PROGRESS WITH THE SPECIATION OF ALUMINUM AND SILICON IN SERUM OF CHRONIC RENAL PATIENTS USING ATOMIC SPECTROSCOPIC TECHNIQUES

In order to provide further evidence on the possible correlation between aluminium and silicon levels in the serum of renal failure patients and the possibility of the reduction of aluminium bioavailability by the presence of silicon in biological fluids, the effects of different factors, including storage conditions, administration of desferrioxamine (DFO) and kidney transplantation on total aluminium and silicon contents and on their distribution in the same serum samples were examined and compared. Ultramicrofiltration was used for the separation of low molecular weight (LMW) and high molecular weight (HMW) serum fractions, and electrothermal atomic absorption spectrometry (ETAAS) for the determination of both elements. Consistent results were obtained, showing that the distribution of aluminium between LMW and HMW serum fractions is a constant factor in the absence of DFO. It was observed that 11 +/- 2% of the total aluminium in serum is ultrafiltrable and this value does not seem to be influenced by the total serum elemental concentration, storage conditions, particular renal pathology of the patients or kidney transplantation. However, kidney transplantation induces a 'clear-up' of serum aluminium and silicon, which is easily observable after a few months. Administration of DFO alters the speciation of aluminium by increasing its relative content in the LMW fraction up to 75 +/- 6% of the total element concentration in serum. Conversely, distribution of silicon in serum proved to be affected only by the storage conditions. If the sample is stored properly (the pH maintained below 7.8), the ultrafiltrable silicon content results were consistent and reproducible (43 +/- 3% of total serum silicon in the LMW fraction was found to be ultrafiltrable). In any case, silicon binding to serum proteins must be different to that observed for aluminium (which is mostly bound to transferrin). Moreover, the observed distribution of aluminium between LMW and HMW serum fractions was neither related to silicon total concentration nor to the distribution of silicon in serum.