Optimization of an Acridine Orange-bisbenzimide procedure for the detection of apoptosis-associated fluorescence colour changes in etoposide-treated cell cultures.

This study was initiated in order to investigate the possibility of improving fluorescence microscopy as a method for evaluating apoptosis in cells by combining two fluorescent dyes with different staining characteristics. Cells were vitally stained with bisbenzimide (1.3 microM) and Acridine Orange (6.6 microM) and observed using the following filter configuration: excitation 380 nm, beamsplitter 395 nm and longpass filter 397 nm. Control cells exhibited clear blue fluorescent nuclei and red fluorescing lysosomes. In cells treated with etoposide to induce apoptosis, two distinct occurrences were observed: a change in the spectrum of emitted light from bisbenzimide bound to the nuclear region and an increase in lysosomal Acridine Orange fluorescence. The two occurrences together permit a more unbiased detection of apoptosis than most assays. Only one filter set is required for evaluation and the resulting images can be easily evaluated visually or processed further by image analysis.