Homocysteine is a sulfur-containing amino acid and a product of the methionine demethylation. Homocysteine appears to be an independent risk factor for coronary heart diseases, stroke, peripheral occlusive arterial diseases and renal insufficiency. Increased homocysteine concentrations in blood can also be caused by deficiency of vitamin B6, B12 and folate.
The aim of this study was to determine the physiological concentration of homocysteine in canine plasma and to record the reference range after statistical calculation. The correlations of homocysteine concentration with plasma parameters, which indicate a renal insufficiency, were studied as well. After 12 hour food-deprivation lithium heparin blood was taken and used for homocysteine determination. The heparin tube was centrifuged by 5000 rpm for 5 min to separate plasma from the cellular fraction. A fully automated HPLC isocratic system purchased from Chromsystems was used.
Homocysteine levels of 51 healthy and 97 sick dogs were analysed. The reference range of homocysteine concentration in canine plasma has been found to be between 5.3 and 22.9 µmol/L (mean=10.9µmol/L, confidence interval =95%).
In the group of sick dogs, the correlations of creatinine, urea and total protein levels with the homocysteine concentration have been studied. No strong association could be observed for the mentioned parameters. This fact indicates, that an increase of these components as a signal for renal insufficiency is not associated with an increase of total plasma homocysteine concentration and is not comparable to the (most) clinical findings of human plasma.
For 2 species an increased creatinine level (351 and 400.5 µmol/L) was associated with an increase of total homocysteine in plasma. In the case of very high creatinine levels (n=9) the homocysteine content was in the normal range (creatinine: 109.6 - 249.3 µmol/L) or below (creatinin:
828.3 µmol/L). Only a few tested sick dogs showed an increased homocysteine level (n =8). In another experiment with 6 healthy beagles, the total homocysteine levels in plasma were analysed after 12 hours food- deprivation. The dogs were fed 4 different low-protein diets for two weeks and 4 hours after feeding blood was taken as well. Protein content of the diets was 15.22, 11.47, 17.78 and 17.44 % in the dry substance. Two of them were dry foods and two canned foods. All of those homocysteine values were in the reference range, there was only a slight increase after feeding observed. After one month feeding of the low-protein diets the homocysteine levels of the beagles decreased.
Conclusion: It was found an association between the plasma homocystein level and the progression of the disease. Survival prognosis is better when hyperhomocysteinemia can be diagnosed compared to hypohomocysteinemia.
The results show, that homocystein is no qualified parameter for clinical diagnosis.
Homocystein / dog / reference range / creatinine / protein reduced diets