PMC10328163_01
Photomicrograph of a hematoxylin and eosin-stained section of a liver biopsy
from a cat with primary copper hepatopathy. Moderate amounts of cytoplasmic
brown-orange pigment (arrow) were evident in hepatocytes, extending from the
central vein to the portal region (bar = 50 microm) with most of the pigment
found in the centrilobular region. The inset is a higher magnification image
of the region closest to the central vein to better demonstrate the
cytoplasmic pigment (bar = 25 microm)
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Histopathologic examination of hematoxylin and eosin-stained biopsy sections identified cytoplasmic copper aggregates in hepatocytes with greatest accumulation in centrilobular regions (Figure 1).
Photomicrograph of a rhodanine-stained section of a liver biopsy from a cat
with primary copper hepatopathy. Copper was appreciable as orange-red
aggregates around the hepatic veins (HVs) (bar = 1 mm). The inset is a
higher magnification image to better demonstrate cytoplasmic copper
aggregates in individual hepatocytes (bar = 100 microm)
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Subsequent copper-specific rhodanine staining (Figure 2) permitted digital quantification of the copper   (dry weight copper = 3051 microg/g, normal <400 microg/g, secondary copper hepatopathy <700 microg/g, primary copper hepatopathy >700 microg/g) and the results were strongly suggestive of primary copper hepatopathy (PCH).   A cytologic re-examination of a modified Wright's-stained smear of a liver aspirate identified cytoplasmic blue-green refractile and non-refractile aggregates in hepatocytes - the former consistent with copper and the latter possibly lipofuscin or a copper variant (Figure 3).
Photomicrograph of a modified Wright's-stained smear of a liver aspirate from
a cat with primary copper hepatopathy. The cytoplasm of several hepatocytes
contained small amounts of blue-green refractile pigment (arrows),
consistent with copper (bar = 10 microm). The more numerous blue-green
non-refractile aggregates could be lipofuscin or a copper variant
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Subsequent copper-specific rhodanine staining (Figure 2) permitted digital quantification of the copper   (dry weight copper = 3051 microg/g, normal <400 microg/g, secondary copper hepatopathy <700 microg/g, primary copper hepatopathy >700 microg/g) and the results were strongly suggestive of primary copper hepatopathy (PCH).   A cytologic re-examination of a modified Wright's-stained smear of a liver aspirate identified cytoplasmic blue-green refractile and non-refractile aggregates in hepatocytes - the former consistent with copper and the latter possibly lipofuscin or a copper variant (Figure 3).
Amino acid sequence alignment of ATP7B across eight species
in the regions of both previously unknown single nucleotide variations
(SNVs) found in a cat with primary copper hepatopathy. The black arrows
indicate the locations of amino acid substitutions owing to the novel SNVs.
(a) The amino acid affected by the c.1268c/t SNV (p.Thr423Ile) was only
conserved across 3/8 species, (b) whereas the amino acid affected by the
c.3670t/a SNV (p.Trp1224Arg) was conserved across 8/8 species. NCBI
Reference Sequences: dog NP_001020438.1, horse XP_005601246.1, cow
XP_002691840.1, pig XP_020920945.1, human NP_000044.2, rat NP_036643.2 and
mouse NP_031537.2
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To determine whether these novel SNVs were pathogenic, the consensus amino acid sequence of the feline ATP7B gene was aligned with seven other species using previously described methods (Figure 4).   Substitutions in functionally important amino acids are more likely to be pathogenic and therefore purged by natural selection (ie, functionally important amino acids are highly conserved across species). While the amino acid affected by the c.1268c/t SNV (p.Thr423Ile) was only conserved across three of the eight species (Figure 4a), the amino acid affected by the c.3670t/a SNV (p.Trp1224Arg) was conserved across all eight species (Figure 4b), which suggests that the c.3670t/a SNV and resulting p.Trp1224Arg substitution could be pathogenic.