A Retrospective Study of Equine Liver Lesions in Western Canada and the Expression of Metallothionein by Immunohistochemistry
Verhoef, Jolanda Nicole Chantal 1976-
Liver disease in equids is often difficult to diagnose, as clinical symptoms are vague and do not appear until there is a functional loss of approximately 75% of the liver. Metallothionein (MT) is a ubiquitously expressed protein with high affinity for binding zinc in the liver. It has been implicated in inflammatory and neoplastic processes in various species, but its role has not been evaluated in horses. To properly appreciate the possible implications of MT expression within the liver, it is crucial to understand, globally, the types of hepatic lesions to which equids are susceptible. Therefore, the first half of this work aimed to describe the histopathologic lesions of the liver from equids of all life stages submitted to the Prairie Diagnostic Services Inc. diagnostic laboratory (Saskatoon, SK) from 1995 to 2014, inclusive. Statistical analysis showed that the odds of being diagnosed with suppurative to mixed hepatitis was greater in juveniles and yearlings (odds ratio (OR) for both = 2.9, 95% confidence interval (CI) = 1.45 to 5.62 and 1.17 to 7.00, respectively), compared to adults. The odds of being diagnosed with multi-focal random hepatocellular necrosis were greater in fetuses and juveniles than in adults (OR = 77.1 and 6.1, CI = 22.6 to 263.2 and 2.1 to 17.8, respectively). The odds of being diagnosed with portal fibrosis and bile duct proliferation was greater in adults than in juveniles (OR = 5.4, 95% CI = 1.2 to 23.6). Neoplasia was diagnosed only in adults, and this was statistically significant (chi-square, P = 0.042). Additionally, equids such as donkeys, ponies, Miniature Horses as well as Coldbloods had significantly increased odds for the presence of hepatocellular vacuolation (OR = 29.5, 15.7, 7.4 and 7.9, 95% CI = 5.3 to 164.2, 2.7 to 90.8, 1.3 to 4.0, and 1.06 to 58.6 respectively). The odds of being diagnosed with suppurative to mixed hepatitis increased by each calendar year (OR = 1.07, 95% CI = 1.02 to 1.13). The second half of this work focused on investigating the expression of MT in the equine liver as detected by immunohistochemistry. In particular, the relationship between MT expression and histopathologic features of liver disease was examined. These histopathologic features included hepatic inflammation, fibrosis, and bile duct proliferation. Also, the relationship between MT expression and cellular regeneration, as determined by Ki-67 immunoreactivity, was determined. Metallothionein expression within hepatocytes was increased in 73 of 77 (94.8%) cases with chronic equine liver lesions. Statistical analysis found that MT expression was significantly associated with Ki-67 expression within bile duct epithelium (P = 0.0004, Mann-Whitney U-test), resident Kupffer cells (P = 0.0045, Mann-Whitney U-test), as well as with the presence of lymphocytic foci (P = 0.0017, Mann-Whitney U-test), suggesting that MT may play a role in inflammation and the cellular regeneration of bile duct epithelium in horses. In conclusion, MT is associated with inflammation and cellular regeneration in equine liver disease. Additionally, the hepatic lesions described herein from animals from western Canada, though regionally specific, are in alignment with what we know about liver disease in equids. From these findings, and from what we currently understand about the pathophysiology of equine liver disease, there is an excellent opportunity to pursue further research into the development of MT-based diagnostics, preventatives, and therapeutics.
DegreeMaster of Science (M.Sc.)
CommitteeSimko, Elemir; Lohmann, Katharina; Blakley, Barry; Allen, Andrew; Wobeser, Bruce
Copyright DateSeptember 2017
equine, chronic, liver, hepatic, fibrosis, inflammation, bile duct proliferation, regeneration, retrospective, metallothionein, immunohistochemistry