Distribution and sequestration of palytoxin in coral reef animals

Characteristics of palytoxin-induced cytotoxicity in neuroblastoma cells

Cation fluxes appear to play a key role in palytoxin-induced signal. There are other cellular targets that have not been described as well as the biochemical signaling cascades that transmit palytoxin-stimulated signals remain to be clarified. Since modifications of cations, mainly calcium, are generally associated to cell death or apoptosis, we wanted to further evaluate the effect of palytoxin on cell death. Then, in vitro cytotoxic effects of palytoxin were characterized on human neuroblastoma cells. By using several techniques, we studied markers of cell death and apoptosis, such as cell detachment, mitochondrial membrane potential, caspases, DNA damage, LDH leakage, propidium iodide uptake, F-actin depolymerization and inhibition of cellular proliferation. Results show that palytoxin triggers a series of toxic responses; it inhibits cell proliferation, induces cell rounding, detachment from the substratum and F-actin disruption. Among the apoptotic markers studied we only detected fall in mitochondrial membrane potential. Neither caspases activation nor chromatin condensation or DNA fragmentation were observed in palytoxin-treated cells.

Effects of the marine toxins okadaic acid and palytoxin on mussel phagocytosis

The present study analyzes the effects of the marine toxins okadaic acid (OA) and palytoxin (PTX) on the phagocytic activity of immunocytes from the mussel Mytilus galloprovincialis. In particular, we describe how the effects of the two biotoxins are influenced by the temperature and experimental stress applied before hemolymph withdrawal. The collected data indicate that OA increases phagocytic activity only when hemolymph incubation is performed at 25 degrees C, but not at 20 degrees C, suggesting a certain degree of dependence of OA effects from the status of mussel immunocytes. Conversely, PTX plays an active role in immunocyte signalling transduction pathways, increases the phagocytic activity and markedly promotes the involvement of p38 mitogen-activated protein (MAP) kinase in phagocytosis. Overall, we conclude that both OA and PTX influence mussel phagocytic activity, and the toxic effects may depend on both the mollusc conditions and the activation of specific signalling pathways.

Toxic polypeptides of the hydra—a bioinformatic approach to cnidarian allomones

Cnidarians such as hydrae and sea anemones are sessile, predatory, soft bodied animals which depend on offensive and defensive allomones for prey capture and survival. These allomones are distributed throughout the entire organism both in specialized stinging cells (nematocytes) and in the body tissues. The cnidarian allomonal system is composed of neurotoxins, cytolysins and toxic phospholipapses. The present bioinformatic survey was motivated by the fact that while hydrae are the most studied model cnidarian, little is known about their allomones. A large-scale EST database from Hydra magnipapillata was searched for orthologs of known cnidarian allomones, as well as for allomones found in other venomous organisms. We show that the hydrae express orthologs of cnidarian phospholipase A2 toxins and cytolysins belonging to the actinoporin family, but could not find orthologs of the 'classic' short chain neurotoxins affecting sodium and potassium conductance. Hydrae also express proteins similar to elapid-like phospholipases, CRISP proteins, Prokineticin-like polypeptides and toxic deoxyribonucleases. Our results illustrate a high level of complexity in the hydra allomonal system, suggest that several toxins represent a basal component of all cnidarian allomones, and raise the intriguing possibility that similar proteins may fulfill both endogenous and allomonal roles in cnidaria.

Prey-capture in Pomacanthus semicirculatus (Teleostei,Pomacanthidae): functional implications of intramandibular joints in marine angelfishes

We examined prey-capture morphology and kinematics in the angelfish, Pomacanthus semicirculatus (Cuvier 1931), to evaluate the magnitude and role of functional specialisation. The feeding apparatus of P. semicirculatus possess three biomechanical mechanisms of particular interest: (1) a novel intramandibular joint, permitting dentary rotation and protruded jaw closure; (2) an opercular linkage facilitating mandible depression; and (3) a suspensorial linkage with two novel points of flexion,permitting anterior rotation of the suspensorium and augmenting mandible protrusion. Prey-capture kinematics were quantified using motion analysis of high-speed video, yielding performance profiles illustrating timing of onset,duration and magnitude of movement in these three biomechanical systems, and other variables traditionally quantified in studies of teleostean ram–suction feeding activity. Mandible depression and suspensorial rotation both augmented mandible protrusion, and coincided during jaw protrusion, typically increasing head length by 30%. Jaw closure appeared to result from contraction of the adductor mandibulae segment A2, which rotated the dentary by approximately 30° relative to the articular. This resulted in jaw closure with the mandible fully depressed and the jaws at peak-protrusion. Feeding events were concluded by a high-velocity jaw retraction (20–50 ms), and completed in 450–750 ms. Feeding kinematics and morphology of Pomacanthus differed from other biting teleosts, and more closely resemble some long-jawed ram–suction feeders. The structural and functional modifications in the Pomacanthusfeeding apparatus are matched to an unusual diet of structurally resilient and firmly attached benthic prey.

Cytotoxic actions of palytoxin on aortic smooth muscle cells in culture

Palytoxin (PTX), isolated from a zoanthid of the genus Palythoa, is the most potent marine toxin known. Intoxication by PTX leads to vasoconstriction, hemorrhage, ataxia, muscle weakness, ventricular fibrillation, pulmonary hypertension, ischemia and death. In this study, clonal A7r5 rat aortic smooth muscle cells were used to study the mechanism of PTX-mediated cytotoxicity. A7r5 cells exposed to PTX for > or = 15 min exhibited surface granularities, vacuoles and rounding. These alterations culminated in a loss of viability as indicated by marked increases in the release of lactate dehydrogenase. Electrophysiological recording from A7r5 cells disclosed a profound membrane depolarization and an increase in conductance to Na+ and K+. PTX-mediated cytotoxicity could not be reversed by washout or by the addition of 10 microM verapamil but was antagonized by 100 microM ouabain or by removal of extracellular Na+ or Ca2+. In light of the involvement of vascular smooth muscle in PTX poisoning, A7r5 cells could serve as a useful model to test specific drugs for treatment of PTX intoxication.

Identification of palytoxin as a principle which causes morphological changes in rat 3Y1 cells in the zoanthid Palythoa aff. margaritae

A very potent cell-bursting principle was isolated from the extract of the zoanthid Palythoa aff. margaritae. The compound was identified as palytoxin by comparing the spectral data and HPLC profile with those of an authentic sample.

Structure elucidation of ostreocin D, a palytoxin analog isolated from the dinoflagellate Ostreopsis siamensis

The structure of ostreocin D, a palytoxin analog isolated from the marine dinoflagellate Ostreopsis siamensis, was found to be 42-hydroxy-3,26-didemethyl-19,44-dideoxypalytoxin by detailed 2D NMR analyses of intact ostreocin D and its ozonolysis products. Partial stereochemical assignments were done. This result indicates that the dinoflagellate O. siamensis is one of the biogenetic origins of palytoxin.

Delayed haemolytic activity by the freshwater puffer Tetraodon sp. toxin

In order to elucidate the toxin composition of the freshwater puffer in Bangladesh, about 230 specimens of Tetraodon sp. were collected from 1997 to 1999 and extracted. After partitioning the toxins between an aqueous layer and a 1-butanol layer, the toxin in the aqueous layer was characterized as paralytic shellfish poison (PSP) (data not shown), while the toxin in the 1-butanol layer was identified as palytoxin (PTX) or PTX-like substance based on the delayed haemolytic activity which was inhibited by an anti-PTX antibody and ouabain (g-strophanthin). This is the first report on the occurrence of PTX or PTX-like substance(s) in puffer fish.

Toxicity in animals. Trends in evolution?

Animals acquire toxicity either by metabolic synthesis of toxins (secondary metabolites), by expression of toxin genes or by the uptake, storage and sequestration of toxins produced by other organisms, i.e., microbes, plants or other animals. Variability of toxin structure and function is high. Peptide toxins in particular, although relying on a limited number of structural frameworks, often exhibit considerable structural hypervariability. An accelerated rate of evolution in the toxin gene structure (conserved introns, but high substitution rates in the exons) leads to the functional diversity of these peptides or proteins. The selective forces which may drive toxin evolution are unknown. Venomousness or the possession of toxins can be essential for survival, but the advantage of toxin biosynthesis may also be of minor importance or has been lost during evolution.