In praise of cold
Some observers believe that cryonics advocates are reluctant to subject their theories to experimental scrutiny because this could damage their (uncritical) belief in future resuscitation. Similarly, one might think that cryonicists would react with a mix of hostility and dismissal to alternative strategies for personal survival. Nothing could be further from the truth. In fact, it is exactly because our personal survival is at stake that forces us to be wary of dogmatism.
For this reason, I have always been interested in chemical fixation as a (low cost) alternative for cryonics. In fact, years before all the talk about the “connectome” and “plastination” I spent considerable time exchanging messages with Michael Perry at Alcor about the technical and practical feasibility of chemical brain preservation. But no matter how open minded I tried to be about this approach, I kept running into the same challenges over and over again.
The challenge that has concerned me the most is whether a delayed start of chemical brain fixation will produce incomplete distribution of the chemical fixative in the brain because of ischemia-induced perfusion impairment. Thinking about the technical problem of “no-reflow” is not the first thing on the mind of someone who first hears about the idea of using chemical fixatives to preserve the brain. In my case, this concern was not just “theoretical.” In my lab I have spent many years looking at the effects of cerebral ischemia on cryopreservation and chemical fixation. Last year we decided to broaden our investigations to delayed chemical fixation and we have not been pleased at what we have observed so far. After 1.5 years of room temperature storage the delayed aldehyde fixed brains are falling apart and continue to decompose. In small animals one might imagine that such perfusion impairment could be overcome by immersing the brains in the fixative instead but human brains are simply too large. By the time that the fixative would have reached the core of the brain, extensive autolysis will have occurred.
Another complex problem is to identify a fixation and polymerization protocol that fixes all identity-critical parts of the brain. If aldehydes do not completely fix the lipids in the brain, should we add strong oxidizing heavy metals to stabilize lipids? This is possible in theory but, as a general rule, these chemicals are either very expensive or dangerous to use (or both). Even if we are able to identify a chemical fixation protocol for the brain that can do the job, how can we know that such brains are stable for very long periods of time? Should we follow fixation by embedding with a polymer to inhibit residual biochemical activity? To my knowledge, there is no known embedding protocol that is scalable to human brains due to the extreme viscosity of these plastics.
Recently these issues took a more personal nature for me when I had to think really hard about a reasonable but affordable longterm preservation protocol for a companion animal. I spent many days reading the electron microscopy and fixation literature to come up with a protocol that was better than aldehyde fixation and low temperature storage. Adding calcium to the fixative? What about phenol? Post-fixation perfusion of a viscous cryoprotectant to allow storage at subzero temperatures? That is when I really started appreciating the “magic” of cold temperatures.
Absent a vitrification agent, cryogenic temperatures can cause extensive damage to cells. But one thing we know: whatever the nature of this damage, as soon the brain is below the glass transition temperature of -130°C, all water is either frozen or a vitrified rigid solid. We do not have to worry about any damage getting worse over time, or whether some biomolecules have not been fixed. Cold may be “crude” in its effects but it is exactly because no biochemical process can escape inhibition at very low temperatures that makes it such a powerful personal survival technology.
Originally published as a column in Cryonics magazine, January, 2013