Molecular and cellular mechanisms of profile changes of charged blood plasma free oligosaccharides in myeloproliferative disorders

Abstract

Free oligosaccharides (FOS) are unbound to proteins or lipids structural analogs of their glycans. FOS appear as by-products of endoplasmic reticulum synthesis, cell control folding with endoplastic reticulum-associated degradation and lysosomal/endosomal breakdown of glycoconjugates. They may be either neutral or negatively charged depending on the way of their formation. Charged FOS appear during degradation of glycoconjugates in the lysosomal/endosomal system and are natural substrates for lysosomal sialidase-1. FOS are formed inside the cell but some of them can get into the extracellular space, and then into the blood and urine, where both neutral and charged structures were found. Secretion of charged FOS outside of the cell is most likely to be caused by the lysosomal exocytosis. The activity of neuraminidase-1 is known to be connected with the intensity of the lysosomal exocytosis. In our previous studies, it was found that HPLC-profiles of charged FOS were specifically changed in acute and chronic myeloproliferative blood disorders. The objective of this work was to analyze the molecular and cellular mechanisms of these changes and to test the hypothesis of their association with the activity change of lysosomal neuraminidase-1. Plasma samples of patients with acute and chronic leukaemia – polycytaemia vera, chronic idiopathic myelofibrosis, hypoplastic anaemia, myelodysplastic syndrome with transformation, acute lymphatic and acute myelomonocytic leukaemia – were collected for investigation. Plasma samples of practically healthy volunteers were obtained and used for comparison. After plasma deproteinization and FOS purification the oligosaccharides were labelled with anthranilic acid (2-AA), separated into the neutral and charged fractions with QAE Sephadex (Q25-120) chromatography and analysed using high-performance liquid chromatography (HPLC). Glucose unit values were determined following comparison with a 2-AA-labelled glucose oligomer ladder derived from a partial hydrolysate of dextran as an external standard. The data were collected and processed using Empower software. The charged FOS were digested with the sialidase from Arthrobacter ureafaciens . 2-AA – labelled free oligosaccharides from transferrin were used as an external standard for the structure decoding. In this paper, the changes in neraminidase-1 activity was first demonstrated on natural substrates, free oligosaccharides, in vivo . Chromatographic profiles of charged plasma FOS of patients with acute and chronic hematological malignancies revealed decreasing of neuraminidase-1 activity and increasing of the lysosomal exocytosis. Thus, chromatographic profiles of charged plasma FOS appeared to be a sensitive parameter of the lysosomal/endosomal status in normal or pathological states and to open up new prospects for their applications to the development of anti-cancer drugs designed to block the work of the lysosomal/endosomal system and monitoring of their action.