Lipids and HCV

Chronic hepatitis C virus (HCV) infection is associated with an increase in hepatic steatosis and a decrease in serum levels of total cholesterol, low-density lipoprotein cholesterol (LDL) and apolipoprotein B (apoB), the main protein constituent of LDL and very low-density lipoprotein (VLDL). These changes are more marked in HCV genotype 3 infection, and effective treatment results in their reversal. Low lipid levels in HCV infection correlate not only with steatosis and more advanced liver fibrosis but also with non-response to interferon-based therapy. The clinical relevance of disrupted lipid metabolism reflects the fact that lipids play a crucial role in the life cycle of hepatitis C virus. HCV assembly and maturation in hepatocytes depend on microsomal triglyceride transfer protein and apoB in a manner that parallels the formation of VLDL. VLDL production from the liver occurs throughout the day with an estimated 10¹⁸ particles produced every 24 h whilst the estimated hepatitis C virion production rate is 10¹² virions per day. HCV particles in the serum exist as a mixture of complete low-density infectious lipo-viral particles (LVP) and a vast excess of apoB-associated empty nucleocapsid-free sub-viral particles that are complexed with anti-HCV envelope antibodies. Apolipoprotein E (apoE) is also involved in HCV particle morphogenesis and is an essential apolipoprotein for HCV infectivity. ApoE is a critical ligand for the receptor-mediated removal of triglyceride rich lipoprotein (TRL) remnants by the liver. The dynamics of apoB-associated lipoproteins, including HCV-LVP, change post-prandially with an increase in large TRL remnants and very low density HCV-LVP which are rapidly cleared by the liver (at least three HCV receptors are cellular receptors for uptake of TRL remnants). In summary, HCV utilises triglyceride-rich lipoprotein pathways within the liver and the circulation to its advantage.     

内源性高甘油三酯血症患者血浆VLDL、LDL及HDL对血凝的影响

目的：研究内源性高甘油三酯血症(HTG)患血浆极低密度脂蛋白(VLDL)、低密度脂蛋白(LDL)及高密度脂蛋白(HDL)是否发生了氧化修饰及其对血凝的影响。方法：对2l例内源性高甘油三酯血症患与2l例年龄性别相近的正常人的血脂、脂质过氧化物进行了分析。用一次性密度梯度超速离心法分离血浆VLDL、LDL及HDL，测定这三种脂蛋白的234nm光吸收、相对电泳迁移率(REM)和硫代巴比妥酸反应物质(TBARS)，分别将这三种脂蛋白加入由正常人新鲜混合血浆构成的反应系统中，按试剂盒分别测定凝血酶原时间(PT)及活化部分凝血酶原时间(APIT)。结果：内源性HTG患血浆TG含量平均升高2．73倍，HDLC下降l.7l倍，同时LPO升高1．22倍;HTG组VLDL、LDL及HDL的REM、234nm光吸收值、TBARS含量均较对照组显增加(P＜0．01)，表明内源性HTG患血浆VLDL、LDL及LDL均发生了氧化修饰生成Ox—VLDL、Ox-LDL.PT及APTT在分别加入HTG组的VLDL、LDL及HDL后均比加入相应正常组脂蛋白明显缩短(P均＜0．05)。相关分析表明，HTG组血浆VLDL及HDL相对电泳迁移率(REM)与PT呈负相关(P＜0．01)。结论：HTG患血浆VLDL、LDL及HDL发生了氧化修饰，并使PT及APTT明显缩短。     

Apolipoprotein B100 quality control and the regulation of hepatic very low density lipoprotein secretion

Apolipoprotein B (apoB) is the main protein component of very low density lipoprotein (VLDL) and is necessary for the assembly and secretion of these triglyceride (TG)-rich particles. Following release from the liver, VLDL is converted to low density lipoprotein (LDL) in the plasma and increased production of VLDL can therefore play a detrimental role in cardiovascular disease. Increasing evidence has helped to establish VLDL assembly as a target for the treatment of dyslipidemias. Multiple factors are involved in the folding of the apoB protein and the formation of a secretion-competent VLDL particle. Failed VLDL assembly can initiate quality control mechanisms in the hepatocyte that target apoB for degradation. ApoB is a substrate for endoplasmic reticulum associated degradation (ERAD) by the ubiquitin proteasome system and for autophagy. Efficient targeting and disposal of apoB is a regulated process that modulates VLDL secretion and partitioning of TG. Emerging evidence suggests that significant overlap exists between these degradative pathways. For example, the insulin-mediated targeting of apoB to autophagy and postprandial activation of the unfolded protein response (UPR) may employ the same cellular machinery and regulatory cues. Changes in the quality control mechanisms for apoB impact hepatic physiology and pathology states, including insulin resistance and fatty liver. Insulin signaling, lipid metabolism and the hepatic UPR may impact VLDL production, particularly during the postprandial state. In this review we summarize our current understanding of VLDL assembly, apoB degradation, quality control mechanisms and the role of these processes in liver physiology and in pathologic states.     

Cellular glycosaminoglycans and low density lipoprotein receptor are involved in hepatitis C virus adsorption

The initial binding of Hepatitis C virus (HCV) to the cell membrane is a critical determinant of pathogenesis. Two putative HCV receptors have been identified, CD81 and low-density lipoprotein receptor (LDLr). CD81 interacts in vitro with the HCV E2 envelope glycoprotein, and LDLr interacts with HCV present in human plasma. In order to characterize these potential receptors for HCV, virus from plasma, able to replicate in cell culture, was inoculated on Vero cells or human hepatocarcinoma cells. HCV adsorption was assessed by quantitating cell-associated viral RNA by a real-time RT-PCR method. Anti-LDLr antibody, low and very low density lipoproteins inhibited significantly HCV adsorption, confirming the role of LDLr as HCV receptor. Only one out of the two anti-CD81 antibodies used in this study led to a partial inhibition of HCV binding. This study also highlights a role for glycosaminoglycans (GAGs) in HCV adsorption: treatment of virus with heparin led to 70% inhibition of attachment, as did desulfation of cellular GAGs. Treatment of Vero cells with heparin-lyase significantly inhibited virus attachment but by only 30%. These results demonstrate the complexity of the HCV binding step in which LDLr interacts strongly with HCV, whereas the interaction of HCV with GAGs and particularly with CD81 seem to be more moderate.     

Binding of human lipoproteins (low, very low, high density lipoproteins) to recombinant envelope proteins of hepatitis C virus

Heterogeneities in the density of hepatitis C virus (HCV)-RNA-carrying material from human sera (1.03–1.20 g/ml) are partially due to the binding of lipoproteins [low density (LDL), very low density (VLDL), high density (HDL) lipoproteins] and immunoglobulins. In this study we demonstrate the binding of recombinant HCV envelope protein (E1/E2) to human LDL, VLDL and HDL on a molecular basis. The binding of lipoproteins was restricted to the middle part of the E1 gene product (amino acids 222–336) and the C-terminal part of the E2 protein (amino acids 523–809). Lipoproteins did not bind to recombinant HCV core protein. Received: 22 December 1999     

Reduced plasma concentrations of total, low density lipoprotein and high density lipoprotein cholesterol in patients with Gaucher type I disease

Plasma lipid and serum apoprotein concentrations were determined in twenty-nine individuals with Gaucher type I disease. Plasma total cholesterol, low density lipoprotein (LDL) cholesterol and high density lipoprotein (HDL) cholesterol were all significantly reduced in the patients with Gaucher disease compared to a group of matched control subjects. Total, LDL and HDL cholesterol were lower in males than in females with Gaucher disease. These sex differences appeared to be inversely correlated with the severity of disease manifestations which were greater in the males. Serum levels of apoprotein-B and apoprotein-AI, the major structural apoproteins of LDL and HDL, respectively, were decreased in the subjects with Gaucher disease. Thus, the reductions in LDL and HDL cholesterol were associated with reduced numbers of lipoprotein particles in plasma. In contrast, apoprotein-E, a protein which is secreted by several tissues, including activated macrophages and which may mediate hepatic catabolism of lipoproteins, was elevated in the patients. Since macrophages may also catabolize lipoproteins, Gaucher disease may serve as a model for the effect of activated macrophages upon human lipoprotein metabolism.
This work was supported by the following grants: USPHS HL 23077, HD 07105, HL 25752, CA 31656 and RR-71 from the National Institutes of Health; 1–273 and 1–578 from the March of Dimes Birth Defects Foundation; grant from the New York Heart Assocation. Dr. Ginsberg is a recipient of a Research Career Development Award HL 00949 and is an Irma T. Hirschl Career Scientist. Dr. Grabowski is a recipient of a Clinical Investigator Award HD 00386.     

Very low density lipoprotein apolipoprotein B metabolism in humans

Summary The human plasma lipoproteins encompass a broad spectrum of particles of widely varying physical and chemical properties whose metabolism is directed by their protein components. Apolipoprotein B₁₀₀ (apo B₁₀₀) is the major structural protein resident in particles within the Svedberg flotation range 0–400. The largest of these, the very low density lipoprotein (VLDL), rich in triglyceride, are metabolised by sequential delipidation through a transient intermediate density lipoprotein (IDL) to cholesterol-rich low density lipoproteins (LDL). Several components contribute to the regulation of this process, including (a) the lipolytic enzymes lipoprotein lipase and hepatic lipase (b), apolipoproteins B, CII, CIII and E, and (c) the apolipoprotein B/E or LDL receptor. Lipoprotein lipase acts primarily on large VLDL of Sf 60–400. Hepatic lipase on the other hand seems to be critical for the conversion of smaller particles (Sf 12–60) to LDL (Sf 0–12). Although most apo B₁₀₀ flux is directed to the production of the delipidation end product LDL, along the length of the cascade there is potential for direct removal of particles from the system, probably via the actions of cell membrane receptors. This alternative pathway is particularly evident in hypertriglyceridaemic subjects, in whom the delipidation process is retarded.VLDL metabolism shows inter subject variability even in normal individuals. In this regard, apolipoprotein E plays an important role. Normolipidaemic individuals homozygous for the apo E₂ variant exhibit gross disturbances in the transit of B protein through the VLDL-IDL-LDL chain.Abbreviations apo B, C, E Apolipoprotein B, C, E - CETP Cholesteryl ester transfer protein - FCH Familial combined hyperlipidaemia - FH Familial hypercholesterolaemia - FHTG Familial hypertriglyceridaemia - HDL High density lipoprotein - HL Hepatic lipase - IDL Intermediate density lipoprotein - LDL Low density lipoprotein - LpL Lipoprotein lipase - RFLP Restriction fragment length polymorphism - Sf Svedberg flotation coefficient - VLDL Very low density lipoprotein - WHHL Watanabe heritable hyperlipidemic     

Apolipoprotein E on hepatitis C virion facilitates infection through interaction with low-density lipoprotein receptor

Hepatitis C virus (HCV) infection is a major cause of liver disease. HCV associates with host apolipoproteins and enters hepatocytes through complex processes involving some combination of CD81, claudin-1, occludin, and scavenger receptor BI. Here we show that infectious HCV resembles very low density lipoprotein (VLDL) and that entry involves co-receptor function of the low-density lipoprotein receptor (LDL-R). Blocking experiments demonstrate that β-VLDL itself or anti-apolipoprotein E (apoE) antibody can block HCV entry. Knockdown of the LDL-R by treatment with 25-hydroxycholesterol or siRNA ablated ligand uptake and reduced HCV infection of cells, whereas infection was rescued upon cell ectopic LDL-R expression. Analyses of gradient-fractionated HCV demonstrate that apoE is associated with HCV virions exhibiting peak infectivity and dependence upon the LDL-R for cell entry. Our results define the LDL-R as a cooperative HCV co-receptor that supports viral entry and infectivity through interaction with apoE ligand present in an infectious HCV/lipoprotein complex comprising the virion. Disruption of HCV/LDL-R interactions by altering lipoprotein metabolism may therefore represent a focus for future therapy.     

Low density lipoprotein receptors in cultured skin fibroblasts from psoriasis patients

Low density lipoprotein (LDL) receptor activity, measured as 125I-LDL association and degradation at 37 degrees C, was determined in cultured fibroblasts from involved as well as uninvolved skin obtained from 20 psoriasis patients. The same analyses were conducted in fibroblasts from two reference groups consisting of 19 heterozygotes for familial hypercholesterolemia and 16 normal subjects, respectively. Psoriasis patients had significantly lower LDL receptor activity than normals, and it was comparable to that of the heterozygotes for familial hypercholesterolemia. The reduced LDL receptor activity was not accompanied by an increase in total serum cholesterol. The psoriasis patients had a significant reduction in apo-B concentration, but did not differ from the normals in the other serum lipid or lipoprotein parameters. There was no difference in LDL receptor activity between involved and uninvolved skin from psoriasis patients. These results suggest that there is an abnormal cell membrane in dermal fibroblasts from psoriasis patients. Since their total serum cholesterol is normal, their low LDL receptor activity may be confined to dermal cells, leaving the hepatic lipid metabolism normal. The pathogenetic significance of this finding is unknown.     

Low density lipoprotein receptor as a candidate receptor for hepatitis C virus

Hepatitis C virus (HCV) binds to different human cell lines in vitro. However, the efficiency of adsorption is very low due mainly to a relatively small fraction of the virus being able to bind to these cells. Free low density lipoprotein (LDL > 200 microg/ml) is able to block the attachment of HCV to human fibroblasts in vitro completely. COS-7 cells being primarily not able to bind HCV were transfected with a vector containing the entire coding sequence of the human LDL-receptor (LDLR). HCV was now bound to these cells. We propose that HCV and LDL are competitive for the cellular LDLR and that LDL in sera of patients may regulate the binding of HCV to this target.     

Binding of liver derived, low density hepatitis C virus to human hepatoma cells

HCV recovered from low density fractions of infected blood is associated with lipid and host apo-lipoproteins in lipo-viro-particles (LVP). It has been proposed that these particles are capable of binding and entering hepatocytes by viral glycoprotein independent mechanisms utilizing uptake pathways of normal host lipoproteins after binding to cell surface glycosaminoglycans (GAG), the low density lipoprotein receptor (LDL-r) or scavenger receptor B1 (SR-B1). In this study binding to human hepatoma cells of HCV low density RNA containing particles, semi-purified from macerates of infected human liver, is compared with that of normal host low density lipoprotein (LDL). Binding of both LDL and HCV low density RNA containing particles paralleled LDL-r but not SR-B1 expression on the recipient cells. Binding of both particle types was sensitive to suramin at 0 degrees C but less so at 37 degrees C suggesting that they both bind initially to GAG but, at 37 degrees C, are internalized or transferred to a suramin resistant receptor. Suramin resistant uptake of both particles was blocked in the presence of excess LDL or oxidized LDL. However, whilst LDL uptake was blocked by anti-apoB-100, HCV low density RNA uptake was enhanced by anti-apoB100 and further enhanced by a cocktail of anti-apo-B100 and anti-apoE. Pre-incubation of HCV low density RNA containing particles with antibodies to the E2 glycoprotein had little or no effect on uptake. These data indicate that whilst liver derived HCV RNA containing particles are taken up by HepG2 cells by a virus glycoprotein independent mechanism, the mechanism differs from that of LDL uptake.     

Acute and delayed effects of prolonged exercise on serum lipoproteins

Summary To investigate the effects of a single period of prolonged exercise on lipoprotein concentration and composition, 13 healthy endurance-trained men were examined before and after (1 h, 20 h) a cross-country run [30 km, time: 130 (SD 7.4) min]. The data show that following acute exercise, serum triglyceride (TG) concentration were reduced (36%) as a consequence of a reduced number (31%) of very low density lipoprotein (VLDL) particles. Changes in composition of VLDL were present but less evident. In contrast to this, acute exercise did not induce significant changes in the average concentration of individual low-density lipoprotein (LDL) subfractions. However, changes in dense LDL [density (d) > 1.044 g · ml^-1}] concentration were significantly correlated to changes in serum TG: a reduction of dense LDL occurred in subjects with large reductions in serum TG. In addition, LDL composition changed significantly. Immediately (1 h) after exercise the TG content of all LDL subfractions was reduced. These reductions were significant in large (d=1.0061.037 g · ml^-1) and small LDL (1.044-1.063 g · ml -1). It can be concluded therefore from our study that acute exercise primarily altered the composition of LDL subfractions while their concentration remained stable.This paper is dedicated to Prof. Dr. J. Keul, Medical Director of our Department, on the occasion of his 60th birthday     

Low density lipoprotein receptor-related protein 1 expression correlates with cholesteryl ester accumulation in the myocardium of ischemic cardiomyopathy patients

ABSTRACT: Our hypothesis was that overexpression of certain lipoprotein receptors might be related to lipid accumulation in the human ischemic myocardium. Intramyocardial lipid overload contributes to contractile dysfunction and arrhythmias in cardiomyopathy. Thus, the purpose of this study was to assess the effect of both hypercholesterolemic dose of LDL and that of hypertrigliceridemic VLDL on LRP1 expression in cardiomyocytes, as well as the potential correlation between LRP1 expression and neutral lipid accumulation in the left ventricle tissue from ischemic cardiomyopathy patients. Cell culture experiments include control and LRP1-deficient cardiomyocytes exposed to lipoproteins under normoxic and hypoxic conditions. Explanted hearts from 18 ICM patients and eight non-diseased hearts (CNT) were included. Low density lipoprotein receptor-related protein 1 (LRP1), very low density lipoprotein receptor (VLDLR) and low density lipoprotein receptor (LDLR) expression was analyzed by real time PCR and Western blotting. Cholesteryl ester (CE), triglyceride (TG) and free cholesterol (FC) content was assess by thin layer chromatography following lipid extraction. Western blotting experiments showed that protein levels of LRP1, VLDLR and HIF-1 were significantly upregulated in ischemic hearts. Immunohistochemistry and confocal microscopy analysis showed that LRP1 and HIF-1 were upregulated in cardiomyocytes of ICM patients. In vitro studies showed that VLDL, LDL and hypoxia exerted an upregulatory effect on LRP1 expression and that LRP1 played a major role in cholesteryl ester accumulation from lipoproteins in cardiomyocytes. Myocardial CE accumulation strongly correlated with LRP1 levels in ischemic hearts Taken together, our results suggest that LRP1 upregulation is key for myocardial cholesterol ester accumulation in ischemic human hearts and that LRP1 may be a target to prevent the deleterious effects of myocardial cholesterol accumulation in ischemic cardiomyopathy.     

Mechanisms of dyslipoproteinemias in systemic lupus erythematosus

Autoimmunity and inflammation are associated with marked changes in lipid and lipoprotein metabolism in SLE. Autoantibodies and cytokines are able to modulate lipoprotein lipase (LPL) activity, a key enzyme in lipid metabolism, with a consequent "lupus pattern" of dyslipoproteinemia characterized by elevated levels of very low-density lipoprotein cholesterol (VLDL) and triglycerides (TG) and lower high-density lipoprotein cholesterol (HDL) levels. This pattern favors an enhanced LDL oxidation with a subsequent deleterious foam cell formation. Autoantibodies and immunocomplexes may aggravate this oxidative injury by inducing accumulation and deposition of oxLDL in endothelial cells. Drugs and associated diseases usually magnify the close interaction of these factors and further promote the proatherogenic environment of this disease.     

Genetics of the low density lipoprotein receptor:

Fibroblast association (plasma membrane binding plus intracellular accumulation) and degradation of radioiodinated low density lipoprotein (125I-LDL) index plasma membrane LDL receptor activity. Cultured fibroblasts from 23 subjects affected with familial hypercholesterolemia (HC) and from 95 subjects without HC (non-HCs) were tested for 125I-LDL association and degradation. Both LDL receptor activity indices were twice as high in non-HC and HC heterozygous cell strains. This is compatible with a major gene effect on LDL receptor activity. However, a considerable overlap between non-HC and HC heterozygous values was found in the 125I-LDL association assay [median (range) 970 (330-2500), and 450 (250-490), respectively] and in the degradation assay [median (range) 810 (280-2020), and 470 (160-790), respectively]. The values are expressed as ng 125I-LDL X mg cell protein-1 X 4.5 h-1. These great overlaps in the LDL receptor activity indices support the view that the influence of LDL receptor activity on the HC phenotype may be smaller than believed previously. Furthermore, for the diagnosis of HC, these LDL receptor activity assays are far more expensive and have less sensitivity and specificity than simple serum cholesterol determination. The LDL receptor-dependent 125I-LDL association values for the HC heterozygous individuals clustered into four groups. Family data supported the hypothesis that this variation could be due to four different LDL receptor variants, each coded for by different alleles at the LDL receptor locus. If confirmed, this finding may have implications for the understanding of the variable expression of HC and also of the genetic impact on lipoprotein metabolism and susceptibility to atherosclerosis in non-HCs.     

Elevated lipoprotein(a) levels in patients with acute myeloblastic leukaemia decrease after successful chemotherapeutic treatment

Summary Twenty-two patients with acute myeloblastic leukaemia (AML) were studied to investigate disease-associated changes in lipid metabolism. Lipoprotein (a) [Lp(a)] levels were found to be elevated at the time of diagnosis (median 23 mg/dl; 41% of patient group had levels greater than 25 mg/dl) and diminished after successful chemotherapeutic treatment in 9 of 10 cases, with a maximum decrease from 56 to 10 mg/dl. In contrast, reduced levels of total cholesterol, low density lipoprotein (LDL) and high density lipoprotein (HDL) (medians 137, 87 and 20 mg/dl, respectively) were observed at the time of diagnosis. Cholesterol and HDL levels increased in all 10 and LDL in 9 cases in which complete remission was achieved. These data suggest that the catabolism of LDL-cholesterol might be even more enhanced than assumed to date. Furthermore, it indicates that the Lp(a) level in acute myeloblastic leukaemia is influenced either directly or indirectly by the leukaemic blasts.Abbreviations AML acute myeloblastic leukaemia - Lp(a) lipoprotein (a) - LDL low density lipoprotein - HDL high density lipoprotein - FAB French-American-British - CALGB cancer and leukaemia group B - CR complete remission - TG triglycerides - VLDL very low density lipoprotein - RIA radioimmunoassay - apo(a) apoprotein (a) - HMG-CoA reductase 3-hydroxy-3-methylglutaryl coenzyme A reductase Supported by the Volkswagen Stiftung with a grant to A.N.     

Altered lipoprotein composition and elevated serum lipids in chicken embryos with hereditary muscular dystrophy

The earliest biochemical changes reported in chickens with hereditary muscular dystrophy are increased cholesterol levels in liver, serum and pectoral muscles at 9 days of embryonic development. We have investigated whether there were concomitant differences in serum lipoprotein composition (VLDL, very low density lipoproteins; LDL, low density lipoproteins; HDL high density lipoproteins)**, and levels of serum triglycerides (TG), free cholesterol (FC) and cholesteryl esters (CE) in normal chicken embryos and in those with hereditary muscular dystrophy between 10 and 16 days in ovo. VLDL and CE content of the serum of dystrophic embryos are significantly elevated compared to those of the normal serum from 10 to 16 days in ovo, and serum TG is significantly increased at 12 and 14 days in ovo. Serum LDL and HDL concentrations are significantly lower in dystrophic embryos at 14, 16 and 12 days respectively. It is proposed that an increased rate of CE synthesis, probably in the liver, induces the formation of CE-rich, TG-poor VDLD-like lipoprotein. Decreased degradation of this lipoprotein by peripheral tissues, especially muscles, may account for the high VLDL levels in the dystrophic embryos. Since dystrophic chickens exhibit hyperlipoproteinemia followed by muscle degeneration, this disease has features in common with human spinal muscular atrophy.     

Lp(a) lipoprotein enters cultured fibroblasts independently of the plasma membrane low density lipoprotein receptor

Lp(a) lipoprotein shares the apoB antigen with low density lipoprotein (LDL). The Lp(a) antigen is unique for Lp(a) lipoprotein. Fibroblast association (i.e. plasma membrane binding plus intracellular accumulation), plasma membrane binding, intracellular accumulation and degradation of 125I-Lp(a) lipoprotein were studied in strains from subjects with or without autosomal dominant hypercholesterolemia (HC). Subjects without HC (non-HCs) have cell surface receptors for low density lipoprotein (LDL receptors). On the average, HC heterozygotes have half-normal LDL receptor activity and "receptor-negative" HC homozygous cell strains lack functional receptors. Fibroblast processing of 125I-Lp(a) lipoprotein was compared to fibroblast processing of 125I-LDL. LDL receptor-dependent processing of 125I-LDL was saturated at about 50 microgram apo 125I-LDL.ml-1 in non-HC fibroblasts. 125I-Lp(a) lipoprotein was, however, largely processed independently of receptor mechanisms by non-HC cells (highest concentration examined 150 microgram apo 125I-Lp(a) lipoprotein . ml-1). Lp(a) lipoprotein did not interfere with 125I-LDL for fibroblast association, but inhibited 125I-LDL degradation. The interference with 125I-LDL degradation was time dependent. Only slightly higher 125I-Lp(a) lipoprotein processing values were found in non-HC and HC heterozygous strains than in "receptor-negative" HC homozygous strains. However, non-HC cells had more than tenfold higher 125I-LDL processing values than "receptor-negative" HC homozygous cells.     

Characterization of low density lipoprotein receptor (LDLR) gene mutations in Albania

Introduction

Familial hypercholesterolaemia (FH) is a clinical syndrome characterised by elevated serum total cholesterol (TCHOL) levels due to an increase in low-density lipoprotein (LDL) cholesterol, by tendon xanthomata and clinical manifestations of ischaemic heart disease in early life. Typically, it results from mutations in the low-density lipoprotein receptor (LDLR) gene. So far, more than 800 mutations have been reported for the LDLR gene and account for FH. The nature of LDLR gene mutations varies among different ethnicities. Until now no mutations of LDLR have been reported in the Albanian population.

Material and methods

We assessed the contribution of the LDLR gene mutations as causes of FH in an Albanian population. Fifty probands with a clinical diagnosis of FH were included. We analysed all the exons and the promoter of the LDLR gene by using restriction isotyping or direct sequencing.

Results

Twenty-one patients were heterozygous for the 1646G>A mutation (FH Genoa) in exon 11 and 9 patients were heterozygous for the 81T>C mutation in exon 2 of the LDLR gene.

Conclusions

This report describes two LDLR gene mutations accounting for FH in Albania (1646G>A, 81T>C).     

Metabolic fate of low density lipoprotein and high density lipoprotein labeled with an ether analogue of cholesteryl ester

Summary Low density lipoprotein (LDL) metabolism by human skin fibroblasts was studied using LDL labeled with a nonhydrolyzable cholesteryl ether analogue,³H-cholesteryl linoleyl ether (CLE). The³H-CLE-LDL was taken up by the apo-B, E receptor mediated endocytosis similar to¹²⁵I-labeled LDL. This was shown by saturation kinetics of uptake with respect to³H-CLE-LDL concentration and very low uptake of³H-CLE-LDL by receptor negative cell strains. When injected into rats,³H-CLE-LDL and¹⁴C- cholesteryl ester (CE)-LDL were cleared at equal rates and about 30% of the injected LDL was recovered in the liver. Treatment with ethinyl estradiol resulted in a three-fold increase in³H-CLE-LDL uptake by the liver. The liver is also the major site of uptake of³H-CLE-high density lipoprotein (HDL) (40%–45% of the injected dose) but its uptake by the liver increased only by 20% with estradiol treatment. As³H-CLE-HDL was cleared from the circulation at a somewhat faster rate than¹²⁵I-HDL it appeared that some dissociation in the tissue uptake of the protein and CE moieties occurs.Abbreviations LDL low density lipoprotein - HDL high density lipoprotein - CLE cholesteryl linoleyl ether - CE cholesteryl ester Presented at the 42nd European Atherosclerosis Group Meeting, Munich, 5–6 March, 1984