Induction of apoptosis pathways in several cell lines following exposure to the marine algal toxin azaspiracid.

Azaspiracids (AZAs) are polyether marine dinoflagellate toxins that accumulate in shellfish and represent an emerging human health risk. Although there have been no deaths associated with the AZA toxins, humans exposed to AZAs experience severe gastrointestinal symptoms. This toxin class has been shown to be highly cytotoxic, a teratogen to developing fish, and a possible carcinogen in mice. Just recently, the AZAs have been shown to be potassium channel inhibitors. This report employed multiple human cell lines [Jurkat T lymphocytes, Caco-2 intestinal cells, and BE(2)-M17 neuroblastoma cells] in characterizing cytotoxicity and pathways of apoptosis. Cytotoxicity experiments were consistent with published literature that has shown that AZA1 is cytotoxic in both a concentration- and time-dependent manner to each cell type tested, with mean EC(50) values ranging between 1.1 and 7.4 nM. Despite the absence of morphological indices indicating apoptosis, caspase-3/7 activity was higher in all cell types treated with AZA1. Furthermore, in T lymphocytes, the most sensitive cell type, the activities of initiator caspase-2 and caspase-10 and concentrations of intracellular cytochrome c were elevated. DNA fragmentation was also observed for T lymphocytes exposed to AZA1-AZA3. Collectively, our data confirm that AZA1 was highly cytotoxic to multiple cell types and that cells exposed to AZA1 underwent atypical apoptosis, possibly in conjunction with necrotic cytotoxicity.

Inhibitory effects of pectenotoxins from marine algae on the polymerization of various actin isoforms.

Pectenotoxins (PTXs) are marine toxins produced by dinoflagellates and which accumulate in shellfish. There are at least 14 different analogs of PTX with slight variations in structure leading to different chemical properties and consequently different toxicities. Since preliminary studies have shown that the parent compound PTX1 targets actin, we investigated the effects of two analogs, PTX2 and PTX2 seco acid, on the polymerization and depolymerization of skeletal muscle actin, smooth muscle actin, cardiac muscle actin, and non-muscle actin. Optimized actin assays using fluorescently labeled skeletal muscle actin and SDS-PAGE were jointly used to determine the relative amounts of filamentous and globular actin formed during polymerization and depolymerization experiments. Our findings suggest that PTX2 causes a dose-dependent decrease in both the rate and yield of skeletal muscle actin polymerization (IC50 values of 44 and 177 nM; respectively), with no significant effects on depolymerization. Moreover, the inhibitory effects of PTX2 are conserved towards other actin isoforms (i.e., smooth muscle, cardiac muscle, and non-muscle), as the inhibitory effects on actin polymerization were also observed with similar IC50 values (range: 19-94 nM). No inhibitory effects on polymerization were observed for PTX2 seco acid, suggesting an intact lactone ring is necessary for bioactivity.