Prognostic significance of chronic myocardial injury diagnosed by three different cardiac troponin assays in patients admitted with suspected acute coronary syndrome

OBJECTIVES

Chronic myocardial injury (CMI) is defined as stable concentrations of cardiac troponin T or I (cTnT or cTnI) above the assay-specific 99th percentile upper reference limit (URL) and signals poor outcome. The clinical implications of diagnosing CMI are unclear. We aimed to assess prevalence and association of CMI with long-term prognosis using three different high-sensitivity cTn (hs-cTn) assays.

METHODS

A total of 1,292 hospitalized patients without acute myocardial injury had cTn concentrations quantified by hs-cTn assays by Roche Diagnostics, Abbott Diagnostics and Siemens Healthineers. The median follow-up time was 4.1 years. The prevalence of CMI and hazard ratios for mortality and cardiovascular (CV) events were calculated based on the URL provided by the manufacturers and compared to the prognostic accuracy when lower percentiles of cTn (97.5, 95 or 90), limit of detection or the estimated bioequivalent concentrations between assays were used as cutoff values.

RESULTS

There was no major difference in prognostic accuracy between cTnT and cTnI analyzed as continuous variables. The correlation between cTnT and cTnI was high (r=0.724-0.785), but the cTnT assay diagnosed 3.9-4.5 times more patients with having CMI based on the sex-specific URLs (TnT, n=207; TnI Abbott, n=46, TnI Siemens, n=53) and had higher clinical sensitivity and AUC at the URL.

CONCLUSIONS

The prevalence of CMI is highly assay-dependent. cTnT and cTnI have similar prognostic accuracy for mortality or CV events when measured as continuous variables. However, a CMI diagnosis according to cTnT has higher prognostic accuracy compared to a CMI diagnosis according to cTnI.

Hollow-microsphere-integrated optofluidic immunochip for myocardial infarction biomarker microanalysis

This work developed an optofluidic immunochip that uses whispering gallery mode with fiber laser enhancement, for the rapid detection of a key biomarker cardiac troponin I for acute myocardial infarction (AMI). The immunochip adopted an innovative design, using perforated hollow glass microspheres (HGMS) as carriers, with antibodies immobilized on the inner surface of the HGMS, thereby achieving ultra-low sample consumption. The performance of the immunochip was improved by fiber laser, including spectral width compression to 0.019 nm, optical signal-to-noise ratio amplification to 63.17 dB, and an enhancement in the limit of detection to 5 pg/mL. Moreover, this immunochip can provide results within 15 min, making it highly suitable for early AMI risk management. Compared to the standard electrochemiluminescence detection method, although some differences exist in the results of the immunochip due to the principle of detection and differences in antibody affinity, its positive reference value can be calculated as 0.0754 ng/mL, with a successful recognition rate of 88% for positive patients. The immunosensor is integrated on a polydimethylsiloxane substrate, with a compact size suitable for use in point-of-care devices and AMI self-screening, as well as rapid disease screening and microanalysis of various biomarkers, offering new possibilities for applications in these fields.

High-sensitivity troponins and mortality in the general population

AIMS

Cardiac troponin T and I can be measured using a number of high-sensitivity (hs) assays. This study aimed to characterize correlations between four such assays and test their comparative associations with mortality.

METHODS AND RESULTS

Among adults without cardiovascular disease in the 1999-2004 National Health and Nutrition Examination Survey, hs-troponin T was measured using one assay (Roche) and hs-troponin I using three assays (Abbott, Siemens, and Ortho). Cox regression was used to estimate associations with all-cause and cardiovascular mortality. Pearson's correlation coefficients comparing concentrations from each assay ranged from 0.53 to 0.77. There were 2188 deaths (488 cardiovascular) among 9810 participants. Each hs-troponin assay [log-transformed, per 1 standard deviation (SD)] was independently associated with all-cause mortality: hazard ratio (HR) 1.20 [95% confidence interval (CI) 1.13-1.28] for Abbott hs-troponin I; HR 1.10 (95% CI 1.02-1.18) for Siemens hs-troponin I; HR 1.23 (95% CI 1.14-1.33) for Ortho hs-troponin I; and HR 1.31 (95% CI 1.21-1.42) for Roche hs-troponin T. Each hs-troponin assay was also independently associated with cardiovascular mortality (HR 1.44 to 1.65 per 1 SD). Associations of hs-troponin T and all-cause and cardiovascular mortality remained significant after adjusting for hs-troponin I. Furthermore, associations of hs-troponin I remained significant after mutually adjusting for hs-troponin I from the other individual assays: e.g. cardiovascular mortality HR 1.46 (95% CI 1.19-1.79) for Abbott after adjustment for the Siemens assay and HR 1.29 (95% CI 1.09-1.53) for Abbott after adjustment for the Ortho assay.

CONCLUSION

This study demonstrates only modest correlations between hs-troponin T and three hs-troponin I assays and that hs-troponin I assays can provide distinct risk information for mortality in the general population.

Cardiac Troponin I in Patients Undergoing Percutaneous and Surgical Myocardial Revascularization: Comparison of Analytical Methods

The myocardial infarction (MI) types 4a and 5 guidelines recommend cardiac troponin (cTn) diagnostic decision limits of 5 and 10 times the 99th percentile, respectively. Different cTn kits elicit different responses, so the MI diagnosis is still challenging. The study aimed to establish the cutoff values and the accuracy of three different cTnI kits in the diagnosis of post-procedural MI. We analyzed 115 patients with multivessel stable chronic coronary artery disease; 26 underwent percutaneous coronary intervention, and 89 underwent coronary artery bypass graft. Delayed-enhancement magnetic resonance imaging was performed before and after each intervention for definitive MI diagnoses. Two contemporary and one high-sensitivity cTnI immunoassays were used. ROC curves determined the accuracy of each assay. Low accuracy was observed after applying the current guidelines recommendations. The three cTnI assays accuracies improved when adjusted by the new ROC cutoffs, reaching 82% for MI type 5 for all assays, and 78%, 88%, and 87% for MI type 4 for Siemens, Beckman, and Abbott, respectively. The ultrasensitive and contemporary tests’ accuracy for MI types 4a and 5 diagnoses are equivalent when adjusted for these new cutoffs. The hs-cTnI assays had lower accuracy than contemporary tests for MI types 4a and 5 diagnoses.

Point-of-Care: Roadmap for Analytical Characterization and Validation of a High-Sensitivity Cardiac Troponin I Assay in Plasma and Whole Blood Matrices

BACKGROUND

High-sensitivity cardiac troponin (hs-cTn) assays enable more precise use of traditional diagnostic strategies and earlier rule-out/rule-in at 0/1 h or 0/2 h after presentation of acute myocardial infarction (AMI). Availability of hs-cTn measurements at point-of-care (POC) can improve timely management of AMI patients. A roadmap for regulatory and analytical validation is exemplified with studies with the Atellica VTLi hs-cTnI at POC.

METHODS

High-sensitivity performance was assessed with AACC/IFCC expert recommendations. Clinical Laboratory Standards Institute protocols were used for characterizing limit of blank, limit of detection (LoD), limit of quantitation (LoQ), 10% CV, precision, linearity, and analytic specificity with several reagent lots. Bland-Altman, Passing-Bablok, and hematocrit bias plots compared hs-cTnI measurement in lithium-heparin plasma (PL) and whole blood (WB) matrices.

RESULTS

LoB was 0.55 ng/L; LoD and LoQ were 1.24 ng/L and 2.1 ng/Lm for PL and 1.60 ng/L and 3.7 ng/L for WB, respectively. The male 99th percentile is 27 ng/L, and female 99th percentile upper reference limit is 18 ng/L; 10% CVs were 6.7 ng/L for PL and 8.9 ng/L for WB. Also ≥50% of hs-cTnI values for healthy cohorts exceeded the LoD, confirming high-sensitivity performance. Linearity spanned from LoQ to 1250 ng/L. Specificity was >90% for 40 potential interferences; no hook effect was detected. WB and PL correlation was WB = 1.02*plasma + 0.3 ng/L (r = 0.996, n = 152). No hs-cTnI association with hematocrit was detected (R2 = 0.003).

CONCLUSION

This analytical roadmap showed high-sensitivity performance, good analytic characteristics, and excellent PL and WB agreement for the Atellica VTLi hs-cTnI POC system. Essential clinical performance studies in patients by intended POC users may now commence.

Fiber-integrated WGM optofluidic chip enhanced by microwave photonic analyzer for cardiac biomarker detection with ultra-high resolution

Cardiac troponin I (cTnI) plays an important role in emergency diagnosis of cardiovascular diseases, which exists predominately in the form of cardiac troponin I-C (cTnI-C) complex. We proposed a fiber-integrated optofluidic chip immunosensor with time-delay-dispersion based microwave photonic analyzer (MPA) for cTnI-C detection. The whispering gallery mode (WGM) fiber probe was fabricated by embedding a polydopamine functionalized hollow glass microsphere (HGMS) into the etched capillary-fiber structure, and the WGMs could be excited through the efficient coupling between the thin-wall capillary and the HGMS. The reflective WGM optofluidic chip functioned as a wavelength tuner to construct fiber ring laser cavity, whose laser output wavelength was cTnI-C concentration-dependent. The tiny wavelength variation of sensing laser was converted into a radio-frequency (RF) response, which was retrieved by measuring the change of RF-domain free spectrum range (FSR) in time-delay-dispersion based MPA, and the quantitative detection of cTnI-C complex can be achieved with high resolution. Experimental results show that this immunosensor had a limit of detection (LOD) of 0.59 ng/mL, and a detection resolution of 1.2 fg/mL. The relative resolving power was 10²-10⁴-fold higher than that of others optical fiber cTnI biosensors. The proposed fiber-integrated optofluidic chip provides an innovative lab-on-chip diagnostic tool for myocardial damage.

Features of the Metabolisms of Cardiac Troponin Molecules-Part 1: The Main Stages of Metabolism, Release Stage

Cardiac troponins (cTns) have long been the most valuable and specific biomarkers for detecting ischemic myocardial cells (MCs) injury, which is one of the key signs of myocardial infarction (MI). Modern methods (highly sensitive and ultra-sensitive immunoassays (hs-cTns)) of detection are an important and indispensable tool for the early diagnosis of MI and the choice of patient management protocols. Timely diagnosis of MI can significantly improve the prognosis of patients. However, in real clinical practice, doctors often face a significant problem when using cTns-the difficulty of differential diagnosis due to frequent and unexplained increases in the concentration of cTns in blood serum. In addition, there is conflicting information that may potentially affect the diagnostic capabilities and value of cTns: the influence of certain biological factors (diurnal rhythm, gender and age) on serum cTns levels; extra-cardiac expression of cTns; the possibilities of non-invasive diagnosis of MI; and other pathological conditions that cause non-ischemic injury to MCs. To solve these problems, it is necessary to concentrate on studying the metabolism of cTns. The review of our current knowledge about cTns metabolism consists of two parts. In this (first) part of the manuscript, the main stages of cTns metabolism are briefly described and the mechanisms of cTns release from MCs are considered in detail.

Effect of Particle Size and Surface Chemistry of Photon-Upconversion Nanoparticles on Analog and Digital Immunoassays for Cardiac Troponin

Sensitive immunoassays are required for troponin, a low-abundance cardiac biomarker in blood. In contrast to conventional (analog) assays that measure the integrated signal of thousands of molecules, digital assays are based on counting individual biomarker molecules. Photon-upconversion nanoparticles (UCNP) are an excellent nanomaterial for labeling and detecting single biomarker molecules because their unique anti-Stokes emission avoids optical interference, and single nanoparticles can be reliably distinguished from the background signal. Here, the effect of the surface architecture and size of UCNP labels on the performance of upconversion-linked immunosorbent assays (ULISA) is critically assessed. The size, brightness, and surface architecture of UCNP labels are more important for measuring low troponin concentrations in human plasma than changing from an analog to a digital detection mode. Both detection modes result approximately in the same assay sensitivity, reaching a limit of detection (LOD) of 10 pg mL^-1 in plasma, which is in the range of troponin concentrations found in the blood of healthy individuals.

Advances in point-of-care testing for cardiovascular diseases

Point-of-care testing (POCT) is a specific format of diagnostic testing that is conducted without accompanying infrastructure or sophisticated instrumentation. Traditionally, such rapid sample-to-answer assays provide inferior analytical performances to their laboratory counterparts when measuring cardiac biomarkers. Hence, their potentially broad applicability is somewhat bound by their inability to detect clinically relevant concentrations of cardiac troponin (cTn) in the early stages of myocardial injury. However, the continuous refinement of biorecognition elements, the optimization of detection techniques, and the fabrication of tailored fluid handling systems to manage the sensing process has stimulated the production of commercial assays that can support accelerated diagnostic pathways. This review will present the latest commercial POC assays and examine their impact on clinical decision-making. The individual elements that constitute POC assays will be explored, with an emphasis on aspects that contribute to economically feasible and highly sensitive assays. Furthermore, the prospect of POCT imparting a greater influence on early interventions for medium to high-risk individuals and the potential to re-shape the paradigm of cardiovascular risk assessments will be discussed.

The role of antibody-based troponin detection in cardiovascular disease: A critical assessment

Cardiovascular disease has remained the world's biggest killer for 30 years. To aid in the diagnosis and prognosis of patients suffering cardiovascular-related disease accurate detection methods are essential. For over 20 years, the cardiac-specific troponins, I (cTnI) and T (cTnT), have acted as sensitive and specific biomarkers to assist in the diagnosis of various types of heart diseases. Various cardiovascular complications were commonly detected in patients with COVID-19, where cTn elevation is detectable, which suggested potential great prognostic value of cTn in COVID-19-infected patients. Detection of these biomarkers circulating in the bloodstream is generally facilitated by immunoassays employing cTnI- and/or cTnT-specific antibodies. While several anti-troponin assays are commercially available, there are still obstacles to overcome to achieve optimal troponin detection. Such obstacles include the proteolytic degradation of N and C terminals on cTnI, epitope occlusion of troponin binding-sites by the cTnI/cTnT complex, cross reactivity of antibodies with skeletal troponins or assay interference caused by human anti-species antibodies. Therefore, further research into multi-antibody based platforms, multi-epitope targeting and rigorous validation of immunoassays is required to ensure accurate measurements. Moreover, with combination and modification of various latest technical (e.g. microfluidics), antibody-based troponin detection systems can be more specific, sensitive and rapid which could be incorporated into portable biosensor systems to be used at point-of care.

Myocardial Injury and the Release of Troponins I and T in the Blood of Patients

BACKGROUND

Cardiac troponin I (cTnI) and cTnT are the established biomarkers of cardiomyocyte damage and the recommended biomarkers for the diagnosis of acute myocardial infarction (MI). High-sensitivity immunochemical diagnostic systems are able to measure the cTn concentrations in the blood of a majority of healthy people. At the same time, the concentration of cTn may be increased not only after MI but also because of other pathologies that might affect myocardium. This effect reduces the clinical specificity of cTn for MI and may complicate the diagnosis.

CONTENT

This review summarizes the existing information regarding the causes and mechanisms that lead to the increase of cTn concentration in blood and the forms of cTn that are present in circulation after MI or other types of myocardial injury.

SUMMARY

Different etiologies of disease associated with increases of cTn above the 99th percentile and various mechanisms of troponin release from myocardium could result in the appearance of different forms of cTn in blood and provide the first clinical evidence of injury. Additional research is needed for the careful characterization of cTn forms that are present in the blood in different clinical settings. That knowledge may lead to the development of immunochemical systems that would differentiate certain forms of troponins and possibly certain types of cardiac disease.

Establishment and Application of a Dual-Labeling Time-Resolved Fluorescence Immunoassay Method for Simultaneous Detection of the Troponin I-C Complex and Full-Size-Troponin I

Background: The measurement of cardiac troponin I (cTnI) is widely used in the diagnosis of acute myocardial infarction (AMI). Although existing cTnI detection methods measure total cTnI, the significance of undegraded full-size-cTnI levels is still not well-understood. In this study, we have established a novel dual-labeling time-resolved fluorescence immunoassay (TRFIA) technique that simultaneously detects the cTnI-C complex and full-size-cTnI, allowing us to explore the clinical value of full-size-cTnI determination.

Methods: An antibody against the 23–43 amino acid region of cTnI protected by endogenous cTnC is coupled to magnetic beads to provide a solid-phase antibody for capturing all cTnI. An antibody against cTnC in the cTnI-C complex labeled with Eu³⁺ was used to detect the cTnI-C complex, and an antibody labeled with Sm³⁺ near the C-terminal 190–203 amino acids of cTnI was used to detect full-size-cTnI. Through dual-labeling TRFIA, cTnI-C complex, full-size-cTnI, and the full-size-cTnI/cTnI-C ratio can be detected simultaneously. The dual-labeling TRFIA technique was used to analyze serum samples collected at different times during treatment and compare their full-size-cTnI/cTnI-C ratios.

Results: The sensitivity for the cTnI-C-TRFIA complex was 0.02 ng/mL, the measurement range was 0.02–40 ng/mL, the average intra-batch coefficient of variation (CV) was 4.35%, and the inter-average CV was 6.23%. The correlation coefficient between cTnI-C-TRFIA and commercial cTnI-CLIA methods was R² = 0.8887. The sensitivity for full-size-cTnI-TRFIA was 0.04 ng/mL, the measurement range was 0.04–40 ng/mL, the average intra-batch CV was 4.95%, and the average inter-batch CV was 7.79%. The correlation coefficient between full-size-cTnI-TRFIA and commercial cTnI-CLIA methods was R² = 0.7247.

Conclusions: Dual-labeling full-size-cTnI/cTnI-C-TRFIA analysis is helpful for determining the length of time of chest pain before admission and the degree of continuous release of cTnI in the myocardium. Thus, it is more for early prognosis than just detecting cTnI.

Nanoproteomics enables proteoform-resolved analysis of low-abundance proteins in human serum

Top-down mass spectrometry (MS)-based proteomics provides a comprehensive analysis of proteoforms to achieve a proteome-wide understanding of protein functions. However, the MS detection of low-abundance proteins from blood remains an unsolved challenge due to the extraordinary dynamic range of the blood proteome. Here, we develop an integrated nanoproteomics method coupling peptide-functionalized superparamagnetic nanoparticles (NPs) with top-down MS for the enrichment and comprehensive analysis of cardiac troponin I (cTnI), a gold-standard cardiac biomarker, directly from serum. These NPs enable the sensitive enrichment of cTnI (<1 ng/mL) with high specificity and reproducibility, while simultaneously depleting highly abundant proteins such as human serum albumin (>1010 more abundant than cTnI). We demonstrate that top-down nanoproteomics can provide high-resolution proteoform-resolved molecular fingerprints of diverse cTnI proteoforms to establish proteoform-pathophysiology relationships. This scalable and reproducible antibody-free strategy can generally enable the proteoform-resolved analysis of low-abundance proteins directly from serum to reveal previously unachievable molecular details.

Implications of the complex biology and micro-environment of cardiac sarcomeres in the use of high affinity troponin antibodies as serum biomarkers for cardiac disorders

Cardiac troponin I (cTnI), the inhibitory-unit, and cardiac troponin T (cTnT), the tropomyosin-binding unit together with the Ca-binding unit (cTnC) of the hetero-trimeric troponin complex signal activation of the sarcomeres of the adult cardiac myocyte. The unique structure and heart myocyte restricted expression of cTnI and cTnT led to their worldwide use as biomarkers for acute myocardial infarction (AMI) beginning more than 30 years ago. Over these years, high sensitivity antibodies (hs-cTnI and hs-cTnT) have been developed. Together with careful determination of history, physical examination, and EKG, determination of serum levels using hs-cTnI and hs-cTnT permits risk stratification of patients presenting in the Emergency Department (ED) with chest pain. With the ability to determine serum levels of these troponins with high sensitivity came the question of whether such measurements may be of diagnostic and prognostic value in conditions beyond AMI. Moreover, the finding of elevated serum troponins in physiological states such as exercise and pathological states where cardiac myocytes may be affected requires understanding of how troponins may be released into the blood and whether such release may be benign. We consider these questions by relating membrane stability to the complex biology of troponin with emphasis on its sensitivity to the chemo-mechanical and micro-environment of the cardiac myocyte. We also consider the role determinations of serum troponins play in the precise phenotyping in personalized and precision medicine approaches to promote cardiac health.

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Serum levels of cardiac TnI and cardiac TnT permit stratification of patients with chest pain.

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Release of troponins into blood involves not only frank necrosis but also programmed necroptosis.

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Genome wide analysis of serum troponin levels in the general population may be prognostic about cardiovascular health.

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Significant levels of serum troponins with exhaustive exercise may not be benign.

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Troponin in serum can lead to important data related to personalized and precision medicine.

Norepinephrine as new functional monomer for molecular imprinting: An applicative study for the optical sensing of cardiac biomarkers

The continuous research for alternatives to antibody-based detection drove, in the last decades, the development of numerous strategies. Molecularly imprinted polymers (MIPs) emerged thanks to the low-cost and long-term stability features, where the choice of natural functional monomer(s) represents the key step for efficient imprinting of biomolecules. The chemical structure of dopamine (DA), one of the most used natural functional monomers, provided the inspiration for this work. We wondered why norepinephrine (NE) that differs from dopamine only for an additional hydroxyl group was not investigated at all in biosensing applications. In fact, there is only one paper exploiting polynorepinephrine (PNE) in molecular recognition applications, taking advantage of molecular imprinting, but not for biosensing purposes. In contrast, hundreds of papers describe polydopamine-based sensors. Therefore, we firstly investigated how the additional hydroxyl group of NE could affect the properties of the resulting polymer, and how these properties could be exploited for biosensing applications. The results highlighted the reduced non-specific adsorption of proteins onto PNE with respect to dopamine polymer. Furthermore, as a case study, we successfully developed a PNE-based imprinted biosensor for the early detection of Troponin I, a crucial biomarker for heart failure, by coupling the MIP biosensor with surface plasmon resonance (SPR) detection. The results indicate the feasible use of imprinted PNE as synthetic receptor for biomolecules, opening new perspectives for this biopolymer, so far not considered, and encouraging further investigations on its potential application in biosensing.

Proteolytic Digestion of Serum Cardiac Troponin I as Marker of Ischemic Severity

BACKGROUND

The serum troponin assay is the biochemical gold standard for detecting myocardial infarction (MI). A major diagnostic issue is that some believe troponin levels can rise with reversible injury, in the absence of radiologically detectable infarct.

HYPOTHESIS

Because cell death activates intracellular proteases, troponin released by irreversible infarct will be more proteolyzed than that released by milder processes. Our goal was to quantify proteolytic digestion of cardiac troponin I in patients with varying degrees of myocardial injury.

METHODS

Serum or plasma samples from 29 patients with cardiac troponin I elevations were analyzed for proteolytic degradation, using 3 different sandwich ELISAs designed to specifically detect the N-terminal, core, or C-terminal regions of cardiac troponin I.

RESULTS

As predicted, the degree of proteolytic digestion increased with increasing severity of injury, as estimated by the total troponin level, and this trend was more pronounced for C-terminal (vs N-terminal) degradation. The highest degree of proteolytic digestion was observed in patients with ST-elevation MI; the least, in type 2 MI (supply-demand ischemia rather than acute thrombus formation).

CONCLUSIONS

The proteolytic degradation pattern of cardiac troponin I may be a better indicator of clinically significant MI than total serum troponin level. Distinguishing between intact and degraded forms of troponin may be useful for (a) identifying those patients with clinically significant infarct in need of revascularization, (b) monitoring intracellular proteolysis as a possible target for therapeutic intervention, and (c) providing an impetus for standardizing the epitopes used in the troponin I assay.

The impact of environmental factors on the production of peptides in mammalian decomposition fluid in relation to the estimation of post-mortem interval: A summer/winter comparison in Western Australia

We report the peptide content of decomposition fluid produced under field-based conditions and in the absence of a soil matrix. Sixteen domestic pig (Sus scrofa domesticus) cadavers were used to model human decomposition in trials conducted in the summer and winter months in Western Australia. Physical characteristics were recorded and the peptide components of decomposition fluid were analysed using high performance liquid chromatography-time of flight mass spectrometry. A range of peptides was consistently detected in both summer and winter. Thirty seven peptides were common to both trials; 22 originating from haemoglobin subunit beta, 1 from haemoglobin subunit alpha, 4 from beta-enolase, and 2 from creatine kinase. In agreement with our previous findings, 13 peptides occurred consistently, regardless of trial conditions. Degradation patterns for haemoglobin subunits alpha and beta in summer and winter were similar when expressed in ADD and when adjusted for differences in temperature. The consistent identification of several protein-specific peptides generated during decomposition trials conducted under different temperature and rainfall regimes suggests that quantitative peptide analysis may be useful in estimating time since death.

Cardiac Troponins Following Repeated Administration of an Iron Chelator – Salicylaldehyd Isonicotinoyl Hydrazone (SIH) – in Rabbits

Both cardiac troponin T (cTnT) and cardiac troponin I (cTnI) are considered to be reliable biomarkers with sufficient sensitivity and specificity for cardiac injury in the majority of laboratory animals. The aim of our study was to compare the diagnostic performance of cTnT and cTnI in three groups of rabbits: 1) control (saline 1 ml/kg i.v.); 2) Salicylaldehyd Isonicotinoyl Hydrazone – SIH (50 mg/kg, once weekly, i.p.; partially dissolved in 10 % Cremophor solution); 3) 10 % Cremophor solution in water (2 ml/kg i.v.). The drugs were given once a week, 10 administrations. The concentration of cTnT was measured using Elecsys Troponin T STAT Immunoassay (Roche). The concentration of cTnI was measured using AxSYM Troponin I (Abbott). The linear regression model was applied to see if there is a dependence between cTnT and cTnI. The coefficient of determination was not acceptable in all groups. The highest value of R2was found in the control group (R2= 0.424). We may conclude that in rabbits meaningful dependence between cTnT and cTnI was not found. According to our long-term experiences cTnT seems to be more suitable cardiomarker in rabbits in comparison with cTnI where the data are characterized by the large scatter.

Studies towards hcTnI Immunodetection Using Electrochemical Approaches Based on Magnetic Microbeads

Different electrochemical strategies based on the use of magnetic beads are described in this work for the detection of human cardiac troponin I (hcTnI). hcTnI is also known as the gold standard for acute myocardial infarction (AMI) diagnosis according to the different guidelines from the European Society of Cardiology (ESC) and the American College of Cardiology (ACC). Amperometric and voltamperometric sandwich magnetoimmunoassays were developed by biofunctionalization of paramagnetic beads with specific antibodies. These bioconjugates were combined with biotinylated antibodies as detection antibodies, with the aim of testing different electrochemical transduction principles. Streptavidin labeled with horseradish peroxidase was used for the amperometric magnetoimmunoassay, reaching a detectability of 0.005 ± 0.002 µg mL-1 in 30 min. Cadmium quantum dots-streptavidin bioconjugates were used in the case of the voltamperometric immunosensor reaching a detectability of 0.023 ± 0.014 µg mL-1.

Full-Size Cardiac Troponin I and Its Proteolytic Fragments in Blood of Patients with Acute Myocardial Infarction: Antibody Selection for Assay Development

BACKGROUND

In the blood of patients with acute myocardial infarction (AMI), cardiac troponin I (cTnI) presents as an intact molecule with a repertoire of proteolytic fragments. The degradation of cTnI might negatively influence its precise immunodetection. In this study we identified cTnI fragments and calculated their ratio in the blood of patients at different times after AMI to discriminate the most stable part(s) of cTnI.

METHODS

Serial serum samples were collected from AMI patients within 1 to 36 h after the onset of chest pain both before and after stenting. cTnI and its fragments were immunoextracted from serum samples and analyzed by Western blotting with monoclonal antibodies (mAbs) specific to the different epitopes of cTnI and by 2 in-house immunoassays specific to the central and terminal portions of cTnI.

RESULTS

Intact cTnI and its 11 major fragments were detected in blood of AMI patients. The ratio of the fragments in serial samples did not show large changes in the period 1–36 h after AMI. mAbs specific to the epitopes located approximately between amino acid residues (aar) 34 and 126 stained all extracted cTnI. mAbs specific to aar 23–36 and 126–196 recognized approximately 80% to 90% (by abundance) of cTnI.

CONCLUSIONS

In addition to mAbs specific to the central part of cTnI (approximately aar 34–126), antibodies specific to the adjacent epitopes (approximately aar 23–36 and 126–196) could be used in assays because they recognize ≥80% of cTnI in patients' blood samples within the first 36 h after AMI.

Quantification of cardiac troponin I in human plasma by immunoaffinity enrichment and targeted mass spectrometry

Quantification of cardiac troponin I (cTnI), a protein biomarker used for diagnosing myocardial infarction, has been achieved in native patient plasma based on an immunoaffinity enrichment strategy and isotope dilution (ID) liquid chromatography-tandem mass spectrometry (LC-MS/MS) method. The key steps in the workflow involved isolating cTnI from plasma using anti-cTnI antibody coupled to magnetic nanoparticles, followed by an enzymatic digestion with trypsin. Three tryptic peptides from cTnI were monitored and used for quantification by ID-LC-MS/MS via multiple reaction monitoring (MRM). Measurements were performed using a matrix-matched calibration system. NIST SRM 2921 Human Cardiac Troponin Complex acted as the calibrant and a full-length isotopically labeled protein analog of cTnI was used as an internal standard. The method was successfully demonstrated on five patient plasma samples, with cTnI concentrations measuring between 4.86 μg/L and 11.3 μg/L (signifying moderate myocardial infarctions). LC-MS/MS measurement precision was validated by three unique peptides from cTnI and two MRM transitions per peptide. Relative standard deviation (CV) from the five plasma samples was determined to be ≤14.3%. This study has demonstrated that quantification of cTnI in native plasma from myocardial infarction patients can be achieved based on an ID-LC-MS/MS method. The development of an ID-LC-MS/MS method for cTnI in plasma is a first step for future certification of matrix-based reference materials, which may be used to help harmonize discordant cTnI clinical assays. Graphical abstract A schematic of the workflow for measuring cardiac troponin I (cTnI), a low-abundant protein biomarker used for diagnosing myocardial infarction, in human plasma by isotope-dilution LC-MS/MS analysis.

Thrombin-Mediated Degradation of Human Cardiac Troponin T

BACKGROUND

Cardiac troponin T (cTnT) is an acknowledged biomarker of acute myocardial infarction (AMI) that is known to be prone to proteolytic degradation in serum. Such degradation is usually explained by the action of μ-calpain, although there could be other candidates for that role. In the current study, we explored the hypothesis that thrombin-mediated cTnT cleavage occurs as a result of the serum sample preparation.

METHODS

cTnT degradation was studied by using immunoblotting and mass spectrometry (MS) analysis.

RESULTS

The comparison of cTnT isolated from AMI heparin plasma and serum samples showed that cTnT in the plasma samples was mainly present as the full-sized molecule (approximately 35 kDa), while in serum samples it was present as a 29-kDa fragment. The incubation of recombinant cTnT, or native ternary cardiac troponin complex with thrombin or in normal human serum (NHS), resulted in the formation of a 29-kDa product that was similar to that detected in AMI serum samples. No cTnT degradation was observed when thrombin or NHS was pretreated with hirudin, a specific inhibitor of thrombin, or during incubation of troponin in normal heparin plasma. When the products of thrombin-mediated cTnT proteolysis were analyzed by MS, 2 fragments consisting of amino acid residues (aar) 2-68 and 69-288 were identified, which suggests that thrombin cleaves cTnT between R68 and S69.

CONCLUSIONS

The results of this study suggest that the 29-kDa fragment of cTnT in AMI serum samples mainly appears due to the cleavage by thrombin during serum sample preparation.

Cardiac Troponin T: Smaller Molecules in Patients with End-Stage Renal Disease than after Onset of Acute Myocardial Infarction

BACKGROUND

We have found previously that in acute myocardial infarction (AMI), cardiac troponin T (cTnT) is degraded in a time-dependent pattern. We investigated whether cTnT forms differed in patients with chronic cTnT increases, as seen with renal dysfunction, from those in the acute phase of myocardial infarction.

METHODS

We separated cTnT forms by gel filtration chromatography (GFC) in end-stage renal disease (ESRD) patients: prehemodialysis (pre-HD) and post-HD (n = 10) and 2 months follow-up (n = 6). Purified (cTnT) standards, quality control materials of the clinical cTnT immunoassay (Roche), and AMI patients' sera also were analyzed. Immunoprecipitation and Western blotting were performed with the original cTnT antibodies from the clinical assay and antibodies against the N- and C-terminal end of cTnT.

RESULTS

GFC analysis revealed the retention of purified cTnT at 27.5 mL, identical to that for cTnT in quality controls. For all ESRD patients, one cTnT peak was found at 45 mL, pre- and post-HD, and stable over time. Western blotting illustrated that this peak corresponded to cTnT fragments &lt;18 kDa missing the N- and C-terminal ends. AMI patients' sera revealed cTnT peaks at 27.5 and 45 mL, respectively, corresponding to N-terminal truncated cTnT of 29 kDa and N- and C-terminal truncated fragments of &lt;18 kDa, respectively.

CONCLUSIONS

We found that cTnT forms in ESRD patients are small (&lt;18 kDa) and different from forms seen in AMI patients. These insights may prove useful for development of a more specific cTnT immunoassay, especially for the acute and diagnostic phase of myocardial infarction.

Advances in Cardiac Biomarkers of Acute Coronary Syndrome

Acute coronary syndrome (ACS) encompasses a pathophysiological spectrum of cardiovascular diseases, all of which have significant morbidity and mortality. ACS was once considered an acute condition; however, new treatment strategies and improvements in biomarker assays have led to ACS being an acute and chronic disease. Cardiac troponin is the preferred biomarker for the diagnosis of myocardial infarction, and there is considerable interest and efforts toward development and implementation of high-sensitivity cardiac troponin (hs-cTn) assays worldwide. Analytical and clinical performance characteristics of hs-cTn assays as well as testing limitations are important for laboratorians and clinicians to understand in order to utilize testing appropriately. Furthermore, expanding the clinical utility of hs-cTn into other cohorts such as asymptomatic community dwelling populations, heart failure, and chronic kidney disease populations supports novel opportunities for improved short- and long-term prognosis.

Identification and Characterization of Cardiac Troponin T Fragments in Serum of Patients Suffering from Acute Myocardial Infarction

BACKGROUND

Cardiac troponin T (cTnT) is the preferred biomarker for the diagnosis of acute myocardial infarction (AMI). It has been suggested that cTnT is present predominantly in fragmented forms in human serum following AMI. In this study, we have used a targeted mass spectrometry assay and epitope mapping using Western blotting to confirm this hypothesis.

METHODS

cTnT was captured from the serum of 12 patients diagnosed with AMI using an immunoprecipitation technique employing the M11.7 catcher antibody and fractionated with SDS-PAGE. Coomassie-stained bands of 4 patients at 37, 29, and 16 kDa were excised from the gel, digested with trypsin, and analyzed on a Q Exactive instrument set on targeted Selected Ion Monitoring mode with data-dependent tandem mass spectrometry (MS/MS) for identification. Western blotting employing 3 different antibodies was used for epitope mapping.

RESULTS

Ten cTnT peptides of interest were targeted. By using MS/MS, all of these peptides were identified in the 37-kDa, intact, cTnT band. In the 29- and 16-kDa fragment bands, 8 and 4 cTnT-specific peptides were identified, respectively. Some of these peptides were "semitryptic," meaning that their C-termini were not formed by trypsin cleavage. The C-termini of these semitryptic peptides represent the C-terminal end of the cTnT molecules present in these bands. These results were confirmed independently by epitope mapping.

CONCLUSIONS

Using LC-MS, we have succeeded in positively identifying the 29- and 16-kDa fragment bands as cTnT-derived products. The amino acid sequences of the 29- and 16-kDa fragments are Ser79-Trp297 and Ser79-Gln199, respectively.

Factors underlying elevated troponin I levels following pacemaker primo-implantation

BACKGROUND

Cardiac troponins are routinely used as markers of myocardial damage. Originally, they were only intended for use in diagnosing acute coronary syndromes; however, we now know that raised serum troponin levels are not always caused by ischemia. There are many other clinical conditions that cause damage to cardiomyocytes, leading to raised levels of troponin. However, the specificity of cardiac troponins towards the myocardium is absolute. Our work focuses on mechanical damage to the myocardium and on monitoring the factors that raise the levels of cardiospecific markers after primo-implantation of a pacemaker with an actively fixed electrode.

AIMS

(i) To determine whether the use of a primo-implanted pacemaker with an electrode system with active fixation will raise troponin levels over baseline. (ii) To assess whether troponin I elevation is dependent on procedure complexity.

METHODS

We enrolled 219 consecutive patients indicated for pacemaker primo-implantation; cardiospecific marker values (troponin I, CKMB, myoglobin) were determined before the implantation procedure and again at 6- and 18-h intervals after the procedure. We monitored duration of cardiac skiascopy, number of attempts to place the electrode (active penetration into the tissue) and intervention range (single-chamber versus dual-chamber pacing), and we assessed the clinical data.

RESULTS

The average age of the enrolled patients was 78.2 ± 8.0 years (median age, 80 years); women constituted 45% of the group. We implanted 128 dual-chamber and 91 single-chamber devices with an average skiascopic time of 38.6 ± 22.0 s (median, 33.5 s). Troponin I serum levels increased from an initial 0.03 ± 0.07 μg/L (median, 0.01) to 0.18 ± 0.17 μg/L (median, 0.13) and 0.09 ± 0.18 μg/L (median, 0.04) at 6 and 18 h, respectively. The differences were statistically significant (P < 0.001 or P < 0.001). We confirmed a correlation between troponin increase and duration of skiascopy (P < 0.001). We also demonstrated a correlation between increased troponin I and number of attempts to place a pacemaker electrode (penetration into the tissue) at 6 h (P < 0.001) post-implantation.

CONCLUSION

We detected slightly elevated troponin I levels in patients with primo-implanted pacemakers using electrodes with active fixation. We demonstrated a direct correlation between myocardial damage (number of electrode penetrations into the myocardium) and troponin I elevation, as well as between complexity (severity) of the implantation procedure (indicated by prolonged skiascopy) and raised troponin I. The described phenomenon demonstrates the loss of the diagnostic role of troponin I early after pacemaker primo-implantation in patients with concomitant chest pain.

A rational approach for generating cardiac troponin I selective Spiegelmers

We report the first protein selective Spiegelmers of diagnostic relevance by rational identification of a target epitope and reverse screening of Spiegelmer candidates following the selection procedure. Application of the presented approach resulted in isolation of cardiac troponin I selective Spiegelmers with low nanomolar dissociation constant and functionality in serum.

Evaluation of standardization capability of current cardiac troponin I assays by a correlation study: results of an IFCC pilot project

As a part of an International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) project to prepare a commutable reference material for cardiac troponin I (cTnI), a pilot study evaluated current cTnI assays for measurement equivalence and their standardization capability.

cTnI-positive samples collected from 90 patients with suspected acute myocardial infarction were assessed for method comparison by 16 cTnI commercial assays according to predefined testing protocols. Seven serum pools prepared from these samples were also assessed.

Each assay was assessed against median cTnI concentrations measured by 16 cTnI assays using Passing-Bablok regression analysis of 79 patient samples with values above each assay’s declared detection limit. We observed a 10-fold difference in cTnI concentrations for lowest to highest measurement results. After mathematical recalibration of assays, the between-assay variation for patient samples reduced on average from 40% to 22% at low cTnI concentration, 37%–20% at medium concentration, and 29%–14% at high concentration. The average reduction for pools was larger at 16%, 13% and 7% for low, medium and high cTnI concentrations, respectively. Overall, assays demonstrated negligible bias after recalibration (y-intercept: –1.4 to 0.3 ng/L); however, a few samples showed substantial positive and/or negative differences for individual cTnI assays.

All of the 16 commercial cTnI assays evaluated in the study demonstrated a significantly higher degree of measurement equivalence after mathematical recalibration, indicating that measurement harmonization or standardization would be effective at reducing inter-assay bias. Pooled sera behaved similarly to individual samples in most assays.

High sensitivity cardiac troponin assays in the clinical laboratories

Immunoassays measuring cardiac troponins I or T have become firmly established as critical tools for diagnosing acute myocardial infarction. While most contemporary assays provide adequate diagnostic performance, the increased sensitivity and precision of the new, high sensitivity assays that have already been introduced into clinical practice, provide the potential to further shorten intervals between blood draws or the time needed to detect the first significant troponin elevation. In addition to the relatively modest benefits at the diagnostic end, the high sensitivity assays and the investigational ultrasensitive cardiac troponin assays offer improvements for predicting major adverse cardiovascular events, development of heart failure or transition to end-stage kidney disease. These novel high sensitivity assays can measure troponin concentrations in 50%–100% of healthy individuals and therefore allow for the distribution of troponin values within a healthy cohort to be measured, patient’s baseline troponin levels to be monitored, and clinicians to be alerted of deteriorating cardiorenal conditions. We envisage that the high sensitivity assays will become important tools for predicting each patient’s risk of future adverse events and for guiding and monitoring corresponding adjustments of preventative therapeutic interventions.

Troponin assays in the assessment of the equine myocardium

In 2000, troponin assays were adopted as the test of choice for detection of myocardial injury in man. This decision was made after extensive testing and followed a 60 year search for a biomarker of myocardial damage with sufficient analytical sensitivity and specificity. This has led to proliferation of assays for use in human medicine, each requiring extensive testing and validation before it could be made available on the open market for human use. The search for ever-more analytically sensitive assays and for a standard reference material continues. The adoption of troponin testing in veterinary medicine followed shortly after its development for use in man, providing a much-needed means of detecting and monitoring myocardial damage in horses. However, application of these tests in veterinary medicine has exclusively involved use of assays designed for and clinically validated in human patients. There is no mandated requirement for test validation in veterinary medicine and, while many of these assays have been shown to be capable of detecting equine troponin, the wide diversity of available tests, lack of validation, absence of protocols for their use and lack of standardisation make their application problematic. The objective of this review article is to address this issue, offering guidance where data are available and encouraging caution where there are none. Ultimately, the overall goal of this review is to examine critically the use of troponin assays in the horse and to promote the accurate and appropriate interpretation of valid results.

Role of anti-CD40 antibody-mediated costimulation blockade on non-Gal antibody production and heterotopic cardiac xenograft survival in a GTKO.hCD46Tg pig-to-baboon model

BACKGROUND

Recently, we have shown that an immunosuppression regimen including costimulation blockade via anti-CD154 antibody significantly prolongs the cardiac xenograft survival in a GTKO.hCD46Tg pig-to-baboon heterotopic xenotransplantation model. Unfortunately, many coagulation disorders were observed with the use of anti-CD154 antibody, and recipient survival was markedly reduced by these complications.

MATERIAL AND METHODS

In this experiment, we replaced anti-CD154 antibody with a more clinically acceptable anti-CD40 antibody while keeping the rest of the immunosuppressive regimen and the donor pig genetics the same. This was carried out to evaluate the antibody's role in xenograft survival and prevention of coagulopathies. Two available clones of anti-CD40 antibody were tested. One mouse anti-human CD40 antibody, (clone 3A8), activated B lymphocytes in vitro and only modestly suppressed antibody production in vivo. Whereas a recombinant mouse non-human primate chimeric raised against macaque CD40, (clone 2C10R4), blocked B-cell activation in vitro and completely blocked antibody production in vivo.

RESULTS

The thrombotic complications seen with anti-CD154 antibody were effectively avoided but the graft survival, although extended, was not as prolonged as observed with anti-CD154 antibody treatment. The longest survival for the 3A8 antibody group was 27 days, and the longest graft survival in the 2C10R4 antibody group was 146 days. All of the grafts except two rejected and were explanted. Only two recipient baboons had to be euthanized due to unrelated complications, and the rest of the baboons remained healthy throughout the graft survival period or after graft explantation. In contrast to our anti-CD 154 antibody-treated baboons, the non-Gal antibody levels started to rise after B cells made their appearance around 8 weeks post-transplantation.

CONCLUSIONS

Anti-CD40 antibody at the current dose does not induce any coagulopathies but while effective, had reduced efficacy to induce similar long-term graft survival as with anti-CD154 antibody perhaps due to ineffective control of B-cell function and antibody production at the present dose. More experiments are required to determine antibody affinity and effective dose for inducing long-term cardiac xenograft survival.

Evaluation of a high-sensitivity assay for measurement of canine and feline serum cardiac troponin I

BACKGROUND

Cardiac troponins are established as the gold standard biomarkers for acute cardiac injury. As even small elevations of cardiac troponins have prognostic relevance in people, it is important to investigate the performance of sensitive assays for use in veterinary medicine.

OBJECTIVES

The aim of this study was to evaluate analytical and overlap performance of a high-sensitivity cardiac troponin I (cTnI) assay, the ADVIA Centaur CP TnI-Ultra assay, in dogs and cats.

METHODS

Serum samples from dogs and cats with cardiac disease or arrhythmias, along with samples of purified canine free cTnI and complexed cTnI, T, and C (cTnI-T-C) were used in the assay validation study. Intra- and inter-assay variation, linearity under dilution, spike-and-recovery analysis, and detection limit were investigated to assess analytical performance. Overlap performance was evaluated based on the ability of the assay to discriminate between healthy animals and animals with cardiac disease or arrhythmias.

RESULTS

Intra-assay variation of cTnI in canine and feline serum ranged from 3.9 to 6.4% and from 4.0 to 4.8%, respectively. Inter-assay variation ranged from 2.7 to 4.7% and from 4.0 to 7.8%, respectively. The assay demonstrated acceptable linearity under dilution within a clinically relevant range of cTnI concentrations. Spike-and-recovery analysis showed excessive recovery in the range 150.7%-242.0% for free cTnI and 121.1-196.3% for complexed cTnI-T-C, partly due to a matrix effect. Overlap performance was acceptable as animals with cardiac disease or arrhythmias (n = 45 dogs, n = 53 cats) had significantly higher cTnI concentrations than healthy controls (P < .0001).

CONCLUSIONS

The results confirm the ADVIA Centaur CP TnI-Ultra assay as a valuable tool for assessing cTnI and thus myocardial injury in dogs and cats.

Time-dependent degradation pattern of cardiac troponin T following myocardial infarction

BACKGROUND

Cardiac troponin T (cTnT) is widely used for the diagnosis of acute myocardial infarction (AMI). However, it is still unclear whether degraded cTnT forms circulate in the patient's blood. We therefore aimed to elucidate which cTnT forms are detected by the clinical assay.

METHODS

Separation of cTnT forms by gel filtration chromatography (GFC) was performed in sera from 13 AMI patients to examine cTnT degradation. The GFC eluates were subjected to Western blot analysis with the original antibodies from the Roche immunoassay used to mimic the clinical cTnT assay. To investigate the degradation pattern with time, standardized serum samples of 18 AMI patients collected 0-72 h after admission were analyzed by Western blot analysis.

RESULTS

GFC analysis of AMI patients' sera revealed 2 cTnT peaks with retention volumes of 5 and 21 mL. Western blot analysis identified these peaks as cTnT fragments of 29 and 14-18 kDa, respectively. Furthermore, the performance of direct Western blots on standardized serum samples demonstrated a time-dependent degradation pattern of cTnT, with fragments ranging between 14 and 40 kDa. Intact cTnT (40 kDa) was present in only 3 patients within the first 8 h after hospital admission.

CONCLUSIONS

These results demonstrate that the Roche cTnT immunoassay detects intact as well as degraded cTnT forms in AMI patients' sera during the period of diagnostic testing. Moreover, following AMI, cTnT is degraded in a time-dependent pattern.

Sensible use of high-sensitivity troponin assays

The first intracellular Ca(2+)-sensor protein to be described was the troponin complex. Only later it was -discovered that cardiac-specific isoforms of troponin I (cTnI) and troponin T (cTnT) exist, and nowadays, measurement of cardiac troponins is a corner stone in the diagnosis of patients with acute coronary syndrome (ACS). High-sensitivity (hs-) assays have been developed that can record slightly elevated plasma concentrations of cardiac troponins as early as 3 h after onset of clinical symptoms. International guidelines defined a diagnostic cut-off at cardiac troponin levels corresponding to the 99th percentile of a healthy reference population and require that hs-assays measure this concentration with an interassay coefficient of variation ≤10%. This review provides an overview of the diagnostic and prognostic use of cardiac troponins.

Application of recombinant antibody fragments for troponin I measurements

The cardiac isoform of troponin I is a reliable biomarker of damaged cardiomyocytes that accompanies such severe cardiovascular diseases as myocardial infarction. Monoclonal antibody 19C7 recognizes troponin I in the bloodstream with high affinity and specificity. Recombinant antibodies can be used to improve detection systems based on monoclonal antibodies produced with hybridoma technology. In the present study, we compare the properties of monoclonal antibody 19C7 and its recombinant fragments. It is shown that the recombinant antibody fragments demonstrate similar affinity values as monoclonal antibodies and can be applied for troponin I detection.

The impact of antibody selection on the detection of cardiac troponin I

BACKGROUND

Cardiac troponin I (cTnI) is the current standard biomarker for diagnosing acute myocardial infarction and for risk-stratification of acute coronary syndromes in patients. However, it remains unclear how the epitope specificity of antibodies in immunoassays influences the detection of various modified forms of cTnI.

METHODS

Four mouse anti-human cTnI monoclonal antibodies targeting different regions of human cTnI were chosen for immunoaffinity purification of cTnI from human and swine cardiac tissue. High-resolution intact protein mass spectrometry was employed to assess the comparative performance of these four antibodies in detecting modified forms of cTnI.

RESULTS

Our data revealed that antibody selection significantly impacts the relative protein yield of cTn from immunoaffinity purification. Remarkably, a single amino acid variation in cTnI (G->S) in the epitope region completely abolished the binding between monoclonal antibody 560 and swine cTnI in solution. Moreover, proteolytic degradation around the epitope region severely compromised the detection of proteolytic fragment forms of cTnI by monoclonal antibodies. In contrast, the phosphorylation status near the epitope region did not significantly affect the antibody recognition of cTnI.

CONCLUSION

Caution needs to be taken in the interpretation of the data produced by immuno-assays with monoclonal antibodies against various epitopes of cTnI.

Evaluation of a modified lateral flow immunoassay for detection of high-sensitivity cardiac troponin I and myoglobin

We prospectively evaluated the use of lateral flow immunoassay (LFIA) test modified with nanoparticles for combined detection of high-sensitivity cardiac troponin I (hs-cTnI) and myoglobin with the aim of excluding acute myocardial infarction (AMI). Specimens from 173 patients with symptoms suggestive of AMI were collected to measure hs-cTnI and myoglobin using an electrochemiluminescence immunoassay (ECLI) and the LFIA test modified with nanoparticles, and a comparison was performed between the modified method and a commercial LFIA test for detection of the two proteins. The accuracy of the modified LFIA test was also evaluated. Consistent agreement was observed in the quantitative comparison of 173 clinical samples using the modified LFIA and ECLI, and the modified method was more sensitive than the commercial LFIA test. The accuracy of the modified LFIA was <12% for both hs-cTnI and myoglobin. Thus, the new approach has great potential to improve LFIAs test, demonstrating its usefulness for simple screening applications and for sensitivity and quantitative immunoassays for diagnosis ofAMI.