Don't Judge A Book About Protein Isoforms By Its Cover

Traditionally, clinical laboratories detect and quantitate many proteins of clinical significance using immunoassay platforms. Let us compare immunoassay methodologies for protein quantitation to a librarian re-shelving books: The librarian can identify a type of book and count how many of that type are on a shelf. However, if a book is missing pages or has typos inside, the librarian won’t know by solely looking at the cover.

If we in the lab use only this librarian’s approach to detecting proteins in the laboratory, we may have a problem. Proteins of the same type may come in many different isoforms, each having individual properties and potential diagnostic utility. Immunoassays may not be able to reliably detect and/or differentiate these proteoforms, even when it is clinically important. This is where mass spectrometry can provide deeper diagnostic information than immunoassay platforms. In today’s session “Quantitative Proteomics in Clinical Care: Development, Deployment and Future Directions,” we will learn how mass spectrometry is revolutionizing quantitative proteomics by specifically isolating and quantitating protein isoforms implicated in human disease.

The first speaker, Christa Cobbaert, PhD, will discuss in her talk “Metrological Traceability & MS-based Apolipoprotein Quantification: Challenges and Opportunities” how mass spectrometry allows us to detect and quantitate clinically relevant protein isoforms or “proteoforms” with specific physiological and pathological functions. These proteoforms can help characterize health and disease of patients at the molecular level, providing a deeper diagnostic opportunity to ultimately improve health outcomes. Cobbaert will shed light on using quantitative proteomics to create a multiplexed, mass spectrometry-based apolipoprotein test that could be used to identify residual cardiovascular risk in patients outside of using traditional LDL cholesterol measurements.

A second speaker, Andre Mattman, PhD, will present “Advantages and Challenges of Immunoglobulin G Subclass Measurement by Mass Spectrometry over Immunonephelometry.” He will discuss the testing of IgG protein isoforms, specifically how IgG isoforms vary in their antigen binding, immuno-complex formation, and complement activation, and how these specific isoforms are implicated in distinctly different disease processes. Mattman will also cover how IgG isoforms or subclasses are differentiated and quantitated using mass spectrometry-based methods.

Jennifer Van Eyk, PhD, will complete the session with her talk “Solving a Clinical Challenge: The Absolute Quantification of B-Type Natriuretic Peptide Proteolysis, a Key Heart Failure Diagnostic and Therapeutic, in Human Plasma by CE-MS.” Van Eyk will provide a unique clinical perspective when analyzing brain natriuretic peptide (BNP) using the synergistic application of both mass spectrometry and capillary electrophoresis to distinguish and monitor multiple BNP peptidoforms.

Van Eyk also will describe how circulating peptides and proteins exist in homeostatic equilibrium. When blood is sampled from the body, this equilibrium is disrupted and may alter the quantitation of the intact protein. This is especially true if enzymes coexist in the sample and may continue to catabolize proteins of interest after the sample is drawn. However, remnant peptides or “peptidoforms” created from this protein degradation still remain intact and stable. She will discuss why traditional antibody-based methodologies are incapable of distinguishing different peptidoforms, which could ultimately provide an erroneous BNP concentration, and where this new mass spectrometry-based application may provide more accurate and useful results.

Although immunoassays still provide a wealth of clinical information, these three speakers will highlight how mass spectrometry-based quantitative proteomic applications are providing us with a deeper clinical understanding of human disease than ever before. Sometimes judging a book by its cover is not enough, and these mass spectrometry applications are a case in point.