# Effects of Post-Treatment Hydrogen Gas Inhalation on Uveitis Induced by Endotoxin in Rats.
> エンドトキシン誘発ブドウ膜炎ラットモデルにおける水素ガス吸入の後処置効果


## Abstract

This animal study examined whether post-treatment inhalation of a 67% H2 / 33% O2 gas mixture could reduce ocular inflammation in Sprague-Dawley rats with lipopolysaccharide-induced uveitis. Compared with a nitrogen-oxygen control group, H2-inhaling rats showed no significant improvement in clinical uveitis scores, dark-adapted electroretinography b-wave peak latency, or the number of infiltrating cells in the iris and ciliary body. However, aqueous humor protein concentration was significantly lower in the H2 group (P<0.05), and Iba1 immunostaining revealed a partial reduction in microglial activation. The findings indicate that H2 inhalation after disease induction exerts selective, rather than comprehensive, anti-inflammatory effects in this endotoxin-driven ocular model.

### Mechanism

H2 inhalation reduced aqueous humor protein leakage and partially suppressed Iba1-positive microglial activation in the iris and ciliary body, without significantly affecting leukocyte infiltration or overall clinical uveitis severity.

## Bibliographic

- **Authors**: Yan W, Chen TX, Long P, Liu Q, Wang X, An J, et al.
- **Journal**: Med Sci Monit
- **Year**: 2018 (2018-06-07)
- **PMID**: [29875353](https://pubmed.ncbi.nlm.nih.gov/29875353/)
- **DOI**: [10.12659/MSM.907269](https://doi.org/10.12659/MSM.907269)
- **PMC**: [PMC6020745](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6020745/)
- **Study type**: animal study
- **Delivery route**: inhalation
- **Effect reported**: mixed
- **H2 concentration**: 67%

## 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 29875353. https://h2-papers.org/en/papers/29875353
> **Source**: PubMed PMID [29875353](https://pubmed.ncbi.nlm.nih.gov/29875353/)