Electroencephalographic and behavioral convulsant effects of hydrobromide and hydrochloride salts of bupropion in conscious rodents

Abstract

A novel bromide salt of the antidepressant bupropion (bupropion HBr) has recently been developed and approved for use in the United States. Given previous use of bromides to treat seizures, and that the existing chloride salt of bupropion (HCl) can cause seizures, it is important to determine if the HBr salt may be less likely to cause seizures than the HCl salt. In the present animal studies this was evaluated by means of quantified electroencephalogram (EEG), observation, and the rotarod test in mice and rats. Both bupropion salts were tested at increasing equimolar doses administered intraperitoneally. The results in mice showed that bupropion HCl 125 mg/kg induced a significantly higher ten-fold increase in the mean number of cortical EEG seizures compared to bupropion HBr (7.50 +/- 2.56 vs 0.75 +/- 0.96; p = 0.045), but neither drug caused any brain injuries. In rats bupropion HBr 100 mg/kg induced single EEG seizure activity in the cortical and hippocampal (depth) electrodes and in significantly (p < 0.05) fewer rats (44%) compared to bupropion HCl, which induced 1 to 4 convulsions per rat in all rats (100%) dosed. The total duration of cortical seizures in bupropion HCl-treated rats was significantly longer than the corresponding values obtained in bupropion HBr-treated rats (424.6 seconds vs 124.5 seconds respectively, p < 0.05). Bupropion HCl consistently induced more severe convulsions at each dose level compared to bupropion HBr. Both treatments demonstrated a similar dose-dependent impairment of rotarod performance in mice. In conclusion, these findings suggest that bupropion HBr may have a significantly lower potential to induce seizures in mice and rats, particularly at higher doses, compared to bupropion HCl. Determination of this potential clinical advantage will require human studies. If confirmed by such studies, it is likely that this potential beneficial clinical benefit would be due to the presence of the bromide salt given the long history of the use of bromide to treat seizure disorders.

Keywords: EEG; bupropion hydrobromide; bupropion hydrochloride; mice; motor impairment; rats; seizures.

Figure 1

Representative 40X lens images of NeuN (red), TUNEL (green) and Fluoro-Jade B (green) staining of hippocampal sections of control mice with kainic acid-induced (KA-seizure) seizures (A, B, C, respectively) and of hippocampal [CA3], substantia nigra [SubNigr] and caudate-putamen [C–P] sections of mice with bupropion HCl- (D, E, F, J, K, L, P, Q, R) and bupropion HBr-induced (G, H, I, M, N, O, S, T, U) seizures 24 hours following the administration of drug (Kainic acid or 125 mg/kg of bupropion salt). A–C: (A) shows NeuN immunostaining of some hippocampal area CA3 neurons particularly in the lower right side of the panel indicating the presence of neurons and the absence of NeuN staining in the upper left part of the panel indicating the loss of NeuN immunoreactivity probably from degradation of NeuN antigen from the degenerative process resulting from kainic acid-induced seizures; (B) a number of TUNEL-positive cells in the upper left part of the panel (arrows) indicating presence of cell death from kainic acid-induced seizures; and (C) Fluoro-Jade B staining of degenerating neurons in hippocampal section stained bright yellow-green (arrows) against a dark background from kainic acid-induced seizures. D-U: NeuN immunostaining of large numbers of cells in sections from the hippocampus (D and G), substantia nigra (J and M) and caudate-putamen (P and S) of mice with bupropion HCl- and bupropion HBr-induced seizures, respectively, confirming the presence of neurons; note absence of TUNEL-positive cells and hence, any cell death resulting from the administration of bupropion HCl or bupropion HBr in the hippocampus (E or H), substantia nigra (K or N), and caudate-putamen (Q or T); and similarly, note absence of Fluoro-Jade B-positive cells indicating the absence of degenerating neurons resulting from the administration of bupropion HCl or bupropion HBr in the hippocampus (F or I), substantia nigra (L or O), and caudate-putamen (R or U). Notes: Bar in A, B, D, E, G, H, J, K, M, N, P, Q, S and T = 45 μm; and bar in C, F, I, L, O, R, and U = 500 μm. Abbreviations: TUNEL, terminal deoxynucleotidyl dUTP nick end labeling; F-JB, Fluoro-Jade B; Bup-HCl, bupropion HCl; Bup-HBr, bupropion HBr.

Figure 2

Five minutes of simultaneously recorded cortical (upper trace) and hippocampal (lower trace) EEG following the administration of bupropion hydrochloride 100 mg/kg intraperitoneally to a rat showing a seizure episode. A) The seizure lasted 35.2 seconds and 30.6 seconds in the cortex and hippocampus, respectively. The time and amplitude calibration bar is indicated between the traces to the left. The initial phase of the seizure activity is shown at higher time resolution. B) Behaviorally, hyperactivity/stereotypical behavior and facial clonus (Racine Class I) were observed simultaneously in the same rat. EEG = electroencephalogram.

Figure 3

Five minutes of simultaneously recorded cortical (upper trace) and hippocampal (lower trace) electroencephalogram (EEG) following the administration of bupropion hydrobromide 100 mg/kg intraperitoneally to a rat showing a seizure episode. A) The seizure lasted 16.9 seconds and 16.7 seconds in the cortex and hippocampus, respectively. The time and amplitude calibration bar is indicated between the traces to the left. The initial phase of the seizure activity is shown at higher time resolution. B) Behaviorally, hyperactivity/stereotypical behavior, facial clonus and forelimb clonus (Racine Class III) were observed simultaneously in the same rat.

Figure 4

Dose-response curves of the percent (%) of convulsing mice following the intraperitoneal (IP) administration of bupropion HCl (closed circles) and bupropion HBr (open circles) in mice. The CD₅₀ or Convulsing Dose₅₀ values, the convulsant doses required to induce convulsions in 50% of mice were 103 (CI: could not be estimated due to lack of data) and 110 (CI: 100.3, 179.9) mg/kg for the dose-response curves for bupropion HCl and bupropion HBr, respectively. Doses of bupropion HCl administered IP were 100, 125, and 150 mg/kg. Bupropion HBr doses were molar equivalents of the bupropion HCl doses. Each data point is the % of convulsing mice in n = 13 mice. Abbreviations: HCl, hydrochloride; HBr, hydrobromide.