Towards an SI-Traceable Reference Measurement System for Seven Serum Apolipoproteins Using Bottom-Up Quantitative Proteomics: Conceptual Approach Enabled by Cross-Disciplinary/Cross-Sector Collaboration

Cardiovascular disease lipids and lipoproteins biomarker standardization

Cardiovascular disease (CVD) is the leading cause of mortality in the United States and globally. This review describes changes in CVD lipid and lipoprotein biomarker measurements that occurred in line with the evolution of clinical practice guidelines for CVD risk assessment and treatment. It also discusses the level of comparability of these biomarker measurements in clinical practice. Comparable and reliable measurements are achieved through assay standardization, which not only depends on correct test calibration but also on factors such as analytical sensitivity, selectivity, susceptibility to factors that can affect the analytical measurement process, and the stability of the test system over time. The current status of standardization for traditional and newer CVD biomarkers is discussed, as are approaches to setting and achieving standardization goals for low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), total cholesterol (TC), triglycerides (TG), lipoprotein(a) (Lp(a)), apolipoproteins (apo) A-I and B, and non-HDL-C. Appropriate levels of standardization for blood lipids are maintained by the Centers for Disease Control and Prevention's (CDC) CVD Biomarkers Standardization Program (CDC CVD BSP) using the analytical performance goals recommended by the National Cholesterol Education Program. The level of measurement agreement that can be achieved is dependent on the characteristics of the analytes and differences in measurement principles between reference measurement procedures and clinical assays. The technical and analytical limitations observed with traditional blood lipids are not observed with apolipoproteins. Additionally, apoB and Lp(a) may more accurately capture CVD risk and residual CVD risk, respectively, than traditional lipids, thus prompting current guidelines to recommend apolipoprotein measurements. This review further discusses CDC's approach to standardization and describes the analytical performance of traditional blood lipids and apoA-I and B observed over the past 11 years. The reference systems for apoA-I and B, previously maintained by a single laboratory, no longer exist, thus requiring the creation of new systems, which is currently underway. This situation emphasizes the importance of a collaborative network of laboratories, such as CDC's Cholesterol Reference Methods Laboratory Network (CRMLN), to ensure standardization sustainability. CDC is supporting the International Federation of Clinical Chemistry and Laboratory Medicine's (IFCC) work to establish such a network for lipoproteins. Ensuring comparability and reliability of CVD biomarker measurements through standardization remains critical for the effective implementation of clinical practice guidelines and for improving patient care. Utilizing experience gained over three decades, CDC CVD BSP will continue to improve the standardization of traditional and emerging CVD biomarkers together with stakeholders.

SysQuan: Repurposing SILAC Mice for the Cost-Effective Absolute Quantitation of the Human Proteome

Relative quantitation, used by most mass spectrometry-based proteomics laboratories to determine protein fold-changes, requires samples being processed and analyzed together for best comparability through minimizing batch differences. This limits the adoption of mass spectrometry-based proteomics in population-wide studies and the detection of subtle but relevant changes in heterogeneous samples. Absolute quantitation circumvents these limitations and enables comparison of results across laboratories, studies, and over time. However, high cost of the essential stable isotope labeled (SIL) standards prevents widespread access and limits the number of quantifiable proteins. Our new approach, called "SysQuan", repurposes SILAC mouse tissues/biofluids as system-wide internal standards for matched human samples to enable absolute quantitation of, theoretically, two-thirds of the human proteome using 157,086 shared tryptic peptides, of which 73,901 with lysine on the c terminus. We demonstrate that SysQuan enables quantification of 70% and 31% of the liver and plasma proteomes, respectively. We demonstrate for 14 metabolic proteins that abundant SIL mouse tissues enable cost-effective reverse absolute quantitation in, theoretically, 1000s of human samples. Moreover, 10,000s of light/heavy doublets in untargeted SysQuan datasets enable unique postacquisition absolute quantitation. SysQuan empowers researchers to replace relative quantitation with affordable absolute quantitation at scale, making data comparable across laboratories, diseases and tissues, enabling completely novel study designs and increasing reusability of data in repositories.

Strategies to verify equimolar peptide release in mass spectrometry-based protein quantification exemplified for apolipoprotein(a)

OBJECTIVES

Quantitative protein mass spectrometry (MS) is ideally suited for precision diagnostics and for reference standardization of protein analytes. At the Leiden Apolipoprotein Reference Laboratory we apply MS strategies to obtain detailed insight into the protein-to-peptide conversion in order to verify that quantifier peptides are not partly concealed in miscleaved protein backbone.

METHODS

Apolipoprotein(a) (apo(a)) was digested in a non-optimal manner to enhance the number of miscleaved peptides that were identified by high resolution liquid chromatography tandem-MS measurements. The protein-to-peptide conversion was carefully mapped with specific attention for miscleaved peptides that contain an apo(a) quantifier peptide. Four different isotopologues of each apo(a)-quantifier peptide were applied to evaluate linearity of internal peptide standards during measurement of specific real-life samples.

RESULTS

Two apo(a) quantifier peptides that were concealed in two different miscleaved peptides were included into a multiple reaction monitoring list in our targeted MS-based apo(a) quantifications to alert for potential protein digestion discrepancies. The presence of miscleaved peptides could be ruled out when applying our candidate reference measurement procedure (RMP) for apo(a) quantification.

CONCLUSIONS

These data further corroborate the validity of our apo(a) candidate RMP as higher order method for certification of commercial Lp(a) tests that is endorsed by the International Federation of Clinical Chemistry and Laboratory Medicine. MS-based molecular detection and quantification of heterogeneous apo(a) proteoforms will allow manufacturers' transitioning from confounded lipoprotein(a) [Lp(a)] mass levels into accurate molar apo(a) levels.

Rethinking cardiovascular risk: The emerging role of lipoprotein(a) screening

Lipoprotein(a) [Lp(a)] is a genetically inherited, independent risk factor for cardiovascular disease (CVD), affecting approximately 20-25% of the global population. Elevated Lp(a) levels are associated with a 2-3-fold increased risk of myocardial infarction and aortic valve stenosis, comparable to the risk seen in individuals with familial hypercholesterolemia. Despite its clinical relevance, the integration of Lp(a) screening into routine practice has been limited by inconsistent measurement techniques and a lack of targeted treatments. Recent advancements, including improved assays and the development of potential Lp(a)-lowering therapies, have renewed focus on the importance of Lp(a) screening. This review aims to clarify the role of Lp(a) in cardiovascular health by examining current evidence on who should be screened, when screening should occur, and the most accurate methods for measuring Lp(a). Key recommendations include universal, one-time screening for adults, selective screening for high-risk pediatric patients, and special considerations for individuals with conditions such as familial hypercholesterolemia and chronic kidney disease. Advances in assay technology now allow for more precise Lp(a) measurement, supporting better risk stratification. Additionally, emerging therapies that specifically target elevated Lp(a) levels could lead to more personalized management of CVD risk. Our findings support the integration of Lp(a) screening into routine cardiovascular risk assessment, highlighting its potential to improve early detection and prevention strategies across diverse patient populations.

Interaction Between Lipoprotein(a) and Other Lipid Molecules: A Review of the Current Literature

Lipoprotein(a) [Lp(a)] is a well-established causal risk factor for cardiovascular diseases (CVDs), as reported by multiple Mendelian randomization studies and large epidemiological studies. When elevated Lp(a) is combined with other risk factors, most notably elevated low-density lipoprotein cholesterol (LDL-C), a synergistic atherogenic effect has been reported. However, the current literature is conflicting regarding how Lp(a) interacts in the context of controlled LDL-C levels (e.g., <70 mg/dL) and whether reducing LDL-C can modify the atherogenic effect of Lp(a). In some studies, elevated Lp(a) was still significantly associated with a higher risk of cardiovascular events, despite controlled levels of LDL-C. In contrast, multiple studies have reported attenuation of the cardiovascular risk mediated by elevated Lp(a) with lower LDL-C levels. Moreover, the relationship between Lp(a) and triglycerides, high-density lipoprotein, and very low-density lipoprotein remains unclear. In this literature review, we summarize and discuss the current evidence regarding the interactions between Lp(a) and other lipid molecules, how they contribute to the pathogenesis of CVD, and future perspectives, particularly in the current era where promising targeted Lp(a)-lowering therapies are under development.

Apolipoprotein B: Bridging the Gap Between Evidence and Clinical Practice

Despite data suggesting that apolipoprotein B (apoB) measurement outperforms low-density lipoprotein cholesterol level measurement in predicting atherosclerotic cardiovascular disease risk, apoB measurement has not become widely adopted into routine clinical practice. One barrier for use of apoB measurement is lack of consistent guidance for clinicians on how to interpret and apply apoB results in clinical context. Whereas guidelines have often provided clear low-density lipoprotein cholesterol targets or triggers to initiate treatment change, consistent targets for apoB are lacking. In this review, we synthesize existing data regarding the epidemiology of apoB by comparing guideline recommendations regarding use of apoB measurement, describing population percentiles of apoB relative to low-density lipoprotein cholesterol levels, summarizing studies of discordance between low-density lipoprotein cholesterol and apoB levels, and evaluating apoB levels in clinical trials of lipid-lowering therapy to guide potential treatment targets. We propose evidence-guided apoB thresholds for use in cholesterol management and clinical care.

Consensus on lipoprotein(a) of the Spanish Society of Arteriosclerosis. Literature review and recommendations for clinical practice

The irruption of lipoprotein(a) (Lp(a)) in the study of cardiovascular risk factors is perhaps, together with the discovery and use of proprotein convertase subtilisin/kexin type 9 (iPCSK9) inhibitor drugs, the greatest novelty in the field for decades. Lp(a) concentration (especially very high levels) has an undeniable association with certain cardiovascular complications, such as atherosclerotic vascular disease (AVD) and aortic stenosis. However, there are several current limitations to both establishing epidemiological associations and specific pharmacological treatment. Firstly, the measurement of Lp(a) is highly dependent on the test used, mainly because of the characteristics of the molecule. Secondly, Lp(a) concentration is more than 80% genetically determined, so that, unlike other cardiovascular risk factors, it cannot be regulated by lifestyle changes. Finally, although there are many promising clinical trials with specific drugs to reduce Lp(a), currently only iPCSK9 (limited for use because of its cost) significantly reduces Lp(a). However, and in line with other scientific societies, the SEA considers that, with the aim of increasing knowledge about the contribution of Lp(a) to cardiovascular risk, it is relevant to produce a document containing the current status of the subject, recommendations for the control of global cardiovascular risk in people with elevated Lp(a) and recommendations on the therapeutic approach to patients with elevated Lp(a).

Canadian Society of Clinical Chemists Harmonized Pediatric Lipid Reporting Recommendations for Clinical Laboratories

Detecting dyslipidemia early is important because atherosclerosis originates in childhood and early treatment can improve outcomes. In 2022, the Canadian Cardiovascular Society (CCS) and Canadian Pediatric Cardiology Association (CPCA) published a clinical practice update to detect, evaluate, and manage pediatric dyslipidemia. However, guidance on its translation into clinical laboratories is lacking. The Canadian Society of Clinical Chemists Working Group on Reference Interval Harmonization Lipid Team aims to assist guideline implementation and promote harmonized pediatric lipid reporting across Canada. The 2022 CCS/CPCA clinical practice update, 2011 National Heart, Lung, and Blood Institute integrated guidelines, and new data analysis (Canadian pediatric reference values from the Canadian Laboratory Initiative on Pediatric Reference Intervals [CALIPER] and retrospective patient data from large community laboratories) were incorporated to develop 5 key recommendations. These include recommendations to: (1) offer nonfasting and fasting lipid testing; (2) offer a lipid panel including total cholesterol, low-density lipoprotein cholesterol (LDL-C), high-density lipoprotein cholesterol (HDL-C), non-HDL-C, and triglycerides, with apolipoprotein B and lipoprotein(a) available as individually orderable tests; (3) flag total cholesterol, LDL-C, and non-HDL-C results ≥ 95th percentile, and HDL-C results < 10th percentile, as recommended by CCS/CPCA/National Heart, Lung, and Blood Institute and validated by CALIPER, and flag apolipoprotein B and nonfasting triglyceride results ≥ 95th percentile on the basis of CALIPER, and do not flag Lp(a) results but mention the adult cutoff in the interpretive comments; (4) implement interpretive comments listed in the current report; and (5) implement the National Institutes of Health LDL-C equation. The Canadian Society of Clinical Chemists Working Group on Reference Interval Harmonization Lipid Team will support clinical laboratories to implement these recommendations using knowledge translation strategies. Harmonizing pediatric lipid reporting across Canadian clinical laboratories will optimize clinical decision-making and improve cardiovascular risk management in youth.

An LC-MS/MS method for serum cystatin C quantification and its comparison with two commercial immunoassays

OBJECTIVES

The standardization of cystatin C (CysC) measurement has received increasing attention in recent years due to its importance in estimating glomerular filtration rate (GFR). Mass spectrometry-based assays have the potential to provide an accuracy base for CysC measurement. However, a precise, accurate and sustainable LC-MS/MS method for CysC is still lacking.

METHODS

The developed LC-MS/MS method quantified CysC by detecting signature peptide (T3) obtained from tryptic digestion. Stable isotope labeled T3 peptide (SIL-T3) was spiked to control matrix effects and errors caused by liquid handling. The protein denaturation, reduction and alkylation procedures were combined into a single step with incubation time of 1 h, and the digestion lasted for 3.5 h. In the method validation, digestion time-course, imprecision, accuracy, matrix effect, interference, limit of quantification (LOQ), carryover, linearity, and the comparability to two routine immunoassays were evaluated.

RESULTS

No significant matrix effect or interference was observed with the CysC measurement. The LOQ was 0.21 mg/L; the within-run and total imprecision were 1.33-2.05 % and 2.18-3.90 % for three serum pools (1.18-5.34 mg/L). The LC-MS/MS method was calibrated by ERM-DA471/IFCC and showed good correlation with two immunoassays traceable to ERM-DA471/IFCC. However, significant bias was observed for immunoassays against the LC-MS/MS method.

CONCLUSIONS

The developed LC-MS/MS method is robust and simpler and holds the promise to provide an accuracy base for routine immunoassays, which will promote the standardization of CysC measurement.

Lipoprotein(a), platelet function and cardiovascular disease

Lipoprotein(a) (Lp(a)) is associated with atherothrombosis through several mechanisms, including putative antifibrinolytic properties. However, genetic association studies have not demonstrated an association between high plasma levels of Lp(a) and the risk of venous thromboembolism, and studies in patients with highly elevated Lp(a) levels have shown that Lp(a) lowering does not modify the clotting properties of plasma ex vivo. Lp(a) can interact with several platelet receptors, providing biological plausibility for a pro-aggregatory effect. Observational clinical studies suggest that elevated plasma Lp(a) concentrations are associated with worse long-term outcomes in patients undergoing revascularization. Furthermore, in these patients, those with elevated plasma Lp(a) levels derive more benefit from prolonged dual antiplatelet therapy than those with normal Lp(a) levels. The ASPREE trial in healthy older individuals treated with aspirin showed a reduction in ischaemic events in those who had a single-nucleotide polymorphism in LPA that is associated with elevated Lp(a) levels in plasma, without an increase in bleeding events. In this Review, we re-examine the role of Lp(a) in the regulation of platelet function and suggest areas of research to define further the clinical relevance to cardiovascular disease of the observed associations between Lp(a) and platelet function.

An LC-MS-based designated comparison method with similar performance to the Lp(a) reference measurement procedure to guide molar Lp(a) standardization

BACKGROUND

The 2022 consensus statement of the European Atherosclerosis Society (EAS) on lipoprotein(a) (Lp(a)) recognizes the role of Lp(a) as a relevant genetically determined risk factor and recommends its measurement at least once in an individual's lifetime. It also strongly urges that Lp(a) test results are expressed as apolipoprotein (a) (apo(a)) amount of substance in molar units and no longer in confounded Lp(a) mass units (mg/dL or mg/L). Therefore, IVD manufacturers should transition to molar units. A prerequisite for this transition is the availability of an Lp(a) Reference Measurement Procedure (RMP) that allows unequivocal molecular detection and quantification of apo(a) in Lp(a). To that end an ISO 17511:2020 compliant LC-MS based and IFCC-endorsed RMP has been established that targets proteotypic peptides of apolipoprotein(a) (apo(a)) in Lp(a). The RMP is laborious and requires highly skilled operators. To guide IVD-manufacturers of immunoassay-based Lp(a) test kits in the transition from mass to molar units, a Designated Comparison Method (DCM) has been developed and evaluated.

METHODS

To assess whether the DCM provides equivalent results compared to the RMP, the procedural designs were compared and the analytical performance of DCM and RMP were first evaluated in a head-to-head comparison. Subsequently, apo(a) was quantified in 153 human clinical serum samples. Both DCM and RMP were calibrated using external native calibrators that produce results traceable to SRM2B. Measurement uncertainty (MU) was checked against predefined allowable MU.

RESULTS

The major difference in the design of the DCM for apo(a) is the use of only one enzymatic digestion step. The analytical performance of the DCM and RMP for apo(a) is highly similar. In a direct method comparison, equivalent results were obtained with a median regression slope 0.997 of and a median bias of - 0.2 nmol/L (- 0.2%); the intermediate imprecision of the test results was within total allowable error (TEa) (CVa of 10.2% at 90 nmol/L).

CONCLUSIONS

The semi-automated, higher throughput, LC-MS-based method for Lp(a) meets the predefined analytical performance specifications and allowable MU and is hence applicable as a higher order Designated Comparison Method, which is ideally suited to guide IVD manufacturers in the transition from Lp(a) mass to molar units.

Developing an SI-traceable Lp(a) reference measurement system: a pilgrimage to selective and accurate apo(a) quantification

In the past decade a remarkable rebirth of serum/plasma lipoprotein(a) (Lp(a)) as an independent risk factor of cardiovascular disease (CVD) occurred. Updated evidence for a causal continuous association in different ethnic groups between Lp(a) concentrations and cardiovascular outcomes has been published in the latest European Atherosclerosis Society (EAS) Lp(a) consensus statement. Interest in measuring Lp(a) at least once in a person's lifetime moreover originates from the development of promising new Lp(a) lowering drugs. Accurate and clinically effective Lp(a) tests are of key importance for the timely detection of high-risk individuals and for future evaluation of the therapeutic effects of Lp(a) lowering medication. To this end, it is necessary to improve the performance and standardization of existing Lp(a) tests, as is also noted in the Lp(a) consensus statement. Consequently, a state-of-the-art internationally endorsed reference measurement system (RMS) must be in place that allows for performance evaluation of Lp(a) field tests in order to certify their validity and accuracy. An ELISA-based RMS from Northwest Lipid Research Laboratory (University of Washington, Seattle, USA) has been available since the 1990s. A next-generation apo(a)/Lp(a) RMS is now being developed by a working group from the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC). The envisioned apo(a) RMS is based on the direct measurement of selected proteotypic fragments generated after proteolytic digestion using quantitative protein mass spectrometry (MS). The choice for an MS-based RMS enables selective measurement of the proteotypic peptides and is by design apo(a) isoform insensitive. Clearly, the equimolar conversion of apo(a) into the surrogate peptide measurands is required to obtain accurate Lp(a) results. The completeness of proteolysis under reaction conditions from the candidate reference measurement procedure (RMP) has been demonstrated for the quantifying apo(a) peptides. Currently, the candidate apo(a) RMP is endorsed by the IFCC and recommendations for suitable secondary reference materials have been made in a recent commutability study paper. Ongoing efforts toward a complete apo(a) RMS that is listed by the Joint Committee on Traceability in Laboratory Medicine (JCTLM) are focused on the peptide-based calibration and the establishment of a network of calibration laboratories running the apo(a) RMS in a harmonized way. Once completed, it will be the holy grail for evaluation and certification of Lp(a) field methods.

Clinical Proteomics for Solid Organ Tissues

The evaluation of biopsied solid organ tissue has long relied on visual examination using a microscope. Immunohistochemistry is critical in this process, labeling and detecting cell lineage markers and therapeutic targets. However, while the practice of immunohistochemistry has reshaped diagnostic pathology and facilitated improvements in cancer treatment, it has also been subject to pervasive challenges with respect to standardization and reproducibility. Efforts are ongoing to improve immunohistochemistry, but for some applications, the benefit of such initiatives could be impeded by its reliance on monospecific antibody-protein reagents and limited multiplexing capacity. This perspective surveys the relevant challenges facing traditional immunohistochemistry and describes how mass spectrometry, particularly liquid chromatography-tandem mass spectrometry, could help alleviate problems. In particular, targeted mass spectrometry assays could facilitate measurements of individual proteins or analyte panels, using internal standards for more robust quantification and improved interlaboratory reproducibility. Meanwhile, untargeted mass spectrometry, showcased to date clinically in the form of amyloid typing, is inherently multiplexed, facilitating the detection and crude quantification of 100s to 1000s of proteins in a single analysis. Further, data-independent acquisition has yet to be applied in clinical practice, but offers particular strengths that could appeal to clinical users. Finally, we discuss the guidance that is needed to facilitate broader utilization in clinical environments and achieve standardization.

High residual cardiovascular risk after lipid-lowering: prime time for Predictive, Preventive, Personalized, Participatory, and Psycho-cognitive medicine

As time has come to translate trial results into individualized medical diagnosis and therapy, we analyzed how to minimize residual risk of cardiovascular disease (CVD) by reviewing papers on "residual cardiovascular disease risk". During this review process we found 989 papers that started off with residual CVD risk after initiating statin therapy, continued with papers on residual CVD risk after initiating therapy to increase high-density lipoprotein-cholesterol (HDL-C), followed by papers on residual CVD risk after initiating therapy to decrease triglyceride (TG) levels. Later on, papers dealing with elevated levels of lipoprotein remnants and lipoprotein(a) [Lp(a)] reported new risk factors of residual CVD risk. And as new risk factors are being discovered and new therapies are being tested, residual CVD risk will be reduced further. As we move from CVD risk reduction to improvement of patient management, a paradigm shift from a reductionistic approach towards a holistic approach is required. To that purpose, a personalized treatment dependent on the individual's CVD risk factors including lipid profile abnormalities should be configured, along the line of P5 medicine for each individual patient, i.e., with Predictive, Preventive, Personalized, Participatory, and Psycho-cognitive approaches.

Exploring Utilization and Establishing Reference Intervals for the Apolipoprotein B Test in the Korean Population

We investigated the reference intervals for Apolipoprotein B (ApoB), a valuable biomarker for cardiovascular diseases, in Korean adults who had undergone health check-ups and showed normal lipid levels under traditional lipid tests, including total cholesterol, triglyceride, and high-density lipoprotein cholesterol, along with ApoB. We compared the findings with different cutoffs for ApoB from international clinical guidelines. Among a total of 264,105 traditional lipid test sets, only 464 (0.2%) included ApoB tests, indicating underutilization of this test in health check-up clinics in Korea. From these 464 samples, 334 ApoB results (164 men and 170 women) with normal traditional lipid test results were used to establish reference intervals. Using the parametric method (mean ± 2 SD), the reference intervals ranged from 46 to 134 mg/dL for men and 49 to 129 mg/dL for women. Employing the non-parametric method (central 95th percentile value), the reference intervals ranged from 50 to 131 mg/dL for men and 51 to 127 mg/dL for women. The prevalence of high ApoB did not significantly differ by sex when considering the established reference intervals for each sex and the cutoffs recommended by international clinical guidelines. This study enhances knowledge on ApoB reference intervals in the Korean population, and it will in aid test result interpretation for clinicians and laboratories.

Consensus document on Lipoprotein(a) from the Italian Society for the Study of Atherosclerosis (SISA)

AIMS

In view of the consolidating evidence on the causal role of Lp(a) in cardiovascular disease, the Italian Society for the Study of Atherosclerosis (SISA) has assembled a consensus on Lp(a) genetics and epidemiology, together with recommendations for its measurement and current and emerging therapeutic approaches to reduce its plasma levels. Data on the Italian population are also provided.

DATA SYNTHESIS

Lp(a) is constituted by one apo(a) molecule and a lipoprotein closely resembling to a low-density lipoprotein (LDL). Its similarity with an LDL, together with its ability to carry oxidized phospholipids are considered the two main features making Lp(a) harmful for cardiovascular health. Plasma Lp(a) concentrations vary over about 1000 folds in humans and are genetically determined, thus they are quite stable in any individual. Mendelian Randomization studies have suggested a causal role of Lp(a) in atherosclerotic cardiovascular disease (ASCVD) and aortic valve stenosis and observational studies indicate a linear direct correlation between cardiovascular disease and Lp(a) plasma levels. Lp(a) measurement is strongly recommended once in a patient's lifetime, particularly in FH subjects, but also as part of the initial lipid screening to assess cardiovascular risk. The apo(a) size polymorphism represents a challenge for Lp(a) measurement in plasma, but new strategies are overcoming these difficulties. A reduction of Lp(a) levels can be currently attained only by plasma apheresis and, moderately, with PCSK9 inhibitor treatment.

CONCLUSIONS

Awaiting the approval of selective Lp(a)-lowering drugs, an intensive management of the other risk factors for individuals with elevated Lp(a) levels is strongly recommended.

Use of Apolipoprotein B in the Era of Precision Medicine: Time for a Paradigm Change?

Atherosclerotic cardiovascular disease (ASCVD) remains the leading cause of death worldwide and the risk of a major cardiovascular event is highest among those with established disease. Ongoing management of these patients relies on the accurate assessment of their response to any prescribed therapy, and their residual risk, in order to optimize treatment. Recent international guidelines and position statements concur that the plasma concentration of apolipoprotein B (apoB) is the most accurate measure of lipoprotein associated ASCVD risk. This is especially true for the growing number of individuals with diabetes, obesity, or the metabolic syndrome, and those on statin therapy. Most guidelines, however, continue to promote LDL-C as the primary risk marker due to uncertainty as to whether the greater accuracy of apoB is sufficient to warrant a paradigm shift. Recommendations regarding apoB measurement vary, and the information provided on how to interpret apoB results is sometimes insufficient, particularly for non-lipid specialists. Misinformation regarding the reliability of the assays is also frequently repeated despite its equivalent or better standardization than many other diagnostic assays. Thus, demand for apoB testing is relatively low, which means there is little incentive to increase its availability or reduce its cost. In this review, we examine the results of recent clinical outcomes studies and meta-analyses on the relative values of apoB, LDL-C, and non-HDL-C as markers of ASCVD risk. Although there is seemingly minimal difference among these markers when only population-based metrics are considered, it is evident from our analysis that, from a personalized or precision medicine standpoint, many individuals would benefit, at a negligible total cost, if apoB measurement were better integrated into the diagnosis and treatment of ASCVD.

Role of lncRNAs in Remodeling of the Coronary Artery Plaques in Patients with Atherosclerosis

INTRODUCTION

Cardiovascular diseases (CVDs) are the leading cause of death worldwide according to World Health Organization (WHO) data. Atherosclerosis is considered as a chronic inflammatory disease that develops in response to damage to the vascular intima-media layer in most cases. In recent years, epigenetic events have emerged as important players in the development and progression of CVDs. Since noncoding RNA (ncRNAs) are important regulators in the organization of the pathophysiological processes of the cardiovascular system, they have the potential to be used as therapeutic targets, diagnostic and prognostic biomarkers. In this study long noncoding RNA (lncRNA) and mRNA gene expression were compared between coronary atherosclerotic plaques (CAP) and the internal mammary artery (IMA)  which has the same genetic makeup and is exposed to the same environmental stress conditions with CAP in the same individual.

METHODS

lncRNA and mRNA gene expressions were determined using the microarray in the samples. Microarray results were validated by RT-qPCR. Differentially expressed genes (DEGs; lncRNAs and mRNAs) were determined by GeneSpring (Ver 3.0) [p values < 0.05 and fold change (FC) > 2]. DAVID bioinformatics program was used for Gene Ontology (GO) annotation and enrichment analyses of statistically significant genes between CAP and IMA tissue.

RESULTS AND CONCLUSIONS

In our study, 345 DEGs were found to be statistically significant (p < 0.05; FC > 2) between CAP and IMA. Of these, 65 were lncRNA and 280 were mRNA. Thirty-three lncRNAs were upregulated, while 32 lncRNAs were downregulated. Some of the important mRNAs are SPP1, CYP4B1, CHRDL1, MYOC, and ALKAL2, while some of the lncRNAs are LOC105377123, LINC01857, DIO3OS, LOC101928134, and KCNA3 between CAP and IMA tissue. We also identified genes that correlated with statistically significant lncRNAs. The results of this study are expected to be an important source of data in the development of new genetically based drugs to prevent atherosclerotic plaque. In addition, the data obtained may contribute to the explanation of the epigenetic mechanisms that play a role in the pathological basis of the process that protects the IMA from atherosclerosis.

Standardization of Apolipoprotein B, LDL-Cholesterol, and Non-HDL-Cholesterol

Concern continues about whether the measurement of apolipoprotein B (apoB) is adequately standardized, and therefore, whether apoB should be applied widely in clinical care. This concern is misplaced. Our objective is to explain why and what the term "standardization" means. To produce clinically valid results, a test must accurately, precisely, and selectively measure the marker of interest. That is, it must be standardized. Accuracy refers to how closely the result obtained with 1 method corresponds to the result obtained with the standard method, precision to how reproducible the result is on repeated testing, and selectivity to how susceptible the method is to error by inclusion of other classes of lipoprotein particles. Multiple expert groups have determined that the measurement of apoB is adequately standardized for clinical care, and that apoB can be measured inexpensively, using widely available automated methods, more accurately, precisely, and selectively than low-density lipoprotein cholesterol or non-high-density lipoprotein cholesterol. ApoB is a standard superior to low-density lipoprotein cholesterol and high-density lipoprotein cholesterol because it is a defined molecule, whereas the cholesterol markers are the mass of cholesterol within lipoprotein particles defined by their density, not by their molecular structure. Nevertheless, the standardization of apoB is being further improved by the application of mass spectrophotometric methods, whereas the limitations in the standardization and, therefore, the accurate, precise, and selective measurement of low-density lipoprotein cholesterol and high-density lipoprotein cholesterol are unlikely to be overcome. We submit that greater accuracy, precision, and selectivity in measurement is a decisive advantage for apoB in the modern era of intensive lipid-lowering therapies.

Daring to dream: Targeting lipoprotein(a) as a causal and risk-enhancing factor

Lipoprotein(a) [Lp(a)], a distinct lipoprotein class, has become a major focus for cardiovascular research. This review is written in light of the recent guideline and consensus statements on Lp(a) and focuses on 1) the causal association between Lp(a) and cardiovascular outcomes, 2) the potential mechanisms by which elevated Lp(a) contributes to cardiovascular diseases, 3) the metabolic insights on the production and clearance of Lp(a) and 4) the current and future therapeutic approaches to lower Lp(a) concentrations. The concentrations of Lp(a) are under strict genetic control. There exists a continuous relationship between the Lp(a) concentrations and risk for various endpoints of atherosclerotic cardiovascular disease (ASCVD). One in five people in the Caucasian population is considered to have increased Lp(a) concentrations; the prevalence of elevated Lp(a) is even higher in black populations. This makes Lp(a) a cardiovascular risk factor of major public health relevance. Besides the association between Lp(a) and myocardial infarction, the relationship with aortic valve stenosis has become a major focus of research during the last decade. Genetic studies provided strong support for a causal association between Lp(a) and cardiovascular outcomes: carriers of genetic variants associated with lifelong increased Lp(a) concentration are significantly more frequent in patients with ASCVD. This has triggered the development of drugs that can specifically lower Lp(a) concentrations: mRNA-targeting therapies such as anti-sense oligonucleotide (ASO) therapies and short interfering RNA (siRNA) therapies have opened new avenues to lower Lp(a) concentrations more than 95%. Ongoing Phase II and III clinical trials of these compounds are discussed in this review.

Frequent questions and responses on the 2022 lipoprotein(a) consensus statement of the European Atherosclerosis Society

In 2022, the European Atherosclerosis Society (EAS) published a new consensus statement on lipoprotein(a) [Lp(a)], summarizing current knowledge about its causal association with atherosclerotic cardiovascular disease (ASCVD) and aortic stenosis. One of the novelties of this statement is a new risk calculator showing how Lp(a) influences lifetime risk for ASCVD and that global risk may be underestimated substantially in individuals with high or very high Lp(a) concentration. The statement also provides practical advice on how knowledge about Lp(a) concentration can be used to modulate risk factor management, given that specific and highly effective mRNA-targeted Lp(a)-lowering therapies are still in clinical development. This advice counters the attitude: "Why should I measure Lp(a) if I can't lower it?". Subsequent to publication, questions have arisen relating to how the recommendations of this statement impact everyday clinical practice and ASCVD management. This review addresses 30 of the most frequently asked questions about Lp(a) epidemiology, its contribution to cardiovascular risk, Lp(a) measurement, risk factor management and existing therapeutic options.

Are we seeing the light at the end of the tunnel for high lipoprotein(a)? Lipoprotein(a)

Lipoprotein (a) (Lp(a)) attests to be of interest as a new lipoprotein target. However, Lp(a) was discovered in 1963 and since then was recognized as a low-density lipoprotein (LDL)-like lipoprotein with a structurally similar domain to plasminogen. We are increasingly recognizing the importance of Lp(a) and cardiovascular pathologies including atherosclerotic cardiovascular disease, aortic valve stenosis, heart failure, and atrial fibrillation. However, we neither have a standardized measurement method nor an appropriate agent to intervene with this old threat that we have recognized for more than 50 years. Herein, we present an up-to-date review of our knowledge about Lp(a) covering measurement methods, its associates, and summary of the currently available therapies and emerging therapeutic agents for the management of high Lp(a) in the light of recent evidence and guideline recommendations

Detection strategies for elevated lipoprotein(a): will implementation let the genie out of the bottle?

PURPOSE OF REVIEW

Elevated Lp(a) level is an important causal risk factor for atherosclerotic cardiovascular disease (ASCVD), principally coronary artery disease. Selective testing for Lp(a) is highly recommended in patients at intermediate and high risk for ASCVD. Lp(a) levels are predominantly genetically determined, and this has implications for cascade testing.

RECENT FINDINGS

Recent studies show that cascade testing is effective in identifying elevated Lp(a) in close relatives of probands with high Lp(a). Apart from selective testing and cascade testing as detection strategies, some recent guidelines recommend testing of Lp(a) in all adults at least once in their lifetime and various implementation strategies have been suggested.

SUMMARY

Hyper-Lp(a) is an important global health problem that can be easily detected. Hyper-Lp(a) meets all the criteria for universal screening except that there is not yet supportive evidence from clinical interventional trials showing a reduction of ASCVD events. The cost-effectiveness of the various detection and implementation strategies need to be further evaluated.

Development of an LC-MRM-MS-Based Candidate Reference Measurement Procedure for Standardization of Serum Apolipoprotein (a) Tests

BACKGROUND

Medical results generated by European CE Marking for In Vitro Diagnostic or in-house tests should be traceable to higher order reference measurement systems (RMS), such as International Federation of Clinical Chemistry and Laboratory Medicine (IFCC)-endorsed reference measurement procedures (RMPs) and reference materials. Currently, serum apolipoprotein (a) [apo(a)] is recognized as a novel risk factor for cardiovascular risk assessment and patient management. The former RMS for serum apo(a) is no longer available; consequently, an International System of Units (SI)-traceable, ideally multiplexed, and sustainable RMS for apo(a) is needed.

METHODS

A mass spectrometry (MS)-based candidate RMP (cRMP) for apo(a) was developed using quantitative bottom-up proteomics targeting 3 proteotypic peptides. The method was provisionally validated according to ISO 15193 using a single human serum based calibrator traceable to the former WHO-IFCC RMS.

RESULTS

The quantitation of serum apo(a) was by design independent of its size polymorphism, was linear from 3.8 to 456 nmol/L, and had a lower limit of quantitation for apo(a) of 3.8 nmol/L using peptide LFLEPTQADIALLK. Interpeptide agreement showed Pearson Rs of 0.987 and 0.984 for peptides GISSTVTGR and TPENYPNAGLTR, and method comparison indicated good correspondence (slopes 0.977, 1.033, and 1.085 for LFLEPTQADIALLK, GISSTVTGR, and TPENYPNAGLTR). Average within-laboratory imprecision of the cRMP was 8.9%, 11.9%, and 12.8% for the 3 peptides.

CONCLUSIONS

A robust, antibody-independent, MS-based cRMP was developed as higher order RMP and an essential part of the apo(a) traceability chain and future RMS. The cRMP fulfils predefined analytical performance specifications, making it a promising RMP candidate in an SI-traceable MS-based RMS for apo(a).

Commutability Assessment of Candidate Reference Materials for Lipoprotein(a) by Comparison of a MS-based Candidate Reference Measurement Procedure with Immunoassays

BACKGROUND

Elevated concentrations of lipoprotein(a) [Lp(a)] are directly related to an increased risk of cardiovascular diseases, making it a relevant biomarker for clinical risk assessment. However, the lack of global standardization of current Lp(a) measurement procedures (MPs) leads to inconsistent patient care. The International Federation for Clinical Chemistry and Laboratory Medicine working group on quantitating apolipoproteins by mass spectrometry (MS) aims to develop a next-generation SI (International system of units)-traceable reference measurement system consisting of a MS-based, peptide-calibrated reference measurement procedure (RMP) and secondary serum-based reference materials (RMs) certified for their apolipoprotein(a) [apo(a)] content. To reach measurement standardization through this new measurement system, 2 essential requirements need to be fulfilled: a sufficient correlation among the MPs and appropriate commutability of future serum-based RMs.

METHODS

The correlation among the candidate RMP (cRMP) and immunoassay-based MPs was assessed by measuring a panel of 39 clinical samples (CS). In addition, the commutability of 14 different candidate RMs was investigated.

RESULTS

Results of the immunoassay-based MPs and the cRMPs demonstrated good linear correlations for the CS but some significant sample-specific differences were also observed. The results of the commutability study show that RMs based on unspiked human serum pools can be commutable with CS, whereas human pools spiked with recombinant apo(a) show different behavior compared to CS.

CONCLUSIONS

The results of this study show that unspiked human serum pools are the preferred candidate secondary RMs in the future SI-traceable Lp(a) Reference Measurement System.

Apolipoprotein Proteomics for Residual Lipid-Related Risk in Coronary Heart Disease

BACKGROUND

Recognition of the importance of conventional lipid measures and the advent of novel lipid-lowering medications have prompted the need for more comprehensive lipid panels to guide use of emerging treatments for the prevention of coronary heart disease (CHD). This report assessed the relevance of 13 apolipoproteins measured using a single mass-spectrometry assay for risk of CHD in the PROCARDIS case-control study of CHD (941 cases/975 controls).

METHODS

The associations of apolipoproteins with CHD were assessed after adjustment for established risk factors and correction for statin use. Apolipoproteins were grouped into 4 lipid-related classes [lipoprotein(a), low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triglycerides] and their associations with CHD were adjusted for established CHD risk factors and conventional lipids. Analyses of these apolipoproteins in a subset of the ASCOT trial (Anglo-Scandinavian Cardiac Outcomes Trial) were used to assess their within-person variability and to estimate a correction for statin use. The findings in the PROCARDIS study were compared with those for incident cardiovascular disease in the Bruneck prospective study (n=688), including new measurements of Apo(a).

RESULTS

Triglyceride-carrying apolipoproteins (ApoC1, ApoC3, and ApoE) were most strongly associated with the risk of CHD (2- to 3-fold higher odds ratios for top versus bottom quintile) independent of conventional lipid measures. Likewise, ApoB was independently associated with a 2-fold higher odds ratios of CHD. Lipoprotein(a) was measured using peptides from the Apo(a)-kringle repeat and Apo(a)-constant regions, but neither of these associations differed from the association with conventionally measured lipoprotein(a). Among HDL-related apolipoproteins, ApoA4 and ApoM were inversely related to CHD, independent of conventional lipid measures. The disease associations with all apolipoproteins were directionally consistent in the PROCARDIS and Bruneck studies, with the exception of ApoM.

CONCLUSIONS

Apolipoproteins were associated with CHD independent of conventional risk factors and lipids, suggesting apolipoproteins could help to identify patients with residual lipid-related risk and guide personalized approaches to CHD risk reduction.

Quantitative protein mass-spectrometry requires a standardized pre-analytical phase

OBJECTIVES

Quantitative protein mass-spectrometry (QPMS) in blood depends on tryptic digestion of proteins and subsequent measurement of representing peptides. Whether serum and plasma can be used interchangeably and whether in-vitro anticoagulants affect the recovery is unknown. In our laboratory serum samples are the preferred matrix for QPMS measurement of multiple apolipoproteins. In this study, we investigated the effect of different matrices on apolipoprotein quantification by mass spectrometry.

METHODS

Blood samples were collected from 44 healthy donors in Beckton Dickinson blood tubes simultaneously for serum (with/without gel) and plasma (heparin, citrate or EDTA). Nine apolipoproteins were quantified according to standard operating procedure using value-assigned native serum calibrators for quantitation. Tryptic digestion kinetics were investigated in the different matrices by following formation of peptides for each apolipoprotein in time, up to 22 h.

RESULTS

In citrate plasma recovery of apolipoproteins showed an overall reduction with a bias of -14.6%. For heparin plasma only -0.3% bias was found compared to serum, whereas for EDTA-plasma reduction was more pronounced (-5.3% bias) and variable with >14% reduction for peptides of apoA-I, A-II and C-III. Digestion kinetics revealed that especially slow forming peptides showed reduced formation in EDTA-plasma.

CONCLUSIONS

Plasma anticoagulants affect QPMS test results. Heparin plasma showed comparable results to serum. Reduced concentrations in citrate plasma can be explained by dilution, whereas reduced recovery in EDTA-plasma is dependent on altered proteolytic digestion efficiency. The results highlight the importance of a standardized pre-analytical phase for accurate QPMS applications in clinical chemistry.

Consensus and guidelines on lipoprotein(a) - seeing the forest through the trees

PURPOSE OF THE REVIEW

Over the past decade, lipoprotein(a) [Lp(a)] made it to several consensus and guideline documents. This review aims to summarize the literature which underlies the various recommendations and compares recent European and North American consensus and guideline documents of the recent 3-4 years.

RECENT FINDINGS

Multiple large epidemiological and genetic studies have provided strong evidence for a causal association between Lp(a) concentrations and atherosclerotic cardiovascular disease (ASCVD) and aortic valve stenosis. There is a dose-dependent linear relationship between Lp(a) and ASCVD risk advocating to consider Lp(a) on a continuous scale rather than using thresholds. The best way to implement this in the clinic is by individualizing the Lp(a)-related risk using tools such as the 'Lp(a) risk calculator' ( http://www.lpaclinicalguidance.com ) that takes into account the Lp(a) level in the context of an individual's traditional risk factors and global risk for ASCVD. There is growing agreement across the guidelines regarding the clinical utility of measuring Lp(a) and more recent expert groups advocate for a general screening approach applied to all adults. As long as the cardiovascular outcomes trials for specific Lp(a)-lowering drugs are in progress, the current management of patients with high Lp(a) should focus on the comprehensive management of all other modifiable ASCVD risk factors which can be therapeutically addressed as per guideline recommendations.

SUMMARY

Since the contribution of high Lp(a) concentrations to global ASCVD risk has been underestimated in the past, a clear recommendation to measure Lp(a) at least once in a person's lifetime is imperative. Recent expert consensus recommendations provide clinicians with direction on how to manage the excess risk associated with elevated Lp(a) concentration by comprehensive and individualized management of modifiable ASCVD risk factors while awaiting the results of clinical trials of Lp(a) targeted therapies.

Advances in rapid detection of SARS-CoV-2 by mass spectrometry

COVID-19 has already been lasting for more than two years and it has been severely affecting the whole world. Still, detection of SARS-CoV-2 remains the frontline approach to combat the pandemic, and the reverse transcription polymerase chain reaction (RT-PCR)-based method is the well recognized detection method for the enormous analytical demands. However, the RT-PCR method typically takes a relatively long time, and can produce false positive and false negative results. Mass spectrometry (MS) is a very commonly used technique with extraordinary sensitivity, specificity and speed, and can produce qualitative and quantitative information of various analytes, which cannot be achieved by RT-PCR. Since the pandemic outbreak, various mass spectrometric approaches have been developed for rapid detection of SARS-CoV-2, including the LC-MS/MS approaches that could allow analysis of several hundred clinical samples per day with one MS system, MALDI-MS approaches that could directly analyze clinical samples for the detection, and efforts for the on-site detection with portable devices. In this review, these mass spectrometric approaches were summarized, and their pros and cons as well as further development were also discussed.

New Horizons: Revival of Lipoprotein (a) as a Risk Factor for Cardiovascular Disease

The status of lipoprotein (a) [Lp(a)] as a cardiovascular risk factor has been resurrected by advances in genetics. Mendelian randomization studies show a causal link of Lp(a) with coronary artery disease (CAD), peripheral artery disease (PAD), and calcific aortic valve stenosis (CAVS). The genetics of Lp(a) is complex and extends beyond the kringle-IV type 2, as it is also dependent on ancestry. The plasma concentration of Lp(a) is determined by the hepatic production of apolipoprotein(a) [apo(a)] component of Lp(a), supporting the use of nucleic acids that inhibit the messenger RNA (mRNA) gene transcript for apo(a). Analytical barriers to measurement of Lp(a) are being addressed using isoform independent assays and a traceable standard. The association of Lp(a) and atherosclerotic cardiovascular disease is higher for myocardial infarction than PAD and CAVS. Increased risk of type 2 diabetes mellitus associated with low Lp(a) levels is perplexing and requires further investigation. The greatest advancement in Lp(a)-lowering therapies is based on using RNA therapeutics that are now being investigated in clinical trials. Proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibition lowers Lp(a) modestly, but whether cardiovascular benefit is independent of low-density lipoprotein lowering remains unclear. Opportunistic and selective testing for Lp(a) is supported by moderate evidence, with the case for universal screening premature. Modification of behavioral and clinical risk factors may be targeted to mitigate Lp(a)-mediated risk of cardiovascular disease. Clinical practice guidelines have been developed to address gaps in care of high Lp(a), but full implementation awaits the findings of clinical outcome trials using RNA-directed therapies currently underway.

Overcoming challenges regarding reference materials and regulations that influence global standardization of medical laboratory testing results

BACKGROUND

Standardized results for laboratory tests are particularly important when their interpretation depends on fixed medical practice guidelines or common reference intervals. The medical laboratory community has developed a roadmap for an infrastructure to achieve standardized test results described in the International Organization for Standardization standard 17511:2020 In vitro diagnostic medical devices - Requirements for establishing metrological traceability of values assigned to calibrators, trueness control materials and human samples. Among the challenges to implementing metrological traceability are the availability of fit-for-purpose matrix-based certified reference materials (CRMs) and requirements for regulatory review that differ among countries. A workshop in December 2021 focused on these two challenges and developed recommendations for improved practices.

DISCUSSION

The participants agreed that prioritization of measurands for standardization should be based on their impact on medical decisions in a clinical pathway. Ensuring that matrix-based CRMs are globally available for more measurands will enable fit-for-purpose calibration hierarchies for more laboratory tests. Regulation of laboratory tests is important to ensure safety and effectiveness for the populations served. Because regulations are country or region specific, manufacturers must submit recalibration changes intended to standardize results for regulatory review to all areas in which a measuring system is marketed.

RECOMMENDATIONS

A standardization initiative requires collaboration and planning among all interested stakeholders. Global collaboration should be further developed for prioritization of measurands for standardization, and for coordinating the production and supply of CRMs worldwide. More uniform regulatory submission requirements are desirable when recalibration is implemented to achieve internationally standardized results.

Ancestry, Lipoprotein(a), and Cardiovascular Risk Thresholds: JACC Review Topic of the Week

This study reviews ancestral differences in the genetics of the LPA gene, risk categories of elevated lipoprotein(a) [Lp(a)] as defined by guidelines, ancestry-specific Lp(a) risk, absolute and proportional risk, predictive value of risk thresholds among different ancestries, and differences between laboratory vs clinical accuracy in Lp(a) assays. For clinical decision-making, the preponderance of evidence suggests that the predictive value of Lp(a) does not vary sufficiently to mandate the use of ancestry-specific risk thresholds. This paper interprets the literature on Lp(a) and ancestral risk to support: 1) clinicians on understanding cardiovascular disease risk in different ancestral groups; 2) trialists for the design of clinical trials to ensure adequate ancestral diversity to support broad conclusions of drug effects; 3) regulators in the evaluation of the design and interpretation of results of Lp(a)-lowering trials with different Lp(a) inclusion thresholds; and 4) clinical laboratories to measure Lp(a) by assays that discriminate risk thresholds appropriately.

Lipoprotein(a) in atherosclerotic cardiovascular disease and aortic stenosis: a European Atherosclerosis Society consensus statement

This 2022 European Atherosclerosis Society lipoprotein(a) [Lp(a)] consensus statement updates evidence for the role of Lp(a) in atherosclerotic cardiovascular disease (ASCVD) and aortic valve stenosis, provides clinical guidance for testing and treating elevated Lp(a) levels, and considers its inclusion in global risk estimation. Epidemiologic and genetic studies involving hundreds of thousands of individuals strongly support a causal and continuous association between Lp(a) concentration and cardiovascular outcomes in different ethnicities; elevated Lp(a) is a risk factor even at very low levels of low-density lipoprotein cholesterol. High Lp(a) is associated with both microcalcification and macrocalcification of the aortic valve. Current findings do not support Lp(a) as a risk factor for venous thrombotic events and impaired fibrinolysis. Very low Lp(a) levels may associate with increased risk of diabetes mellitus meriting further study. Lp(a) has pro-inflammatory and pro-atherosclerotic properties, which may partly relate to the oxidized phospholipids carried by Lp(a). This panel recommends testing Lp(a) concentration at least once in adults; cascade testing has potential value in familial hypercholesterolaemia, or with family or personal history of (very) high Lp(a) or premature ASCVD. Without specific Lp(a)-lowering therapies, early intensive risk factor management is recommended, targeted according to global cardiovascular risk and Lp(a) level. Lipoprotein apheresis is an option for very high Lp(a) with progressive cardiovascular disease despite optimal management of risk factors. In conclusion, this statement reinforces evidence for Lp(a) as a causal risk factor for cardiovascular outcomes. Trials of specific Lp(a)-lowering treatments are critical to confirm clinical benefit for cardiovascular disease and aortic valve stenosis.

Canadian Society of Clinical Chemists Harmonized Clinical Laboratory Lipid Reporting Recommendations on the Basis of the 2021 Canadian Cardiovascular Society Lipid Guidelines

There is limited guidance on laboratory reporting and interpretation of lipids and lipoproteins used in cardiovascular risk stratification. This contributes to inconsistencies in lipid reporting across clinical laboratories. Recently, the Canadian Cardiovascular Society (CCS) published the 2021 CCS guidelines for the management of dyslipidemia for the prevention of cardiovascular disease in the adult. A subcommittee of the Working Group on Reference Interval Harmonization of the Canadian Society of Clinical Chemists has developed harmonized lipid reporting recommendations that are aligned with the 2021 CCS guidelines, to improve the standardization of lipid assessment and clinical decision-making. The proposed harmonized lipid reporting recommendations were critically reviewed by a broad range of laboratory and clinical experts across Canada. Feedback from approximately 30 expert reviewers was reviewed by the Working Group on Reference Interval Harmonization lipid subcommittee, and consensus decisions were incorporated into the 2021 harmonized lipid reporting recommendations. In this position statement, we provide 6 recommendations for laboratory reporting of lipid parameters. These recommendations include implementing the new National Institutes of Health equation to replace the Friedewald equation for calculating low-density lipoprotein cholesterol, offering lipoprotein (a), either as an in-house or send-out test, and using assays that report lipoprotein (a) in molar units (nmol/L). We also developed a harmonized lipid reporting format with interpretive comments that includes flagging results based on screening patients using treatment decision thresholds in a primary prevention setting. Overall, harmonized lipid reporting will help bridge the gap between clinical guideline recommendations and clinical laboratory reporting and interpretation, and will improve cardiovascular risk assessment across Canada.

Hypertriglyceridemia, a causal risk factor for atherosclerosis, and its laboratory assessment

Epidemiological and clinical studies show a causal association between serum triglyceride (TG) level, the number of triglyceride-rich lipoproteins (TRLs) and their remnants, and the increased risk of atherosclerosis and cardiovascular disease (CVD) development. In light of current guidelines for dyslipidemia management, the laboratory parameters reflecting TRL content are recommended as part of the routine lipid analysis process and used for CVD risk assessment, especially in people with hypertriglyceridemia (HTG), diabetes mellitus, obesity and low levels of low-density lipoprotein cholesterol (LDL-C), in which high residual CVD risk is observed. The basic routinely available laboratory parameters related with TRL are serum TG and non-high-density lipoprotein cholesterol (non-HDL-C) levels, but there are also other biomarkers related to TRL metabolism, the determination of which can be helpful in identifying the basis of HTG development or assessing CVD risk or can be the target of pharmacological intervention. In this review, we present the currently available laboratory parameters related to HTG. We summarise their link with TRL metabolism and HTG development, the determination methods as well as their clinical significance, the target values and interpretation of the results in relation to the current dyslipidemia guidelines.

Simultaneous Mass Spectrometry-Based Apolipoprotein Profiling and Apolipoprotein E Phenotyping in Patients with ASCVD and Mild Cognitive Impairment

Apolipoprotein E (apoE) occurs on the majority of plasma lipoproteins and plays a major role in the lipid metabolism in the periphery and in the central nervous system. ApoE is a polymorphic protein with three common isoforms, apoE2, apoE3 and apoE4, derived from respective alleles ε2, ε3 and ε4. The aim of this study was to develop a sample pretreatment protocol combined with rapid mass spectrometry (MS)-based assay for simultaneous apolipoprotein profiling and apoE phenotype identification. This assay was validated in 481 samples from patients with stable atherosclerotic cardiovascular disease (ASCVD) and applied to study association with mild cognitive impairment (MCI) in the LIFE Adult study, including overall 690 study subjects. Simultaneous quantification of 8−12 major apolipoproteins including apoA-I, apoB-100 and apoE could be performed within 6.5 min. Phenotyping determined with the developed MS assay had good agreement with the genotyping by real-time fluorescence PCR (97.5%). ApoE2 isoform was associated with the highest total apoE concentration compared to apoE3 and apoE4 (p < 0.001). In the subgroup of diabetic atherosclerotic cardiovascular disease (ASCVD) patients, apoE2 isoform was related to higher apoC-I levels (apoE2 vs. apoE3, p < 0.05), while in the subgroup of ASCVD patients under statin therapy apoE2 was related to lower apoB-100 levels (apoE2 vs. apoE3/apoE4, p < 0.05). A significant difference in apoE concentration observed between mild cognitive impairment (MCI) subjects and controls was confirmed for each apoE phenotype. In conclusion, this study provides evidence for the successful implementation of an MS-based apoE phenotyping assay, which can be used to assess phenotype effects on plasma lipid and apolipoprotein levels.

Development and Validation of an Isoform Independent Monoclonal Antibody-Based ELISA for Measurement of Lipoprotein(a)

The study aims were to develop a new isoform-independent enzyme-linked immunoassay (ELISA) for the measurement of lipoprotein(a) [Lp(a)], validate its performance characteristics, and demonstrate its accuracy by comparison with the gold-standard ELISA method and an LC-MS/MS candidate reference method, both developed at the University of Washington. The principle of the new assay is the capture of Lp(a) with monoclonal antibody LPA4 primarily directed to an epitope in apolipoprotein(a) KIV₂ and its detection with monoclonal antibody LPA-KIV9 directed to a single antigenic site present on KIV₉. Validation studies were performed following the guidelines of the Clinical Laboratory Improvement Amendments and the College of American Pathologists. The analytical measuring range of the LPA4/LPA-KIV9 ELISA is 0.27–1,402 nmol/L, and the method meets stringent criteria for precision, linearity, spike and recovery, dilutability, comparison of plasma versus serum, and accuracy. Method comparison with both the gold-standard ELISA and the LC-MS/MS method performed in 64 samples with known apolipoprotein(a) isoforms resulted in excellent correlation with both methods (r=0.987 and r=0.976, respectively). Additionally, the variation in apolipoprotein(a) size accounted for only 0.2% and 2.2% of the bias variation, respectively, indicating that the LPA4/LPA-KIV9 ELISA is not affected by apolipoprotein(a) size polymorphism. Peptide mapping and competition experiments demonstrated that the measuring monoclonal antibodies used in the gold-standard ELISA (a-40) and in the newly developed ELISA (LPA-KIV9) are directed to the same epitope, ⁴⁰⁷⁶LETPTVV⁴⁰⁸², on KIV₉. In conclusion, no statistically or clinically significant bias was observed between Lp(a) measurements obtained by the LPA4/LPA-KIV9 ELISA and those obtained by the gold-standard ELISA or LC-MS/MS, and therefore, the methods are considered equivalent.

Simultaneous quantification of apolipoproteins A-I, E, and J in human plasma by LC-MS/MS for clinical application to diabetes mellitus complicated with cardiovascular disease

Apolipoproteins (Apos) play an important role in regulating plasma lipid concentration. Complex disorders of Apos are highly related with diabetes mellitus, cardiovascular and other diseases. Direct measures of lipoprotein fractions for risk assessment suffer from inaccuracy in the dyslipidemia and pathological states. Therefore, a reliable precise assay will be of high clinical utility. LC-MS/MS methods with multiple reaction monitoring modes have proven suitable for multiplexed quantification. We aimed to develop a simple, cost-effective and amenable LC-MS/MS assay for quantification of ApoA-I, ApoE and ApoJ in human plasma. Standards were constructed from substitute matrix and proteotypic peptides for external calibration and corresponding stable isotope labeled peptides were added as internal standards to remove matrix effects. Analytical validation of the assay included the assessment of linearity, accuracy (RE: −3.02% to 5.32%), intra-assay precision (RSD: 2.50% to 6.56%), inter-assay precision (RSD: 0.78% to 6.68%), spiking recovery rate (accuracy: 87.17% to 112.71%), matrix effect (accuracy: 88.03% to 114.87%), and reproducibility and repeatability of sample preparation (RSD: 1.95% to 7.26%). The performance of proteotypic peptides ApoA-I, ApoE and ApoJ was sufficient for triplex quantitation within a linear range from 16.26 to 1626.41 pmol mL⁻¹, 1.03 to 103.35 pmol mL⁻¹ and 0.86 to 86.46 pmol mL⁻¹ respectively. For all quantified peptides, the determination coefficient (R²) was >0.997. Besides, the validated LC-MS/MS method has been successfully applied to the quantification of plasma samples in diabetes mellitus and cardiovascular diseases. We anticipate that this assay may provide an alternative method for future clinical applications.

Simultaneous quantification of apolipoproteins A-I, E, and J in human plasma by LC-MS/MS.

Lipoprotein(a) measurement issues: Are we making a mountain out of a molehill?

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

Review of the Use of Liquid Chromatography-Tandem Mass Spectrometry in Clinical Laboratories: Part I-Development

The process of method development for a diagnostic assay based on liquid chromatography-tandem mass spectrometry (LC-MS/MS) involves several disparate technologies and specialties. Additionally, method development details are typically not disclosed in journal publications. Method developers may need to search widely for pertinent information on their assay(s). This review summarizes the current practices and procedures in method development. Additionally, it probes aspects of method development that are generally not discussed, such as how exactly to calibrate an assay or where to place quality controls, using examples from the literature. This review intends to provide a comprehensive resource and induce critical thinking around the experiments for and execution of developing a clinically meaningful LC-MS/MS assay.

Lipoprotein(a): Pathophysiology, measurement, indication and treatment in cardiovascular disease. A consensus statement from the Nouvelle Société Francophone d'Athérosclérose (NSFA)

Lipoprotein(a) is an apolipoprotein B100-containing low-density lipoprotein-like particle that is rich in cholesterol, and is associated with a second major protein, apolipoprotein(a). Apolipoprotein(a) possesses structural similarity to plasminogen but lacks fibrinolytic activity. As a consequence of its composite structure, lipoprotein(a) may: (1) elicit a prothrombotic/antifibrinolytic action favouring clot stability; and (2) enhance atherosclerosis progression via its propensity for retention in the arterial intima, with deposition of its cholesterol load at sites of plaque formation. Equally, lipoprotein(a) may induce inflammation and calcification in the aortic leaflet valve interstitium, leading to calcific aortic valve stenosis. Experimental, epidemiological and genetic evidence support the contention that elevated concentrations of lipoprotein(a) are causally related to atherothrombotic risk and equally to calcific aortic valve stenosis. The plasma concentration of lipoprotein(a) is principally determined by genetic factors, is not influenced by dietary habits, remains essentially constant over the lifetime of a given individual and is the most powerful variable for prediction of lipoprotein(a)-associated cardiovascular risk. However, major interindividual variations (up to 1000-fold) are characteristic of lipoprotein(a) concentrations. In this context, lipoprotein(a) assays, although currently insufficiently standardized, are of considerable interest, not only in stratifying cardiovascular risk, but equally in the clinical follow-up of patients treated with novel lipid-lowering therapies targeted at lipoprotein(a) (e.g. antiapolipoprotein(a) antisense oligonucleotides and small interfering ribonucleic acids) that markedly reduce circulating lipoprotein(a) concentrations. We recommend that lipoprotein(a) be measured once in subjects at high cardiovascular risk with premature coronary heart disease, in familial hypercholesterolaemia, in those with a family history of coronary heart disease and in those with recurrent coronary heart disease despite lipid-lowering treatment. Because of its clinical relevance, the cost of lipoprotein(a) testing should be covered by social security and health authorities.

Apolipoprotein B and Cardiovascular Disease: Biomarker and Potential Therapeutic Target

Apolipoprotein (apo) B, the critical structural protein of the atherogenic lipoproteins, has two major isoforms: apoB48 and apoB100. ApoB48 is found in chylomicrons and chylomicron remnants with one apoB48 molecule per chylomicron particle. Similarly, a single apoB100 molecule is contained per particle of very-low-density lipoprotein (VLDL), intermediate density lipoprotein, LDL and lipoprotein(a). This unique one apoB per particle ratio makes plasma apoB concentration a direct measure of the number of circulating atherogenic lipoproteins. ApoB levels indicate the atherogenic particle concentration independent of the particle cholesterol content, which is variable. While LDL, the major cholesterol-carrying serum lipoprotein, is the primary therapeutic target for management and prevention of atherosclerotic cardiovascular disease, there is strong evidence that apoB is a more accurate indicator of cardiovascular risk than either total cholesterol or LDL cholesterol. This review examines multiple aspects of apoB structure and function, with a focus on the controversy over use of apoB as a therapeutic target in clinical practice. Ongoing coronary artery disease residual risk, despite lipid-lowering treatment, has left patients and clinicians with unsatisfactory options for monitoring cardiovascular health. At the present time, the substitution of apoB for LDL-C in cardiovascular disease prevention guidelines has been deemed unjustified, but discussions continue.

Genetically-engineered hamster models: applications and perspective in dyslipidemia and atherosclerosis-related cardiovascular disease

Cardiovascular disease is the leading cause of morbidity and mortality in both developed and developing countries, in which atherosclerosis triggered by dyslipidemia is the major pathological basis. Over the past 40 years, small rodent animals, such as mice, have been widely used for understanding of human atherosclerosis-related cardiovascular disease (ASCVD) with the advantages of low cost and ease of maintenance and manipulation. However, based on the concept of precision medicine and high demand of translational research, the applications of mouse models for human ASCVD study would be limited due to the natural differences in metabolic features between mice and humans even though they are still the most powerful tools in this research field, indicating that other species with biological similarity to humans need to be considered for studying ASCVD in future. With the development and breakthrough of novel gene editing technology, Syrian golden hamster, a small rodent animal replicating the metabolic characteristics of humans, has been genetically modified, suggesting that gene-targeted hamster models will provide new insights into the precision medicine and translational research of ASCVD. The purpose of this review was to summarize the genetically-modified hamster models with dyslipidemia to date, and their potential applications and perspective for ASCVD.

Quantification of SARS-CoV-2 spike and nucleocapsid proteins using isotope dilution tandem mass spectrometry

The emergence and subsequent global outbreak of the novel coronavirus SARS-CoV-2 prompted our laboratory to launch efforts to develop methods for SARS-CoV-2 antigen detection and quantification. We present an isotope dilution mass spectrometry method (IDMS) for rapid and accurate quantification of the primary antigens, spike and nucleocapsid proteins. This IDMS method utilizes liquid chromatography-tandem mass spectrometry (LC-MS/MS) to analyze sample tryptic digests for detection and quantification of selected conserved peptides of SARS-CoV-2 spike and nucleocapsid proteins. The IDMS method has the necessary attributes to be successfully utilized for accurate quantification in SARS-CoV-2 protein-based vaccines and as targets of rapid diagnostic tests. Absolute quantification was achieved by quantifying and averaging 5 peptides for spike protein (3 peptides in the S1 subunit and 2 peptides in the S2 subunit) and 4 peptides for nucleocapsid protein. The overall relative standard deviation of the method was 3.67% for spike protein and 5.11% for nucleocapsid protein. IDMS offers speed (5 h total analysis time), sensitivity (LOQ; 10 fmol/µL) and precision for quantification of SARS-CoV-2 spike and nucleocapsid proteins.

The Time Has Come for Quantitative Protein Mass Spectrometry Tests That Target Unmet Clinical Needs

Protein mass spectrometry (MS) is an enabling technology that is ideally suited for precision diagnostics. In contrast to immunoassays with indirect readouts, MS quantifications are multiplexed and include identification of proteoforms in a direct manner. Although widely used for routine measurements of drugs and metabolites, the number of clinical MS-based protein applications is limited. In this paper, we share our experience and aim to take away the concerns that have kept laboratory medicine from implementing quantitative protein MS. To ensure added value of new medical tests and guarantee accurate test results, five key elements of test evaluation have been established by a working group within the European Federation for Clinical Chemistry and Laboratory Medicine. Moreover, it is emphasized to identify clinical gaps in the contemporary clinical pathways before test development is started. We demonstrate that quantitative protein MS tests that provide an additional layer of clinical information have robust performance and meet long-term desirable analytical performance specifications as exemplified by our own experience. Yet, the adoption of quantitative protein MS tests into medical laboratories is seriously hampered due to its complexity, lack of robotization and high initial investment costs. Successful and widespread implementation in medical laboratories requires uptake and automation of this next generation protein technology by the In-Vitro Diagnostics industry. Also, training curricula of lab workers and lab specialists should include education on enabling technologies for transitioning to precision medicine by quantitative protein MS tests.