Very Low Density Lipoprotein Triglyceride Research Articles

Effect of a new HMG-CoA reductase inhibitor, atorvastatin, on lipids, apolipoproteins and lipoprotein particles in patients with elevated serum cholesterol and triglyceride levels

The effects of atorvastatin (lipitor) on cholesterol-rich and triglyceride-rich lipoproteins were evaluated in this multicenter trial. Following a 6-week baseline period, 47 patients with elevated cholesterol and triglyceride levels were treated with atorvastatin 10 mg once daily (QD) for the initial 12 weeks (Period 1) increasing to 20 mg QD for the following 12 weeks (Period 2). At both the 10 and 20 mg doses, atorvastatin treatment resulted in significant reductions compared to pretreatment levels in low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), very low-density lipoprotein cholesterol (VLDL-C), apolipoprotein (apo) B, apoB in LDL (LDL-apo B), apo B in VLDL (VLDL-apo B), lipoprotein (Lp)B, lipoprotein B-complex (LpB c), triglycerides (TG), low-density lipoprotein triglycerides (LDL-TG), very low-density lipoprotein triglyceride (VLDL-TG), high-density lipoprotein triglycerides (HDL-TG), and apo C-III. Atorvastatin 10 and 20 mg QD also resulted in significant increases in high-density lipoprotein cholesterol (HDL-C), apo AI, and LpAII:B:C:D:E. Due to its unique ability to normalize both cholesterol-rich and triglyceride-rich particles, atorvastatin is a promising candidate for monotherapy in a broad range of patients including those with varying degrees of hypercholesterolemia and hypertriglyceridemia.

On the interrelationship between hepatic carnitine, fatty acid oxidation, and triglyceride biosynthesis in nephrosis.

The nephrotic syndrome is associated with disturbances in plasma lipid pattern and metabolism. However, the reason for these perturbations is poorly understood. In the present study, we have investigated hepatic triglyceride metabolism in puromycin aminonucleoside-induced nephrotic syndrome in rats. Nephrotic rats displayed a 70% increase in hepatic triglyceride levels compared to controls (16.9 +/- 1.6 vs. 9.8 +/- 0.6 mumol/g liver; means +/- SEM, P < 0.01). The capacity for hepatic mitochondrial beta-oxidation of fatty acids was substantially elevated (80%). This was associated with a rise in the liver content of the fatty acid carrier carnitine (1.24 +/- 0.06 vs. 0.85 +/- 0.07 mumol/g dry weight, P < 0.05). A positive correlation between the levels of acetylcarnitine and acetyl-CoA was found in normal as well as in nephrotic rats, implying that carnitine plays an important role as an acetyl group acceptor in the liver under normo- and hyperlipidemic conditions. Changes in carnitine levels seem to be tightly coupled to the rate of fatty acid oxidation. There was a significant elevation in the activity of phosphatidate phosphohydrolase (E.C. 3.1.3.4) in liver microsomes from nephrotic rats (1.07 +/- 0.09 vs. 0.81 +/- 0.04 nmol/min.mg protein, P < 0.02). Hepatic very low density lipoprotein (VLDL)-triglyceride secretion rate was 18% higher in nephrotic rats than in controls. The results demonstrate a deranged hepatic triglyceride metabolism in nephrosis, with an increased hepatic triglyceride biosynthesis, a sizable accumulation of hepatic triglycerides, and only a modest increase in VLDL triglyceride secretion. In addition, mitochondrial beta-oxidation of fatty acids was enhanced, associated with an increased availability of carnitine.

EFFECTS OF SHORT-TERM EXERCISE ON LIPIDS AND LIPOPROTEINS IN MEN WITH ABDOMINAL OBESITY 35

Eleven sedentary men with central pattern of obesity [mean (SE): Mass, 119.1 (5.4) kg; BMI, 37.7 (1.8) kg·m-2; WHR, 0.97(0.01); age, 31.7 (2.4) years] were studied before and after 10 d of exercise in order to determine effects of short-term exercise on triglycerides (Tg), very low density lipoprotein-triglyceride (VLDL-Tg), total cholesterol (TC), low density lipoprotein-cholesterol (LDL-C), and high density lipoprotein-cholesterol (HDL-C) and its subfractions HDL2-C and HDL3-C. Blood chemistry was performed prior to participation and 24 h after the last exercise session. Daily exercise bouts were 40 min. in duration and consisted of treadmill walking and cycle ergometry at 70 - 80% age-predicted HR max, with an average energy expenditure or 1837 (70.5) kJ. Three-day dietary recalls were used to evaluate the subjects' diets during the exercise period. Average caloric intake during the study period was 2729 kcal(46% CHO; 37% fat; 17% protein). No significant changes (p > 0.05) in body mass were noted following 10 d of exercise [(119.1 (5.4) kg vs. 118.9 (5.4) kg]. TC and LDL-C were significantly decreased following 10 d of exercise as compared to pre-exercise with values of 185.4 (6.8) mg·dl-1 vs. 170.2 (9.3) mg·dl-1 (p<0.05), and 119.2 (6.6) mg·dl-1 vs. 111.9 (7.3) mg·dl-1 (p = 0.05), respectively. Exercise also resulted in significant reductions (p < 0.05) in TG [168.3 (18.2) mg·dl-1 vs. 131.6 (15.8) mg·dl-1] and VLDL-TG [138.0 (17.3) mg·dl-1 vs. 105.6 (15.5) mg·dl-1]. No significant changes (p >0.05) in HDL-C [34.7 (2.3) mg·dl-1 vs. 35.5 (2.3) mg·dl-1] were observed following 10 d of exercise as compared to pre-exercise, despite a significant increase (p < 0.05) in HDL2-C [1.5 (0.6) mg·dl-1 vs. 2.6 (0.8) mg·dl-1]. No changes in HDL3-C [33.4 (1.9) mg·dl-1 vs. 33.0 (1.8) mg·dl-1] were noted when comparing pre-exercise to post-exercise samples. These data suggest that daily short-term exercise induced favorable changes in the lipoprotein profile of adult men with abdominal obesity.

Magnesium pyridoxal-5′-phosphate glutamate, "A vitamin B 6 derivative", does not affect lipoprotein levels in patients with familial hypercholesterolaemia

In this double-blind, randomized, placebo-controlled, dose-finding study we assessed the short-term efficacy and safety of increasing dosages of magnesium pyridoxal-5'-phosphate glutamate (MPPG) compared to placebo in patients with familial hypercholesterolaemia (FH). Twenty-three patients of either sex, over the age of 18 years and suffering from heterozygous FH, were treated with MPPG for a period of 16 weeks. Baseline characteristics and lipoprotein profiles of the patients were comparable in the two treatment groups. Overall compliance was 90%. Neither after the first 8 weeks treatment period with 450 mg MPPG daily nor after the second 8 weeks treatment period with 600 mg MPPG daily were statistically significant changes in plasma total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol or triglyceride levels observed between the treatment and placebo groups. Plasma levels of lipoprotein (Lp)(a), apolipoprotein (apo) A1, apo B100, very low density lipoprotein (VLDL) cholesterol and VLDL triglyceride also did not change. Although it has been demonstrated that MPPG improves lipoprotein levels in patients with different forms of dyslipidaemia, MPPG is not effective for the treatment of FH patients.

Hepatic storage and transport of n-3 and n-6 polyunsaturated fatty acids by very-low-density lipoproteins in growing rats fed low- or adequate-protein diets with sunflower, soybean, coconut, and salmon oils

Protein and essential fatty acid (EFA) deficiencies may both occur in chronic malnutrition and have common symptoms. To determine the interactions between dietary protein intake and EFA availability, rats were fed purified diets containing 20% or 2% casein and 5% as one of four fats (sunflower, soybean, coconut, or salmon oil) that differed particularly in their n-6 and n-3 polyunsaturated fatty acids (PUFAs). Protein malnutrition enhanced hepatic triacylglycerol and cholesterol concentrations while decreasing hepatic protein and phospholipid contents and mass and components of very-low-density lipoprotein (VLDL). The ratio of PUFAs to saturated fatty acids (SFAs) was consistently depressed by protein malnutrition in liver and VLDL triacylglycerol and phospholipid. Total n-6 and n-3 fatty acids were diminished by protein malnutrition, except with salmon oil, with which a decrease in 20:5n-3 was compensated for by an increase in 22:6n-3. The ratio of 20:4n-6 to 18:2n-6 was enhanced in liver phospholipid and VLDL triacylglycerol, and modified little in liver triacylglycerol. Generally, the ratio of 20:3n-9 to 20:4n-6, an index for EFA deficiency, was raised with protein malnutrition in liver triacylglycerol and phospholipid and in VLDL triacylglycerol. The extent of changes in each fatty acid proportion varied according to the oil fed. Overall, VLDL-apolipoprotein concentrations were, in general, strongly reduced with protein malnutrition. In conclusion, protein malnutrition may accelerate marginal EFA deficiency and decrease long-chain PUFA bioavailability and thus increase EFA requirement.

Plasma lipoproteins and incidence of non-insulin-dependent diabetes mellitus in Pima Indians: protective effect of HDL cholesterol in women

The role of plasma lipoproteins in the development of non-insulin-dependent diabetes mellitus (NIDDM) was studied in 787 non-diabetic (2-h glucose<11.1 mmol/l) Pima Indians (265 men and 522 women). Subjects were followed for a mean of 9.8 (range: 1.8–16.4) years, during which 261 (76 men and 185 women) developed NIDDM. In men and women, very-low-density lipoprotein (VLDL) cholesterol, VLDL triglyceride, low-density lipoprotein triglyceride and total triglyceride, controlled for age, predicted NIDDM (P<0.01 for each). These effects diminished when controlled for age, sex, body mass index, systolic blood pressure and 2-h glucose. However, high-density lipoprotein (HDL) cholesterol, controlled for age, body mass index, systolic blood pressure and 2-h glucose, was a significant protective factor for NIDDM in women (hazard rate ratio (HRR)=0.35, 95% CI (0.23–0.54), P<0.001, 90th compared with 10th percentile) but not in men (HRR=1.04, 95% CI (0.53–2.05), P=0.915). This association remained significant in women when controlled for fasting or 2-h plasma insulin concentrations, other estimates of insulin resistance or alcohol consumption. The protective effect of HDL cholesterol was similar among women with normal (2-h glucose<7.8 mmol/l) or impaired (7.8 mmol/l≤2-h glucose<11.1 mmol/l) glucose tolerance at baseline. These results indicate that lipoprotein disorders are an early accompaniment of the abnormalities that lead to NIDDM.

Origin of hepatic very-low-density lipoprotein triacylglycerol: the contribution of cellular phospholipid.

When rat hepatocytes were cultured for 24 h in the absence of exogenous fatty acid, the amount of very-low-density lipoprotein (VLDL) triacylglycerol (TAG) secreted (114 +/- 14 micrograms/mg of cell protein) could not be accounted for by the mass of TAG lost from the cells (29 +/- 6.1 micrograms/mg of cell protein) during this period (n = 12). Of the balance (85 +/- 14 micrograms/mg; 94 +/- 15 nmol/mg), a maximum of only 37 nmol/mg of cell protein of TAG could be accounted for by fatty acids synthesized de novo. When labelled exogenous oleate (initial concentration, 0.75 nM) was present in the culture medium, the net gain in cellular plus VLDL TAG (253 +/- 38 micrograms/mg of cell protein per 24 h) was greater than that contributed by the exogenous fatty acid (155 +/- 18.2 micrograms/mg of cell protein, n = 5). Again, the balance (98.8 +/- 18.2 micrograms/mg of cell protein per 24 h) was too great to be accounted for by fatty acid synthesis de novo. In experiments in which cellular glycerolipids were prelabelled with [9, 10(n)-3H]oleic acid, following removal of the labelled fatty acid, there was a net increase in labelled cellular plus VLDL TAG over the next 24 h. That cellular phospholipids are the source of a substantial part of the excess TAG synthesized is supported by the following evidence. (1) The loss of prelabelled cellular phospholipid during culture was greater than could be accounted for by secretion into the medium. (2) During culture of cells prelabelled with 1,2-di-[l-14C]palmitoyl phosphatidylcholine, a substantial amount of label was secreted as VLDL TAG. (3) In pulse-chase experiments, the kinetics of labelled phospholipid turnover were consistent with conversion into a non-phospholipid pool. The enzymology involved in the transfer of phospholipid fatty acids into TAG is probably complex, but the present results suggest that this pathway may represent an important route by which extracellular fatty acids are channelled into VLDL TAG.

Adenoviral delivery of low-density lipoprotein receptors to hyperlipidemic rabbits: Receptor expression modulates high-density lipoproteins

Plasma concentrations of low-density lipoproteins (LDLs) and high-density lipoproteins (HDLs) are inversely related in several dyslipoproteinemias. To elucidate the interactions between these lipoproteins, we used a recombinant adenovirus (hLDLR-rAdV) to express human LDL receptors (hLDLRs) in LDL receptor-deficient rabbits. hLDLR-rAdV administration resulted in hepatocyte expression and a reduction of total, intermediate-density lipoprotein (IDL), and LDL cholesterol. In addition, we found that hLDLR-rAdV treatment induced (1) increased very-low-density lipoprotein (VLDL) cholesterol, (2) increased VLDL, IDL and LDL triglycerides, (3) decreased α- and pre-β-migrating apolipoprotein E (apo E) and decreased pre-β-migrating apo A-I at 2 to 4 days posttreatment, and (4) increased total plasma apo A-I and pre-β-migrating apo A-I beginning 8 to 10 days posttreatment. Virtually all plasma apo A-I was present on α- and pre-β-HDL. Pre-β-HDL particles with size and electrophoretic properties consistent with nascent HDL demonstrated the greatest relative apo A-I enrichment following hLDLR-rAdV treatment. In summary, enhanced expression of hepatocyte LDLRs by hLDLR-rAdV treatment markedly altered apo A-I-containing lipoproteins and IDL and LDL. The use of recombinant viruses to express physiologically relevant genes in intact animals, analogous to transfection of cells in culture, provides a new strategy for the evaluation of effects of specific gene products on metabolic systems in vivo.

Effect of apolipoprotein E and insulin resistance on VLDL particles in combined hyperlipidemic patients

Apolipoprotein (apo) E2 and high insulin levels are associated with the severity of hypertriglyceridemia in patients with combined hyperlipidemia. To study how these determinants affect very low-density lipoprotein (VLDL) in combined hyperlipidemic patients, we characterized VLDL particles in 106 unrelated patients with combined hyperlipidemia. The study was performed after 9 weeks of standardized dietary intake and after an overnight fast. Patients heterozygous for apoE2 had significantly higher mean levels of VLDL cholesterol by 0.71 mmol/l (95% CI, 0.30 to 1.12 mmol/l, P < 0.005) and VLDL triglycerides by 0.88 mmol/l (95% CI, 0.30 to 1.47 mmol/l, P < 0.005) compared to patients without apoE2. The VLDL triglyceride content per particle and the calculated diameter of the VLDL particles were similar in both groups, which indicate a higher number of circulating VLDL particles in heterozygous apoE2 carriers. Patients with high fasting insulin levels (≥ 80 pmol/l) had a higher mean serum VLDL triglyceride level by 0.56 mmol/l (95% CI, 0.04 to 1.07 mmol/l, P < 0.05). The calculated VLDL diameter was larger by 3.7 nm (95% CI, 1.2 to 6.2 nm, P < 0.005) and the particles contained more triglycerides by 2.7 weight percent (95% CI, 0.3 to 5.1 weight percent, P < 0.05). These insulin-dependent changes in VLDL particles were only present in the absence of apoE2. In conclusion, patients heterozygous for apoE2 have higher numbers of circulating VLDL particles, whereas patients with high fasting insulin levels have larger, triglyceride enriched VLDL particles.

Complete Phenotypic Characterization of apobec-1 Knockout Mice with a Wild-type Genetic Background and a Human Apolipoprotein B Transgenic Background, and Restoration of Apolipoprotein B mRNA Editing by Somatic Gene Transfer of Apobec-1

We have produced gene knockout mice by targeted disruption of the apobec-1 gene. As recently reported by Hirano et al. (Hirano, K.-I., Young, S. G., Farese, R. V., Jr., Ng, J., Sande, E., Warburton, C., Powell-Braxton, L. M., and Davidson, N. O. (1996) J. Biol. Chem. 271, 9887-9890), these animals do not edit apolipoprotein (apo) B mRNA or produce apoB-48. In this study we have performed a detailed analysis of the lipoprotein phenotypic effects of apobec-1 gene disruption that were not examined in the previous study. We first analyzed the plasma lipoproteins in knockout animals with a wild-type genetic background. Although there was no difference in plasma cholesterol between apobec-1(-/-), +/-, or +/+ mice, there was a marked (176%) increase in plasma apoB-100, from 1.8 +/- 1.2 mg/dl in apobec-1(+/+) mice to 2.7 +/- 0.6 mg/dl in apobec-1(+/-) and 5.0 +/- 1.4 mg/dl in apobec-1(-/-) mice. Plasma apoE was similar in these animals. By fast protein liquid chromatography (FPLC) analysis, there was a significant decrease in plasma high density lipoprotein (HDL) cholesterol in apobec-1(-/-) mice. We further fractionated the plasma lipoproteins into d < 1.006, 1.006-1.02, 1.02-1.05, 1.05-1.08, 1.08-1.10, and 1.10-1.21 g/ml classes, and found a marked (30-40%) reduction in the cholesterol and protein content in the (d 1.08-1.10 and 1.10-1.21) HDL fractions, corroborating the FPLC data. SDS-gel analysis revealed an absence of apoB-48, an increase in apoB-100 in the very low density lipoprotein (VLDL) and low density lipoprotein (LDL) fractions, and a small decrease in apoA-I in the HDL fractions in the apobec-1(-/-) samples. We next raised the basal plasma apoB levels in the apobec-1(-/-) animals by cross-breeding them with human apoB transgenic (TgB) mice. The plasma apoB-100 was 3-fold higher in apobec-1(-/-)/TgB+/- mice (26.6 +/- 18.3 mg/dl) than in apobec-1(+/+)/TgB+/- mice (9.8 +/- 3.9 mg/dl, p < 0.05). The apobec-1(-/-)/TgB+/- mice had a plasma cholesterol levels of 170 +/- 28 mg/dl and triglyceride levels of 106 +/- 31 mg/dl, which are 80% and 58% higher, respectively, than the corresponding values of 94 +/- 21 mg/dl and 67 +/- 11 mg/dl in apobec+/+/TgB+/- mice. By FPLC, the apobec-1(-/-)/TgB+/- animals developed markedly elevated plasma LDL cholesterol (518.5 +/- 329.5 microg/ml) that is 373% that of apobec1(+/+)/TgB+/- mice (139.0 +/- 87.0 microg/ml) (p < 0.05). The elevated plasma triglyceride was accounted for mainly by a 97% increase in VLDL triglyceride in the apobec1(-/-)/TgB+/- mice. We conclude that apobec-1(-/-) animals have a distinctive lipoprotein phenotype characterized by significant hyperapoB-100 and HDL deficiency in mice with a wild-type genetic background. Furthermore, the abolition of apoB mRNA editing elevates plasma total cholesterol and LDL cholesterol in apobec-1(-/-) animals with a TgB background. Finally, to exclude the possibility that absence of apoB mRNA editing was a secondary effect of chronic Apobec-1 deficiency, we treated apobec-1(-/-) mice with a replication-defective mouse Apobec-1 adenoviral vector and found that we could acutely restore apoB mRNA editing in the liver. These experiments indicate that Apobec-1 is an essential component of the apoB mRNA editing machinery and absence of editing in the knockout animals is a direct consequence of the absence of functional Apobec-1.

Urapidil treatment decreases plasma fibrinogen concentration in essential hypertension

The effects of antihypertensive drugs on cardiovascular metabolic risk factors were monitored in 42 patients with essential hypertension (diastolic blood pressure [DBP] >95 mm Hg). In a double-blind randomized parallel-group study, they were treated with atenolol 50 mg once per day (n = 25) or urapidil 60 mg twice per day (n = 17), a peripheral α 1-receptor blocker with an additional central serotonin 1A (5HT1A) receptor agonistic effect, for 12 weeks. Plasma fibrinogen concentration decreased by 24% ( P < .0001) during urapidil treatment and by 9% ( P = .05) during atenolol treatment, with the effects of the two drugs differing significantly. Plasminogen activator inhibitor (PAI) activity tended to increase by 17% (nonsignificant [NS]) in the atenolol-treated group and to decrease by 4% (NS) in the urapidil group. Differences between the effects of the two drugs on very—low-density lipoprotein (VLDL) triglycerides (TG) and on total TG were significant. During urapidil medication, these two parameters were reduced by 22% and 13%, respectively, but the changes were nonsignificant ( P = .11 and P = .14, respectively). In contrast, atenolol treatment caused a significant increase in both VLDL TG and total TG of 31% and 21%, respectively. Hemoglobin A 1c (HbA 1c) increased by 4% ( P = .06) during atenolol treatment, but was unaffected by urapidil. There were no significant changes within or between atenolol- and urapidil-treated groups regarding glucose disposal on an oral glucose tolerance test (OGTT) or the insulin sensitivity index on a hyperinsulinemic-euglycemic clamp test. In conclusion, urapidil treatment was characterized by neutral or favorable effects on several variables associated with the metabolic syndrome. Atenolol treatment had neutral properties in some metabolic aspects, but deleterious effects on lipid status.

Effects of gemfibrozil or simvastatin on apolipoprotein-B-containing lipoproteins, apolipoprotein-CIII and lipoprotein(a) in familial combined hyperlipidaemia

Background: Familial combined hyperlipidaemia (FCH), characterized by elevated very-low-density lipoprotein (VLDL) and/or low-density lipoprotein (LDL), is associated with an increased prevalence of premature cardiovascular disease. Therefore, lipid-lowering is frequently indicated. Methods: We evaluated in a parallel, double-blind randomized fashion the effect of gemfibrozil (1200 mg/day) (n = 40) or simvastatin (20 mg/day) (n = 41) on lipids, apolipoprotein-B (apo-B)-containing lipoproteins, apo-CIII and lipoprotein(a) [Lp(a)], in 81 well-defined FCH patients. Results: While both drugs lowered plasma cholesterol and triglyceride levels, gemfibrozil lowered plasma triglycerides more effectively by reduction of triglycerides in VLDL and LDL, whereas simvastatin was more effective in its reduction of total plasma cholesterol by exclusively decreasing LDL cholesterol. High-density lipoprotein (HDL) increased to an equal extent on both therapies. Total serum apo-B levels were reduced with both drugs; however, gemfibrozil decreased apo-B only in VLDL + IDL, whereas simvastatin decreased apo-B in both VLDL + IDL and LDL. In keeping with a more effective reduction of VLDL particles, a more pronounced reduction of apo-CIII also was observed after gemfibrozil, which correlated with the reduction in plasma triglycerides. Baseline concentrations of Lp(a) showed a wide range in both treatment groups. Median Lp(a) levels increased after simvastatin, but were not affected by gemfibrozil. Conclusion: Both therapies exhibited their specific effects, although none of the drugs alone completely normalized the lipid profiles of these patients with FCH. Therefore, the choice of treatment should be based on the most elevated lipoprotein fraction, and in some cases a combination of the two drugs may be indicated.

Effects of inherent responsiveness to diet and day-to-day diet variation on plasma lipoprotein concentrations

We studied the biological variability and responsiveness to dietary fat of plasma lipoprotein cholesterol and triacylglycerol concentrations. Ten normal persons were studied on 3 consecutive days while they were eating their unrestricted usual diets and after 8, 9, and 10 d of eating a constant high-fat and low-fat diet administered in a crossover design. The changes in plasma low-density-lipoprotein (LDL)-cholesterol concentrations from baseline with the high-fat diet were inversely correlated with the changes from baseline with the low-fat diet (r = -0.74, P = 0.01), as well as with the changes from the low-fat to high-fat diet (r = -0.93, P < 0.001). The extent of increases in plasma LDL-cholesterol concentrations from the baseline to the high-fat diet were positively correlated with the increases from the low-fat to the high-fat diet (r = 0.93, P < 0.001). The responses of high-density-lipoprotein (HDL) cholesterol were not consistently correlated. The within-person between-day CV of LDL decreased from 10% with the unrestricted diet to 6% (P < 0.05) with the high-fat diet and to 7% with the low-fat diet (NS). The CV of total triacylglycerol (22%) and very-low-density-lipoprotein (VLDL) triacylglycerol (48%) on the unrestricted diet significantly decreased by 51-59% during both controlled diets (P = 0.03-0.06). The CV of HDL cholesterol was 5.3% during baseline, 4.2% during the high-fat diet, and 3.2% during the low-fat diet (P = 0.4, 0.19, respectively). In summary, individuals have a reproducible plasma LDL-cholesterol response when changing their dietary fat intake. The day-to-day variation in total triacylglycerol, VLDL triacylglycerol, and LDL-cholesterol concentrations decreases when day-to-day dietary variation is eliminated.

Decreased sensitivity of very-low-density lipoprotein secretion to the inhibitory effect of insulin in cultured hepatocytes from lactating rats.

Hepatocytes were prepared from 10-11-day lactating rat dams and from lactating dams which had been weaned for periods of either 1-2 days or 7 days. Hepatocytes from each group were cultured for periods of up to 48 h in a chemically defined medium. Compared with those from the 7-day weaned animals, hepatocytes from the lactating rats were resistant to the inhibitory effects of insulin on the secretion of very-low-density lipoprotein (VLDL) triacylglycerol (TAG). These differences persisted for up to 48 h in culture. Hepatocytes from the 1-2 day weaned animals remained relatively insulin-resistant in this respect. Similar differences in the response to insulin were not observed for the secretion of VLDL apolipoprotein B. TAG production increased and ketogenesis decreased in the hepatocytes from the lactating compared with those from the 7-day weaned rats. Insensitivity of the liver to the normal effects of insulin on the secretion of VLDL TAG may arise from a need to maintain an adequate flux of hepatic lipids to the lactating mammary gland in order to meet the large demand for milk-fat production.

Endotoxin and cytokines decrease serum levels and extra hepatic protein and mRNA levels of cholesteryl ester transfer protein in syrian hamsters.

Endotoxin alters the metabolism of lipoproteins, including that of high density lipoprotein (HDL). Cholesteryl ester transfer protein (CETP) facilitates exchange of HDL cholesterol for very low density lipoprotein (VLDL) triglyceride, leading to catabolism of HDL. We investigated the effects of endotoxin and cytokines on CETP in Syrian hamsters. Endotoxin induced a rapid and progressive decrease in serum CETP levels, by 48 h CETP had decreased to < 20% of control levels. Endotoxin also decreased CETP mRNA and protein levels in adipose tissue, heart, and muscle, the tissues with highest levels of CETP mRNA, providing a plausible mechanism for the endotoxin-induced decrease in circulating CETP. Dexamethasone did not mimic the effects of endotoxin on CETP, but the combination of tumor necrosis factor and interleukin-1 did, indicating that these cytokines may in part mediate the effects of endotoxin on CETP. The endotoxin-induced decrease in CETP may help maintain HDL cholesterol levels during infection and inflammation when increased triglyceride levels could drive the exchange of HDL cholesteryl ester for VLDL triglyceride. Maintaining circulating HDL may be important because HDL protects against the toxic effects of endotoxin and provides cholesterol for peripheral cells involved in the immune response and tissue repair.

Probing structure and function of VLDL by synthetic amphipathic helical peptides

Class A amphipathic helical peptides have been shown to mimic many properties of exchangeable apolipoproteins. The three analogs of the class A amphipathic peptides were used to probe the structure and function of human very low density lipoproteins (VLDL): 1) 18 residue peptide possessing a single helical domain (18A) with the sequence Asp-Trp-Leu-Lys-Ala-Phe-Tyr-Asp-Lys-Val-Ala-Glu-Lys-Leu-Lys-Glu-Ala-Phe; 2) two domains of 18A separated by a Pro (37pA); and 3) and 18A analog with the end groups protected to increase helicity (Ac-18A-NH2). Upon incubation of the peptides with VLDL at a peptide to VLDL, (protein) ratio of 1:1, the 37pA and Ac-18A-NH2 were able to displace most of apolipoprotein (apo) Cs and E from VLDL without alteration in its lipid composition and morphology while 18A had minimal effect. The extent of displacement was a function of the peptide to VLDL ratio. The rank order of displaceability of apolipoproteins on VLDL was apoE > C-III > C-II. The displacement of apoE and/or Cs from VLDL by peptides variably affected the ability of VLDL to interact with purified bovine milk lipoprotein lipase (LpL) and cultured macrophages. Treatment of VLDL with Ac-18A-NH2 markedly lowered its reactivity to LpL and its ability to induce lipid accumulation in cultured macrophages: however, treatment of VLDL with 37pA or 18A only minimally lowered their abilities. Ac-18A-NH2 treatment of VLDL resulted in the increase of apparent K(m) and a decrease of Vmax for lipoprotein lipase (LpL)-catalyzed hydrolysis of VLDL triglycerides. When an artificial triglyceride emulsion was used as a substrate of LpL, 37pA, but not Ac-18A-NH2, activated LpL. The above data indicate that 1) amphipathic helical peptides can alter the metabolic and functional properties of VLDL by dissociating the functionally important exchangeable apolipoproteins from VLDL as well as by acting as a functional element of VLDL after their incorporation; and 2) the class A amphipathic peptides having different lipid-associating properties exert significantly different effect on VLDL function.

Characterization of lipoprotein composition in rats fed different dietary lipids and of the effects of lipoproteins upon lymphocyte proliferation

Weanling Lewis rats were fed for 10 weeks on a low fat (2.5% by weight; LF) diet or on diets containing 20% by weight of hydrogenated coconut oil (HCO), olive oil (OO), safflower oil (SO), evening primrose oil (EPO), or menhaden (fish) oil (MO); all other components of the diets were identical. The chylomicron (CM), very low density lipoprotein (VLDL), low density lipoprotein (LDL), and high density lipoprotein (HDL) fractions were isolated from the serum. The serum from MO-fed animals had lower LDL and HDL cholesterol concentrations than the serum from animals fed each of the other diets. The apolipoprotein A-1 concentration in the HDL fraction from animals fed the MO diet was also low. The serum from HCO-fed animals had a higher CM triacylglycerol concentration than serum from animals fed each of the other diets. The serum from OO-fed animals had a higher VLDL triacylglycerol concentration than serum from animals fed each of the other diets. The concentration of apolipoprotein B was also high in the VLDL fraction from OO-fed animals. The fatty acid composition of each lipoprotein fraction was affected by the nature of the lipid in the diet; the greatest effects were observed in the CM and VLDL fractions. Each lipoprotein fraction isolated from LF-fed rats inhibited mitogen-stimulated rat spleen lymphocyte proliferation in a concentration-dependent manner; LDL and HDL caused greater inhibition than CM and VLDL. Dietary lipid manipulation did not alter the inhibitory effects of any of the lipoprotein fractions upon lymphocyte proliferation, except that CM and HDL from MO-fed animals and HDL from OO-fed animals resulted in enhanced proliferation compared with either CM or HDL from animals fed the other diets. We conclude that the inhibition of lymphocyte proliferation caused by feeding rats certain dietary lipids (OO, EPO, MO) may be mediated by non-lipoprotein serum components.

Two weeks of daily injections and continuous infusion of recombinant human growth hormone (GH) in GH-deficient adults. II. Effects on serum lipoproteins and lipoprotein and hepatic lipase activity

Recombinant human growth hormone (GH) administered as daily subcutaneous (SC) injections has been shown to affect serum lipoproteins in GH-deficient subjects. However, the effects of continuous infusion of GH on serum lipoproteins have not been investigated in GH-deficient adults. The aim of the present study was to compare effects of daily injections and continuous infusion of GH on lipoprotein metabolism. Recombinant human GH (0.25 U/kg/wk) was administered to nine GH-deficient adult men during a period of 14 days in two different ways, ie, as a daily SC injection at 8:00 pm and as a continuous SC infusion, with 1 month of washout between the treatments. Blood samples and tests were performed in the morning after an overnight fast before the start of GH treatment (day 0) and on day 2 and day 14 of treatment. Abdominal SC adipose tissue lipoprotein lipase (LPL), postheparin plasma LPL, and hepatic lipase (HL) activity were measured 120 minutes after the intake of 100 g glucose. Adipose tissue LPL activity decreased and postheparin plasma HL activity increased after 14 days of GH treatment irrespective of the mode of GH administration, whreas GH treatment had no effect on postheparin plasma LPL activity. Serum triglyceride and very-low-density lipoprotein (VLDL) triglyceride concentrations increased during GH treatment. However, VLDL triglyceride concentrations increased to a greater degree during treatment with daily GH injections than during continuous infusion of GH. Serum apolipoprotein (apo) B and low-density lipoprotein (LDL) cholesterol concentrations decreased during treatment with daily GH injections, but were not significantly affected by continuous GH infusion. Thus, apo B and LDL cholesterol concentrations were lower after daily GH injections versus continuous GH infusion. Serum lipoprotein(a) [Lp(a)] and apo E concentrations increased during both modes of GH treatment. However, continuous infusion of GH resulted in a more marked increase in Lp(a) and apo E concentrations than daily GH injections. Minor effects were observed on serum apo A-I concentrations, but high-density lipoprotein (HDL) cholesterol concentrations were not affected. In conclusion, GH treatment of GH-deficient men influenced adipose tissue LPL and postheparin plasma HL activity, as well as serum lipoprotein concentrations. Moreover, continuous GH infusion and daily GH injections differed with respect to the magnitude of effects on several lipoprotein fractions including VLDL triglycerides, LDL cholesterol, apo B, apo E, and Lp(a) concentrations.

Angiographic assessment of effects of bezafibrate on progression of coronary artery disease in young male postinfarction patients

Summary Background Bezafibrate has effects on lipid metabolism and haemostatic function. We undertook a double-blind, placebo-controlled intervention trial, the Bezafibrate Coronary Atherosclerosis Intervention Trial (BECAIT), to establish whether bezafibrate (200 mg three times daily) could retard or prevent the progression of atherosclerotic lesions in dyslipidaemic male survivors of myocardial infarction who were younger than 45 years at the time of the event. Methods 92 patients completed an initial 3-month period of dietary intervention and were randomly assigned to treatment with bezafibrate or placebo. Dietary intervention continued throughout the trial. Coronary angiography was done at baseline and after 2 and 5 years. 81 patients (42 bezafibrate treated and 39 placebo treated) who underwent baseline angiography and at least one posttreatment angiogram were included in the efficacy analysis. The primary endpoint was change in mean minimum lumen diameter. Findings The mean minimum lumen diameter decreased from baseline to the last angiographic assessment (2 or 5 years) by 0·06 mm (95% Cl 0·15 reduction to 0·01 increase) in the bezafibrate group and by 0·17 mm (0·33 reduction to 0·09 increase) in the placebo group. The treatment effect was therefore 0·13 mm (95% Cl 0·10 to 0·15; p=0·049). Parallel treatment effects, although not statistically significant, were observed for the secondary angiographic endpoints (mean segment diameter 0·02 mm [0·01-0·04] and percentage stenosis -3·41% [-4·00 to -2·98]). The cumulative coronary event rate was significantly lower among bezafibrate-treated than among placebo-treated patients (three vs 11 patients; p=0·02). There were significant treatment effects of bezafibrate for serum concentrations of cholesterol (-9%; p<0·001), very-low-density-lipoprotein (VLDL) cholesterol (-35%; p<0·001), serum triglycerides (-31%; p<0·001), VLDL triglycerides (-37%; p<0·001), and plasma fibrinogen (-12%; p=0·001), whereas low-density (LDL) cholesterol concentrations did not change. High density lipoprotein (HDL) cholesterol increased significantly with bezafibrate (9%; p=0·02). Interpretation The results show that bezafibrate improves dyslipidaemia, lowers plasma fibrinogen, slows the progression of focal coronary atherosclerosis, and reduces coronary events in young survivors of myocardial infarction.

Chronic exogenous hyperinsulinaemia does not modify the acute inhibitory effect of insulin on the secretion of very-low-density lipoprotein triacylglycerol and apolipoprotein B in primary cultures of rat hepatocytes.

Male Wistar rats were fitted with subcutaneous osmotic mini-pumps that delivered insulin at a constant rate of 0.20 i.u./h for 7 days. This treatment raised the plasma insulin concentration from 31 +/- 4 to 201 +/- 64 micro-i.u./ml. Hepatocytes prepared from the hyperinsulinaemic animals secreted very-low-density lipoprotein (VLDL) triacylglycerol (TAG) at a higher rate (172 +/- 21 microgram per 24 h per mg cell protein) than did those from sham-operated controls (109 +/- 12 microgram per 24 h per mg) (P<0.05). However, chronic exogenous hyperinsulinaemia had no stimulatory effect on the secretion of VLDL apolipoprotein B (apoB) in derived hepatocytes compared with those from the sham-operated controls (2.32 +/- 0.38 compared with 3.09 +/- 0.40 microgram per 24 h per mg). Hepatocytes from the hyperinsulinaemic rats thus secreted larger VLDL particles as evidenced by the increased TAG:apoB ratio (78.4 +/- 13.1 compared with 38.4 +/- 7.6; P<0.05). In hepatocytes from the hyperinsulinaemic rats a larger proportion of the newly synthesized TAG was secreted as VLDL. Hepatocytes from the hyperinsulinaemic and the sham-operated control animals were equally sensitive to the inhibitory effect of insulin added in vitro on the secretion of VLDL TAG. Insulin added in vitro to the culture medium of hepatocytes from hyperinsulinaemic animals significantly decreased the TAG:apoB ratio of the secreted VLDL. This change did not occur in hepatocytes from sham-operated rats. These results suggest that, in vivo, chronic hyperinsulinaemia is not in itself sufficient to desensitize the liver to the acute inhibitory effect of insulin on the secretion of VLDL.