Pharmacokinetic and pharmacodynamic properties of aerosolized ("vaped") THC in adolescent male and female rats

Abstract

Rationale: Adolescent exposure to ∆⁹-tetrahydrocannabinol (THC), the psychotropic constituent of cannabis, might affect brain development, and in rodent models leads to long-term behavioral and physiological alterations. Yet, the basic pharmacology of this drug in adolescent rodents, especially when ingested via ecologically relevant routes like aerosol inhalation, commonly referred to as "vaping," is still poorly characterized. Moreover, sex differences exist in THC metabolism, kinetics, and behavioral effects, but these have not been rigorously examined after vapor dosing in adolescents.

Objectives: We investigated the pharmacokinetics and pharmacodynamics of aerosolized THC (30 min inhalation exposure, 25 or 100 mg/ml) in adolescent Wistar rats of both sexes.

Methods: Liquid chromatography/mass spectrometry analysis of THC and its major metabolites was conducted on blood plasma and brain tissue at 5, 30, 60, and 120 min following a 30-min aerosol dosing session. Effects on activity in a novel environment for 120 min after aerosol, and temperature, were measured in separate rats.

Results: We found sex-dependent differences in the pharmacokinetics of THC and its active (11-OH-THC) and inactive (11-COOH-THC) metabolites in the blood and brain, along with dose- and sex-dependent effects on anxiety-like and exploratory behaviors; namely, greater 11-OH-THC levels accompanied by greater behavioral effects in females at the low dose but similar hypothermic effects in both sexes at the high dose.

Conclusions: These results provide a benchmark for dosing adolescent rats with aerosolized (or "vaped") THC, which could facilitate adoption by other labs of this potentially human-relevant THC exposure model to understand cannabis effects on the developing brain.

Keywords: Anxiety; Blood; Brain; E-cigarette; Inhalation; Locomotion; Pharmacodynamics; Pharmacokinetics; THC; Vapor.

Figure 1:. Aerosol Apparatus and Experimental Timeline

The experimental timeline is shown, with aerosol (‘vapor’) exposure in occurring over 30 min (ten 5-sec THC puffs at regular intervals). Rats used for pharmacokinetic (PK) experiments were killed at the timepoints indicated by red lines. Rats used for pharmacodynamic experiments were placed in a novel environment for 2 hrs following aerosol dosing; the first 5 min was analyzed for center/surround time, and locomotion/rearing was measured for the remainder of the 2 hr test.

Figure 2.

Plasma concentrations of Δ⁹-THC and its first-pass metabolites, 11-OH-THC and 11-COOH-THC, after 30 min (t = 0) aerosol exposure of Δ⁹-THC. (A-C) show the lower, 25 mg/mL dose, (D-F) show the higher 100 mg/mL dose in male (black squares) or female (red circles) adolescent rats. Symbols represent the mean ± SEM, n = 4–5. Dashed line represents limit of quantification (LOQ; 20 pmol/mL), dotted line represents limit of detection (LOD; 5 or 10 pmol/mL) for each analyte respectively.

Figure 3.

Brain concentrations of Δ⁹-THC and its active first-pass metabolite, 11-OH-THC, after 30 min (t = 0) aerosol exposure of Δ⁹-THC. A) and B) show the lower, 25 mg/mL dose, B) and C) show the higher 100 mg/mL dose in male (black squares) or female (red circles) adolescents. Symbols represent the mean ± SEM, n = 4–5. Dashed line represents LOQ (20 pmol/mL), dotted line represents LOD (5 pmol/mL) for each analyte respectively. At both exposure levels, 11-COOH-THC was undetectable in brain tissue.

Figure 4:. Aerosolized THC Reduces Temperature and Increases Anxiety-Like Behavior:

A) Body temperature prior to aerosol exposure and after the 120min locomotor session held immediately after aerosol exposure is shown, with significant reductions present at the 100mg/ml (dark green) but not 25mg/ml dose. B) Change in body temperature from pre-aerosol to post locomotor testing is shown separately in females and males. No significant sex difference in THC vapor-induced hypothermia was observed. C) Percent time in the first 5min of exposure to a novel locomotor testing chamber spent in the exposed center of the chamber, an inverse assay of anxiety-like behavior is shown for both sexes, and each sex separately. D) Locomotor behavior (top) and rearing (bottom) during this initial 5 min period in which center-surround behavior was analyzed is depicted. *p<0.05 compared to vehicle.

Figure 5:. Aerosolized THC Suppresses Locomotion and Rearing:

A) Locomotion, as measured by distance travelled in the 2hr locomotor test, is shown in both sexes, as well as separately for females and males. B) The time course of locomotion is depicted in 30min bins across the 2hr session. Vertical rearing is shown using the same scheme, for C) the entire 2hr session, and D) in 30min bins. *p<0.05 compared to vehicle.