Intrinsic enzymes of high-density lipoprotein

Several lines of evidence are available to support the protective effects of high-density lipoproteins (HDL) on atherosclerosis. The exact mechanisms by which HDL protects against atherosclerotic disease development are not understood. In addition to its role in the reverse transport of cholesterol from the peripheral sites to the liver for excretion, HDL also carries a number of enzymes that contribute to the remodeling of plasma lipoproteins and to the protection of other lipoproteins against oxidative modification. Many of these enzymes can play a role in determining the composition of circulating HDL, while others appear to affect specific biologic activities associated with HDL. It is not clear whether the concentrations of HDL particles or the activities associated with this class of particles are more important. One of the problems is that HDL constitutes a heterogeneous population of particles, and analytical tools to characterize the various subpopulations are not widely available. In this article, we will review the enzymes that are associated with plasma HDL and possible mechanisms as to how these may contribute to the protective properties of HDL in humans.     

High-density lipoproteins: marker of cardiovascular risk and therapeutic target

The high-density lipoproteins (HDLs) are complex, polymolecular assemblies produced by the jejunum, liver, in serum, and on the surface of macrophages. HDL cholesterol (HDL-C) levels are an independent predictor of risk for cardiovascular events in both men and women. High serum levels of this lipoprotein are associated with reduced risk for atherosclerosis and its clinical sequelae, such as myocardial infarction, ischemic stroke, and death. The molecular basis for the apparent vasculoprotection afforded by elevated HDL-C is widely attributed to the ability of HDL particles to drive reverse cholesterol transport. The proteosome (protein cargo) of HDL also appears to endow this lipoprotein with a capacity to reduce oxidized lipids, promote endothelial cell nitric oxide production, reduce adhesion molecule expression, inhibit platelet activation, stimulate endothelial proliferation and inhibit apoptosis, and reduce inflammatory mediator expression, among other functions. Recent investigation suggests that among patients with coronary artery disease, HDL can also be dysfunctional, yielding a pro-inflammatory and pro-oxidative phenotype. Numerous drugs are currently in development in an effort to devise the means by which to optimally increase serum levels of functional, antiatherogenic HDL species. These drugs exploit a diverse range of mechanisms with potential for beneficially impacting the development and progression of atherosclerotic disease.     

HDL signaling and protection against coronary artery atherosclerosis in mice

Atherosclerosis is a leading underlying factor in cardiovascular disease and stroke, important causes of morbidity and mortality across the globe. Abundant epidemiological studies demonstrate that high levels of high density lipoprotein (HDL) are associated with reduced risk of atherosclerosis and preclinical, animal model studies demonstrate that this association is causative. Understanding the molecular mechanisms underlying the protective effects of HDL will allow more strategic approaches to development of HDL based therapeutics. Recent evidence suggests that an important aspect of the ability of HDL to protect against atherosclerosis is its ability to trigger signaling responses in a variety of target cells including endothelial cells and macrophages in the vessel wall. These signaling responses require the HDL receptor, scavenger receptor class B type 1 (SR-B1), an adaptor protein (PDZK1) that binds to the cytosolic C terminus of SR-B1, Akt1 activation and (at least in endothelial cells) activation of endothelial NO synthase (eNOS). Mouse models of atherosclerosis, exemplified by apolipoprotein E or low density lipoprotein receptor gene inactivated mice (apoE or LDLR KO) develop atherosclerosis in their aortas but appear generally resistant to coronary artery atherosclerosis. On the other hand, inactivation of each of the components of HDL signaling (above) in either apoE or LDLR KO mice renders them susceptible to extensive coronary artery atherosclerosis suggesting that HDL signaling may play an important role in protection against coronary artery disease.     

Simultaneous transfer of cholesterol, triglycerides, and phospholipids to high-density lipoprotein in aging subjects with or without coronary artery disease

OBJECTIVE:

To verify whether the capacity of high-density lipoprotein (HDL) to simultaneously receive non-esterified cholesterol, triglycerides, cholesteryl esters, and phospholipids changes with aging and the presence of coronary artery disease.

DESIGN:

Cross-sectional study with biochemical analyses.

SUBJECTS:

Eleven elderly patients with coronary artery disease (74±5 years) were compared with the following groups of non-coronary artery disease subjects (referred to as “healthy”): 25 young (25±5 years), 25 middle-aged (42±6 years), and 25 elderly subjects (75±8 years).

METHODS:

Plasma samples were incubated with a nanoemulsion labeled with radioactive lipids; the transfer of the lipids from the nanoemulsion to the HDL was measured in chemically precipitated HDL. HDL size and paraoxonase-1 activity were also determined.

RESULTS:

The transfer of cholesteryl esters and phospholipids to high-density lipoprotein was significantly greater (p<0.001) in healthy elderly subjects than in the middle-aged and younger subjects. Non-esterified cholesterol and triglyceride transfer was not different among these three groups. The HDL size was significantly greater (p<0.001) in healthy elderly subjects than in the middle-aged and younger subjects. The paraoxonase-1 activity was similar among the groups. Compared with healthy elderly subjects, coronary artery disease elderly subjects had significantly less (p<0.05) transfer of non-esterified cholesterol, triglycerides, and cholesteryl esters to the HDL and a significantly smaller (p<0.05) HDL size.

CONCLUSION:

Because lipid transfer is enhanced in healthy elderly subjects but not in those with coronary artery disease, increasing lipid transfer to HDL may be a protective mechanism against the disease.     

Elevated high-density-lipoprotein cholesterol and normal triglycerides as markers of longevity

Summary Serum cholesterol, high-density lipoprotein (HDL) cholesterol and triglycerides of 85 year old home-living persons were compared to those of controls and of patients who had severe coronary artery disease (CAD) at an early age. Eightyfive-year-olds had higher serum HDL cholesterol than controls and patients with CAD. Patients with severe CAD had higher serum total cholesterol and serum triglycerides and lower HDL-cholesterol than other groups. When 85-year-old persons were divided into quintiles according to serum HDL cholesterol, women with highest HDL cholesterol had lowest mortality, men with lowest HDL cholesterol had highest mortality. We conclude that elevated HDL cholesterol is correlating with longevity and low HDL cholesterol with CAD at an early age.Abbreviations HDL high density lipoprotein - CAD coronary artery disease     

Is HDL function as important as HDL quantity in the coronary artery disease risk assessment?

Over the past several decades, it has been clearly established that higher plasma concentrations of high-density lipoprotein (HDL) are related to lower risk of coronary artery disease (CAD). According to the National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) guidelines, the HDL level of <40 mg/dL is considered low and is one of the CAD risk predictors. However, in the last decade, several studies have indicated the importance of the quality of HDL as another potential measure for CAD risk assessment. The loss of normal biological function of HDL particles as a result of multifactorial actions of chronic inflammation and acute phase responses has suggested a new potential pathway in the pathophysiology of atherosclerosis. The concept of “dysfunctional HDL” or “proinflammatory HDL,” which exhibits chameleon-like properties of converting a positive force protecting arteries to a negative one, enhancing atherogenesis is now under active investigation. Measurements of this dysfunctional quality of HDL in cell-based or cell-free assays by analyzing anti-inflammatory functions may link these changes to in vivo assessments of vascular disease. This review provides details on functional and dysfunctional HDL and summarizes recent studies into dysfunctional HDL and its potential links to CAD.     

Effects of ethanol on lipids and atherosclerosis.

Moderate alcohol consumption is associated with an increase in plasma high density lipoprotein (HDL) cholesterol concentration and a decrease in low density lipoprotein (LDL) cholesterol concentration. Changes in the concentration and composition of lipoproteins are estimated to account for more than half of alcohol's protective effect for coronary heart disease. Alcohol intake also affects plasma proteins involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, and phospholipases. In addition, alcohol intake may result in acetaldehyde modification of apolipoproteins. Furthermore, "abnormal" lipids, phosphatidylethanol and fatty acid ethyl esters are formed in the presence of ethanol and are associated with lipoproteins in plasma. Ethanol and ethanol-induced modifications of lipids may modulate the effects of lipoproteins on the cells in the arterial wall. The molecular mechanisms involved in these processes are complex, requiring further study to better understand the specific effects of ethanol in the pathogenesis of atherosclerosis. This review discusses the effects of ethanol on lipoproteins and lipoprotein metabolism, as well as the novel effects of lipoproteins on vascular wall cells.     

Functions of cholesterol ester transfer protein and relationship to coronary artery disease risk

The protective role of HDL in atherosclerotic cardiovascular disease reflects in part its ability to promote cholesterol efflux via ATP binding cassette transporters ABCA1 and ABCG1 in macrophage foam cells. This initiates a process of reverse cholesterol transport from the arterial wall to the liver. Inhibition of cholesteryl ester transfer protein (CETP) raises HDL and probably stimulates cholesterol efflux and anti-inflammatory effects in macrophage foam cells but does not increase the overall process of reverse cholesterol transport. Single nucleotide polymorphisms in the CETP gene are associated with lower CETP, higher HDL and probably with reduced CAD. Initial clinical trials with the CETP inhibitor torcetrapib were associated with an adverse outcome that mainly seemed to arise from offtarget toxicity.     

Comparative study of LpAI lipoparticles, HDL cholesterol and apolipoprotein AI in a control population, in a group of subjects with coronary diseases, and in a group of subjects with angiographically normal coronary vessels]

A new method for directly measuring LpAI lipoparticles containing apolipoprotein AI, but not apolipoprotein AII, is now disponible for laboratories. Concentrations of LpAI were measured in serum from 158 presumably healthy normolipidemic subjects (72 male, 86 female), for the age group 30-60 years. Concentrations of LpAI were also measured in subjects with angiographically defined coronary artery disease (coro+) and without angiographically defined coronary artery disease (coro-). After comparison of the groups, lipoprotein particle LpAI did not appear to be a better discriminative marker than HDL cholesterol or apolipoprotein AI for atherogen risk.     

Simvastatin and niacin, antioxidant vitamins, or the combination for the prevention of coronary disease.

BACKGROUND: Both lipid-modifying therapy and antioxidant vitamins are thought to have benefit in patients with coronary disease. We studied simvastatin-niacin and antioxidant-vitamin therapy, alone and together, for cardiovascular protection in patients with coronary disease and low plasma levels of HDL. METHODS: In a three-year, double-blind trial, 160 patients with coronary disease, low HDL cholesterol levels and normal LDL cholesterol levels were randomly assigned to receive one of four regimens: simvastatin plus niacin, vitamins, simvastatin-niacin plus antioxidants; or placebos. The end points were arteriographic evidence of a change in coronary stenosis and the occurrence of a first cardiovascular event (death, myocardial infarction, stroke, or revascularization). RESULTS: The mean levels of LDL and HDL cholesterol were unaltered in the antioxidant group and the placebo group; these levels changed substantially (by -42 percent and +26 percent, respectively) in the simvastatin-niacin group. The protective increase in HDL2 with simvastatin plus niacin was attenuated by concurrent therapy with antioxidants. The average stenosis progressed by 3.9 percent with placebos, 1.8 percent with antioxidants (P=0.16 for the comparison with the placebo group), and 0.7 percent with simvastatin-niacin plus antioxidants (P=0.004) and regressed by 0.4 percent with simvastatin-niacin alone (P<0.001). The frequency of the clinical end point was 24 percent with placebos; 3 percent with simvastatin-niacin alone; 21 percent in the antioxidant-therapy group; and 14 percent in the simvastatin-niacin-plus-antioxidants group. CONCLUSIONS: Simvastatin plus niacin provides marked clinical and angiographically measurable benefits in patients with coronary disease and low HDL levels. The use of antioxidant vitamins in this setting must be questioned.     

Coronary computed tomography angiography evaluation of plaque morphology and its relationship to HDL and total cholesterol to HDL ratio

BackgroundWhile population studies have demonstrated that high density lipoprotein cholesterol (HDL-C) and the ratio of total cholesterol to HDL (TC/HDL) improve cardiovascular risk prediction, the mechanism by which these parameters protect the cardiovascular system remains uncertain.ObjectiveTo investigate the relationship between the HDL-C level and the total cholesterol to HDL (TC/HDL) ratio with the morphology of coronary artery plaque as determined by coronary computed tomography angiography (CCTA).MethodsThis is a cross-sectional study involving 190 subjects with stable coronary artery disease. Semi-automated plaque analysis software was utilized to quantify plaque and plaque volumes are presented as total atheroma volume normalized (TAV_norm). Multivariate regression models were used to evaluate the association of HDL-C and TC/HDL ratio with coronary plaque volumes.ResultsOf the 190 subjects the average (SD) age was 58.9 (9.8) years, with 63% being male. After adjustment for cardiovascular risk factors, HDL- C (>40 mg/dl) is inversely associated with fibrous (p = 0.003), fibrous fatty (p = 0.007), low attenuation plaque (LAP) (p = 0.007), total non-calcified plaque (TNCP) (p = 0.002) and total plaque (TP)(p = 0.004) volume. Furthermore, the TC/HDL ratio (> 4.0) is associated with fibrous (p = 0.047) and total non-calcified plaque (p = 0.039), but not with fibrofatty, LAP, dense calcified plaque, or TP volume.ConclusionThere is a strong association between low HDL-C levels and increasing TC/HDL ratio with certain types of coronary plaque characteristics, independent of traditional risk factors. The findings of this study suggest mechanistic evidence supporting the protective role of HDL-C and the TC/HDL ratio's clinical relevance in coronary artery disease management.     

Rethinking reverse cholesterol transport and dysfunctional high-density lipoproteins

Human plasma high-density lipoprotein cholesterol concentrations are a negative risk factor for atherosclerosis-linked cardiovascular disease. Pharmacological attempts to reduce atherosclerotic cardiovascular disease by increasing plasma high-density lipoprotein cholesterol have been disappointing so that recent research has shifted from HDL quantity to HDL quality, that is, functional vs dysfunctional HDL. HDL has varying degrees of dysfunction reflected in impaired reverse cholesterol transport (RCT). In the context of atheroprotection, RCT occurs by 2 mechanisms: one is the well-known trans-hepatic pathway comprising macrophage free cholesterol (FC) efflux, which produces early forms of FC-rich nascent HDL (nHDL). Lecithin:cholesterol acyltransferase converts HDL-FC to HDL-cholesteryl ester while converting nHDL from a disc to a mature spherical HDL, which transfers its cholesteryl ester to the hepatic HDL receptor, scavenger receptor B1 for uptake, conversion to bile salts, or transfer to the intestine for excretion. Although widely cited, current evidence suggests that this is a minor pathway and that most HDL-FC and nHDL-FC rapidly transfer directly to the liver independent of lecithin:cholesterol acyltransferase activity. A small fraction of plasma HDL-FC enters the trans-intestinal efflux pathway comprising direct FC transfer to the intestine. SR-B1^?/? mice, which have impaired trans-hepatic FC transport, are characterized by high plasma levels of a dysfunctional FC-rich HDL that increases plasma FC bioavailability in a way that produces whole-body hypercholesterolemia and multiple pathologies. The design of future therapeutic strategies to improve RCT will have to be formulated in the context of these dual RCT mechanisms and the role of FC bioavailability.     

Apolipoprotein A-I gene polymorphism associated with premature coronary artery disease and familial hypoalphalipoproteinemia

Decreased plasma high-density-lipoprotein (HDL) cholesterol and apolipoprotein A-I levels have been associated with premature coronary artery disease. We identified a PstI restriction-endonuclease site flanking the human apolipoprotein A-I gene at its 3' end that is polymorphic. The absence and presence of this site, as determined by genomic blotting analysis of PstI-digested chromosomal DNA with the use of an apolipoprotein A-I gene probe, were associated with 3.3-kb and 2.2-kb hybridization bands, respectively. The 3.3-kb band appeared in 4.1 percent of 123 randomly selected control subjects and in 3.3 percent of 30 subjects with no angiographic evidence of coronary artery disease. In contrast, among 88 patients who had severe coronary disease before the age of 60, as documented by angiography, the 3.3-kb band occurred in 32 percent (P less than 0.0001). It was also found in 8 of 12 index cases (P less than 0.0001) of kindreds with familial hypoalphalipoproteinemia. In the two patient groups, the allele frequencies of the site that produced the 3.3-kb band were 17 and 42 percent, respectively, as compared with an allele frequency of only 2 percent in the control populations. Within kindreds with familial hypoalphalipoproteinemia and among first-degree relatives of patients with coronary artery disease, the 3.3-kb band was associated with decreased HDL cholesterol levels. Among all patients with coronary artery disease, 58 percent had HDL cholesterol levels below the 10th percentile of normal values; however, this frequency increased to 73 percent when patients with the 3.3-kb band were considered. These findings indicate that the polymorphism in the region between the apolipoprotein A-I and apolipoprotein C-III genes may be a useful marker for the risk of premature coronary artery disease and familial hypoalphalipoproteinemia.     

Cholesterol changes in coronary patients after a short behavior modification program

Serum cholesterol changes after an 8-week behavior modification program for patients with coronary artery disease (CAD) were studied in a randomized controlled clinical trial. Acute myocardial infarction (AMI) or coronary artery bypass grafting (CABG) patients were randomly assigned to the intervention (N = 94) or to usual care (N = 90). After 9 months’ follow-up the intervention was effective in reducing total cholesterol and LDL cholesterol levels, particularly in patients with high baseline lipid levels. After correcting for changes in dose of statins during follow-up, effects were weakened, but for patients with high baseline cholesterol levels favorable effects remained. In these patients, the intervention group showed a decline of total cholesterol and LDL cholesterol levels of 20% and 29%, respectively, compared to a 12% and 19% reduction in the control group (p < .01). These effects could not be explained by changes in dietary fat consumption. An unexpected finding was a lower increase in HDL cholesterol in the intervention group than in the control group.     

Lecithin-cholesterol acyltransferase activity in patients with coronary artery disease examined by coronary angiography

This study grew out of observations of certain lecithin:cholesterol acyltransferase (LCAT) abnormalities in patients with atherosclerosis. We studied the interrelationships among LCAT, and total cholesterol, free and esterified cholesterol, cholesterol in individual lipoprotein fractions, triglycerides, phospholipids, free fatty acids, L-lactates in 90 angiographically examined patients with coronary artery disease and 30 control subjects without clinical manifestations of coronary artery disease. Results of the study showed LCAT activity to be significantly decreased (P<0.05) in patients with single-, double-, or triple-vessel disease than in disease-free subjects. LCAT was also found to follow the stage of coronary artery disease in angiographically examined patients. Decreased LCAT activity was accompanied by lower high-density lipoprotein cholesterol, elevated ratio of unesterified to esterified cholesterol, and increased levels of L-lactates, free fatty acids, and low-density lipoprotein cholesterol. Total cholesterol and triglycerides were within or slightly above the normal limits. The results show LCAT to be a significantly better indicator of the risk of coronary artery disease than either total cholesterol or triglycerides.Abbreviations LCAT lecithin:cholesterol acyltransferase - CAD coronary artery disease - UC/EC ratio of esterified to unesterified cholesterol - MI myocardial infarction - HDL high-density lipoprotein Correspondence to: A. Stavljenic-Rukavina     

Myeloperoxidase-derived chlorinating species induce protein carbamylation through decomposition of thiocyanate and urea: novel pathways generating dysfunctional high-density lipoprotein

Abstract Aims: Protein carbamylation through cyanate is considered as playing a causal role in promoting cardiovascular disease. We recently observed that the phagocyte protein myeloperoxidase (MPO) specifically induces high-density lipoprotein (HDL) carbamylation, rather than chlorination, in human atherosclerotic lesions, raising the possibility that MPO-derived chlorinating species are involved in cyanate formation. Results: Here, we show that MPO-derived chlorinating species rapidly decompose the plasma components thiocyanate (SCN) and urea, thereby promoting (lipo)protein carbamylation. Strikingly, the presence of physiologic concentrations of SCN completely prevented MPO-induced 3-chlorotyrosine formation in HDL. SCN scavenged a 2.5-fold molar excess of hypochlorous acid, promoting HDL carbamylation, but not chlorination. Cyanate significantly impaired (i) HDL's ability to activate lecithin-cholesterol acyltransferase; (ii) the activity of paraoxonase, a major HDL-associated anti-inflammatory enzyme; and (iii) the antioxidative activity of HDL. Innovation: Here, we report that MPO-derived chlorinating species preferentially induce protein carbamylation-rather than chlorination-in the presence of physiologically relevant SCN concentrations. The carbamylation of HDL results in the loss of its anti-inflammatory and antioxidative activities. Conclusion: MPO-mediated decomposition of SCN and/or urea might be a relevant mechanism for generating dysfunctional HDL in human disease. Antioxid. Redox Signal. 00, 000-000.     

Coronary artery disease, lipid disorders and genetic polymorphisms

Coronary artery disease (CAD) is the leading cause of morbidity and mortality in most industrialized countries, accounting for one out of every two deaths in the United States. Disorders of the lipid transport system resulting from complex interactions among nutritional, environmental and genetic factors, play a very important role in the development of this disease. It has been proposed that low density lipoproteins (LDL) cause cholesterol deposition in the arterial wall, whereas high density lipoproteins (HDL) promote efflux of cholesterol from this site. Thus, low levels of HDL and/or high levels of LDL, have been associated with increased risk of CAD. Apolipoprotein A-I (Apo A-I) is the major protein component of HDL, and it has been proposed that the levels of this protein are a better predictor of risk of CAD than the level of cholesterol in HDL. The human Apo A-I gene has been characterized, and it has been found to be adjacent to the genes for apolipoproteins C-lll and A-lV on the long arm of chromosome 11. The cloning of these genes provides the appropriate tools to apply molecular genetic techniques to find differences between individuals at the gene level (restriction fragment length polymorphisms, RFLP) and to identify specific alleles at this particular gene locus which may be associated with a clinical phenotype, more specifically, premature CAD and familial hypoalphalipoproteinemia. In a preliminary study we have identified a Pst I restriction-endonuclease site flanking the human apolipoprotein A-I gene at its 3' end that is polymorphic.(ABSTRACT TRUNCATED AT 250 WORDS)     

Familial occurrence of abnormalities of high-density lipoprotein cholesterol

In families, well-known monogenic high-density lipoprotein cholesterol (HDL-C) disorders characterized by extreme HDL-C levels on both ends of the continuum occur in multiple HDL pathways and can confer increased risk for atherosclerotic disease. Polygenic HDL-C variants have been more difficult to identify. In many family and twin studies in different populations, HDL-C levels have been shown to be highly heritable, explaining, on average, between 40% and 60% of between-individual variation. This review of abnormal HDL in families addresses known monogenic HDL disorders and HDL-C heritability in the general population, and presents novel data on the heritability of HDL-C in families with a history of premature coronary artery disease. We conclude that levels of HDL-C and HDL abnormalities are largely under genetic control and environmental and behavioral factors alone have only a modest impact. While rare, monogenic disorders offer considerable insight into the genetics of HDL regulation. Moderate to high heritability estimates across different family populations suggest that future genetic studies will be successful in identifying HDL genetic trait loci and that translational studies will ultimately lead to therapies that optimize the cardiovascular protective benefits of HDL.     

Problems with the measurement of apolipoproteins AI and AII

There is considerable evidence demonstrating that increased levels of low density lipoprotein (LDL) cholesterol and decreased levels of high density lipoprotein (HDL) cholesterol are associated with coronary artery disease (CAD). Yet, these lipoprotein markers are insensitive for identifying risk of CAD. Measurement of subcomponents of HDL may offer more sensitive markers. Investigators have focused on protein components (apolipoproteins) of HDL as a potentially important marker. Unfortunately, because much of the immunoreactivity of apolipoproteins is hidden as a result of an association with lipids, it is difficult to measure them accurately. Detergents and other denaturing agents have been used to expose immunoreactivity. Poor correlations among different methods suggest that some detergents presently used may not be adequate for effective measurement of apolipoprotein (APO) AI. Studies using denaturing agents to probe HDL particles indicate that APO AII immunoreactivity is more resistant to exposure than that of APO AI. Data presented here indicate that the immunoreactivity of APO AII can be increased up to 50 percent by treatment with 4M guanidine provided the concentration of guanidine is diluted to less than 50 mM in the assay system. Previous studies failed to notice this effect because high levels of guanidine inhibited the antibody-antigen reaction in the immunoassay, making it appear that APO AII had not been exposed. It is concluded that with our present state of knowledge, it is unclear which, if any apolipoprotein assays, are adequately designed to achieve optimal exposure of antigenic sites, but that pretreatment with guanidine may be a simple, effective way to optimize APO AI and APO AII assays for clinical purposes.     

Apolipoprotein E polymorphism is not associated with lipid levels and coronary artery disease in Greek patients with familial hypercholesterolaemia

Abstract Familial hypercholesterolaemia is a genetic disorder characterised by high low-density lipoprotein (LDL) cholesterol concentrations, which frequently gives rise to premature coronary artery disease (CAD). The clinical expression of familial hypercholesterolaemia is highly variable even in patients carrying the same LDL receptor gene mutation. This variability may be due to environmental and other genetic factors. Apolipoprotein E (Apo-E) has been extensively studied for its effects on the phenotype of familial hypercholesterolaemia. In this study we examined the influence of Apo-E genotype on lipid parameters and the incidence of CAD in 93 Greek patients with familial hypercholesterolaemia. Apo-E E2, E3 and E4 allele frequencies were 0.06, 0.86 and 0.09 respectively. The levels of total cholesterol, LDL cholesterol, HDL cholesterol, triglycerides, apolipoproteins A and B and lipoprotein α did not differ significantly among carriers and non-carriers of the E4 allele. The prevalence of CAD and hypertension did not differ either. Our results suggest that the E4 allele is not associated with lipid levels or with the prevalence of CAD among familial hypercholesterolaemia patients of the Greek population. *The two authors were equally involved in the work