Apolipoprotein J polymorphisms and serum HDL cholesterol levels in African blacks

Apolipoprotein J (apoJ, protein; APOJ, gene) is found in serum associated with high-density lipoprotein (HDL) subfractions, which also contain apolipoprotein A-I (apoA1) and cholesteryl ester transfer protein. ApoJ has been shown to be involved in a variety of physiological functions, including lipid transport. In earlier studies we reported the existence of a common genetic polymorphism (APOJ*1 and APOJ*2 alleles) using isoelectric focusing (IEF) and immunoblotting. In this study we determined the molecular basis of this polymorphism and together with another polymorphism at codon 328 (G-->A) evaluated its relationship with serum HDL cholesterol and apoA1 levels in 767 African blacks stratified by staff level: junior (less affluent, n = 450) and senior (more affluent, n = 317). The molecular analysis of the cathodally shifted APOJ*2 allele on IEF gels revealed an amino acid substitution of asparagine by histidine resulting from a missense mutation (A-->C) at codon 317 in exon 7. The frequency of the APOJ*2 (C) allele of codon 317 in the total sample was 0.267, whereas that of the less common allele A of codon 328 was 0.04. Despite their close proximity, no linkage disequilibrium was observed between the 2 polymorphisms. The impact of the codon 317 polymorphic variation was significant on serum HDL cholesterol (p = 0.003) and HDL3 cholesterol (p = 0.001) in junior staff. The adjusted mean values of these traits were higher in the codon 317 APOJ*2/*2 genotype than in the *1/*1 and *1/*2 genotypes. Overall, the APOJ codon 317 polymorphism explained 10.2% and 8.3% of the phenotypic variation in HDL cholesterol and HDL3 cholesterol, respectively, in junior staff. The codon 328 polymorphism showed a significant effect on HDL2 cholesterol (p = 0.039) and apoA1 (p = 0.007) only in junior women and accounted for 2.5% and 4.2% of the phenotypic variation in HDL2 cholesterol and apoA1, respectively. We also analyzed the combined effects of these genotypes at the 2 polymorphic sites. Significant effects on HDL cholesterol (p = 0.004) and HDL3 cholesterol (p = 0.008) in junior men and on HDL2 cholesterol (p = 0.003) in junior women were observed in the combined genotype data. The 2-locus genotypes explained 6.0% and 5.3% of the residual phenotypic variation of HDL cholesterol and HDL3 cholesterol in junior men and 10.4% of HDL2 cholesterol in junior women. These data indicate that the effect of the APOJ polymorphism on HDL cholesterol levels is modulated by socioeconomic status, as measured by staff level. Given the association of HDL and its subfractions with cardiovascular disease, these polymorphisms may lead to a better understanding of interracial differences in the risk of cardiovascular disease.     

Promoter polymorphisms of hepatic lipase gene influence HDL(2) but not HDL(3) in African American men: CARDIA study

Hepatic lipase encoded by the hepatic lipase gene (LIPC) is involved in the metabolism of several lipoproteins. Four promoter polymorphisms in LIPC have been found to be in complete disequilibrium and associated with high density lipoprotein cholesterol (HDL-C) and apolipoprotein (apo)A-I levels in both white and black populations. We investigated the association between the promoter polymorphism and lipid profiles as well as anthropometric phenotypes in African American men in the Coronary Artery Risk Development in Young Adults study. We performed serial cross-sectional analyses and longitudinal analyses of lipids from 578 subjects in five examinations over 10 years of follow-up. Results showed that the allele frequency (0.52) in our black population was consistent with that reported in black subjects but much higher than that reported (approximately 0.2) in white populations. Analysis of covariance tests of the three genotypic means in each examination showed that the P values ranged from 0.01 to 0.08 for HDL-C (except P = 0.54 in the fourth examination), from 0.006 to 0.01 for HDL(2)-C, and from 0.06 to 0.07 for apoA-I. Mean HDL(3)-C levels were essentially identical among the three genotypes. Total cholesterol, low density lipoprotein cholesterol (LDL-C), triglycerides, and apoB, which are mainly involved in the very low density lipoprotein-LDL pathway, were not significantly different according to the promoter polymorphism, except for triglycerides in the third examination (P = 0.01). No significant association was found between anthropometric phenotypes and the LIPC polymorphism in any of five examinations. The change of the anthropometric variables was not significantly associated with genotypes. In conclusion, our results indicated that the LIPC promoter polymorphism has exclusive effects on HDL(2)-C but not HDL(3)-C levels.     

Association of metabolic and genetic factors with cholesterol esterification rate in HDL plasma and atherogenic index of plasma in a 40 years old Slovak population

We assessed association between novel biomarkers of cardiovascular disease and conventional factors in 40 years old subjects (208 men and 266 women) from the general population of Slovakia. FER(HDL) (cholesterol esterification rate in HDL plasma), AIP--Atherogenic Index of Plasma [Log(TG/HDL-C)] as markers of lipoprotein particle size, and CILP2, FTO and MLXIPL polymorphisms, were examined in relation to biomarkers and conventional risk factors. Univariate analyses confirmed correlation between AIP, FER(HDL) and the most of measured parameters. Relations between AIP and CILP2, FTO and MLXIPL were not significant. However, CILP2 was significantly related to FER(HDL) in both genders. In multivariate analysis BMI was the strongest correlate of AIP levels. In multivariate model variability of FER(HDL) was best explained by AIP (R(2) = 0.55) in both genders with still significant effect of CILP2 SNP in men. In a model where AIP was omitted, TG levels explained 43 % of the FER(HDL) variability in men, while in women HDL-C was the major determinant (42 %). In conclusions, FER(HDL) and AIP related to the known markers of cardiovascular risk provide means to express their subtle interactions by one number. Our novel finding of association between CILP2 polymorphism and FER(HDL) supports its role in lipid metabolism.     

Cellular SR-BI and ABCA1-mediated cholesterol efflux are gender-specific in healthy subjects

We evaluated the impact of gender differences in both the quantitative and qualitative features of HDL subspecies on cellular free cholesterol efflux through the scavenger receptor class B type I (SR-BI), ABCA1, and ABCG1 pathways. For that purpose, healthy subjects (30 men and 26 women) matched for age, body mass index, triglyceride, apolipoprotein A-I, and high density lipoprotein-cholesterol (HDL-C) levels were recruited. We observed a significant increase (+14%; P < 0.03) in the capacity of whole sera from women to mediate cellular free cholesterol efflux via the SR-BI-dependent pathway compared with sera from men. Such enhanced efflux capacity resulted from a significant increase in plasma levels of large cholesteryl ester-rich HDL2 particles (+20%; P < 0.04) as well as from an enhanced capacity (+14%; P < 0.03) of these particles to mediate cellular free cholesterol efflux via SR-BI. By contrast, plasma from men displayed an enhanced free cholesterol efflux capacity (+31%; P < 0.001) via the ABCA1 transporter pathway compared with that from women, which resulted from a 2.4-fold increase in the plasma level of prebeta particles (P < 0.008). Moreover, in women, SR-BI-mediated cellular free cholesterol efflux was significantly correlated with plasma HDL-C (r = 0.72, P < 0.0001), whereas this relationship was not observed in men. In conclusion, HDL-C level may not represent the absolute indicator of the efficiency of the initial step of the reverse cholesterol transport.     

Targeted next-generation sequencing to diagnose disorders of HDL cholesterol

A low level of HDL cholesterol (HDL-C) is a common clinical scenario and an important marker for increased cardiovascular risk. Many patients with very low or very high HDL-C have a rare mutation in one of several genes, but identification of the molecular abnormality in patients with extreme HDL-C is rarely performed in clinical practice. We investigated the accuracy and diagnostic yield of a targeted next-generation sequencing (NGS) assay for extreme levels of HDL-C. We developed a targeted NGS panel to capture the exons, intron/exon boundaries, and untranslated regions of 26 genes with highly penetrant effects on plasma lipid levels. We sequenced 141 patients with extreme HDL-C levels and prioritized variants in accordance with medical genetics guidelines. We identified 35 pathogenic and probably pathogenic variants in HDL genes, including 21 novel variants, and performed functional validation on a subset of these. Overall, a molecular diagnosis was established in 35.9% of patients with low HDL-C and 5.2% with high HDL-C, and all prioritized variants identified by NGS were confirmed by Sanger sequencing. Our results suggest that a molecular diagnosis can be identified in a substantial proportion of patients with low HDL-C using targeted NGS.     

High levels of human apolipoprotein A-I in transgenic mice result in increased plasma levels of small high density lipoprotein (HDL) particles comparable to human HDL3

Five lines of transgenic mice, which had integrated the human apolipoprotein (apo) A-I gene and various amounts of flanking sequences, were established. Normally, apoA-I is expressed mainly in liver and intestine, but all of the transgenic lines only expressed apoA-I mRNA in liver, strongly suggesting that 256 base pairs of 5'-flanking sequence was sufficient for liver apoA-I gene expression but that 5.5 kilobase pairs was not sufficient for intestinal expression. Mean plasma levels of human apoA-I varied in different lines from approximately 0.1 to 200% of normal mouse levels. This was not dependent on the amount of flanking sequence. Lipoprotein levels were studied in detail in one of the lines with a significantly increased apoA-I pool size. In one study, the total plasma apoA-I level (mouse plus human) was 381 +/- 43 mg/dl in six animals from this line, compared to 153 +/- 17 mg/dl in matched controls. Total and high density lipoprotein cholesterol (HDL-C) levels were increased 60% in transgenic animals, compared to controls (total cholesterol: 125 +/- 12 versus 78 +/- 13 mg/dl, p = 0.0001; HDL-C 90 +/- 7 versus 55 +/- 11 mg/dl, p = 0.0001). The molar ratio of HDL-C/apoA-I was significantly lower in transgenic animals, 17 +/- 1 versus 25 +/- 2 (p = 0.0001), suggesting the increase was in smaller HDL particles. This was confirmed by native gradient gel electrophoresis. This was not due to aberrant metabolism of human apoA-I in the mouse, since human apoA-I was distributed throughout the HDL particle size range and was catabolized at the same rate as mouse apoA-I. In another study of 23 transgenic mice, HDL-C and human apoA-I levels were highly correlated (r = 0.87, p less than 0.001). The slope of the correlation line also indicated the additional HDL particles were in the smaller size range. We conclude that human apoA-I can be incorporated into mouse HDL, and excessive amounts increase HDL-C levels primarily by increasing smaller HDL particles, comparable to human HDL3 (HDL-C/apoA-I molar ratio = 18).     

Polymorphisms in the gene encoding lipoprotein lipase in men with low HDL-C and coronary heart disease: the Veterans Affairs HDL Intervention Trial

Our goal was to further define the role of LPL gene polymorphisms in coronary heart disease (CHD) risk. We determined the frequencies of three LPL polymorphisms (D9N, N291S, and S447X) in 899 men from the Veterans Affairs HDL Intervention Trial (VA-HIT), a study that examined the potential benefits of increasing HDL with gemfibrozil in men with established CHD and low high density lipoprotein cholesterol (HDL-C; < or =40 mg/dl), and compared them with those of men without CHD from the Framingham Offspring Study (FOS). In VA-HIT, genotype frequencies for LPL D9N, N291S, and S447X were 5.3, 4.5, and 13.0%, respectively. These values differed from those for men in FOS having an HDL-C of >40, who had corresponding values of 3.2% (P = 0.06), 1.5% (P < 0.01), and 18.2% (P < 0.01). On gemfibrozil, carriers of the LPL N9 allele in VA-HIT had lower levels of large LDL (-32%; P < 0.01) but higher levels of small, dense LDL (+59%; P < 0.003) than did noncarriers. Consequently, mean LDL particle diameter was smaller in LPL N9 carriers than in noncarriers (20.14 +/- 0.87 vs. 20.63 +/- 0.80 nm; P < 0.003). In men with low HDL-C and CHD: 1) the LPL N9 and S291 alleles are more frequent than in CHD-free men with normal HDL-C, whereas the X447 allele is less frequent, and 2) the LPL N9 allele is associated with the LDL subclass response to gemfibrozil.     

The T111I mutation in the EL gene modulates the impact of dietary fat on the HDL profile in women

The objective of the present study was to examine the impact of the T111I missense mutation in exon 3 of the endothelial lipase (EL) gene on HDL and its potential interaction effect with dietary fat. The study sample included 281 women and 216 men aged between 17 and 76 years from the Québec Family Study. Plasma HDL3-C levels of I111I homozygote women were higher compared with those of women carrying the wild-type allele (P = 0.03). These differences were not attenuated when adjusted for levels of obesity and were not observed among men. Dietary PUFA interacted with the T111I mutation to modulate apolipoprotein A-I (apoA-I) and HDL3-C levels among women. Specifically, a diet rich in PUFA was associated with increased apoA-I levels among women carriers of the I111 allele and with decreased apoA-I among women homozygotes for the wild-type allele (P = 0.002). A similar interaction was observed with plasma HDL3-C levels (P = 0.003). These interactions were not observed among men. In conclusion, the EL T111I mutation appears to have a modest effect on plasma HDL levels. The gene-diet interaction among women, however, suggests that the T111I missense mutation may confer protection against the lowering effect of a high dietary PUFA intake on plasma apoA-I and HDL3-C levels.     

Gaucher disease: A G+1----A+1 IVS2 splice donor site mutation causing exon 2 skipping in the acid beta-glucosidase mRNA.

Gaucher disease is the most frequent lysosomal storage disease and the most prevalent Jewish genetic disease. About 30 identified missense mutations are causal to the defective activity of acid beta-glucosidase in this disease. cDNAs were characterized from a moderately affected 9-year-old Ashkenazi Jewish Gaucher disease type 1 patient whose 80-year-old, enzyme-deficient, 1226G (Asn370----Ser [N370S]) homozygous grandfather was nearly asymptomatic. Sequence analyses revealed four populations of cDNAs with either the 1226G mutation, an exact exon 2 (delta EX2) deletion, a deletion of exon 2 and the first 115 bp of exon 3 (delta EX2-3), or a completely normal sequence. About 50% of the cDNAs were the delta EX2, the delta EX2-3, and the normal cDNAs, in a ratio of 6:3:1. Specific amplification and characterization of exon 2 and 5' and 3' intronic flanking sequences from the structural gene demonstrated clones with either the normal sequence or with a G+1----A+1 transition at the exon 2/intron 2 boundary. This mutation destroyed the splice donor consensus site (U1 binding site) for mRNA processing. This transition also was present at the corresponding exon/intron boundary of the highly homologous pseudogene. This new mutation, termed "IVS2 G+1----A+1," is the first splicing mutation described in Gaucher disease and accounted for about 3.4% of the Gaucher disease alleles in the Ashkenazi Jewish population. The occurrence of this "pseudogene"-type mutation in the structural gene indicates the role of acid beta-glucosidase pseudogene and structural gene rearrangements in the pathogenesis of this disease.     

Differential effects of HDL subpopulations on cellular ABCA1- and SR-BI-mediated cholesterol efflux

Our objective was to evaluate the associations of individual apolipoprotein A-I (apoA-I)-containing HDL subpopulation levels with ABCA1- and scavenger receptor class B type I (SR-BI)-mediated cellular cholesterol efflux. HDL subpopulations were measured by nondenaturing two-dimensional gel electrophoresis from 105 male subjects selected with various levels of apoA-I in pre-beta-1, alpha-1, and alpha-3 HDL particles. ApoB-containing lipoprotein-depleted serum was incubated with [(3)H]cholesterol-labeled cells to measure efflux. The difference in efflux between control and ABCA1-upregulated J774 macrophages was taken as a measure of ABCA1-mediated efflux. SR-BI-mediated efflux was determined using cholesterol-labeled Fu5AH hepatoma cells. Fractional efflux values obtained from these two cell systems were correlated with the levels of individual HDL subpopulations. A multivariate analysis showed that two HDL subspecies correlated significantly with ABCA1-mediated efflux: small, lipid-poor pre-beta-1 particles (P=0.0022) and intermediate-sized alpha-2 particles (P=0.0477). With regard to SR-BI-mediated efflux, multivariate analysis revealed significant correlations with alpha-2 (P=0.0004), alpha-1 (P=0.0030), pre-beta-1 (P=0.0056), and alpha-3 (P=0.0127) HDL particles. These data demonstrate that the small, lipid-poor pre-beta-1 HDL has the strongest association with ABCA1-mediated cholesterol even in the presence of all other HDL subpopulations. Cholesterol efflux via the SR-BI pathway is associated with several HDL subpopulations with different apolipoprotein composition, lipid content, and size.     

ABCA1 gene promoter DNA methylation is associated with HDL particle profile and coronary artery disease in familial hypercholesterolemia

High-density lipoproteins cholesterol (HDL-C) level, a strong coronary artery disease (CAD) clinical biomarker, shows significant interindividual variability. However, the molecular mechanisms involved remain mostly unknown. ATP-binding cassette A1 (ABCA1) catalyzes the cholesterol transfer from peripheral cells to nascent HDL particles. Recently, a differentially methylation region was identified in ABCA1 gene promoter locus, near the first exon. Therefore, we hypothesized that DNA methylation changes at ABCA1 gene locus is one of the molecular mechanisms involved in HDL-C interindividual variability. The study was conducted in familial hypercholesterolemia (FH), a monogenic disorder associated with a high risk of CAD . Ninety-seven FH patients (all p.W66G for the LDLR gene mutation and not under lipid-lowering treatment) were recruited and finely phenotyped for DNA methylation analyses at ABCA1 gene locus. ABCA1 DNA methylation levels were found negatively correlated with circulating HDL-C (r = -0.20; p = 0.05), HDL2-phospholipid levels (r = -0.43; p = 0.04), and with a trend for association with HDL peak particle size (r = -0.38; p = 0.08). ABCA1 DNA methylation levels were also found associated with prior history of CAD (CAD = 40.2% vs. without CAD = 34.3%; p = 0.003). These results suggest that epigenetic changes within the ABCA1 gene promoter contribute to the interindividual variability in plasma HDL-C concentrations and are associated with CAD expression. These findings could change our understanding of the molecular mechanisms involved in the pathophysiological processes leading to CAD.     

Testosterone replacement in hypogonadal men alters the HDL proteome but not HDL cholesterol efflux capacity

The effects of androgens on cardiovascular disease (CVD) risk in men remain unclear. To better characterize the relationship between androgens and HDL, we investigated the effects of testosterone replacement on HDL protein composition and serum HDL-mediated cholesterol efflux in hypogonadal men. Twenty-three older hypogonadal men (ages 51-83, baseline testosterone < 280 ng/dl) were administered replacement testosterone therapy (1% transdermal gel) with or without the 5α-reductase inhibitor dutasteride. At baseline and after three months of treatment, we determined fasting lipid concentrations, HDL protein composition, and the cholesterol efflux capacity of serum HDL. Testosterone replacement did not affect HDL cholesterol (HDL-C) concentrations but conferred significant increases in HDL-associated paraoxonase 1 (PON1) and fibrinogen α chain (FGA) (P = 0.022 and P = 0.023, respectively) and a decrease in apolipoprotein A-IV (apoA-IV) (P = 0.016). Exogenous testosterone did not affect the cholesterol efflux capacity of serum HDL. No differences were observed between men who received testosterone alone and those who also received dutasteride. Testosterone replacement in older hypogonadal men alters the protein composition of HDL but does not significantly change serum HDL-mediated cholesterol efflux. These effects appear independent of testosterone conversion to dihydrotestosterone. Further research is needed to determine how changes in HDL protein content affect CVD risk in men.     

C323 of SR-BI is required for SR-BI-mediated HDL binding and cholesteryl ester uptake

Scavenger receptor BI (SR-BI) is an HDL receptor. It binds HDL and mediates the uptake of cholesteryl ester from HDL. Early studies have pointed out that the extracellular domain of SR-BI is critical for SR-BI-mediated cholesteryl ester uptake. However, the extracellular loop of SR-BI is large: it contains 403 amino acids. The HDL binding site and the modulation of SR-BI-mediated cholesteryl ester uptake remain to be identified. In this study, using C323G mutant SR-BI, we showed that C323G mutant SR-BI lost its HDL binding and cholesteryl ester uptake activity, indicating that the highly conserved C323 is required for SR-BI-mediated HDL binding and cholesteryl ester uptake. Using a blocking antibody against C323 region, we demonstrated that C323 is directly involved in HDL binding and likely an HDL binding site. Using C323G mutant transgenic mouse model, we further demonstrated that C323 of SR-BI is required for regulating plasma cholesterol levels in vivo. Using redox reagents, we showed that physiological relevant levels of H(2)O(2) upregulated the SR-BI-mediated cholesteryl ester uptake activity by 65%, whereas GSH or DTT significantly downregulated SR-BI-mediated cholesteryl ester uptake activity by 45%. C323 of SR-BI is critical for SR-BI-mediated HDL binding and cholesteryl ester uptake, and changes in redox status may be a regulatory factor modulating SR-BI-mediated cholesterol transport.     

Cholesteryl ester transfer protein (CETP) expression enhances HDL cholesteryl ester liver delivery, which is independent of scavenger receptor BI, LDL receptor related protein and possibly LDL receptor

Cholesteryl ester transfer protein (CETP) is a hydrophobic plasma glycoprotein that mediates the transfer and exchange of cholesteryl ester (CE) and triglyceride (TG) between plasma lipoproteins, and also plays an important role in HDL metabolism. Previous studies have indicated that, compared to wild type mice, human CETP transgenic mice had significantly lower plasma HDL CE levels, which was associated with enhancement of HDL CE uptake by the liver. However, the mechanism of this process is still unknown. To evaluate the possibility that this might be directly mediated by CETP, we utilized CETP transgenic (CETPTg) mice with liver scavenger receptor BI (SR-BI) deficiency [i.e., PDZK1 gene knockout (PDZK1O)], and with receptor associated protein (RAP) overexpression, to block LDL receptor-related protein (LRP) and LDL receptor (LDLR). We found that (1) CETPTg/PDZK1O mice have significantly lower HDL-C than that of PDZK1 KO mice (36%, p<0.01); (2) CETPTg and CETPTg/PDZK1O mice have same HDL-C levels; (3) CETPTg/PDZK1O/RAP mice had significant lower plasma HDL-C levels than that of PDZK1O/RAP ones (50%, p<0.001); (4) there is no incremental transfer of HDL CE radioactivity to the apoB-containing lipoprotein fraction in mice expressing CETP; and (5) CETPTg/PDZK1O/RAP mice had significant higher plasma and liver [(3)H]CEt-HDL turnover rates than that of PDZK1O/RAP ones (50% and 53%, p<0.01, respectively). These results suggest that CETP expression in mouse increases direct removal of HDL CE in the liver and this process is independent of SR-BI, LRP, and possibly LDLR.     

Low levels of high density lipoproteins in Turks, a population with elevated hepatic lipase. High density lipoprotein characterization and gender-specific effects of apolipoprotein e genotype

Turks have strikingly low levels of high density lipoprotein cholesterol (HDL-C) (10-15 mg/dL lower than those of Americans or Western Europeans) associated with elevated hepatic lipase mass and activity. Here we report that Turks have low levels of high density lipoprotein subclass 2 (HDL(2)), apoA-I-containing lipoproteins (LpA-I), and pre-beta-1 HDL and increased levels of HDL(3) and LpA-I/A-II particles (potentially an atherogenic lipid profile). The frequency distributions of HDL-C and LpA-I levels were skewed toward bimodality in Turkish women but were unimodal in Turkish men. The apoE genotype affected HDL-C and LpA-I levels in women only. In women, but not men, the varepsilon2 allele was strikingly more prevalent in those with the highest levels of HDL-C and LpA-I than in those with the lowest levels. The higher prevalence of the epsilon2 allele in these subgroups of women was not explained by plasma triglyceride levels, total cholesterol levels, age, or body mass index. The modulating effects of apoE isoforms on lipolytic hydrolysis of HDL by hepatic lipase (apoE2 preventing efficient hydrolysis) or on lipoprotein receptor binding (apoE2 interacting poorly with the low density lipoprotein receptors) may account for differences in HDL-C levels in Turkish women (the epsilon2 allele being associated with higher HDL levels). In Turkish men, who have substantially higher levels of hepatic lipase activity than women, the modulating effect of apoE may be overwhelmed. The gender-specific impact of the apoE genotype on HDL-C and LpA-I levels in association with elevated levels of hepatic lipase provides new insights into the metabolism of HDL.     

Binding of high density lipoprotein (HDL) and discoidal reconstituted HDL to the HDL receptor scavenger receptor class B type I. Effect of lipid association and APOA-I mutations on receptor binding

The binding of apoA-I-containing ligands to the HDL receptor scavenger receptor class B type I (SR-BI) was characterized using two different assays. The first employed conventional binding or competition assays with (125)I-labeled ligands. The second is a new nonradioactive ligand binding assay, in which the receptor-associated ligand is detected by quantitative immunoblotting ("immunoreceptor assay"). Using both methods, we observed that the K(d) value for spherical HDL (density = 1.1-1.13 g/ml) was approximately 16 microgram of protein/ml, while the values for discoidal reconstituted HDL (rHDL) containing proapoA-I or plasma apoA-I were substantially lower (approximately 0.4-5 microgram of protein/ml). We also observed reduced affinity and/or competition for spherical (125)I-HDL cell association by higher relative to lower density HDL and very poor competition by lipid-free apoA-I and pre-beta-1 HDL. Deletion of either 58 carboxyl-terminal or 59 amino-terminal residues from apoA-I, relative to full-length control apoA-I, resulted in little or no change in the affinity of corresponding rHDL particles. However, rHDL particles containing a double mutant lacking both terminal domains competed poorly with spherical (125)I-HDL for binding to SR-BI. These findings suggest an important role for apoA-I and its conformation/organization within particles in mediating HDL binding to SR-BI and indicate that the NH(2) and COOH termini of apoA-I directly or indirectly contribute independently to binding to SR-BI.     

Large-scale candidate gene analysis of HDL particle features

Background

HDL cholesterol (HDL-C) is an established marker of cardiovascular risk with significant genetic determination. However, HDL particles are not homogenous, and refined HDL phenotyping may improve insight into regulation of HDL metabolism. We therefore assessed HDL particles by NMR spectroscopy and conducted a large-scale candidate gene association analysis.

Methodology/Principal Findings

We measured plasma HDL-C and determined mean HDL particle size and particle number by NMR spectroscopy in 2024 individuals from 512 British Caucasian families. Genotypes were 49,094 SNPs in >2,100 cardiometabolic candidate genes/loci as represented on the HumanCVD BeadChip version 2. False discovery rates (FDR) were calculated to account for multiple testing. Analyses on classical HDL-C revealed significant associations (FDR<0.05) only for CETP (cholesteryl ester transfer protein; lead SNP rs3764261: p = 5.6*10⁻¹⁵) and SGCD (sarcoglycan delta; rs6877118: p = 8.6*10⁻⁶). In contrast, analysis with HDL mean particle size yielded additional associations in LIPC (hepatic lipase; rs261332: p = 6.1*10⁻⁹), PLTP (phospholipid transfer protein, rs4810479: p = 1.7*10⁻⁸) and FBLN5 (fibulin-5; rs2246416: p = 6.2*10⁻⁶). The associations of SGCD and Fibulin-5 with HDL particle size could not be replicated in PROCARDIS (n = 3,078) and/or the Women''s Genome Health Study (n = 23,170).

Conclusions

We show that refined HDL phenotyping by NMR spectroscopy can detect known genes of HDL metabolism better than analyses on HDL-C.     

Association of three polymorphisms of scavenger receptor class BI gene (exon8, exon1, intron5) with coronary stenosis in a coronary Tunisian population

Background

The potential role of scavenger receptor class BI (gene name SCARB1) in the regulation of lipoproteins metabolism and atherosclerosis has attracted considerable interest. We tested the relationship of SCARB1 polymorphisms with significant coronary stenosis (SCS) and lipid profile in a coronary Tunisian population.

Methods

Three SCARB1 polymorphisms (exon8 (C/T), exon1 (G/A), intron5 (C/T)) were studied in 316 Tunisian patients undergoing coronary angiography. SCS was defined as a luminal narrowing of ≥ 50% in at least one major coronary artery. Lipid profile was measured. Genotyping was performed using PCR–RFLP.

Results

Individuals with TT genotypes of exon8 were associated with higher concentrations of plasma HDL-C and ApoAI in the group without SCS. Carriers of T allele of exon8 were associated with 41% lower risk of SCS. This protective effect seemed to be particularly significant in women, nondiabetics and nonsmokers. Subjects homozygous for the variant allele of intron5 were significantly associated with an increased risk of SCS, particularly in smokers. AA genotype of exon1 was associated with an increased risk of SCS in diabetics and in patients with metabolic syndrome. The (CAT) haplotype was associated with increase in the risk of SCS compared to the wild haplotype and had a 4-fold greater risk of SCS than patients with haplotype (TGC) which seems to be the most protective against SCS.

Conclusion

Carriers of T allele of exon8 in SCARB1 seemed to increase HDL-C and ApoAI concentrations and reduce the risk of SCS. The intron5, exon1 and (CAT) haplotype seemed to have an atherogenic effect.