Myocardial infarct size by serum troponin T and myosin light chain 1 concentration

Combined subthreshold dose inhibition of myosin light chain phosphorylation and MMP-2 activity provides cardioprotection from ischaemic/reperfusion injury in isolated rat heart

BACKGROUND AND PURPOSE

Phosphorylation and degradation of myosin light chain 1 (MLC1) during myocardial ischaemia/reperfusion (I/R) injury is a well-established phenomenon. It has been established that MMP-2 is involved in MLC1 degradation and that this degradation is increased when MLC1 is phosphorylated. We hypothesized that simultaneous inhibition of MLC1 phosphorylation and MMP-2 activity will protect hearts from I/R injury. As phosphorylation of MLC1 and MMP-2 activity is important for normal heart function, we used a cocktail consisting combination of low (subthreshold for any protective effect alone) doses of MLC kinase, MMP-2 inhibitors and subthreshold dose of an MLC phosphatase activator.

EXPERIMENTAL APPROACH

Isolated rat hearts were subjected to 20 min of global, no-flow ischaemia and 30 min reperfusion in the absence and presence of inhibitors of MLC1 phosphorylation and degradation.

KEY RESULTS

The recovery of cardiac function was improved in a concentration-dependent manner by the MLC kinase inhibitor, ML-7 (1-5 μM), the MLC phosphatase activator, Y-27632 (0.05-1 μM) or the MMP inhibitor, doxycycline (Doxy, 1-30 μM). Co-administration of subthreshold doses of ML-7 (1 μM) and Y-27632 (0.05 μM) showed a potential synergistic effect in protecting cardiac contractility and MLC1 levels in I/R hearts. Further combination with a subthreshold concentration of Doxy (1 μM) showed additional protection that resulted in full recovery to control levels.

CONCLUSIONS AND IMPLICATIONS

The results of this study exemplify a novel low-dose multidrug approach to pharmacological prevention of reperfusion injury that will enable a reduction of unwanted side effects and/or cytotoxicity associated with currently available MMP-2 and kinase inhibiting drugs.

Unspecific elevation of plasma troponin-T and CK-MB after coronary surgery

OBJECTIVE

Biochemical markers of myocardial injury are frequently elevated after cardiac surgery. It is generally accepted that release unrelated to permanent myocardial damage explains a proportion of these elevations. However, little is known about the magnitude and temporal characteristics of this diagnostic noise. One way to address this issue would be to study a group without permanent myocardial injury.

DESIGN

The unique release kinetics of troponin-T (permanent myocardial injury causes a sustained release of structurally bound troponin) were used to identify patients with no or minimal permanent myocardial injury. Blood was sampled from patients undergoing coronary artery bypass grafting (CABG) with cardiopulmonary bypass (CPB) before surgery, 3 and 8 h after unclamping the aorta, and each morning until postoperative day 4, for analysis of enzymes and troponin-T. From 302 consecutive patients a subgroup was identified that fulfilled the following criteria: (a) normalized troponin-T levels < or = postoperative day 4; (b) no ECG changes indicating myocardial injury.

RESULTS

Seventy-seven patients fulfilled the criteria above and in this subgroup troponin-T (2.08 +/- 1.42 microg/l; range 0.35-8.99 microg/l) peaked at the 3 h recording and creatine kinase monobasic (CK-MB) (28.6 +/- 11.3 microg/l; range 11.9-86.0 microg/l) peaked at the 8 h recording after unclamping the aorta.

CONCLUSION

Substantial early elevations of plasma CK-MB and troponin-T occurred in patients with no or minimal permanent myocardial injury after CABG. Unspecific release was most pronounced during the timeframe that is usually studied to evaluate myocardial protective strategies or to compare revascularization procedures.

Test strategies for the detection of myocardial damage

In the space of half a century, cardiac marker testing has advanced incrementally from enzymes present in nearly all tissues to proteins having remarkable specificity for myocardium. Markers with other desirable properties, such as earlier release, have also been introduced and others may be anticipated, although a single perfect marker is not on the horizon. Optimum application of these new markers still requires improved robustness and harmonization of commercial assays, and continuing insights in the pathophysiology of acute coronary syndromes. As these advances occur, future testing will likely focus more on therapeutic decisions than on arbitrary diagnostic classifications.

Early identification of permanent myocardial damage after coronary surgery is aided by repeated measurements of CK-MB

OBJECTIVE

ECG diagnosis of myocardial infarction after cardiac surgery is associated with major pitfalls and enzyme diagnosis is interfered by unspecific elevation unrelated to permanent myocardial injury. Sustained release of troponin-T is a marker of permanent myocardial injury if renal function is maintained. However, early identification of perioperative myocardial infarction is desirable and therefore the usefulness of creatine kinase monobasic (CK-MB) kinetics to detect myocardial injury early after coronary surgery was investigated.

DESIGN

Two hundred and eighty-six patients undergoing coronary surgery were studied with respect to release of enzymes and troponin-T preoperatively and postoperatively 3 and 8 h after unclamping the aorta, and every morning postoperative days 1-4.

RESULTS

CK-MB peak was found at 3 h (n = 145), 8 h (n = 103) and 16-20 h after unclamping (n = 38). Depending on when the CK-MB peak was recorded different demographic and perioperative characteristics were found. A sustained release of troponin-T was characteristic for the group with the CK-MB peak at 16-20 h after unclamping.

CONCLUSION

If CK-MB is measured only once it may be advisable to do it on the first postoperative morning as these measurements provided the best discrimination between patients with and without sustained elevation of troponin-T. However, repeated sampling provides additional information that aids in the early identification of permanent myocardial injury particularly in patients with borderline elevations of CK-MB.

Reduction of myocardial infarct size with sCR1sLe(x), an alternatively glycosylated form of human soluble complement receptor type 1 (sCR1), possessing sialyl Lewis x

1 This study investigated the effects of soluble complement receptor type 1 (sCR1) or sCR1sLex, agents which function as a complement inhibitor or as a combined complement inhibitor and selectin adhesion molecule antagonist, respectively, on the infarct size and cardiac troponin T (cTnT) release caused by regional myocardial ischaemia and reperfusion in the rat. 2 Eighty-two, male Wistar rats were subjected to 30 min occlusion of the left anterior descending coronary artery (LAD) followed by 2 h of reperfusion. Haemodynamic parameters were continuously recorded and at the end of the experiments infarct size (with p-nitro-blue tetrazolium) and cTnT release were determined. 3 Infusion of sCR1 (1, 5 or 15 mg kg-1, each n=7) or sCR1sLe(x) (1, 5 or 15 mg kg-1, n=7, 13 or 13, respectively) 5 min prior to LAD-reperfusion caused a reduction in infarct size from 59+/-2% (PBS - control, n=12) to 46+/-6%, 25+/-9% and 37+/-6% or 42+/-6%, 35+/-6% and 35+/-4%, respectively. 4 Infusion of sCR1 (15 mg kg-1, n=5) or sCR1sLe(x) (15 mg kg-1, n=5) also reduces the myocardial TnT release from 80+/-20 ng ml-1 (control) to 13+/-7 or 4+/-1 ng ml-1, respectively. 5 Thus, sCR1 or sCRsLe(x) significantly reduce infarct size and cardiac TnT release caused by 30 min of regional myocardial ischaemia and 2 h of reperfusion in the rat. The mechanisms of the cardioprotective effects of sCR1 or sCR1sLe(x) are not entirely clear, but may be due complement inhibition and/or prevention of the adhesion and activation of neutrophils.

Comparison of troponin-I and troponin-T after pediatric cardiovascular operation

BACKGROUND

Although the diagnostic value of troponin-T in childhood is documented, little is known about the significance of troponin-I. It was the aim of this study to compare the diagnostic value of troponin-I and troponin-T in children and newborns to assess the perioperative potential myocardial damage.

METHODS

Forty-eight children, mean, 51+/-54 months (mean value +/-1 standard deviation) (range, 1 day to 204 months) undergoing cardiac operation were prospectively enrolled in the present study. Troponin-I, troponin-T, creatine kinase (CK), and the MB isoenzyme were measured before operation and postoperatively within 2 days.

RESULTS

Postoperative values of troponin-I for children undergoing extracardiac operation were in the normal range. In children with interventions through the right atrium (n = 10) the mean value increase to 6.5+/-6.1 microg/L (range, 1.8 to 24.3 microg/L) and even to a mean of 29.9+/-21.1 microg/L (range, 7.5 to 90 microg/L) (p<0.01) in children with atrial and additional ventricular surgical approach (n = 23). Troponin-I was of equal specificity and sensitivity compared to troponin-T, excepted in patients with postoperative renal failure in whom troponin-T raised to false pathological results.

CONCLUSIONS

For detection of perioperative myocardial damage troponin-I shows a higher specificity than CK-MB activity and CK-MB mass. The diagnostic value of troponin-I is similar to troponin-T, but compared with troponin-T, it has the advantage of not being influenced by renal failure.

Troponin-T: improved diagnostic assessment of myocardial damage in childhood

Troponin-T (cTnT) as a marker of myocardial damage is well established in adults, but not yet in children. cTnT was measured in 85 children (aged 1 day-204 months, mean 46 months). Twenty-five children were non-surgical patients, with possible myocardial damage suspected on clinical grounds. The other 60 patients had cardiac surgery leading to a defined myocardial damage. In these children, troponin-T (cTnT), creatine kinase activity (CK), creatine kinase-MB activity (CK-MB), and creatine kinase-MB-Mass (CK-MB-Mass) were measured preoperatively and 3-4 times during the first 55 postoperative h. Except in four children with probable preoperative myocardial damage, all troponin-T values were in the normal range (< 0.1 microg/l). All children with intracardiac surgery showed a postoperative increase in troponin-T. Children with extracardiac surgery of the great vessels showed no postoperative increase of troponin-T. For the assessment of myocardial damage, troponin-T was more specific and more sensitive than the other markers tested, troponin-T might significantly improve the diagnostic assessment of myocardial damage in children.

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.