Cardiac myosin-binding protein-C: assessing fragmentation patterns to differentiate between forms of myocardial injury

Abstract

Abstract Background Cardiac myosin-binding protein-C (cMyC) is a novel biomarker of myocardial injury. We hypothesize that fragmentation of cMyC differs according to aetiology of myocardial injury. Assessing the fragmentation pattern of the protein may aid diagnosis of these conditions. Purpose This work represents an examination of cMyC fragmentation in human serum, and studies its utility in differentiating between forms of myocardial injury. Methods Patients who were admitted to a hospital during October-November 2023 with acute myocardial injury were recruited. Acute myocardial injury was defined as a dynamic troponin rise above the 99th centile (Abbott Alinity: cTnI>34ng/L male, cTnI >16ng/L female). Following collection, samples were left at room temperature for 30 minutes and then centrifuged. Serum was separated for cMyC measurement, frozen in liquid nitrogen and stored at -80 °C. Recruited patients were followed up during their inpatient journey. Their final diagnosis was defined using the 4th universal definition of MI by two cardiologists, with a third cardiologist acting as adjudicator, if required. The serum samples were analysed using two separate electrochemiluminescence sandwich ELISA assays detecting different portions of cMyC. One assay formulated for total concentration of cMyC using high affinity mouse N-terminal monoclonal antibodies (mAb) targeting epitopes in close proximity (Limit of Detection (LoD) = 9.0ng/L). The other assay uses a N-terminal and a C-terminal mouse mAb which straddle the major proteolytic cleavage site of cMyC. This assay detects the intact (fuller-length) cMyC (LoD= 14.2ng/L). Both assays perform with good sensitivity, low variability and are capable of detecting cMyC at concentrations well below the 99th centile. Results 11 patient samples were collected with final diagnoses of; type 1 MI (STEMI n=3, NSTEMI n=4), type 4 MI (alcohol septal ablation n=1), acute myocardial injury (myocarditis n=2) and type 2 MI (chest sepsis with known coronary disease n=2). Figure one details the percentage of intact cMyC relative to total cMyC measured in serum for each patient, and is split into their adjudicated diagnosis. The bars display the median and interquartile range (IQR). Our findings suggest that the fragmentation pattern of cMyC could help differentiate between forms of myocardial injury. The ratio of intact: total cMyC was higher in the type 2 MI than any other condition. The results did not reach statistical significance (p = 0.06) due to the small sample size. Conclusions The fragmentation pattern of cMyC is dependent on the type of myocardial injury and could aid in the differentiation between type 2 MI and other forms of myocardial injury.Figure One