ИСТИНА

Ternary troponin complex consists of three proteins: troponin I (TnI), troponin T (TnT) and troponin C (TnC). Cardiac isoforms of TnT (cTnT) and TnI (cTnI) that are expressed exclusively in heart are actively used as biomarkers of heart disorders. Heparin is a highly negatively charged polysaccharide that is used to prevent blood coagulation in the treatment of acute myocardial infarction (AMI) and to prepare heparin plasma samples used for immunodiagnostics. The work aimed to study the interaction of heparin with ternary cTnI­cTnT­TnC complex (ITC) and its effect on the immunochemical determination of cardiac troponins. To reach the goal, we spiked ITC, сTnI­TnC complex (IC) or free cTnT to normal heparin and citrate plasmas and analyzed the samples by gel­filtration (GF). In resulting profiles, the peaks of ITC and free cTnT but not IC shifted to a higher molecular weight region in heparin plasma compared to citrate plasma. In the GF profiles of heparin and citrate plasma samples of AMI patients, the peak of the full­size ITC also shifted to a higher molecular weight region in heparin plasma whereas peaks of the low­molecular weight (LMW) ITC eluted in the same volume in heparin and citrate plasmas. Since LMW ITC contains only a C­terminal fragment of TnT, we conclude that heparin binds to cTnT via its N­terminal and/or central part of the molecule. The recovery of spiked ITC and free cTnT by some antibodies specific to cTnT was significantly lower in heparin plasma than in citrate plasma samples, which may indicate the sites of heparin binding. We identified four regions of cTnT that are affected by heparin, and antibodies specific to these regions should be carefully checked prior to use in immunochemical tests. To sum up, here we show that the binding of heparin to ITC is due to the interaction of heparin with N­ and/or central part of cTnT in ITC and these interactions may have a profound effect on the immunochemical detection of cTnT.