Philippe Amade

Chemical defence of the mediterranean alga Caulerpa taxifolia: variations in caulerpenyne production

Abstract Caulerpenyne (Cyn) is the major secondary metabolite involved in the chemical defence of Caulerpa taxifolia. A fast chromatography technique for Cyn quantification in algal samples of fronds and stolons collected monthly at Cap Martin (France), from depth of 5–30 m, is reported. Temperature influenced Cyn production in this alga of subtropical origin and the maximum concentration was in fronds at 5 m depth in summer period when the water temperature rose above 19°C. The amount of Cyn decreased at increasing depths and Cyn concentrations were always higher in fronds than in stolons. Variations in Cyn concentration explained seasonal changes in (1) feeding behaviour of the sea urchin Paracentrotus lividus and (2) biomass of fouling organisms of C. taxifolia. Tropical strains of this alga always contain less Cyn than the mediterranean strain. Geographical, seasonal, depth and intraplant variations of Cyn concentrations are discussed versus influences of biotic and abiotic factors.

Bioactive guanidine alkaloids from two Caribbean marine sponges.

Seven new guanidine alkaloids (1-7) together with the known batzelladines A, F, H, and L, ptilomycalin A, and fromiamycalin were isolated from the Caribbean marine sponges Monanchora arbuscula and Clathria calla. Molecular structures were assigned on the basis of detailed analysis of 1D and 2D NMR spectra and mass spectrometry data, and bioactivities of the alkaloids were evaluated against human cancer cell lines and malaria protozoa.

Antiprotozoal steroidal saponins from the marine sponge Pandaros acanthifolium.

The chemical composition of the Caribbean sponge Pandaros acanthifolium was reinvestigated and led to the isolation of 12 new steroidal glycosides, namely, pandarosides E-J (1-6) and their methyl esters (7-12). Their structures were determined on the basis of extensive spectroscopic analyses, including two-dimensional NMR and HRESIMS data. Like the previously isolated pandarosides A-D (13-16), the new compounds 1-12 share an unusual oxidized D-ring and a cis C/D ring junction. The absolute configurations of the aglycones were assigned by interpretation of CD spectra, whereas the absolute configurations of the monosaccharide units were determined by chiral GC analyses of the acid methanolysates. The majority of the metabolites showed in vitro activity against three or four parasitic protozoa. Particularly active were the compounds 3 (pandaroside G) and its methyl ester (9), which potently inhibited the growth of Trypanosoma brucei rhodesiense (IC(50) values 0.78 and 0.038 microM, respectively) and Leishmania donovani (IC(50)s 1.3 and 0.051 microM, respectively).

Parazoanthines A-E, hydantoin alkaloids from the Mediterranean sea anemone Parazoanthus axinellae.

Five new hydantoin alkaloids, named parazoanthines A-E (1-5), were isolated as the major constituents of the Mediterranean sea anemone Parazoanthus axinellae. Their structural elucidation was achieved through NMR spectroscopic and mass spectrometric analyses. The absolute configuration of the chiral compounds 1 and 4 was determined by comparison between experimental and TDDFT-calculated CD spectra. The configuration of the trisubstituted double bond of 2, 3, and 5 was deduced from the (3)J(H6-C4) coupling constant value. This family of alkaloids represents the first example of natural 3,5-disubstituted hydantoins that do not exhibit a methyl at N-3. All compounds were tested for their natural toxicity (Microtox assay), and parazoanthine C (3) exhibited the highest natural toxicity.

Hanishin, a Semiracemic, Bioactive C9 Alkaloid of the Axinellid Sponge Acanthella carteri from the Hanish Islands. A Shunt Metabolite?

The C9 alkaloid hanishin (2), isolated from a collection in the Hanish Islands (Red Sea) of the highly polymorphic sponge Acanthella carteri, has low enantiomeric purity and may be viewed as a shunt metabolite, albeit biologically active, from co-occurring oroidin (1).

Effects of caulerpenyne, the major toxin from Caulerpa taxifolia on mechanisms related to sea urchin egg cleavage

Abstract Caulerpenyne (CYN), the major metabolite synthesized by the alga Caulerpa taxifolia (Vahl), inhibited the first cleavage of sea urchin eggs without affecting fertilization. The effect was dose-dependent with a half maximal dose of 33 μM. Blockage of cleavage was observed when the toxin was added within 40 min of insemination. A preliminary search for the cellular targets of this toxin showed that ionic signals involved in the cell dynamics are altered: caulerpenyne reduced the intracellular ATP-dependent Ca 2+ accumulation in a dose-dependent manner but did not provoke a release of sequestered Ca 2+ . This effect is similar to that of thapsigargin, a specific inhibitor of reticular Ca 2+ -ATPase. CYN had no effect on the incorporation of 35 S-methionine into proteins. 3 H-thymidine incorporation into DNA was inhibited by CYN in a dose-dependent manner: an effect well correlated with cell division kinetics. A CYN concentration of 30 μM, which delayed the first cleavage, inhibited overall protein phosphorylation but did not affect histone kinase phosphorylating activity. Thus, CYN appears to alter the main events of sea urchin egg cleavage, and may therefore constitute an ecological risk for microorganisms and eggs of pluricellular animals living close to these algae. Moreover, this compound is of potential pharmacological interest in view of its antiproliferative properties.

Elysia subornata (Mollusca) a potential control agent of the alga Caulerpa taxifolia (Chlorophyta) in the Mediterranean Sea

The biological characteristics of Elysia subornata (Mollusca: Opisthobranchia) were studied in an aquarium to assess its risks and chance of success as a potential biological control agent against the invasive alga Caulerpa taxifolia (Chlorophyta) in the Mediterranean Sea. This species feeds only on Caulerpa and has benthic larval development. Dietary switching is possible on some Mediterranean Caulerpales but feeding on other algae and sea grass is unlikely. The main limiting factor for the success of studied Caribbean strain of E. subornata are the Mediterranean winter temperatures which are lethal for that species. For the five months of the year which are favourable for feeding, growth and reproduction, the tested strain of E. subornata cannot reach a population density capable of controlling C. taxifolia .

MICROALGAE : A MODEL TO INVESTIGATE THE ECOTOXICITY OF THE GREEN ALGA CAULERPA TAXIFOLIA FROM THE MEDITERRANEAN SEA

Abstract The spectacular development of the green alga Caulerpa taxifolia (Vahl) C. Agardh, introduced in the Mediterranean in 1984, represents a biological pollution which threatens the biodiversity of the marine ecosystem. The weak pressure from grazers and the presence of repulsive secondary metabolites make the problem worse. Whereas the anti-appetant effect of these metabolites is well known, their role in competition between algae has not been extensively studied. Using a microalgal model representing the initial stage of the marine food chain, we studied the effects of C. taxifolia metabolites. We showed that organic extracts of C. taxifolia and caulerpenyne inhibit or delay the proliferation of several phytoplanktonic strains to various degrees. Seasonal variations of the toxicity were observed with a maximal effect in the summer. Experiments with Dunaliella minuta showed that caulerpenyne did not affect the protein content but strongly reduced that of the cell chlorophyll A.

EVALUATION OF THE TOXICOLOGICAL RISK TO HUMANS OF CAULERPENYNE USING HUMAN HEMATOPOIETIC PROGENITORS, MELANOCYTES, AND KERATINOCYTES IN CULTURE

The extensive growth of Caulerpa taxifolia in the Mediterranean sea produces important quantities of bioactive secondary metabolites unable to enter the food chain. The cytotoxic effects of caulerpenyne, the major secondary metabolite from C. taxifolia, was studied in different in vitro models: skin cells, primary cultures of melanocytes and keratinocytes, immortalized keratinocytes (HaCaT and HESV), and bone marrow cells (hematopoietic progenitors CFU-GM). Typical dose-response curves from neutral red uptake and MTT assays were recorded in all models with IC50 ranging from 6 to 24 microM. Hematopoietic progenitors were more sensitive to caulerpenyne than melanocyte and keratinocyte cell lines, which could be due to their higher proliferative rate. The distribution of aggregates in colonies, macroclusters, and microclusters of hematopoietic progenitors was also altered in the presence of caulerpenyne. From our evaluation of the caulerpenyne concentrations required to result in cellular toxicity, the risks of cutaneous and/or food intoxication to humans may be considered minimal.

Plumisclerin A, a Diterpene with a New Skeleton from the Soft Coral Plumigorgia terminosclera

A novel compound, named plumisclerin A (1), was isolated from samples of the soft coral Plumigorgia terminosclera collected at Mayotte Island. The compound possesses the novel plumisclerane carbon skeleton, including a tricyclo[4,3,1,0(1,5)]decane ring. Its structure and relative stereochemistry were elucidated by extensive spectroscopic analysis, including HREIMS, COSY, HSQC, HMBC, TOCSY, and NOESY experiments. In addition, the novel compound displayed in vitro cytotoxicity against selected cancer cell lines.