Protective effects of erythropoietin on infection induced neonatal rat brain injury using at different times

Abstract

Objective To explore the influence of erythropoietin(EPO) on infection induced neonatal rat brain injury at different starting time and its related mechanism. Methods Postnatal day 2(P2) newborn SD rats were randomly divided into 4 groups: control group(group A), lipopolysaccharide(LPS) group(group B), the early EPO group(group C)and the later EPO group(group D). Pups in group A, B and C were injected different drugs intraperitoneally(group A for saline, group B for 0.6 mg/kg of LPS, and group C for 0.6 mg/kg of LPS and 5 000 U/kg of EPO)once a day for consecutive 5 days(P2-P6). LPS in group D were injected 0.6 mg/kg of LPS intraperitoneally once a day for consecutive 5 days(P2-P6), and with 5 000 U/kg of EPO once a day for consecutive 5 days(P7-P11). Rats in each group were given different drugs starting at corresponding time by intraperitoneal injection for 5 consecutive days.Every 10 newborn rats in group A and B were selected randomly on P2(6 h after intraperitoneal injection of drugs for the first time), P7 and P12, the brains were divided into the left and the right hemispheres marked by sagittal suture, using enzyme-linked immunosorbent assay method to evaluate the erythropoietin receptor(EPOR) protein level with the right cerebral hemisphere and reverse transcription-polymerase chain reaction(RT-PCR) method was used to investigate EPOR mRNA level of the left cerebral hemisphere.Immunohistochemical method was adopted to evaluate the expression of myelin basic protein(MBP), glial fibrillary acidic protein(GFAP) and EPOR at specified time point, and HE dyeing for the pathological changes of brain damage in different groups. Results HE staining of the group A pre-sented the normal structure in the neonatal rat brain.Reduced numbers of hippocampal pyramidal cells, expansion of the lateral ventricles and periventricular leukomalacia were found in group B. No leukomalacia or lateral ventricles's expansion in EPO administrated groups and it was more obvious in group C. The EPOR protein and mRNA of group B was increased compared with the group A. The EPOR protein and mRNA levels had a tendency to decline with the increase of age.The MBP expression of group B(107.46±3.65)was significantly reduced compared with the group A(146.78±3.13)(P 0.05). Conclusions EPO shows a protective effect on the cerebral white matter injury caused by postpartum infection, it is superior to administer EPO at early time than later time.The mechanism of the protective effect may be connected with the fact that the infection can induce the expression of brain EPOR and the EPOR expression level has a tendency to decline with the increase of age. Key words: Erythropoietin; Erythropoietin receptor; Myelin basic protein; Glial fibrillary acidic protein; Neonatal rat