Reduction of Neurological Damage by a Peptide Segment of the Amyloid β/A4 Protein Precursor in a Rabbit Spinal Cord Ischemia Model

Abstract

Although found as a precursor of Alzheimer amyloid, substantial evidence suggests that β/A4 protein precursor (APP) is involved in regulation of neuronal growth and survival. Recently, we have obtained evidence that the trophic properties of APP are fully preserved in a 17-amino acid sequence. If APP is neurotrophic, then it would be anticipated that administration of the growth-promoting segment of the APP 17-mer peptide might attenuate the neuronal dysfunction or loss or behavioral deficits associated with neuronal injury, such as that accompanying central nervous system ischemia. We evaluated this 17-mer peptide in a rabbit spinal cord ischemia model and found that this peptide alleviates paraplegia resulting from ischemia/reperfusion. Ischemia of the distal lumbar cord was produced by temporary occlusion of the abdominal aorta. Saline, 17-mer APP peptide, or a control peptide (200, 500, or 1000 n M) was administered intrathecally 20 min prior to ischemia and once daily for 3 days thereafter. The neurologic and morphologic outcomes were evaluated after 4 days. Durations of ischemia encompassing all grades of neurologic function were included. The 500 n M dose of 17-mer APP peptide significantly reduced neurologic damage. The average ischemia duration necessary to produce permanent neurologic damage increased from 27.9 ± 1.9 min in saline-injected controls and 27.7 ± 2.0 in scrambled sequence peptide-injected controls to 40.2 ± 4.0 min in the 500 n M 17-mer APP-injected group. The 200 n M dose produced a nonsignificant trend toward reduced neurologic damage. This effect to reduce the neurologic dysfunction was observed 4 days after ischemic insult, but not at 18 h after ischemia, suggesting a restorative rather than protective effect of the APP 17-mer peptide. Consistent with this hypothesis, increased synaptophysin-like immunoreactivity, a presynaptic marker, despite the neuronal loss, was observed in the APP-injected animals subjected to ischemia/reperfusion, suggesting synaptic sprouting. Our results demonstrate that this 17-mer peptide is capable of reducing neurologic damage in vivo in a model of central nervous system ischemia, possibly through its effect on synaptic plasticity.