SummaryStudies on the cord serum lipid transport system were initiated to determine whether there is a correlation between decreased cord serum lipid levels and the absence or diminished level of some or all of the human serum apolipoproteins. Immunologic studies indicated the presence of all the well-characterized apolipoproteins and provided evidence that these apolipoproteins occurred primarily as distinct lipoprotein species with a paucity of association complexes or what others have termed "triglyceride-rich" lipoproteins. Quantitation of the apolipoproteins present in cord serum by electroimmunoassay yielded the following mean levels: A-I = 730 mg/liter; A-11 = 410 &liter; apolipoprotein B = 280 mg/ liter; C-I = 59 mg/liter; C-I1 = 32 &liter; C-111 = 65 mg/liter; apolipoprotein D = 37 &liter; and apolipoprotein E = 85 mg/ liter. Levels of C-I, C-11, and apolipoprotein E approached adult levels (83 to 86% of the adult levels), whereas apolipoproteins B and D were most reduced when compared to the adult concentrations, 29 and 37%, respectively. The three other apolipoproteins were present at approximately one-half the levels found in adults.
SpeculationThe immunochemical studies on the apolipoprotein levels and lipoprotein forms of cord serum provide part of the data necessary for studying the progressive changes in the human lipid transport system from its fetal form to that of the adult.Studies on the human adult serum lipid transport system have established that the major serum lipids (triacylglycerol, cholesterol, cholesteryl esters, and phospholipids) are bound to particular protein constituents (14, 32). designated apolipoproteins. Such lipid-protein complexes (lipoproteins) have been most commonly classified on the basis of two of their characteristic physical properties. i.e., hydrated density (26) and charge (30).Studies on the antigenic components of the major lipoprotein density classes and electrophoretic bands in the human adult have clearly demonstrated their protein heterogeneity (4, 37) and lead to a classification system based on apolipoproteins as the only distinct chemical markers of this system (1, 2). This concept has been developed into the lipoprotein family theory and has been described elsewhere (2). Recently, the levels of all well-recognized apolipoproteins have been reported (3).Application of these physicochemical techniques to cord sera has established that compared to normal adult levels, very low density lipoprotein (VLDL) is virtually absent (39) or present in low concentrations (13, 15), low-density lipoprotein (LDL) is markedly decreased (8,42), and the predominant lipoprotein density class is high-density lipoprotein (49). In addition, the lipid levels of cord sera are also lower than the corresponding levels in adult sera (42,49,50). However, it has not been established whether there is a correlation between the decreased cord serum lipid levels (42,49,50) and the absence or diminished level of some or all of the apolipoproteins. The studies described herein are the first...