We scientists are difficult, cranky, and above all, maddeningly frustrating people. Want to turn lead into gold? No problem, we can tell you how to do that, and in fact have even done it already: the only catch is that the cost of such ‘nuclear transmutation’ is many times that of even the most expensive mined gold. You say you want to travel to the moon? Done! That will be ~$80 billion (in 2005 US dollars). Want to increase average life expectancy from ~45 to ~80 years? Your wish is our command, but be mindful, you will, on average, spend the last few of those years as a fleshpot in the sunroom garden of an extended care facility.
And so it has been with an effective treatment for cerebral ischemia-reperfusion injury following cardiac arrest. Thirty years ago, laboratory scientists found a way to ameliorate most (and in many cases all) of the damage that would result from ~15 minutes of cardiac arrest, and what’s more, it was simple! All that is required is that the brain be cooled just 3oC within 15 minutes of the restoration of circulation. The catch? Well, this is surprisingly difficult thing to do because the brain is connected to the body and requires its support in order to survive. And the body, as it turns out, represents an enormous heat sink from which it is very difficult to remove the necessary amount of heat in such short time. Thus, the solution exists and has been proven in the laboratory, but it has been impossible to implement clinically. This may be about to change as a variety of different cooling technologies, such as cold intravenous saline and external cooling of the head begin to be applied in concert with each other. Separately, they cannot achieve the required 3oC of cooling, but when added together they may allow for such cooling in a way that is both effective and practical to apply in the field. A newly developed modality that cools the brain via the nasal cavity may provide the technological edge required to achieve the -3oC philosopher’s stone of cerebroprotection.
In his article entitled ‘Evidence Based Cryonics’ Aschwin de Wolf unassailably argues that: “There is an urgent need to move from extrapolation based cryonics to evidence based cryonics. This will require a comprehensive research program aimed at creating realistic cryonics research models. It will also require vast improvements in the monitoring and evaluation of cryonics cases. The current debate should no longer be between advocates and opponents of standby and stabilization but about what stabilization procedures should be used by cryonics organizations given our current knowledge”.
Unfortunately, much of the rest of what he has to say is incomplete or lacks the necessary context required to allow for a fair and technically sound evaluation. Perhaps the brevity of the blog format was the reason for these shortcomings? In any event, I would like to comment on these remarks and provide a somewhat different perspective on the complex and important issues discussed in ‘Evidence Based Cryonics.’
The best place to start is to define what evidence based medicine is, and then proceed to attempt to describe what might constitute ‘evidenced based cryonics.’ Webster’s New World Medical Dictionary, 3rd Edition (2008) defines evidence-based medicine as, “the judicious use of the best current evidence in making decisions about the care of the individual patient. Evidence-based medicine (EBM) is mean to integrate clinical expertise with the best available research evidence and patient values. EBM was initially proposed by Dr. David Sackett and colleagues at McMasters University in Ontario, Canada.” Having defined what EBM is, the next question is, what constitutes “the best current evidence?”
The United States uses the U.S. Preventive Services Task Force (USPSTF) system for evaluating evidence about the effectiveness of medical interventions. The USPSTF classifies evidence in terms of reliability for use in decision making as follows:
* Level I: Evidence obtained from at least one properly designed randomized controlled trial.
* Level II-1: Evidence obtained from well-designed controlled trials without randomization.
* Level II-2: Evidence obtained from well-designed cohort or case-control analytic studies, preferably from more than one center or research group.
* Level II-3: Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled trials might also be regarded as this type of evidence.
* Level III: Opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.
* While beyond the scope of discussion here, it is worth noting (and referencing) the work of Guyatt, et al., and the GRADE Working Group in further defining what constitutes the quality and strength of scientific evidence; a formidable and controversial task (1- 6).
* To anyone knowledgeable in the areas of medicine applicable to human cryopatient stabilization and transport procedures (i.e., resuscitation/reanimatology, ischemia-reperfusion injury, solid organ preservation, deep hypothermic cardiopulmonary bypass and whole animal asanguineous perfusion) it will immediately be apparent that none of the 5 classes of evidence presented above can be directly applied to cryonics cases. Arguably, Level III evidence, the “opinions of respected authorities, based on clinical experience, descriptive studies, or reports of expert committees” might apply were there any acknowledged ‘respected authorities’ in the sphere of cryonics standby, stabilization or transport patient care. Alas, no such authorities, respected or otherwise, are currently ‘acknowledged’ to exist.
Thus, the first statement Aschwin makes in opening his article, “Cryonics patients can greatly benefit from rapid stabilization after pronouncement of legal death,” which he defines as “procedures that aim to rapidly restore blood circulation and drop the patient’s temperature” is itself unsupported by either conventional medical research or by cryonics research or case reporting using EBM criteria. If the information-theorertic criteria, as validated by ultrastructural preservation of the brain (7), or the demonstrated recovery of function of the brain are to be used as the gold standards for determining the efficacy of cryonics stabilization and transport procedures, then there currently exists no EBM quality (scientifically robust) data to support “restoration of blood circulation” following pronouncement of medico-legal death in cryopatients.
More specifically, assuming such an intervention is warranted, the question then becomes,’ under what circumstances and in which patients should it be applied?’ Is the patient with 30 minutes of post-arrest warm ischemia better off with simple external cooling followed by cryoprotective perfusion, as opposed to undergoing in-the-field reperfusion using closed chest cardiopulmonary support? What about the patient with profound peri-arrest hypoperfusion with evidence of failed or inadequate brain perfusion, such as the presence of fixed and unresponsive pupils for many minutes, or even for an hour or more, before cardiac arrest occurs and medico-legal death can be pronounced? At what point in the complex and difficult to quantify spectrum of warm ischemic injury should cardiopulmonary support be withheld? Or, given that the benefits of rapid post arrest cooling are unequivocally supported by Level II-2 and Level II-3 evidence from conventional medicine, should such support be modified to mitigate or prevent oxygen-driven reperfusion injury by carrying out CPS under anoxic conditions, and if so, under what circumstances and by what procedures? We have no rigorous answers to these questions and Aschwin is certainly on-point in calling for well designed, cryonics-appropriate studies to answer these and myriad other questions of great importance.
The problem is, as it has been since the inception of clinical cryonics in 1967, “what, if anything, do we do in the meantime?” Indeed, forty-two years later, we have little direct evidence even that cryoprotective perfusion results in superior conservation of identity-critical information under the real-world conditions encountered by today’s cryopatients than would be the case were they subjected to more timely straight freezing!
Is a patient who has suffered hours of warm ischemia better off simply being rapidly cooled and rendered into the solid state, as opposed to being subjected to 24, 48 or 72 hours of cold ischemia, followed by cryoprotective perfusion and freezing or vitrification? How do we even determine what the ultrastructural condition of a brain is following straight freezing? Freezing in the absence of fairly large amounts of colligative cryoprotectant agent(s) results in the collapse of tissue ultrastructure into dense channels of material, the structural condition of which it is currently not possible to determine by techniques such as transmission electron microscopy. Reaching conclusions based on the post-thaw ultrastructure (or lack thereof) of straight frozen tissue is complicated by the potentially myriad artifacts introduced during rewarming, thawing, fixation and embedding required to image tissue ultrastructure.
Given the extreme resource constraints that have historically been present in cryonics, and the lack of directly applicable mainstream medical research, the answer to the question of ‘what to do’ has been to apply reasoned extrapolation of high quality, peer-reviewed biomedical research to the care of the individual cryonics patient, and where possible, to conduct on-point in-house research to validate such armchair speculation.
It is important to point out that since the inception of cryonics in 1964, until approximately 1976, efforts to establish patient care protocols were a group effort between the then extant cryonics societies. The first of these efforts was organized by Robert Ettinger in 1966 and resulted in the protocol developed by Dante Brunol (8). Beginning in 1972, Fred and Linda Chamberlain, Art Quaife, Greg Fahy, Peter Gouras, M.D., Robert Ettinger, and I engaged in an extensive and largely public effort to reach a consensus about what should constitute a good standard of care for cryonics patients based upon extrapolation (and where feasible) experimental validation of findings in the peer-reviewed biomedical literature. This was done via extensive private correspondence, via publication of findings and recommendations in Manrise Technical Review and The Immortalist, as well as in the form of a detailed procedure manual for administering human cryopreservation entitled Instructions for the Induction of Solid State Hypothermia in Humans published by Fred and Linda Chamberlain and available, in part, on-line at: http://www.lifepact.com/mm/mrm001.htm (Readers interested in obtaining a copy of the full manual, for private use, may contact the author at ).
During the 1980s this effort continued and was both documented and subjected to review by the American Cryonics Society, Trans Time, Alcor and Cryovita Laboratories in the form of detailed technical presentations made at the annual Lake Tahoe Life Extension Conferences hosted by Fred and Linda Chamberlain’s Lake Tahoe Life Extension Festivals from 1979 to 1985[1.] An example of such disclosures is available at: http://www.lifepact.com/tahoe.htm.
In short, these efforts were public, largely collegial, and consisted of a best effort to apply insights from the scientific literature to human cryopatients. Furthermore, both Jerry Leaf and I made a sustained and detailed effort to document, by both presentations and publications, the outcomes achieved in detailed human cryopatient case reports (10-20) and in animal studies of post-cryopreservation ultrastructure, including those designed to reproduce conditions encountered under real-world conditions (21, 22).
These efforts resulted in a number of cryopatient stabilization protocols that incorporated multiple drugs to address the multiple mechanisms of ischemia-reperfusion injury as identified in the literature; an approach which Aschwin describes as administration of “an unorthodox number of medications to protect the brain and prevent impairment of circulation. While there are peer reviewed papers that combine a number of medications, there is no precedent in mainstream medicine or biomedical research in using such a large number of medications (in contemporary cryonics, medications protocol exceeds 12 different drugs and fluids).” This statement deserves further scrutiny.
Are poly-drug approaches to treatment unprecedented in medicine? As an example, let’s consider the case of a hyperkalemic hemodialysis patient who experiences cardiac arrest while preparations are being made for emergency hemodialysis. How many and what kind of medications will this patient likely receive in the setting of refractory cardiac arrest? Per the American Heart Association (AHA) Guidelines the patient will initially receive 1 mg epinephrine IV every 3 to 5 minutes during CPR. This may be substituted (after the first dose) with 40 IU of vasopressin IV. Since the patient is in aystole 1mg atropine IV is also given. Concurrent with the administration of these drugs the patient is given 30,000 IU of sodium heparin to allow for the institution of hemodialysis to definitively reduce the serum potassium level. The patient is given an unsuccessful 360 Joule shock at this point. Point of care evaluation of blood electrolytes discloses blood potassium of 12 mmol/L: a level that is incompatible with the return of spontaneous circulation. A decision is made to administer calcium chloride: 5 mL of 10% solution IV over 2 min and 2 amps (60 mlL) of 50% dextrose in water along with 10 IU regular insulin IV (glucose and insulin facilitate a transient profound cellular uptake of potassium from the interstitial and intravascular spaces). CPR is continued for 8 cycles and the patient is again defibrillated with a resulting non-perfusing rhythm consistent with hyperkalemic cardioplegia. CPR is continued while hemodialysis proceeds. After 4 minutes of hemodialysis a third defibrillation attempt is made with the result being coarse ventricular fibrillation. Following another unsuccessful defibrillation attempt, and confirmation by point of care testing that serum potassium has decreased to 7.8 mmol/L with blood pH at 6.95, 300 mg of amiodarone is given in addition to 1 mEq/kg sodium bicarbonate: by slow IV push; the latter to correct the acidosis that has resulted from prolonged CPR and dialysis with a low pH bicarbonate-acetate dialysate.. Following 5 additional cycles of CPR the patient is successfully defibrillated and recovers with a mild neurological deficit as a consequence of extended, low flow perfusion during CPR.
This patient, undergoing routine resuscitation from hyperkalemia cardiac arrest, has just received 9 discrete drugs, all of them indicated, and all of them within the current guidelines for the treatment of hyperkalemic cardiac arrest (23-24). Interestingly, none of these drugs was administered to ameliorate vital organ ischemia-reperfusion injury. The reason for this is that no such drugs are currently clinically available for this indication.
Similarly, patients undergoing acute fluid resuscitation and initial; treatment for septic shock may receive a dozen or more drugs including pressors, ionotropes, a vasodilator, 2-3 antibiotics, insulin, rAPC, and any ancillary drugs required to facilitate renal replacement therapy or mechanical ventilation (see: http://www.leedspicu.org/Documents/Septic%20shock.pdf). So, it is clearly not the case that, “there is no precedent in mainstream medicine” for a multimodal drug treatment approach to complex illness, since multi-drug interventions constitute the standard of care for resuscitation from both cardiac arrest and septic shock and increasingly serve as the backbone of a wide range of successful cancer chemotherapies.
However, it is the case that, at least until recently, multi-drug interventions in biomedical research to treat cerebral ischemia-reperfusion injury have been virtually nonexistent. This is beginning to change as there is increasing understanding of the complex, multifactorial nature of cerebral ischemia-reperfusion injury. Examples of this are the recent successful work of Buckberg, et al in recovering piglets from 90 minutes of deep hypothermic circulatory arrest using a protocol that employed 5 primary therapeutic drugs (plus leukodepletion using a Leukoguard filter in the arterial line during cardiopulmonary bypass) (25), the work of Liu, et al., demonstrating the effectiveness of a combination of cerebral blood flow promoting drugs and the administration of phenyl-N-tert-butyl-nitrone (a free radical inhibitor) and cyclosporine-A (a mitochondrial poration inhibitor) in improving 24 hour neurological outcome after 8 min of experimental normothermic cardiac arrest in pigs (26) and the work of Gupta, et al., combining melatonin and poly (ADP-ribose) polymerase inhibitors in a rat model of stroke – a study that employed 6 drugs in the most successfully treated group (27).Other research combining multiple drugs and other interventions, such as mild therapeutic hypothermia, have also shown positive results (28, 29).
Aschwin goes on to state, “The only existing justification for using current protocol reflects work done at Critical Care Research (CCR) in the 1990s. Although scattered reports exist about the effectiveness of this protocol in resuscitating dogs from up to 17 minutes of normothermic global ischemia, no detailed (peer reviewed) paper has been published about these experiments “
I do not know what is meant by the term “scattered reports” to describe disclosure of this work and would note that there have been two formal public disclosures, the first in the form of United States Patent 5700828 issued on 12/23/1997, and the second in the form of a public seminar which was subsequently distributed as a videotape: Darwin M, Harris, SB, Russell, SR, O’Farrell, Rasch, C, J, Pengelle, C, Fletcher, M. Routine Resuscitation of Dogs from 15-17 Minutes of Normothermic Ischemia (37.5°C) With Long Term Survival (>6 weeks). In: 21st Century Medicine Seminar on Recent Breakthroughs in Cryobiology and Resuscitation Research, Ontario, CA; 1998.
As the principal investigator on this study, I would be the first to agree that it is both regrettable and unacceptable that it has not been either peer reviewed or published. However, as I do not have access to either the primary or the reduced data from this study, I am personally powerless to remedy this situation. Further, I think it extremely unlikely either that I will be given access to this data, or that the results of this study will be published in any meaningful time frame, if at all, by those at CCR who control the study data.
The question thus arises as to whether the drugs identified in this study are of use, either singly or in combination, in the stabilization of cryonics patients? The only certain way to answer that question is to apply them in well designed animal models that closely approximate the spectrum of real-world conditions under which cryopatients eligible for cardiopulmonary support and pharmacological treatment of ischemia-reperfusion injury present for care. Such studies will take tens of thousands of dollars and several years to complete. So, again, the questions arise, ‘what do we do in the meantime ‘and ‘how do we judge the evidence that we use to justify any interventions we undertake?’
It is not possible to answer these questions without considering the specifics of the work in question. Aschwin states that, “in contemporary cryonics, medications protocol exceeds 12 different drugs and fluids” with the implication that the CCR canine resuscitation series (CRS) research was the source of these 12 drugs/fluids, presumably those described by Aschwin in his January 2007 article Human Cryopreservation Stabilization Medications (http://www.alcor.org/Library/html/stabilizationmeds.html).
In fact, the original CRS protocol included a total of 22 drugs!
o Hemodiluent: defined electrolyte-dextran-40 containing solution
o Hypertensives: 3 primary drugs, 1 secondary drug
o Buffer: tromethamine (THAM), 1 drug
o Antiglycemic: 1 drug
o Free radical inhibitors: 6 drugs
o Excitotoxicity Inhibitors: 3 drugs
o Ca++ Antagonists: 1 drug
o Bradykinin Inhibitor: 1 drug
o Leukotriene Antagonists/Inhibitors: 2 drugs
o COX I&II Inhibitors: 1 drug
o Phospholipase Inhibitor: 1 drug
o Antiplatelet: 1 drug
o PARS Inhibitor: 1 drug
o Metabolic Support: 2 drugs
TOTAL: 22 drugs
Of these, 6 drugs (not including the anticoagulant heparin, the hyperosmotic agent mannitol, the flow promoting agent dextran-40, and the buffer THAM, all of which were previously in use in cryonics) were retained in the protocol licensed by CCR to Alcor and to Suspended Animation, Inc. These drugs are s-methylthiourea (SMT), d-alpha tocopherol (Vitamin E), melatonin, alpha Phenyl t-Butyl Nitrone (PBN), kynurenine, and carprofen. How should the utility of these drugs be judged? The first step in such a process is to determine which patients might benefit based on the available information. By definition, only patients eligible for CPS can be treated, since effective use of all of these drugs requires thorough systemic distribution. Patients with 20 minutes or less of normothermic cardiac arrest are probably the only suitable candidates based on the limited ability of closed chest CPS to generate adequate pressure and flow over increasingly long intervals of cardiac arrest. Beyond this general criterion, it is necessary to consider the evidence for the utility of each drug individually, on the basis not only of the CCR study, but in the context of the published literature.
The patent which first discloses the core drugs used in the CCR protocol was United States Patent 5700828 which was filed on 12/07/1995. This is significant because two of the primary cerebroprotective drugs described in this patent, melatonin and PBN, had not been previously demonstrated to be neuroprotective in cerebral ischemia-reperfusion injury. It was not until 2003 that the first peer-reviewed paper documenting the effectiveness of melatonin in ischemia-reperfusion appeared (30) and not until 1999 that the effectiveness of PBN in cerebral ischemia was documented in the literature (31). Since these papers first appeared a vast literature supporting the effectiveness of melatonin in both focal and global cerebral ischemia-reperfusion injury has appeared, and the PBN analog NXY-059 was demonstrated as effective in a wide range of animal models of cerebral ischemic injury (32)., although the drug failed in a RCT of stroke (33).
The utility of vitamin E, mannitol and of dextran-40 in cerebral ischemia reperfusion injury predate the 1995 patent and are extensively documented in the cerebral resuscitation literature. There are few papers documenting the effectiveness of kynurenine, and no papers supporting the effectiveness of carprofen in cerebral ischemia-reperfusion injury, although there are many papers documenting the utility of other non-steroidal anti-inflammatory and NF-kappa B inhibiting drugs in cerebral resuscitation.
Should any or all of these drugs be applied to cryopatients? Aschwin raises a number of possible contraindications which merit consideration: “The lack of relevant published data to support the administration of large numbers of drugs…in cryonics is not just a matter of risking performing redundant procedures. A lot of time and resources are being spent in cryonics on obtaining and maintaining equipment and supplies for these procedures, in addition to the licensing fees paid to use some of these technologies and the training and recruiting of people to perform them. But perhaps the most troublesome problem is that the preparation and execution of these procedures during actual cryonics cases can seriously interfere with rapid and effective cardiopulmonary support and induction of hypothermia.”
It is clear from the foregoing that Aschwin considers immediate post arrest cooling in the presence of CPS to be an essential element of effective cryopatient stabilization. Unfortunately, the use of CPS in this setting carries with it the risks of return of consciousness (33) as well as the return of ‘signs of life’ such as agonal gasping (34, 35), spontaneous movement (36, 37) and even the return of spontaneous circulation. (38). This implies that the cryopatient undergoing CPS must be protected against these undesirable effects by pharmacological intervention. At a minimum, this means that intravenous (IV) or intraosseous (IO) vascular access must be established and at least 3 drugs must be administered (e.g., an anesthetic, a paralytic, and a cardioplegic). Thus, much of the skill, equipment and added personnel required to administer cerebroprotective drugs to cryopatients are, in fact, a requirement of delivering CPS assisted cooling. When Aschwin writes: “the preparation and execution of these procedures during actual cryonics cases can seriously interfere with rapid and effective cardiopulmonary support and induction of hypothermia” it is not clear what he means? Is it establishing IV or IO access, or the administration of a large number of drugs, or both that constitutes a threat to rapid post-arrest CPS and cooling?
CPS and vascular access must, necessarily, proceed together, with CPS (properly) trumping vascular access where any conflict occurs. It should also be noted that CPS, given in the absence of an effective pressor, and (in most cryopatients) volume expansion, will not achieve perfusion that is effective; either for supplying adequate cerebral blood flow to prevent ongoing ischemic injury, or to facilitate heat exchange. CPS implies not only vascular access and the attendant skills, complexity and hardware, but also the administration of at least half a dozen drugs in order to render it both safe and effective. Given this requirement, what are the additional burdens and costs of delivering cerebroprotective medication?
Currently, melatonin, PBN, vitamin E, and carprofen are combined into a single parenteral product by CCR (Vital-Oxy) which can be administered IV or IO via a stopcock manifold using a pressure infuser. Heparin (anticoagulant), vercuronium (paralytic), magnesium sulfate (cardioplegic) and the first dose of vasopressin (pressor) can similarly be combined to create a single parenteral product shortly before use and may be administered ‘push’ via the stopcock manifold. Dexrtran-40 and mannitol may also be combined into a single parenteral product with a total volume of ~550 mL which can also be given via pressure infuser and the stopcock manifold. Bolus, or continuous doses of vasopressin and THAM (buffer), can be given via the same stopcock manifold using battery operated infusion or syringe pumps.
The broader issue to be addressed is how these multiple medications may be given rapidly, accurately, and with the least use of personnel. Compact, battery operated infusion pumps for in-field use are now available, but they cost a fortune. The same is true of programmable, battery operated syringe pumps. I think the solution to this problem is to computerize it. A laptop computer should already be in use during cryopatient stabilization and transport to acquire data from the patient and it can and should be used to give the meds as well. One simple system for doing this would be to use pressure infusers, and syringes under pressure, with open/close line-clamp solenoids under computer control. Meds would be dispensed by the interval of solenoid opening; push meds would be a full open solenoid, and interval bolus meds would be given by briefly, and for a fixed time, opening the solenoid(s). This is an extremely simple system to implement from both the hardware and software standpoints. A schematic of this type of system is shown below:
Of course, this presumes that the multidrug approach to cerebroprotection of the cryopatient is economically justified. I would be the first to agree that it is not necessary to pay costly licensing fees to derive most of the benefit from the CRS protocol. It is clear from reviewing the literature that the most widely validated and likely most potent drugs in this protocol (in the context of preventing ultrastructural injury secondary to ischemia-reperfusion injury) are melatonin, PBN[2], and, arguably, vitamin E. These are readily available molecules and may be used by any cryonics organization, absent licensing, on the basis of their documented protective effects in the literature. Other likely useful drugs such as dextran-40, THAM and mannitol have a long history of use in cryonics which predates the CCR research and these drugs may also be used at little cost (Darwin M. Transport Protocol for Cryonic Suspension of Humans, Fourth Edition. 1990, http://www.alcor.org/Library/html/1990manual.html).
In the nearly decade and a half that have elapsed since the CCR canine resuscitation series was undertaken many other promising experimental drugs for the inhibition or moderation of cerebral ischemia-reperfusion injury have emerged. I am in complete agreement with Aschwin that the best way to evaluate the potential utility of these drugs to cryopatients is in animal models that are truly relevant and which simulate the actual condition of cryonics patients who present for stabilization and transport. Such patients are typically suffering from extensive activation of the immune-inflammatory cascade, are often severely dehydrated or fluid overloaded, and invariably suffer from serious disturbances in cerebral microcirculation which begin hours or even days before medico-legal death is pronounced. As a consequence, these patients will typically have pre-arrest ischemic injury which will likely be compounded by post-arrest reperfusion. Evaluation of pharmacological interventions should, and indeed properly must be, carried out in animals models that reflect these facts.
Finally, Aschwin writes: “Even more complexity is introduced when cryonics organizations make an attempt to wash out the blood and substitute it with a universal organ preservation solution. The rationale for this procedure is found in conventional organ preservation and emergency medicine research. The question in organ preservation research is no longer whether hypothermic organs benefit from blood substitution with a synthetic solution, but what the ideal composition of such a solution should be. In emergency medicine research asanguineous hypothermic circulatory arrest is increasingly being investigated to stabilize trauma victims. But it is a major step from these developments to the practice of remote blood washout of ischemic patients with expected transport times of 24 hours or more. At present the only sure benefit of remote blood washout is that it enables more rapid cooling of the patient, a benefit that should not be underestimated. But when liquid ventilation becomes available to cryonics patients, rapid cooling rates will be possible without extracorporeal circulation.”
There can be no argument that blood washout followed by long delays to cryoprotective perfusion is deleterious (as currently practiced) on the basis of both clinical experience with cryopatients and recent unpublished animal research by Fahy, et al., of 21st Century Medicine (39). This practice should probably be abandoned until such time as effective solutions are developed for use in cryopatient transports. The statement that “when liquid ventilation becomes available to cryonics patients, rapid cooling rates will be possible without extracorporeal circulation,” is by no means assured. As the primary inventor of fractional tidal liquid assisted pulmonary cooling (40), I feel it is critical to point out that this technique has been validated only in the setting of healthy animals with spontaneous circulation. The reduced flow state attending external CPS and the typically severely injured lungs of the cryopatient present the twin challenges of greatly reduced blood flow coupled with greatly reduced pulmonary surface area (as a consequence of pre-existing or emergent lung injury; i.e., acute respiratory distress syndrome or acute lung injury resulting from closed chest CPS). which will dramatically reduce the efficacy of heat exchange achievable with this technique.
Once again, as Aschwin correctly notes in the context of pharmacological intervention, it is imperative that modalities developed for application in conventional clinical medicine be validated in the very different setting of the patient presenting for cryopreservation after succumbing to prolonged terminal illness – as well as the added insults of peri- and post-arrest systemic and cerebral ischemia.
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39. Fahy, GM The Whole-Body Vitrification Project at 21st Century Medicine. In the Suspended Animation conference held in Fort Lauderdale, Florida, from May 18th through May 20th May 2007.
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ENDNOTES:
[1] The Cryonics Institute declined repeated invitations to participate in these colloquiums.
[2] It is important to note that the PBN used in the CCR study was prepared by dissolving it in boiling water with concurrent microwave heating in the presence of atmospheric oxygen. This is very likely significant because such handling would inevitably create breakdown products of PBN, such as NtBHA and its oxidation product the spin-trap MNP. As Proctor, et al., have pointed out, (Peter H. Proctor and Lynsey P. Tamborello, SAINT-I Worked, But the Neuroprotectant Is Not NXY-059, Stroke 2007 38:e109; published online before print August 23 2007.) it is possible that the failure of NXY-059 in the SAINT-II trial was due to the fact that material used in this trial differed from that used in the successful SAINT-I trial in that it was stabilized and protected against oxidation. It may well be that it is not PBN, per se, that is cerebroprotective, but rather its oxidation and/or break-down products.
In “The chemistry of neuroprotection”, the author argues convincingly that there could be great benefit from a systematic and rigorously scientific study of the physical chemistry of putative neuroprotectants vis-à-vis their pharmacological effect. However, the first example used of the earliest thinking in this direction (which comes, not surprisingly via V. A. Negovskii, the father of resuscitation (1) medicine) is instructive as to some of the potential barriers standing in the way of this approach.
“It is not surprising that all the agents which are effective in shock carry a negative charge. This applies both to heparin, which possesses a very strong negative charge, and to hypertonic glucose solution. The same may be said about a substance now in wide use – dextran – which has small, negatively charged molecules, and also about the glucocorticoids 21, 17, and 11, which also have a negative charge.” – Professor Laborit in: Acute problems in resuscitation and hypothermia; proceedings of a symposium on the application of deep hypothermia in terminal states, September 15-19, 1964. Edited by V. A. Negovskii.
In the intervening decades since Laborit wrote the words quoted above, supraphysiologic (high) steroids have not only failed to demonstrate benefit in cerebral resuscitation and shock, they have been found to be actively harmful in every well designed RCT undertaken to test their utility (a). This also extends to their lack of utility in trauma, spinal cord injury and sepsis. Similarly, the utility of heparin in treating the encephalopathy of the post-resuscitation syndrome, or improving survival after cardiac arrest has recently been called into question. Glucose, hypertonic or otherwise, was long ago demonstrated to markedly increase neurological injury if given immediately after reperfusion following cardiac arrest, and elevated blood levels of glucose, both pre- and post cardiac arrest have a strong negative correlation with both survival and neurological outcome.
Determining the seriously harmful effects of steroid administration in critical illness took decades. Despite the compelling evidence for their injurious effects, administration of large, supraphysiologic doses of steroids is still a practice both used and defended by some clinicians (albeit not ones who rely on evidence based criteria) and the use of glucose in shock, trauma and cardiac arrest took a nearly comparable period of time to discredit. These two examples are noteworthy because they comprised mainstays of therapy for most kinds of neuroinjury for decades, and they had compelling theoretical appeal, as well as many positive small clinical and animal research studies. Indeed, the debate continues to this day with controversy centred mostly on the use of low or “physiological replacement” doses of steroids in critical illness. As the eminent pulmonologist and intensivist Neil Macintyre observed in 2005, “Patients die, but steroids never do.” This raises the twin problems of bad research (i.e., junk science) and statistically under powered or otherwise flawed studies. Combined, it has been estimated that these two types of defective studies comprise the bulk of published peer-reviewed scientific work.
High dose corticosteroid therapy for neuroinjury offers another complication in determining the therapeutic efficacy of any drug that merits consideration as a neuroprotectant (new or old). While there is no doubt that high-dose corticosteroids are ineffective and deleterious in the clinical setting, there is also little doubt that these agents are neuroprotective in the laboratory setting under certain conditions and for discrete subpopulations of neurons. The reasons for the failure of translational research in the case of corticosteroids are complex, but are mostly attributable to crucial differences between the laboratory and the real world of clinical medicine. In the case of corticosteroids these differences are most significantly:
a. Delay from time of insult to time of treatment; in the laboratory the timing of interventions is uniform and is typically much shorter than is the case in the clinic where delays in both presentation and treatment are both long and highly variable.
b. Heterogeneity of injury in humans compared to animals; animal models of neuroinjury are highly standardized (location, extent, mechanics) whereas human patients present with diverse injuries inflicted in many complex and often poorly understood ways.
c. Species differences; not only are there large genetic differences between humans and rodents in general, there are dramatic differences in the native ability of rodents to both resist and overcome infection in comparison to humans.
d. Demographics and comorbidities: laboratory animals are comparatively very uniform genetically, are typically young and healthy and of the same age, do not have comorbid conditions such as hypertension, diabetes, atherosclerosis, obesity or the diminished physiological capacity and repair and regenerative capacity increasingly present in humans over the age of 25.
e. Rodents aren’t people and do not interact with investigators in ways that facilitate straightforward determination of an adverse affect such loss of short term memory, or other cognitive deficits. It is now understood that the corticosteroids are toxic to the neurons of the hippocampus in both rodents and men. However, injury from this adverse effect is not only more evident in men than in mice (or rats for that matter), it is only men who are capable of complaining about it.
It is notable that all of these effects, with the possible exception of increased resistance to steroid-induced immunosuppression-mediated infection, obtain in the case of other translational models of drug development. The conclusion that corticosteroids are very likely neuroprotective in humans (in terms of the direct pharmacological effect on selected subpopulations of neurons in injured central nervous tissues under ideal conditions) is highly likely. However, the confounding realities of the clinic and the genetic differences between men and rodents (the animals almost exclusively used in this type of research) mask this effect. This poses yet another serious challenge to investigators seeking to establish common moieties in prospective neuroprotective molecules.
Clinical trials of putative neuroprotective substances have been overwhelmingly negative. This has been the outcome despite often stellar results achieved in animal models; often in diverse species in studies conducted by multiple investigators in different institutions and sometimes in different countries; none of whom have any obvious relationship, let alone one that might raise the specter of conflict of interest. In the last 6 years alone, over 1000 experimental papers and over 400 clinical articles have appeared on this subject. What this suggests is that the same deficiencies seen in studies reported upon in rest of the peer-reviewed biomedical literature also apply to studies of pharmacological intervention in neuroprotection. An inevitable conclusion is that until the signal to noise ratio improves, attempts to draw general conclusions about the shared, essential properties of neuroprotective molecules will be difficult at best, and unreliable or misleading at worst.
Perhaps a good place to start this kind of analysis is in an area where the molecular structure of the agent(s) is extraordinarily simple and the animal and clinical data are both robust and show good to fair agreement. Hypertonic sodium chloride solutions have demonstrated efficacy in providing both systemic (splanchnic) and cerebral protection in a broad class insults including hemorrhagic/hypovolemic shock, closed head injury and less robustly in stroke and global cerebral ischemia. Interestingly, other cation salts of chloride given at comparably high tonicity do not have this effect. Furthermore, animal as well as small human clinical studies have demonstrated isochloremic hypertonic solutions to be as effective as hypertonic sodium chloride at restoring microcirculatory flow and reversing metabolic acidosis in haemorrhagic shock without the potentially troublesome side-effect of raising the mean arterial pressure to levels where re-bleeding may occur in trauma or subarachnoid haemorrhage. A relative lack of effectiveness of the chloride salt of magnesium compared to the sulfate salt of this ion has also been noted. Understanding the mechanics of these paradoxes would seem to be a worthwhile and comparatively straightforward place to begin such structure-activity relationship analyses.
17β-Estradiol
Cerebroprotective drugs not infrequently possess a multiplicity of pharmacological effects that are known to be neuroprotective but that may be accomplished by very different and even indirect means in terms of their structure-function relationship. Some cerebroprotective molecules, such as the female hormone 17β-estradiol and the mixed estrogen antagonist-agonist tamoxifen share common physiochemical properties such as free radical scavenging, N-methyl-d-aspartate (NMDA) receptor inhibition, and modulation of volume regulated anion channels (VRAC); which play a role in ischemia-induced release of excitatory amino acids. There is considerable evidence that some of 17β-estradiol’s neuroprotective effect is via signal transduction as well as its neurotrophic effects, even at doses below those necessary for its direct effects on reactive oxygen species production and its NMDA receptor inhibiting effects. While the structure of the molecules shares some important features, they are also structurally very different and the signal transduction and neurohormonal effects are almost certainly very different. Thus, these molecules also present a fascinating opportunity to probe structure-function relationships in neuropharmacology.
Tamoxifen
Finally, an admission, or perhaps a confession is order in ending this discussion. This author has been responsible for the application of at least one putative neuroprotective drug to cryopatients which ultimately proved ineffective in human clinical trials when administered during and after cardiopulmonary resuscitation (CPR). This drug, nimodipine, performed well in animal trials, but failed to show benefit in human trials, possibly as a result of its hypotension-inducing effect. Adequate mean arterial pressure (MAP) following resuscitation from cardiac arrest is essential to survival and a post arrest bout of hypertension has been demonstrated to provide substantial cerebral rescue in animal models of global cerebral ischemia. Reduction of MAP in cryopatients is a serious concern because achieving adequate perfusion pressure is problematic under the best of conditions. It is also worth noting that cryopatients have been given a variety of other ineffective neuroprotective drugs over the past 30 years, including the opiate agonist naloxone, the corticosteroid methylprednisolone and the iron chelating drug desferroxamine.
While these drugs, with the possible exception of nimodipine, are not likely to have been injurious (except perhaps to the pocketbook), their use raises important questions about when and how promising animal research should be translated to the setting of clinical cryonics. Unique among all other populations of human and animal patients, cryopatients have the opportunity to be treated with neuroprotective drugs that show great promise, absent the long delays of regulatory vetting, and independent of the economic pressure experienced by pharmaceutical companies to not only market drugs that are effective, but to market ones that are also profitable. The question thus becomes what criteria do we use in applying these drugs absent the extensive pre- and post marketing evaluation that obtains with approved ethical drugs? In essence the question we must ask and answer is “can we do better, much better in fact, than our colleagues in conventional critical care medicine?
Michael G. Darwin, Independent Critical Care Consultant
Click here for this entry with references in PDF format.
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(1) Resuscitation medicine is properly termed reanimatology, and is so-called in the non-English speaking world
(a) The one condition in which there is unequivocal benefit to supraphysiologic administration of steroids is meningococcal meningitis with substantial evidence also supporting a similar degree of efficacy in Typhoid and Pneumocystis carinii pneumonia.
“The presentations impressed upon me how much witchcraft and how little science has gone into the study of cryoprotectant agents (CPAs). This might be understandable in light of the fact that most cryobiologists are, in fact, biologists. I suspect that a great deal could be accomplished by a thorough study of the physics of the chemistry of CPAs.”
Such an observation could equally apply to the study of neuroprotectants in cerebral ischemia. There has been a growing literature investigating the potential of numerous molecules for the treatment of stroke and cardiac arrest. Although some approaches have been more successful than others, systematic reviews of the chemical and physical characteristics of effective drugs are lacking and discussion of the topic is often confined to isolated remarks.
A number of examples:
“It is not surprising that all the agents which are effective in shock carry a negative charge. This applies both to heparin, which possesses a very strong negative charge, and to hypertonic glucose solution. The same may be said about a substance now in wide use – dextran – which has small, negatively charged molecules, and also about the glucocorticoids 21, 17, and 11, which also have a negative charge.” – Professor Laborit in: Acute problems in resuscitation and hypothermia; proceedings of a symposium on the application of deep hypothermia in terminal states, September 15-19, 1964. Edited by V. A. Negovskii.
“We report that estrogen and estrogen derivatives within the hydroxyl group in the C3 position on the A ring of the steroid molecule can also act as powerful neuroprotectants in an estrogen-receptor-independent short term manner because of to their antioxidative capacity.” Christian Behl et al. Neuroprotection against Oxidative Stress by Estrogens: Structure-Activity Relationship. Molecular Pharmacology 51:535-541 (1997).
“Minocycline’s direct radical scavenging property is consistent with its chemical structure, which includes a multiply substituted phenol ring similar to alpha-tocopherol (Vitamin E)” – Kraus RL et al. Antioxidant properties of minocycline: neuroprotection in an oxidative stress assay and direct radical-scavenging activity. Journal of Neurochemistry. 2005 Aug;94(3):819-27.
“It is notable, however, that NAD+ and minocycline share a carboxamide and aromatic ring structure. A common structural feature of competitive PARP inhibitors is a carboxamide group attached to an aromatic ring or the carbamoyl group built in a polyaromatic heterocyclic skeleton. This structure is also present in each of the tetracycline derivatives with demonstrated PARP-1 inhibitory activity. Alano CC et al. Minocycline inhibits poly(ADP-ribose) polymerase-1 at nanomolar concentrations. Proceedings of the National Academy of Sciences of the United States of America. 2006 Jun 20;103(25):9685-90.
Systematic study of structure-activity relationship of neuroprotectants would not only contribute towards the development of a general theory of neuroprotection in cerebral ischemia, it would also contribute to the design of multi-functional neuroprotectants. Although it is now increasingly accepted that combination therapy offers more potential for successful treatment of stroke and cardiac arrest than mono-agents, parallel or sequential administration of multiple drugs present non-trivial challenges in research design and clinical application. Such problems may be better addressed by designing molecules with different mechanisms of action in the same structure, an approach that is currently recognized and investigated by forward-looking biomedical researchers.
Although the field of cerebral resuscitation has known some notable researchers like Vladimir Aleksandrovich Negovskii and Peter Safar, who devoted their lives to a thorough study of the mechanisms of cerebral ischemia and its treatment, the field as a whole shows a never ending stream of trial and error publications to investigate yet another drug (before moving on to other areas in neuroscience and medicine). Although there is an increased interest in meta-analysis of all these experiments, meta-analysis that places its findings in a broader biochemical and pharmacological context is rare.
The emphasis on theory and research design can be taken too far. As Nassim Nicholas Taleb recently argued, the role of design in biotechnology is overestimated at the expense of chance observations and unexpected directions. But in the area of cerebral resuscitation the risk of too much theory and systematization is low at this point. As evidenced by the successful development of vitrification agents with low toxicity in cryobiology, a committed long-term and systematical effort to find solutions to human medical needs can pay off.
A recent study in Rejuvenation Research reports that a combination of dietary supplements confer neuroprotection in stroke. Over a 2 week period rats received either a proprietary formulation of blueberry, green tea, Vitamin D3, and carnosine called NT-020 or vehicle (i.e., the same solution minus the compounds of interest) before stroke was induced through middle cerebral artery occlusion (MCAo). Two weeks after the insult the rats were subjected to behavioral tests and histological examination. Rats treated with the dietary supplements scored better on behavioral tests, had less histological damage, and showed evidence of neurogenesis.
This study is interesting for a number of reasons. Foremost, it highlights the possibility that dietary choices can positively affect outcome after ischemic insults. These findings complement research that found that caloric restriction improves behavioral and histological outcome after stroke. The findings also reinforce that some of the most effective neuroprotective agents to date are ordinary nutrients, vitamins, and hormones. In this study the investigators combine a number of these agents to greater effect. Although the authors do not present specific data on bioavailability in the brain for these compounds, they argue that a multi-agent approach relaxes the dosage requirements for individual agents.
The paper reviews assays that demonstrate improved neurogenesis in the rats that received NT-020 such as endogenous birth of new neurons, neuronal phenotype expression of newly formed cells, and alterations in neurogenic factors. Pharmacological modulation of neurogenesis after ischemia is a young research field and the results reported in this paper provide additional evidence for the (only recently accepted) phenomenon of adult neurogenesis. Unresolved questions at this point include how neurogenesis differs among species and whether post-ischemic neurogenesis can improve long term outcome in humans.
The design of the current study does not allow a rigorous answer to the question of whether neurogenesis contributed to or accompanied improved outcome. The possibility that other mechanisms (such as increased free radical scavenging) were primarily responsible for the observed improvements cannot be ruled out based on this study.
Induction of hypothermia can reduce injury to the brain when it is deprived of oxygen. How fast do we need to cool a patient during cardiac arrest or stroke to prevent irreversible injury to the brain?
It is an established fact that induction of hypothermia prior, during, or after circulatory arrest can reduce brain injury. As a general rule, the lower the temperature is dropped, the longer the brain can tolerate circulatory arrest. The neuroprotective effects of hypothermia are often expressed using the Q10 rule which says that for every 10 degrees Celsius drop in temperature metabolic rate decreases by 50%. Or to put it differently, the Q10 rule states that ischemic damage susceptibility is decreased by a factor of 2 for every 10 degrees Celsius temperature drop. Q10 may vary between species and in different organs and cells. For example, different temperature sensitivities were observed for release of the neurotransmitters glutamate, aspartate, glycine, and GABA during cerebral ischemia by Nakashima et al. Because even very modest reductions of brain temperature can have profound neuroprotective effects, the Q10 rule may not tell the complete story.
Other things being equal, it would be very useful to have a measure of brain injury when hypothermia is induced prior and/or during cardiac arrest. At least two authors have made an attempt to produce such a measure of ischemic exposure. In Cryonics Magazine (2nd Quarter, 1996), Michael Perry started initial work on this in an article called “Toward a Measure of Ischemic Exposure” (PDF). Perry’s Measure of Ischemic Exposure (MIX) calculates how long the patient has been at a given temperature, with a higher weighting used for higher temperatures. A related measure has been proposed be Steve Harris called the E-HIT. E-HIT stands for Equivalent Homeothermic Ischemic Time. In his (unpublished) manuscript, Harris uses the E-HIT formula to calculate the equivalent normothermic ischemic time for different cryonics case scenarios and real cases. Clearly, the availability of such a measure (and its routine calculation in case reports) would constitute a major contribution to cryonics as evidence based medicine. It could aid in deciding if viability of the brain was maintained during cryonics procedures by estimating the equivalent warm ischemic time.
What makes such a measure complicated during cardiopulmonary resuscitation (CPR), or cardiopulmonary support (CPS) in cryonics stabilization procedures is that hypothermia may only constitute one intervention to mitigate brain injury. In an ideal cryonics case, pronouncement of legal death is followed by rapid restoration of oxygenated blood flow to the brain by (mechanical) cardiopulmonary support, administration of neuroprotective drugs and induction of hypothermia. Such a combination of interventions might avoid any injury to the brain, reducing the equivalent warm ischemic time to zero. A more realistic scenario is that such a combination of interventions may reduce the extent of ischemic injury compared to cooling only. Another complicating factor is that oxygenation in combination with low perfusion pressures might produce more injury than “anoxic cardiopulmonary support” (chest compressions without ventilation). It is clear that calculating a measure of equivalent ischemic time for real cryonics cases can become very complicated.
It would be interesting to know the cooling rate that would be necessary to stay ahead of brain injury, using contemporary medical criteria, during circulatory arrest. For this purpose we use some very simplifying assumptions:
1.The patient is not ischemic prior to pronouncement of legal death.
2. Cooling is initiated immediately after pronouncement of legal death.
3. There is no cardiopulmonary support or administration of neuroprotective agents.
4. Brain injury starts at 5 minutes of warm ischemia.
5. Q10 is 2.0: for every 10 degrees Celsius we decrease the temperature , metabolism is dropped 50% , which doubles the time a patient can tolerate ischemia.
6. No other forms of injury occur other than ischemic injury.
7. Ischemic injury is completely eliminated at the glass transition temperature of the vitrification agent M22 (-123.3°C).
8. A constant cooling rate is assumed.
Using these assumptions, Alcor’s Mike Perry calculates that a cooling rate of 2.89 degrees Celsius per minute is necessary to stay ahead of the equivalent of 5 minutes of warm ischemia.
Let Ehit = total ischemic time limit in hours, 1/12 corresponding to 5 min
Q10 = factor of decrease in metabolism per 10 degrees
Tdrop = desired temperature drop, from 37 degrees (body temp) down to -123.3= 160.3 degrees Celsius
ch=desired cooling rate in deg/hour
cm=desired cooling rate in deg/min = ch/60
Then
ch = 10*(1-exp(-Tdrop*ln(Q10)/10))/(Ehit*ln(Q10))
For Q10=2, Tdrop = 160.3, cm = 2.89 deg/min
If some of the assumptions are slightly changed we find the following for Q10=2.2
For Q10=2.2, Tdrop = 160.3, cm = 2.54 deg/min
If we assume negligible ischemic insult below 0 Celsius and only worry about cooling down to that temperature, so Tdrop is only 37 rather than 160.3, it doesn’t change these amounts drastically:
For Q10=2, Tdrop = 37, cm = 2.66 deg/min
For Q10=2.2, Tdrop = 37, cm = 2.40 deg/min
Clearly, such high cooling rates cannot be achieved during either conventional cardiopulmonary resuscitation or cardiopulmonary support in cryonics. The cooling rates we can hope for during the initial stages of cryonics procedures may exceed 1.0 degrees Celsius per minute at best. It is therefore not realistic to assume that cooling alone may be able to limit brain injury to a degree that allows resuscitation without adverse neurological effects using contemporary medical criteria. This should strengthen the case for the use of other interventions such as administration of neuroprotective agents and oxygenation of the patient. Although the latter intervention may produce adverse effects on the brain itself, the calculations above indicate that anoxic cardiopulmonary support is not compatible with maintaining viability of the brain as the objective of cryonics stabilization procedures. The case for rapid stabilization of cryonics patients remains strong.
