Elsevier

Neuropharmacology

Volume 58, Issue 2, February 2010, Pages 404-412
Neuropharmacology

COX-2 inhibition controls P-glycoprotein expression and promotes brain delivery of phenytoin in chronic epileptic rats

https://doi.org/10.1016/j.neuropharm.2009.09.012Get rights and content

Abstract

Epileptic seizures drive expression of the blood–brain barrier efflux transporter P-glycoprotein via a glutamate/cyclooxygenase-2 mediated signalling pathway. Targeting this pathway may represent an innovative approach to control P-glycoprotein expression in the epileptic brain and to enhance brain delivery of antiepileptic drugs.

Therefore, we tested the effect of specific cyclooxygenase-2 inhibition on P-glycoprotein expression in two different status epilepticus models. Moreover, the impact of a cyclooxygenase-2 inhibitor on expression of the efflux transporter and on brain delivery of an antiepileptic drug was evaluated in rats with recurrent spontaneous seizures.

The highly selective cyclooxygenase-2 inhibitors SC-58236 and NS-398 both counteracted the status epilepticus-associated increase in P-glycoprotein expression in the parahippocampal cortex and the ventral hippocampus. In line with our working hypothesis, a sub-chronic 2-week treatment with SC-58236 in the chronic epileptic state kept P-glycoprotein expression at control levels. As described previously, enhanced P-glycoprotein expression in chronic epileptic rats was associated with a significant reduction in the brain penetration of the antiepileptic drug phenytoin. Importantly, the brain delivery of phenytoin was significantly enhanced by sub-chronic cyclooxygenase-2 inhibition in rats with recurrent seizures.

In conclusion, the data substantiate targeting of cyclooxygenase-2 in the chronic epileptic brain as a promising strategy to control the expression levels of P-glycoprotein despite recurrent seizure activity. Cyclooxygenase-2 inhibition may therefore help to increase concentrations of antiepileptic drugs at the target sites in the epileptic brain. It needs to be further evaluated whether the approach also enhances efficacy.

Introduction

Resistance to antiepileptic drugs continues to be a major challenge in the pharmacotherapy of epilepsy. Limitation of antiepileptic drug brain penetration is discussed as a putative contributor to therapeutic failure (Loscher and Potschka, 2005a). Several studies indicate that overexpression of blood–brain barrier efflux transporters occurs in response to epileptic seizure activity. Recently, it has been demonstrated that selective inhibition of the major efflux transporter P-glycoprotein (Pgp) enhances the brain uptake of antiepileptic drugs and improves the anticonvulsant response (Brandt et al., 2006, Clinckers et al., 2005, van Vliet et al., 2006). These findings point to a role of seizure-induced Pgp overexpression as a limiting factor in epilepsy pharmacotherapy.

Prevention of seizure-induced transporter overexpression may therefore render an elegant strategy to improve the outcome of antiepileptic drug therapy. Recently, we were able to identify cyclooxygenase as a central factor of a cascade that drives the transcriptional activation of the Pgp-encoding gene in the epileptic brain (Bauer et al., 2008). Cyclooxygenase-2 proved to mediate Pgp regulation in response to excess glutamate concentrations such as those occurring during epileptic seizures. In initial in vivo experiments, the non-selective COX inhibitor indomethacin as well as the COX-2 inhibitor celecoxib attenuated the status epilepticus-induced increase in capillary Pgp expression in the acute phase of the pilocarpine model (Bauer et al., 2008).

These data suggest that selective COX-2 inhibition constitutes a promising strategy to control Pgp expression despite recurrent seizure activity in the epileptic brain and to promote delivery of antiepileptic drugs to the brain. To test this hypothesis we determined the effect of selective COX-2 inhibition on Pgp expression and on phenytoin brain penetration in the chronic phase of a electrical post-status epilepticus model. In preparation for this experiment we evaluated the efficacy of two different highly-selective COX-2 inhibitors in the acute phase of two models with electrical or chemical induction of a status epilepticus.

Regarding our efforts to develop a preventive strategy it is of specific interest to further elucidate the complex mechanisms which drive Pgp expression in response to seizure activity. It has been speculated that enhanced expression of efflux transporters in the epileptic brain may represent a compensatory mechanism in response to a preceding seizure-associated leakiness of the blood–brain barrier. In line with this hypothesis, we addressed the question whether disturbance of BBB integrity triggers enhanced COX-2 signalling and subsequent induction of Pgp.

Section snippets

Animals

Ninety-seven female Wistar Unilever rats and 103 male Sprague–Dawley rats (Harlan-Winkelmann, Borchen, Germany, and Harlan Netherlands, Horst, The Netherlands) were used in the present study. Animals were kept under controlled environmental conditions (22 ± 2 °C, 50–60% humidity, 12-h dark/light cycle) with free access to tap water and standard feed. Animals for experiments were allowed to adapt to the new environment for at least 1 week. All animal protocols were approved by the Institutional

Onset and course of status epilepticus

Seventy-two percent of NS-398 treated animals (n = 16 out of 22) developed a status epilepticus in response to repeated injections of the cholinomimetic pilocarpine. In the vehicle-treated group a status epilepticus was successfully induced in 63% of the animals (n = 20 out of 32). No significant difference was observed in the amount of pilocarpine required to induce a status epilepticus. In NS-398 treated rats a mean pilocarpine dosage of 39.4 ± 6.0 mg/kg was administered prior to onset of

Discussion

Our study demonstrates that selective COX-2 inhibition efficaciously controls Pgp expression in the epileptic brain. Consistent with these data selective COX-2 inhibition was substantiated as a promising strategy to promote delivery of the antiepileptic drug phenytoin to the brain.

Numerous studies have indicated that seizure-associated induction of the BBB efflux transporter Pgp is a common feature in a variety of acute seizure and chronic epilepsy models (Potschka et al., 2004, Rizzi et al.,

Acknowledgements

We acknowledge Pfizer for providing SC-58236, Merial for providing NS-398, Rien de Rijke and Wouter Dieters for phenytoin analysis in plasma and brain samples as well as Heidrun Zankl and Andrea Wehmeyer for their excellent technical assistance. This research was supported by the Epilepsy Institute in The Netherlands (SEIN)-Lopes da Silva fellowship (to EAvV), the EU-FP7-project NeuroGlia Grant Agreement No. 202167 (to EA), Nationaal Epilepsie Fonds grant 07-19 (to JG) and the grant DFG PO

References (32)

  • H.A. Volk et al.

    Increased expression of the multidrug transporter P-glycoprotein in limbic brain regions after amygdala-kindled seizures in rats

    Epilepsy Res.

    (2004)
  • B. Bauer et al.

    Seizure-induced up-regulation of P-glycoprotein at the blood–brain barrier through glutamate and cyclooxygenase-2 signaling

    Mol. Pharmacol.

    (2008)
  • R. Clinckers et al.

    Quantitative in vivo microdialysis study on the influence of multidrug transporters on the blood–brain barrier passage of oxcarbazepine: concomitant use of hippocampal monoamines as pharmacodynamic markers for the anticonvulsant activity

    J. Pharmacol. Exp. Ther.

    (2005)
  • A. Dhir et al.

    Rofecoxib potentiates the anticonvulsant effect of topiramate

    Inflammopharmacology

    (2008)
  • A. Dhir et al.

    Rofecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor potentiates the anticonvulsant activity of tiagabine against pentylenetetrazol-induced convulsions in mice

    Inflammopharmacology

    (2006)
  • J.A. Gorter et al.

    Progression of spontaneous seizures after status epilepticus is associated with mossy fibre sprouting and extensive bilateral loss of hilar parvalbumin and somatostatin-immunoreactive neurons

    Eur. J. Neurosci.

    (2001)
  • Cited by (125)

    • Microglia in epilepsy

      2023, Neurobiology of Disease
    • Astrocyte-neuron circuits in epilepsy

      2023, Neurobiology of Disease
    View all citing articles on Scopus
    View full text