Environmental Hydrogen Concentration as a Novel Factor Determining Changes in Redox Potential

Intracellular oxidation–reduction (redox) potential is a key factor regulating various physiological phenomena in the cell. Monitoring this potential change is therefore important for understanding physiological homeostasis in cells. Herein, we propose a new approach for the real-time, non-invasive estimation of the redox potential impacting biological metabolism and reactive oxygen species generation. Enzymes, specifically oxidoreductases, play a crucial role in catalyzing redox reactions by facilitating the transfer of electrons and hydrogen atoms between molecules. The redox potential of substrates, such as nicotinamide adenine dinucleotide, is determined by the ratio of its oxidized and reduced forms, while that of enzymes, such as succinate dehydrogenase, is determined using the reference electrode in protein-film voltammetry. Although the standard hydrogen electrode potential is defined as zero under standard conditions, the electrode potential of a reversible hydrogen electrode changes according to the ratio of the hydrogen ions (H+) and hydrogen gas (H2) in the biological fluids, as a reference electrode. The pH is maintained at 7.4 ± 0.1 in the arterial blood and the H2 that produced by the gut microbiota is measured in the endo-tidal breath for clinical diagnosis. The H2 in the endo-tidal breath equilibrates arterial blood during gas exchange in the lungs, as well as in whole-body tissues, due to the systemic circulation. In this study, H2 can be measured in the environmental gas compared to the atmosphere, and may serve as a novel factor for redox potential changes in redox enzymes, impacting biological metabolism and reactive oxygen species generation.