&Delta;⁹-Tetrahydrocannabinol Produced Positive Place Preference in Mice without Significant <i>Ex-Vivo</i> Effect on Hepatic Arylamine N-Acetyltransferase Activity: Implications for Its Addictive Liability and Absence of Effect on Xenobiotic Metabolism

Abstract

Aim: Δ 9 -Tetrahydrocannabinol (Δ 9 -THC) is a potentially addictive cannabinoid. Its impact on the activity of liver arylamine N-Acetyltransferase (NAT) has not been reported. This study investigated the rewarding effects of Δ 9 -THC in mice and whether Δ 9 -THC had any impact ex-vivo and in-vitro on NAT activity. Methods: Thirty-six Swiss albinomice randomly assigned to six groups (n = 6) completed a biased, 8-week Conditioned Place Preference (CPP) paradigm. Mice exhibiting ~80% preference for the black chamber at pre-conditioning were selected. Treatment groups were administered Δ 9 -THC (0.10, 0.50 or 2.0 mg/kg/mL, ip ) or amphetamine (AMP, 5.0 mg/kg/mL, ip ); while untreated groups (controls) received vehicle solutions (coconut oil or 0.9% saline). Entries and time spent in the white, drug-paired chamber during a 15-min post-conditioning exploration of the CPP apparatus were compared with the pre-conditioning exploratory scores. Livers from Δ 9 -THC treated and untreated mice were excised and NAT enzyme activity determined ex-vivo using a spectrophotometric assay with p-anisidine as substrate. The impact of varying concentrations of Δ 9 -THC (0.00 - 162 μM) on the activities of NAT from untreated mice livers were also investigated in-vitro . Results: Δ 9 -THC treated mice entered and spent significantly more time in the drug-paired CPP chamber (p ≤ 0.05) at post-conditioning vs pre-conditioning (F = 11.22). Mice treated with 2.0 mg/kg Δ 9 -THC made significantly more entries into the drug-paired chamber (p ≤ 0.05) as compared with their vehicle controls. AMP-treated mice displayed significant (p < 0.001) increases in both entries and time spent in the drug-paired chamber at post-conditioning (positive place preference). In-vitro NAT evaluations revealed a dose-dependent inhibitory impact of Δ 9 -THC on NAT activity with an IC50 value of 34.97 ±1.58 μM. Ex-vivo evaluations of livers from Δ 9 -THC treated mice showed no significant impact on liver NAT enzyme activity. Conclusion: Δ 9 -THC induced significant conditioned place preference (drug reward) and produced a moderate dose-dependent inhibition on NAT activity in-vitro , but not ex-vivo .