Exposure to the excitotoxin domoic acid (DOM) has been shown to produce cardiac lesions in both clinical and animal studies. We have previously shown that DOM failed to directly affect cardiomyocyte viability and energetics, but the development of this cardiomyopathy has remained unexplained. The present study compared effects of high-level seizure induction obtained by intraperitoneal (2 mg/kg) or intrahippocampal (100 pmol) bolus administration of DOM on development of cardiac pathologies in a rat model. Assessment of cardiac pressure derivatives and coronary flow rates revealed a significant time-dependent decrease in combined left ventricular (LV) systolic and diastolic function at 1, 3, 7, and 14 days after intraperitoneal administration and at 7 and 14 days after intrahippocampal DOM administration. LV dysfunction was matched by a similar time-dependent decrease in mitochondrial respiratory control, associated with increased proton leakage, and in mitochondrial enzyme activities. Microscopic examination of the LV midplane revealed evidence of progressive multifocal ischemic damage within the subendocardial, septal, and papillary regions. Lesions ranged from reversible early damage (vacuolization) to hypercontracture and inflammatory necrosis progressing to fibrotic scarring. Plasma proinflammatory IL-1␣, IL-1␤, and TNF-␣ cytokine levels were also increased from 3 days after seizure induction. The observed cardiomyopathies did not differ between intraperitoneal and intrahippocampal groups, providing strong evidence that cardiac damage after DOM exposure is a consequence of a seizure-evoked autonomic response.

Excitatory mediated neuronal injury has been shown to involve a complex cascade of events. However, the associated cardiac damage reported in humans and marine animals following exposure to excitotoxins has not been well characterized. We hypothesized that the excitotoxin domoic acid can traverse cardiac cell membranes and elicit a deleterious effect on cardiac mitochondrial energetics. Domoic acid (0.05-0.25 microM; 10 min) treatment of isolated rat cardiac mitochondria produced a marked decrease of both mitochondrial flavin adenine dinucleotide (FAD)- and nicotinamide adenine linked respiratory control indices (p < 0.001). Enzymatic assays of the mitochondrial electron transport chain (complexes I-V) and the mitochondrial matrix marker enzyme citrate synthase, showed marked concentration-dependent impairment in activity and integrity following exposure to domoic acid (p < 0.01). Similar mitochondrial effects were seen following exposure to the glutamic acid analog, kainic acid (0.5-2 microM). Domoic acid (0.05-10 microM; 40 min) was shown by competitive enzyme-linked immunosorbent assay to traverse the cellular membrane of H9c2 rat cardiac myoblasts. Exposure of intact H9c2 cells to domoic acid (10 microM; 24 h) impaired complex II-III activity but did not compromise cellular viability as assessed using cell quantification or lactate dehydrogenase leakage assays. Assessment of reactive oxygen species (superoxide and hydrogen peroxide) production in both isolated cardiac mitochondria and H9c2 cardiomyocytes failed to show any significant differences following exposure to domoic acid (0.05-5 microM). This is the first study to demonstrate a direct effect of domoic acid on cardiac mitochondrial energetics. However, the absence of substantial damage to intact cardiomyocytes raises questions regarding direct toxicological effects on cardiac energetics or viability under conditions of natural domoic acid exposure.