Analytical approaches to the problem of protein binding of aluminium in blood serum

Abstract

Ultrafiltration and chromatographic techniques were used to study protein binding and aluminium speciation in blood serum. Ultrafiltration studies were carried out using both a stirred Amicon ultrafiltration cell and an Amicon Centrifree Micropartition Unit (MPS-1). The latter device proved to be less prone to contamination and results obtained showed that only about 8% of the aluminium in normal serum is ultrafilterable. Experiments with patients undergoing desferrioxamine (DFO) chelation therapy showed that the ultrafilterable aluminium in their serum increased by up to 74% because of the formation of a low relative molecular mass chelate with the DFO. High-performance liquid chromatography (HPLC) separation of serum proteins was carried out with an ion-exchange column of TSK DEAE-3SW (150 mm long × 7.5 mm i.d., 10-µm particle size) using a sodium acetate gradient (0–0.5 M) at pH 7.4 (Tris-HCl buffer). Proteins were detected spectrophotometrically at 280 nm and the aluminium was determined by electrothermal atomisation atomic absorption spectrometry of 0.5-ml fractions collected at the end of the HPLC column. Results obtained with this system suggest that transferrin is the only aluminium binding protein in normal serum. However, in the presence of DFO in serum, most of the aluminium proved to be bound to the drug. Only a very small fraction remains bound to the transferrin for a 2 mg l^–1 concentration of DFO in serum.