A preliminary study on the cytotoxic activity of the edible sea hare Dolabella auricularia in Fiji

The sea hare Dolabella auricularia and it egg masses are eaten in a number of countries in the Pacific Islands although they can contain poisonous and cytotoxic compounds. In Fiji, some parts of the digestive gland of the animals are initially removed before it is cooked and eaten. Egg masses on the other hand, are eaten raw after marinating with lemon. Several biologically active metabolites have been isolated from Dolabella auricularia, including the highly toxic and biologically active dolastatin family of cylic peptides. The current preliminary study evaluates the toxicity level of the secondary metabolites present in the local animals and investigates the anatomical distribution of biologically active compounds particularly in its digestive glands and the exterior, which includes the skin and mantle. Three extracts of Dolabella auricularia were subjected to a bioscreening study to detect cytotoxic activity by the brine shrimp lethality bioassay. The extracts studied were: (1) metabolites from the digestive glands (internal organs), (2) metabolites from the whole organism, and (3) metabolites from the skin and mantle (external organs) of the animal. Extracts (1), (2) and (3) were shown to be toxic to brine shrimps with lethality levels found at <100 ppm, 480 ppm and 2000 ppm respectively. Although further works needs to be completed, our preliminary results show that the metabolites extracted from the digestive organs were significantly more toxic than those obtained from the skin and mantle of the animal. This result is not surprising as many researchers have shown that sea hares are a rich source of bioactive substances believed to be of dietary origin. In Fiji, where this sea hare is sold at the local market, the high lethality levels found for the digestive glands suggest that it is crucial that the digestive gland of the animal be removed before the animal is consumed. Although low lethality levels are found from the extracts of the skin and mantle, further research is needed to ascertain whether the sea hares as sold and consumed locally have acceptable toxicity levels.