Properties of the plasma very low and low density lipoproteins in Tangier disease

The absence of normal high density lipoproteins (HDL) in Tangier disease is well established, but the properties of very low density lipoproteins (VLDL) and low density lipoproteins (LDL) in this disorder have not been well defined. The profiles obtained by analytic ultracentrifugation and the chemical composition, morphology, and electrophoretic mobility of Tangier and normal VLDL and LDL were compared. Apolipoproteins were fractionated by gel chromatography and characterized by amino acid analysis, polyacrylamide-gel electrophoresis, and immunochemical reactivity. Concentrations of low density lipoproteins of S(f) (o) 0-12 were reduced in three of six Tangier plasmas studied by analytic ultracentrifugation. Accumulation of intermediate density lipoproteins (S(f) (o) 12-20) was not observed. Two subjects with hypertriglyceridemia had normal VLDL (S(f) (o) 20-400) levels, suggesting that abnormalities of chylomicron metabolism probably account for the hypertriglyceridemia frequently observed in this disorder. Tangier VLDL migrate more slowly than normal VLDL on paper electrophoresis, yet their morphology, gross chemical composition, and qualitative apolipoprotein content are similar. Quantitative abnormalities in C-apolipoproteins, however, were observed in Tangier VLDL. When patients were consuming unrestricted diets, C apoproteins accounted for 19-49% of the protein in lipoproteins of d < 1.006 g/ml. Ingestion of low-fat, high-carbohydrate diets reduced the VLDL-C-apoprotein content in all Tangier patients (mean = 17% of VLDL protein vs. 43% in controls). These findings suggested that a major proportion of the C apoproteins in Tangier plasma is associated with chylomicrons or their remnants, perhaps because the C-apoprotein reservoir normally provided by HDL is absent. This secondary mechanism for C-apoprotein conservation is lost when dietary fat is withdrawn.LDL-2 (1.035 < d < 1.063) from Tangier and control plasma had identical electrophoretic mobilities. Tangier LDL-2 had slightly smaller median diameters (210-225 A vs. 230-240 A in controls) and a quite different composition than normal LDL-2. Triglyceride accounted for a mean of 29% of Tangier LDL-2 mass (control = 6%) and the cholesteryl ester content was reduced by about 50%. Thus, HDL may be required for the generation of chemically normal LDL. Alternatively, the fundamental defect in Tangier disease may involve all lipoprotein classes.