Does plasma-induced methionine degradation provide alternative reaction paths for cell death?

Abstract

Cold atmospheric pressure plasma is a promising technology for surface wound healing. Its antimicrobial effect is correlated to chemical modifications of methionine (Met) caused by reactive oxygen and nitrogen species. To minimize unwanted side effects on healthy tissue it is of utmost importance to unravel the origin of the antimicrobial plasma effects.In this study, we employed confocal Raman spectroscopy on Met and Met glutathione (GSH) mixtures to obtain a chemical picture of how plasma affects Met as a function of treatment time (t = 0–600 s). We were able to observe a hitherto unknown reaction path that leads to a disulfide (MSSM) via a thiol (MSH) in addition to the well-known Met degradation route involving sulfur oxidation to methionine disulfide (Met(O)) and methionine sulfone (Met(O2)). We propose that the anti-microbial effect of plasma treatment is caused by two alternative reaction routes. The first one leads to protein damage caused by sulfur bridge formation (S-S). A second pathway is provided by MSH and dimethyl sulfoxide precursor species (detected via their characteristic Raman bands) that cause DNA damage due to strand breaks. Addition of GSH shifts the Met decay in time by 70 s while the general reaction pathways are preserved.