- WASHINGTON (Reuters) - A
non-human molecule found in red meat and milk makes its way into the human
system when eaten -- and seems to build up especially in tumors, U.S. researchers
reported on Monday.
- The compound, called sialic acid, is found on the surfaces
of animal cells but is not found in people, and may be one reason why animal-to-human
organ and tissue transplants do not work well. Animals have a version called
Neu5Gc, while humans carry Neu5Ac.
-
- But researchers at the University of California San Diego
found it does show up in the human body, and showed it can be absorbed
from eating red meat and milk.
-
- They also showed that the body produces an immune response
against the molecule.
-
- Dr. Ajit Varki and colleagues, reporting in the Proceedings
of the National Academy of Sciences (news - web sites), say it is too soon
to make any recommendations based on their findings.
-
- "Of course, there are already existing recommendations
that people should not consume too much food containing saturated fats,
such as dairy products and red meats," Varki said in a statement.
-
- "The highest amount (of Neu5Gc) was found in lamb,
pork, and beef (so-called 'red meat')," the researchers wrote. Levels
were very low or undetectable in poultry and fish, vegetables and hen's
eggs.
-
- Varki, who is not a vegetarian, noted that many studies
have linked a diet rich in meat and milk with cancer, heart disease and
other diseases.
-
- AUTOIMMUNE DISEASE
-
- "The small amounts of Neu5Gc in normal tissues also
raise the possibility that anti-Neu5Gc antibodies are involved in autoimmunity,"
the researchers said.
-
- Autoimmune disease occur when the body mistakenly attacks
healthy tissue and include type-1 or juvenile diabetes and some types of
arthritis. "In this regard, it is interesting that vegetarian diet
has been suggested to improve rheumatoid arthritis," they wrote.
-
- But much research has focused on the fat content of animal
fat or byproducts of cooking meat as the cause of disease.
-
- Varki's collaborator Dr. Elaine Muchmore developed an
antibody -- an immune system targeting protein -- that would hook onto
Neu5Gc. The team found Neu5Gc in human tumor samples and to a much lower
degree in healthy tissue.
-
- More tests showed that most people had made their own
antibodies that recognized Neu5Gc, and thus could potentially initiate
an inflammatory immune response.
-
- Varki and two colleagues drank Neu5Gc purified from pork
sources, and the molecule showed up in their urine, blood, hair and saliva.
-
- "We need to find out if there is any association
between the presence of Neu5Gc and/or the anti-Neu5Gc antibodies with any
disease," Varki said. "This will require large-scale population
studies."
-
- In some cases the human immune response was similar to
that seen when people are exposed to another animal molecule, this one
a cell surface molecule called alpha galactose.
-
- Varki noted that the molecule is almost certainly not
immediately toxic to people.
-
- "Meat eating has certainly been a feature of human
ancestors for many hundreds of thousands of years," he said.
-
- "Thus, it is indeed possible that humans have developed
some kind of tolerance or indifference to Neu5Gc. However, most humans
are continuing to make antibodies against Neu5Gc."
-
- It could be that the damage only builds up over years
-- and that as people live longer, the consequences make themselves felt.
-
- "However, we are now living longer and the question
arises whether the gradual accumulation of Neu5Gc and the simultaneous
presence of antibodies against could be involved in some diseases of later
life," he said.
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