Effects of Novel Antagonists of Polyetherbrevetoxin (pbtx)-induced Bronchoconstriction in Allergic Sheep

Florida red tide brevetoxins are potent sodium channel neurotoxins produced by the dinoflagellate Karenia brevis (K.brevis). When aerosolized, lysed cultures of K. brevis (crude PbTx) cause bronchoconstriction, especially in people withunderlying airway diseases, such as asthma. PbTx2 and PbTx-3 are two of the structurally–related toxins present inhighest concentration during the growth phase of K. brevis. In this study, we used sheep with airway hypersensitivity to Ascarissuum antigen, as a surrogate for asthmatic patients, to determined if inhalation challenge with purified PbTx-2 and PbTx-3 causes bronchoconstriction and if this effect could be blocked by B-Naphthoyl-PbTx-3, which antagonizes the effects of PbTx-3 in vitro, and AJB 6.0P, a newly described antagonist, which is produced by the organism, itself. Changes in mean pulmonary airflow resistance (RL) were measured before and after inhalation challenge with increasing concentrations (20 breaths 0.1-10 pg/ml) of PbTx-2 and PbTx-3 or after challenge with crude PbTx (20 breaths 0.1-1.0 pg/ml). Challenge with PbTx-2 and PbTx3 produced 226±21 % and 204±26% (mean ±se, n=7) increases in RL over baseline, respectively (P<0.05) at 10 pg/ml, whereas 1.0 pg/ml of crude PbTx induced a 201±9% (n=4) increase. Treating the animals with either B Naphthoyl-PbTx-3 or AJB 6.0P (20 breaths of increasing concentrations 15 min before challenge) significantly reduced the bronchial responses to crude PbTx, PbTx-2 and PbTx3 in a dose-dependent fashion. Neither of the antagonists alone affected RL. We conclude that aerosols of K. brevis that contain PbTx-2 and PbTx-3 are potent airway constrictors and so could adversely affect human health. The identification of agents that inhibit the effects of these toxins may lead to therapies for affected individuals.