Surface fitting of 2D diffusion-edited 1H NMR spectroscopy data for the characterisation of human plasma lipoproteins

Abstract

Determining the concentration and size of lipoprotein complexes is very important due to their role in cardiovascular diseases and metabolic disorders. However, standard methods for lipoprotein fractionation are manual and time consuming and cannot be used as standard diagnostic tools. Because different subclasses of lipoproteins have different radii and, hence, different diffusion velocities, we propose a fast and reliable method that uses 2D diffusion-edited 1 H NMR spectroscopy to acquire a set of 2D spectra of plasma samples, followed by a surface fitting algorithm based on Lorentzian functions to estimate the sizes and the relative proportions of different lipoprotein subclasses. We were able to demonstrate that the derived sizes and positions related to the Lorentzian functions follow an exponential relationship for normolipidaemic and dislipaemic samples with coefficients of determination (r 2 ) of 0.85 and 0.81, respectively. Moreover, we found a linear relationship between the width and size of the Lorentzian functions for normolipidaemic samples (r 2 = 0.88) while for dislipaemic samples this relation was nonlinear (r 2 = 0.62). Dividing our samples set into four different lipoprotein profiles (normal lipid values, low HDL/LDL ratio, high triglycerides values and both risk factors) and using principal component analysis (PCA) followed by multivariate analysis of variance (MANOVA), our method was able to statistically discriminate between those groups, with p-values of 0.0016, 0.0006, \1e -4 and 0.0035, respectively. These parameters are characteristic and indicative of different lipoprotein profiles and can be used to distinguish between normolipidaemic, hypercholesterolaemic, hypertriglyceridaemic and chylomicronaemic profiles.

Lipidomic changes of LDL in overweight and moderately hypercholesterolemic subjects taking phytosterol- and omega-3-supplemented milk

“…LDL size was directly measured in plasma-EDTA (500 l) by NMR (Biosfer Teslab, Reus, Spain), as described by Mallol et al ( 28 ). Briefl y, particle concentration and the diffusion coeffi cients were obtained from the measured amplitudes and attenuation of by guest, on www.jlr.org (AT-DYSL) (supplementary Table 2B).…”

Liposcale: a novel advanced lipoprotein test based on 2D diffusion-ordered 1H NMR spectroscopy

“…Though different lipoprotein subclasses may in theory be deconvoluted within the 1D-NMR spectrum according to their chemical shift positions, it has proven to be complicated in practice due to significant spectral overlap as different lipoprotein subclasses contribute to NMR resonance at the same frequency ( 18 ). This is of great importance for LDL subclasses, which are particularly diffi cult to characterize due to the effect of neighboring lipoprotein classes (i.e., VLDL and HDL) ( 26,27 ).…”

“…The gradient pulse strength was increased from 5 to 95% of the maximum strength of 53.5 Gauss cm Surface fi tting. The methyl signal was surface fi tted using a previously reported procedure ( 18 ). The number of functions was increased to account for the nine lipoprotein subclasses.…”

“…As a result, we obtained unique solutions for all samples after 10 runs. Normalized root mean square errors of the fi ttings were calculated as previously described ( 18 ). The initial values of the signal intensities were taken to be the mean solution values of all samples.…”

Advanced lipoprotein testing for cardiovascular diseases risk assessment: a review of the novel approaches in lipoprotein profiling

“…using data-processing software similar to that of LipoProfile ® . This software was however further developed and modified to improve peak deconvolution using statistical approaches [82].…”