Determination, stable isotope enrichment and kinetics of direct-reacting copper in blood plasma

Abstract

Direct-reacting Cu is defined as Cu 2+ and other forms of Cu that readily exchange with Cu 2+ in blood plasma. An analytical method was developed for 1) quantification of direct-reacting Cu by stable isotope dilution and 2) determination of 65Cu enrichment of direct-reacting Cu in plasma samples from in vivo tracer studies. The method involved addition of enriched 65Cu to plasma, extraction with sodium diethyldithiocarbamate in mineral oil, and analysis by inductively coupled plasma mass spectrometry. Optimum sodium diethyldithiocarbamate concentration for the extraction was 0.16 mM. Direct-reacting Cu (means ± SD) varied from 3.4 ± 0.5% of whole plasma Cu in dairy cows (n = 7) and 3.4 ± 0.3% in healthy men ( n = 10) to 16.6 ± 3.7% in dogs ( n = 3). After intravenous infusion of enriched 65Cu into two healthy men, biological half-lives of 8.7 and 12.3 min were determined for direct-reacting Cu.