Hydrogen sulfide (H2S), which has a characteristic rotten egg smell, is a colorless, flammable, water-soluble gas that is primarily considered a toxic agent due to its ability to inhibit mitochondrial respiration through blockade of cytochrome c oxidase. Recent research has demonstrated that H2S in low quantities may have the potential to limit cell death (Lefer, 2007). Inhibition of respiration is potentially toxic; however, if depression of respiration occurs in a controlled manner, it may allow non-hibernating species exposed to inhaled H2S to enter a state akin to suspended animation (i.e., a slowing of cellular activity to a point where metabolic processes are inhibited but not terminal) and thereby increase tolerance to stress. H2S also may cause activation of ATP-dependent K+ channels, cause vasodilation properties, and serve as a free radical scavenger. H2S has been shown to protect against whole-body hypoxia, lethal hemorrhage, and ischemia-reperfusion injury in various organs including the kidney, lung, liver, and heart. Currently, effort is underway for development of gas-releasing molecules that could deliver H2S and other therapeutic gases to diseased tissue (Bannenberg and Vieira, 2009). Though H2S has clinical potential, further verification in preclinical models is necessary as is more information regarding the route of delivery, timing, formulation, and concentration of H2S.
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