The Neuroprotective Effects of Aspirin and MK-801 Against Un-Caged Caged-Glutamate for Use in a Visual Prosthetic Device

Abstract

Abstract: : Purpose: While glutamate is the primary excitatory neurotransmitter in the retina and CNS, overstimulation may lead to excitotoxic cell death. A novel approach to retinal stimulation in the field of artificial vision employs the use of caged-glutamate, a pro-drug form of L-glutamate. Prior studies have shown that the caging of glutamate confers a degree of neuroprotection from glutamate excitotoxicity however, in some cases, the uncaged glutamate was slightly more toxic than glutamate alone. The purpose of this study was to examine aspirin, a free radical scavenger, and MK-801, a noncompetitive NMDA receptor antagonist, and their ability to attenuate the toxicity observed with L-glutamate and uncaged hydroxyphenacyl derivatives for their potential use in a neurotransmitter based visual prosthetic device. Methods: Visual cortical neurons were cultured from embryonic Sprague-Dawley rat pups incubated for 8 days before exposure to either 50 uM L-glutamate, 50 uM p-hydroxyphenacyl (hPA) glutamate, 50 uM p-hydroxy-m-methoxyphenacyl (mPA) glutamate, 100uM aspirin, 25 uM MK-801 and combinations of each. Cellular viability was assessed 24 hours after the initial exposure using a trypan blue dye exclusion assay. Results: L-glutamate, uncaged hPA or uncaged mPA treated cultures that were exposed with aspirin or MK-801 demonstrated a statistically significant increase in neuronal survival as compared to glutamate, uncaged hPA or uncaged mPA (p<.001). Glutamate, uncaged hPA or uncaged mPA treated cultures exposed to aspirin and MK-801 conferred no additional improvements in neuronal viability as compared to glutamate, uncaged hPA or uncaged mPA and MK-801. Conclusions: Aspirin and MK-801 are both neuroprotective against glutamate, uncaged mPA glutamate, and uncaged hPA glutamate. However, aspirin is not as neuroprotective as MK-801. Aspirin and MK-801 in combination do not improve cell viability as compared to MK-801 alone.

Keywords: cell death/apoptosis • excitatory neurotransmitters • neuroprotection