Metabolism, CB1 cannabinoid receptor binding and in vivo activity of synthetic cannabinoid 5F-AKB48: Implications for toxicity.

AKB48 and its fluorinated derivative 5F-AKB48 are synthetic cannabinoids (SCs) which have caused hospitalizations and deaths in human users. Abuse of SCs is dangerous because users may mistake them for natural cannabis, which is generally considered to be unlikely to elicit adverse effects. The present studies were designed to investigate the in vitro oxidative metabolism of 5F-AKB48 by human microsomal fractions from different organs and sexes as well as recombinant human cytochrome P450s (P450s). Mass spectrometry data tentatively provides evidence for the existence of mono-, di-, and trihydroxylated metabolites in a successive metabolism. Experiments utilizing P450s revealed that the most active enzymes (CYP2D6, CYP2J2, CYP3A4, and CYP3A5) effectively produced mono- and dihydroxylated metabolites, while CYP3A4/5 also produced significant amounts of the trihydroxylated metabolite. Moreover, although the affinity and potency of Phase I metabolite 4OH-5F-AKB48 is reduced when compared to that of the parent drug, this metabolite nevertheless retains similar high affinity for CB1 receptors, and greater efficacy for G protein activation, when compared to THC. Finally, 5F-AKB48 produced time- and dose-dependent cannabimimetic effects in mice which were more potent, but shorter acting, than those of Δ9-THC, and were attenuated by prior treatment with the CB1 antagonist rimonabant. Based on our data, we hypothesize that while many cases of toxicity result from genetic mutations, which can lead to a decrease or even absence of activity for Phase I drug-metabolizing enzymes, other P450s could potentially increase their role in the metabolism of these SCs. Because many metabolites of SCs remain biologically active, they could contribute to the deleterious effects of these substances.