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International journal of molecular medicine

The analgesic effect of rolipram is associated with the inhibition of the activation of the spinal astrocytic JNK/CCL2 pathway in bone cancer pain.


PMID 28025994

Abstract

Bone cancer pain (BCP) is one of the most difficult and intractable tasks for pain management, which is associated with spinal 'neuron-astrocytic' activation. The activation of the c-Jun N-terminal kinasexa0(JNK)/chemokine (C-Cxa0motif) ligandxa0(CCL2) signaling pathway has been reported to be critical for neuropathic pain. Rolipramxa0(ROL), a selective phosphodiesterasexa04 inhibitor, possesses potent anti-inflammatory and anti-nociceptive activities. The present study aimed to investigate whether the intrathecal administration of ROL has an analgesic effect on BCP in rats, and to assess whether the inhibition of spinal JNK/CCL2 pathway and astrocytic activation are involved in the analgesic effects of ROL. The analgesic effects of ROL were evaluated using the Vonxa0Frey and Hargreaves tests. Immunofluorescence staining was used to determine the number of c-Fos immunoreactive neurons, and the expression of spinal astrocytes and microglial activation on dayxa014 after tumor cell inoculation. Enzyme‑linked immunosorbent assayxa0(ELISA) was used to detect the expression of pro-inflammatory cytokines [interleukinxa0(IL)-1β, IL-6 and tumor necrosis factorxa0(TNF)-α] and chemokinesxa0(CCL2), and western blot analysis was then used to examine the spinal phosphodiesterasexa04xa0(PDE4), ionized calcium binding adapter molecule-1xa0(IBA-1) and JNK levels on dayxa014 after tumor cell inoculation. The results revealed that ROL exerted a short-term analgesic effect in a dose-dependent manner, and consecutive daily injections of ROL exerted continuous analgesic effects. In addition, spinal 'neuron‑astrocytic' activation was suppressed and was associated with the downregulation of spinal IL-1β, IL-6 and TNF-α expression, and the inhibition of PDE4B and JNK levels in the spine was also observed. In addition, the level of CCL2 was decreased in the rats with BCP. The JNK inhibitor, SP600125, decreased CCL2 expression and attenuated pain behavior. Following co-treatment with ROL and SP600125, no significant increases in thermal hyperalgesia and CCL2 expression were observed compared with the ROL group. Thus, our findings suggest that the analgesic effects of ROL in BCP are mainly mediated through the inhibition of 'neuron‑astrocytic' activation, which occurs via the suppression of spinal JNK/CCL2 signaling.