Inhalation of water electrolysis-derived hydrogen ameliorates cerebral ischemia–reperfusion injury in rats – A possible new hydrogen resource for clinical use

Highlights

• Water electrolysis-derived hydrogen is effective in cerebral I/R injury.

• Water electrolysis-derived hydrogen prevents oxidative stress and inflammation.

• Water electrolysis-derived hydrogen is safe for inhalation.

• Water electrolysis-derived hydrogen is a new hydrogen resource for clinical use.

Abstract

Hydrogen is a kind of noble gas with the character to selectively neutralize reactive oxygen species. Former researches proved that low-concentration of hydrogen can be used to ameliorating cerebral ischemia/reperfusion injury. Hydrogen electrolyzed from water has a hydrogen concentration of 66.7%, which is much higher than that used in previous studies. And water electrolysis is a potential new hydrogen resource for regular clinical use. This study was designed and carried out for the determination of safety and neuroprotective effects of water electrolysis-derived hydrogen. Sprague–Dawley rats were used as experimental animals, and middle cerebral artery occlusion was used to make cerebral ischemia/reperfusion model. Pathologically, tissues from rats in hydrogen inhalation group showed no significant difference compared with the control group in HE staining pictures. The blood biochemical findings matched the HE staining result. TTC, Nissl, and TUNEL staining showed the significant improvement of infarction volume, neuron morphology, and neuron apoptosis in rat with hydrogen treatment. Biochemically, hydrogen inhalation decreased brain caspase-3, 3-nitrotyrosine and 8-hydroxy-2-deoxyguanosine-positive cells and inflammation factors concentration. Water electrolysis-derived hydrogen inhalation had neuroprotective effects on cerebral ischemia/reperfusion injury in rats with the effect of suppressing oxidative stress and inflammation, and it is a possible new hydrogen resource to electrolyze water at the bedside clinically.

Introduction

Cerebral ischemia/reperfusion (I/R) injury is closely related to stroke, which is a serious disease with poor blood flow to the brain. A large number of deaths result from stroke (Ono et al., 2012). I/R injuries may happen when stroke patients are treated with rapid brain–blood reperfusion (Srivastava et al., 2008, Huang et al., 2010). As brain–blood reperfusion is the standard treatment for stroke with no other effective replacement, it is very important to find effective therapies for IR injury.

It’s not easy to figure out the exact mechanisms of cerebral I/R injury, because it is really complex and there are many factors involved, such as oxidative stress, inflammation, immunity, apoptosis, and autophagy. It is believed that the effects of oxidative stress including the increase of reactive oxygen species (ROS) are related to I/R injury pathophysiology. One of the effects of ROS is to modify the chemical structure of protein, lipid, and DNA, if the ROS cannot be cleaned up effectively, it causes damages. On the other hand, ROS can also trigger chain reactivity of cell apoptosis after ischemic attack (Broughton et al., 2009). The expression of inflammatory cytokines may be elevated by ROS, and inflammation bursts subsequently (Lakhan et al., 2009). In summary, oxidative stress causes a complicated series of biochemical cascades after ischemic/reperfusion insult, which will ultimately aggravate the damage of stroke (Piotrowska et al., 2012).

In recent years, hydrogen is considered as a novel antioxidant, and it has been proven that molecular hydrogen (H₂) can be effective to protect various ischemia/reperfusion injuries (Ohsawa et al., 2007). It is demonstrated by many researches that hydrogen selectively neutralizes several certain ROS, which are ONOO^- and ^·OH (Yu et al., 2011, Hong et al., 2012), and protects the tissue from oxidative stress and inflammatory cascades injury (Ono et al., 2012, Kawamura et al., 2013). Both inhalation of hydrogen (2%, 4%) and administration of hydrogen-rich saline are effective.

However, in daily practice, water electrolysis is the most convenient means to obtain hydrogen and theoretically the concentration is much higher than that previously used. We hypothesized that water electrolysis-derived hydrogen could ameliorate cerebral ischemia/reperfusion injury in rats through inhibition of oxidative stress and inflammation.