X-Message-Number: 15451 From: Date: Thu, 25 Jan 2001 14:24:25 EST Subject: more on toxicity etc. Some misunderstandings seem to persist about toxicity of CPAs and related matters, so I'll try once again to clarify this. If I have made any mistakes, I'll welcome correction, as always. First, from historical perspective, for many years it was believed that relatively large tissue masses could not be vitrified except with concentrations of CPA so high as to produce unacceptable toxicity. That changed in recent years with the use of CPAs (methoxylated compounds) that were not new in themselves, but were new in the context of new methods of rapid cooling and warming. With these, toxicity was reported to be lower than with glycerol--meaning, I believe, the glycerol concentration that Alcor had for some years been using. That, if memory serves, was reported as 7.5 M, which I believe works out to about 690 grams of glycerol per liter of solution, or roughly 60% by weight or 55% by volume. A couple of people expressed the opinion that the toxicity must also be much lower than that of the current CI solution, which is 75% glycerol by volume (i.e., 750 ml glycerol added to 250 ml water at room temperature, later refrigerated). However, our one-pass does not result in equilibration. Our measurements indicate a final average concentration in the brain tissue of around 26% by weight, hence obviously a much lower toxicity than the previous Alcor standard. How were measurements of toxicity of glycerol made? I don't know; if someone can direct me to reports on this, good. We do know, from recent reports, that estimates of toxicity of solutions similar to the current Alcor solution (but less concentrated, according to Fred Chamberlain's report in CRYONICS, which would imply that the Alcor solution is more toxic) were made from rat brain slices using the K/Na ratio criterion, which most recently showed 66% of normal function, probably meaning an average over the cells in a sample. I also have the impression-and again will welcome correction if I am wrong--that the K/Na test requires very fresh specimens, virtually no post mortem delay. This means that the relevance to cryonics patients is problematic. In the two Alcor cases that were "vitrified," the delay was reported as more than a full day, and there is small likelihood of any significant number of patients being treated with no delay. This does not mean that I personally think the "viability" criterion is the most important one. My guess is that histology is more important, and neuronal electrical activity the most important of all. As previously noted, Pichugin's rabbit brain studies were encouraging in this respect, using glycerol and rewarming the specimens from liquid nitrogen temperature. Finally, yet again, to my knowledge there have been no reports--anywhere, by anyone, ever--of results evaluated by any criterion after application of the current Alcor procedure to brains, cooling to liquid nitrogen temperature (or even the hoped-for intermediate temperature in the range of - 135 C) and then rewarmed. And yet again, we still do not claim that the current CI procedure is better than the current Alcor procedure. We can't, because we don't know, and neither does anybody else. All we say is that we choose the demonstrated best procedure out of those we have tried, as evaluated by independent professionals. The Alcor people and their consultants, based on indirect evidence, think their current procedure is the best available. Maybe they are right, and maybe they will soon prove it. But they haven't proven it yet, as far as we know, and we can't test their methods, even on small samples, because of the secrecy. We will continue our policy of testing all promising methods, choosing our priorities carefully, and from time to time will change or modify our procedures according to the results. Robert Ettinger Cryonics Institute Immortalist Society http://www.cryonics.org Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=15451