A sugar that naturally occurs in animals but not humans could be the reason why people are at higher risk for cancer when they consume red meat, researchers at the UC San Diego School of Medicine reported Monday.
The scientists found that feeding the sugar Neu5Gc to mice engineered to be deficient in it — like humans — significantly promoted spontaneous cancers. Their study did not involve exposure to carcinogens or artificially inducing cancers, further implicating Neu5Gc as a key link between red meat consumption and cancer, according to UCSD.
"Until now, all of our evidence linking Neu5Gc to cancer was circumstantial or indirectly predicted from somewhat artificial experimental setups," said Dr. Ajit Varki, a professor of medicine and cellular and molecular medicine. "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."
Red meats like beef, pork and lamb are rich in that type of sugar, according to the Varki, a co-founder of SiaMab Therapeutics Inc., a biotech with an interest in Neu5Gc and anti-Neu5Gc antibodies.
The researchers had previously discovered that animal Neu5Gc can be absorbed into human tissues.
In the newest study — published in the early edition of Proceedings of the National Academy of Sciences — 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 their theory, the scientists engineered mice to mimic humans in that they lacked their own Neu5Gc and produced antibodies against it. When the mice were fed Neu5Gc, they developed systemic inflammation, spontaneous tumor formation increased fivefold and Neu5Gc accumulated in the tumors, according to Varki.
"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."
Varki said moderate amounts of red meat can be a source of good nutrition for young people, so the data could lead to solutions for what he called a "catch-22."
The research was funded, in part, by the Ellison Medical Foundation, the National Cancer Institute, a Samuel and Ruth Engelberg Fellowship from the Cancer Research Institute and a Swiss National Science Foundation fellowship.
