The glycosylation of AGP and its associations with the binding to methadone.

Methadone remains the most common form of pharmacological therapy for opioid dependence; however, there is a lack of explanation for the reports of its relatively low success rate in achieving complete abstinence. One hypothesis is that in vivo binding of methadone to the plasma glycoprotein alpha-1-acid glycoprotein (AGP), to a degree dependent on the molecular structure, may render the drug inactive. This study sought to determine whether alterations present in the glycosylation pattern of AGP in patients undergoing various stages of methadone therapy (titration < two weeks, harm reduction < one year, long-term > one and a half years) could affect the affinity of the glycoprotein to bind methadone. The composition of AGP glycosylation was determined using high pH anion exchange chromatography (HPAEC) and intrinsic fluorescence analysed to determine the extent of binding to methadone. The monosaccharides galactose and N-acetyl-glucosamine were elevated in all methadone treatment groups indicating alterations in AGP glycosylation. AGP from all patients receiving methadone therapy exhibited a greater degree of binding than the normal population. This suggests that analysing the glycosylation of AGP in patients receiving methadone may aid in determining whether the therapy is likely to be effective.

The analysis of glycosylation: a continued need for high pH anion exchange chromatography.

An appreciation of the structures of the oligosaccharide chains which become attached to biomolecules (the process known as glycosylation), and their relevance to the biological function of the molecule concerned, has progressed rapidly in recent years with developments in site-selective protein glycosylation, oligosaccharide synthesis and in vivo targeting of oligosaccharides. These developments have necessitated the parallel development of effective analytical tools for the determination of the structures of glycosylation. The conclusion of studies in the 1980s and 1990s was that high pH anion exchange chromatography (HPAEC) was the most effective HPLC mode for the analysis of glycosylation. It allowed the fractionation of complex mixtures of monosaccharides or oligosaccharides, the latter in terms of charge, size, composition, anomerity and intra-chain linkages. This review reinvestigates whether HPAEC still appears to offer the most effective means of analysing glycosylation.