Suspending life

[Opethian]

I thought this was pretty interesting, although it's mostly speculation.

In the deep history of our planet, there have been at least five short intervals in which the majority of living species suddenly went extinct. Biologists are used to thinking about how environmental pressures slowly select the organisms most fit for survival through natural selection, shaping life on Earth like an artist sculpting clay. However, mass extinctions are drastic examples of natural selection at its most ruthless, killing off vast numbers of species at one time in a way that is hardly typical of evolution.
In the 1980s, Nobel Prize-winning physicist Luis Alvarez and his son first hypothesized that the impact of comets or asteroids caused the mass extinctions of the past. Most scientists slowly came to accept this theory of extinction, and since then a great scar in the Earth--an impact crater--has been discovered off the coast of Mexico that dates to around the time the dinosaurs went extinct. An asteroid probably did kill off the dinosaurs, but the causes of the other four mass extinctions are still obscured beneath the accumulated weight of hundreds of millions of years, and no one has found any other credible evidence of impact craters.
But now, together with Mark Roth of the Fred Hutchinson Cancer Research Center in Seattle, I believe we have found a possible biochemical scar, present within living animals, that links Earth's greatest mass extinction to a single substance: hydrogen sulfide (H2S). Hydrogen sulfide is a relatively simple molecule that gives rotten eggs their distinctive foul odor and is quite toxic--in high concentrations a single breath can kill. And it looks like that is what happened: Hundreds of millions of years ago, hydrogen sulfide probably saturated our oceans and atmosphere, poisoning nearly every creature on Earth.
Yet some creatures, like our very distant ancestors, must have somehow survived this toxic environment. What Roth has discovered is that H2S, incredibly, also has the ability to preserve and save lives. In small doses the chemical puts many animals into a state of "suspended animation," a useful adaptation that would have allowed creatures to, in essence, hibernate through the catastrophe of mass extinction. If this idea is correct, our understanding of the deep past could lead to a dramatic medical revolution very soon.

http://www.seedmagazine.com/news/2008/04/suspending_life.php

 

[Opethian]

There doesn't seem to be much hope for a medical application in humans though:

In a widely publicized series of experiments by Blackstone et al., hydrogen sulfide (H2S) was found to induce hypometabolism in mice. These experiments raised interest in whether such “suspended animation” could be achieved in humans. If administration of H2S would be able to reduce metabolic rate in humans to the same extent as observed in mice, the practical applications could range from management of trauma victims to space travel.
Recent work by Haouzi et al. is not encouraging. The researchers were able to induce hypometabolism in mice but did not find any change in metabolic rate in sedated sheep after exposing them to 60 ppm H2S. What the investigators did report, and which was left implicit in previous experiments with mice, is that H2S-induced hypometabolism preceded hypothermia. H2S-induced hypometabolism in mice is not just the result of hypothermia, so the inability of H2S to produce hypometabolism in sheep cannot be attributed to thermal inertia of large animals.
How can H2S induce hypometabolism in mice? The authors state that “the present results have little to offer on the pathways that are responsible for H2S-induced decrease of metabolism.” They raise the point that in small animals such as mice a large portion of metabolism is devoted to heat production instead of ATP production. In contrast, small reductions in oxygen utilization in humans, as produced by H2S exposure, will affect ATP generation. Or as Ikaria’s Csaba Szabo speculates in “Hydrogen sulphide and its therapeutic potential”, “the window of opportunity to compromise oxidative phosphorylation in a human, therefore, must be smaller than in the mouse.“
The authors do not expect that higher dosages of H2S will produce hypometabolism in large mammals because the 60 ppm that was administered to sheep already exceeds what is known to be toxic in humans.
The search for molecules that induce hypometabolism, let alone hibernation-on-demand, in humans remains elusive. So far most research in this area involves attempts to activate conserved metabolic pathways of hibernating animals in non-hibernating animals instead of direct pharmacological inhibition of high energy consuming physiological activities.

http://depressedmetabolism.com/2007/11/12/hydrogen-sulfide-does-not-induce-hypometabolism-in-sheep/