Biochemical and Biophysical Research Communications, Vol.522, No.4, 965-970, 2020
Molecular hydrogen suppresses superoxide generation in the mitochondrial complex I and reduced mitochondrial membrane potential
Molecular hydrogen (H-2) is recognized as a medical gas applicable to numerous diseases including neurodegenerative diseases, metabolic disorders, and rheumatoid arthritis. Although the efficacy of H2 is reportedly attributed to its scavenging capability against the hydroxyl radical, the mechanisms underlying its therapeutic efficacy are not fully understood. Herein, we estimated the role of H-2 in the energy converting system of the mitochondria, the source of reactive oxygen species. To investigate the effects of H-2 on mitochondrial function, direction of electron flow, superoxide generation, and mitochondrial membrane potential were investigated. Forward electron transport (FET) or reverse electron transport (RET) was assessed by monitoring the decrease or increase of beta-nicotin-amide adenine dinucleotide hydrate (NADH, - or +, mu M, respectively) in the presence of beta-nicotinamide adenine dinucleotide (NAD(+)) and/or succinate in the isolated mitochondria. H2O2 converted from superoxide by superoxide dismutase (SOD) was measured to estimate electron leakage in the mitochondria. The effects of H-2 on mitochondrial membrane potential were observed by staining cells with the fluorescence probe, teramethylrhodamine ethyl ester (TMRE). Despite the absence of succinate, a distinct RET was observed (from +0.0313 +/- 0.0106 mu M to +1.20 +/- 0.302 mu M) by adding 25 mM H-2. In the presence of 5 mu M NADH, RET by succinate inverted to FET from +1.62 +/- 0.358 mu M to -1.83 +/- 0.191 mu M, accompanied by a suppression of superoxide generated predominantly from complex I by 51.1%. H-2 solely reduced mitochondrial membrane potential of the cultured cells by 11.3% as assessed by TMRE. The direction of electron flow was altered by H-2 depending on the NAD(+)/NADH ratio, accompanied by suppression of superoxide generation H-2 could suppress superoxide generation in complex I in vitro and reduce membrane potential in vivo. H-2 may also neutralize semiquinone radicals to reduce superoxide produced in complex III. H-2 may function as a rectifier of the electron flow affecting the mitochondrial membrane potential to suppress oxidative damage in mitochondria. (C) 2019 The Authors. Published by Elsevier Inc.