Hydrogen Gas and the Gut Microbiota as Potential Biomarkers for the Development of Experimental Colitis in Mice
Inflammatory Bowel Disease (IBD) is a chronic inflammatory condition that primarily includes Ulcerative Colitis (UC) and Crohn’s Disease (CD). The incidence of IBD has been increasing globally, imposing significant health and economic burdens on patients and society. Currently, the diagnosis of IBD relies mainly on endoscopy, but this method is expensive, invasive, and inconvenient for continuous use. Therefore, there is an urgent need to develop a more convenient and non-invasive diagnostic approach.
In recent years, the relationship between gut microbiota and the pathogenesis of IBD has garnered widespread attention. Metabolites of gut microbiota, such as hydrogen (H₂), ammonia (NH₃), and hydrogen sulfide (H₂S), may enter the respiratory system through the blood-lung barrier and eventually be exhaled. These gas components could serve as biomarkers for IBD. However, most current studies focus on high-molecular-weight Volatile Organic Compounds (VOCs), while low-molecular-weight gas components, such as hydrogen, have not been thoroughly investigated.
Source of the Paper
The study was conducted by a research team from Keio University and The University of Tokyo, with primary authors including Yuta Fujiki, Takahisa Tanaka, Kyosuke Yakabe, and others. The paper was accepted on October 20, 2023, and published in the journal Gut Microbiome with the DOI 10.1017/gmb.2023.17.
Research Process
1. Experimental Design and Animal Model
The study used a Dextran Sulphate Sodium (DSS)-induced colitis mouse model to simulate the inflammatory process of IBD. The experiment was divided into two groups: one group of mice was treated with DSS, while the other group received Dextran (a DSS analogue) as a negative control. The experiment lasted for 15 days, during which changes in body weight and fecal Lipocalin-2 (LCN2) levels—a biomarker of intestinal inflammation—were monitored daily.
2. Biogenic Gas Measurement
The research team designed a gas sampling system to continuously measure five biogenic gases in the mouse cages: hydrogen (H₂), ammonia (NH₃), hydrogen sulfide (H₂S), methanethiol (CH₃SH), and ethanethiol (C₂H₅SH). The system used sensor gas chromatographs for real-time monitoring of gas concentrations, with a sampling frequency of 10 times per hour. The gas concentrations reflected the mice’s breath, skin gases, and fecal gas components.
3. Gut Microbiota Analysis
At different time points during the experiment (days 0, 1, 3, 5, 7, 9, 12, and 15), fecal samples were collected from the mice for 16S rRNA gene sequencing to analyze the composition and diversity of the gut microbiota. The sequencing data were processed using Qiime2 software to construct Amplicon Sequence Variants (ASVs), and species classification was performed using the Silva database.
4. Data Analysis
The study used Pearson correlation analysis to assess the relationship between biogenic gas concentrations and colitis phenotypes (body weight changes and LCN2 levels). Additionally, Receiver Operating Characteristic (ROC) curves were used to evaluate the diagnostic potential of each gas in predicting colitis development.
Key Findings
1. Correlation Between Biogenic Gases and Colitis Phenotypes
In DSS-treated mice, hydrogen (H₂) levels were negatively correlated with LCN2 levels and positively correlated with body weight changes. This suggests that H₂ levels decrease with the progression of colitis, potentially serving as a biomarker for intestinal inflammation. Furthermore, hydrogen sulfide (H₂S) had the highest area under the ROC curve (AUC), indicating its strong diagnostic value in predicting colitis development.
2. Changes in Gut Microbiota
In DSS-treated mice, the diversity and richness of the gut microbiota gradually decreased. The relative abundance of Akkermansiaceae and Rikenellaceae was positively correlated with LCN2 levels and negatively correlated with body weight changes, while the relative abundance of Tannerellaceae was negatively correlated with LCN2 levels and positively correlated with H₂ levels. This suggests that Tannerellaceae may play a positive role in alleviating colitis symptoms.
3. Correlation Between Biogenic Gases and Gut Microbiota
The relative abundance of Tannerellaceae was positively correlated with H₂ levels, while the relative abundance of Akkermansiaceae and Rikenellaceae was negatively correlated with H₂ levels. This finding further supports the potential of H₂ as a biomarker for intestinal inflammation.
Conclusion and Significance
The study demonstrates that hydrogen (H₂) levels are closely related to the development of experimental colitis and may serve as a non-invasive biomarker for IBD. Additionally, specific gut microbiota (e.g., Tannerellaceae) are associated with changes in H₂ levels and may play a significant role in the pathogenesis of IBD. This discovery provides new insights for the diagnosis and treatment of IBD.
Research Highlights
- Innovative Research Methodology: The research team developed a system for continuous measurement of biogenic gases, enabling real-time monitoring of gas components in mouse cages, providing a technical reference for similar studies.
- Study of Low-Molecular-Weight Gases: Unlike previous research, this study focused on low-molecular-weight gas components (e.g., H₂), filling a gap in this field.
- Association Between Gut Microbiota and Gas Metabolism: The study is the first to reveal the correlation between specific gut microbiota and biogenic gas levels, offering a new perspective for understanding the pathogenesis of IBD.
Other Valuable Information
The study also found that hydrogen sulfide (H₂S) has high diagnostic value in predicting colitis development, providing a new direction for future research. Additionally, the research team plans to establish an experimental model that measures only exhaled breath components in the future to further improve diagnostic accuracy.
This study not only provides new biomarkers for IBD diagnosis but also offers important clues for understanding the complex relationship between gut microbiota and gas metabolism, holding significant scientific and practical value.