Neu5Gc: A Sugar Molecule That May Not Be So Sweet
Neu5Gc: A Sugar Molecule That May Not Be So Sweet
Parents often complain that the food their children eat does not "stick with them." That might seem like an advantage if they were aware of what you're about to read. Recent research shows specific constituents of certain foods go beyond sticking to us. These substances are more like intruders, uninvited guests that can wreak havoc on our bodies instead of nourishing them.
What's at Steak
This new experimental evidence demonstrates, perhaps for the first time, how and why certain foods can promote cancer growth. Red meat was identified as one of those foods.
Numerous epidemiological studies support the findings. Populations who commonly consume significant amounts of meat, especially red, have reported a higher incidence of certain cancers, compared to populations whose diet is predominantly fish, vegetables, fruit and legumes. But what, exactly, is the connection between red meat and cancer?
Not-so-sweet Molecules
For some time, scientists studying cancerous tissues have observed that cells of malignant growths contain abnormal sugar and sugar-like molecules, which extrude on the cell's surface. One of these, a sialic acid sugar called Neu5Gc, is normally present in most mammals but lacking in humans, due to the absence of a gene necessary for its synthesis.
In spite of the human inability to make the sialic acid sugar, Neu5Gc, its presence has been reported in human tumors, including colon carcinomas, retinoblastomas, breast cancers, and melanomas. So the team of investigators, who undertook the recent research, asked: where does the Neu5Gc originate?
Their study suggests the probable source of the Neu5Gc is diet, more specifically foods containing high levels of this sialic acid sugar, among them red meat and milk products. Both of these foods also have a significant association with cancer risk.
Exception and Explanation
If diet is the key, why do some red-meat/milk-product consumers seem to be disease-free? Blood analyses detected antibodies to the sialic acid sugar, indicating its presence. The key determinant seemed to be the absence of precancerous cells.
This observation led to further in vitro cancer cell study. Although the researchers didn't conclusively demonstrate that Neu5Gc causes cancer, they do present strong evidence that Neu5Gc stimulates pre-existing cancerous growth through the following processes:
The Neu5Gc on the cell's surface is recognized as a foreign substance. (Remember, humans don't produce it.) In response, the immune system is mildly activated in an attempt to destroy it. As with many immune reactions, there is associated inflammation. Certain growth factors are secreted by the invading inflammatory cells.
One of these, VEGF, initiates the growth of new blood vessels, which function as conduits, bringing more nutrition to the cells in the area, both malignant and normal. In other words, the foreign Neu5Gc sugar, adhering to the exterior of the tumor cell, indirectly feeds the cancer.
Immune System Malfunction?
Our immune system is supposed to protect us from disease, including cancer. However, it seems to be most effective when it defends with rapid and overwhelming force. On the other hand, an immune response resulting in chronic, low-grade inflammation has long been associated with many diseases (diabetes, heart disease, Alzheimer's disease, etc.), most prominently cancer.
It appears, from the study summarized here and others, that a mild or chronic inflammation is just what the malignant cell requires to grow. This hypothesis is also upheld by studies showing decreased cancer risk in people who take non-steroidal, anti-inflammatory drugs such as aspirin and the COX-2 inhibitors.
Experiments with mice, exhibiting tumors bearing the Neu5Gc sugar, corroborated the effectiveness of anti-inflammatory drugs. Tumor growth increased after the mice were injected with the antibody to Neu5Gc. However, if the animals were treated with an anti-inflammatory agent then injected with the antibody, the stimulatory effect was largely eliminated.
Which brings us to the question of the relationship between Neu5Gc, its antibody and cancer. Our cousins, the chimpanzees, may actually hold another clue. Unlike humans, chimps can synthesize this sialic acid sugar. Since it is not foreign to their immune systems, antibodies aren't produced. Interestingly, chimpanzees rarely develop the types of cancers associated with Neu5Gc-bearing tumors.
Eat No Evil
Although the research results described here are impressive, they are not conclusive. Still, humans may benefit from mimicking the chimps' condition. The less Neu5Gc we ingest, the fewer antibodies and related chronic low-grade inflammation will be produced.
In other words, it may be prudent to consume modest amounts of red meat and milk, favoring other protein sources (fish, poultry, legumes) instead. By simply changing our food choices, we could reduce the incidence of certain cancers as well as other diseases associated with inflammation.
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