The anti-hyperalgesic activity of retigabine is mediated by KCNQ potassium channel activation

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Abstract
Retigabine (N-(2-amino-4-(4-fluorobenzylamino)-phenyl) carbamic acid ethyl ester) has a broad anticonvulsant spectrum and is currently in clinical development for epilepsy. The compound has an opening effect on neuronal KCNQ channels. At higher concentrations an augmentation of gamma-aminobutyric acid (GABA) induced currents as well as a weak blocking effect on sodium and calcium currents were observed. The goal of this study was to characterise the activity of retigabine in models of acute and neuropathic pain and to investigate if the potassium channel opening effect of retigabine contributes to its activity. Retigabine was tested in mice and rats in the tail flick model of acute pain and in the nerve ligation model with tight ligation of the 5th spinal nerve (L5) using both thermal and tactile stimulation. While retigabine like gabapentin had almost no analgesic effect in mice it showed some analgesic effects in rats in the tail flick model. These effects could not be antagonised with linopirdine, a selective KCNQ potassium channel blocker, indicating a different mode of action for this activity. In L5-ligated rats retigabine significantly and dose-dependently elevated the pain threshold and prolonged the withdrawal latency after tactile and thermal stimulation, respectively. In the L5 ligation model with thermal stimulation retigabine 10 mg/kg p.o. was as effective as 100 mg/kg gabapentin or 10 mg/kg tramadol. The L5 model with tactile stimulation was used to test the role of the KCNQ potassium channel opening effect of retigabine. If retigabine 10 mg/kg p.o. was administered alone it was as effective as tramadol 10 mg/kg p.o. in elevating the pain threshold. Linopirdine (1 and 3 mg/kg i.p.) had nearly no influence on neuropathic pain response. If we administered both retigabine and linopirdine the effect of retigabine was abolished or diminished depending on the dose of linopirdine used. In summary, retigabine is effective in predictive models for neuropathic pain. The activity is comparable to tramadol and is present at lower doses compared with gabapentin. Since the anti-allodynic effect can be inhibited by linopirdine we can conclude that the potassium channel opening properties of retigabine are critically involved in its ability to reduce neuropathic pain response.