We describe the development of chronic hepatitis from hepatic copper accumulation in general, as well as our research on copper associated chronic hepatitis (CACH) in Labrador retrievers. We investigated family members of dogs with CACH for participation in prospective studies, characterized the disease, determined the heritability, and performed molecular genetic research, as well as treatment studies.
Copper and the Liver
The liver is essential for copper metabolism, because it is the principal recipient of absorbed copper, has the highest stored copper content, delivers copper in protein-bound form to other tissues and is the principal organ of excessive copper elimination via biliary excretion. Transport and sequestration of copper are tightly controlled. Essentially no free copper is available in the cytoplasm of liver cells.
Copper is a transition metal which is able to cycle between two redox states, oxidized copper (Cu2+, cupric) and reduced copper (Cu+, cuprous). The metal can therefore function as a redox co-factor in different enzymes.
Free copper ions are able to catalyze the formation of hydroxyl radicals via the Haber-Weiss reaction.
The hydroxyl-radical can directly damage lipids, proteins and nucleic acids. Oxidative damage can induce inflammation, and oxidative stress affects transcription factors, resulting in deregulated gene expressions which ultimately can lead to liver damage. In addition oxidative stress is a major inducer of cytokine production. Profibrotic cytokines favour the accumulation of collagen.
Copper-Associated Chronic Hepatitis
Hepatic copper accumulation can result from increased uptake of copper, a primary metabolic defect in hepatic copper metabolism or from altered biliary excretion of copper.
Toxicity of copper is dependent upon the molecular association and subcellular localization of the molecule as well as its total concentration in liver tissue. In inherited copper storage disorders copper accumulation is always localized centrolobularly (zone 3 of the liver lobule, e.g., Bedlington terrier copper toxicosis, Wilson's disease in humans, liver disease in LEC-rats). This disease is unlike secondary copper loading of liver cells during cholestasis or cholatestasis, where copper is mainly restricted to the periportal parenchyma.1-3
Copper-Associated Chronic Hepatitis in Dogs
Inherited copper toxicosis is a well described disease in the Bedlington terrier, where a deletion of exon 2 in the COMMD1 gene (previously called MURR1) causes accumulation of copper in hepatocytes, resulting in chronic hepatitis.4-8 Moreover, hepatic copper storage and associated hepatitis are breed-associated in the West Highland White terrier, Skye terrier, Doberman Pincher, Dalmatian, and Labrador retriever.9-19
The average canine liver copper concentration is 200-400 ppm (ppm= μg/g = mg/kg) per dry weight (dw) liver. Hepatic copper levels in breeds with primary copper storage disease vary between individual animals and between breeds from 600 to above 2,200 ppm.9,13,17,20-22
Clinical Signs and Laboratory Results of Dogs with Copper-Associated Chronic Hepatitis
Dogs with hepatic copper accumulation can appear normal over years before they develop clinical signs late in disease, although copper may begin to accumulate at 5-6 months of age. One investigator had followed dogs with the COMMD1 deletion from birth to 3 years of age, and copper accumulated in the liver by 1 year of age, whereas histologic signs of hepatitis did not occur before affected dogs were 2 years old.9 Therefore dogs with inherited copper storage disorders may be subject to a prolonged first delay period of several years between severe accumulation of copper and development of histologic signs of inflammation, as well as a second delay between histologic signs of inflammation consolidate and clinical signs of disease are recognized.
With the exception of hemolysis from copper release into blood, which is only described for Bedlington terriers, signs of the disease are all non-specific results of liver dysfunction. The clinical problem may start with a mildly calmer behaviour or less appetite. In most cases the owner will only recognize these intermittent signs retrospectively. Over weeks to months dogs may change between days of decreased playfulness and long periods were they behave completely normal. After months to years signs become more prominent. The dog may salivate with intermittent vomiting and nausea. Polyuria and polydipsia, icterus, diarrhea, and ascites may develop in advanced disease.
Due to a greater relative increase in alanine aminotransferase (ALT) activity compared to alkaline phosphatase (ALP), a primary hepatocellular liver disease appears most likely in the clinic.
Copper Associated Chronic Hepatitis in Labrador Retrievers
We investigated the genes involved in copper metabolism as candidate genes for CACH in Labradors. We invited family members of dogs with CACH for participation in a prospective study, in order to characterize the disease, to determine the heritability of traits of the disorder, and to perform molecular genetic research, as well as treatment studies.
Females are more commonly affected than male dogs, and generally present around 7 years of age (range 2-10 years). The clinical signs including salivation, intermittent vomiting, and weight loss are all non-specific results of liver dysfunction. PU/PD, icterus, diarrhea, ascites, and disseminated intravascular coagulation (DIC) may develop in advanced disease.
In most cases there is a greater relative increase in alanine transferase (ALT) activity compared to alkaline phosphatase (ALP).
Histopathologic evaluation of liver tissue is the only method for diagnosis of the disease.
Hepatic copper concentrations generally range between 650 to 3000 µg/g dry weight liver (histologically above 2+ with rubeanic acid staining). The chronic hepatitis is characterized by hepatocellular apoptosis, necrosis, regeneration, and fibrosis, as well as inflammatory infiltrates, that can be mononuclear or mixed. Cirrhosis results as the end-stage of the disease.
Penicillamine (10-15mg/kg BID PO) chelates copper from tissues and promotes copper excretion in urine. We have tested copper chelation therapy with penicillamine (10-15mg/kg twice daily PO for 3-6 months) in Labrador retrievers in a randomized, double blinded, placebo-controlled study and found the drug to be effective for treatment of hepatic copper accumulation in this breed. Adverse effects like inappetance, vomiting, and diarrhea can be avoided by mixing the drug with food, and dividing the dosage in more frequent applications per day. Clinical improvement from penicillamine treatment might take weeks to months, and there occur large inter-individual variations with respect to the effectiveness of the drug. Follow-up liver biopsies are required to determine the length of penicillamine therapy.
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