Investigation of release and degradation of cardiac troponin T in patients with acute myocardial infarction

Highly Sensitive Immunoassay for Long Forms of Cardiac Troponin T Using Upconversion Luminescence

BACKGROUND

Long cardiac troponin T (cTnT) has been proposed to be a promising and more specific biomarker of acute myocardial infarction (AMI). As it represents a subfraction of circulating cTnT, detection of very low concentrations is a requirement. The aim of this study was to develop a novel, highly sensitive immunoassay for long cTnT.

METHODS

A two-step sandwich-type immunoassay for long cTnT was developed, utilizing upconverting nanoparticles (UCNPs) as reporters. The limits of detection and quantitation were determined for the assay. Linearity and matrix effects were evaluated. Performance with clinical samples was assessed with samples from patients with non-ST elevation myocardial infarction (NSTEMI, n = 30) and end-stage renal disease (ESRD, n = 37) and compared to a previously developed time-resolved fluorescence (TRF)-based long cTnT assay and a commercial high-sensitivity cTnT assay.

RESULTS

The novel assay reached a 28-fold lower limit of detection (0.40 ng/L) and 14-fold lower limit of quantitation (1.79 ng/L) than the previously developed TRF long cTnT assay. Li-heparin and EDTA plasma, but not serum, were found to be suitable sample matrixes for the assay. In a receiver operating characteristics curve analysis, the troponin ratio (long/total cTnT) determined with the novel assay showed excellent discrimination between NSTEMI and ESRD with an area under the curve of 0.986 (95% CI, 0.967-1.000).

CONCLUSIONS

By utilizing upconversion luminescence technology, we developed a highly sensitive long cTnT assay. This novel assay can be a valuable tool for investigating the full potential of long cTnT as a biomarker for AMI. ClinicalTrials.gov Registration Number: NCT04465591.

Low Level of First Morning Urine Cardiac Troponin I: A Specific Hallmark of Aortic Stenosis Severity

Background: It has recently been shown that cardiac-specific troponin I concentrations in first morning urine samples can be measured with commercially available tests. Due to their accumulation in the first morning urine, scientific papers indicate a potential predictive value for cardiovascular diseases. Therefore, the aim of this study was to compare the concentration of cardiac troponin I in the first morning urine in patients with severe aortic stenosis and the healthy population. Patients and Methods: Blood and first morning urine samples were collected from 34 healthy individuals (17 female) at University Hospital Merkur and 25 patients with severe aortic stenosis (14 female) before surgical treatment at University Hospital Dubrava. Cardiac troponin I and T values were determined using high-sensitivity assays using commercially available Abbott and Roche tests. Results: Patients with severe aortic stenosis had significantly lower troponin I concentrations in the first morning urine samples (0.3 ng/L (0.1-0.6)) as compared to the healthy population (15.2 ng/L (8.4-19.9)) (p < 0.001). There was no statistically significant difference in troponin T concentrations between healthy individuals and patients with severe aortic stenosis. In parallel, both I and T plasma troponin concentrations were significantly higher in patients with severe aortic stenosis. Conclusions: In patients with severe aortic stenosis, cardiac troponin I values in the first morning urine are significantly lower than in healthy subjects.

Fragmentation of human cardiac troponin T after acute myocardial infarction

BACKGROUND

Blood measurement of cardiac troponin T (cTnT) is one of the most widespread methods of acute myocardial infarction (MI) diagnosis. cTnT degradation may have a significant influence on the precision of cTnT immunodetection; however, there are no consistent data describing the level and sites of cTnT proteolysis in the blood of MI patients. In this study, we bordered major cTnT fragments and quantified their relative abundance in the blood at different times after MI.

METHODS

Serial heparin plasma samples were collected from 37 MI patients 2-37 h following the onset of MI. cTnT and its fragments were studied by western blotting and immunofluorescence analysis using monoclonal antibodies specific to various cTnT epitopes.

RESULTS

cTnT was present in the blood of MI patients as 23 proteolytic fragments with an apparent molecular mass of ∼ 8-37 kDa. Two major sites of cTnT degradation were identified: between amino acid residues (aar) 68 and 69 and between aar 189 and 223. Analysis of the abundance of cTnT fragments showed an increase in the fraction of free central fragments in the first few hours after MI, while the fraction of the C-terminal fragments of cTnT remained almost unchanged.

CONCLUSION

cTnT progressively degrades after MI and appears in the blood as a mixture of 23 proteolytic fragments. The cTnT region approximately bordered by aar 69-158 is a promising target for antibodies used for measurement of total cTnT.

Cardiac troponins: Mechanisms of release and role in healthy and diseased subjects

The cardiac troponins (cTns), cardiac troponin C (cTnC), cTnT, and cTnI are key elements of myocardial apparatus, fixed as protein complex on the thin filament of sarcomere and are involved in the regulation of excitation-contraction coupling of cardiomyocytes in the presence of Ca²⁺ . Circulating cTnT and cTnI (cTns) increase following cardiac tissue necrosis, and they are consolidated biomarkers of acute myocardial infarction (AMI). However, the use of high sensitivity (hs)-immunoassay tests for cTnT and cTnI has made it possible to identify a multitude of other clinical conditions associated with increased circulating levels of cTns. cTns can be measured also in the peripheral circulation of healthy subjects or athletes, suggesting that different mechanisms are involved in the release of cTns in the blood independently of cardiac cell necrosis. In this review, the molecular/cellular mechanisms involved in cTns release in blood and the exploitation of cTnI and cTnT as biomarkers of cardiac adverse events, in addition to cardiac necrosis, are discussed.

Prognostic Implications of a Second Peak of High-Sensitivity Troponin T After Myocardial Infarction

BACKGROUND

After an acute myocardial infarction (MI), repeated measurement of cardiac biomarkers is commonly performed, although not recommended in current guidelines. There is only limited data on the kinetics of troponin in this phase. For high-sensitivity cardiac troponin T (hs-cTnT), but not high-sensitivity cardiac troponin I (hs-cTnI), late increases in terms of a second peak have been described. Their impact on the prognosis of patients with MI remains unclear.

METHODS

We included 2,305 patients presenting to the emergency department with symptoms suggestive of MI. Five hundred and seven were diagnosed with MI. Hs-cTnT, creatine kinase (CK) and the MB fraction of CK (CK-MB) were measured at admission, after 1 and 3 h and thereafter as indicated by the treating physician. A mixed-model approach was applied for modeling the biomarker kinetics. All patients were followed up to assess a composite endpoint of mortality, recurrent MI, revascularization and rehospitalization and to investigate the effect of a second hs-cTnT peak on prognosis.

RESULTS

Out of 507 patients with MI, 192 had a sufficient amount of hs-cTnT measurements after the index MI. In 111 (57.8%) patients a second hs-cTnT peak was found after 4.48 days. For CK and CK-MB a second peak could not be identified. Regarding the composite endpoint there was no significant difference between patients with and without a second hs-cTnT peak.

CONCLUSION

In our analyses, a second peak of hs-cTnT after an acute MI was common, but not associated with poorer outcome. Thus, the clinical value of hs-cTnT for monitoring myocardial ischemia might be limited in this phase and other biomarkers might be more suitable.Trial Registration: www.ClinicalTrials.gov, identifier: NCT02355457, Date of registration: February 4, 2015.

Use of high-sensitivity cardiac troponins in the emergency department for the early rule-in and rule-out of acute myocardial infarction without persistent ST-segment elevation (NSTEMI) in Italy

Serial measurements of cardiac troponin are recommended by international guidelines to diagnose myocardial infarction (MI) since 2000. However, some relevant differences exist between the three different international guidelines published between 2020 and 2021 for the management of patients with chest pain and no ST-segment elevation. In particular, there is no agreement on the cut-offs or absolute change values to diagnose non-ST-segment elevation MI (NSTEMI). Other controversial issues concern the diagnostic accuracy and cost-effectiveness of cut-off values for the most rapid algorithms (0 h/1 h or 0 h/2 h) to rule-in and rule-out NSTEMI. Finally, another important point is the possible differences between demographic and clinical characteristics of patients enrolled in multicenter trials compared to those routinely admitted to the Emergency Department in Italy. The Study Group of Cardiac Biomarkers, supported by the Italian Scientific Societies Società Italiana di Biochimica Clinica, Italian Society of the European Ligand Assay Society, and Società Italiana di Patolgia Clinica e Medicina di Laboratorio decided to revise the document previously published in 2013 about the management of patients with suspected NSTEMI, and to provide some suggestions for the use of these biomarkers in clinical practice, with a particular focus on the Italian setting.

Cardiac Troponin Composition Characterization after Non ST-Elevation Myocardial Infarction: Relation with Culprit Artery, Ischemic Time Window, and Severity of Injury

BACKGROUND

Troponin composition characterization has been implicated as a next step to differentiate among non-ST elevation myocardial infarction (NSTEMI) patients and improve distinction from other conditions with troponin release. We therefore studied coronary and peripheral troponin compositions in relation to clinical variables of NSTEMI patients.

METHODS

Samples were obtained from the great cardiac vein (GCV), coronary sinus (CS), and peripheral circulation of 45 patients with NSTEMI. We measured total cTnI concentrations, and assessed both complex cTnI (binary cTnIC + all ternary cTnTIC forms), and large-size cTnTIC (full-size and partially truncated cTnTIC). Troponin compositions were studied in relation to culprit vessel localization (left anterior descending artery [LAD] or non-LAD), ischemic time window, and peak CK-MB value.

RESULTS

Sampling occurred at a median of 25 hours after symptom onset. Of total peripheral cTnI, a median of 87[78-100]% consisted of complex cTnI; and 9[6-15]% was large-size cTnTIC. All concentrations (total, complex cTnI, and large-size cTnTIC) were significantly higher in the CS than in peripheral samples (P < 0.001). For LAD culprit patients, GCV concentrations were all significantly higher; in non-LAD culprit patients, CS concentrations were higher. Proportionally, more large-size cTnTIC was present in the earliest sampled patients and in those with the highest CK-MB peaks.

CONCLUSIONS

In coronary veins draining the infarct area, concentrations of both full-size and degraded troponin were higher than in the peripheral circulation. This finding, and the observed associations of troponin composition with the ischemic time window and the extent of sustained injury may contribute to future characterization of different disease states among NSTEMI patients.

Diagnostic algorithms for non-ST-segment elevation myocardial infarction: open issues

The use of serial measurement of cardiac troponin (cTn) is recommended by international guidelines for the diagnosis of myocardial infarction (MI) since 2000. This article focuses on factors influencing temporal changes in high-sensitive cTn (hs)-cTn and the impact of these factors on the diagnosis of non-ST-segment elevation MI (NSTEMI). The recommendations proposed by three different international guidelines published in 2020-2021 for the management of acute coronary syndromes (ACS) in patients presenting without persistent ST-segment elevation (NSTE) show some discrepancies. In particular, there is no agreement among these guidelines about cut-off or absolute change values to be used for the rule-in, especially regarding the use of sex-specific cut-off values. Furthermore, there are no sufficient evidences on the diagnostic accuracy and cost effectiveness related to cut-off values suggested for algorithms to be used by some hs-cTnI methods.

Ultrafast, Ultrasensitive Detection and Imaging of Single Cardiac Troponin-T Molecules

The fluorescence-based methods of single-molecule optical detection have opened up unprecedented possibilities for imaging, monitoring, and sensing at a single-molecule level. However, single-molecule detection methods are very slow, making them practically inapplicable. In this paper, we show how to overcome this key limitation using the expanded laser spot, laser excitation in a nonfluorescent spectral window of biomolecules, and more binding fluorescent molecules on a biomolecule that increases the detection volume and the number of collected photons. We demonstrate advantages of the developed approach unreachable by any other technique using detection of single cardiac troponin-T molecules: (i) 1000-fold faster than by known approaches, (ii) real-time imaging of single troponin-T molecules dissolved in human blood serum, (iii) measurement of troponin-T concentration with a clinically important sensitivity of about 1 pg/mL. The developed approach can be used for ultrafast, ultrasensitive detection, monitoring, and real-time imaging of other biomolecules as well as of larger objects including pathogenic viruses and bacteria.

Early kinetic profiles of troponin I and T measured by high-sensitivity assays in patients with myocardial infarction

The early concentration kinetic profiles of cardiac troponin in patients with non-ST-elevated myocardial infarction (NSTEMI) measured by high-sensitivity cardiac troponin I (hs-cTnI) and T (hs-cTnT) assays have not been described. In intermediate-to-high-risk of NSTEMI patients we measured serial cTn concentrations on ED arrival, at 1, 2, 3, 6-12, 24 and 48-hours with hs-cTnI and hs-cTnT assays. Log-normal curves were fitted to concentrations from time from symptom onset, and the time to rule-out decision thresholds estimated (hs-cTnI: 2 ng/L and 5 ng/L; hs-cTnT: 5 ng/L). Among 164 patients there were 58 NSTEMI. The hs-cTnI to hs-cTnT ratio increased linearly over the first 6-12 h following symptom onset. The estimated times from symptom onset to the 2 ng/L and 5 ng/L thresholds for hs-cTnI were 1.8 (0.1-3.1) and 1.9 (1.1-3.5) hours, and to the 5 ng/L threshold for hs-cTnT 1.9 (1.1-3.8) hours. The estimated time to exceed 5 ng/L was ≥3 hours in 32.6% (95%CI: 20.0% to 48.1%) cases for hs-cTnI and 33.3% (19.6% to 50.0%) for hs-cTnT. cTnI concentrations increased at a much more rapid rate than cTnT concentrations in patients with NSTEMI. Concentrations of a high proportion of patients took longer than 3 hours from symptom onset to exceed the 5 ng/L rule-out decision threshold.

Relationship between hemoglobin A1c and serum troponin in patients with diabetes and cardiovascular events

OBJECTIVES

Diabetes mellitus is a group of metabolic disorders associated with high risk for cardiovascular disease. Although troponins are primarily clinically used for the diagnosis of acute coronary syndrome, they are also used in risk assessment in patients with acute coronary syndrome as well as in a number of other conditions. The aim of this review was to investigate the relationship between hemoglobin A1c and serum troponin in patients with diabetes and cardiovascular events.

METHODS

Hemoglobin A1c has been chosen as the best clinical indicator of glucose control and risk of micro and macrovascular complications. We investigated cardiac troponins as a group of markers of muscle injury which includes troponin T, troponin I and troponin C. Troponin T and I are specific for myocardial injury, compared to C which is specific for skeletal muscle.

RESULTS

In this review, we showed that there was a causal relation between hemoglobin A1c levels and serum troponin concentrations. Hemoglobin A1c has shown to be a positive predictive factor of incidence, mortality and morbidity of conditions such as acute coronary syndrome, arrhythmias, stroke, pulmonary embolism and other conditions that causes troponin elevation by its release in circulation.

CONCLUSIONS

Chronic hyperglycemia decreases glomerular filtration and consequently decreases troponin elimination and also by affecting the heart microcirculation it leads to microvascular damage and consequently to ischemia which contribute to troponin concentration elevation. Furthermore, correlation between hemoglobin A1c and troponin concentration manifests in their prognostic value for mortality.

Multi-Site Coronary Vein Sampling Study on Cardiac Troponin T Degradation in Non-ST-Segment-Elevation Myocardial Infarction: Toward a More Specific Cardiac Troponin T Assay

Background Cardiac troponin T ( cTnT ) is seen in many other conditions besides myocardial infarction, and recent studies demonstrated distinct forms of cTnT . At present, the in vivo formation of these different cTnT forms is incompletely understood. We therefore performed a study on the composition of cTnT during the course of myocardial infarction, including coronary venous system sampling, close to its site of release. Methods and Results Baseline samples were obtained from multiple coronary venous system locations, and a peripheral artery and vein in 71 non- ST -segment-elevation myocardial infarction patients. Additionally, peripheral blood was drawn at 6- and 12-hours postcatheterization. cTnT concentrations were measured using the high-sensitivity- cTnT immunoassay. The cTnT composition was determined via gel filtration chromatography and Western blotting in an early and late presenting patient. High-sensitivity - cTnT concentrations were 28% higher in the coronary venous system than peripherally (n=71, P<0.001). Coronary venous system samples demonstrated cT n T-I-C complex, free intact cTnT , and 29 kD a and 15 to 18 kD a cTnT fragments, all in higher concentrations than in simultaneously obtained peripheral samples. While cT n T-I-C complex proportionally decreased, and disappeared over time, 15 to 18 kD a cTnT fragments increased. Moreover, cT n T-I-C complex was more prominent in the early than in the late presenting patient. Conclusions This explorative study in non- ST -segment-elevation myocardial infarction shows that cTnT is released from cardiomyocytes as a combination of cT n T-I-C complex, free intact cTnT , and multiple cTnT fragments indicating intracellular cTnT degradation. Over time, the cT n T-I-C complex disappeared because of in vivo degradation. These insights might serve as a stepping stone toward a high-sensitivity- cTnT immunoassay more specific for myocardial infarction.

Mass Spectrometric Identification of Cardiac Troponin T in Urine of Patients Suffering from Acute Myocardial Infarction

BACKGROUND

Because of its high cardiospecificity, cardiac troponin T (cTnT) is one of the first-choice biomarkers to diagnose acute myocardial infarction (AMI). cTnT is extensively fragmented in serum of patients suffering from AMI. However, it is currently unknown whether all cTnT is completely degraded in the body or whether some cTnT fragments can leave the body via urine. The aim of the present study is to develop a method for the detection of cTnT in urine and to examine whether cTnT is detectable in patient urine.

METHODS

Proteins in urine samples of 20 patients were precipitated using a cTnT-specific immunoprecipitation technique and a nonspecific acetonitrile protein precipitation. After in-solution digestion of the precipitated proteins, the resulting peptides were separated and analyzed using HPLC and mass spectrometry with a targeted selected ion monitoring assay with data-dependent tandem mass spectrometry (t-SIM/dd-MS2).

RESULTS

The t-SIM/dd-MS2 assay was validated using a synthetic peptide standard containing 10 specific cTnT peptides of interest and with purified human intact cTnT spiked in urine from healthy individuals. Using this assay, 6 different cTnT-specific peptides were identified in urine samples from 3 different patients, all suffering from AMI.

CONCLUSIONS

We show here for the first time that cTnT can be present in the urine of AMI patients using a targeted LC-MS/MS assay. Whether the presence of cTnT in urine reflects a physiological or pathophysiological process still needs to be elucidated.

What to do when you question cardiac troponin values

High-sensitivity cardiac troponin assays enable cardiac troponin measurement with a high degree of analytical sensitivity and a low level of analytical imprecision at the low measuring range. One of the most important advantages of these new assays is that they allow novel, more rapid approaches for ruling in or ruling out acute myocardial infarctions. The increase in the early diagnostic sensitivity of high-sensitivity cardiac troponin assays comes at the cost of a reduced acute myocardial infarction specificity of the biomarker, because more patients with other causes of acute or chronic myocardial injury without overt myocardial ischaemia are detected than with previous cardiac troponin assays. Increased troponin concentrations that do not fit with the clinical presentation are seen in the daily routine, mainly as a result of a variety of pathologies, and if tested in the same sample, even discrepancies between high-sensitivity cardiac troponin I and troponin T test results may sometimes be found as well. In addition, analytically false-positive test results occasionally may occur since no assay is perfect. In this review, we summarise the biochemical, pathophysiological and analytical background of the work-up for such a clinical setting.

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.

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.

Impact of Modifiable Risk Factors on B-type Natriuretic Peptide and Cardiac Troponin T Concentrations

Alcohol use, physical activity, diet, and cigarette smoking are modifiable cardiovascular risk factors that have a substantial impact on the risk of myocardial infarction, stroke, and cardiovascular death. We hypothesized that these behaviors may alter concentrations of cardiac troponin, a marker of myocyte injury, and B-type natriuretic peptide, a marker of myocyte stress. Both markers have shown strong association with adverse cardiovascular outcomes. In 519 women with no evidence of cardiovascular disease, we measured circulating concentrations of cardiac troponin T, using a high-sensitivity assay (hsTnT), and the N-terminal fragment of B-type natriuretic peptide (NT-proBNP). We used logistic regression to determine if these behaviors were associated with hsTnT ≥ 3 ng/l or with NT-proBNP in the highest quartile (≥ 127.3 ng/l). The median (Q1 to Q3) NT-proBNP of the cohort was 68.8 ng/l (40.3 to 127.3 ng/l), and 30.8% (160 of 519) of the cohort had circulating hsTnT ≥ 3 ng/l. In adjusted models, women who drank 1 to 6 drinks/week had lower odds of having a hsTnT ≥ 3 ng/l (odds ratio 0.58, 95% confidence interval 0.34 to 0.96) and lower odds of having an elevated NT-proBNP (odds ratio 0.55, 95% confidence interval 0.32 to 0.96). We were subsequently able to validate the results for B-type natriuretic peptide in a large independent cohort. In conclusion, our results suggest that regular alcohol consumption is associated with lower concentrations of hsTnT and NT-proBNP, 2 cardiovascular biomarkers associated with cardiovascular risk, and raise the hypothesis that the beneficial effects of alcohol consumption may be mediated by direct effects on the myocardium.

The effect of elapsed time on cardiac troponin-T (cTnT) degradation and its relation to postmortem interval in cases of electrocution

BACKGROUND

The estimation of postmortem interval (PMI) is of paramount importance for the police in their investigation when arriving at the scene of a questionable death. The aim of present study is to evaluate the effect of elapsed time on cardiac Troponin-T degradation and its association with PMI in cases of death due to electrocution.

METHODS

Cardiac tissue samples were collected from medico-legal autopsies, after informed consent from the relatives. The cases included were the subjects of electrocution without any prior history of disease who died in the hospital and their exact time of death was known. The analysis involves extraction of the protein at room temperature for different time periods (∼5, 26, 50, 84, 132, 157, 180, 205 and 230 Hrs), separation by SDS-PAGE and visualization by Western blot using cTnT specific monoclonal antibodies.

RESULTS

The results specify a characteristic banding pattern amongst human cadavers (n = 5), a pseudo-linear relationship between percent cTnT degraded and the time since death (R(2) = 0.87, p = 0.0001) was observed. The area of the bands within a lane was quantified by scanning and digitizing the image using Gel Doc (Universal Hood II).

CONCLUSIONS

The post-mortem Troponin-T fragmentation observed in this study reveals a sequential, time-dependent process with the potential for use as a predictor of PMI in cases of electrocution.

Kinetics of high-sensitivity cardiac troponin T and I differ in patients with ST-segment elevation myocardial infarction treated by primary coronary intervention

PURPOSE

Cardiac biomarkers including troponins are the cornerstone of the biological definition of acute myocardial infarction. New high-sensitivity cardiac assays determining troponin T (hs-cTnT) as well as I ((hs-cTnI) from Abbott and s-cTnI from Siemens) raise concerns because of their unclear kinetics following the peak.

AIMS

This study aims to compare kinetics of creatine kinases, hs-cTnT, hs-cTnI and s-cTnI in patients with ST-segment elevation myocardial infarction (STEMI) treated by percutaneous coronary intervention.

METHODS

We prospectively studied 106 consecutive patients admitted in our institution for STEMI and treated by percutaneous coronary intervention. We evaluated for all the patients simultaneously kinetics of creatine kinases, hs-cTnT (Roche) and two different cTnIs (hs-cTnI from Abbott and s-cTnI from Siemens). Modelling of kinetics was realized using mixed effects with cubic splines.

RESULTS

Kinetics of markers showed a first peak at 10.7h (8.0-12.0) for creatine kinases, 11.8h (10.4-13.3) for hs-cTnT (Roche); 11.8h (10.7-11.8) for hs-cTnI from Abbott and 10.2h (8.7-11.6) for s-cTnI from Siemens, respectively. This peak was followed by a nearly log linear decrease for hs-cTnI/s-cTnI and creatine kinases in contrast to hs-cTnT, which appeared with a biphasic shape curve marked by a second peak at 76.9h (69.5-82.8). The analysis of the decrease in percentage of the peak value at 77h showed that hs-cTnT follows a twice lower decrease than other markers.

CONCLUSION

Kinetics of hs-cTnT, hs-cTnI and s-cTnI differ significantly with a linear decrease regarding both cTnI assays contrasting with a biphasic shape curve for hs-cTnT. This is of importance for clinical management of patients in routine settings especially in follow-up after STEMI including the suspicion of reinfarction.

Kinetics of high-sensitivity cardiac troponin T or troponin I compared to creatine kinase in patients with revascularized acute myocardial infarction

Cardiac biomarkers are the cornerstone of the biological definition of acute myocardial infarction (AMI). The key role of troponins in diagnosis of AMI is well established. Moreover, kinetics of troponin I (cTnI) and creatine kinase (CK) after AMI are correlated to the prognosis. New technical assessment like high-sensitivity cardiac troponin T (hs-cTnT) raises concerns because of its unclear kinetic following the peak. This study aims to compare kinetics of cTnI and hs-cTnT to CK in patients with large AMI successfully treated by percutaneous coronary intervention (PCI).

We prospectively studied 62 patients with anterior AMI successfully reperfused with primary angioplasty. We evaluated two consecutive groups: the first one regularly assessed by both CK and cTnI methods and the second group by CK and hs-cTnT. Modeling of kinetics was realized using mixed effects with cubic splines.

Kinetics of markers showed a peak at 7.9 h for CK, at 10.9 h (6.9–12.75) for cTnI and at 12 h for hs-cTnT. This peak was followed by a nearly log linear decrease for cTnI and CK by contrast to hs-cTnT which appeared with a biphasic shape curve marked by a second peak at 82 h. There was no significant difference between the decrease of cTnI and CK (p=0.63). CK fell by 79.5% (76.1–99.9) vs. cTnI by 86.8% (76.6–92.7). In the hs-cTnT group there was a significant difference in the decrease by 26.5% (9–42.9) when compared with CK that fell by 79.5% (64.3–90.7).

Kinetic of hs-cTnT and not cTnI differs from CK. The role of hs-cTnT in prognosis has to be investigated.

Effects of moderate strength cold air exposure on blood pressure and biochemical indicators among cardiovascular and cerebrovascular patients

The effects of cold air on cardiovascular and cerebrovascular diseases were investigated in an experimental study examining blood pressure and biochemical indicators. Zhangye, a city in Gansu Province, China, was selected as the experimental site. Health screening and blood tests were conducted, and finally, 30 cardiovascular disease patients and 40 healthy subjects were recruited. The experiment was performed during a cold event during 27–28 April 2013. Blood pressure, catecholamine, angiotensin II (ANG-II), cardiac troponin I (cTnI), muscle myoglobin (Mb) and endothefin-1 (ET-1) levels of the subjects were evaluated 1 day before, during the 2nd day of the cold exposure and 1 day after the cold air exposure. Our results suggest that cold air exposure increases blood pressure in cardiovascular disease patients and healthy subjects via the sympathetic nervous system (SNS) that is activated first and which augments ANG-II levels accelerating the release of the norepinephrine and stimulates the renin-angiotensin system (RAS). The combined effect of these factors leads to a rise in blood pressure. In addition, cold air exposure can cause significant metabolism and secretion of Mb, cTnI and ET-1 in subjects; taking the patient group as an example, ET-1 was 202.7 ng/L during the cold air exposure, increased 58 ng/L compared with before the cold air exposure, Mb and cTnI levels remained relatively high (2,219.5 ng/L and 613.2 ng/L, increased 642.1 ng/L and 306.5 ng/L compared with before the cold air exposure, respectively) 1-day after the cold exposure. This showed that cold air can cause damage to patients’ heart cells, and the damage cannot be rapidly repaired. Some of the responses related to the biochemical markers indicated that cold exposure increased cardiovascular strain and possible myocardial injury.

Peak and fixed-time high-sensitive troponin for prediction of infarct size, impaired left ventricular function, and adverse outcomes in patients with first ST-segment elevation myocardial infarction receiving percutaneous coronary intervention

The clinical use of advanced imaging modalities for early determination of infarct size and prognosis is limited. As a specific indicator of myocardial necrosis, cardiac troponin T (cTnT) can be used as a surrogate measure for this purpose. The present study sought to investigate the use of peak and serial 6-hour fixed-time high-sensitive (hs) cTnT for estimation of infarct size, left ventricular (LV) function, and prognosis in consecutive patients with ST-segment elevation myocardial infarction. The infarct size was expressed as the 48-hour cumulative creatine kinase release. LV function at 3 months was assessed using the echocardiographic wall motion score index and LV ejection fraction using radionuclide ventriculography. Adverse outcomes, comprising all-cause death, implantable cardioverter-defibrillator implantation, or hospitalization for heart failure, were recorded at 1 year of follow-up. In 188 patients, the peak and all fixed-time values correlated significantly with the 48-hour cumulative creatine kinase release, wall motion score index, and LV ejection fraction. The hs-cTnT value at 24 hours demonstrated the greatest correlation (r = 0.86, r = 0.47, and r = -0.59, respectively; p <0.001 for all). In the multivariate regression models adjusted for the clinical parameters, almost all were independently associated with the 48-hour cumulative creatine kinase release, wall motion score index, and LV ejection fraction, with the hs-cTnT value at 24 hours having the largest effect. Moreover, all cTnT values independently predicted adverse outcomes, again, with the hs-cTnT value at 24 hours showing the largest influence (hazard ratio 3.77, 95% confidence interval 2.12 to 6.73, p <0.001). In conclusion, not only peak, but all fixed-time hs-cTnT values were associated with infarct size, LV function at 3 months, and adverse outcomes 1 year after ST-segment elevation myocardial infarction. The value 24 hours after the onset of symptoms had the closest associations with all outcomes. Therefore, serial sampling for a peak value might be redundant.

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.

Myofilament proteins: From cardiac disorders to proteomic changes

Myofilament proteins of the cardiac sarcomere house the molecular machinery responsible for generating tension and pressure. Release of intracellular Ca(2+) triggers myofilament tension generation and shortening, but the response to Ca(2+) is modulated by changes in key regulatory proteins. We review how these proteomic changes are essential to adaptive physiological regulation of cardiac output and become maladaptive in cardiac disorders. We also review the essentials of proteomic techniques used to study myofilament protein changes, including degradation, isoform expression, phosphorylation and oxidation. Selected proteomic studies illustrate the applications of these approaches.

Serum high-sensitivity cardiac troponin T is a significant biomarker of left-ventricular diastolic dysfunction in subjects with non-diabetic chronic kidney disease

Background

Chronic kidney disease (CKD) is associated with left-ventricular (LV) diastolic dysfunction (LVDD) which progresses to diastolic heart failure. However, biomarkers predicting LVDD in patients with CKD are largely unknown.

Methods

In 93 patients with non-diabetic CKD, the relationships among echocardiography, high-sensitivity cardiac troponin T (hs-cTnT), B-type natriuretic peptide (BNP), and renal function were evaluated. LV mass index, peak early diastolic mitral filling velocity (E), peak early diastolic mitral annular velocity (E′), and E/E′ were recorded.

Results

The E′ values were significantly decreased and E/E′, BNP, and hs-cTnT increased with increasing CKD stage. The CKD patients with LVDD with E′ <5 cm/s had a significantly higher hs-cTnT level as well as a significantly higher BNP level compared to those with E′ ≥5 cm/s. The area under the receiver-operating characteristic curve for hs-cTnT and BNP to detect E′ <5 cm/s was 0.880 (p = 0.0101) and 0.741 (p = 0.0570), respectively. In multivariate analysis, hs-cTnT and albuminuria were significantly associated with E′, and estimated glomerular filtration rate with the hs-cTnT level, after adjusting for age, cause of CKD, and other parameters.

Conclusions

These data suggest that hs-cTnT may be a useful biomarker of LVDD in non- diabetic CKD patients.

Automated heart-type fatty acid-binding protein assay for the early diagnosis of acute myocardial infarction

We compared an automated quantitative heart-type fatty acid-binding protein (H-FABP) assay with other cardiac-marker assays to examine its usefulness as an early diagnostic marker of acute myocardial infarction (AMI). Serum samples for cardiac troponin T (cTnT), creatine kinase-MB isozyme (CK-MB), myoglobin, and H-FABP were obtained from 64 patients with AMI and 53 patients with other conditions (control group). H-FABP was measured by using 2 immunoassays, the H-FABP enzyme-linked immunosorbent assay (ELISA; Biocheck, Foster City, CA) and the H-FABP latex turbidimetric immunoassay (LTIA; HBI, Anyang, Korea). Sensitivities of assays for cTnT, CK-MB, myoglobin, H-FABP (by ELISA), H-FABP (by LTIA), and electrocardiogram (ECG) for the diagnosis of AMI at hospital admission were 39.1%, 59.4%, 64.1%, 68.7%, 70.3%, and 54.7%, respectively. Specificities of cTnT, CK-MB, myoglobin, H-FABP (by ELISA), H-FABP (by LTIA), and ECG were 98.1%, 71.7%, 81.1%, 77.4%, 90.6%, and 92.5%, respectively. The automated H-FABP (by LTIA) is superior to cTnT, CK-MB, myoglobin, and H-FABP (by ELISA) tests for the diagnosis of AMI in patients admitted within 4 hours from the onset of chest pain.

Circulating Immunoreactive Cardiac Troponin Forms Determined by Gel Filtration Chromatography after Acute Myocardial Infarction

Background: Cardiac troponin I (cTnI) and cTnT measurements are used in the diagnosis of acute myocardial infarction (AMI). Together with troponin C (TnC), the cTnI and cTnT forms make up the ternary cTnT-cTnI-TnC (TIC) complex found within myocardium. Whether cTn occurs in the circulation after AMI as ternary TIC, binary cTnI-TnC (IC) complexes, or free troponin forms has not been thoroughly investigated.

Methods: Blood samples from 10 AMI patients were collected at hospital admission and then at 12, 24, and 48 h after onset of chest pain. Serum was subjected to gel filtration chromatography and cTnT (Roche cTnT) and cTnI (Siemens Centaur UltraTnI and Beckman Access AccuTnI) concentrations were measured in the gel filtration chromatography fractions.

Results: cTnT was present predominantly as free cTnT and cTnI as binary IC complex. These 2 forms were present at every time point. Lesser quantities of TIC complex (6%–32% of total cTnT and &lt;50% of total cTnI) were detected in 4 patients at varying times. Minor quantities of a high molecular mass form of cTnI were detected occasionally. No free cTnI was found. Both cTnI assays identified a similar pattern of cTnI forms.

Conclusions: After AMI, cTnI is present in serum as TIC and IC complexes. cTnT may be present as a combination of TIC and free cTnT or exclusively as free cTnT.

Protein kinase Cθ is required for cardiomyocyte survival and cardiac remodeling

Protein kinase Cs (PKCs) constitute a family of serine/threonine kinases, which has distinguished and specific roles in regulating cardiac responses, including those associated with heart failure. We found that the PKCθ isoform is expressed at considerable levels in the cardiac muscle in mouse, and that it is rapidly activated after pressure overload. To investigate the role of PKCθ in cardiac remodeling, we used PKCθ^−/− mice. In vivo analyses of PKCθ^−/− hearts showed that the lack of PKCθ expression leads to left ventricular dilation and reduced function. Histological analyses showed a reduction in the number of cardiomyocytes, combined with hypertrophy of the remaining cardiomyocytes, cardiac fibrosis, myofibroblast hyper-proliferation and matrix deposition. We also observed p38 and JunK activation, known to promote cell death in response to stress, combined with upregulation of the fetal pattern of gene expression, considered to be a feature of the hemodynamically or metabolically stressed heart. In keeping with these observations, cultured PKCθ^−/− cardiomyocytes were less viable than wild-type cardiomyocytes, and, unlike wild-type cardiomyocytes, underwent programmed cell death upon stimulation with α1-adrenergic agonists and hypoxia. Taken together, these results show that PKCθ maintains the correct structure and function of the heart by preventing cardiomyocyte cell death in response to work demand and to neuro-hormonal signals, to which heart cells are continuously exposed.

Usefulness of peak troponin-T to predict infarct size and long-term outcome in patients with first acute myocardial infarction after primary percutaneous coronary intervention

In acute myocardial infarction cardiac troponin-T (cTnT) is the preferred biomarker to detect myocardial necrosis. Our aim was to investigate the prognostic value of peak plasma cTnT in patients with ST-elevation myocardial infarction treated by primary percutaneous coronary intervention (PCI). Patients were eligible if ST-elevation myocardial infarction symptoms started <9 hours before the primary PCI. During the first 48 hours after primary PCI, cTnT and creatine kinase were measured repeatedly. Main outcome measures were left ventricular ejection fraction assessed by myocardial scintigraphy at 90 days, and clinical outcomes through 1-year follow-up after primary PCI in a dedicated outpatient clinic; 168 consecutive patients (79% men) with first ST-elevation myocardial infarction were studied. Mean age +/- SD was 59 +/- 12 years. Peak cTnT values were reached within 24 hours after primary PCI in all patients. The enzymatic infarct size, measured by cumulative 48-hours creatine kinase release, correlated positively with peak cTnT (r = 0.73, p <0.001). Left ventricular ejection fraction at 3 months was negatively correlated with peak cTnT (r = -0.52, p <0.001). A peak plasma cTnT > or = 6.5 microg/L predicted a left ventricular ejection fraction < or = 40% at follow-up with 86% sensitivity and 74% specificity. Multivariable Cox regression analysis identified peak cTnT as an independent predictor of major adverse cardiac events (hazard ratio 1.07, 95% confidence limits 1.01 to 1.12) and heart failure (hazard ratio 1.12, 95% confidence limits 1.05 to 1.20) during follow-up. In conclusion, peak cTnT after primary PCI for ST-elevation myocardial infarction offers a good estimation of infarct size and is a prognostic indicator in patients with first acute myocardial infarction.

Reference population and marathon runner sera assessed by highly sensitive cardiac troponin T and commercial cardiac troponin T and I assays

BACKGROUND

Endurance exercise can increase cardiac troponin (cTn) concentrations as high as those seen in cases of minor myocardial infarction. The inability of most cTn assays to reliably quantify cTn at very low concentrations complicates a thorough data analysis, and the clinical implications of such increases remain unclear. The application of recently developed highly sensitive cTn immunoassays may help resolve these problems.

METHODS

We evaluated the precommercial highly sensitive cardiac troponin T (hs-cTnT) assay from Roche Diagnostics and the Architect cardiac troponin I (cTnI-Architect) assay from Abbott Diagnostics by testing samples from a reference population of 546 individuals and a cohort of 85 marathon runners. We also measured the samples with the current commercial cTnT assay for comparison.

RESULTS

Although the hs-cTnT and cTnI-Architect assays were capable of measuring cTn concentrations at low concentrations (<0.01 microg/L), only the hs-cTnT assay demonstrated a CV of <10% at the 99th percentile of the reference population and a near-gaussian distribution of the measurements. After a marathon, 86% of the runners had cTnT concentrations greater than the 99th percentile with the hs-cTnT assay, whereas only 45% of the runners showed increased concentrations with the current cTnT assay. cTn concentrations remained significantly increased the day after the marathon. A multiple regression analysis demonstrated marathon experience and age to be significant predictors of postmarathon cTn concentrations (P < 0.05).

CONCLUSIONS

The hs-cTnT assay was the only assay tested with a performance capability sufficient to detect cTn concentrations in healthy individuals. The number of runners with increased cTn concentrations after a marathon depends highly on an assay's limit of detection (LOD). The assay with the lowest LOD, the hs-cTnT assay, showed that almost all runners had increased cTn concentrations. The clinical implications of these findings require further investigation.

Release kinetics of intact and degraded troponin I and T after irreversible cell damage

PURPOSE

We characterized the release kinetics of cardiac troponin I and T in relation to lactate dehydrogenase (LDH) from cardiomyocytes before and after the transition from reversible to irreversible cell damage.

METHODS

Cardiomyocytes were exposed to mild metabolic inhibition (1 mmol/L sodium azide) to induce a necrotic cell death process that is characterized by a reversible (0-12 h) and irreversible phase (12-30 h). At various time intervals cells and media were collected and analyzed for LDH activity, intact cTnI and cTnT, and their degradation products.

RESULTS

During the first 12 h of metabolic inhibition, cell viability was unchanged with no release of intact cTnI and cTnT nor their degradation products. Between 12 and 30 h of azide treatment, cardiomyocytes showed progressive cell death accompanied by release of intact cTnI (29 kDa), intact cTnT (39 kDa), four cTnI degradation products of 26, 20, 17 and 12 kDa, and three cTnT degradation products of 37, 27 and 14 kDa. Possibly due to degradation, there is progressive loss of cTnI and cTnT protein that is obviously undetected by the antibodies used.

CONCLUSIONS

Metabolic inhibition of cardiomyocytes induces a parallel release of intact cTnI and cTnT and their degradation products, starting only after onset of irreversible cardiomyocyte damage.

Absolute quantification of cardiac troponin T by means of liquid chromatography/triple quadrupole tandem mass spectrometry

A liquid chromatography/tandem mass spectrometric method for absolute quantification of cardiac troponin T (cTnT) in mouse heart tissue is presented. Even in such a complex biological sample, the multiple reaction monitoring acquisition mode allowed the selective and sensitive determination of a specific peptide, obtained by cTnT enzymatic digestion. The concentration of this cTnT-specific peptide was considered as a representation of the concentration of its parent protein. Quantification was carried out by means of the matrix-matched calibration curve, constructed by adding the synthetic standard of the target peptide and another synthetic structurally analogous peptide as internal standard. Method identification limit and method quantification limit were estimated as 60 and 110 ng of cTnT per mg of total extracted proteins, respectively. The developed label-free approach has been applied for the absolute quantitation of cTnT because of its diagnostic and prognostic value as cardiac disease marker. However, the method could be of general application, since it requires only the synthesis of two suitable peptides, a protein tryptic cleavage product and an internal standard.