No abstract

No abstract

N-linked oligosaccharides obtained from total serum of mice with implanted head and neck tumors were analyzed and compared with those from control samples of healthy mice. Methods used include a combination of a derivatization procedure with phenylhydrazine (PHN) and analysis by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). Oligosaccharides were enzymatically released from total serum with PNGaseF and purified by high-performance liquid chromatography (HPLC) on a reversed-phase column. Mass spectra contained ion peaks of labeled oligosaccharides and MS/MS experiments provided useful data for the structural elucidation of these compounds. More than 40 N-glycans with compositions characteristic of high-mannose, hybrid, complex, neutral, and sialylated structures were identified in the serum of tumoral mice. Significant differences between samples were observed with respect to the abundances of high mannose and hybrid glycans. These oligosaccharides showed higher relative intensities in the spectra obtained from the cancer sera. Complex sialylated oligosaccharides had similar abundances in both types of sera, with the exception of fucosylated biantennary disialylated oligosaccharide, which was mostly detected with lower abundance in control samples. In the MALDI spectra, several minor species corresponded to uncommon carbohydrates. These structures have been investigated in detail by MS/MS. Among these novel glycoforms, a few sialylated oligosaccharides without a free reducing end were identified. Also, glycans with an extra 60 u were observed and likely feature the presence of a 2-acetamido-2-deoxyoctose residue attached on antennae of 3-or 6-linked mannose. . It has been recognized that altered glycosylation is an universal feature of living cells and several studies have demonstrated that the changes in cellular glycosylation profiles can be also related to aggressive cancer cell behavior, such as tumor cell invasion and metastasis [2][3][4][5][6][7][8]. As cancer cells can produce oligosaccharides that are significantly different from those in normal cells, comparative studies between glycoprotein carbohydrates produced by malignant cells and normal cells may provide useful information for diagnosis, prognosis, and immunotherapy of tumors [9].Mass spectrometry (MS) has been used extensively as the most sensitive method for the analysis of carbohydrate molecules [10 -14]. Moreover, modern MS instruments allow the measurement of unseparated mixtures, and make possible the identification of trace amounts of glycans in biological materials [15]. Nonetheless, biochemical analysis of carbohydrates is generally complicated, not only because of their lower concentration relative to with proteins, but also because of the structural diversity of molecules, anomericity, linkage positions, and branching patterns of monosaccharides. Moreover, carboxylic groups cause sialylated oligosaccharides to ionize with less efficiency than neutral oligosaccharides, making MS analysis of glycans more difficu...

No abstract