Recent Studies on the Pathological Effects of Purified Sea Urchin Toxins

Sea urchins are the popular name for marine invertebrates that belong to the phylum Echinodermata. Approximately 200 species of sea urchin are found on the coast of Japan, while several species of echinoids are dangerous to humans. Envenomations are caused by stings from either pedicellariae or spines. In our search for bioactive compounds we have been investigating mitogenicity and/or cytotoxicity from the venoms of the four sea urchins: Toxopneustes pileolus, Tripneustes gratilla, Diadema setosum, and Asthenosoma species. The toxopneustid sea urchins have well‐developed globiferous pedicellariae with bioactive substances. The hollow primary spines of diadematid sea urchins are suggested to contain bioactive substances. Two D‐galactose‐binding lectins (SUL‐I and SUL‐II ) and a heparin‐binding lectin (TGL‐I) were purified from the globiferous pedicellariae of T. pileolus and T. gratilla. Furthermore, a novel hemolytic lectin with a molecular mass of 29 kDa was isolated from the coelomic fluid of T. gratilla. More recently, we found that a mannose‐containing glycoprotein, Contractin A (18 kDa) is also a novel lectin that caused smooth muscle contraction and relaxation. SUL‐I and Contractin A induced mitogenic stimulation on murine splenocytes, but SUL‐II and TGL‐I did not. SUL‐I promoted chemotaxis of guinea‐pig macrophages and human morphonuclear leukocytes. In murine myeloid leukemic cells (M1 cells) SUL‐I showed not only cytotoxic effect, but also differentiating ability. In addition, SUL‐I partially induced apoptosis to M1 cells. SUL‐I did not show a sequence homology to SUL‐II. However, SUL‐I is related to fisg egg lectins. On the other hand, SUL‐II showed a sequence homology to Contractin A and UT841 from T. pileolus, which may be a phopholipase A2‐like substance. Our data suggest an extracellular function for SUL‐I and Contractin A that may have wide‐ranging effects, and suggest that sea urchin venoms may be regarded as useful bioactive substances.