The decellularization
process, step by step
Photo credit: University
of Minnesota |
"We just took nature's own building
blocks to build a new organ. When we saw the first contractions
we were speechless." — study author Dr Harald
Ott, Massachusetts General Hospital
The recent announcement that a
"bioartificial" rat heart had been grown in a Minnesota
lab, and had actually been prompted to start beating,
proved two concepts that many doctors have suspected
for a long time. First, you can grow real organs in
the lab using progenitor cells, and second, you shouldn't
believe everything you read in the papers.
The breakthrough is real enough,
but the widely-repeated claim that this scientific first
- published January 13 in Nature Medicine —
could herald an end to donor organs and anti-rejection
drugs is simply not true. In fact, several further breakthroughs
will be necessary before anyone can feel safe claiming
that.
OUT
WITH THE OLD
To generate this bioartificial heart, American researchers,
led by Doris Taylor, PhD, director of the University
of Minnesota's Centre for Cardiovascular Repair, came
up with a revolutionary technique called perfusion-decellularization.
They used detergent to remove all of the actual cells
in a dead heart, leaving only the "decellularized" matrix,
the basic architecture of the heart with four chambers,
valves and the three coronary arteries. The structure
is then repopulated with progenitor cells, which are
encouraged to grow in a nutrient bath that takes the
place of normal circulation.
They applied the technique to a
rat's heart and not only did the cells grow into heart
cells, but the heart actually beat when stimulated with
electricity. Stem cells drawn from a heart failure patient
could be used to build new organs using the same technique,
Dr Taylor noted, launching a flurry of excitement.
Dr Doris Taylor shows
off the decellularized rat heart
Photo credit: University
of Minnesota |
STEM
THE ENTHUSIASM
But though the researchers got the heart to beat, that's
not the same as pumping blood, critics rushed to point
out. The highest contractile force achieved by the bioartificial
heart was 2.4mm Hg. The heartbeat of a human fetus at
about 16 weeks' gestation is already four times stronger
than this.
Moreover, even a strong heart can
only pump as much blood as its arteries can carry. The
team's efforts at re-lining the decellularized blood
vessels with endothelial progenitor cells were less
successful than their efforts with the heart tissue
itself. One hundred rat hearts were processed to harvest
the progenitor cells used in this study to build one
working rat heart.
OBSTACLES
AHEAD
And that brings up two other problems. First, this is
a real heart, but not a living heart, because it has
never been implanted in an animal. Hardly surprising,
given that the poor rat would immediately die from circulatory
failure, even before the immune reaction could get him.
Secondly, the effort and expense
required are a major stumbling block. Dr Taylor believes
she could build a single human heart right now, but
"creating the larger bioreactors and generating the
reagents and growing enough cells would cost tens of
thousands of dollars for each heart at this point,"
she told the Telegraph. The team is currently looking
for new funding to move in that direction
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