Sequence polymorphisms in the apolipoprotein(a) gene and their association with lipoprotein(a) levels and myocardial infarction. The ECTIM Study

The kringle IV type 2 domain variant 4925G>A causes the elusive association signal of the LPA pentanucleotide repeat

Lipoprotein(a) [Lp(a)] concentrations are regulated by the LPA gene mainly via the large kringle IV-type 2 (KIV-2) copy number variation and multiple causal variants. Early studies suggested an effect of long pentanucleotide repeat (PNR) alleles (10 and 11 repeats, PNR10 and PNR11) in the LPA promoter on gene transcription and found an association with lower Lp(a). Subsequent in vitro studies showed no effects on mRNA transcription, but the association with strongly decreased Lp(a) remained consistent. We investigated the isolated and combined effect of PNR10, PNR11, and the frequent splice site variant KIV-2 4925G>A on Lp(a) concentrations in the Cooperative Health Research in the Region of Augsburg F4 study by multiple quantile regression in single-SNP and joint models. Data on Lp(a), apolipoprotein(a) Western blot isoforms, and variant genotypes were available for 2,858 individuals. We found a considerable linkage disequilibrium between KIV-2 4925G>A and the alleles PNR10 and PNR11. In single-variant analysis adjusted for age, sex, and the shorter apo(a) isoform, we determined that both PNR alleles were associated with a highly significant Lp(a) decrease (PNR10: β = -14.43 mg/dl, 95% CI: -15.84, -13.02, P = 3.33e-84; PNR11: β = -17.21 mg/dl, 95% CI: -20.19, -14.23, P = 4.01e-29). However, a joint model, adjusting the PNR alleles additionally for 4925G>A, abolished the effect on Lp(a) (PNR10: β = +0.44 mg/dl, 95% CI: -1.73, 2.60, P = 0.69; PNR11: β = -1.52 mg/dl, 95% CI: -6.05, 3.00, P = 0.51). Collectively, we conclude that the previously reported Lp(a) decrease observed in pentanucleotide alleles PNR10 or PNR11 carriers results from a linkage disequilibrium with the frequent splicing mutation KIV-2 4925G>A.

Organic Cation Transporters in Health and Disease

The organic cation transporters (OCTs) OCT1, OCT2, OCT3, novel OCT (OCTN)1, OCTN2, multidrug and toxin exclusion (MATE)1, and MATE kidney-specific 2 are polyspecific transporters exhibiting broadly overlapping substrate selectivities. They transport organic cations, zwitterions, and some uncharged compounds and operate as facilitated diffusion systems and/or antiporters. OCTs are critically involved in intestinal absorption, hepatic uptake, and renal excretion of hydrophilic drugs. They modulate the distribution of endogenous compounds such as thiamine, L-carnitine, and neurotransmitters. Sites of expression and functions of OCTs have important impact on energy metabolism, pharmacokinetics, and toxicity of drugs, and on drug-drug interactions. In this work, an overview about the human OCTs is presented. Functional properties of human OCTs, including identified substrates and inhibitors of the individual transporters, are described. Sites of expression are compiled, and data on regulation of OCTs are presented. In addition, genetic variations of OCTs are listed, and data on their impact on transport, drug treatment, and diseases are reported. Moreover, recent data are summarized that indicate complex drug-drug interaction at OCTs, such as allosteric high-affinity inhibition of transport and substrate dependence of inhibitor efficacies. A hypothesis about the molecular mechanism of polyspecific substrate recognition by OCTs is presented that is based on functional studies and mutagenesis experiments in OCT1 and OCT2. This hypothesis provides a framework to imagine how observed complex drug-drug interactions at OCTs arise. Finally, preclinical in vitro tests that are performed by pharmaceutical companies to identify interaction of novel drugs with OCTs are discussed. Optimized experimental procedures are proposed that allow a gapless detection of inhibitory and transported drugs.

Lipoprotein (a) as a cause of cardiovascular disease: insights from epidemiology, genetics, and biology

Human epidemiologic and genetic evidence using the Mendelian randomization approach in large-scale studies now strongly supports that elevated lipoprotein (a) [Lp(a)] is a causal risk factor for cardiovascular disease, that is, for myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis. The Mendelian randomization approach used to infer causality is generally not affected by confounding and reverse causation, the major problems of observational epidemiology. This approach is particularly valuable to study causality of Lp(a), as single genetic variants exist that explain 27-28% of all variation in plasma Lp(a). The most important genetic variant likely is the kringle IV type 2 (KIV-2) copy number variant, as the apo(a) product of this variant influences fibrinolysis and thereby thrombosis, as opposed to the Lp(a) particle per se. We speculate that the physiological role of KIV-2 in Lp(a) could be through wound healing during childbirth, infections, and injury, a role that, in addition, could lead to more blood clots promoting stenosis of arteries and the aortic valve, and myocardial infarction. Randomized placebo-controlled trials of Lp(a) reduction in individuals with very high concentrations to reduce cardiovascular disease are awaited. Recent genetic evidence documents elevated Lp(a) as a cause of myocardial infarction, atherosclerotic stenosis, and aortic valve stenosis.

The Distribution of Apolipoprotein E Gene Polymorphism and Apolipoprotein E Levels among Coronary Artery Patients Compared to Controls

OBJECTIVE

Coronary artery disease (CAD) is a multifactorial disease that is caused by various genetics and environmental factors. Genetically, predisposition is an important component for CAD. The candidate apolipoprotein E (apoE) gene is the most studied one. ApoE is composed of e2, e3, e4 alleles and E2/2, E2/3, E2/4, E3/3, E3/4, E4/4 genotypes. In this study, the relationship between CAD and apoE polymorphism and apoE level has been studied in Tokat region.

MATERIALS AND METHODS

The study population is composed of 100 CAD patients diagnosed by coronary angiography and 100 control patients of whom fifty have normal coronary angiography and fifty did not have any CAD symptoms. The serum lipid and apoE levels and apoE genotypes of all participants have been measured, and the relationship between these parameters has been evaluated.

RESULTS

Apolipoprotein E, total cholesterol, HDL cholesterol and LDL cholesterol levels were statistically low at CAD patients than control patients (p=0.0004, p=0.0005, p=0.0107, p=0.0052 respectively). There was not any significant difference between triglyceride levels (p=0.0848). Waist circumferences were significantly high at CAD patients (p=0.0012). Allele frequencies were as e2 (7.25%), e3 (83.5%), e4 (9.25%) and genotype distributions were as E2/2 (0.5%), E2/3 (13%), E2/4 (0.5%), E3/3 (68.5%), E3/4 (16.5%), E4/4 (1%). The distribution of alleles and genotypes were not significantly different (p>0.05). ApoE levels were higher at e2 allele carriers than e3 and e4 allele carriers (p<0.05). However, there was no significant difference between e3 and e4 allele carriers.

CONCLUSION

In conclusion, the distribution of apoE genotype and allele at our region is similar to the general of Turkey. The low apoE levels in CAD patients may show the influence of apoE on CAD by local and systemic mechanisms.

Towards a molecular systems model of coronary artery disease

Coronary artery disease (CAD) is a complex disease driven by myriad interactions of genetics and environmental factors. Traditionally, studies have analyzed only 1 disease factor at a time, providing useful but limited understanding of the underlying etiology. Recent advances in cost-effective and high-throughput technologies, such as single nucleotide polymorphism (SNP) genotyping, exome/genome/RNA sequencing, gene expression microarrays, and metabolomics assays have enabled the collection of millions of data points in many thousands of individuals. In order to make sense of such 'omics' data, effective analytical methods are needed. We review and highlight some of the main results in this area, focusing on integrative approaches that consider multiple modalities simultaneously. Such analyses have the potential to uncover the genetic basis of CAD, produce genomic risk scores (GRS) for disease prediction, disentangle the complex interactions underlying disease, and predict response to treatment.

When should we measure lipoprotein (a)?

Recently published epidemiological and genetic studies strongly suggest a causal relationship of elevated concentrations of lipoprotein (a) [Lp(a)] with cardiovascular disease (CVD), independent of low-density lipoproteins (LDLs), reduced high density lipoproteins (HDL), and other traditional CVD risk factors. The atherogenicity of Lp(a) at a molecular and cellular level is caused by interference with the fibrinolytic system, the affinity to secretory phospholipase A2, the interaction with extracellular matrix glycoproteins, and the binding to scavenger receptors on macrophages. Lipoprotein (a) plasma concentrations correlate significantly with the synthetic rate of apo(a) and recent studies demonstrate that apo(a) expression is inhibited by ligands for farnesoid X receptor. Numerous gaps in our knowledge on Lp(a) function, biosynthesis, and the site of catabolism still exist. Nevertheless, new classes of therapeutic agents that have a significant Lp(a)-lowering effect such as apoB antisense oligonucleotides, microsomal triglyceride transfer protein inhibitors, cholesterol ester transfer protein inhibitors, and PCSK-9 inhibitors are currently in trials. Consensus reports of scientific societies are still prudent in recommending the measurement of Lp(a) routinely for assessing CVD risk. This is mainly caused by the lack of definite intervention studies demonstrating that lowering Lp(a) reduces hard CVD endpoints, a lack of effective medications for lowering Lp(a), the highly variable Lp(a) concentrations among different ethnic groups and the challenges associated with Lp(a) measurement. Here, we present our view on when to measure Lp(a) and how to deal with elevated Lp(a) levels in moderate and high-risk individuals.

Effects of SNPs at newly identified lipids loci on blood lipid levels and risk of coronary heart disease in Chinese Han population: a case control study

Associations between "lipid-related" candidate genes, blood lipid concentrations and coronary artery disease (CHD) risk are not clear. We aimed to investigate the effect of three newly identified lipids loci from genome-wide association studies on CHD and blood lipid levels in Chinese Han population. The genotypes of SNPs at three newly identified lipid loci and blood lipids concentrations were examined in 1360 CHD patients and 1360 age- and sex-frequency matched controls from an unrelated Chinese Han population. Allele T of rs16996148 occurred less frequently in CHD patients with the odds ratio (OR) being 0.64 (95% CI 0.50 to 0.81), after adjusting for conventional risk factors and was associated with a 33% decreased CHD risk (P<0.01) comparing with the major allele G. Individuals with GT genotype had the lowest CHD risk. No associations were found between the polymorphisms of other two loci with CHD risk and all three SNPs had no effect on lipid profile in this population. SNP rs16996148 on chromosome 19p13 is significantly associated with lower risk for CHD in Chinese Han population. However, it remains unresolved why these lipid-related loci had significantly less effects than the correspondingly expected effects on blood lipids levels in this population.

Lipoprotein(a) and risk of myocardial infarction--genetic epidemiologic evidence of causality

Elevated levels of lipoprotein(a) are associated with an increased risk of myocardial infarction. Our study aimed to test whether genetic data are consistent with this association being causal. Accordingly, we developed a high-throughput realtime PCR assay to genotype for the lipoprotein(a) kringle IV type 2 (KIV-2) repeat polymorphism in the LPA gene in > 40,000 individuals. The LPA KIV-2 genotype associated with plasma levels of lipoprotein(a) (trend p < 0.001), and the LPA KIV-2 genotype associated with risk of myocardial infarction (trend p < 0.001 to 0.03) in a manner consistent with its effect on plasma levels of lipoprotein(a). The association of LPA KIV-2 genotypes raising plasma levels of lipoprotein(a) with increased risk of myocardial infarction strongly supports a causal association of lipoprotein(a) with risk of myocardial infarction.

Atherogenic lipids and lipoproteins trigger CD36-TLR2-dependent apoptosis in macrophages undergoing endoplasmic reticulum stress

Macrophage apoptosis in advanced atheromata, a key process in plaque necrosis, involves the combination of ER stress with other proapoptotic stimuli. We show here that oxidized phospholipids, oxidized LDL, saturated fatty acids (SFAs), and lipoprotein(a) trigger apoptosis in ER-stressed macrophages through a mechanism requiring both CD36 and Toll-like receptor 2 (TLR2). In vivo, macrophage apoptosis was induced in SFA-fed, ER-stressed wild-type but not Cd36⁻(/)⁻ or Tlr2⁻(/)⁻ mice. For atherosclerosis, we combined TLR2 deficiency with that of TLR4, which can also promote apoptosis in ER-stressed macrophages. Advanced lesions of fat-fed Ldlr⁻(/)⁻ mice transplanted with Tlr4⁻(/)⁻Tlr2⁻(/)⁻ bone marrow were markedly protected from macrophage apoptosis and plaque necrosis compared with WT →Ldlr⁻(/)⁻ lesions. These findings provide insight into how atherogenic lipoproteins trigger macrophage apoptosis in the setting of ER stress and how TLR activation might promote macrophage apoptosis and plaque necrosis in advanced atherosclerosis.

The role of endoplasmic reticulum stress in the progression of atherosclerosis

Prolonged activation of the endoplasmic reticulum (ER) stress pathway known as the unfolded protein response (UPR) can lead to cell pathology and subsequent tissue dysfunction. There is now ample evidence that the UPR is chronically activated in atherosclerotic lesional cells, particularly advanced lesional macrophages and endothelial cells. The stressors in advanced lesions that can lead to prolonged activation of the UPR include oxidative stress, oxysterols, and high levels of intracellular cholesterol and saturated fatty acids. Importantly, these arterial wall stressors may be especially prominent in the settings of obesity, insulin resistance, and diabetes, all of which promote the clinical progression of atherosclerosis. In the case of macrophages, prolonged ER stress triggers apoptosis, which in turn leads to plaque necrosis if the apoptotic cells are not rapidly cleared. ER stress-induced endothelial cell apoptosis may also contribute to plaque progression. Another potentially important proatherogenic effect of prolonged ER stress is activation of inflammatory pathways in macrophages and, perhaps in response to atheroprone shear stress, endothelial cells. Although exciting work over the last decade has begun to shed light on the mechanisms and in vivo relevance of ER stress-driven atherosclerosis, much more work is needed to fully understand this area and to enable an informed approach to therapeutic translation.

Lipoprotein(a) and ischemic heart disease--a causal association? A review

The aim of this review is to summarize present evidence of a causal association of lipoprotein(a) with risk of ischemic heart disease (IHD). Evidence for causality includes reproducible associations of a proposed risk factor with risk of disease in epidemiological studies, evidence from in vitro and animal studies in support of pathophysiological effects of the risk factor, and preferably evidence from randomized clinical trials documenting reduced morbidity in response to interventions targeting the risk factor. Elevated and in particular extreme lipoprotein(a) levels have in prospective studies repeatedly been associated with increased risk of IHD, although results from early studies are inconsistent. Data from in vitro and animal studies implicate lipoprotein(a), consisting of a low density lipoprotein particle covalently bound to the plasminogen-like glycoprotein apolipoprotein(a), in both atherosclerosis and thrombosis, including accumulation of lipoprotein(a) in atherosclerotic plaques and attenuation of t-PA mediated plasminogen activation. No randomized clinical trial of the effect of lowering lipoprotein(a) levels on IHD prevention has ever been conducted. Lacking evidence from randomized clinical trials, genetic studies, such as Mendelian randomization studies, can also support claims of causality. Levels of lipoprotein(a) are primarily determined by variation in the LPA gene coding for the apolipoprotein(a) moiety of lipoprotein(a), and genetic epidemiologic studies have documented association of LPA copy number variants, influencing levels of lipoprotein(a), with risk of IHD. In conclusion, results from epidemiologic, in vitro, animal, and genetic epidemiologic studies support a causal association of lipoprotein(a) with risk of IHD, while results from randomized clinical trials are presently lacking.

Identification of copy number variants defining genomic differences among major human groups

Background

Understanding the genetic contribution to phenotype variation of human groups is necessary to elucidate differences in disease predisposition and response to pharmaceutical treatments in different human populations.

Methodology/Principal Findings

We have investigated the genome-wide profile of structural variation on pooled samples from the three populations studied in the HapMap project by comparative genome hybridization (CGH) in different array platforms. We have identified and experimentally validated 33 genomic loci that show significant copy number differences from one population to the other. Interestingly, we found an enrichment of genes related to environment adaptation (immune response, lipid metabolism and extracellular space) within these regions and the study of expression data revealed that more than half of the copy number variants (CNVs) translate into gene-expression differences among populations, suggesting that they could have functional consequences. In addition, the identification of single nucleotide polymorphisms (SNPs) that are in linkage disequilibrium with the copy number alleles allowed us to detect evidences of population differentiation and recent selection at the nucleotide variation level.

Conclusions

Overall, our results provide a comprehensive view of relevant copy number changes that might play a role in phenotypic differences among major human populations, and generate a list of interesting candidates for future studies.

Genome-wide haplotype association study identifies the SLC22A3-LPAL2-LPA gene cluster as a risk locus for coronary artery disease

We identify the SLC22A3-LPAL2-LPA gene cluster as a strong susceptibility locus for coronary artery disease (CAD) through a genome-wide haplotype association (GWHA) study. This locus was not identified from previous genome-wide association (GWA) studies focused on univariate analyses of SNPs. The proposed approach may have wide utility for analyzing GWA data for other complex traits.

Apolipoprotein gene polymorphisms and plasma levels in healthy Tunisians and patients with coronary artery disease

Aim

To analyze apolipoprotein gene polymorphisms in the Tunisian population and to check the relation of these polymorphisms and homocysteine, lipid and apolipoprotein levels to the coronary artery disease (CAD).

Methods

In healthy blood donors and in patients with CAD complicated by myocardial infarction (MI) four apolipoprotein gene polymorphisms [APO (a) PNR, APO E, APO CI and APO CII] were determined and plasma levels of total homocysteine, total cholesterol (TC), triglycerides (TG), HDL-cholesterol (HLD-C) and apolipoproteins (apo A-I, Apo B, Apo E) were measured.

Results

Analysis of the four apolipoprotein gene polymorphisms shows a relative genetic homogeneity between Tunisian population and those on the other side of Mediterranean basin. Compared to controls, CAD patients have significantly higher main concentrations of TC, TG, LDL-C, apo B and homocysteine, and significantly lower ones of HDL-C, apo A-I and apo E. The four apolipoprotein gene polymorphisms have not showed any significant differences between patients and controls. However, the APO E4 allele appears to be associated to the severity of CAD and to high levels of atherogenic parameters and low level of apo E, which has very likely an anti-atherogenic role.

Conclusion

Although APO (a) PNR, APO CI and APO CII genes are analyzed in only few populations, they show a frequency distribution, which is not at variance with that of APO E gene and other widely studied genetic markers. In the Tunisian population the APO E 4 appears to be only indirectly involved in the severity of CAD. In the routine practice, in addition of classic parameters, it will be useful to measure the concentration of apo E and that of Homocysteine and if possible to determine the APO E gene polymorphism.

Pentanucleotide repeat polymorphism, lipoprotein(a) levels, and risk of ischemic heart disease

CONTEXT

Lipoprotein(a) is a cardiovascular risk factor. Levels of lipoprotein(a) are predominantly determined by apolipoprotein(a) gene variation, including a pentanucleotide repeat promoter polymorphism.

OBJECTIVE

We tested the hypothesis that apolipoprotein(a) pentanucleotide repeat genotype predicts elevated lipoprotein(a) levels and risk of myocardial infarction (MI) and ischemic heart disease (IHD) in the general population.

DESIGN

We used a cohort study of the Danish general population, The Copenhagen City Heart Study, including 10,276 individuals of which 860 and 1,781 developed MI and IHD, respectively, during up to 31 yr of follow-up, and a case-control study including 1,814 IHD patients and 5,076 controls. Follow-up was 100% complete.

RESULTS

Allele frequencies were 0.0018, 0.0018, 0.6750, 0.1596, 0.1465, 0.0146, and 0.0004 for 6, 7, 8, 9, 10, 11, and 12 repeats, respectively. Mean lipoprotein(a) levels were 40, 36, and 27 mg/dl for individuals with 14-15, 16, and 17-22 repeats (sum of repeats on both alleles), respectively (trend, P < 0.001). Cumulative incidence of MI and IHD was increased for individuals with 14-15 vs. at least 16 repeats (log rank, P < 0.001 and P = 0.002). Multifactorially adjusted hazard ratios for 14-15 and 17-22 vs. 16 repeats were 3.1 (95% confidence interval, 1.6-5.8) and 1.0 (0.9-1.2) for MI and 2.2 (1.3-3.6) and 1.0 (0.9-1.1) for IHD. In the case-control study, multifactorially adjusted odds ratios for 14-15 and 17-22 vs. 16 repeats were 2.9 (1.1-7.8) and 0.9 (0.8-1.0) for MI and 2.5 (1.0-6.0) and 0.9 (0.8-1.0) for IHD.

CONCLUSIONS

Apolipoprotein(a) 14-15 pentanucleotide repeats predict elevated levels of lipoprotein(a) and a 3- and 2-fold increased risk of MI and IHD in the general population.

Detection of variability in apo(a) gene transcription regulatory sequences using the DGGE method

BACKGROUND

Increased lipoprotein(a), Lp(a), concentration is an independent risk factor for premature atherosclerosis. Apolipoprotein(a), apo(a), determines properties of the lipoprotein and its production rate is the limiting step in Lp(a) particle formation.

METHODS

Subjects covering the whole range of Lp(a) concentration were separated into quintiles. A randomly chosen sample from each quintile was derived, there being a total number of 713 individuals. The DGGE method was used to scan the known transcription regulatory regions of apo(a) gene (promoter; DHII and DHIII enhancers) for variability and its distribution across quintiles.

RESULTS

Besides 5 previously reported nucleotide substitutions (+121 G>A; +93 C>T; -1712 G>T; -1617 C>A; -1230 A>G) 16 unreported rare sequence variants were detected. All polymorphic variants were distributed throughout the quintiles with several significant differences. The novel +62 C variant was found only among individuals with Lp(a) levels over 16 mg/dl.

CONCLUSION

The apo(a) gene transcription regulatory regions were not revealed to be extremely polymorphic. However, we should consider a combined effect of all polymorphic sites from the whole apo(a) gene locus, including the apo(a) gene length polymorphism, when dealing with high population variability of Lp(a) levels.

Apolipoprotein(a) size and lipoprotein(a) concentration and future risk of angina pectoris with evidence of severe coronary atherosclerosis in men: The Physicians' Health Study

BACKGROUND

The relationship of lipoprotein (a) [Lp(a)] concentrations with risk of coronary heart disease needs clarification, especially for threshold values for increased risk and for possible interactions with LDL-cholesterol concentrations and apolipoprotein (a) [apo(a)] size polymorphism. This study was designed to examine the ability of baseline Lp(a) concentration and apo(a) size to predict future severe angina pectoris in apparently healthy men.

METHODS

Baseline Lp(a) concentration and apo(a) size were determined in 195 men who subsequently developed angina and in 195 men who remained free of cardiovascular disease for 5 years.

RESULTS

Cases had higher median Lp(a) concentrations than did controls (30.6 vs 22.5 nmol/L; P = 0.02). Lp(a) concentration was predictive of angina [relative risk (RR) from lowest to highest quintiles: 1.0, 1.5, 1.0, 1.8, and 2.6; P for trend = 0.015]. The increased risk was approximately 4-fold (95% confidence interval, 1.4- to 11-fold) among men who had Lp(a) above the 95th percentile (>158 nmol/L). Men with Lp(a) concentrations in the highest quintile and LDL-cholesterol concentrations >1600 mg/L had a 12-fold increased risk (95% confidence interval, 1.5- to 43-fold). Small apo(a) size isoforms also significantly predicted risk of angina (RR for lowest quintile = 4.1; P for trend = 0.004). When the independent effect of Lp(a) concentration and apo(a) size was assessed by including them in the same multivariate model, only the association between apo(a) size and risk remained significant.

CONCLUSIONS

High Lp(a) predicts risk of angina, and the risk is substantially increased with high concomitant LDL-cholesterol. Small apo(a) size predicts angina with greater strength and independence than Lp(a) concentration.

Regulation of the expression of the apolipoprotein(a) gene: evidence for a regulatory role of the 5' distal apolipoprotein(a) transcription control region enhancer in yeast artificial chromosome transgenic mice

OBJECTIVE

The apolipoprotein(a) [apo(a)] gene locus is the major determinant of the circulating concentration of the atherothrombogenic lipoprotein Lp(a). In vitro analysis of the intergenic region between the apo(a) and plasminogen genes revealed the presence of a putative apo(a) transcription control region (ACR) approximately 20 kb upstream of the apo(a) gene that significantly increases the minimal promoter activity of the human apo(a) gene.

METHODS AND RESULTS

To examine the function of the ACR in its natural genomic context, we used the Cre-loxP recombination system to generate 2 nearly identical apo(a)-yeast artificial chromosome transgenic mouse lines that possess a single integration site for the human apo(a) transgene in the mouse genome but differ by the presence or absence of the ACR enhancer. Analysis of the 2 groups of animals revealed that the deletion of the ACR was associated with 30% reduction in plasma and mRNA apo(a) levels. Apo(a)-yeast artificial chromosome transgenic mice with and without the ACR sequence were similar in all other aspects of apo(a) regulation, including liver-specific apo(a) expression and alteration in expression levels in response to sexual maturation and a high-fat diet.

CONCLUSIONS

This study provides the first experimental in vivo evidence for a functional role of the ACR enhancer in determining levels of apo(a) expression.

Pentanucleotide TTTTA repeat polymorphism of apolipoprotein(a) gene and plasma lipoprotein(a) are associated with ischemic and hemorrhagic stroke in Chinese: a multicenter case-control study in China

BACKGROUND AND PURPOSE

It is still inconclusive whether high plasma lipoprotein(a) [Lp(a)] level is a risk factor for stroke. Small sample size and different ethnic groups and methodologies might be contributors to the conflicts in study results. The purpose of the present study was to investigate the association between plasma Lp(a) levels, pentanucleotide TTTTA repeat (PNTR) polymorphism of the apolipoprotein(a) [apo(a)] gene, and Chinese stroke in a case-control study.

METHODS

We recruited 1825 cases with stroke (44.3% cerebral atherothrombosis, 28.3% lacunar infarction, and 27.3% intracerebral hemorrhage) and 1817 controls from 7 centers in China. Lp(a) concentrations were quantified by enzyme-linked immunosorbent assay. The PNTR polymorphism of the apo(a) gene was determined by polymerase chain reaction-polyacrylamide gel electrophoresis. Conditional multivariate logistic regression analysis was used to identify independent risk factors for stroke and its subtypes.

RESULTS

Lp(a) levels were significantly higher in cases than in controls (median, 28.5 versus 23.1 mg/dL; P<0.001), leading to a 1.97-fold (95% CI, 1.64 to 2.37) increase in risk for overall stroke, 2.0-fold (95% CI, 1.59 to 2.52) increase for atherothrombotic type, 2.05-fold increase (95% CI, 1.59 to 2.63) for lacunar type, and 1.64-fold increase (95% CI, 1.21 to 2.21) for hemorrhagic type. The number of PNTR negatively correlated with Lp(a) levels. Low-number repeats (sum of both alleles <16) of apo(a) PNTR were associated with both atherothrombotic stroke (odds ratio, 1.41; 95% CI, 1.04 to 1.91) and hemorrhagic stroke (odds ratio, 1.62; 95% CI, 1.09 to 2.37).

CONCLUSIONS

Our results indicate for the first time that low numbers of apo(a) PNTR and plasma Lp(a) levels are independently associated with both ischemic and hemorrhagic stroke in Chinese.

Analysis of the apo(a) size polymorphism in Asian Indian populations: association with Lp(a) concentration and coronary heart disease

Most studies aiming to detect associations of genetic variation with common complex diseases, e.g. coronary heart disease (CHD) have been performed in populations with a western lifestyle but it is unclear whether associations detected in one geographic group exist also in others. We here have determined lipoprotein(a) levels and apo(a) K-IV-2 repeat genotypes in CHD patients (N=254) and controls (N=480) from two Asian Indian populations (Tamil Nadu and New Delhi). In both populations and also in the pooled dataset median Lp(a) levels were significantly elevated in the patients (27.4 mg/dl) compared with the controls (17.6 mg/dl). Apo(a) K-IV-2 allele frequencies were not different between the CHD patients and controls and thus did not explain the increased Lp(a) levels in CHD patients. Contrary to what has recently been observed in Black and White men short (K-IV<or=22) alleles associated with high Lp(a) concentration were not overrepresented in the patients. Rather, short (K-IV<or=22), intermediate (K-IV 23-29) and long (K-IV>or=30) apo(a) alleles were all associated with higher Lp(a) levels in the patients. Accordingly relative risk (estimated as odds ratio) for CHD rose continuously with increasing Lp(a) but was independent of apo(a) allele length. Together with previous studies our results indicate that the relation between apo(a) genotypes, Lp(a) levels, and CHD may be heterogeneous across ethnic groups and that it depends on the genetic architecture of the Lp(a) trait in a given population whether an association of K-IV-2 repeat length with CHD exists or not.

Helicobacter pylori is associated with modified lipid profile: impact on Lipoprotein(a)

OBJECTIVES

Helicobacter pylori is a controversial risk factor for atherosclerosis. We investigated whether the bacterium persistent inflammation or the expression of the cytotoxin-associated gene A (CagA) may affect serum lipids as well as Lipoprotein(a).

DESIGN AND METHODS

Two hundred-eleven healthy volunteers were evaluated for lipids and Lipoprotein(a). Helicobacter pylori was characterized by Urea Breath Test and IgG-anti-CagA. apo(a) Kringle-IV polymorphism was genotyped.

RESULTS

Prevalence of the infection was 72%; 43% of subjects expressed CagA reactivity. Infected subjects showed increased levels of cholesterol, LDL-cholesterol, and cholesterol/HDL-cholesterol atherogenic index. Association with the Helicobacter pylori CagA(-) strains persisted after the adjustment for covariates. Significant difference between infected and uninfected subjects was found in Lipoprotein(a) levels. This difference did not arise from the Kringle-IV genotype.

CONCLUSIONS

The infection per se significantly modified serum lipid and Lipoprotein(a) concentrations. CagA does not seem to be a reliable marker of pathogenicity for the atherogenic complications of H. pylori infection.

Studies of apolipoprotein (a) promoter from subjects with different plasma lipoprotein (a) concentrations

OBJECTIVE

High plasma lipoprotein (a) [Lp(a)] level is closely related to coronary heart disease and cerebral thrombosis. The Lp(a) concentration is determined primarily by apolipoprotein (a) [apo(a)] gene and APO(a) mRNA abundance has been found to vary with apo(a) isoform. Our objective is to investigate whether APO(a) promoter activity is related to plasma Lp(a) level.

DESIGN AND METHODS

The 5' 1.4 kilobases (kb) promoter region of APO(a) was cloned into plasmid pGL-2 basic that carries luciferase reporter system. The promoter activity was assayed in HepG2 cells. DNA sequence of the promoter was also determined.

RESULTS

Few nucleotide changes besides the variations at the five polymorphic sites: -1270 (TTTTA repeat), -868 (T repeat), -772 (A/G variation), +93 (C/T variation) and +121 (A/G variation) were observed in these promoters. APO(a) promoter activity differed in subjects with different plasma Lp(a) levels.

CONCLUSION

The sequence variation of APO(a) promoter region may contribute to the variation of its transcription activity.

Pentanucleotide TTTTA and G/A -914 DNA polymorphisms in apolipoprotein(a) promoter: genotyping by single-tube PCR

It is known that pentanucleotide repeat polymorphism, consisting of varying number of (TTTTA) repeats in a promoter, is associated with plasma lipoprotein(a) levels. G/A -914 base substitution has also been correlated with pentanucleotide repeat polymorphism in individuals with high and low lipoprotein(a) levels. To facilitate future analysis of these polymorphisms we have developed a quick and reliable assay for the detection of both polymorphisms in a single polymerase chain reaction.

Genetic testing for coronary heart disease: the approaching frontier

The prospect for genetic testing to better delineate the risk for coronary heart disease will become a reality in the next decade. Advances in this area will follow the accelerated trajectory in our ability to dissect the genetics of complex diseases including coronary heart disease. A brief overview of the present state of knowledge will follow the discussion of present approaches in discovering these genetic predispositions. The key issues that will likely shape the field in the near future will also be presented.

Association of polymorphisms of the apolipoprotein(a) gene with lipoprotein(a) levels and myocardial infarction

BACKGROUND

Serum lipoprotein(a) [Lp(a)] concentration is largely determined by variability at the apolipoprotein(a) gene locus. Most prominent effects relate to polymorphisms in the promoter (a pentanucleotide [PN] repeat) and coding regions (a kringle IV [K4] repeat), the latter of which also affects Lp(a) particle size. The impact of these polymorphisms on cardiovascular risk is poorly understood.

METHODS AND RESULTS

We studied both polymorphisms and Lp(a) levels in 834 registry-based myocardial infarction (MI) patients (38% women) and 1548 population-based controls. Lp(a) concentrations were inversely related with the numbers of K4 and PN repeats. However, the effect of the PN polymorphism was restricted to subjects producing small Lp(a) particles (<or=8 PN 66.1 mg/dL versus >8 PN 8.7 mg/dL; P<0.0001). The odds to present with MI were elevated in individuals producing small Lp(a) particles (<or=22 K4 repeats; OR 1.47 for men and 1.69 for women; P<0.002) and in women with <or=8 PN repeats (OR 1.46, P=0.009). Interestingly, in women, the frequent haplotype with <or=8 PN and <or=22 K4 repeats, which is related to high levels of small Lp(a) particles, resulted in an elevated OR for MI (1.79; P=0.01) independently of Lp(a) serum concentration.

CONCLUSIONS

The K4 and PN repeat polymorphisms largely explain the high variability of serum Lp(a) levels. A haplotype with <or=8 PN and <or=22 K4 repeats is characterized by high concentrations of small Lp(a) particles. Our observation that this haplotype was associated with MI independently of Lp(a) serum levels may suggest that Lp(a) particle size in addition to its concentration may modulate MI risk in women.

Lipoprotein(a): an emerging cardiovascular risk factor

Lipoprotein(a) is a cholesterol-enriched lipoprotein, consisting of a covalent linkage joining the unique and highly polymorphic apolipoprotein(a) to apolipoprotein B100, the main protein moiety of low-density lipoproteins. Although the concentration of lipoprotein(a) in humans is mostly genetically determined, acquired disorders might influence synthesis and catabolism of the particle. Raised concentration of lipoprotein(a) has been acknowledged as a leading inherited risk factor for both premature and advanced atherosclerosis at different vascular sites. The strong structural homologies with plasminogen and low-density lipoproteins suggest that lipoprotein(a) might represent the ideal bridge between the fields of atherosclerosis and thrombosis in the pathogenesis of vascular occlusive disorders. Unfortunately, the exact mechanisms by which lipoprotein(a) promotes, accelerates, and complicates atherosclerosis are only partially understood. In some clinical settings, such as in patients at exceptionally low risk for cardiovascular disease, the potential regenerative and antineoplastic properties of lipoprotein(a) might paradoxically counterbalance its athero-thrombogenicity, as attested by the compatibility between raised plasma lipoprotein(a) levels and longevity.

APO(a) variants and lipoprotein(a) in men with or without myocardial infarction

The lipoprotein Lp(a) with high plasma concentration is an independent genetic determinant for cardiovascular diseases. It was investigated as a quantitative factor of risk for myocardial infarction. A total of 345 Italian subjects, 127 Cases and 218 Controls, were studied. Lipids and lipoproteins were compared. Cases had atherogenic traits, such as lower HDL cholesterol and higher triglycerides than Controls. In particular, they had Lp(a) concentrations over the risk threshold, (median, 27 mg/dl in Cases vs 17 mg/dl in Controls; P = 0.0075, Mann-Whitney test) which confirmed the association of this parameter with the disease. Two main functional variants of the apo(a) gene, KringleIV and penta-nucleotide repeat, (PNR) were analyzed. Allele and genotype frequency distributions differed between Cases and Controls. Lp(a) concentrations differed according to PNR genotypes in Controls: subjects having alleles >8 showed lower Lp(a). This was not found in Cases. They had a higher prevalence of the smaller KringleIV alleles, the high Lp(a)-expressing ones. In Cases, genotypes consisting of two small KringleIV alleles were prevalently associated to PNR 8/9 and 8/10, thus preventing Lp(a) lowering. The putative apo(a) enhancer within LINE1 in the apo(a)-plasminogen intergenic region was investigated for functional polymorphisms. No variants that could be associated to the Lp(a) variability were found.

Heterozygous apolipoprotein (a) status and protein expression as a risk factor for premature coronary heart disease

Exactly how apolipoprotein a [APO(a)] isoform size affects the degree of cardiovascular risk associated with high lipoprotein a [LP(a)] levels is not fully understood. Using a sodium dodecyl sulfate-agarose APO(a) & LP(a) phenotyping method, we assessed the role of APO(a) size heterogeneity according to the number of kringle 4 repeats and the differential APO(a) protein expression in 91 male Spanish patients with premature coronary heart disease (CHD) compared with 99 healthy Spanish men. CHD patients had significantly increased median plasma LP(a) levels (0.31 g/L) and a higher percentage of subjects with LP(a) levels of 0.30 g/L or greater (51%) than controls (0.15 g/L and 23%, respectively). Patients with the double-band phenotype had significantly higher plasma LP(a) levels (median 0.37 g/L) compared with those expressing a single-band phenotype (median 0.20 g/L; P =.018) and with their corresponding controls (median 0.15 g/L; P <.001). The double-band phenotype and LP(a) values of 0.30 g/L or greater had a significant association with CHD (odds ratio [OR] 6.47, 95% confidence interval [CI] 2.51-16.7), stronger than that observed for the entire group (OR 4.19, 95% CI 1.97-8.90). The adjusted OR for the APO(a) protein pattern that equally expressed both isoforms indicates an independent association with premature CHD (OR 3.33; 95% CI 1.08-10.3). These results suggest that APO(a) phenotyping might be used in subjects with hyperlipoproteinemia a as a powerful marker to assess the risk of premature CHD because heterozygous status, mainly when both isoforms are equally expressed, is associated with higher cardiovascular risk.

The association of serum lipoprotein(a) levels, apolipoprotein(a) size and (TTTTA)(n) polymorphism with coronary heart disease

BACKGROUND

The association between lipoprotein(a) levels, apolipoprotein(a) size and the (TTTTA)(n) polymorphism which is located in the 5' non-coding region of the apo(a) gene was studied in 263 patients with severe coronary heart disease and 97 healthy subjects.

METHODS

Lp(a) levels were measured by ELISA, apo(a) isoform size was determined by SDS-agarose gel electrophoresis, and analysis of the (TTTTA)(n) was carried out by PCR. For statistical calculation, both groups were divided into low (at least one apo(a) isoform with < or = 22 Kringle IV) and high (both isoforms with >22 KIV) apo(a) isoform sizes, and into low number (<10 in both alleles) and high number of (> or =10 at least one allele) TTTTA repeats.

RESULTS

Lp(a) levels were higher (P=0.007), apo(a) isoforms size < or =22 KIV and TTTTA repeats > or = 10 were more frequent (P=0.007 and 0.01) in cases than in controls. Lp(a) levels were found to be increased with low apo(a) weight in both groups (both P<0.0001). In multivariate logistic regression analysis, only the Lp(a) levels (P=0.005) and (TTTTA)(n) polymorphism (P=0.002) were found to be significantly associated with CHD.

CONCLUSION

Nevertheless, these results indicate that in CHD patients the (TTTTA)(n) polymorphism has an effect on Lp(a) levels which is independent of the apo(a) size.

Functional analysis of the chimpanzee and human apo(a) promoter sequences: identification of sequence variations responsible for elevated transcriptional activity in chimpanzee

Lp(a) concentrations vary considerably among individuals and are primarily determined by the apo(a) gene locus. We have previously shown that mean plasma Lp(a) levels in the chimpanzee are significantly higher than those observed in humans (Doucet, C., Huby, T., Chapman, J., and Thillet, J. (1994) J. Lipid Res 35, 263-270). To evaluate the possibility that this difference may result from a high level of expression of chimpanzee apo(a), we cloned and sequenced 1.4 kilobase (kb) of the 5'-flanking region of the gene and compared promoter activity to that of its human counterpart. Sequence analysis revealed 98% homology between chimpanzee and human apo(a) 5' sequences; among the differences observed, two involved polymorphic sites associated with Lp(a) levels in humans. The TTTTA repeat located 1.3 kb 5' of the apo(a) gene, present in a variable number of copies (n = 5-12) in humans, is uniquely present as four copies in the chimpanzee sequence. The second position concerns the +93 C>T polymorphism that creates an additional ATG start codon in the human apo(a) gene, thereby impairing translation efficiency. In chimpanzee, this position did not appear polymorphic, and a base difference at position +94 precluded the presence of an additional ATG. In transient transfection assays, the chimpanzee apo(a) promoter exhibited a 5-fold elevation in transcriptional activity as compared with its human counterpart. This marked difference in activity was maintained with either 1.4 kb of 5' sequence or the minimal promoter region -98 to +141 of the human and chimpanzee apo(a) genes. Using point mutational analyses, nucleotides present at positions -3, -2, and +8 (relative to the start site of transcription) were found to be essential for the high transcription efficiency of the chimpanzee apo(a) promoter. High transcriptional activity of the chimpanzee apo(a) gene may therefore represent a key factor in the elevated plasma Lp(a) levels characteristic of this non-human primate.

Lipoprotein(a), atherosclerosis, and apolipoprotein(a) gene polymorphism

High plasma lipoprotein(a) [Lp(a)] levels have been implicated as an independent risk factor for coronary artery disease in Caucasians, Chinese, Africans, and Indians. Apo(a) that evolved from a duplicated plasminogen gene during recent primate evolution is responsible for the concentration of Lp(a) in the artery wall leading to atherosclerosis, by virtue of its ability to bind to the extracellular matrix and its role in stimulating the proliferation and migration of human smooth muscle cells. Several types of polymorphisms, size as well as sequence changes both in the coding and regulatory sequences, have been reported to influence the variability of Lp(a) concentration. Apo(a) exhibits genetic size polymorphism varying between 300 and 800 kDa that could be attributed to the number of k-4 VNTR (variable number of transcribed kringle-4 repeats). An inverse relationship between Lp(a) level and apo(a) allele sizes is a general trend in all ethnic populations although apo(a) allele size distribution could be significantly variable in ethnic types. A negative correlation between the number of pentanucleotide TTTTA(n) repeat (PNR) sequences in the regulatory region of the apo(a) gene and Lp(a) level has also been observed in Caucasians and Indians, but not in African Americans. However, a significant linkage disequilibrium was noted between the PNR number and k-4 VNTR. In order to correlate the role of apo(a) gene polymorphisms to apo(a) gene regulation, we have proposed that liver-specific transcriptional activators and repressors might contribute to the differential expression of apo(a) gene, in an individual-specific manner.

Simultaneous mutations (A/G(-418) and C/T(-384)) in the apo(a) promoter of individuals with low Lp(a) levels

High plasma levels of Lp(a), a low-density lipoprotein particle with an attached apo(a), are associated with the development of atherosclerosis. We present two simultaneous mutations in the apo(a) promoter (A/G(-418) and C/T(-384)) in healthy Indians with a low Lp(a) level (<5 mg/dl). No such mutations were detected in coronary artery disease positive individuals with very high Lp(a) levels (>200 mg/dl). The mutations described here might be useful in understanding the transcriptional regulation of the apo(a) gene.

Single effects of apolipoprotein B, (a), and E polymorphisms and interaction between plasminogen activator inhibitor-1 and apolipoprotein(a) genotypes and the risk of coronary artery disease in Czech male caucasians

To evaluate whether polymorphisms in genes whose products are involved in lipid metabolism and fibrinolysis alter the risk of coronary artery disease (CAD), allele frequencies of four genetic polymorphisms were ascertained by PCR-based methods in 175 Czech male patients with coronary artery disease and in 222 Czech men with no symptoms of CAD. The following polymorphisms were studied: apolipoprotein B (apo B) signal peptide insertion/deletion polymorphism, 5' apolipoprotein(a) [apo(a)] TTTTA repeat polymorphism, apolipoprotein E (apo E) varepsilon2, varepsilon3, varepsilon4 polymorphism, and plasminogen activator inhibitor-1 (PAI-1) 4G/5G promoter polymorphism. Apo B and apo(a) allele frequencies differed significantly between the CAD and the control groups (P<0.01 each), with higher frequencies of apo B deletion and apo(a) shorter repeat alleles in the CAD group. We did not observe any differences in allele frequencies of either PAI-1 or apo E polymorphisms but the genotype frequencies of apo E were slightly different between the two groups (P<0.05). In addition, we observed a gene-gene interaction between the PAI-1 and apo(a) polymorphisms with respect to the risk of CAD. None of the polymorphisms studied were associated with the severity of CAD or a history of myocardial infarction. Our findings support the idea that several polymorphisms in apolipoprotein genes may by themselves and/or in interaction with other polymorphisms contribute to risk factors for CAD in men.