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Using NMR Spectroscopy to Quantify Lipoprotein Profiles

“The development of NMR- specific SOPs will allow the comparison of different cohorts and will generate new knowledge on the lipoprotein particle distribution with the possibility of turning it into a biomarker”

 Cardiovascular disease (CVD) is the most common cause of death worldwide. According to the World Health Organization, 17.7 million CVD-related deaths occurred in 2015, which represented 31% of all deaths globally.

Important behavioral risk factors for CVD are an unhealthy diet and a lack of physical activity, which may be indicated in a blood sample by an abnormal lipid profile.

Lipids are hydrophobic and cannot be carried in the bloodstream independently. Instead they bind to a protein to form a complex called a lipoprotein, which transports lipids around the body delivering them to tissues where they can be stored or used for energy.

Lipoproteins are classified based on their composition and density into five categories: chylomicrons (CMs); very low-density lipoproteins (VLDLs); intermediate density lipoproteins (IDLs), low density lipoproteins (LDLs) and high-density lipoproteins (HDLs).

These different lipoprotein fractions have different effects on the cardiovascular system, which may be harmful or beneficial. These fractions can also be further refined into subfractions that can indicate CVD risk.

Current standard approaches to blood lipoprotein profiling are time consuming and labor intensive and there is an increasing demand from clinicians for effective fractionation and quantification methods that will improve lipoprotein screening and the prevention and diagnosis of CVD.

In a recent review by Søren Engelsen and colleagues, these approaches are compared, with a focus on the use of NMR spectroscopy. Engelsen and team believe NMR spectroscopy could revolutionize lipoprotein profiling in the future.

The method currently considered the gold standard for lipoprotein profiling is density gradient ultra-centrifugation (UC). This approach requires distinct separation and quantification steps, whereas NMR spectroscopy performs lipoprotein classification and quantification within just one measurement.

With NMR spectroscopy, both lipoprotein fraction and subfractions can be determined, owing to the method’s sensitivity to the chemical and physical properties of lipoproteins. The various lipoprotein fractions and subfractions differ in their chemical composition and size, which results in different magnetic susceptibilities. This gives rise to distinctive NMR signals with individual amplitudes that directly reflect the concentration of the LP particle. This enables blood lipoproteins to be identified and quantified within one rapid experiment.

Engelson and team say another advantageous feature of NMR-spectroscopy is its non-destructive nature, which means a sample’s natural chemical equilibria can be preserved. Furthermore, according to the most recent Standard Operating Procedures, serum and plasma samples can be stored for nine months at −80°C, without NMR profiles being altered.

With the UC method, samples need to be fresh, which means having to perform separation as soon as possible after samples have been collected.

One drawback when using NMR-spectroscopy for lipoprotein profiling is that NMR spectra must be calibrated to a primary method of reference such as UC, using multivariate regression methods.

However, great efforts are being made to do this and when NMR spectroscopy is combined with multivariate regression, efficient and accurate determination of lipoprotein concentration and the cholesterol and triglyceride content of specific lipoprotein fractions is achievable, as displayed in for Bruker’s AVANCE IVDr.

Engelsen and team acknowledge that there are still some challenges to overcome surrounding the idea of using NMR-based lipoprotein profiling in clinical practice, but they believe that with the current efforts that are being made to standardize NMR measurements and reference methods, this technology could revolutionize the field of lipoprotein profiling.

Contact Bruker for more information about the AVANCE IVDr.

Reference:

  • Engelson, S.B et al. Quantification of lipoprotein profiles by nuclear magnetic resonance spectroscopy and multivariate data analysis. Trends in Analytical Chemistry 2017;94: 210-219. https://doi.org/10.1016/j.trac.2017.07.009