Troponin I composition

Abstract

The present invention relates to stable compositions useful as primary standards and calibrators and controls comprising a cardiac troponin I (cTnI) such as native, recombinant, addition and deletion forms thereof, whether or not complexed with other troponin subunits such as TnC and/or TnT, in an inactivated human serum. The compositions are obtained by incubating troponin complexes with human serum. The compositions are characterized by an immunodetectability ratio of epitopes on the N-terminal segment to epitopes on the C-terminal segment substantially equivalent to that of pooled, fresh serum from acute myocardial infarction patients.

What is claimed is:  
     
         1 . A substantially stable composition for use as a cardiac troponin I standard comprising a proteolytically-degraded cardiac troponin I in proteinase-inactivated human serum, the immunodetectability ratio of N-terminal epitopes to C-terninal epitopes of said proteolytically-degraded cardiac troponin I being substantially equivalent to the immunodetectability ratio of N-terninal epitopes to C-terminal epitopes of cardiac troponin I in pooled, fresh serum of acute myocardial infarction patients.  
     
     
         2 . The composition of  claim 1  wherein said standard comprising proteolytically-degraded cardiac troponin I is derived from a cardiac troponin I selected from the group consisting of a complex of a cardiac troponin I, troponin C and troponin T; a complex of a cardiac troponin I and troponin C; and a cardiac troponin I.  
     
     
         3 . The composition of  claim 2  wherein said cardiac troponin I is selected from the group consisting of native troponin I, recombinant troponin I, synthetic troponin I, modified troponin I, and combinations thereof.  
     
     
         4 . The composition of  claim 1  wherein the immunodetectability ratio is determined using at least two antibodies which recognize the N-terminal region of troponin I, and at least two antibodies which recognize the C-terminal region of troponin I.  
     
     
         5 . The composition of  claim 1  wherein said proteinase-inactivated human serum comprises human serum wherein proteinase activity therein is inactivated to the extent that said composition is substantially stable.  
     
     
         6 . The composition of  claim 5  wherein proteinase activity therein is inactivated by a method selected from the group consisting of addition of protease inhibitors and heat inactivation of said composition to inactivate proteinases therein.  
     
     
         7 . The composition of  claim 1  wherein said cardiac troponin I is recombinant human cardiac troponin I.  
     
     
         8 . An assay kit for determining a level of troponin I in a patient sample relative to the cardiac troponin I standard of  claim 1  comprising 
 (i) means for measuring troponin I in said sample; and  
 (ii) said troponin I composition.  
 
     
     
         9 . A method for preparing a substantially stable proteolytically-degraded cardiac troponin I composition comprising sequential steps of 
 (a) incubating a cardiac troponin I in human serum for a period of time to undergo proteolytic degradation sufficient to achieve an immunodetectability ratio of N-termninal epitopes to C-terminal epitopes substantially equivalent to the immunodetectability ratio of cardiac troponin I in pooled, fresh serum of acute myocardial infarction patients; and    (b) inactivating proteinases in said serum.    
     
     
         10 . The method of  claim 9  wherein said cardiac troponin I is selected from the group consisting of a complex of a cardiac troponin I, troponin C and troponin T; a complex of a cardiac troponin I and troponin C; and a cardiac troponin I.  
     
     
         11 . The method of  claim 9  wherein said cardiac troponin I is selected from the group consisting of native, recombinant, synthetic, modified, and combinations thereof.  
     
     
         12 . The method of  claim 9  wherein said cardiac troponin I is recombinant human cardiac troponin I.  
     
     
         13 . The method of  claim 9  wherein said incubation is performed at from about 35° C. to about 44° C.  
     
     
         14 . The method of  claim 9  wherein proteinases are added to said human serum.  
     
     
         15 . The method of  claim 9  wherein said human serum is processed to inactivate proteinases by a method selected from the group consisting of addition of protease inhibitors to said cardiac troponin I composition and heat-inactivation of proteinases in said cardiac troponin I composition.  
     
     
         16 . A method for preparing the cardiac troponin I composition of  claim 1  comprising incubating cardiac troponin I in human serum at a temperature of from about 35 C. to about 44 C. for a period of time to achieve said immunodetectability ratio.  
     
     
         17 . The composition of  claim 3  wherein said modified troponin I is an addition or deletion analog thereof.  
     
     
         18 . The method of  claim 11  wherein said modified troponin I is an addition or deletion analog thereof.