Determination of Cardiac Troponin I Forms in the Blood of Patients with Acute Myocardial Infarction and Patients Receiving Crystalloid or Cold Blood Cardioplegia

Abstract

To determine the forms of cardiac troponin I (cTnI) circulating in the bloodstream of patients with acute myocardial infarction (AMI) and patients receiving a cardioplegia during heart surgery, we developed three immunoenzymatic sandwich assays. The first assay involves the combination of two monoclonal antibodies (mAbs) specific for human cTnI. The second assay involves the combination of a mAb specific for troponin C (TnC) and an anti-cTnI mAb. The third assay was a combination of a mAb specific for human cardiac troponin T (cTnT) and an anti-cTnI mAb. Fifteen serum samples from patients with AMI, 10 serum samples from patients receiving crystalloid cardioplegia during heart surgery, and 10 serum samples from patients receiving cold blood cardioplegia during heart surgery were assayed by the three two-site immunoassays. We confirmed that cTnI circulates not only in free form but also complexed with the other troponin components (TnC and cTnT). We showed that the predominant form in blood is the cTnI-TnC binary complex (IC). Free cTnI, the cTnI-cTnT binary complex, and the cTnT-cTnI-TnC ternary complex were seldom present, and when present, were in small quantities compared with the binary complex IC. Similar results were obtained in both patient populations studied. These observations are essential for the development of new immunoassays with improved clinical sensitivity and for the selection of an appropriate cTnI primary calibrator.

Fetal Cardiac Troponin I in Relation to Intrapartum Events and Umbilical Artery pH

“…It is unlikely that cardiac troponin I crosses the placenta, given its molecular weight of 24,000 kd and the fact that it exists in the circulation predominantly as a binary complex. 12 No data exist describing placental production of cardiac troponin I, and its specificity for cardiac muscle, as distinct from vascular smooth muscle, would make this improbable. It therefore seems likely that the cardiac troponin I levels measured in this study are the result of endogenous fetal production.…”

Biochemical markers of myocardial injury

“…The maximal amount of free cTnI was released shortly after the injury. The presence of cTnI/ cTnT complex has also been demonstrated, 43 although in very small amounts. In blood, it is probable that the T/I/C complex dissociates with time into free cTnT and I/C complex.…”

The Diagnostic Value of Biochemical Cardiac Markers in Acute Myocardial Infarction

“…Recent studies have found that in patients after AMI the predominant form of cTnI exhibited in blood is the binary troponin IC complex with slight concentrations of ternary ITC complex, binary IT complex and free cTnI [82][83][84][85]. The release pattern of these forms in MI is still under investigation.…”