Quantification and isotopic analysis of bulk and of exchangeable and ultrafiltrable serum copper in healthy and alcoholic cirrhosis subjects

Information on the Cu speciation in blood serum can be valuable for a better understanding of the metabolism of this essential transition metal, but Cu speciation analysis and, to an even larger extent, compound-specific high precision Cu isotopic analysis are challenging. In this work, quantification and isotopic analysis of Cu were carried out in bulk serum and in both its exchangeable + ultrafiltrable (EXCH + UF) Cu fraction and its non-exchangeable + non-ultrafiltrable (NEXCH + NUF) fraction using quadrupole and multi-collector ICP-mass spectrometry, respectively. The EXCH + UF serum Cu represents the labile Cu pool, ie. Cu loosely bound to proteins, such as albumin, alpha-2 macroglobulin and other low molecular weight compounds, while the NEXCH + NUF serum Cu contains the Cu firmly bound to ceruloplasmin (Cp). The method was evaluated using human, goat and fetal bovine serum and applied to serum samples from assumed healthy subjects and from patients with alcoholic liver cirrhosis (AC). The healthy subjects showed an isotopic composition of EXCH + UF serum Cu heavier (by on average + 0.4 parts per thousand) than that of their total serum Cu. In general, patients with AC showed higher EXCH + UF serum Cu concentrations and significantly lower delta Cu-65(EXCH) + up and delta Cu-65(serum) values than did healthy subjects. Within the AC population, delta Cu-65(EXCH+UF) values were comparable to or lower than the corresponding delta Cu-65 rum values, potentially reflecting the extent of labile Cu deregulation. As to be expected, the NEXCH + NUF serum Cu isotopic composition was similar to that of the total serum Cu, as most of the serum Cu is firmly bound to Cp.