Biliary excretion of copper, metallothionein, and glutathione into Long-Evans Cinnamon rats: a convincing animal model for Wilson disease.

ABSTRACT

Long-Evans Cinnamon (LEC) rats, characterized by a gross accumulation of hepatic Cu and the spontaneous onset of hepatitis, have been established to be an animal model for Wilson disease. They were used to estimate the relationships among copper (Cu), metallothionein (MT), and reduced glutathione (GSH) in biliary excretion in this study. Even though a huge amount of MT existed in the LEC rat liver (5016 micrograms/g liver) compared to that (63 micrograms/g liver) of controls (Fischer rats), the biliary excretion of MT (65 ng/ml bile) did not reflect the accumulated MT level in LEC rats. It seems likely that MT does not excrete intrinsically into the bile. Biliary excretion of Cu (0.17 microgram/ml) in LEC rats was significantly lower than that (0.57 microgram/ml) in Fischer rats. The difference in biliary excretion of GSH between the two groups was significant but slight. The reduced excretion of GSH into bile in LEC rats may be due to increased hepatic gamma-glutamyltransferase but not to hepatic GSH levels. There were no differences in biliary potassium and inorganic phosphorous between the two groups. On the other hand, excretion of lysosomal enzymes such as beta-N-acetylglucosaminidase into bile was much lower in LEC rats (15.6 units/liter) than in controls (42.5 units/liter). The defective biliary excretion of Cu may be due to impaired lysosomal exocytosis, rather than canalicular membrane impairment. The LEC rat is very useful for research into the dynamics of metal excretion via the hepatobiliary system.