Expression of the cobalamin receptor subunit AMN in dogs with idiopathic inflammatory bowel disease
17 February 2020 (online)
Background Idiopathic inflammatory bowel disease (IBD) in dogs is often associated with cobalamin deficiency. Hypocobalaminemia is also a risk factor for negative clinical outcome in dogs with IBD, and affected dogs may not respond to treatment unless receiving supplemental cobalamin. It is proposed that the uptake of cobalamin from the intestinal lumen is compromised in dogs with IBD. However, the pathophysiology of cobalamin deficiency in canine IBD has not been fully elucidated. Thus, the aim of this study was to quantify the expression of the cobalamin receptor subunit amnionless (AMN) in ileal biopsies from healthy dogs and dogs with IBD.
Material and methods Endoscopic biopsies from the ileum were evaluated from dogs that were assigned to one of the following groups: (1) dogs with IBD and severe hypocobalaminemia, (2) dogs with IBD and suboptimal cobalamin status, (3) dogs with IBD and normocobalaminemia, and (4) healthy control dogs. Formalin-fixed and paraffin embedded sections of ileal biopsies were stained for the AMN using commercially available fluorescence-labelled polyclonal antibodies, and the expression of AMN was quantified (blinded) using laser scanning microscopy.
Results Expression of AMN was significantly higher in severely hypocobal-aminemic dogs with IBD (median: 4.97 counts, n = 6) compared to healthy control dogs (median: 3.40 counts, n = 8; p = 0.0118), and a large variation in the AMN expression was seen in the first group. There were no significant differences among any other groups of dogs (all p > 0.05).
Conclusion The expression of the cobalamin receptor subunit AMN appears to be altered in severely hypocobalaminemic dogs with IBD. Contrary to current believe, AMN receptor downregulation may not be the primary cause of severe hypocobalaminemia in canine IBD. The underlying mechanisms and clinical implications of these findings, and also the effect of selected patient characteristics (e. g., age, sex) on AMN expression, warrant further investigation.