Effective active vaccination against methamphetamine in female rats

Abstract

Background: Immunotherapies directed against methamphetamine (MA) abuse have shown success in rodent models, however only a limited number of studies have investigated active vaccination in female mice and none in female rats. It is critical to determine if potential immunotherapeutic strategies generalize across sex, particularly for drugs that may produce significant sex-differences on behavioral or physiological endpoints.

Methods: Female Wistar rats were initially vaccinated with keyhole-limpet hemocyanin (KLH) or an anti-methamphetamine-KLH conjugate (MH6-KLH) three times over five weeks and implanted with radiotelemetry devices to assess locomotor activity and body temperature responses to MA. Rats were first exposed to MA via vapor inhalation (100mg/mL in propylene glycol) and then by injection (0.25-1.0mg/kg, i.p.) and vapor after a final vaccine boost.

Results: The MH6-KLH vaccine generated an increase in antibody titers across the initial 6-week, 3 immunization protocol and a restoration of titer after a week 14 booster. Locomotor stimulation induced by 0.25mg/kg MA, i.p, in the KLH group was prevented in the MH6-KLH group. MH6-KLH animals also exhibited an attenuated locomotor stimulation produced by 0.5mg/kg MA, i.p. No group differences in locomotion induced by vapor inhalation of MA were observed and body temperature was not differentially affected by MA across the groups, most likely because vapor inhalation of MA that produced similar locomotor stimulation resulted in ∼10-fold higher plasma MA levels.

Conclusions: This study confirms the efficacy of the MH6-KLH vaccine in attenuating the effects of MA in female rats.

Keywords: Female; Methamphetamine; Rat; Vaccine; Vapor inhalation.

Figure 1

Mean (N=8; ±SEM) antibody titer for female Wistar rats treated with the MH6-KLH vaccine (as indicated by vertical arrows). The timing of methamphetamine (MA) challenge experiments are indicated in shaded bars. A significant difference from week 1 is indicated by #, from week 14 by # and from week 20 by §.

Figure 2

Mean (±SEM) activity rates and body temperature for MH6-KLH (N=7) and KLH (N=8) female rats after inhalation of PG or d-methamphetamine (100 mg/mL in PG) vapor. A significant difference from both the baseline and PG vehicle is indicated by the open symbols and from the baseline by the gray shaded symbols. A significant difference between groups is indicated by & and between PG and MA inhalation within-group by #. Base= pre-inhalation baseline.

Figure 3

Mean (±SEM) activity rates for KLH (N=8) and MH6-KLH (N=5) female rats after administration of the Vehicle or d-methamphetamine (0.25, 0.5, 1.0 mg/kg, i.p.). Significant differences from the baseline and vehicle within group are indicated by the open symbols, from the baseline (only) by the gray shaded symbols and from the vehicle by *.

Figure 4

Mean (±SEM) activity rates for KLH (N=8) and MH6-KLH (N=5) female rats after administration of the Vehicle (Veh) or d-methamphetamine (MA; 0.25, 0.5, 1.0 mg/kg, i.p.) are directly compared for the first two hours. Significant differences from the Vehicle and 0.25 mg/kg within Group and Hour are indicated by §, from Vehicle (only) by # and from the 0.5 mg/kg condition by &.

Figure 5

Mean activity rates and body temperature for MH6-KLH (N=5) and KLH (N=6–8) female rats after inhalation of PG (20 minutes) or d-methamphetamine (100 mg/mL in PG; 40 or 20 minutes) vapor. Bars indicate SEM. A significant difference from both the baseline and PG vehicle within group is indicated by the open symbols and from the baseline (only) by the gray shaded symbols. A significant difference from the PG within group is indicated by * and a significant difference from the 60 minute time point within-group by #. Base= pre-inhalation baseline.

Figure 6

A) Standard curve generated for MA using blank plasma samples and known concentration of drug (0 – 500 ng/mL). Mean (N=4; ±SEM) Concentrations of MA in plasma 1 and 2 hours after B) i.p. injection and C) vapor inhalation. Plasma concentrations were determined by LCMS analysis. A significant effect of dose is indicated by *.