Interesting paper in
EMBO Reports describing successful growth of human arteries in vitro. This is likely to become a widely used application once its perfected, since lots of people will need an extra chunk of artery for bypass surgeries, and taking the artery from other parts of the body, such as the femoral artery, is painful and causes its own problems. One interesting aspect of the research is that they inserted human telomerase reverse transcriptase (hert) into the smooth muscle cells that form the bulk of the artery, which makes them live longer.
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There is a pressing need to develop methods to engineer small-calibre arteries for bypass surgery. We hypothesized that the rate-limiting step that has thwarted previous attempts to engineer such vessels from non-neonatal tissues is the limited proliferative capacity of smooth muscle cells (SMCs), which are the main cellular component of these vessels. Ectopic expression of the human telomerase reverse transcriptase subunit (hTERT) has been shown recently to extend the lifespan of certain human cells. We therefore introduced hTERT into human SMCs and found that the resulting cells proliferated far beyond their normal lifespan but retained characteristics of normal control SMCs. Importantly, using these non-neonatal SMCs, we were able to engineer mechanically robust human vessels, a crucial step towards creating arteries of clinical value for bypass surgery.
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McKee et al, Human arteries engineered in vitro. EMBO reports 4, 6, 633–638 (2003).
From
Nature science update:
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First they encourage ordinary human muscle cells to multiply. Then they add a gene called hTERT to make them live longer. Next they seed the cells on a hose-shaped scaffold of biodegradable polymer. After 2 months, the support dissolves leaving a "dense, muscular, tubular structure," says Niklason. Lining cells are then dropped inside to complete the artificial artery.
"We need to determine whether such vessels are safe [before they are transplanted]," says Asif Ahmed who works on veins and arteries at the UK's University of Birmingham. 90% of human tumours contain hTERT. Although the gene doesn't cause cancer by itself, it might encourage cells to continue to grow inside a vessel and block it, he cautions.
Another step is to test the prototype arteries in the lab to see whether they can "withstand millions of cycles of the heart pumping," advises David Williams, head of the UK Centre for Tissue Engineering at Liverpool University. We need to find out "what it takes to burst them," he says.
If all goes well cardiac patients might not be the only ones to profit. Every year, up to 150,000 US patients have leg bypass surgery as an alternative to amputation and lab-reared arteries could connect kidney patients to dialysis machines.
With donor tissue hard to come by, researchers are racing to create a new generation of synthetic transplant organs including livers, lungs and kidneys. As these become reality, artificial blood vessels will be in demand. After all, "they're all going to need a blood supply," says Niklason.
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Patrick
06-06-2003, 08:11 AM
Tissue engineering: Human arteries engineered in vitro
