Umbilical cord blood lipoproteins. Isolation and characterization of high density lipoproteins.

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Abstract
High density lipoproteins (HDL) (d = 1.063-1.21 g/ml) were isolated from both individual and pooled [human] umbilical cord blood plasma by sequential preparative ultracentrifugation. Mean total HDL concentration was 139 .+-. 9.1 mg/dl, with mean values for cholesterol and triglyceride of 24.9 mg/dl and 5.0 mg/dl, respectively. The particle size distribution of HDL particles was examined by gradient gel electrophoresis (GGE) on 4-30% gels; the range of particle sizes was broader than that reported for adult HDL and showed a deficiency of material in the region defined as (HDL3a)gge. In contrast, the latter is a major peak in adult HDL. The total HDL isolated from the pooled samples were subfractionated by density gradient ultracentrifugation. The subfractions, as well as the total HDL used as starting material, were analyzed for size (both GGE and EM), chemical composition and apolipoprotein [apo] content by both sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis and radioimmunoassay for apo E. Apo E concentration of 1.76 mg/dl in cord blood HDL is highly relative to the low HDL cholesterol values of 24.9 mg/dl. In addition to increased amounts of apo E, cord blood HDL contained apo A-I, apo A-II and traces of apo C. The less dense HDL (d .ltoreq. 1.115) were large (12.0 nm), were enriched in unesterified cholesterol, and contained the bulk of the apo E which was present as a reducible mixed disulfide complex (E-A-II). The more dense HDL (d .gtoreq. 1.115) were smaller and were enriched in total protein and cholesteryl ester. The unusual HDL size distribution, as determined by GGE, and the elevated apo E and apo E-A-II complex content of cord blood HDL point to an altered metabolism of lipoproteins with densities of 1.063-1.21 g/ml in the fetus.