Development of Immunochemical Systems for Detection of Human Skeletal Troponin I Isoforms

Troponin I (TnI), together with troponin T (TnT) and troponin C (TnC), forms the troponin complex, a thin filament protein of the striated muscle that plays a key role in regulation of muscle contraction. In humans, TnI is represented by three isoforms: cardiac, which is synthesized only in myocardium, and fast and slow skeletal, which are synthesized in fast- and slow-twitch muscle fibers, respectively. Skeletal TnI isoforms could be used as biomarkers of skeletal muscle damage of various etiologies, including mechanical trauma, myopathies, muscle atrophy (sarcopenia), and rhabdomyolysis. Unlike classical markers of muscle damage, such as creatine kinase or myoglobin, which are also present in other tissues, skeletal TnIs are specific for skeletal muscle. In this study, we developed a panel of monoclonal antibodies for immunochemical detection of skeletal TnI isoforms using Western blotting (sensitivity: 0.01-1 ng per lane), immunohistochemical assays, and fluorescence immunoassays. Some of the designed fluorescence immunoassays enable quantification of fast skeletal (limit of detection [LOD] = 0.07 ng/mL) and slow skeletal (LOD = 0.1 ng/mL) TnI isoforms or both isoforms (LOD = 0.1 ng/ml). Others allow differential detection of binary (with TnC) or ternary (with TnT and TnC) complexes, revealing composition of troponin forms in the human blood.