- NEW YORK (Reuters Health)
- The abnormal proteins linked to "mad cow" disease and other
brain-wasting illnesses can form in muscle much more easily than previously
thought, new research suggests.
-
- The accumulation of these proteins, known as prions,
has been thought to be concentrated mainly in the central nervous system
and lymphatic tissues, but California researchers have demonstrated that
high levels of prions can form in muscles throughout the body.
-
- The report suggests that current strategies aimed at
protecting the food supply, which include taking precautions to ensure
that meat does not contain any neurological or lymphatic tissues, may not
be adequate for reducing the risk of prion diseases. However, the study's
authors caution that the results are preliminary, and it is too soon to
know whether prions naturally form in the muscle of animals infected with
brain-wasting diseases.
-
- Mad cow disease, or bovine spongiform encephalopathy
(BSE), is one of several fatal brain-wasting diseases thought to be caused
by the build-up of prions in the brain. In 1996, a new form of
Creutzfeldt-Jakob
disease (CJD), a human brain-wasting disease, was reported in young adults
in the UK. There is strong evidence that this new type of CJD arose when
people ate meat from cows infected with BSE.
-
- Since the discovery of the apparent link between mad
cow and the new type of CJD, there has been a push to exclude meat from
prion-infected animals from the food supply. Besides slaughtering herds
of infected cattle, this strategy has included banning brains, spinal cord
and certain other tissues from meat products.
-
- Now, Dr. Stanley B. Prusiner and colleagues from the
University of California at San Francisco report that, in mice at least,
high levels of prions can accumulate in muscles, too.
-
- Prusiner and his colleagues injected brain tissue from
prion-infected mice and hamsters into the muscles of uninfected mice. The
researchers found that these injected prions were able to reproduce
extensively
in muscle. This accumulation of the abnormal proteins varied widely from
muscle to muscle, with muscles in the hind legs having the highest
levels.
-
- A report on the findings appears in the March 19th issue
of the journal Proceedings of the National Academy of Sciences.
-
- The research demonstrates that skeletal muscle in mice
is "intrinsically capable" of forming high levels of the abnormal
proteins, Prusiner and his colleagues conclude. The fact that high levels
of prions may accumulate in muscle even when neural and lymphatic tissue
is excluded "raises the concern that humans consuming meat from
prion-infected
animals are at risk for acquiring infection," according to the
authors.
-
- But the risk of contracting a prion disease by eating
meat is still uncertain, Prusiner and his colleagues note. They point out
that the accumulation of prions may vary from species to species and from
disease to disease. Also, compared to being injected with infected tissue,
it is much more difficult to become infected with prions by eating infected
tissue, they note. The researchers also point out that not all types of
prions can move from species to species, so the risk to people is
uncertain.
-
- The study challenges the conventional thinking on where
prions accumulate in the body, Dr. Giuseppe Legname, who is a co-author
of the study, told Reuters Health in an interview. "We thought that
they were only accumulating in the nervous system and lymphatic
system,"
he said.
-
- The formation of prions in muscle could have larger
implications,
according to Legname. He stressed, however, that the study was conducted
in laboratory mice, so it does not prove that prions can form in the
muscles
of other animals. To find this out, researchers will have to perform
similar
experiments in other species, he said.
-
- People should not panic about the results, Legname
explained.
There is "no reason to worry yet," he said. Still, he added,
"We need to be aware that there might be a possibility" that
prions could be present in the muscles of other animals.
-
- The findings may have a silver lining. If significant
numbers of prions do accumulate in muscle, than it would be easier to
diagnose
prion diseases by analyzing a small sample of muscle tissue, the
investigators
note.
-
- SOURCE: Proceedings of the
National Academy of Sciences 2002;99:3812-
-
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