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The frequent occurrence of Moorea producens (formerly Lyngbya majuscula) blooms has been associated with adverse effects on human health. Hoiamide A is a structurally unique cyclic depsipeptide isolated from an assemblage of the marine cyanobacteria M. producens and Phormidium gracile. We examined the influence of hoiamide A on neurite outgrowth in neocortical neurons and found that it suppressed neurite outgrowth with an IC50 value of 4.89 nM. Further study demonstrated that hoiamide A stimulated lactic acid dehydrogenase (LDH) efflux, nuclear condensation and caspase-3 activity with EC50 values of 3.66, 2.55 and 4.33 nM, respectively. These data indicated that hoiamide A triggered a unique neuronal death profile that involves both necrotic and apoptotic mechanisms. The similar potencies and similar time-response relationships between LDH efflux and caspase-3 activation/nuclear condensation suggested that both necrosis and apoptosis may derive from interaction with a common molecular target. The broad-spectrum caspase inhibitor, Z-VAD-FMK completely inhibited hoiamide A-induced neurotoxicity. Additionally, hoiamide A stimulated JNK phosphorylation, and a JNK inhibitor attenuated hoiamide A-induced neurotoxicity. Collectively, these data demonstrate that hoiamide A-induced neuronal death requires both JNK and caspase signaling pathways. The potent neurotoxicity and unique neuronal cell death profile of hoiamide A represents a novel neurotoxic chemotype from marine cyanobacteria.

Voltage-gated sodium channels (VGSCs) are responsible for the generation of the action potential. Among nine classified VGSC subtypes (Nav1.1–Nav1.9), Nav1.7 is primarily expressed in the sensory neurons, contributing to the nociception transmission. Therefore Nav1.7 becomes a promising target for analgesic drug development. In this study, we compared the influence of an array of VGSC agonists including veratridine, BmK NT1, brevetoxin-2, deltamethrin and antillatoxin (ATX) on membrane depolarization which was detected by Fluorescence Imaging Plate Reader (FLIPR) membrane potential (FMP) blue dye. In HEK-293 cells heterologously expressing hNav1.7 α-subunit, ATX produced a robust membrane depolarization with an EC50 value of 7.8 ± 2.9 nM whereas veratridine, BmK NT1, and deltamethrin produced marginal response. Brevetoxin-2 was without effect on membrane potential change. The ATX response was completely inhibited by tetrodotoxin suggesting that the ATX response was solely derived from hNav1.7 activation, which was consistent with the results where ATX produced a negligible response in null HEK-293 cells. Six VGSC antagonists including lidocaine, lamotrigine, phenytoin, carbamazepine, riluzole, and 2-amino-6-trifluoromethylthiobenzothiazole all concentration-dependently inhibited ATX response with IC50 values comparable to that reported from patch-clamp experiments. Considered together, we demonstrate that ATX is a unique efficacious hNav1.7 activator which offers a useful probe to develop a rapid throughput screening assay to identify hNav1.7 antagonists.

Voltage-gated sodium channels (VGSCs) are responsible for the generation of the action potential. Among nine classified VGSC subtypes (Nav1.1-Nav1.9), Nav1.7 is primarily expressed in the sensory neurons, contributing to the nociception transmission. Therefore Nav1.7 becomes a promising target for analgesic drug development. In this study, we compared the influence of an array of VGSC agonists including veratridine, BmK NT1, brevetoxin-2, deltamethrin and antillatoxin (ATX) on membrane depolarization which was detected by Fluorescence Imaging Plate Reader (FLIPR) membrane potential (FMP) blue dye. In HEK-293 cells heterologously expressing hNav1.7 α-subunit, ATX produced a robust membrane depolarization with an EC50 value of 7.8 ± 2.9 nM whereas veratridine, BmK NT1, and deltamethrin produced marginal response. Brevetoxin-2 was without effect on membrane potential change. The ATX response was completely inhibited by tetrodotoxin suggesting that the ATX response was solely derived from hNav1.7 activation, which was consistent with the results where ATX produced a negligible response in null HEK-293 cells. Six VGSC antagonists including lidocaine, lamotrigine, phenytoin, carbamazepine, riluzole, and 2-amino-6-trifluoromethylthiobenzothiazole all concentration-dependently inhibited ATX response with IC50 values comparable to that reported from patch-clamp experiments. Considered together, we demonstrate that ATX is a unique efficacious hNav1.7 activator which offers a useful probe to develop a rapid throughput screening assay to identify hNav1.7 antagonists. [ABSTRACT FROM AUTHOR]