High density lipoproteins from bovine plasma and follicular fluid do not possess a high affinity for glycosaminoglycans

Distribution of apolipoprotein E among lipoprotein fractions in the lactating cow

Apolipoprotein (apo) E plays a key role in regulating plasma levels of lipoproteins. We investigated the serum apoE concentrations in cows during different lactating stages by ELISA. To confirm the distribution of apoE in lipoprotein fractions, cow plasma was separated by gel filtration, ultracentrifugation and agarose gel electrophoresis. The apoE concentrations during early, mid- and late lactating stages in cows were significantly higher than that during the non-lactating stage. In lactating plasma, apoE eluted in high-density lipoprotein (HDL) fractions separated by gel filtration increased. The portion of this apoE in plasma was 49%. However, when lactating plasma was separated by ultracentrifugation, less then 5% apoE was recovered in the HDL fraction, and more apoE was recovered in the non-lipoprotein fraction (d>1.21 g/ml, 46%). In agarose gel electrophoresis, plasma apoE was found in beta-migrating lipoprotein, but it was not present in alpha-migrating lipoprotein. To purify apoE-containing particles, the HDL fraction separated by gel filtration was pooled and the fraction retained on Heparin-Sepharose chromatography collected. Cholesterol was absent from this fraction. These results suggest that apoE-containing particles, which increased during the lactating stage, were not associated with HDL particles, and that lipid-free forms were included in cow plasma.

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.

Characterization of proteoglycans and glycosaminoglycans in bovine renal AA-type amyloidosis

Highly sulfated glycosaminoglycans (GAG) or proteoglycans (PG), especially heparan sulfate (HS) and heparan sulfate proteoglycan (HSPG), are considered to be intimately associated with amyloid deposits in different types of amyloidosis. Based on this relationship an important role for HS has been suggested in amyloidogenesis. The present immunohistological and ultrastructural study shows that in bovine renal AA-amyloidosis, sulfated GAG/PG was not restricted to amyloid deposits proper and that areas without GAP/PG were also present within the amyloid. Both glomerular and papillary amyloid contained HS (PG), and the latter also contained chondroitin sulfate (CS) and dermatan sulfate (DS), suggesting a correlation between the location of the amyloid and the type of GAG/PG deposited. Amyloid P component (AP) had a distribution similar to that of HSPG, confirming their affinity-based relationship. The GAG types found ultrastructurally in amyloid fibril preparations of glomerular and papillary amyloid isolated from the same kidney, reflected the immunohistological findings. HS was shown to be the predominant GAG in all papillary amyloid fibril extracts. Taking into account the chemico-physical properties of HS, it cannot be excluded that this predominance is introduced by the purification procedure. These results suggest that the association of GAG/PG and amyloid is not necessarily mutually obligatory and that the proposed importance of GAG in amyloidogenesis is disputable.

Assessment of lipoprotein activators of skim milk lipoprotein lipase and the relationship between lipoprotein lipase activity and milk fat synthesis

Bovine plasma and lipoproteins isolated by gel filtration chromatography were examined for their ability to activate skim milk lipoprotein lipase. Addition of equal amounts of protein from either triglyceride-rich lipoprotein, low density lipoprotein, high density lipoprotein or plasma to a lipoprotein lipase assay resulted in 6.0, 2.2, 2.5, or 1.1% hydrolysis of radiolabelled triglyceride emulsion. Lipoprotein lipase activity in skim milk was evaluated as an indicator of mammary lipid secretory capacity. Skim milk lipoprotein lipase activity was significantly lower immediately prepartum as compared with activity immediately postpartum (.2 vs. 5.4% of substrate hydrolyzed). Skim milk lipoprotein lipase was significantly higher during the final 12 d of lactation than in samples obtained 12 d after machine milking was terminated (5.6 vs. less than 1% of substrate hydrolyzed). Although skim milk lipoprotein lipase activity appeared positively related to mammary lipid secretory capacity during the time immediately surrounding initiation and cessation of copious milk production, activity between those periods was not correlated to milk fat percentage, milk fat yield, or stage of lactation.