brevetoxin and Brain-Neoplasms

Previously, we analyzed Eastern oysters (Crassostrea virginica) naturally exposed to a Karenia brevis red tide and found that brevetoxins (PbTx) are rapidly accumulated and metabolized. Several metabolites were isolated and later identified, including a cysteine-PbTx conjugate (MH(+): m/z 1018) and its sulfoxide product (m/z 1034). In the present study, we confirm and extend those findings by examining PbTx metabolism and elimination in oysters exposed to pure toxins (PbTx-2 and -3) under controlled conditions. Waterborne PbTx-3 was rapidly accumulated, but not metabolized, in the oyster and was largely eliminated within 2 weeks after exposure. In contrast, PbTx-2 was accumulated and rapidly metabolized. Metabolites of PbTx-2 included the reduction product PbTx-3 (m/z 897), and the cysteine conjugates (m/z 1018 and 1034) isolated previously from the field samples. Levels of the metabolite PbTx-3 in PbTx-2-exposed oysters were highest immediately after exposure and declined at a rate similar to parent PbTx-3 in PbTx-3-exposed oysters. Cysteine-PbTx persisted for 8 weeks after exposure. The same metabolites were confirmed in oysters exposed to laboratory cultures of K. brevis. PbTx metabolites contribute to neurotoxic shellfish poisoning (NSP) and should be included in analytical protocols for monitoring shellfish toxicity after a K. brevis red tide event.

Topics: Animals; Brain Neoplasms; Cell Survival; Chromatography, Liquid; Dinoflagellida; Dose-Response Relationship, Drug; Marine Toxins; Mice; Neuroblastoma; Ostreidae; Oxocins; Spectrometry, Mass, Electrospray Ionization; Tumor Cells, Cultured

Ciguatoxins (CTXs) and brevetoxins (PbTxs) modify the activation and inactivation processes of voltage-sensitive sodium channels (VSSC). In this study, the specific binding to rat brain synaptosomes of two commercial PbTxs, five purified CTXs and their derivatives was evaluated in competition with various concentrations of radiolabelled brevetoxin ([3H]PbTx-3). The results indicate that all CTXs bind specifically and with high affinity to sodium channels. Statistical analysis of the calculated inhibition constants identified two classes of toxins: the PbTxs and the less polar CTXs, and a group of CTXs of very high affinity. Relatively small chemical differences between the CTXs gave rise to significant differences in their affinity to the rat brain sodium channels. Cytotoxic effects associated with sodium channel activation were evaluated for the two classes of toxins on murine neuroblastoma cells, and their acute toxicity was determined in mice. CTXs have shown high affinities to VSSC of rat brain membranes and strong cytotoxic effects on neuroblastoma cells which correlate with their very low LD50 in mice. For PbTxs, it is different. Although binding with high affinity to VSSC and giving rise to significant cytotoxic effects, they are known to be poorly toxic intraperitoneally to mice. Furthermore, within the CTXs family, even though the most toxic compound (CTX-1B) has the highest affinity and the less toxic one (CTX-4B) the lowest affinity, a detailed analysis of the data pointed out a complex situation: (i) high affinity and toxicity seem to be related to the hydroxylation of the molecule on the A-ring rather than to the backbone type, (ii) acute toxicity in mice does not follow exactly the sodium-dependent cytotoxicity on neuroblastoma cells. These data suggest that the high toxicity of CTXs is related to sodium-dependent disturbances of the excitable membranes but might also involve other cellular mechanisms.

Topics: Animals; Brain Neoplasms; Ciguatoxins; Female; In Vitro Techniques; Ion Channel Gating; Lethal Dose 50; Male; Marine Toxins; Mice; Neuroblastoma; Neurotoxins; Oxocins; Rats; Rats, Sprague-Dawley; Sodium Channel Blockers; Structure-Activity Relationship; Synaptosomes

In October of 1996, a Gymnodinium breve bloom occurred in shellfish harvesting waters of Alabama, Mississippi and Louisiana, Gulf of Mexico, USA. Bloom densities reached 5.6x10(5) cells liter(-1) and bloom residence at shellfish sampling stations ranged from 3 to 28 days. Brevetoxin-2 dominated G. breve toxin profiles in bloom seawater extracts. Shellfish toxicity, assessed by mouse bioassay, exceeded the guidance level for up to 75 days after the bloom had dissipated. Cytotoxicity assays and mouse bioassays showed similar temporal patterns of shellfish toxicity, but the two methods differed in estimations of brevetoxin-3 equivalent toxicity by a factor of 93 to 1. LC-ESI-MS showed the temporal patterns in shellfish toxicity reflected metabolism of G. breve toxins. The molecular ions m/z 1004, 1017 and 1033 dominated LC-ESI-MS spectra of toxic chromatographic fractions from the extracts and were identified as brevetoxin metabolites on the basis of LC-APCI-MS-MS. The discrepancy between cytotoxicity and mouse bioassay estimates of brevetoxin-3 equivalent toxicity resulted from the difference in extraction efficiency of solvents used in the respective methods and the relative sensitivity of the assays to toxin metabolite mixtures present in the extracts. The normalized cytotoxicity assay showed 75% agreement with mouse bioassay positive test samples and 64% agreement with mouse bioassay negative test samples. Published in 1999 by John Wiley & Sons, Ltd.

Topics: Animals; Biological Assay; Brain Neoplasms; Cell Line; Cell Survival; Chromatography, High Pressure Liquid; Dinoflagellida; Marine Toxins; Mass Spectrometry; Mice; Neuroblastoma; Ostreidae; Oxocins; Seawater; Sodium Channels; Time Factors