Pharmacokinetics of a single inhalation of hydrogen gas in pigs

The impact of hydrogen inhalation therapy on blood reactive oxygen species levels: A randomized controlled study

Reactive Oxygen Species (ROS) play a key role in physiological processes. However, the imbalance between ROS and antioxidants in favor of the former causes oxidative stress linked to numerous pathologies. Due to its unique attributes, including distinguished permeability and selective antioxidant capability, molecular hydrogen (H2) has become an essential therapeutic agent. Hydrogen Inhalation Therapy (HIT) has come to light as a promising strategy to counteract oxidative stress. In this randomized controlled study, we aimed to evaluate the effectiveness of HIT in reducing blood ROS levels. 37 participants with elevated ROS levels (d-ROMs value > 350 U.CARR) were enrolled in the study. Participants were divided into test and control groups. The test group participants received HIT, and then their blood ROS levels were measured immediately post-treatment and after 24 h. Their results were compared to those of the control group participants who did not undergo HIT. The test group demonstrated a significant reduction in blood ROS levels after the treatment. These findings suggested the efficacy of HIT in reducing oxidative stress.

Combination of Hydrogen Inhalation and Hypothermic Temperature Control After Out-of-Hospital Cardiac Arrest: A Post hoc Analysis of the Efficacy of Inhaled Hydrogen on Neurologic Outcome Following Brain Ischemia During PostCardiac Arrest Care II Trial

OBJECTIVE

The Efficacy of Inhaled Hydrogen on Neurologic Outcome Following Brain Ischemia During Post-Cardiac Arrest Care (HYBRID) II trial (jRCTs031180352) suggested that hydrogen inhalation may reduce post-cardiac arrest brain injury (PCABI). However, the combination of hypothermic target temperature management (TTM) and hydrogen inhalation on outcomes is unclear. The aim of this study was to investigate the combined effect of hydrogen inhalation and hypothermic TTM on outcomes after out-of-hospital cardiac arrest (OHCA).

DESIGN

Post hoc analysis of a multicenter, randomized, controlled trial.

SETTING

Fifteen Japanese ICUs.

PATIENTS

Cardiogenic OHCA enrolled in the HYBRID II trial.

INTERVENTIONS

Hydrogen mixed oxygen (hydrogen group) versus oxygen alone (control group).

MEASUREMENTS AND MAIN RESULTS

TTM was performed at a target temperature of 32-34°C (TTM32-TTM34) or 35-36°C (TTM35-TTM36) per the institutional protocol. The association between hydrogen + TTM32-TTM34 and 90-day good neurologic outcomes was analyzed using generalized estimating equations. The 90-day survival was compared between the hydrogen and control groups under TTM32-TTM34 and TTM35-TTM36, respectively. The analysis included 72 patients (hydrogen [n = 39] and control [n = 33] groups) with outcome data. TTM32-TTM34 was implemented in 25 (64%) and 24 (73%) patients in the hydrogen and control groups, respectively (p = 0.46). Under TTM32-TTM34, 17 (68%) and 9 (38%) patients achieved good neurologic outcomes in the hydrogen and control groups, respectively (relative risk: 1.81 [95% CI, 1.05-3.66], p < 0.05). Hydrogen + TTM32-TTM34 was independently associated with good neurologic outcomes (adjusted odds ratio 16.10 [95% CI, 1.88-138.17], p = 0.01). However, hydrogen + TTM32-TTM34 did not improve survival compared with TTM32-TTM34 alone (adjusted hazard ratio: 0.22 [95% CI, 0.05-1.06], p = 0.06).

CONCLUSIONS

Hydrogen + TTM32-TTM34 was associated with improved neurologic outcomes after cardiogenic OHCA compared with TTM32-TTM34 monotherapy. Hydrogen inhalation is a promising treatment option for reducing PCABI when combined with TTM32-TTM34.

Protective Effects of Hydrogen Gas Inhalation for Hindlimb Ischaemia-Reperfusion Injury in a Mouse Model

OBJECTIVE

Ischaemia-reperfusion (I/R) injury is a severe post-operative complication that triggers an inflammatory response and causes severe damage. Hydrogen gas has anti-oxidant and anti-apoptotic properties and has been shown to be safe in humans. The study aimed to investigate whether hydrogen gas protects against skeletal muscle I/R injury.

METHODS

Experimental basic research using mice. A total of 160 eight to 10 week old albino laboratory bred strain of house mice (25.8 ± 0.68 g) were used in this study. The mice were cable tied to the hindlimb under anaesthesia and then placed in an anaesthesia box filled with air and 2% isoflurane (control group); 80 mice were additionally subjected to 1.3% hydrogen gas in this mix (hydrogen group). After two hours, the cable ties were removed to initiate reperfusion, and hydrogen inhalation lasted for six hours in the hydrogen group. After six hours, the mice were taken out of the box and kept in cages under standard conditions until time for observation at 16 different time points after reperfusion: zero, two, four, six, eight, and 10 hours and one, two, three, four, five, six, seven, 14, 21, and 28 days. Five mice were sacrificed using excess anaesthesia at each time point, and the bilateral hindlimb tissues were harvested. The inflammatory effects of the I/R injury were assessed by evaluating serum interleukin-6 concentrations using enzyme linked immunosorbent assay, as well as histological and immunohistochemical analyses. Untreated mice with I/R injury were used as controls.

RESULTS

Hydrogen gas showed protective effects associated with a reduction in inflammatory cell infiltration (neutrophils, macrophages, and lymphocytes), a reduced area of damaged muscle, maintenance of normal muscle cells, and replacement of damaged muscle cells with neoplastic myocytes.

CONCLUSION

Inhalation of hydrogen gas had a protective effect against hindlimb I/R injury in mice, in part by reducing inflammatory cell infiltration and in part by preserving normal muscle cells.

Molecular Hydrogen Therapy-A Review on Clinical Studies and Outcomes

With its antioxidant properties, hydrogen gas (H2) has been evaluated in vitro, in animal studies and in human studies for a broad range of therapeutic indications. A simple search of "hydrogen gas" in various medical databases resulted in more than 2000 publications related to hydrogen gas as a potential new drug substance. A parallel search in clinical trial registers also generated many hits, reflecting the diversity in ongoing clinical trials involving hydrogen therapy. This review aims to assess and discuss the current findings about hydrogen therapy in the 81 identified clinical trials and 64 scientific publications on human studies. Positive indications have been found in major disease areas including cardiovascular diseases, cancer, respiratory diseases, central nervous system disorders, infections and many more. The available administration methods, which can pose challenges due to hydrogens' explosive hazards and low solubility, as well as possible future innovative technologies to mitigate these challenges, have been reviewed. Finally, an elaboration to discuss the findings is included with the aim of addressing the following questions: will hydrogen gas be a new drug substance in future clinical practice? If so, what might be the administration form and the clinical indications?

Hydrogen Inhalation Reduces Lung Inflammation and Blood Pressure in the Experimental Model of Pulmonary Hypertension in Rats

Hydrogen has been shown to exhibit selective antioxidant properties against hydroxyl radicals, and exerts antioxidant and anti-inflammatory effects. The monocrotaline-induced model of pulmonary hypertension is suitable for studying substances with antioxidant activity because oxidative stress is induced by monocrotaline. On day 1, male Wistar rats were subcutaneously injected with a water-alcohol solution of monocrotaline or a control with an only water-alcohol solution. One group of monocrotaline-injected animals was placed in a plastic box that was constantly ventilated with atmospheric air containing 4% of molecular hydrogen, and the two groups of rats, injected with monocrotaline or vehicle, were placed in boxes ventilated with atmospheric air. After 21 days, hemodynamic parameters were measured under urethane narcosis. The results showed that, although hydrogen inhalation had no effect on the main markers of pulmonary hypertension induced by monocrotaline injection, there was a reduction in systemic blood pressure due to its systolic component, and a decrease in TGF-β expression, as well as a reduction in tryptase-containing mast cells.

Attenuation of pulmonary damage in aged lipopolysaccharide-induced inflammation mice through continuous 2 % hydrogen gas inhalation: A potential therapeutic strategy for geriatric inflammation and survival

INTRODUCTION

With the global population aging, there is an increased prevalence of sepsis among the elderly, a demographic particularly susceptible to inflammation. This study aimed to evaluate the therapeutic potential of hydrogen gas, known for its anti-inflammatory and antioxidant properties, in attenuating inflammation specifically in the lungs and liver, and age-associated molecular markers in aged mice.

METHODS

Male mice aged 21 to 23 months, representative of the human elderly population, were subjected to inflammation via intraperitoneal injection of lipopolysaccharide (LPS). The mice were allocated into eight groups to examine the effects of varying durations and concentrations of hydrogen gas inhalation: control, saline without hydrogen, saline with 24-hour 2 % hydrogen, LPS without hydrogen, LPS with 24-hour 2 % hydrogen, LPS with 6-hour 2 % hydrogen, LPS with 1-hour 2 % hydrogen, and LPS with 24-hour 1 % hydrogen. Parameters assessed included survival rate, activity level, inflammatory biomarkers, and organ injury.

RESULTS

Extended administration of hydrogen gas specifically at a 2 % concentration for 24 h led to a favorable prognosis in the aged mice by reducing mRNA expression of inflammatory biomarkers in lung and liver tissue, mitigating lung injury, and diminishing the expression of the senescence-associated protein p21. Moreover, hydrogen gas inhalation selectively ameliorated senescence-related markers in lung tissue, including C-X-C motif chemokine 2, metalloproteinase-3, and arginase-1. Notably, hydrogen gas did not alleviate LPS-induced liver injury under the conditions tested.

CONCLUSION

The study highlights that continuous inhalation of hydrogen gas at a 2 % concentration for 24 h can be a potent intervention in the geriatric population for improving survival and physical activity by mitigating pulmonary inflammation and modulating senescence-related markers in aged mice with LPS-induced inflammation. This finding paves the way for future research into hydrogen gas as a therapeutic strategy to alleviate severe inflammation that can lead to organ damage in the elderly.

Hydrogen Therapy and Its Future Prospects for Ameliorating COVID-19: Clinical Applications, Efficacy, and Modality

Molecular hydrogen is renowned as an odorless and colorless gas. The recommendations developed by China suggest that the inhalation of hydrogen molecules is currently advised in COVID-19 pneumonia treatment. The therapeutic effects of molecular hydrogens have been confirmed after numerous clinical trials and animal-model-based experiments, which have expounded that the low molecular weight of hydrogen enables it to easily diffuse and permeate through the cell membranes to produce a variety of biological impacts. A wide range of both chronic and acute inflammatory diseases, which may include sepsis, pancreatitis, respiratory disorders, autoimmune diseases, ischemia-reperfusion damages, etc. may be treated and prevented by using it. H₂ can primarily be inoculated through inhalation, by drinking water (which already contains H₂), or by administrating the injection of saline H₂ in the body. It may play a pivotal role as an antioxidant, in regulating the immune system, in anti-inflammatory activities (mitochondrial energy metabolism), and cell death (apoptosis, pyroptosis, and autophagy) by reducing the formation of excessive reactive O₂ species and modifying the transcription factors in the nuclei of the cells. However, the fundamental process of molecular hydrogen is still not entirely understood. Molecular hydrogen H₂ has a promising future in therapeutics based on its safety and possible usefulness. The current review emphasizes the antioxidative, anti-apoptotic, and anti-inflammatory effects of hydrogen molecules along with the underlying principle and fundamental mechanism involved, with a prime focus on the coronavirus disease of 2019 (COVID-19). This review will also provide strategies and recommendations for the therapeutic and medicinal applications of the hydrogen molecule.

Efficacy of inhaled hydrogen on neurological outcome following brain ischaemia during post-cardiac arrest care (HYBRID II): a multi-centre, randomised, double-blind, placebo-controlled trial

Background

Inhaled molecular hydrogen gas (H₂) has been shown to improve outcomes in animal models of cardiac arrest (CA). H₂ inhalation is safe and feasible in patients after CA. We investigated whether inhaled H₂ would improve outcomes after out-of-hospital CA (OHCA).

Methods

HYBRID II is a prospective, multicentre, randomised, double-blind, placebo-controlled trial performed at 15 hospitals in Japan, between February 1, 2017, and September 30, 2021. Patients aged 20-80 years with coma following cardiogenic OHCA were randomly assigned (1:1) using blinded gas cylinders to receive supplementary oxygen with 2% H₂ or oxygen (control) for 18 h. The primary outcome was the proportion of patients with a 90-day Cerebral Performance Category (CPC) of 1 or 2 assessed in a full-analysis set. Secondary outcomes included the 90-day score on a modified Rankin scale (mRS) and survival. HYBRID II was registered with the University Hospital Medical Information Network (registration number: UMIN000019820) and re-registered with the Japan Registry for Clinical Trials (registration number: jRCTs031180352).

Findings

The trial was terminated prematurely because of the restrictions imposed on enrolment during the COVID-19 pandemic. Between February 1, 2017, and September 30, 2021, 429 patients were screened for eligibility, of whom 73 were randomly assigned to H₂ (n = 39) or control (n = 34) groups. The primary outcome, i.e., a CPC of 1 or 2 at 90 days, was achieved in 22 (56%) and 13 (39%) patients in the H₂ and control groups (relative risk compared with the control group, 0.72; 95% CI, 0.46-1.13; P = 0.15), respectively. Regarding the secondary outcomes, median mRS was 1 (IQR: 0-5) and 5 (1-6) in the H₂ and control groups, respectively (P = 0.01). An mRS score of 0 was achieved in 18 (46%) and 7 (21%) patients in the H₂ and control groups, respectively (P = 0.03). The 90-day survival rate was 85% (33/39) and 61% (20/33) in the H₂ and control groups, respectively (P = 0.02).

Interpretation

The increase in participants with good neurological outcomes following post-OHCA H₂ inhalation in a selected population of patients was not statistically significant. However, the secondary outcomes suggest that H₂ inhalation may increase 90-day survival without neurological deficits.

Funding

Taiyo Nippon Sanso Corporation.

Translation

For the Japanese translation of the abstract see Supplementary Materials section.

Molecular Hydrogen: From Molecular Effects to Stem Cells Management and Tissue Regeneration

It is known that molecular hydrogen is a relatively stable, ubiquitous gas that is a minor component of the atmosphere. At the same time, in recent decades molecular hydrogen has been shown to have diverse biological effects. By the end of 2022, more than 2000 articles have been published in the field of hydrogen medicine, many of which are original studies. Despite the existence of several review articles on the biology of molecular hydrogen, many aspects of the research direction remain unsystematic. Therefore, the purpose of this review was to systematize ideas about the nature, characteristics, and mechanisms of the influence of molecular hydrogen on various types of cells, including stem cells. The historical aspects of the discovery of the biological activity of molecular hydrogen are presented. The ways of administering molecular hydrogen into the body are described. The molecular, cellular, tissue, and systemic effects of hydrogen are also reviewed. Specifically, the effect of hydrogen on various types of cells, including stem cells, is addressed. The existing literature indicates that the molecular and cellular effects of hydrogen qualify it to be a potentially effective agent in regenerative medicine.

Pharmacokinetics of hydrogen administered intraperitoneally as hydrogen-rich saline and its effect on ischemic neuronal cell death in the brain in gerbils

Intraperitoneal administration of hydrogen (H2)-containing saline inhibited neuronal cell death in ischemic stroke in a number of animal models, but it is unknown whether H2 is absorbed from the abdominal cavity into the blood and reaches the brain. In this study, we investigated whether intraperitoneal administration of saline containing H2 inhibits neuronal cell death caused by cerebral ischemia and measured the concentration of H2 in the carotid artery and inferior vena cava (IVC). Gerbils were subjected to transient unilateral cerebral ischemia twice, and saline or H2-rich saline was administered intraperitoneally three or seven times every 12 hours. We evaluated the number of apoptotic cells in the hippocampus and cerebral cortex on day 3 and the number of viable neurons in the hippocampus and cerebral cortex on day 7. In addition, a single dose of saline or H2-rich saline was administered intraperitoneally, and blood H2 levels in the carotid artery and IVC were measured. On day 3 of ischemia/reperfusion, the number of neurons undergoing apoptosis in the cortex was significantly lower in the H2-rich saline group than in the saline group, and on day 7, the number of viable neurons in the hippocampus and cerebral cortex was significantly higher in the H2-rich saline group. Intraperitoneal administration of H2-rich saline resulted in large increases in H2 concentration in the IVC ranging from 0.00183 mg/L (0.114%) to 0.00725 mg/L (0.453%). In contrast, carotid H2 concentrations remained in the range of 0.00008 mg/L (0.0049%) to 0.00023 (0.0146%). On average, H2 concentrations in carotid artery were 0.04 times lower than in IVC. These results indicate that intraperitoneal administration of H2-rich saline significantly suppresses neuronal cell death after cerebral ischemia, even though H2 hardly reaches the brain.

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.

Drinking hydrogen water improves photoreceptor structure and function in retinal degeneration 6 mice

Retinitis pigmentosa (RP) is a genetically heterogeneous group of inherited retinal disorders involving the progressive dysfunction of photoreceptors and the retinal pigment epithelium, for which there is currently no treatment. The rd6 mouse is a natural model of autosomal recessive retinal degeneration. Given the known contributions of oxidative stress caused by reactive oxygen species (ROS) and selective inhibition of potent ROS peroxynitrite and OH·by H₂ gas we have previously demonstrated, we hypothesized that ingestion of H₂ water may delay the progression of photoreceptor death in rd6 mice. H₂ mice showed significantly higher retinal thickness as compared to controls on optical coherence tomography. Histopathological and morphometric analyses revealed higher thickness of the outer nuclear layer for H₂ mice than controls, as well as higher counts of opsin red/green-positive cells. RNA sequencing (RNA-seq) analysis of differentially expressed genes in the H₂ group versus control group revealed 1996 genes with significantly different expressions. Gene and pathway ontology analysis showed substantial upregulation of genes responsible for phototransduction in H₂ mice. Our results show that drinking water high in H₂ (1.2-1.6 ppm) had neuroprotective effects and inhibited photoreceptor death in mice, and suggest the potential of H₂ for the treatment of RP.

Hydrogen, a Novel Therapeutic Molecule, Regulates Oxidative Stress, Inflammation, and Apoptosis

Molecular hydrogen (H₂) is a colorless and odorless gas. Studies have shown that H₂ inhalation has the therapeutic effects in many animal studies and clinical trials, and its application is recommended in the novel coronavirus pneumonia treatment guidelines in China recently. H₂ has a relatively small molecular mass, which helps it quickly spread and penetrate cell membranes to exert a wide range of biological effects. It may play a role in the treatment and prevention of a variety of acute and chronic inflammatory diseases, such as acute pancreatitis, sepsis, respiratory disease, ischemia reperfusion injury diseases, autoimmunity diseases, etc.. H₂ is primarily administered via inhalation, drinking H₂-rich water, or injection of H₂ saline. It may participate in the anti-inflammatory and antioxidant activity (mitochondrial energy metabolism), immune system regulation, and cell death (apoptosis, autophagy, and pyroptosis) through annihilating excess reactive oxygen species production and modulating nuclear transcription factor. However, the underlying mechanism of H₂ has not yet been fully revealed. Owing to its safety and potential efficacy, H₂ has a promising potential for clinical use against many diseases. This review will demonstrate the role of H₂ in antioxidative, anti-inflammatory, and antiapoptotic effects and its underlying mechanism, particularly in coronavirus disease-2019 (COVID-19), providing strategies for the medical application of H₂ for various diseases.

Pharmacokinetics of hydrogen after ingesting a hydrogen-rich solution: A study in pigs

Drinking hydrogen (H₂)-rich water is a common way to consume H₂. Although many studies have shown efficacy of drinking H₂-rich water in neuropsychiatric and endocrine metabolic disorders, their authenticity has been questioned because none examined the associated pharmacokinetics of H₂. Therefore, we performed the first study to investigate the pharmacokinetics of H₂ in pigs given an H₂-rich glucose solution with the aim to extrapolate the findings to humans. We inserted blood collection catheters into the jejunal and portal veins, suprahepatic inferior vena cava, and carotid artery of 4 female pigs aged 8 weeks. Then, within 2 min we infused 500 ml of either H₂-rich or H₂-free glucose solution into the jejunum via a percutaneous gastrostomy tube and measured changes in H₂ concentration in venous and arterial blood over 120 min. After infusion of the H₂-rich glucose solution, H₂ concentration in the portal vein peaked at 0.05 mg/L and remained at more than 0.016 mg/L (H₂ saturation level, 1%) after 1 h; it also increased after infusion of H₂-free glucose solution but remained below 0.001 mg/L (H₂ saturation level, 0.06%). We assume that H₂ was subsequently metabolized in the liver or eliminated via the lungs because it was not detected in the carotid artery. In conclusion, drinking highly concentrated H₂-rich solution within a short time is a good way to increase H₂ concentration in portal blood and supply H₂ to the liver.

Molecular Hydrogen as Medicine: An Assessment of Administration Methods

Since the late 18th century, molecular hydrogen (H2) has been shown to be well tolerated, firstly in animals, and then in humans. However, although research into the beneficial effects of molecular hydrogen in both plant and mammalian physiology is gaining momentum, the idea of utilising this electrochemically neutral and non-polar diatomic compound for the benefit of health has yet to be widely accepted by regulatory bodies worldwide. Due to the precise mechanisms of H2 activity being as yet undefined, the lack of primary target identification, coupled with difficulties regarding administration methods (e.g., dosage and dosage frequencies, long-term effects of treatment, and the patient’s innate antioxidant profile), there is a requirement for H2 research to evidence how it can reasonably and most effectively be incorporated into medical practice. This review collates and assesses the current information regarding the many routes of molecular hydrogen administration in animals and humans, whilst evaluating how targeted delivery methods could be integrated into a modern healthcare system.

A Comparison of the Antioxidant Effects Between Hydrogen Gas Inhalation and Vitamin C Supplementation in Response to a 60-Min Treadmill Exercise in Rat Gastrocnemius Muscle

The reactive oxygen species (ROS) produced during exercise act as a double-edged sword because they may cause oxidative damage but also play a role in the signaling pathways. A supplementation of exogenous antioxidants can reduce the total amount of ROS during exercise while it may also affect the ROS’ role in the signaling pathways of mitochondrial biogenesis. It has been suggested that hydrogen gas, as an antioxidant, can selectively scavenge hydroxyl radicals but does not affect superoxide anion’s signal transduction. The aim of this study was to compare the effects of 1-h hydrogen gas inhalation 30min prior to a treadmill exercise on the key biomarkers of mitochondrial biogenesis and related signaling pathways, and the activities of endogenous antioxidant enzymes, with those of vitamin C, in the rat skeletal muscle. Eighty-one 8-week-old male Sprague–Dawley (SD) rats were randomly assigned to three interventions (exercise-only, exercise+4%H₂, and exercise+vitamin C at 500mg/kg weight, with 27 rats under each intervention), and sampled at pre-, immediately post and 4h post a 60-min treadmill exercise at speed of 27m/min and flat inclination, with nine rats in each sub-group. Expression of mitochondrial biogenetic markers and related signaling molecules in gastrocnemius muscle, and concentrations of oxidative stress markers in serum were measured. Two-way ANOVA or Kruskal–Wallis analyses showed that both hydrogen inhalation and vitamin C supplementation significantly reduced serum levels of MDA immediately after exercise and AGEs 4h after exercise. The pre-exercise supplement of vitamin C significantly reduced mitochondrial complex IV concentrations and PGC-1α, NRF-1, TFAM gene expression levels compared to the pre-exercise group, but the hydrogen gas intervention did not result in a reduction in these measurements. Unlike vitamin C, hydrogen inhalation did not blunt post-exercise mitochondrial biogenetic signals, but resulted in an increase in complex IV concentration, activation of PGC-1α, and TFAM and NRF-2 gene transcription, and up-regulation of PGC-1α protein expression. The findings indicated that hydrogen gas inhalation could play the role as an effective antioxidant in response to the exercise, whilst it did not significantly affect mitochondrial biogenesis. The dose–response relationship and antioxidant effects in different types of exercise for hydrogen inhalation require further investigation.

Inhalation of Molecular Hydrogen, a Rescue Treatment for Noise-Induced Hearing Loss

Noise exposure is the most important external factor causing acquired hearing loss in humans, and it is strongly associated with the production of reactive oxygen species (ROS) in the cochlea. Several studies reported that the administration of various compounds with antioxidant effects can treat oxidative stress-induced hearing loss. However, traditional systemic drug administration to the human inner ear is problematic and has not been successful in a clinical setting. Thus, there is an urgent need to develop rescue treatment for patients with acute acoustic injuries. Hydrogen gas has antioxidant effects, rapid distribution, and distributes systemically after inhalation.The purpose of this study was to determine the protective efficacy of a single dose of molecular hydrogen (H₂) on cochlear structures. Guinea pigs were divided into six groups and sacrificed immediately after or at 1 or 2 weeks. The animals were exposed to broadband noise for 2 h directly followed by 1-h inhalation of 2% H₂ or room air. Electrophysiological hearing thresholds using frequency-specific auditory brainstem response (ABR) were measured prior to noise exposure and before sacrifice. ABR thresholds were significantly lower in H₂-treated animals at 2 weeks after exposure, with significant preservation of outer hair cells in the entire cochlea. Quantification of synaptophysin immunoreactivity revealed that H₂ inhalation protected the cochlear inner hair cell synaptic structures containing synaptophysin. The inflammatory response was greater in the stria vascularis, showing increased Iba1 due to H₂ inhalation.Repeated administration of H₂ inhalation may further improve the therapeutic effect. This animal model does not reproduce conditions in humans, highlighting the need for additional real-life studies in humans.

Biological Responses to Hydrogen Molecule and its Preventive Effects on Inflammatory Diseases

Because multicellular organisms do not have hydrogenase, H₂ has been considered to be biologically inactive in these species, and enterobacteria to be largely responsible for the oxidation of H₂ taken into the body. However, we showed previously that inhalation of H₂ markedly suppresses brain injury induced by focal ischemia-reperfusion by buffering oxidative stress. Although the reaction constant of H₂ with hydroxyl radical in aqueous solution is two to three orders of magnitude lower than that of conventional antioxidants, we showed that hydroxyl radical generated by the Fenton reaction reacts with H₂ at room temperature without a catalyst. Suppression of hydroxyl radical by H₂ has been applied in ophthalmic surgery. However, many of the anti- inflammatory and other therapeutic effects of H₂ cannot be completely explained by its ability to scavenge reactive oxygen species. H₂ administration is protective in several disease models, and preculture in the presence of H₂ suppresses oxidative stress-induced cell death. Specifically, H₂ administration induces mitochondrial oxidative stress and activates Nrf2; this phenomenon, in which mild mitochondrial stress leaves the cell less susceptible to subsequent perturbations, is called mitohormesis. Based on these findings, we conclude that crosstalk between antioxidative stress pathways and the anti-inflammatory response is the most important molecular mechanism involved in the protective function of H₂, and that regulation of the immune system underlies H₂ efficacy. For further medical applications of H₂, it will be necessary to identify the biomolecule on which H₂ first acts.

Daily inhalation of hydrogen gas has a blood pressure-lowering effect in a rat model of hypertension

A recent clinical study demonstrated that haemodialysis with a dialysate containing hydrogen (H₂) improves blood pressure control in end-stage kidney disease. Herein, we examined whether H₂ has a salutary effect on hypertension in animal models. We subjected 5/6 nephrectomised rats to inhalation of either H₂ (1.3% H₂ + 21% O₂ + 77.7% N₂) or control (21% O₂ + 79% N₂) gas mixture for 1 h per day. H₂ significantly suppressed increases in blood pressure after 5/6 nephrectomy. The anti-hypertensive effect of H₂ was also confirmed in rats in a stable hypertensive state 3 weeks after nephrectomy. To examine the detailed effects of H₂ on hypertension, we used an implanted telemetry system to continuously monitor blood pressure. H₂ exerted an anti-hypertensive effect not only during daytime rest, but also during night-time activities. Spectral analysis of blood pressure variability revealed that H₂ improved autonomic imbalance, namely by suppressing the overly active sympathetic nervous system and augmenting parasympathetic nervous system activity; these effects co-occurred with the blood pressure-lowering effect. In conclusion, 1-h daily exposure to H₂ exerts an anti-hypertensive effect in an animal model of hypertension.

Low-Flow Nasal Cannula Hydrogen Therapy

BACKGROUND

Molecular hydrogen (H2) is a biologically active gas that is widely used in the healthcare sector. In recent years, on-site H2 gas generators, which produce high-purity H2 by water electrolysis, have begun to be introduced in hospitals, clinics, beauty salons, and fitness clubs because of their ease of use. In general, these generators produce H2 at a low-flow rate, so physicians are concerned that an effective blood concentration of H2 may not be ensured when the gas is delivered through a nasal cannula. Therefore, this study aimed to evaluate blood concentrations of H2 delivered from an H2 gas generator via a nasal cannula.

METHODS

We administered 100% H2, produced by an H2 gas generator, at a low-flow rate of 250 mL/min via a nasal cannula to three spontaneously breathing micro miniature pigs. An oxygen mask was placed over the nasal cannula to administer oxygen while minimizing H2 leakage, and a catheter was inserted into the carotid artery to monitor the arterial blood H2 concentration.

RESULTS

During the first hour of H2 inhalation, the mean (standard error (SE)) H2 concentrations and saturations in the arterial blood of the three pigs were 1,560 (413) nL/mL and 8.85% (2.34%); 1,190 (102) nL/mL and 6.74% (0.58%); and 1,740 (181) nL/mL and 9.88% (1.03%), respectively. These values are comparable to the concentration one would expect if 100% of the H2 released from the H2 gas generator is taken up by the body.

CONCLUSIONS

Inhalation of 100% H2 produced by an H2 gas generator, even at low-flow rates, can increase blood H2 concentrations to levels that previous non-clinical and clinical studies demonstrated to be therapeutically effective. The combination of a nasal cannula and an oxygen mask is a convenient way to reduce H2 leakage while maintaining oxygenation.