X-Message-Number: 16560
From: 
Date: Sun, 17 Jun 2001 01:13:04 EDT
Subject: Apoptosis and Crummy Sciemce

In a message dated 6/16/01 Driven From the Pack writes:


> Correct me if I am wrong, but as I understand it from
>  previous cryonet discussions, the mechanisms that
>  allowed the little girl to survive had nothing to do
>  with preventing cell apoptosis. 

You are correct. Apoptosis is a major player in cerebral ischemic injury and 
in injury associated with prolonged hypothermic storage of organs and tissues 
(for transplant). It's relevance to cryonics is probably primarily as a 
marker for severe free radical damage which may or may not be of relevance to 
the destruction of structure critical to memory, personality and identity. It 
certainly is not an event which causes cell death (destruction) during the 
interval of interest to cryonicists between the time legal death is 
pronounced and cryopreservation is achieved.

Apoptosis, or programmed cell death, is a common and vital event in the 
healthy functioning of all mammals. Most people think of cancer as a disease 
of uncontrolled cell division and visualize it as hordes of rapidly dividing 
cells growing out of control and overwhelming their "normal" neighbors. While 
many cancers are characterized by up-regulated cell division, most 
adenocarcinomas (the common major lethal cancers like those of the lung, 
breast, colon and skin) show only modestly increased rates of cell division 
over those present in normal tissue. 

At least as big a problem and in many cases a bigger problem than rampant 
cell division is that malignant cells do not undergo apoptosis at the 
appropriate interval after cell division. This is also true of many of the 
leukemias and lymphomas. The normal lifespan of a white blood cell is under 
two weeks. The lifespan of a leukemic blast cell can be months, or longer. 
The most aggressive cancers combine up-regulated cell division and defective 
apoptosis with activation of genes promoting angiogenisis (new blood vessel 
formation), metastasis (invasive colonization of tissues in multiple 
locations in the host) and resistance to normal immune surveillance. 
Activation of apoptosis in cancer cells is a promising line of therapy and 
will probably reach the clinic within the next 3-5 years.

In cerebral ischemia, apoptosis is usually triggered as a result of severe 
damage to nuclear and mitochondrial DNA as a result of free radical injury. 
Severe damage to the mitochondria can lead to their poration or 
disintegration releasing enzymes called caspases which signal the cell 
nucleus to in effect shut down. In relevant mammalian models of brain 
ischemia apoptosis is often seen as late 3 to 6 weeks following the insult. 
Rescue of brain cells with drugs which prevent necrotic cell death often 
result in early "good" results which disappear within 2-3 months of treatment 
as these temporarily salvaged cells undergo apoptotic cell death.

This raises the issue of the relevance of apoptosis to cryonics patients 
since animals who recover from acute ischemic insults often do well until 
apoptosis kicks in days or weeks later. This implies a considerable window of 
time to intervene in inhibiting this kind of damage.

Having said this, and being the person who developed the most successful 
cerebroprotective strategy yet reported (with recovery of dogs from 17 
minutes of normothermic ischemia without lasting neurological deficit) I 
would hasten to add that I dealt with apoptosis largely by preventing the 
mitochondrial injury which causes it both by direct free radical inhibition 
and by polyADPribose polymerase synthase (PARP) inhibition.

>When a person dies at
>  low temps, and then is later revived, the reasons why
>  he/she can be revived has nothing to do with cell
>  apoptosis, but instead with the inhibtion of certain
>  chemical reactions which in ordinary cases of death at
>  other temperatures and conditions, cause the clogging
>  of certain ion channels in the brain; this clogging of
>  ion channels is what causes a person who has been
>  revived after being dead for more than 10 minutes or
>  so, to often be brain damaged. The effects of cell
>  apoptosis do not begin taking a significant toll until
>  several hours (perhaps 24 hours or so). The little
>  girl was not yet in danger of cell apoptosis. 

>  Am I correct? Is this article completely off base?

You are partially correct. Actually, the ion channels are not clogged they 
are wide open and this is a major source of injury. The problem isn't so much 
that the ion channels are open as it is they the ion pumps are shut down from 
lack of energy to operate them either due to hypothermia or ischemia, or 
both. Hibernators keep their pumps running and seem to actually close ion 
channels! More incredible are estivators; animals who shut down metabolic 
activity at normal temperatures and just sit there and wait for external 
conditions to improve. The African lungfish is the archetype estivator and 
appears to use ion channel "plugging" or modulation as a key strategy to 
prevent cell injury from ionic imbalances.

Calcium is a key cell regulatory molecule and it is normally kept outside the 
cell with the concentration outside being about 10,000 times greater than 
inside. When cell ion pumping stops (which accounts of 1/3rd of your daily 
energy expenditure!) due to hypothermia or ischemia, calcium and sodium flood 
into the cells. The sodium causes cell swelling and the calcium unleashes an 
incredibly diverse cascade of biochemical events most of which are acutely 
injurious. Proteolytic enzymes which tear cell structures apart are activated 
and the release of neurotransmitters that cause the cell to become 
hypermetabolic upon restoration of metabolism after resuscitation are both 
immediate effects of calcium entry into brain cells. 

It is ironic that calcium influx from outside the cells and its release from 
stores inside brain cells is a key player in ischemic cell death because this 
same mechanism, carefully moderated, is probably one of the principal steps 
by which memories are first encoded in the brain (i.e., activation of the 
NMDA receptors and long-term potentiation (LTP)).

I hope this answers your questions. And, BTW the zebra fish paper is yet 
another example of crummy science writ large.

Mike Darwin

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