TOXICITY AND CELL-DENSITY MONITORING IN MONOLAYER AND 3-DIMENSIONAL CULTURES WITH THE XTT ASSAY

The application of viability criteria (MTT and XTT tests) to monolayer cultures and immobilised cells in three-dimensional systems was inves tigated in order to assess cell viability and cell proliferation. The suitability and accuracy of these tests were compared with the convent ional criteria (cellular protein and DNA content) used in monolayer cu ltures for the same purpose. The colorimetric assay based on the metab olic reduction of the tetrazolium salt XTT to a water-soluble formazan proved to be very useful, rapid and sensitive. This automated spectro photometric enzymatic method, due to its lack of toxicity, also permit s repeated nondestructive assays on a single cellular culture for the long-term monitoring of cytotoxicity, cell survival and cell prolifera tion, and can be performed in 96-well plates with minimal handling. Th is method could offer a solution for cellular density evaluation in co mplex cell cultures that do not permit visual examination; it is also the best choice for protein-based, three-dimensional systems such as c ollagen gels.