Blocking of cytokines signalling attenuates evoked and spontaneous neuropathic pain behaviours in the paclitaxel rat model of chemotherapy‐induced neuropathy

BACKGROUND: Chemotherapy-induced peripheral neuropathic pain (CIPNP) is a serious dose-limiting neurotoxic effect of cancer drug treatment. The underlying mechanism(s) of this debilitating condition, which lacks effective drug treatment, is incompletely understood. However, neural-immune interactions, involving increased expression and release of cytokines, are believed to be involved. Here, we examined, in the paclitaxel rat model of CIPNP, whether plasma levels of 24 cytokines/chemokines change after paclitaxel treatment, and whether blocking of signalling of some of those cytokines would reverse/attenuate behavioural signs of CIPNP. METHODS: To achieve these objectives luminex, pharmacological and behavioural experiments were performed on male Wistar rats (250-300 g) 31 days after the last injection of paclitaxel (1 mg/kg, i.p. on four alternate days) as well as on control (vehicle-treated) rats. RESULTS: Compared with control rats, plasma levels of IL-1α, IL-1β, IL-6, TNF-α, INF-γ and MCP-1 were significantly upregulated in paclitaxel-treated rats. Blocking of TNF-α signalling with etanercept (2 mg/kg, i.p.) or IL-1β with IL-1 receptor antagonist (IL-1ra; 3 mg/kg, i.p.), significantly attenuated established mechanical and cold hypersensitivity as well as spontaneous pain behaviour (spontaneous foot lifting) 24 and 48 h postdrug treatment. Pharmacological blockade of MCP-1/CCL2 signalling with a highly selective CCR2 receptor antagonist (S504393, 5 mg/kg, i.p.) also significantly reduced evoked, but not spontaneous, pain behaviours of CIPNP in paclitaxel-treated rats at the same time points. CONCLUSIONS: The findings support the notion that cytokines/chemokines, particularly TNF-α, IL-1 and MCP-1, are involved in the pathophysiology of CIPNP and suggest that strategies that target their inhibition may be effective in treating CIPNP. SIGNIFICANCE: This study demonstrates that paclitaxel-treated rats exhibit, in addition to indices of mechanical and cold hypersensitivity, a behavioural sign of spontaneous pain, the principal compliant of patients with neuropathic pain. This was accompanied by upregulation in plasma levels of key cytokines/chemokines (IL-1α, IL-1β, IL-6, TNF-α, INF-γ and MCP-1) 31 days post-treatment. However, it is noteworthy that cytokine release, rather than nerve injury per se, may be causative of NP in this model of CIPNP. Nevertheless, our findings that pharmacological blockade of TNF-α, IL-1β and MCP-1 attenuated both evoked and spontaneous pain suggest that strategies that target inhibition of these cytokines may be effective in treating CIPNP.