Combination therapy with methylprednisolone and brain-derived neurotrophic factor for acute spinal cord injury

Abstract

Daniel Kim, MD, Stanford, CA, USA; Tae-Ahn Jahng, MD, Chonbuk, South Korea; Lixin Li, Nanjing, ChinaObjective: Spinal cord injury produced by trauma results in immediate paralysis as well as subsequent progressive worsening of the injured spinal cord. Despite intensive preventive efforts, none of the pharmacological approaches tried alone has been able to promote significant recovery. To refine current treatments and develop a new combination strategy for acute spinal cord injury, we tested the efficacy of combination therapy with methylprednisolone (MP) + brain-derived neurotrophic factor (BDNF; Alomone Company, Israel) in injured rat spinal cord. The present study was designed to investigate whether combination therapy with MP and BDNF could effectively enhance motor axonal regeneration and locomotor functional recovery.Materials and methods: Contusion injury to adult rat spinal cord (18 animals) was produced at the T10 vertebra level after laminectomy using a weight drop model. Immediately after spinal cord contusion injury, rats received 60 mg/kg intravenous MP injection, and they received another intravenous 30 mg/kg MP injection 4 hours later. BDNF was dissolved in an artificial cerebrospinal fluid solution. For continuous infusion of the injured site, each rat was implanted with an osmotic minipump-brain infusion assembly. Animals survived for 10 weeks for functional testing using a BBB scale. After sacrifice, spinal cord from the contused site was cut and fixed for immunohistochemical analysis and gene expression of GAP-43 using RT-PCR. All histological outcome measures were analyzed using univariate analysis of variance followed by Tukey's HSD test if main effects were significant. Behavioral measures were compared using general linear model with repeated measures.Results: Combination therapy with MP+BDNF+vehicle resulted in a significant decrease in ED-1 positive hematogenous inflammatory cellular infiltration compared with vehicle only (p<.05). Concomitantly, a significant amount of increased motor axonal regeneration was observed in the injured spinal cord infused with MP+BDNF+vehicle compared with MP+vehicle and vehicle only (p<.05). Furthermore, increased expression of GAP-43 gene, an endogenous indicator of axonal regeneration, was demonstrated in the MP+BDNF+vehicle infused spinal cord. In addition, combination therapy with MP+BDNF+vehicle resulted in stimulation of hindlimb activity as well as improvement in the rate of recovery in open field locomotion from the third week after injury (p<.05).Discussion: Some studies have shown that MP depresses the production of growth-promoting factors, such as BDNF and NT3. Thus, MP treatment alone has not been sufficient to induce or may hinder functional recovery after spinal cord injury. Furthermore, there are no means for functional recovery after megadose MP treatment in the clinical situation. Thus, it is reasonable to combine nerve growth factor with MP after acute spinal cord injury. In this study, we examined the efficacy of chronic BDNF infusion (6 weeks) with MP treatment. Our results showed that combination therapy could improve functional recovery through a mechanism that includes attenuating inflammatory cellular infiltration and enhancing motor axonal regeneration at the injury site. Furthermore, our results demonstrate that combination therapy stimulates hindlimb stepping and improves functional recovery. The present study offers a rational approach to treating spinal cord injury, in which both the attenuation of initial inflammation and the regeneration of motor axons are required. Further study involving a large number of animals is needed for proper concentration and infusion duration of BDNF.