X-Message-Number: 26201 From: "Brian Wowk" <> Subject: Recent Suspended Animation Research Date: Thu, 19 May 2005 07:20:41 -0700 Questions have been asked about the recent Science paper, and related Scientific American article, discussing a suspended animation breakthough. The subject has been discussed extensively on the Imminst website. In my opinion, the implications of this work as it currently stands have been overstated. The researches used H2S to inhibit the cell energy producing enzyme cytochrome oxidase. This is the same mechanism as cyanide poisoning, except that H2S "poisoning" is apparently more easily reversible. When the energy producing ability of cells is inhibited, animals can no longer obtain normal body temperature. Their temperature falls to match that of the environment. This is no surprise. In a cold state, the animals require less energy and a lower metabolic rate to stay alive. This is also no surprise. In fact, the metabolic reduction claimed at +11 degC is similar to what would be expected had the animals been simply cooled to that temperature by the methods of conventional clinical hypothermia. (The world record for human hypothermia survival is +7 degC, by the way.) This highlights the greatest weakness of the Science paper: no controls. They did not show that metabolic inhibition and cooling facilitated by H2S gives better results than what would be obtained by a combination of anesthesia, paralytic drugs, and cooling by conventional means. If we suppose that this approach does give better results in mice than ordinary cooling, there are still many questions about the extendability of the work to larger animals. For example, even if you turn off all energy production inside a human, a human will only passively cool at approximatley one degree C per hour (the rate at which a dead body cools in room air). A human with metabolism that is merely inhibited will cool even slower, which leads to questions of whether cells will have sufficient energy to maintain basic housekeeping (homeostasis) in a high temperature state with their metabolism inhibited. To implement this protocol in a human, it would have to be done either very slowly, or with the aid of conventional heart-lung bypass cooling. If the latter, then we get back to the question of whether H2S is actually providing a protective effect, or merely facilitating cooling that we can do more expeditiously by other means. In other words, does H2S actually reduce *the need for energy*, or merely inhibit the body's *ability to produce energy*. There are a host of pathologies known to afflict large animals in ultraprofound hypothermia, ranging from blood cell agglutination (why hemodiluation is used in clinical hypothermia), altered ion balances, and cardiac arrythmias. It would be a miracle if simply inhibiting one energy producing enzyme could address all these problems and more. Stranger things have happened, but it hasn't been shown yet. It's remarkable that a simple molecule can reversibly inhibit biological energy production. At a minimum, this should be useful to treat malignant hyperthermia. But it is premature to call this work a "suspended animation breakthough" based on what has been reported so far. ---Brian Wowk -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.322 / Virus Database: 266.11.12 - Release Date: 5/17/2005 Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=26201