Is Biomolecule Oxidation by Plasma-Derived Reactive Species Restricted to the Gas-Liquid Interphase?

Biomolecules such as amino acids, lipids, and proteins are relevant targets for reactive species due to the presence of sensitive chemical structures, such as electron-rich heteroatoms, (conjugated) double bonds, or aromatic rings. In plasma medicine, the successful application of plasmas for curative or preventive measures has been established. Besides electrical fields, predominantly reactive oxygen and nitrogen species were attributed to be most relevant for the observed effects. While it is accepted that long-lived species such as hydrogen peroxide can penetrate into (model) tissues, the fate of atomic and singlet oxygen or peroxynitrite remains to be clarified. Starting from amino acids (tyrosine, cysteine) and phospholipids (POPC), we found distinctive oxidation products and could show the incorporation of gas-and liquid phase derived atoms indicative for gas-liquid interphase reactions. Via model peptides, isolated proteins, and complex protein samples a site and sub-structure specificity of plasma-derived reactive species could be shown. In catalase, phospholipase, or filamentary proteins, the newly introduced chemical modifications modulated protein activity and recognition and subsequently changed cell physiology. Accordingly, it can be stated that the oxidative modification of biomolecules is a regular event in plasma medicine that modulates or even controls downstream physiologic processes.