(Circulation. 2001;103:58.)
© 2001 American Heart Association, Inc.
Clinical Investigation and Reports |
Cardiac Troponin I Is Modified in the Myocardium of Bypass Patients
From the Departments of Physiology (J.L.M., R.L.), Community Health and Epidemiology (W.P.), Anatomy and Cell Biology (M.Y.T., S.C.P.), Medicine (S.M.), and Physiology and Biochemistry (J.E.V.E.), Queen’s University, and Department of Surgery, Kingston General Hospital (G.R.), Kingston, Ontario, Canada; and the Heart Center, Division of Cardiology, Rigshospitalet (State University Hospital), Copenhagen, Denmark (D.A.).
Correspondence to Dr J.E. Van Eyk, Room 429, Botterell Hall, Department of Physiology, Queen’s University, Kingston, Ontario, Canada, K7L 3N6. E-mail jve1{at}post.queensu.ca
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Abstract |
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Background—Selective proteolysis of cardiac troponin I (cTnI) is a proposed mechanism of contractile dysfunction in stunned myocardium, and the presence of cTnI degradation products in serum may reflect the functional state of the remaining viable myocardium. However, recent swine and canine studies have not demonstrated stunning-dependent cTnI degradation.
Methods and Results—To address the universality of cTnI modification, myocardial biopsy samples were obtained from coronary artery bypass patients (n=37) before and 10 minutes after removal of cross-clamp. Analysis of biopsy samples for cTnI by Western blotting revealed a spectrum of modified cTnI products in myocardium both before and after cross-clamp, including degradation products (7 products resulting from differential N- and C-terminal processing) and covalent complexes (3 products). In particular, a 22-kDa cTnI degradation product with C-terminal proteolysis was identified, which may represent an initial ischemia-dependent cTnI modification, similar to cTnI1–193 observed in stunned rat myocardium. Although no systematic change in amount of modified cTnI was observed, subgroups of patients displayed an increase (n=10, 85±5% of cTnI remaining intact before cross-clamp versus 75±5% after) or a decrease (n=12, 67±5% before versus 78±5% after). Electron microscopy demonstrated normal ultrastructure in biopsy samples, which suggests no necrosis was present. In addition, cTnI modification products were observed in serum through a modified SDS-PAGE methodology.
Conclusions—cTnI modification, in particular proteolysis, occurs in myocardium of bypass patients and may play a key role in stunning in some bypass patients.
Key Words: ischemia • proteins • cardiopulmonary bypass
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Introduction |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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Myocardial ischemic injury produces a spectrum of damage, ranging from myocardial stunning (reversible contractile dysfunction in the absence of cell death) to infarction (irreversible dysfunction accompanied by cell death). The specific and selective proteolysis of cardiac troponin I (cTnI) has recently been proposed to play a key role in the contractile dysfunction observed in myocardial ischemia/reperfusion injury, including myocardial stunning.1 2 3 4 5 6
In the isolated perfused rat heart, cTnI is progressively and selectively posttranslationally modified through proteolysis, the formation of covalent cross-links, and phosphorylation, with increases in the severity of the ischemic insult1 2 3 (see Reference 44 for review). In particular, myocardial stunning (15 minutes of ischemia followed by 45 minutes of reperfusion), in which no myocardial protein release occurs, results in the proteolysis of cTnI from the C-terminus to produce a degradation product comprising amino acid residues 1 to 193 (rat isoform).1 2 3 More severe ischemia/reperfusion (60 minutes of ischemia followed by 45 minutes of reperfusion) produces further cTnI degradation from the N-terminus to cTnI residues 63 to 193 and 73 to 193.1
The importance of cTnI proteolysis over other protein modifications is suggested by its crucial role in the control of calcium-dependent muscle contraction.7 This theory is supported by a recently developed line of transgenic mice that express cTnI1–193, the cTnI degradation product found in stunned rat myocardium.8 These mice exhibited ventricular dilation and decreased myofilament contractility, demonstrating that cTnI proteolysis alone is sufficient to recapitulate the cellular phenotype of stunning.8 However, in vivo swine and canine models of stunning have failed to demonstrate stunning-dependent cTnI degradation.9 10 Therefore, the universality of cTnI degradation as a mechanism of contractile dysfunction is in question.
However, if these various disease-induced cTnI modification products are present in human cardiac diseases, they may be necrotically released into the blood. A profile of modified cTnI products in serum may be observed that reflects the progression of the disease, as well as the functional status of the remaining viable myocardium. This information could affect treatment of patients, enabling more precise and individualized long-term prognosis and management.
To address this issue of universality of cTnI modification in stunning, we have previously demonstrated cTnI proteolysis in myocardial biopsy samples taken from 2 coronary artery bypass patients.8 Here, we present analysis of biopsy samples from 37 bypass patients, providing further evidence that cTnI undergoes extensive modification in the myocardium of bypass patients into 7 degradation products and 3 covalent complexes, all of which have a C-terminal proteolytic cleavage. In particular, an initial, or first, 22-kDa degradation product was observed with a similar C-terminal cleavage to TnI1–193. Although no systematic change in cTnI modification was observed with cross-clamp, subgroups of patients experienced an increase or decrease in the amount of modified cTnI, and modified cTnI products were observed in postoperative serum samples when a modified SDS-PAGE protocol was used. Electron microscopy (EM) on a subset of myocardial biopsy samples demonstrated normal cellular ultrastructure within biopsy samples, which suggests that cTnI degradation can occur in the absence of necrosis. Therefore, TnI is specifically and selectively modified in the myocardium of bypass patients.
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Methods |
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Surgical Technique
Thirty-seven patients undergoing elective coronary bypass were recruited at Kingston General Hospital (KGH) between June 1998 and February 1999. The Human Research Ethics Board of Queen’s University approved this study, and all patients gave informed consent. Exclusion criteria were age under 21 or over 75 years and congenital heart defects or valvular heart disease. Patients underwent multiple coronary artery bypass grafts (n=3 to 7) with internal mammary artery and saphenous vein grafts. Briefly, a single cross-clamp technique was performed on full cardiopulmonary bypass (flow rate 5 to 6 L/min, perfusion pressure 50 to 70 mm Hg) using blood cardioplegia at a 4:1 crystalloid-to-blood ratio (High K; Plasma-Lyte 56 with 5% dextrose, 50 mmol/L NaHCO3, 50 mmol/L KCl, and 200 mg of lidocaine) infused at 37°C (n=13) or 4°C (n=24) with an initial bolus of 600 or 1000 mL (High K) followed by intermittent boluses of 400 or 250 mL after each proximal vein anastomosis. On completion of the mammary anastomosis, a hotshot of 400 mL (Low K; Plasma-Lyte 56 with 5% dextrose, 50 mmol/L NaHCO3, 6 mmol/L KCl, and 50 mg of lidocaine) at 37°C was infused before cross-clamp removal. No statistical differences existed between patients with the 2 cardioplegic methodologies (data not shown). Systemic normothermia was maintained, and standard anesthetic techniques with a neuromuscular blocking agent were used. Cardiopulmonary bypass was maintained with moderate hemodilution (hematocrit 20 to 25) with a centrifugal pump and membrane oxygenator via single arterial and venous (2-stage) cannulae. Preoperative and postoperative serial ECGs were assessed, and the diagnosis of myocardial infarction was made based on new Q waves or loss of R wave.
Tissue and Blood Sampling
Epicardial biopsy samples (50 to 100 µg) were
obtained from both the right (anterior or inferior) and left
(anterolateral) ventricles in areas remote to the visually
underperfused muscle, with no visible scar or epicardial fat, after
initiation of bypass before clamping (RVpre and
LVpre) and 10 minutes after cross-clamp removal
(RVpost and LVpost);
these samples were immediately frozen in liquid nitrogen and stored at
-70°C. No clinical complications resulted from the procurement of
biopsy samples. An additional subset of patients (n=3) were recruited,
and biopsy samples were analyzed by EM. For EM, biopsy samples were
fixed immediately by immersion in 2.4% glutaraldehyde in 0.1 mol/L
PBS, pH 7.2, and processed according to a previously published
protocol.11
Blood samples (5 mL) were analyzed at KGH laboratories for creatine kinase–MB (CK-MB) (Technicon Immunol, Bayer Corporation) and cTnI (ACCESS system, Sanofi Diagnostics Pasteur SA) after initiation of bypass before clamping (time=0) and at 10 and 30 minutes and 3, 24, and 72 hours after cross-clamp removal. Aliquots of serum were retained and frozen at -70°C for further analysis.
Gel Electrophoresis and Western Blot
Analysis
Biopsy samples were homogenized in 25 µL of
homogenization buffer (100 mmol/L Tris-HCl, pH 6.8, 6 mol/L urea, 3.6
µmol/L leupeptin, 2.1 µmol/L pepstatin A, and 50 µmol/L
phenylmethylsulfonyl fluoride) at 4°C and boiled. Aliquots of
LVpre homogenate were dephosphorylated with
alkaline phosphatase conjugated to sepharose beads (Sigma) for 30
minutes at 37°C in 100 mmol/L Tris-HCl, 1 mmol/L magnesium chloride,
pH 7.5, according to the manufacturer’s protocol. All samples were
diluted 1:2 in sample buffer A (200 mmol/L Tris-HCl, 2% SDS, 20 mmol/L
dithiothreitol [DTT], and 0.05% bromophenol blue, pH 6.8), boiled,
and separated by 12.5% SDS-PAGE.
Serum samples (2 µL) were diluted 12.5-fold in sample buffer B (0.33% SDS, 0.33% CHAPS, 0.33% Nonidet NP-40, 0.1 mol/L DTT, 4 mol/L urea, and 50 mmol/L Tris-Cl, pH 6.8 in 50% glycerol), boiled, and separated by 12% SDS-PAGE (14 cmx14 cmx0.75 mm; 90 V for 5.5 hours).
All samples were transferred to nitrocellulose in 10 mmol/L CAPS (3-cyclohexylamino-1-propanesulfonic acid), pH 11.0 (27 V for 16 hours). Western blots were performed according to an established protocol1 with 8I-7, 3E3, and 3I-35, which are monoclonal anti-cTnI antibodies (MABs) (Spectral Diagnostics Inc) whose epitopes comprise human cTnI amino acid residues 136 to 154,1 1 to 54 (determined by protocol in Reference 11 ), and 175 to 199,1 respectively. In addition, MP, a rabbit polyclonal anti-peptide antibody raised in our laboratory against a synthetic peptide of human cTnI residues 193 to 209 (see method in Reference 1212 ), was used. The 8I-7 Western blots were quantified within the linear range as described previously,1 with the TnI products in each sample expressed as a percentage of the total amount of TnI in the sample.1 Competitive Western blotting with MAB 8I-7 in the presence or absence of recombinant hcTnI demonstrated that MAB 8I-7 is cTnI specific and that all immunoreactive bands are cTnI products (data not shown). The small biopsy size (50 µg) prevented absolute protein measurements, but the specificity of MAB 8I-7 suggests that quantification of cTnI products as a proportion of total cTnI is a viable measurement under these conditions. Measurement error was estimated at <2% by quantification of repeat samples, and changes were considered only if >2%. Significant differences in the amount of cTnI modification before versus after surgery were determined by paired 2-tailed nonparametric t tests. Differences between subgroups were determined by 2-tailed nonparametric t tests.
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Results |
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cTnI Is Specifically and Selectively Modified in Human Myocardium
To determine whether cTnI is modified in bypass patients in a similar manner to isolated rat heart, epicardial biopsy samples from bypass patients (n=37, Table 1
) were analyzed for cTnI by Western blot (MAB
8I-7,
Figure 1A). Biopsy samples were obtained from the inferior
or anterior right ventricle (RV) and anterolateral left ventricle (LV)
before application of cross-clamp (LVpre,
RVpre) and 10 minutes after cross-clamp removal
(LVpost, RVpost) from
regions of the heart remote to the coronary occlusions.
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cTnI was extensively modified into both degradation
products and covalent complexes
(Figure 1A
) in the myocardium of 
70% of bypass patients
(Table 2). In fact, many patients had modified cTnI products
in the myocardium even before application of the cross-clamp. A maximum
of 7 degradation products (molecular weight [MW] 22, 18, 16, 15, 12,
10, and 9 kDa; Deg 1 through Deg 7, respectively) and 3 covalent
complexes (MW 60, 50, and 40 kDa; Cov 1 through Cov 3, respectively)
(TnI MW 26 kDa by SDS-PAGE;
Figure 1A) were present. Competitive Western blotting with
recombinant cTnI confirmed that all immunoreactive bands were indeed
cTnI products (data not shown). Although the number and quantity of
cTnI modification products varied between patients, the products (when
present) were the same across all patients, which suggests that the
modification process is specific and selective. The particular products
Deg 1, Deg 2, and Deg 4, corresponding to MW 22, 18, and 15 kDa, were
the most abundant in individual patients
(Table 3) and were also seen most frequently across patients
(Table 2), and so they were considered the best candidates
for further analysis.
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Characterization of cTnI Modification
Products
The most prominent degradation products (Deg 1, Deg 2,
and Deg 4) were characterized in part through Western blotting with a
variety of anti-cTnI antibodies, with different epitopes on cTnI. An
LVpre biopsy sample (LV,
Figure 1B), both native and dephosphorylated by treatment
with alkaline phosphatase (LV-dephos,
Figure 1B), was analyzed with the anti-cTnI antibodies 8I-7,
3E3, 3I-35, and MP. 3E3 binds to the extreme N-terminus of cTnI, where
protein kinase A (PKA)–dependent and protein kinase C (PKC)–dependent
phosphorylations occur (serine residues 23 and 24 and serine residues
42 and 44, respectively), whereas 3I-35 and MP bind to the
extreme C-terminus, where cTnI is specifically proteolyzed in stunned
rat heart (amino acid residue 193 in rat, 192 in human).
Deg 1, Deg 2, and Deg 4 did not interact with MP or 3I-35,
and therefore these products likely have a C-terminal truncation in the
region of cTnI amino acid residue 192. Because all but 1 patient with
cTnI modification had Deg 1
(Table 2), Deg 1 likely represents the first, or initial,
degradation product with a C-terminal proteolytic cleavage.
The smaller cTnI degradation products were modified at both N-termini and C-termini, but each product was modified to different degrees. Dephosphorylation significantly increased the immunoreactivity of Deg 1, Deg 2, and Deg 4 to the anti-TnI antibody 3E3, which suggests phosphorylation at the PKA and/or PKC (amino acid residues 22 and 23 and residues 42 and 44, respectively) sites. Further characterization of the individual modification products is ongoing and will require extensive biochemical analysis.
cTnI Modification Is a Progressive
Process
To determine whether cTnI degradation in bypass
patients is ischemia/reperfusion dependent, the quantity of modified
cTnI in the myocardium was compared before versus after the cross-clamp
episode. Each modification product was quantified as a percentage of
the total amount of cTnI, in the same manner as previous reports in
isolated rat hearts.1 The
amount of intact cTnI remaining was therefore a direct (inverse)
measure of the total amount of modified cTnI. For example, if intact
cTnI represents 85% of total cTnI, then 15% of total cTnI is
posttranslationally modified. Therefore, increases in the proportion of
intact cTnI from 75% to 85% do not indicate increases in the absolute
amount (ie, micrograms) of intact cTnI but rather show that the
proportion of cTnI remaining intact has increased relative to total
cTnI. Interestingly, we found on average that there was no difference
between values before and after cross-clamp for any of the cTnI
modification products (including intact cTnI, data not shown). However,
on an individual level, most patients (60%) did experience a change in
cTnI modification during cross-clamp, but the changes varied
extensively
(Figure 2), comprising 3 subgroups of patients: those who
experienced an increase in degradation after surgery
(Figure 2 A and D; n=10), those who experienced a decrease in
degradation after surgery
(Figure 2 B and E; n=12), and those who experienced no change
after surgery (change <2%,
Figure 2C; n=10). Before cross-clamp, patients who
experienced an increase in cTnI modification with surgery were
equivalent to those who did not experience a change
(Table 3), but patients who experienced a decrease in
modification with surgery initially demonstrated extensive modification
(P<0.05,
Table 3). During cross-clamp, increases or decreases in
cTnI modification, when they occurred, were significant
(P<0.05,
Table 3). After cross-clamp removal, differences between
subgroups did not reach significance
(Table 3).
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To determine whether the loss of degradation products in a
subset of patients
(Figure 3, B and E;
Table 3) results from necrotic release, serum cTnI was
observed by 2 methods: the diagnostic kit used by KGH laboratories
(ACCESS, Sanofi Diagnostics, Pasteur SA) and a newly developed SDS-PAGE
methodology for the electrophoretic separation and immunoblot
visualization of serum proteins. Under normal SDS-PAGE conditions,
serum albumin overwhelms all other proteins on the blot (owing to its
high concentration) and interferes with the proper separation of
lower-abundance proteins such as cTnI and CK-MB. Through the use of a
combination of detergents, the effect of albumin on the separation of
lower-abundance and lower-MW proteins is minimized.
Figure 3 shows serum cTnI (and CK-MB) release profiles as
detected by diagnostic kit
(Figure 3A) and by an anti-cTnI Western blot using our new
approach (2 µL of serum per lane), with the diagnostic kit cTnI
values given below the blot
(Figure 3B) (note: 0 minutes indicates measurement taken
before cross-clamp). Although both methods clearly show a postoperative
rise in total serum cTnI, our new methodology demonstrates that cTnI
modification products are present in addition to intact cTnI, including
a degradation product similar to Deg 1. Surprisingly, cTnI was detected
in a presurgery serum sample (0 minutes) at levels below the detection
limit of the diagnostic kit.
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Serum cTnI and CK-MB release, however, cannot be directly
attributed to specific myocardial regions and may not reflect the local
environment of the biopsy samples. Therefore, 3 additional patients
were recruited, and the biopsy samples were analyzed by EM
(Figure 4). Cardiac muscle fibers in both longitudinal and
cross-sectional orientations were examined. In general, all ventricular
samples examined showed normal ultrastructure, and there were no
detectable differences before versus after cross-clamp. Many muscle
fibers showed a serrated sarcolemma
(Figure 4A). Bundles of myofibrils were arranged along the
length of each muscle fiber and interspersed with numerous mitochondria
(Figure 4B). Within each myofibril, thin and thick
myofilaments were organized into typical sarcomeres; however, the I
bands of nearly all muscle fibers examined were in a contracted stage,
rendering them invisible unless the fibers were cut in cross section.
Intercalated disks were found adjoining adjacent muscle fibers
(Figure 4A), and gap junctions were located at the
longitudinal portion of the sarcolemma of adjacent myocytes
(Figure 4C). Overall, this suggests that at least 1
subpopulation of patients does not experience necrosis either before or
after cross-clamp. However, measurements of regional function in the
area of biopsy and biochemical analysis on EM-analyzed samples were not
performed, which prevents any conclusive determinations regarding cTnI
degradation in myocardial stunning.
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Discussion |
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TopAbstractIntroductionMethodsResultsDiscussionReferences |
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The specific and selective posttranslational modification of cTnI has been proposed to play an important role in the contractile dysfunction observed in stunned and ischemia/reperfused myocardium.1 2 3 4 5 6 However, in vivo swine and canine models of stunning have failed to demonstrate the ischemia-dependent cTnI degradation observed in isolated rat heart models.9 10 Thus, demonstrating selective and progressive ischemia/reperfusion-dependent modification of cTnI in human disease is of fundamental importance.
Previously, we demonstrated that cTnI is specifically modified in the myocardium of 2 bypass patients, without modification to other myofilament proteins (actin and the regulatory myosin light chain).8 In the present study, analysis of myocardial biopsy samples from 37 bypass patients demonstrated that cTnI is modified in a selective and progressive manner, both before and after cross-clamp. Importantly, myocardial cTnI is degraded in approximately two thirds of patients before cross-clamp, when there is little or no cell necrosis at the site of the biopsy. This is the first study to demonstrate ischemia-dependent TnI modification in human myocardium.
The first, or initial, degradation product in bypass patients (Deg 1) is similar in MW (22 kDa) and immunogenicity to the C-terminal degradation product found in stunned rat myocardium. In the isolated rat heart, this product has been identified as cTnI1–193, resulting from proteolytic cleavage of 17 C-terminal amino acids.1 This suggests that ischemia/reperfusion activates similar processes (ie, the activation of Ca2+-dependent proteases) in both rats and bypass patients.
The presence of modified cTnI in the myocardium of so many
patients before application of cross-clamp, which suggests myocardial
injury (possibly stunning) in "normally" perfused myocardium, is
both intriguing and unexpected. This basal level of modified cTnI may
result from 2 processes: (1) undetected prior or ongoing disease, not
necessarily directly resulting from the repaired coronary occlusions;
and (2) pre–cross-clamp myocardial damage resulting from surgical
preparation (including anesthetic influences). The relative influence
of these 2 processes cannot be established at this time; however, it is
known that anesthetics such as halothanes can modulate myocardial
preconditioning in animal
models.13 14 On
the other hand, all patients had preexisting cardiac diseases,
including previous myocardial infarction, or cardiovascular risk
factors such as smoking and hypertension
(Table 1). The overall profile of proteins in the damaged or
diseased myocyte, known as its proteome, likely comprises a spectrum of
protein modifications resulting from numerous overlapping disease
processes, drug therapies, and surgical interventions in any given
patient.
cTnI modification did not change systematically across all patients with bypass surgery. However, particular patient populations, of undetermined clinical characteristics but representing two thirds of bypass patients, experienced ischemia/reperfusion-dependent changes in the amount of modified cTnI, with some patients experiencing an increase in cTnI modification and others experiencing a decrease. The extent of cTnI modification present in the myocardium before cross-clamp may influence the change observed. A larger prospective study will be necessary to address the role of specific preexisting and surgical conditions on the progression of cTnI modification.
Our ability to detect cTnI and its modification products in the serum of bypass patients, even at levels below detection limits of the ACCESS diagnostic kit, suggests that some cTnI modification products are released from dead and/or dying cardiomyocytes after bypass surgery. If the amount of cTnI modification in the myocardium reflects the progress of myocardial ischemia/reperfusion injury, then the presence of modified cTnI products in the serum may prove useful in the risk stratification of patients with coronary syndromes. From a diagnostic perspective, the most useful biomarkers are those that are key to the phenotypic expression of the cardiac disease, especially in the design of a marker that might indicate functional prognosis. Indeed, cTnI (along with cTnT) has already proved to be an excellent organ-specific marker of myocardial damage.15
Determining whether these patients experience stunned
myocardium is not trivial. The key lies in 2 factors: (1) myocardial
contractile dysfunction and (2) the absence of myocardial necrosis. All
of these patients experienced some degree of myocardial dysfunction
stemming from coronary artery disease, as evidenced by depressed LV
ejection fraction
(Table 1). EM analysis suggests that the myocardium at the
biopsy site was not necrotic in a subset of patients, either before or
after aortic cross-clamp, and none of the patients had detectable serum
cTnI before cross-clamp. However, without assessments of regional
function in the biopsy site or biochemical analysis of EM-analyzed
samples, conclusive statements about the presence of stunned myocardium
cannot be made. Despite shortcomings, these results suggest that many
bypass patients experience cTnI modification in the absence of necrosis
before cross-clamp, whereas after cross-clamp, subsets of patients
experience either no necrosis or necrotic loss of cellular contents,
depending on the extent of TnI modification present in the myocardium
before
cross-clamp.
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Acknowledgments |
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This work was supported by grants from The Heart and Stroke Foundation of Canada (grant-in-aid No. T-3759, Dr Van Eyk), The Medical Research Council of Canada (grant-in-aid No. MT-14375, Dr Van Eyk), the National Institutes of Health (United States, Dr Van Eyk), and the Swiss National Science Foundation (grant 32-49126.96, Dr Atar), as well as a Heart and Stroke Foundation of Canada research scholarship (Dr Van Eyk) and research traineeship (J.L. McDonough). The authors would like to thank Spectral Diagnostics (Toronto, Canada) for anti-cTnI monoclonal antibodies; Dr Anne Murphy, Pediatric Cardiology, The Johns Hopkins University, for advice; and John DaCosta for his assistance in processing and sectioning cardiac tissue samples.
Received June 21, 2000; revision received August 11, 2000; accepted August 14, 2000.
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V. L.J.L. Thijssen, J. Ausma, L. Gorza, H. M.W. van der Velden, M. A. Allessie, I. C. Van Gelder, M. Borgers, and G. J.J.M. van Eys Troponin I Isoform Expression in Human and Experimental Atrial Fibrillation Circulation, August 17, 2004; 110(7): 770 - 775. [Abstract] [Full Text] [PDF]
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D. A Colantonio, J. E Van Eyk, and K. Przyklenk Stunned peri-infarct canine myocardium is characterized by degradation of troponin T, not troponin I Cardiovasc Res, August 1, 2004; 63(2): 217 - 225. [Abstract] [Full Text] [PDF]
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C. Chen-Scarabelli, T. M. Scarabelli, J. B. Selvanayagam, S. E. Petersen, J. M. Francis, M. D. Robson, A. Kardos, S. Neubauer, and D. P. Taggart Myocardial Injury and Cardiac Troponin I Release After Off-Pump Versus On-Pump Coronary Surgery * Response Circulation, July 27, 2004; 110(4): e36 - e36. [Full Text] [PDF]
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J. H.C. Diris, C. M. Hackeng, J. P. Kooman, Y. M. Pinto, W. T. Hermens, and M. P. van Dieijen-Visser Impaired Renal Clearance Explains Elevated Troponin T Fragments in Hemodialysis Patients Circulation, January 6, 2004; 109(1): 23 - 25. [Abstract] [Full Text] [PDF]
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S. B. Marston and C. S. Redwood Modulation of Thin Filament Activation by Breakdown or Isoform Switching of Thin Filament Proteins: Physiological and Pathological Implications Circ. Res., December 12, 2003; 93(12): 1170 - 1178. [Abstract] [Full Text] [PDF]
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D. B. Foster, T. Noguchi, P. VanBuren, A. M. Murphy, and J. E. Van Eyk C-Terminal Truncation of Cardiac Troponin I Causes Divergent Effects on ATPase and Force: Implications for the Pathophysiology of Myocardial Stunning Circ. Res., November 14, 2003; 93(10): 917 - 924. [Abstract] [Full Text] [PDF]
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P. Ping Identification of Novel Signaling Complexes by Functional Proteomics Circ. Res., October 3, 2003; 93(7): 595 - 603. [Abstract] [Full Text] [PDF]
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A. Lavoinne, B. Cauliez, H. Eltchaninoff, C. Tron, and A. Cribier Release of Macromolecular Cardiac Troponin I Complex after Successful Percutaneous Transluminal Coronary Angioplasty in Acute Myocardial Infarction Clin. Chem., March 1, 2003; 49(3): 505 - 507. [Full Text] [PDF]
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A. van der Laarse Hypothesis: troponin degradation is one of the factors responsible for deterioration of left ventricular function in heart failure Cardiovasc Res, October 1, 2002; 56(1): 8 - 14. [Abstract] [Full Text] [PDF]
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O. Zeitz, A. E. Maass, P. Van Nguyen, G. Hensmann, H. Kogler, K. Moller, G. Hasenfuss, and P. M.L. Janssen Hydroxyl Radical-Induced Acute Diastolic Dysfunction Is Due to Calcium Overload via Reverse-Mode Na+-Ca2+ Exchange Circ. Res., May 17, 2002; 90(9): 988 - 995. [Abstract] [Full Text] [PDF]
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D. A. Colantonio, W. Pickett, R. J. Brison, C. E. Collier, and J. E. Van Eyk Detection of Cardiac Troponin I Early after Onset of Chest Pain in Six Patients Clin. Chem., April 1, 2002; 48(4): 668 - 671. [Full Text] [PDF]
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R. C. Payne, B. I. Bluestein, D. L. Morris, R. Labugger, L. Organ, C. Collier, J. E. Van Eyk, and D. Atar Extensive Troponin I and T Modification Detected in Serum From Patients With Acute Myocardial Infarction Response Circulation, July 31, 2001; 104 (5): e26 - e27. [Full Text] [PDF]
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J. Feng, B. J. Schaus, J. A. Fallavollita, T.-C. Lee, and J. M. Canty Jr Preload Induces Troponin I Degradation Independently of Myocardial Ischemia Circulation, April 24, 2001; 103(16): 2035 - 2037. [Abstract] [Full Text] [PDF]
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S.-J. Kim, R. K. Kudej, A. Yatani, Y.-K. Kim, G. Takagi, R. Honda, D. A. Colantonio, J. E. Van Eyk, D. E. Vatner, R. L. Rasmusson, et al. A Novel Mechanism for Myocardial Stunning Involving Impaired Ca2+ Handling Circ. Res., October 26, 2001; 89(9): 831 - 837. [Abstract] [Full Text] [PDF]
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