Research article

Effect of a short-term in vitro exposure to the marine toxin domoic acid on viability, tumor necrosis factor-alpha, matrix metalloproteinase-9 and superoxide anion release by rat neonatal microglia

Alejandro MS Mayer¹ , Mary Hall¹ , Michael J Fay¹ , Peter Lamar¹ , Celeste Pearson¹ , Walter C Prozialeck¹ , Virginia KB Lehmann² , Peer B Jacobson³ , Anne M Romanic⁴ , Tolga Uz⁵ and Hari Manev⁶

¹Department of Pharmacology, Chicago College of Osteopathic Medicine, Midwestern University, 555 31st Street, Downers Grove, Illinois 60515, USA

²School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA

³Abbott Laboratories, Abbott Park, Illinois 60064, USA

⁴GlaxoSmithKline Pharmaceuticals, Department of Cardiovascular Pharmacology, King of Prussia, Pennsylvania 19406, USA

⁵The Psychiatric Institute, University of Illinois at Chicago, Chicago, Illinois 60612, USA

⁶The Psychiatric Institute, University of Illinois at Chicago, Chicago, Illinois 60612, USA

author email corresponding author email

BMC Pharmacology 2001, 1:7doi:10.1186/1471-2210-1-7

Published:	2 October 2001

Abstract

Background

The excitatory amino acid domoic acid, a glutamate and kainic acid analog, is the causative agent of amnesic shellfish poisoning in humans. No studies to our knowledge have investigated the potential contribution to short-term neurotoxicity of the brain microglia, a cell type that constitutes circa 10% of the total glial population in the brain. We tested the hypothesis that a short-term in vitro exposure to domoic acid, might lead to the activation of rat neonatal microglia and the concomitant release of the putative neurotoxic mediators tumor necrosis factor-α (TNF-α), matrix metalloproteinases-2 and-9 (MMP-2 and -9) and superoxide anion (O₂-).

Results

In vitro, domoic acid [10 μM-1 mM] was significantly neurotoxic to primary cerebellar granule neurons. Although neonatal rat microglia expressed ionotropic glutamate GluR4 receptors, exposure during 6 hours to domoic acid [10 μM-1 mM] had no significant effect on viability. By four hours, LPS (10 ng/mL) stimulated an increase in TNF-α mRNA and a 2,233 % increase in TNF-α protein In contrast, domoic acid (1 mM) induced a slight rise in TNF-α expression and a 53 % increase (p < 0.01) of immunoreactive TNF-α protein. Furthermore, though less potent than LPS, a 4-hour treatment with domoic acid (1 mM) yielded a 757% (p < 0.01) increase in MMP-9 release, but had no effect on MMP-2. Finally, while PMA (phorbol 12-myristate 13-acetate) stimulated O₂- generation was elevated in 6 hour LPS-primed microglia, a similar pretreatment with domoic acid (1 mM) did not prime O₂- release.

Conclusions

To our knowledge this is the first experimental evidence that domoic acid, at in vitro concentrations that are toxic to neuronal cells, can trigger a release of statistically significant amounts of TNF-α and MMP-9 by brain microglia. These observations are of considerable pathophysiological significance because domoic acid activates rat microglia several days after in vivo administration.