In dogs, chronic hepatitis is a clinical syndrome for which the causal factors remain poorly defined.1–4 Etiopathogenic mechanisms of chronic hepatitis include chronic exposure to infectious agents (eg, Leptospira spp and Adenovirus), hepatotoxins (eg, mycotoxins, drugs, and industrial agents), and pathological retention of transition metals, especially copper. Excessive accumulation of copper in the liver has been documented in various breeds of dogs, including Bedlington Terriers, in which a genetic mutation has been identified that predisposes affected dogs to accumulate excessive copper in the liver.1–9 A similar gene mutation has not been identified in Labrador Retrievers, although investigators of multiple studies6,7,9 have reported pathological accumulation of copper in the livers of Labrador Retrievers with chronic hepatitis, with 1 group suggesting that pathological copper accumulation may be a heritable condition of the breed. Generally, copper-storage hepatopathy in Bedlington Terriers is the result of an autosomal recessive deletion of exon 2 of COMMD1 (the gene responsible for binding cupric ions in 1:1 stoichiometry); however, copper-storage hepatopathy has also been diagnosed in Bedlington Terriers that do not have that genetic deletion, which suggests that additional causal factors are involved in the pathogenesis of the disease.10
Our clinical impression during an ongoing study at Cornell University involving dogs with chronic hepatitis has been that hepatic copper concentrations have increased in both purebred and mixed-breed dogs during the last decade (based on qualitative and quantitative tissue copper assessments). Also during that time, the number of Labrador Retrievers examined at the veterinary teaching hospital at Cornell University and on which liver biopsies have been performed has increased, perhaps because of the increased popularity of the breed as a family pet. However, during the period between 2006 and 2009, investigators of 3 studies6,7,9 performed at 3 different academic institutions reported an association between excessive hepatic copper concentration and chronic hepatitis in Labrador Retrievers. Whether the increased recognition of excessive hepatic copper concentrations in Labrador Retrievers reflects a genetic mutation or other factors, such as increased intake or bioavailability of copper in food or increased breed popularity, remains unclear.
Accumulation of copper in the liver, especially in its cupric form, is extremely toxic and increases oxidant stress. This compromises glutathione availability and damages nucleic acids, proteins, and lipids, which in turn promote hepatocyte apoptosis.11,12 Common histologic features of hepatic copper toxicosis include microvesicular steatosis in damaged hepatocytes and accelerated hepatocyte turnover associated with cytolytic necrosis and apoptosis. Copper bound to metallothionein within the cytoplasm or aggregated in lysosomes of hepatocytes can be identified via histochemical staining methods.13
Currently, the physiologic hepatic copper concentration reported for dogs is ≤ 400 μg/g of dry weight, and hepatic copper concentrations > 1,800 μg/g of dry weight are considered pathogenic.1,14–16 The physiologic reference limit for hepatic copper concentration (on a dry-weight basis) in dogs has progressively increased from 7 μg/g in 1929 to 80 μg/g in 1956 to 400 μg/g since the late 1970s.15,17 Some investigators1,15 have suggested that this increase in the physiologic reference limit for hepatic copper concentration reflects increased feeding of industrially produced dog food to pet dogs. In 1996, AAFCO recommended the elimination of the use of cupric oxide as supplemental copper in dog food premixes because of its poor absorption in favor of more bioavailable forms of copper such as copper sulfate or copper chelates.18,19 The purpose of the study reported here was to evaluate changes in the hepatic copper concentrations of Labrador Retrievers with and without chronic hepatitis over a 30-year period. Liver tissue specimens from Labrador Retrievers with and without chronic hepatitis obtained between 1980 and 2010 were evaluated for qualitative and quantitative copper concentrations. We hypothesized that there would be a significant increase in hepatic copper concentration in Labrador Retrievers with and without chronic hepatitis during that time period corresponding with the switch to more bioavailable forms of supplemental copper in commercially produced dog food. Moreover, on the basis of our observation that hepatic copper concentrations for all breeds of dogs has increased during the recent decade, we postulated that Labrador Retrievers might represent a risk sentinel for hepatic copper accumulation for all dogs.
Association of American Feed Control Officials
Varian AA-1275, Varian Inc, Palo Alto, Calif.
Statistix, version 9.0, Analytical Software, Tallahassee, Fla.
Analyse-It, 2.22 Excel +, Analyse-It Software Ltd, Leeds, West Yorkshire, England.
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Scoring system for grading and staging chronic hepatitis in dogs that was developed at Cornell University to rank histologic features of and assign qualitative copper scores for liver tissue sections.
|Interface hepatitis—inflammatory cells within the portal tract extending through the limiting plate and associated with individual hepatocyte necrosis|
|Normal (no inflammation)||0|
|Mild (focal, in < 50% of all portal areas)||1|
|Mild to moderate (focal, in ≥ 50% of all portal regions)||2|
|Moderate (continuous around < 50% of portal regions or septa)||4|
|Severe (continuous around ≥ 50% of portal regions or septa)||5|
|Portal inflammation—inflammatory cells in the portal tract|
|Mild (< 5 inflammatory cells in some or all portal regions)||1|
|Moderate (≥ 5 but < 20 inflammatory cells in some or all portal regions)||2|
|Moderate to severe (≥ 20 but < 75 inflammatory cells in > 50% of all portal regions)||3|
|Severe (≥ 75 inflammatory cells in > 50% of all portal regions)||4|
|Lobular activity—intermittent necrosis, apoptosis, focal inflammation and hydropic degeneration (excluding fatty change and vacuolar hepatopathy)|
|< 2 foci/10 × field||1|
|2 4 foci/10 × field||2|
|5 10 foci/10 × field||3|
|> 10 foci/10 × field||4|
|Zonal necrosis in < 50% of lobules||1|
|Zonal necrosis in ≥ 50% of lobules||2|
|Zonal necrosis with occasional bridging||3|
|Zonal necrosis with frequent bridging||4|
|Panlobular or multilobular necrosis||5|
|Fibrous expansion of < 50% of portal regions with no fibrous septaa||1|
|Fibrous expansion of ≥ 50% of portal regions with no fibrous septaa||2|
|Fibrous expansion of ≥ 50% of portal regions with fibrous septaa||3|
|Fibrous expansion of ≥ 50% of portal regions with < 50% bridging septab||4|
|Fibrous expansion of ≥ 50% of portal regions with ≥ 50% bridging septab||5|
|Copper in hepatocytes, macrophages, and lipogranuloma cells within each zone (1, 2, and 3)|
|A few copper granules in an occasional cell||1|
|Obvious copper granules in some cells||2|
|Numerous copper granules in < 50% of cells||3|
|Numerous copper granules in ≥ 50% but < 75% of cells||4|
|Numerous copper granules in ≥ 75% of cells||5|
The scoring system is a modification of the Ishak-Knodell scoring system.
Consists of bands of fibrosis that distort hepatic architecture but do not bridge between zones.
Consists of bands of fibrosis that extend between portal regions (zone 1 to zone 1), portal regions and terminal hepatic venules (zone 1 to zone 3), or terminal hepatic venules (zone 3 to zone 3).
Architecture of the entire liver is disrupted by fibrous septa.
Because focal damage can mimic true cirrhosis, information obtained via physical examination, diagnostic imaging, or a biopsy specimen from another region of the liver is critical. Fibrous septa may bridge or may occur as broad fibrous tracts that obliterate multiple adjacent lobules (extinction of parenchyma). Regenerative nodules may not be present if the fibrosis has developed rapidly.