Quantitative analysis of site-specific N-glycans on sera haptoglobin β chain in liver diseases

The site-specific characterization of N-glycans in glycoproteins with the potential of clinical application is important. In our previous report, the overall N-glycans of sera haptoglobin (Hp) beta chain were found to be different in liver diseases. Hp beta chain contains four potential sites of N-glycosylation. In this study, we investigated the potential change of N-glycans on Hp beta chain in a site-specific fashion. Sera Hp beta chain in healthy individuals as well as patients with hepatitis B virus (HBV), liver cirrhosis (LC) and hepatocellular carcinoma (HCC) were purified, digested and subjected to liquid chromatography-electrospray ionization-higher energy collision dissociation mass spectrometry, which allowed identification and structure determination of the glycopeptide, as well as the relative quantification of glycans present on each glycopeptide. The quantitative results revealed that the sialylation of NLFLN(207)HSEN(211)ATAK and the fucosylated structure at all glycopeptides increased significantly in LC and HCC patients compared with those in HBV patients and healthy individuals. A set of different N-glycan patterns of Hp beta chain in various liver diseases has been determined. Thus, the sialylated and fucosylated glycoforms of Hp beta chain might be related to early hepatocarcinogenesis and also might be useful as novel differential markers for LC and HCC patients.