Apoptosis versus cytotoxicity in HeLa cells exposed to paracetamol

Apoptosis is a programmed form of cell death which occurs in response to sp ecific stimuli. It is distinguished from necrotic or accidental cell death by unique events, including the degradation of chromatin and a loss of cell ular volume. In contrast to necrotic cell death, cell membrane integrity an d mitochondrial function are thought to be maintained until the apoptotic p rocess is well advanced. One of the novel assays for detecting apoptosis is flow cytometry. In our experiments, we used a flow cytometric assay to det ect DNA changes in a human cell line (HeLa) exposed to paracetamol, by meas uring propidium iodide binding. We were able to detect the apoptotic proces s in cells exposed to paracetamol. Apoptosis did not correlate with cytotox icity, and was only found in samples exposed to 4-5mg/ml paracetamol for 8 hours in minimum essential medium and incubated in fresh medium without par acetamol for 14-19 hours. The greatest effect was noted 18 hours after para cetamol exposure. These results were confirmed by studying cell morphology and chromatin condensation by fluorescent microscopy with the fluorochromes acridine orange and ethidium bromide. Our results support the hypothesis t hat, in cultured cells, apoptosis is induced by a relatively narrow range o f chemical concentrations which are known to inhibit the cell cycle, and th at apoptosis and inhibition of cell proliferation coincide to some degree.