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Lipoprotein(a): new insights into an atherogenic lipoprotein.

Lipoprotein(a) constitutes a macromolecular complex in human plasma that combines structural features from the blood clotting and the lipoprotein systems. Aside from the discovery of lipoprotein(a) [Lp(a)] as a potential independent risk factor for premature cardiovascular disease its physiological role and activity remains obscure. Since the site of catabolism has not yet been fully characterized, there is intensive search for factors which influence plasma Lp(a) levels. Several clinical conditions and metabolic states have been identified to be added to the disorders of the lipid metabolism itself that modulate Lp(a) plasma levels. Diseases of the kidney and their accompanying factors (proteinuria and nephrotic syndrome) as well as end-stage renal disease and their treatment modalities (hemodialysis, peritoneal dialysis, and kidney transplantation) have all been found to increase Lp(a) plasma levels substantially. Fluctuations in Lp(a) also seem to occur in states of hormonal changes, such as in diabetes mellitus, after estrogen treatment, and during pregnancy. Recently a plausible mechanism for the atherogenic activity of Lp(a) has been ascribed to the inhibiting effect of Lp(a) on plasminogen activation, thus decreasing plasmin formation which in turn reduces the activation of transforming growth factor beta, a potent inhibitor of smooth muscle cell proliferation. Lp(a) exerts its pathological effect at plasma levels in the range of 20-30 mg/dl. Therefore, it seems mandatory to quantitate Lp(a) levels in patients who are at risk of developing progressive atherosclerotic disease to identify those with high levels of this unique atherogenic lipoprotein.(ABSTRACT TRUNCATED AT 250 WORDS)

Arteriosclerosis↗

Lipoprotein metabolism in the extravascular space. Cyclophosphamide inhibits modification of low-density lipoproteins in interstitial inflammatory fluid of the rabbit.

We have recently reported preferential modification and reduction in low-density lipoproteins (LDL) of inflammatory exudates in the rabbit. In an attempt to establish the role of inflammatory cells in these specific alterations, using the sponge-implanted rabbit model we characterized extravascular lipoproteins in animals with severely induced leukopenia. Under these conditions we were unable to demonstrate alterations in the distribution of lipoproteins in inflammatory fluid as compared to homologous plasma. Characterization of LDL from both plasma and inflammatory fluids revealed close similarity in molecular composition and electrophoretic mobility. These studies further implicate the role of scavenger cell systems as a significant component of daily lipoprotein homeostasis.

Animals↗

The C766T low-density lipoprotein receptor related protein polymorphism and coronary artery disease, plasma lipoproteins, and longevity in the Czech population.

Low-density lipoprotein receptor related protein (LRP) is a multifunctional endocytic receptor involved in various biological processes including the regulation of the coagulation-fibrinolysis balance, the lipoprotein metabolism, and cellular migration, all of which relate to the development of atherosclerosis. Polymorphisms affecting the function or expression of LRP may thus influence the individual risk of atherosclerosis development. This study investigated the association between the C766T LRP polymorphism, coronary artery disease (CAD), and plasma lipoprotein levels in a large sample of Caucasian subjects of Czech nationality. In addition, the 4G/5G promoter polymorphism of the gene coding for plasminogen activator inhibitor 1 (PAI-1), the known ligand of LRP with strong antifibrinolytic potential, was ascertained to investigate its possible association with CAD. Both polymorphisms were studied using polymerase chain reaction analysis in 654 patients with angiographically confirmed CAD and in 525 controls. No statistically significant differences in allele frequencies of the polymorphisms studied were detected between patients and controls, even when men, women, hypertonic, and type II diabetic subjects were compared separately. However, the frequency of the T allele of the LRP polymorphism was significantly higher in patients than controls when only subjects with the 5G/5G PAI-1 genotype were analyzed. In addition, the T LRP allele frequency was significantly lower in subjects aged 60 years or over than in those who were younger in both groups. No significant association was observed between the LRP or PAI-1 polymorphisms and plasma lipoprotein levels in the CAD patients. Our results demonstrate that the T allele of the C766T LRP polymorphism is negatively related to longevity, and that it increases the risk of CAD development in subjects with the 5G/5G PAI-1 genotype.

Aged↗

Lipoprotein(a) and atherosclerosis: new perspectives on the mechanism of action of an enigmatic lipoprotein.

Although elevated plasma concentrations of lipoprotein(a) (Lp(a)) have been identified as a risk factor for coronary heart disease, the pathophysiologic and physiologic roles of Lp(a) continue to elude basic researchers and clinicians alike. Lp(a) is a challenging lipoprotein to study because it has a complex structure consisting of a low-density lipoprotein-like moiety to which is covalently attached the unique glycoprotein apolipoprotein(a) (apo(a)). Apo(a) contains multiply repeated kringle domains that are similar to a sequence found in the fibrinolytic proenzyme plasminogen; differing numbers of kringle sequences in apo(a) give rise to Lp(a) isoform size heterogeneity. In addition to elevated plasma concentrations of Lp(a), apo(a) isoform size has been identified as a risk factor for coronary heart disease, although studies addressing this relationship have been limited. The similarity of Lp(a) to low-density lipoprotein and plasminogen provides an enticing link between the processes of atherosclerosis and thrombosis, although a clear demonstration of this association in vivo has not been provided. Clearly, Lp(a) is a risk factor for both atherothrombotic and purely thrombotic events; a plethora of mechanisms to explain these clinical findings has been provided by both in vitro studies as well as animal models for Lp(a).

Animals↗

Receptor-independent low-density lipoprotein catabolism. Evaluation of 2-hydroxyacetaldehyde-treated lipoprotein as a probe for its measurement.

This study examines the protein modification procedures available for inhibiting receptor recognition of low-density lipoprotein (LDL). Glycosylation with glucose, idose or ribose blocks the interaction of the lipoprotein with the high-affinity LDL receptor on cultured fibroblast membranes and delays its clearance from the plasma of rabbits. However, the prolonged incubation required in the process also changes the metabolic properties of the lipoprotein. An alternative approach using 2-hydroxyacetaldehyde-treated LDL completely blocks receptor recognition. This modified tracer has the same metabolic properties as the reductively methylated lipoprotein in rabbits and appears to be a suitable probe for the measurement of the receptor-independent LDL catabolic pathway in humans.

Acetaldehyde↗

The expressed human hepatic receptor for low-density lipoproteins differs from the fibroblast low-density lipoprotein receptor.

The role of the cellular receptor for the low-density lipoproteins (LDL) in cholesterol transport was initially defined through the study of nonhepatic cells in vitro. Since the liver is central in plasma lipoprotein metabolism, an investigation of hepatic lipoprotein receptors is important for understanding normal lipoprotein transport. Utilizing human hepatic and fibroblast membranes, the characteristics of receptors for LDL from hepatic and nonhepatic tissues were directly compared. Human hepatic membranes reversibly bound LDL within 5 min. Although both fibroblast and hepatic membranes saturably bound LDL at 37 degrees C, the fibroblast LDL receptor affinity (Kd = 2.5 X 10(-8) M) and number (5.5 X 10(12) sites/mg membrane protein) were greater than the hepatic receptor affinity (Kd = 10.8 X 10(-8) M) and number (0.5 X 10(12) sites/mg membrane protein). In contrast to the fibroblast LDL receptor which was unable to bind LDL in the presence of EDTA, the hepatic LDL receptor binding of LDL was only partially blocked by EDTA. The binding of LDL to its hepatic receptor is highly temperature-dependent, and studies utilizing both radiolabeled LDL and colloidal gold-labeled LDL indicate that little, if any, binding of LDL hepatic membranes occur at 0-4 degrees C. The hepatic membrane receptor(s) (Mr approximately equal to 270 000 and 330 000) differ from that of the fibroblast LDL receptor (Mr approximately equal to 130 000) and these proteins are present in hepatic membranes from a patient lacking the fibroblast LDL receptor. These data indicate that an expressed hepatic LDL receptor has unique properties different from those of the fibroblast LDL receptor and that the expressed protein(s) is genetically distinct from the fibroblast receptor.

Biological Transport, Active↗

A screening method for abnormally high lipoprotein(a) concentrations by agarose lipoprotein electrophoresis.

A routine electrophoretic method detecting plasma lipoprotein(a) (Lp(a)) is described. Plasma lipoproteins were electrophoresed using an agarose gel film containing cations which retard migration of beta-, prebeta- and alpha-bands. When present, the Lp(a)-band was detected between prebeta- and alpha-bands. This extra-band lipoprotein has been demonstrated to be Lp(a), by an immunofixation technique using anti-Lp(a) antibodies. This original procedure allows a distinct separation of Lp(a) from prebeta even after samples have been stored at 4 degrees C for several days, or in cases of hyperlipemic samples with increased prebeta lipoproteins. The reliability of this detection test has been tested in comparison with an Lp(a) electroimmunoassay. Both these techniques have been performed on 719 randomly selected subjects. With electrophoresis, the Lp(a)-positive subjects accounted for 34.2% of the subjects and although this method does not distinguish between different levels of positivity (depending on the sample), the presence of Lp(a)-band was always perceptible at concentrations that belong to the upper 15th percentile of values as determined by electroimmunodiffusion; inversely, all Lp(a)-positive plasma was measurable. In consequence, since it is reliable and relatively inexpensive, this detection test on modified agarose gel appears very useful for revealing the presence of abnormally high values of Lp(a) in populations.

Adolescent↗

Metabolism of lipoproteins in nonhuman primates. Reduced secretion of very low density lipoproteins in squirrel monkeys with diet-induced hypercholesterolemia.

We have studied the effects of diet-induced hypercholesterolemia on the rates of secretion of triglycerides into the plasma of fasted squirrel monkeys. Two groups of monkeys were studied: control animals which were fed a semipurified diet not associated with hyperlipemia (plasma cholesterol 127 +/- 8 mg/100 ml), and animals made hypercholesterolemic (plasma cholesterol 307 +/- 31 mg/100 ml) by being fed a diet containing 25% butter and 0.5% cholesterol. After intravenous infusion of Triton WR 1339 (300 mg/kg body wt), plasma triglycerides increased almost linearly for 9-12 hours. Analysis of individual lipoproteins separated by ultracentrifugation showed that newly secreted triglycerides were present almost exclusively in the very low density lipoprotein fraction. The rates of triglyceride secretion in the hypercholesterolemic group of monkeys (5.15 +/- 0.86 mg/kg/hr) were less than half those of the control animals (10.96 +/- 2.15 mg/kg/hr). We suggest that in monkeys with diet-induced hypercholesterolemia high concentrations of plasma low density lipoproteins may inhibit the synthesis and/or secretion of their parent very low density lipoprotein molecules into the circulation.

Animals↗

Heterozygous familial hypercholesterolemia in children: low-density lipoprotein receptor mutational analysis and variation in the expression of plasma lipoprotein-lipid concentrations.

The phenotypic expression of heterozygous familial hypercholesterolemia (FH) is variable form biochemical and clinical standpoints and several genetic and environmental factors could contribute to explain this variability. We have compared, in a cohort of 266 heterozygous FH children and adolescents (1-19 years), the variation in plasma lipoprotein-lipid levels among patients defined by three mutations in the low density lipoprotein receptor (LDLR) gene. Comparison of the plasma total and LDL-cholesterol (LDL-C) levels among the three mutation groups revealed significant differences. Plasma total and LDL-C levels were significantly higher (P < 0.05) in the group bearing the French-Canadian delta > 15 kb null allele mutation (8.17 +/- 1.45 and 6.58 +/- 1.42 mmol/l) and in the group with the defective allele C646Y missense mutation (8.18 +/- 1.53 and 6.65 +/- 1.50 mmo/l) compared to the group with the defective allele W66G missense mutation (7.19 +/- 1.23 and 5.62 +/- 1.16 mmol/l). Comparisons of other lipoprotein-lipid parameters between FH heterozygotes and normolipemic (n = 120) children indicated that all mutation groups had significantly (P = 0.0001) lower plasma HDL-cholesterol (HDL-C) levels and a higher total cholesterol (TC) to HDL-C ratio (P < 0.05). Among FH heterozygote groups, the W66G group had the lowest TC to HDL-C ratio. Multivariate analyses revealed that in FH heterozygotes as well as in controls, HDL-C levels contributed to a greater proportion of the variation in TC to HDL-C ratio than TC. In order to examine the age effect, control and FH heterozygote delta > 15 kb groups were then subdivided into four groups (1-4; 5-8; 9-13, and 14-19 years). The variation in HDL-C and triglycerides with age in heterozygous FH children showed a pattern which was similar to the one noted in the control group. In conclusion, the present study demonstrated that the overall contribution of age to variation in the lipoprotein profile of heterozygous FH children is similar to the effect observed among healthy children. The effect of LDLR gene in FH is dominant and there was no difference in plasma TC and LDL-C due to gender. Finally, this study indicates that the LDLR gene type mutations are a modulator of the magnitude of the increase in plasma TC and LDL-C levels noted among FH heterozygote children.

Adolescent↗

Treatment of E2E2 homozygous familial dysbetalipoproteinemic subjects with gemfibrozil does not enhance the binding of their d < 1.019 lipoprotein fraction to the low-density lipoprotein receptor.

Six E2E2 homozygous familial dysbetalipoproteinemic (FD) patients were treated with gemfibrozil (2 x 600 mg/d) for a period of 4 weeks. For all subjects, normalization of serum cholesterol concentrations with treatment did not result in a significant change in the cholesterol/triglyceride ratio of the d < 1.019 lipoprotein fraction. In addition, the binding efficiency of this lipoprotein fraction to the low-density lipoprotein (LDL) receptor on HepG2 cells did not change consistently with treatment. We conclude that normalization of serum cholesterol concentrations in FD patients by treatment with gemfibrozil is the result of an effect of gemfibrozil on the synthesis of d < 1.019 lipoproteins rather than an effect on the receptor-mediated clearance of these particles.

Apolipoproteins A↗

Effects of a moderate exercise session on postprandial lipoproteins, apolipoproteins and lipoprotein remnants in middle-aged men.

Prior moderate exercise reduces postprandial triglyceride concentrations. Its effects on the concentrations, compositions and potential atherogenicity of lipoprotein subfractions were investigated in the present study. Twenty normoglycaemic middle-aged men each underwent two fat tolerance tests (blood taken fasting and for 8 h after a meal containing 80 g fat and 70 g carbohydrate). On the afternoon before one test, subjects performed a 90-min treadmill walk (exercise); no exercise was performed before the control test. Prior exercise significantly reduced postprandial concentrations of chylomicrons (Sf >400) by 28.6% (absolute reduction 14.6 mg dl(-1)), of large VLDL1 (Sf 60-400) by 34.4% (39.7 mg dl(-1)) and of small VLDL2 (Sf 20-60) by 23.0% (9.6 mg dl(-1)). Over 95% of VLDL1 and VLDL2 comprised apolipoprotein (apo) B100-containing particles. Exercise also reduced postprandial remnant-like lipoprotein cholesterol (by 35%) and triglyceride concentrations (by 29%). Postprandial apo CIII/apo B and apo E/apo B ratios in VLDL1 were lower following exercise. Postprandial cholesteryl ester/triglyceride ratios were lower in VLDL1 and VLDL2 and higher in HDL2 following exercise. These data suggest that the effect of prior moderate exercise on VLDL1 is quantitatively greater than its effect on chylomicrons and that, in addition to reducing lipoprotein concentrations, exercise induces compositional changes to lipoprotein species which are likely to influence their metabolism and atherogenicity.

Apolipoproteins↗

The plasma parameter log (TG/HDL-C) as an atherogenic index: correlation with lipoprotein particle size and esterification rate in apoB-lipoprotein-depleted plasma (FER(HDL)).

OBJECTIVES: To evaluate if logarithm of the ratio of plasma concentration of triglycerides to HDL-cholesterol (Log[TG/HDL-C]) correlates with cholesterol esterification rates in apoB-lipoprotein-depleted plasma (FER(HDL)) and lipoprotein particle size. DESIGN AND METHODS: We analyzed previous data dealing with the parameters related to the FER(HDL) (an indirect measure of lipoprotein particle size). In a total of 1433 subjects from 35 cohorts with various risk of atherosclerosis (cord plasma, children, healthy men and women, pre- and postmenopausal women, patients with hypertension, type 2 diabetes, dyslipidemia and patients with positive or negative angiography findings) were studied. RESULTS: The analysis revealed a strong positive correlation (r = 0.803) between FER(HDL) and Log(TG/HDL-C). This parameter, which we propose to call "atherogenic index of plasma" (AIP) directly related to the risk of atherosclerosis in the above cohorts. We also confirmed in a cohort of 35 normal subjects a significant inverse correlation of LDL size with FER(HDL) (r = -0.818) and AIP (r = -0.776). CONCLUSION: Values of AIP correspond closely to those of FER(HDL) and to lipoprotein particle size and thus could be used as a marker of plasma atherogenicity.

Adult↗

Lipoprotein desialylation simultaneously enhances the cell cholesterol uptake and impairs the reverse cholesterol transport system: in vitro evidences utilizing neuraminidase-treated lipoproteins and mouse peritoneal macrophages.

Desialylation of low density lipoprotein (LDL) brings about accumulation of cholesterol in cultured cells. The influence of the neuraminidase-treated lipoprotein (LP) on the reverse cholesterol transport system was investigated in vitro utilizing very low density lipoprotein (VLDL), LDL, total high density lipoprotein (HDL) and its subfractions, HDL2 and HDL3, isolated from healthy donor plasma and mouse peritoneal macrophages. It was found that LP desialylation significantly: (1) decreased the capacity of total HDL and of HDL2, but not of HDL3, to efflux cellular cholesterol; (2) lowered the cholesterol esterification rate by lecithin:cholesterol acyltransferase (LCAT) without modifying the intrinsic LCAT activity of HDL; (3) increased the cholesteryl ester transfer from HDL to apo B-containing LP mediated by cholesteryl ester transfer protein (CETP); (4) enhanced the uptake by macrophages of cholesterol from HDL and LDL, although the amount of cholesterol taken up by the cells was much greater from the desialylated LDL than from desialylated HDL. Taken together, these in vitro evidences indicate that, in addition to enhancing the cell cholesterol LP uptake, desialylation may contribute to the premature development of atherosclerosis by impairing the reverse cholesterol transport system.

Animals↗

Long-term effect of low-density lipoprotein apheresis on plasma lipoproteins and coronary heart disease in native vessels and coronary bypass in severe heterozygous familial hypercholesterolemia.

Low-density lipoprotein (LDL) apheresis is a potent treatment for patients with coronary heart disease and severe hereditary forms of LDL hypercholesterolemia not adequately responsive to drug treatment. Until now, the beneficial effect of aggressive reduction of LDL cholesterol by LDL apheresis on the course of coronary heart disease has been demonstrated in one 3-year study and several studies lasting 2 years. We now report on the clinical course, lipoprotein concentrations, coronary angiograms, and side effects in patients undergoing LDL apheresis for as long as 8.6 years. Thirty-four patients (21 men and 13 women) with coronary heart disease and heterozygous familial hypercholesterolemia (FH) not adequately responsive to lipid-lowering drugs received weekly (four patients biweekly) LDL apheresis for 4.6 +/- 2.6 years under diet and lipid-lowering drug therapy; after 0.5 to 3 years, simvastatin in the maximal tolerable dose was added. The baseline LDL cholesterol concentration was 6.9 +/- 1.6 mmol/L. Combined treatment in the steady state yielded a pretreatment and posttreatment LDL cholesterol concentration of 4.8 +/- 0.9 and 1.8 +/- 0.4 mmol/L, respectively. The calculated interval mean LDL cholesterol was 3.3 +/- 0.6 mmol/L. Evaluation of the coronary angiographies revealed a definite regression of coronary lesions in four patients (11.8%); in 19 patients, there was a cessation of progression. Two patients developed atheromatous lesions in bypass grafts (L.H., 60% stenosis; S.M., occlusion). Of 23 patients eligible for the scoring of anginal symptoms, five (21.7%) reported a reduction of the frequency and severity of angina pectoris. The mean coronary symptom score in 23 patients changed from 1.65 +/- 0.83 at baseline to 1.39 +/- 0.66 at the end of the study. During the whole observation period, we observed three sudden deaths, one nonfatal myocardial infarction, and five patients requiring hospital admission because of unstable angina pectoris, one of which was followed by a transluminal coronary angioplasty. Aggressive reduction of LDL cholesterol with combined LDL apheresis and drugs induced regression of coronary lesions in four of 34 patients and prevented progression in 29 patients for as long as 8.6 years. The effect on LDL and high-density lipoprotein (HDL) cholesterol and lipoprotein(a) [Lp(a)] was comparable with all three apheresis techniques. Therefore, no obvious difference between the three techniques was found regarding changes in coronary lesions.

Adult↗

Susceptibility to oxidation of copper-induced plasma lipoproteins from Japanese eel: protective effect of vitellogenin on the oxidation of very low density lipoprotein.

The susceptibility to oxidation of copper-induced plasma lipoproteins from Japanese eel Anguilla japonica was examined with the guidance of thiobarbituric acid-reactive substances (TBARS). The TBARS values of copper-induced plasma lipoproteins increased with increasing the lipid-to-apolipoprotein ratios and very low density lipoprotein (VLDL) exhibited the highest TBARS value. On the other hand, vitellogenin, estrogen-induced precursor of egg yolk proteins, was resistant to copper-induced oxidation and seemed to chelate low concentrations of copper ion. Vitellogenin also protected the copper-induced oxidation of VLDL because of its antioxidant function. Vitellogenin seemed to serve as transition metals-binding lipoprotein by which free-radical reactions in the oocytes were extensively depressed.

Anguilla↗

Intensification of free radical oxidation of low-density lipoproteins in the plasma of patients with ischemic heart disease receiving beta-hydroxy-beta-methylglutaryl-coenzyme A reductase inhibitor cerivastatin and inhibition of low-density lipoprotein peroxidation with antioxidant probucol.

Inhibitors of the key enzyme of cholesterol biosynthesis beta-hydroxy-beta-methylglutaryl-coenzyme A reductase (statins) decrease cholesterol content in atherogenic low-density lipoproteins in patients with coronary heart disease and hypercholesterolemia, but inhibited biosynthesis of ubiquinone Q10 protecting low-density lipoproteins from free radical oxidation. Cerivastatin in a daily dose of 0.4 mg markedly increased the content of lipid peroxides in low-density lipoproteins. However, complex therapy with cerivastatin and antioxidant probucol (250 mg/day) was accompanied by a sharp decrease in the content of lipid peroxides in low-density lipoproteins in patients with coronary heart disease in vivo. These data indicate that antioxidant agents should be used in combination with inhibitors of beta-hydroxy-beta-methylglutaryl-coenzyme A reductase (hypolipidemic preparations) for the therapy of patients with coronary heart disease.

Antioxidants↗

Two common mutations (D9N, N291S) in lipoprotein lipase: a cumulative analysis of their influence on plasma lipids and lipoproteins in men and women.

We assessed the effect of two common mutations in the lipoprotein lipase gene (LPL), D9N and N291S, which have been shown to modulate plasma lipids in a wide spectrum of patients. A total of 1114 men and 1 144 women from the Framingham Offspring Study (FOS) were analyzed for these two LPL variants. Subsequently, the association with fasting plasma lipids and risk of coronary artery disease (CHD) was determined. We extended our study by calculating weighed means of lipids and lipoproteins in carriers and non-carriers for these LPL mutations in patients with genetic dyslipidemias, CHD patients and healthy controls. In the FOS sample, the D9N and N291S alleles were associated with lower high-density lipoprotein-cholesterol (HDL-C) (delta = - 0.07 mmol/ 1, p = 0.03) and a trend towards increased triglycerides (delta = 0.25 mmol/ 1, p = 0.07). In women, a trend towards the high triglyceride, low HDL-C phenotype was evident (delta = - 0.02 mmol/1 for HDL-C and delta = 0.14 mmol/l for triglycerides, respectively). Cumulative analysis of other studies of male carriers of the D9N and N291S revealed higher levels of triglycerides (D291N; 2.60(1.85) mmol/l vs. 1.62(1.18) mmol/l: p < 0.0001) (D9N; 1.94 (1.19) mmol/l vs. 1.74(1.17) mmol/l: p < 0.001) and lower HDL-C (N291S; 1.04(0.32) mmol/l vs. 1.15(0.28) mmol/l: p < 0.0001) (D9N; 1.08(0.24) mmol/l vs. 1.16(0.28) mmol/l: p < 0.0001). In females, results differed with higher TG levels (N291S; 1.70(0.99) mmol/l vs. 1.10(0.63) mmol/l: p < 0.001) (D9N; 1.08(0.76) mmol/l vs. 0.96(0.51) mmol/l: p < 0.01) and lower HDL-C levels (N291S; 1.27(0.33) mmol/l vs. 1.51(0.32) mmol/l: p < 0.0001); however, the HDL-C levels for D9N carriers were similar to non-carriers (D9N; 1.52(0.29) mmol/l vs. 1.53(0.35) mmol/l: p = 0.83). Our data provide evidence that common variants of the LPL gene are significant modulators of lipid and lipoprotein levels in both men and women.

Cholesterol, HDL↗

Degradation of lipoproteins by human monocyte-derived macrophages. Evidence for two distinct processes for the degradation of abnormal very-low-density lipoprotein from subjects with type III hyperlipidaemia.

Human blood monocyte-derived macrophages that had been cultured in medium containing human serum for 7 days degraded the abnormal very-low-density lipoproteins (VLDL) from the plasma of subjects with type III hyperlipoproteinaemia by two distinct saturable processes. One process was stimulated when cells from normal subjects were preincubated with lipoprotein-free medium, was inhibited by excess unlabelled low-density lipoproteins (LDL) and was absent from cells from subjects with homozygous familial hypercholesterolaemia; on these criteria it was identified as an LDL-receptor-dependent process. Degradation by the second process was of equal magnitude in both cell types and was unaffected by excess unlabelled LDL or acetylated LDL. The activity of this process was reduced when the cells were preincubated in lipoprotein-free medium. The abnormal VLDL from the plasma of cholesterol-fed rabbits were also degraded by this process, which was similar to that in mouse peritoneal macrophages mediated by the receptor for VLDL of beta-electrophoretic mobility [Goldstein, Ho, Brown, Innerarity & Mahley (1980) J. Biol. Chem. 255, 1839-1848].

Animals↗