Determination of physical properties of bovine serum lipoproteins by analytical ultracentrifugation

Agarose gel electrophoresis determination of bovine lipoproteins compared with a wet chemistry method

Quantification of serum lipoproteins provides information relative to the overall metabolic health, degree of lipid mobilization, and hepatic function of dairy cattle. Automated assays performed on benchtop chemistry analyzers and commercially available kits use reagents developed for human lipoproteins. The substantial physical and chemical differences between bovine and human lipoproteins potentially confounds the use of these assays in evaluating bovine lipoproteins. In this study, we prospectively analyzed serum lipoproteins from 56 Holstein cows using horizontal slab agarose gel electrophoresis to semi-quantify the high-density lipoprotein (HDL) and low-density lipoprotein (LDL) fractions by optical densitometry. Ultracentrifugation was used to confirm the electrophoretic separation pattern of the lipoproteins. The values obtained using the electrophoretic method were compared with values obtained by direct measure of HDL cholesterol, total cholesterol, and triglyceride (TG) concentrations on a Roche chemistry analyzer, and calculated LDL cholesterol. Correlation between these methods was poor for HDL (Passing-Bablok regression line: y = 30.31 + 0.853x) and could not be calculated for LDL. Automated HDL values were equal to, or higher than, the total cholesterol concentration in 25 of the 56 samples. The TG concentrations were above the reference interval in 18 samples, and these samples had an average of 96% of the cholesterol measured as HDL by the automated method, and 78% HDL by electrophoresis. Given that it is physiologically impossible to have more cholesterol within the HDL fraction than in the total serum fraction, and the increased proportion of TG found in LDL and very-low-density lipoprotein, our results draw into question the accuracy of the Roche automated assay in quantifying bovine lipoprotein fractions.

Characterization of Particle Size Distribution of Plasma Lipoproteins in Dairy Cattle Using High-Resolution Polyacrylamide Electrophoresis

Plasma lipoproteins play critical roles in energy metabolism and inflammation. Concentrations of high-density lipoproteins (HDL) are linked to reproductive outcomes and milk yields in dairy cattle. Low-density lipoproteins (LDL), which are enzymatically formed in the blood from very low-density lipoproteins (VLDL) following secretion by the liver, have been used as a surrogate marker of liver function due to the rapid influx of circulating VLDL into the lactating mammary gland. In humans, the composition of plasma lipoproteins is reflected in lipoprotein particle size distribution, and both of these parameters are highly predictive of disease development and related health outcomes. Bovine HDL are overall larger, less dense particles compared to human HDL. Lipoprotein particle size distribution in both health and disease is understudied in the bovine. We hypothesize that a more detailed analysis of lipoproteins could hold diagnostic and/or prognostic value in the study of dairy cattle health and production. In this study, we took the first steps in this characterization and used a high-resolution polyacrylamide gel electrophoretic assay to better define LDL and HDL at the subfraction level in Holstein cows at different stages of lactation. We extensively characterized the lipoprotein particle size distribution in healthy lactating dairy cattle. We identified subfractions of LDL that were prominent only in the dry period and subfractions of HDL that were highest in cows during mid-lactation. Use of this method could be informative in the study of multiple herds and management strategies, including longitudinal evaluation of animals and production parameters.

Uptake and intracellular degradation of fluorescent sphingomyelin by fibroblasts from normal individuals and a patient with Niemann-Pick disease

Sphingomyelin, labelled with a fluorescent probe, pyrene, in the fatty acyl residue was associated with fetal calf serum; approx. 80% of the sphingomyelin was found in the low- and high-density lipoproteins. This was added to the growth medium of cultured human skin fibroblasts from normal individuals and a patient with Niemann-Pick disease type A, devoid of acid sphingomyelinase activity. The fluorescent sphingomyelin was taken up by both cell types, but only the former degraded it to produce fluorescent ceramide. Differences between normal and Niemann-Pick cells in sphingomyelin content or ceramide production were observed after several hours uptake. A more pronounced difference was noted when cells were incubated for 1 day with fluorescent sphingomyelin and then for two to three days in medium devoid of this compound. Under these conditions, the fluorescence intensity of the Niemann-Pick cells remained practically constant while that of their normal counterparts was almost completely eliminated from the cells. Comparison of fluorescence intensities of these two cell types could be made directly on aqueous suspensions of whole cells or, alternatively, on their lipid extracts. For evaluation of the degradation of fluorescent sphingomyelin to ceramide within the cells, several procedures were developed for the rapid isolation of the latter compound from the total lipid extract. The results suggest that when associated with the constituents of the fetal calf serum, sphingomyelin is taken up by the cells and transported into the lysosomal compartment where it is degraded to ceramide. Use of the fluorescent derivative of sphingomyelin provided a simple and rapid procedure for following the uptake by and degradation within the cultured cells. It also permitted the establishment of differences in the rates of degradation of the fluorescent sphingomyelin by cells with a normal metabolism and others lacking sphingomyelinase (i.e., Niemann-Pick disease type A cells).

The serum lipoprotein pattern of water buffalo (Bubalus bubalis)

1. The serum lipoprotein pattern of water buffalo was studied by means of electrophoresis and the lipoproteins were isolated by ultracentrifugation on the basis of their hydrated density. 2. High density lipoproteins (HDL) showed a higher level of cholesterol than did the other lipoproteins. Moreover, the level of phospholipids was higher in HDL than in very low density lipoproteins (VLDL). 3. The buffalo B100 apoprotein was similar to that of man and rat. Three apoproteins similar to human apo E, apo AI and AII were found in buffalo HDL, buffalo VLDL contained essentially apo B protein.

Comparison of ultracentrifugation and gel filtration for the isolation of bovine lipoproteins

Lipoproteins from the plasma of three nonlactating Holstein cows were isolated using either preparative ultracentrifugation or gel filtration chromatography. Lipoprotein classes obtained by ultracentrifugation were very low density plus chylomicra, less than 1.006 g/ml; low density, 1.007-1.039 g/ml; high density1, 1.040-1.063 g/ml; and high density, 1.064-1.22 g/ml. These lipoprotein classes were individually applied to an agarose gel column to determine at what volume they eluted in comparison to lipoproteins that were separated after applying total bovine lipoproteins to the column. Three major peaks corresponding to very low density lipoproteins plus chylomicra, low density, and high density lipoproteins resulted after gel filtration of total lipoproteins. Very low density lipoproteins plus chylomicra, obtained by ultracentrifugation, eluted as a single peak, as did low density and high density lipoproteins. However, high density1 lipoproteins eluted as two peaks. The first peak eluted at the same volume as low density lipoproteins, and the second peak eluted at a volume similar to that of the ascending slope of the high density lipoprotein peak. Results from disc polyacrylamide gel electrophoresis, immunoelectrophoresis and double immunodiffusion of lipoprotein fractions, and SDS polyacrylamide gel electrophoresis of their apoproteins, similarly indicated that the lipoproteins present in the 1.040-1.063 g/ml density interval are a mixture of low and high density lipoproteins rather than a unique class of lipoproteins.

Dietary lipid metabolism in lactating dairy cows

Effects of feeding an oil seed supplement treated with formalin upon lipid patterns of blood and synthesis of milk fat were evaluated. Percentages and yields of fatty acids of milk fat with chain lengths between 6 and 16 carbons were decreased while percentages and yields of stearate and linoleate were increased when the lipid supplement was fed. Calculations in cows fed control and supplement, 60% and 80%, respectively, of fatty acids of milk were derived from lipids of blood were supported by arterial-venous differences. Comparisons of the fatty acid compositions of triacylglycerol of plasma and milk fat suggested that triacylglycerol may not be the sole source of linoleate transferred from blood to milk fat. A preliminary evaluation of supplement effects upon lipoprotein patterns of serum indicated two peaks in the low density lipoprotein class and that the increase in total cholesterol of blood caused by feeding lipid supplement is due to increases in cholesterol content of the low density and high density lipoprotein classes.

Immunological properties of bovine serum lipoproteins and chemical analysis of their protein moieties

Four classes of bovine serum lipoproteins were isolated by precipitation with dextran sulfate, ultracentrifugation, and preparative electrophoresis on polyacrylamide gel. Very low density lipoprotein (d less than 1.019 g/ml) was related immunologically to low density lipoprotein-two (d 1.039 to 1.060 g/ml) and high density lipoprotein (d 1.060 to 1.210 g/ml) was related immunologically to low density lipoprotein-one (d 1.019 to 1.039 g/ml), but the two pairs were immunologically distinct. The major N-terminal amino acid of both high density lipoprotein and low density lipoprotein-one was aspartic acid, and that of low density lipoprotein-two was glutamic acid. Very low density lipoprotein had both aspartic acid and glutamic acid as the major N-terminal amino acids. None of the lipoproteins was identical with any other with respect to amino acid composition, but high density lipoprotein and low density lipoprotein-one were similar to each other and different from low density lipoprotein-two. Very low density lipoprotein was similar to both low density lipoprotein-one and low density lipoprotein-two. It is concluded that the proteins of high density lipoprotein and of low density lipoprotein-one are related and are different from that of low density lipoprotein-two. The protein of very low density lipoprotein is related to that of low density lipoprotein-two but may contain polypeptides of high density lipoprotein or low density lipoprotein-one.