Comparison of different types of non-thermal plasma treatment of mammalian cells

Abstract

Summary form only given. Non-thermal plasma is now being widely developed for various clinical applications, e.g. cancer treatment, blood coagulation and tissue sterilization. However, the effects of non-thermal plasma on mammalian cells are still unclear. In this paper we investigate the effects of the plasma on mammalian cells. One of the most critical of such effects could be DNA damage, since DNA damage is the most threatening to cell survival. We studied the physical mechanisms of interaction of non-thermal plasma treatment of living cells by comparing direct treatment of cells with indirect treatment of cells by placing a grounded mesh between the sample being treated and the high voltage electrode. The mesh only allows neutral species to come in contact with the cells. We also compared direct treatment of cells with exposure of cells to separately treated medium. In this case cell growth medium was treated separately from the cells and then was poured on top of untreated cells. We measured DNA damage in mammalian cells using immunofluorescence and western blots to detect phosphorylation of the histone protein H2AX (gamma-H2AX), which is a marker of DNA damage. Hydrogen peroxide was used as a positive control since it is known to induce DNA damage. The level of DNA damage induced by indirect treatment was almost similar to that induced by direct treatment of cells. This suggests that neutral species produced by plasma play a major role in inducing damage rather than charged particles. Also separated treatment induced DNA damage similar to direct treatment, indicating that non-thermal plasma interacts with cells indirectly by modifying the cell culture medium. Further, the results indicate that short exposure of non-thermal plasma at low power produces DNA damage in mammalian cells, suggesting that somehow the effects of plasma penetrate the cells. The level of DNA damage as measured by gamma-H2AX was dependent on the dose of non-thermal plasma, at a low dose of plasma treatment, the damage is reversible, whereas at higher doses, cells undergo apoptosis. The cells remain viable after treatment at low dose as measured by colony assay. Future work will involve the determination of the specific pathways through which the effects of non-thermal plasma penetrate cells and interact with cellular DNA.