CYTOTOXIC QUANTIFICATION OF MAITOTOXIN-LIKE ACTIVITY FROM THE DINOFLAGELLATE GAMBIERDISCUS-TOXICUS

Gambierdiscus toxicus is a marine dinoflagellate involved in the food- borne disease ciguatera. Its toxicity is mainly due to maitotoxin, a h ydrophilic toxin, the chemical structure of which has recently been de scribed. This toxin increases internal Ca2+ concentration and triggers phosphoinositide breakdown. Three cytotoxic tests were set for the de tection and quantification of toxicity in G. toxicus extracts, further purified by HPLC: the neutral red uptake assay (NRU), observation of morphological alterations on baby hamster kidney fibroblasts (BHK 21/C 13) and the measurement of internal Ca2+ concentration on human lympho cytes (Jurkat D). In order to evaluate cytotoxicity tests, results wer e compared with the mouse bioassay. A positive correlation was observe d between the minimum lethal dose (MLD), estimated at 24 hr by the mou se bioassay, and the IC50, estimated by the NRU assay, for extracts of increasing degree of purity. By the use of the NRU assay, a precise d etection and quantification of toxicity in multiple extracts was possi ble after 8 hr. Cell blebbing was generally highest for extracts that strongly inhibited NRU. The analysis of the correlation between the tw o cytological tests facilitates monitoring of the progression of purif ication. An indication of the presence of maitotoxin activity was supp orted by the increase of internal Ca2+ concentration in Jurkat D lymph ocytes, which was maximal in cells exposed to the purest extracts.