Lipoproteins and apolipoprotein patterns in rat plasma after liver injury induced by D-galactosamine

The effect of galactosamine administration on the concentration and composition of plasma lipoproteins was studied in female rats. After a single intraperitoneal injection of 3.48 mmol galactosamine/kg the following alterations occurred within 24 h: Disappearance of alpha-lipoproteins as shown by agarose electrophoresis, increase of abnormal lipoproteins in the beta- and pre-beta-region. These changes corresponded to a two- to three-fold increase of VLDL and LDL and a decrease of HDL to 20-30% of normal after sequential ultracentrifugation. When compared to control animals, galactosamine-treated rats exhibited an abnormal chemical composition of their plasma lipoproteins: A nearly total loss of cholesterol esters, but an increase of free cholesterol and phospholipids, particularly in the LDL and HDL density classes. Moreover, polyacrylamide gel electrophoresis in 8M urea revealed a clear diminution of all C-apoproteins in the VLDL and HDL density class and a complete disappearance of the A II band in the HDL fraction 24-48 h after galactosamine administration. These lacking apoprotein bands reappeared 72-168 h after galactosamine treatment. The same effects could be obtained by lower doses of galactosamine (2.32 and 1.16 mmol/kg, respectively) which led only to slight increases of hepatocellular enzymes in the plasma. It is concluded therefore, that galactosamine administration in experimental animals leads to profound, but reversible alterations in the synthesis and/or secretion of plasma lipoproteins.

[HDL cholesterol: biochemical aspects (author's transl)]

High density lipoproteins are a heterogeneous mixture of spherical macromolecules which differ in size (80-120 A), chemical composition (apolipoprotein A-I: 30-35%; apolipoprotein A-II: 10-15%; apolipoprotein C: 3-5%; phospholipids 25-30%; cholesterol/cholesterol esters: 15-20%; triglycerides: 3-5%) and physico-chemical properties. They can be isolated through selective precipitation of apolipoprotein B-containing lipoproteins (very low density lipoproteins, low density lipoproteins, lipoprotein (a)) and, under routine conditions, quantitation can be performed by the determination of their cholesterol or apolipoprotein content. A considerable portion of high density lipoproteins originates in plasma from discoidal phospholipid-apolipoprotein bilayers (thickness: 46 A; diameter: 190 A). These bilayers are in part synthesized by the liver and in part derived from the surface of chylomicrons during lipolysis. The role of discoidal precursors of high density lipoproteins in cholesterol-uptake from peripheral cells will be discussed.

[HDL cholesterol: clinical and pathobiochemical aspects (author's transl)]

The determination of high density lipoprotein (HDL)-cholesterol in patients with mild hypercholesterolemia (240-300 mg/dl) allows one to distinguish between hyperbetalipoproteinemia (= high atherogenic risk) and hyperalphalipoproteinemia (= low atherogenic risk). In addition, analysis of HDL-cholesterol is of value in the prediction and early recognition of coronary heart disease, particularly in combination with known risk factors (hypertriglyceridemia, adipositas, smoking). This prognostic value of HDL-cholesterol is a result of its negative correlation to coronary heart disease which has been recognized in epidemiologic and clinical studies. The study of Tangier disease (analphalipoproteinemia) and tissue culture experiments will provide opportunities for the further elucidation of the role of HDL in atherogenesis.

[Screening and therapy control of lipid metabolism disturbances in general practice (author's transl)]

The determination of total cholesterol and triglycerides in fasting serum is the basic program for routine diagnosis and therapy control of lipid metabolic defects. With the introduction of routine determination of HDL-cholesterol and LDL-cholesterol into the laboratory of the general practitioner, differential diagnosis of lipid metabolism disorders and therefore an improved recognition of the coronary risk becomes possible. The combination of hypertriglyceridemia and a low HDL-cholesterol as a possible indicator of diminished intravascular lipolysis is especially significant for the recognition of individual risks. The indications for the diagnosis and therapeutic control of hyperlipidemia as well as the value of the lipid parameters for the prediction and early diagnosis of coronary heart disease is discussed.

Lipoprotein and apoprotein values in coronary angiography patients

In this study the lipoprotein and apoprotein patterns of patients with coronary artery disease were evaluated. The patient population consisted of 179 men who underwent coronary arteriography. On the basis of the results of coronary arteriography these patients were subdivided into a control group (score 0) with normal arteriograms and three groups each having coronary artery disease (CAD) of increasing severity (scores 1 to 3). The patients with coronary artery disease had significantly higher plasma concentrations of total cholesterol, LDL cholesterol, triglycerides and apolipoprotein B (apo B) than the controls. HDL cholesterol as well as apolipoprotein A-I (apo A-I) were significantly lower in patients with coronary artery disease. However, no difference was found in apolipoprotein A-II (apo A-II) values. Apo B and LDL cholesterol increased with the degree of coronary atherosclerosis. In the discriminant function analysis, apo B was the best separating parameter between control patients and CAD patients (scores 1-3).

Role of low-density and high-density lipoproteins in atherogenesis

Among the cholesterol-carrying lipoproteins, low-density lipoproteins (LDL) have been associated with coronary heart disease as a risk factor while high-density lipoproteins (HDL) appear to protect against coronary heart disease. According to studies with cells in tissue culture, control mechanisms of receptor-mediated LDL uptake are important in maintaining the cholesterol balance within the arterial cells. HDL may be a vehicle for transporting cholesterol from peripheral cells to the liver. Recent results, derived from studies of patients affected with Tangier disease (absence of HDL in plasma), favor the hypothesis that HDL precursors (e.g. surface remnants of chylomicrons) may be more potent in cholesterol uptake than mature HDL.

Demonstration of human apolipoprotien A in isolated mucosal cells from small intestine and isolated hepatocytes

Isolated mucosal cells from the human jejunum and stomach, cryostat sections from the jejunum, isolated parenchymal liver cells and lymphocytes were investigated for the presence of apolipoprotien A (apoA). Antisera against purified human apoA-I and apoA-II were raised in rabbits and conjugated with fluorescein-isothiocyanate (FITC). Mucosal cells from jejunum and stomach were isolated with pronase from tissue obtained from operated patients. ApoA-I and apoA-II could be demonstrated in isolated mucosal cells as well as in cryostat sections from the jejunum. The fluorescence pattern in isolated jejunal cells was coarse granular. In the radial gel diffusion test the homogenate from mucosal cells of jejunum showed a single precipitation line with anti-apoA-I and with anti-apoA-II, respectively. The reaction was more intensive with anti-apoA-I than with anti-apoA-II. Isolated gastric cells were negative for apoA. Hepatocytes incubated with FITC anti-apoA-I showed a fine granular fluorescence pattern in the cytoplasm. Anti-apoA-II did not react with hepatocytes. There was no evidence for an in vivo fixation of serum-apoA at the surface of isolated mucosal cells from jejunum or isolated hepatocytes. The results support the hypotheses that in man apoA is synthesised in the epithelial cells of the small intestine and in parenchymal liver cells.

[Tangier-disease (author's transl)]

Tangier disease is a rare autosomal recessive lipid transport disease characterized by the absence of the usual high density lipoproteins from plasma and cholesteryl ester storage in many organs. 25 cases of Tangier disease have been described so long. The predominant clinical symptoms include tonsilar hypertrophy, splenomegaly and peripheral neuropathy. The cholesteryl ester storage is limited to macrophages, Schwann's cells and intestinal smooth muscle cells. Hypocholest erolemia (less than 80mg/dl), hypertriglyceridemia (greater than 200 mg/dl), and the absence of high density lipoproteins in agarose electrophoresis are the major plasma abnormalities. The protein moiety of normal high density lipoprotein consists of apoprotein A-I and apoprotein A-II. In Tangier disease, serum concentrations of these apoproteins are reduced to less than 1% and 5-10%, respectively. Theories concerning the pathogenesis of Tangier disease are only incomplete and unproved up to now; however, a structural abnormality of apoprotein A-I causing an inability to bind to lipid or other proteins (apoprotein A-II) is consistent with several of the recent biochemical findings. The imbalance of cellular cholesterol metabolism caused by the absence of high density lipoproteins as well as the presumed role of these lipoproteins in cholesterol removal from cells are discussed in this article.

Characterization of the oligosaccharide side chain of apolipoprotein C-III from human plasma very low density lipoproteins

Apolipoprotein C-III1 and apolipoprotein C-III2 each contain one oligosaccharide side chain, bound O-glycosidically to threonine in position 74 of the amino acid sequence. The studies reported in this paper characterize these alkali labile oligosaccharides, thereby demonstrating the complete structure of apolipoprotein C-III. Monosaccharide analysis revealed the following sugar composition: D-galactose/N-acetyl-D-galactosamine/sialic acid 1 : 1 : 1 and 1 : 1 : 2 for apolipoprotein C-III1 and apolipoprotein C-III2, respectively. Treatment of desialylated apolipoproteins with alkaline borohydride released the reduced disaccharide beta-D-galactosyl-(1 leads to 3)-N-acetyl-D-galactosaminitol, which was detected by gas-liquid chromatography. Further studies employing periodate oxidation and Smith degradation indicated that the structure of the trisaccharide from apolipoprotein C-III1 was alpha-N-acetylneuraminyl-(2 leads to 3)-beta-D-galactosyl-(1 leads to 3)-N-acetyl-D-galactosaminitol. The tetrasaccharide structure from apolipoprotein C-III2 is made up of this trisaccharide plus one sialic acid residue linked to C6 of N-acetyl-D-galactosaminitol, as was shown by the assessment of chromogens formed upon alkaline degradation.

High density lipoprotein infusion and partial plasma exchange in Tangier disease

High density lipoprotein (HDL) infusion and partial plasma exchange were undertaken in two patients homozygous for Tangier disease. Serum samples and ultracentrifugally isolated serum fractions were analysed over a period of 7 days post infusion by agarose electrophoresis, two-dimensional immunoelectrophoresis (employing antibodies to HDL, HDL3, Apoprotein A-I, and Apoprotein A-II), Apoprotein A radioimmunoassay, and analytical polyacrylamide electrophoresis. The following observations were made: (a) immediately after HDL substitution the broad-beta band, normally visible upon agarose electrophoresis of Tangier plasma, resolved into a distinct beta and pre-beta band; (b)as HDL was catabolized, an abnormal alpha-migrating lipoprotein was generated which contained Apoprotein A-II as protein constituent; and (c) there was a proferential loss of Apoprotein A-I from HDL and the plasma compartment in the course of HDL catabolism. The results suggest that the defect in Tangier disease resides with enhanced catabolism or defective synthesis of Apoprotein A-I.

Characterization of high density lipoproteins in patients heterozygous for Tangier disease

In this study a large family group affectd with Tangier disease has been investigated. Besides two homozygous propositi, several heterozygous patients have been identified on the basis of quantitative measurements of high density lipoproteins and their constitutive polypeptides. By a variety of quantitative immunological methods, such as one-dimensional Laurell eletrophoresis, two-dimensional immunoelectrophoresis, and double-antibody radioimmunoassay, the total amount of apoprotein A-I and apoprotein A-I contained in the serum of heterozygous patients and the distribution of these A apoproteins among serum lipoproteins have been determined. The molar ration of apoprotein A-I and apoprotein A-II contained in high density lipoproteins of heterozygous patients did not significantly differ from that of control preparations, although the total mass of high density lipoproteins was reduced by approximately 50%. The elution profile of high density lipoproteins from agarose columns and their morphological appearance, as ascertained by electron microscopy, were similar to control preparations. In addition to the quantitative alterations of serum lipoproteins, lipid storage in histiocytes of the rectal mucosa obtained from heterozygous patients has been documented. It is concluded that patients heterozygous for Tangier disease have normal high density lipoproteins in circulation, the total mass of which is reduced by approximately 50%.

Isolation and characterization of an abnormal high density lipoprotein in Tangier Diesase

The nature of the high density lipoproteins has been investigated in five patients homozygous for Tangier disease (familial high density lipoprotein deficiency). It has been established that Tangier high density lipoproteins, as isolated by ultracentrifugation, are morphologically heterogenous and contain several proteins (Apo B, albumin, and Apo A-II). An abnormal lipoprotein has been isolated from the d = 1.063-1.21 g/ml ultracentrifugal fraction by agarose-column chromatography which contains apoprotein A-II as the sole protein constituent. In negative-stain electron microscopy, these lipoproteins appeared as spherical particles 55-75 A in diameter. By a variety of criteria (immunochemical, polyacrylamide electrophoresis, amino acid composition, and fluorescence measurements), apoprotein A-I the major apoprotein of normal high density lipoproteins and the C apoproteins were absent from this lipoprotein. As demonstrated by (125)I very low density lipoprotein incubation experiments with Tangier plasma, C apoproteins did not associate with lipoproteins of d = 1.063-1.21 g/ml. Tangier apoprotein A-II, isolated to homogeneity by delipidation of the apoprotein A-II-containing lipoprotein or Sephadex G-200 guanidine-HCl chromatography of the d = 1.063-1.21 g/ml fraction, was indistinguishable from control apoprotein A-II with respect to amino acid composition and migration of tryptic peptides in urea-polyacrylamide electrophoresis. The ability of Tangier apoprotein A-II to bind phospholipid was demonstrated by in vitro reconstitution experiments and morphological and chemical analysis of lipid-protein complexes. It is concluded that normal high density lipoproteins, as defined by polypeptide composition and morphological appearance, are absent from Tangier plasma and that as a consequence, the impairment of C apoprotein metabolism contributes to the hypertriglyceridemia and fasting chylomicronemia observed in these patients.

The lipoprotein abnormality in Tangier disease: quantitation of A apoproteins

In this study we have determined by radioimmunoassay and double immunoelectrophoresis the total quantities and distributions of A apoproteins in three adult patients affected with Tangier disease (hereditary alpha-lipoprotein deficiency). Compared with normal plasma, the total quantities of apoproteins A-I and A-II in Tangier plasma were determined to be less than 1% and 5-7%, respectively. In Tangier patients, approximately 90% of the apoprotein A-I sedimented when ultracentrifugations of plasma were carried out at density 1.21 g/ml KBr. By contrast, more than 95% of the apoprotein A-II floated under those conditions. In normal plasma, approximately 90% of both apoproteins A-I and A-II is found in the 1.063-1.21-g/ml KBr density fraction. These findings suggest that complete dissociation of A apoproteins occurs in Tangier plasma. This dissociation of apoproteins was confirmed by double immunoelectrophoresis with monospecific antisera. Immunochemical and electrophoretic experiments did not provide evidence for a structural abnormality of apoprotein A-I in these patients, The results taken together strongly suggest that normal high-density lipoproteins are absent from Tangier plasma.

Swine aortic smooth muscle in tissue culture. Some effects of purified swine lipoproteins on cell growth and morphology

Smooth muscle cells (SMC) were grown from inner media explants of swine aorta and used as a model for studying the role of lipoproteins in atherogenesis. These cultured cells retain the characteristics of SMC through multiple passages. Cell growth curves, in time, were obtained by using standard counting techniques, SMC grew slowly (0.019 cycle/day) in modified Dulbecco-Vogt medium supplemented with 1.5% swine serum. Purified lipoproteins were prepared from three normolipidemic and two hyperlipidemic (cholesterol-fed) swine. When the medium of 84 growth experiments was supplemented with these lipoproteins, SMC growth rate increased linearly with lipoprotein cholesterol concentration up to 10 mg/dl. At 10 mg/dl of lipoprotein cholesterol, very low density lipoproteins (VLDL) increased growth rate 7.2-fold (P less than 0.01); low density lipoproteins (LDL) 5.7-fold (P less than 0.01); high density lipoproteins (HDL2) 3,4-fold (P less than 0.02); and HDLc, and lipoprotein appearing in the hyperlipidemic swine, 3.0-fold (P less than 0.01). Addition of 10% lipoprotein-free serum stimulated growth rate 6.0-fold (P less than 0.01). There was no difference between normo- and hyperlipidemic lipoproteins with respect to cell growth rate. Factors present in the ultracentrifugal bottom, and factors appearing during the platelet release reaction, were shown to contribute to the SMC growth response. Morphological alterations characteristic of intimal foam cells occurred in SMC grown in VLDL at triglyceride levels in excess of 15 mg per 100 ml. Thus there are distinct parallels between SMC response in this model in vitro and atherogenesis in vivo.

Swine lipoproteins and atherosclerosis. Changes in the plasma lipoproteins and apoproteins induced by cholesterol feeding

Cholesterol feeding in miniature swine resulted in a hypercholesterolemia with a distinctive hyperlipoproteinemia and the subsequent development of atherosclerosis. Alterations in the type and distribution of plasma lipoproteins induced by cholesterol feeding were as follows: (a) the occurrence of beta-migrating lipoproteins (B-VLDL) as well as very low density lipoproteins in the d less than 1.006 ultracentrifugal fraction; (b) an increased prominence of the intermediate lipoproteins (d = 1.006-1.02); (c) an increased prominence of low density lipoproteins; and (d) the occurrence of a distinctive lipoprotein with alpha mobility which was referred to as HDLc (cholesterol induced). Characterization of the various plasma lipoproteins included chemical composition, size by electron microscopy, and apoprotein content. The B-VLDL resembled the beta-migrating lipoproteins of human Type III hyperlipoproteinemia and contained a prominent protein equivalent to the arginine-rich apoprotein in addition to the B apoprotein, apo-A-I, and the fast-migrating apoproteins (apo-C). The HDLc were rich in cholesterol, ranged in size from 100 to 240 A in diameter, and contained the arginine-rich apoprotein and apo-A0I but lacked the B apoprotein. The arginine-rich apoproteins isolated from B-VLDL and HDLc by gel chromatography were similar in amino acid analyses, with glutamic acid as their amino-terminal residue. The occurrence of a spectrum of cholesterol-rich lipoproteins which contained the arginine-rich apoprotein with the occurrence of accelerated atherosclerosis suggested an interesting, although speculative, association.

Accumulation of oxygenated steryl esters in Wolman's disease

7alpha- and 7beta-hydroxycholesteryl esters, 7-ketocholesteryl esters, and 5,6alpha- and 5,6beta-epoxycholesteryl esters have been identified in tissues of patients affected by Wolman's disease. Their structural identities were determined by mass spectroscopy and nuclear magnetic resonance spectroscopy and confirmed by chemical synthesis. It is postulated that cholesteryl ester hydrolase deficiency in Wolman's disease might lead to accumulation of oxygenated steryl esters in vivo and impairment of bile acid formation.

13C nuclear magnetic resonance spectroscopy of native and recombined lipoproteins

(13)C nuclear magnetic resonance data on native and recombined lipoproteins are reported. [Methyl-(13)C]phosphatidylcholine, [methyl-(13)C]sphingomyelin, 1,2-[dioleoyl-1-(13)C]-sn-phosphatidylcholine and cholesteryl-[1-(13)C]oleate were enriched with 90% carbon-13 in respective molecules by chemical synthesis and used for recombination experiments with high density lipoprotein apoproteins. Relaxation times for these specifically enriched lipids in organic solvents, (2)H(2)O, and lipid-protein complexes isolated by ultracentrifugal flotation, were measured. The results show that both the phosphatidylcholine and sphingomyelin polar headgroups have the same hydrophilic environment in either sonicated lipid particles or reassembled lipoproteins, and suggest that ionic interaction of lipid and apolipoproteins is of minor importance in the formation of plasma lipoprotein complexes. Our experiments indicate that (13)C nuclear magnetic resonance spectroscopy will contribute to the understanding of lipidprotein interaction in lipoproteins and membranes.

A molecular model of high density lipoproteins

Based on the analysis of recombined lipidapoprotein complexes by C-13 and P-31 nuclear magnetic resonance spectroscopy and circular dichroism [Assmann, G., Sokoloski, E. A. & Brewer, H. B., Jr. (1974) Proc. Nat. Acad. Sci. USA 71, 549-553; Assmann, G., Highet, R. J., Sokoloski, E. A. & Brewer, H. B., Jr. (1974) Proc. Nat. Acad. Sci. USA 71, in press; Assmann, G. & Brewer, H. B., Jr. (1974) Proc. Nat. Acad. Sci. USA 71, 989-993] and the identification of conformational amphipathic regions in apoproteins, a new model for human high density lipoproteins is proposed. This model is analogous to membrane models proposed by Singer, in that protein "icebergs" are embedded in a "sea" of lipid.

Lipid-protein interactions in high density lipoproteins

Delipidated high density lipoprotein (apo-HDL), isolated apolipoproteins apoA-I and apoA-II, S-carboxymethylated apoA-II, apoC-III, the NH(2)- and COOH-terminal CNBr peptides of apoA-II, and the COOH-terminal CNBr peptide of apoA-I were recombined in vitro with [N-C(3)H(3)-choline]phosphatidylcholine (PC) and [N-(14)CH(3)-choline]sphingomyelin (SPM). The lipid-protein complexes were analyzed by ultracentrifugal flotation, agarose gel chromatography and circular dichroism. ApoHDL, apoA-II, and S-carboxymethylated apoA-II readily recombined with PC or SPM to form particles that were similar in size to native HDL. The COOH- but not the NH(2)-terminal CNBr peptide of apoA-II recombined with lipid. ApoA-I and the COOH-terminal CNBr peptide of apoA-I, however, recombined with PC or SPM to only a limited extent, suggesting that protein-protein interactions between apoA-I and apoA-II are important in the integration of apoA-I into recombined lipoprotein particles. Analysis of the recombined lipid-protein complexes by circular dichroism indicated that there was an increase in helical structure concomitant with lipid-protein binding. The reconstituted particles had many of the physical and chemical properties of the native lipoprotein.

31P nuclear magnetic resonance spectroscopy of native and recombined lipoproteins

Native and recombined lipoproteins have been studied by (31)P nuclear magnetic resonance spectroscopy. Very low-, low-, and high-density lipoproteins exhibited characteristic spectra. The main resonances were assigned to phosphatidylcholine and sphingomyelin. Relaxation times for these phospholipids were separately measured in low-density lipoproteins and high-density lipoproteins. The effect of paramagnetic ions (Eu(+++)) on the nuclear magnetic resonance spectrum of high-density lipoproteins is reported.