Yessotoxin, a shellfish biotoxin, is a potent inducer of the permeability transition in isolated mitochondria and intact cells. (33/156)

The diarrhetic poisoning by bivalve molluscs, diarrhetic shellfish poisoning, is due to consumption of mussels containing biotoxins produced by some Dinoflagellate species. Toxic effects of yessotoxin (YTX) include morphological alterations of mitochondria from heart and liver but the biochemical basis for these alterations is completely unknown. This paper demonstrates that YTX is a very powerful compound that opens the permeability transition pore (PTP) of the inner mitochondrial membrane of rat liver mitochondria at nanomolar concentrations. The effect requires the presence of a permissive level of calcium, by itself incapable of opening the pore. The direct effect of YTX on PTP is further confirmed by the inhibition exerted by cyclosporin A (CsA) that is known as a powerful inhibitor of PTP opening. Moreover, YTX induces membrane depolarization as shown by the quenching of tetramethylrhodamine methyl ester (TMRM), also prevented by the addition of CsA. YTX caused PTP opening in Morris Hepatoma 1C1 cells, as shown by the occurrence of CsA-sensitive depolarization within minutes of the addition of submicromolar concentrations of the toxin. These results provide a biochemical basis for the mitochondrial alterations observed in the course of intoxication with YTX, offering the first clue into the pathogenesis of diseases caused by YTX, and providing a novel tool to study the PTP in situ.  (+info)

Brevenal is a natural inhibitor of brevetoxin action in sodium channel receptor binding assays. (34/156)

1. Florida red tides produce profound neurotoxicity that is evidenced by massive fish kills, neurotoxic shellfish poisoning, and respiratory distress. Red tides vary in potency, potency that is not totally governed by toxin concentration. The purpose of the study was to understand the variable potency of red tides by evaluating the potential for other natural pharmacological agents which could modulate or otherwise reduce the potency of these lethal environmental events. 2. A synaptosome binding preparation with 3-fold higher specific brevetoxin binding was developed to detect small changes in toxin binding in the presence of potential antagonists. Rodent brain labeled in vitro with tritiated brevetoxin shows high specific binding in the cerebellum as evidenced by autoradiography. Synaptosome binding assays employing cerebellum-derived synaptosomes illustrate 3-fold increased specific binding. 3. A new polyether natural product from Florida's red tide dinoflagellate Karenia brevis, has been isolated and characterized. Brevenal, as the nontoxic natural product is known, competes with tritiated brevetoxin for site 5 associated with the voltage-sensitive sodium channel (VSSC). Brevenal displacement of specific brevetoxin binding is purely competitive in nature. 4. Brevenal, obtained from either laboratory cultures or field collections during a red tide, protects fish from the neurotoxic effects of brevetoxin exposure. 5. Brevenal may serve as a model compound for the development of therapeutics to prevent or reverse intoxication in red tide exposures.  (+info)

Inhalation toxicity of brevetoxin 3 in rats exposed for 5 days. (35/156)

Brevetoxins are potent neurotoxins produced by the marine dinoflagellate Karenia brevis. Exposure to brevetoxins may occur during a K. brevis red tide when the compounds become aerosolized by wind and surf. This study assesses possible adverse health effects associated with short-term inhalation exposure to brevetoxin 3. Male F344/Crl/Br rats were exposed to 500 microg brevetoxin 3/m3 by nose-only inhalation for 0.5 or 2 h/d for 5 consecutive days. Control rats were sham exposed for 2 h to vehicle. Calculated deposited brevetoxin doses were 8.3 and 33 microg/kg/d for the low- and high-dose groups, respectively. At the termination of exposures, only body weights of the high-dose group (Group B) were significantly below control values. By immunohistochemistry (IHC), small numbers of splenic and peribronchiolar lymphoid tissue macrophages stained positive for brevetoxin, while nasal mucosa, liver, and brain were IHC negative for brevetoxin. No gross or microscopic lesions were observed in any tissue examined. There was no biochemical evidence of cytotoxicity or inflammation in bronchoalveolar lavage fluid. Alveolar macrophages showed some evidence of activation following brevetoxin exposure. Humoral-mediated immunity was suppressed in brevetoxin-exposed rats as indicated by a >70% reduction in splenic plaque-forming cells in brevetoxin-exposed animals compared to controls. Results suggest that the immune system may be a target of toxicity following brevetoxin inhalation. Future studies will focus on identification of a no-effect level and mechanisms underlying brevetoxin-induced immune suppression.  (+info)

Maitotoxin induces biphasic interleukin-1beta secretion and membrane blebbing in murine macrophages. (36/156)

Maitotoxin (MTX) is a potent shellfish toxin widely used as an in vitro tool for increasing intracellular Ca2+ and studying Ca2+ -dependent processes. MTX also induces membrane blebbing and nonselective pores similar to those elicited by the P2X7 receptor (P2X7R), an ATP-gated cation channel expressed in inflammatory leukocytes. We therefore tested whether MTX treatment of lipopolysaccharide-primed murine macrophages would mimic the ability of activated P2X7R to induce secretion of the proinflammatory cytokine interleukin-1beta (IL-1beta). MTX at < or = 0.6 nM predominantly induced processing and nonlytic release of mature IL-1beta (mIL-1beta), whereas >0.6 nM of MTX induced cytolytic release of unprocessed proIL-1beta. MTX-dependent release of mIL-1beta (but not cytolysis) was inhibited by the elimination of the trans-plasma membrane K+ gradient. MTX-induced cytokine release and cytolysis were both abrogated in the absence of extracellular Ca2+. On the other hand, extracellular glycine (5 mM) blocked MTX-induced cytolytic release of proIL-1beta without affecting regulated secretion of mIL-1beta. Because MTX has profound effects on plasma membrane permeability, we used time-lapse videography to examine the morphologic response of individual macrophages to MTX. MTX treatment led to biphasic propidium dye uptake and dilated blebbing coincident with cytolysis. Glycine completely blocked the second, lytic phase of dye uptake and prevented MTX-induced bleb dilation. These results indicate that the inflammatory macrophage can assemble the necessary signaling components to initiate both regulated and lytic release of IL-1beta in response to MTX. This suggests that the hyperactivation of proinflammatory cytokine secretion may be a significant component of the in vivo response to MTX during shellfish seafood poisoning.  (+info)

Airway responses to aerosolized brevetoxins in an animal model of asthma. (37/156)

Florida red tide brevetoxins are sodium channel neurotoxins produced by the dinoflagellate Karenia brevis. When aerosolized, the toxin causes airway symptoms in normal individuals and patients with airway disease, but systematic exposures to define the pulmonary consequences and putative mechanisms are lacking. Here we report the effects of airway challenges with lysed cultures of Karenia brevis (crude brevetoxin), pure brevetoxin-2, brevetoxin-3, and brevetoxin-tbm (brevetoxin-2 minus the side chain) on pulmonary resistance and tracheal mucus velocity, a marker of mucociliary clearance, in allergic and nonallergic sheep. Picogram concentrations of toxin caused bronchoconstriction in both groups of sheep. Brevetoxin-tbm was the least potent, indicating the importance of the side chain for maximum effect. Both histamine H(1)- and cholinergic-mediated pathways contributed to the bronchoconstriction. A synthetic antagonist, beta-naphthoyl-brevetoxin-3, and brevenal, a natural antagonist, inhibited the bronchoconstriction. Only crude brevetoxin and brevetoxin-3 decreased tracheal mucus velocity; both antagonists prevented this. More importantly, picomolar concentrations of the antagonists alone improved tracheal mucus velocity to the degree seen with mM concentrations of the sodium channel blocker amiloride. Thus, Karenia brevis, in addition to producing toxins that adversely affect the airways, may be a source of agents for treating mucociliary dysfunction.  (+info)

Uptake and elimination of brevetoxin in blood of striped mullet (Mugil cephalus) after aqueous exposure to Karenia brevis. (38/156)

There is a critical need to simply and reliably monitor brevetoxins routinely in the blood of humans and aquatic animals. We used striped mullet as laboratory test animals to better define the uptake and elimination kinetics of brevetoxin during an aqueous exposure to the brevetoxin-producing dinoflagellate Karenia brevis. Striped mullet were first exposed to sublethal densities of K. brevis (approximately 250,000 cells/L) for 1, 4, 8, 12, and 24 hr. No mortality was observed in the aquaria, and at each time point blood samples were taken and applied to blood collection cards for brevetoxin analysis using radioimmunoassay (RIA). The RIA indicated that blood levels of brevetoxin (PbTx-3) increased to values significantly different from that of the controls at all five time points during exposure (p < 0.05). Striped mullet were then exposed to a K. brevis culture with a known brevetoxin concentration of 0.5 ng/mL. Even after exposures at a low brevetoxin concentration, RIA was able to detect 2.25 +/- 0.62 ng/mL PbTx-3 equivalents in the blood of the mullet at 8 hr of exposure. When exposed to higher brevetoxin concentrations (3.5 and 5.4 ng/mL), blood brevetoxin increased to peak levels at 12 hr and then reached equilibrium after 24 hr in the continued presence of K. brevis. During this time of equilibrium, the mullet maintained brevetoxins with a blood:water coefficient of 2.2. To define the elimination of brevetoxin, striped mullet were next exposed for 8-10 hr and then transferred to fresh seawater containing no K. brevis for up to 116 hr. Blood brevetoxin levels remained elevated and decreased only by 50% 116 hr after transfer. The rate of elimination fit best to a two-phase exponential decay with a biologic half-life of 12 and 266 hr. This study, using RIA in conjunction with blood collection cards, demonstrates an effective means to monitor blood brevetoxin levels in finfish and provides a foundation to characterize biologically relevant levels of brevetoxin in other species impacted by red tide events.  (+info)

A new polyether ladder compound produced by the dinoflagellate Karenia brevis. (39/156)

A new ladder-frame polyether compound containing five fused ether rings was isolated from laboratory cultures of the marine dinoflagellate Karenia brevis. This compound, named brevenal, and its dimethyl acetal derivative both competitively displace brevetoxin from its binding site in rat brain synaptosomes. Significantly, these compounds are also nontoxic to fish and antagonize the toxic effects of brevetoxins in fish. The structure and biological activity of brevenal, as well as the dimethyl acetal derivative, are described in this paper.  (+info)

Identification of a rapid detoxification mechanism for brevetoxin in rats. (40/156)

We examined detoxification of brevetoxin in rats through metabolic activities and key elimination routes by analyzing samples from individual rats exposed to two brevetoxin congeners (PbTx-2 and PbTx-3). Brevetoxins were detected by radioimmunoassay in methanolic extracts of blood within 1 h post intraperitoneal (ip) administration. The toxin assay response was about three times higher in PbTx-2-treated rats versus the same dose (180 microg/kg) of PbTx-3. This difference persisted for up to 8 h postexposure. When the blood samples were reextracted with 20% methanol to enhance recovery of potential polar brevetoxin metabolites, 25-fold higher assay activity was present in the PbTx-2-treated rats. Analysis of urine from the same animals identified 7-fold more activity in the PbTx-2-treated rats that accumulated over the course of 24 h. Radioimmunoassay-guided high performance liquid chromatographic analysis of urine from PbTx-2-treated rats yielded three major peaks of activity. The first peak was attributed to the two cysteine adducts, cysteine-PbTx sulfoxide and cysteine-PbTx (MH(+): m/z 1034 and 1018). The second peak was attributed to the oxidized form of PbTx-2 (MH(+): m/z 911) and its reduction product PbTx-3. The third peak remains unidentified. Brevetoxin cysteine conjugate and its sulfoxide product contributed nearly three-quarters of the brevetoxin immunoactivity. Our findings indicate the most commonly occurring PbTx-2 is rapidly transformed to a polar metabolite of a reduced biological activity that appears in blood and remains for up to 8 h, yet is cleared mostly to the urine within 24 h.  (+info)