Perhaps because of this evolutionary pressure, different species can have different kinds of sialic acids. In mammals, there are two major types: Neu5Gc and Neu5Ac, which differ by one oxygen atom. Humans have only the "Ac" version; other mammals also have the "Gc" version. This human-specific change likely happened two or three million years ago, said Varki, who also co-directs the Center for Academic Research Training in Anthropogeny at UCSD. "No one knows why, but this may have been selected by an infectious disease, like malaria"
Although the Ac and Gc versions are very similar in structure, the single oxygen atom difference is recognized by the human immune system, which develops antibodies to the non-human sugar.
And therein lies the problem, said Varki. Antibodies are naturally circulating proteins that identify and neutralize invaders, such as viruses or bacteria. Part of that process involves inflammation, the host's attempt to kill and remove invasive cells or tissues perceived to be harmful. If there is a strong antibody response to diet-incorporated Neu5Gc, the resulting inflammation could cause harm to the person. This may partially explain associations between certain foods and increased risk of diseases associated with inflammation, such as cancer and heart attacks diseases that are rare in other primates.
The problem may also be exacerbated by the presence of Neu5Gc in drugs developed through recombinant biotechnology, some of which are actually used to treat inflammatory disorders. Neu5Gc cont
|Contact: Scott LaFee|
University of California - San Diego