Sialic acids are a family of 9-carbon carboxylated sugars, where different substitutions of the backbone define over 30 members. Biological roles of these substitutions have been missed until recently because of their low abundance and lability to conventional isolation/purification methods. This new approach characterizes sialic acids using electrospray ionization-mass spectrometry (ESI-MS) to monitor the HPLC separation of their DMB (1,2-diamino-4,5-methylenedioxy-benzene) derivatives (quinoxalinones). A combination of retention times and spectra characteristics allows definition of the type and position of the various substituents. This approach requires no previous purification, involving a simple derivatization reaction followed by direct injection on the microbore HPLC column. A complete spectrum, including molecular ions and CAD fragments of a sialic acid quinoxalinone, is obtained by injecting 10-20 pmol of the compound. Individual quinoxalinones can be purified by regular RP-HPLC and analyzed by direct-injection ESI-MS or LSIMS. Using this approach, we identified 28 different sialic acids, including the following new species: Neu5Gc9Lt (BSM), anhydro derivatives of Neu5Ac other than the 4,8-anhydro (horse serum hydrolyzates), KDN5(7)Ac and KDN5(7),9Ac2 (amphibian Pleurodeles waltl), four isomers of Neu5Gc8MexAc and three anhydro derivatives of Neu5Gc8Me (glycolipids of the starfish Pisaster brevispinus), and Neu5Ac8S (in addition to Neu5Gc8S, in the glycolipids of the sea urchin Lovenia cordiformis). Results show the usefulness of LC-ESI-MS to study sialic acid diversity, and identification of small amounts of unexpected sialic acids or new members of their family.

Bronchial mucins were purified from the sputum of 14 patients suffering from cystic fibrosis and 24 patients suffering from chronic bronchitis, using two CsBr density-gradient centrifugations. The presence of DNA in each secretion was used as an index to estimate the severity of infection and allowed to subdivide the mucins into four groups corresponding to infected or noninfected patients with cystic fibrosis, and to infected or noninfected patients with chronic bronchitis. All infected patients suffering from cystic fibrosis were colonized by Pseudomonas aeruginosa. As already observed, the mucins from the patients with cystic fibrosis had a higher sulfate content than the mucins from the patients with chronic bronchitis. However, there was a striking increase in the sialic acid content of the mucins secreted by severely infected patients as compared to noninfected patients. Thirty-six bronchial mucins out of 38 contained the sialyl-Lewis x epitope which was even expressed by subjects phenotyped as Lewis negative, indicating that at least one alpha1,3 fucosyltransferase different from the Lewis enzyme was involved in the biosynthesis of this epitope. Finally, the sialyl-Lewis x determinant was also overexpressed in the mucins from severely infected patients. Altogether these differences in the glycosylation process of mucins from infected and noninfected patients suggest that bacterial infection influences the expression of sialyltransferases and alpha1,3 fucosyltransferases in the human bronchial mucosa.

There is increasing evidence that inflammation may affect glycosylation and sulfation of various glycoproteins. The present study reports the effect of tumor necrosis factor ␣ (TNF-␣), a proinflammatory cytokine, on the glycosyl-and sulfotransferases of the human bronchial mucosa responsible for the biosynthesis of Lewis x epitope and of its sialylated and/or sulfated derivatives, which are expressed in human bronchial mucins. Fragments of macroscopically normal human bronchial mucosa were exposed to TNF-␣ at a concentration of 20 ng/ml. TNF-␣ was shown to increase ␣1,3-fucosyltransferase activity as well as expression of the two ␣1,3-fucosyltransferase genes expressed in the human airway, FUT3 and FUT4. It had no influence on ␣1,2-fucosyltransferase activity or FUT2 expression. It also increased ␣2,3-sialyltransferase activity and the expression of ST3Gal-III and, more importantly, ST3Gal-IV and both N-acetylglucosamine 6-O-sulfotransferase and galactose 3-O-sulfotransferase. These results are consistent with the observation of oversialylation and increased expression sialyl-Lewis x epitopes on human airway mucins secreted by patients with severe lung infection such as those with cystic fibrosis, whose airways are colonized by Pseudomonas aeruginosa. However, other cytokines may also be involved in this process.

Human respiratory mucins consist of a family of glycoproteins with different peptides in which glycosylation, the major post-translational phenomenon, is responsible for about 70 to 80% of the weight of these molecules. This glycosylation generates a remarkable diversity of O-glycosidically linked carbohydrate chains, which are expressed as several hundreds of different chains in a single person. These chains, which can vary from one to about 20 sugars, may be neutral, sialylated, or sulfated. They bear multiple epitopes. Some antigenic determinants such as ABO, Leb antigens in secretor individuals, Lea, or X or Y antigens have been identified. There is increasing evidence that, among other functions, this diversity of chains allows many interactions with microorganisms and may be an important factor in maintaining the sterility of the respiratory tree. In certain pathologic situations such as cystic fibrosis, which is associated with colonization by Pseudomonas aeruginosa, the hypothesis of an alteration of this interaction is open.