Evolution of Exchangeable Copper and Relative Exchangeable Copper through the Course of Wilson's Disease in the Long Evans Cinnamon Rat

Abstract

BackgroundWilson's disease (WD) is an inherited disorder of copper metabolism leading to liver failure and/or neurological impairment. Its diagnosis often remains difficult even with genetic testing. Relative exchangeable copper (REC) has recently been described as a reliable serum diagnostic marker for WD.Methodology/Principal FindingsThe aim of this study was to validate the use of REC in the Long Evans Cinnamon (LEC) rat, an animal model for WD, and to study its relevance under different conditions in comparison with conventional markers. Two groups of LEC rats and one group of Long-Evans (LE) rats were clinically and biologically monitored from 6 to 28 weeks of age. One group of LEC rats was given copper-free food. The other groups had normal food. Blood samples were collected each month and different serum markers for WD (namely ceruloplasmin oxidase activity, exchangeable copper (CuEXC), total serum copper and REC) and acute liver failure (serum transaminases and bilirubinemia) were tested. Every LEC rat under normal food developed acute liver failure (ALF), with 40% global mortality. Serum transaminases and bilirubinemia along with total serum copper and exchangeable copper levels increased with the onset of acute liver failure. A correlation was observed between CuEXC values and the severity of ALF. Cut-off values were different between young and adult rats and evolved because of age and/or liver failure. Only REC, with values >19%, was able to discriminate LEC groups from the LE control group at every time point in the study. REC sensitivity and specificity reached 100% in adults rats.Conclusions/SignificanceREC appears to be independent of demographic or clinical data in LEC rats. It is a very simple and reliable blood test for the diagnosis of copper toxicosis owing to a lack of ATP7B function. CuEXC can be used as an accurate biomarker of copper overload.

Relative exchangeable copper: A valuable tool for the diagnosis of Wilson disease

“…Thus, it could be a very interesting marker when starting a chelating treatment and especially in the neurological forms. In LEC rats, a correlation was observed between CuEXC values and the severity of acute liver failure . Interestingly, in our study, when considering patients at diagnosis, CuEXC was normal in only the patient who was diagnosed as presymptomatic.…”

“…Exchangeable copper concentration was also higher in neurological patients compared to pure hepatic WD patients . Recently, in an animal model for WD, REC with values >19% was able to discriminate Long‐Evans Cinnamon (LEC) rats from the Long‐Evans control group with a sensitivity and specificity of 100% . With the same determination procedure, we found that all new or non‐compliant patients had a REC>18.5% whereas none of the control population of chronic liver diseases had a REC>18.5%.…”

Clinical considerations for an effective medical therapy in Wilson's disease

“…An easy solution would be the direct determination of this lower affinity or noncovalent‐bound copper pool by ultrafiltration or other techniques . A promising approach has been put forward with exchangeable copper (CuEXC) and its derived relative exchangeable copper (REC, ratio CuEXC/total copper%) . The published studies to date demonstrate its usefulness primarily in the diagnostic setting, but its value for monitoring purposes is obvious.…”

Exchangeable copper: a reflection of the neurological severity in Wilson's disease

“…Indeed, the only patient with acute liver failure and Coombs-negative haemolytic anaemia in the hepatic group had a very high CuEXC. Moreover, in Long-Evans Cinnamon rats, a referenced WD animal model that does not develop neurological impairment, Schmitt et al demonstrated that CuEXC levels were correlated with acute liver failure[23]. So interpretation of a high CuEXC in the context of fulminant or acute liver failure should be carefully interpreted.…”