The DIRE (DIffusional and Relaxation Editing) experiment was used in 2021 to measure the glycoprotein levels (GlycA and GlycB) in COVID-19 patients. In the resulting NMR spectrum, we discovered the Supramolecular Phospholipid Composite (SPC) peak. Further characterisation of SPC revealed three distinct subregions (SPC1, SPC2, SPC3). The SPC signal arises in the NMR spectrum from the choline headgroups of phospholipids within lipoproteins. SPC1 from the phospholipid contained in HDL subfraction 4, SPC2 from the phospholipid contained within HDL subfractions 1-3 and SPC3 from the subfractions contained within LDL. Due to the editing nature of the NMR experiment quantification of these regions simply means spectral integration.
Further investigation of the glycoproteins and SPC offers nuanced insights into inflammatory processes. Our recent findings suggest GlycA, GlycB and the clinical marker of inflammation C-Reactive Protein are directly correlated with inflammation regardless of the cause. However, when chronic inflammation is present using cardiovascular disease and diabetes as two exemplars, SPC2 and SPC3 levels reduce while SPC1 remains unchanged. While in acute inflammation such as COVID-19 infection and sepsis it was found SPC1 was directly correlated to the severity of inflammation. In addition, the ratio SPC3/SPC2 is highly correlated with the clinical biomarker of atherosclerotic risk ApolipoproteinB100/Apolipoprotein A1 (ABA1).
An advantage of using SPC3/SPC2 over the ABA1 ratio is that if determined using NMR, the SPC parameter is model-free, allowing its determination simply by integration of the SPC region of the spectrum, which can be acquired on an 80MHz benchtop NMR making it clinically deployable.
These recent observations highlight the potential of the SPC subregions as novel inflammatory markers, and a measure of cardiovascular risk based on a single NMR experiment. This has widespread diagnostic applicability to many disease states associated with systemic inflammation.