Pharmacokinetics and central accumulation of delta-9-tetrahydrocannabinol (THC) and its bioactive metabolites are influenced by route of administration and sex in rats

Abstract

Up to a third of North Americans report using cannabis in the prior month, most commonly through inhalation. Animal models that reflect human consumption are critical to study the impact of cannabis on brain and behaviour. Most animal studies to date utilize injection of delta-9-tetrahydrocannabinol (THC; primary psychoactive component of cannabis). THC injections produce markedly different physiological and behavioural effects than inhalation, likely due to distinctive pharmacokinetics. The current study directly examined if administration route (injection versus inhalation) alters metabolism and central accumulation of THC and metabolites over time. Adult male and female Sprague-Dawley rats received either an intraperitoneal injection or a 15-min session of inhaled exposure to THC. Blood and brains were collected at 15, 30, 60, 90 and 240-min post-exposure for analysis of THC and metabolites. Despite achieving comparable peak blood THC concentrations in both groups, our results indicate higher initial brain THC concentration following inhalation, whereas injection resulted in dramatically higher 11-OH-THC concentration, a potent THC metabolite, in blood and brain that increased over time. Our results provide evidence of different pharmacokinetic profiles following inhalation versus injection. Accordingly, administration route should be considered during data interpretation, and translational animal work should strongly consider using inhalation models.

Figure 1

Vapor delivery system. (A) Illustration of passive vapor delivery system: Schematic of vapor apparatus components with direction of air-flow (adapted from Freels et al.). Briefly, the vapor inhalation system uses machinery similar to electronic cigarettes to deliver distinct “puffs” of vapor within airtight chambers. A vacuum compressor pulls ambient room air through an intake valve at a constant rate of 1 L per minute. At set intervals THC-dominant cannabis extract is vaporized combining with the constant ambient air flow for delivery into the chamber. Air (and vapor) are evacuated through the back of the chamber via the vacuum compressor, filtered and ventilated out of the building. (B) Image of passive vapor exposure: Picture of a male SD rat within the vapor apparatus.

Figure 2

Body temperature. (A) Male temperature: Data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) with a solid and dashed green line indicates that THC-INH and THC-INJ respectively differ from one or more other groups. THC-INH resulted in immediate hypothermia at 30-min (THC-INH < all groups at *p < 0.05) and at 60-min (THC-INH < CON-INJ and THC-INJ at *p < 0.05), whereas THC-INJ resulted in delayed hypothermia at 90-min (THC-INJ < CON-INJ and THC-INH at *p < 0.05) and at 240-min (THC-INJ < all groups at **p < 0.01). (B) Female temperature: data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) with a solid and dashed green line indicates that THC-INH and THC-INJ respectively differ from one or more other groups. THC-INH resulted in immediate hypothermia at 30-min (THC-INH < all groups at **p < 0.01) and at 60-min (THC-INH < all groups at *p < 0.05), whereas THC-INJ resulted in delayed hypothermia at 90-min (THC-INJ < all groups at *p < 0.05) and at 240-min (THC-INJ < CON-INJ and THC-INH at **p < 0.01).

Figure 3

THC Chromatogram and levels in blood and brain. (A) LC-MS Chromatogram: THC (black line) and THC-d3 (grey line) overlapping peaks at 2.7 min. (B) Blood levels: data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) indicates an administration difference with INH > INJ at 15-min at ****p < 0.0001. Presence of (^#) indicates a timepoint difference with green and purple lines indicating an INH and INJ difference respectively; specifically, INH-15 > all timepoints and INH-30 > INH-60/90/240 at ^#p < 0.05, whereas INJ-30 > all timepoints and INJ-240 < all timepoints at ^##p < 0.01. Presence of (^$) indicates a sex difference; specifically, female-INH > female-INJ at ^$$$p < 0.001 and male-INJ > female-INJ at ^$$$p < 0.001). (C) Brain levels: data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) indicates an administration difference with INH > INJ at 15, 30, and 60-min at **p < 0.01. Presence of (^#) indicates a timepoint difference with green and purple lines indicating an INH and INJ difference respectively; specifically, INH-15, 30, and 60 > INH-90 and 240 at ^##p < 0.01, whereas INJ-90 > INJ-15 and 240 at ^##p < 0.01. Presence of (^$) indicates a sex difference with males > females at ^$$p < 0.01.

Figure 4

11-OH-THC chromatogram and levels in blood and brain. (A) LC-MS Chromatogram: 11-OH-THC (black line) and 11-OH-THC-d3 (grey line) peaks at 2.0 min. (B) Blood levels: data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) indicates an administration difference with INH < INJ at all timepoints at *p < 0.05. Presence of (^#) indicates a timepoint difference with purple lines indicating an INJ difference where INJ-15 < INJ-30, 60, and 90 at ^#p < 0.05 and INJ-240 < INJ-30, 60, and 90 at ^###p < 0.001. Presence of (^$) indicates a sex difference; specifically, females > males at ^$p < 0.05. (C) Brain levels: data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) indicates an administration difference with INH < INJ at 30, 60, and 90-min at ***p < 0.001. Presence of (^#) indicates a timepoint difference with purple lines indicating an INJ difference where INJ-15 and 240 < INJ-30, 60, and 90 at ^###p < 0.001. Presence of (^$) indicates a sex difference; specifically, male-INH < male-INJ at ^$$$p < 0.001, female-INH < female-INJ at ^$$$$p < 0.0001, and male-INJ < female-INJ at ^$$$$p < 0.0001.

Figure 5

THC-COOH chromatogram and levels in blood and brain. (A) LC-MS Chromatogram: THC-COOH (black line) and THC-COOH-d3 (grey line) peaks at 2.0 min. (B) Blood levels: Data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) indicates an administration difference with INH < INJ at 30, 60, 90 and 240-min at *p < 0.05. Presence of (^#) indicates a timepoint difference with purple lines indicating an INJ difference where INJ-15 < all timepoints at ^##p < 0.01. Presence of (^$) indicates a sex difference; specifically, male-INH < male-INJ and female-INH < female-INJ at ^$$$$p < 0.0001, and male-INJ < female-INJ at ^$$$$p < 0.0001. (C) Brain levels: Data are presented as mean ± SEM; n = 5–6 for each group. Presence of (*) indicates an administration difference with INH > INJ at ****p < 0.0001. Presence of (^$) indicates a sex difference with males < females at ^$$$p < 0.001.