Search

Oxidized phospholipids (OxPL) are key mediators of the pro-atherosclerotic effects of oxidized lipoproteins. They are particularly important for the pathogenicity of lipoprotein(a) (Lp(a)), which is the preferred lipoprotein carrier of phosphocholine-containing OxPL in plasma. Indeed, elevated levels of OxPL-apoB, a parameter that almost entirely reflects the OxPL on Lp(a), are a potent risk factor for atherothrombotic diseases as well as calcific aortic valve stenosis. A substantial fraction of the OxPL on Lp(a) are covalently bound to the KIV

Elevated plasma concentrations of lipoprotein(a) (Lp(a)) are a causal risk factor for the development of atherothrombotic disorders including coronary heart disease. However, the pathological mechanisms underlying this causal relationship remain incompletely defined. Lp(a) consists of a lipoprotein particle in which apolipoproteinB100 is covalently linked to the unique glycoprotein apolipoprotein(a) (apo(a)). The remarkable homology between apo(a) and the fibrinolytic proenzyme plasminogen strongly suggests an antifibrinolytic role: apo(a) contains a strong lysine binding site and can block the sites on fibrin and cellular receptors required for plasminogen activation, but itself lacks proteolytic activity. While numerous in vitro and animal model studies indicate that apo(a) can inhibit plasminogen activation and fibrinolysis, this activity may not be preserved in Lp(a). Moreover, elevated Lp(a) does not reduce the efficacy of thrombolytic therapy and is not a risk factor for some non-atherosclerotic thrombotic disorders such as venous thromboembolism. Accordingly, different prothrombotic mechanisms for Lp(a) must be contemplated. Evidence exists that Lp(a) binds to and inactivates tissue factor pathway inhibitor and stimulates expression of tissue factor by monocytes. Moreover, some studies have shown that Lp(a) promotes platelet activation and aggregation, at least in response to some agonists. Lp(a) alters the structure of the fibrin network to make it less permeable and more resistant to lysis. Finally, Lp(a) may promote the development of a vulnerable plaque phenotype that is more prone to rupture and hence the precipitation of atherothrombotic events. Further study, especially in animal models of thrombosis, is required to clarify the prothrombotic effects of Lp(a).

Lipoprotein(a) [Lp(a)] has been established as an independent and causal risk factor for cardiovascular disease. Individuals with elevated levels of Lp(a) (>125 nmol/L; >50 mg/dl) display increased arterial wall inflammation characterized by activation of the endothelium by Lp(a)-carried oxidized phospholipids and recruitment of circulating monocytes. This results in increased secretion of chemoattractants and cytokines, upregulation of adhesion molecules and increased migration of leukocytes through the vessel wall. In addition, Lp(a) is also pivotal in the initiation phase of aortic valve stenosis. The oxidized phospholipids associated, in part, with the apolipoprotein(a) [apo(a)] moiety of Lp(a) stimulate the aortic valve residential cell, the valve interstitial cells (VICs), to either induce osteoblastic differentiation or apoptosis, thereby initiating the process of aortic valve calcification. Lastly, Lp(a) has been linked to systemic inflammation, including the acute phase response. Specifically, the cytokine interleukin 6 (IL-6) has a unique relationship with Lp(a), since the LPA gene contains IL-6 response elements. In this review, we will discuss the pathways and cell types affected by Lp(a) in the context of atherosclerosis, aortic valve stenosis and the acute phase response, highlighting the role of Lp(a) as an inflammatory mastermind. ispartof: Atherosclerosis vol:349 pages:101-109 ispartof: location:Ireland status: published

Epidemiological studies investigating the association between a biomarker and a disease have many limitations. The most prominent among these is that we cannot impute causality purely from a statistical association. If we observe an association, the biomarker might really be causal for the development of the disease, the association might be caused by a confounding variable or by reverse causation. With Mendelian Randomization (MR) methods, we have a potent tool at hand to derive evidence for a direct causal relationship. One of the core assumptions of MR studies is that genetic variants can be identified, which are strongly associated with the biomarker of interest, and can serve as an instrument indicating lifetime exposure. Since Lp(a) is primarily genetically determined by KIV-2 repeats, that in turn determine apo(a) isoform size, and by numerous single nucleotide polymorphisms (SNPs) and SNP-scores, this assumption is definitely fulfilled and it is probably one of the best phenotypes to be studied with Mendelian Randomization methods. The first studies evaluating the causal role of Lp(a) for cardiovascular diseases were performed in the early 1990s and more recently gained interest after several Lp(a)-increasing SNPs were identified in genome wide association studies. In this review, the principles behind MR methods are explained, together with their important role for Lp(a) research, particularly reconsidered in their historic context. MR methods have also been used to estimate the extent of Lp(a) reduction that would be required to yield a clinically meaningful reduction in outcomes in clinical intervention trials.

Lipoprotein(a) [Lp(a)] became besides LDL cholesterol one of the most attractive targets for intervention in cardiovascular disease. Strong genetic evidence supports the causal association between high Lp(a) concentrations and cardiovascular outcomes. Since specific Lp(a)-lowering therapies are under clinical investigation, the interest in measuring Lp(a) has markedly increased. However, the special structure of the lead protein component of Lp(a), named apolipoprotein(a), creates difficulties for an accurate measurement of Lp(a). A highly homologous repetitive structure, called kringle IV repeat with up to more the 40 repeats, causes a highly polymorphic protein. Antibodies raised against apolipoprotein(a) are mostly directed against the repetitive structure of this protein, which complicates the measurement of Lp(a) in molar terms. Both measurements in mass (mg/dL) and molar terms (nmol/L) are described and a conversion from one into the another unit is only approximately possible. Working groups for standardization of Lp(a) measurements are going to prepare widely available and improved reference materials, which will be a major step for the measurement of Lp(a). This review discusses many aspects of the difficulties in measuring Lp(a). It tries to distinguish between academic and practical concerns and warns to make a mountain out of a molehill, which does no longer allow to see the patient behind that mountain by simply staring at the laboratory issues. On the other hand, the calibration of some assays raises major concerns, which are anything else but a molehill. This should be kept in mind and we should start measuring Lp(a) with the aim of a better risk stratification for the patient and to identify those patients who might be in urgent need for a specific Lp(a)-lowering therapy as soon as it becomes available.

Lp(a) and diabetes are both known and established risk factors for the development of cardiovascular disease. However, studies trying to link both risk factors find an inverse association between Lp(a) and risk of prevalent and incident diabetes. It is not yet clear though whether this association is causal and whether this possible causal link is due to Lp(a) concentration itself, to length of the apo(a) isoforms, or both. The results of Mendelian Randomisation studies are highly heterogeneous. This review aims to shed light on the most recent findings of epidemiological and Mendelian Randomisation studies and disentangle the contradictory results. Only part of the observed association of Lp(a) with diabetes can likely be explained by causality and may also be driven by reverse causation, co-morbidities, or medications. Furthermore, this review also summarizes the role of Lp(a) within patients with diabetes. Several studies suggest that elevated Lp(a) is a causal independent risk factor for CVD in patients. Although therapies that specifically target and lower Lp(a) have not been evaluated in diabetic patients, analysis of the large PCSK9 clinical outcomes trials suggest they are beneficial on cardiovascular outcomes.

Lipoprotein (a) (Lp(a)) is a strange lipoprotein species causatively independently and significantly associated with cardiovascular diseases and calcified aortic valve stenosis. Elevated plasma Lp(a) levels increase the rate of cardiovascular events at any achieved low-density lipoprotein (LDL) level. The major structural difference between Lp(a) and LDL is that Lp(a) has a second large protein, apolipoprotein (a) (apo(a)), bound to the apolipoprotein B100 moiety of an LDL sized particle by a single disulfide bond. Over the past decades, several investigators have tried to elucidate the molecular, cellular and metabolic pathways governing the production of Lp(a), the contribution of Lp(a) to lipid transport in the plasma, and the catabolic fate of Lp(a). The metabolism of this enigmatic lipoprotein nevertheless still remains poorly understood. The objectives of the present manuscript are to comprehensively review the knowns and unknowns of the complexities of Lp(a) metabolism with a focus on apo(a) biosynthesis in hepatocytes, Lp(a) assembly, and Lp(a) plasma clearance and catabolism. We also discuss the controversy surrounding the exact role of the LDL receptor in mediating Lp(a) cellular uptake by reviewing seminal in vitro and in vivo data, the metabolism of Lp(a) in familial hypercholesterolemia, as well as the divergent effects of statins and proprotein convertase subtilisin kexin type 9 inhibitors in modulating Lp(a) plasma concentrations. We also provide new insights into the physiology and pathophysiology of Lp(a) metabolism from human kinetic studies in the context of contemporary molecular and cell biological investigations.

High lipoprotein(a) [Lp(a)] concentrations are one of the most important genetically determined risk factors for cardiovascular disease. Lp(a) concentrations are an enigmatic trait largely controlled by one single gene (LPA) that contains a complex interplay of several genetic elements with many surprising effects discussed in this review. A hypervariable coding copy number variation (the kringle IV type-2 repeat, KIV-2) generates40 apolipoprotein(a) protein isoforms and determines the median Lp(a) concentrations. Carriers of small isoforms with up to 22 kringle IV domains have median Lp(a) concentrations up to 5 times higher than those with large isoforms (22 kringle IV domains). The effect of the apo(a) isoforms are, however, modified by many functional single nucleotide polymorphisms (SNPs) distributed over the complete range of allele frequencies (0.1% to20%) with very pronounced effects on Lp(a) concentrations. A complex interaction is present between the apo(a) isoforms and LPA SNPs, with isoforms partially masking the effect of functional SNPs and, vice versa, SNPs lowering the Lp(a) concentrations of affected isoforms. This picture is further complicated by SNP-SNP interactions, a poorly understood role of other polymorphisms such as short tandem repeats and linkage structures that are poorly captured by common R

Antisense oligonucleotides (ASOs) targeting LPA to lower lipoprotein(a) [Lp(a]] are in clinical trials. Patients have been recruited according to various Lp(a) thresholds, but the prevalence of LPA genetic variants and their effect on efficacy of these ASOs are not well described.We analyzed data from 4 clinical trials of the ASO pelacarsen targeting apolipoprotein(a) that included 455 patients. Common LPA genetic variants rs10455872 and rs3798220, major and minor isoform size, and changes in Lp(a), LDL-C, apoB, OxPL-apoB and OxPL-apo(a) were analyzed according to categories of baseline Lp(a).The prevalence of carrier status for rs10455872 and rs3798220 combined ranged from 25.9% in patients with Lp(a) in the 75 -125 nmol/L range to 77.1% at Lp(a) ≥375 nmol/L. The prevalence of homozygosity for rs3798220, rs10455872 and for double heterozygosity in category of Lp(a) ≥375 nmol/L was 6.3%, 14.6% and 12.5%, respectively. Isoform size decreased with increasing Lp(a) plasma levels, with 99.3% of patients with Lp(a) ≥175 nmol/L having ≤20 KIV repeats in the major isoform. The mean percent reduction from baseline in Lp(a), OxPL-apoB and OxPL-apo(a) in response to pelacarsen was not affected by the presence of rs10455872 and rs3798220, isoform size or baseline Lp(a) at all doses studied.In patients randomized to Lp(a) lowering trials, LPA genetic variants are common, but a sizable proportion do not carry common variants associated with elevated Lp(a). In contrast, the major isoform size was almost uniformly ≤20 KIV repeats in patients with Lp(a) ≥175 nmol/L. The Lp(a) and OxPL lowering effects of pelacarsen were independent of both LPA genetic variants and isoform size.

Background and aims Circulating lipoprotein (a) [Lp(a)] level relates inversely to apolipoprotein (a) [apo(a)] size. Both smaller apo(a) isoforms and higher Lp(a) levels have been linked to coronary heart disease and stroke, but their independent contributions are less well defined. We examined the role of Lp(a) in younger adults with cryptogenic stroke. Methods Lp(a) and apo(a) isoforms were evaluated in a prospectively designed case-control study of patients with unexplained ischemic stroke and stroke-free controls, ages 18 to 64. Serum Lp(a) was measured among 255 cases and 390 controls with both apo(a)-size independent and dependent assays. Apo(a) size was determined by agarose gel electrophoresis. Results Cases and controls were similar in socio-demographic characteristics, but cases had more hypertension, diabetes, smoking, and migraine with aura. In race-specific analyses, Lp(a) levels showed positive associations with cryptogenic stroke in whites, but not in the smaller subgroups of blacks and Hispanics. After full adjustment, comparison of the highest versus lowest quartile in whites was significant for apo(a)-size-independent (OR = 2.10 [95% CI = 1.04, 4.27], p = 0.040), and near-significant for apo(a)-size-dependent Lp(a) (OR = 1.81 [95% CI = 0.95, 3.47], p = 0.073). Apo(a) size was not associated with cryptogenic stroke in any race-ethnic subgroup. Conclusions This study underscores the importance of Lp(a) level, but not apo(a) size, as an independent risk factor for unexplained ischemic stroke in young and middle-aged white adults. Given the emergence of effective Lp(a)-lowering therapies, these findings support routine testing for Lp(a) in this setting, along with further research to assess the extent to which such therapies improve outcomes in this population.

The aim of this study is to investigate the relation between lipoprotein(a) [Lp(a)] and proprotein convertase subtilisin/kexin type 9 (PCSK9) concentrations, and their complex, in patients with potential familial hypercholesterolemia (FH), depending on apo(a) phenotype.The study included 205 patients with total cholesterol (TC) 7.5 mmol/L and/or low density lipoprotein cholesterol (LDL-C)4.9 mmol/L, 32 (15%) patients suffered from ischemic heart disease (IHD), 64 were taking statins. The diagnosis of FH was estimated according to the Dutch Lipid Clinics Network criteria. Lipid parameters, apoB-containing lipoprotein subfractions, Lp(a), PCSK9, Lp(a)-PCSK9 complex levels and apo(a) phenotype were determined. Depending on the apo(a) phenotype, all patients were divided into 2 groups: with high molecular weight (HMW) (n = 145) and low molecular weight (LMW) (n = 60) apo(a) phenotype.The groups were comparable by all major clinical characteristics and biochemical parameters. In the whole group, PCSK9 concentration correlated with age, statins intake, Lp(a), TC and TG levels. Correlation between Lp(a) and PCSK9 levels was found only in the LMW apo(a) phenotype group independently of statins intake (r = 0.46, p 0.001). Associations between Lp(a)-PCSK9 complex and large subfractions of intermediate (r = 0.30) and low-density lipoproteins (r = 0.30, p 0.05 for both) were observed, with more significance in group 2 (r = 0.59, p 0.005 and r = 0.40, p 0.05, respectively).In patients with potential familial hypercholesterolemia, positive correlations between concentrations of Lp(a) and PCSK9, as well as of Lp(a)-PCSK9 plasma complex with large subfractions of intermediate and low-density lipoproteins (IDL-1 and LDL-C), were determined by the LMW apo(a) phenotype.

Lipoprotein(a) [Lp(a)] is an emerging genetic risk factor for cardiovascular disease (CVD). We examined whether plasma Lp(a) concentration and apolipoprotein(a) [apo(a)] isoform size are associated with extent and severity of coronary artery disease (CAD), and the presence of carotid artery plaque.We included in our study male participants (n = 263) from a cohort with angiographically defined premature CAD (Carotid Ultrasound in Patients with Ischemic Heart Disease). The angiographic extent and severity of CAD were determined by the modified Gensini and Coronary Artery Stenosis≥20% (CAGE) scores. Carotid artery plaque was assessed by bilateral carotid B-mode ultrasound. Apo(a) isoform size was determined by LPA Kringle IV-2 copy number (KIV-2 CN).Lp(a) concentration, but not KIV-2 CN, was positively associated with the Gensini score. The association remained significant following adjustment for conventional CVD risk factors (all p 0.05). Lp(a) concentration and elevated Lp(a) [≥50 mg/dL] were positively associated with the CAGE≥20 score, independent of conventional CVD risk factors. KIV-2 C N Q1 (lowest KIV-2 CN quartile) was associated with CAGE≥20 score and KIV-2 CN, with the CAGE≥20 score in those without diabetes. In multivariate models that included phenotypic familial hypercholesterolemia or low-density lipoprotein cholesterol, Lp(a) concentration, but not KIV-2 CN, was independently associated with the Gensini and CAGE≥20 scores. No significant associations between Lp(a) concentration and KIV-2 CN with carotid artery plaque were observed.Lp(a) concentration, but not apo(a) isoform size, is independently associated with angiographic extent and severity of CAD. Neither Lp(a) nor apo(a) isoform size is associated with carotid artery plaque.

Lipoprotein(a) (Lp(a)) is a causal risk factor for cardiovascular disorders including coronary heart disease and calcific aortic valve stenosis. Apolipoprotein(a) (apo(a)), the unique glycoprotein component of Lp(a), contains sequences homologous to plasminogen. Plasminogen activation is markedly accelerated in the presence of cell surface receptors and can be inhibited in this context by apo(a).We evaluated the role of potential receptors in regulating plasminogen activation and the ability of apo(a) to mediate inhibition of plasminogen activation on vascular and monocytic/macrophage cells through knockdown (siRNA or blocking antibodies) or overexpression of various candidate receptors. Binding assays were conducted to determine apo(a) and plasminogen receptor interactions.The urokinase-type plasminogen activator receptor (uPAR) modulates plasminogen activation as well as plasminogen and apo(a) binding on human umbilical vein endothelial cells (HUVECs), human acute monocytic leukemia (THP-1) cells, and THP-1 macrophages as determined through uPAR knockdown and overexpression. Apo(a) variants lacking either the kringle V or the strong lysine binding site in kringle IV type 10 are not able to bind to uPAR to the same extent as wild-type apo(a). Plasminogen activation is also modulated, albeit to a lower extent, through the Mac-1 (αThese results indicate cell type-specific roles for uPAR, α

To evaluate the relationships of lipoprotein(a) (Lp(a)) concentration and apolipoprotein(a) (apo(a)) phenotype to major adverse cardiovascular events after coronary artery bypass grafting (CABG) in long-term follow-up.This single-center study included 356 patients with stable coronary heart disease (CHD) who underwent successful CABG. At baseline, we assessed the patient's risk factor profile for atherosclerosis, Lp(a) concentration and apo(a) phenotype. The primary endpoint was the composite of cardiovascular death and non-fatal myocardial infarction (MI). The secondary endpoint also included hospitalization for recurrent or unstable angina and repeat revascularization.Over a mean of 8.5 ± 3.5 years (range 0.9-15.0 years), the primary and secondary endpoints were registered in 46 (13%) and 107 (30%) patients, respectively. Patients with Lp(a) ≥30 mg/dL were at significantly greater risk for the primary endpoint (hazard ratio (HR) 2.98, 95% confidence interval (CI) 1.76-5.03, p 0.001) and secondary endpoint (HR 3.47, 95% CI 2.48-4.85, p 0.001) than patients with Lp(a) values30 mg/dL. The low molecular-weight apo(a) phenotype was also associated with higher risk of both primary and secondary endpoints (3.57 (1.87-6.82) and 3.05 (2.00-4.62), respectively; p 0.001 for both), regardless of conventional risk factors and statins use.In stable CHD patients Lp(a) concentration and low molecular-weight apo(a) phenotype are independently associated with three-fold increase in risk of major adverse cardiovascular events within 15 years after CABG. Lp(a) levels may provide an additional information for postoperative cardiovascular risk assessment.

Lipoprotein(a) (Lp(a)) is an independent, genetically regulated cardiovascular risk factor. Lp(a) plasma levels are largely determined by the apolipoprotein(a) (apo(a)) component, and differ across ethnicity. Although a number of polymorphisms in the apo(a) gene have been identified, apo(a) genetic regulation is not fully understood. To study the relation between apo(a) gene variants, we constructed haplotypes and assessed linkage equilibrium in African Americans and Caucasians for three widely studied apo(a) gene polymorphisms (apo(a) size, +93 C/T and pentanucleotide repeat region (PNR)). Apo(a) size allele frequency distributions were different across ethnicity (p0.01). For African Americans, PNR frequencies were similar across apo(a) sizes, suggesting linkage equilibrium. For Caucasians, the PNR and the PNR-C/T haplotype frequencies differed for large and small apo(a), with the T and PNR 9 alleles associated with large apo(a) size (p0.0002); also, the PNR 9 allele was more common on a T allele, while PNR 8 was more common on a C allele. On a C allele background, small PNR alleles were more common and the PNR 10 allele less common among African Americans than Caucasians (p0.001). The ethnic difference in apo(a) size distribution remained controlling for C/T and PNR alleles (p=0.023). In conclusion, allele and haplotype frequencies and the nature of the linkage disequilibrium differed between African Americans and Caucasians at three apo(a) gene polymorphisms.

Introduction: Cardio- and/or cerebro-vascular risk are associated with high lipoprotein (a) [Lp(a)] levels and low-molecular-weight (LMW) apo(a) isoforms. Aims of this study were to evaluate the deposition of apo(a) isoforms and apoprotein B (apo B) in atherosclerotic plaque from patients (males and females) who had carotid endarterectomy for severe stenosis, and to identify differences between patients classified by gender and divided according to the stability or instability of their plaques. Materials and methods: We determined lipids, apo B and Lp(a) in serum and plaque extracts from 55 males and 25 females. Apo(a) was phenotyped and isoforms were classified by number of kringle IV (KIV) repeats. Results: Lp(a) levels were higher in female serum and plaque extracts than in male samples, while apo B levels were lower. More Lp(a) than apo B deposition was observed in plaque after normalization for serum levels. Thirty-one different apo(a) isoforms were detected in our patients, with a double band phenotype in 94% of cases. In both sexes, the low/high (L/H) molecular weight apo(a) isoform expression ratio was significantly higher in plaque than in serum. Females with unstable plaques had higher Lp(a) levels in both serum and tissue extracts, and fewer KIV repeats of the principal apo(a) isoform in the serum than the other female group or males. Conclusions: In both sexes, the same apo(a) isoforms are found in serum and atherosclerotic plaque, but in different proportions: in plaque, LMW apo(a) is almost always more strongly accumulated than HMW apo(a), irrespective of any combination of apo(a) isoforms in double band phenotypes or Lp(a) serum levels. Moreover, serum and tissue Lp(a) levels were higher in females than in males, and particularly in the group with unstable plaques.

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-IVor=22) alleles associated with high Lp(a) concentration were not overrepresented in the patients. Rather, short (K-IVor=22), intermediate (K-IV 23-29) and long (K-IVor=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.

Lipoprotein(a) (Lp(a)), which is generated through the covalent association of apolipoprotein(a) (apo(a)) and apo B-100-LDL, is an independent risk factor for several vascular diseases. Therefore, there is interest in developing therapies for lowering Lp(a). This investigation was carried out to determine the effect of CI-1011, a potent lipid regulator in rodents, on Lp(a) and other lipid parameters in cynomolgus monkeys (Macaca fascicularis). Nine healthy male monkeys on a normal chow diet were orally treated with CI-1011 at 30 mg/kg per day for 3 weeks. Lp(a) and total cholesterol levels were significantly decreased after 1 week and maximally reduced to 68 and 73% of control levels, respectively, after 3 treatment weeks. The decreases in total cholesterol were mainly due to changes in low density lipoprotein (LDL). The LDL:HDL ratio decreased by 30%. Triglycerides were unaffected by treatment. Lp(a) and total cholesterol levels returned to pretreatment values after stopping treatment suggesting a direct effect of the compound on their inhibition. Further studies demonstrated that CI-1011 was effective at a low dose of 3 mg/kg per day after 1 week of administration. CI-1011 also decreased apo B-100 to 80% of control levels, but this change was not sufficient to account for the Lp(a) lowering. There was also no correlation between the changes in Lp(a) and apo B-100 levels. Treatment of cynomolgus monkey primary hepatocyte cultures with CI-1011 resulted in a dose-dependent inhibition of Lp(a) levels suggesting a direct hepatic effect of the compound. Western blot analysis of the samples showed that changes in Lp(a) were associated mainly with decreased apo(a) (47%), but not apo B-100 (17%). These results demonstrate that CI-1011 effectively decreases Lp(a) levels both in vivo and in vitro.

Numerous epidemiological studies have shown that lipoprotein(a) (Lp(a)) is an independent risk factor for the premature development of cardiovascular disease. In spite of such evidence, the structural and functional features of this atherogenic, cholesterol-rich particle are not clearly understood. We have demonstrated the presence of two distinct structural domains in apolipoprotein(a) (apo(a)), which are linked by a flexible and accessible region located between kringles 4-4 and 4-5. We have isolated the Lp(a) particle following removal of the N-terminal domain by proteolytic cleavage; the residual particle, containing the C-terminal domain (comprising the region from Kr 4-5 to the protease domain), is linked to apo B-100 by disulphide linkage, and is termed 'mini-Lp(a)'. Mini-Lp(a) exhibited the same binding affinity to fibrin as the corresponding Lp(a). This finding indicated that the kringles responsible for fibrin binding are restricted to Kr 4-5 to Kr 4-10, an observation consistent with the failure of the N-terminal domain to bind to fibrin. N-terminal fragments of apo(a) have been detected in the urine of normal subjects, thereby indicating that part of the catabolism of Lp(a), which is largely indeterminate, could occur via the renal route.

Serum lipoprotein (a) concentrations (Lp(a)) are largely under genetic control, and are strong predictors of coronary heart disease. It has been hypothesised that Lp(a) may contribute to the increased risk of coronary heart disease in familial Type 2 diabetes mellitus. We therefore examined the Lp(a) concentrations and the apolipoprotein (a) (apo(a)) phenotypes in 126 normoglycaemic first degree relatives from families with two or more living Type 2 diabetic patients. These were compared with 147 sex matched normoglycaemic control subjects with no family history of diabetes. Lp(a) concentrations were measured using an enzyme-linked immunosorbent assay (ELISA), and apo(a) isoforms were determined and classified according to the relative mobility of apo(a) on sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE), relative to that of apolipoprotein B-100. There were no significant differences in Lp(a) concentrations between the relatives (R) and controls (C): 11.2 (R) vs. 11.1 (C) mg/dl (median). The distribution of apo(a) phenotypes was not significantly different between groups 0.65 (R) vs. 0.67 (C). These results show that first degree relatives at risk of developing Type 2 diabetes do not have abnormal Lp(a) concentrations or apo(a) phenotypes.

The relationship of Lp(a) with manifestations of coronary heart disease (CHD) has not been studied extensively in women. There is little information as to the association of the unique Lp(a) apolipoprotein moiety (apo(a)) with CHD in either men or women. We therefore assessed the association of the apo(a) polymorphism and of Lp(a) with first acute myocardial infarction (MI) in a population-based case-control study in Jewish residents of Jerusalem between the ages of 25 and 64. The patients consisted of 238 men and 47 women hospitalized for a first acute MI in the 4 hospitals of Jerusalem serving the population (70% response rate among all first MI patients). The control subjects comprised 318 men and 159 women sampled from the national population registry and who were free of CHD (75% response). Lp(a) and apo(a) were measured in plasma stored at -20 degrees C for 6-24 months. Among men, plasma Lp(a) concentrations were higher in cases than controls in both univariate and multivariate analyses. The elevated risk was limited to the upper fifth of the Lp(a) distribution (unadjusted odds ratio = 1.65, P0.01 vs. the lower four quintiles, multivariable odds ratio = 1.82, P0.01). Among women, Lp(a) was not elevated in acute MI patients. Apo(a) isoforms with a B, S1 or S2 band (associated with higher Lp(a) values and having lower molecular weights) were more prevalent in female MI cases than controls (unadjusted odds ratio = 2.5, P = 0.016). This association could not be attributed to the higher Lp(a) concentrations associated with these isoforms and was not seen in men. In conclusion, our study points to an association of the apo(a) isoforms with acute MI in women, not evident in this population sample in men. Previously described associations of elevated Lp(a) with acute MI were confirmed in men but not in women. While the role of chance and inadequate statistical power cannot be excluded, the suggestion of a sex difference in the strength of these associations deserves further investigation, as does the question of whether apo(a) phenotype contributes to risk independently of Lp(a) level.

Objective: LPA encodes apolipoprotein(a), and a CCTC haplotype in the LPA locus is associated with CHD. The 4399Met variant (rs3798220) of LPA has a risk estimate for CHD similar to that of the CCTC haplotype. We asked whether co-incidence with the 4399Met variant explained the association of the haplotype with CHD. Methods: We stratified by the 4399Met variant and another LPA SNP (rs10455872) associated with CHD and tested the association between CHD and 4 SNPs that define two haplotypes associated with CHD: CCTC and CTTG. Results: For CCTC, in the presence of the rs3798220 risk allele the OR was 1.68 (95% CI: 1.05–2.68, P = 0.03) versus 0.30 (95% CI: 0.06–1.59, P = 0.16) with the non-risk allele. For CTTG, in the presence of the rs10455872 risk allele the OR was 1.57 (95% CI: 1.15–2.13, P = 0.004) versus 1.04 (95% CI: 0.79–1.35, P = 0.77) with the non-risk allele. Conclusion: The rs3798220 and rs10455872 SNPs explain the association of the CCTC and CTTG haplotypes with CHD.

A previous study has shown that complement component C3 binds to recombinant apolipoprotein(a) (r-apo(a)). In the present report we have investigated the interactions between lipoprotein(a) (Lp(a)), r-apo(a) and C3 in relation to complement activation and degradation. Neither Lp(a) nor r-apo(a) affected complement activation as indicated by sheep and rabbit red blood cell hemolytic assays, and by assessment of the amount of C3a generated in zymosan-activated human serum in the presence or absence of Lp(a). Crossed immunoelectrophoretic analyses indicated that Lp(a) retarded the migration of iC3b in complement-activated serum but had no effects on C3, C3b, C3c or C3dg. Recombinant apo(a) exhibited the same properties as intact Lp(a) indicating that it is the apo(a) portion of Lp(a) that mediates this effect and not the lipid moiety. Low density lipoprotein had no effect on the migration of C3 cleavage fragments. Treatment of Lp(a) or apo(a) with neuraminidase abolished their capacity to alter iC3b migration. SDS-PAGE immunoblotting analysis of C3 activation fragments generated in the presence of Lp(a) demonstrated the usual physiologic C3 cleavage fragments. Rocket intermediate gel immunoelectrophoresis of complement-activated serum demonstrated that Lp(a) did not hinder or accelerate the generation of C3c and C3dg breakdown fragments of iC3b. The results indicate that the apo(a) moiety of Lp(a) alters the migration of iC3b in an electric field but does not affect complement activation or degradation of activated C3. The sialic acid residues on apo(a) are necessary for the apo(a)-iC3b interaction.

Patients with end-stage renal failure (ESRF) on renal replacement therapy are at significantly increased risk of cardiovascular disease. To determine whether altered concentrations of apolipoprotein(a) (apo(a)), the plasminogen-like protein moiety of the atherogenic particle lipoprotein(a), contributed to this increased risk, apo(a) concentrations were measured in 48 non-diabetic patients with ESRF treated by continuous ambulatory peritoneal dialysis (CAPD) therapy and compared with 65 controls. Apo(a) concentration was increased in CAPD patients compared to controls (geometric mean 419 units/1 versus 137 units/l; ratio of means 3.06 (95% CI 1.95-4.80). We conclude that CAPD patients have increased apo(a) concentrations which may contribute to their increased risk of cardiovascular disease.

Atherosclerosis is associated with arterial deposition of low density lipoprotein (LDL) and lipoprotein(a), Lp(a). Both lipoproteins have been detected in atherosclerotic vessels; however, while LDL has been shown to be only blood-derived, it is not clear whether Lp(a) is also produced within the vessel wall. In the present investigation we studied gene expression of apo(a) and apoB in human blood vessels. Aorta, carotid arteries and liver specimens from 29 adult and pediatric autopsy cases were studied by RT–PCR and Southern blot analysis with primers and probes specific for apo(a), apoB and GAPDH (a control housekeeping gene). The mRNA of apo(a), but not apoB, was found within the vessel wall in both adult atherosclerotic arterial vessels and in pediatric non atherosclerotic vessels. Neither apo(a) nor apoB mRNA was detected in femoral veins. To verify the nature of the detected transcripts, we cloned the 162 base pair (bp) RT–PCR product derived from the arterial wall total RNA. Nucleotide sequencing revealed 100% homology with the apo(a) gene. Thus, while LDL in atherosclerotic arteries is exclusively blood-derived, the accumulation of Lp(a) within the artery may be due in part to in situ production of apo(a) within the vessel wall.

Several studies indicate that the inter-individual variation in plasma concentrations of lipoprotein(a) (Lp(a)) is mainly under genetic control. To define the effect of three DNA polymorphisms on apolipoprotein(a) (apo(a)) expression, we have determined plasma Lp(a) concentrations, apo(a) isoform size, KpnI allele size, the TTTTA pentanucleotide repeat number in the 5' control region of the apo(a) gene and the +93 C/T polymorphism in a European Caucasian population. The simultaneous determination of the kringle 4 (K4) number by genotyping and by phenotyping revealed that the size distribution of non-expressed apo(a) alleles was markedly skewed towards alleles with greater than 25 K4 repeats. This is consistent with the inverse relationship frequently described between the kringle 4 number and the plasma Lp(a) level. Apportioning the Lp(a) concentration from the surface of the peaks on apo(a) phenotyping blots, we have observed that the Lp(a) plasma concentration associated with alleles having more than 25 K4 units does not exceed 400 mg/l, whereas the range of Lp(a) concentrations associated with smaller alleles was broad, from 0 to more than 1000 mg/l. It can thus be concluded that the number of K4 repeats is the main determinant of Lp(a) concentration when this number is more than 25, whereas other polymorphisms may be involved in the alleles with fewer than 26 K4. Analyses of the TTTTA repeat number and of the +93 C/T polymorphism were performed in subjects with KpnI alleles of the same length: low Lp(a) concentrations were shown to be preferentially associated with the presence of apo(a) alleles with more than eight pentanucleotide repeats while no association was revealed between Lp(a) plasma levels and the C/T polymorphism. These results demonstrate that the (TTTTA)(n) polymorphism affects the Lp(a) expression independently of apo(a) size polymorphism.

High serum lipoprotein(a) (Lp(a)) concentration which is largely determined by genetic factors, mainly the apolipoprotein(a) (apo(a)) polymorphism, is associated with ischemic cerebrovascular disease. The aim of this study was to investigate whether apo(a) size was associated with acute ischemic stroke in young adults for which causal factors often remain undetermined. Lipid parameters, Lp(a) concentration and apo(a) isoform size distribution were determined in 90 young patients (37.4+/-8.7 years) with acute cerebral ischemia, and compared to those of control subjects with similar age and sex ratio. Apo(a) size was expressed as its apparent number of kringle 4 (Kr 4) repeats. Serum Lp(a) concentrations were significantly higher in patients than in controls (median values: 0.18 vs. 0.07 g/l, P=0.009) and were as expected inversely related to the number of kringle 4 repeats in both controls (r2=-0.61, P0.001) and patients (r2=-0.56, P0.001). However there was no difference in the apo(a) isoform size distributions between the two groups (median isoform size: 27 vs. 27 Kr 4, P=0.25). Lp(a) levels were increased as well in patients with size apo(a) isoformor = 22 Kr 4 as in those with isoforms25 Kr 4. Multivariate analysis showed that apo(a) phenotype did not appear as a risk factor for cerebrovascular infarction. Thus, our results indicate that serum Lp(a) was significantly increased in young people with ischemic stroke but fail to reveal a role of small-sized apo(a) isoforms in the occurrence of this event. They suggest that other factors, genetic or environmental in nature, than the apo(a) size contribute to increase the serum Lp(a) concentrations in these young patients.

Non-insulin dependent diabetes (NIDDM) is associated with an increased risk of peripheral vascular disease (PVD), but within the diabetic population the relationship between lipid profile and PVD has not been clearly defined. In this study we examined the association of lipid parameters and in particular low density lipoprotein (LDL) particle size, with the presence of PVD in subjects with and without NIDDM. 41 NIDDM patients and 31 non-diabetic subjects with PVD in the absence of rest pain or ulceration, defined by ankle-brachial index measurements and duplex scanning, were compared with 41 NIDDM and 31 euglycemic control subjects of comparable age and sex, without PVD. In both groups those with PVD were found to have significantly elevated triglycerides (2.7 [2.2-3.3] versus 1.9 [1.6-2.2] mmol/l; P0.05 in the diabetic group and 2.0 [1.6-2.3] versus 1.4 [1.1-1.5] mmol/l; P0.05 in the non-diabetic group), decreased apolipoprotein A1 (124 +/- 3 versus 139 +/- 5 mg/dl; P0.01 in the diabetic group and 133 +/- 4 versus 147 +/- 4 mg/dl; P0.05 in the non-diabetic group) and decreased LDL particle size (25.4 +/- 0.1 versus 25.8 +/- 0.1 nm; P0.01 in the diabetic group and 26.0 +/- 0.1 versus 26.3 +/- 0.1 nm; P0.05 in the non diabetic group). In the non-diabetic group apolipoprotein[a] (365 [239-554] versus 184 [17-266] U/l; P0.01), total cholesterol (6.3 +/- 0.2 versus 5.6 +/- 0.2 mmol/l; P0.05), LDL cholesterol (4.1 +/- 0.2 versus 3.6 +/- 0.2 mmol/l; P0.05) and apolipoprotein B (146 +/- 8 versus 117 +/- 5 mg/dl; P0.05) were also found to be associated with PVD although these associations were not observed in the group with diabetes. In addition, 11 NIDDM subjects and 11 non-diabetic subjects with rest pain or ulceration were compared to the corresponding groups with uncomplicated PVD and had lipid profiles with significantly lower levels of total cholesterol and LDL cholesterol. We conclude that the dyslipidemic profile characterized by increased triglyceride level, decreased apolipoprotein A1 level and small dense LDL is associated with uncomplicated PVD in both NIDDM and non-diabetic subjects.

The objective of the present study was to examine the possible associations between low molecular weight (LMW) apolipoprotein(a) (apo(a)) isoforms (F,B,S1,S2) and coronary heart disease (CHD). We conducted a nested case-control (prospective) study of five cohorts of white men: The 1936 cohort (baseline 1976, n = 548) and four cohorts from MONICA I born in 1923 (n = 463), 1933 (n = 491), 1943 (n = 504) and 1953 (n = 448) studied at baseline in 1983. At follow up in 1991, 52 subjects had developed a first myocardial infarction and 22 had been hospitalized with angina pectoris. Plasma samples obtained at baseline were stored frozen until 1993-94, when case samples (n = 74) were analyzed together with samples from matched (disease free) controls (n = 190). In a statistical model (conditional logistic regression) including all age groups, cholesterol (or apo B) level (P0.01), systolic blood pressure (P = 0.05) and smoking (P = 0.02) predicted CHD. In the statistical model Lp(a) interacted significantly with age (OR = 5.7; 95% CI: 1.4-23.6; P = 0.016), and high Lp(a) (over 45 mg/dl) was associated with significantly increased risk in subjects under 60 years (OR = 3.82; 95% CI: 1.47-9.96), but not in older men (OR = 0.67; 95% CI: 0.235-1.89). Therefore, we studied the impact of Lp(a)/apo(a) and other variables in subjects who had been under 60 years when they became cases. Among the younger subjects the presence of LMW apo(a) isoforms significantly predicted the development of CHD (OR = 3.83; 95% CI: 1.18-12.4). The increased risk pertained to high Lp(a) (above versus below 45 mg/dl: OR = 3.68; 95% CI: 1.03-13.10), and to Lp(a) concentrations when entered into the model as a continuous variable (P = 0.04). Cholesterol or apo B (P0.01), smoking (P = 0.02), systolic blood pressure (P = 0.05) and low alcohol consumption (under nine drinks/week) (P = 0.04) were also significant predictors of CHD. We conclude that LMW apo(a) isoforms are significantly associated with increased risk of CHD in men under 60 years.

Analyses of 1163 samples from the San Antonio Family Heart Study revealed several elements of genetic control of lipoprotein(a) (Lp(a)) concentrations in Mexican Americans. Apolipoprotein(a) (apo(a)) isoform size variation was inversely related to Lp(a) concentrations and explained about 22% of total phenotypic variation. Segregation analyses suggested the existence of a major gene that influenced an additional 41% of total Lp(a) variation. A G→A polymorphism in the LPA promoter was in strong disequilibrium with apo(a) isoform size, but did not contribute a significant amount of additional information about Lp(a) variation. However, about 25% of variation in Lp(a) concentrations was influenced by additive polygenic effects, which include the effects of null phenotype alleles. Altogether, these genetic components explained 89% of Lp(a) variation, similar to heritability estimates made in several other studies. Apo(a) size variation and the major gene (explaining a total of about 62% of Lp(a) variation) were linked to each other and, as expected, to the plasminogen locus. Thus, together with the well-established null phenotype allele, these different genetic factors represent at least three distinct elements of control exerted at the LPA locus, which encodes the apo(a) protein.

To evaluate whether a high level of lipoprotein(a) (Lp(a)) is a risk for the development of coronary heart disease (CHD), 94 Japanese patients and 64 age-matched Japanese controls, diagnosed after coronary angiography (CAG), were analyzed wuth special reference to the relations between the degree of atherosclerosis, Lp(a) levels and the apolipoprotein(a) (apo(a)) genotypes. The degree of atherosclerosis was evaluated based on CAG findings in the following three ways: the number of diseased vessels, the Gensini score, and the presence or absence of vascular ulcers and/or irregular outlines of coronary stenotic lesions. Apo(a) protein sizes and the pentanucleotide (TTTTA) repeat polymorphism in the 5′ control region of the apo(a) gene were analyzed. Multivariate predictors for the number of diseased vessels were, in decreased order of significance, plasma Lp(a) levels, history of smoking, hypertension, diabetes mellitus and body mass index (BMI). Independent factors associated with the Gensini score were Lp(a) levels, BMI, hypertension, and diabetes mellitus. A negative association of Lp(a) levels with apo(a) protein sizes, and higher Lp(a) levels in those homozygous for an allele with 8 (TTTTA)-repeats than in those homozygous for an allele with 9 (TTTTA)-repeats, was found in both the controls and patients. In decreasing order of significance, apo(a) protein sizes, the degree of atherosclerosis, the genotype of the pentanucleotide repeat, and gender were independent predictors of Lp(a) levels in stepwise regression models. Apo(a) protein sizes were a significant predictor, and the genotype homozygous for the 8 (TTTTA)-repeats was a possible predictor, for the degree of atherosclerosis in CHD. These findings support the notion that a high Lp(a) level is a risk for the development of atherosclerosis in CHD.

Northern blotting and hybridisation with specific probes was used to detect and quantitate apolipoprotein(a) (apo(a)) mRNA in total RNA isolated from 25 human liver samples. A total of 14 different transcripts were identified suggesting that there are at least 15 different alleles at the apo(a) locus including a probable null allele. Apo(a) mRNA sizes were linearly correlated with the electrophoretic mobility of plasma apo(a) glycoprotein isoforms, and differed, in many cases, by the equivalent of one Kringle 4 unit. To investigate the relationship between apo(a) mRNA size and its concentration in the liver, and between hepatic apo(a) mRNA concentration and plasma lipoprotein(a) (Lp(a)) levels, apo(a) mRNA was quantified by densitometric scanning of autoradiograms of Northern blots. Overall, there was a significant inverse correlation between apo(a) mRNA size and its concentration in the liver, despite a marked interindividual variability in the relative amounts of similar-sized transcripts. In each heterozygous individual, the difference in concentration between the two mRNA species was determined by the difference in size. However, there was not a significant relationship between hepatic apo(a) mRNA concentration and plasma Lp(a) levels in this group. These findings emphasise the importance of mechanisms other than the rate of transcription of the apo(a) gene in the reggulation of Lp(a) synthesis.

Homozygous familial hypercholesterolemia (FH) is a genetic disorder featuring a functional defect in cellular LDL receptors, marked elevation in circulating LDL concentrations, and premature atherosclerosis. The potential atherogenic role of apo B-containing lipoproteins other than LDL in this disease is indeterminate. We describe the quantitative and qualitative characteristics of Lp(a) as a function of apo(a) phenotype in a group of eight, unrelated homozygous FH patients. Plasma Lp(a) levels were significantly elevated (2.5-fold; mean 50 +/- 32 mg/dl) as compared to those in healthy subjects. The S2 isoform of apo(a) occurred most frequently (6 of eight patients); the rare B isoform presented in three patients. Plasma Lp(a) levels in homozygous FH did not correspond to those predicted by apo(a) phenotype. Analyses of the density distribution of Lp(a) and of Lp(a) particle size and heterogeneity as a function of density did not reveal any anomalies characteristic of homozygous FH. However, comparison of the hydrated density of Lp(a) particles as a function of apo(a) isoform content revealed a clear influence of isoform on this parameter; thus, in a B/S2 heterozygous patient, the density distribution of Lp(a) fractions containing isoform B alone, B and S2, and S2 alone, demonstrated that the apparent molecular weight of apo(a) plays a determining role in controlling the hydrated density and size of the resulting Lp(a) particle. Indeed, patients expressing the high molecular weight, S2 isoform uniformly displayed a dense form of Lp(a) (hydrated density approximately 1.055 g/ml). In subjects presenting two apo(a) isoforms, each isoform resided on distinct lipoprotein particles; in such cases, the plasma levels of the denser isoform predominated, suggesting differences in rates of formation, or rates of tissular catabolism, or in the plasma stability of the particles, or a combination of these mechanisms. Considered together, our data may be interpreted to suggest that the elevated circulating levels of Lp(a) in homozygous FH patients may reflect either an increased biosynthesis, or diminished catabolism via the cellular LDL receptor pathway, or a combination of both.

In 10 hyperlipidaemic subjects who had been satisfactorily treated with clofibrate, stopping treatment led to significant reductions in plasma apoprotein A-I and high density lipoprotein cholesterol concentrations; resumption of treatment significantly raised both. The changes were therefore inversely related to those in the plasma cholesterol and triglyceride levels and were most prominent in hypertriglyceridaemic subjects.