Hydrogen: An Endogenous Regulator of Liver Homeostasis

Basic and clinical studies have shown that hydrogen (H(2)), the lightest gas in the air, has significant biological effects of anti-oxidation, anti-inflammation, and anti-apoptosis. The mammalian cells have no abilities to produce H(2) due to lack of the expression of hydrogenase. The endogenous H(2) in human body is mainly produced by anaerobic bacteria, such as Firmicutes and Bacteroides, in gut and other organs through the reversible oxidation reaction of 2 H(+) + 2 e(-) ⇌ H(2). Supplement of exogenous H(2) can improve many kinds of liver injuries, modulate glucose and lipids metabolism in animal models or in human beings. Moreover, hepatic glycogen has strong ability to accumulate H(2), thus, among the organs examined, liver has the highest concentration of H(2) after supplement of exogenous H(2) by various strategies in vivo. The inadequate production of endogenous H(2) play essential roles in brain, heart, and liver disorders, while enhanced endogenous H(2) production may improve hepatitis, hepatic ischemia and reperfusion injury, liver regeneration, and hepatic steatosis. Therefore, the endogenous H(2) may play essential roles in maintaining liver homeostasis.