Tetrachloroaurate (III)–induced oxidation increases nonthermal plasma-induced aldehydes

Research on nonthermal plasma (NTP) devices first began almost five decades ago. NTP devices discharge electrons, positive ions, ultraviolet light, reactive oxygen species (ROS) and reactive nitrogen species (RNS) at near-physiological temperatures. Advances in plasma science have enabled the manipulation of ROS/RNS irradiation for medical applications. During preclinical stages and in human clinical trials, NTP promotes blood coagulation, eradication of bacterial, viral, and biofilm-related infections, wound healing, and cancer therapy. Previously, tetrachloroaurate (III) increased NTP-induced oxidative stress that was attenuated by reduced and oxidized glutathione, indicating that the presence of interactions between metal ions and biomolecules may modulate biological effects. In this study, using 3,3,5,5-tetramethyl-1-pyrroline-N-oxide (M4PO) as a spin probe in electron paramagnetic resonance (EPR), we observed that the tetrachloroaurate-induced M4PO-X spin adduct was significantly suppressed by ascorbate and α-tocopherol, while dehydroascorbate (DHA) and Trolox were ineffective. Tetrachloroaurate-induced lipid peroxidation, which was measured by 2-thiobarbituric acid-reactive substances (TBARS) in combination with NTP exposure, was suppressed by ascorbate, α-tocopherol and Trolox, while DHA was ineffective. Furthermore, N-acetyl-l-cysteine and dithiothreitol efficiently suppressed tetrachloroaurate-induced M4PO-X spin adduct and lipid peroxidation. LC‒MS/MS analyzes identified hexanal that was significantly elevated by NTP exposure and/or tetrachloroaurate. However, 25 and 250 μM ascorbate did not significantly suppress the formation of aldehydes, such as acetaldehyde, hexanal, nonanal, nonenal, and 4‑hydroxy-2-nonenal. Further studies are warranted to elucidate the redox reactions between metal ions, including gold (III), and biomolecules to expand the possibility of NTP application in medicine and agriculture.