During the acute phase response (APR) to tissue injury or infection, the liver is responsible for the level of mediators such as cytokines required at the site of inflammation and providing the essential components for wound healing and tissue repair. Additionally there are substantial alterations in the expression of plasma proteins of hepatic origin such as alpha-1-acid glycoprotein (AGP). The APR also results in alterations to the branching, sialylation and fucosylation of the oligosaccharide chains of AGP. This study investigated whether liver damage could be correlated with changes in AGP glycosylation in groups of patients with various liver diseases (alcoholic liver disease, hepatitis B, hepatitis C, cirrhosis). Hyperfucosylation occurred in all cases of liver disease, although the hepatitis B and C samples showed a more significant increase in comparison with the others. Additionally N-acetylgalactosamine (GalNAc) was detected in the majority of the hepatitis C samples, which was unexpected since this monosaccharide is not a usual component of the N-linked oligosaccharide chains. It was also determined by concanavalin (con) A chromatography that there is a shift towards the increased branching of the oligosaccharide chains in inflammatory liver diseases compared to normal serum.
Alpha-1-acid glycoprotein (AGP) is a plasma glycoprotein produced by the liver that undergoes increased production and altered glycosylation in several physiological and pathological conditions including rheumatoid arthritis. To date, although present in the synovial fluid of rheumatoid arthritis patients, there has been no evidence for the separate extra-hepatic production of AGP. This study indicates that there could be a localized production of AGP in rheumatoid synovial fluid by demonstrating that the glycosylation patterns of AGP differed between the serum and synovial fluid in the same rheumatoid patient. Serum AGP was largely composed of fucosylated tri- and tetra-antennary oligosaccharide chains while the synovial fluid contained mainly bi-antennary chains that were fucosylated to a lesser extent. This structural heterogeneity of glycosylation resulted in functional diversity; serum but not synovial AGP is able to inhibit binding to the cell adhesion molecule E-selectin through expression of antigen sialyl Lewis X.
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