Integrated regulation of very low density lipoprotein triglyceride and apolipoprotein-B kinetics in man: Normolipemic subjects,familial hypertriglyceridemia and familial combined hyperlipidemia

Turnover kinetics of triglycerides (TG) and apolipoprotein-B (apo-B) of plasma very low density lipoprotein (VLDL) and their relationship to plasma VLDL composition and VLDL apo-B conversion to low density lipoprotein (LDL) were determined in age and weight-matched groups of normolipemic (NL) healthy subjects, patients with familial combined hyperlipidemia (FCHL) and patients with familial hypertriglyceridemia (FHTG). In NL subjects, a significant correlation as observed between VLDL TG or VLDL apo-B turnover rate and its circulating mass, suggesting that the plasma level of VLDL was determined by the secretion rate of VLDL TG and apo-B. The positive significant correlation between VLDL TG and apo-B also suggests that the production of these moieties was integrated at the synthetic and/or secretory sites to maintain the ratio of TG to apo-B in plasma VLDL. In moderately obese NL subjects, proportionate increases in VLDL TG and apo-B turnover rates resulted in enhanced secretion of VLDL particles. Both groups with genetic hypertriglyceridemia had increased VLDL TG and VLDL apo-B turnover rates. This increase accounted for the increase in circulating VLDL TG and apo-B mass. In patients with FCHL, turnover rates of VLDL TG and apo-B were equally increased, hence, the ratios between major VLDL constituents were within normal limits. On the other hand, the increase in VLDL TG turnover in patients with FHTG was disproportionately greater than that of apo-B resulting in a higher ratio of TG to other VLDL components. In NL subjects, approximately 72% of VLDL apo-B released into plasma was converted to LDL. This conversion correlated positively with VLDL apo-B turnover rate and inversely with VLDL TG turnover rate. Formation of LDL from VLDL was significantly greater in the obese individuals. In FCHL, conversion of VLDL to LDL represented the major pathway for VLDL apo-B catabolism. The increased VLDL apo-B load was predominantly catabolized to LDL. The greater increase in VLDL TG turnover relative to apo-B in FHTG, on the other hand, resulted in a smaller fraction of VLDL apo-B recovered in LDL, most of the VLDL apo-B being removed via a pathway that did not involve this conversion. We conclude that the composition and metabolic fate of plasma VLDL may be greatly influenced by the secretion rates of VLDL TG and apo-B. If VLDL conversion to LDL and the subsequent catabolism of the latter provides a major route for delivery of cholesterol ester to peripheral tissues, then the increased LDL production in FCHL compared to FHTG may account for a higher cardiovascular risk.     

Low density lipoprotein metabolism in familial combined hyperlipidemia and familial hypercholesterolemia: kinetic analysis using an integrated model

Several models for low density lipoprotein (LDL) apo B metabolism were applied to LDL turnover data from subjects with two distinct genetic forms of hyperlipidemia, familial hypercholesterolemia (FH), and familial combined hyperlipidemia (FCHL). Of the first two models tested, there was good agreement between the observed and predicted data for FH in one (model A), and for FCHL in the other (model B). The major difference between these two models is that LDL is kinetically homogeneous in model A and heterogeneous in model B, raising the possibility that LDL subspecies differences may occur between these two disorders. The findings are consistent with LDL homogeneity in FH and LDL heterogeneity in FCHL. Two other integrated models (models C and D) provided good agreement between observed and predicted data in both disorders. Although neither could be rejected outright on the basis of known physiology, parameter estimates were more variable with model D. Analysis of the data using model C was consistent with the known pathophysiologic defect in LDL catabolism in FH and suggests that individuals with FH as well as FCHL have more than one LDL subpopulation in plasma. The urine/plasma (U/P) ratio was shown to be constant from day 4 to day 14 of the study in FH, while in FCHL this value declined in all cases. Thus, determination of LDL fractional catabolic rates (FCR) by the U/P ratio method may be invalid in certain groups of patients. The other traditional method for calculating LDL FCR, the Matthews' analysis, overestimated FCR in some instances, and could lead to systematic errors when used to determine LDL FCR and production rates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Carotid atherosclerosis and lipoprotein particle subclasses in familial hypercholesterolaemia and familial combined hyperlipidaemia

Background and AimsFamilial hypercholesterolaemia (FH) and familial combined hyperlipidaemia (FCH) are common atherogenic disorders with great variability in cardiovascular disease (CVD). No direct atherosclerosis burden comparisons have been performed between FH and FCH in relation to lipoprotein particle distribution.Methods and ResultsRisk factors and three measures of carotid intima-media thickness (IMT) in both sides were determined in 572 FH, 250 FCH and 200 controls. Lipoproteins were assessed by nuclear magnetic resonance (NMR) spectroscopy. Compared with controls, IMT measures were increased in FH and FCH. FCH had the highest adjusted mean–maximum IMT. FH had twice low-density lipoprotein (LDL) particles than controls, but similar LDL subclass size and distribution. FCH subjects also had increased LDL particles and the highest number of small LDL (1519 ± 731 nmol l^?1 vs. 887 ± 784 nmol l^?1 in FH and 545 ± 409 nmol l^?1 in controls). Age, gender, cholesterol/high-density lipoprotein (HDL) ratio, smoking and systolic blood pressure were independently associated with IMT in FH (r² = 0.38). The same variables, except cholesterol/HDL ratio, were associated with IMT in FCH (r² = 0.40). Among NMR lipoproteins, only VLDL and chylomicrons increased IMT prediction in FCH by 0.8%.ConclusionFH and FCH subjects show increased carotid atherosclerosis in relation to classical risk factors. Lipoprotein subclasses do not substantially contribute to IMT variability.     

家族性混合型高脂血症与脂蛋白脂酶基因的连锁分析

目的 探讨脂蛋白脂酶基因与家族性混合型高脂血症是否连锁，以期发现家族性混合型高脂血症遗传易感位点。方法 从北京地区搜集12个（81人）家族性混合型高脂血症家系选择脂蛋白脂酶基因及其附近的微卫星遗传标记（LPLGZ14／15与D8S282）进行连锁分析。结果 CENEHUNTER软件包多点连锁分析显示微卫星遗传标记最大LOD score(HLOD)值如下：HLODLPLGZ14／15＝－8．9及HLODD8S282＝－10．5。结论 中国北京地区家族性混合型高脂血症家系提示，脂蛋白脂酶基因不是影响家族性混合型高脂血症表型的遗传易感基因。     

Effects of fenofibrate on high and low density lipoprotein metabolism in heterozygous familial hypercholesterolemia

This study investigates the influence of pharmacological doses of fenofibrate on HDL and LDL metabolism in 5 familial hypercholesterolemia heterozygotes. Fenofibrate lowered plasma low density lipoprotein cholesterol (20%, P less than 0.025), triglycerides (37%: P less than 0.005) and apolipoprotein B (14%: P less than 0.05) but increased apo A-I (20%; P = 0.01). Kinetic studies showed that the drug markedly increased the fractional catabolic rate of LDL-apo B by 59% and its synthetic rate by 36%. Fractional catabolic rate of apo A-I was also increased by 26% but accompanied by a much greater increase of its synthetic rate (49%). Thus the change in balance between catabolism and synthesis of both apoproteins affected by fenofibrate accounts for the observed plasma concentration changes, which may be considered as favourable with regard to the management of atherosclerosis.     

Why very low density lipoprotein levels are normal in familial hyperchylomicronaemia.

The anomalous finding that very low density lipoprotein levels are relatively normal in patients with familial hyperchylomicronaemia has never been satisfactorily explained, particularly in view of the marked reduction or absence of peripheral lipoprotein lipase activity characteristic of this condition. I propose that the discrepancy between the plasma levels of the two triglyceride-rich lipoprotein fractions in these patients is due to the secretion by the liver of triglyceride in the form of chylomicron-like particles, rather than as very low density lipoprotein. The proposed "switch" in the spectrum of lipoproteins secreted by the liver is probably contingent upon the activity of the hepatic lipase present on the liver cell plasma membrane.     

Pulse wave velocity in familial combined hyperlipidemia

BACKGROUND: In the present cross-sectional study we investigated whether familial combined hyperlipidemia (FCH) is associated with an increased arterial wall stiffness, and whether measures of arterial wall stiffness in FCH family members could contribute to cardiovascular risk stratification. METHODS: Ninety-eight subjects with FCH and 230 unaffected relatives filled out a questionnaire about their smoking habits, medical history, and medication use. Fasting venous blood was drawn after discontinuation of any lipid-lowering medication. Pulse wave velocity (PWV) and augmentation index (AIx) were determined by applanation tonometry as surrogate markers of arterial stiffness. RESULTS: Patients with FCH had a significantly increased PWV compared to their unaffected relatives (9.07 +/- 2.75 v 8.28 +/- 2.62 m/sec, P = .005), whereas AIx was not increased (21.6 +/- 12.7 v 15.6 +/- 14.1, P = .96). Age- and gender-adjusted PWV was an equally good predictor of the presence of cardiovascular disease (CVD) in FCH family members as the most predictive combination of age- and gender-adjusted clinical and biochemical risk factors, including total cholesterol, HDL-cholesterol, and systolic blood pressure (area under the receiver operating curve (ROC) [AUC] 0.83 [0.76-0.90] v AUC 0.84 [0.78-0.91], P = .83). Addition of PWV to the multivariable prognostic model, including these age- and gender-adjusted traditional risk factors, did not increase the predictive ability for CVD (AUC 0.84 [0.79-0.89]). CONCLUSIONS: Patients with FCH are characterized by an increased arterial stiffness. The PWV predicts the presence of CVD equally well as any combination of clinical and traditional biochemical risk factors, but PWV has no additional value in addition to traditional risk factor screening in FCH families.     

高密度脂蛋白亚类与心血管疾病的现状分析

高密度脂蛋白是一类异质性脂蛋白,其亚类表现出在抗动脉粥样硬化功能和心血管保护作用方面的差异性,并随年龄、性别等的差异也发生动态变化。影响高密度脂蛋白功能和亚类分布的药物或许是改善心血管风险更有效的方法。文章就高密度脂蛋白亚类的检测、抗动脉粥样硬化功能以及与心血管疾病的相关性等进行综述,为人类心血管疾病的防治提供新视角。     

The effects of low density lipoprotein and high density lipoprotein on phosphoinositide hydrolysis in bovine aortic endothelial cells.

Low density lipoprotein (LDL) and high density lipoprotein (HDL3) were tested for their ability to induce inositol phospholipid turnover and inositol phosphate production in bovine aortic endothelial cells (BAEC). The production of inositol phosphates following hydrolysis of the phosphoinositides was demonstrated by two methods; release of [3H]inositol phosphates after labelling with [3H]myo-inositol and by a direct binding assay for inositol 1,4,5-trisphosphate (InsP3). Acute exposure to LDL induced InsP3 release at low concentrations of the lipoprotein within the physiological range of LDL in tissues. HDL3 did not cause any release of the inositol phosphates. Pre-incubation of BAEC with HDL3 suppressed bradykinin- and LDL-induced inositol phosphate production in BAEC in a concentration-dependent manner. It is concluded that LDL acutely stimulates phosphoinositide breakdown and that pre-incubation of cells with HDL3 inhibits this effect. The mechanism responsible for these effects remains to be elucidated.     

Coexistence of familial dysalbuminemic hyperthyroxinemia with familial hypercholesterolemia and multiple lipoprotein type hyperlipidemia

Familial dysalbuminemic hyperthyroxinemia (FDH), an autosomal disorder characterized by an increase in serum albumin binding of thyroxine, has been encountered in a family who was also found to have both familial hypercholesterolemia (FHC) and multiple lipoprotein type hyperlipidemia (MLH). One subject with FHC and two subjects with MLH had FDH. Although some of the laboratory parameters in hyperlipidemic patients with FDH were suggestive of hyperthyroidism, the dialyzable free thyroxine concentrations were in the normal range and the patients were clinically euthyroid. The significance of the occurrence of FDH in hyperlipidemic subjects with hypothyroidism has been discussed, especially in regard to the longer time interval that may be needed to achieve an amelioration of the hypothyroid state during treatment with a normal maintenance dose of thyroxine. Treatment of FDH patients with other drugs may require an altered dosage if the drug binds to the atypical albumin fragments characterizing this disorder.     

Beneficial effects of blood donation on high density lipoprotein concentration and the oxidative potential of low density lipoprotein

According to some authors blood donors have a lower risk of cardiovascular incidents. This may be associated with the risk of cardiovascular disease reported by some authors, as well as with the oxidative changes caused by iron. The aim of this study was to determine, what happens to some of the factors contributing to atherosclerosis after the lowering of body iron. Blood was drawn from 23 healthy males after overnight fasting and the parameters described below determined. These persons donated blood (500 ml) on three occasions with 6 weeks intervals. Six to eight weeks after the third and final donation, blood was again drawn after overnight fasting and the following parameters measured for the second time: various parameters of body iron; lipid profile; anti-oxidants; and oxidative parameters of low density lipoprotein (LDL). Blood donation has various beneficial effects, such as increasing high density lipoprotein (HDL) and apoA; a higher oxidative potential of LDL; a lower level of LDL peroxidation resulting in a LDL particle with a higher oxidative potential, and a higher NO(3) concentration. We conclude that blood donation, and thereby a lowered body iron concentration, is an effective way to increase the oxidative potential of LDL, as well as the HDL and apoA concentrations.     

Angiographically silent atherosclerosis detected by intravascular ultrasound in patients with familial hypercholesterolemia and familial combined hyperlipidemia: Correlation with high density lipoproteins

Objectives. This study sought to evaluate the extent of atherosclerosis in coronary and iliac arteries in patients with heterozygous familial hypercholesterolemia or familial combined hyperlipidemia, using intravascular ultraound imaging.

Background. Intravascular ultrasound imaging provides cross-sectional tomographic views of the vessel wall and allows quantitative assessment of atherosclerosis.

Methods. Forty-eight nonsmoking, asymptomatic patients with heterozygous familial hypercholesterolemia or familial combined hyperlipidemia underwent intravascular ultrasound imaging of the left anterior descending coronary, left main coronary and common iliac arteries. Angiography showed only minimal or no narrowing in these vessels. Intravascular ultrasound images obtained during catheter pullback underwent morphometric analysis. Plaque burden was expressed as the mean and maximal intimal index (ratio of plaque area and area within the internal elastic lamina) and as the percent of vessel surface covered by plaque.

Results. Intravascular ultrasound detected plaque more frequently than angiography in the left anterior descending (80% vs. 29%, respectively), left main (44% vs. 16%) and iliac arteries (33% vs. 27%). Plaque burden was higher in the left anterior descending (mean intimal index [±SD] 0.25 ± 0.16) than in the left main (0.11 ± 0.16, p < 0.001) and iliac arteries (0.02 ± 0.04, p < 0.001). Angiography detected lumen narrowing only in coronary arteries with a maximal intimal index 0.42 (left anterior descending artery) and 0.43 (left main artery). The area within the internal elastic lamina increased with plaque area in the left anterior descending (r = 0.82, p < 0.001) and left main arteries (r = 0.53, p < 0.001). By stepwise multiple regression analysis, the strongest predictor for plaque burden in the left anterior descending artery was the level of high density lipoprotein (HDL) cholesterol and total/HDL cholesterol ratio for the left main artery.

Conclusions. In patients with heterozygous familial hypercholesterolemia and familial combined hyperlipidemia, extensive coronary plaque is present despite minimal or no angiographic changes. Compensatory vessel enlargement and diffuse involvement with eccentric plaque may account for the lack of angiographic changes. Levels of HDL cholesterol and total/HDL cholesterol ratio are far more powerful predictors of coronary plaque burden than are low density lipoprotein cholesterol levels in these patients with early, asymptomatic disease.     

Defects of receptor-mediated low density lipoprotein catabolism in homozygous familial hypercholesterolemia and hypothyroidism in vivo

The role of low density lipoprotein (LDL) receptors in the pathogenesis of hereditary and acquired forms of hypercholesterolemia has been investigated in vivo by simultaneously determining total and receptor-independent LDL catabolism with 125I-labeled LDL and 131I-labeled LDL coupled with cyclohexanedione. Receptor-mediated catabolism of LDL, determined as the difference between the turnover of 125I and 131I, was found to be virtually absent in two homozygotes with familial hypercholesterolemia and markedly reduced in a hypothyroid patient. Treatment of the latter with L-thyroxine markedly stimulated receptor-mediated catabolism and reduced LDL levels as did cholestyramine administration in a control subject. Reduction of LDL levels by plasma exchange in a control subject and homozygote had no such effect. These results demonstrate the existence of an intrinsic and almost total defect of receptor-mediated LDL catabolism in homozygous familial hypercholesterolemia and demontrate an analogous but reversible abnormality in hypothyroidism.