Gene expression profiling in brain of mice exposed to the marine neurotoxin ciguatoxin reveals an acute anti-inflammatory, neuroprotective response

<p>Abstract</p> <p>Background</p> <p>Ciguatoxins (CTXs) are polyether marine neurotoxins and potent activators of voltage-gated sodium channels. This toxin is carried by multiple reef-fish species and human consumption of ciguatoxins can result in an explosive gastrointestinal/neurologic illness. This study characterizes the global transcriptional response in mouse brain to a symptomatic dose of the highly toxic Pacific ciguatoxin P-CTX-1 and additionally compares this data to transcriptional profiles from liver and whole blood examined previously. Adult male C57/BL6 mice were injected with 0.26 ng/g P-CTX-1 while controls received only vehicle. Animals were sacrificed at 1, 4 and 24 hrs and transcriptional profiling was performed on brain RNA with Agilent whole genome microarrays. RT-PCR was used to independently validate gene expression and the web tool DAVID was used to analyze gene ontology (GO) and molecular pathway enrichment of the gene expression data.</p> <p>Results</p> <p>A pronounced 4°C hypothermic response was recorded in these mice, reaching a minimum at 1 hr and lasting for 8 hrs post toxin exposure. Ratio expression data were filtered by intensity, fold change and p-value, with the resulting data used for time course analysis, K-means clustering, ontology classification and KEGG pathway enrichment. Top GO hits for this gene set included acute phase response and mono-oxygenase activity. Molecular pathway analysis showed enrichment for complement/coagulation cascades and metabolism of xenobiotics. Many immediate early genes such as Fos, Jun and Early Growth Response isoforms were down-regulated although others associated with stress such as glucocorticoid responsive genes were up-regulated. Real time PCR confirmation was performed on 22 differentially expressed genes with a correlation of 0.9 (Spearman's Rho, p < 0.0001) with microarray results.</p> <p>Conclusions</p> <p>Many of the genes differentially expressed in this study, in parallel with the hypothermia, figure prominently in protection against neuroinflammation. Pathologic activity of the complement/coagulation cascade has been shown in patients suffering from a chronic form of ciguatera poisoning and is of particular interest in this model. Anti-inflammatory processes were at work not only in the brain but were also seen in whole blood and liver of these animals, creating a systemic anti-inflammatory environment to protect against the initial cellular damage caused by the toxin.</p

Brevenal Inhibits Pacific Ciguatoxin-1B-Induced Neurosecretion from Bovine Chromaffin Cells

Ciguatoxins and brevetoxins are neurotoxic cyclic polyether compounds produced by dinoflagellates, which are responsible for ciguatera and neurotoxic shellfish poisoning (NSP) respectively. Recently, brevenal, a natural compound was found to specifically inhibit brevetoxin action and to have a beneficial effect in NSP. Considering that brevetoxin and ciguatoxin specifically activate voltage-sensitive Na+ channels through the same binding site, brevenal has therefore a good potential for the treatment of ciguatera. Pacific ciguatoxin-1B (P-CTX-1B) activates voltage-sensitive Na+ channels and promotes an increase in neurotransmitter release believed to underpin the symptoms associated with ciguatera. However, the mechanism through which slow Na+ influx promotes neurosecretion is not fully understood. In the present study, we used chromaffin cells as a model to reconstitute the sequence of events culminating in ciguatoxin-evoked neurosecretion. We show that P-CTX-1B induces a tetrodotoxin-sensitive rise in intracellular Na+, closely followed by an increase in cytosolic Ca2+ responsible for promoting SNARE-dependent catecholamine secretion. Our results reveal that brevenal and β-naphtoyl-brevetoxin prevent P-CTX-1B secretagogue activity without affecting nicotine or barium-induced catecholamine secretion. Brevenal is therefore a potent inhibitor of ciguatoxin-induced neurotoxic effect and a potential treatment for ciguatera

Brevetoxins: Toxicological Profile

Brevetoxins (PbTxs) are polyether ladder-shaped neurotoxins produced by the dinoflagellate Karenia brevis. Blooms of K. brevis have been recorded since the mid-1800s, principally in the Gulf of Mexico but occasionally along the mid and south Atlantic coasts. Blooms may be accompanied by public health issues as well as significant mortalities of marine mammals, such as bottlenose dolphins and manatees, fishes, sea birds, and sea turtles. PbTxs bind to the voltage-gated sodium channels (VGSCs), leading to persistent activation of neuronal, muscle, and cardiac cells. In humans, after consumption of contaminated shellfish (oysters, clams, whelks), these toxins cause a syndrome known as neurotoxic shellfish poisoning (NSP), characterized by nausea, diarrhea, vomiting, abdominal pain, paresthesia, myalgia, ataxia, bradycardia, loss of coordination, vertigo, and mydriasis. The ingestion of contaminated seafood represents the most dangerous route of exposure for humans. However, when PbTxs are aerosolized through the disruption of K. brevis cells by breaking waves or winds, people can suffer from respiratory effects such as conjunctivitis, rhinorrhea, and bronchoconstriction. Due to successful shellfish monitoring programs managed by the Gulf coast states, cases of human intoxications are fortunately rather rare, and no human fatalities have been attributed to NSP

Neuroprotective Effects of Rosmarinic Acid on Ciguatoxin in Primary Human Neurons

International audienceCiguatoxin (CTX), is a toxic compound produced by microalgae (dinoflagellate) Gambierdiscus spp., and is bio-accumulated and bio-transformed through the marine food chain causing neurological deficits. To determine the mechanism of CTX-mediated cytotoxicity in human neurons, we measured extracellular lactate dehydrogenase (LDH) activity, intracellular levels of nicotinamide adenine dinucleotide (NAD(+)) and H2AX phosphorylation at serine 139 as a measure for DNA damage in primary cultures of human neurons treated with Pacific (P)-CTX-1B and P-CTX-3C. We found these marine toxins can induce a time and dose-dependent increase in extracellular LDH activity, with a concomitant decline in intracellular NAD(+) levels and increased DNA damage at the concentration range of 5-200 nM. We also showed that pre- and post-treatment with rosmarinic acid (RA), the active constituent of the Heliotropium foertherianum (Boraginaceae) can attenuate CTX-mediated neurotoxicity. These results further highlight the potential of RA in the treatment of CTX-induced neurological deficits

Ciguatoxin and ciguatera

Ciguatera is a disease caused by the consumption of fishes from tropical and subtropical waters that have accumulated lipophilic sodium channel activator toxins known as ciguatoxins (CTXs) to levels sufficient to cause human poisoning. Consumption of these temperature-stable, orally active polycyclic ether compounds leads to the activation of neuronal sodium channels that produces a range of characteristic neurological, gastrointestinal, and cardiovascular signs and symptoms that clinically define the illness. Ciguatera is estimated to affect similar to 50,000 people annually worldwide after accounting for misdiagnosis and non-reporting. Currently there are no clinically validated treatments and no routine tests that can cost-effectively detect ciguatoxins prior to consumption, with government bans on capture or personal avoidance of risk fish species providing the only effective means to mitigate the risk currently. A recently developed rapid extraction method for ciguatoxins coupled to LC/MS/MS detection has potential for surveillance and confirmation of ciguatera outbreaks