The 10 essential questions regarding lipoprotein(a)

PURPOSE OF REVIEW

Lp(a) is one of the most atherogenic lipoproteins, and significant progress has been made to understand its pathophysiology over the last 20 years. There are now selective therapies in late-stage clinical trials to lower Lp(a). Yet there are many outstanding questions about Lp(a). This review outlines 10 of the most burning questions and tries to answer some of them.

RECENT FINDINGS

Antisense oligonucleotide (ASO) treatment is currently the most advanced therapy to lower plasma Lp(a) by 60-80%. There are, however, also two small molecule medications in early stage of development with similar efficacy.

SUMMARY

This review aims to answer important preclinical and clinical questions about the metabolism and physiological role of Lp(a) and also outlines possible therapeutic approaches with nutraceuticals, currently available lipid-lowering therapies and new medications. In addition, ways are illustrated to use Lp(a) as a marker to better predict cardiovascular risk.

Australian Atherosclerosis Society Position Statement on Lipoprotein(a): Clinical and Implementation Recommendations

This position statement provides guidance to cardiologists and related specialists on the management of adult patients with elevated lipoprotein(a) [Lp(a)]. Elevated Lp(a) is an independent and causal risk factor for atherosclerotic cardiovascular disease (ASCVD) and calcific aortic valve disease (CAVD). While circulating Lp(a) levels are largely determined by ancestry, they are also influenced by ethnicity, hormones, renal function, and acute inflammatory events, such that measurement should be done after accounting for these factors. Further, circulating Lp(a) concentrations should be estimated using an apo(a)-isoform independent assay that employs appropriate calibrators and reports the results in molar units (nmol/L). Selective screening strategies of high-risk patients are recommended, but universal screening of the population is currently not advised. Testing for elevated Lp(a) is recommended in all patients with premature ASCVD and those considered to be at intermediate-to-high risk of ASCVD. Elevated Lp(a) should be employed to assess and stratify risk and to enable a decision on initiation or intensification of preventative treatments, such as cholesterol lowering therapy. In adult patients with elevated Lp(a) at intermediate-to-high risk of ASCVD, absolute risk should be reduced by addressing all modifiable behavioural, lifestyle, psychosocial and clinical risk factors, including maximising cholesterol-lowering with statin and ezetimibe and, where appropriate, PCSK9 inhibitors. Apheresis should be considered in patients with progressive ASCVD. New ribonucleic acid (RNA)-based therapies which directly lower Lp(a) are undergoing clinical trials.

Lp(a) and the Risk for Cardiovascular Disease: Focus on the Lp(a) Paradox in Diabetes Mellitus

Lipoprotein(a) (Lp(a)) is one of the strongest causal risk factors of atherosclerotic disease. It is rich in cholesteryl ester and composed of apolipoprotein B and apo(a). Plasma Lp(a) levels are determined by apo(a) transcriptional activity driven by a direct repeat (DR) response element in the apo(a) promoter under the control of (HNF)4α Farnesoid-X receptor (FXR) ligands play a key role in the downregulation of APOA expression. In vitro studies on the catabolism of Lp(a) have revealed that Lp(a) binds to several specific lipoprotein receptors; however, their in vivo role remains elusive. There are more than 1000 publications on the role of diabetes mellitus (DM) in Lp(a) metabolism; however, the data is often inconsistent and confusing. In patients suffering from Type-I diabetes mellitus (T1DM), provided they are metabolically well-controlled, Lp(a) plasma concentrations are directly comparable to healthy individuals. In contrast, there exists a paradox in T2DM patients, as many of these patients have reduced Lp(a) levels; however, they are still at an increased cardiovascular risk. The Lp(a) lowering mechanism observed in T2DM patients is most probably caused by mutations in the mature-onset diabetes of the young (MODY) gene and possibly other polymorphisms in key transcription factors of the apolipoprotein (a) gene (APOA).

Lp(a) and the Risk for Cardiovascular Disease: Focus on the Lp(a) Paradox in Diabetes Mellitus

Lipoprotein(a) (Lp(a)) is one of the strongest causal risk factors of atherosclerotic disease. It is rich in cholesteryl ester and composed of apolipoprotein B and apo(a). Plasma Lp(a) levels are determined by apo(a) transcriptional activity driven by a direct repeat (DR) response element in the apo(a) promoter under the control of (HNF)4α Farnesoid-X receptor (FXR) ligands play a key role in the downregulation of APOA expression. In vitro studies on the catabolism of Lp(a) have revealed that Lp(a) binds to several specific lipoprotein receptors; however, their in vivo role remains elusive. There are more than 1000 publications on the role of diabetes mellitus (DM) in Lp(a) metabolism; however, the data is often inconsistent and confusing. In patients suffering from Type-I diabetes mellitus (T1DM), provided they are metabolically well-controlled, Lp(a) plasma concentrations are directly comparable to healthy individuals. In contrast, there exists a paradox in T2DM patients, as many of these patients have reduced Lp(a) levels; however, they are still at an increased cardiovascular risk. The Lp(a) lowering mechanism observed in T2DM patients is most probably caused by mutations in the mature-onset diabetes of the young (MODY) gene and possibly other polymorphisms in key transcription factors of the apolipoprotein (a) gene (APOA).

Essentials of a new clinical practice guidance on familial hypercholesterolaemia for physicians

Familial hypercholesterolaemia (FH) is a common, heritable and preventable cause of premature coronary artery disease. New clinical practice recommendations are presented to assist practitioners in enhancing the care of all patients with FH. Core recommendations are made on the detection, diagnosis, assessment and management of adults, children and adolescents with FH. Management is under-pinned by the precepts of risk stratification, adherence to healthy lifestyles, treatment of non-cholesterol risk factors and appropriate use of low-density lipoprotein (LDL)-cholesterol-lowering therapies including statins, ezetimibe and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. The recommendations need to be utilised using judicious clinical judgement and shared decision-making with patients and families. New government-funded schemes for genetic testing and use of PCSK9 inhibitors, as well as the National Health Genomics Policy Framework, will enable adoption of the recommendations. However, a comprehensive implementation science and practice strategy is required to ensure that the guidance translates into benefit for all families with FH.

Synopsis of an integrated guidance for enhancing the care of familial hypercholesterolaemia: an Australian perspective

Introduction

Familial hypercholesterolaemia (FH) is a common, heritable and preventable cause of premature coronary artery disease, with significant potential for positive impact on public health and healthcare savings. New clinical practice recommendations are presented in an abridged guidance to assist practitioners in enhancing the care of all patients with FH.

Main recommendations

Core recommendations are made on the detection, diagnosis, assessment and management of adults, children and adolescents with FH. There is a key role for general practitioners (GPs) working in collaboration with specialists with expertise in lipidology. Advice is given on genetic and cholesterol testing and risk notification of biological relatives undergoing cascade testing for FH; all healthcare professionals should develop skills in genomic medicine. Management is under-pinned by the precepts of risk stratification, adherence to healthy lifestyles, treatment of non-cholesterol risk factors, and appropriate use of low-density lipoprotein (LDL)-cholesterol lowering therapies, including statins, ezetimibe and proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors. Recommendations on service design are provided in the full guidance.

Potential impact on care of FH

These recommendations need to be utilised using judicious clinical judgement and shared decision making with patients and families. Models of care need to be adapted to both local and regional needs and resources. In Australia new government funded schemes for genetic testing and use of PCSK9 inhibitors, as well as the National Health Genomics Policy Framework, will enable adoption of these recommendations. A broad implementation science strategy is, however, required to ensure that the guidance translates into benefit for all families with FH.

Integrated Guidance for Enhancing the Care of Familial Hypercholesterolaemia in Australia

Familial hypercholesterolaemia (FH) is a dominant and highly penetrant monogenic disorder present from birth that markedly elevates plasma low-density lipoprotein (LDL)-cholesterol concentration and, if untreated, leads to premature atherosclerosis and coronary artery disease (CAD). There are approximately 100,000 people with FH in Australia. However, an overwhelming majority of those affected remain undetected and inadequately treated, consistent with FH being a leading challenge for public health genomics. To further address the unmet need, we provide an updated guidance, presented as a series of systematically collated recommendations, on the care of patients and families with FH. These recommendations have been informed by an exponential growth in published works and new evidence over the last 5 years and are compatible with a contemporary global call to action on FH. Recommendations are given on the detection, diagnosis, assessment and management of FH in adults and children. Recommendations are also made on genetic testing and risk notification of biological relatives who should undergo cascade testing for FH. Guidance on management is based on the concepts of risk re-stratification, adherence to heart healthy lifestyles, treatment of non-cholesterol risk factors, and safe and appropriate use of LDL-cholesterol lowering therapies, including statins, ezetimibe, proprotein convertase subtilisin/kexin type 9 inhibitors and lipoprotein apheresis. Broad recommendations are also provided for the organisation and development of health care services. Recommendations on best practice need to be underpinned by good clinical judgment and shared decision making with patients and families. Models of care for FH need to be adapted to local and regional health care needs and available resources. A comprehensive and realistic implementation strategy, informed by further research, including assessments of cost-benefit, will be required to ensure that this new guidance benefits all Australian families with or at risk of FH.

Gaps in the Care of Familial Hypercholesterolaemia in Australia: First Report From the National Registry

BACKGROUND

Familial hypercholesterolaemia (FH) is under-diagnosed and under-treated worldwide, including Australia. National registries play a key role in identifying patients with FH, understanding gaps in care and advancing the science of FH to improve care for these patients.

METHODS

The FH Australasia Network has established a national web-based registry to raise awareness of the condition, facilitate service planning and inform best practice and care services in Australia. We conducted a cross-sectional analysis of 1,528 FH adults enrolled in the registry from 28 lipid clinics.

RESULTS

The mean age at enrolment was 53.4±15.1 years, 50.5% were male and 54.3% had undergone FH genetic testing, of which 61.8% had a pathogenic FH-causing gene variant. Only 14.0% of the cohort were family members identified through cascade testing. Coronary artery disease (CAD) was reported in 28.0% of patients (age of onset 49.0±10.5 years) and 64.9% had at least one modifiable cardiovascular risk factor. The mean untreated LDL-cholesterol was 7.4±2.5 mmol/L. 80.8% of patients were on lipid-lowering therapy with a mean treated LDL-cholesterol of 3.3±1.7 mmol/L. Among patients receiving lipid-lowering therapies, 25.6% achieved an LDL-cholesterol target of <2.5 mmol/L without CAD or <1.8 mmol/L with CAD.

CONCLUSION

Patients in the national FH registry are detected later in life, have a high burden of CAD and risk factors, and do not achieve guideline-recommended LDL-cholesterol targets. Genetic and cascade testing are under-utilised. These deficiencies in care need to be addressed as a public health priority.

Molecular, Population, and Clinical Aspects of Lipoprotein(a): A Bridge Too Far?

There is now significant evidence to support an independent causal role for lipoprotein(a) (Lp(a)) as a risk factor for atherosclerotic cardiovascular disease. Plasma Lp(a) concentrations are predominantly determined by genetic factors. However, research into Lp(a) has been hampered by incomplete understanding of its metabolism and proatherogeneic properties and by a lack of suitable animal models. Furthermore, a lack of standardized assays to measure Lp(a) and no universal consensus on optimal plasma levels remain significant obstacles. In addition, there are currently no approved specific therapies that target and lower elevated plasma Lp(a), although there are recent but limited clinical outcome data suggesting benefits of such reduction. Despite this, international guidelines now recognize elevated Lp(a) as a risk enhancing factor for risk reclassification. This review summarises the current literature on Lp(a), including its discovery and recognition as an atherosclerotic cardiovascular disease risk factor, attempts to standardise analytical measurement, interpopulation studies, and emerging therapies for lowering elevated Lp(a) levels.

Is Lp(a) ready for prime time use in the clinic? A pros-and-cons debate

Lipoprotein (a) (Lp(a)) is a cholesterol-rich lipoprotein known since 1963. In spite of extensive research on Lp(a), there are still numerous gaps in our knowledge relating to its function, biosynthesis and catabolism. One reason for this might be that apo(a), the characteristic glycoprotein of Lp(a), is expressed only in primates. Results from experiments using transgenic animals therefore may need verification in humans. Studies on Lp(a) are also handicapped by the great number of isoforms of apo(a) and the heterogeneity of apo(a)-containing fractions in plasma. Quantification of Lp(a) in the clinical laboratory for a long time has not been standardized. Starting from its discovery, reports accumulated that Lp(a) contributed to the risk of cardiovascular disease (CVD), myocardial infarction (MI) and stroke. Early reports were based on case control studies but in the last decades a great deal of prospective studies have been published that highlight the increased risk for CVD and MI in patients with elevated Lp(a). Final answers to the question of whether Lp(a) is ready for wider clinical use will come from intervention studies with novel selective Lp(a) lowering medications that are currently underway. This article expounds arguments for and against this proposition from currently available data.

Lipoprotein (a): a historical appraisal

Initially, lipoprotein (a) [Lp(a)] was believed to be a genetic variant of lipoprotein (Lp)-B. Because its lipid moiety is almost identical to LDL, Lp(a) has been deliberately considered to be highly atherogenic. Lp(a) was detected in 1963 by Kare Berg, and individuals who were positive for this factor were called Lpa⁺ Lpa⁺ individuals were found more frequently in patients with coronary heart disease than in controls. After the introduction of quantitative methods for monitoring of Lp(a), it became apparent that Lp(a), in fact, is present in all individuals, yet to a greatly variable extent. The genetics of Lp(a) had been a mystery for a long time until Gerd Utermann discovered that apo(a) is expressed by a variety of alleles, giving rise to a unique size heterogeneity. This size heterogeneity, as well as countless mutations, is responsible for the great variability in plasma Lp(a) concentrations. Initially, we proposed to evaluate the risk of myocardial infarction at a cut-off for Lp(a) of 30-50 mg/dl, a value that still is adopted in numerous epidemiological studies. Due to new therapies that lower Lp(a) levels, there is renewed interest and still rising research activity in Lp(a). Despite all these activities, numerous gaps exist in our knowledge, especially as far as the function and metabolism of this fascinating Lp are concerned.

Relation of reduced preclinical left ventricular diastolic function and cardiac remodeling in overweight youth to insulin resistance and inflammation

Insulin resistance (IR) and inflammation are associated with an increased risk of cardiovascular disease and may contribute to obesity cardiomyopathy. The earliest sign of obesity cardiomyopathy is impaired left ventricular (LV) diastolic function, which may be evident in obese children and adolescents. However, the precise metabolic basis of the impaired LV diastolic function remains unknown. The aims of this study were to evaluate cardiac structure and LV diastolic function by tissue Doppler imaging in overweight and obese (OW) youth and to assess the relative individual contributions of adiposity, IR, and inflammation to alterations in cardiac structure and function. We studied 35 OW (body mass index standard deviation score 2.0±0.8; non-IR n=19, IR n=16) and 34 non-OW youth (body mass index standard deviation score 0.1±0.7). LV diastolic function was reduced in OW youth compared with non-OW controls, as indicated by lower peak myocardial relaxation velocities (p<0.001) and greater filling pressures (p<0.001). OW youth also had greater LV mass index (p<0.001), left atrial volume index, and LV interventricular septal thickness (LV-IVS; both p=0.02). IR-OW youth had the highest LV filling pressures, LV-IVS, and relative wall thickness (all p<0.05). Homeostasis model of assessment-insulin resistance and C-reactive protein were negative determinants of peak myocardial relaxation velocity and positive predictors of filling pressure. Adiponectin was a negative determinant of LV-IVS, independent of obesity. In conclusion, OW youth with IR and inflammation are more likely to have adverse changes to cardiovascular structure and function which may predispose to premature cardiovascular disease in adulthood.

When should we measure lipoprotein (a)?

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

Acute elevation of lipids does not alter exercise hemodynamics in healthy men: A randomized controlled study

OBJECTIVE

Exaggerated exercise blood pressure (BP) predicts mortality. Some studies suggest this could be explained by chronic hyperlipidemia, but whether acute-hyperlipidemia effects exercise BP has never been tested, and was the aim of this study.

METHODS

Intravenous infusion of saline (control) and Intralipid were administered over 60 min in 15 healthy men by double-blind, randomized, cross-over design. Brachial and central BP (including, pulse pressure, augmentation pressure and augmentation index), cardiac output and systemic vascular resistance were recorded at rest and during exercise.

RESULTS

Compared with control, Intralipid caused significant increases in serum triglycerides, very low density lipoproteins and free fatty acids (p < 0.001 for all). However, there was no significant difference for any exercise hemodynamic variable (p > 0.05 for all).

CONCLUSION

Acute-hyperlipidemia does not significantly change exercise hemodynamics in healthy males. Therefore, the association between raised lipids and increased exercise BP is likely due to the chronic effects of hyperlipidemia.

Nicotinic acid inhibits hepatic APOA gene expression: studies in humans and in transgenic mice

Elevated plasma lipoprotein(a) (LPA) levels are recognized as an independent risk factor for cardiovascular diseases. Our knowledge on LPA metabolism is incomplete, which makes it difficult to develop LPA-lowering medications. Nicotinic acid (NA) is the main drug recommended for the treatment of patients with increased plasma LPA concentrations. The mechanism of NA in lowering LPA is virtually unknown. To study this mechanism, we treated transgenic (tg) APOA mice with NA and measured plasma APOA and hepatic mRNA levels. In addition, mouse and human primary hepatocytes were incubated with NA, and the expression of APOA was followed. Feeding 1% NA reduced plasma APOA and hepatic expression of APOA in tg-APOA mice. Experiments with cultured human and mouse primary hepatocytes in addition to reporter assays performed in HepG2 cells revealed that NA suppresses APOA transcription. The region between -1446 and -857 of the human APOA promoter harboring several cAMP response element binding sites conferred the negative effect of NA. In accordance, cAMP stimulated APOA transcription, and NA reduced hepatic cAMP levels. It is suggested that cAMP signaling might be involved in reducing APOA transcription, which leads to the lowering of plasma LPA.

FGF19 signaling cascade suppresses APOA gene expression

OBJECTIVE

Lipoprotein(a) is a highly atherogenic lipoprotein, whose metabolism is poorly understood. Currently no safe drugs exists that lower elevated plasma lipoprotein(a) concentrations. We therefore focused on molecular mechanisms that influence apolipoprotein(a) (APOA) biosynthesis.

METHODS AND RESULTS

Transgenic human APOA mice (tg-APO mice) were injected with 1 mg/kg of recombinant human fibroblast growth factor 19 (FGF19). This led to a significant reduction of plasma APOA and hepatic expression of APOA. Incubation of primary hepatocytes of tg-APOA mice with FGF19 induced ERK1/2 phosphorylation and, in turn, downregulated APOA expression. Repression of APOA by FGF19 was abrogated by specific ERK1/2 phosphorylation inhibitors. The FGF19 effect on APOA was attenuated by transfection of primary hepatocytes with siRNA against the FGF19 receptor 4 (FGFR4). Using promoter reporter assays, mutation analysis, gel shift, and chromatin immune-precipitation assays, an Ets-1 binding element was identified at -1630/-1615bp region in the human APOA promoter. This element functions as an Elk-1 binding site that mediates repression of APOA transcription by FGF19.

CONCLUSIONS

These findings provide mechanistic insights into the transcriptional regulation of human APOA by FGF19. Further studies in the human system are required to substantiate our findings and to design therapeutics for hyper lipoprotein(a).

Expression of fat mobilizing genes in human epicardial adipose tissue

BACKGROUND

Epicardial adipose tissue (EAT) mass correlates with metabolic syndrome and coronary artery disease (CAD). However, little is known about the expression of genes involved in triglyceride (TG) storage and mobilization in EAT. We therefore analyzed the expression of genes involved in fat mobilization in EAT in comparison to subcutaneous abdominal adipose tissue (AAT) in CAD patients and in controls.

METHODS

EAT and AAT were obtained during coronary artery bypass graft (CABG) surgery from 16 CAD patients and from 14 non-CAD patients presenting for valve surgery. The state of atherosclerosis was assessed by angiography. RNA from tissues were extracted, reversibly transcribed and quantified by real time polymerase chain reaction (RT-PCR). The following genes were analyzed: perilipin-1 and -5 (PLIN1, PLIN5), lipoprotein lipase (LPL), hormone sensitive lipase (HSL), adipose triglyceride lipase (ATGL), comparative gene identification-58 (CIG-58), angiopoietin like protein 4 (ANGPTL4), in addition to interleukine-6 (IL-6), leptin (LEP) and adiponectin (ADPN).

RESULTS

A significant expression of all listed genes could be observed in EAT. The relative expression pattern of the 10 genes in EAT was comparable to the expression in AAT, yet there was a significantly higher overall expression in AAT. The expression of the listed genes was not different between CAD patients and controls.

CONCLUSION

It is suggested that the postulated difference in EAT volume between CAD patients and non-CAD patients is not caused by a differential mRNA expression of fat mobilizing genes. Further work on protein levels and enzyme activities will be necessary to get a complete picture.

Farnesoid X receptor represses hepatic human APOA gene expression

High plasma concentrations of lipoprotein(a) [Lp(a), which is encoded by the APOA gene] increase an individual's risk of developing diseases, such as coronary artery diseases, restenosis, and stroke. Unfortunately, increased Lp(a) levels are minimally influenced by dietary changes or drug treatment. Further, the development of Lp(a)-specific medications has been hampered by limited knowledge of Lp(a) metabolism. In this study, we identified patients suffering from biliary obstructions with very low plasma Lp(a) concentrations that rise substantially after surgical intervention. Consistent with this, common bile duct ligation in mice transgenic for human APOA (tg-APOA mice) lowered plasma concentrations and hepatic expression of APOA. To test whether farnesoid X receptor (FXR), which is activated by bile acids, was responsible for the low plasma Lp(a) levels in cholestatic patients and mice, we treated tg-APOA and tg-APOA/Fxr-/- mice with cholic acid. FXR activation markedly reduced plasma concentrations and hepatic expression of human APOA in tg-APOA mice but not in tg-APOA/Fxr-/- mice. Incubation of primary hepatocytes from tg-APOA mice with bile acids dose dependently downregulated APOA expression. Further analysis determined that the direct repeat 1 element between nucleotides -826 and -814 of the APOA promoter functioned as a negative FXR response element. This motif is also bound by hepatocyte nuclear factor 4α (HNF4α), which promotes APOA transcription, and FXR was shown to compete with HNF4α for binding to this motif. These findings may have important implications in the development of Lp(a)-lowering medications.

Implications of the Obesity Epidemic for Statin Therapy: Shifting Cholesterol Metabolism to a High Synthesis and Low Dietary Absorption State

Obesity and the metabolic syndrome are becoming one of the biggest health challenges of the 21(st) century. Cholesterol metabolism is significantly altered in both obesity and metabolic syndrome in that cholesterol synthesis is increased and absorption reduced and this has important implications for the treatment of lipid disorders in both obesity and the metabolic syndrome. In the present review we discuss these changes in detail especially in the context of a more standardized approach for cholesterol reduction like the TARGET LDL trial. Customized care is topical in lipidology as we strive to achieve LDL cholesterol and non-HDL cholesterol targets in every patient.

Therapy of hyper-Lp(a)

Lipoprotein (a) [Lp(a)] appears to be one of the most atherogenic lipoproteins. It consists of a low-density lipoprotein (LDL) core in addition to a covalently bound glycoprotein, apolipoprotein (a) [apo(a)]. Apo(a) exists in numerous polymorphic forms. The size polymorphism is mediated by the variable number of kringle-4 Type-II repeats found in apo(a). Plasma Lp(a) levels are determined to more than 90% by genetic factors. Plasma Lp(a) levels in healthy individuals correlate significantly high with apo(a) biosynthesis and not with its catabolism. There are several hormones known to have a strong impact on Lp(a) metabolism. In certain diseases, such as kidney disease, Lp(a) catabolism is impaired leading to up to fivefold elevations. Lp(a) levels rise with age but are otherwise influenced only little by diet and lifestyle. There is no safe and efficient way of treating individuals with elevated plasma Lp(a) concentrations. Most of the lipid-lowering drugs have either no significant influence on Lp(a) or exhibit a variable effect in patients with different forms of primary and secondary hyperlipoproteinemia. There is without doubt a strong need to concentrate on the development of specific medications to selectively target Lp(a) biosynthesis, Lp(a) assembly and Lp(a) catabolism. So far only anabolic steroids were found to drastically reduce Lp(a) plasma levels. This class of substance cannot, of course, be used for treatment of patients with hyper-Lp(a). We recommend that the mechanism of action of these drugs be studied in more detail and that the possibility of synthesizing derivatives which may have a more specific effect on Lp(a) without having any side effects be pursued. Other strategies that may be of use in the development of drugs for treatment of patients with hyper-Lp(a) are discussed in this review.

Inflammation, complement activation and endothelial function in stable and unstable coronary artery disease

BACKGROUND

Endothelial dysfunction plays an important role in the pathogenesis of coronary artery disease (CAD). Apart from traditional risk factors complement activation and inflammation may trigger and sustain endothelial dysfunction. We sought to assess the association between endothelial function, high sensitivity C-reactive protein (hs-CRP) and markers of complement activation in patients with either stable or unstable coronary artery disease.

METHODS

We prospectively recruited 78 patients, 35 patients with stable angina pectoris (SAP) and 43 patients with unstable angina pectoris (UAP). Endothelial function was assessed as brachial artery reactivity (BAR). Hs-CRP, C3a, C5a and C1-Inhibitor (C1 inh.) were measured enzymatically.

RESULTS

Patients with UAP showed higher median levels of hs-CRP and C3a compared to patients with SAP, while BAR was not significantly different between patient groups. In UAP patients, hs-CRP was significantly correlated with cholesterol (r=0.27, p<0.02), C3a (r=0.32, p<0.001) and C1 INH.(r=0.41, p<0.003), but not with flow mediated dilatation (r=0.09, P=0.41). Hs-CRP and C1 INH.were found to be independent predictors of UAP in a backward stepwise logistic regression model.

CONCLUSIONS

We conclude that both hs-CRP, a marker of inflammation and C3a, a marker of complement activation are elevated in patients with UAP, but not in patients with SAP.

Plasma delipidation process induces rapid regression of atherosclerosis and mobilisation of adipose tissue

Cholesterol is a major component of atherosclerotic plaques. Cholesterol accumulation within the arterial intima and atherosclerotic plaques is determined by the difference of cellular cholesterol synthesis and/or influx from apo B-containing lipoproteins and cholesterol efflux. In humans, apo A-1 Milano infusion has led to rapid regression of atherosclerosis in coronary arteries. We hypothesised that a multifunctional plasma delipidation process (PDP) would lead to rapid regression of experimental atherosclerosis and probably impact on adipose tissue lipids. In hyperlipidemic animals, the plasma concentrations of cholesterol, triglyceride and phospholipid were, respectively, 6-, 157-, and 18-fold higher than control animals, which consequently resulted in atherosclerosis. PDP consisted of delipidation of plasma with a mixture of butanol-diisopropyl ether (DIPE). PDP removed considerably more lipid from the hyperlipidemic animals than in normolipidemic animals. PDP treatment of hyperlipidemic animals markedly reduced intensity of lipid staining materials in the arterial wall and led to dramatic reduction of lipid in the adipose tissue. Five PDP treatments increased apolipoprotein A1 concentrations in all animals. Biochemical and hematological parameters were unaffected during PDP treatment. These results show that five PDP treatments led to marked reduction in avian atherosclerosis and removal of lipid from adipose tissue. PDP is a highly effective method for rapid regression of atherosclerosis.

HDL therapy: the next big step in the treatment of atherosclerosis?

Despite significant reductions in mortality with statins and increasingly lower targets of low-density-lipoprotein cholesterol, two thirds of cardiovascular events cannot be prevented with current treatments. Therefore, a clear need for additional therapeutic interventions to complement the results of low-density lipoprotien lowering, exists. One prime target for new interventions is high-density lipoprotein (HDL) and/or its apolipoproteins. While lifestyle interventions and well-established drugs, such as fibrates and nicotinic acid, modestly increase HDL, the most promising current approaches are direct infusion of HDL-like particles (e.g., apolipoprotein AI Milano-phospholipid complexes) and inhibition of one of the key enzymes in HDL metabolism, cholesterol ester transfer protein. These methods have been shown to have dramatic effects on the incidence of atherosclerosis and/or HDL cholesterol. This review will focus on treatments that raise HDL cholesterol or enhance reverse cholesterol transport. Old and new drugs will be discussed as well as combination therapy and novel approaches such as plasma delipidation and recombinant apolipoprotein AI.

Effects of simvastatin on blood lipids, vitamin E, coenzyme Q10 levels and left ventricular function in humans

BACKGROUND

As statin therapy has been reported to reduce antioxidants such as vitamin E and coenzyme Q10 and there are indications that this reduction may cause impairment of left ventricular function (LVF), we studied the influence of simvastatin on LVF and serum vitamin E and coenzyme Q10 levels in humans.

MATERIAL AND METHODS

We assessed the effect of simvastatin on left ventricular function and coenzyme Q10 levels in 21 (11 male, 10 female) hypercholesterolaemic subjects (mean age = 56 years) with normal LVF, over a period of 6 months. Subjects were re-tested after a 1-month wash-out period (7 months). Echocardiography was performed on all subjects before commencement of simvastatin (20 mg day(-1)), and at 1, 3, 6 and 7 months after initiation of treatment. Fasting blood samples were also collected at these intervals to assess lipids, apoproteins, vitamin E and coenzyme Q10.

RESULTS

Serum lipids showed the expected reductions. Plasma vitamin E and coenzyme Q10 levels were reduced by 17 +/- 4% (P < 0.01) and 12 +/- 4% (P < 0.03) at 6 months. However, the coenzyme Q10/LDL-cholesterol ratio and vitamin E/LDL-cholesterol ratio increased significantly. Left ventricular ejection fraction (EF) decreased transiently after 1 month, while no significant change was observed at 3 and 6 months. Other markers of left ventricular function did not change significantly at any time point.

CONCLUSION

Despite reduced plasma vitamin E and coenzyme Q10, 20 mg of simvastatin therapy is associated with a significantly increased coenzyme Q10/LDL-cholesterol ratio and vitamin E/LDL-cholesterol ratio. Simvastatin treatment is not associated with impairment in left ventricular systolic or diastolic function in hypercholesterolaemic subjects after 6 months of treatment.

Factors affecting plasma lipoprotein(a) levels: role of hormones and other nongenetic factors

Lp(a) appears to be one of the most atherogenic lipoproteins. It consists of an low-density lipoprotein core in addition to a covalently bound glycoprotein, apo(a). Apo(a) exists in numerous polymorphic forms. The size of the polymorphism is mediated by the variable number of kringle-4 Type 2 repeats found in apo(a). Plasma Lp(a) levels are determined to more than 90% by genetic factors. Plasma Lp(a) levels in healthy individuals correlate significantly highly with apo(a) biosynthesis, and not with its catabolism. There are several hormones that are known to have a strong effect on Lp(a) metabolism. In certain diseases, such as kidney disease, the Lp(a) catabolism is impaired, leading to elevations that are up to a fivefold increase. Lp(a) levels rise with age but are otherwise only little influenced by diet and lifestyle. There is no safe and efficient way of treating individuals with elevated plasma Lp(a) concentrations. Most of the lipid-lowering drugs have either no significant influence on Lp(a) or exhibit a variable effect in patients with different forms of primary and secondary hyperlipoproteinemia.

Lipoprotein(a): still an enigma?

PURPOSE OF REVIEW

Lipoprotein(a) belongs to the class of the most atherogenic lipoproteins. Despite intensive research - in the last year more than 80 papers have been published on this topic - information is still lacking on the physiological function of lipoprotein(a) and the site of its catabolism. Important advances have been made in the knowledge of these points, which may have some therapeutic implications.

RECENT FINDINGS

The association of high lipoprotein(a) values with an increase in risk for coronary events has been documented in further prospective studies. This increased risk may relate to recent findings that apolipoprotein(a) is produced in situ within the vessel wall. In addition, lipoprotein(a) binds and inactivates the tissue factor pathway inhibitor and induces plasminogen activator inhibitor type 2 expression in monocytes. A new antisense oligonucleotide strategy has been proposed which efficiently inhibits apolipoprotein(a) expression in vitro and in vivo. Apolipoprotein(a), however, suppresses angiogenesis and thus may interfere with the infiltration of tumor cells. Finally, the enzymatic activity leading to the formation of apolipoprotein(a) fragments in plasma and their catabolism have been further elucidated.

SUMMARY

We are still far away from understanding the pathways involved in lipoprotein(a) catabolism, and the physiological function of this lipoprotein. Recent findings, however, provide new insight into pathomechanisms in patients with increased lipoprotein(a) related to hemostasis, which may serve as a basis for designing new treatment strategies.

The Physiological Role of Lipoprotein (a)

Lipoprotein (a) (Lp(a)) is one of the most atherogenic lipoproteins, and, although we know plenty about the pathophysiology of Lp(a), its physiological function and metabolism remain elusive. From our previous results and more recent reports, the following model of Lp(a) metabolism emerges: apolipoprotein a (apo(a)) is biosynthesized in liver cells and the size of the isoform determines its rate of synthesis and excretion. In a first step, specific kringle IV domains in apo(a), mainly T-6 and T-7, bind to circulating low-density lipoproteins, followed by a second step in which stabilization of the newly formed Lp(a) complex is achieved by a disulfide bridge. Circulating Lp(a) interacts specifically with kidney cells, or possibly other tissues, causing cleavage of 2/3­3/4 of the N-terminal part of apo(a) by a collagenase-type protease. Part of these apo(a) fragments are found as excretory products of Lp(a) in urine, but there are indications that they, in fact, represent the biologically active form of apo(a) and are possibly responsible for the atherogenicity of Lp(a). Strategies for reducing this atherogenic lipoprotein with medication should, therefore, aim at interfering with either the assembly of Lp(a) or the stimulation of apo(a) fragmentation. (c) 2002 Prous Science. All rights reserved.

[Aggressive therapy and combination therapy in severe hyperlipidemia]

In cases of severe hyperlipidemia, we have very effective therapeutic tools nowadays. LDL-apheresis is still the most effective therapy for familial hypercholesterolemia, especially in its homocygous form. In combination with statins, LDL-cholesterol can be lowered by 80%. Most other genetic and secondary hyperlipidemias can effectively be treated by lipid lowering drugs. This aggressive treatment gains more and more on importance in view of the tough recommendations of specific scientific societies. Atorvastatin and simvastatin can lower LDL-cholesterol by 60%. In this report different therapies and combination therapies for hyperlipidemia are discussed.

[Lowering cholesterol 1998. Cholesterol synthesis inhibitors compared]

Large scale primary and secondary prevention trials in recent years have revealed that the effective lipid reducing therapy with statins can reduce mortality of coronary heart disease by up to 30%. For the first time it has become possible to reduce LDL-cholesterol pharmacologically by more than 50%, a reduction that was only achieved by LDL-apheresis so far. Cost-effectiveness is becoming an important issue since this varies widely between patients according to the coronary risk. Treating the patients with the highest coronary risk is most cost effective. Currently, there are six statins on the market. Reduction of LDL-cholesterol is mainly mediated by the induction of LDL-receptor activity in the liver. In addition, some statins at high doses also reduce LDL-cholesterol synthesis. Due to variations in the molecular structure of the active compounds these 6 statins have important pharmacological differences, such as their capacity to reduce plasma triglycerides, their interaction with other drugs. The daily recommended doses of the statins range from 0.1 mg (cerivastatin) to 80 mg (atorvastatin). In this review the differences in the pharmacological and clinical actions of the statins are analyzed.

Urinary apolipoprotein (a) excretion in patients with proteinuria

Increased plasma lipoprotein (a) (Lp(a)) levels are strongly associated with premature cardiovascular disease and stroke. Recently we, as well as other groups, found that apolipoprotein (a) (apo(a)) fragments appear in the urine of healthy individuals, and that renal transplant patients with impaired renal function excrete fewer apo(a) fragments into their urine compared with controls. As the excretion mode of apo(a) is presently unknown, we determined plasma Lp(a) levels and urinary apo(a) excretion in relation to kidney function in 58 proteinuric patients and 58 healthy controls. For the first time, urinary apo(a) excretion was related to apo(a) isoforms. Plasma Lp(a) values were higher in the proteinuric patients compared with the controls, independent of their renal function. The patients with low-molecular-weight apo(a) isoforms had higher Lp(a) plasma levels, whereas the patients with high-molecular-weight apo(a) isoforms had lower Lp(a) plasma levels. Urinary apo(a) showed a very similar pattern to that of plasma Lp(a), being significantly higher in patients with low-molecular-weight isoforms as compared with patients with high-molecular-weight isoforms. Urinary apo(a) excretion was significantly decreased in the patient group when compared with healthy controls. There was a close correlation (P < 0.001) between the plasma Lp(a) and urinary apo(a) excretion in both the patient group and the control group. Urinary apo(a) excretion did not correlate with protein excretion, creatinine clearance or plasma creatinine levels. We conclude that urinary apo(a) excretion correlates with plasma Lp(a) and Lp(a) isoforms, and that proteinuric patients excrete significantly less apo(a) into their urine than healthy controls, a factor that might contribute to increased plasma Lp(a) levels in these patients.

Decreased urinary apolipoprotein (a) excretion in patients with impaired renal function

BACKGROUND

Plasma lipoprotein (a) [Lp(a)] levels are elevated in patients with kidney disease and are strongly associated with premature cardiovascular disease and stroke.

METHODS

As the kidney is suggested to play an important role in apolipoprotein (a) [apo(a)] catabolism and as apo(a) fragments appear in urine, we determined plasma Lp(a) levels and urinary apo(a) excretion in relation to kidney function in a large cohort of renal patients. A total of 368 renal patients with normal or different degrees of impaired renal function and 163 healthy control subjects matched for age and sex were investigated. Plasma Lp(a) and urinary apo(a) were analysed immunochemically.

RESULTS

Renal patients were found to have significantly elevated total cholesterol and low-density lipoprotein (LDL)-C values but lower high-density lipoprotein (HDL)-C values than control subjects. Plasma Lp(a) values were significantly higher only in patients with creatinine clearance < 70 mL min-1. There was a significant correlation between urinary apo(a) and plasma Lp(a) in patients and control subjects. Urinary apo(a) excretion was significantly lower in patients than in control subjects and showed no correlation with urinary protein excretion.

CONCLUSION

Although it is unlikely that impaired renal excretion of apo(a) fragments largely contributes to increased plasma Lp(a) levels in patients suffering from impaired kidney function, these data suggest that urinary apo(a) excretion is significantly decreased in renal patients and that this might contribute to increased plasma Lp(a) levels in this patient group.

Urinary excretion of apo(a) in patients after kidney transplantation

BACKGROUND

Increased plasma Lipoprotein (a) (Lp(a)) levels are strongly associated with premature cardiovascular disease and stroke. The kidney is purported to play an important role in apo(a) catabolism. Therefore we investigated plasma Lp(a) levels in relation to kidney function and urinary apo(a) excretion.

METHODS

One hundred and sixteen kidney transplant patients with normal or impaired renal function and 109 age- and sex-matched healthy controls were investigated. Plasma Lp(a) and urinary apo(a) levels were determined immunochemically and all other parameters were determined by routine laboratory methods.

RESULTS

Transplant recipients were found to have significantly elevated total cholesterol and LDL-C values, but equal HDL-C values compared to controls. Plasma Lp(a) values were higher and urinary apo(a) excretion was lower in transplant recipients compared to controls, independent of renal function. When the patient group was subdivided into 'normal' and 'impaired creatinine clearance', only the latter group secreted less apo(a) than normal controls.

CONCLUSION

These data suggest that urinary apo(a) excretion is reduced in transplant recipients with impaired excretory graft function, which may contribute to the elevation of plasma Lp(a) levels in these patients.

Lecithin-cholesterol acyltransferase activity in normocholesterolaemic and hypercholesterolaemic roosters: modulation by lipid apheresis

Lipid apheresis, a recently described procedure for the elimination of lipid but not apolipoproteins from plasma, was applied to normocholesterolaemic and hypercholesterolaemic roosters. Lipid apheresis resulted in an immediate reduction in plasma unesterified cholesterol concentration, which was sustained for 150 min. The reduction in unesterified cholesterol concentration was higher in the normocholesterolaemic animals than in the hypercholesterolaemic animals. Lipid apheresis induced changes in the ratio of plasma unesterified to total cholesterol in normocholesterolamic animals but not in hypercholesterolaemic animals. In hypercholesterolaemic animals, lecithin-cholesterol acyltransferase (LCAT) activity was not affected by lipid apheresis, whereas in normocholesterolaemic animals LCAT activity was acutely reduced for 150 min after lipid apheresis. Saturated LCAT kinetics occurred in the hypercholesterolaemic animals but not in the normocholesterolaemic animals. LCAT obeyed Michaelis-Menten kinetics. After lipid apheresis, there was a pool of unesterified cholesterol that was available as substrate for LCAT to a greater extent in hypercholesterolaemic animals than in normocholesterolaemic animals. These observations may have important implications for lipid apheresis as a treatment for atherosclerosis.

Urinary apo(a) discriminates coronary artery disease patients from controls

Increased plasma lipoprotein (a) (Lp(a)) levels are associated with premature cardiovascular diseases and stroke. Since Lp(a) immune reactivity is found in urine we compared urinary apolipoprotein (a) (apo(a)) with plasma Lp(a) levels in 116 patients suffering from angiographically proven coronary artery diseases with that of 109 controls. Urinary apo(a) investigated by immuno blotting, revealed a distinct apo(a) fragmentation pattern with molecular weights between 50 and 160 kDa. Apolipoprotein B however was not secreted into urine. Lp(a) and apo(a) were measured by a fluorescence immuno assay. Within single individuals, urinary apo(a) levels correlated significantly with creatinine (Rho, 0.98; P < 0.0005). Medians and 25/75 percentiles of urinary apo(a) in coronary artery disease (CAD) patients were 5.70, 3.25 and 10.35 microg/dl and in controls 2.64, 1.43 and 3.50 microg/dl respectively. At cut-off levels of 30 mg/dl for plasma Lp(a) and 10 microg/dl of urinary apo(a) respectively, both paramenters showed comparable sensitivities (33.8% vs. 26.7%), yet the specificity (76.1% vs. 91.7%) and the positive predictive value (60.0% vs.76.4%) of urinary apo(a) were much higher. In receiver-operating characteristic plots, urinary apo(a) was much more sensitive at high specificities i.e. greater than 60% as compared to Lp(a). Urinary secretion of apo(a) fragments normalized to creatinine is stable in a given individual and significantly associated with coronary artery disease.

LDL-apheresis significantly reduces urinary apo(a) excretion

Increased plasma Lp(a) is an established risk factor for atherosclerosis. We recently described the presence of apo(a) fragments in urine and the significant correlation between urinary apo(a) concentrations and plasma Lp(a). Here we investigated urinary apo(a) in patients suffering from familial hypercholesterolaemia (FH), treated with LDL apheresis. Before treatment, plasma Lp(a) levels and urinary apo(a) normalized to creatinine were > 2-fold increased in FH patients (P < 0.0001) as compared to controls. LDL-apheresis led to a reduction of plasma Lp(a) by 75% and a concomitant immediate reduction of urinary apo(a) by 45%. We conclude that a steady state condition for urinary apo(a) is rapidly achieved via LDL-apheresis.

Urinary excretion of apo(a) fragments. Role in apo(a) catabolism

The biosynthesis and assembly of lipoprotein(a) [Lp(a)], a marker for atherosclerotic disease, appears to be well understood. However, information is lacking concerning the mode and site of Lp(a) catabolism. Apo(a) is reported to be excreted into the urine. To study the effect of this pathway on the overall catabolism of Lp(a), urinary apo(a) was characterized by immunoblotting. More than 10 distinct apo(a) bands with molecular masses between 30 and 160 kD were observed. Apo(a) fragments were not complexed to apoB. In more than 30 individuals the size of apo(a) bands was comparable irrespective of their apo(a) phenotype, although marked differences in the relative intensities of the bands were observed. Eight batches of 24-hour urine collections collected from one proband at 2-week intervals exhibited a significant correlation between creatinine and apo(a) concentrations as measured by DELFIA (r = .93; P < .01). In 193 healthy volunteers a highly significant correlation was found between urinary apo(a) concentrations normalized to creatinine levels and plasma Lp(a) values (p = 0.659; P < .0001). Of the total plasma apo(a), 0.073%, i.e., 121 micrograms apo(a), was excreted in the form of apo(a) fragments in 24-hour urine samples from 12 healthy volunteers. We conclude that the catabolism of Lp(a) via excretion of apo(a) fragments accounts for < 1% of the daily Lp(a) catabolism.

Lipid apheresis in an animal model causes in vivo changes in lipoprotein electrophoretic patterns

Lipid apheresis, a new extracorporeal procedure based on plasma delipidation and showing promise as a possible treatment for atherosclerosis, was recently reported for the first time from this laboratory [Cham et al., J Clin Apheresis 10:61-69, 1995]. In the present study lipid apheresis was applied to hypercholesterolemic and normocholesterolemic roosters to examine its effect on plasma lipoprotein particles. This procedure resulted in conspicuous changes in electrophoretic patterns of plasma lipoproteins. The electrophoretic mobilities of all the lipoprotein fractions had changed considerably. Lipid stainable material was present in at least three bands in the alpha-globulin area. In particular, changes in the electrophoretic region of high-density lipoproteins were observed. Lipid apheresis markedly induced the anti-atherogenic pre- beta-high-density lipoproteins. The observed changes induced by lipid apheresis were more pronounced in the hyperlipidemic animals compared with the normocholesterolemic controls. A novel pre-alpha-lipoprotein band was observed soon after lipid apheresis. This lipoprotein band had a density larger than 1.21. At approximately 150 minutes after lipid apheresis, the electrophoretic pattern had almost returned to its original base pattern. Lipid apheresis results in plasma lipoprotein changes which may induce reverse cholesterol transport and shows promise as a possible treatment of atherosclerosis.

Lipid apheresis: an in vivo application of plasma delipidation with organic solvents resulting in acute transient reduction of circulating plasma lipids in animals

Despite primary and secondary prevention of coronary disease with lowering plasma cholesterol by diet and drug therapy, coronary heart disease remains the major cause of death in Western countries. Low density lipoprotein apheresis had the potential to make a significant impact as it acutely leads to a marked reduction in plasma cholesterol. However, recent preliminary results suggest that low density lipoprotein apheresis may not be more effective in preventing progression of coronary disease than current drug therapy. We have devised a new technique, termed lipid apheresis, which removes cholesterol and triglycerides from plasma but retains the apolipoproteins. This procedure shows great promise in stimulating regression beyond current therapy. Lipid apheresis, a new extracorporeal procedure based on plasma delipidation with the organic solvent mixture butanol-diisopropyl ether, was applied to hypercholesterolemic and normocholesterolemic roosters. Approximately 25% of the calculated blood volume was removed from the animals. The plasma was separated from the blood cells. The plasma was delipidated for 20 min with the organic solvent mixture. The delipidated plasma containing all proteins, including the apolipoproteins and other ionic constituents, was remixed with the blood cells and infused back into the identical donor animals. Analyses of serial blood samples collected from lipid apheresed and sham treated animals up to 16 h after infusion revealed that lipid apheresis caused acute, marked reductions in plasma lipids. The pattern and extent of the plasma levels of cholesterol were different in the hypercholesterolemic animals when compared with normocholesterolemic animals, indicating that a readily extraplasma cholesterol pool in the hypercholesterolemic animals was rapidly mobilized into the plasma pool.(ABSTRACT TRUNCATED AT 250 WORDS)