Investigation of human low-density lipoprotein by (1)H nuclear magnetic resonance spectroscopy: mobility of phosphatidylcholine and sphingomyelin headgroups characterizes the surface layer

Exploration of Human Serum Lipoprotein Supramolecular Phospholipids Using Statistical Heterospectroscopy in n-Dimensions (SHY-n): Identification of Potential Cardiovascular Risk Biomarkers Related to SARS-CoV-2 Infection

SARS-CoV-2 infection causes a significant reduction in lipoprotein-bound serum phospholipids give rise to supramolecular phospholipid composite (SPC) signals observed in diffusion and relaxation edited ¹H NMR spectra. To characterize the chemical structural components and compartmental location of SPC and to understand further its possible diagnostic properties, we applied a Statistical HeterospectroscopY in n-dimensions (SHY-n) approach. This involved statistically linking a series of orthogonal measurements made on the same samples, using independent analytical techniques and instruments, to identify the major individual phospholipid components giving rise to the SPC signals. Thus, an integrated model for SARS-CoV-2 positive and control adults is presented that relates three identified diagnostic subregions of the SPC signal envelope (SPC₁, SPC₂, and SPC₃) generated using diffusion and relaxation edited (DIRE) NMR spectroscopy to lipoprotein and lipid measurements obtained by in vitro diagnostic NMR spectroscopy and ultrahigh-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The SPC signals were then correlated sequentially with (a) total phospholipids in lipoprotein subfractions; (b) apolipoproteins B100, A1, and A2 in different lipoproteins and subcompartments; and (c) MS-measured total serum phosphatidylcholines present in the NMR detection range (i.e., PCs: 16.0,18.2; 18.0,18.1; 18.2,18.2; 16.0,18.1; 16.0,20.4; 18.0,18.2; 18.1,18.2), lysophosphatidylcholines (LPCs: 16.0 and 18.2), and sphingomyelin (SM 22.1). The SPC₃/SPC₂ ratio correlated strongly (r = 0.86) with the apolipoprotein B100/A1 ratio, a well-established marker of cardiovascular disease risk that is markedly elevated during acute SARS-CoV-2 infection. These data indicate the considerable potential of using a serum SPC measurement as a metric of cardiovascular risk based on a single NMR experiment. This is of specific interest in relation to understanding the potential for increased cardiovascular risk in COVID-19 patients and risk persistence in post-acute COVID-19 syndrome (PACS).

Alterations of endogenous sphingolipid metabolism in cardiometabolic diseases: Towards novel therapeutic approaches

The increasing prevalence of obesity and metabolic diseases is a worldwide public health concern, and the advent of new analytical technologies has made it possible to highlight the involvement of some molecules, such as sphingolipids (SL), in their pathophysiology. SL are constituents of cell membranes, lipoproteins and lipid droplets (LD), and are now considered as bioactive molecules. Indeed, growing evidence suggests that SL, characterized by diverse families and species, could represent one of the main regulators of lipid metabolism. There is an increasing amount of data reporting that plasma SL profile is altered in metabolic diseases. However, less is known about SL metabolism dysfunction in cells and tissues and how it may impact the lipoprotein metabolism, its functionality and composition. In cardiometabolic pathologies, the link between serum SL concentrations and alterations of their metabolism in various organs and LD is still unclear. Pharmacological approaches have been developed in order to activate or inhibit specific key enzymes of the SL metabolism, and to positively modulate SL profile or related metabolic pathways. Nevertheless, little is known about the long-term impact of such approaches in humans and the current literature still focuses on the decomposition of the different parts of this complex system rather than performing an integrated analysis of the whole SL metabolism. In addition, since SL can be provided from exogenous sources, it is also of interest to evaluate their impact on the homeostasis of endogenous SL metabolism, which could be beneficial in prevention or treatment of obesity and related metabolic disorders.

Evaluation of Methods for the Measurement of Low-Density Lipoprotein Cholesterol

A high concentration of low-density lipoprotein cholesterol (LDL-C) in plasma is one of the strongest risk factors for atherosclerotic cardiovascular disease and mortality. The most common approach to determining LDL-C in the clinical laboratory is the Friedewald calculation. There is an increased interest to improve the accuracy of LDL-C estimated by this equation. The expert panel convened by National Cholesterol Education Program has recommended the development of accurate direct methods to measure LDL-C. Several homogeneous and fully automated methods have been introduced in recent years that show improved precision and accuracy over earlier methods, especially the Friedewald calculation. Each of the atherogenic particles in plasma—very-low, intermediate-, and low-density lipoprotein—as well as lipoprotein (a), contain one molecule of apolipoprotein B (apoB) and thus, plasma total concentration of apoB reflects the number of atherogenic particles. Several studies suggested that the measurement of apoB could improve the prediction of risk of coronary artery disease. Thus, in addition to the newly developed direct assays, alternative calculation procedures have been proposed that also take into consideration total serum apoB concentration for the estimation of LDL-C and the presence of small, dense LDL particles. The new generation of homogenous methods for the measurement of LDL-C and the use of serum apoB concentration for the estimation of LDL-C can contribute to the accurate LDL-C determination.

Role of apolipoprotein E genotype in coronary artery disease

Recent gene-targeting technology has provided good animal models that provide insight into the pathology of complex diseases such as atherosclerosis. The apolipoprotein E gene polymorphism is one of the most extensively studied in cardiovascular medicine. The scope of the present review is to briefly outline the biochemical characteristics and the genetic variation of apolipoprotein E. Apolipoprotein E is best known for its role in modulating lipoprotein metabolism as a ligand for cellular receptors. Other functions unrelated to lipid transport are becoming known, including reverse cholesterol transport, immunoregulation and modulation of cell growth. This review will examine recent work that addresses how apolipoprotein E participates in atherosclerosis. Genotypic variation of apolipoprotein E has been associated with certain phenotypes regarding vascular disease, such as the presence of atherosclerosis and coronary heart disease outcomes. This article will also review evidence regarding the association between apolipoprotein E gene polymorphisms and coronary artery disease based upon experimental and clinical studies.

1H NMR at 800MHz facilitates detailed phospholipid follow-up during atherogenic modifications in low density lipoproteins

The structure of low density lipoprotein (LDL) particles and, particularly, the enzymatic and oxidative modifications of their surface is crucial in the initiation of atherosclerosis. Due to the structural complexity of LDL, there is a lack of suitable methods for dynamic follow-up studies of the molecular mechanisms in native and modified particles in physiological conditions. Here, we report that phosphatidylcholine (PC), lysophosphatidylcholine (lyso-PC), and sphingomyelin (SM) can all be identified and quantified in LDL particles by (1)H NMR spectroscopy at 800 MHz. The signal assignment for the lyso-PC is novel and we illustrate the applicability of the methodology in the case of lipid peroxidation that is generally considered as one of the key proatherogenic modifications of LDL. It was found, somewhat surprisingly, that the LDL-associated phospholipase A(2) is activated in the very beginning of the formation of PC-hydroperoxides. The (patho)physiological rationale of the resulting lyso-PC generation is also briefly discussed.

Lipid–protein interactions in human plasma LDL evidenced by magnetic resonance

Low density lipoprotein (LDL) particles exhibit extremely complex three-dimensional structural organization which is still not understood at the molecular level. The aim of this study was to provide the experimental evidence of a direct non-covalent interaction of the protein part with the lipid matrix. The approach was based on the combination of (1)H NMR (600 MHz) spectroscopy with thiol-specific spin labeling of the protein (apoB). It is shown that the spectral peaks assigned to the methyl head groups of phosphatidylcholine and sphingomyelin in the (1)H spectra of LDL exhibit line broadening when otherwise free thiol groups of apoB are covalently modified by methanethiosulfonate spin label. The effect is similar in the presence of water soluble paramagnetic compound. These results indicate that fragments of apoB, which are part of the receptor binding region, are directly in contact with the solvated phospholipid head groups of the lipid matrix.

Absorption and lipoprotein transport of sphingomyelin

Dietary sphingomyelin (SM) is hydrolyzed by intestinal alkaline sphingomyelinase and neutral ceramidase to sphingosine, which is absorbed and converted to palmitic acid and acylated into chylomicron triglycerides (TGs). SM digestion is slow and is affected by luminal factors such as bile salt, cholesterol, and other lipids. In the gut, SM and its metabolites may influence TG hydrolysis, cholesterol absorption, lipoprotein formation, and mucosal growth. SM accounts for approximately 20% of the phospholipids in human plasma lipoproteins, of which two-thirds are in LDL and VLDL. It is secreted in chylomicrons and VLDL and transferred into HDL via the ABCA1 transporter. Plasma SM increases after periods of large lipid loads, during suckling, and in type II hypercholesterolemia, cholesterol-fed animals, and apolipoprotein E-deficient mice. SM is thus an important amphiphilic component when plasma lipoprotein pools expand in response to large lipid loads or metabolic abnormalities. It inhibits lipoprotein lipase and LCAT as well as the interaction of lipoproteins with receptors and counteracts LDL oxidation. The turnover of plasma SM is greater than can be accounted for by the turnover of LDL and HDL particles. Some SM must be degraded via receptor-mediated catabolism of chylomicron and VLDL remnants and by scavenger receptor class B type I receptor-mediated transfer into cells.

1H NMR spectroscopic evidence of interaction between ibuprofen and lipoproteins in human blood plasma

Recent studies have suggested that ibuprofen inhibits low-density lipoprotein oxidation in a high dose-dependent manner and is a promising drug for treatment of the conditions associated with atherosclerosis. In this article, we present the NMR spectroscopic evidence for the interaction between ibuprofen and phospholipids in lipoprotein particles in intact human plasma. Ibuprofen caused chemical shift upfield drifts for the protons of -N(+)(CH(3))(3) moieties of phosphatidylcholine and sphingomyelin, olefinic chains (-CH[double bond]CH[bond], [bond]CH[triple bond]CHCH(2)CH[triple bond]CH[bond], [bond](CH(2))(n)CH(2)CH[double bond]), and (CH(2))(n) and CH(3) groups, from unsaturated lipids in lipoprotein particles. The ibuprofen may interact directly with the above-mentioned groups of phospholipids or induce structural changes in the lipoproteins. This may shed light on the mechanism by which the drug protects against oxidative modification of lipoproteins.