Temporal trends in the secondary metabolite production of the sponge Aplysina aerophoba

Temporal changes in the production of secondary metabolites are far from being fully understood. Our study quantified, over a two-year period, the concentrations of brominated alkaloids in the ectosome and the choanosome of Aplysina aerophoba, and examined the temporal patterns of these natural products. Based on standard curves, we quantified the concentrations of aerophobin-2, aplysinamisin-1, and isofistularin-3: three of the four major peaks obtained through chemical profiling with high-performance liquid chromatography. Our results showed a striking variation in compound abundance between the outer and inner layers of the sponge. The ectosome showed high concentrations of bromocompounds during the summer months, while the choanosome followed no pattern. Additionally, we found that, from the outer layer of the sponge, aerophobin-2 and isofistularin-3 were significantly correlated with water temperature. The present study is one of the first to document quantitative seasonal variations in individual compounds over multiple years. Further studies will clarify the role of environmental, biological, and physiological factors in determining the seasonal patterns in the concentration of brominated alkaloids.

Relevance of an integrative approach for taxonomic revision in sponge taxa: case study of the shallow-water Atlanto-Mediterranean Hexadella species (Porifera:Ianthellidae:Verongida)

The identification of sponges that lack a mineral skeleton is always highly challenging, especially for Hexadella species, which are also fibreless. Recently, the yellow species Hexadella pruvoti Topsent was identified as a cryptic species complex while the pink coloured Hexadella racovitzai Topsent showed two highly divergent lineages. We performed a COI phylogenetic reconstruction using 27 new Mediterranean Hexadella samples in order to confirm the presence of divergent lineages within both shallow-water species. Specimens were described with an integrative approach combining morphological and cytological investigations, biochemical profiling and assessment of natural toxicity in order to identify diagnostic characters for each taxon. H. topsenti, sp. nov. is distinguished from H. racovitzai by its colour, its surface network shape, divergent secondary metabolite patterns and toxicity values. H. crypta, sp. nov. differs from H. pruvoti by a different encrusting growth form when alive, and by distinctively colouring the ethanol fixative solution. In addition, H. pruvoti and H. crypta show different types of cells with inclusions as well as distinct metabolic fingerprints. Natural toxicity values, however, do not permit the separation of H. pruvoti and H. crypta. Our work shows that only the use of a combination of complementary tools can provide relevant descriptions for some problematic taxa.

Structures and antimicrobial activities of pyridoacridine alkaloids isolated from different chromotypes of the ascidian Cystodytes dellechiajei

Three new pentacyclic alkaloids were isolated from different chromotypes of the western Mediterranean ascidian Cystodytes dellechiajei. The purple color morph collected in Catalonia contained the known compounds kuanoniamine D (1), shermilamine B (2), N-deacetylkuanoniamine D (3), and styelsamine C (4) and a new alkaloid named N-deacetylshermilamine B (5). The green color morph collected in the Balearic Islands contained the known compounds 11-hydroxyascididemin (6) and 8,9-dihydro-11-hydroxyascididemin (7) and two new alkaloids named cystodimine A (8) and cystodimine B (9). The blue color morph collected in Catalonia yielded the known compound ascididemin (10). The structures of all compounds were elucidated on the basis of spectroscopic data, mainly 1D and 2D NMR data. The antimicrobial potential of the pyridoacridine alkaloids isolated from each color morph was evaluated and compared.

Halocyntin and papillosin, two new antimicrobial peptides isolated from hemocytes of the solitary tunicate, Halocynthia papillosa

We report here the screening of five marine invertebrate species from two taxa (tunicates and echinoderms) for the presence of cationic antimicrobial peptides (AMP) in defence cells (hemocytes). Antimicrobial activities were detected only in the two tunicates Microcosmus sabatieri and Halocynthia papillosa. In addition, we report the isolation and characterization of two novel peptides from H. papillosa hemocytes. These molecules display antibacterial activity against Gram-positive and Gram-negative bacteria. Complete peptide characterization was obtained by a combination of Edman degradation and mass spectrometry. The mature molecules, named halocyntin and papillosin, comprise 26 and 34 amino acid residues, respectively. Their primary structure display no significant similarities with previously described AMP.

Antimitotic activity of methoxyconidiol, a meroterpene isolated from an ascidian

Methoxyconidiol is a meroterpene previously extracted from the ascidian Aplidium aff. densum [A. Simon-Levert, A. Arrault, N. Bontemps-Subielos, C. Canal, B. Banaigs. Meroterpenes from the ascidian Aplidium aff. densum, J. Nat. Prod. 68 (2005) 1412-1415]. In the present work we investigated its antimitotic effect on eukaryotic cells by using a bioassay based on the sea urchin early embryo. This bioassay has been successfully used to evaluate the efficacy of antiproliferative agents and to rapidly determine the affected cell cycle phase. We demonstrated that methoxyconidiol inhibits the cleavages of sea urchin Sphaerechinus granularis and Paracentrotus lividus fertilized eggs. This meroterpene disrupts M-phase progression and completely blocks cytokinesis without having any effect on DNA replication. The treatment severely disturbs the establishment of a mitotic spindle, most likely by affecting microtubule dynamics. Moreover, while the cell cycle regulatory kinase cyclin B/CDK1 is activated, cyclin B proteolysis is inhibited, impeding the output of M-phase. This characteristic cell cycle arrest induced by methoxyconidiol in sea urchin eggs emphasizes the interest for this drug as a putative antiproliferative agent for tumor cells.

Total structure and inhibition of tumor cell proliferation of laxaphycins

From a mixed assemblage of Lyngbya majuscula rich marine cyanobacteria, we isolated a series of cell growth inhibitory cyclic peptides. The structures of the two major components, laxaphycins A (1) and B (2), and of two minor peptides, laxaphycins B2 (3) and B3 (4), were determined by spectroscopic methods and degradative analysis. Absolute configurations of natural and nonproteinogenic amino acids were determined by a combination of hydrolysis, synthesis of noncommercial residues, chemical derivatization, and HPLC analysis. The organism producing the laxaphycins was identified as the cyanobacterium Anabaena torulosa. The antiproliferative activity of laxaphycins was investigated on a panel of solid and lymphoblastic cancer cells. Our results demonstrate that in contrast to laxaphycin A, laxaphycin B inhibits the proliferation of sensitive and resistant human cancer cell lines and that this activity is strongly increased in the presence of laxaphycin A. This effect appears to be due to an unusual biological synergism.

Temporal Variation in the Production of Four Secondary Metabolites in a Colonial Ascidian

The ecological and applied importance of ascidian secondary metabolites is well reported, but little is known about temporal variation in the production of these compounds. Here, we examined seasonal variation in the production of the four main pyridoacridine alkaloids (shermilamine B, kuanoniamine D, and their deacetylated forms) of the purple morph of the ascidian Cystodytes sp. Five replicate samples were taken monthly from July 2004 to February 2006, and analyzed by high-performance liquid chromatography. Our results showed a high degree of intercolony variability in secondary metabolite concentration and a lack of statistically significant seasonal variation in the production of the four compounds. Minimum values, however, were consistently recorded over the studied years in late summer, after the reproductive period. These minima may be attributable to sexual exhaustion and seasonally varying biotic interactions or abiotic parameters.

Meroterpenes from the ascidian Aplidium aff. densum

Chemical investigation of the ascidian Aplidium aff. densum collected at Masirah Island, Oman, has resulted in the isolation of five meroterpenes: two new ones, methoxyconidiol (1) and didehydroconicol (2), and three related, known compounds, 3-5. The structures of 1 and 2 were determined by a combination of mass spectrometry and one- and two-dimensional high-field NMR techniques. Their biological activities against bacteria and human lymphoblastic cell lines were evaluated.

Distribution of a new rosmarinic acid derivative in Eryngium alpinum L. and other Apiaceae

The roots of Eryngium alpinum L. (Apiaceae) demonstrated radical scavenging properties toward the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical in a TLC autographic assay. Isolation of the bioactive compounds allowed the identification of R-(+)-3'-O-beta-D-glucopyranosyl rosmarinic acid, a new rosmarinic acid derivative. The quantitative determination of the antioxidant capacity of the compound by chemoluminescence demonstrated half the activity of R-(+)-rosmarinic acid. To find another source richer in this compound, a chemotaxonomic study was conducted. The higher content was found in the aerial parts of Sanicula europeae L., also belonging to the Saniculoideae subfamily. Although present in most of the Eryngium species, this compound was not detected in Imperatoria ostruthium L., Pimpinella peregrina L., and Levisticum officinalis L. species from the Apioideae subfamily and Hydrocotyle asiatica L. from the Hydrocotyloideae subfamily. The results indicate that the new derivative R-(+)-3'-O-beta-D-glucopyranosyl rosmarinic acid is a potential chemotaxonomic marker of the Saniculoideae subfamily.

Cytotoxic effect of Laxaphycins A and B on human lymphoblastic cells (CCRF-CEM) using digitised videomicrofluorometry

Laxaphycin A (laxa A) and Laxaphycin B (laxa B), cyclic peptides isolated from the terrestrial blue-green alga Anabaena laxa or the marine cyanobacterium Lyngbya majuscula have antifungal and cytotoxic activities. We used numerical videomicrofluorometry and a protocol of multiple labelling with Hoescht 33342 (nuclear DNA), Rhodamine 123 (mitochondria) and Nile Red (plasma membrane) to study the cytotoxicity of these substances in human lymphoblastic cells sensitive (CEM-WT) or resistant (CEM-VLB and CEM-VM1) to anticancer agents. The results indicate a low resistance index of 2 for CEM-VLB cells treated with laxa B or laxa A + lava B. For the three cell strains, following laxa B treatment, we observed an increase of a polyploid cell subpopulation that could result from the alteration of topoisomerase-II activity. On the contrary, the simultaneous treatment by laxa A and laxa B led to a decrease of that subpopulation with increasing laxa A doses. However, the effect of laxa A was less pronounced in the CEM-VM1 cells, which present a low intrinsic topoisomerase-II activity. For CEM-VLB cells, the higher doses needed can be attributed to their MDR resistance. Though we observed a synergistic effect between laxa B and laxa A (the latter is inactive by itself), these results indicate a different mode of action for laxa B and laxa A + laxa B. A more precise study of the mode of action of these compounds is warranted.

Larval sensory abilities and mechanisms of habitat selection of a coral reef fish during settlement

Sensory abilities and preferences exhibited by mobile larvae during their transition to juvenile habitats can establish spatial heterogeneity that drives subsequent species interactions and dynamics of populations. We conducted a series of laboratory and field experiments using coral reef fish larvae (Chromis viridis) to determine: ecological determinants of settlement choice (conspecifics vs. heterospecifics vs. coral substrates); sensory mechanisms (visual, acoustic/vibratory, olfactory) underlying settlement choice; and sensory abilities (effective detection distances of habitat) under field conditions. C. viridis larvae responded positively to visual, acoustic/vibratory, and olfactory cues expressed by conspecifics. Overall, larvae chose compartments of experimental arenas containing conspecifics in 75% of trials, and failed to show any significant directional responses to heterospecifics or coral substrates. In field trials, C. viridis larvae detected reefs containing conspecifics using visual and/or acoustic/vibratory cues at distances <75 cm; detection distances increased to <375 cm when olfactory capacity was present (particularly for reefs located up-current). We conducted high performance liquid chromatography (HPLC) analyses of seawater containing C. viridis juveniles and isolated high concentrations of several organic compounds. Subsequent laboratory trials demonstrated that C. viridis larvae responded positively to only one of these organic compounds. This compound was characterized by a weak polarity and was detected at 230 nm with a 31-min retention time in HPLC. Overall, our results suggest that fishes may use a range of sensory mechanisms effective over different spatial scales to detect and choose settlement sites, and species-specific cues may play a vital role in establishment of spatial patterns at settlement.

Culture of the marine cyanobacterium, Lyngbya majuscula (Oscillatoriaceae), for bioprocess intensified production of cyclic and linear lipopeptides

Cyanobacteria are an ancient and diverse group of photosynthetic microorganisms, which inhabit many different and extreme environments. This indicates a high degree of biological adaptation, which has enabled these organisms to thrive and compete effectively in nature. The filamentous cyanobacterium, Lyngbya majuscula, produces several promising antifungal and cytotoxic agents, including laxaphycin A and B and curacin A. Samples of L. majuscula collected from Moorea Island, Tahiti (French Polynesia) and from the Culture Collection of Algae and Protozoa (CCAP 1446/4) were studied and adapted to large scale laboratory culture (5 l). This constitutes a 100-fold scale-up for the culture of this particular strain of L. majuscula. The effect of culture vessel configurations, growth conditions and media compositions on growth of L. majuscula was examined. Using optimised culture conditions, two strains of L. majuscula are currently being evaluated for their production of secondary metabolites. Results will be compared with those obtained from four environmental extracts. Comparisons were made by thin layer chromatography (TLC), high performance liquid chromatography (HPLC) and fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). It was shown that varying the culture conditions under which L. majuscula was grown had the greatest effect on secondary metabolite production, thus providing potential for future bioprocess intensified production.

Structure-activity relationship for bromoindole carbaldehydes: effects on the sea urchin embryo cell cycle

Natural derivatives of indole-3-carbaldehyde were isolated from the tropical marine ascidian Stomoza murravi. A series of 13 derivatives, three natural and 10 synthetic (brominated and N-methylated), were examined for their effects on cell division of sea urchin eggs. These derivatives were shown to inhibit the first mitotic cycle in a concentration-dependent manner. By comparing the IC50 values with the structure of the various molecules, we were able to determine that bromination increased the cytotoxicity of the compound with a maximum occurring when bromine was added to carbon number 2, while addition of N-methylation was shown to markedly reduce the cytotoxicity of these same compounds brominated at carbon 2 only. Biological activity of this family of compounds has been characterized, via detailed study of addition of the most active derivative, 2,5,6-tribromoindole-3-carbaldehyde, on macromolecule synthesis and cytoskeleton reorganization during the first mitotic cycle of fertilized sea urchin eggs. Fluorescence localization of chromatin and microtubules revealed that 2,5,6-tribromoindole-3-carbaldehyde allowed pronuclei migration and fusion but prevented the condensation of chromatin, nuclear envelope breakdown, and bipolar mitotic spindle assembly, inducing an arrest of sea urchin embryogenesis at the beginning of mitosis. It is postulated here that this phenotype is likely to be due to a strong inhibition of DNA replication and protein synthesis.

Inhibition of topoisomerase II by the marine alkaloid ascididemin and induction of apoptosis in leukemia cells

Ascididemin (ASC) is a pentacyclic DNA-intercalating agent isolated from the Mediterranean ascidian Cystodytes dellechiajei. This marine alkaloid exhibits marked cytotoxic activities against a range of tumor cells, but its mechanism of action remains poorly understood. We investigated the effects of ASC on DNA cleavage by human topoisomerases I and II. Relaxation assays using supercoiled DNA showed that ASC stimulated double-stranded cleavage of DNA by topoisomerase II, but exerted only a very weak effect on topoisomerase I. ASC is a conventional topoisomerase II poison that significantly promoted DNA cleavage, essentially at sites having a C on the 3' side of the cleaved bond (-1 position), as observed with etoposide. The stimulation of DNA cleavage by topoisomerase I in the presence of ASC was considerably weaker than that observed with camptothecin. Cytotoxicity measurements showed that ASC was even less toxic to P388 leukemia cells than to P388CPT5 cells resistant to camptothecin. In addition, the marine alkaloid was found to be equally toxic to HL-60 leukemia cells sensitive or resistant to mitoxantrone. It is therefore unlikely that topoisomerases are the main cellular targets for ASC. This alkaloid was found to strongly induce apoptosis in HL-60 and P388 leukemia cells. Cell cycle analysis showed that ASC treatment was associated with a loss of cells in the G1 phase accompanied with a large increase in the sub-G1 region. Cleavage experiments with poly(ADP-ribose) polymerase (PARP) revealed that caspase-3 was a mediator of the apoptotic pathway induced by ASC. The DNA of ASC-treated cells was severely fragmented. Collectively, these findings indicate that ASC is a potent inducer of apoptosis in leukemia cells.

Matemone, a new bioactive bromine-containing oxindole alkaloid from the indian ocean sponge Iotrochota purpurea

A new bioactive bromine-containing oxindole alkaloid, matemone (1), was isolated from the Indian Ocean sponge Iotrochota purpurea, together with the known 6-bromoindole-3-carbaldehyde. The structures were elucidated on the basis of spectral and chemical data. Compound 1 shows mild cytotoxicity against three cancer cell lines and marginal antibacterial activity against Staphyloccocus aureus. DNA intercalant screening demonstrated DNA interactions with 1. Both compounds inhibit division of sea-urchin eggs.