Comparison of the Neurotoxic and Seizure-Inducing Effects of Synthetic and Endogenous Cannabinoids with Δ9-Tetrahydrocannabinol
Chris S. Breivogel, Jacob R. Wells, Amreen Jonas, Artik H. Mistry, Morgan L. Gravley, Rajul M. Patel, Brianna E. Whithorn, and Bonnie M. Brenseke
Cannabis and Cannabinoid Research, 2019, Volume X, Number X
Introduction : Synthetic cannabinoids (SCs) are commonly found in preparations used as recreational drugs. Although severe adverse health effects are not generally associated with cannabis use, a rising number of studies document seizures and even death after SC use. In this study, a mouse model is used to investigate the hypothesis that SCs are more toxic than Δ9-tetrahydrocannabinol (THC), the principal psychoactive constituent of cannabis.
Materials and Methods : Beginning with the SCs, JWH-073 and AM-2201, dose–response curves were generated to find the dose of each drug that was similarly efficacious to 50 mg/kg THC. Mice were given daily intraperitoneal (IP) injections of vehicle, 50 mg/kg THC, 30 mg/kg JWH-073, or 1 mg/kg AM-2201 until tolerance to the antinociceptive and hypothermic effects was complete, and then were assessed for spontaneous and antagonist-precipitated withdrawal and potential organ damage. No differences in tolerance were noted, but AM-2201 showed more rearing in the spontaneous and antagonist-precipitated withdrawal phases than either vehicle or the other two drug treatments. Histopathological examination of these mice revealed no drug-induced lesions. In a subsequent set of experiments, various doses of THC, methanandamide (mAEA), and of a variety of SCs (HU-210, CP55940, JWH-073, AM-2201, and PB-22) were given IP, and convulsions and change in body temperature were quantified.
Discussion : The treatments yielded varying numbers of convulsions and a range of changes in body temperature. JWH-073 and AM-2201 produced significantly more convulsions than THC, HU-210, mAEA, or cannabidiol (CBD) (the latter two producing none). HU-210, CP55940, JWH-073, and mAEA produced greater hypothermia than THC or CBD. Convulsions and hypothermia induced by several agonists were prevented by pretreatment with a CB1 antagonist, but not a CB2 antagonist.
Conclusions : In agreement with human studies and case reports, this study found that SCs generally produced more seizures than THC. Of particular significance was the finding that mAEA produced far greater hypothermia than THC (similar to most SCs), but unlike the SCs and THC, produced no seizures.
Keywords : AM-2201; HU-210; JWH-073; methanandamide; PB-22; tetrahydrocannabinol
It has been estimated that synthetic cannabinoids (SCs) are 30 times more likely than cannabis to result in the need for emergency medical treatment.1 Increased use of SCs, sold under brand names such as Spice and K2, and their apparent toxicity2 has led to an urgent need for in vivo toxicological studies.
There are several chemical classes of cannabinoid receptor agonists. The phytocannabinoids from Cannabis sativa3 include Δ9-tetrahydrocannabinol (THC) and related compounds such as cannabidiol (CBD). Although THC is an agonist for the cannabinoid CB1 receptor, CBD appears to be a negative allosteric modulator of this receptor.4,5 Synthetic CB1 agonists belong to different chemical classes, and include close analogs of THC such as HU-210, and more distantly related classes such as alkyl phenols (e.g., CP55940) and aminoalkylindoles (e.g., JWH-073).
The endogenous cannabinoids termed “endocannabinoids” are the arachidonic acid derivatives, arachidonoyl ethanolamide (AEA or anandamide), and 2-arachidonoyl glycerol (2-AG).6 Methanandamide (mAEA), a semisynthetic metabolism-resistant methyl analog of anandamide, has similar pharmacology to anandamide.7
In animals, activation of CB1 produces hypothermia, antinociception, decreased spontaneous activity, and catalepsy.8 In humans, cannabinoid effects on the psyche and perception include fatigue, euphoria, anxiety or anxiolysis, increased appetite, decreased nausea, amnesia, depersonalization, and hallucinations.9 Cannabinoid somatic effects include tachycardia, analgesia, xerostomia, conjunctivitis, decreased intraocular pressure, and unsteady gait.9 Recreational use of SCs is reported to cause seizures,10 an acute toxic symptom seen with increasing prevalence in hospital emergency rooms.2,11–13
Two recent studies showed that THC and the aminoalkylindoles, JWH-018 and AM-2201, produced seizures in mice. The first showed that seizures, recorded visually and by electroencephalogram (EEG), were induced by THC or JWH-018 and prevented by the CB1-selective antagonist, AM-251.14 The second study found that AM-2201 produced seizures, which were prevented by AM-251 or a metabotropic glutamate receptor antagonist, but not CB2 or vanilloid receptor antagonists.15 These studies concluded that cannabinoid-induced seizures are mediated by CB1, and antagonists such as AM-251 are potential treatments for acute cannabinoid toxicity.
This study extends the findings of previous studies to include additional agonists. It began by comparing JWH-073 and AM-2201 with THC. JWH-073 and AM-2201 are among the SCs found in products sold to the public and in patients admitted to the emergency room.16 This study then examined the seizure-inducing activity of these and additional cannabinoids representing a range of chemical classes (Fig. 1), and exhibiting a range of affinities and efficacies for activating G-proteins through CB1.17,18 It also confirmed the roles of cannabinoid CB1 receptors in mediating seizure activity.
As the use of cannabis has not been associated with seizures (and may even decrease the risk of seizures)10 in humans or tissue damage in humans or animals, it was hypothesized that, compared with THC, SCs would cause greater or more rapid levels of tolerance, dependence, tissue damage, hypothermia, and seizures.