Impaired biliary excretion of copper and lysosomal enzymes in Long-Evans cinnamon

Abstract

Although impaired biliary excretion of copper through hepatocyte lysosomes has been postulated as a pathogenesis of Wilson's disease, direct evidence has been lacking. Our aim was to investigate the dynamics of biliary excretion of copper and lysosomal enzymes in the Long-Evans Cinnamon (LEC) rat, a recently established rodent model of Wilson's disease. Liver homogenate and bile were obtained from 12 week-old LEC rats (n = 7), Long-Evans Agouti rats (n = 3) and Sprague-Dawley rats (n = 8) and analyzed for copper and lysosomal enzymes. Structural integrity of hepatic lysosomes was assessed by the latency of N-acetyl-beta-glucosaminidase. Compared with the controls, LEC rats exhibited a 43-fold increase in hepatic copper concentration (p < 0.001), a significant increase in hepatic activities of lysosomal enzymes (p < 0.001) and reduction of lysosomal latency (p < 0.05). In contrast, biliary excretion of copper and lysosomal enzymes were significantly impaired in LEC rats (p < 0.05). These results suggest a coupled alteration between copper and lysosomal enzymes in both the liver and bile of LEC rats (i.e., increase in liver and decrease in bile). Defective biliary excretion of copper via hepatocyte lysosomes may play a role in part in spontaneous copper accumulation in LEC rats.