Fluorescent dyes for cell viability: an application on prefixed conditions.

In recent years increasing attention has been given to apoptosis for its role in pathologic, organogenetic and homeostatic phenomena. Acridine orange (AO), Hoechst 33342 (HO) and propidium iodide (PI) are among the most used fluorescent dyes used to analyse cell culture viability. In fact, they respectively show specificity for living, apoptotic and late apoptosis/necrosis states. We explored whether HO, AO and PI can be used on prefixed monolayers of three commonly used cell lines. Here we mainly describe the metachromatic effects obtained by fluorescence microscopy with double and triple dye combinations. Furthermore, we propose an easy staining method in which a balanced sequential treatment with HO, AO and PI allows identification of different viability states onto fixed cells by using a long-pass FITC filter. This method extends the spectrum of suitable applications for these dyes in fluorescence viability detection onto previously fixed (prefixed) samples.