26 March 2008

Hydrogen sulfide for prolonging life: possible mechanism of action

You can't eat a lot of rotten eggs
Pyotr Smirnov, "Newspaper.Ru»

Scientists have figured out how to save on food and oxygen when sending astronauts on a trip to Mars. As it turned out, hydrogen sulfide, a gas that gives rotten eggs their unique smell, is able to reduce the intensity of metabolism and slow down the work of the heart.

Hydrogen sulfide, harmful in large quantities to the body, in small doses can not only prolong life, but also save the body's resources and significantly reduce the need for food and oxygen. This conclusion was reached by scientists from the Massachusetts General Hospital after completing work on the study of the effect of this gas on the functioning of the cardiovascular system in mice, published in the journal Anesthesiology (Gian Paolo Volpato et al., Inhaled Hydrogen Sulfide A Rapidly Reversible Inhibitor of Cardiac and Metabolic Function in the Mouse).

The very idea of using hydrogen sulfide to prolong life is not new. Last year, two research groups reported on the "beneficial" effect of this gas. Specialists from the Fred Hutchinson Cancer Center showed its inhibitory effect on mice, and their colleagues Mark Roth and Dana Miller in December with the help of this gas extended the life of roundworms.

Since until then several ways of prolonging the life of C.elegans have been described using manipulations on three groups of genes, it would be logical to assume that hydrogen sulfide affects one of these mechanisms. The first is to control the production of insulin, the second is to control the work of mitochondria, and the third modulates various physiological effects depending on the restriction of access to nutrients.

Then none of these hypotheses could be confirmed. This time, the team led by Jean Paolo Volpato focused on the study of the effect of microconcentrations on the cardiovascular system.

Their wards inhaled hydrogen sulfide at a concentration of 80 ppm (parts per million) – that is, 80 volume fractions of gas were added to a million volume fractions of air. Unlike numerous previous works in this field, Massachusetts scientists allowed their wards to breathe this mixture for a long time – 6 hours.

At the same time, the researchers assessed the performance of the heart, blood vessels and the content of gases and ions in the blood, and most importantly, the temperature of the whole body and the so–called "core" – that is, the internal temperature. They were able to show that by the second hour, the pulse of mice dropped from 500 beats per minute to 260 beats, while blood pressure remained at the same level, which is extremely necessary to maintain the viability of organs and tissues.

The same downward trend was observed in breathing (from 115 breaths per minute to 34), the formation of carbon dioxide and carbon monoxide, oxygen absorption. After 10 minutes of the experiment, the formation of CO 2 decreased by 46%.

Despite the fact that normal oxygen concentration was maintained in the inhaled mixture, most of it was simply not needed by the mice.

The temperature of the mice decreased from 37.5 degrees to 29 degrees, and the scientists measured the temperature of the "core" – an indicator of the intensity of metabolism. The body surface temperature also depends on the environment and the condition of the vessels, and therefore it cannot be considered a reliable indicator in such experiments.

Снижение температуры тела, частоты сердцебиения и практически неизменное артериальное давление у мышей при дыхании содержащим сероводород воздухомA decrease in the temperature of the "core" of the body, heart rate with preserved blood pressure (in order).
On the abscissa axis – the time of the experiment, on the ordinate axes – degrees Celsius, beats per minute and mmHg, respectively.

Black figures highlight data for data for experiments conducted at an ambient temperature of 27 degrees, contour (empty) – 35 degrees.

Hypothermia also has all the effects described above – a controlled decrease in body temperature used during heart operations, organ transplants and when taking donor organs. But a decrease in body temperature is fraught with an increased risk of infection and blood clotting.

The method proposed by the Massachusetts is much more perfect. They conducted all their experiments at two ambient temperatures – 27 and 35 degrees Celsius. All the described changes are valid for both, with a few exceptions.

If the air temperature is maintained at 35 degrees, then the body temperature will remain at the same level (37 degrees), while the heartbeat, breathing and metabolism will be much lower – all the benefits without the slightest risks.

The prospects are the brightest: these are already described applications in medicine, and life support systems in space – after all, the traditional ration of oxygen and food can theoretically be cut more than twice.

By the way, the concentration of sulfides in blood plasma did not change during the experiment, which, firstly, indicates the relative safety of such a concentration of hydrogen sulfide in the air, and, secondly, makes the mechanism of all the phenomena described above even more incomprehensible.

As before, scientists suggest that sulfur becomes an alternative to oxygen in metabolism – just as it happens in sulfobacteria. However, the latter cannot switch from sulfur to oxygen and when they get into an oxygen environment, they instantly die.

Partly ignorance of the mechanisms prevents the introduction of this method into practice; in addition, it is not known what effect hydrogen sulfide has on the central nervous system and what such procedures are fraught with.

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