Evaluation of lipoprotein(a) as a prothrombotic factor: progress from bench to bedside

Association of Lipoprotein(a) Levels With Myocardial Fibrosis in the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Lipoprotein(a) (Lp[a]) has been identified as an emerging risk factor for adverse cardiovascular (CV) outcomes, including heart failure. However, the connections among Lp(a), myocardial fibrosis (interstitial and replacement), and cardiac remodeling as pathways to CV diseases remains unclear.

OBJECTIVES

This study investigated the relationship between Lp(a) levels and myocardial fibrosis by cardiac magnetic resonance (CMR) T1 mapping and late gadolinium enhancement, as well as cardiac remodeling by cine CMR, in the MESA (Multi-Ethnic Study of Atherosclerosis) cohort.

METHODS

The study included 2,040 participants with baseline Lp(a) measurements and T1 mapping for interstitial myocardial fibrosis (IMF) evaluation in 2010. Lp(a) was analyzed as a continuous variable (per log unit) and using clinical cutoff values of 30 and 50 mg/dL. Multivariate linear and logistic regression were used to assess the associations of Lp(a) with CMR measures of extracellular volume (ECV fraction [ECV%]), native T1 time, and myocardial scar, as well as parameters of cardiac remodeling, in 2,826 participants.

RESULTS

Higher Lp(a) levels were associated with increased ECV% (per log-unit Lp[a]; β = 0.2%; P = 0.007) and native T1 time (per log-unit Lp[a]; β = 4%; P < 0.001). Similar relationships were observed between elevated Lp(a) levels and a higher risk of clinically significant IMF defined by prognostic thresholds per log-unit Lp(a) of ECV% (OR: 1.20; 95% CI: 1.04-1.43) and native T1 (OR: 1.2; 95% CI: 1.1-1.4) equal to 30% and 955 ms, respectively. Clinically used Lp(a) cutoffs (30 and 50 mg/dL) were associated with greater prevalence of myocardial scar (OR: 1.85; 95% CI: 1.1-3.2 and OR: 1.9; 95% CI: 1.1-3.4, respectively). Finally, higher Lp(a) levels were associated with left atrial enlargement and dysfunction.

CONCLUSIONS

Elevated Lp(a) levels are linked to greater subclinical IMF, increased myocardial scar prevalence, and left atrial remodeling.

Lipoprotein(a) during COVID-19 hospitalization: Thrombosis, inflammation, and mortality

Background and aims

Methods

Results

Conclusions

Lipoprotein(a) and calcific aortic valve stenosis: A systematic review

Calcific aortic valve stenosis (AS) is the most common form of acquired valvular heart disease needing intervention and our understanding of this disease has evolved from one of degenerative calcification to that of an active process driven by the interplay of genetic factors and chronic inflammation modulated by risk factors such as smoking, hypertension and elevated cholesterol. Lipoprotein(a) [Lp (a)] is a cholesterol rich particle secreted by the liver which functions as the major lipoprotein carrier of phosphocholine-containing oxidized phospholipids. Lp(a) levels are largely genetically determined by polymorphisms in the LPA gene. While there is an extensive body of evidence linking Lp(a) to atherosclerotic cardiovascular disease, emerging evidence now suggests a similar association of Lp(a) to calcific AS. In this article, we performed a systematic review of all published literature to assess the association between Lp(a) and calcific aortic valve (AV) disease. In addition, we review the potential mechanisms by which Lp(a) influences the progression of valve disease. Our review identified a total of 21 studies, varying from case-control studies, prospective or retrospective observational cohort studies to Mendelian randomized studies that assessed the association between Lp(a) and calcific AS. All but one of the above studies demonstrated significant association between elevated Lp(a) and calcific AS. We conclude that there is convincing evidence supporting a causal association between elevated Lp(a) and calcific AS. In addition, elevated Lp(a) predicts a faster hemodynamic progression of AS, and increased risk of AV replacement, especially in younger patients. Further research into the clinical utility of Lp(a) as a marker for predicting the incidence, progression, and outcomes of sclerodegenerative AV disease is needed.

Identification and analyses of inhibitors targeting apolipoprotein(a) kringle domains KIV-7, KIV-10, and KV provide insight into kringle domain function

Increased plasma concentrations of lipoprotein(a) (Lp(a)) are associated with an increased risk for cardiovascular disease. Lp(a) is composed of apolipoprotein(a) (apo(a)) covalently bound to apolipoprotein B of low-density lipoprotein (LDL). Many of apo(a)'s potential pathological properties, such as inhibition of plasmin generation, have been attributed to its main structural domains, the kringles, and have been proposed to be mediated by their lysine-binding sites. However, available small-molecule inhibitors, such as lysine analogs, bind unselectively to kringle domains and are therefore unsuitable for functional characterization of specific kringle domains. Here, we discovered small molecules that specifically bind to the apo(a) kringle domains KIV-7, KIV-10, and KV. Chemical synthesis yielded compound AZ-05, which bound to KIV-10 with a K_d of 0.8 μm and exhibited more than 100-fold selectivity for KIV-10, compared with the other kringle domains tested, including plasminogen kringle 1. To better understand and further improve ligand selectivity, we determined the crystal structures of KIV-7, KIV-10, and KV in complex with small-molecule ligands at 1.6-2.1 Å resolutions. Furthermore, we used these small molecules as chemical probes to characterize the roles of the different apo(a) kringle domains in in vitro assays. These assays revealed the assembly of Lp(a) from apo(a) and LDL, as well as potential pathophysiological mechanisms of Lp(a), including (i) binding to fibrin, (ii) stimulation of smooth-muscle cell proliferation, and (iii) stimulation of LDL uptake into differentiated monocytes. Our results indicate that a small-molecule inhibitor targeting the lysine-binding site of KIV-10 can combat the pathophysiological effects of Lp(a).

Lipoproteins in Atherosclerosis Process

BACKGROUND

Dyslipidaemias is a recognized risk factor for atherosclerosis, however, new evidence brought to light by trials investigating therapies to enhance HDLcholesterol have suggested an increased atherosclerotic risk when HDL-C is high.

RESULTS

Several studies highlight the central role in atherosclerotic disease of dysfunctional lipoproteins; oxidised LDL-cholesterol is an important feature, according to "oxidation hypothesis", of atherosclerotic lesion, however, there is today a growing interest for dysfunctional HDL-cholesterol. The target of our paper is to review the functions of modified and dysfunctional lipoproteins in atherogenesis.

CONCLUSION

Taking into account the central role recognized to dysfunctional lipoproteins, measurements of functional features of lipoproteins, instead of conventional routine serum evaluation of lipoproteins, could offer a valid contribution in experimental studies as in clinical practice to stratify atherosclerotic risk.

A novel lipoprotein (a) lowering drug, D-47, decreases neointima thickening after vascular injury

Although Lp(a) have been thought to be a cardiovascular risk factor, it is unclear whether lowering Lp(a) levels reduces the risk of cardiovascular diseases. No pharmacological agents which selectively reduce serum Lp(a) levels, and Lp(a) is present in primate but absent in common laboratory animals such as mice and pigs. In the present study we used transgenic mice of human Lp(a) and tested effect a novel Lp(a) lowering drug D-47 on neointima formation after vascular injury. D-47 successfully decreased plasma levels of Lp(a) and possibly inhibited neointima formation in Lp(a) transgenic mice. The results indicate that we can modulate plasma Lp(a) levels by pharmacologic agents and inhibit atherogenic properties of Lp(a) by reducing plasma levels of Lp(a). J. Med. Invest. 64: 64-67, February, 2017.

Effect of Two Lipoprotein (a)-Associated Genetic Variants on Plasminogen Levels and Fibrinolysis

Two genetic variants (rs3798220 and rs10455872) in the apolipoprotein (a) gene (LPA) have been implicated in cardiovascular disease (CVD), presumably through their association with lipoprotein (a) [Lp(a)] levels. While Lp(a) is recognized as a lipoprotein with atherogenic and thrombogenic characteristics, it is unclear whether or not the two Lp(a)-associated genetic variants are also associated with markers of thrombosis (i.e., plasminogen levels and fibrinolysis). In the present study, we genotyped the two genetic variants in 2919 subjects of the Old Order Amish (OOA) and recruited 146 subjects according to the carrier and noncarrier status for rs3798220 and rs10455872, and also matched for gender and age. We measured plasma Lp(a) and plasminogen levels in these subjects, and found that the concentrations of plasma Lp(a) were 2.62- and 1.73-fold higher in minor allele carriers of rs3798220 and rs10455872, respectively, compared with noncarriers (P = 2.04 × 10⁻¹⁷ and P = 1.64 × 10⁻⁶, respectively). By contrast, there was no difference in plasminogen concentrations between carriers and noncarriers of rs3798220 and rs10455872. Furthermore, we observed no association between carrier status of rs3798220 or rs10455872 with clot lysis time. Finally, plasminogen mRNA expression in liver samples derived from 76 Caucasian subjects was not significantly different between carriers and noncarriers of these two genetic variants. Our results provide further insight into the mechanism of action behind two genetic variants previously implicated in CVD risk and show that these polymorphisms are not major modulating factors for plasma plasminogen levels and fibrinolysis.

Long-term Effect of Glimepiride and Rosiglitazone on Non-conventional Cardiovascular Risk Factors in Metformin-treated Patients Affected by Metabolic Syndrome: A Randomized, Double-blind Clinical Trial

We evaluated the effect of glimepiride plus metformin and rosiglitazone plus metformin on glucose, and on cardiovascular risk parameters such as lipoprotein(a) (Lp[a]) and homocysteine (HCT) in patients with type 2 diabetes and metabolic syndrome. Ninety-nine patients in the multicentre, randomized, double-blind study took metformin (1500 mg/day) plus glimepiride (2 mg/day) or rosiglitazone (4 mg/day) for 12 months. Changes in body mass index, glycosylated haemoglobin (HbA1c), Lp(a) and HCT were primary efficacy variables. Fasting plasma glucose (FPG), post-prandial plasma glucose (PPG) and homeostasis model assessment index were also used to assess efficacy. On average, HbA1c decreased by 9.1% and 8.1%, FPG decreased by 7.3% and 10.9%, and PPG decreased by 7.6% and 10.5%, respectively, in the glimepiride and rosiglitazone groups after 12 months. Patients receiving rosiglitazone experienced more rapid improvement in glycaemic control than those on glimepiride, and showed a significant improvement in insulin resistance-related parameters. There was a statistically significant decrease in basal homocysteinaemia in glimepiride-treated patients (−27.3%), but not in rosiglitazone-treated patients. Rosiglitazone plus metformin significantly improved long-term control of insulin resistance-related parameters compared with glimepiride plus metformin, although glimepiride treatment was associated with a slight improvement in cholesterolaemia, not observed in the rosiglitazone-treated patients, and with significant improvements in non-traditional risk factors for cardiovascular disease, such as basal homocysteinaemia and plasma Lp(a) levels.

Distinct metabolism of apolipoproteins (a) and B-100 within plasma lipoprotein(a)

OBJECTIVES

Lipoprotein(a) [Lp(a)] is mainly similar in composition to LDL, but differs in having apolipoprotein (apo) (a) covalently linked to apoB-100. Our purpose was to examine the individual metabolism of apo(a) and apoB-100 within plasma Lp(a).

MATERIALS AND METHODS

The kinetics of apo(a) and apoB-100 in plasma Lp(a) were assessed in four men with dyslipidemia [Lp(a) concentration: 8.9-124.7nmol/L]. All subjects received a primed constant infusion of [5,5,5-(2)H3] L-leucine while in the constantly fed state. Lp(a) was immunoprecipitated directly from whole plasma; apo(a) and apoB-100 were separated by gel electrophoresis; and isotopic enrichment was determined by gas chromatography/mass spectrometry.

RESULTS

Multicompartmental modeling analysis indicated that the median fractional catabolic rates of apo(a) and apoB-100 within Lp(a) were significantly different at 0.104 and 0.263 pools/day, respectively (P=0.04). The median Lp(a) apo(a) production rate at 0.248nmol/kg·day(-1) was significantly lower than that of Lp(a) apoB-100 at 0.514nmol/kg·day(-1) (P=0.03).

CONCLUSION

Our data indicate that apo(a) has a plasma residence time (11days) that is more than twice as long as that of apoB-100 (4days) within Lp(a), supporting the concept that apo(a) and apoB-100 within plasma Lp(a) are not catabolized from the bloodstream as a unit in humans in the fed state.

Targeting lipoprotein (a): an evolving therapeutic landscape

Robust epidemiologic and genetic studies have solidified the role of lipoprotein (a) [Lp(a)] as an independent and causal risk factor for cardiovascular disease. The increased cardiovascular risk of Lp(a) is mediated through both proatherogenic and prothrombotic/antifibrinolytic mechanisms. Several societies recommend Lp(a) screening for patients with high cardiovascular risk, although no consensus exists on the management of patients with elevated Lp(a). However, numerous pharmacologic approaches are being evaluated that have the potential to reduce Lp(a) and will be the focus of this review. The majority of these interventions have been developed for other lipid-lowering indications, but also lower Lp(a). There are also novel therapies in development that specifically target Lp(a). The efficacy of these therapies varies, and their role in the evolving lipoprotein therapeutic landscape has yet to be determined. Nevertheless, targeted Lp(a) reduction is certainly intriguing and will likely continue to be an active area of investigation in the future.

Evidence for several independent genetic variants affecting lipoprotein (a) cholesterol levels

Lipoprotein (a) [Lp(a)] is an independent risk factor for atherosclerosis-related events that is under strong genetic control (heritability = 0.68-0.98). However, causal mutations and functional validation of biological pathways modulating Lp(a) metabolism are lacking. We performed a genome-wide association scan to identify genetic variants associated with Lp(a)-cholesterol levels in the Old Order Amish. We confirmed a previously known locus on chromosome 6q25-26 and found Lp(a) levels also to be significantly associated with a SNP near the APOA5-APOA4-APOC3-APOA1 gene cluster on chromosome 11q23 linked in the Amish to the APOC3 R19X null mutation. On 6q locus, we detected associations of Lp(a)-cholesterol with 118 common variants (P = 5 × 10(-8) to 3.91 × 10(-19)) spanning a ∼5.3 Mb region that included the LPA gene. To further elucidate variation within LPA, we sequenced LPA and identified two variants most strongly associated with Lp(a)-cholesterol, rs3798220 (P = 1.07 × 10(-14)) and rs10455872 (P = 1.85 × 10(-12)). We also measured copy numbers of kringle IV-2 (KIV-2) in LPA using qPCR. KIV-2 numbers were significantly associated with Lp(a)-cholesterol (P = 2.28 × 10(-9)). Conditional analyses revealed that rs3798220 and rs10455872 were associated with Lp(a)-cholesterol levels independent of each other and KIV-2 copy number. Furthermore, we determined for the first time that levels of LPA mRNA were higher in the carriers than non-carriers of rs10455872 (P = 0.0001) and were not different between carriers and non-carriers of rs3798220. Protein levels of apo(a) were higher in the carriers than non-carriers of both rs10455872 and rs3798220. In summary, we identified multiple independent genetic determinants for Lp(a)-cholesterol. These findings provide new insights into Lp(a) regulation.

Guidelines for the primary prevention of stroke: a statement for healthcare professionals from the American Heart Association/American Stroke Association

The aim of this updated statement is to provide comprehensive and timely evidence-based recommendations on the prevention of stroke among individuals who have not previously experienced a stroke or transient ischemic attack. Evidence-based recommendations are included for the control of risk factors, interventional approaches to atherosclerotic disease of the cervicocephalic circulation, and antithrombotic treatments for preventing thrombotic and thromboembolic stroke. Further recommendations are provided for genetic and pharmacogenetic testing and for the prevention of stroke in a variety of other specific circumstances, including sickle cell disease and patent foramen ovale.

Lipoprotein(a) as a therapeutic target in cardiovascular disease

INTRODUCTION

Recent advances in genetics and epidemiology have once again thrust lipoprotein(a) (Lp(a)) into the clinical spotlight. Elevated plasma concentrations of Lp(a) are an independent, causal risk factor for coronary heart disease. The mechanisms underlying the pathogenicity of Lp(a) remain obscure, and uncertainty continues to surround the appropriate use of Lp(a) in the clinic.

AREAS COVERED

We summarize the most recent findings on the biology and epidemiology of Lp(a), and use this as a platform to discuss strategies to lower plasma Lp(a) concentrations. The majority of the existing approaches are not Lp(a) specific since they also improve other aspects of the lipid profile. It is possible, however, that the unique characteristics of Lp(a) can be exploited to design therapeutics to specifically lower Lp(a).

EXPERT OPINION

Lp(a) should be measured in selected patients, including those with a family history of cardiovascular disease (CVD), those with several risk factors for CVD and those who exhibit resistance to statins. Lp(a) lowering should not be the primary driver of choice of therapy, as it has not yet been established through randomized controlled trials that Lp(a) lowering per se has clinical benefit. The development of agents that specifically lower Lp(a) will allow interrogation of this question.

Review of lipid and lipoprotein(a) abnormalities in childhood arterial ischemic stroke

National organizations recommend cholesterol screening in children to prevent vascular disease in adulthood. There are currently no recommendations for cholesterol and lipoprotein (a) testing in children who experience an arterial ischemic stroke. While dyslipidemia and elevated lipoprotein (a) are associated with ischemic stroke in adults, the role of atherosclerotic risk factors in childhood arterial ischemic stroke is not known. A review of the literature was performed from 1966 to April 2012 to evaluate the association between childhood arterial ischemic stroke and dyslipidemia or elevated lipoprotein (a). Of 239 citations, there were 16 original observational studies in children (with or without neonates) with imaging-confirmed arterial ischemic stroke and data on cholesterol or lipoprotein (a) values. Three pairs of studies reported overlapping subjects, and two were eliminated. Among 14 studies, there were data on cholesterol in 7 and lipoprotein (a) in 10. After stroke, testing was performed at >three-months in nine studies, at ≤three-months in four studies, and not specified in one study. There were five case-control studies: four compared elevated lipoprotein (a) and one compared abnormal cholesterol in children with arterial ischemic stroke to controls. A consistent positive association between elevated lipoprotein (a) and stroke was found [Mantel-Haenszel OR 4·24 (2·94-6·11)]. There was no association in one study on total cholesterol, and a positive association in one study on triglycerides. The literature suggests that elevated lipoprotein (a) may be more likely in children with arterial ischemic stroke than in control children. The absence of confirmatory study on dyslipidemia should be addressed with future research.

Apolipoprotein(a) inhibits in vitro tube formation in endothelial cells: identification of roles for Kringle V and the plasminogen activation system

Elevated plasma concentrations of lipoprotein(a) are associated with increased risk for atherothrombotic diseases. Apolipoprotein(a), the unique glycoprotein component of lipoprotein(a), is characterized by the presence of multiple kringle domains, and shares a high degree of sequence homology with the serine protease zymogen plasminogen. It has been shown that angiostatin, a proteolytic fragment of plasminogen containing kringles 1–4, can effectively inhibit angiogenesis. Moreover, proteolytic fragments of plasminogen containing kringle 5 are even more potent inhibitors of angiogenesis than angiostatin. Despite its strong similarity with plasminogen, the role of apolipoprotein(a) in angiogenesis remains controversial, with both pro- and anti-angiogenic effects reported. In the current study, we evaluated the ability of apolipoprotein(a) to inhibit VEGF- and angiopoietin-induced tube formation in human umbilical cord endothelial cells. A 17 kringle-containing form of recombinant apo(a) (17K), corresponding to a well-characterized, physiologically-relevant form of the molecule, effectively inhibited tube formation induced by either VEGF or angiopoietin-1. Using additional recombinant apolipoprotein(a) (r-apo(a)) variants, we demonstrated that this effect was dependent on the presence of an intact lysine-binding site in kringle V domain of apo(a), but not on the presence of the functional lysine-binding site in apo(a) kringle IV type 10; sequences within in the amino-terminal half of the molecule were also not required for the inhibitory effects of apo(a). We also showed that the apo(a)-mediated inhibition tube formation could be reversed, in part by the addition of plasmin or urokinase plasminogen activator, or by removal of plasminogen from the system. Further, we demonstrated that apo(a) treated with glycosidases to remove sialic acid was significantly less effective in inhibiting tube formation. This is the first report of a functional role for the glycosylation of apo(a) although the mechanisms underlying this observation remain to be determined in the context of angiogenesis.

Lipoprotein(a) and family history of cardiovascular disease in children with familial dyslipidemias

OBJECTIVE

To investigate in children and adolescents with familial dyslipidemias the association between lipoprotein(a) [Lp(a)] level and family history of cardiovascular disease (CVD), and whether this association is independent of the disturbed lipid profile.

STUDY DESIGN

Lp(a) level, lipid profile, and a 2-generation genealogic tree to detect cardiovascular events were evaluated in 231 patients with familial dyslipidemias. Lp(a) levels were stratified according to presence, age of occurrence, and number and type of cardiovascular events in the patient's kindreds.

RESULTS

Lp(a) and other plasma lipid fractions did not differ between patients with and those without a family history of cardiovascular events. However, the percentage of patients with elevated Lp(a) level (≥85th percentile) was higher in those with a positive family history for early cardiovascular events (P = .01). Lp(a) level was a significant independent predictor of the number of premature cardiovascular events (β = 0.17; P = .01) and of cerebrovascular events in kindreds (OR, 2.5; 95% CI, 1.05-6.03; P = .039), independent of plasma lipid fractions and other cardiovascular risk factors.

CONCLUSIONS

In children and adolescents with familial dyslipidemias, the overall association between Lp(a) level and family history of early CVD may be due to a threshold effect in those with the highest Lp(a) levels. However, multiple cardiovascular events and cerebrovascular events are predicted by any increase in plasma Lp(a) level, independent of other cardiovascular risk factors.

Proteomics of Lipoprotein(a) identifies a protein complement associated with response to wounding

Lipoprotein(a) [Lp(a)] is a major independent risk factor for cardiovascular disease. Twenty percent of the general population exhibit levels above the risk threshold highlighting the importance for clinical and basic research. Comprehensive proteomics of human Lp(a) will provide significant insights into Lp(a) physiology and pathogenicity. Using liquid chromatography-coupled mass spectrometry, we established a high confidence Lp(a) proteome of 35 proteins from highly purified particles. Protein interaction network analysis and functional clustering revealed proteins assigned to the two major biological processes of lipid metabolism and response to wounding. The latter includes the processes of coagulation, complement activation and inflammatory response. Furthermore, absolute protein quantification of apoB-100, apo(a), apoA1, complement C3 and PON1 gave insights into the compositional stoichiometry of associated proteins per particle. Our proteomics study has identified Lp(a)-associated proteins that support a suggested role of Lp(a) in response to wounding which points to mechanisms of Lp(a) pathogenicity at sites of vascular injury and atherosclerotic lesions. This study has identified a high confidence Lp(a) proteome and provides an important basis for further comparative and quantitative analyses of Lp(a) isolated from greater numbers of plasma samples to investigate the significance of associated proteins and their dynamics for Lp(a) pathogenicity.

Enigmatic role of lipoprotein(a) in cardiovascular disease

Lipoprotein (a), [Lp(a)] has many properties in common with low-density lipoprotein, (LDL) but contains a unique protein apolipoprotein(a), linked to apolipoprotein B-100 by a single disulfide bond. There is a substantial size heterogeneity of apo(a), and generally smaller apo(a) sizes tend to correspond to higher plasma Lp(a) levels, but this relation is far from linear, underscoring the importance to assess allele-specific apo(a) levels. The presence of apo(a), a highly charged, carbohydrate-rich, hydrophilic protein may obscure key features of the LDL moiety and offer opportunities for binding to vessel wall elements. Recently, interest in Lp(a) has increased because studies over the past decade have confirmed and more robustly demonstrated a risk factor role of Lp(a) for cardiovascular disease. In particular, levels of Lp(a) carried in particles with smaller size apo(a) isoforms are associated with coronary artery disease (CAD). Other studies suggest that proinflammatory conditions may modulate risk factor properties of Lp(a). Further, Lp(a) may act as a preferential acceptor for proinflammatory oxidized phospholipids transferred from tissues or from other lipoproteins. However, at present only a limited number of agents (e.g., nicotinic acid and estrogen) has proven efficacy in lowering Lp(a) levels. Although Lp(a) has not been definitely established as a cardiovascular risk factor and no guidelines presently recommend intervention, Lp(a)-lowering therapy might offer benefits in subgroups of patients with high Lp(a) levels.

Antiangiogenic kringles derived from human plasminogen and apolipoprotein(a) inhibit fibrinolysis through a mechanism that requires a functional lysine-binding site

Many proteins in the fibrinolysis pathway contain antiangiogenic kringle domains. Owing to the high degree of homology between kringle domains, there has been a safety concern that antiangiogenic kringles could interact with common kringle proteins during fibrinolysis leading to adverse effects in vivo. To address this issue, we investigated the effects of several antiangiogenic kringle proteins including angiostatin, apolipoprotein(a) kringles IV(9)-IV(10)-V (LK68), apolipoprotein(a) kringle V (rhLK8) and a derivative of rhLK8 mutated to produce a functional lysine-binding site (Lys-rhLK8) on the entire fibrinolytic process in vitro and analyzed the role of lysine binding. Angiostatin, LK68 and Lys-rhLK8 increased clot lysis time in a dose-dependent manner, inhibited tissue-type plasminogen activator-mediated plasminogen activation on a thrombin-modified fibrinogen (TMF) surface, showed binding to TMF and significantly decreased the amount of plasminogen bound to TMF. The inhibition of fibrinolysis by these proteins appears to be dependent on their functional lysine-binding sites. However, rhLK8 had no effect on these processes owing to an inability to bind lysine. Collectively, these results indicate that antiangiogenic kringles without lysine binding sites might be safer with respect to physiological fibrinolysis than lysine-binding antiangiogenic kringles. However, the clinical significance of these findings will require further validation in vivo.

Guidelines for the primary prevention of stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association

BACKGROUND AND PURPOSE

This guideline provides an overview of the evidence on established and emerging risk factors for stroke to provide evidence-based recommendations for the reduction of risk of a first stroke.

METHODS

Writing group members were nominated by the committee chair on the basis of their previous work in relevant topic areas and were approved by the American Heart Association (AHA) Stroke Council Scientific Statement Oversight Committee and the AHA Manuscript Oversight Committee. The writing group used systematic literature reviews (covering the time since the last review was published in 2006 up to April 2009), reference to previously published guidelines, personal files, and expert opinion to summarize existing evidence, indicate gaps in current knowledge, and when appropriate, formulate recommendations using standard AHA criteria (Tables 1 and 2). All members of the writing group had the opportunity to comment on the recommendations and approved the final version of this document. The guideline underwent extensive peer review by the Stroke Council leadership and the AHA scientific statements oversight committees before consideration and approval by the AHA Science Advisory and Coordinating Committee.

RESULTS

Schemes for assessing a person's risk of a first stroke were evaluated. Risk factors or risk markers for a first stroke were classified according to potential for modification (nonmodifiable, modifiable, or potentially modifiable) and strength of evidence (well documented or less well documented). Nonmodifiable risk factors include age, sex, low birth weight, race/ethnicity, and genetic predisposition. Well-documented and modifiable risk factors include hypertension, exposure to cigarette smoke, diabetes, atrial fibrillation and certain other cardiac conditions, dyslipidemia, carotid artery stenosis, sickle cell disease, postmenopausal hormone therapy, poor diet, physical inactivity, and obesity and body fat distribution. Less well-documented or potentially modifiable risk factors include the metabolic syndrome, excessive alcohol consumption, drug abuse, use of oral contraceptives, sleep-disordered breathing, migraine, hyperhomocysteinemia, elevated lipoprotein(a), hypercoagulability, inflammation, and infection. Data on the use of aspirin for primary stroke prevention are reviewed.

CONCLUSIONS

Extensive evidence identifies a variety of specific factors that increase the risk of a first stroke and that provide strategies for reducing that risk.

Serum lipoprotein (a) levels in patients with first unprovoked venous thromboembolism is not associated with subsequent risk of recurrent VTE

INTRODUCTION

Case-control studies suggest that elevated lipoprotein (a) (Lp(a)) is a risk factor for first venous thromboembolism (VTE). Lp(a) has not been prospectively investigated as a possible risk factor for recurrent VTE in first unprovoked VTE patients. We sought to determine if serum Lp(a) levels in patients with unprovoked VTE who discontinue anticoagulants after 5 to 7 months of therapy predict VTE recurrence in a prospective cohort study.

MATERIALS AND METHODS

Serum Lp(a) measurements were obtained from 510 first unprovoked VTE patients treated for 5 -7 months with anticoagulants in a 12 center study. Patients were subsequently followed for a mean of 16.9 months (SD+/-11.2) for symptomatic VTE recurrence which was independently adjudicated with reference to baseline imaging.

RESULTS

There was no significant association between Lp(a) as a continuous variable and recurrent VTE nor in gender stratified subgroups. No statistically significant differences were observed in the median Lp(a) concentrations between patients who recurred and those who did not recur (median (interquartile range): 0.09 g/L (0.17) versus 0.06 g/L (0.11) respectively; p=0.15). The Lp(a) cut-off point of 0.3g/L was not significantly associated with recurrent VTE for the overall population nor in gender stratified subgroups.

CONCLUSIONS

Elevated serum Lp(a) does not appear to be associated with recurrent VTE in patients with history of first unprovoked VTE and may not play a role in identifying patients with unprovoked VTE at high risk of recurrence. There was no optimal predictive threshold for the overall population or for sex sub-groups and Lp(a)>or=0.3 g/L was not a significant predictor of recurrent VTE.

Association of Apo(a)isoform size with dyslipoproteinemia in male venous thrombosis patients

BACKGROUND

Lp(a) is a proatherogenic lipoprotein that may also be prothrombotic. Apo(a) size isoforms have differential effects on fibrinolysis. Whereas Lp(a) concentrations have been linked to venous thromboembolic disease (VTE) risk, apo(a) polymorphisms in VTE have not been studied.

METHODS

We used a standardized high resolution agarose gel electrophoresis technique to determine apo(a) isoform size, and a Lp(a) immunoassay insensitive to apo(a) size to measure Lp(a) concentration in 46 men with VTE and 46 age-matched healthy controls.

RESULTS

Apo(a) isoform distribution in VTE cases and controls was bimodal and VTE patients tended to have more medium-sized isoforms K(4)-(19-27) (54.3% vs. 34.8%, p=0.06). Cases and controls had the same median predominant apo(a) size isoform (23.5 K(4) repeats) and comparable Lp(a) concentrations. However, subgroup analysis based on apo(a) isoform size (K(4)< or =23 or K(4)> or =24) revealed that cases in the K(4)> or =24 subgroup had higher Lp(a) concentrations than the controls in this isofrom subgroup (14.5 mmol vs. 6.6 mmol, p=0.029). Also, dyslipoproteinemia (smaller LDL and HDL particles, higher LDL and lower HDL parameters) was strongly associated with VTE only in this larger apo(a) isoform group.

CONCLUSIONS

These observations provide the first evidence that determination of apo(a) isoforms may provide useful novel insights into VTE risk.

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.

Targeting cerebrovascular Rho-kinase in stroke

BACKGROUND

Rho and Rho-associated kinase (ROCK) play pivotal roles in pathogenesis of vascular diseases including stroke. ROCK is expressed in all cell types relevant to stroke, and regulates a range of physiological processes.

OBJECTIVE

To provide an overview of ROCK as an experimental therapeutic target in cerebral ischemia, and the translational opportunities and obstacles in the prophylaxis and treatment of stroke.

METHODS

Relevant literature was reviewed.

RESULTS

ROCK activity is upregulated in chronic vascular risk factors such as diabetes, hyperlipidemia and hypertension, and more acutely by cerebral ischemia. ROCK activation is predicted to increase the risk of cerebral ischemia, and worsen the ischemic tissue outcome and functional recovery. Evidence suggests that ROCK inhibition is protective in models of cerebral ischemia. The benefit is mediated through multiple mechanisms.

CONCLUSION

ROCK is a promising therapeutic target in all stages of stroke.

Apolipoprotein(a) inhibits the conversion of Glu-plasminogen to Lys-plasminogen: a novel mechanism for lipoprotein(a)-mediated inhibition of plasminogen activation

BACKGROUND

Elevated plasma concentrations of lipoprotein(a) [Lp(a)] are associated with an increased risk for thrombotic disorders. Lp(a) is a unique lipoprotein consisting of a low-density lipoprotein-like moiety covalently linked to apolipoprotein(a) [apo(a)], a homologue of the fibrinolytic proenzyme plasminogen. Several in vitro and in vivo studies have shown that Lp(a)/apo(a) can inhibit tissue-type plasminogen activator-mediated plasminogen activation on fibrin surfaces, although the mechanism of inhibition by apo(a) remains controversial. Essential to fibrin clot lysis are a number of plasmin-dependent positive feedback reactions that enhance the efficiency of plasminogen activation, including the plasmin-mediated conversion of Glu-plasminogen to Lys-plasminogen.

OBJECTIVE

Using acid-urea gel electrophoresis to resolve the two forms of radiolabeled plasminogen, we determined whether apo(a) is able to inhibit Glu-plasminogen to Lys-plasminogen conversion.

METHODS

The assays were performed in the absence or presence of different recombinant apo(a) species, including point mutants, deletion mutants and variants that represent greater than 90% of the known apo(a) isoform sizes.

RESULTS

Apo(a) substantially suppressed Glu-plasminogen conversion. Critical roles were identified for the kringle IV types 5-9 and kringle V; contributory roles for sequences within the amino-terminal half of the molecule were also observed. Additionally, with the exception of the smallest naturally-occurring isoform of apo(a), isoform size was found not to contribute to the inhibitory capacity of apo(a).

CONCLUSION

These findings underscore a novel contribution to the understanding of Lp(a)/apo(a)-mediated inhibition of plasminogen activation: the ability of the apo(a) component of Lp(a) to inhibit the key positive feedback step of plasmin-mediated Glu-plasminogen to Lys-plasminogen conversion.

Elevated Lp(a) with a small apo(a) isoform in children: risk factor for the development of premature coronary artery disease

BACKGROUND

levels of Lp(a) and low-molecular-weight apolipoprotein(a) isoform are strongly associated with the development of early cardiovascular disease. Certain types of apo(a) isoforms in combination with elevated levels of Lp(a) may be important in the determining of premature coronary artery disease. Therefore, we investigated the association of familial history of premature coronary artery disease and apo(a) size and Lp(a) levels in children and adolescents with hypercholesterolemia using a novel method determining apo(a) isoforms.

METHODS AND RESULTS

Isoforms were classified in six phenotype patterns: S1-S4, B, F and according to their K-IV repeats. Apo(a) isoforms were divided into two groups: low-molecular- and high-molecular apo(a) isoforms. In subjects with double-banded apo(a) isoforms containing a small- and a large-isoform Lp(a) each contribution was based on the intensity of staining of the two bands. The percentage of patients with elevated levels of Lp(a) and a small apo(a) isoform (i.e. elevated small-isoform Lp(a)) was 46% in the risk group and 20% in the control group, p < 0.05. The percentage number of children and adolescents with elevated Lp(a) levels was higher in the risk group, reaching statistical significance (p < 0.05).

CONCLUSION

Elevated levels of small-isoform Lp(a) might be a strong and independent risk factor for the development of premature coronary artery disease in children and adolescents with hypercholesterolemia.

Hypercoagulability markers in patients with peripheral arterial disease: association to ankle-brachial index

Peripheral arterial disease is diagnosed by measuring the ankle-brachial index. Values lower than 0.90 define the disease being usually related to its severity. Patients with peripheral arterial disease may show a hypercoagulability state. The aim of this study was to assess hemostatic variables and to correlate them with the presence of peripheral arterial disease and its severity as assessed by ankle-brachial index values. Plasma levels of D dimer, plasminogen, prothrombin fragment 1+2, plasminogen activator inhibitor and thrombomodulin were measured in 36 patients with peripheral arterial disease (group 1) and 30 without disease (group 2). Significant differences for D dimer, plasminogen, prothrombin fragment 1+2 and plasminogen activator inhibitor type 1 between the 2 groups were found (P<0.05). Significant and inverse correlations were also observed (Pearson correlation, P<0.05) between ankle-brachial index values and levels of both plasminogen and plasminogen activator inhibitor type 1. Although there was no significant correlation between ankle-brachial index and levels of D dimer, higher D dimer values were observed in patients with lower ankle-brachial index values. The results confirm a trend to hypercoagulability and hypofibrinolysis in patients with peripheral arterial disease. Increased levels of plasminogen activator inhibitor type 1 seem to be associated with the severity of the disease, considering the inverse correlation between this inhibitor and ankle-brachial index.

Relationship of apoE polymorphism with lipoprotein(a), apoA, apoB and lipid levels in atherosclerotic infarct

BACKGROUND AND PURPOSE

Apolipoprotein E (apoE) polymorphism is suggested to be a risk factor in stroke in some populations, either by affecting lipid parameters or independently. Its effect on lipoprotein(a) [Lp(a)] is not known. The roles of apoE polymorphism and of high Lp(a) levels in atherosclerotic stroke (AS) in the Turkish population are unclear. Our aim was to investigate the relationship of apoE alleles and Lp(a) level with AS and the relationship of apoE alleles with Lp(a) and other lipid parameters.

METHODS

ApoE polymorphisms and lipid parameters were prospectively evaluated in 85 patients and 77 controls with normal brain imaging.

RESULTS

Only hypertension, diabetes mellitus, associated vascular diseases and decreased high-density lipoprotein cholesterol levels were found to be independent risk factors for stroke. However, in the presence of apoE/E4 allele, increased low-density lipoprotein cholesterol (LDL-chol), apolipoprotein B (apoB) and Lp(a) levels and in the presence of apo E/E3 allele, only Lp(a) levels were determined as risk factors.

CONCLUSION

This study showed that while apoE polymorphism was not a risk factor itself, high Lp(a), LDL-chol and apoB were determined to be risk factors in E3 or E4 carriers.

Inherited Thrombophilia

Inherited thrombophilia can be defined as a genetically determined predisposition to the development of thromboembolic complications. Since the discovery of activated protein C resistance in 1993, several additional disorders have been described and, at present, it is possible to identify an inherited predisposition in about 60 to 70% of patients with such complications. These inherited prothrombotic risk factors include qualitative or quantitative defects of coagulation factor inhibitors, increased levels or function of coagulation factors, defects of the fibrinolytic system, altered platelet function, and hyperhomocysteinemia. In this review, the main inherited prothrombotic risk factors are analyzed from epidemiological, laboratory, clinical, and therapeutic points of view. Finally, we discuss the synergism between genetic and acquired prothrombotic risk factors in particular conditions such as childhood and pregnancy.

Polymorphism in the apolipoprotein(a) gene, plasma lipoprotein(a), cardiovascular disease, and low-dose aspirin therapy

OBJECTIVE

A minor allele variant (rs3798220) of apolipoprotein(a) has been reported to be associated with elevated plasma lipoprotein(a) [Lp(a)] and increased cardiovascular risk. We investigated whether this allele was associated with elevated Lp(a) and cardiovascular risk in the Women's Health Study, a randomized trial of low-dose aspirin, and whether aspirin reduced cardiovascular risk in minor allele carriers.

METHODS AND RESULTS

Genotypes of rs3798220 were determined for 25,131 initially healthy Caucasian participants. Median Lp(a) levels at baseline were 10.0, 79.5, and 153.9mg/dL for major allele homozygotes, heterozygotes, and minor allele homozygotes, respectively (P<0.0001). During the 9.9 years of follow-up, minor allele carriers (3.7%) in the placebo group had twofold higher risk of major cardiovascular events than non-carriers (age-adjusted hazard ratio (HR)=2.21, 95% CI: 1.39-3.52). Among carriers, risk was reduced more than twofold by aspirin: for aspirin compared with placebo the age-adjusted HR was 0.44 (95% CI: 0.20-0.94); risk was not significantly reduced among non-carriers (age-adjusted HR=0.91, 95% CI: 0.77-1.08). This interaction between carrier status and aspirin allocation was significant (P=0.048).

CONCLUSIONS

In the Women's Health Study, carriers of an apolipoprotein(a) variant had elevated Lp(a), doubled cardiovascular risk, and appeared to benefit more from aspirin than non-carriers.

Lipoprotein[a] and cancer: Anti-neoplastic effect besides its cardiovascular potency

While the death rate from cancer has substantially decreased over the past decade, the search for effective and tolerable therapies is a great challenge as yet. The evidence that malignant cells cannot grow to a clinically detectable tumor mass and spread in the absence of an adequate vascular support, has opened a new area of research towards the selective inhibition or even destruction of tumor vessels. Angiostatin and angiostatin-related proteins are a family of specific angiogenesis inhibitors produced by tumors from a family of naturally occurring proteins, which also includes plasminogen and lipoprotein[a]. The anti-angiogenic activity of these proteins resides in cryptic and highly-repetitive molecular domains hidden within the protein moiety, called kringles. Lipoprotein[a] is an intriguing molecule consisting of a low-density lipoprotein core in addition to the covalently bound apolipoprotein[a]. Apolipoprotein[a] is characterized by an inactive protease domain, a single copy of the plasminogen kringle V and multiple repeats of domains homologous to the plasminogen kringle IV. Reliable studies on animal models indicate that the proteolytic break-down products of apolipoprotein[a] would posses anti-angiogenic and anti-tumoral properties both in vitro and in vivo, a premise to develop novel therapeutic modalities which may efficiently suppress tumor growth and metastasis. This review is focused on the biochemical structure, metabolism and the anti-angiogenic activity of this unique and elusive kringle-containing lipoprotein.

Plasma Lipoprotein(a) Indicates Risk for 4 Distinct Forms of Vascular Disease

Background: Increased lipoprotein(a) [Lp(a)] concentrations are predictive for coronary artery disease (CAD). The risk conferred by Lp(a) for other types of vascular disease compared with CAD has not been investigated within a single population. This study aimed to investigate Lp(a) risk association for 4 different types of vascular disease (including CAD) within a predominantly white population.

Methods: We used an Lp(a) ELISA that measures Lp(a) independently of apolipoprotein(a) size to measure plasma Lp(a) in patients [384 CAD, 262 peripheral vascular disease, 184 ischemic stroke (stroke), 425 abdominal aortic aneurysm] and 230 disease-free controls. We then conducted association studies with logistic regression, integrating the potential confounding effects of age, sex, diabetes, plasma lipids, and a history of previous hypertension, hypercholesterolemia, and smoking.

Results: Multivariate analyses with Lp(a) concentrations of &gt;45 nmol/L (the 75th percentile value for controls) as the clinical cutoff showed increased Lp(a) concentrations to be a risk factor for all disease groups, with adjusted odds ratios ranging from 1.96 [95% confidence interval (CI) 1.24–3.08] for CAD to 2.33 (95% CI 1.39–3.89) for PVD. The risk conferred by Lp(a) appeared to be independent of other confounders, including exposure to statin/fibrate therapies. Similar odds ratios and CIs between disease groups indicated that increased Lp(a) conferred a similar risk for all groups studied.

Conclusions: Lp(a) constitutes a stable risk factor of similar magnitude for 4 major forms of vascular disease. This association was not altered by exposure to standard lipid-lowering therapy.

Lipoprotein(a) as a risk factor associated with ischemic heart disease: Ouro Preto Study

Evidences suggest that lipoprotein(a) [Lp(a)] is an important risk factor for cardiovascular disease. However, literature has been controversial in confirming its role as an independent risk factor for cardiovascular disease. The objective of the present study is to evaluate the association between serum levels of Lp(a) and ischemic heart disease as well as other cardiovascular risk factors in a population-based study conducted on a local cohort of the Brazilian population. Lp(a) serum levels were measured in 400 individuals selected from a larger sample of a populational survey carried out in Ouro Preto, a city in the southeast of Brazil. Lipid profile, fasting blood glucose, anthropometric and clinical parameters were analyzed. Lp(a) levels were significantly associated with the presence of ischemic heart disease. In relation to other cardiovascular risk factors, it was verified that Lp(a) levels were statistically associated with age, total cholesterol, LDL-cholesterol and percentage of body fat determined by bioelectric impedance. Lp(a) was also highly associated with the Framingham risk score (p=0.003). In a multivariate analysis two significant interactions were revealed; one involving ischemic heart disease, sex and age and other associating ischemic heart disease, age and total cholesterol. In summary, in the present analysis Lp(a) serum levels were correlated with the occurrence of ischemic heart disease and other cardiovascular risk factors.

Lipoprotein (a) and risk of ischemic stroke in young adults

Lipoprotein (a) [Lp(a)] is a LDL-particle linked to apoprotein (a) [apo(a)]. High Lp(a) plasma level is a risk factor for coronary heart disease and, in older men, for ischemic stroke. The role of Lp(a) as a risk factor for ischemic stroke in young adults is uncertain.

METHODS

Lp(a) concentration was prospectively measured in 100 consecutive patients with acute ischemic stroke (58 men and 42 women) aged 18-55 years, and in 100 controls matched for age and gender.

RESULTS

The distribution of Lp(a) concentration was skewed toward the highest and median tertiles in male patients. In multivariate logistic regression analyses adjusting on classical risk factors for ischemic stroke and lipid variables, Lp(a) concentration in the highest and medium tertiles compared with the lowest tertile was significantly associated with ischemic stroke in men (OR 3.55, 95% CI 1.33-9.48, p = 0.012), but was not in women (OR 0.42, 95% CI 0.14-1.26, p = 0.12). Although large vessel atherosclerosis was more common in men than in women, there were no differences in Lp(a) concentration according to the cause of ischemic stroke.

CONCLUSION

Among subjects aged 18-55 years, a slightly elevated Lp(a) concentration was strongly and independently associated with ischemic stroke in men, but not in women. Further studies are required to elucidate the mechanisms underlying this gender-specific association.

Lipoprotein(a): A Unique Risk Factor for Cardiovascular Disease

Lipoprotein(a) (Lp(a)) is present in humans and primates. It has many properties in common with low-density lipoprotein, but contains a unique protein moiety designated apo(a), which is linked to apolipoprotein B-100 by a single disulfide bond. International standards for Lp(a) measurement and optimized Lp(a) assays insensitive to isoform size are not yet widely available. Lp(a) is a risk factor for coronary artery disease, and smaller size apo(a) is associated with coronary artery disease. The physiologic role of Lp(a) is unknown.