Goniodomin A, an antifungal polyether macrolide, increases the filamentous actin content of 1321N1 human astrocytoma cells

Effects of the toxic dinoflagellate, Alexandrium pacificum, on the marine diatom, Chaetoceros muelleri, and mussel (Perna canaliculus) sperm and hemocytes

Harmful algal blooms (HABs) of Alexandrium pacificum have affected the Marlborough Sounds in New Zealand since 2010, posing a threat to green-lipped mussel (GLM, Perna canaliculus) farming. Previous studies have shown A. pacificum has negative effects GLM embryos and larvae. To further investigate these toxic mechanisms, in vitro bioassays were conducted on GLM spermatozoa, hemocytes, and the diatom, Chaetoceros muelleri. The three cell types were exposed to several treatments of A. pacificum for 2 h and responses were measured using flow cytometry and pulse amplitude-modulated fluorometry. Significant spermatozoa mortality was recorded in treatments containing A. pacificum cells or fragments, while hemocyte and C. muelleri mortality was recorded in cell-free treatments of A. pacificum which contained paralytic shellfish toxins (PSTs). Variation in sensitivity between cell types as well as the sublethal effects observed, emphasise the diverse toxic mechanisms of A. pacificum on co-occurring species in the environment.

Alexandrium spp.: From Toxicity to Potential Biotechnological Benefits

Many dinoflagellates of the genus Alexandrium are well known for being responsible for harmful algal blooms (HABs), producing potent toxins that cause damages to other marine organisms, aquaculture, fishery, tourism, as well as induce human intoxications and even death after consumption of contaminated shellfish or fish. In this review, we summarize potential bioprospecting associated to the genus Alexandrium, including which Alexandrium spp. produce metabolites with anticancer, antimicrobial, antiviral, as well as anti-Alzheimer applications. When available, we report their mechanisms of action and targets. We also discuss recent progress on the identification of secondary metabolites with biological properties favorable to human health and aquaculture. Altogether, this information highlights the importance of studying which culturing conditions induce the activation of enzymatic pathways responsible for the synthesis of bioactive metabolites. It also suggests considering and comparing clones collected in different locations for toxin monitoring and marine bioprospecting. This review can be of interest not only for the scientific community, but also for the entire population and industries.

Mass spectrometric characterization of the seco acid formed by cleavage of the macrolide ring of the algal metabolite goniodomin A

Goniodomin A (GDA) is a polyketide macrolide produced by multiple species of the marine dinoflagellate genus Alexandrium. GDA is unusual in that it undergoes cleavage of the ester linkage under mild conditions to give mixtures of seco acids (GDA-sa). Ring-opening occurs even in pure water although the rate of cleavage accelerates with increasing pH. The seco acids exist as a dynamic mixture of structural and stereo isomers which is only partially separable by chromatography. Freshly prepared seco acids show only end absorption in the UV spectrum but a gradual bathochromic change occurs, which is consistent with formation of α,β-unsaturated ketones. Use of NMR and crystallography is precluded for structure elucidation. Nevertheless, structural assignments can be made by mass spectrometric techniques. Retro-Diels-Alder fragmentation has been of value for independently characterizing the head and tail regions of the seco acids. The chemical transformations of GDA revealed in the current studies help clarify observations made on laboratory cultures and in the natural environment. GDA has been found to reside mainly within the algal cells while the seco acids are mainly external with the transformation of GDA to the seco acids occurring largely outside the cells. This relationship, plus the fact that GDA is short-lived in growth medium whereas GDA-sa is long-lived, suggests that the toxicological properties of GDA-sa in its natural environment are more important for the survival of the Alexandrium spp. than those of GDA. The structural similarity of GDA-sa to that of monensin is noted. Monensin has strong antimicrobial properties, attributed to its ability to transport sodium ions across cell membranes. We propose that toxic properties of GDA may primarily be due to the ability of GDA-sa to mediate metal ion transport across cell membranes of predator organisms.

Phytoplankton Toxins and Their Potential Therapeutic Applications: A Journey toward the Quest for Potent Pharmaceuticals

Phytoplankton are prominent organisms that contain numerous bioactive substances and secondary metabolites, including toxins, which can be valuable to pharmaceutical, nutraceutical, and biotechnological industries. Studies on toxins produced by phytoplankton such as cyanobacteria, diatoms, and dinoflagellates have become more prevalent in recent years and have sparked much interest in this field of research. Because of their richness and complexity, they have great potential as medicinal remedies and biological exploratory probes. Unfortunately, such toxins are still at the preclinical and clinical stages of development. Phytoplankton toxins are harmful to other organisms and are hazardous to animals and human health. However, they may be effective as therapeutic pharmacological agents for numerous disorders, including dyslipidemia, obesity, cancer, diabetes, and hypertension. In this review, we have focused on the properties of different toxins produced by phytoplankton, as well as their beneficial effects and potential biomedical applications. The anticancer properties exhibited by phytoplankton toxins are mainly attributed to their apoptotic effects. As a result, phytoplankton toxins are a promising strategy for avoiding postponement or cancer treatment. Moreover, they also displayed promising applications in other ailments and diseases such as Alzheimer’s disease, diabetes, AIDS, fungal, bacterial, schizophrenia, inflammation, allergy, osteoporosis, asthma, and pain. Preclinical and clinical applications of phytoplankton toxins, as well as future directions of their enhanced nano-formulations for improved clinical efficacy, have also been reviewed.

Macrolides: From Toxins to Therapeutics

Macrolides are a diverse class of hydrophobic compounds characterized by a macrocyclic lactone ring and distinguished by variable side chains/groups. Some of the most well characterized macrolides are toxins produced by marine bacteria, sea sponges, and other species. Many marine macrolide toxins act as biomimetic molecules to natural actin-binding proteins, affecting actin polymerization, while other toxins act on different cytoskeletal components. The disruption of natural cytoskeletal processes affects cell motility and cytokinesis, and can result in cellular death. While many macrolides are toxic in nature, others have been shown to display therapeutic properties. Indeed, some of the most well known antibiotic compounds, including erythromycin, are macrolides. In addition to antibiotic properties, macrolides have been shown to display antiviral, antiparasitic, antifungal, and immunosuppressive actions. Here, we review each functional class of macrolides for their common structures, mechanisms of action, pharmacology, and human cellular targets.

Algal Toxin Goniodomin A Binds Potassium Ion Selectively to Yield a Conformationally Altered Complex with Potential Biological Consequences

The marine toxin goniodomin A (GDA) is a polycyclic macrolide containing a spiroacetal and three cyclic ethers as part of the macrocycle backbone. GDA is produced by three species of the Alexandrium genus of dinoflagellates, blooms of which are associated with "red tides", which are widely dispersed and can cause significant harm to marine life. The toxicity of GDA has been attributed to stabilization of the filamentous form of the actin group of structural proteins, but the structural basis for its binding is not known. Japanese workers, capitalizing on the assumed rigidity of the heavily substituted macrolide ring, assigned the relative configuration and conformation by relying on NMR coupling constants and NOEs; the absolute configuration was assigned by degradation to a fragment that was compared with synthetic material. We have confirmed the absolute structure and broad features of the conformation by X-ray crystallography but have found GDA to complex with alkali metal ions in spite of two of the heterocyclic rings facing outward. Such an arrangement would have been expected to impair the ability of GDA to form a crown-ether-type multidentate complex. GDA shows preference for K⁺, Rb⁺, and Cs⁺ over Li⁺ and Na⁺ in determinations of relative affinities by TLC on metal-ion-impregnated silica gel plates and by electrospray mass spectrometry. NMR studies employing the K⁺ complex of GDA, formed from potassium tetrakis[pentafluorophenyl]borate (KBArF₂₀), reveal a major alteration of the conformation of the macrolide ring. These observations argue against the prior assumption of rigidity of the ring. Alterations in chemical shifts, coupling constants, and NOEs indicate the involvement of most of the molecule other than ring F. Molecular mechanics simulations suggest K⁺ forms a heptacoordinate complex involving O_A, O_B, O_C, O_D, O_E, and the C-26 and C-27 hydroxy groups. We speculate that complexation of K⁺ with GDA electrostatically stabilizes the complex of GDA with filamentous actin in marine animals due to the protein being negatively charged at physiological pH. GDA may also cause potassium leakage through cell membranes. This study provides insight into the structural features and chemistry of GDA that may be responsible for significant ecological damage associated with the GDA-producing algal blooms.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Cytotoxicity of goniodomin A and B in non contractile cells

Goniodomin A is a phycotoxin produced by the dinoflagellates Alexandrium hiranoi (formerly Goniodoma pseudogoniaulax) and Alexandrium monilatum. This polyether macrolide exerts a potent antifungal effect and disturbs the actomyosin ATPase activity and the F-actin meshwork in diverse cell types. Goniodomin B is a fused acetal isomer isolated with goniodomin A with unknown activity. Histopathological changes induced by goniodomin A postulated hepatocytes as target cells. In this study both compounds induce a time and concentration dependent fall in the viability of Clone 9 rat hepatocytes. Furthermore, for both compounds, primary rat hepatocytes are almost 10 folds less sensitive than Clone 9 cells. Goniodomin A is highly effective in the nanomolar range while micromolar concentrations of goniodomin B are necessary to observe cytoxicity. Additionally, goniodomin A induced a significant increase in the F-actin and decrease in the G-actin content of Clone 9 cells but did not change the actin of primary cultured hepatocytes. However, goniodomin B could not exert significant alterations in the cytoskeleton of neither cell type. Futhermore goniodomin A as well as goniodomin B are cytotoxic to excitable cells. Both analogues triggered a time dependent decrease on viability in BE(2)-M17 human neuroblastoma cells. In this cell model goniodomin A increased the intracellular calcium and depolarized cells. We conclude that goniodomins A and B are biologically active molecules in hepatocytes and also in excitable cells BE(2)-M17. However, the analogue goniodomin B, whose activity is described in this work for the first time, is a much less potent compound.

Synthesis of macrocyclic shellfish toxins containing spiroimine moieties

An overview of the structure and biological activity of macrocyclic polyketides derived from dinoflagellates that contain unusual cyclic imine units is provided. The total and partial syntheses of these molecules are discussed with an emphasis on the construction of the spiroimine functionality thought to be the key pharmacophore of these fact-acting shellfish toxins.

Goniodomin A, an antifungal polyether macrolide, exhibits antiangiogenic activities via inhibition of actin reorganization in endothelial cells

Goniodomin A (GDA) is an antifungal polyether macrolide isolated from the dinoflagellate Goniodoma pseudogoniaulax. Previous studies revealed that GDA profoundly affected cytoskeletal reorganization. We examined the effect of GDA on the angiogenic properties of vascular endothelial cells. GDA itself did not affect proliferation of, migration of, and tube formation in type I collagen gels by, bovine aortic endothelial cells (BAECs). Proliferation of BAECs stimulated by bFGF was not affected by GDA at concentrations of up to 10 nM. However, at similar concentrations, GDA significantly inhibited bFGF-induced migration and tube formation in type I collagen gels by BAECs. Actin reorganization is required for cell migration. GDA caused the perinuclear aggregation of filamentous actin and inhibited stress fiber formation in bFGF- or VEGF-stimulated BAECs and lysophosphatidic acid-stimulated HeLa cells. However, GDA did not affect stress fiber structures already formed through Gbetagamma expression or in constitutively active RhoA mutant HeLa cells. Finally, GDA inhibited forming of vasucular system in a chorioallantoic membrane. Our results indicated that GDA suppressed angiogenic properties of ECs at least in part through the inhibition of actin reorganization and inhibited angiogenesis in vivo.