Background: Folate and cobalamin are essential cofactors for homocysteine (HCY) metabolism. Hyperhomocysteinemia, a multifactorial condition, may reflect B vitamin deficiency and is associated with increased risk of cardiovascular disease, thrombosis, and neurodegenerative and chronic gastrointestinal diseases in humans. Hyperhomocysteinemia has been reported in Greyhounds with suspected chronic enteropathy. Objectives: To evaluate the frequencies of and the association between hypofolatemia and hyperhomocysteinemia in Greyhounds. Animals: Data and serum samples from 559 Greyhounds. Methods: Nested case-control study. The frequency of hypofolatemia in Greyhounds was determined by a laboratory database search. The relationship between hyperhomocysteinemia (measured by gas chromatography-mass spectrometry) and hypocobalaminemia and hypofolatemia was evaluated, and its frequency compared between healthy Greyhounds and Greyhounds with thrombosis or chronic diarrhea. Results: Hypofolatemia was identified in 172 of 423 (41%) Greyhounds and was more common in hypo- than in normocobalaminemic dogs (49% vs. 35%; P = .0064). Hyperhomocysteinemia was detected in 53 of 78 (68%) of Greyhounds, being more common in hypo- than in normofolatemic dogs (88% vs. 59%; P = .0175). All healthy Greyhounds, 21 of 30 (70%) of dogs with chronic diarrhea and 6 of 8 (75%) of those with thrombosis, were hyperhomocysteinemic. Serum HCY concentrations were inversely correlated with serum folate concentration (q = -0.28; P = .0386) and were positively associated with serum albumin concentration (q = 0.66; P = .0022). Conclusions and Clinical Relevance: Hyperhomocysteinemia occurs frequently in the Greyhound population. Its association with hypofolatemia suggests decreased intracellular availability of B vitamins, but the functional implications warrant further investigation. Hyperhomocysteinemia in Greyhounds potentially may serve as a spontaneous canine model to further investigate hyperhomocysteinemia in humans.

Background: Folate and cobalamin are essential cofactors for homocysteine (HCY) metabolism. Hyperhomocysteinemia, a multifactorial condition, may reflect B vitamin deficiency and is associated with increased risk of cardiovascular disease, thrombosis, and neurodegenerative and chronic gastrointestinal diseases in humans. Hyperhomocysteinemia has been reported in Greyhounds with suspected chronic enteropathy. Objectives: To evaluate the frequencies of and the association between hypofolatemia and hyperhomocysteinemia in Greyhounds. Animals: Data and serum samples from 559 Greyhounds. Methods: Nested case-control study. The frequency of hypofolatemia in Greyhounds was determined by a laboratory database search. The relationship between hyperhomocysteinemia (measured by gas chromatography-mass spectrometry) and hypocobalaminemia and hypofolatemia was evaluated, and its frequency compared between healthy Greyhounds and Greyhounds with thrombosis or chronic diarrhea. Results: Hypofolatemia was identified in 172 of 423 (41%) Greyhounds and was more common in hypo- than in normocobalaminemic dogs (49% vs. 35%; P = .0064). Hyperhomocysteinemia was detected in 53 of 78 (68%) of Greyhounds, being more common in hypo- than in normofolatemic dogs (88% vs. 59%; P = .0175). All healthy Greyhounds, 21 of 30 (70%) of dogs with chronic diarrhea and 6 of 8 (75%) of those with thrombosis, were hyperhomocysteinemic. Serum HCY concentrations were inversely correlated with serum folate concentration (q = -0.28; P = .0386) and were positively associated with serum albumin concentration (q = 0.66; P = .0022). Conclusions and Clinical Relevance: Hyperhomocysteinemia occurs frequently in the Greyhound population. Its association with hypofolatemia suggests decreased intracellular availability of B vitamins, but the functional implications warrant further investigation. Hyperhomocysteinemia in Greyhounds potentially may serve as a spontaneous canine model to further investigate hyperhomocysteinemia in humans.

Background: Chronic inflammatory enteropathy (CIE) in dogs is often associated with cobalamin deficiency. Hypocobalaminemia is also a risk factor for negative clinical outcomes in dogs with CIE and affected dogs may not respond to treatment unless receiving supplemental cobalamin. It has been proposed that the uptake of cobalamin from the intestinal lumen is compromised as a result of receptor deficiency in dogs with CIE, but the expression of the cobalamin receptor in dogs with chronic intestinal inflammation has not been studied. In addition to cobalamin deficiency, increased serum cobalamin concentrations could also be linked to relevant health conditions if not resulting from cobalamin supplementation. Cobalamin is essential for many cell functions, and both under- and oversupply may be associated with severe disease. Objectives: The study aimed to quantify protein and mRNA abundances of components involved in intestinal cobalamin uptake (i.e., amnionless [AMN], cubilin [CUBN], and the basolateral efflux transporter multi-drug resistance protein 1 [MRP1]) in ileal biopsies from dogs diagnosed with CIE compared to healthy dogs. These receptor levels were also evaluated in relation to the patient clinical, clinicopathologic, and histologic variables. Further, the study aimed to retrospectively determine the prevalence of hypercobalaminemia compared to hypocobalaminemia and its potential association with pathologies in a large group of dogs and cats. Material and Methods: The intestinal expression of the cobalamin receptor subunits AMN and CUBN, as well as MRP1, was evaluated in dogs with CIE (n=22) compared to healthy control dogs (n=9 for protein and n=11 for mRNA analysis). Epithelial CUBN and AMN levels were quantified by confocal laser scanning microscopy using immunofluorescent stainings in endoscopic ileal biopsies from dogs with (i) CIE and normocobalaminemia, (ii) CIE and suboptimal serum cobalamin status, (iii) CIE and severe hypocobalaminemia, and (iv) healthy controls. Expression of CUBN and MRP1 was also quantified by RT-qPCR. Receptor expression levels were analyzed for correlation with clinical patient data using non-parametric two- or multiple-group comparison or likelihood ratio tests and calculating correlation coefficients, applying a Bonferroni correction (significance at P<0.05) if indicated. For the second part of the study, medical records of all dogs and cats that presented at the Small Animal Clinic of the Leipzig University between 2007 and 2019 and had the serum cobalamin concentration measured were reviewed (1,227 cobalamin measurements). Patients receiving prior cobalamin supplementation or with incomplete medical record data were excluded from further analysis. The proportion of animals with hypercobalaminemia (serum cobalamin concentration >908 ng/L in dogs and >1,334 ng/L in cats) was calculated, and the association of hypercobalaminemia with individual patient characteristics and pathologic findings was evaluated. Results: Ileal mucosal protein levels of AMN and CUBN, as well as mRNA levels of CUBN and MRP1, were significantly increased in dogs with CIE, particularly those dogs with hypocobalaminemia, compared to healthy controls (all P=0.05). Ileal cobalamin receptor expression was positively correlated with age, clinical disease activity index (CCECAI) score, and lacteal dilation in the ileum, inversely correlated with serum folate concentrations but was not associated with serum cobalamin concentrations. Of the 654 dogs included in the second part of the study, 3% (n=21) were hypercobalaminemic, and 48% of these dogs had chronic gastrointestinal signs. Two of the 21 hypercobalaminemic dogs (10%) were diagnosed with hypoadrenocorticism, and adrenal insufficiency was significantly associated with hypercobalaminemia (P=0.031). Of the 315 cats included in the final analysis, 11% (n=34) were hypercobalaminemic. Of these cats, 65% (n=22) were diagnosed with chronic enteropathy, 24% (n=8) with acute or chronic pancreatitis, and 18% (n=6) with cholangiohepatopathy. Conclusions: Contrary to the previously proposed pathogenetic mechanism, cobalamin receptor downregulation does not appear to be the primary cause of hypocobalaminemia in canine CIE. Especially in dogs of older age, with severe clinical signs and/or more pronounced microscopic intestinal lesions, intestinal upregulation of the cobalamin receptor may be a mechanism to compensate for CIE-associated hypocobalaminemia. These findings also support an oral supplementation strategy in canine hypocobalaminemic patients with CIE. Hypercobalaminemia occurs infrequently in cats and less often in dogs. Increased serum cobalamin concentrations in patients without prior supplementation should not be ignored as they may indicate severe inflammatory, immunemediated, or neoplastic diseases.