Accurate in vivo real-time determination of the hydrogen concentration in different tissues of mice after hydrogen inhalation

As an antioxidant, anti-inflammatory and anti-apoptotic agent, hydrogen (H2) shows a promising potential in basic and clinical research against various diseases owing to its safety and efficacy. However, knowledge involving its underlying mechanisms of action, dosage effects, and dose duration remains limited. Previously, the dynamics of H2 concentrations in different tissues of rats after exogenous H2 inhalation had been detected by our team. Here, sequential changes of H2 concentrations in different tissues of another most commonly used experimental rodent mice were monitored in real time with an electrochemical H2 gas sensor during continuous different concentrations of H2 inhalation targeting on five tissues including brain, liver, spleen, kidney, and gastrocnemius. The results showed that the H2 saturation concentrations varied among tissues significantly regardless of the concentration of H2 inhaled, and they were detected the highest in the kidney but the lowest in the gastrocnemius. Meantime, it required a significant longer time to saturate in the thigh muscle. By comparing the H2 saturation concentrations of mice and rats, we found that there were no differences detected in most tissues except the kidney and spleen. Both gas diffusion and bloodstream transport could help the H2 reach to most organs. The results provide data reference for dosage selection, dose duration determination to ensure optimal therapeutic effects of H2 for mice experiments.

Hydrogen-rich water alleviates cyclosporine A-induced nephrotoxicity via the Keap1/Nrf2 signaling pathway

Oxidative stress induced by long-term cyclosporine A (CsA) administration is a major cause of chronic nephrotoxicity, which is characterized by tubular atrophy, tubular cell apoptosis, and interstitial fibrosis in the progression of organ transplantation. Although hydrogen-rich water (HRW) has been used to prevent various oxidative stress-related diseases, its underlying mechanisms remain unclear. This study investigated the effects of HRW on CsA-induced nephrotoxicity and its potential mechanisms. After administration of CsA (25 mg/kg/day), rats were treated with or without HRW (12 mL/kg) for 4 weeks. Renal function and vascular activity were investigated. Histological changes in kidney tissues were analyzed using Masson’s trichrome and terminal deoxynucleotidyl transferase dUTP nick-end labeling stains. Oxidative stress markers and the activation of the Kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway were also measured. We found that CsA increased the levels of reactive oxygen species (ROS) and malonaldehyde (MDA), but it reduced glutathione (GSH) and superoxide dismutase (SOD) levels. Such alterations induced vascular dysfunction, tubular atrophy, interstitial fibrosis, and tubular apoptosis. This was evident secondary to an increase in urinary protein, serum creatinine, and blood urea nitrogen, ultimately leading to renal dysfunction. Conversely, HRW decreased levels of ROS and MDA while increasing the activity of GSH and SOD. This was accompanied by an improvement in vascular and renal function. Moreover, HRW significantly decreased the level of Keap1 and increased the expression of Nrf2, NADPH dehydrogenase quinone 1, and heme oxygenase 1. In conclusion, HRW restored the balance of redox status, suppressed oxidative stress damage, and improved kidney function induced by CsA via activation of the Keap1/Nrf2 signaling pathway.