Non-thermal plasma-induced DMPO-OH yields hydrogen peroxide.

Recent developments in electronics have enabled the medical applications of non-thermal plasma (NTP), which elicits reactive oxygen species (ROS) and reactive nitrogen species (RNS), such as hydroxyl radical (OH), hydrogen peroxide (HO), singlet oxygen (O), superoxide (O), ozone, and nitric oxide at near-physiological temperatures. In preclinical studies or human clinical trials, NTP promotes blood coagulation, eradication of bacterial, viral and biofilm-related infections, wound healing, and cancer cell death. To elucidate the solution-phase biological effects of NTP in the presence of biocompatible reducing agents, we employed electron paramagnetic resonance (EPR) spectroscopy to quantify OH using a spin-trapping probe, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO); O using a fluorescent probe; and O and HO using luminescent probes in the presence of thiols or tempol. NTP-induced OH was significantly scavenged by dithiothreitol (DTT), reduced glutathione (GSH), and oxidized glutathione (GSSG) in 2 or 5 mM DMPO. NTP-induced O was significantly scavenged by 10 μM DTT and GSH, while O was not efficiently scavenged by these compounds. GSSG degraded HO more effectively than GSH and DTT, suggesting that the disulfide bonds reacted with HO. In the presence of 1-50 mM DMPO, NTP-induced HO quantities were unchanged. The inhibitory effect of tempol concentration (50 and 100 μM) on HO production was observed in 1 and 10 mM DMPO, whereas it became ineffective in 50 mM DMPO. Furthermore, DMPO-OH did not interact with tempol. These results suggest that DMPO and tempol react competitively with O. Further studies are warranted to elucidate the interaction between NTP-induced ROS and biomolecules.