Insights in the pathogenesis of Dobermann hepatitis

Abstract

The pathogenesis of Dobermann hepatitis has been under debate for several years. In this thesis two hypotheses were formulated and discussed.

Hypothesis 1: In Dobermann dogs exists an autosomal genetic error in metabolism that leads to an abnormal copper metabolism which results in an increased hepatic copper concentration and leads to a (subclinical) hepatitis.

Hypothesis 2: Some Dobermann dogs may have a specific DLA (dog leukocyte antigen) configuration that is associated with an abnormal or inadequate response on an (normal) immune-stimulation which prones to autoimmune hepatitis.

To investigate morbidity and mortality in this breed questionnaires were sent randomly to owners of 928 Dobermann dogs registered over seven different years. A proportional mortality of 3.7% was found for Dobermann hepatitis and in the group alive a prevalence of 0.8%. The prevalence of subclinical hepatitis was also investigated in a group of 106 randomly selected 3 year old Dobermann dogs. Histopathologic examination of liver samples revealed subclinical hepatitis in 22 dogs (19 females and 3 males). Liver copper concentrations measured using instrumental neutron activation analysis (INAA), was significantly higher (419 ± 414 mg/kg dry matter; mean ± SD) (p=0.0008) in dogs with hepatitis than those without liver disease (197 ± 113 mg/kg; mean ± SD). At 2.6 ± 0.6 years hepatitis persisted in 6 and the average copper concentration (939 ± 299 mg/kg) had continued to rise significantly (p=0.02). The hepatitis was associated with apoptotic hepatocytes and copper-laden Kupffer cells in centrolobular regions. The hepatobiliary copper excretion is examined by means of an intravenously administered radioactive copper isotope (64Cu) in both normal Dobermanns as well as patients. Plasma clearance values were in all dogs comparable without significant differences. The excretion of 64Cu into the bile was significantly less for the Dobermann dogs with subclinical hepatitis compared to the normal dogs which suggests an impaired copper excretion. Cholestasis was excluded by means of a 99mTc- Bis-IDA hepatobiliary scintigraphy.

A quantitative Real-Time PCR was used to determine differentially expressed genes involved in copper metabolism and ROS defences. Most mRNA levels of proteins were around control values in the CASH group. In contrast, many of these proteins were significantly reduced in the DH group. We also performed a candidate gene scan for CTR1, Ceruloplasmin, Metallothionein, ATP7A, ATP7B, Murr1, COX17, ATOX1 and all had to be excluded.

Since Dobermann hepatitis might also be (partly) immune-mediated we used an androgen (double blinded placebo controlled) for 4 months but no effect was found. We also treated five female Dobermann dogs with increased hepatic copper concentrations and persistent subclinical hepatitis with D-penicillamine for 4 months. The copper concentrations had decreased in all of the dogs (P=0.03) and histopathology returned to normal. Lastly DLA Class II allele variations are described. There was no prevalent DLA allele or haplotype in either of the disease groups. The majority of dogs was homozygous for one haplotype that had a frequency of 88.75% in the entire group of Dobermans.

We concluded that Dobermann dogs have an inborn error of metabolism that results in a decreased biliary copper excretion. Since Dobermann dogs with CASH or DH do not show a variation in DLA haplotypes if compared with normal Dobermann dogs we did not found proof to support the second hypothesis.