Effects of repeated milnacipran and fluvoxamine treatment on mechanical allodynia in a mouse paclitaxel-induced neuropathic pain model

Abstract

Paclitaxel is widely used in cancer chemotherapy for the treatment of solid tumors, but it frequently causes peripheral neuropathy. Milnacipran, a serotonin/noradrenaline reuptake inhibitor and fluvoxamine, a selective serotonin reuptake inhibitor, have shown efficacy against several chronic pain syndromes. In this study, we investigated the attenuation of paclitaxel-induced mechanical allodynia in mice by milnacipran and fluvoxamine. Paclitaxel was administered once per day (2 mg/kg, intraperitoneally (i.p.)) for 5 days to mice. Mechanical allodynia was evaluated by measuring the withdrawal response to stimulation with a von Frey filament. In paclitaxel-treated mice, mechanical allodynia was observed on days 3-15 of paclitaxel administration. A single administration of milnacipran (20 mg/kg, i.p.) or fluvoxamine (40 mg/kg, i.p.) had no effect on paclitaxel-induced mechanical allodynia. However, repeated administration of milnacipran (10, 20 mg/kg, once per day, i.p.) for 5 days significantly reduced paclitaxel-induced mechanical allodynia. In contrast, repeated fluvoxamine administration (40 mg/kg, once per day, i.p.) for 5 days resulted in a weak attenuation of paclitaxel-induced mechanical allodynia. These results suggest that chronic paclitaxel administration induces mechanical allodynia, and that repeated milnacipran administration may be an effective therapeutic approach for the treatment of neuropathic pain caused by paclitaxel treatment for cancer.Peripheral neurotoxicity induced by antineoplastic drugs (taxanes, vinca-alkaloids and platin-based compounds) is a clinically significant complication that can be dose-limiting and can substantially diminish quality of life. Paclitaxel is commonly used for the treatment of solid tumors and ovarian and breast cancers. Paclitaxel induces antimitotic actions by impeding the cell cycle in the late phases of mitosis, stabilizing microtubule formation, and ultimately inducing apoptosis (26). However, paclitaxelinduced peripheral neuropathy is a side-effect of chemotherapeutic treatment which often manifests as bilateral pain in the extremities in a stocking and glove-type distribution (6), sometimes greatly impairing the patients' quality of life and their ability to perform normal activities of daily living. To date, therapeutic drugs have been evaluated using various animal models of paclitaxel-induced allodynia. Ethosuximide (7), gabapentin (14), thalidomide and minocycline (3), neurotropin (11) and acetyl-L-carnitine (8) have been examined against the paclitaxelinduced neuropathic pain model, although studies regarding their efficacy have not been conclusive. Supplementary analgesics (antidepressants and anticonvulsants) have suppressive effects on opioid-resistant neuropathic pain (16,24), and antidepressants are widely used for the treatment of neuropathic pain. Antidepressants, especially tricyclic antidepressants (TCAs), are regarded as first-line drugs for the treatment of neuropathic pain (16). Recently, more selective monoamine reuptake inhibitors...

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