Cell Response to He, He-O2 Plasma and Plasma Electric Field Alone Treatments
Résumé
Cold atmospheric pressure plasmas (CAPs) are promising therapeutic strategies in numerous biomedical fields such as, oncology and dermatology (wound healing, disinfection of tissues). CAPS are constituted by different components that may have effects on cells (e.g. photons, charged particles, reactive oxygen and nitrogen species, electric field, etc.). Among them, reactive oxygen and nitrogen species (RONS) are often considered as main actors responsible for the effects of plasma treatment on treated cells [1]. Depending on their gaseous composition, plasmas generated with similar electrical conditions could act in a very different way on cells and so, potentially, have completely different applications.The exact effects of plasma treatment on living cells are not very well characterized. This study aimed to investigate those effects in both human keratinocytes and HeLa cancer cell line. Particular attention was paid to the contribution of the electric field (EF) and RONS in cellular response to plasma treatment. Indeed, if the cell membrane gets charged, an electric stress could cause its rupture leading to cell death [2]. It is also well known that the electric field alone is able to cause either a reversible or irreversible depolarization of cell membrane, favorable to the increase of membrane permeability to certain species [3].In this work, plasmas were generated using a Plasma Gun feeded with helium or He-0.5% O2 mixtures. An electro optic electric field sensor was used to measure the electric field exposure of cell and culture media. It was measured that pure He plasma was more toxic than He-0.5% O2 plasma. H2O2 and NO2- were the main species detected in treated PBS post treatment, in higher concentrations following He than He-O2 plasmas exposure. Electric field alone treatment, achieved either with inserting a dielectric plate between the plasma jet and the well plates, or by irradiating the well plates from their bottom, lead to much less but still significant cell death.Regarding He-0.5% O2, EF measured was lower but plasmic membrane depolarization observed was much more important than that obtained with He plasma. Following the exposure to only a few thousands of plasma shots, He and He-O2 plasmas were also shown to induce potent permeabilization of HeLa plasma membrane, revealed through 4 kDa Dextran fluorescence detected in the cell nucleus. He-O2 plasma was the more efficient, leading to up to a 30% uptake for this dextran small molecule. Plasma or electric field alone exposure during a few thousands pulses was finally shown to allow for very limited but unambiguous penetration of much larger molecules as plasmid DNA in the HeLa cells.This work supports that strong cell depolarization with He-O2 plasmas can be obtained, same as plasma electric field which permeabilization effect does favor the penetration of chemical species such as RONS or larger molecules, but surprisingly leads to a much lower cell death.References[1] M. Ishaq, M. Evans, K. Ostrikov, International Journal of Cancer.,134, 1517 (2014). [2] N. Babaeva, N. Ning, D. Graves, M. Kushner, Journal of Physics, 45 11 115203 (2012)[3] Leduc M, Guay D, Leask RL, Coulombe S. New Journal of Physics, 11 115021 (2009)