Tuesday, March 09, 2004

Cool Science - Freeze-dried Blood

I've recovered from my little rhinovirus and I'm back for blogging. I just can't bring myself to mention the E word and my least favorite Democratic candidate. There's plenty of mocking of J Freakin' K going on around in the blogosphere, and I just don't care enough to try to be clever. Sigh! Only 8 months to go.

Anyway, I saw this story in Nature about scientists developing methods to freeze-dry cells, including red blood cells.

Cell Biology: Just add water

Thanks to a sugar found in yeast, it may be possible to provide 'freeze-dried' blood cells to treat injured soldiers. The technique could also find applications in the cell-biology lab. Geoff Brumfiel reports.

The US military is one of the most bloodthirsty organizations on Earth. The troops hold regular blood drives to keep a required 70,000 units on hand at all times; and a veritable small army is needed to transport this blood to remote battle zones in Iraq or Afghanistan. It can take more than a week for refrigerated supplies to reach the field. That's a critical delay, explains Joe Bielitzki, a programme manager at the Defense Advanced Research Projects Agency (DARPA), which oversees speculative research for the Pentagon. "Typically, by that point nobody's bleeding," he says.

Bloodthirsty? Ha, ha. I suppose Brumfiel is trying to be clever. What better adjective to apply to a group of men and women that are spilling their blood over in Iraq and Afganistan for the freedom of others? Gimme a break and please get to the point of the article ASAP.

Ideally, the military needs blood supplies that can be stored and moved easily. So DARPA has assembled a team of US researchers to develop technology that will allow blood to be freeze-dried, rather like instant coffee, and stored at room temperature for years rather than days or weeks. It might seem an impossible task, but in just three years the group has achieved an impressive result — it has extended the shelf-life of human blood platelets, cells critical to wound healing, from a week to almost two years.

Medical applications aside, members of the DARPA team claim that their work could have wider uses in the laboratory. For example, it may be possible to store experimental cell lines for years at a time on a shelf, rather than in expensive liquid-nitrogen freezers. And it could become easier to ship cells of all types, including precious embryonic stem cells, to and from labs around the world.

This would be quite a breakthrough for medicine and medical research. Remember all the people that lined up to give blood on 9-11? Since all that blood couldn't be used before it went bad, a lot of it was thrown out. Now if that blood could have been freeze-dried, some of it might still be available for use. And the cost of storing other types of cells for research would be greatly reduced. We have 2 or 3 -80 C freezers just in my lab for storing cells and other reagents. Some cells have to be stored in liquid nitrogen freezers. If the power goes out and the cells warm up even a little bit, you are SOL. With freeze-dried cells, you could store them at room temperature.

Imagine if you could have packets of freeze-dried blood for each member of your family in your home first-aid kit. And the blood could be donated by each member of your family for future use. The blood would be perfectly typed also, reducing the possible adverse side effects. Your doctor or local hospital could also keep some on hand for you in the case of an emergency. This could reduce the need for blood because people could donate in advance for themselves and also donate less often for others because of the extended shelf-life.

So what exactly does freeze-drying a bunch of cells entail? Why haven't we been able to freeze cells before?

Putting cells into a freezer exposes them to all sorts of danger. As water inside and outside the cells cools, ice crystals form and their jagged edges can rip the cells apart. Partial dehydration is a side effect of cooling, and if it is not controlled it causes the cells' membranes to shrivel and stick together. Rapidly cooling cells to liquid-nitrogen temperatures can prevent lethal ice crystals from forming by transforming the watery cytoplasm into an amorphous glass. But even if the cells survive freezing, the deathblow often occurs during thawing and rehydration, when they are subjected to new stresses.

This is why, if you're dying of an incurable disease, you can't just get yourself frozen and then have someone thaw you out in the future when a cure has been found. A chemical called a cryoprotectant has to be used to protect the cells from damage.

Enter trehalose, a simple sugar found in organisms such as baker's yeast (Saccharomyces cerevisiae) and brine shrimps (Artemia species) that allows them to survive severe dehydration. Its properties are almost miraculous, says John Crowe, co-director of the Center for Biostabilization at the University of California, Davis, who has devoted most of his career to its study. "We've spent a lot of time looking at how it works," he says. It also has the virtue of being naturally non-toxic.

After two decades of probing the structure of trehalose and how it interacts with cellular components, Crowe's team has worked out the main ways in which the sugar protects cells during drying and freezing. First, it replaces some of the water in the cell so that, as the temperature drops, trehalose prevents uncontrolled dehydration. Second, the sugar stabilizes the cell's membrane and stops it from disintegrating. Then, as the temperature falls below water's freezing point, trehalose forms an amorphous glass inside the cell, which prevents ice crystals from forming. If the cell is subsequently fully dehydrated, the glass becomes stable, and the cell can be kept at room temperature for long periods of time.

So far, Crowe's group has been able to freeze-dry platelets (cells essential for blood clotting), store them for 2 years at room temp, and reconstitute 90% of the cell. They've have not yet achieved this success for red blood cells, stem cells, or human egg cells. But I expect within the next 10 years they'll be able to freeze dry various cells, tissues, and organs for medical or research use. Maybe some day you'll be able freeze Grandap until scientists can reverse the aging process.

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