| Thermal plasmas and lasers have been widely used in medicine to cut, ablate and cauterize tissues through heating in contrast, non-thermal plasma produces various highly active molecules and atoms without heat. As a result, its effects on living cells and tissues could be selective and tunable. This makes non-thermal plasma very attractive for medical applications. However, despite several interesting demonstrations of non-thermal plasma in blood coagulation and tissue sterilization, the biological and physical mechanisms of its interaction with living cells are still poorly understood impeding further development of non-thermal plasma as a clinical tool. Although several possible mechanisms of interaction have been suggested, no systematic experimental work has been performed to verify these hypotheses.Using cells in culture, it is shown in this work that non-thermal plasma created by dielectric barrier discharge (DBD) has dose-dependent effects ranging from increasing cell proliferation to inducing apoptosis which are consistent with the effects of oxidative stress. DNA damage is chosen as a marker to assess the effects of oxidative stress in a quantitative manner. It is demonstrated here that plasma induced DNA damage as well as other effects ranging from cell proliferation to apoptosis are indeed due to production of intracellular reactive oxygen species (ROS). We found that DNA damage is initiated primarily by plasma generated active neutral species which cannot be attributed to ozone alone. Moreover, it is found that extracellular media and its components play a critical role in the transfer of the non-thermal plasma initiated oxidative stress into cells. Specifically, it is found that the peroxidation efficiency of amino acids is the sole predictor of the ability of the medium to transfer the oxidative stress induced by non-thermal plasma.Phosphorylation of H2AX, a DNA damage marker, following plasma treatment is found to be ATR dependent and ATM independent, suggesting that non-thermal plasma may induce formation of bulky lesions unlike ionizing radiation (IR) or H2O2 which primarily produce DNA double strand breaks. Moreover, it is found that the pathway by which plasma generated oxidative stress is transferred across cellular membranes does not involve lipid peroxidation by-products, although lipid peroxidation does occur. |
