Marine brevetoxin induces IgE-independent mast cell activation

Abstract

Brevetoxins (PbTx) are sodium channel neurotoxins produced by the marine dinoflagellate Karenia brevis during red tide blooms. Inhalation of PbTx in normal individuals and individuals with pre-existing airways disease results in adverse airway symptoms including bronchoconstriction. In animal models of allergic inflammation, inhalation of PbTx results in a histamine H₁-mediated bronchoconstriction suggestive of mast cell activation. How mast cells would respond directly to PbTx is unknown. We thus explored the activation of mouse bone marrow-derived mast cells (BMMCs) following exposure to purified PbTx-2. Following in vitro exposure to PbTx-2, we examined cellular viability, mast cell degranulation (β-hexosaminidase release), intracellular Ca²+ and Na+ flux, and the production of inflammatory mediators (IL-6). PbTx-2 induced significant cellular toxicity within 24 h as measured by LDH release and Annexin-V staining. However, within 1 h of exposure, PbTx-2 induced BMMC degranulation and an increase in IL-6 mRNA expression independent of the high-affinity IgE receptor (FcεRI) stimulation. Activation of BMMCs by PbTx-2 was associated with altered intracellular Ca²+ and Na+ levels. Brevenal, a naturally produced compound that antagonizes the activity of PbTx, prevented changes in intracellular Na+ levels but did not alter activation of BMMCs by PbTx-2. These findings demonstrate that PbTx-2 activates mast cells independent of FcεRI providing insight into critical events in the pathogenesis and a potential therapeutic target in brevetoxin-induced airway symptoms.