Photosensitivity in mice caused by pyropheophorbide in the midgut gland of the scallop Patinopecten yessoensis observed in diarrhetic shellfish poisoning mouse bioassays

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Photosensitivity was observed in the mice used in bioassays of diarrhetic shellfish poisoning. The mice were intraperitoneally injected with the extracts from the midgut glands of cultured scallops Patinopecten yessoensis fished in early spring in Funka Bay, Hokkaido, Japan. The injections induced untypical symptoms in the mice within 24 h. The symptoms included piloerection, substantial eye discharge, swelling of the ears and head, and ear scratching. They were similar to those reported in study of photosensitivity caused by pyropheophorbide in the midgut glands of abalones, which are herbivorous gastropods. The problematic scallops also accumulated a large amount of pyropheophorbide-a. The amount determined with high-performance liquid chromatography was 300 to 530 μg per 1 g of the homogenate of the midgut glands. The dose of pyropheophorbide is estimated to be 0.99 to 2.3 mg per a mouse with 20-g body weight. It is sufficient to cause the photosensitivity in a mouse. Moreover, comparative mouse tests showed that the onset of the symptoms needs light and a substantial amount of pyropheophorbide. Therefore, we defined that the symptoms were photosensitivity caused by pyropheophorbide. Scallops, which are suspension-feeding bivalves, also accumulate a large amount of pyropheophorbide in the midgut glands depending on the habitat environment.