UCSD. US: Neu5Gc, a non-human sugar found in red meat, promotes inflammation and cancer progression in rodentsWhile
people who eat a lot of red meat are known to be at higher risk for
certain cancers, other carnivores are not, prompting researchers at the
University of California, San Diego School of Medicine to investigate
the possible tumor-forming role of a sugar called Neu5Gc, which is
naturally found in most mammals but not in humans.
In a study published in the Dec. 29 online early edition of the Proceedings of the National Academy of Sciences,
the scientists found that feeding Neu5Gc to mice engineered to be
deficient in the sugar (like humans) significantly promoted spontaneous
cancers. The study did not involve exposure to carcinogens or
artificially inducing cancers, further implicating Neu5Gc as a key link
between red meat consumption and cancer.
“Until now, all of our evidence linking Neu5Gc to cancer was
circumstantial or indirectly predicted from somewhat artificial
experimental setups,” said principal investigator Ajit Varki, MD,
Distinguished Professor of Medicine and Cellular and Molecular Medicine
and member of the UC San Diego Moores Cancer Center. “This is the first
time we have directly shown that mimicking the exact situation in humans
— feeding non-human Neu5Gc and inducing anti-Neu5Gc antibodies —
increases spontaneous cancers in mice.”
Varki’s team first conducted a systematic survey of common foods.
They found that red meats (beef, pork and lamb) are rich in Neu5Gc,
affirming that foods of mammalian origin such as these are the primary
sources of Neu5Gc in the human diet. The molecule was found to be
bio-available, too, meaning it can be distributed to tissues throughout
the body via the bloodstream.
The researchers had previously discovered that animal Neu5Gc can be
absorbed into human tissues. In this study, they hypothesized that
eating red meat could lead to inflammation if the body’s immune system
is constantly generating antibodies against consumed animal Neu5Gc, a
foreign molecule. Chronic inflammation is known to promote tumor
formation.
To test this hypothesis, the team engineered mice to mimic humans in
that they lacked their own Neu5Gc and produced antibodies against it.
When these mice were fed Neu5Gc, they developed systemic inflammation.
Spontaneous tumor formation increased fivefold and Neu5Gc accumulated in
the tumors.
“The final proof in humans will be much harder to come by,” Varki
said. “But on a more general note, this work may also help explain
potential connections of red meat consumption to other diseases
exacerbated by chronic inflammation, such as atherosclerosis and type 2
diabetes.
“Of course, moderate amounts of red meat can be a source of good
nutrition for young people. We hope that our work will eventually lead
the way to practical solutions for this catch-22.”
Study co-authors include Annie N. Samraj, Oliver M. T. Pearce, Heinz
Läubli, Alyssa N. Crittenden, Anne K. Bergfeld, Kalyan Banda,
Christopher J. Gregg, Andrea E. Bingman, Patrick Secrest, Sandra L. Diaz
and Nissi M. Varki, all at UC San Diego School of Medicine.
This research was funded, in part, by the Ellison Medical Foundation,
the National Cancer Institute (grant R01CA38701), a Samuel and Ruth
Engelberg Fellowship from the Cancer Research Institute and a Swiss
National Science Foundation Fellowship.
Disclosure: Ajit Varki and Nissi Varki are
co-founders and have equity interest in SiaMab Therapeutics, Inc., a
biotech company with an interest in Neu5Gc and anti-Neu5Gc antibodies.
In addition, Ajit Varki is a member of SiaMab Therapeutics, Inc.’s Board
of Directors and is a Scientific Advisor to the company. The terms of
this arrangement have been reviewed and approved by the University of
California, San Diego in accordance with its conflict of interest
policies.