Electrophoretic characterization of bovine serum lipoproteins throughout gestation and lactation

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.

High Density Lipoprotein: Assembly, Structure, Cargo, and Functions

Cardiovascular disease (CVD) is the leading cause of death globally. For close to four decades, we have known that high density lipoprotein (HDL) levels are inversely correlated with the risk of CVD. HDL is a complex particle that consists of proteins, phospholipids, and cholesterol and has the ability to carry micro-RNAs. HDL is constantly undergoing remodelling throughout its life-span and carries out many functions. This review summarizes many of the different aspects of HDL from its assembly, the receptors it interacts with, along with the functions it performs and how it can be altered in disease. While HDL is a key cholesterol efflux particle, this review highlights the many other important functions of HDL in the innate immune system and details the potential therapeutic uses of HDL outside of CVD.

Effects of supplemental parenteral administration of vitamin E and selenium to Jerseys and Holsteins during the nonlactating period

OBJECTIVE

To determine effects of breed and supplemental administration of vitamin E and selenium (Se) during late gestation on circulating concentrations of these micronutrients in periparturient Jerseys and Holsteins.

DESIGN

Randomized controlled clinical study.

ANIMALS

16 Jersey and 36 Holstein cows.

PROCEDURE

Cows were allotted to blocks on the basis of breed and expected parturition date. Cows within blocks were randomly assigned to be given vitamin E or Se parenterally 3 to 4 weeks prior to anticipated parturition in a 2 x 2 factorial design.

RESULTS

Results of ANOVA indicated Jerseys had higher blood concentrations of Se and lower serum concentrations of vitamin E than Holsteins at the end of lactation. Jerseys had higher blood concentrations of Se than Holsteins 3 to 4 weeks prior to parturition and at parturition. Selenium administration increased blood concentrations of Se at parturition. Administration of nutrients did not affect serum concentrations of vitamin E at parturition or 2 to 3 weeks after parturition or blood concentrations of Se 2 to 3 weeks after parturition.

CONCLUSIONS AND CLINICAL RELEVANCE

Jerseys and Holsteins consuming rations of comparable Se content differ in blood concentrations of Se during the nonlactating period, suggesting breed-related differences in Se metabolism during late lactation and the nonlactating period. Parenteral administration of Se 3 to 4 weeks prior to anticipated parturition increased blood concentrations of Se at parturition; however, Se concentrations of both groups at parturition were considered within the reference range for clinically normal cattle.

Dietary vitamin A modulates the concentrations of RRR-alpha-tocopherol in plasma lipoproteins from calves fed milk replacer

The practice of supplementing milk replacers fed to neonatal calves with high concentrations of vitamin A has raised concerns regarding the effect of excess vitamin A on the bioavailability of vitamin E. A 4 x 2 factorial experiment evaluated the effects of four dietary amounts of vitamin A [0, 1.78 [National Research Council (NRC)(6) requirement, control], 35.6 and 71.2 micromol daily as retinyl acetate] and two forms of vitamin E (RRR-alpha-tocopherol and RRR-alpha-tocopheryl acetate, 155 micromol daily) on plasma RRR-alpha-tocopherol and RRR-gamma-tocopherol and RRR-alpha-tocopherol associated with plasma lipoproteins (Lp) from milk replacer-fed Holstein calves from birth to 28 d of age. The VLDL, LDL, HDL and very high-density lipoprotein (VHDL) fractions were separated by ultracentrifugal flotation, and the amount of vitamin E associated with each fraction was determined by normal-phase HPLC. The amount and distribution of RRR-alpha-tocopherol in Lp fractions were unaffected by the form of dietary vitamin E. Plasma and Lp RRR-alpha-tocopherol concentrations increased with age (P < 0.0001) and were maximal at 28 d of age. Concentrations of RRR-alpha-tocopherol associated with Lp were 25% (P < 0.01) to 39% (P < 0.0001) lower in calves fed 35.6 and 71.2 micromol of vitamin A daily than in control calves at 28 d of age. The RRR-gamma-tocopherol concentrations were unaffected by dietary vitamin A (P >/= 0.05). In conclusion, dietary vitamin A modulated the amount and distribution of RRR-alpha-tocopherol in the circulation of milk replacer-fed neonatal calves. Because of the essential antioxidant role of vitamin E, the health-related consequences associated with the depression of the LP RRR-alpha-tocopherol concentrations in calves fed vitamin A at 35.6 and 71.2 micromol need to be investigated.

Serum cholesterol and triglycerides in postpartum beef cows and their relationship to the resumption of ovulation

The variations in lipid metabolism according to the physiological stage and their relationship to the resumption of postpartum ovarian cyclicity were assessed in Limousine beef cows fed a grass diet over 3 yr. Weekly blood samples were collected from 59 cows beginning 10 wk before to 20 wk after calving to evaluate serum cholesterol and triglyceride concentrations and electrophoretic lipoprotein fractions. After parturition, progesterone concentrations were also measured at weekly intervals to determine time of resumption of ovulation. Cows were categorized by resumption of postpartum ovarian cyclicity into 3 groups: early (4 to 6 wk post partum, n = 36); mid (7 to 10 wk post partum, n = 46) and late (after 11 wk post partum, n = 38). Higher serum triglyceride values (P<0.05) were observed during the last 10 wk of pregnancy (0.36+/-0.15 g/L) than during the first 20 wk of suckling (0.29+/-0.09 g/L). Cholesterol values decreased significantly (P<0.05) at the end of pregnancy, were minimal (1.01+/-0.03 g/L) at parturition, and increased again up to 9 wk post calving. Increased cholesterolemia and low serum triglyceride values after calving could be linked to the increased bovine alpha-lipoprotein fraction and decreased beta fraction. Serum triglyceride concentrations were not related to the resumption of postpartum ovarian cyclicity. Higher serum cholesterol values were observed from 2 wk before to 4 wk after calving in cows with early rather than mid and late resumption of ovarian cyclicity. Therefore, modifications in lipid metabolism during the puerperium seem to be related to resumption of cyclicity during the early postpartum period.

Lipoprotein lipase activity of post-heparin plasma in Japanese black cattle affected with fat necrosis

Post-heparin plasma (PHP) lipoprotein lipase (LPL) activity and serum lipoprotein concentration were examined in Japanese Black cows affected with fat necrosis. The PHP-LPL activity in the affected cows was significantly (P < 0.001) higher than in normal animals and tended to reduce 4 weeks after treatment with isoprothiolane. This finding indicates that affected cows have a predisposition to deposit more fat into adipose tissue than normal animals. The serum concentrations of triglyceride in beta-lipoprotein and of cholesterol, phospholipid and total lipid in alpha-lipoprotein were significantly (P < 0.05) lower in the affected cows. Elevated levels of phospholipid and total lipid in alpha-lipoprotein as well as decreased levels of non-esterified fatty acid (NEFA) were observed after medication. It is suggested that isoprothiolane produces an improvement in hepatic lipid metabolism including acceleration of plasma NEFA uptake and alpha-lipoprotein secretion in affected cows.

Blood-lipid and lactation-stage factors affecting serum vitamin E concentrations and vitamin E cholesterol ratios in dairy cattle

The distribution of cholesterol and vitamin E among the various lipoprotein density fractions in bovine blood was measured. The percentage of total plasma vitamin E and cholesterol in the various lipoprotein fractions was very-low-density lipoprotein, 2% and 2%, respectively; low-density lipoprotein, 17% and 22%, respectively, and high-density lipoprotein. 77% and 72%, respectively. Only 3% of plasma vitamin E was not associated with the lipoproteins. Vitamin E cholesterol ratios were not significantly different among lipoprotein fractions (P = 0.3). These results indicate that vitamin E and cholesterol are distributed in equal proportions among lipoprotein fractions. Moreover, the results suggest that variation in the proportions of lipoproteins in the different density fractions would not affect the overall vitamin E cholesterol ratio of plasma. The results further imply that the total plasma vitamin E cholesterol ratio is a valid relative estimator of the vitamin E concentration per lipoprotein particle, regardless of the density distribution of particles. Total serum vitamin E and cholesterol concentrations and their ratio were then determined in commercial diary cattle in various phases of the lactation cycle. There was a significant lactation-stage effect on the serum concentration of each analyte, as well as on their ratio. However, the magnitude of the effect was much less for the ratio than for either vitamin E or cholesterol alone. These results imply that lactation stage affects serum vitamin E concentrations by influencing both the concentration of lipoprotein particles and the concentration of vitamin E within individual particles.

Lipid absorption and transport in ruminants

The objective of this paper is to review new insights on the biological mechanisms of absorption and transport of lipid in ruminants, especially the modern concepts and analytical methods used in studies on structural properties and intravascular and tissue metabolism of lipoproteins and their factors of variation. The intestinal absorption of lipids (including long-chain fatty acids) is detailed, and variations in the qualitative and the quantitative aspects of absorption with diet composition, especially for high fat diets, are presented. Also, structural properties and distribution characteristics of lipoprotein classes in different lymphatic and blood vessels are compared across several animal species. Physicochemical and hydrodynamic properties of the lipoprotein particles and their apolipoprotein moieties are given for the main classes of lipoproteins. Finally, lipoprotein metabolism is discussed in relation to development and physiological, nutritional, and hormonal status. Intravascular metabolism of lipoproteins, including the role of lipolytic enzymes and lipid transfer proteins, is presented. Characteristics of the intestinal and hepatic synthesis of lipoproteins and apolipoprotein fractions are compared, especially through experiments stimulating the hepatic secretion of triglyceride-rich lipoproteins. Different methods of measurement of lipoprotein tissue uptake or secretion in ruminants are discussed.

Plasma lipoproteins in dairy cows with naturally occurring severe fatty liver: evidence of alteration in the distribution of apo A-I-containing lipoproteins

The relationships between fatty liver in dairy cows and reduced levels of plasma lipoproteins, and particularly of low density lipoproteins (LDL), has been previously described. Since electrophoretic heterogeneity of ultracentrifugally isolated LDL (d, 1.006-1.063 g/ml) has been found, the exact nature of this reduction in cows with fatty liver was investigated. Lipoproteins from control and severely afflicted animals were isolated by ultracentrifugation and affinity chromatography on heparin-Sepharose CL 6 B. Gradient gel electrophoresis of lipoproteins on 4-30% gels and an immunolocalization study of apoprotein A-I (apo A-I) showed that control animals have two subpopulations of apo A-I-containing particles with a mean radius of 6.52 and 5.05 nm. In the fatty liver cows, the former was clearly shifted toward smaller particles. We concluded that the depressed level and compositional modifications of LDL in severe fatty liver cows result from a decrease in the oversized apo A-I-containing lipoproteins which can be isolated in the LDL density range. This could stem from the decreased supply of triglyceride-rich lipoprotein surface components for the production of these lipoproteins. The modifications can be plausibly explained by a reduced synthesis or secretion of very low density lipoproteins (VLDL) by the liver.

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.

Isolation and characterization of lipoprotein lipase activators from bovine blood serum

Bovine serum lipoproteins were fractionated into high density and low and very low density lipoproteins by precipitation with sodium phosphotungstate and magnesium chloride. From each lipoprotein fraction seven apo C peptides were isolated by gel filtration and ion exchange chromatography. The two lipoprotein fractions probably contain identical apo C peptides but in different proportions. Two of the apo C peptides activated lipoprotein lipase from milk in vitro. Their specific activities were about 2000 times as high as that of the original serum. The apo C fraction from low-very low density lipoproteins had a specific activity three times that from high density lipoproteins. Also, the activator peptides from low and very low density lipoproteins gave one band on alkaline urea gel electrophoresis whereas corresponding peptides from high density lipoproteins were slightly heterogeneous. The low and very low density lipoproteins, therefore, seem to be the fraction of choice for isolation of activators for lipoprotein lipase.

Fractionation of plasma triglyceride-rich lipoproteins of the dairy cow: evidence of chylomicron-size particles

Electron micrographs of bovine triglyceride-rich lipoproteins demonstrated spherical particles with diameters up to 3000 A. Chylomicron-size particles (larger than 750 A) were isolated specifically by rate zonal centrifugation. Subfractionation by rate zonal centrifugation, isopycnic centrifugation, and gel filtration chromatography all indicated a wide range of bovine triglyceride-rich lipoproteins from chylomicrons to very low density lipoproteins. Chemical analysis of subfractions from gel filtration showed changes in the ratio of triglyceride/protein characteristic of chylomicrons versus very low density lipoproteins. Electrophoretic analysis on agarose gels of bovine chylomicrons obtained by centrifugation and gel filtration showed migrating bands similar to very low density lipoproteins, unlike human chylomicrons. Evidence of bovine chylomicrons provides support for the concept of a significant contribution to milk fat from intestinally absorbed lipid in the dairy cow.

Babesia bovis (Argentina): studies of plasma lipids and lipoproteins during acute infections in cattle

Preliminary studies have demonstrated changes to the lipid metabolism of cattle acutely infected with Babesia bovis. Total lipid, total cholesterol, and phospholipids decreased significantly during infection. Associated with this was a decrease in concentration of serum lipoproteins and a loss of their electrophoretic heterogeneity. These changes are discussed in relation to the pathophysiological changes during infection.

Effect of pregnancy and lactation on triglycerides of very-low-density lipoproteins of rat plasma

Triglyceride in the blood of rats increased during pregnancy, decreased to control during lactation, and increased again on weaning. The triglyceride content of the very-low-density lipoproteins (d less than 1.006 g/ml) changed in parallel with that of the plasma, and its magnitude indicated that it was chiefly responsible for the transport of triglycerides in the blood. These changes were accompanied by changes in the electrophoretic pattern of the lipoproteins of rat plasma, but no such changes were observed in lipoproteins of ovine and caprine serum.

A kinetic concepto of lipid transport in ruminants

Summarization of the literature shows a strong correlation between dietary fatty acid intake and total lipid concentration in plasma in lactating cows whereas total milk fat secreted is related to neither of these. In the process of plasma triglyceride removal, chylomicra and very low density lipoproteins are converted to low density lipoproteins. Limited kinetic data indicate that the fractional removal rates for chulomicra and very low density lipoproteins are rapid in lactating cows whereas fractional removal of low density lipoproteins is slower, resulting in accumulation of the latter in plasma. Under such conditions, low density lipoprotein concentrations of plasma would not be expected to reflect quantitatively the transfer of plasma triglyceride fatty acids to milk fat. Quantitative analysis or triglyceride fatty acid turnover in density less than 1.006 lipoproteins should delineate the role of plasma lipid transport in milk fat synthesis. High fat diets protected from rumen biohydrogenation have proven to be a useful approach in studying ruminant fat metabolism and may be used more extensively to elucidate the role of cholesterol in plasma lipid transport and the metabolism of essential fatty acids in ruminants.

Determination of physical properties of bovine serum lipoproteins by analytical ultracentrifugation

Pure samples of low density lipoprotein-one (d 1.019 to 1.039 g/ml), low density lipoprotein-two (d 1.039 to 1.060 g/ml), and high density lipoprotein (d 1.060 to 1.210 g/ml) were isolated from bovine serum and their properties studied in the analytical ultracentrifuge. Approach-to-equilibrium experiments indicated that the lipoprotein classes were homogeneous. Molecular weights of the lipoproteins given by this method (low density lipoprotein-one, 1.14 x 10(6); low density lipoprotein-two, 2.37 x 10(6); high density lipoprotein, .576 x 10(6)) agreed well with those obtained by a high-speed-equilibrium method (1.03 x 10(6), 2.15 x 10(6), and .567 x 10(6)). Linear plots of flotation rate (corrected for viscosity) against the density of the medium were obtained in sedimentation velocity experiments and on extrapolation gave values for the hydrated density of 1.032 g/ml for low density lipoprotein-one, 1.044 g/ml for low density lipoprotein-two, and 1.071 g/ml for high density lipoprotein. The density of the material which would have to be added to high density lipoprotein to give it the physical properties of low density lipoprotein one was less than 1 g/ml, which suggested that it was predominantly lipid.

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.