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Departments of
1
Physiology,
2 Pathology, and
3 Biochemistry, Queens University, Kingston, Ontario, K7L 3N6 Canada
4 Kingston General Hospital, Kingston, Ontario, K7L 3N6 Canada.
aAddress correspondence to this author at: Rm 429, Botterell Hall, Department of Physiology, Queens University, Kingston, Ontario, K7L 3N6 Canada. Fax 613-533-6880; e-mail jve1{at}post.queensu.ca.
Background: Cardiac troponins are modified during ischemic injury and are found as a heterogeneous mixture in blood of patients with cardiovascular diseases. We present a strategy to isolate cardiac troponins from human biological material, by use of affinity chromatography, and to provide samples ready for direct analysis by mass spectrometry.
Methods: Cardiac troponins were isolated from human left ventricular tissue by affinity chromatography. Isolated troponins were either eluted and analyzed by Western blot or enzymatically digested while bound to affinity beads. The resulting peptide mixture was subjected to mass spectrometry for protein identification and characterization. The same method was used to analyze serum from patients with acute myocardial infarction (AMI).
Results: Affinity chromatography with antibodies specific for one cardiac troponin subunit facilitated the isolation of the entire cardiac troponin complex from myocardial tissue. The three different proteases used for enzymatic digestion increased the total protein amino acid sequence coverage by mass spectrometry for the three cardiac troponin subunits. Combined amino acid sequence coverages for cardiac troponin I, T, and C (cTnI, cTnT, cTnC) were 54%, 48%, and 40%, respectively. To simulate matrix effects on the affinity chromatographymass spectrometry approach, we diluted tissue homogenate in cardiac troponin-free serum. Sequence coverages in this case were 44%, 41%, and 19%, respectively. Finally, affinity chromatographymass spectrometry analysis of AMI serum revealed the presence of cardiac troponins in a wide variety of its free and/or complexed subunits, including the binary cTnI-cTnC and cTnI-cTnC-cTnT complexes.
Conclusions: Affinity chromatographymass spectrometry allows the extraction and analysis of cardiac troponins from biological samples in their natural forms. We were, for the first time, able to directly confirm the presence of cardiac troponin complexes in human serum after AMI. This approach could assist in more personalized risk stratification as well as the search for reference materials for cardiac troponin diagnostics.
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