left panels) and hCB₂ expressing (right panels) HEK293 cell membranes. In the top panels, Δ⁹-THC (filled squares), Δ⁸-THC (unfilled circles), (6aR,9R)-Δ¹⁰-THC (filled inverted triangles), THCV (unfilled squares), and CBD (filled circles) displaced [³H]CP55,940 with a wide range of affinities at both receptors. In the bottom panels at both receptors, CBN (unfilled squares) displayed modest affinity, whereas CBC (filled triangles) and CBCV (unfilled inverted triangles) exhibited low affinity, and β-caryophylline (unfilled circles) and β-caryophylline oxide (unfilled triangles) exhibited negligible affinity with the latter two only partially displacing [³H]CP55,940 binding at concentrations of 31.6 μM. Each curve represents the mean (± SEM) of at least N=3 experiments performed in duplicate.

Figure 3.

Effects of phytocannabinoids on percentage of responding on the Δ⁹-THC-associated aperture (top panels) and response rates (responses/s; bottom panels) in adult male and female C57BL/6J mice (left and right panels, respectively) trained to discriminate 5.6 mg/kg Δ⁹-THC from vehicle. Dose-effect curves were determined for the training drug (Δ⁹-THC, filled squares) and for six minor cannabinoids: Δ⁸-THC (unfilled circles), CBD (filled circles), CBC (filled triangles), CBCV (unfilled inverted triangles), CBN (unfilled squares), and (6aR,9R)-Δ¹⁰-THC (filled inverted triangles; tested only in males). Control tests with vehicle (V) and 5.6 mg/kg Δ⁹-THC (T) were conducted prior to each dose-effect curve, with results shown at the left side of the panels. For the Δ⁹-THC dose-effect curve, each point represents the mean (± SEM) of data from 27 male mice (left panels) or 24 female mice (right panels). For the dose-effect curves with minor cannabinoids, each point represents the mean (± SEM) of data from 7–8 male mice (left panels) or 7–8 female mice (right panels), except for CBD (n=12 male mice) and Δ⁸-THC (n=5 male mice). # indicates significant main effect of dose across sex, with post-hoc difference in response rate between vehicle and the indicated dose (p<0.05). * indicates a significant difference in response rate between vehicle and the indicated dose of (6aR,9R)-Δ¹⁰-THC (p<0.05) for male mice.

Figure 4.

Effects of THCV on percentage of responding on the Δ⁹-THC-associated aperture (top panels) and response rates (responses/s; bottom panels) in adult male and female C57BL/6J mice (left and right panels, respectively) trained to discriminate 5.6 mg/kg Δ⁹-THC from vehicle. Dose-effect curves were determined for the training drug (Δ⁹-THC, filled squares) and for THCV alone (unfilled squares). In addition, combinations of THCV (30 and 100 mg/kg) with 5.6 mg/kg Δ⁹-THC were used to evaluate antagonism. Control tests with vehicle (V) and 5.6 mg/kg Δ⁹-THC (THC) were conducted prior to each dose-effect curve, with results shown at the left side of the panels. Each point represents the mean (± SEM) of data from 7 male mice (left panels) or 7 female mice (right panels). # indicates significant main effect of dose across sex, with post-hoc difference in response rate between vehicle and the indicated dose (p<0.05).

Figure 5.

Effects of the terpenoids, β-caryophylline and β-caryophylline oxide, on percentage of responding on the Δ⁹-THC-associated aperture (top panels) and response rates (responses/s; bottom panels) in adult male and female C57BL/6J mice (left and right panels, respectively) trained to discriminate 5.6 mg/kg Δ⁹-THC from vehicle. Dose-effect curves were determined for the training drug (Δ⁹-THC, filled squares) and for each terpenoid alone, β-caryophylline (unfilled circles) and β-caryophylline oxide (unfilled triangles). In addition, 30 mg/kg of each terpenoid (β-caryophylline, filled circles; β-caryophylline oxide, filled triangles) was assessed in combination with a range of Δ⁹-THC doses (on X-axis). Control tests with vehicle (V) and 5.6 mg/kg Δ⁹-THC (THC) were conducted prior to each dose-effect curve, with results shown at the left side of the panels. For the Δ⁹-THC dose-effect curve, each point represents the mean (± SEM) of data from 7–8 male mice (left panels) or 6–7 female mice (right panels), with exception that 100 mg/kg β-caryophylline was tested in only 2 mice of each sex.