Development of the stable isotope tracer approach for studies of copper turnover in the rat and mouse

Abstract

The stable isotope tracer approach was explored for long-term investigations of copper turnover in the adult rat and mouse, with inductively coupled plasma mass spectrometry for isotope measurements. The isotopic measurement method permitted precision and accuracy of <1.0%, with an overall sample blank of <0.05 μg copper. Rats were fed a copper-deficient diet and deionized water with (+Cu) or without (−Cu) copper (20 μg/ml). Both groups underwent a single-day replacement of drinking water with 20 μg/ml of 65Cu. Compared with the baseline isotope ratio ( 65Cu/ 63Cu) of 0.462 ± 0.002, blood plasma ratios for the +Cu group on days 2, 7, and 14 postdosing were 0.702 ± 0.021, 0.557 ± 0.004, and 0.474 ± 0.001, respectively. The corresponding data for liver were 0.652 ± 0.018, 0.560 ± 0.005, and 0.482 ± 0.001, respectively. For the −Cu group, respective plasma ratios were 1.580 ± 0.04, 0.917 ± 0.02, and 0.664 ± 0.01 for days 2, 7, and 14 postdosing, and the ratios for liver were 0.978 ± 0.02, 0.876 ± 0.04, and 0.739 ± 0.03. Mice previously made copper deficient to varying degrees were given a single-day replacement with the label. When the 24-hour postdosing isotope ratios in the livers of these mice were correlated with the activity of plasma ceruloplasmin, a negative correlation ( r = −0.85) was observed. Isotope enrichment in both rats and mice was greater in the copper-deficient animals compared with the controls.