Antillatoxin is a marine cyanobacterial toxin that potently activates voltage-gated sodium channels

Abstract

M arine cyanobacteria represent a particularly rich source of structurally unique neurotoxic secondary metabolites (1-5). Lyngbya majuscula is a pantropical marine cyanobacterium that is the source of antillatoxin (ATX), a structurally unusual lipopeptide (1) (Fig. 1). Blooms of L. majuscula have been associated with adverse effects on human health. These blooms have been reported to cause respiratory irritation, eye inflammation, and severe contact dermatitis in exposed fishermen and swimmers (6). ATX has been shown to be among the most ichthyotoxic metabolites isolated to date from a marine microalga (1) and, more recently, has been demonstrated to be neurotoxic in primary cultures of rat cerebellar granule cells (4). In the latter study, morphologic evidence of ATX-induced neurotoxicity included swelling of neuronal somata, thinning of neurites, and blebbing of neurite membranes. ATX also induced a concentration-dependent cytotoxicity in cerebellar granule neurons as monitored by lactate dehydrogenase efflux (ATX EC 50 ϭ 20.1 Ϯ 6.4 nM) (4). This neurotoxic response of ATX was prevented by coexposure with noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) receptor such as MK-801 and dextrorphan.Voltage-gated sodium channels are responsible for generation of the rising phase of the action potential in membranes of neurons as well as in most other electrically excitable cells. Sodium channels consist of a pore-forming ␣ subunit of 260 kDa associated with auxiliary ␤ subunits of 33-36 kDa (7,8). Voltagegated sodium channels represent the molecular target for an array of natural products including marine neurotoxins. Marine neurotoxins such as tetrodotoxin (TTX), saxitoxin, conotoxins, sea anemone toxins, brevetoxin, and ciguatoxin all bind with high affinity and specificity to at least six distinct receptor sites on sodium channel ␣ subunits (8). Collectively, these toxins have served as important tools to explore the structure and function of voltage-dependent sodium channels. These marine neurotoxins produce characteristic alterations in the two major properties of sodium channels, namely ion permeation and gating (8).The objective of the present study was to test the hypothesis that ATX acts as an activator of voltage-dependent sodium channels. This hypothesis emanated from our previous studies which were consistent with ATX acting as an autocrine excitotoxic agent in cerebellar granule neurons. In this study we have used a combination of neurochemical and pharmacological approaches to show that ATX is a structurally unusual lipopeptide activator of neuronal voltage-gated sodium channels. Materials and MethodsMaterials. Tritiated batrachotoxin A 20-␣-benzoate ([ 3 H]BTX) and 22 Na ϩ were obtained from DuPont͞NEN. Deltamethrin was purchased from Biomol (Plymouth Meeting, PA). Veratridine, brevetoxin-1 (PbTx-1), and ouabain were obtained from Sigma. Sea anemone toxin was purchased from Calbiochem. Fluo-3 AM and pluronic acid were obtained from Molecular Probes. ATX was either authentic natural (Ϫ)-ant...

Antillatoxin is a sodium channel activator that displays unique efficacy in heterologously expressed rNav1.2, rNav1.4 and rNav1.5 alpha subunits

“…ATX has been demonstrated to allosterically stimulate [ 3 H]BTX binding in cerebellar granule cells [11]. This enhancement can be further augmented by PbTx-2 suggesting a positive allosteric interaction between neurotoxin site 5 and the ATX site [11]. In the present study we demonstrated that a subthreshold concentration of ATX significantly potentiated PbTx-2-induced sodium influx in rNa v 1.4 α-subunit expressing cells.…”

“…ATX binds to a site on the sodium channel α-subunit that remains to be defined and stimulates sodium influx in cerebellar granule and neocortical neurons [11,12]. Veratridine is a steroid-derived alkaloid purified from the plant Liliaceae family.…”

Pharmacology and toxicology of pahayokolide A, a bioactive metabolite from a freshwater species of Lyngbya isolated from the Florida Everglades

“…Pharmacological activity of such Lyngbya-derived compounds ranges from microtubule inhibitors, such as curacin A (Gerwick et al, 1994), to potent sodium channel blockers and activators, such as kalkitoxin (Wu et al, 2000) and antillatoxin (Li et al, 2001). On the other hand, exposure to Lyngbya toxins have also been associated with various human health effects (Izumi and Moore, 1987;Osborne et al, 2001).…”

Marine diazotrophic cyanobacteria: Out of the blue

“…Some bloomforming cyanobacteria also produce toxins, which are actually more toxic to human and terrestrial mammals than to aquatic biota. Neurotoxins and hepatotoxins produced by some of the bloom-forming cyanobacteria, such as Nodularia (Laamanen et al 2001;Sivonen et al 1989) and Lyngbya majuscula (Li et al 2001), cause economic losses to the surrounding societies, ranging from disturbance in tourism due to the unpleasant smell, skin irritation and gastrointestinal problems of the swimmers, to death of fish and domestic animals drinking the water. Interestingly, and for an unknown reason, blooms of toxic cyanobacterial species may contain both toxic and non-toxic strains.…”