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.

Lipoprotein Particle Size Distributions in Response to a 6-Week Dietary Intervention Using Different Dairy Food Matrices Including Cheese and Butter

Objectives Most dietary guidelines recommend saturated fat (SFA) intakes to be < 10% of total energy intake, since SFA increase low-density lipoprotein cholesterol (LDL-c) levels, a known risk factor for cardiovascular disease (CVD). However, within LDL-c, small, dense LDL particles are more strongly related to CVD risk than large buoyant particles, and response to SFA vary for different foods. Dairy fat, when eaten as cheese, significantly lowers total cholesterol compared to butter. Here, we aimed to test the effect of the cheese matrix on lipoprotein particle size distribution response in overweight adults aged ≥ 50 years. Methods In this secondary analysis of a 6-week randomised parallel intervention(1); participants received ∼40g dairy fat in 1 of 4 treatments: (A) 120 g of full-fat cheddar cheese (FFCC); (B) reduced-fat cheese plus butter (RFC + B); (C) butter, calcium caseinate powder, and calcium supplement (CaCO3) (BCC); or (D) 120 g FFCC as per (A). Fasting EDTA blood samples at wk. 0 (baseline) and wk. 6 were analysed for lipoprotein particle size distribution via nuclear magnetic resonance (NMR) spectroscopy. To examine extremes in response, those with greatest reduction in LDL-c (n = 15, ‘positive’ responders) were compared to those with the greatest increase in LDL-c (n = 15, ‘negative’ responders). Results Correlation analyses between the change in cholesterol levels and change in particle size distribution suggest a relationship between change in LDL-c, HDL-c, and corresponding particle sizes, which differs dependent on the dairy fat matrix. The correlation of LDL-c and LDL particle (LDL-p) concentration weakened as less fat was present within a cheese matrix, as LDL-c decreased so did total LDL-p, due to larger LDL particles. The positive responders displayed a stronger relationship between change in cholesterol and lipoprotein levels, with the changes in cholesterol driven by the large LDL-p and large HDL-p. Conclusions Lipoprotein particle distribution is correlated with change in cholesterol levels after a 6-week intervention of dairy fat. The changes in LDL-c and HDL-c were driven by the less atherogenic, large LDL-p and large HDL-p which are inversely associated with CVD risk. The overall response in LDL-p to SFA appears to vary, dependent on the dairy food matrix in which the fat was eaten. Funding Sources Food for Health Ireland (FHI). Enterprise Ireland.