Skeletal troponin I cross-reactivity in different cardiac troponin I assay versions

Intact Transition Epitope Mapping-Force Differences between Original and Unusual Residues (ITEM-FOUR)

Antibody-based point-of-care diagnostics have become indispensable for modern medicine. In-depth analysis of antibody recognition mechanisms is the key to tailoring the accuracy and precision of test results, which themselves are crucial for targeted and personalized therapy. A rapid and robust method is desired by which binding strengths between antigens and antibodies of concern can be fine-mapped with amino acid residue resolution to examine the assumedly serious effects of single amino acid polymorphisms on insufficiencies of antibody-based detection capabilities of, e.g., life-threatening conditions such as myocardial infarction. The experimental ITEM-FOUR approach makes use of modern mass spectrometry instrumentation to investigate intact immune complexes in the gas phase. ITEM-FOUR together with molecular dynamics simulations, enables the determination of the influences of individually exchanged amino acid residues within a defined epitope on an immune complex's binding strength. Wild-type and mutated epitope peptides were ranked according to their experimentally determined dissociation enthalpies relative to each other, thereby revealing which single amino acid polymorphism caused weakened, impaired, and even abolished antibody binding. Investigating a diagnostically relevant human cardiac Troponin I epitope for which seven nonsynonymous single nucleotide polymorphisms are known to exist in the human population tackles a medically relevant but hitherto unsolved problem of current antibody-based point-of-care diagnostics.

A review of cardiac troponin I detection by surface enhanced Raman spectroscopy: Under the spotlight of point-of-care testing

Cardiac troponin I (cTnI) is a biomarker widely related to acute myocardial infarction (AMI), one of the leading causes of death around the world. Point-of-care testing (POCT) of cTnI not only demands a short turnaround time for its detection but the highest accuracy levels to set expeditious and adequate clinical decisions. The analytical technique Surface-enhanced Raman spectroscopy (SERS) possesses several properties that tailor to the POCT format, such as its flexibility to couple with rapid assay platforms like microfluidics and paper-based immunoassays. Here, we analyze the strategies used for the detection of cTnI by SERS considering POCT requirements. From the detection ranges reported in the reviewed literature, we suggest the diseases other than AMI that could be diagnosed with this technique. For this, a section with information about cardiac and non-cardiac diseases with cTnI release, including their release kinetics or cut-off values are presented. Likewise, POCT features, the use of SERS as a POCT technique, and the biochemistry of cTnI are discussed. The information provided in this review allowed the identification of strengths and lacks of the available SERS-based point-of-care tests for cTnI and the disclosing of requirements for future assays design.

False-Positive Causes in Serum Cardiac Troponin Levels

Cardiac troponins (cTns) are the most valuable and specific markers of cardiovascular diseases, including acute myocardial infarction. These biomarkers can also be used to assess the degree of myocardial damage in non-cardiac diseases that can negatively affect the cells of cardiac muscle tissue. However, in everyday clinical practice, doctors often encounter with false-positive cases of increased cTns. False-positive cases of increased cTns can contribute to incorrect diagnosis and subsequent inadequate treatment, which causes significant harm to the patient. This review discusses some common causes of a false-positive increase in the level of cTns in the blood serum. Such causes are fibrin clots, heterophilic antibodies, alkaline phosphatase, rheumatoid factor, and cross-reactions of diagnostic (anti-cTn) antibodies with skeletal troponins. Detailed attention is focused on the mechanisms of false-positive increase, and ways to identify and combat these false-positive causes of increased cTns. This has an important practical significance in modern clinical practice.

Some Common Causes of False Positive Increases in Serum Levels of Cardiac Troponins

Cardiac troponin molecules (cTnI and cTnT) are the most valuable and in-demand biomarkers for detecting various types of myocardial damage (reversible and irreversible, ischemic, inflammatory, toxic, etc.) in current clinical practice. These biomarkers are widely used for early diagnosis of acute myocardial infarction (AMI) and risk stratification of patients suffering from a number of cardiac (such as myocarditis, heart failure, cardiomyopathy, etc.) and extra-cardiac diseases (such as sepsis, renal failure, pulmonary embolism, neurological pathologies, etc.) that negatively affect the cells of cardiac muscle tissue. However, in daily routine clinical activities, internists and cardiologists often encounter cases of false increases in the concentrations of cardiospecific troponins. A false increase in the concentration of troponins contributes to an incorrect diagnosis and incorrect therapy, which can harm the patient. A false increase in the concentration of troponins contributes to an incorrect diagnosis and incorrect therapy, which can harm the patient, therefore, internists and cardiologists should be well aware of the main reasons and mechanisms for false-positive results cTnI and cTnT. This review article mainly focuses on the causes of falsepositive increases in serum levels of cTnI and cTnT, which provide helpful clues for the accurate diagnosis of AMI and evidence for the differential diagnosis.

Exercise-Induced Cardiac Troponin Elevations: From Underlying Mechanisms to Clinical Relevance

Supplemental Digital Content is available in the text.

Serological assessment of cardiac troponins (cTn) is the gold standard to assess myocardial injury in clinical practice. A greater magnitude of acutely or chronically elevated cTn concentrations is associated with lower event-free survival in patients and the general population. Exercise training is known to improve cardiovascular function and promote longevity, but exercise can produce an acute rise in cTn concentrations, which may exceed the upper reference limit in a substantial number of individuals. Whether exercise-induced cTn elevations are attributable to a physiological or pathological response and if they are clinically relevant has been debated for decades. Thus far, exercise-induced cTn elevations have been viewed as the only benign form of cTn elevations. However, recent studies report intriguing findings that shed new light on the underlying mechanisms and clinical relevance of exercise-induced cTn elevations. We will review the biochemical characteristics of cTn assays, key factors determining the magnitude of postexercise cTn concentrations, the release kinetics, underlying mechanisms causing and contributing to exercise-induced cTn release, and the clinical relevance of exercise-induced cTn elevations. We will also explain the association with cardiac function, correlates with (subclinical) cardiovascular diseases and exercise-induced cTn elevations predictive value for future cardiovascular events. Last, we will provide recommendations for interpretation of these findings and provide direction for future research in this field.

Generation, selection and modification of anti-cardiac troponin I antibodies with high specificity and affinity

Current diagnosis of acute myocardial infarction involves quantification of circulating cTn levels. This work endeavoured to generate and enhance recombinant antibody fragments targeting various epitopes on the N- and C-terminals of the cTnI molecule, thereby facilitating highly sensitive detection of the troponin molecule. From this approach, two anti-cTnI scFv antibodies were successfully selected using either phage display or structural reformatting of full length anti-cTnI IgG. Their antibody binding affinity was further optimised via chain shuffling and/or site directed mutagenesis, resulting in scFv with heightened sensitivity when compared to the wild-type scFv. If used in conjunction with existing anti-mid fragment cTnI antibodies, these N- and C- terminal-targeting scFvs show high potential for the enhancement of current cTnI detection assays by limiting the effects from cTnI degradation or troponin complex formation.

Troponin elevation in the setting of exercise-induced rhabdomyolysis in an athletic teenager

Troponin levels are often obtained when chest pain is evaluated in the paediatric emergency department. Elevations in troponin levels can be due to different causes, and it is important to fully understand all of these possible causes to help streamline further evaluation and therapy. We present the case of a teenager who had two episodes of troponin elevation in the setting of rhabdomyolysis.

Evaluation of Molecularly Imprinted Polymers for Point-of-Care Testing for Cardiovascular Disease

Molecular imprinting is a rapidly growing area of interest involving the synthesis of artificial recognition elements that enable the separation of analyte from a sample matrix and its determination. Traditionally, this approach can be successfully applied to small analyte (<1.5 kDa) separation/ extraction, but, more recently it is finding utility in biomimetic sensors. These sensors consist of a recognition element and a transducer similar to their biosensor counterparts, however, the fundamental distinction is that biomimetic sensors employ an artificial recognition element. Molecularly imprinted polymers (MIPs) employed as the recognition elements in biomimetic sensors contain binding sites complementary in shape and functionality to their target analyte. Despite the growing interest in molecularly imprinting techniques, the commercial adoption of this technology is yet to be widely realised for blood sample analysis. This review aims to assess the applicability of this technology for the point-of-care testing (POCT) of cardiovascular disease-related biomarkers. More specifically, molecular imprinting is critically evaluated with respect to the detection of cardiac biomarkers indicative of acute coronary syndrome (ACS), such as the cardiac troponins (cTns). The challenges associated with the synthesis of MIPs for protein detection are outlined, in addition to enhancement techniques that ultimately improve the analytical performance of biomimetic sensors. The mechanism of detection employed to convert the analyte concentration into a measurable signal in biomimetic sensors will be discussed. Furthermore, the analytical performance of these sensors will be compared with biosensors and their potential implementation within clinical settings will be considered. In addition, the most suitable application of these sensors for cardiovascular assessment will be presented.

A glass fibre membrane platform for ultra-sensitive detection of cardiac troponin T

A glass fibre membrane platform that allows quantification of circulating cTnT with a LoD of 0.87 pg mL^-1 is described. The proposed platform uses a glass fibre membrane, DNA-guided detection method, and antibody-conjugated fluorescent beads for the quantification of cTnT in the analytical detection range of 1-120 pg mL^-1 at room temperature in 30 min. Glass fibre membranes were chemically modified to immobilize the oligonucleotide probes that catch a biomolecular complex (FB-dAB-cTnT-cAB-DNA) containing complementary oligonucleotides. There were no interferences from human cTnI, cTnC, skTnT, biotin, and hemoglobin (each 1 μg mL^-1). The linearity in the serial dilution test of plasma samples indicates that this platform is highly applicable for regular health check-up to assess the risk of AMI and HF.

Elevation of cardiac troponins measured after recreational resistance training

BACKGROUND

Whereas elevated cardiac troponin (cTn) concentrations i.e. above the 99th percentile of healthy reference population (recommended cutoff for the diagnosis of myocardial infarction) are well-documented in healthy individuals after prolonged and/or intensive exercises such as marathons, data on less-strenuous sports are scarce. Therefore, our aim was to investigate cTnI and cTnT release in response to recreational resistance training, here a single-bout of 1-h kettlebell workout.

METHODS

Serum samples were collected from 11 apparently healthy volunteers the previous day (pre-exercise), three hours after the kettlebell class (post-exercise), the next day and three days later. The aliquoted samples were analyzed with Abbott Laboratories' Architect high-sensitivity (hs)-cTnI assay (limit of detection, LoD = 2 ng/L), our 3+1-type cTnI assay free from cTn-specific autoantibody interference (LoD = 3 ng/L) and Roche Diagnostics' hs-cTnT assay (LoD = 5 ng/L).

RESULTS

The post-exercise cTn concentrations were significantly higher than the pre-exercise values (median 5.5-9.6 ng/L vs. <LoD, P<0.05 for all) and they correlated strongly between the three assays (Spearman r = 0.881-0.960, P<0.001 for all). Furthermore, a few post-exercise concentrations even exceeded the 99th percentile of Architect hs-cTnI (>26 ng/L, n = 2) and/or hs-cTnT (>14 ng/L, n = 4). The cTn concentrations returned to baseline during the three days of follow-up.

CONCLUSIONS

Our study demonstrates abnormally elevated cTns with well-validated sensitive cTn assays after resistance training. This confirms that different kinds of recreational physical activity are yet another confounder that may affect the determination and use of 99th percentile reference values. Therefore, exercise-associated changes should be carefully addressed as part of the evaluation what is "normal cTn".