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Tuesday, 1 July 2008

Bloody Wednesday

An edition dedicated to out lovely blood. Ok, alien DNA, cloned hearts and the harm of blood transfusion. All very interesting subjects.
I'm personally most trilled by the arsenic DNA which suggests an alternative way of creating DNA in different environment-for example, the conditions of another planet. So, UFO-maniacs and just decent alien-believers, now you know it's possible not only on paper.

Early life could have relied on 'arsenic DNA'

  • 26 April 2008
A DEADLY poison, arsenic is best known for snuffing out life. But could it have played a key
role in the origins of life on Earth?
Felisa Wolfe-Simon of Harvard University thinks so because the toxin behaves so
similarly to phosphorus, an essential ingredient in nearly all living things. Much more arsenic
would have been available in Earth's primordial oceans than phosphorus. And while microbial
activity was necessary later to unlock phosphorus from rocks, arsenic could have
dissolved in water from hydrothermal vents.
Phosphorus binds to four oxygen atoms to form a negatively charged phosphate ion that is
used to build the backbone of DNA's double helix. Phosphate is also key in adenosine
triphosphate (ATP), the "universal energy currency" that supplies energy to most life on
Earth.

Wolfe-Simon and Paul Davies of Arizona State University in Tempe think arsenic could do the same jobs. Just as phosphorus forms phosphate ions, so arsenic readily forms arsenate ions. Arsenate isn't suitable for life today, because it tends to latch onto adenosine diphosphate molecules, blocking the production of ATP. However, without much phosphorus available, the first life might have evolved to make use of the next best thing, Wolfe-Simon says.
"If you put arsenic in a test tube with adenosine, you immediately get lots of adenosine monoarsenate," which is structurally similar to adenine, the "A" letter in DNA's code of A, C, G and T, says Wolfe-Simon.

If early life did use arsenate, single-celled organisms with arsenate-based DNA may still be around today wherever phosphorus is scarce.
The only stumbling block to the idea is that arsenic-based DNA tends to break down quickly. "You don't want to build your DNA out of a compound with a half-life in the order of a couple of minutes," points out Steve Benner of the Foundation For Applied Molecular Evolution in Gainesville, Florida.
However, he points out that it could be a good thing in extreme cold, where chemical reactions move very slowly. Microbes living in Antarctica or on Saturn's moon Titan might find phosphate-based DNA too sluggish to work with and have evolved to take advantage of faster-reacting arsenate instead(pdf) .source

My comment: Aliens, anyone? I mean what better use of that theory than in extra-solar planets. And it only add up to the knowledge of how different life can be.

Be still my beating stem cell heart

Movie Camera
  • 18:00 23 April 2008
Muscles that make up the human heart have been made from embryonic stem cells for the first time

There's a new recipe in the embryonic stem cell cookbook. Scientists have announced the creation of a human master heart cell, able to transform into all the different cells that make up a beating heart.

Though the cells can repair a damaged mouse heart, it's too soon to say whether they will help treat humans who have suffered a heart attack, says Gordon Keller, a cell biologist at McEwen Centre for Regenerative Medicine in Toronto.

Embryonic stem cells are an exciting technology because, in the right environment, they transform into any human tissue. But the human heart, made of three different kinds of tissue, has thus far proved elusive.

By tweaking an existing recipe that makes one kind of heart cell, Keller's team coaxed stem cells into forming all three types: cardiac muscle cells that pump blood, smooth muscle cells that form blood vessels, and endothelial cells that line coronary blood vessels.

Beginning with human embryonic stem cells grown in the lab, Keller's team added proteins important to cell growth and differentiation. After two weeks, the researchers had created a culture that included all three kinds of heart cells, and – importantly – no others. Even in a Petri dish, the cells beat.

When implanted into mice, the cells improved their damaged hearts. Just as importantly, the cells did not form teratomas, tumours that are a common problem with stem cell therapies.

"It's extremely interesting to think about having one cell that could do it all," says Chuck Murry, a cell biologist at the University of Washington in Seattle, whose lab converted embryonic stem cells into heart muscle cells last year.

The next step will be to derive the master heart cells from normal human tissue, Murry says. Last year, researchers in the US and Japan transformed ordinary human cells into stem cells, called induced pluripotent stem cells (iPS). With iPS cells, scientists could make heart cells from a patient's own tissue, avoiding the risk of immune rejection.

Keller's team has begun experiments to transform iPS cells into the heart cells. But he says drug tests will probably be the first application of the new cells. Currently, researchers have no source of human heart cells to test the effects of drugs that combat heart disease and other conditions.

"This gives us an endless supply of human heart cells," he says.

Journal reference: Nature (DOI: 10.1038/nature06894) source

My comment: I'm kind of confused on this one, because I remember posting about a new heart made by using the form of an cadaver heart. And now we have those cells...Well, anyway, it's great to hear they are making progress. I just prefer not to see that progress only as a field for perfecting drugs. It will be a waste, especially if they can inject the cells and wait for them to repair the heart. But it will be a good way to check for side-effects, I guess.

Could blood transfusions cause harm?

“FOR the life of the flesh is in the blood. No soul of you shall eat blood.” So says the Bible’s book of Leviticus, and it is for this reason that Jehovah’s Witnesses shun blood transfusions. They do not, however, shun surgery. As long as surgeons use special techniques, Jehovah’s Witnesses can have surgery - including operations with the greatest potential for blood loss, such as open-heart surgery - without ever receiving a drop of someone else’s blood.

Now some surgeons and anaesthetists are questioning whether every patient shouldn’t get the same treatment. Over the past decade a number of studies have found that, far from saving lives, blood transfusions can actually harm many patients.

The problem is not the much-publicised risk of blood-borne infectious agents, such as HIV, but the blood itself. Study after study has shown that transfusions, particularly those containing red blood cells, are linked to higher death rates in patients who have had a heart attack, undergone heart surgery, or who are in critical care. The exact nature of the link is uncertain, but it seems likely that chemical changes in ageing blood, their impact on the immune system, and the blood’s ability to deliver oxygen are key.

In fact, most experts now agree that the risk posed by the transfused blood itself is far greater than that of a blood-borne infection. “Probably 40 to 60 per cent of blood transfusions are not good for the patients,” says Bruce Spiess, a cardiac anaesthesiologist at Virginia Commonwealth University in Richmond.

Such claims have led this week to the US National Institutes of Health issuing a call for proposals to study the problem.

Blood transfusion became a mainstay of medicine during the two world wars, where it was used as a last resort to save soldiers who had suffered massive blood loss. But now, far from being restricted to catastrophic bleeding, transfusions are routinely used as an optional treatment, most commonly for patients in intensive care or undergoing major surgery. In these situations, mostly small volumes of red cells are transfused, usually after they have been stored at 4 °C for anything up to 42 days.

The rationale behind such blood transfusions seems incontrovertible. Red cells deliver vital oxygen to tissues, and seriously ill patients who are also anaemic fare less well, so a transfusion should help. Those assumptions went untested for the better part of a century.

Things started to change in 1999 with a randomised controlled trial on 838 critical care patients in Canada that used haemoglobin levels to determine when a blood transfusion was given. Normal levels of haemoglobin, the oxygen-carrying protein in red cells, range from 120 to 170 grams per litre. A normal haematocrit - the proportion of red cells in the blood - ranges from 36 to 50 per cent. Doctors decide whether to give a transfusion based on a number of factors, including haemoglobin levels and haematocrit, and the patient’s overall robustness. Many guidelines exist, and practice varies from one hospital or doctor to another, but it is common for patients to receive transfusions when their haemoglobin dips to between 70 and 100 g/l or their haematocrit to 21 to 30 per cent.

But the Canadian study found significantly fewer patients died in hospital, 22 versus 28 per cent, if they received transfusions only when their haemoglobin fell below 70 g/l rather than when it fell below 100 g/l.

A more recent study has found that in heart attack patients with haematocrits of over 25 per cent, a transfusion is associated with more than three times the risk of death or a second heart attack within 30 days compared with not having a transfusion (Journal of the American Medical Association, vol 292, p 1555).

For almost 9000 patients who had heart surgery in the UK between 1996 and 2003, receiving a red cell transfusion was associated with three times the risk of dying in the following year and an almost sixfold risk of dying within 30 days of surgery compared with not receiving one. Transfusions were also associated with more infections and higher incidences of stroke, heart attack and kidney failure Р complications usually linked to a lack of oxygen in body tissues (Circulation, vol 116, p 2544).

“There is virtually no high-quality study in surgery, or intensive or acute care - outside of when you are bleeding to death - that shows that blood transfusion is beneficial, and many that show it is bad for you,” says Gavin Murphy, a cardiac surgeon at the Bristol Heart Institute, who ran the UK study.

Organisations such as the American Society of Anaesthesiologists have started recommending that doctors be more conservative about ordering transfusions. But many experts worry that the recommendations are being ignored, and don’t go far enough. Transfusion, they say, should only be used as a last resort, and far greater effort should go into preventing blood loss in the first place and ensuring patients are not anaemic before surgery.

A priority is to find out how transfusions can be harmful. One possibility is that they affect the patient’s immune system. Blood transfusions are typically teeming with cytokines - chemicals that modify immune cells - and both the cytokines and white blood cells in donated blood have been shown to affect the action of “recipient” immune cells in the lab. Before modern immunosuppressant drugs were developed, blood transfusions were sometimes used to achieve immunosuppression during kidney transplants.

Several of the recent studies have found an association between contracting infections in hospital and transfusions, which seems to support the theory. “The more units of blood patients receive, the more likely they are to get infections,” says Mary Rogers at the University of Michigan in Ann Arbor, who has studied transfusions in US heart surgery patients.

But people should not stop donating blood, stress experts. “Transfusion is critical in several situations such as severe haemorrhage. We also need blood for essential products such as antibodies and clotting factors for people with haemophilia,” says Isbister (article). NewScientist

My comment: I didn't suspect that. It's interesting the body would reject foreign blood when it doesn't really need it. Very interesting indeed. Mostly that people haven't noticed until now. And blood transfusions are so often.

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