Lp(a) Awareness Day 2024

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Lp(a) Awareness Day 2024

Lp(a) Awareness Day

Novel and classical insights into Lp(a) concentration and the effects on various cardiovascular conditions.

Despite advances in understanding and technology, cardiovascular diseases (CVDs) remain a major source of mortality across the world. The World Health Organisation (WHO) estimate that 17.9 million people died due to CVDs in 2019, accounting for around 32% of deaths that year1. First described in 1963, Lipoprotein(a) (Lp(a)) is a macromolecular lipoprotein complex2 which is thought to display proatherogenic, proinflammatory3 and prothrombotic4 potential and is considered an independent causal risk factor for various types of CVD5. These properties provide several mechanisms in which elevated Lp(a) levels may contribute to CVD however the true nature of Lp(a)s relationship to CVD remains largely enigmatic.

Lp(a) concentrations in plasma are principally regulated by variation in LPA gene and levels remain relatively stable throughout one’s lifetime with lifestyle factors having little effect on their concentration6. Due to the highly heritable nature of Lp(a) concentration, those with a family history of Familial Hypercholesterolaemia (FH), elevated LDL-C levels, or Atherosclerotic cardiovascular disease (ASCVD) should be screened, their plasma Lp(a) concentration determined, and their risk of CVD established.

In the last 10 years, there have been many advances in the understanding of this ambiguous lipoprotein which support the causal association with CVD, clarify the established evidence and introduce novel mechanisms of action in relation to Lp(a), shedding light on its obscure pathophysiology. However, there are still diagnostic complications associated with Lp(a) measurement as there is little standardisation in methods of determination5.

Physiology and Genetics

Synthesised mainly in the liver, Lp(a), like LDL, is composed of a lipid centre made of cholesteryl esters and triacylglycerols, surrounded by a shell of phospholipids, free cholesterol, and an apoB-100 molecule. The major difference between other LDL molecules and Lp(a) is the presence of a polymorphic glycoprotein, apo(a), bound to apoB-100 by a single disulphide bond5. It is this apo(a) molecule which contributes to Lp(a)s pathophysiology.

Apo(a) is thought to have evolved from the plasminogen gene (PLG) around 40 million years ago and shares 78-100% sequence homology within the untranslated and coding regions of the fibrinolytic enzyme2. Like plasminogen, apo(a) contains unique domains named kringles5. While plasminogen contains 5 different kringle structures (KI to KV), apo(a) has lost KI to KIII and instead contains several forms of KIV, namely, 1 copy of KIV1 and KIV3-10, 1-40 copies of KIV2, 1 copy of KV and an inactive protein domain at the carboxyl terminus of the molecule7. These hydrophilic subunits are highly polymorphic due to the variation in KIV2 repeats. Individuals may possess two different isoforms of apo(a) one of which will have been passed down from each parent and are expressed codominantly2. These isoforms are dependent on the number of KIV2 repeats they contain2. Isoforms with less KIV2 repeats produce smaller apo(a) isoforms which are found at a higher concentration compared with larger isoforms8 due to the increased rate at which the smaller molecules can be synthesised5. The polymorphisms in KIV2 repeats account for up to 70% of the variation seen in concentration between individuals, with the remainder being attributed to differences in protein folding, transport, and single nucleotide polymorphisms (SNPs)5. SNPs are central in the heterogeneity of apo(a), effecting RNA splicing, nonsense mutations and 5’ untranslated region of the LPA gene resulting in shorter gene translation5,8.

Lp(a) vs LDL-C

Lp(a) Pathophysiology

Lp(a) is thought to contribute to the risk of CVD through multiple mechanisms. Firstly, Lp(a) molecules display all the same atherosclerotic risk as LDL-C molecules due to their similar fundamental composition, for example, their propensity for oxidisation upon entering the vessel wall, and promotion of atherosclerosis through inflammatory and immunogenic mechanisms 9. However, Lp(a) displays more proatherogenic potential due to the presence of the apo(a) molecule. The structure of apo(a) results in decreased fibrinolysis. Due to its structural similarities, apo(a) competes with plasminogen for binding sites, competitively inhibiting plasminogen, ultimately resulting in reduced fibrinolysis9.

Lp(a) is thought to be a preferential carrier of oxidised phospholipids2 (OxPLs) which covalently bind to apo(a), increase expression of inflammatory proteins, and stimulate the secretion of IL-8 and monocyte chemoattractant protein-1, enhancing its ability to cross the vessel wall9. Some claims require further investigation, however, studies have been carried out which show inhibition of plasminogen activation in the presence of Lp(a)10. It is this indirect mechanism that Lp(a) is thought to conduct its prothrombotic activity8,9.

Clinical Evidence

Many studies have been carried out to determine the association of Lp(a) concentration and CVD risk. Studies such as the Copenhagen General Population Study, the Copenhagen City Heart Study, Dallas Heart Study, and Ischemic Heart Disease Studies provide strong evidence for Lp(a) as a causal risk factor for CVD. Data analysis of the Copenhagen General Population Study reveal that 20% of subjects displayed Lp(a) concentrations of more than 42mg/dl, or around 105nmol/L11, which is considered to result in increased risk of atherosclerotic disease5. It is important to note, there is no accepted conversion factor for converting Lp(a) concentration from mg/dl to nmol/L due to the variability of apo(a) kringles. The unitage will depend on the assay method used5. Another study in a healthcare organisation in Israel showed that Myocardial Infarction (MI) and Coronary Artery Disease was 2.5 times more common in those with high levels of Lp(a) than in the age and sex matched control group3. This study3, along with others5,6,12 describes a linear relationship between Lp(a) concentration and CVD risk, showing at least a 3-fold increase in ASCVD and MI events in adults with Lp(a) concentrations in the top 1% when compared with those in the with concentrations in the bottom 20%3.

The major variation in Lp(a) concentration seen throughout the population, is further evident between ethnicities and sexes. On average, Caucasian subjects display the lowest Lp(a) concentrations, with Black subjects displaying the highest concentrations5. However, the large number of functional variants are consistent across ethnicities suggesting that it is the KIV2 repeats and SNPs that are the major factors contributing to Lp(a) concentration regardless of ethnicity. Lp(a) concentrations are higher in women than men8 with levels increasing post-menopause thought to be caused by a decrease in oestrogen3.

Lp(a) Testing and Screening

The European Atherosclerosis Society (EAS) recommend that all adults are tested at least once in their lifetime to identify individuals who have high levels of Lp(a) and therefore high CVD risk. Screening is also recommended in children who have a family history of Ischaemic stroke, premature ASCVD or high Lp(a) levels in the absence of other identifiable risk factors8. Testing has been associated with reduced mortality rates. This is thought to be because of increased and intensified therapy for those who are identified as high risk due to high plasma Lp(a) concentration6.

There are various assays available for the determination of Lp(a) concentration which vary in accuracy and precision. Many of these assays utilise polyclonal antibodies which recognise different antigenic determinants8. Due to the variability in apo(a) structure and KIV repeats, these assays often overestimate the concentration of large isoforms and underestimate concentration of small isoforms when determining the true Lp(a) levels9. This variation can be partially nullified by using a calibrator series and by selecting a method which is traceable to WHO/IFCC reference material. This allows laboratories to confidently identify individuals considered high risk but may still prove problematic when patients’ results report closer to the assay thresholds.

One study13 compared 5 commercially available Lp(a) assays on an automated clinical chemistry analyser. The assays tested were manufactured by Diazyme, Kamiya, MedTest, Roche, and Randox. The authors show that all the assays tested met the manufacturers claims for sensitivity, linearity, and precision. However, significant bias was observed in 4 out of 5 assays. The only assay which did not display significant bias was the Randox Lp(a) Assay which is traceable to WHO/IFCC reference material. This report highlights the importance of measuring and reporting Lp(a) in molar concentration rather than in mass units to facilitate standardisation and harmonisation in Lp(a) testing13.

Current and Emerging Therapies

Statins are one of the most potent treatments for the primary prevention of ASCVD through the reduction of LDL-C concentration. However, recent studies reveal that statins have no effect on Lp(a) concentration3 and others suggest that statin administration can increase Lp(a) concentration by up to 11%5,9. Nonetheless, EAS do not recommend statin therapy be halted as their strong ameliorative effects on CVD risk are well established and surmount the risk related to increased Lp(a) concentration8.

Niacin (Nicotinic acid) is another established treatment for the reduction of CVD events and act by increasing HDL levels. Niacin can reduce Lp(a) concentration though the reduction of gene expression in a dose-dependent manner5. However, Niacin therapy has not been proven to have beneficial effects on CVD risk8.

A recent metanalysis showed a 26% reduction in serum Lp(a) concentration through treatment with PCSK9 inhibitors. This is thought to be due to a shortage of apoB-100 molecules either because of reduced synthesis or competitive binding with other LDL receptors, resulting in reduced Lp(a) concentration5. Several studies show the efficacy of PCSK9 inhibitors in reducing CVD risk, but this is not yet an approved therapy5,8.

New therapeutic strategies aim to target hepatocytes, the site of apo(a) synthesis, to reduce Lp(a) concentration. Antisense Oligonucleotides (ASOs) inhibit apo(a) mRNA in the nucleus and cytoplasm, ultimately inhibiting Lp(a) secretion5 through the cleavage of the sense strand by ribonuclease H19. While still in clinical trials, ASO therapies show promise in the battle to reduce CVD risk with some studies displaying an overall reduction in Lp(a) concentration of more than 80%9.

Conclusions

There have been major advances in the understanding of Lp(a) pathophysiology in the last 10 years establishing this macromolecular complex as an independent causal risk factor for various forms of CVD, however, more investigation is required to fully understand the mechanisms responsible for this association. With many national healthcare organisations and the EAS recommending universal testing for Lp(a) in adults, more emphasis should be placed on raising awareness of the importance of Lp(a) screening. Finally, more research is needed into therapies which succeed at lowering Lp(a) concentration. While some therapies are in clinical trials, there are currently no approved therapies that achieve this goal.

The Randox Lp(a) assay is calibrated in nmol/L, traceable to the WHO/IFCC reference material, and displays an excellent correlation coefficient of r=0.995 with when compared with other commercially available methods. To accompany this liquid ready-to-use reagent we also offer a dedicated 5 point calibrator with accuracy-based assigned target values (in nmol/l) is available, accurately reflecting the heterogeneity of the apo(a) isoforms.

For more information on this revolutionary assay, visit randox.com/lipoproteina/ or reach out to us at marketing@randox.com.

References

  1. World Health Organization. Cardiovascular Diseases. World Health Organization. Published June 11, 2021. https://www.who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds)
  2. Schmidt K, Noureen A, Kronenberg F, Utermann G. Structure, function, and genetics of lipoprotein (a). Journal of Lipid Research. 2016;57(8):1339-1359. doi:https://doi.org/10.1194/jlr.r067314
  3. Zafrir B, Aker A, Saliba W. Extreme lipoprotein(a) in clinical practice: A cross sectional study. International Journal of Cardiology Cardiovascular Risk and Prevention. 2023;16:200173. doi:https://doi.org/10.1016/j.ijcrp.2023.200173
  4. Pino BD, Gorini F, Gaggini M, Landi P, Pingitore A, Vassalle C. Lipoprotein(a), Cardiovascular Events and Sex Differences: A Single Cardiological Unit Experience. Journal of Clinical Medicine. 2023;12(3):764. doi:https://doi.org/10.3390/jcm12030764
  5. Stürzebecher PE, Schorr JJ, Klebs SHG, Laufs U. Trends and consequences of lipoprotein(a) testing: Cross-sectional and longitudinal health insurance claims database analyses. Atherosclerosis. 2023;367:24-33. doi:https://doi.org/10.1016/j.atherosclerosis.2023.01.014
  6. Lampsas S, Xenou M, Oikonomou E, et al. Lipoprotein(a) in Atherosclerotic Diseases: From Pathophysiology to Diagnosis and Treatment. Molecules. 2023;28(3):969. doi:https://doi.org/10.3390/molecules28030969
  7. Vuorio A, Watts GF, Schneider WJ, Tsimikas S, Kovanen PT. Familial hypercholesterolemia and elevated lipoprotein(a): double heritable risk and new therapeutic opportunities. Journal of Internal Medicine. 2019;287(1):2-18. doi:https://doi.org/10.1111/joim.12981
  8. Kronenberg F, Mora S, Stroes ESG, et al. Lipoprotein(a) in atherosclerotic cardiovascular disease and aortic stenosis: a European Atherosclerosis Society consensus statement. European Heart Journal. 2022;43(39):3925-3946. doi:https://doi.org/10.1093/eurheartj/ehac361
  9. Tsimikas S. A Test in Context: Lipoprotein(a): Diagnosis, Prognosis, Controversies, and Emerging Therapies. Journal of the American College of Cardiology. 2017;69(6):692-711. doi:https://doi.org/10.1016/j.jacc.2016.11.042
  10. Boffa MB, Koschinsky ML. Lipoprotein (a): truly a direct prothrombotic factor in cardiovascular disease? Journal of Lipid Research. 2016;57(5):745-757. doi:https://doi.org/10.1194/jlr.r060582
  11. Enkhmaa B, Anuurad E, Berglund L. Lipoprotein (a): impact by ethnicity and environmental and medical conditions. Journal of Lipid Research. 2016;57(7):1111-1125. doi:https://doi.org/10.1194/jlr.r051904
  12. Svilaas T, Klemsdal TO, Bogsrud MP, et al. High levels of lipoprotein(a) – assessment and treatment. Tidsskrift for Den norske legeforening. Published online January 12, 2023. doi:https://doi.org/10.4045/tidsskr.21.0800
  13. Wyness SP, Genzen JR. Performance evaluation of five lipoprotein(a) immunoassays on the Roche cobas c501 chemistry analyzer. Practical Laboratory Medicine. 2021;25:e00218. doi:https://doi.org/10.1016/j.plabm.2021.e00218

Randox Health announce partnership with Simplyhealth

Simplyhealth is now offering customers of its Health Plan discounted access to 10 Randox Health home testing kits able to detect common lifestyle related conditions including high cholesterol, vitamin deficiencies or diabetes.

24.4% of the UK population were at risk of at least one underlying health condition in 2019*. Reports from Randox Health home test kits will enable members to act early by suggesting simple lifestyle changes or directing them to a GP for further advice and guidance.

Simplyhealth Health Plan members can purchase discounted tests via the SimplyPlan app or the online Simplyhealth portal, under the SimplyRewards section. Members can choose from 10 Randox Health home test kits that measure up to twenty-four biomarkers related to heart, kidney, liver, iron, diabetes, thyroid, and nutritional health, providing fast, accurate, and convenient insights into their health.

The ten discounted at home test kits are: Vitamin D, Vitamin B12, Heart Health, Thyroid Health, General Health, Male Hormones, Female Hormones, STI, Anti-mullerian hormone (AMH), and Prostate-specific Antigen (PSA). Full details of each test can be found on the Simplyhealth and Randox websites.

David Ferguson, Chief Operations Officer for Randox Health said: “We are pleased to announce this partnership with Simplyhealth, providing their members with discounted Randox Health home testing kits.

“Our range of specialised health packages enable you to take control of your health, using our innovative diagnostic technologies which can give a comprehensive overview of an individual’s health, helping to detect the earliest signs of illness. Together we can work towards preventative healthcare.”

Claudia Nicholls, Chief Customer Officer for Simplyhealth said “A better understanding of the body can empower people to make diet and lifestyle changes that could help prevent future illness. We are passionate about making healthcare more accessible to all and our partnership with Randox Health is just one of the ways we are helping people to take more control of their health and prevent them from becoming ill.

Simplyhealth’s Health Plan for businesses can be tailored to meet the specific needs of any workforce and is available for under £5 per employee, per month, making it more accessible and easier to offer the entire workforce cover. Individuals can access the service as part of Simplyhealth’s 1-2-3 Health Plan from just £20 a month.

 


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