Dimethyl sulfoxide's impact on epileptiform activity in a mouse model of chronic temporal lobe epilepsy

Abstract

In the quest for novel treatments for patients with drug-resistant seizures, poor water solubility of potential drug candidates is a frequent obstacle. Literature indicated that the highly efficient solvent dimethyl sulfoxide (DMSO) may have a confounding influence in epilepsy research, reporting both pro- and antiepileptic effects. In this study, we aim to clarify the effects of DMSO on epileptiform activity in one of the most frequently studied models of chronic epilepsy, the intrahippocampal kainic acid (IHKA) mouse model, and in a model of acute seizures. We show that 100 % DMSO (in a volume of 1.5 µl/g corresponding to 1651 mg/kg) causes a significant short-term anti-seizure effect in epileptic IHKA mice of both sexes, but does not affect the threshold of acute seizures induced by pentylenetetrazol (PTZ). These findings highlight that the choice of solvent and appropriate vehicle control is crucial to minimize undesirable misleading effects and that drug candidates exclusively soluble in 100 % DMSO need to be modified for better solubility already at initial testing.

Keywords: DMSO; Dimethyl sulfoxide; Intrahippocampal kainic acid model; Pentylenetetrazol-induced acute seizures; Temporal lobe epilepsy.

Fig. 1

Effect of different concentrations of DMSO on spike trains and HPDs in the IHKA mouse model of TLE. (A) Experimental timeline for testing of different concentrations of DMSO (1 %, 10 %, 30 % and 100 % in a volume of 1.5 μl/g corresponding to 16.5 mg/kg, 165.1 mg/kg, 495.2 mg/kg and 1651 mg/kg) vs. 0.9 % saline (sal) s.c. in mice with established chronic epilepsy 4–8 weeks after IHKA. Treatment schedules were designed according to a Latin square crossover design with 72 h minimum resting period between injections. (B) Number [% of pre] and (D) cumulative duration [% of pre] of spike trains and (C) number [% of pre] and (E) cumulative duration [% of pre] of HPDs in female and male IHKA mice in the 5–34 min after treatment with 1 %, 10 %, 30 % and 100 % DMSO compared to saline. Regarding HPDs, number and cumulative duration were significantly reduced after 100 % DMSO in both females and males in comparison to saline. 100 % DMSO in male mice resulted in a significant reduction of the cumulative duration of spike trains compared to saline. Data (females n = 9, males n = 8) are presented as % normalized to the pretreatment period (mean ± SD) and were analyzed with a 2-way linear mixed model for repeated measures followed by Dunnett’s multiple comparisons test. * p < 0.05; * * p < 0.01.

Fig. 2

Banded power after different concentrations of DMSO in the IHKA mouse model of TLE. Power in the (A) 1–4 Hz, (B) 4–8 Hz, (C) 8–13 Hz, (D) 13–30 Hz and (E) 30–80 Hz frequency bands as well as the (F) coastline were calculated for the 5–34 min after treatment normalized to the pretreatment period. 100 % DMSO caused a significant decrease in the 4–8 Hz, 8–13 Hz and 13–30 Hz bands in both sexes and in the females additionally in the 30–80 Hz band. Data (females n = 9, males n = 8) are presented as % normalized to the pretreatment period (mean ± ŞD) and were analyzed with a 2-way linear mixed model for repeated measures followed by Dunnett’s multiple comparisons test. * p=<0.05; ** p=<0.01. (G) Representative spectrogram before and after 100 % DMSO showing a reduction.

Fig. 3

PTZ-induced acute seizure threshold after different concentrations of DMSO. Seizure threshold [mg PTZ/kg] determined by PTZ tail-vein infusion in untreated animals or pretreated with 30 % or 100 % DMSO showed no statistically significant differences. Data (n = 3–5) are expressed as mean ± SD and were analyzed with ordinary 2-way ANOVA.