The lysosomal copper concentration in the liver in primary biliary cirrhosis

Wilson disease

Wilson disease (WD) is an autosomal recessive disorder of copper metabolism. Since daily copper intake exceeds the body's requirements, effective means of excreting excess copper are essential. These are accomplished by ATP7B, a new member of the cation-transporting p-type ATPase family, which is mainly expressed in the liver and mediates both copper secretion into plasma (coupled with ceruloplasmin synthesis) and its excretion into bile. Thus far, more than 200 mutations of the WD gene have been detected, causing impairment of ATP7B function and, ultimately, copper accumulation. Excess copper, however, induces free-radical reactions and lipid peroxidation. Resultant liver damage leads to steatosis, inflammation, cirrhosis, and, occasionally, fulminant liver failure. The diagnosis of WD is commonly made on the basis of typical clinical and laboratory findings, including low serum ceruloplasmin, increased urinary copper excretion, and increased hepatic copper content. Since liver morphology is non-specific, and copper histochemistry may lead to both false-negative and false-positive results, the pathologist usually only suspects the disease or assists in its confirmation. Although the value of molecular genetic testing is limited due to the high number of possible gene mutations, polymerase chain reaction may be useful for the evaluation of family members of homozygous index patients.

Copper transport and its defect in Wilson disease: characterization of the copper-binding domain of Wilson disease ATPase

Copper is an essential trace element which forms an integral component of many enzymes. While trace amounts of copper are needed to sustain life, excess copper is extremely toxic. An attempt is made here to present the current understanding of the normal transport of copper in relation to the absorption, intracellular transport and toxicity. Wilson disease is a genetic disorder of copper transport resulting in the accumulation of copper in organs such as liver and brain which leads to progressive hepatic and neurological damage. The gene responsible for Wilson disease (ATP7B) is predicted to encode a putative copper-transporting P-type ATPase. An important feature of this ATPase is the presence of a large N-terminal domain that contains six repeats of a copper-binding motif which is thought to be responsible for binding this metal prior to its transport across the membrane. We have cloned, expressed and purified the N-terminal domain (approximately 70 kD) of Wilson disease ATPase. Metal-binding properties of the domain showed the protein to bind several metals besides copper; however, copper has a higher affinity for the domain. The copper is bound to the domain in Cu(I) form with a copper: protein ratio of 6.5:1. X-ray absorption studies strongly suggest Cu(I) atoms are ligated to cysteine residues. Circular dichroism spectral analyses suggest both secondary and tertiary structural changes upon copper binding to the domain. Copper-binding studies suggest some degree of cooperativity in binding of copper. These studies as well as detailed structural information of the copper-binding domain will be crucial in determining the specific role played by the copper-transporting ATPase in the homeostatic control of copper in the body and how the transport of copper is interrupted by mutations in the ATPase gene.

Isolation, characterization, and determination of human liver (copper/zinc) metallothionein

A copper-containing protein was purified from the liver of a patient with primary biliary cirrhosis by a combination of gel filtration and anion exchange chromatography. This copper-protein had UV absorption and emission spectra, an amino acid composition, and a molecular mass which were characteristic for metallothionein (MT). From 8 livers (3 control, 1 fetal and 4 primary biliary cirrhosis) MT was extracted with non-reducing buffer and centrifuged, and pellets were re-extracted with a 1% 2-mercaptoethanol-containing buffer. The non-reducing buffer extracted a predominantly copper-containing MT from the livers of patients with primary biliary cirrhosis and a predominantly zinc-containing MT from control livers and the fetal liver. Only from the fetal liver was a copper/zinc containing MT solubilized during the re-extraction with 2-mercaptoethanol-containing buffer. These results indicate that human MT is a unique metalloprotein with age and disease-dependent characteristics.

Developmental changes in hepatic copper proteins in the guinea pig

We have suggested that Wilson's disease is caused by failure to adapt from the fetal to adult mode of copper metabolism and that the study of liver copper ontogeny might provide clues to the pathogenesis of Wilson's disease. This study traces the developmental changes in hepatic copper binding proteins in the guinea pig. During the last trimester, as fetal hepatic copper increases, metallothionein is the major copper binding peak in both the soluble and particulate supernatant fractions. After birth this peak decreases in parallel with the fall in liver copper. Metallothionein is absent from adult soluble supernatant and copper is associated with superoxide dismutase and a high molecular weight protein. A novel low molecular weight copper binding component is present in the particulate supernatant of neonatal liver, but is absent from the adult. Unlike many other animals, but similar to man, the switch from the fetal to adult mode of copper metabolism occurs at birth. Comparison of the copper protein profiles of the fetus and neonate with Wilson's disease are required to test the hypothesis that Wilson's disease is caused by developmental arrest of copper ontogeny.

Hepatitis and copper accumulation in Skye terriers

Livers of nine related Skye terriers with liver disease were evaluated for histological changes and copper content. Lesions ranged from hepatocellular degeneration and necrosis (zone 3) with intracanalicular cholestasis and mild inflammation, to chronic hepatitis with cholangioplasia and cirrhosis. Excess copper (801-2,257 micrograms/g) was related to the severity of cholestasis. Skye terrier hepatitis is a distinct disease entity and may be derived from a disorder of intracellular bile metabolism culminating in disturbed bile secretion and the accumulation of copper.