Erythropoietin Accelerates Functional Recovery After Peripheral Nerve Injury

Abstract

Erythropoietin is a naturally occurring hormone with multiple effects on a number of different cell types. Recent data have suggested neuroprotective and perhaps even neurotrophic roles for erythropoietin. We hypothesized that these functional effects could be demonstrable in standard models of peripheral nerve injury. Experiments were undertaken to evaluate the effect of erythropoietin on the previously reported standard course of healing of sciatic injuries in mice. The injury groups included mice that were subjected to (1) sham surgery, (2) a calibrated sciatic crush injury, (3) transection of the sciatic nerve followed by epineural repair, or (4) a transection followed by burial of the proximal stump in the adjacent muscle tissue (neurectomy). Either erythropoietin or saline solution was administered to the mice in each of these experimental groups twenty-four hours preinjury, immediately after surgical creation of the injury, twenty-four hours postinjury, or one week postinjury. All mice were evaluated on the basis of the published model for recovery of sciatic nerve motor function by measuring footprint parameters at specific times after the injury. Immunohistochemistry was also performed to assess the erythropoietin-receptor expression profile at the site of injury. In general, the mice treated with erythropoietin recovered sciatic nerve motor function significantly faster than did the untreated controls. This conclusion was based on a sciatic function index that was 60% better in the erythropoietin-treated mice at seven days postinjury (p < 0.05). Although the group that had been given the erythropoietin immediately postinjury showed the best enhancement of recovery, the timing of the administration of the drug was not critical. Histological analysis demonstrated enhanced erythropoietin-receptor positivity in the nerves that recovered fastest, suggesting that accelerated healing correlates with expression of the receptor in nerve tissue. Erythropoietin treatment of an acute sciatic nerve crush injury leads to an effect consistent with functional neuroprotection. This protective effect may have clinical relevance, especially since it was detectable even when erythropoietin had been administered up to one week after injury.