Cardiac troponin I increases in parallel to cardiac troponin T, creatine kinase and lactate dehydrogenase in effluents from isolated perfused rat hearts after hypoxia-reoxygenation-induced myocardial injury

The Coadministration of Levosimendan and Exenatide Offers a Significant Cardioprotective Effect to Isolated Rat Hearts against Ischemia/Reperfusion Injury

(1) Background: The present study aims to investigate the effect of administration of Levosimendan and Exenatide in various concentrations, as well as of the coadministration of those agents in an ischemia–reperfusion injury isolated heart model. (2) Methods: After 30 min of perfusion, the hearts underwent a 30 min period of regional ischemia followed by a 120 min period of reperfusion. All animals were randomly divided into 12 experimental groups of nine animals in each group: (1) Control, (2) Sham, (3) Digox (Negative control, Digoxin 1.67 μg/min), (4) Levo 1 (Levosimendan 0.01 μg/min), (5) Levo 2 (Levosimendan 0.03 μg/mL), (6) Levo 3 (Levosimendan 0.1 μg/min), (7) Levo 4 (Levosimendan 0.3 μg/min), (8) Levo 5 (Levosimendan 1 μg/min), (9) Exen 1 (Exenatide 0.001 μg/min), (10) Exen 2 (Exenatide 0.01 μg/min), (11) Exen 3 (Exenatide 0.1 μg/min) and (12) Combi (Levosimendan 0.1 µg/mL + Exenatide 0.001 μg/min). The hemodynamic parameters were recorded throughout the experiment. Arrhythmias and coronary flow were also evaluated. After every experiment the heart was suitably prepared and infarct size was measured. Markers of myocardial injury were also measured. Finally, oxidative stress was evaluated measuring reactive oxygen species. (3) Results: A dose-dependent improvement of the haemodynamic response was observed after the administration of both Levosimendan and Exenatide. The coadministration of both agents presented an even greater effect, improving the haemodynamic parameters further than the two agents separately. Levosimendan offered an increase of the coronary flow and both agents offered a reduction of arrhythmias. A dose-dependent reduction of the size of myocardial infarction and myocardial injury was observed after administration of Levosimendan and Exenatide. The coadministration of both agents offered a further improving the above parameters. Levosimendan also offered a significant reduction of oxidative stress. (4) Conclusions: The administration of Levosimendan and Exenatide offers a significant benefit by improving the haemodynamic response, increasing the coronary flow and reducing the occurrence of arrhythmias, the size of myocardial injury and myocardial oxidative stress in isolated rat hearts.

RNase1 prevents the damaging interplay between extracellular RNA and tumour necrosis factor-α in cardiac ischaemia/reperfusion injury

Despite optimal therapy, the morbidity and mortality of patients presenting with an acute myocardial infarction (MI) remain significant, and the initial mechanistic trigger of myocardial "ischaemia/reperfusion (I/R) injury" remains greatly unexplained. Here we show that factors released from the damaged cardiac tissue itself, in particular extracellular RNA (eRNA) and tumour-necrosis-factor α (TNF-α), may dictate I/R injury. In an experimental in vivo mouse model of myocardial I/R as well as in the isolated I/R Langendorff-perfused rat heart, cardiomyocyte death was induced by eRNA and TNF-α. Moreover, TNF-α promoted further eRNA release especially under hypoxia, feeding a vicious cell damaging cycle during I/R with the massive production of oxygen radicals, mitochondrial obstruction, decrease in antioxidant enzymes and decline of cardiomyocyte functions. The administration of RNase1 significantly decreased myocardial infarction in both experimental models. This regimen allowed the reduction in cytokine release, normalisation of antioxidant enzymes as well as preservation of cardiac tissue. Thus, RNase1 administration provides a novel therapeutic regimen to interfere with the adverse eRNA-TNF-α interplay and significantly reduces or prevents the pathological outcome of ischaemic heart disease.

Frequent biomarker analysis in the isolated perfused heart reveals two distinct phases of reperfusion injury

BACKGROUND

Reperfusion injury and its modulation are incompletely characterized. The purpose of the present study was to characterize the dynamics of reperfusion injury by portraying the temporal release of lactate dehydrogenase (LDH) during ischemia-reperfusion injury in an isolated heart model.

METHODS

We studied infarct size and LDH release in the following groups: I) Effect of reperfusion length was evaluated in 79 rats subjected to 40 minute ischemia and 60, 90, 120 or 180 minute reperfusion and a) ischemic preconditioning (IPC) or b) No IPC (control). II) LDH release kinetics was studied in 6 rats subjected to calcium-paradox to verify the applicability of LDH as a dynamic marker of cellular injury. III) Ischemia-reperfusion injury modification was studied in 36 rats subjected to: a) ischemic postconditioning, b) prolonged ischemia, c) Reperfusion Injury Salvage Kinase (RISK) pathway inhibition with wortmannin in IPC hearts, d) RISK activation with insulin or e) mitochondrial permeability transition pore (mPTP) inhibition with cyclosporine A.

RESULTS

Infarct size increased from 60 to 180 minute reperfusion in control hearts. LDH was released in two separate peaks from 2 to 20 and 30 to 120 min of reperfusion. IPC attenuated both peaks. Postconditioning and agents known to modify reperfusion injury attenuated the second peak.

CONCLUSIONS

Frequent measurement of myocardial ischemia markers for 120 min of reperfusion allows identification of two phases of reperfusion injury that are affected by cardioprotective stimuli. The second phase contributes significantly to final infarct size, which is modifiable and a potential target for cardioprotective interventions.

Can early cardiac troponin I measurement help to predict recent coronary occlusion in out-of-hospital cardiac arrest survivors?

OBJECTIVE

Recent guidelines recommend the immediate performance of a coronary angiography when an acute myocardial infarction is suspected as a cause of out-of-hospital cardiac arrest. However, prehospital factors such as postresuscitation electrocardiogram pattern or clinical features are poorly sensitive in this setting. We searched to evaluate if an early measurement of cardiac troponin I can help to detect a recent coronary occlusion in out-of-hospital cardiac arrest.

DESIGN

Retrospective analysis of a prospective electronic registry database.

SETTING

University cardiac arrest center.

PATIENTS

Between January 2003 and December 2008, 422 out-of-hospital cardiac arrest survivors without obvious extra-cardiac cause have been consecutively studied. An immediate coronary angiography has been systematically performed. The primary outcome was the finding of a recent coronary occlusion.

INTERVENTION

First, blood cardiac troponin I levels at admission were analyzed to assess the optimum cutoff for identifying a recent coronary occlusion. Second, a logistic regression was performed to determine early predictive factors of a recent coronary occlusion (including cardiac troponin I) and their respective contribution.

MEASUREMENTS AND MAIN RESULTS

An ST-segment elevation was present in 127 of 422 patients (30%). During coronary angiography, a recent occlusion has been detected in 193 of 422 patients (46%). The optimum cardiac troponin I threshold was determined at 4.66 ng·mL(-1) (sensitivity 66.7%, specificity 66.4%). In multivariate analyses, in addition of smoking and epinephrine initial dose, cardiac troponin I (odds ratio 3.58 [2.03-6.32], p < .001) and ST-segment elevation (odds ratio 10.19 [5.39-19.26], p < .001) were independent predictive factors of a recent coronary occlusion.

CONCLUSIONS

In this large cohort of out-of-hospital cardiac arrest patients, isolated early cardiac troponin I measurement is modestly predictive of a recent coronary occlusion. Furthermore, the contribution of this parameter even in association with other factors does not seem helpful to predict recent occlusion. As a result and given the high benefit of percutaneous coronary intervention for such patients, the dosage of cardiac troponin I at admission could not help in the decision of early coronary angiogram.

Correlation among Clinicopathological Parameters of Myocardial Damage in Rats Treated with Isoproterenol

The correlation among clinicopathological parameters of myocardial damage was investigated in rats administered a single subcutaneous dose of isoproterenol at 0 (saline), 0.04, 0.4 and 4 mg/kg. Total lactate dehydrogenase (LDH), creatine kinase (CK), and their isoenzymes (LDH-1, LDH-2 and CK-MB), as well as troponin I and tropinin T, were measured 4 h after the administration of the drug. Troponin I was determined by a chemiluminescence method using Bayer Centaur and DPC Immulyze, as well as by ELISA. Troponin T was assayed semi-quantitatively using Trop T Sensitive. A high correlation was found among LDH isoenzymes, troponin I (Centaur) and troponin T. The present result provides a baseline for interpreting changes in the different parameters of myocardial damage assayed by different methods in toxicity studies.

Protective effects of dantrolene against myocardial injury induced by isoproterenol in rats: biochemical and histological findings

PURPOSE

We investigated whether dantrolene might protect the heart against myocardial injury (MI) induced by isoproterenol (ISO), using an experimental model in rats.

METHODS

Twenty-eight rats were randomized to treatment with saline only (control group, n=8), ISO only (ISO group, n=8), low-dose dantrolene (LDD)+ISO (LDD group, n=6) and high-dose dantrolene (HDD)+ISO (HDD group, n=6). ISO (150 mg/kg/day, s.c.), LDD (5 mg/kg/day, i.p.) and HDD (10 mg/kg/day, i.p.) were given once a day for two consecutive days. At the end of the second day, blood samples were taken from abdominal aorta shortly after the rats were anesthetised for cardiac troponins T (cTnT) and I (cTnI) assay, and the hearts were removed and observed microscopically.

RESULTS

cTnT and cTnI levels were increased in the ISO group when compared with the control group (p<0.001). LDD and HDD significantly reduced cTnT and cTnI levels when compared with the ISO group. Elevations of cTnT and cTnI appeared to relate to the severity of histological changes. The rate of animals that exhibited marked MI was higher in the ISO group than in the control group (p<0.001). The rats in both LDD and HDD groups showed less histological changes when compared to the ISO group (p<0.01). There was no significant difference between the control group and both LDD and HDD groups.

CONCLUSIONS

This study shows that dantrolene has a significant effect in the protection of the heart against MI induced by ISO. We believe that pretreatment with dantrolene may contribute to developing novel strategies in the cardiotoxicity animal models and in the prevention of the cardiotoxic effects of elevated levels of catecholamines.

Respiratory muscle injury, fatigue and serum skeletal troponin I in rat

To evaluate injury to respiratory muscles of rats breathing against an inspiratory resistive load, we measured the release into blood of a myofilament protein, skeletal troponin I (sTnI), and related this release to the time course of changes in arterial blood gases, respiratory drive (phrenic activity), and pressure generation. After approximately 1.5 h of loading, hypercapnic ventilatory failure occurred, coincident with a decrease in the ratio of transdiaphragmatic pressure to integrated phrenic activity (P(di)/ integral Phr) during sighs. This was followed at approximately 1.9 h by a decrease in the P(di)/ integral Phr ratio during normal loaded breaths (diaphragmatic fatigue). Loading was terminated at pump failure (a decline of P(di) to half of steady-state loaded values), approximately 2.4 h after load onset. During 30 s occlusions post loading, rats generated pressure profiles similar to those during occlusions before loading, with comparable blood gases, but at a higher neural drive. In a second series of rats, we tested for sTnI release using Western blot-direct serum analysis of blood samples taken before and during loading to pump failure. We detected only the fast isoform of sTnI, release beginning midway through loading. Differential detection with various monoclonal antibodies indicated the presence of modified forms of fast sTnI. The release of fast sTnI is consistent with load-induced injury of fast glycolytic fibres of inspiratory muscles, probably the diaphragm. Characterization of released fast sTnI may provide insights into the molecular basis of respiratory muscle dysfunction; fast sTnI may also prove useful as a marker of impending respiratory muscle fatigue.

Protective effects of melatonin against myocardial injury induced by isoproterenol in rats

This study was performed to determine whether melatonin could have a protective effect against myocardial injury (MI) induced by isoproterenol (ISO) in rats. Twenty-four rats were divided into three treatment groups: (1) control (n = 8): saline solution. (2) ISO (n = 8): ISO only. (3) melatonin + ISO (n = 8). Melatonin (10 mg/kg/day, i.p.) was administered 30 min before the initiation of ISO (150 mg/kg/day, s.c.). Drugs and saline were given at 14:00 hr for two consecutive days. At the end of the second day, blood samples were taken from the abdominal aorta shortly after the rats were anesthetized for the purpose of measuring cardiac troponins T (cTnT) and I (cTnI); hearts were removed, preserved and examined microscopically. Additionally, based on the histological changes in myocardial tissue, the rats were divided into three groups: no change, mild changes and moderate and/or marked changes. The mean cTnT and cTnI values were significantly increased in ISO group compared with control group [(1.29 +/- 0.22 ng/mL versus 0.46 +/- 0.07 ng/mL, P < 0.0001) and (0.56 +/- 0.11 ng/mL versus 0.21 +/- 0.01 ng/mL, P < 0.001)], respectively, and were significantly reduced in the ISO + melatonin group (0.65 +/- 0.06 ng/mL for cTnT and 0.25 +/- 0.01 ng/mL for cTnI) compared with the ISO only group (P < 0.01), respectively. cTnT and cTnI values were significantly increased in rats with moderate and/or marked cardiac changes compared with hearts where there were mild changes and no change (P < 0.05). ISO + melatonin group showed less histological changes than the ISO group (P < 0.01). In conclusion, this study revealed a protective effect of melatonin against ISO-induced MI in rats, and its potential clinical application in the treatment of MI.

Effects of cardiac contusion in isolated perfused rat hearts

Myocardial contusion is frequently suspected after blunt chest trauma, but the exact mechanisms of resulting cardiac dysfunction and the time course for enzymatic alterations have not yet been fully understood. Therefore, we investigated pathophysiological aspects of myocardial contusion in a controlled animal model. Male Wistar rat hearts were studied in an isolated perfusion model and were divided into two groups: control (n = 4) and heart contusion (n = 6) groups. The cardiac contusion was produced by a single blow with a weighted pendulum (m = 44 g, height = 20 cm). Functional implications of the contusion were examined in an "isolated perfused heart" model. Troponin 1 concentrations were determined in the perfusate. Cardiac contusion resulted in an increase of coronary perfusion pressure (CPP) of 9 mmHg (P < 0.05, 20 min postcontusion versus baseline and control), followed by a significant increase of left ventricular end-diastolic pressure (LVEDP) of 6 mmHg (P < 0.05, 20 min postcontusion versus baseline and control). Heart contusion was followed by an early increase of troponin 1 (+0.82 ng/mL). The troponin 1 concentration decreased again and, after 20 min, baseline levels were reached. The control group showed no such changes. In this model, high troponin 1 levels after cardiac contusion suggest direct damage to the myocardium. First functional response was shown by the alteration of the coronary perfusion, followed by impaired diastolic function, which persisted even after lowering of the troponin 1 levels.

Factors contributing to troponin exchange in myofibrils and in solution

The troponin complex in a muscle fiber can be replaced with exogenous troponin by using a gentle exchange procedure in which the actin-tropomyosin complex is never devoid of a full complement of troponin (Brenner et al. (1999) Biophys J 77: 2677-2691). The mechanism of this exchange process and the factors that influence this exchange are poorly understood. In this study, the exchange process has now been examined in myofibrils and in solution. In myofibrils under rigor conditions, troponin exchange occurred preferentially in the region of overlap between actin and myosin when the free Ca2+ concentration was low. At higher concentrations of Ca2+, the exchange occurred uniformly along the actin. Ca2+ also accelerated troponin exchange in solution but the effect of S1 could not be confirmed in solution experiments. The rate of exchange in solution was insensitive to moderate changes in pH or ionic strength. Increasing the temperature resulted in a two-fold increase in rate with each 10 degrees C increase in temperature. A sequential two step model of troponin binding to actin-tropomyosin could simulate the observed association and dissociation transients. In the absence of Ca2+ or rigor S1, the following rate constants could describe the binding process: k1 = 7.12 microM(-1) s(-1), k(-1) = 0.65 s(-1), k2 = 0.07 s(-1), k(-2) = 0.0014 s(-1). The slow rate of detachment of troponin from actin (k(-2)) limits the rate of exchange in solution and most likely contributes to the slow rate of exchange in fibers.

Cardiac troponins and creatine kinase content of striated muscle in common laboratory animals

Animal models are important for the investigation of human heart pathology, novel treatments, and medical or surgical interventions for disease. Serum markers of myocardial damage may also be important tools within this field of research. In order to assess the cardiac specificity of widely utilised serum markers, we measured the cardiac troponins and creatine kinase (CK) isoenzymes in cardiac and skeletal muscle samples taken from dog, monkey, pig and rat. These samples were also analysed by immunoblotting for cardiac troponin I (cTnI) and cardiac troponin T (cTnT). The content of cTnI and cTnT in skeletal muscle was below 0.6% of that found in heart for all animal species studied. This low immunoreactivity in skeletal muscle was confirmed by immunoblot analysis. The content of CK was higher in skeletal muscle than in heart muscle for all species. The CK-MB/total CK ratio was lower in skeletal muscle than in cardiac muscle for all species. The differences in CK-MB content of skeletal muscle and heart muscle were much less pronounced than the tissue differences in the amounts of the cardiac troponins. The cardiac troponins are potentially useful serum markers of myocardial damage, with high specificity for myocardial muscle in these common laboratory animals. Creatine kinase-MB is much less cardiac-specific.

Comparison of the diagnostic value of cardiac troponin I and T determinations for detecting early myocardial damage and the relationship with histological findings after isoprenaline-induced cardiac injury in rats

Cardiac troponins I (cTnI) and T (cTnT) have been shown to be highly sensitive and specific markers of myocardial cell injury. The purpose of this study was to investigate the diagnostic value of cTnI and cTnT with regard to creatine kinase (CK) and lactate dehydrogenase (LD) and to determine whether they can be used for early diagnosis of myocardial damage in rats, and to examine the relationship between cTnl and cTnT release with histological examinations, using isoprenaline-induced cardiac muscle damage as an experimental model in the rat. Eighteen Wistar rats per group were treated with a single dose of either isoprenaline (iso) or with normal saline as a control group. The anti-cTnI and cTnT monoclonal antibodies (mAbs) employed in the cTnI (Access) and cTnT (Elecsys) assays cross-react with cTnI and cTnT of the rat. A highly significant rise of cTnl or cTnT was found already 2 h after iso. The time-courses of cTnI and cTnT were monophasic in form. The highest cTnI (mean+/-S.D., 1.1+/-2.3 ng/ml) and cTnT (mean+/-S.D. 3.6+/-30 ng/ml) were found 4 h after iso. cTnI and cTnT significantly increased in iso-treated rats in comparison with controls whether the differences between 2-, 4- and 6-h levels and basal levels were considered or not. The areas under cTnl and cTnT curves (AUC) (0-6 h) and the maximal cTnI and cTnT (0-6 h) after iso were significantly different from the controls. For CK and LD, no elevation in comparison with controls could be detected (except a trend for LD whether or not the difference between 6-h levels and basal levels were considered (P=0.08) and for LD AUC (0-6 h) (P=0. 059)). Correlations between maximal cTnI and cTnT and AUC were 0.69 (P=0.0001) and 0.60 (P=0.0066), respectively. Histological examinations of iso-treated rats revealed acute focal or multifocal myofibrillar degeneration of the myocardial tissue in ten out of 14 rats and showed the earliest alterations 4 h after iso in one treated rat. Only four of the controls exhibited evidence of mild changes and slight mononuclear cell infiltration. cTnl and cTnT peak values to at least 0.35 and 1.3 ng/ml, respectively, were necessary to detect histological myocardial cell injury after iso. cTnI and cTnT were found to be early markers for diagnosing iso-induced myocardial damage in comparison with CK and LD. Elevations of cTnI and cTnT appeared to relate to the severity of histologic changes after myocardial injury. Although there was a difference in the absolute concentration of results between cTnI and cTnT assays, due to a lack of standardization and heterogeneity in the cross-reactivities of mAbs to various troponin I and T forms, cTnI and cTnT can be used as easily measurable target parameters for detection of cardiotoxic and/or cardiodegenerative effects in rats.

Cardiac troponin I and cardiac troponin T increases in pigs during ischemia-reperfusion damage

In this study we addressed the question of whether the measurement of cardiac Troponin T (cTnT) and cardiac Troponin I (cTnI) is able to detect myocardial cell damage in an ischemia-reperfusion model in pigs. To answer the question 3 pigs were anaesthesized and a cardiac arrest was induced by electric fibrillation. After 5 minutes of global ischemia the cardiac arrest was reversed by electric defibrillation until normal perfusion was restored. We could clearly demonstrate an increase of cTnT and cTnI 30 minutes after reperfusion indicating myocardial injury during ischemia and subsequent reperfusion. The cTnT as well as the cTnI serum levels increased till 180 minutes after reperfusion. This ischemia-reperfusion injury is likely induced by oxygen radicals generated during hypoxia and subsequent reperfusion We conclude from our first results that troponin measurements with commercial available test kits may also reflect myocardial cell damage in pigs as it was recently demonstrated in rats. Further studies are needed for correlation of troponin serum levels and histopathological damage in this model especially if it is used to test beneficial or toxicological effects of radical neutralizing drugs.

Tissue release of cardiac markers: from physiology to clinical applications

The early release of cardiac markers is influenced by a variety of factors, the most important influence being their intracellular compartmentation. In contrast to the release of cytosolic proteins, the release of structurally bound proteins requires both a leaky plasma membrane and a dissociation or degradation of the subcellular structure, which is a slower process. Another major impact is the susceptibility to the degradation by cytosolic proteases, such as the calpains. The lysosomes are stable within the first 3-4 hours after onset of ischemia, and, therefore, their enzymes are not involved in the early degradation of structurally bound proteins. Troponin I and troponin T are substrates of micro-calpain. Current experimental as well as clinical results suggest that the molecular mass seems to be of minor importance for the pattern of appearance of myocardial proteins in blood after myocardial infarction. However, within the family of molecules with a certain intracellular compartmentation, the molecular mass is an influence on the appearance in blood, because heavier molecules diffuse at a slower rate, and particularly smaller molecules, such as myoglobin, may enter the vascular system to an even larger extent directly via the microvascular endothelium. The higher the concentration gradient of a marker between the cardiomyocytes and the interstitial space, the faster a parameter will translocate from sarcoplasma to the interstitial space as soon as the plasma membrane permeability is increased. Another influence is local blood and lymphatic flow. Recent experimental studies showed that reperfusion causes a true acceleration of cellular protein leakage by an acute manifestation of plasmalemmal disruptions and not just an enhanced wash out. Marker protein time-courses after myocardial damage are also markedly influenced by their disappearance rate from blood. Most proteins appear to be catabolized in organs with a high metabolic rate, such as liver, pancreas, kidneys, and the reticuloendothelial system. Smaller molecules, such as myoglobin, also pass the glomerular membranes of the kidneys and are reabsorbed and subsequently metabolized in tubular epithelial cells.

Post-ischaemic dysfunction does not correlate with release of cardiac troponin T in isolated rat hearts

Cardiac troponin T (cTnT) is a highly sensitive and specific serum marker of irreversible cardiomyocyte injury. It is not clear whether cTnT also is a suitable marker of subtle, reversible injury. In the present investigation the relationship between cTnT release and function during the first 30 min of reperfusion after 30 min of global ischaemia, was investigated in isolated, retrogradely perfused rat hearts. Left ventricular systolic (LVSP), end-diastolic (LVEDP) and developed (LVDP) pressures, heart rate (HR), and coronary flow (CF) were measured. In one series of experiments (n=7) the kinetics of cTnT release during 30 min of reperfusion was investigated. An early, short-lasting peak of cTnT release appeared after 30 s of reperfusion. Then cTnT release gradually increased with a maximum after 20 min (from 0.08 +/- 0.03 before ischaemia to 2.16 +/- 0.40 ng min-1) (mean +/- SEM). In a second series of experiments (n=52) the relationship between cTnT release and cardiac function was investigated after 20 min of reperfusion. At this time point LVEDP increased (0 to 62 +/- 3 mmHg) and LVDP decreased (84 +/- 2 to 33 +/- 3 mmHg), but without any correlation with cTnT release. cTnT release was positively correlated to LVSP (P < 0.04, r=0.29), and negatively correlated to HR (P < 0.03, r=-0.31). cTnT concentration in the coronary effluent increased in parallel to increasing CF (P < 0.03, r=0.31). In conclusion, during the early reperfusion period there was no consistent correlation between cTnT release and dysfunction after global ischaemia in the isolated rat heart. Release of cTnT and post-ischaemic function appear to provide supplementary information in this particular model.

Release kinetics of cardiac troponin I and cardiac troponin T in effluents from isolated perfused rabbit hearts after graded experimental myocardial contusion

BACKGROUND

Few experimental studies report effects of direct contusion on cardiac enzyme release. Cardiac troponins I (cTnI) and T (cTnT) have been shown to be highly sensitive and specific markers of myocardial cell injury. This investigation was designed to determine and compare the acute effects of quantified magnitudes of blunt cardiac trauma upon release of cTnI and cTnT in comparison with creatine kinase (CK) and lactate dehydrogenase (LD).

METHODS

In 24 rabbit hearts prepared on a standard Langendorff apparatus, myocardial contusion (MC) was produced by a single blow with a ball falling from a predefined height, delivered directly to the surface of the heart. Hearts were divided into control (n = 6) and various quantified impacts: 75 mJoules (mJ) (n = 6), 100 mJ (n = 6), 200 mJ (n = 6). Coronary effluent samples for cTnI, cTnT, CK, and LD were collected at baseline, immediately after MC and 5, 15, 30, 45, and 60 minutes after MC. At the end of experiment, histologic condition was evaluated.

RESULTS

The anti-cTnI and cTnT MAbs used in the cTnI (Access) and cTnT (Elecsys) assays cross-react with cTnI and cTnT of the rabbit. The time-courses of cTnI, cTnT, CK, and LD were monophasic in form. After MC, all parameters rose significantly compared with baseline and with control group. The maximal release occurred immediately after MC. The area under the cTnI curve and the maximal cTnI concentration were linked to the contusion energy when increased at 200 mJ. Maximal concentrations and areas under cTnT, CK, LD time activity curve were not linked to the contusion energy level and showed no between-energy group differences. The correlation found between maximal cTnI and maximal cTnT concentrations was 0.70 (p = 0.0001). Histologic examination showed cellular disruption and after the more severe impact, the extent of pathologic changes was more extensive.

CONCLUSION

After graded experimental MC, maximal cTnI concentration and area under cTnI curve increase with the power of impact kinetic energy. Levels of cTnI allow a much higher accuracy in detecting the extent of myocardial injury postMC in comparison with cTnT, CK, and LD in this experimental study. These results should be consistent with the more extensive cTnI release with more severe impact in patients with blunt chest trauma. Furthermore, because specificity and time-course of release, both cTnI and cTnT should have a role in the diagnosis and evaluation of such patients.

Release of cardiac troponin in acute coronary syndromes: ischemia or necrosis?

Analysis of cardiac troponin T and I have been shown to be effective in detecting minor myocardial injury in cardiac patients who present with acute coronary syndromes (ACS). Determination of minor myocardial injury is significant, as these patients have a higher short-term morbidity and mortality than other unstable angina patients with normal concentrations for these markers. In this report, two theories are given as to why cardiac troponin is superior to other markers such as CK-MB for risk stratification. The 'low cut-off concentration model' is based on the fact that troponin is not increased in patients with skeletal muscle disease or injury, resulting in low baseline concentrations of the cardiac isoforms in the absence of active cardiac disease. This enables the use of low decision limits. Troponin also has a higher myocardial tissue content relative to CK-MB, thereby also increasing its clinical sensitivity to irreversible injury. In the 'reversible ischemia model', cytoplasmic free troponin T and I leak across the membrane of myocytes as the result of reduced coronary blood flow. Jeopardized myocardial tissue can recover with acute recanalization. Support for this model comes from clinical observations and animal studies.

Impact of Antibody Specificity and Calibration Material on the Measure of Agreement between Methods for Cardiac Troponin I

Background: Available assays for cardiac troponin I (cTnI) yield numerically different results. The aim of this study was to compare patient values obtained from four cTnI immunoassays.

Methods: We studied the Stratus® II assay, the Opus® II assay, the Access® assay, and a research-only cTnI heterogeneous immunoassay that uses the Dade Behring aca® plus immunoassay system equipped with two new noncommercial monoclonal antibodies. Because the aca plus cTnI assay is for research only, we first evaluated and analytically validated it for serum and citrated plasma. Initially, each method was calibrated using the method-specific calibrator supplied by each manufacturer; however, the aca plus cTnI assay was calibrated using patient serum pools containing cTnI and selected on the basis of increased creatine kinase MB isoenzyme and with values assigned by use of the Stratus cTnI assay. For method comparisons, individual patient sample cTnI values were determined and compared with the Stratus II assay.

Results: Passing and Bablock regression analysis yielded slopes of 1.44 (r = 0.96; n = 72) for the Opus II vs Stratus II assays; 0.07 (r = 0.91; n = 72) for the Access vs Stratus II assays; and 0.90 (r = 0.91, n = 72) for the aca plus vs Stratus II assays. The recalibration of each method with a Stratus II-assigned serum pool improved, but did not entirely eliminate, the slope differences between the different assays (range, 1.00–1.16). The observed scatter in the correlation curves remained.

Conclusion: There is a need to further explore the specificities of these assays with respect to the different circulating forms of cTnI.

Time-course of cardiac troponin I release from isolated perfused rat hearts during hypoxia/reoxygenation and ischemia/reperfusion

The study was designed to determine the time-course of cardiac troponin I (cTn-I) release in isolated and Langendorff-perfused rat hearts during hypoxia and reoxygenation (H/Reox), and after various durations of total ischemia and subsequent reperfusion (I/R). For this purpose, in H/Reox, cTn-I was measured with the conventional Access immunoassay (ng/ml) and a new immunoassay which operates at pg/ml, and compared with creatine kinase (CK), lactate dehydrogenase (LD) and cardiac troponin T (cTn-T). In I/R, cTn-I was compared with CK and LD. The anti-Tn-I mAbs used in cTn-I assays cross-react with cTn-I of the rat. A clear difference between time-courses and concentration levels of cTn-I in I/R and H/Reox models was found. In I/R, maximum release of cTn-I, CK and LD similarly occurred within minutes following reperfusion; however cTn-I did not return to baseline values. cTn-I levels were not linked to the duration of ischemia. In I/R, we were only able to detect small cTn-I concentrations. In H/Reox experiments, cTn-I, CK and LD increased time-dependently. We found higher cTn-I maximal peak levels detected with the Access immunoassay than with the new assay (median, 0.346 ng/ml per min/g dry wt vs 132 pg/ml per min/g dry wt). cTn-T maximal concentrations were lower than maximal cTn-I levels (median, 0.117 ng/ml per min/g dry wt). Time-courses of cTn-I release were roughly similar with both assays in the H/Reox model (r = 0.90). These data indicate that the cTn-I time-course is related to experimental model (I/R or H/Reox), but also likely depends on the sensitivity of cTn-I assays in such experimental conditions.

Different intracellular compartmentations of cardiac troponins and myosin heavy chains: a causal connection to their different early release after myocardial damage

We investigated the net myocardial release of creatine kinase isoenzyme MB (CKMB), myoglobin, cardiac troponin T (cTnT), cardiac troponin I (cTnI), and cardiac β-type myosin heavy chain (β-MHC) into the coronary circulation after cardioplegic cardiac arrest in humans. Cardiac markers were measured in paired arterial, central venous, and coronary sinus blood in 19 patients undergoing elective coronary artery bypass grafting (CABG) before aortic cross-clamping and 1, 5, 10, and 20 min after aortic declamping. cTnT and cTnI were released into the coronary sinus in parallel to each other and almost simultaneously to myoglobin and CKMB within 20 min of reperfusion. In contrast, no β-MHC was released in the same patients during the study period. The average soluble cTnT and cTnI pools in right atrial appendages of 11 patients with right atrial and right ventricular pressures within reference values were comparable and were ∼8% of total myocardial troponin content. The soluble β-MHC pool was &lt;0.1% in all patients. Our results demonstrate the impact of the different intracellular compartmention of regulatory and contractile proteins on their early release from damaged myocardium.

Comparison of cardiac Troponin T and cardiac Troponin I concentrations in peripheral blood during orciprenaline induced tachycardia in rats

In this study we addressed the question of whether the measurement of the cardiac structure protein cardiac Toponin I (cTnI) in serum is also able to detect marked myocardial cell damage in rats like cardiac Troponin T (cTnT). To answer this question 5 male rats and 5 female rats were injected with orciprenaline to induce myocardial cell damage. Further 5 animals of each sex received physiological saline as control. We could demonstrate that troponin I was rised significantly 6 hours after injection in serum as well as cTnT. 24 hours after injection cTnI was elevated on a lower significance level compared to cTnT. All values returned to normal 96 hours after the injection. We conclude that cTnI was also able to detect a marked myocardial cell damage in rats but we could show that cTnI was elevated on a lower significance level compared to cTnT. Furthermore we found that a cTnI increase to at least 4.1 ng/ml is necessary to detect marked myocardial cell injury in this rat tachycardia model.

Cardiac troponin I and troponin T: are enzymes still relevant as cardiac markers?

Creatine kinase (CK) MB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms, one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT). cTnI and cTnT are usually not detectable in patients without myocardial damage, which is a prerequisite for high diagnostic performance. After acute myocardial infarction (AMI) cTnI, cTnT, and CKMB mass have a comparable early sensitivity. cTnI and cTnT usually peak in parallel except for patients without reperfusion in whom cTnI peaks about 1 day and cTnT approximately 3-4 days after onset of AMI. Both stay increased for at least 4-5 days. cTnT tends to stay increased longer than cTnI. Because the sensitivities of cTnI and cTnT for myocardial injury are comparable, their specificities are the main topic of current debate. Recent reports on mismatches of cTnI and cTnT in patients with renal failure and myopathy without other evidence for myocardial injury suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. In contrast to cTnT, CKMB, and LDH-1, cTnI is not expressed in skeletal muscle during fetal development. So far, an increase in cTnI has been reported only after myocardial damage. Because of currently higher costs, troponin measurement should be restricted at present to clinical settings that really require their high specificity. Based on its distinct functional association with the metabolism of acute ischemic myocardium and according to initial clinical results, glycogen phosphorylase isoenzyme BB is a promising enzyme for the early detection of ischemic myocardial damage.

Progress in myocardial damage detection: new biochemical markers for clinicians

New clinical requirements for triaging chest pain patients challenge the abilities of the current cardiac markers. Serial measurements of myoglobin, creatine kinase (CK) isoenzyme MB (CKMB) mass, or CK isoforms in emergency rooms help to rapidly rule out acute myocardial infarction (AMI). However, within the first 3 to 4 h from chest pain onset, their sensitivities are too low to contribute significantly to AMI diagnosis during this period. CKMB and lactate dehydrogenase (LDH) isoenzyme 1 are not heart-specific, which hampers reliable diagnosis in patients with concomitant skeletal muscle damage. By contrast, the regulatory proteins troponin I and troponin T are expressed in three different isoforms: one for slow-twitch skeletal muscle fibers, one for fast-twitch skeletal muscle fibers, and one for cardiac muscle (cTnI, cTnT); cardiac-specific cTnI and cTnT assays are already available for routine use. cTnT and cTnI are the most promising markers for risk stratification in patients with unstable angina pectoris. Recent reports on increased cTnT in patients with renal failure or myopathy without evidence of myocardial injury and undetectable cTnI suggest that cTnT could be reexpressed similar to CKMB and LDH-1 in chronically damaged human skeletal muscle. Therefore, cTnI is probably the most heart-specific marker. Among the recently proposed new markers for early AMI diagnosis: glycogen phosphorylase isoenzyme BB (GPBB), fatty acid binding protein, phosphoglyceric acid mutase isoenzyme MB, enolase isoenzyme alpha beta, S100a0, and annexin V, GPBB is the most promising because it increases as early as 1 to 4 h from chest pain onset and its early release appears to be essentially dependent on ischemic myocardial injury.