Mechanisms of tolerance in the copper-loaded rat liver

The aim of this study was to contribute to the understanding of the pathogenesis of copper-induced damage and subsequent recovery and tolerance to copper in the copper-loaded rat liver. Male Wistar rats were allocated randomly into groups of four, fed a pelleted diet containing 1500 mg/g copper, and killed at 1, 5, 6, 10, and 15 weeks. Two additional groups were treated as follows: (a) 5 weeks copper loading followed by 5 weeks with normal rodent diet (group 5-0), (b) 5 weeks copper loading followed by 5 weeks normal diet and 5 weeks of copper reloading (group 5-0-5). Control rats were fed a normal rodent diet that contained 18 mg/kg of copper. Tissues were collected for histology, histochemistry, immunocytochemistry, and copper analysis by atomic absorption spectrophotometry and X-ray microanalysis. In the rats continuously fed the high copper diet, copper concentration rose to 444 +/- 32 micrograms/g of liver (wet weight) by Week 1 and to 726 +/- 170 micrograms/g at Week 5, decreasing to 417 +/- 9 micrograms/g at Week 15. X-ray microanalysis and dot mapping microanalysis demonstrated copper within the nucleus, nucleolus, and lysosomes of these continuously loaded rats. Recovery with unloading of liver copper was demonstrated by both qualitative and quantitative methods in group 5-0 (41.32 +/- 19 micrograms/g). Recovery and tolerance were associated with a reduction in nucleolar copper. Copper tolerance was demonstrated in group 5-0-5 and in continuously copper-loaded rats by Weeks 10 and 15. Copper tolerance was reflected by a change in intracellular levels and distribution of copper and an efficient copper unloading mechanism.