# Combination therapy with nitric oxide and molecular hydrogen in a murine model of acute lung injury.
> 急性肺傷害マウスモデルにおける一酸化窒素と水素ガスの併用吸入効果の検討


## Abstract

Using a mouse model of acute lung injury (ALI) induced by intratracheal lipopolysaccharide (LPS) administration, this study examined the effects of inhaled nitric oxide (NO at 20 ppm), hydrogen gas (H2 at 2%), and their combination over a 3-hour period beginning 5 minutes post-LPS. Both single-agent inhalations improved histopathological scores, wet-to-dry weight ratios, oxygenation index (PaO2/FiO2), and bronchoalveolar lavage fluid (BALF) protein levels. Notably, nitrotyrosine accumulation in lung tissue—elevated by NO inhalation alone—was markedly reduced when H2 was co-administered, consistent with H2-mediated peroxynitrite scavenging. The combined regimen produced greater suppression of neutrophil recruitment, myeloperoxidase activity, pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, HMGB1), chemokines, NF-κB activation, and pulmonary cell apoptosis compared with either agent alone. Protective effects were also observed in a polymicrobial sepsis model, and even subthreshold concentrations of both gases in combination retained significant efficacy, suggesting additive or synergistic interactions between NO and H2 in attenuating ALI.

### Mechanism

H2 scavenges peroxynitrite generated from inhaled NO, reducing nitrotyrosine formation in lung tissue. This, combined with suppression of NF-κB activation and attenuation of apoptotic signaling, collectively diminishes neutrophil-driven inflammatory injury in the lung.

## Bibliographic

- **Authors**: Liu H, Liang X, Wang D, Zhang H, Liu L, Chen H, et al.
- **Journal**: Shock
- **Year**: 2015
- **PMID**: [25643010](https://pubmed.ncbi.nlm.nih.gov/25643010/)
- **DOI**: [10.1097/SHK.0000000000000316](https://doi.org/10.1097/SHK.0000000000000316)
- **Study type**: animal study
- **Delivery route**: inhalation
- **Effect reported**: positive
- **H2 concentration**: 2%

## Delivery context

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

## Safety notes

For inhalation applications of molecular hydrogen, the lower flammability limit (LFL) deserves careful handling. The classical 4% figure applies to closed-system mixtures; the practical inhalation-environment threshold is 10%. Even pure-hydrogen output (the UFL 75% paradox) passes through the flammable range at the air–gas boundary. High-concentration (66% / 100%) inhalers are documented in the Japanese Consumer Affairs Agency accident-information database and are not recommended.

See also:
- [Inhalation concentration and LFL / UFL](https://h2-papers.org/en/safety-notes/inhalation-concentration)
- [Consumer Affairs Agency accident cases](https://h2-papers.org/en/safety-notes/accident-cases)
- [LFL / UFL terminology](https://h2-papers.org/en/safety-notes/lfl-ufl-explained)
- [Inhalation safety threshold lineage](https://h2-papers.org/en/safety-notes/lineage)

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> **Cite as**: H2 Papers — PMID 25643010. https://h2-papers.org/en/papers/25643010
> **Source**: PubMed PMID [25643010](https://pubmed.ncbi.nlm.nih.gov/25643010/)