Objective  This study was designed to investigate the effects of low concentration hydrogen inhalation on asthma and sleep function in mice and the potential mechanism.

  Methods  In the asthma experiment, BALB/c mice were randomly divided into normal control group, asthma model group and hydrogen treatment group. After establishing ovalbumin (OVA)-induced asthma model, the hydrogen treatment group mice were treated by inhalation of hydrogen (24-26 mL/L per day) for 7 consecutive days, and the normal control group and asthma model group mice received similar treatment by inhalation of air. The levels of interleukin (IL)-4, IL-13, and interferon-γ (IFN-γ) in bronchoalveolar lavage fluid (BALF) were measured by commercially available ELISA kits. The levels of malondialdehyde (MDA) and glutathione (GSH), as well as the activity of superoxide dismutase (SOD) in lung tissue were detected by colorimetric assays. The pathological changes in lung tissue were assessed by HE staining. In the sleep experiment, ICR mice were randomly divided into blank control group and 1 d, 3 d, 5 d hydrogen treatment groups and diazepam group. The effects of inhalation of 24-26 mL/L per day hydrogen on the sleep duration induced by intraperitoneal injection of upper-threshold dose of sodium pentobarbital and the sleep latency in response to subthreshold dose were evaluated.

  Results  In the asthma experiment, the asthma model group showed higher levels of IL-4 and IL-13 (P<0.05) and lower levels of IFN-γ (P<0.001) in BALF, as compared to the normal control group. The content of MDA in lung tissue was also significantly increased (P<0.01), companied by a decreased GSH concentration (P <0.05) and a mildly reduced SOD activity (P>0.05). Compared to the asthma model group, treatment with hydrogen significantly decreased the levels of IL-4 and IL-13 and increased the level of IFN-γ in BALF (P<0.05). Moreover, without alteration of the MDA production (P>0.05), hydrogen inhalation greatly increased GSH level and restored the SOD activity (P<0.05) in lung tissue. Additionally, the HE staining data showed that the hydrogen treatment attenuated the pulmonary histopathological changes. In the sleep experiment, compared with the blank control group, the sleep latency was significantly shorter (P<0.05) and the sleep duration was longer (P<0.001) in all the hydrogen treatment groups after receiving an upper-threshold dose of sodium pentobarbital. Meanwhile, in all the hydrogen treatment groups, the sleep latency was significantly longer (P<0.001) and the sleep duration was shorter (P<0.001) when compared to the diazepam group. Compared with the blank control group, after intraperitoneal injection of a subthreshold dose of sodium pentobarbital, the sleep latency was significantly increased in both 1 d and 5 d hydrogen treatment groups, and there was no significant difference as compared to the diazepam group. In the 3 d hydrogen treatment group, the sleep latency was only slightly increased (P>0.05), which was significantly lower than that of the diazepam group (P<0.05).

  Conclusion  Low concentration hydrogen inhalation could alleviate OVA-induced asthma in mice, and the mechanism might be related to the anti-oxidative and anti-inflammatory effects of hydrogen. Also, low concentration hydrogen inhalation could improve sleep function in mice.