Changes in Oxygen Level Upon Cold Plasma Treatments: Consequences for RONS Production

Despite the large number of papers showing the biological effect of cold atmospheric plasmas (CAPs) on skin treatment and although their ability to produce a cocktail of reactive oxygen and nitrogen species (RONS) is largely known, the deep knowledge of these ionized gas sources is far to be uncovered. Many parameters take part in the complex mechanisms induced by plasma, such as voltage, frequency, feeding gas flow rate, temperature, air humidity, and atmospheric gas composition. In this paper, we focus our attention on the influence of oxygen dissolved in the medium in RONS generation during CAP treatment. We evaluate RONS production in Dulbecco's phosphate-buffered saline equilibrated with two different percentages of oxygen: 18% and 3% O2. The former oxygen concentration is that usually used in most of cell culture and treatment (normoxia) while the latter is close to the physiological level measured inside human skin (physioxia). Intracellular RONS generation upon CAP treatment was also measured in two human skin cell lines maintained either in normoxic or in physioxic conditions. Our data suggest that RONS generation induced by plasma either in the medium or inside cells is influenced by oxygen dissolved in the treated target.