Extensive troponin I and T modification detected in serum from patients with acute myocardial infarction

Background-Cardiac troponin I and T (cTnI and cTnT) are specific biochemica l serum markers for acute myocardial infarction (AMI). However, cTnI diagno stic assays are plagued by difficulties, resulting in greater than or equal to 20-fold differences in measured values. These discrepancies may result from the release of the numerous cTnI modification products that are presen t in ischemic myocardium. The resolution of these discrepancies requires an investigation of the exact forms of cTnI present in the bloodstream of pat ients after myocardial injury. Methods and Results-A western blot-direct serum analysis protocol was devel oped that allowed us to detect intact cTnI and a spectrum of up to 11 modif ied products in the serum from patients with AMI. For the first time, we do cument both a cTnI degradation pattern and the existence of phosphorylated cTnT, in serum. The number and extent of these modifications reflect patter ns similar to the time profiles of the routine clinical serum markers of to tal creatine kinase, creatine kinase-MB, and cTnI (determined by ELISA). Da ta from in vitro experiments, which were undertaken to study the degradatio n of human recombinant cTnI and cTnT when spiked in serum, indicate that so me modification products present in patient serum existed in the myocardium and that recombinant cTnI alteration dramatically reduces the detectabilit y of cTnI by the Immunol assay over time (our assay was unaffected). Conclusions-This pilot study defines, for the first time, what forms of cTn I and cTnT appear in the bloodstream of AMI patients, and it clarifies the lack of standardization between different cTnI diagnostic assays.