Menadione-mediated WST1 reduction assay for the determination of metabolic activity of cultured neural cells

Cellular reduction of tetrazolium salts to their respective formazans is frequently used to determine the metabolic activity of cultured cells as an indicator of cell viability. For membrane-impermeable tetrazolium salts such as WST1 the application of a membrane-permeable electron cycler is usually required to mediate the transfer of intracellular electrons for extracellular WST1 reduction. Here we demonstrate that in addition to the commonly used electron cycler M-PMS, menadione can also serve as an efficient electron cycler for extracellular WST1 reduction in cultured neural cells. The increase in formazan absorbance in glial cell cultures for the WST1 reduction by menadione involves enzymatic menadione reduction and was twice that recorded for the cytosolic enzyme-independent WST1 reduction in the presence of M-PMS. The optimized WST1 reduction assay allowed within 30 min of incubation a highly reliable detection of compromised cell metabolism caused by 3-bromopyruvate and impaired membrane integrity caused by Triton X-100, with a sensitivity as good as that of spectrophotometric assays which determine cellular MTT reduction or lactate dehydrogenase release. The short incubation period of 30 min and the observed good sensitivity make this optimized menadione-mediated WST1 reduction assay a quick and reliable alternative to other viability and toxicity assays.