Small molecule antioxidants in marine organisms from the Great Barrier Reef, Japan and USA

Specimens of the zoanthid, Palythoa tuberculosa and the ascidian, Lissoclinum patella were collected using SCUBA from 2-4 m depth at Davies Reef in June 1990. Specimens were stored at -20°C until extracted. Coral trout (Plectropomus leopardus) were caught by handline at the same reef and the ocular lenses excised and frozen. Freeze dried red alga samples were sourced from 2 locations: Porphyra tenera was a gift from the Yamamoto Nori Research Institute, Ota-ku, Tokyo, and Mastocarpus stellatus, collected from Schoodic Point, Maine, USA, was provided by Professor JM Shick.

Methanolic aqueous extracts containing mycosporine-like amino acids (MAAs) were prepared from tissue samples from each species and the MAAs were separated and quantified by reverse-phase, isocratic high-performance liquid chromotography (HPLC).

Phosphatidylcholine peroxidation inhibition assay (PC-assays) were conducted using 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) and soybean phosphatidylcholine (PC) as radical inititor and lipid substrate, respectively.

AAPH-initiated oxidation reactions of MAAs in sample tissue extracts were conducted without phosphatidylcholine as a competing substrate.

Mycosporine-Gly was fractionated from the Palythoa extract and after processing was quantified by photometric analysis using published molar absorptivity data. The antioxidant activity of mycosporine-Gly was determined with the addition of appropriate quantities of sample to give 15 and 30 µM concentrations of mycosporine-Gly in the PC-assay. Ascorbic and uric acids were used for comparison of PC peroxidation inhibition rates.

In these sample extracts, mycosporine-glycine was reactive to peroxyl radicals whereas iminomycosporine-like amino acids (shinorine, porphyra-334, palythine, asterina-330 and palythinol) were oxidatively robust. Purified mycosporine-glycine inhibited peroxyl radical-initiated autoxidation of phosphaditylcholine in a concentration-dependent manner. These results suggest that mycosporine-glycine may function as a biological antioxidant in marine organisms.