Mass Spectrometry Based Analysis Of The Oxidation Compounds Produced By Cold Atmospheric Plasma (CAP) Interaction With Cysteine

Abstract

Several studies confirm the effectiveness of cold physical plasmas in cancer treatment and the underlying mechanisms are currently under study. They involve redox signaling processes, with the deposition of reactive oxygen and nitrogen species (RONS) in body fluids and other liquids [1]. A way to clarify the biochemistry of CAP’s anti-cancer action can be to monitor the reactions between the deposited species and small organic molecules (MW<1kDa), which can be used as chemical traps. The resulting product spectra can be used to disentangle key RONS produced under different plasma parameters. Here, we focused on cysteine as model compound: an amino acid with a strong reactivity towards RONS due to the presence of a thiol moiety in its structure. Since the oxidation state of cysteine determines protein structure, function and subcellular localization, studying cysteine oxidation pathway could help in understanding dynamics of plasma-liquid interaction and in identification of a protein behavior during physiological, pathological or plasma related redox processes [2]. In this study, cysteine model solutions were treated with various argon plasma jets, with and without gas shield, and varying working gas conditions. The structure, the origin and the kinetic profiles of appearing cysteine oxidation products were determined using an ion trap triple quadrupole (QTrap5500) and a time-of-flight high-resolution (TripleTOF5600) mass spectrometers. Major trajectories of observed cysteine products (shown in Figure 1) include the oxygen dominated oxidation of the thiol group, with cysteine sulfonic acid (168 m/z) as a dominant product and the disulfide cystine (271.01 m/z) as transient intermediate. Depending on the treatment conditions, various products of cysteine and cystine were observed, which can be used as fingerprint identifying each plasma source. Potentially bioactive oxidized sulfoxides have been detected for moderately oxidative conditions, e.g. when using a nitrogen gas shield. Overall, these observations imply a profound impact on protein thiol groups when treated by plasma in vivo, with subsequent consequences on cellular redox signaling pathways.Download : Download high-res image (167KB)Download : Download full-size image Figure 1. MS spectra of cysteine solutions (300 μM) acquired before (A) and after plasma treatment (B). Treatment conditions: 5 minutes, 3 slm Ar/N2/O2 feed gas (99-0.5-0.5%).