Potential mechanism for hyperhomocysteinemia in Greyhound dogs.

BACKGROUND: Greyhounds have been reported to have hyperhomocysteinemia (HHC), but the underlying mechanisms and clinical implications are unclear. HYPOTHESIS: Our primary aim was to assess serum concentrations of homocysteine (HCy) and related analytes in Greyhounds and to identify a likely metabolic pathway for HHC. A secondary aim was to determine whether HHC is associated with evidence of oxidative stress. ANIMALS: Healthy pet Greyhounds (n = 31) and non-sighthound control dogs (n = 15). METHODS: Analysis of serum HCy, cobalamin, folate, and methionine, and plasma cysteine, glutathione, and total 8-isoprostane concentrations. RESULTS: Homocysteine concentrations were higher in Greyhounds (median, 25.0 µmol/L) compared to controls (13.9 µmol/L; P < .0001). Cobalamin concentrations were lower in Greyhounds (median, 416 ng/L) compared to controls (644 ng/L; P = .004) and were inversely correlated with HCy (r = -0.40, P = .004). Serum concentrations of folate, which is regenerated when HCy is converted to methionine, also were inversely correlated with HCy (r = -0.47, P = .002). Serum methionine concentrations were more than 4-fold lower in Greyhounds (median, 3.2 µmol/L) compared to controls (median, 15.0 µmol/L), but this difference was not significant (P = .3). Plasma cysteine, glutathione, and 8-isoprostane concentrations did not differ significantly between groups. CONCLUSIONS AND CLINICAL IMPORTANCE: Our findings suggest a primary defect in conversion of HCy to methionine in Greyhounds, with related impaired folate generation. Ineffective cycling by methionine synthase could lead to secondary cobalamin depletion. Notably, low serum folate and cobalamin concentrations can be observed in Greyhounds without signs of intestinal disease.

Serum concentration of homocysteine in spontaneous feline chronic kidney disease.

Serum homocysteine (Hcy) increases in people and dogs with chronic kidney disease (CKD). Hyperhomocysteinemia (HHcy) has also been associated with CKD-related hypertension and proteinuria. The aims of this study were to: (1) validate an enzymatic method for quantification of Hcy in feline serum; (2) evaluate whether HHcy was associated with the presence and severity of CKD, proteinuria or hypertension; and (3) determine whether HHcy could predict disease progression. The intra- and inter-assay coefficients of variation (CVs) and the recovery rates of linearity under dilution and spiking recovery tests of the enzymatic method were 3.1-6.7%, 11.6-12.5%, 96.9±5.4% and 96.9±5.4%, respectively. Healthy cats at risk of CKD (n=17) and cats with CKD (n=19) were sampled over a 6-month period (63 samples in total). Cats with CKD had significantly higher Hcy concentrations (P=0.005) than cats at risk. The concentration of Hcy was higher (P=0.002) in moderate-severe CKD than in mild CKD and correlated moderately with serum creatinine (P<0.0001; r=0.51). The concentration of Hcy increased with the magnitude of proteinuria and correlated weakly with urinary protein to creatinine ratio (P=0.045; r=0.26). HHcy was not associated with hypertension. At the time of enrollment, Hcy concentration was significantly higher (P=0.046) in cats that developed CKD compared to cats that remained stable. The enzymatic method for Hcy measurement in feline serum was precise and accurate. HHcy was relatively common in cats with advanced CKD and seemed to predict disease progression, but further studies are warranted.

Hyperhomocysteinemia in Greyhounds and its Association with Hypofolatemia and Other Clinicopathologic Variables.

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 (ρ = -0.28; P = .0386) and were positively associated with serum albumin concentration (ρ = 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.

The contribution of portal drained viscera to circadian homocysteinemia in pigs.

Homocysteine (Hcy) is an intermediary S-containing amino acid produced by the methylation process within all cells. It is known as a powerful pro-oxidant with multiple deleterious effects on immune and physiological functions. Blood plasma total Hcy (tHcy), the most common indicator of Hcy status, can be reduced by dietary folates or vitamin B(12) in pigs as in most mammalians. In humans, homocysteinemia is routinely assessed after an overnight fast (≥ 12 h) although information is not available on circadian tHcy changes. Using a subgroup of pigs from a study on portal appearance of vitamin B(12) after a single meal containing 0, 25 or 250 µg of cyanocobalamin, the present study aimed to report the circadian profile of postmeal blood plasma tHcy and estimate the contribution of portal drained viscera (PDV) to the systemic tHcy. Four pigs (39.7 ± 1.1 kg BW) were surgically equipped at 101.0 ± 8.2 d of age with catheters in the portal vein and carotid artery; an ultrasonic flow probe was also fitted around the portal vein for blood flow recordings. Blood samples were collected simultaneously from the 2 catheters once before meal and at least every hour during 24 h after ingestion of 1.2 kg of a vitamin-free semipurified diet. Arterial tHcy changed considerably during the 24-h postmeal period (P < 0.001; SE = 0.8). In fact, from 12.3 µM 10 min before meal, tHcy gradually reached a maximum of 23.4 µM 13 h postmeal and returned to 15.5 µM 23 h after the meal. Net fluxes of tHcy across PDV were not influenced by levels of dietary vitamin B(12), postprandial time, or their interaction (P > 0.25); average net flux did not differ from zero (P > 0.08). These results suggest that systemic Hcy following a meal originates from metabolic pools other than PDV. It appears that an overnight fast of 12 h will reflect the peak rather than the basal value for tHcy. The duration of the fasting period is therefore a critical factor for a reliable interpretation of tHcy homeostasis in pigs. Such information may be also relevant for human health and nutrition because pig is recognized as a reliable model for Hcy metabolism.

Cobalt-deficiency-induced hyperhomocysteinaemia and oxidative status of cattle.

In ruminants, Co is required for the synthesis of vitamin B12, which in turn is needed for the resynthesis of methionine by methylation of homocysteine and thus, cobalamin deficiency may induce hyperhomocysteinaemia which is brought into context with perturbations of the antioxidative-prooxidative balance. The present study was conducted to explore whether Co deficiency in cattle is also associated with homocysteine-induced disturbances of oxidative status. Co deficiency was induced in cattle by feeding two groups of animals on either a basal maize-silage-based diet that was moderately low in Co (83 micrograms Co/kg DM), or the same diet supplemented with Co to a total of 200 micrograms Co/kg DM, for 43 weeks. Co deficiency was apparent from a reduced vitamin B12 status in serum and liver and an accumulation of homocysteine in plasma which was in excess of 4.8 times higher in Co-deprived cattle than in controls. The much increased level of circulating homocysteine did not indicate severe disturbances in antioxidant-prooxidant balance as measured by individual markers of lipid peroxidation, protein oxidation, and the antioxidative defence system. There were no quantitative difference in plasma thiol groups, nor were there significant changes in concentrations of alpha-tocopherol, microsomal thiobarbituric acid-reactive substances and carbonyl groups in liver. However, there was a trend toward increased plasma carbonyl levels indicating a slight degradation of plasma proteins in the hyperhomocysteinaemic cattle. Analysis of the hepatic catalase (EC 1.11.1.6) activity revealed an 11% reduction in Co-deficient cattle relative to the controls. These results indicate that long-term moderate Co deficiency may induce a severe accumulation of plasma homocysteine in cattle, but considerable abnormalities in oxidative status failed to appear.