Edinburgh Napier University

  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.