Acetate labeling patterns of dinoflagellate polyketides, amphidinols 2, 3 and 4

Membrane-permeabilizing activities of amphidinol 3, polyene-polyhydroxy antifungal from a marine dinoflagellate

Amphidinols, which are polyene-polyhydroxy metabolites produced by the marine dinoflagellate Amphidinium klebsii, possess potent antifungal and hemolytic activities. The membrane permeabilizing actions of amphidinol 3, the most potent homologue, were compared with those of polyene antibiotics, amphotericin B (AmB) and filipin, in hemolytic tests, 23Na nuclear magnetic resonance (NMR)-based membrane permeabilizing assays, and UV spectroscopy for liposome-bound forms. In Na+ flux experiments using large unilamellar vesicles (LUVs), ion efflux by amphidinol 3 was inhibited by cholesterol or ergosterol, which was opposed to previous results [J. Mar. Biotechnol., 5 (1997) 124]. When the effect of the agents on the size of vesicles was examined by light scattering experiments, amphidinol 3 did not significantly alter their size while filipin and synthetic detergent Triton X-100 did. The observations implied that the activity of amphidinol 3 was mainly due to formation of large pores/lesions in liposomes rather than detergent-like disruption of membrane. The pore/lesion size was estimated to be 2.0-2.9 nm in diameter on the basis of osmotic protection experiments using blood cells. The UV spectra in liposomes, which revealed the close interaction of polyene moieties in a lipid bilayer, further implied that the membrane activity of amphidinol 3 is caused by the molecular assemblage formed in biomembrane. These results disclose that amphidinol 3 is one of few non-ionic compounds that possess potent membrane permeabilizing activity with non-detergent mechanism.

Biosynthetic studies of the DSP toxin skeleton

Marine toxins have drawn wide interest because their economical impact and disastrous effect upon the shellfish industry and public health in many parts of the world. One of the most interesting group of substances of marine toxins, from structural and pharmacological points of view are polyether compounds, which generally present a great diversity in size and potent biological activities. The subject of this work was about to biosynthesis of okadaic acid skeleton as leader as DSP toxins. Its biosynthesis attracts considerable attention since the carbon skeleton has been shown to be synthesised via an unusual route. In this paper we report on stable isotope incorporation experiments on DSP toxin in artificial cultures of dinoflagellate. The comparison of the degrees of incorporation in these samples measured by different methods led to contradictory results. This implies that further experimental data is needed in order to propose a logical biogenetic scheme.