Recombinant human erythropoietin attenuates spinal neuroimmune activation of neuropathic pain in rats.

Neuropathic pain is a complex syndrome resulting from damage to the peripheral nervous system. Central neuroimmune activation contributes to the generation and maintenance of chronic pain after nerve injury. The current study determined the effects of recombinant human erythropoietin (rhEPO) on behavioral hyperalgesia and neuroimmune activation in a rat model of neuropathic pain induced by L5 spinal nerve transection. Animals were randomly assigned into 3 groups: sham-operation with saline; L5 spinal nerve transection with rhEPO (5000 units/kg); or L5 transection with saline. The rhEPO or saline was given ip on the day before surgery and continued daily to day 7 post-transection. The paw pressure threshold and paw withdrawal latencies were measured before surgery and on days 1, 3, and 7 post-operation. Glial activation markers such as macrophage antigen complex-1 (Mac-1, OX-42) and glial fibrillary acidic protein (GFAP), production of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-10, as well as nuclear factor-kappa B (NF-kappaB) activation were determined in the lumbar spinal cord. Administration of rhEPO resulted in attenuation of mechanical and thermal hyperalgesia. Furthermore, rhEPO markedly inhibited neuroimmune activation characterized by glial activation, production of proinflammatory cytokines like TNF-alpha, IL-1beta, and NF-kappaB activation, but rhEPO enhanced the level of IL-10. These results support the significance of neuroinflammation and neuroimmune activation in the initiation and persistence of behavioral pain responses. The data indicate that rhEPO attenuates behavioral hyperalgesia and neuroimmune activation in neuropathic pain induced by L5 nerve transection.