ABSTRACT
Cytotoxicity refers to the cell-killing potential of a test compound independent of the mechanisms of death. There are predominantly two distinct mechanisms of cell death: necrosis, the "accidental" cell death, and apoptosis, the "programmed" cell death. Light microscopy aids in detecting different morphological alterations that occur in the early stages of apoptosis of a cell. Activation of caspase enzymes, which aids in protein cleavage eventually leading to cellular disassembly, is a unique feature observed in the initial phases of apoptosis. Another distinguishing feature of apoptotic cell death is the translocation of phosphatidylserine (PS) that is typically restricted to the inner leaflet of plasma membrane to the exterior of cell membrane in response to pro-apoptosis stimuli. The DNA laddering technique allows visualizing the DNA fragmentation that occurs due to endonuclease cleavage during apoptosis. Terminal deoxynucleotidyl transferase nick end labeling (TUNEL) is designed to identify apoptotic cells that endure extensive degradation of DNA during the late phase of apoptosis.
