Abstracts

Rationale: Retigabine is a new-generation anticonvulsant drug that exerts therapeutic action through the activation of KCNQ channel dependent M-type potassium currents. While retigabine has been extensively studied in adult animals using a wide variety of seizure models, its effects in developing animals have only recently been examined. Because many anticonvulsant drugs, with diverse mechanisms of action, induce profound increases in developmental apoptosis in the brains of immature rats, we examined retigabine for this effect. In parallel we examined the pharmacokinetic profile of retigabine in the neonatal rat.Methods: Postnatal day (P) 7 rat pups (Sprague-Dawley) were treated with vehicle or with doses of retigabine (5, 15, 30 mg/kg) which fall within the anticonvulsant range (Forcelli et al, Epilepsy Res, 2012). As a positive control for the induction of apoptosis, animals were treated with phenobarbital (75mg/kg). Animals survived for 6h or 24h and then were perfused and brains processed using the AminoCupricSilver method. Because pilot studies showed that toxicity induced by retigabine was detectable at 6h but not 24h and because retigabine has a short half-life (as described below) we also examined other drugs with short half-lifes (levetiracetam, lamotrigine) to determine if a similar pattern existed. Blood was collected 1 to 24 h after administration and analyzed for levels of retigabine and n-acetylretigabine by mass spectroscopy.Results: Phenobarbital induced neuronal apoptosis in cingulate, orbitofrontal, retrosplenial, motor, and somatosensory cortices, as well as thalamus, nucleus accumbens and striatum. Retigabine induced cell dearth only in a subset of these regions: at each dose tested it increased cell death in nucleus accumbens and orbitofrontal cortex. At 15mg/kg and 30mg/kg cell death was also detected in frontal cortex and retrosplenial cortex. We found that the 5mg/kg dose yielded a Cmax of 2334ng/ml, 15mg/kg = 4859ng/ml, 30mg/kg = 10859ng/ml. The serum half-life ranged from 4.6-5.2h, which is longer than the half-life reported in adult animals.Conclusions: Our data suggest that retigabine, like many other AEDs, can induce acute cellular neurotoxicity in the developing brain in a region-specific and dose-dependent manner. These findings also underscore the importance of evaluating early time points for assessment of drug toxicity. Study supported by a Research Grant from GlaxoSmithKline.