Elsevier

Biochemical Pharmacology

Volume 155, September 2018, Pages 403-418
Biochemical Pharmacology

Can toxicokinetics of (synthetic) cannabinoids in pigs after pulmonary administration be upscaled to humans by allometric techniques?

https://doi.org/10.1016/j.bcp.2018.07.029Get rights and content

Abstract

Being advertised and distributed as attractive substitutes of cannabis, synthetic cannabinoids (SC) are gaining increasing relevance in forensic and clinical toxicology. As no data from controlled human studies are available, SC are sold and consumed without the knowledge of their toxicokinetic (TK) and toxicodynamic properties. Hence, animal models coupled with mathematical approaches should be used to ascertain those properties. Therefore, a controlled pig TK study allowing for extrapolation to human data was performed. For this purpose, eleven pigs received a single pulmonary dose of 200 µg/kg body weight each of Δ9-tetrahydrocannabinol (THC), 4-ethylnaphthalene-1-yl-(1-pentylindole-3-yl)methanone (JWH-210) as well as 2-(4-methoxyphenyl)-1-(1-pentyl-indole-3-yl)methanone (RCS-4) via an ultrasonic nebulizer. Blood and urine samples were repeatedly drawn over 8 h. Serum-concentration-time profiles of the parent compounds were determined using LC-MS/MS. Urine specimens were analyzed by LC-HR-MS/MS in order to elucidate the main metabolites. Maximum serum concentrations were reached 10–15 min after beginning of nebulization and amounted to 66 ± 36 ng/mL for THC, 41 ± 11 ng/mL for JWH-210, and 34 ± 8.9 ng/mL for RCS-4. The serum-concentration-time profiles of THC, JWH-210, and RCS-4 were best described by three-compartment models with first order absorption and elimination processes. Absorption from the lungs to serum was modeled by first-order processes. The determination of the bioavailability yielded 23.0%, 24.2%, and 45.7% for THC, JWH-210, and RCS-4, respectively. Furthermore, the developed THC model was upscaled to humans using allometric scaling techniques. A successful prediction of human concentration-time profiles could be done. Also the metabolic patterns were in good agreement with human data. In conclusion, these findings are the first reported regarding the TK properties of SC after pulmonary administration to pigs. The presented method of TK serves as an appropriate predictor of human TK of cannabinoids.

Introduction

Synthetic cannabinoids (SC) were originally synthesized in the context of structure–activity relationship studies [1], [2], [3], but have increasingly been consumed as a substitute of cannabis to elude the narcotics law. Especially during the last six years, the number of newly emerged SCs has significantly increased in Europe [4]. SC often exhibit higher affinities to the cannabinoid receptor (CB) 2 as well as CB1. This receptor is responsible for the psychoactive, but also antiemetic and analgesic effects [5], explaining the usefulness in the treatment of i.e. nausea during cancer treatment or cachexia in the context of an acquired immune deficiency syndrome. Beyond that, even higher potencies have been observed as compared to Δ9-tetrahydrocannabinol (THC) [6], [7], [8], resulting in unpredictable psychoactive effects, ending up in intoxications with life-threatening conditions or even death [5], [9]. Regarding these issues, SC have become a tremendous public health concern and are gaining increasing relevance in clinical and forensic toxicology. Unlike THC, whose toxicokinetic (TK) and toxicodynamic properties have extensively been examined [10], [11], [12], [13], [14], [15], [16], [17], neither preclinical safety-data nor TK data from controlled studies are available for SC. However, explicit TK data are indispensable when interpreting analytical data from individuals who are either impaired or have overdosed following drug use (i.e. time of ingestion and plasma concentrations related to clinical observations), but in addition and especially if precise expert opinion in forensic cases is required (i.e. driving under the influence of drugs). Only few SC TK data have been obtained so far, which are based on in-vitro or few systematic animal studies, single case reports, or self-experiments with only one or two participants [18], [19], [20]. Recently, Toennes et al. [21] conducted a systematic human study in order to assess adverse effects and TK of JWH-018 after inhalation. However, this database obtained in these pioneer studies has to be supplemented for a even more comprehensive characterization of the TK properties of this drug class.

A pilot study to establish a pig model suitable for cannabinoid TK studies after intravenous (i.v.) administration of THC, 4-ethylnaphthalene-1-yl-(1-pentylindole-3-yl)methanone (JWH-210), and 2-(4-methoxyphenyl)-1-(1-pentyl-indole-3-yl)methanone (RCS-4) [22], [23], [24], [25] and allowing for prediction of human data applying a mathematical approach and allometric scaling techniques [23] has provided first knowledge concerning that issue. In this study, a three compartment model as well as an allometric scaling exponent of 0.75 on each TK parameter described the data best [23].

Nevertheless, the most common route of SC consumption is smoking [6]. Furthermore, inhalation of vaporized cannabinoids via electronic cigarettes has also been reported [26]. Thus, an administration set-up reflecting authentic user habits should be established using the former developed pig model in order to supplement the data obtained after i.v. administration. Therefore, the aim of the present study was to elucidate the TK of THC as well as the two SC JWH-210 and RCS-4 after standardized pulmonary administration to ventilated anesthetized pigs using an ultrasonic-assisted nebulizer [27]. For this purpose, the concentration-time profiles should be determined in a first step. For evaluation of the bioavailability, the data obtained from the pulmonary administration experiments should be compared to those determined in the i.v. study. In a second step, the concentration-time profiles should be modeled and assessed whether the THC model can predict published data in humans by upscaling the THC pig model to humans using allometric techniques. In a third step, simulations of different human dosing scenarios should be performed for JWH-210 and RCS-4. At last, the main urinary metabolites should be identified by liquid-chromatography high-resolution mass spectrometry (LC-HR-MS/MS). Results should be compared with those detected after i.v. administration and finally correlated to human data.

Section snippets

Chemicals and reagents

Glacial acetic acid per analysis (p.a.), isopropanol p.a., acetone Supra Solv, methanol Supra Solv, formic acid EMSURE, and di-potassium hydrogen phosphate EMSURE were obtained from Merck (Darmstadt, Germany). High pressure (HP) LC grade water was purchased from VWR-International (Darmstadt, Germany) and ethanol p.a. and HPLC grade acetonitrile from Sigma-Aldrich (Steinheim, Germany). Ammonium formate (analytical grade) was obtained from Fluka (Neu-Ulm, Germany), methanolic solution of THC

Serum concentration-time profiles

Following pulmonary administration of 200 µg/kg BW to male domestic pigs, Cmax were reached 10–15 min (tmax) after the beginning of nebulization and amounted to 66 ± 36 ng/mL for THC, 41 ± 11 ng/mL for JWH-210, and 34 ± 8.9 ng/mL for RCS-4. Concentrations rapidly declined within the first hour, indicating a distribution into tissues. After 60 min, mean concentrations of 14 ± 5.7 ng/mL for THC, 12 ± 6.9 ng/mL for JWH-210, and 6.5 ± 2.2 ng/mL for RCS-4 were observed. Subsequently, a slower

Pulmonary administration

To establish an authentic consumption scenario, we present a novel standardized experimental method of pulmonary drug administration by using a nebulizer operating in an inspiration-triggered mode. Unlike a permanent nebulization, the triggered mode allowed for successive nebulization (<0.2 mL/min) of the drug solution synchronized with each inspiratory phase resulting in a 12 min administration process of the whole dose. Applying this protocol, a set-up similar to that used for systematic PK

Acknowledgements

The authors thank Benjamin Peters and the staff of the Institute for Clinical & Experimental Surgery at Saarland University for their support and help during the study as well as the Saarland University for the research grant (Anschubfinanzierung von Forschungsprojekten, 61-cl/Anschub 2017/bew-Schäfer).

Conflict of interest

There are no financial or other relations that could lead to a conflict of interest.

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