Studies on cellular resilience and adaptation following acute and repetitive exposure to ozone in cultured human epithelial (HeLa) cells

Ozone is used to treat several medical conditions, while the underlying mechanisms of action are sometimes poorly understood. In the current study, we exposed cultured human epithelial (HeLa) cells acutely and repeatedly to ozone and investigated the effects thereof on cell viability. The involvement of anti-apoptotic pathways in observed adaptive responses to ozone were investigated by employing the Akt inhibitor (-)-deguelin. Cells were exposed to an ozone-saturated physiological solution using various dosing regimens, including acute exposure and various repetitive exposures. Cell viability was determined with Trypan Blue or MTT tests, or by a DNA-fragmentation (comet) assay. Acute ozone exposure compromised cell membrane integrity severely, while adaptation to reverse an initial reduction in mitochondrial activity was observed. Repetitive, short-duration exposures followed by a single long-duration exposure to ozone furnished a protective adaptation that was reversed by Akt inhibition. Extracellular and intracellular damage (and adaptation) occurs differentially. While acute ozone may decrease cell viability, multiple preexposures up-regulates cellular plasticity via induction of anti-apoptotic pathways in a treatment regimen-specific manner.