Administration of ONO-2506 suppresses neuropathic pain after spinal cord injury by inhibition of astrocytic activation.

BACKGROUND CONTEXT

Spinal cord injury (SCI) results in not only motor dysfunction but also chronic neuropathic pain. Allodynia, an abnormal sensation that evokes pain against non-noxious stimuli, is a major symptom of post-SCI neuropathic pain. Astrocytic activation is a cause of post-SCI neuropathic pain and is considered a key treatment target. However, no effective treatment for these problems is available to date. ONO-2506 is a novel agent that suppresses astrocytic activation by inhibition of S100B production from astrocytes. Recently, it has been demonstrated that ONO-2506 inhibits secondary injury and improves motor function after SCI.

PURPOSE

This study aimed to investigate the effect of ONO-2506 on post-SCI neuropathic pain.

STUDY DESIGN

Animal study of a rat model of spinal cord contusion.

METHODS

A total of 22 male Sprague-Dawley rats aged 6 weeks were used. Incomplete SCI was created at T10 level. Animals were divided into two groups: Saline group and ONO-2506 group. Nine animals in each group were finally included for this study. Intraperitoneal administration of ONO-2506 (20 mg/kg) or saline was continued daily for 1 week following SCI. Recovery of hind limb motor function was assessed using the Basso, Beattie, and Bresnahan (BBB) score. Mechanical and thermal allodynia of hind paws were evaluated by the withdrawal threshold using a von Frey filament and the withdrawal latency using the plantar test device. At 6 weeks after SCI, sagittal sections at the injured site and axial sections at L 4/5 were evaluated by fluorescent immunohistochemistry staining using S100B and glial fibrillary acidic protein (GFAP) antibodies.

RESULTS

The improvement course of BBB scores was similar between the two groups. However, the withdrawal thresholds for mechanical stimuli and the withdrawal latency for thermal stimuli were significantly higher in the ONO-2506 group than in the Saline group over 6 weeks after SCI. The histologic assessments at the injured site demonstrated a significant reduction in the cross-sectional area of the cysts and a high fluorescence intensity area of S100B and GFAP in the ONO-2506 group. By correlation analysis, a high absolute value of the correlation coefficient was confirmed between the intensity of S100B expression at the injured site and the allodynia severity.

CONCLUSION

Administration of ONO-2506 attenuated post-SCI neuropathic pain in a rat model of incomplete SCI. Histologic results support that the inhibition of S100B production and subsequent suppression of astrocytic activation contributed to the reduction in neuropathic pain.