Abstract
Cord serum lipoproteins were characterized in terms of lipid and apoprotein compositions in comparison with adult lipoproteins.
Cord sera were obtained from normal babies of normal mothers and sera were also taken from the same babies one and five days after the births. Adult sera were obtained from normal subjects. Lipoproteins were separated by sequential ultracentrifugation by adjusting density with KBr, and in some experiments a density gradient centrifugation was used to obtain each lipoprotein. Apoprotein (apo) A-I, A-II, B, C-II, C-III, and E were determined by single radial immunodiffusion method. Apo B subclasses were analyzed by polyacrylamide gel electrophoresis in the presence of SDS. HDL subclasses were separated by gradient gel electrophoresis using Pharmacia PAA 4/30 gels. Cord serum total cholesterol (TC), triacylglycerol (TG) and phospholipid (PL) levels were significantly lower than those of adult serum; one-third, one-fourth, and a half of that of adult serum respectively. Baby serum lipid levels increased rapidly with time in as few as five days. Lipid contents of each lipoprotein in cord serum were significantly lower than those of adult lipoproteins, but HDL lipids were in a lower range of normal adult HDL lipids, while cord serum VLDL and LDL lipids were extremely lower. The same amount of TC was found in HDL and LDL in cord serum, which shows that cord serum is relative hyperalpha-lipoproteinema. Cord serum VLDL contains less TG/protein compared with adult VLDL, while the TC/protein ratio was comparable to that of adult VLDL. In cord LDL TC/protein was similar to that in adult LDL, but the PL/protein was twice as high as that of adult LDL. Apoprotein composition of each lipoprotein in cord serum was very similar to that in adult serum. However, cord serum HDL contained more apo E than adult HDL. Cord serum HDL was rich in smaller-sized subclasses compared with adult HDL. SDS-PAGE disclosed that the molecular weight of apo B of both adult and cord sera was mainly composed of a 290k to 300k dalton particle corresponding to apo B-48. In adult apo B a band of 120k dalton, which was thought of as apo B-48, was recognized. In cord serum apo B, there was a trace amount of B-48.
Cord serum was poor in VLDL and rich in HDL, and the amount of TC in HDL and in HDL was the same. Cord serum HDL contained more apo E than adult HDL. These data may imply that HDL can play a role in cholesterol supply to peripheral cells by virtue of apo E in fetus, because apo E is able to bind apo B, E receptor in peripheral cells. The fact that fetus serum contains apo B-48 shows that apo B-48 could be also synthesized in fetal liver or secreted from the intestine without food ingestion. Lipoprotein metabolism in fetus should be further investigated in a system including cells.
