Identification of aluminium fractions in serum using the techniques of high performance liquid chromatography, ultrafiltration and Zeeman atomic absorption spectrometry.

Abstract

In order to ascertain the distribution of aluminium in normal and occupationally exposed sera, size-exclusion chromatography using two fractionation techniques was applied: gel filtration (Sephadex G-100 SF) and HPLC (TSK G4000 SW). For each of the techniques, protein profiles obtained for control and exposed sera did not differ and aluminium was found to be associated with the same fractions. Ultrafiltration of sera using Centricon concentrators having a nominal cut-off of M(r) = 10,000 confirmed the presence of high molecular mass and ultrafiltrable low molecular mass aluminium complexes in serum. Absolute quantitation and relative distribution of aluminium in the aforementioned complexes in original and spiked sera were determined using Zeeman atomic absorption spectrometry. It was found that the relative distribution of aluminium between high molecular mass and low molecular mass fractions was 79.1% and 19.6% in controls, compared to 91.3% and 8.7% in exposed sera, which is highly significant for both high molecular mass (p < 0.026) and low molecular mass (p < 0.004). After spiking both control and exposed sera with 400 micrograms/l of Al, the distribution changed. The percentage of the aluminium bound to high molecular mass increased from 79.1% to 98.9% for controls, and from 91.3% to 98.4% for exposed sera, confirming the affinity of high molecular mass proteins, especially transferrin for aluminium. On the other hand, the percentage of aluminium bound to low molecular mass decreased after spiking to 1.12% for controls and to 1.6% for exposed sera. These differences were not statistically significant. This suggests that at high concentrations of total aluminium in serum, the percentage of the aluminium bound to the low molecular mass is lower but the absolute quantity of aluminium circulating as the low molecular mass complex is increased. This low molecular mass aluminium complex is thought to play an important role in intracellular accumulation of aluminium.