Erythropoietin and carbamylated erythropoietin are neuroprotective following spinal cord hemisection in the rat

Abstract

The cytokine erythropoietin (EPO) has been shown to be neuroprotective in a variety of models of central and peripheral nervous system injury. Derivatives of EPO that lack its erythropoietic effects have recently been developed, and the initial reports suggest that they have a neuroprotective potential comparable to that of EPO. One such derivative is carbamylated EPO (CEPO). In the current study we compared the effects of treatment with EPO and CEPO on some of the early neurodegenerative events that occur following spinal cord injury (SCI) induced by hemisection. Adult male Wistar rats received a unilateral hemisection of the spinal cord. Thirty minutes and 24 h following injury, animals received an intraperitoneal injection of saline, EPO (40 microg/kg) or CEPO (40 microg/kg). Results indicated that 3 days post-injury, both CEPO and EPO decreased to a similar extent the size of the lesion compared with control animals. Both compounds also decreased the number of terminal transferase-mediated dUTP nick-end labelling (TUNEL)-labelled apopotic nuclei around the lesion site, as well as the number of axons expressing the injury marker beta-amyloid precursor protein. EPO and CEPO also increased Schwann cell infiltration into the lesion site, although neither compound had any effect on macrophage infiltration either within the lesion site itself or in the surrounding intact tissue. In addition, immunohistochemistry showed an increased expression of both the EPO receptor and the beta common receptor subunit, the components of the receptor complex proposed to mediate the neuroprotective effects of EPO and CEPO in neurons near the site of the injury. The results show that not only does CEPO have an efficacy comparable to that of EPO in its neuroprotective potential following injury, but also that changes in the receptors for these compounds following SCI may underlie their neuroprotective efficacy.