Anticonvulsant and reproductive toxicological studies of the imidazole-based histamine H3R antagonist 2-18 in mice

Abstract

The imidazole-based H3R antagonist 2-18 with high in vitro H3R antagonist affinity, excellent in vitro selectivity profile, and high in vivo H3R antagonist potency was tested for its anticonvulsant effect in maximal electroshock (MES)-induced convulsions in mice having valproic acid (VPA) as a reference antiepileptic drug (AED). Additionally, H3R antagonist 2-18 was evaluated for its reproductive toxicity in the same animal species. The results show that acute systemic administration (intraperitoneal; i.p.) of H3R antagonist 2-18 (7.5, 15, 30, and 60 mg/kg, i.p.) significantly and dose dependently protected male as well as female mice against MES-induced convulsion. The protective action observed for H3R antagonist 2-18 in both mice sexes was comparable to that of VPA and was reversed when mice were pretreated with the selective H3R agonist (R)-alpha-methylhistamine (RAMH, 10 mg/kg, i.p.). Moreover, the results show that acute systemic administration of single (7.5, 15, 30, or 60 mg/kg, i.p.) or multiple doses (15×3 mg/kg, i.p.) of H3R antagonist 2-18 on gestation day (GD) 8 or 13 did not affect the maternal body weight of mice when compared with the control group. Furthermore, no significant differences were observed in the average number of implantations and resorptions between the control and H3R antagonist 2-18-treated group at the early stages of gestation and the organogenesis period. However, oral treatment with H3R antagonist 2-18 (15 mg/kg) on GD 8 induced a reduced number of live embryos when compared with the i.p.-treated mice. In addition, no significant changes in the fetal body and placental weights were observed after injection of H3R antagonist 2-18 with all selected doses. However, three dose groups of i.p. and oral 15 mg/kg on GD 13 significantly affected the placental weight when compared with control group. Notably, the treatment of pregnant female with the H3R antagonist 2-18 did not produce significant malformation in the fetus in both groups. In conclusion, the novel H3R antagonist 2-18 proves to be a very safe compound and displays a low incidence of malformations, demonstrating that H3R antagonist 2-18 may have a potential future therapeutic value in epilepsy.

Keywords: H3R receptor antagonist; anticonvulsant; gestation; malformation; maximal electroshock; mice.

Figure 1

Chemical structure, in vitro affinities, and in vivo H3R antagonist potency of 2-18. Note: Values previously published. Abbreviations: ED₅₀, effective dose affecting 50% of mice receiving the compound 2-18; p.o., peroral.

Figure 2

Anticonvulsant effect of acute systemic administration of H3R antagonist 2-18 on MES-induced seizure in male adult mice. Notes: Anticonvulsant effects of VPA (300 mg/kg, i.p.), test compound 2-18 (7.5, 15, 30, and 60 mg/kg, i.p.), and co-injection of test compound 2-18 (60 mg/kg, i.p.) with RAMH (10 mg/kg, i.p.) on duration of THLE induced in MES model in male adult mice. Each value represents mean ± SEM (n=8). ***P<0.001 versus saline- and 2-18 (7.5 mg)-treated groups. ^#P<0.001 versus 2-18 (7.5 mg)- and 2-18 (15 mg)-treated groups. ^$P<0.05 versus 2-18 (30 mg)-treated group. Abbreviations: MES, maximal electroshock; VPA, valproic acid; i.p., intraperitoneal; RAMH, R-(α)-methylhistamine; THLE, tonic hind limb extension; SAL, saline; SEM, standard error of mean.

Figure 3

Anticonvulsant effect of acute systemic administration of H3R antagonist 2-18 on MES-induced seizure in female adult mice. Notes: Anticonvulsant effects of VPA (300 mg/kg, i.p.), test compound 2-18 (7.5, 15, 30, and 60 mg/kg, i.p.), and co-injection of test compound 2-18 (60 mg/kg, i.p.) with RAMH (10 mg/kg, i.p.) on duration of THLE induced in MES model in female adult mice. Each value represents mean ± SEM (n=8). ***P<0.001 versus saline- and 2-18 (7.5 mg)-treated groups. ^#P<0.001 versus 2-18 (7.5 mg)- and 2-18 (15 mg)-treated groups. ^$P<0.05 versus 2-18 (30 mg)-treated group. ^&Full protection. Abbreviations: MES, maximal electroshock; VPA, valproic acid; i.p., intraperitoneal; RAMH, R-(α)-methylhistamine; THLE, tonic hind limb extension; SAL, saline; SEM, standard error of mean.

Figure 4

Comparison of dose-dependent anticonvulsant effect of acute systemic administration of H3R antagonist 2-18 on MES-induced seizure in male and female adult mice. Notes: Each value represents mean ± SEM (n=8). ^&Full protection. Abbreviations: MES, maximal electroshock; THLE, tonic hind limb extension; VPA, valproic acid; SAL, saline; SEM, standard error of mean.