Assessment of the marine toxins by monitoring the integrity of human intestinal Caco-2 cell monolayers.

The effects of marine substances with various cytotoxic mechanisms on the integrity of the human intestinal Caco-2 cell monolayer were examined by measuring the transepithelial electrical resistance (TEER). TEER was rapidly decreased by apical exposure of the monolayers to discodermin A, a membrane pore-forming substance. The decrease in TEER occurred in an earlier stage of incubation than the release of intracellular lactate dehydrogenase (LDH) which is commonly used as a parameter of cell damage or death. Mycalolide B (an actin-depolymerizing substance), calyculin A and okadaic acid (protein phosphatase inhibitors) also rapidly decreased the TEER value, although no cell membrane damage or resultant LDH release by these toxicants were detected. The TEER decrease caused by the toxicants was associated with the increased transepithelial permeability of the cell monolayer. Treatment with these toxicants, except calyculin A, caused morphological changes in the intracellular actin filament, suggesting that these toxicants altered the cytoskeletal structure, by which the tight junction was opened. Calyculin A was likely to loosen the cellular junctions rapidly and induce cell detachment from the monolayer. Although onnamide A, a protein synthesis inhibitor, did not cause any decrease in TEER, at least during a 90-min incubation, TEER sensitively reflects the cytotoxic effects of various types of toxicants with acute toxicity.