Neuroprotective effects of recombinant human erythropoietin on facial motoneurons after facial nerve injury in rats

BACKGROUND: Erythropoietin and recombinant human erythropoietin (rhEPO) inhibit apoptosis of motor neurons caused by spinal cord injury and brain damage in rats. However, it still remains to be shown whether rhEPO can protect facial motoneurons (FMNs) as well.OBJECTIVE: To test the neuroprotective effects of rhEPO on injured FMNs, as well as the influence on Caspase-3 expression.DESIGN, TIME AND SETTING: Randomized, controlled, animal experiment. This study was performed at the Central Laboratory of Basic Medical College, Chongqing Medical University from January to October 2007.MATERIALS: Seventy-five female SD rats, weighing 210-230g. rhEPO injection was provided by Sansheng pharmaceuticals company, Shenyang City, Liaoning Province, China, and the License number was HMLN S20010001.METHODS: A total of 75 female rats were randomly divided into rhEPO treatment, control, and sham operation groups, with 25 rats in each group. Rat models of facial nerve injury were established in the rhEPO treatment group and the control group by crushing the main trunk of the left facial nerve. Surgical microscopic observation of the facial nerve damage displayed perineurial disruption. The left stylomastoid foramen of the sham operation group were only exposed, but without nerve injury. The rhEPO treatment group was treated with rhEPO (5000U/kg, i. p.) once following injury and once a day for two weeks. The control and sham operation groups were treated with the same dose of normal saline (i. p.), once following injury and once a day for two weeks.MAIN OUTCOME MEASURES: Rats were sacrificed 3, 7, 14, 21, and 28 days after injury, FMN survival after facial nerve injury was analyzed by Toluidine blue staining, and then survival ratios (L/R) were calculated. The number of apoptotic profiles in the injured FMNs were evaluated by TUNEL staining. Expression of Caspase-3 in the facial nucleus was detected by immunohistochemistry methods.RESULTS: A total of 75 rats were included in the final analysis. FMN survival ratios, both in rhEPO treatment group and control group, decreased gradually between seven and 28 days; however, FMN survival ratios were significantly greater in the rhEPO treatment group compared to the control group (P<0.05). No TUNEL-positive cells were observed three days after injury in the rhEPO treatment and control groups; however, by seven days after injury, apoptotic cells were observed and peaked by 14 days in the control group. Between seven and 21 days, apoptotic cell numbers were significantly lower in the rhEPO treatment group compared to the control group (P<0.05). The expression of Caspase-3 increased three days after injury and peaked at 14 days in the control group. Nevertheless, Caspase-3 expression was significantly lower in the rhEPO treatment group compared to the control group at each time point (P<0.05).CONCLUSION: Treatment with rhEPO can effectively protect facial motoneurons by reducing expression of Caspase-3 and inhibiting apoptosis.