Total metal concentrations in serum of dialysis patients and fractionation of Cu, Rb, Al, Fe and Zn in spent continuous ambulatory peritoneal dialysis fluids

Total metal concentrations were determined in the serum of 12 continuous ambulatory peritoneal dialysis (CAPD) patients and in fresh and spent CAPD fluids by electrothermal and flame atomic absorption spectrometry (ETAAS, FAAS). Concentrations of Cu in serum of CAPD patients ranged from 720 to 1780 ng cm⁻³, Rb from 128 to 346 ng cm⁻³, Al from 10 to 72 ng cm⁻³, Fe from 800 to 2300 ng cm⁻³ and Zn from 659 to 1310 ng cm⁻³. The accuracy of the analytical procedure was checked by the analysis of the reference material Seronom™, Trace Elements in Serum. Good agreement between the certified and determined values was obtained for Al, Cu, Fe and Zn. The data on the total metal concentrations in CAPD fluids indicated that during CAPD fluid exchange the losses of Cu from 5.0 to 35 ng cm⁻³, of Rb from 50 to 110 ng cm⁻³ and of Al from 3.0 to 14.0 ng cm⁻³ occurred through the peritoneal membrane. Although fresh CAPD fluids contained traces of Fe (3.0-5.0 ng cm⁻³), the transfer of this element took place through the peritoneal membrane into spent CAPD fluid (13.0-38.0 ng cm⁻³). Zn concentrations were in general lower in spent (20.0-80 ng cm⁻³) than in fresh CAPD fluids (∼100 ng cm⁻³). To follow the mechanisms of the transfer of trace elements through the peritoneal membrane of CAPD patients, fractionation of metals was carried out in spent CAPD fluids by size exclusion chromatography with UV and AAS detection, applying Superdex HR 10/30 column. The chromatographic run was followed at 278 nm and separated metal species also determined ‘off line’ in 1 cm³ fractions by ETAAS or FAAS. From the UV chromatograms and AAS analysis of trace elements in the separated fractions it was demonstrated that Cu, Al, Fe and Zn were bound to proteins and only partially to low molecular weight (LMW) species, while Rb was associated exclusively with LMW species. For characterisation of the high molecular weight (HMW) binding proteins, fractions containing trace elements were subjected to SDS-PAGE electrophoresis. Al and Fe were presumably bound to transferrin, but due to its low concentration in spent CAPD fluids, it was not possible to confirm its presence in the separated fractions. About 10% of Al and 15% of Fe corresponded to LMW species. A fraction of HMW proteins of Cu in spent CAPD fluids was most probably bound to albumin and Zn to albumin and globulins. About 50% of Cu and Zn existed in LMW proteins, while Zn was also found partially in ionic form.