Specific biochemical analyses (such as DNA ladders) should not be employed as an exclusive
means to define apoptosis, because this type of cell death can occur without oligonucleosomal
DNA fragmentation. Similarly, the presence of proteolytically active caspases or of cleavage
products of their substrates is not sufficient to define apoptosis. Frequently, the active
suppression (by pharmacological and/or genetic means) of DNA fragmentation and/or caspase
activation demonstrates that these changes are not required for the execution of the cell death
program, although caspase activation may be necessary for the acquisition of the apoptotic
morphology.22-24 Moreover, the presence of active caspases and/or of specific products of
their enzymatic activity can be linked to non-lethal biological processes.9,10 The measurement
of DNA fragmentation and/or of caspase activation, however, may be helpful in diagnosing
apoptosis. Thus, it may be reasonable to use caspase activation not only to diagnose but also
to better define (together with other features) the type of cell death.