Hydrogen peroxide and beyond-the potential of high-voltage plasma-activated liquids against cancerous cells

Background: The use of plasma-activated liquids such as PBS, medium or simply plasma-activated water (PAW) has been receiving increasing attention for applications in cancer treatments. Amongst the reactive species contained in these solutions, hydrogen peroxide appears to play a pivotal role in causing cytotoxic effects. H₂O₂ concentrations can be correlated with reduced cell viability and growth and used as an indicator of the potential efficacy of a plasma-activated liquid. Objective: To investigate the cytotoxic mediators generated in water specific to high-voltage DBD-ACP. Method: Using a high-voltage dielectric barrier atmospheric cold plasma (DBD-ACP) system, we examined PAW-mediated cytotoxic effects on different mammalian cell lines employing a set-up where short-lived reactive species can be discounted and activated liquids with long-term stability are generated. Results: The PAW potency could be modulated using voltage level, treatment time and post-treatment storage time and target-related characteristics such as surface to volume ratio. All of these parameters effected cell viability in a hydrogen peroxide concentration correlated manner. The susceptibility of two cancer cell lines to PAW was similar to that observed for two non-cancer cell lines and the toxicity of plasma-activated water exceeded that of the corresponding hydrogen peroxide concentrations. Conclusion: In cytotoxic plasma activated water an essential role for H₂O₂ has been demonstrated multi-fold, yet further contributing factors are apparent and remain to be identified.