Studies on the production of prostaglandin E2(PGE2) and its related substances in red algae of the genus Gracilaria

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There have been three official poisoning incidents in Japan, including three deaths, due to the ingestion of raw red algae of the genus Gracilaria have occurred in Japan. In October 1993, a food poisoning incident due to the ingestion of 'ogonori'(Gracilaria verrucosa), an edible red alga occurred at Yokohama, Kanagawa Prefecture. Japan, resulting in two victims, including one death (female). No causative agent present in the ogonori was found from a routine bioassay for marine toxins. Responsibility of prostaglandins(PGs), particularly mainly PGE2, for the "ogonori" poisoning has been suggested. This type of poisoning is very unusual, and differs from the more familiar forms of poisoning occurring after ingestion of marine organisms.From a food hygienic point of view, the production of PGE2 and its related substances was examined in five species of red algae such as G.verrucosa, G.bursa-pastoris, Gracilariopsis chorda, G. textorii and Gracilaria sp. in Seto Inland Sea, Japan in this research project. In the specimens of G.verrucosa, 0.1-57.9μg/g of PGE2 was found in fresh alga and, on addition of araohidonate, its amount increased from 1.8 to 90μg/g. The production of increased amount of PGE2 from the specimens treated with liquid nitrogen was several times larger in comparison with that of untreated speoimens. But the production of PGE2 was extremely decreased by acid treatment of the algae. In the red algae except for G.verrucosa, PGE2 was not detected. However, unidentified PGE2 related substances were detected, whose UV absorption maxima was near 240nm. One of these gave rise to a positive ESI mass spectrum, showing a protonated molecule ion of (M+H)ィイD1+ィエD1 at m/z 372 and other ions of (M+H-HィイD22ィエD2O)ィイD1+ィエD1 at m/z 355, (M+H-2HィイD22ィエD2O)ィイD1+ィエD1 at m/z 337, (M+H-3HィイD22ィエD2O)ィイD1+ィエD1 at m/z 319 and (M+H-4HィイD22ィエD2O)ィイD1+ィエD1 at m/z 301.