Changes of ICE protease activities caused by toxic supernatants of dinoflagellates (Prorocentrum species) from marine algal blooms

Marine phytotoxins may become a major health problem for humans because of their ability to contaminate seafood and to cause shellfish poisoning. In t his report, the cytotoxic effects and the effects on intracellular caspase activities of culture supernatants from different dinoflagellate Prorocentr um clones were determined. Among the clones tested, I? tepsium BAH ME-140 a nd P. lima BAH ME-130 K1 and K2 clones but not P. minimum and I! micans wer e found to be toxic on rat pheochromocytoma PC12 cells, mouse lymphoma L517 8Y cells and rat primary neurons. A significant increase in the specific ac tivities of caspase 1 (ICE), caspase 3 (CPP32) and caspase 6 (Mch2) to 149- 167% was observed after treatment of neurons with P. lima BAH ME-130 K2 sup ernatant for 72 h; in PC12 cells, the increase in these enzyme activities w as much smaller. An even stronger and faster effect on caspase activities, compared to the K2 clone, was observed following treatment of PC12 cells an d neuronal cells with P. lima BAH ME-130 K1 supernatant. The maximal increa se in caspase activities in PC12 cells (CPP32, 364%; and Mch2, 166%) and in neurons (CPP32, 162%; and Mch2, 111%)was observed after 24 h; no significa nt change of ICE activity was found during that incubation period. After 48 h the specific activities of all caspases strongly decreased. Incubation o f PC12 cells with I! tepsium BAH ME-140 for 24 h had almost no effect on ca spase activities, while a small increase in CPP32- (148%) and Mch2- (115%) but not in ICE-activity was detected after 48 h. In neurons, only an increa se in CPP32 activity (to 130%) was observed with this dinoflagellate supern atant after 24 h. The P. lima protein phosphatase inhibitor okadaic acid (0 .5 ng/ml) caused a time-dependent increase in caspase activities in PC12 ce lls. A much higher effect was observed in neuronal cells; after 72 h, the s pecific activities of ICE, CPP32 and Mch2 increased to 295%, 146% and 235%, respectively. These results indicate that disturbances of caspase activiti es may contribute to the neurotoxic effects of certain dinoflagellate super natants.