Human breast milk lipoproteins: A preliminary biochemical characterization

Human breast milk (BM) is an essential fluid for infant development, with a dynamic composition adapted to the infant's needs. It contains bioactive lipids like cholesterol, typically transported by lactosomes, extracellular vesicles, and milk fat globules. However, classic cholesterol-carrying lipoproteins have not been described in BM. This study included BM from 22 healthy women attending paediatric follow-up. BM lipoproteins were isolated by ultracentrifugation, and their density was determined by refractometry. Cholesterol and triglyceride levels in whole milk and from BM-lipoproteins were quantified using commercial kits. The main lipoproteins were quantified by western blot and Luminex assays. Native gel electrophoresis was used to identify lipoprotein migration patterns. BM lipoproteins exhibited densities between 0.999 and 1.043 g/mL, consistent with very low-density lipoproteins, intermediate-density lipoproteins, and low-density lipoproteins (LDLs). No classic high-density lipoproteins (HDLs) were detected by density, but apolipoproteins AI and B, markers of HDL and LDL, respectively, were detected. BM lipoproteins contained significantly less cholesterol and triglycerides than whole milk and showed migration patterns similar to adult serum HDL and LDL. This study provides the first evidence of classical BM lipoprotein classes, expanding knowledge of lipid transport in BM and suggesting a potential role in neonatal lipid metabolism and cholesterol homeostasis.