Excitotoxicity at both NMDA and non-NMDA glutamate receptors is antagonized by aurintricarboxylic acid: evidence for differing mechanisms of action.

In this study, the endonuclease inhibitor aurintricarboxylic acid (ATA) was examined for its ability to attenuate both acute and delayed excitotoxicity mediated through NMDA and non-NMDA glutamate receptors. Ex vivo embryonic chick retina, a model system frequently used for studies of excitotoxicity, was exposed to either 100 microM NMDA or kainate (KA) +/- various concentrations of ATA for 60 min, then allowed to recover for 24 h. Lactate dehydrogenase release into the medium and histology were assessed as measures of delayed toxicity. ATA attenuated lactate dehydrogenase release due to NMDA or KA in a dose-dependent manner. Histology revealed that ATA decreased the number of pyknotic profiles in response to either glutamate agonist. The mechanism of ATA protection was addressed. ATA was found to block NMDA- but not KA-mediated 22Na+ influx and cyclic GMP formation. In membrane binding studies, ATA was relatively selective for displacement at the NMDA receptor. The IC50 values for displacement of [3H]CGS 19755, alpha-[3H]amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), or [3H]KA were 29.9 +/- 1.3, 313 +/- 46, and > 1,000 microM +/- SEM, respectively. ATA also fully attenuated NMDA-induced and partially attenuated KA-induced acute excitotoxicity as monitored histologically by tissue swelling and by the increase in GABA in the medium. Temporal studies of ATA efficacy indicated that ATA needed to be present during NMDA exposure to afford protection but, versus KA, was equally effective if administered immediately after KA exposure. Questions regarding the cellular penetration of ATA were raised because incubation with 100 microM ATA for 60 min had no effect on lactate formation or [3H]leucine incorporation into trichloroacetic acid-precipitable material, even though, in cell-free systems, ATA is a potent inhibitor of phosphofructokinase activity and protein synthesis. These studies demonstrate that ATA can protect against excitotoxicity mediated through NMDA or non-NMDA glutamate receptors. The mechanism of protection versus NMDA is through interruption of NMDA receptor interactions. ATA has no direct effect at the KA receptor; thus, its mechanism of protection versus KA is distinct from that versus NMDA and is, at present, unknown.