Abstract: This study aimed to investigate the antioxidant properties of hydrogen-rich water and its impact on the intestinal flora of simulated weightlessness rats. A tail-suspension rat model was established to simulate the physiological effects of weightlessness in the space environment. SYBR GreenⅠ real-time fluorescent quantitative PCR was used to detect the effects of hydrogen-rich water on various common bacteria in the cecal and colonic contents of rats. The results showed that hydrogen-rich water had a certain scavenging ability against ·OH and ·O₂⁻ free radicals, significantly improved the antioxidant and immune capacities of the liver and spleen, and had a marked inhibitory effect on harmful bacteria in the intestinal flora of rats under simulated weightlessness conditions, which is of great significance for maintaining intestinal flora balance and preventing intestinal microecological imbalance.

Keywords: hydrogen-rich water; antioxidant properties; simulated weightlessness; intestinal flora

1. Introduction

With the continuous development of the aerospace industry, the health issues of astronauts in the space environment have attracted increasing attention. Special environments such as simulated weightlessness can lead the body to a chronic stress state, causing changes in the intestinal flora and intestinal microecological imbalance, which in turn affects the health of astronauts. Hydrogen-rich water, as an aqueous solution containing a high hydrogen gas solubility, has received widespread attention in recent years due to its potential antioxidant and anti-inflammatory effects. Studies have shown that hydrogen gas has the function of selectively neutralizing oxygen free radicals, namely the selective antioxidant effect of hydrogen, which may have a potential role in improving intestinal microecological imbalance caused by the space environment. Therefore, this study aims to explore the antioxidant properties of hydrogen-rich water and its effects on the intestinal flora of simulated weightlessness rats, providing a theoretical basis for preventing intestinal microecological imbalance in astronauts.

2. Antioxidant Properties of Hydrogen-Rich Water

2.1 Antioxidant Mechanism

Hydrogen gas is a strong antioxidant that can selectively neutralize harmful free radicals in the body, especially strongly oxidizing reactive oxygen species such as hydroxyl radicals (·OH) and superoxide anion radicals (·O₂⁻). These free radicals are closely related to various diseases and aging processes, and the antioxidant effect of hydrogen gas helps to reduce the damage caused by oxidative stress to the body.

2.2 Experimental Research

A tail-suspension rat model was constructed to simulate the physiological effects of weightlessness in the space environment, and the effects of hydrogen-rich water on the antioxidant indexes of rat liver and spleen were studied. The results showed that hydrogen-rich water had a certain scavenging ability against ·OH and ·O₂⁻ free radicals but had almost no effect on DPPH· free radicals. In the results of the effects on liver and spleen antioxidant indexes, hydrogen-rich water significantly improved the antioxidant and immune capacities of the liver and spleen. This indicates that hydrogen-rich water has significant antioxidant properties and can enhance the body's antioxidant defense system.

3. Effects of Hydrogen-Rich Water on the Intestinal Flora of Simulated Weightlessness Rats

3.1 Experimental Design

The tail-suspension method was used to simulate the weightlessness effect, and the effects of hydrogen-rich water on the intestinal flora of Wistar male rats were studied. Recombinant plasmids containing the 16S rRNA gene sequences of the bacteria to be tested were constructed as standard samples. SYBR GreenⅠ real-time fluorescent quantitative PCR was used to detect the effects of hydrogen-rich water on enterococcus, bifidobacterium, clostridium perfringens, escherichia coli, lactobacillus, and the total intestinal flora in the cecal and colonic contents of rats. Additionally, the changes in the copy number of escherichia coli in the feces over 8 weeks of rat feeding were tracked.

3.2 Experimental Results

3.2.1 Changes in Intestinal Flora Quantity

Simulated weightlessness increased the copy numbers of enterococcus and escherichia coli in the intestine and decreased the copy number of clostridium perfringens. Hydrogen-rich water had a marked inhibitory effect on enterococcus. When rats were fed hydrogen-rich water, the total intestinal flora and lactobacillus remained basically unchanged, while the conditionally pathogenic enterococcus was significantly inhibited.

3.2.2 Changes in Escherichia coli in Feces

The changes in the copy number of escherichia coli in the feces over time were tracked. The results showed that hydrogen-rich water may have a certain effect on the growth and reproduction of escherichia coli, but the specific mechanism needs further study.

3.3 Mechanism Discussion

The mechanism by which hydrogen-rich water affects the intestinal flora is currently unclear, and one or more mechanisms may act together. Hydrogen molecules may affect the intestinal flora through the following mechanisms:

1. Regulating the endocrine and metabolic network: Hydrogen molecules may improve the intestinal flora by regulating the endocrine and metabolic network, affecting the absorption and metabolism of nutrients in the intestine, thereby influencing the growth and reproduction of intestinal flora.
2. Regulating the immune system: The regulatory effect of hydrogen molecules on the immune system may contribute to the health of the intestinal flora. The normal function of the immune system can maintain the balance of the intestinal flora and prevent the overgrowth of harmful bacteria.
3. Regulating the neural network: The regulatory effect of hydrogen molecules on the neural network may indirectly affect the flora structure by improving intestinal motility and glandular secretion. Intestinal motility and glandular secretion can affect the intestinal environment, such as pH value and nutrient concentration, thereby influencing the survival and reproduction of intestinal flora.

4. Application Prospects of Hydrogen-Rich Water in the Field of Aerospace Health

4.1 Preventing Intestinal Microecological Imbalance

Special space environments (weightlessness, noise, vibration, radiation, high and low temperatures, hypoxia, etc.) can lead the body to a chronic stress state, causing changes in the intestinal flora and intestinal microecological imbalance. Hydrogen-rich water has a marked inhibitory effect on harmful bacteria in the intestinal flora of rats under simulated weightlessness conditions, can maintain intestinal flora balance, and prevent intestinal microecological imbalance. Therefore, providing hydrogen-rich water to astronauts during space missions may help protect their intestinal health and prevent the occurrence of related diseases.

4.2 Promoting the Recovery of Microecological Balance After Flight

Astronauts who have performed space missions may need a certain amount of time to recover their intestinal microecological balance after flight. Hydrogen-rich water may have a positive effect on promoting the recovery of intestinal microecological balance after flight, helping astronauts recover their physical health as soon as possible and adapt to the Earth environment.

5. Conclusion

This study proved through experiments that hydrogen-rich water has significant antioxidant properties, can scavenge harmful free radicals in the body, and improve the body's antioxidant capacity. At the same time, hydrogen-rich water has a marked inhibitory effect on harmful bacteria in the intestinal flora of simulated weightlessness rats, can maintain intestinal flora balance, and prevent intestinal microecological imbalance. These research results provide a theoretical basis for the application of hydrogen-rich water in the field of aerospace health, indicating that hydrogen-rich water may become an effective means of preventing and treating space-related intestinal diseases. However, the specific mechanism by which hydrogen-rich water affects the intestinal flora is currently unclear and requires further in-depth study. Future research can further explore the mechanism of action of hydrogen-rich water, conduct clinical trials, and verify its practical application effects in the field of aerospace health.