Revision of the Troponin T Release Mechanism from Damaged Human Myocardium

Influence of Anticoagulants on the Dissociation of Cardiac Troponin Complex in Blood Samples

Immunodetection of cardiac isoforms of troponin I (cTnI) and troponin T (cTnT) in blood samples is widely used for the diagnosis of acute myocardial infarction. The cardiac troponin complex (ITC-complex), comprising cTnI, cTnT, and troponin C (TnC), makes up a large portion of troponins released into the bloodstream after the necrosis of cardiomyocytes. However, the stability of the ITC-complex has not been fully investigated. This study aimed to investigate the stability of the ITC-complex in blood samples. A native ITC-complex was incubated in buffer solutions, serum, and citrate, heparin, or EDTA plasma at various temperatures. Western blotting and gel filtration were performed, and troponins were detected using specific monoclonal antibodies. The ITC-complex dissociated at 37 °C in buffers with or without anticoagulants, in citrate, heparin, and EDTA plasmas, and in serum, into a binary cTnI-TnC complex (IC-complex) and free cTnT. In plasma containing heparin and EDTA, the IC-complex further dissociated into free TnC and cTnI. No dissociation was found at 4 °C or at room temperature (RT) in all matrices within 24 h except for EDTA plasma. After incubation at 37 °C in EDTA plasma and serum, dissociation was accompanied by proteolytic degradation of both cTnI and cTnT. The presence of anti-troponin autoantibodies in the sample impeded dissociation of the ITC-complex. The ITC-complex dissociates in vitro to form the IC-complex and free cTnT at 37 °C but is mostly stable at 4 °C or RT. Further dissociation of the IC-complex occurs at 37 °C in plasmas containing heparin and EDTA.

Role of Antitroponin Antibodies and Macrotroponin in the Clinical Interpretation of Cardiac Troponin

Cardiac troponin is extensively used as a biomarker in modern medicine due to its diagnostic capability for myocardial injury, as well as its predictive and prognostic value for cardiac diseases. However, heterophile antibodies, antitroponin antibodies, and macrotroponin complexes can be observed both in seemingly healthy individuals and patients with cardiac diseases, potentially leading to false positive or disproportionate elevation of cTn (cardiac troponin) assay results and introducing discrepancies in clinical interpretations with impact on medical management. In this review article, we describe the possible mechanisms of cTn release and the sources of variations in the assessment of circulating cTn levels. We also explore the pathophysiological mechanisms underlying antitroponin antibody development and discuss the influence exerted by macrotroponin complexes on the results of immunoassays. Additionally, we explore approaches to detect these complexes by presenting various clinical scenarios encountered in routine clinical practice. Finally, unsolved questions about the development, prevalence, and clinical significance of cardiac autoantibodies are discussed.

Kinetics of cardiac troponin and other biomarkers in patients with ST elevation myocardial infarction

Objective

To examine changes in concentration, time-to-peak and the ensuing half-life of cardiac biomarkers in patients with myocardial infarction.

Methods

Blood sampling was performed every third hour within 24 h after percutaneous coronary intervention (PCI) on a cohort of patients with ST elevation myocardial infarction. Cardiac troponin (cTn) was measured by the Dimension Vista, Vitros, Atellica, and Alinity high-sensitivity (hs) cTnI assays, and the Elecsys hs-cTnT assay. Further, creatine kinase (CK), myoglobin, creatine kinase MB (CKMB) and other biomarkers were analyzed.

Results

A total of 36 patients completed blood sampling (median age 60 years, IQR 56.4-66.5 years; seven women, 19.4%). Hs-cTnI measured by the Vitros assay was the first hs-cTn to peak at 9.1 h (95%-CI 6.2-10.1) after PCI and 11.7 h (95%-CI 10.4-14.8) after symptoms onset. There were no notable differences between hs-cTn assays in regard to time-to-peak. Also, Vitros hs-cTnI reached the highest median ratio of concentration to upper reference level of nearly 2,000. The median half-life from peak concentration ranged from 7.6 h for myoglobin (CI 6.8-8.6) to 17.8 h for CK (CI 6.8-8.6). For hs-cTn assays the median T½ ranged from 12.4 h for the Vista hs-cTnI assay (95%-CI 11.0-14.1 h) to 17.3 h for the Elecsys hs-cTnT (95%-CI 14.9-20.8 h).

Conclusions

This study updates knowledge on the kinetics of cardiac biomarkers in current clinical use. There was no notable difference in trajectories, time-to-peak or half-life between hs-cTn assays.

Periprocedural myocardial infarction in patients undergoing percutaneous coronary intervention

Percutaneous coronary intervention (PCI) in addition to guideline-directed medical therapy reduces the risk of spontaneous myocardial infarction (MI), urgent revascularization, and improves angina status; however, PCI is associated with an increased risk of periprocedural myocardial injury and MI. Numerous studies have investigated the mechanisms, predictors, and therapeutic strategies for periprocedural MI. Various definitions of periprocedural MI have been proposed by academic groups and professional societies requiring different cardiac biomarker thresholds and ancillary criteria for myocardial ischemia. The frequency and clinical significance of periprocedural MI substantially varies according to the definitions applied. In daily practice, accurate diagnosis of clinically-relevant periprocedural MI is essential because it may have a substantial impact on subsequent patient management. In the clinical trial setting, only clinically relevant periprocedural MI definitions should be applied as a clinical endpoint in order to avoid obscuring meaningful outcomes. In this review, we aim to summarize the mechanisms, predictors, frequency, and prognostic impact of periprocedural MI in patients undergoing PCI and to provide the current perspective on this issue.

Effects of high-intensity interval exercise on cardiac troponin elevation when comparing with moderate-intensity continuous exercise: a systematic review and meta-analysis

Background

This systematic review and meta-analysis aimed to compare the effects of high-intensity interval exercise (HIIE) with different recovery modes versus moderate-intensity continuous exercise (MICE) on cardiac troponin (cTn) elevation.

Methodology

A literature search was conducted in four databases: Scopus, PubMed, EBSCO and Web of Science from January 2010 to June 2022. The articles were screened, evaluated for quality before data were extracted. The review protocol was registered at PROSPERO (CRD42021245649). Standardized mean differences (SMD) of peak cTn were analyzed with a 95% confidence interval (95% CI) using Revman 5.4 software.

Results

Six studies satisfied the inclusion criteria with a total of 92 and 79 participants for HIIE and MICE, respectively. Overall, there was no significant difference between HIIE and MICE in the elevation of cardiac troponin T (SMD: 0.41 [95% CI [-0.21, 1.03]], p = 0.20, I 2 = 77%, p for heterogeneity <0.01). In subgroup analysis, HIIE with passive recovery elicits greater release of cardiac troponin T than MICE (SMD: 0.85 [95% CI [0.44, 1.27]], p < 0.01, I 2 = 32%, p for heterogeneity = 0.22). Changes of cardiac troponin T (SMD: 0.41 [95% CI [-0.21, 1.03]], p = 0.20, I 2 = 77%, p for heterogeneity < 0.01) after HIIE with active recovery were not significantly different from those of MICE.

Conclusions

There was no significant difference between HIIE and MICE in the elevation of cardiac troponin T. However, HIIE with passive recovery elicited more cardiac troponin T elevation than MICE, which should be considered when developing exercise programs.

Cardiac troponin release following coronary artery bypass grafting: mechanisms and clinical implications

The use of biomarkers is undisputed in the diagnosis of primary myocardial infarction (MI), but their value for identifying MI is less well studied in the postoperative phase following coronary artery bypass grafting (CABG). To identify patients with periprocedural MI (PMI), several conflicting definitions of PMI have been proposed, relying either on cardiac troponin (cTn) or the MB isoenzyme of creatine kinase, with or without supporting evidence of ischaemia. However, CABG inherently induces the release of cardiac biomarkers, as reflected by significant cTn concentrations in patients with uncomplicated postoperative courses. Still, the underlying (patho)physiological release mechanisms of cTn are incompletely understood, complicating adequate interpretation of postoperative increases in cTn concentrations. Therefore, the aim of the current review is to present these potential underlying mechanisms of cTn release in general, and following CABG in particular (Graphical Abstract). Based on these mechanisms, dissimilarities in the release of cTnI and cTnT are discussed, with potentially important implications for clinical practice. Consequently, currently proposed cTn biomarker cut-offs by the prevailing definitions of PMI might warrant re-assessment, with differentiation in cut-offs for the separate available assays and surgical strategies. To resolve these issues, future prospective studies are warranted to determine the prognostic influence of biomarker release in general and PMI in particular.

High-Sensitivity Cardiac Troponin I and T Kinetics Differ following Coronary Bypass Surgery: A Systematic Review and Meta-Analysis

Background

Cardiac troponin I and T are both used for diagnosing myocardial infarction (MI) after coronary artery bypass grafting (CABG), also known as type 5 MI (MI-5). Different MI-5 definitions have been formulated, using multiples of the 99th percentile upper reference limit (10×, 35×, or 70× URL), with or without supporting evidence. These definitions are arbitrarily chosen based on conventional assays and do not differentiate between troponin I and T. We therefore investigated the kinetics of high-sensitivity cardiac troponin I (hs-cTnI) and T (hs-cTnT) following CABG.

Methods

A systematic search was applied to MEDLINE and EMBASE databases including the search terms “coronary artery bypass grafting” AND “high-sensitivity cardiac troponin.” Studies reporting hs-cTnI or hs-cTnT on at least 2 different time points were included. Troponin concentrations were extracted and normalized to the assay-specific URL.

Results

For hs-cTnI and hs-cTnT, 17 (n = 1661 patients) and 15 studies (n = 2646 patients) were included, respectively. Preoperative hs-cTnI was 6.1× URL (95% confidence intervals: 4.9–7.2) and hs-cTnT 1.2× URL (0.9–1.4). Mean peak was reached 6–8 h postoperatively (126× URL, 99–153 and 45× URL, 29–61, respectively). Subanalysis of hs-cTnI illustrated assay-specific peak heights and kinetics, while subanalysis of surgical strategies revealed 3-fold higher hs-cTnI than hs-cTnT for on-pump CABG and 5-fold for off-pump CABG.

Conclusion

Postoperative hs-cTnI and hs-cTnT following CABG surpass most current diagnostic cutoff values. hs-cTnI was almost 3-fold higher than hs-cTnT, and appeared to be highly dependent on the assay used and surgical strategy. There is a need for assay-specific hs-cTnI and hs-cTnT cutoff values for accurate, timely identification of MI-5.

Strenuous Endurance Exercise and the Heart: Physiological versus Pathological Adaptations

Although the benefits of regular physical activity on cardiovascular health are well established, the effects of strenuous endurance exercise (SEE) have been a matter of debate since ancient times. In this article, we aim to provide a balanced overview of what is known about SEE and the heart-from epidemiological evidence to recent cardiac imaging findings. Lifelong SEE is overall cardioprotective, with endurance master athletes showing in fact a youthful heart. Yet, some lines of research remain open, such as the need to elucidate the time-course and potential relevance of transient declines in heart function (or increases in biomarkers of cardiac injury) with SEE. The underlying mechanisms and clinical relevance of SEE-associated atrial fibrillation, myocardial fibrosis, or high coronary artery calcium scores also remain to be elucidated. © 2022 American Physiological Society. Compr Physiol 12:1-19, 2022.

Type 2 MI and Myocardial Injury in the Era of High-sensitivity Troponin

Troponin has been the cornerstone of the definition of MI since its introduction to clinical practice. High-sensitivity troponin has allowed clinicians to detect degrees of myocardial damage at orders of magnitude smaller than previously and is challenging the definitions of MI, with implications for patient management and prognosis. Detection and diagnosis are no doubt enhanced by the greater sensitivity afforded by these markers, but perhaps at the expense of specificity and clarity. This review focuses on the definitions, pathophysiology, prognosis, prevention and management of type 2 MI and myocardial injury. The five types of MI were first defined in 2007 and were recently updated in 2018 in the fourth universal definition of MI. The authors explore how this pathophysiological classification is used in clinical practice, and discuss some of the unanswered questions in this era of availability of high-sensitivity troponin.

The ratio of cardiac troponin T to troponin I may indicate non-necrotic troponin release among COVID-19 patients

BACKGROUND

Although cardiac troponin T (cTnT) and troponin I(cTnI) are expressed to similar amount in cardiac tissue, cTnI often reach ten-times higher peak levels compared to cTnT in patients with myocardial necrosis such as in acute myocardial infarction (MI). In contrast, similar levels of cTnT and cTnI are observed in other situations such as stable atrial fibrillation and after strenuous exercise.

OBJECTIVE

Examine cTnT and cTnI levels in relation to COVID-19 disease and MI.

METHODS

Clinical and laboratory data from the local hospital from an observational cohort study of 27 patients admitted with COVID-19 and 15 patients with myocardial infarction (MI) that were analyzed with paired cTnT and cTnI measurement during hospital care.

RESULTS

Levels of cTnI were lower than cTnT in COVID-19 patients (TnI/TnT ratio 0.3, IQR: 0.1-0.6). In contrast, levels of cTnI were 11 times higher compared to cTnT in 15 patients with MI (TnI/TnT ratio 11, IQR: 7-14). The peak cTnI/cTnT ratio among the patients with MI following successful percutaneous intervention were 14 (TnI/TnT ratio 14, IQR: 12-23). The 5 COVID-19 patient samples collected under possible necrotic events had a cTnI/cTnT ratio of 5,5 (IQR: 1,9-8,3).

CONCLUSIONS

In patients with COVID-19, cTnT is often elevated to higher levels than cTnI in sharp contrast to patients with MI, indicating that the release of cardiac troponin has a different cause in COVID-19 patients.

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.

Outcomes of decreasing versus increasing cardiac troponin in patients admitted with non-ST-segment elevation myocardial infarction: the Atherosclerosis Risk in Communities Surveillance Study

BACKGROUND

The fourth universal definition of myocardial infarction requires an increase or decrease in cardiac troponin for the classification of non-ST-segment elevation myocardial infarction. We sought to determine whether the characteristics, management, and outcomes of patients admitted with non-ST-segment elevation myocardial infarction differ by the initial biomarker pattern.

METHODS

We identified patients in the Atherosclerosis Risk in Communities Surveillance Study admitted with chest pain and an initially elevated cardiac troponin I, who presented within 12 hours of symptom onset and were classified with non-ST-segment elevation myocardial infarction. A change in cardiac troponin I required an absolute difference of at least 0.02 ng/mL on the first day of hospitalization, prior to invasive cardiac procedures.

RESULTS

A total of 1926 hospitalizations met the inclusion criteria, with increasing cardiac troponin I more commonly observed (78%). Patients with decreasing cardiac troponin I were more often black (45% vs. 35%) and women (54% vs. 40%), and were less likely to receive non-aspirin antiplatelets (44% vs. 63%), lipid-lowering agents (62% vs. 80%), and invasive angiography (38% vs. 64%). Inhospital mortality was 3%, irrespective of the cardiac troponin I pattern. However, patients with decreasing cardiac troponin I had twice the 28-day mortality (12% vs. 5%; P=0.01). Fatalities within 28 days were more often attributable to non-cardiovascular causes in those with decreasing versus increasing cardiac troponin I (75% vs. 38%; P=0.01).

CONCLUSION

Patients presenting with chest pain and an initially elevated cardiac troponin I which subsequently decreases are less often managed by evidence-based therapies and have greater mortality, primarily driven by non-cardiovascular causes. Whether associations are attributable to type 2 myocardial infarction or a subacute presentation merits further investigation.

Outcomes of decreasing versus increasing cardiac troponin in patients admitted with non-ST-segment elevation myocardial infarction: the Atherosclerosis Risk in Communities Surveillance Study

BACKGROUND

The fourth universal definition of myocardial infarction requires an increase or decrease in cardiac troponin for the classification of non-ST-segment elevation myocardial infarction. We sought to determine whether the characteristics, management, and outcomes of patients admitted with non-ST-segment elevation myocardial infarction differ by the initial biomarker pattern.

METHODS

We identified patients in the Atherosclerosis Risk in Communities Surveillance Study admitted with chest pain and an initially elevated cardiac troponin I, who presented within 12 hours of symptom onset and were classified with non-ST-segment elevation myocardial infarction. A change in cardiac troponin I required an absolute difference of at least 0.02 ng/mL on the first day of hospitalization, prior to invasive cardiac procedures.

RESULTS

A total of 1926 hospitalizations met the inclusion criteria, with increasing cardiac troponin I more commonly observed (78%). Patients with decreasing cardiac troponin I were more often black (45% vs. 35%) and women (54% vs. 40%), and were less likely to receive non-aspirin antiplatelets (44% vs. 63%), lipid-lowering agents (62% vs. 80%), and invasive angiography (38% vs. 64%). Inhospital mortality was 3%, irrespective of the cardiac troponin I pattern. However, patients with decreasing cardiac troponin I had twice the 28-day mortality (12% vs. 5%; P=0.01). Fatalities within 28 days were more often attributable to non-cardiovascular causes in those with decreasing versus increasing cardiac troponin I (75% vs. 38%; P=0.01).

CONCLUSION

Patients presenting with chest pain and an initially elevated cardiac troponin I which subsequently decreases are less often managed by evidence-based therapies and have greater mortality, primarily driven by non-cardiovascular causes. Whether associations are attributable to type 2 myocardial infarction or a subacute presentation merits further investigation.

Dynamic changes of high-sensitivity troponin T concentration during infancy: Clinical implications

Cardiac troponin T determination plays a dominant role in diagnosis of myocardial pathologies. Despite generally accepted use of high-sensitive cardiac troponin T assays (hscTnT) and clearly defined cut-off limit in adults, the uncertainty persists in infants. The aim of this study was to assess plasmatic concentrations of hscTnT and describe sequential age-related dynamic changes of hscTnT in healthy infants and toddlers. Seventy-eight children (52 males/26 females) from Czech Republic aged 44 to 872 days (median, interquartile range 271; 126 to 486 days) were consecutively enrolled in the single-center, prospective observational study. Plasma concentrations of hscTnT were analyzed by the electrochemiluminescent method, age-related reference intervals were calculated using the polynominal regression model. Amongst the study population (n=78), the upper limit of hscTnT concentration defined as the 99th percentile was calculated. The 99th percentile with 95 % confidence interval at the end of 2nd, 3rd, 4th, 5th, 6th and 7th month of postnatal life were: 81 (40.6 to 63.6), 61 (36.0 to 55.3), 47 (31.9 to 48.3), 37 (28.1 to 42.3), 30 (24.7 to 37.2) and 25 (21.5 to 32.7) ng/l, respectively. Concentration of adults 99th percentile (14 ng/l) was achieved approximately at 1 year of postnatal life. Statistically significant negative correlation of hscTnT concentration with age (r=-0.81, p<0.001) was found. Significant gender differences were not found (p>0.07). The study revealed substantially increased reference intervals of hscTnT levels in infants when compared with adult population. Based on our preliminary results, the age-related interpretation of hscTnT plasmatic concentration is recommended.

High-sensitivity troponins in dialysis patients: variation and prognostic value

Background

Dialysis patients have a high prevalence of cardiovascular mortality but also elevated cardiac troponins (cTns) even without signs of cardiac ischaemia. The study aims to assess variation and prognostic value of high-sensitivity cTnI and cTnT in prevalent dialysis patients.

Methods

In 198 prevalent haemodialysis (HD) and 78 peritoneal dialysis (PD) patients, 4-monthly serum troponin I and T measurements were obtained. Reference change values (RCVs) were used for variability assessment and competing-risk regression models for survival analyses; maximal follow-up was 50 months.

Results

HD and PD patients had similar troponin levels [median (interquartile range) troponin I: 25 ng/L (14–43) versus 21 ng/L (11–37), troponin T: 70 ng/L (44–129) versus 67 ng/L (43–123)]. Of troponin I and T levels, 42% versus 98% were above the decision level of myocardial infarction. RCVs were +68/−41% (troponin I) and +29/−23% (troponin T). Increased variability of troponins related to higher age, male sex, protein-energy wasting and congestive heart failure, but not ischaemic heart disease or dialysis form. Elevated troponin T, but not troponin I, predicted death after adjusting for confounders.

Conclusions

A large proportion of prevalent dialysis patients without current established or ongoing cardiac events have elevated levels of high-sensitivity cTns. Mortality risk was doubled in patients with persistently high troponin T levels. The large intraindividual variation of cTns suggests that serial measurements and reference change levels may be used to improve diagnostic utility. However, evidence-based recommendations require more data from large studies of dialysis patients with cardiac events.

Novel clearance of muscle proteins by muscle cells

Blood levels of cardiac troponins (cTn) and myoglobin are analysed when myocardial infarction (MI) is suspected. Here we describe a novel clearance mechanism for muscle proteins by muscle cells. The complete plasma clearance profile of cTn and myoglobin was followed in rats after intravenous or intermuscular injections and analysed by PET and fluorescence microscopy of muscle biopsies and muscle cells. Compared with intravenous injections, only 5 % of cTnT, 0.6 % of cTnI and 8 % of myoglobin were recovered in the circulation following intramuscular injection. In contrast, 47 % of the renal filtration marker FITC-sinistrin and 81 % of cTn fragments from MI-patients were recovered after intramuscular injection. In addition, PET and biopsy analysis revealed that cTn was taken up by the quadriceps muscle and both cTn and myoglobin were endocytosed by cultured muscle cells. This local clearance mechanism could possibly be the dominant clearance mechanism for cTn, myoglobin and other muscle damage biomarkers released by muscle cells.

High-Sensitivity Cardiac Troponin I and T Response Following Strenuous Activity is Attenuated by Smokeless Tobacco: NEEDED (North Sea Race Endurance Exercise Study) 2014

Background

Use of snus, a smokeless tobacco product, is increasing in Scandinavia. Strenuous physical activity is associated with an acute increase in high‐sensitivity cardiac troponin (swhs‐cTn) concentrations. Current smoking is associated with lower hs‐cTn, but whether this also holds true for smokeless tobacco and whether tobacco affects the hs‐cTn response to exercise remain unknown.

Methods and Results

We measured hs‐cTnI and hs‐cTnT concentrations in 914 recreational athletes before and 3 and 24 hours after a 91‐km bicycle race. Self‐reported snus tobacco habits were reported as noncurrent (n=796) and current (n=118). The association between snus use and change in log‐transformed hs‐cTnI and hs‐cTnT concentrations (ie, the differences between concentrations at baseline and 3 hours and 24 hours ) were assessed by multivariable linear regression analysis. Concentrations of hs‐cTn at baseline were lower in current than in noncurrent snus users (hs‐cTnI median, 1.7 ng/L; Q1 to Q3: 1.6–2.3 versus 2.0 ng/L; Q1 to Q3: 1.6–3.2 [P=0.020]; and hs‐cTnT: median, 2.9 ng/L, Q1 to Q3: 2.9–3.5 versus 2.9 ng/L, Q1 to Q3: 2.9–4.3 [P=0.021]). In fully adjusted multivariable models, use of snus was associated with lower change in hs‐cTn concentrations from baseline to 3 hours (hs‐cTnI: −29% [P=0.002], hs‐cTnT: −18% [P=0.010]) and 24 hours (hscTnI: −30% [P=0.010], hs‐cTnT −19%, [P=0.013]).

Conclusions

Resting hs‐cTn concentrations are lower and the exercise‐induced cardiac troponin response is attenuated in current users of smokeless tobacco compared with nonusers. Further insight into the pathophysiological processes underlying the attenuated cardiac troponin response to exercise in tobacco users is needed.

Registration

URL: https://www.clini​caltr​ials.gov; Unique identifier: NCT02166216.

Urinary troponin concentration as a marker of cardiac damage in pregnancies complicated with preeclampsia

Pregnant women with preeclampsia experience significant hemodynamic changes which lead to an increased myocardial workload. In response to increased demands in pregnancy, the heart muscle responds with ventricular remodeling process which involves cardiac muscle hypertrophy. Opposed to occurrence of eccentric ventricular hypertrophy in normal pregnancy, myocardial remodeling in a form of concentric hypertrophy will occur in pregnant patients with preeclampsia. Increased myocardial workload is manifested by an increased troponin release. As process of troponin degradation continue, filtration of degradation fragment through glomerular membrane occur, raising the possibility of it's detection in urine. Degradation fragments of troponin molecules are estimated to be 20 kDa with preserved immunoreactivity to high-sensitivity assays. Some of the authors suggest that serum levels of cardiac troponin I might be elevated in patients with hypertension, as well as in preeclamptic pregnant women. It is to be expected that evaluation of severity of the myocardial damage in pregnant woman with preeclampsia may be performed by measuring levels of troponin in the urine using high-sensitivity assays. Designing of urine dipstick will help to detect an early phase of myocardial involvement in preeclamptic pregnancies.

Exercise-induced release of troponin

It is well established that regular physical activity reduces cardiovascular disease risk; however, numerous studies have demonstrated postexercise elevations in cardiac troponin (cTn), indicative of cardiac injury in apparently healthy individuals. The prevalence of these findings in different exercise settings and population groups, as well as potential underlying mechanisms and clinical significance of exercise-induced cTn release are not yet quite determined. The present review will discuss the cTn response to exercise in light of developing cTn assays and the correlation between postexercise cTn release and cardiac function. Additionally, recent data regarding the potential link between strenuous endurance exercise and its relationship with unfavorable cardiac effects in athletes, as well as the management of patients presenting at emergency care after sport events will be briefly reviewed.

A Possible Mechanism behind Faster Clearance and Higher Peak Concentrations of Cardiac Troponin I Compared with Troponin T in Acute Myocardial Infarction

BACKGROUND

Although cardiac troponin I (cTnI) and troponin T (cTnT) form a complex in the human myocardium and bind to thin filaments in the sarcomere, cTnI often reaches higher concentrations and returns to normal concentrations faster than cTnT in patients with acute myocardial infarction (MI).

METHODS

We compared the overall clearance of cTnT and cTnI in rats and in patients with heart failure and examined the release of cTnT and cTnI from damaged human cardiac tissue in vitro.

RESULTS

Ground rat heart tissue was injected into the quadriceps muscle in rats to simulate myocardial damage with a defined onset. cTnT and cTnI peaked at the same time after injection. cTnI returned to baseline concentrations after 54 h, compared with 168 h for cTnT. There was no difference in the rate of clearance of solubilized cTnT or cTnI after intravenous or intramuscular injection. Renal clearance of cTnT and cTnI was similar in 7 heart failure patients. cTnI was degraded and released faster and reached higher concentrations than cTnT when human cardiac tissue was incubated in 37°C plasma.

CONCLUSION

Once cTnI and cTnT are released to the circulation, there seems to be no difference in clearance. However, cTnI is degraded and released faster than cTnT from necrotic cardiac tissue. Faster degradation and release may be the main reason why cTnI reaches higher peak concentrations and returns to normal concentrations faster in patients with MI.

Acute total body ionizing gamma radiation induces long-term adverse effects and immediate changes in cardiac protein oxidative carbonylation in the rat

Radiation-induced heart disease presents a significant challenge in the event of an accidental radiation exposure as well as to cancer patients who receive acute doses of irradiation as part of radiation therapy. We utilized the spontaneously hypertensive Wistar-Kyoto rat model, previously shown to demonstrate drug-induced cardiomyopathy, to evaluate the acute and long-term effects of sub-lethal total body gamma irradiation at two, four, and fifty-two weeks. We further examined irreversible oxidative protein carbonylation in the heart immediately following irradiation in the normotensive Wistar-Kyoto rat. Both males and females sustained weight loss and anemic conditions compared to untreated controls over a one-year period as reflected by reduced body weight and low red blood cell count. Increased inflammation was detected by elevated IL-6 serum levels selectively in males at four weeks. Serum cardiac troponin T and I analyses revealed signs of cardiomyopathy at earlier timepoints, but high variability was observed, especially at one year. Echocardiography at two weeks following 5.0Gy treatment revealed a significant decrease in cardiac output in females and a significant decrease in both diastolic and systolic volumes in males. Following 10.0Gy irradiation in the normotensive Wistar-Kyoto rat, the heart tissue showed an increase in total protein oxidative carbonylation accompanied by DNA damage indicated by an increase in γ-H2AX. Using proteomic analyses, we identified several novel proteins which showed a marked difference in carbonylation including those of mitochondrial origin and most notably, cardiac troponin T, one of the key proteins involved in cardiomyocyte contractility. Overall, we present findings of acute oxidative protein damage, DNA damage, cardiac troponin T carbonylation, and long-term cardiomyopathy in the irradiated animals.

The Liver and Kidneys mediate clearance of cardiac troponin in the rat

Cardiac-specific troponins (cTn), troponin T (cTnT) and troponin I (cTnI) are diagnostic biomarkers when myocardial infarction is suspected. Despite its clinical importance it is still not known how cTn is cleared once it is released from damaged cardiac cells. The aim of this study was to examine the clearance of cTn in the rat. A cTn preparation from pig heart was labeled with fluorescent dye or fluorine 18 (¹⁸ F). The accumulation of the fluorescence signal using organ extracts, or the 18 F signal using positron emission tomography (PET) was examined after a tail vein injection. The endocytosis of fluorescently labeled cTn was studied using a mouse hepatoma cell line. Close to 99% of the cTnT and cTnI measured with clinical immunoassays were cleared from the circulation two hours after a tail vein injection. The fluorescence signal from the fluorescently labeled cTn preparation and the radioactivity from the 18F-labeled cTn preparation mainly accumulated in the liver and kidneys. The fluorescently labeled cTn preparation was efficiently endocytosed by mouse hepatoma cells. In conclusion, we find that the liver and the kidneys are responsible for the clearance of cTn from plasma in the rat.

How is cardiac troponin released from injured myocardium?

Cardiac troponin I and cardiac troponin T are nowadays the criterion biomarkers for the laboratory diagnosis of acute myocardial infarction due to their very high sensitivities and specificities for myocardial injury. However, still many aspects of their degradation, tissue release and elimination from the human circulation are incompletely understood. Myocardial injury may be caused by a variety of different mechanisms, for example, myocardial ischaemia, inflammatory and immunological processes, trauma, drugs and toxins, and myocardial necrosis is preceded by a substantial reversible prelethal phase. Recent experimental data in a pig model of myocardial ischaemia demonstrated cardiac troponin release into the circulation from apoptotic cardiomyocytes as an alternative explanation for clinical situations with increased cardiac troponin without any other evidence for myocardial necrosis. However, the comparably lower sensitivities of all currently available imaging modalities, including cardiac magnetic resonance imaging for the detection of particularly non-focal myocardial necrosis in patients, has to be considered for cardiac troponin test result interpretation in clinical settings without any other evidence for myocardial necrosis apart from increased cardiac troponin concentrations as well.

Cardioprotective effect of Notch signaling on the development of myocardial infarction complicated by diabetes mellitus

The present study aimed to elucidate the role of Notch signaling in the development of myocardial infarction (MI) concomitant with diabetes in vivo and in vitro and evaluated the therapeutic effect of the Notch signaling in vitro. Streptozotocin-induced diabetic rats were subjected to 25 min of ischemia and 2 h of reperfusion. Cardiac troponin T (cTnT) and creatine kinase-MB (CK-MB) isoenzyme levels were detected. Infarct size was measured by 2,3,5-triphenyltetrazolium chloride staining. Myocardial apoptosis and fibrosis were examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and Masson Trichrome staining, respectively. The mRNA and protein levels of Notch signaling components, including Notch1, Notch4, Delta-like 1, Jagged1, Mastermind-like protein 1 and p300, were quantified by reverse transcription-quantitative polymerase chain reaction and western blotting analyses, respectively. H9c2 cells were treated with/without 33 mM high glucose (HG) and/or subjected to hypoxia in the presence/absence of Jagged1. Cell viability and apoptosis were determined by MTT assay and Annexin V-fluorescein isothiocyanate/propidium iodide assay. Levels of the Notch signaling pathway members were examined. The present findings revealed that diabetes elevated CK-MB and cTnT, increased infarct size, induced myocardial apoptosis and inhibited the Notch signaling pathway in vivo after ischemia/reperfusion. Ischemia/reperfusion augmented the severity of MI in diabetic rats. Furthermore, HG reduced cell viability and induced cell apoptosis in H9c2 cells after hypoxia exposure, which was inhibited by Jagged1. We also found that HG inhibited Notch signaling in H9c2 cells after hypoxia, whereas Jagged1 exerted its cardioprotective effect on hypoxic injury (in HG environments or not) by activating the Notch signaling pathway. In conclusion, these findings suggest that diabetes promoted the progression of MI in vivo and in vitro via the inhibition of the Notch signaling pathway. Jagged1 may protect against MI in in vitro models by activating Notch signaling.

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.

Quantifying the Release of Biomarkers of Myocardial Necrosis from Cardiac Myocytes and Intact Myocardium

BACKGROUND

Myocardial infarction is diagnosed when biomarkers of cardiac necrosis exceed the 99th centile, although guidelines advocate even lower concentrations for early rule-out. We examined how many myocytes and how much myocardium these concentrations represent. We also examined if dietary troponin can confound the rule-out algorithm.

METHODS

Individual rat cardiac myocytes, rat myocardium, ovine myocardium, or human myocardium were spiked into 400-μL aliquots of human serum. Blood was drawn from a volunteer after ingestion of ovine myocardium. High-sensitivity assays were used to measure cardiac troponin T (cTnT; Roche, Elecsys), cTnI (Abbott, Architect), and cardiac myosin-binding protein C (cMyC; EMD Millipore, Erenna^®).

RESULTS

The cMyC assay could only detect the human protein. For each rat cardiac myocyte added to 400 μL of human serum, cTnT and cTnI increased by 19.0 ng/L (95% CI, 16.8-21.2) and 18.9 ng/L (95% CI, 14.7-23.1), respectively. Under identical conditions cTnT, cTnI, and cMyC increased by 3.9 ng/L (95% CI, 3.6-4.3), 4.3 ng/L (95% CI, 3.8-4.7), and 41.0 ng/L (95% CI, 38.0-44.0) per μg of human myocardium. There was no detectable change in cTnI or cTnT concentration after ingestion of sufficient ovine myocardium to increase cTnT and cTnI to approximately 1 × 10⁸ times their lower limits of quantification.

CONCLUSIONS

Based on pragmatic assumptions regarding cTn and cMyC release efficiency, circulating species, and volume of distribution, 99th centile concentrations may be exceeded by necrosis of 40 mg of myocardium. This volume is much too small to detect by noninvasive imaging.

The current status of heart failure diagnostic biomarkers

Heart failure (HF) affects approximately 23 million individuals worldwide and this number is increasing, due to an aging and growing population. Early detection of HF is crucial in the management of this debilitating disease. Current diagnostic methods for HF rely heavily on clinical imaging techniques and blood analysis, which makes them less than ideal for population-based screening purposes. Studies focusing on developing novel biomarkers for HF have utilized various techniques and biological fluids, including urine and saliva. Promising results from these studies imply that these body fluids can be used in evaluating the clinical manifestation of HF and will one day be integrated into a clinical workflow and facilitate HF management.

Experimental determination of diagnostic window of cardiac troponins in the development of chronic anthracycline cardiotoxicity and estimation of its predictive value

BACKGROUND

Cardiac troponins (cTns) seem to be more sensitive for the detection of anthracycline cardiotoxicity than the currently recommended method of monitoring LV systolic function. However, the optimal timing of blood sampling remains unknown. Hence, the aims of the present study were to determine the precise diagnostic window for cTns during the development of chronic anthracycline cardiotoxicity and to evaluate their predictive value.

METHODS

Cardiotoxicity was induced in rabbits with daunorubicin (3mg/kg, weekly, for 8 weeks). Blood samples were collected 2-168 h after the 1st, 5th and 8th drug administrations, and concentrations of cTns were determined using highly sensitive assays: hs cTnT (Roche) and hs cTnI (Abbott).

RESULTS

The plasma levels of cTns progressively increased with the rising number of chemotherapy cycles. While only a mild non-significant increase in both cTn levels occurred after the first daunorubicin dose, a significant rise was observed after the 5th and 8th administrations. Two hours after these administrations, a significant increase occurred with a peak between 4-6h and a decline until 24h. Discrete cTn release continued even after cessation of the therapy. While greater variability of cTn levels was observed around the peak concentrations, the values did not correspond well with the severity of LV systolic dysfunction. Unlike AMI in cardiotoxicity, cTn elevations may be better associated with cumulative dose and concentrations at steady state than cmax.

CONCLUSIONS

To the best of our knowledge, this is the first study to precisely describe the diagnostic window and predictive value of cTns in anthracycline cardiotoxicity.

Analytical validation of novel cardiac biomarkers used in clinical trials

BACKGROUND

Blood-based biomarkers such as cardiac troponin and B-natriuretic peptides are widely used in clinical practice for the diagnosis, rule out, and risk stratification for patients with acute coronary syndromes and heart failure. Because neither these nor any other laboratory test meets all clinical needs, there are many novel biomarkers that are proposed and evaluated each year for possible implementation into clinical practice. Results of clinical trials are used as a means to validate their effectiveness and to obtain regulatory approval.

METHODS AND RESULTS

Novel biomarkers are discovered through a targeted approach using knowledge of the pathophysiology disease process and an untargeted approach where proteins from tissues or blood of disease patients are compared against healthy subjects or those with benign conditions. Once a candidate biomarker has been identified, it is important to understand where the protein is located and how it is released into blood. In designing trials, the requirements for Food and Drug Administration clearance and approval should be taken into consideration. There are preanalytical studies that should be considered including the preservative used to collect samples and in vivo and in vitro analyte stability. If the analyte is not stable, a surrogate marker could be used such as stable "pro" molecules (precursor proteins) may be preferred. Assay imprecision and bias, biological variation and criteria for the establishment of a reference range are important analytical attributes. The need for harmonization and commutability and correlation of results to other markers and clinical outcomes are important postanalytical attributes of novel biomarkers.

CONCLUSIONS

Inadequate adherence to these variables when conducting clinical trials reduces the quality and value of the information contained in literature reports of novel serum/plasma-based biomarkers.

Fundamental concepts of effective troponin use: important principles for internists

Troponin testing is an essential component of our diagnostic approach to patients in acute medical care settings. With the advent of high-sensitivity troponin assays, its importance will extend to patients in chronic disease settings. Although elevated troponin levels provide diagnostic information, inform treatment decisions, and influence patient prognosis, proper interpretation of the values is essential. This requires an understanding of the operating characteristics of troponin testing; the likelihood ratios associated with a positive/negative test result and the pre- and post-test probabilities related to individual clinical settings. These principles will become more important as high-sensitivity assays become introduced over the coming years in the United States. This article reviews the important principles of troponin testing focusing in particular on acute settings and is aimed at internal medicine and hospital specialists.