Multi‐Site Coronary Vein Sampling Study on Cardiac Troponin T Degradation in Non–ST‐Segment–Elevation Myocardial Infarction: Toward a More Specific Cardiac Troponin T Assay

Abstract

Background Cardiac troponin T ( cTnT ) is seen in many other conditions besides myocardial infarction, and recent studies demonstrated distinct forms of cTnT . At present, the in vivo formation of these different cTnT forms is incompletely understood. We therefore performed a study on the composition of cTnT during the course of myocardial infarction, including coronary venous system sampling, close to its site of release. Methods and Results Baseline samples were obtained from multiple coronary venous system locations, and a peripheral artery and vein in 71 non– ST ‐segment–elevation myocardial infarction patients. Additionally, peripheral blood was drawn at 6‐ and 12‐hours postcatheterization. cTnT concentrations were measured using the high‐sensitivity‐ cTnT immunoassay. The cTnT composition was determined via gel filtration chromatography and Western blotting in an early and late presenting patient. High‐sensitivity ‐ cTnT concentrations were 28% higher in the coronary venous system than peripherally (n=71, P <0.001). Coronary venous system samples demonstrated cT n T‐I‐C complex, free intact cTnT , and 29 kD a and 15 to 18 kD a cTnT fragments, all in higher concentrations than in simultaneously obtained peripheral samples. While cT n T‐I‐C complex proportionally decreased, and disappeared over time, 15 to 18 kD a cTnT fragments increased. Moreover, cT n T‐I‐C complex was more prominent in the early than in the late presenting patient. Conclusions This explorative study in non– ST ‐segment–elevation myocardial infarction shows that cTnT is released from cardiomyocytes as a combination of cT n T‐I‐C complex, free intact cTnT , and multiple cTnT fragments indicating intracellular cTnT degradation. Over time, the cT n T‐I‐C complex disappeared because of in vivo degradation. These insights might serve as a stepping stone toward a high‐sensitivity‐ cTnT immunoassay more specific for myocardial infarction.

Molecular signatures of myocardial infarction

“…The composition of circulating cTnT after MI has been previously described [20][21][22][23][24], showing the presence of intact cTnT, either as part of the ternary cTn T-I-C complex or as a free form, and two fragments (29 kDa and 15-18 kDa, respectively) (Figure 1.2B). Also, it was observed that the cTnT conformation changed over time [20,23]. On the other hand, in patients with end-stage renal disease (ESRD) only the smaller fragments (15-18 kDa) were observed [25].…”

“…NSTEMI patients as part of the TRAMICI study (n=71, Transcardiac Assessment of Myocardial Injury and Coronary Inflammation) were selected for the present study based on previously described criteria [23,243]. For an in-depth analysis, two patients with a culprit lesion in the left anterior descending coronary artery were selected: one with the shortest time interval between symptom onset and study procedure (patient 1); and another with the longest time interval (patients 2).…”

“…The molecular cTnI forms were separated using GFC, as was previously described for cTnT [23]. In short, GFC was performed on the AKTA Prime Plus (GE Healthcare, Chicago, Illinois, USA), equipped with a HiPrep TM 16/60 Sephacryl TM S-300 HR column (#17-1167-01, GE Healthcare).…”

“…For each purified standard, 0.25 mL was loaded on the GFC column, 83 fractions of 1 mL were collected and kept on ice until hs-cTnI measurement. This was similar for NSTEMI patients, though fractions were stored at -80 °C for further analysis with one freeze-thaw cycle [23]. For ESRD patients and marathon runners 1.0-2.0 mL serum was loaded on the GFC column, 70 fractions of 1.25 mL were collected and stored at -80 °C [25,236].…”

“…To further validate the cTnI composition, Western blotting (WB) was performed as described before [23]. In short, samples and Precision Plus Protein molecular weight marker were loaded on 12% criterion XT precast gel and run for 60 min.…”