retinol-palmitate and Hyperlipoproteinemia-Type-II

A 49 year-old hypercholesterolemic male with marked electrocardiographic ST segment depression on exercise testing was found to have an apo E E3/3 phenotype by isoelectric focusing, but an APOE E4/3 genotype using HhaI restriction isotyping. DNA sequence analysis of the proband's APOE gene found a G-->C point mutation at codon 251. This predicted a change in the amino acid encoded by codon 251, from arginine to glycine. The mutation occurred on an allele that encoded arginine at position 112 and this variant was named APOE R112; R251G. The R251G change altered a recognition site for the endonuclease StuI and was the basis for a restriction isotyping method to rapidly screen for this mutation. In relatives of the proband, APOE R112; R251G was consistently found in subjects with both hyperlipidemia and atherosclerosis. Apo E R112; R251G-containing very low density lipoproteins bound normally to macrophages in vitro. However, the proband had an abnormal post-prandial lipoprotein response to a dietary fat challenge. The association of APOE R112; R251G with abnormal phenotypes suggests that the amino acid change in the carboxy-terminal, perhaps in combination with the common amino acid polymorphism at codon 112, has a functional impact upon lipoprotein metabolism in members of this family.

Topics: Animals; Apolipoproteins E; Cell Line; Cholesterol; Cholesterol Esters; Coronary Disease; Diterpenes; Female; Humans; Hyperlipidemia, Familial Combined; Hyperlipoproteinemia Type II; Isoelectric Focusing; Lipoproteins, VLDL; Macrophages; Male; Mice; Middle Aged; Oleic Acid; Pedigree; Polymorphism, Restriction Fragment Length; Postprandial Period; Retinyl Esters; Sequence Analysis, DNA; Triglycerides; Vitamin A

The behavior of native retinyl palmitate labeled intestinally derived lipoproteins and their remnants was studied in 8 NZW and 8 WHHL (5 homo- and 3 heterozygote) normal-fed rabbits and in 3 cholesterol-fed NZW, after 1 month of cholesterol feeding, and 3 and 5 months after resuming normal feeding. Palmitate labeled lipoproteins were produced by the intestine after administration of 50,000 IU of Vitamin A, together with olive oil via gastric intubation. Blood was drawn before and 3,6,9,12,24, and in some instances, 48 h later. Retinol (R) and retinyl palmitate (RP) were measured in whole serum and in the chylomicron, d less than 1006, d greater than 1006 less than 1019, d greater than 1019 less than 1063, d greater than 1063 less than 1210 g/ml lipoprotein fractions and in the infranatant. The R content of the serum was almost all concentrated in the infranatant, it did not change during the vitamin A test and was similar in WHHL, and normal- or cholesterol-fed NZW rabbits. In the normal-fed NZW the RP content of the serum increased within 6 h after giving the vitamin A fat meal (peak value less than 200 microgram/100 ml) and then decreased. In the WHHL homozygotes, the RP increased to a much greater degree (peak value 600-1820 micrograms) and for a much longer time, as it was still increased in the 5 cases studied after 24 h, and in 3 cases studied after 48 h. Similar RP curves were obtained in NZW rabbits, after 1 month of cholesterol feeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Diterpenes; Hyperlipoproteinemia Type II; Lipoproteins; Male; Rabbits; Retinyl Esters; Vitamin A

The retinyl palmitate fat tolerance test was used to measure chylomicron remnant clearance in 10 normal subjects (apolipoprotein E [apo E] isotypes 3 or 4 only), 6 normolipidemic apo E2/2 homozygotes and 5 familial hypercholesterolemic homozygotes. Skin fibroblasts with fully upregulated LDL receptors from the latter subjects degraded rabbit 125I-beta VLDL in vitro at rates ranging from less than 10-48% of normal. Experiments in vivo revealed no significant differences between the normal and homozygous familial hypercholesterolemic (FHH) subjects in chylomicron remnant clearance assessed on the basis of "areas under the curves" for retinyl palmitate levels present in post-prandial serum, chylomicron remnants (Sf. less than 1,000), or chylomicrons (Sf. greater than 1,000). Remnant clearance was greatly decreased at all times in the apo E2/2 homozygotes, indicative of an important degree of flux control exerted by a receptor-mediated step involving apo E as ligand. The absence of any excess remnant accumulation in FHH subjects with varying "impairment" of LDL receptor-mediated degradation of apo E-containing lipoproteins, permits the conclusion that chylomicron remnants are initially cleared from the plasma by apo E-recognizing receptors which are genetically distinct from LDL receptors.

Topics: Adolescent; Adult; Cells, Cultured; Chylomicrons; Diterpenes; Female; Homozygote; Humans; Hyperlipoproteinemia Type II; Lipoproteins, LDL; Lipoproteins, VLDL; Male; Metabolic Clearance Rate; Receptors, LDL; Retinyl Esters; Vitamin A