Serum Very Low Density Lipoprotein Research Articles

Lipoprotein profile in men with peripheral vascular disease. Role of intermediate density lipoproteins and apoprotein E phenotypes.

The role of lipoprotein disturbances in the development of peripheral vascular disease (PVD) has not been sufficiently clarified. The relations among concentrations of intermediate density lipoproteins (IDL), apoprotein (apo) B, apo E, and other lipoproteins were studied in 102 men with PVD and 100 healthy men who formed the control group. Patients with PVD had significantly higher levels of serum triglycerides, very low density lipoprotein (VLDL) cholesterol, VLDL triglycerides, VLDL proteins, IDL cholesterol, and IDL triglycerides and lower levels of high density lipoproteins (HDL) than controls. Serum cholesterol and triglycerides were normal in 30 patients (cholesterol, less than 5.2 mmol/l; triglycerides, less than 2.3 mmol/l), who had significant increases in IDL triglycerides and significant decreases in HDL cholesterol compared with the 47 controls, who had normal cholesterol and triglyceride levels. Patients with more severe distal involvement showed higher cholesterol and triglycerides carried by IDL and a greater reduction in HDL cholesterol. Smoking patients with PVD showed increased VLDL cholesterol and VLDL triglycerides and lower HDL concentrations. Apo E polymorphism in our study population does not differ from that reported for other European populations. Alleles epsilon 2 and epsilon 4 had a major impact on serum triglycerides and VLDL lipids in our patients with PVD. Lipoprotein disturbances are a major risk factor for PVD. IDL abnormalities play an important role in the development and severity of PVD and should also be considered a vascular risk factor in normocholesterolemic and normotriglyceridemic patients.

Serum Lipid Levels in Thyroid Dysfunction with Special Reference to Transient Elevation During Treatment in Hyperthyroid Graves' Disease

Lipid metabolism was examined in patients with hyper- or hypothyroidism. Compared with corresponding age and sex matched controls, serum total cholesterol (T-chol), low density lipoprotein cholesterol (LDL-chol), phospholipid (PL) and LDL levels were significantly low and free fatty acid (FFA) levels were high with apparently normal triglyceride (TG), very low density lipoprotein (VLDL) and high density lipoprotein cholesterol (HDL-chol) levels in 61 hyperthyroid patients, while T-chol, LDL-chol, TG, PL, VLDL and LDL levels were high with normal FFA and HDL-chol levels in 31 hypothyroid patients. Serum lipid levels were then repeatedly measured in 7 men and 7 women with hyperthyroid Graves' disease before treatment (stage I), just after the patients became euthyroid with anti-thyroid drug (stage II) and more than 2 months after the patients remained euthyroid (stage III). Serum T-chol, LDL-chol, PL and LDL levels were low at stage I, significantly elevated at stage II and then normalized at stage III. Transient but significant elevation of serum TG, VLDL and HDL-chol levels at stage II were also observed in men. Accelerated catabolism and anabolism of lipid has been reported in hyperthyroidism. Transient elevation of serum lipid levels suggests a more rapid improvement in catabolism than in anabolism of lipid in an early stage of the medical treatment for hyperthyroidism.

Abnormalities of composition and of in vitro lipolysis products of human small very low density lipoproteins in hypertriglyceridemia

Small (S f 20–100) very low density lipoprotein (VLDL) particles were prepared by density gradient ultracentrifugation of plasma from normolipidemic and type IV hypertriglyceridemic post-infarction patients and healthy controls. The small VLDL separated from the plasma of severely hypertriglyceridemic post-infarction patients were found to contain twice the amount of cholesteryl esters per particle, compared with small VLDL from normolipidemic patients and healthy controls. There was a linear increase in the percentage of cholesterol that was esterified in the small VLDL with the serum VLDL triglyceride concentration (r = 0.66). When incubated for two hours with bovine lipoprotein lipase in excess and bovine albumin as a free fatty acid acceptor at one and the same triglyceride concentration in the medium, the end-product isolated by ultracentrifugation varied as a function of the serum VLDL triglyceride level. The amount of glyceride-glycerol recovered after two hours of incubation with lipoprotein lipase was 13.3 ± 1.3% (mean ± SEM) of the initial values and did not correlate with the VLDL triglyceride level. With rising serum VLDL triglyceride concentration, the product isolated in the low density lipoprotein (LDL) density region (1.006 < d < 1.063 kg/1) contained more total cholesterol and phospholipids. The linear correlation coefficients for these relations were 0.65 and 0.58 for cholesterol and phospholipids respectively. The ratio of total cholesterol to insoluble protein in the LDL density range after lipolysis rose with increasing serum VLDL triglyceride level ( r = 0.68). The end-product was further characterized by density gradient ultracentrifugation of the incubate. In vitro LDL derived by lipolysis of normolipidemic small VLDL was denser than in vitro LDL of hypertriglyceridemic small VLDL. A significant relation was found between the percentage of cholesteryl esters of total cholesterol in the substrate and the relative amount of total cholesterol recovered in the LDL density fraction after lipolysis ( r = 0.69). We suggest that the enrichment with cholesteryl esters of small VLDL from type IV hypertriglyceridemic patients is caused by lipid transfer from LDL and high density lipoprotein (HDL) and that the change in VLDL particle composition influences the precursor-product relationship to LDL.

Bezafibrate Retard in Patients with Insulin-Dependent Diabetes

The effects of a sustained-release preparation of bezafibrate (Bezalip Mono) 400 mg once daily and placebo administered for 3 months were compared in 36 patients with stable type 1 diabetes and hypercholesterolemia and/or hypertriglyceridemia. There was a significant decrease in fasting glucose levels with bezafibrate, but not in glycosylated hemoglobin. The serum cholesterol concentration decreased on bezafibrate [from 7.1 ± 0.2 (mean ± SEM) to 6.3 ± 0.3 mmol/L; p < 0.05] predominantly due to a reduction in low-density lipoprotein (LDL) cholesterol [from 4.8 ± 0.3 to 4.2 ± 0.3 mmol/L; p < 0.05. There was also a decrease in fasting serum triglycerides with bezafibrate [1.82 to 1.26 mmol/L (geometric mean)] and in very-low-density lipoprotein (VLDL) cholesterol. Plasma fibrinogen decreased significantly with bezafibrate (from 4.1 ± 0.2 to 2.9 ± 0.2 g/L; p < 0.001). Serum apolipoproteins B and A showed no statistically significant changes. Overall, there was no change in high-density lipoprotein (HDL). However, in patients who were initially hypertriglyceridemic, there was a significant increase in the cholesterol content of total HDL and the HDL2 subfraction (both p < 0.05). It is concluded that in insulin-dependent diabetic patients with hyperlipidemia, bezafibrate is effective in lowering both serum VLDL and LDL. In addition, it has a potentially important action in decreasing plasma fibrinogen levels.

Bezafibrate Retard in Patients with Insulin-Dependent Diabetes

The effects of a sustained-release preparation of bezafibrate (Bezalip Mono) 400 mg once daily and placebo administered for 3 months were compared in 36 patients with stable type 1 diabetes and hypercholesterolemia and/or hypertriglyceridemia. There was a significant decrease in fasting glucose levels with bezafibrate, but not in glycosylated hemoglobin. The serum cholesterol concentration decreased on bezafibrate [from 7.1 +/- 0.2 (mean +/- SEM) to 6.3 +/- 0.3 mmol/L; p less than 0.05] predominantly due to a reduction in low-density lipoprotein (LDL) cholesterol [from 4.8 +/- 0.3 to 4.2 +/- 0.3 mmol/L; p less than 0.05. There was also a decrease in fasting serum triglycerides with bezafibrate [1.82 to 1.26 mmol/L (geometric mean)] and in very-low-density lipoprotein (VLDL) cholesterol. Plasma fibrinogen decreased significantly with bezafibrate (from 4.1 +/- 0.2 to 2.9 +/- 0.2 g/L; p less than 0.001). Serum apolipoproteins B and A showed no statistically significant changes. Overall, there was no change in high-density lipoprotein (HDL). However, in patients who were initially hypertriglyceridemic, there was a significant increase in the cholesterol content of total HDL and the HDL2 subfraction (both p less than 0.05). It is concluded that in insulin-dependent diabetic patients with hyperlipidemia, bezafibrate is effective in lowering both serum VLDL and LDL. In addition, it has a potentially important action in decreasing plasma fibrinogen levels.

Association of DNA polymorphism at the apolipoprotein B gene locus with coronary heart disease and serum very low density lipoprotein levels.

The role of genetic variation at the 3' end of the apolipoprotein B gene locus in the development of coronary heart disease and the regulation of the serum levels of various lipoproteins was studied by using two common restriction fragment length polymorphisms detected with the enzymes Xba I and EcoR I. A group of 106 male patients with coronary heart disease and 118 matched controls of Austrian origin were investigated. The frequency of the R2 allele of the EcoR I polymorphism at cDNA position 12,669 defined by the absence of the polymorphic EcoR I cutting site was significantly higher among patients than among controls. The controls with the R2 allele had significantly higher levels of total triglycerides, very low density lipoprotein (VLDL) triglycerides, and VLDL cholesterol than did the controls without this allele. Among the patients, the R2 allele was associated with higher serum VLDL apolipoprotein B levels. The chemical composition of VLDL in individuals with different genotypes for the EcoR I polymorphism did not differ significantly. For the Xba I polymorphism at cDNA position 7673, no correlation with coronary risk could be demonstrated. Patients and controls homozygous for the X2 allele characterized by the presence of the polymorphic Xba I cutting site showed a higher total and low density lipoprotein cholesterol level than did subjects with the genotype X1X1 or X1X2. This difference, however, was not statistically significant. These findings indicate that the R2 allele of the EcoR I polymorphism is associated with the occurrence of coronary heart disease and that variation at the 3' end of the apo B gene is involved in the regulation of VLDL metabolism.

Investigation of the role of serum lipoprotein-associated peroxides in adriamycin® cardiotoxicity: Release of reduced glutathione from rat hearts perfused with lipase-hydrolyzed very low density lipoprotein fractions obtained from adriamycin®-treated and control rats

In a previous study, we demonstrated that the serum of rats treated chronically with the anticancer agent Adriamycin® contains lipid peroxides associated with neutral lipids (W.S. Thayer, Biochem Pharmacol 33: 2259–2263, 1984). In the present study, hearts from untreated control rats were perfused with medium containing serum or very low density lipoprotein (VLDL) fractions obtained from either Adriamycin®-treated rats or control rats. Release of endogenous glutathione from the perfused heart was tested to evaluate possible metabolism of the serum lipid peroxides through the glutathione peroxidase/glutathione reductase redox cycle. Perfusion with lipoprotein lipase-hydrolyzed serum or VLDL caused glutathione release, the extent of which increased with increasing VLDL concentration in the perfusate. The effect was not unique for VLDL from Adriamycin®-treated rats, but instead appeared to be a more general phenomenon since it was also observed with VLDL from control rats. Glutathione was released in the reduced form (GSH), rather than the oxidized form (GSSG) observed during perfusions with model peroxides. Pretreatment of the VLDL with lipoprotein lipase in vitro prior to perfusion was necessary in order to obtain GSH release. Neither lipase alone nor palmitate in the absence of lipase was as effective in promoting GSH release. Simultaneous release of lactate dehydrogenase was quantitatively less than that of GSH. The results suggest an action of components of serum VLDL on cardiac membrane permeability. Peroxide metabolism-linked perturbation of the cardiac glutathione redox cycle does not appear to be the mode of action for the serum lipid peroxides found in Adriamycin®-treated rats.

Relationship of angiographically defined coronary artery disease to serum lipoproteins and apolipoproteins in young survivors of myocardial infarction.

The relationship of serum lipoprotein and apolipoprotein concentrations to angiographically determined coronary artery disease was investigated in 105 consecutive male survivors of myocardial infarction under the age of 45. Concentrations and composition of lipoproteins, lipid indexes, and nonlipid risk factors (tobacco consumption, hypertension, reduced glucose tolerance, and obesity) were related to a recently developed scoring system for semiquantitative estimation of diffuse coronary atheromatosis, as well as to the number and severity of significant coronary artery stenoses. The concentrations of cholesterol in very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), and high-density lipoprotein (HDL), in combination with serum triglyceride or VLDL triglyceride level, comprised the best set of independent discriminatory lipid variables between patients and control subjects. In the patients, LDL cholesterol and apolipoprotein B levels showed strong relationships to the extent and severity of coronary atheromatosis but not to the number and severity of distinct coronary stenoses. HDL2 cholesterol concentration correlated inversely with the coronary atheromatosis score, whereas other variables reflecting HDL concentration and composition or VLDL lipids were not independently related to any of the coronary scores. The LDL triglyceride level, an index of intermediate-density lipoprotein (IDL) accumulation, was significantly correlated to the coronary atheromatosis score in univariate analysis. Nonlipid risk factors were correlated neither to coronary atheromatosis nor to severity of stenoses. Stepwise multiple regression analyses of data adjusted for age, cumulative tobacco consumption, and weight indicated that 18% of the variation in the coronary atheromatosis score could be accounted for by levels of apolipoprotein B. Addition of other lipoprotein variables or the nonlipid variables hypertension and glucose tolerance did not significantly increase the value of R2. When ratios of lipoprotein lipids and apolipoproteins were included in the regression model, the highest multiple correlation coefficient was obtained with the LDL/HDL cholesterol ratio alone (R2 = .22). The present data demonstrate the importance of elevated LDL cholesterol and apolipoprotein B concentrations for the development of coronary atheromatosis in young male survivors of myocardial infarction. The lack of correlations between the levels of lipoprotein lipids and serum apolipoproteins and the severity of coronary stenoses suggests that mechanisms other than disturbances of lipoprotein metabolism may be involved in the progression of more advanced coronary lesions.

Effects of castration and testosterone administration on serum lipoproteins and their apoproteins in male spontaneously hypertensive rat.

Serum triglyceride and very low density lipoprotein (VLDL) concentrations were higher in male spontaneously hypertensive rat than in male control Wistar Kyoto rat, whereas serum cholesterol, phospholipids, and high density lipoprotein (HDL) concentrations were lower. Castration of hypertensive rats induced an increase in serum cholesterol, phospholipids, and HDL, and a decrease in serum triglyceride and VLDL. The cholesterol content of HDL increased, whereas the triglycerides decreased after gonadectomy of hypertensive rats. These changes in serum lipids and lipoproteins could be reversed by the administration of testosterone. Apolipoprotein E contents in VLDL and HDL of hypertensive rats were low when compared with control rats but rose after castration and could be reduced by testosterone administration. Hypertensive rats accumulated triglycerides and cholesterol in the liver, which resulted in an increase of liver weight. Castration reduced the hepatic lipids as well as liver weight. The effects of castration and testosterone treatment on lipids and lipoproteins were more prominent in spontaneously hypertensive rats than in control rats. These results suggest that testosterone reduces VLDL catabolism which is related to changes of apolipoprotein composition, and that hypertensive rats are more sensitive to testosterone than control rats.

Correction by insulin of disturbed TG-rich LP metabolism in rats with chronic renal failure.

To define the role of insulin in lipid disturbances of chronic renal failure, chronically uremic rats (U+) were supplemented by continuous insulin infusion over a 35-day experimental period and compared with control ad libitum-fed rats (C) and uremic rats without insulin (U). Uremic rats were characterized by hypoinsulinemia, an increase in both circulating very low-density lipoprotein (VLDL) and their cholesterol concentration, a normal hepatic triglyceride secretion rate (TGSR) determined with Triton WR 1339, and a low adipose tissue lipoprotein lipase (LPL) activity. Chronic insulin infusion at low rate (0.5 IU/24 h) to U+ rats normalized serum insulin (from 17.0 +/- 0.6 mU/l in U rats to 23.4 +/- 1.7 mU/l in U+ rats), serum VLDL triglycerides (from 804 +/- 65 to 410 +/- 36 mg/l), and serum VLDL cholesterol (from 43 +/- 8 to 16 +/- 3 mg/l). Hepatic TGSR decreased significantly after insulin treatment (from 0.58 +/- 0.03 to 0.44 +/- 0.03 mumol/min). Moreover, adipose tissue LPL was restored to normal by insulin supplementation (from 460 +/- 60 to 860 +/- 150 mU per total epididymal fat in U and U+ rats, respectively). Correction of the disturbed VLDL metabolism was associated with multiple actions of insulin including 1) a decrease of peripheral lipolysis, 2) a decrease of hepatic TGSR, and 3) an increase of adipose tissue LPL activity. Because cholesterol-rich VLDL are potentially atherogenic, their normalization with insulin treatment in this animal model suggests a viable area of investigation for the prevention of accelerated atherogenesis in chronic renal failure.

高トリグリセライド血症における超低比重リポ蛋白のアポ蛋白異常

The percentages of apo C-II and C-III proteins in very low density lipoprotein (VLDL) were high in the patients with hypertriglyceridemia (type IIb and IV) when compared with normal control subjects and those of apo A-I, A-II and B proteins were low. Positive correlation was shown between serum VLDL concentration and the percentage of apo C proteins, and the inverse relationship was between VLDL concentration and the percent apo B protein. Consequently, C/B and C/E ratios were higher in these patients than in healthy control.By contrast, there were no significant difference in high density lipoprotein apoprotein composition between normal subjects and the patients with high triglyceride concentration.

Comparison of very-low-density lipoproteins isolated from rat liver perfusate, rat serum and human plasma as acceptors for cholesteryl ester transfer

Using two methods, we have compared the ability of three types of very-low-density lipoprotein (VLDL), namely, rat hepatic perfusate VLDL, rat serum VLDL and human plasma VLDL, to accept cholesteryl esters from human plasma high-density lipoprotein (HDL). Both net mass and isotopic transfers of cholesteryl ester were evaluated. The VLDL concentration in the incubation media was adjusted on the basis of equivalent amounts of either cholesteryl ester, apolipoprotein B or triacylglycerol. In each case, the net mass transfer of cholesteryl ester was found to be greatest to rat hepatic VLDL, lower to rat serum VLDL and lowest to human plasma VLDL. Similar results were obtained with the isotopic transfer method when the VLDL concentration was adjusted on the basis of cholesteryl ester or apolipoprotein B. However, when VLDL were matched on the basis of triacylglycerol concentration, the isotopic transfer rate into human plasma VLDL was twice as high as into rat hepatic VLDL which presumably reflects the decreased number of hepatic VLDL particles by this criterion. In conclusion under fasted conditions (chylomicron excluded), nascent VLDL have been shown to be the best cholesteryl ester acceptor compared to their plasma counterpart.

サル灌流肝によるVLDLアポ蛋白Bの生成に対する脂肪酸の影響

In vitro perfused liver from rhesus monkey generated very low density lipoprotein (VLDL) similar to serum VLDL, except for the existance of three kinds of high molecular weight apoproteins. These three kinds of high molecular weight apoprotein were considered to be isoproteins of apoprotein B, because of their molecular weight, amino acid composition, and their immunological character. They were designated as B100, B74, and B42 in a centile system on SDS polyacrylamide gel electrophoresis.Although the B42 ran a little bit faster than the B48 did, which was found in hyperlipemic monkey VLDL, it was considered that the B42 could be a modified B48.Oleic acid supplement in perfusate resulted in the increase of triacylglycerol secretion in perfusate VLDL, indicating that fatty acid supplement results in the secretion of larger VLDL from perfusedliver.The larger VLDL produced by the liver perfused with fatty acid supplement contained the more B42. Considering that the specific activity of B42 decreased with time over the course of perfusion, while that of B100 increased, the B42 is not considered to be degradative product of B100.Besides, with increase of B42 in VLDL secreted by the liver perfused with fatty acid supplement, the ratio of apoprotein E to apoprotein B in VLDL increased, indicating that enlargement of VLDL secreted by the liver results in enrichment of apoprotein E and B42.It is very important to explore the metabolic fate and the role in atherogeneity of such B42 and apoprotein E rich VLDL produced by fatty acid supplement.

Evaluation of the hypocholesterolemic effect of vegetable proteins

The hypocholesterolemic effect of dietary vegetable proteins was studied by comparing egg-white protein and fava bean protein concentrate in one normal and seven hypercholesterolemic (six type II A, one II B) persons; five completed the crossover design. To maintain stable body weight, subjects were kept on an isocaloric diet (20% protein, 48% carbohydrate (CH), 32% fat, P S = 2 ) for 1 month and then hospitalized for two consecutive 18-day periods while receiving an isocaloric diet of different composition (15% protein, 50% CH, 26% fat, P S = 2 ). Women were provided 50 g and men 70 g daily of egg-white or fava bean protein concentrate during the two crossover periods. Hematocrit and fasting plasma or serum were analyzed every 3 days for glucose, insulin, uric acid, creatinine, total and low-density lipoprotein (LDL), very low-density lipoprotein (VLDL), and high-density lipoprotein (HDL) cholesterols, and for total and VLDL triglyceride. Dietary adequacy of both proteins was evaluated by measuring plasma concentration of prealbumin, transferrin, and retinol-binding globulin. Insulin and hematocrit did not show any change, nor did any other biochemical variables show significant differences when results were compared at the end of each crossover period. Compared with baseline, fasting plasma glucose significantly decreased on the fava bean diet. Serum total and LDL cholesterol decreased during both diets but were statistically significant only on the egg-white diet. Serum HDL cholesterol significantly decreased only on the fava bean diet. Serum total and VLDL triglyceride did not show any significant change. Labile plasma protein concentration was significantly reduced only on the fava bean diet. In conclusion, the fava bean diet did not show a significant effect on lowering serum total and LDL cholesterol. Such an effect was mild but significant on the egg-white diet, compared with baseline.

The origin of lipid accumulated in liver lysosomes after administration of triton WR-1339.

The origin of the lipids accumulated in liver lysosomes after administration of Triton WR-1339 was investigated. When Triton WR-1339 was injected into rats, serum triglyceride and cholesterol increased markedly. The highest content of triglyceride was observed in the second-day serum, from which very-low-density lipoprotein (VLDL) was isolated. The VLDL was administered to normal rats, then the light mitochondrial fraction of the liver at 24 h was centrifuged in a sucrose density gradient. The activities of lysosomal enzymes, acid phosphatase, N-acetyl-beta-D-glucosaminidase and acid lipase, were all shifted to less dense fractions as compared with those of normal lysosomes. [3H]Triglyceride-labeled VLDL was injected similarly, and at 12 and 24 h after the administration, the light mitochondrial fraction of the liver was fractionated by sucrose gradient centrifugation. Protein content and radioactivity in the immunoprecipitate with anti-VLDL serum at 12 h showed almost the same distribution as acid phosphatase activity. At 24 h, though acid phosphatase activity, immunoprecipitable protein content and radioactivity were all found in less dense fractions than in the case of normal lysosomes, the former two distributions were significantly different from the latter. The anti-VLDL serum reacted in Ouchterlony tests not only with Triton-induced VLDL and normal VLDL but also with the extract from low-density lysosomes. These results suggest that the lipids accumulated in low-density lysosomes following the administration of Triton WR-1339 were probably derived from the elevated serum VLDL induced by the treatment.

Intestinal very low density lipoprotein secretion in rats fed various amounts of fat

1. The effect of a high-fat diet (30% fat by wt.) on intestinal very low density lipoprotein (VLDL) secretion was studied in male rats after specific inhibition of hepatic VLDL secretion by dietary orotic acid. Total VLDL secretion (from liver and intestine) was measured in animals not receiving orotic acid. 2. Fat-feeding resulted in a 32% decreased post-Triton secretion of total serum VLDL triacylglycerols as compared to a control (low fat) diet. Concomitantly, a large stimulation of post-Triton intestinal VLDL triacylglycerols secretion was measured in fat-fed rats. Thus, the major part (64%) of circulating triacylglycerols transported as VLDL originated from the intestine in these animals, leading presumably to an increased secretion of intestinal apolipoproteins. 3. Intestinal VLDL and chylomicron secretion rates increased with the amount of fat in the diet (7,13,20 or 30% fat by wt.). Whereas the chylomicron secretion was linearly related to the dietary fat content, the relationship between intestinal VLDL secretion and fat content of the diet was sigmoidal. The highest stimulation of intestinal VLDL formation was observed within a narrow range of dietary fat content (between 10 and 20%).

Characterization of a very-low-density lipoprotein (VLDL)-associated cytotoxic factor.

A VLDL-associated cytotoxic factor was isolated from sera of pregnant rats and characterized. The inhibitory effect of this factor on the macromolecular synthesis of rat prostate adenocarcinoma cells (PA-III) was also examined. VLDL (Sf 20-400) was subfractionated by differential ultracentrifugal flotation and the Sf 100-400 fraction was associated with most of the oncolytic activity. Chemical analysis of serum VLDL at various stages of pregnancy indicated that the 4 major constituents of VLDL (protein, triglyceride, cholesterol, and phospholipid), and the cytotoxic titre, were increased significantly before parturition and restored to normal levels by 24 h post partum. The delipidation of lyophilized VLDL by n-heptane suggested that the cytotoxic component was associated with the neutral lipid core of VLDL. Kinetic studies of colony inhibition and the incorporation of radioactive thymidine and leucine into 10% TCA precipitates of PA-III cells showed that VLDL induced irreparable cellular damage during the initial 15 h of incubation. The cytotoxic activity of VLDL was not due to the association with PGF2 alpha, beta-oestradiol, progesterone, 25-hydroxycholesterol, or free fatty acids (oleic, stearic, palmitic, linoleic, linolenic and arachidonic acids), monopalmitolein, elaidyl and alpha-linolenyl alcohol. The role of this factor in host defence against neoplasia is discussed.

Serum and hepatic nascent lipoproteins in normal and hypercholesterolemic rats.

The lipids and apoproteins of serum, hepatic Golgi cisternae, and secretory vesicle lipoproteins from hypothyroid, hypercholesterolemic rats were analyzed and compared to homologous lipoprotein fractions from euthyroid rats fed a low fat chow diet in order tao determine the nature of the nascent lipoprotein particles and indicate post-secretory modifications. Normal rat hepatic Golgi and secretory vesicles contained predominantly triglyceride-rich very low density lipoprotein (VLDL) which had little associated apoC-II or C-III and was deficient in apoE when compared to serum VLDL. Small quantities of cholesteryl ester-enriched low density lipoprotein (LDL) containing apoB and apoE were also present. Hepatic fractions from hypercholesterolemic rats contained cholesteryl ester- and apoE-rich, triglyceride-depleted VLDL of similar size, immunodiffusion characteristics, ratio of immunoassayable apoB to apoE, and lipid composition, to hypercholesterolemic serum VLDL. Hepatic levels of LDL in hypercholesterolemic rats were markedly elevated and enriched in cholesteryl ester and apoE when compare to normal hepatic LDL. Cholesteryl ester-rich hepatic VLDL and LDL increased in size and in cholesteryl ester and apoE content during transit from the Golgi cisternae into the secretory vesicles. Triglyceride-rich VLDL only acquired apoE which was further supplemented upon secretion. Nascent VLDL and LDL represented LpB-LpE association complexes and no deficiency in any apoE isoprotein within the cholesteryl ester-rich serum lipoproteins was observed. Thus, dietary-induced hypercholesterolemia in hypothyroid rats results in a fatty liver whose lipoprotein secretory products contribute to the plasma pool of abnormal cholesteryl ester- and apoE-enriched lipoproteins.

Apoproteins of avian very low density lipoprotein: demonstration of a single high molecular weight apoprotein

The high molecular weight apoproteins of very low density lipoprotein (VLDL) were compared after preparation of VLDL from plasma and sera of diethylstilbestrol-treated roosters. When prepared from plasma with adequate control of endogenous proteolytic activity, VLDL contained a single high molecular weight apoprotein (apo-VLDL-B) as judged by electrophoresis in polyacrylamide gels containing sodium dodecyl sulfate. Serum VLDL contained multiple apoprotein species, the largest of which corresponded to apo-VLDL-B. Immunological analyses showed that the multiple apoproteins of serum VLDL were quantitatively and qualitatively indistinguishable from plasma apo-VLDL-B. These data indicate that apo-VLDL-B can be cleaved during VLDL isolation to produce an apparent heterogeneity of high molecular weight apoproteins. The molecular weight of plasma apo-VLDL-B was estimated to be 350 000. This protein was stable to reduction and S-carboxymethylation and showed no association with apo-VLDL-II [Chan, L., Jackson, R.L., O'Malley, B. W., & Means, A.R. (1976) J. Clin. Invest. 58, 368] through disulfide linkage. Apo-VLDL-B and apo-VLDL-II represented 54% and 46%, respectively, of the total VLDL protein recovered following gel filtration chromatography in sodium dodecyl sulfate. Protein recovery in the chromatographic analyses (92%) was sufficient to conclude that apo-VLDL-B and apo-VLDL-II are the major and possibly the only apoproteins of chicken VLDL. The molar ratio of the apo-VLDL-II monomer to apo-VLDL-B was estimated to be 32.

The effect of a low-cholesterol, high-polyunsaturate diet on serum lipid levels, apolipoprotein B levels and triglyceride fatty acid composition

1. (1) Seven healthy normolipaemic men aged 28–46 years (mean 33 years) were studied for four weeks on their usual diet, the mean polyunsaturated to saturated fat (P : S) ratio of which was approximately 0.23 and the cholesterol content 667 mg/day, and for four weeks on an isocaloric diet, containing similar proportions of protein, carbohydrate and fat, but with a mean P : S ratio of approximately 2.82 and a cholesterol content of 112 mg/day. 2. (2) Total serum cholesterol levels decreased by 18.7 ± 5.2% (mean ± SEM) on the polyunsaturated fat (PUF) diet. This was attributable to a similar reduction in serum low density lipoprotein (LDL) cholesterol. Serum very low density lipoprotein (VLDL) cholesterol showed no clear change. Total serum triglyceride levels decreased by 19.7 ± 7.1% due to a reduction in both serum VLDL and LDL triglyceride concentration. 3. (3) Total serum apolipoprotein B concentration fell by 23 ± 2.6% during the PUF diet. There was a decrease of similar magnitude in serum LDL apolipoprotein B, but no sustained effect on serum VLDL apolipoprotein B. 4. (4) Serum VLDL and LDL lipid to apolipoprotein B ratios did not change significantly during the study. 5. (5) Serum triglyceride fatty acid composition significantly altered during the PUF diet. The percentage of linoleic acid rose from 16 ± 0.90% to 36 ± 0.89%, whilst the percentage of combined saturated and monounsaturated acids fell correspondingly. These changes took place within 2 days of starting the PUF diet.