Isolated Lipoprotein Fractions Research Articles

Effects of lipoproteins on plasma viscosity

Patients with hypertriglyceridemia and mixed hyperlipidemia have been found to have mean plasma viscosities significantly higher than controls ( P < 0.005). In a group of 70 hyperlipidemic patients and controls, plasma viscosity was correlated with plasma triglyceride concentration (r = 0.56, P < 0.01) and to a lesser extent with the concentration of plasma cholesterol (r = 0.29, P 0.05). When isolated lipoprotein fractions were added to lipoprotein-free plasma in increasing concentration over a physiological range, a highly significant linear relationship between plasma viscosity and chylomicron concentrations (r = 0.98, P < 0.001) was apparent. Furthermore, when chylomicrons were removed by ultracentrifugation, viscosity returned to baseline levels. Added VLDL produced a lesser effect (r = 0.70, P < 0.001) and added LDL, over the range of cholesterol concentration studied, had no influence on viscosity. These studies indicate that chylomicrons in particular can increase plasma viscosity. Viscosity increases of the magnitude demonstrated may in turn alter blood flow and thus contribute to symptoms such as intermittent claudication. Chylomicron-induced increases in plasma viscosity and subsequent decreases in local pancreatic blood flow may be one of the factors involved in the known relationship between severe chylomicronemia and acute pancreatitis.

Low density lipoprotein receptor activity in human monocyte-derived macrophages and its relation to atheromatous lesions.

Human peripheral monocytes, isolated from a previously unused source (a leukocyte concentrate byproduct of the plateletphoresis procedure for platelet transfusion), transformed into macrophages while cultured with 5% human serum or isolated lipoprotein fractions. Used for the study of their cholesterol (Chol) metabolism, these human monocyte-derived macrophages had a high-affinity receptor that is saturable, specific for low density lipoprotein (LDL) and maximally induced by incubation for as little as 24 hr in medium devoid of lipoproteins or Chol. Macrophages were shown to have separate receptor activity for 125I-labeled LDL and 125I-labeled acetylated LDL; macrophages that had been incubated with lipoprotein-depleted serum degraded native and acetylated LDL at similar rates. The receptor for LDL was functional in maintaining Chol homeostasis, as demonstrated by feedback inhibition of Chol synthesis after culture with LDL or very low density lipoprotein (VLDL). The Chol content of macrophages was doubled by incubation with medium containing VLDL compared to incubation with LDL (60 microgram of Chol per ml of medium). Incubation with native lipoproteins did not lead to accumulation of esterified Chol by macrophages. Changes in the Chol metabolism of macrophages, rather than modifications in circulating LDL, may cause these cells to store cholesteryl ester and take on the characteristics of cholesteryl ester-laden macrophages of atheromatous lesions.

アスコルビン酸の血清リポ蛋白に及ぼす影響

Effects of hypovitamin C on chemical composition in serum lipoprotein and contents of lipids in the aorta were studied.Guinea pigs were made hypovitamin C by scorbutogenic diet (group 1) or cholesterol and coconut oil added scortogenic diet (group 3) for two weeks. The controls for the experimental animals were fed on a similar diet and supplemented with 25mg of vitamin C daily (group 2 and 4). Lipoproteins were isolated with ultracentrifuge according to Hatch's method. Lipids contents in isolated lipoprotein fractions were estimated with conventional methods described elsewhere. Protein contents in the lipoproteins were estimated by Hartree's method. Amounts of chylmicron, very low density lipoprotein (VLDL), low density lipoprotein (LDL) and high density lipoprotein (HDL) classes were significantly elevated as compared with the control, group 2. Concentration of triglyceride in VLDL, cholesterol ester in LDL were also increased in group 1. Increased amount of LDL, lower cholesterol and higher apoprotein levels in HDL of group 3 were observed as compared with the control, group 4. Eight bands of apoprotein were separated with triton containing polyacrylamide gel disc electorophoresis. The first band of group 1 was stained strongly dark and the others were faint as compared with those of group 2. First band of group 3 was also stained very dark as group 1. The staining intensity of other bands of group 3 were decreased relatively as compared with those of the control, group 4.Total cholesterol, phospholipid and triglyceride tontents in the aorta of group 1 were increased significantly than those of group 2. There was a tendency of elevation of total cholesterol and phospholipid contents in the aorta of group 3, but no statistical difference were found against group 4.From these results, impaired clearance of chylomiron remnants and accumulation of cholesterol ester rich chylomicron and LDL by hypovitamin C were assumed. Altered apoprotein constituents in HDL also may concern with changes of lipoprotein metabolism in hypovitamin C. Thus, hypovitamin C is pathogenic to atherosclerosis not only by decreased integrity of the vascular wall as previously reported, but also by altered lipid metabolism as observed in the present study.

Abnorme low density Lipoproteine bei Kindern mit famili�rer Hypocholesterin�mie ? Ergebnis einer Behandlung mit Anionenaustauscherharzen auf Lipoproteinkonzentration und -zusammensetzung

In 20 children and adolescents with familial Type II a hyperlipoproteinemia, serum lipids and lipoproteins were examined before and during treatment with polyanion exchange resins. The composition of LDL was compared to that of helthy siblings. The patients were given Colestyramine (0.6 g/kg body weight) and Colestipol (0.5 g/kg body weight) in a cross-over study for 8 weeks each, after they had been under dietary treatment for at least 12 months. In 6 children, drug treatment had to be stopped due to side-effects. The most common complaints were gastrointestinal discomfort and constipation. Cholesterol, triglycerides and phopholipids were measured in whole serum and cholesterol, triglycerides and Apolipoprotein-B in isolated lipoprotein fractions after ultracentrifugation. Apo-B was determined by radial immunodiffusion. The Apo-B: cholesterol ratio in whole serum and in the LDL fraction was identical in the patients and in the controls. The LDL triglyceride: Apo-B ratio, however, was about 50% lower in the patients. This abnormal LDL composition was not altered by therapy with polyanion exchange resins. HDL cholesterol levels were significantly lower in the patients than in healthy children, and remained low during therapy. The decrease of total and LDL cholesterol (25%) and Apo-B (20%) was similar under both Colestipol and Colestyramine. Triglycerides and phospholipids showed no significant changes in therapy.

Serum lipoprotein abnormalities in renal allograft recipients

Detailed lipid composition of serum and isolated lipoprotein fractions in male and female transplant recipients has been determined. Results have been compared with appropriate controls and a number of abnormalities have become apparent: 1. (i) Serum total cholesterol, triglyceride and phospholipid levels were significantly elevated in transplant recipients. 2. (ii) All lipid classes in VLDL were significantly increased in both male and female patients. 3. (iii) LDL-total cholesterol, triglyceride and phospholipid were significantly raised in female transplant patients, but this was true only for LDL-triglyceride in male patients. 4. (iv) In female patients, HDL-total cholesterol and -triglyceride were significantly elevated, while in male patients, HDL-total cholesterol, but not HDL-triglyceride, was significantly greater than in controls. 5. (v) The ratio of esterified to free cholesterol was significantly reduced in HDL of female transplant recipients. Results from correlation analysis suggest a relationship between some of the lipid abnormalities and renal function in female patients, while in male patients only immunosuppressive therapy is implicated.

Studies of plasma viscosity in primary hyperlipoproteinaemia

Using an Ubbelohde capillary viscometer, viscosity was determined in the plasma of 39 patients with a primary hyperlipoproteinaemia (type IIa, n = 13; type IV, n = 12; type IIb, n = 14), in isolated lipoprotein fractions as well as in sera which differed only in their lipoprotein concentration. Plasma viscosity of the patients with hyperlipoproteinaemia was compared to that of a normolipidaemic control group and correlated with the lipid fractions characteristic of the different hyperlipoproteinaemia types. Plasma viscosity in types IIa, IV and IIb was found to be significantly higher than in the control group. Of the different hyperlipoproteinaemia types, IIa exhibited the lowest and IIb the highest plasma viscosity levels. The elevation of plasma viscosity was correlated with the concentration of lipoproteins (lipid fractions). In viscosity measurements of sera which varied only in lipoprotein concentrations, a correlation between the increase of viscosity and lipoprotein concentration as well as a greater efficiency of VLDL fractions was observed, similar to the viscosity results from isolated lipoproteins.

Transfer of cholesterol in vitro between normal arterial smooth muscle tissue and serum lipoproteins of normo-lipidemic rabbits

During incubation of normal arterial tissue with serum lipoproteins, net transfer of cholesterol was observed in the direction from the lipoproteins into the arterial tissue. Such transfer was only observed during incubations with single, isolated lipoprotein fractions. It was independent of the type of lipoprotein, VLDL, LDL or HDL, which was incubated with the arterial tissue. On the other hand, no net transfer of cholesterol was observed during incubations of arterial tissue with a combination of serum lipoproteins equivalent to that in native serum. Studies on the transfer of radioactive cholesterol suggested that cholesterol elimination from arterial tissue in vitro was not affected by the composition of the incubation medium. Therefore, it is suggested that cholesterol accumulation more easily is influenced by the serum lipoprotein composition, and that serum lipoprotein dysbalance may promote cholesterol accumulation in the tissue. This effect may be present even when the dysbalance involves a decrease of specific serum lipoprotein fractions.

Studies on the synthesis and intracellular transport of lipoprotein particles in rat liver.

Lipoprotein particles (d less than 1.03 g/ml) were isolated from rough and smooth microsomes and from the Golgi apparatus of rat liver, and were characterized chemically and morphologically. The rough endoplasmic reticulum (ER) particles were rich in protein (50%) and contained phospholipids (PLP) and triglycerides (TG) in smaller amounts, whereas the lipoprotein particles emanating from the smooth ER, and especially the Golgi apparatus, were rich in TG and PLP, resembling very low density lipoproteins (VLDL) of serum. The difference in chemical composition among the particles was associated with change in size both in situ and in isolated lipoprotein fractions. The rough ER particles were 200-800 A in diameter (mean similar to 420 A); the smooth er particles 200-900 A (mean similar to 520 A); the Golgi particles 350-950 A (mean similar to 580A); and serum VLDL 300-800 A (mean similar to 450 A). Generally, lipoprotein particles were rare in the rough ER, frequent but diffusely dispersed in smooth ER, and occurring mainly in clusters in "secretory vesicles" of the Golgi complex. They were seldom observed in the cisternal compartments of the Golgi complex. At short intervals (less than 15 min), intravenously injected radioactive glycerol was preferentially channelled into TG, whereas at later time points the majority of the isotope was recovered in the PLP. Three TG pools were distinguished: (a) a cytoplasmic pool with a slow turnover rate; (b) a membrane-associated TG pool; and (c) a pool corresponding to the TG moiety of lipoprotein particles, which showed the highest initial rate of labeling and fastest turnover. When, after pulse labeling, the appearance of incorporation of radioactive glycerol into TG or PLP of isolated lipoproteins was followed from one subcellular fraction to the other, a sequence of labeling was noted. During the first interval, TG from both rough and smooth microsomal lipoproteins displayed a high rate of labeling with peak value at 6 min, followed by a quick fall-off, while the Golgi lipoproteins reached maximal level at 10-20 min after administration. There was an interval of 10-15 min before the appearance of labeled VLDL in serum. It is concluded that the assembly of the apoproteins and lipid moieties into lipoprotein particles-presumed to be precursors of liver VLDL-begins in the rough ER and continues in the smooth ER. Also, there is a parallel change in chemical composition and size of the lipoprotein particles as they make their way through the ER and the Golgi apparatus. Some remodeling of the particles may take place in the Golgi apparatus before discharge into the circulation.

Gonadal steroid effects on plasma lipoproteins and individual phospholipids.

ABSTRACT The previously established effects of gonadal steroids on individual plasma phospholipids have been studied further in isolated lipoprotein fractions. For this purpose an estrogenic steroid (ethinylestradiol) alone and in combination with a gestagen with androgenic effect (norethisterone) was given for 3-week periods to 6 oophorectomized women. During ethinylestradiol administration the increase in plasma phospholipids was due mainly to an increase in the phospholipid fraction of highdensity- and very-high-density-lipoproteins (HDL-VHDL), (D > 1.063 g/ml) and the reduction in plasma cholesterol to a reduction in low-densitylipoproteins (LDL) (D 1.006–1.063 g/ml). The increase in plasma lecithin and cephalin and the decrease in plasma lysolecithin mirrored mainly corresponding changes in the HDL-VHDL. The addition of the gestagen-androgen used reversed the changes produced by the estrogen. The results obtained suggest an influence of these steroids on a) the liver synthesis of HDL-VHDL phospholipi...

Mouvements de cholesterol in vitro entre les α- et les β- lipoproteines plasmatiques du rat et entre chacune d'elles et les globules rouges

After administration of [4- 14C]cholesterol to rats, blood was obtained and eventually the labeled plasma subdivided into α- and β-lipoprotein classes ( d > 1.063 and d < 1.063). Incubation of plasma, or of α- or β-lipoproteins with unlabeled erythrocytes, was performed at 37° for 7h or less. The changes in free and esterified cholesterol content and specific activity were studied. On the basis of these data, models of exchange were proposed, and checked by analogue computer. 1. 1. Incubation of α- lipoprotein solutions in the presence of erythrocytes, results, first, in exchange of free cholesterol and, second, in a net loss of erythrocyte cholesterol (42%) which is related to an increase of free and esterified cholesterol in the α- lipoproteins. From the isotopic results, it is calculated that 80% of cholesterol which become esterified derives from cholesterol lost by erythrocytes, and only 20% from α- lipoprotein- free cholesterol. Similar observations can be made about β- lipoproteins during their incubation with erythrocytes, but the changes are smaller. 2. 2. The fitting of the experimental curves, by analogue computer, is performed varying the value of the exchange rate of free cholesterol, and that of the partition coefficient in relation with the esterification pathway. The rate of exchange, determined by this method, is not constant during the course of incubation. Considering 1 g of red cells, the rate decreases from 0.029 to 0.007 mg/h in the case of α-lipoproteins and from 0.024 to 0.019 mg/h in that of β- lipoproteins. The repartition of the amount of cholesterol esterified by the way of erythrocytes or lipoprotein cholesterol, calculated from isotopic results, is close to that obtained by analogue computer. 3. 3. During short-time incubation of plasma (2 h), the newly formed cholesterol esters are associated only with the α-lipoproteins. The rate of exchange of free cholesterol between α- and β- lipoproteins is about 0.06 mg/h in 1 g of plasma. Furthermore, the results suggest the occurrence of exchange of ester cholesterol. 4. 4. Finally, dialysis carried out at 5° before incubation is followed by a net esterification of only α- lipoproteins (37 %). Moreover, addition of erythrocytes to a solution of α- lipoproteins results in a picking up of free cholesterol by the erythrocytes. This phenomenon is not so obvious in the case of β- lipoproteins. All these results are discussed keeping in mind the heterogeneity of isolated lipoprotein fractions.

Lowered serum concentration of high density lipoproteins in cholesterol-fed rats

Holtzman rats were fed a solid semisynthetic diet both with and without cholesterol. The serum lipoproteins were determined by disc electrophoresis of prestained staum, preparative ultracentrifugation at several solution densities (1.006, 1.050, 1.063, 1.125, and 1.21 g/ml), disc electrophoresis of isolated lipoprotein fractions using a lipid stain as well as a protein stain, and by chemical analyses of lipoprotein proctions for their total lipid, cholesterol, phospholipid, and protein content. The data obtained have convincingly shown that, while there was an increase in serum low density lipoproteins, the serum high density lipoproteins, particularly HDL 1, and HDL 2 were substantially decreased in cholesterol-fed rats. A speculative hypothesis for the decline in rat serum high density lipoproteins has been proposed, and, as an extension, it is further speculated that human atherosclerosis may be primarily the result of hepatic disorder, as originally suggested by Olson.