| ironjustice@aol.com 2005-06-10, 9:02 am |
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Source: Case Western Reserve University
Date: 2004-12-30
New Study Shows How Mad Cow Prions Hitch A Ride Into Intestine
A new study from the Department of Pathology at Case Western Reserve
University School of Medicine shows that the infectious version of
prion proteins, the main culprits behind the human form of mad cow
disease or variant Creutzfeldt-Jakob Disease (vCJD), are not destroyed
by digestive enzymes found in the stomach. Furthermore, the study finds
that the infectious prion proteins, also known as prions, cross the
normally stringent intestinal barrier by riding piggyback on ferritin,
a protein normally absorbed by the intestine and abundantly present in
a typical meat dish. The study appears in the Dec. 15 issue of the
Journal of Neuroscience.
Prions are a modified form of normal proteins, the prion proteins,
which become infectious and accumulate in the nervous system causing
fatal neurodegenerative disease. Variant CJD results from eating
contaminated beef products from cattle infected with mad cow disease.
To date, 155 cases of confirmed and probable vCJD in the world have
been reported, and it is unclear how many others are carrying the
infection.
According to the study's senior author Neena Singh, M.D., Ph.D.,
associate professor of pathology, little is known about the mechanism
by which prions cross the human intestinal barrier, which can be a
particularly difficult obstacle to cross.
"The mad cow epidemic is far from over, and the continuous spread of a
similar prion disease in the deer and elk population in the U.S. raises
serious public health concerns," said Singh. "It is therefore essential
to understand how this disease is transmitted from one species to
another, especially in the case of humans where the infectious prions
survive through stages of cooking and digestion."
Using brain tissues infected with the spontaneously occurring version
of CJD which is also caused by prions, the researchers simulated the
human digestive process by subjecting the tissue to sequential
treatment with digestive fluids as found in the human intestinal tract.
They then studied how the surviving prions are absorbed by the
intestine using a cell model. The prions were linked with ferritin, a
cellular protein that normally binds excess cellular iron to store it
in a soluble, non-toxic form within the cell.
"Since ferritin shares considerable similarity between species, it may
facilitate the uptake of prions from distant species by the human
intestine,"said Singh."This important finding provides insight into the
cellular mechanisms by which infectious prions ingested with
contaminated food cross the species barrier, and provides the
possibility of devising practical methods for blocking its uptake," she
said. "If we can develop a method of blocking the binding of prions to
ferritin, we may be able to prevent animals from getting this disease
through feed, and stop the transmission to humans."
Currently, Singh's group is checking whether prions from distant
species such as deer and elk can cross the human intestinal barrier.
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The study was supported by National Institutes of Health grants.
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This story has been adapted from a news release issued by Case Western
Reserve University
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