Researchers at the University of Wisconsin–Madison (WISC) have developed a method combining sticky nanoparticles with high-precision protein measurement to capture and analyze a common marker of heart disease to reveal details that were previously inaccessible, according to a press release from WISC.
The new method, a system known as nanoproteomics, effectively captures and measures various forms of the protein cardiac troponin I, or cTnI, a biomarker of heart damage currently used to help diagnose heart attacks and other heart diseases. An effective test of cTnI variations could one day provide doctors with a better ability to diagnose heart disease, the leading cause of death in the U.S.
Measuring low-concentration proteins in the blood like cTnI is a classic needle-in-a-haystack problem. Rare, meaningful biomarkers of disease are completely overwhelmed by common and diagnostically useless proteins in the blood. Current methods use antibodies to enrich and capture proteins in a complex sample to identify and quantify proteins. But antibodies are expensive, have batch-to-batch variations, and can generate inconsistent results.
To capture cTnI and overcome some of the limitations of antibodies, the researchers designed nanoparticles of magnetite, a magnetic form of iron oxide, and linked it to a peptide of 13 amino acids long designed to specifically bind to cTnI. The peptide latches onto cTnI in a blood sample, and the nanoparticles can be collected together using a magnet. Nanoparticles and peptides are easily made in the lab, making them cheap and consistent.
Using the nanoparticles, the researchers were able to effectively enrich cTnI in samples of human heart tissue and blood. Then they used advanced mass spectrometry, which can distinguish different proteins by their mass, to not only get an accurate measurement of cTnI, but also to assess the various modified forms of the protein.
The researchers decided to test if they could distinguish the various forms of cTnI that can be found in patient blood samples. They spiked blood serum with proteins from donor hearts that were normal, diseased, or from a dead donor. Then they used their nanoparticles to capture cTnI and measured the protein using mass spectrometry.
As hoped, the scientists could observe clearly different patterns in the types of cTnI prevalent in each type of heart tissue. The healthy hearts tended to have lots of cTnI with multiple phosphate groups attached, for example, while diseased hearts had cTnI that had less phosphate and the post-mortem heart had cTnI broken into pieces.
