Identification of β1-3 galactosylglucose-core free-glycans in human urine

Combination of urinary free-glycan markers for the diagnosis of various malignant tumors

Many urinary free-glycan markers were identified in our previous studies. Here, the clinical utility of these markers was examined. Urine samples taken from 120 healthy subjects and 503 patients with various malignant tumors were analyzed. Four lactose-core glycans containing N-glycolylglucosamine (GlcNGc) were synthesized and used as internal standards (ISs). Free-glycans were isolated using a two-step column purification procedure, pyridylaminated, and subjected to LC-selected reaction monitoring. Assay validation was performed using four ISs and eight reference glycans. Twelve markers composed of three sialyl lactose-core glycans, three sulfated glycans, four Gn1-core free-N-glycans, and two glycans with unusual structures were selected to investigate their effectiveness for cancer diagnosis. Markers were simultaneously measured and the relative area ratio (marker/IS) quantified. This method was shown to be accurate and precise by repeated analysis of calibrators and quality control samples in urine. Receiver operating characteristic curve analyses revealed that individual markers were not sufficient for highly accurate diagnosis. However, a combination of four markers resulted in higher area under curves of 0.910, 0.867, and 0.914 for gastric, colorectal, and pancreatic cancers, respectively. Moreover, levels of these markers were elevated in various other malignancies. These analyses demonstrated high clinical utility of the free-glycan markers.

Occurrence of free glycans in salmonid serum

Free N-glycans (FNGs) are oligosaccharides that are structurally related to N-linked glycans, and are widely found in nature. The mechanisms responsible for the formation and degradation of intracellular FNGs are well characterized in mammalian cells. More recent analysis in mammalian sera shows that there are various types of extracellular free glycans, including FNGs. However, it is unknown whether these free glycans are widely distributed in vertebrates. In this study, we investigated the occurrence of free glycans in salmonid serum. We found that it contained sialyl or neutral FNGs and sialyl lactose/N-acetyllactosamine (LacNAc)-type glycans, which was consistent with that found in mammalian sera. Many of the structures of FNGs matched those of N-glycans from serum glycoproteins. This study revealed that various types of free glycans are present in fish serum, demonstrating their wide occurrence among vertebrates.

Rat hepatocytes secrete free oligosaccharides

We recently established a method for the isolation of serum-free oligosaccharides, and characterized various features of their structures. However, the precise mechanism for how these glycans are formed still remains unclarified. To further investigate the mechanism responsible for these serum glycans, here, we utilized rat primary hepatocytes to examine whether they are able to secrete free glycans. Our findings indicated that a diverse array of free oligosaccharides such as sialyl/neutral free N-glycans (FNGs), as well as sialyl lactose/LacNAc-type glycans, were secreted into the culture medium by primary hepatocytes. The structural features of these free glycans in the medium were similar to those isolated from the sera of the same rat. Further evidence suggested that an oligosaccharyltransferase is involved in the release of the serum-free N-glycans. Our results indicate that the liver is indeed secreting various types of free glycans directly into the serum.

Occurrence of a D-arabinose-containing complex-type free-N-glycan in the urine of cancer patients

Urinary free-glycans are promising markers of disease. In this study, we attempted to identify novel tumor markers by focusing on neutral free-glycans in urine. Free-glycans extracted from the urine of normal subjects and cancer patients with gastric, colorectal, pancreatic and bile duct were fluorescently labeled with 2-aminopyridine. Profiles of these neutral free-glycans constructed using multidimensional high performance liquid chromatography separation were compared between normal controls and cancer patients. The analysis identified one glycan in the urine of cancer patients with a unique structure, which included a pentose residue. To reveal the glycan structure, the linkage fashion, monosaccharide species and enantiomer of the pentose were analyzed by high performance liquid chromatography and mass spectrometry combined with several chemical treatments. The backbone of the glycan was a monoantennary complex-type free-N-glycan containing β1,4-branch. The pentose residue was attached to the antennal GlcNAc and released by α1,3/4-l-fucosidase. Intriguingly, the pentose residue was consistent with d-arabinose. Collectively, this glycan structure was determined to be Galβ1-4(d-Araβ1-3)GlcNAcβ1-4Manα1-3Manβ1-4GlcNAc-PA. Elevation of d-arabinose-containing free-glycans in the urine of cancer patients was confirmed by selected reaction monitoring. This is the first study to unequivocally show the occurrence of a d-arabinose-containing oligosaccharide in human together with its detailed structure.