3.2.1. Sample preparation for fluorometric analysis
Cells are seeded the day before analysis at 5–20 103 cells in
100 ll per well in 96-well adherent plates using L15 medium
(Leibovitz), which allows CO2-independent buffering. The next
day the cells should be 80% confluent at the most when inducing
cell death. Add a cell impermeant dye 30 min before measurement
(e.g. Sytox Green to obtain a final concentration of 5 lM), and put
the cells back at 37 C. Sytox Green intensity can then be
measured on a fluorescence plate reader in function of time. The
choice of excitation and emission filters depends on the probe
used. To ensure an average value that accurately reflects the extent
of cell death per well, it is advised to set up multiple reads per well
via orbital averaging with a diameter of 3 mm for 96-well plates to
avoid border effects. The obtained value is referred to as ICD (induced
cell death). To obtain the maximum Sytox Green intensity
per well, which corresponds to 100% cell death (MCDn), Triton
X-100 is added to each well to a final concentration of 0.1%. Cells
are incubated for 1 h at 37 C and Sytox Green intensity is
measured again [27]. The value obtained is referred to as MCD
(max cell death). Results are expressed as percentage cell death
per well (Fig. 1), which can be calculated by the following formula: