Development of immunochemical systems for detection of human skeletal troponin i isoforms

Troponin I (TnI), together with troponin T and troponin C (TnC), forms the troponin complex, a thin filament protein of the striated muscle that plays a key role in the regulation of muscle contraction. In humans, TnI is represented by three isoforms: cardiac, which is synthesised only in the myocardium, and fast and slow skeletal, which are synthesised in fast- and slow-twitch muscle fibres, respectively. Skeletal TnI isoforms can be used as biomarkers of skeletal muscle damage of various aetiologies, 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 in Western blotting (sensitivity: 0.01-1 ng per lane), in immunohistochemistry, and in fluorescence immunoanalysis. Some of the designed fluorescence immunoanalyses enable the quantification of fast skeletal (limit of detection [LOD]=0.07 ng/mL) and slow skeletal TnI (LOD=0.1 ng/mL) or both isoforms (LOD=0.1 ng/ml). Others allow the differential detection of binary (with TnC) or ternary (with troponin T and TnC) complexes, revealing the composition of troponin forms in human blood.