Abstract
The exposure of aqueous solutions to atmospheric plasmas results in the generation of relatively long-lived secondary products such as hydrogen peroxide which are biologically active and have demonstrated anti-microbial and cytotoxic activity. The use of plasma-activated solutions in applications such as microbial decontamination or anti-cancer treatments requires not only adequate performance on target cells but also a safe operating window regarding the impact on surrounding tissues. Furthermore the generation of plasma-activated fluids needs to be considered as a by-stander effect of subjecting tissue to plasma discharges. Cytotoxicity and mutagenicity assays using mammalian cell lines were used to elucidate the effects of solutions treated with di-electric barrier discharge atmospheric cold plasma. Plasma-treated PBS inhibited cell growth in a treatment time-dependent manner showing a linear correlation to the solutions’ peroxide concentration which remained stable over several weeks. Plasma-treated foetal bovine serum (FBS) acting as a model for complex bio-fluids showed not only cytotoxic effects but also exhibited increased mutagenic potential as determined using the mammalian HPRT assay. Further studies are warranted to determine the nature, causes and effects of the cyto- and genotoxic potential of solutions exposed to plasma discharges to ensure long-term safety of novel plasma applications in medicine and healthcare.
Highlights
Found both faster and higher cytotoxic effects of ozone on fibroblast cells but did not show if similar amounts of ozone were produced in the plasma discharge[16]
Cells treated in normal growth medium Dulbecco’s Modified Eagle’s Medium (DMEM) supplemented with 10% foetal bovine serum (FBS) showed much lower sensitivity to plasma treatment, where the effects were reversible by replacement of the medium after treatment (Fig. 1a,b), suggesting a retention of cytotoxic effects in the medium to have a stronger impact on the cells
Cytotoxic effects were dependent on the medium composition with serum (FBS) supplementation providing protective effects and strong differences were observed between different formulations of even the same cell culture medium (DMEM), where DMEM D5796 containing 4.5 g/l glucose showed much higher cytotoxic effects than DMEM D5546 with 1.0 g/l glucose and containing pyruvate at 0.11 g/l
Summary
Found both faster and higher cytotoxic effects of ozone on fibroblast cells but did not show if similar amounts of ozone were produced in the plasma discharge[16]. Pre-treatment with catalase prevented cytotoxic effects induced by either type of medium with the authors suggesting H2O2 to be the main stable chemical species responsible for cytotoxicity[17]. Other studies have observed differences in cell viability with varying nitrogen to oxygen ratios which is attributed to the effect of other cytotoxic reactive species such as nitrites or nitrates, when H2O2 concentrations remained unchanged[18,20]. Hydrogen peroxide generation as one of the main effector molecules produced in aqueous solution during plasma discharge in air is correlated to the observed cytotoxic effects. The potential of high-voltage plasma exposure to induce mutagenic effects in plasma treated solutions - both simple buffered saline solutions and complex bio-fluids - was assessed and compared to supplementation with hydrogen peroxide
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