Distribution of Defensive Metabolites in Nudibranch Molluscs.

Many plants and animals store toxic or unpalatable compounds in tissues that are easily encountered by predators during attack. Defensive compounds can be produced de novo, or obtained from dietary sources and stored directly without selection or modification, or can be selectively sequestered or biotransformed. Storage strategies should be optimized to produce effective defence mechanisms but also prevent autotoxicity of the host. Nudibranch molluscs utilize a diverse range of chemical defences, and we investigated the accumulation and distribution of defensive secondary metabolites in body tissues of 19 species of Chromodorididae nudibranchs. We report different patterns of distribution across tissues, where: 1) the mantle had more or different (but structurally related) compounds than the viscera; 2) all compounds in the mantle were also in the viscera; and 3) the mantle had fewer compounds than the viscera. We found no further examples of species that selectively store a single compound, previously reported in Chromodoris species. Consistent with other studies, we found high concentrations of metabolites in mantle rim tissues compared to the viscera. Using bioassays, compounds in the mantle were more toxic than compounds found in the viscera for Glossodoris vespa Rudman, 1990 and Ceratosoma brevicaudatum Abraham, 1876. In G. vespa, compounds in the mantle were also more unpalatable to palaemonid shrimp than compounds found in the viscera. This indicates that these species may modify compounds to increase bioactivity for defensive purposes and/or selectively store more toxic compounds. We highlight clear differences in the storage of sequestered chemical defences, which may have important implications for species to employ effective defences against a range of predators.

The Sequestration of Oxy-Polybrominated Diphenyl Ethers in the Nudibranchs Miamira magnifica and Miamira miamirana.

A series of oxy-polybrominated diphenyl ethers (O-PBDEs) has been isolated from the extracts of Miamira magnifica and Miamira miamirana collected from Queensland, Australia. M. magnifica sequesters the new OH-PBDE 1 and six known OH-PBDEs containing four to six bromines (2-7). M. miamirana also accumulates known tribromo- and tetrabromo OMe-PBDEs 8-10 in both mantle and viscera tissues. To date, Miamira is the only genus of the family Chromodorididae that is known to incorporate O-PBDEs, rather than terpenes, in the mantle where the metabolites may play a putative role in chemical defense. The extract of M. magnifica was tested in a brine shrimp lethality assay and exhibited an LD50 of 58 µg/mL.

Oxygenated Diterpenes from the Indo-Pacific Nudibranchs Goniobranchus splendidus and Ardeadoris egretta.

Five new diterpenes (1-5), each with a highly oxygenated spongian framework, were characterized from an organic extract of a specimen of the nudibranch Goniobranchus splendidus collected from Eastern Australia. The new diterpene 7α-hydroxydendrillol-3 (6) was identified from specimens of Ardeodoris egretta. The structures and relative configurations of the six new metabolites have been elucidated by analysis of their spectroscopic data.

In silico study of fucoxanthin as a tumor cytotoxic agent.

BACKGROUND: Fucoxanthin is a potential tumor cytotoxic compound. However, mechanisms underlying the activities are unclear. AIM: This in silico study aimed to predict the main mechanism of fucoxanthin; whether with its binding to p53 gene, CDK2, or tubulin. MATERIALS AND METHODS: In silico was studied by using Autodock-Vina's algorithms. The mechanisms being analyzed by comparison of fucoxanthin and native ligands binding energies in p53 gene (1RV1), CDK2 (1AQ1), and three binding sites of tubulin (1JFF-paclitaxel, 1SA0-colchicine, and 1Z2B-vinblastine site). RESULTS: Autodock-Vina's algorithms were valid, as re-docking the native ligands to their receptors showed a RSMD value less than 2 A with binding energies of -11.5 (1RV1), -14.4 (1AQ1), -15.4 (1JFF), -9.2 (1SA0), and -9.7 (1Z2B) kcal/mol. Docking of fucoxanthin to subjected receptors were -6.2 (1RV1), -9.3 (1AQ1), -8.1 (1JFF), -9.2 (1SA0), and -7.2 (1Z2B) kcal/mol. Virtual analysis of fucoxanthin and tubulin binding structure showed the carboxyl moiety in fucoxanthin make a hydrogen bound with 355Val (2.61 A) and 354Ala (2.79 A) at tubulin. CONCLUSION: The results showed that binding energy of fucoxanthin could only reach the same level as with colchicine ligand in tubulin. Therefore, it may predict that the most probable fucoxanthin main mechanism is to bind tubulin, which causes microtubules depolimerization and cell cycle arrest.