Accurate evaluation of drug effect on the LDH activity of live cells: dual measurement of live cell number by fluorescent staining of nucleus and LDH activity by formazan.

Effect of drugs on the intracellular activity of lactate dehydrogenase (LDH) has been measured by using water-soluble tetrazolium (WST). Because the assay is usually conducted in the presence of dead cells, net activity of live cells is not evaluated. Here, we reported the assay of the net intracellular LDH activity of live cells by counting the live cells using fluorescent staining of nucleus. By using a deep red fluorescent dye, dual measurements of fluorescence signal of nucleus and absorbance of WST could be conducted with transparent 96-well-plates. We found that conventional assay in the presence of dead cells overestimate the effect of drugs on the LDH activity.