Sialic acids (Sia) are a family of about 50 derivatives of neuraminic acid, an acid amino sugar with a chain of 9 carbon atoms. Sia occur in body fluids, especially in blood, in mucous secretions and in cell membranes. As components of sugar-protein and sugar-lipid compounds (glycoconjugates) they cover all cells of higher animals and man with an electro-negatively charged coat and exert a variety of different biological functions, among which the regulation of cellular communications prevails.
In the developmental history, Sia regularly occur since the echinoderms.However, they sporadically were also found in lower animals including developing insects, and Sia genes even occur in plants. These monosaccharides are frequently expressed in microorganisms, too. It is supposed that Sia contributed successfully to the development of higher animals including man.
The quantity and quality of sialic acid is tissue- and organ-specific. A change in the amount of sialic acids on the cell surface, or in organs and tissues, or a disturbance of the sialic acid metabolism is very dangerous to the health of inviduals. For example, a reduction of sialic acids in red blood cells leads to their being entrapped in liver and spleen and thus to anemia. On the other hand, sialic acids may be increased in cancerous tissues, which can stimulate tumor growth and facilitate the formation of metastases. Sia also play a role in inflammation caused by viruses or other microorganisms which use sialic acids to attach to cells and to infect them. An inhibitor of influenza virus sialidase was created which is a derivative of natural Sia and stops virus spreading. This drug has the potential to fight against the threat of flu. Sialic acids are involved in immunological reactions, in signalling, apoptosis, ion transport, growth, differentiation and ageing. Correspondingly, their pathophysiological significance cannot be underestimated.
Exploration of the role of sialic acids and the regulation of their expression will thus lead to the early diagnosis of diseases and their successful treatment. Sialopharmacy is an upcoming area, not only in the treatment of inflammation, but, for example, also in transplantation medicine, protectin of epithelia from microbial attack (innate immunity), and the design of more potent peptide hormones, e.g. erythropoietin.

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Biochemisches Institut der Christian-Albrechts-Universität zu Kiel, Olshausenstrasse 40, D-24098 Kiel
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