December 30, 2005

MRI tracks transplanted islets in mice

By Karla Gale

NEW YORK (Reuters Health) - Researchers at Harvard Medical
School have developed a protocol in mice in which
insulin-producing islet cells are labeled with a magnetic
imaging probe that can be detected by MRI, thus representing a
potential easy noninvasive way for doctors to follow islet cell
transplantation in humans.

Islet cell transplantation is a promising therapy for
insulin-dependent or type 1 diabetes. "Right now, all we can do
to follow the fate of transplanted islet cells is monitor blood
glucose," senior investigator Dr. Anna Moore told Reuters

The problem with that approach, she explained, is that
blood sugar "doesn't give direct information about the health
of those transplanted islets."

The advantage of using a magnetic probe along with MRI is
that it may detect inflammation, immune rejection, and toxicity
resulting from elevated blood sugar or "hyperglycemia" without
performing a biopsy, she added.

According to a report in Nature Medicine, Moore's group
incubated islet cells with magnetic nanoparticles. Their
testing showed that the cells' sugar-stimulated insulin
secretion was unchanged, and that treatment resulted in a loss
of signal on MRI images.

When treated human pancreatic islets were implanted into
the kidney of mice, MRI showed a marked decrease in signal
intensity on imaging at the implantation site. Moreover, the
change in the image remained stable in the labeled graft over a
188-day study period.

The labeled cells were also capable of restoring
normoglycemia in diabetic mice, with no difference between
labeled and unlabeled islets.

Similar results were obtained when labeled islets were
infused through a vein into the liver of mice. The cells were
readily visualized by MRI, and normoglycemia was restored
within 1 week.

"Now we are trying to see if we can obtain similar results
with a contrast agent approved by the FDA for imaging of the
liver," the researcher said. If all goes well, she hopes that a
human trial can be started within the next year.

SOURCE: Nature Medicine, December 2005.