Gene Expression Profiles in Zebrafish Brain after Acute Exposure to Domoic Acid at Symptomatic and Asymptomatic Doses

Abstract

Domoic acid (DA) is a neuroexcitatory amino acid that is naturally produced by some marine diatom species of the genus Pseudo-nitzschia. Ingestion of DA-contaminated seafood by humans results in a severe neurotoxic disease known as amnesic shellfish poisoning (ASP). Clinical signs of ASP include seizures and neuronal damage from activation of ionotropic glutamate receptors. However, the impacts of DA exposure at levels below those known to induce outward signs of neurobehavioral exicitotoxicity have not been well characterized. To further understand the mechanisms of neurotoxic injury associated with DA exposure, we examined the transcriptome of whole brains from zebrafish (Danio rerio) receiving intracoelomic (IC) injection of DA at both symptomatic and asymptomatic doses. A majority of zebrafish exposed to high-dose DA (1.2 microg DA/g) exhibited clinical signs of neuroexcitotoxicity (EC(50) of 0.86 microg DA/g) within 5-20 min of IC injection. All zebrafish receiving low-dose DA (0.47 microg DA/g) or vehicle only maintained normal behavior. Microarray analysis of symptomatic and asymptomatic exposures collectively yielded 306 differentially expressed genes (1.5-fold, p </= 0.05) predominately represented by signal transduction, ion transport, and transcription factor functional categories. Transcriptional profiles were suggestive of neuronal apoptosis following an overwhelming of protective adaptive pathways. Further, potential molecular biomarkers of neuropathic injury, including the zebrafish homolog of human NDRG4, were identified and may be relevant to DA exposure levels below that causing neurobehavioral injury. In general, DA-modulated gene expression was consistent with other model species thereby validating zebrafish as an appropriate vertebrate model to study mechanisms of DA neurotoxicity. These data provide a basis for identifying pathways of DA-induced injury as well as biomarkers of asymptomatic and symptomatic DA exposure levels.

Magnetic resonance imaging reveals that brain atrophy is more severe in older California sea lions with domoic acid toxicosis

“…Toxicity studies with the zebrafish (Danio rerio) have revealed that exposure to low levels of DA caused different patterns of gene expression than the patterns observed in fish exposed to high doses (Lefebvre et al, 2009). One specific gene, the zebrafish homolog of human N-myc downstreamregulated gene or NDRG4, was markedly downregulated in fish exposed to low levels (Lefebvre et al, 2009). Interestingly, in a separate study, mice that were made NDRG4 protein-deficient had impaired spatial learning and memory in the Morris water maze test (Yamamoto et al, 2011).…”

Characterization of Renal Toxicity in Mice Administered the Marine Biotoxin Domoic Acid

“…[7][8][9][10][11][12][13][14] Although the overt gastrointestinal and neurologic manifestations have defined the disease, emerging evidence from animal and human studies support previously unrecognized threats and novel toxicologic syndromes caused by subclinical toxicity from acute and chronic DA exposures, which may ultimately challenge the adequacy of the current acceptable limit. [15][16][17][18] DA is a potent activator of kainate receptors (KRs) as well as a subpopulation of a-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid receptors (AMPARs). 19 The toxic response produced by DA is a coordinated effort, which involves initial activation of KR and AMPAR by DA and secondary activation of N-methyl-D-aspartate receptors (NMDARs) by glutamate, and it is associated with an influx of Ca 2+ across the plasma membrane, inflammation, neuronal cell injury and death, and neurobehavioral alterations.…”

Angler exposure to domoic acid via consumption of contaminated fishes

“…Low DA levels (0.002 to 0.11 µg g -1 ) detected in the urine of California sea lions have been associated with a novel neurological syndrome characterized by epilepsy (Goldstein et al 2008). More recently, Lefebvre et al (2009) showed that DA doses below those that cause observable signs of behavioral injury in zebrafish can downregulate several genes involved in important biochemical processes, suggesting potential neurological risk associated with asymptomatic DA exposures. In contrast, experiments with rats have demonstrated that low DA doses can precondition the brain and induce tolerance against higher DA doses in young, but not aged, rats (Kerr et al 2002, Hesp et al 2004.…”