Nanoparticle System Captures Heart-Disease Biomarker From Blood

Physicians currently use an antibody-based test called enzyme-linked immunosorbent assay (ELISA) to help diagnose heart attacks based on elevated levels of cardiac troponin I (cTnI) in the patient's blood sample. While the ELISA test is sensitive, patients can have high levels of cTnI in the blood without having heart disease, which can lead to expensive and unnecessary treatments for patients.

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 impractical 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.

Chemists at the University of Wisconsin-Madison (Madison, WI, USA) 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 laboratory, making them cheap and consistent.

The team, by using the nanoparticles, was 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. Samples were analyzed by direct infusion using a TriVersa NanoMate system (Advion BioSciences, Ithaca, NY, USA) coupled to a solariX XR 12-Tesla Fourier Transform Ion Cyclotron Resonance mass spectrometer (FTICR-MS, Bruker Daltonics, Bremen, Germany).

Like many proteins, cTnI can be modified by the body depending on factors like an underlying disease or changes in the environment. In the case of cTnI, the body adds various numbers of phosphate groups, small molecular tags that might change the function of cTnI. These variations are subtle and hard to track.

Ying Ge, PhD, a Professor of Chemistry and senior author of the study, said, “So we want to use our nanoproteomics system to look into more details at various modified forms of this protein rather than just measuring its concentration. That will help reveal molecular fingerprints of cTnI from each patient for precision medicine. with high-resolution mass spectrometry, We can now 'see' these molecular details of proteins, like the hidden iceberg beneath the surface.” The study was published on August 6, 2020 in the journal Nature Communications.

Related Links:

University of Wisconsin-Madison
Advion BioSciences
Bruker Daltonics