Hidrogeno Actua Como Terapia Antioxidante

ARTICLES

© 2007 Nature Publishing Group http://www.nature.com/naturemedicine

Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals
Ikuroh Ohsawa1, Masahiro Ishikawa1, Kumiko Takahashi1, Megumi Watanabe1,2, Kiyomi Nishimaki1, Kumi Yamagata1, Ken-ichiro Katsura2, Yasuo Katayama2, Sadamitsu Asoh1 & Shigeo Ohta1
Acute oxidative stress induced byischemia-reperfusion or inflammation causes serious damage to tissues, and persistent oxidative stress is accepted as one of the causes of many common diseases including cancer. We show here that hydrogen (H2) has potential as an antioxidant in preventive and therapeutic applications. We induced acute oxidative stress in cultured cells by three independent methods. H2 selectively reduced the hydroxylradical, the most cytotoxic of reactive oxygen species (ROS), and effectively protected cells; however, H2 did not react with other ROS, which possess physiological roles. We used an acute rat model in which oxidative stress damage was induced in the brain by focal ischemia and reperfusion. The inhalation of H2 gas markedly suppressed brain injury by buffering the effects of oxidative stress. Thus H2can be used as an effective antioxidant therapy; owing to its ability to rapidly diffuse across membranes, it can reach and react with cytotoxic ROS and thus protect against oxidative damage.

Oxidative stress arises from the strong cellular oxidizing potential of excess reactive oxygen species (ROS), or free radicals1–5. Most of the superoxide anion radical (O–) produced is generated inmitochondria 2 by electron leakage from the electron transport chain and the Krebs cycle6. O– is also produced by metabolic oxidases, including NADPH 2 oxidase and xanthine oxidase7. Superoxide dismutase converts O– 2 into hydrogen peroxide (H2O2)8, which is detoxified into H2O by either glutathione peroxidase or catalase. Excess O– reduces transition 2 metal ions such as Fe3+ and Cu2+ (ref. 2), thereduced forms of which in turn can react with H2O2 to produce hydroxyl radicals (OH) by the Fenton reaction. OH is the strongest of the oxidant species and reacts indiscriminately with nucleic acids, lipids and proteins. There is no known detoxification system for OH; therefore, scavenging OH is a critical antioxidant process9. Despite their cytotoxic effects, O– and H2O2 play important 2physiological roles at low concentrations: they function as regulatory signaling molecules that are involved in numerous signal transduction cascades and also regulate biological processes such as apoptosis, cell proliferation and differentiation7,10. At higher concentrations, H2O2 is converted into hypochlorous acid by myeloperoxidase; hypochlorous acid defends against bacterial invasion5. Nitric oxide(NO), another ROS, functions as a neurotransmitter and is essential for the dilation of blood vessels11. Thus, cytotoxic radicals such as OH must be neutralized without compromising the essential biological activities of other, physiologically beneficial, ROS. Here we demonstrate that molecular hydrogen (dihydrogen, H2) can alleviate OH-induced cytotoxicity without affecting the other ROS, andpropose that H2 has potential as an antioxidant for preventive and therapeutic applications.
1Department

RESULTS H2 selectively reduces OH in cultured cells H2 reduces the OH that is produced by radiolysis or photolysis of water12; however, whether H2 can effectively neutralize OH in living cells has not been directly investigated. As the cellular damage produced by spontaneous generationof OH is not sufficient to be detectable, we induced O– production in PC12 cultured cells. To do 2 this, we treated the cells with a mitochondrial respiratory complex III inhibitor, antimycin A (ref. 13); following such treatment, O– in 2 these cells is rapidly converted into H2O2. The addition of antimycin A increased levels of O– and H2O2, as judged by the fluore2 scence signals emitted by...