Copper-associated hepatopathy (CAH) is an increasingly recognized syndrome in dogs, characterized by pathologic copper accumulation within hepatocytes, resulting in oxidative stress, cell death, and inflammation. Copper overload can lead to chronic hepatitis, end-stage liver disease, and even death. Risk factors are genetic or environmental. Clinical signs are initially nonspecific; however, as the disease progresses, they become more overt and are usually associated with liver failure.<\/p>\n
Hepatic enzyme (alanine aminotransferase and alkaline phosphatase) activities are nonspecific for detection of CAH; definitive diagnosis is obtained by histologic assessment of the hepatic copper distribution and copper quantification. Treatment is focused mainly on creating a negative copper balance by restricting copper intake through dietary modifications and increasing copper excretion by administering copper-chelating agents. Outcomes are best when treatment is started early in the course of the disease.<\/p>\n
Take-Home Points<\/strong><\/p>\n Copper is a trace element that serves as a cofactor for enzymes involved in many metabolic processes throughout the body. Although essential for life, free copper can be toxic because it can potentially lead to formation of reactive oxygen species via the Fenton reaction; therefore, its absorption, distribution, and excretion are tightly regulated.1<\/sup> The major organ for copper metabolism is the liver, which is responsible for copper storage, redistribution of copper in the protein-bound form to other tissues and organs, and elimination of excess copper via biliary excretion.2<\/sup> After copper enters the hepatocyte, it is immediately bound to specialized copper scavenger proteins (called copper chaperones) that assure safe handling and specific delivery of copper to its destination molecules. Copper chaperone antioxidant 1 (ATOX1) is responsible for shuttling copper to the trans-Golgi network, where the adenosine triphosphatase (ATPase) copper-transporting <\/span>\u03b1<\/span> and <\/span>\u03b2<\/span> (ATP7A <\/i>and <\/i>ATP7B) reside. Under certain conditions under which copper accumulates, ATP7B will interact with the copper metabolism Murr1<\/i> domain containing 1 (COMMD1) protein, facilitating excess copper excretion into the bile.3<\/sup><\/span><\/p>\n Abnormal hepatic copper accumulation can result from primary genetic defects in hepatic copper metabolism, increased dietary copper intake, or both. When hepatic copper transport\/binding capacities are overwhelmed, free copper within the hepatocytes will lead to oxidative stress, resulting in hepatocellular cell death and inflammation that commonly begins in the centrilobular regions of the liver (zone 3) but can also affect midzonal and portal regions as damage progresses. This pattern is a useful finding when interpreting liver histology for suspected copper-associated hepatopathy (CAH). In cases of severe chronic injury, parenchymal remodeling and fibrosis associated with formation of regenerative nodules can be found.4,5<\/sup> Generally, normal hepatic copper concentrations are 120 to 400 mg\/kg dry weight (DW), and potentially harmful concentrations are considered those >600 mg\/kg DW.5<\/sup><\/span><\/p>\n Predisposition to development of CAH can be affected by breed, sex (for some breeds), and diet. Historically, Bedlington terriers, Labrador retrievers, and Doberman pinschers have been considered to be predisposed, but other breeds with a suspected predisposition include West Highland white terriers, Dalmatians, Skye terriers, Anatolian shepherds, Welsh corgis, and Clumber spaniels.6<\/sup> CAH can also develop in dogs of other breeds or of mixed breed.5<\/sup> Usually, dogs of both sexes are equally predisposed, with the exception of Labrador retrievers and Doberman pinschers, for which a predisposition to females has been reported. In Doberman pinschers, immune-mediated chronic hepatitis is also suspected to occur, which may explain the sex predisposition for CAH as autoimmune conditions are generally more common in females.7-9 <\/sup><\/span><\/p>\n Bedlington terriers are predisposed to CAH. The main cause has been identified as a mutation responsible for creating a large deletion of the second exon in the COMMD1 <\/i>gene. This autosomal recessive disorder will cause altered copper excretion, inducing hepatic copper concentrations of \u226510<\/span>\u2009<\/span>000 \u00b5g\/g DW, which results in copper toxicosis and chronic hepatitis.10<\/sup> Genetic screening for this COMMD1 <\/i>deletion, along with selective breeding of Bedlington terriers, has reduced prevalence of CAH. Recently, mutations of a candidate gene (ABCA12 <\/i>[adenosine triphosphate\u2013binding cassette subfamily A member 12]), independent of the COMMD1<\/i> deletion, <\/i>have been implicated in the development of CAH in Bedlington terriers.11<\/sup><\/span><\/p>\n A genome-wide association study performed on 235\u00a0Labrador retrievers revealed mutations in the chromosome region coding for the ATP7B<\/i> gene significantly associated with increased hepatic copper levels.12<\/sup> The study also reported a mutation in the gene coding for ATP7A<\/i>, which partly protects against copper accumulation; these mutations accounted for only 12% of heritability. A similar study revealed that homozygous mutant offspring in which both parents had a least 1 copy of the ATP7B<\/i> mutation had elevated hepatic copper concentrations with normal alanine aminotransferase (ALT) activity.13<\/sup> Mutations of the ATP7B <\/i>gene have also been reported in a population of Doberman pinschers from the Netherlands and the United States with increased hepatic copper concentrations.14<\/sup><\/span><\/p>\n Over the past 3 decades, prevalence of CAH among dogs has risen considerably; several studies have associated this phenomenon with changes in the quantity and bioavailability of copper in commercial dog foods.5,15<\/sup> First, since the mid- to late-1990s, use of copper chelates (acetate, sulfate, and carbonate), which have relatively high bioavailability, in premix formulations has substantially increased the amount of copper absorbed.16<\/sup> Second, many commercial foods contain large variations in copper concentrations and often exceed (by 2 to 4 times) the minimum allowances for dietary copper intake (0.067 mg\/kg\/d) recommended by the Association of American Food Control Officials and the National Research Council.17<\/sup> Third, no upper limit for dietary copper is in place in the United States. Last, a proposed contributing factor is the current trend for owners to feed \u201calternative diets\u201d<\/a> (evolutionary or vegetarian diets) that use animal-based ingredients or vegetables with high copper content.15<\/sup><\/span><\/p>\n Dogs with CAH can appear healthy for years before clinical signs develop. The duration of the subclinical period depends mainly on the rate of hepatic copper accumulation, genetic predisposition, and dietary copper intake and can vary between breeds and individuals.18<\/sup> The liver has a substantial reserve capacity; therefore, clinical signs usually appear when the disease is more advanced. Because of the long subclinical period, many dogs exhibit no clinical signs, and the first sign of disease may be increased liver enzymes on routine blood work. Initial clinical signs are nonspecific and commonly include anorexia, lethargy, nausea, vomiting, and weight loss. Signs of more advanced disease are compatible with hepatic failure (e.g., ascites, hepatic encephalopathy, polyuria\/polydipsia, icterus).18<\/sup> In rare cases, an acute hemolytic crisis can occur when massive amounts of hepatic copper are released into the bloodstream; however, this phenomenon has only been reported in Bedlington terriers.19<\/sup><\/span><\/p>\n Routine serum biochemical analyses can reveal increased activity of liver enzymes (e.g., ALT or alkaline phosphatase [ALP]), but these alterations are not specific for CAH.5<\/sup> Furthermore, measurement of hepatic enzyme activity has not been shown to be sensitive for detecting subclinical stages of CAH.20<\/sup> In later stages of the disease, when a considerable amount of hepatic parenchyma has been lost, activity of other enzymes (e.g., <\/span>\u03b3<\/span>-glutamyl transpeptidase [GGT]) can be slightly elevated, and markers of liver function may be abnormal (e.g., hypoalbuminemia, hypoglycemia, hypocholesterolemia, decreased urea). In patients with end-stage liver disease, liver enzyme activity may decrease and even fall within normal reference intervals.21<\/sup> Hepatic function tests (e.g., total serum bile acids, ammonia, bilirubin, coagulation testing) are useful parameters for detecting liver disease, but, unfortunately, none are specific or sensitive for CAH.6<\/sup> In dogs with CAH, copper can also accumulate within the proximal renal tubular epithelium and lead to tubular injury and dysfunction, triggering a Fanconi-like syndrome exhibited by low urinary specific gravity, proteinuria<\/a>, and normoglycemic glucosuria.22<\/sup><\/span><\/p>\n Abdominal radiographs can be used to assess overall hepatic size, shape, and opacity as well as the presence of ascites, but they lack sensitivity to subtle changes or usefulness for diagnosing a given specific parenchymal disease. The initial imaging tool for hepatic parenchyma evaluation is commonly ultrasonography; however, although it can be sensitive for identifying certain liver and biliary abnormalities, ultrasonography lacks specificity for the diagnosis of CAH. Hepatic ultrasonography images can appear normal in dogs with CAH; common changes associated with chronic inflammation and remodeling that can be observed in dogs with CAH include heterogeneous echotexture, irregular margins, and microhepatica (<\/span>FIGURE 1<\/b><\/span>). Ultrasonography enables identification of alternative diagnoses (e.g., congenital portosystemic shunts) or complicating factors (e.g., portal hypertension, acquired portosystemic collateral blood vessels, ascites, thrombi) and can also be useful for needle biopsy sampling<\/a>.23<\/sup><\/span><\/p>\n Figure 1. Hepatic ultrasonography image of a dog with copper-associated hepatopathy. The liver appears heterogenous (asterisk) and hyperechoic, with irregular margins (arrows), suggestive of regenerative changes and concurrent fibrous tissue. Courtesy Dr. Lauren Ann Russell, Texas A&M University<\/p><\/div>\n Cytologic detection of copper-laden hepatocytes can be achieved via fine needle aspiration<\/a> and copper staining (with rhodanine or rubeanic acid). Although this noninvasive approach can be used to detect copper in individual hepatocytes, it has many limitations, such as the inability to evaluate copper distribution, degree of hepatocellular injury, and exact amount of copper. The negative predictive value of this method is, therefore, uncertain.24<\/sup><\/span><\/p>\n The only way to diagnose CAH is by histologic examination of a liver biopsy sample. Hepatic samples can be obtained via laparotomy<\/a>, laparoscopy (<\/span>FIGURE\u00a02<\/b><\/span>), or percutaneous needle biopsy guided by ultrasonography.6<\/sup> Before biopsy acquisition, bleeding risk assessment is recommended and can be performed by evaluating prothrombin time, activated partial thromboplastin time, plasma fibrinogen concentration, platelet count, viscoelastic coagulation monitor, and, possibly, buccal mucosal bleeding time. Despite the risk for serious postbiopsy hemorrhage, prevalence of this complication seems relatively low.25<\/sup> Generally, greater diagnostic quality is achieved with larger biopsy specimens obtained during laparoscopy or laparotomy than with those collected by percutaneous needle biopsy. Biopsy specimens should be obtained from the central and peripheral regions of the hepatic lobes; severely cirrhotic or fibrotic regions should be avoided. Current recommendations for adequate histopathologic examination suggest obtaining a minimum of 5\u00a0laparoscopic or surgical biopsy specimens from at least 2 liver lobes.5,26<\/sup><\/span><\/p>\n Figure 2. Acquisition of hepatic biopsy sample via laparoscopy from a dog with copper-associated hepatopathy. The liver is of normal size and has smooth margins. A probe is being used to displace the omentum. Courtesy Dr. Jes\u00fas Mendez-Flores, Hospital Veterinario de Alta Especialidad Delta, M\u00e9xico.<\/p><\/div>\n When the primary driving force of liver damage is copper toxicity, the centrilobular regions of the hepatic lobule are initially affected (<\/span>FIGURE 3<\/b><\/span>). Copper overload will trigger a mixed inflammatory infiltrate (lymphohistiocytic infiltrate) that can accumulate at the interface of the perivascular adventitia and regional hepatocytes. As the disease progresses, damage can extend into midzonal and portal regions, eventually affecting hepatocytes in all zones. Affected hepatocytes may display cytosolic copper aggregates. Advanced stages of disease may lead to centrilobular parenchymal collapse and obstruction of sinusoidal flow through hepatic venules with parenchymal remodeling and fibrosis. End-stage disease involves severe cirrhosis, massive necrosis, and lobular collapse, which will distort the architecture of the liver lobule, making it difficult to differentiate between zones.5,15,27<\/sup> Given that copper visualization is not optimal with routine staining (hematoxylin and eosin), use of high-affinity copper-binding stains (e.g., rhodanine, rubeanic acid) is required for an accurate diagnosis.5,6<\/sup><\/span><\/p>\n Figure 3. Microscopic image of a dog liver. Centrilobular copper distribution (brown granules) of a liver biopsy sample stained with rhodanine from a dog with copper-associated hepatopathy. Courtesy Dr. Jo\u00e3o Pedro Cavasin, Gastrointestinal Laboratory at Texas A&M University.<\/p><\/div>\n Semiquantitative grading schemes to characterize hepatic copper content and distribution correlate well with other quantitative measures. These scoring systems focus mainly on grading the zonal location and the number of hepatocytes and macrophages containing copper granules on a scale from 0 to 5 (<\/span>FIGURE 4<\/b><\/span>). Scores greater than 2 are considered abnormal.18,27<\/sup><\/span><\/p>\n\n
Etiopathogenesis of Copper Hepatopathy<\/h2>\n
Predisposing Factors for Copper Hepatopathy<\/h2>\n
Bedlington Terriers<\/h3>\n
Labrador Retrievers and Doberman Pinschers<\/h3>\n
Dietary Factors<\/h3>\n
Clinical Presentation of Copper Hepatopathy<\/h2>\n
Diagnostic Evaluation<\/h2>\n
Clinicopathologic Findings<\/h3>\n
Imaging<\/h3>\n
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<\/a>Cytology<\/h3>\n
Liver Biopsy<\/h3>\n
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<\/a>Histopathologic Analysis<\/h3>\n
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<\/a>Histologic Grading of Copper<\/h3>\n
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Figure 4. Histochemical hepatic copper scoring system. (A) Score 0: normal liver tissue with no copper; stained with hematoxylin and eosin.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/02\/Lidbury_TVPMarApr23_CopperHepatopathy_Fig4B.png\")
Figure 4B. Score 1: isolated hepatocytes containing copper granules; stained with rhodanine.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/02\/Lidbury_TVPMarApr23_CopperHepatopathy_Fig4C.png\")
Figure 4C. Score 2: small groups of hepatocytes containing moderate amounts of copper granules; stained with rhodanine.<\/span><\/a><\/div><\/div>![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/02\/Lidbury_TVPMarApr23_CopperHepatopathy_Fig4D.png\")
Figure 4D. Score 3: larger groups of hepatocytes containing moderate amounts of copper granules; stained with rhodanine.<\/span><\/a><\/div><\/div>
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![\"\"](\"https:\/\/navc.sitepreview.app\/todaysveterinarypractice.com\/wp-content\/uploads\/sites\/4\/2023\/02\/Lidbury_TVPMarApr23_CopperHepatopathy_Fig4F.png\")