Evidences for pharmacokinetic interaction of riluzole and topiramate with pilocarpine in pilocarpine-induced seizures in rats

Riluzole is Effective on Spinal Decompression for Treating Acute Spinal Injury When Compared With Methylprednisolone and the Combination of Two Drugs: In Vivo Rat Model

STUDY DESIGN

Randomized controlled animal experiment.

OBJECTIVES

To determine and compare the efficacy of riluzole, MPS and the combination of two drugs in a rat model with acute spinal trauma, electrophysiologically and histopathologically.

METHODS

59 rats were divided into 4 groups as control, riluzole (6 mg/kg, every 12 hours for 7 days), MPS (30 mg/kg, 2nd and 4th hours after injury) and riluzole + MPS. Spinal trauma was created and the subjects were followed for 7 days. Electrophysiological recordings were made via neuromonitoring. The subjects were sacrificed and histopathological examination was made.

RESULTS

For the amplitude values, mean alteration in the period from the spinal cord injury to the end of the 7th day is 15.89 ± 20.00%, 210.93 ± 199.44%, 24.75% ± 10.13% increase and 18.91 ± 30.01% decrease for the control, riluzole, riluzole + MPS and MPS groups, respectively. Although the riluzole treatment group produced the greatest increase in amplitude, it was observed that no treatment provided a significant improvement compared to the control group, in terms of latency and amplitude. It was observed that there was significantly less cavitation area in the riluzole treatment group compared to the control group (P = .020). (P < .05).

CONCLUSIONS

Electrophysiologically, no treatment was found to provide significant improvement. Histopathologically, it was observed that riluzole provided significant neural tissue protection.

An In Vivo Electroencephalographic Analysis of the Effect of Riluzole against Limbic and Absence Seizure and Comparison with Glutamate Antagonists

BACKGROUND

Riluzole (RLZ) has demonstrated neuroprotective effects in several neurological disorders. These neuroprotective effects seem to be mainly due to its ability to inhibit the excitatory glutamatergic neurotransmission, acting on different targets located both at the presynaptic and postsynaptic levels.

METHODS

In the present study, we evaluated the effects of Riluzole (RLZ) against limbic seizures, induced by AMPA, kainate, and NMDA receptor agonists in Sprague-Dawley rats, and in a well-validated genetic model of absence epilepsy, the WAG/Rij rat. Furthermore, in this latter model, we also studied the effect of RLZ in co-administration with the competitive NMDA receptor antagonist, CPP, or the non-competitive AMPA receptor antagonist, THIQ-10c, on spike-wave discharges (SWDs) in WAG/Rij rats, to understand the potential involvement of AMPA and NMDA receptors in the anti-absence effect of RLZ.

RESULTS

In Sprague-Dawley rats, RLZ pretreatment significantly reduced the limbic seizure severity induced by glutamatergic agonists, suggesting an antagonism of RLZ mainly on NMDA rather than non-NMDA receptors. RLZ also reduced SWD parameters in WAG/Rij rats. Interestingly, the co-administration of RLZ with CPP did not increase the anti-absence activity of RLZ in this model, advocating a competitive effect on the NMDA receptor. In contrast, the co-administration of RLZ with THIQ-10c induced an additive effect against absence seizure in WAG/Rij rats.

CONCLUSIONS

these results suggest that the antiepileptic effects of RLZ, in both seizure models, can be mainly due to the antagonism of the NMDA glutamatergic receptors.

Comparative Anticonvulsant Study of Epoxycarvone Stereoisomers

Stereoisomers of the monoterpene epoxycarvone (EC), namely (+)-cis-EC, (-)-cis-EC, (+)-trans-EC, and (-)-trans-EC, were comparatively evaluated for anticonvulsant activity in specific methodologies. In the pentylenetetrazole (PTZ)-induced anticonvulsant test, all of the stereoisomers (at 300 mg/kg) increased the latency to seizure onset, and afforded 100% protection against the death of the animals. In the maximal electroshock-induced seizures (MES) test, prevention of tonic seizures was also verified for all of the isomers tested. However, the isomeric forms (+) and (-)-trans-EC showed 25% and 12.5% inhibition of convulsions, respectively. In the pilocarpine-induced seizures test, all stereoisomers demonstrated an anticonvulsant profile, yet the stereoisomers (+) and (-)-trans-EC (at 300 mg/kg) showed a more pronounced effect. A strychnine-induced anticonvulsant test was performed, and none of the stereoisomers significantly increased the latency to onset of convulsions; the stereoisomers probably do not act in this pathway. However, the stereoisomers (+)-cis-EC and (+)-trans-EC greatly increased the latency to death of the animals, thus presenting some protection. The four EC stereoisomers show promise for anticonvulsant activity, an effect emphasized in the isomers (+)-cis-EC, (+)-trans-EC, and (-)-trans-EC for certain parameters of the tested methodologies. These results serve as support for further research and development of antiepileptic drugs from monoterpenes.

Pilocarpine-induced convulsive activity is limited by multidrug transporters at the rodent blood-brain barrier

As a result of the growing availability of genetically engineered mouse lines, the pilocarpine post-status epilepticus (SE) model of temporal lobe epilepsy is increasingly used in mice. A discrepancy in pilocarpine sensitivity in FVB/N wild-type versus P-glycoprotein (PGP)-deficient mice precipitated the investigation of the interaction between pilocarpine and two major multidrug transporters at the blood-brain barrier. Doses of pilocarpine necessary for SE induction were determined in male and female wild-type and PGP-deficient mice. Brain and plasma concentrations were measured following low (30-50 mg⋅kg(-1) i.p.) and/or high (200 mg⋅kg(-1) i.p.) doses of pilocarpine in wild-type mice, and mice lacking PGP, breast cancer resistance protein (BCRP), or both transporters, as well as in rats with or without pretreatment with lithium chloride or tariquidar. Concentration equilibrium transport assays (CETA) were performed using cells overexpressing murine PGP or BCRP. Lower pilocarpine doses were necessary for SE induction in PGP-deficient mice. Brain-plasma ratios were higher in mice lacking PGP or PGP and BCRP, which was also observed after pretreatment with tariquidar in mice and in rats. Lithium chloride did not change brain penetration of pilocarpine. CETA confirmed transport of pilocarpine by PGP and BCRP. Pilocarpine is a substrate of PGP and BCRP at the rodent blood-brain barrier, which restricts its convulsive action. Future studies to reveal whether strain differences in pilocarpine sensitivity derive from differences in multidrug transporter expression levels are warranted.

Riluzole attenuates the effects of chemoconvulsants acting on glutamatergic and GABAergic neurotransmission in the planarian Dugesia tigrina

Planarians, the non-parasitic flatworms, display dose-dependent, distinct (C-like and corkscrew-like) hyperkinesias upon exposure to 0.001-10 mM aqueous solutions of glutamatergic agonists (L-glutamate and N-methyl-D-aspartate (NMDA)) and 0.001-5 mM concentrations of the glutamate decarboxylase (GAD) inhibitor (semicarbazide). In the planarian seizure-like activity (PSLA) experiments the three chemoconvulsants displayed the following order of potency (EC50): L-glutamate (0.6mM)>NMDA (1.4 mM)>semicarbazide (4.5mM). Planarian hyperkinesias behavior counting experiments also revealed that riluzole (0.001 to 1mM), an anti-convulsive agent, displayed no significant behavioral activity by itself, but attenuated hyperkinesias elicited by the three chemoconvulsants targeting either glutamatergic or GABAergic neurotransmission with the following order of potency (IC50): NMDA (44.7 µM)>semicarbazide (88.3 µM)>L-glutamate (160 µM). Further, (+)-MK-801, a specific NMDA antagonist, alleviated 3mM NMDA (47%) or 3mM L-glutamate (27%) induced planarian hyperkinesias. The results provide pharmacological evidence for the presence of glutamatergic receptor-like and semicarbazide sensitive functional GAD enzyme-like proteins in planaria in addition to demonstrating, for the first time, the anti-convulsive effects of riluzole in an invertebrate model. High performance liquid chromatography coupled with fluorescence detection (HPLC-F) analysis performed on planarian extracts post no drug treatment (control) or treatment with 3mM semicarbazide, combination of 3mM semicarbazide and 0.1 mM riluzole, or 0.1 mM riluzole revealed that 3 mM semicarbazide induced 35% decrease in the GABA levels and a combination of 3mM semicarbazide and 0.1 mM riluzole induced 42% decrease in glutamate levels with respect to the control group.

Effect of ciprofloxacin and grapefruit juice on oral pharmacokinetics of riluzole in Wistar rats

Objectives

The objective of this study was to explore potential drug–drug/food interactions of ciprofloxacin and grapefruit juice, known hepatic cytochrome P450 (CYP) 1A2 inhibitors, on single-dose oral pharmacokinetics of riluzole, a substrate of CYP 1A2 enzymes.

Methods

Pharmacokinetic parameters of riluzole were determined in Wistar rats after single-dose co-administration with ciprofloxacin and grapefruit juice. In-vitro metabolic inhibition studies using rat and human liver microsomes and intestinal absorption studies of riluzole in a rat everted gut-sac model were conducted to elucidate the mechanism of interaction. A validated HPLC method was employed to quantify riluzole in the samples obtained in various studies.

Key findings

Co-administration of ciprofloxacin with riluzole caused significant increase in systemic exposure of riluzole (area under the curve, maximum plasma concentration and mean residence time were found to increase). Co-administration of grapefruit juice with riluzole did not cause any significant difference in the pharmacokinetic parameters of riluzole. In-vitro metabolism studies demonstrated significant inhibition of riluzole metabolism when it was co-incubated with ciprofloxacin or grapefruit juice. No significant change was observed in apparent permeability of riluzole.

Conclusions

Co-administration of ciprofloxacin with riluzole increases the systemic levels of riluzole and thereby the oral pharmacokinetic properties of riluzole while co-administration of grapefruit juice with riluzole has no significant effect.

Characterizing the effects of Eugenol on neuronal ionic currents and hyperexcitability

RATIONALE

Eugenol (EUG, 4-allyl-2-methoxyphenol), the main component of essential oil extracted from cloves, has various uses in medicine because of its potential to modulate neuronal excitability. However, its effects on the ionic mechanisms remains incompletely understood.

OBJECTIVES

We aimed to investigate EUG's effects on neuronal ionic currents and excitability, especially on voltage-gated ion currents, and to verify the effects on a hyperexcitability-temporal lobe seizure model.

METHODS

With the aid of patch-clamp technology, we first investigated the effects of EUG on ionic currents in NG108-15 neuronal cells differentiated with cyclic AMP. We then used modified Pinsky-Rinzel simulation modeling to evaluate its effects on spontaneous action potentials (APs). Finally, we investigated its effects on pilocarpine-induced seizures in rats.

RESULTS

EUG depressed the transient and late components of I(Na) in the neurons. It not only increased the degree of I(Na) inactivation, but specifically suppressed the non-inactivating I(Na) (I(Na(NI))). Its inhibition of I (Na(NI)) was reversed by tefluthrin. In addition, EUG diminished L-type Ca(2+) current and delayed rectifier K(+) current only at higher concentrations. EUG's effects on APs frequency reduction was verified by the simulation modeling. In pilocarpine-induced seizures, the EUG-treated rats showed no shorter seizure latency but a lower seizure severity and mortality than the control rats. The EUG's effect on seizure severity was occluded by the I(Na(NI)) antagonist riluzole.

CONCLUSION

The synergistic blocking effects of I (Na) and I(Na(NI)) contributes to the main mechanism through which EUG affects the firing of neuronal APs and modulate neuronal hyperexcitability such as pilocarpine-induced temporal lobe seizures.

Recent developments regarding voltage-gated sodium channel blockers for the treatment of inherited and acquired neuropathic pain syndromes

Chronic and neuropathic pain constitute significant health problems affecting millions of individuals each year. Pain sensations typically originate in sensory neurons of the peripheral nervous system which relay information to the central nervous system (CNS). Pathological pain sensations can arise as result of changes in excitability of these peripheral sensory neurons. Voltage-gated sodium channels are key determinants regulating action potential generation and propagation; thus, changes in sodium channel function can have profound effects on neuronal excitability and pain signaling. At present, most of the clinically available sodium channel blockers used to treat pain are non-selective across sodium channel isoforms and can contribute to cardio-toxicity, motor impairments, and CNS side effects. Numerous strides have been made over the last decade in an effort to develop more selective and efficacious sodium channel blockers to treat pain. The purpose of this review is to highlight some of the more recent developments put forth by research universities and pharmaceutical companies alike in the pursuit of developing more targeted sodium channel therapies for the treatment of a variety of neuropathic pain conditions.

Inhibition of Navβ4 peptide-mediated resurgent sodium currents in Nav1.7 channels by carbamazepine, riluzole, and anandamide

Paroxysmal extreme pain disorder (PEPD) and inherited erythromelalgia (IEM) are inherited pain syndromes arising from different sets of gain-of-function mutations in the sensory neuronal sodium channel isoform Nav1.7. Mutations associated with PEPD, but not IEM, result in destabilized inactivation of Nav1.7 and enhanced resurgent sodium currents. Resurgent currents arise after relief of ultra-fast open-channel block mediated by an endogenous blocking particle and are thought to influence neuronal excitability. As such, enhancement of resurgent currents may constitute a pathological mechanism contributing to sensory neuron hyperexcitability and pain hypersensitivity associated with PEPD. Furthermore, pain associated with PEPD, but not IEM, is alleviated by the sodium channel inhibitor carbamazepine. We speculated that selective attenuation of PEPD-enhanced resurgent currents might contribute to this therapeutic effect. Here we examined whether carbamazepine and two other sodium channel inhibitors, riluzole and anandamide, exhibit differential inhibition of resurgent currents. To gain further insight into the potential mechanism(s) of resurgent currents, we examined whether these inhibitors produced correlative changes in other properties of sodium channel inactivation. Using stably transfected human embryonic kidney 293 cells expressing wild-type Nav1.7 and the PEPD mutants T1464I and M1627K, we examined the effects of the three drugs on Navβ4 peptide-mediated resurgent currents. We observed a correlation between resurgent current inhibition and a drug-mediated increase in the rate of inactivation and inhibition of persistent sodium currents. Furthermore, although carbamazepine did not selectively target resurgent currents, anandamide strongly inhibited resurgent currents with minimal effects on the peak transient current amplitude, demonstrating that resurgent currents can be selectively targeted.