The Serum Immunoglobulin G Glycosylation Signature of Gastric Cancer.

Biomarkers may facilitate detection of gastric cancer at an earlier stage and reduce mortality. Here we sought to determine if the glycosylation profile of serum immunoglobulin G (IgG) could distinguish patients with non-atrophic gastritis (NAG), duodenal ulcer (DU) and gastric cancer (GC). Serum IgG was released and analyzed using nano-LC-TOF mass spectrometry. Statistically significant false discovery rate (FDR)-adjusted p-values were observed for 18 glycans, eight that differed significantly between NAG and GC, three that distinguished NAG from DU, and eight that differed between DU and GC. The IgG glycosylation signature may be useful as a predictive marker for gastric cancer.

Serum glycan signatures of gastric cancer.

Glycomics, a comprehensive study of glycans expressed in biologic systems, is emerging as a simple yet highly sensitive diagnostic tool for disease onset and progression. This study aimed to use glycomics to investigate glycan markers that would differentiate patients with gastric cancer from those with nonatrophic gastritis. Patients with duodenal ulcer were also included because they are thought to represent a biologically different response to infection with Helicobacter pylori, a bacterial infection that can cause either gastric cancer or duodenal ulcer. We collected 72 serum samples from patients in Mexico City that presented with nonatrophic gastritis, duodenal ulcer, or gastric cancer. N-glycans were released from serum samples using the generic method with PNGase F and were analyzed by matrix-assisted laser desorption/ionization Fourier transform-ion cyclotron resonance mass spectrometry. The corresponding glycan compositions were calculated based on accurate mass. ANOVA-based statistical analysis was performed to identify potential markers for each subgroup. Nineteen glycans were significantly different among the diagnostic groups. Generally, decreased levels of high-mannose-type glycans, glycans with one complex type antenna, bigalactosylated biantennary glycans, and increased levels of nongalactosylated biantennary glycans were observed in gastric cancer cases. Altered levels of serum glycans were also observed in duodenal ulcer, but differences were generally in the same direction as gastric cancer. Serum glycan profiles may provide biomarkers to differentiate gastric cancer cases from controls with nonatrophic gastritis. Further studies will be needed to validate these findings as biomarkers and identify the role of protein glycosylation in gastric cancer pathology.

Biomarkers of Helicobacter pylori-associated gastric cancer.

Helicobacter pylori-associated gastric cancer is a major cause of morbidity and mortality worldwide, and is predicted to become even more common in developing countries as the population ages. Since gastric cancer develops slowly over years to decades, and typically progresses though a series of well-defined histologic stages, cancer biomarkers have potential to identify asymptomatic individuals in whom surgery might be curative, or even those for whom antibiotics to eradicate H. pylori could prevent neoplastic transformation. Here we describe some of the challenges of biomarker discovery, summarize current approaches to biomarkers of gastric cancer, and explore some recent novel strategies.

Functional plasticity in the type IV secretion system of Helicobacter pylori.

Helicobacter pylori causes clinical disease primarily in those individuals infected with a strain that carries the cytotoxin associated gene pathogenicity island (cagPAI). The cagPAI encodes a type IV secretion system (T4SS) that injects the CagA oncoprotein into epithelial cells and is required for induction of the pro-inflammatory cytokine, interleukin-8 (IL-8). CagY is an essential component of the H. pylori T4SS that has an unusual sequence structure, in which an extraordinary number of direct DNA repeats is predicted to cause rearrangements that invariably yield in-frame insertions or deletions. Here we demonstrate in murine and non-human primate models that immune-driven host selection of rearrangements in CagY is sufficient to cause gain or loss of function in the H. pylori T4SS. We propose that CagY functions as a sort of molecular switch or perhaps a rheostat that alters the function of the T4SS and "tunes" the host inflammatory response so as to maximize persistent infection.

Modification of gastric mucin oligosaccharide expression in rhesus macaques after infection with Helicobacter pylori.

BACKGROUND & AIMS: Helicobacter pylori attaches to mucin oligosaccharides that are expressed on host gastric epithelium. We used the rhesus macaque model to characterize the effect of H. pylori infection on gastric mucin oligosaccharides during acute and chronic infection. METHODS: Specific pathogen (H. pylori)-free rhesus macaques were inoculated with H. pylori J166. Biopsy specimens of the gastric antrum were obtained 2 and 4 weeks before and 2, 8, and 24 weeks after infection with H. pylori. O-linked mucin oligosaccharides were released from gastric biopsy samples by beta-elimination and profiled by matrix-assisted laser desorption/ionization mass spectrometry. Similar studies were performed on gastric biopsy samples from H. pylori-infected and uninfected humans. Formalin-fixed, paraffin-embedded sections of rhesus antrum biopsy samples were stained with H&E, periodic acid-Schiff stain, and antibody to MUC5AC, the predominant mucin expressed in the stomach. RESULTS: H. pylori-induced gastritis was accompanied by an acute and dramatic decrease in diversity and relative abundance of O-linked mucin oligosaccharides in the rhesus stomach, which largely recovered during the 24-week observation period. These variations in oligosaccharide abundance detected by mass spectrometry were reflected by changes in periodic acid-Schiff-positive material and expression of MUC5AC over time. Relatively few differences were seen in gastric mucin oligosaccharide composition between H. pylori-infected and uninfected patients, which is consistent with the results in rhesus macaques because infection occurs in childhood. CONCLUSIONS: Acute H. pylori infection is accompanied by a dramatic but transient loss in mucin oligosaccharides that may promote colonization and persistence.

Method for profiling mucin oligosaccharides from gastric biopsies of rhesus monkeys with and without Helicobacter pylori infection.

A method for in vivo analysis of gastric mucin oligosaccharides was developed and applied to rhesus monkeys with and without Helicobacter pylori infection. Mucin-type O-linked oligosaccharides were directly released by reductive beta-elimination from gastric biopsies from rhesus monkeys. The released oligosaccharides were structurally characterized by matrix-assisted laser desorption/ionozation and electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. A diverse profile of neutral and acidic oligosaccharides was observed with these techniques. The most predominant core structure detected in all of the samples at relatively high abundance corresponded to core 2 (2HexNAc-1Hex, m/z = 611.227). The spectra generated from H. pylori-infected monkey samples showed fewer oligosaccharides collectively. Peaks corresponding to 1HexNAc-1Hex (m/z = 408.148) and 2HexNAc (m/z = 449.174), which most likely represent core structures, were absent in all infected monkeys studied, although present in all uninfected monkeys. Unsupervised cluster analysis demonstrated clear differences between the peaks detected in uninfected and naturally infected monkey samples. The results suggest that H. pylori infection is associated with lower relative abundance of oligosaccharides and loss of mucin-type core structures. This method can be applied to characterize the glycans associated with the mucin lining of live animals and allows for repeated analysis of the same animal over the course of infection.