Cell transplant hope for diabetes sufferers
30 July 2007
Iron-based 'magnetocapsules' of insulin-producing cells could help
doctors use cell transplants to treat type I diabetes.
The disease is caused when the immune system destroys insulin-
producing beta cells in the pancreas. Without insulin, blood sugar
levels become dangerously high, so regular insulin injections are
needed. But treating the disease with implanted beta cells would be
preferable, as they continually adjust insulin levels to regulate
blood sugar.
While attempts have been made to transplant beta cells to treat
people with type I diabetes before, results have been mixed. In 80 to
90 per cent of cases, the implanted cells stop producing insulin
within five years, for reasons yet to be discovered. Part of the
problem is an inability to track the cells once they're inside the
body.
A team of scientists at Johns Hopkins University in Baltimore,
Maryland, US, have now developed a magnetic casing to protect
transplanted beta cells. The capsules have small pores, which let the
insulin out into the body but cloak the cell from the recipient's
immune system, preventing rejection. The team can also follow the
fate of their magneto-encapsulate
magnetic resonance imaging (MRI).
An encapsulated pancreatic beta cell (shell stained green, cell
nucleus stained blue). Scale bar: 150?m
© Nature
'We're really excited because we can track where we put the cells,
and make sure their protective housing stays intact and that the
cells don't move,' said Aravind Arepally, assistant professor of
radiology and surgery at John Hopkins. 'This could solve the mystery
of why current transplantation techniques work only for so long.'
The team encapsulated the beta cells in a mixture of Feridex, a
clinically approved, iron oxide-containing MRI contrast agent, and
alginate, a gum isolated from algae. The outer shell hardens to
create a pellet about a tenth of a millimetre across, containing 500
to 1000 cells. In trials of the encapsulated human beta cells in
pigs, the scientists could accurately place the cells in the liver
using real-time MRI fluoroscopy imaging. Three weeks after
implantation, MRI and blood tests showed the capsules remained in
place, and that the cells were still producing insulin.
Jo Brodie, Islets Project Coordinator at Diabetes UK, said: 'If this
research can be safely applied to people it could bring a huge
benefit in allowing doctors to monitor the health of the transplanted
cells. At the moment this isn't really possible as there are no
markers - for example, urinary or blood products - that indicate
islet damage.'
'Combining this with encapsulation technology will hopefully minimise
rejection episodes in the first place, and could provide an
additional platform for stem cell transplantation in the future,' she
added.
James Mitchell Crow
http://www.rsc.
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