Determination of d-Mannose in Serum by Capillary Electrophoresis

Abstract

Congenital disorders of glycosylation (CDG) are a newly delineated group of inherited multisystem disorders associated with abnormal glycosylation of glycoproteins (1). In CDG group I, which includes all defects in N -glycan assembly (2), the subgroup CDG type Ib, attributable to phosphomannose isomerase (EC 5.3.1.8.) deficiency, is treatable by mannose supplementation (3). Monitoring of this treatment necessitates the availability of methods to quantify d-mannose in serum. The determination of mannose in serum is hampered by the presence of an ∼100-fold excess of glucose. Jolley et al. (4) used high-resolution liquid chromatography, whereas Aloia (5) used gas-liquid chromatography after treating the sera with glucose oxidase. Soyama (6) and Akazawa et al. (7) used enzymatic methods that involved treatment with glucose oxidase. In all of these studies, the presence or elimination of glucose remained critical. Pitkanen and Kanninen (8) were able to measure mannose using gas chromatography-mass spectrometry. However, this method is not suitable for routine purposes. The assay proposed by Etchison and Freeze (9) involves the elimination of glucose by glucokinase (EC 2.7.1.2), followed by the removal of anionic products by a subtle ion-exchange chromatography step. Finally, the mannose concentration is determined enzymatically. We investigated whether capillary electrophoresis (CE) of fluorophore-labeled carbohydrates was an appropriate method. In the resulting procedure, d-mannose can be determined in small amounts of serum in the presence of d-glucose without loss of selectivity, accuracy, and sensitivity. 1-Aminopyrene-3,6,8-trisulfonate (APTS) was purchased from Lambda Fluoreszenz Technologie GmbH. Sodium cyanoborohydride (1.0 mol/L in tetrahydrofuran) was …