Improved detection of minor ischemic myocardial injury with measurement of serum cardiac troponin I

This study compared the diagnostic accuracy of the measurement of serum cardiac troponin I (cTnI) with creatine kinase (CK) MB mass in patients with minor myocardial injury whose measured total CK activity did not exceed twice the upper reference limit (300 U/L for men; 200 U/L for women). Forty-eight consecutive patients presenting with chest pain and with in-hospital documentation of myocardial injury were enrolled. Electrocardiogram, echocardiogram, and serial serum CK-MB mass, cTnI, and total CK were measured over 36 h after admission. Peak total CK activity was within normal limits in 28 patients (58%). The mean (+/- SD) peak CK-MB mass and cTnI concentrations were: 16.4 (11.8) micrograms/L and 132 (13.0) micrograms/L; respectively. The peak biochemical marker index (defined as CK-MB or cTnI divided by its respective upper reference limit) was significantly (P < 0.05) higher for cTnI than for CK-MB from 7 to 36 h. The clinical sensitivity for detection of myocardial injury for cTnI was 100% [95% confidence interval (CI): 87.2% to 100%], compared with 81.8% (CI: 67.3% to 91.8%) for CK-MB. Thus, cTnI was more sensitive than CK-MB mass for detection of myocardial injury in patients with small increases of total CK.     

Role of cardiac troponin I in the evaluation of myocardial injury

Congenital fibrosarcoma is a rare soft tissue sarcoma. A 22-year-old woman in the 22nd week of her first pregnancy underwent sonographic examination, which revealed a soft tissue swelling of the fetus's left thigh. The pregnancy was terminated, and congenital fibrosarcoma was diagnosed by pathologic examination. To our knowledge, this is the first published report of the intrauterine sonographic observation of this tumor in a fetal extremity.     

Cardiac troponin I (cTn I) and the postmortem diagnosis of myocardial infarction

KH 1060 is the 20-epi-22-oxa-24a-homo-26,27-dimethyl analogue of the natural hormone, 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3). We have previously shown that after topical application in hairless mice both KH 1060 and 1 alpha,25(OH)2D3 cause epidermal hyperproliferation. MC 1582 differs from KH 1060 by the lack of hydroxyl group in the side chain which is required for receptor binding. We found that MC 1582 strongly stimulates epidermal hyperplasia in hairless mice after topical application in vivo, approaching in potency KH 1060. A similar, although much weaker response was also obtained with 1 alpha-hydroxyvitamin D3 (1 alpha(OH)D3). Since only the vitamin D compounds which possess hydroxyl groups both in the position 1 alpha and in the side chain, bind to the vitamin D receptor, we suggest that a local metabolism of MC 1582 and 1 alpha(OH)D3 takes place in the skin to the active, side-chain-hydroxylated species, probably to KH 1060 and 1 alpha,25(OH)2D3. This study suggests that 1 alpha hydroxylated prodrugs may be of use in the dermatological treatment of the future.     

Cardiac troponin I phosphorylation increases the rate of cardiac muscle relaxation

Cardiac troponin (Tn) I (CTnI), compared with skeletal TnI, contains extra amino acids (32 to 33) at its amino terminus, including two adjacent serine residues. These two serine residues are believed to be phosphorylated by protein kinase A (PKA) upon stimulation of the heart by beta-agonists. In this study, we found that phosphorylation of a cardiac skinned muscle preparation by PKA, mainly at CTnI, results in a decrease in the Ca2+ sensitivity of muscle contraction. The pCa50 decreased by approximately 0.27 +/- 0.06 pCa units upon phosphorylation. To study cardiac muscle relaxation, we used diazo-2, a photolabile Ca2+ chelator with a low Ca2+ affinity in its intact form that is converted to a high-affinity form after photolysis. We found that the rate of cardiac muscle relaxation increased from a time of half-relaxation (t1/2) = 110 +/- 10 milliseconds to t1/2 = 70 +/- 8 milliseconds after CTnI phosphorylation. This result demonstrates that CTnI phosphorylation can be linked with the increased rate of muscle relaxation in a relatively intact muscle preparation. Since CTnI phosphorylation has been shown previously to affect the Ca2+ affinity and Ca2+ off-rate of CTnC in vitro, it is likely that the faster relaxation seen here reflects faster dissociation of Ca2+ from cardiac TnC (CTnC). Model calculations show that increased dissociation of Ca2+ from CTnC, coupled with the faster uptake of Ca2+ by the sarcoplasmic reticulum stimulated by PKA phosphorylation of phospholamban, can account for the faster relaxation seen in the inotropic response of the heart to catecholamines.     

Serum levels of cardiac troponin I and troponin T in estimating myocardial infarct size soon after reperfusion

BACKGROUND: Cardiac troponin I (TnI) and troponin T (TnT) are highly specific myocardial markers. OBJECTIVE: To determine whether their serum levels can be used to estimate myocardial infarct size soon after reperfusion. METHODS: We measured the serum levels of TnI, TnT, and creatine kinase every 3 h, and the serum cardiac myosin light chain I (MLCI) every 24 h, in 42 patients with acute myocardial infarction in whom reperfusion therapy had successfully been performed. We calculated the severity of regional hypokinesis by analyzing the follow-up ventriculograms with the centerline method. RESULTS: The time from reperfusion to the peak level for TnI was 6.1 +/- 3.5 h, significantly shorter than those for creatine kinase (7.5 +/- 4.1 h) and MLCI (55 +/- 28 h). The time to peak level for TnT (6.8 +/- 4.0 h) differed significantly from that for MLCI but not from that for creatine kinase. There was a significant correlation between the peak levels of TnI and TnT (r = 0.86). The peak TnI and TnT levels were correlated well to the peak creatine kinase level (r = 0.67 and 0.69, respectively), total creatine kinase release (r = 0.66 and 0.66), and the peak MLCI level (r = 0.71 and 0.80). We observed excellent correlations between the peak levels of TnI and TnT, and regional hypokinesis (r = -0.84 and -0.85, respectively). These were comparable to the correlations between regional hypokinesis and the peak creatine kinase level (r = 0.75), total creatine kinase release (r = -0.72), and the peak MLCI level (r = -0.76). CONCLUSIONS: These results suggest that the peak serum levels of TnI and TnT in patients with successful reperfusion are accurate and early indices of infarct size.     

Clinical utility of cardiac troponin I and cardiac troponin T measurements

The measurement of CK-MB remains the test of choice for confirmation or exclusion of AMI and probably will remain the test of choice for routine diagnosis in the near future. Nowadays determination of cardiac troponin T (cTnT) and cardiac troponin I (cTnI) as a method relatively expensive and time-consuming should be restricted to clinical settings that really require their high specificity.     

Assay of cardiac troponin T on Elecsys 2010: comparison with cardiac troponin I

Cardiac troponin T (troponin Tc) of second generation has been measured on the Boehringer Elecsys 2010 analyzer. Cardiac specificity has been studied in patients presenting a rhabdomyolysis syndrome and the results compared with those obtained for cardiac troponin I (troponin Ic) measured on the Dade-Behring Stratus analyzer. The results clearly demonstrated that both troponin Tc and Ic showed similar cardiac specificity. Moreover, troponin Tc and troponin Ic can be indifferently used for the biological diagnostic of myocardial infarction or to asses reperfusion after percutaneous transluminal coronary angioplasty for acute myocardial infarction. In renal disease, troponin Tc was upper the reference limit (0.10 microgram/l) in 25% of the patients studied (20 patients). By contrast, troponin Ic was upper the reference limit (0.6 microgram/l) in only one patient.     

Cardiac troponin T and cardiac troponin I: relative values in short-term risk stratification of patients with acute coronary syndromes. GUSTO-IIa Investigators

We compared cardiac troponins T (cTnT) and I (cTnI) collected within 3.5 h of ischemic symptoms for predicting clinical outcomes in 770 patients. cTnT (cutoff > 0.1 microgram/L) and cTnI (cutoff > 1.5 micrograms/L) were concordant (both positive or negative) in 90.4% of patients. Among discordant results, 66 were cTnT positive and cTnI negative vs 8 who showed the reverse (P < 0.001). Five cTnT-positive and cTnI-negative patients died within 30 days; none who were cTnT negative and cTnI positive died. cTnT showed a slightly greater association (chi 2 = 18.0, P < 0.001) with 30-day mortality than cTnI (chi 2 = 12.5, P = 0.002). The area of the ROC curve for predicting 30-day mortality was significantly larger (Z = 2.08; P = 0.0375) for cTnT, at 0.68 [95% confidence interval (CI) 0.60-0.75], compared with cTnI, at 0.64 (95% CI 0.56-0.72). When cTnI and the electrocardiogram (ECG) were put in a logistic multiple regression model, cTnT added significant information (chi 2 = 8.03, P = 0.045); however, cTnI did not add to a model containing cTnT and the ECG (chi 2 = 0.84, P = 0.657). cTnT provided more information than cTnI for predicting 30-day mortality early after presentation with acute coronary syndromes.     

Phosphorylation-induced distance change in a cardiac muscle troponin I mutant

Phosphorylation of two adjacent serine residues in the unique N-terminal extension of cardiac muscle troponin I (cTnI) is known to decrease the Ca2+-sensitivity of cardiac myofilaments. To probe the structural significance of the N-terminal extension, we have constructed two cTnI mutants each containing a single cysteine: (1) a full-length cTnI mutant (S5C/C81I/C98S) and (2) a truncated cTnI mutant (S9C/C50I/C67S) in which the N-terminal 32 amino acid residues were deleted. We determined the apparent binding constants for the complex formation between IAANS-labeled cardiac troponin C (cTnC) and the two cTnI mutants. The affinities of the cTnC for the truncated cTnI mutant were: (1) 1.5 x 10(6) M(-1) in EGTA, (2) 28.9 x 10(6) M(-1) in Mg2+, and (3) 87.5 x 10(6) M(-1) in Mg2+ + Ca2+. These binding constants were approximately 1.4-fold smaller than the corresponding values obtained with the full-length cTnI mutant, suggesting a very small contribution of the N-terminal extension to the binding of cTnI to cTnC. Cys-5 in the full-length cTnI mutant was labeled with IAANS, and the distribution of the separation between this site and Trp-192 was determined by analysis of the efficiency of fluorescence resonance energy transfer from Trp-192 to IAANS. The following mean distances were obtained with the unphosphorylated full-length mutant: 44.4 A (cTnI alone), 48.3 A (cTnI + cTnC), 46.3 A (cTnI + cTnC in Mg2+), and 51.6 A (cTnI + cTnC in Mg2+ + Ca2+). The corresponding values of the mean distance determined with the phosphorylated full-length cTnI mutant were 35.8, 36.6, 34.8, and 37.3 A. The phosphorylation of cTnI reduced the half-width of the distribution from 9.5 to 3.7 A. Similar but less pronounced decreases of the half-widths were also observed with the phosphorylated cTnI complexed with cTnC in different ionic conditions. Thus, phosphorylation of cTnI resulted in a decrease of 9-12 A in the mean distance between the sites located at the N- and C-terminal portion of cTnI. Our results indicate that phosphorylation elicits a change in the conformation of cTnI which underlies the basis of the phosphorylation-induced modulation of cTnI activity.     

Assessment of left ventricular function using serum cardiac troponin I measurements following myocardial infarction

The FhuA protein of Escherichia coli K-12 transports ferrichrome and the structurally related antibiotic albomycin across the outer membrane and serves as a receptor for the phages T1, T5, and phi 80 and for colicin M. In this paper, we show that chimeric proteins consisting of the central part of FhuA and the N- and C-terminal parts of FhuE (coprogen receptor) or the N- and/or C-terminal parts of FoxA (ferrioxamine B receptor), function as ferrichrome transport proteins. Although the hybrid proteins contained the previously identified gating loop of FhuA, which is the principal binding site of the phages T5, T1, and phi 80, only the hybrid protein consisting of the N-terminal third of FoxA and the C-terminal two thirds of FhuA conferred weak phage sensitivity to cells. Apparently, the gating loop is essential, but not sufficient for wild-type levels of ferrichrome transport and for phage sensitivity. The properties of FhuA-FoxA hybrids suggest different regions of the two receptors for ferric siderophore uptake.     

A new method of human cardiac troponin I and troponin T purification

Neurotrophins (NTFs) are a family of structurally related proteins with specific effects on the developing nervous system and a wide range of non-neuronal differentiating cells. To date, four NTFs have been characterized: nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4). To perform their biological effects, the NTFs must bind to appropriate receptors on the surface of responsive cells. High- and low-affinity receptors for NTFs have been identified. The high-affinity receptors are members of the trk protein tyrosine kinase receptor family. The low-affinity neurotrophin receptor gp75NTFR is a common receptor for all NTFs. Here we summarize some of our previous findings on the expression patterns of NGF, gp75NTFR, TrkB, and TrkC in the developing molar tooth of the rat. Both NGF and gp75NTFR are localized in dental epithelium and mesenchyme but often their expression patterns differ. Concomitant expression of NGF and gp75NTFR in mesenchyme is correlated with odontoblast differentiation. The trkB and trkC receptors show distinct cell-specific expression patterns in developing tooth, suggesting that other NTFs, apart from NGF, may be involved in odontogenesis. These data demonstrate that NTFs participate in the cascade of molecular events that direct tooth development, and support the notion that NTFs may have multiple and distinct roles in dental tissues.     

Differential reactivity of cardiac and skeletal muscle from various species in a cardiac troponin I immunoassay

The effects of 2-butoxyethanol (2-BE) on poly(ADP-ribosyl)ation were studied in Syrian hamster embryo (SHE) cells by measuring the cellular concentrations of the polymer poly(ADP-ribose) (pADPr) and of NAD+, the substrate of poly(ADP-ribose) polymerase (PARP). As biotransformation pathways of ethylene glycol ethers involve NAD+-dehydrogenases, it was hypothesized that 2-BE could reduce poly(ADP-ribosyl)ation by consuming NAD+. As a result DNA repair could be altered, which would explain that 2-BE had been shown to potentiate the effects of clastogenic substances such as methyl-methanesulfonate (MMS). In this study, the effects of 2-BE on MMS-induced pADPr metabolism were analyzed. The results indicated that: (i) 2-BE (5 mM) by itself did not influence significantly pADPr or NAD+ levels. (ii) 2-BE inhibited pADPr synthesis in MMS (0.2 mM)-pretreated cells, without any change in NAD+ concentrations. (iii) MMS treatment, which rapidly increased pADPr levels, also affected the poly(ADP-ribosyl)ation system as a secondary effect by damaging cell structures. Membrane permeabilization, which occurred at concentrations >1 mM MMS, led to a dramatic leakage of cellular NAD+ resulting in a strong reduction in pADPr levels. (iv) A bleomycin pulse (100 microM) applied after MMS and/or 2-BE treatment confirmed that 2-BE reduced poly(ADP-ribosyl)ation capacities of MMS-treated cells, though the glycol ether had no effect alone. This study confirmed that the inhibition of pADPr synthesis could be responsible for the synergistic effects of 2-BE with genotoxic substances. The mechanism of this inhibition cannot be explained by a lack of NAD+ at the concentrations of 2-BE tested.     

Degradation of cardiac troponin I: implication for reliable immunodetection

We have analyzed by different immunological methods the proteolytic degradation of cardiac troponin I (cTnI) in human necrotic tissue and in serum. cTnI is susceptible to proteolysis, and its degradation leads to the appearance of a wide diversity of proteolytic peptides with different stabilities. N- and C-terminal regions were rapidly cleaved by proteases, whereas the fragment located between residues 30 and 110 demonstrated substantially higher stability, possibly because of its protection by TnC. We conclude that antibodies selected for cTnI sandwich immunoassays should preferentially recognize epitopes located in the region resistant to proteolysis. Such an approach can be helpful for a much needed standardization of cTnI immunoassays and can improve the sensitivity and reproducibility of cTnI assays.     

Incidence of myocardial lesions after vascular surgery: diagnosis by troponin Ic

OBJECTIVE: To compare the incidence of myocardial damages diagnosed following vascular surgery using the cardiac troponin I measurement technique and conventional methods. STUDY DESIGN: Prospective epidemiological study. PATIENTS: Fifty-four patients who underwent surgery for either aneurysmal disease in 28 cases or occlusive aortic disease in 26 cases. METHODS: Plasma concentration of cardiac troponin I (significant at a concentration > 1.5 ng.mL-1) was measured by immunoenzymofluorimetry on the second and fifth postoperative days. Conventional monitoring methods included daily electrocardiogram (ECG), enzymatic assay of total-PCK, and measurement of plasma levels of the MB isoenzyme of phosphokinase creatine (MB-PCK) (significant at > 1 ng.mL-1 and RI > 1.5). RESULTS: The cardiac troponin I measurement technique allowed the diagnosis of minor myocardial damages during the postoperative period in five patients, whereas with the conventional methods (clinical signs. ECG, and MB-PCK) only three myocardial lesions were diagnosed. CONCLUSION: The cardiac troponin I measurement technique allows diagnosis of minor myocardial damages following vascular surgery. Conventional methods underestimate the incidence of these damages.     

Expression of regulated cardiac troponin I in Escherichia coli

The study of the functional effects of troponin isoform changes would be greatly aided by the development of a strategy permitting protein engineering and mutational analysis. To assess the role of troponin isoforms in regulating myofibrillar ATPase activity, we have expressed rat cardiac troponin I (cTnI) in E. coli and purified the protein to near homogeneity. We utilized the inducible expression vector pGEX-KG to create a glutathione-S-transferase fusion protein which can be cleaved with thrombin. Approximately 6 mg of cTnI can be purified from 1 l of culture. Ca2+Mg2+ ATPase activity was measured using the bacterially synthesized cTnI and the remaining components of the regulated actomyosin complex (troponin T, troponin C, tropomyosin, actin, and myosin) purified to homogeneity from mammalian hearts. In the presence of free Ca2+ ranging from 10(-2) to 10(-8) M, bacterially synthesized cTnI exhibits specific activity similar to that observed for control cTnI isolated from rat hearts. The bacterially synthesized protein is capable of stoichiometric phosphorylation and demonstrates appropriately regulated specific activity. These results establish the feasibility of using bacterial expression to study functional consequences of changes in expression of troponin isoforms.     

Comparison of myoglobin, creatine kinase-MB, and cardiac troponin I for diagnosis of acute myocardial infarction

Serial plasma concentrations of myoglobin, creatine kinase MB (CK-MB) isoenzyme, and cardiac troponin I (cTnI) were measured in 25 patients with a confirmed diagnosis of acute myocardial infarction (AMI), and 74 patients who were suspected of AMI but were subsequently ruled out for this diagnosis. The cutoff concentration for the cTnI assay was optimally determined to be 2.5 ng/mL. Of the three markers, myoglobin had the highest clinical sensitivity (50 percent) when blood was collected between 0 to 6 h after the onset of chest pain. Assays for all serum markers used had high clinical sensitivity (> 93 percent) 6 to 24 h after onset. The CK-MB remained highly sensitive for 48 h, while cTnI was sensitive for up to 72 h. Between 72 and 150 h, cTnI had a clinical sensitivity of 70 percent as compared to 21 percent and 18 percent for myoglobin and CK-MB, respectively. The clinical specificity of cTnI for non-AMI patients was equivalent to CK-MB and significantly higher than for myoglobin. The clinical efficiency of cTnI for all samples was better than either CK-MB or myoglobin, owing mainly to the wider diagnostic window. The specificity of cTnI for 59 patients with chronic renal failure, skeletal muscle trauma and disease was better than all of these markers including cardiac troponin T (cTnT). Results of this study show that cTnI is an effective marker for the retrospective diagnosis of AMI, and consideration should be given to its use in place of CK-MB.     

Cardiac markers in the early hours of acute myocardial infarction: clinical performance of creatine kinase, creatine kinase MB isoenzyme (activity and mass concentration), creatine kinase MM and MB subform ratios, myoglobin and cardiac troponin T

We compared early markers of acute myocardial infarction (AMI) in the first 6 h from the onset of symptoms in 133 non-traumatized patients arriving at the emergency department with chest pain suggestive of AMI. Clinical performance parameters were calculated on the basis of 45 patients with AMI and 88 patients with a non-AMI diagnosis. At admission and in the first 0-3 h after the onset of chest pain the creatine kinase-MB (CK-MB) subform ratio was the most sensitive test at a comparable specificity level of 0.95. In the time interval of 3-5 h, myoglobin, the CK-MB mass concentration and the CK-MB subform ratio were associated with the greatest areas under receiver operating characteristic (ROC) curves, but differences between these tests were small and non-significant. At 6 h from the onset of pain, differences in clinical performance between the same three tests were even smaller whether or not samples drawn after the start of thrombolytic treatment were included in the test comparison. For confirmation of AMI at 6 h after onset of pain, CK-MB (activity and mass concentration) demonstrated the highest positive likelihood ratio, and for exclusion of AMI at 6 h the CK-MB subform ratio was associated with the highest negative likelihood ratio. However, differences between the CK-MB subform ratio, CK-MB mass concentration and myoglobin were not significant as estimated by the substantial overlap between the confidence intervals of the likelihood ratios and the ROC areas at 6 h. Cardiac troponin T (cTnT) demonstrated an ROC area equal to the CK-MB isoform ratio and myoglobin at 6 h. However, the likelihood ratio for ruling out AMI was lower, mostly due to the elevated cTnT in unstable coronary disease not defined as AMI. We conclude that the CK-MB subform ratio, CK-MB mass concentration and myoglobin do not demonstrate any significant differences in clinical performance for ruling in or ruling out acute myocardial infarction at 6 h after the onset of chest pain.