Particle number analysis of lipoprotein subclasses by gel permeation HPLC in patients with cholesteryl ester transfer protein deficiency

The Sizes and Composition of HDL-Cholesterol Are Significantly Associated with Inflammation in Rheumatoid Arthritis Patients

Rheumatoid arthritis (RA), a chronic inflammatory disease, carries a significant burden of atherosclerotic cardiovascular diseases (ASCVD). With their heterogeneous composition, high-density lipoprotein (HDL) particles have varied athero-protective properties, and some may even increase ASCVD risk. In this prospective and cross-sectional study, we aimed to examine the relationship between HDL sizes/metabolites and inflammation in RA. Using ¹H-NMR-based lipid/metabolomics, differential HDL-related metabolites were identified between RA patients and healthy control (HC) subjects and between RA patients with and without anti-citrullinated peptide antibodies (ACPA). The correlation between the discriminative HDL-related metabolites and C-reactive protein (CRP) was evaluated in RA patients. RA patients demonstrated higher particle number, lipids, cholesterol, cholesterol ester, free cholesterol, and phospholipids in large/very large-sized HDLs. ACPA-positive patients had higher L-HDL-C and L-HDL-CE but lower small-/medium-sized HDL-TG levels than ACPA-negative patients. An inverse correlation was found between CRP levels and small-sized HDLs. Janus kinase inhibitor treatment was associated with increased serum small-sized HDL-related metabolites and decreased CRP levels. We are the first to reveal the significant associations between RA inflammation and HDL sizes/metabolites. A potential link between ACPA positivity and changes in serum levels of HDL-related metabolites was also observed in RA patients.

Dalcetrapib and anacetrapib increase apolipoprotein E-containing HDL in rabbits and humans

The large HDL particles generated by administration of cholesteryl ester transfer protein inhibitors (CETPi) remain poorly characterized, despite their potential importance in the routing of cholesterol to the liver for excretion, which is the last step of the reverse cholesterol transport. Thus, the effects of the CETPi dalcetrapib and anacetrapib on HDL particle composition were studied in rabbits and humans. The association of rabbit HDL to the LDL receptor (LDLr) in vitro was also evaluated. New Zealand White rabbits receiving atorvastatin were treated with dalcetrapib or anacetrapib. A subset of patients from the dal-PLAQUE-2 study treated with dalcetrapib or placebo were also studied. In rabbits, dalcetrapib and anacetrapib increased HDL-C by more than 58% (P < 0.01) and in turn raised large apo E-containing HDL by 66% (P < 0.001) and 59% (P < 0.01), respectively. Additionally, HDL from CETPi-treated rabbits competed with human LDL for binding to the LDLr on HepG2 cells more than control HDL (P < 0.01). In humans, dalcetrapib increased concentrations of large HDL particles (+69%, P < 0.001) and apo B-depleted plasma apo E (+24%, P < 0.001), leading to the formation of apo E-containing HDL (+47%, P < 0.001) devoid of apo A-I. Overall, in rabbits and humans, CETPi increased large apo E-containing HDL particle concentration, which can interact with hepatic LDLr. The catabolism of these particles may depend on an adequate level of LDLr to contribute to reverse cholesterol transport.

Dietary-Induced Elevations of Triglyceride-Rich Lipoproteins Promote Atherosclerosis in the Low-Density Lipoprotein Receptor Knockout Syrian Golden Hamster

Elevated triglycerides are associated with an increased risk of cardiovascular disease (CVD). Therefore, it is very important to understand the metabolism of triglyceride-rich lipoproteins (TRLs) and their atherogenic role in animal models. Using low-density lipoprotein receptor knockout (LDLR^-/-) Syrian golden hamsters, this study showed that unlike LDLR^-/- mice, when LDLR^-/- hamsters were fed a high cholesterol high-fat diet (HFD), they had very high plasma levels of triglycerides and cholesterol. We found that LDLR^-/- hamsters exhibited increased serum TRLs and the ApoB100 and 48 in these particles after being fed with HFD. Treatment with ezetimibe for 2 weeks decreased these large particles but not the LDL. In addition, ezetimibe simultaneously reduced ApoB48 and ApoE in plasma and TRLs. The expression of LRP1 did not change in the liver. These findings suggested that the significantly reduced large particles were mainly chylomicron remnants, and further, the remnants were mainly cleared by the LDL receptor in hamsters. After 40 days on an HFD, LDLR^-/- hamsters had accelerated aortic atherosclerosis, accompanied by severe fatty liver, and ezetimibe treatment reduced the consequences of hyperlipidemia. Compared with the serum from LDLR^-/- hamsters, that from ezetimibe-treated LDLR^-/- hamsters decreased the expression of vascular adhesion factors in vascular endothelial cells and lipid uptake by macrophages. Our results suggested that in the LDLR^-/- hamster model, intestinally-derived lipoprotein remnants are highly atherogenic and the inflammatory response of the endothelium and foam cells from macrophages triggered atherosclerosis. The LDL receptor might be very important for chylomicrons remnant clearance in the Syrian golden hamster, and this may not be compensated by another pathway. We suggest that the LDLR^-/- hamster is a good model for the study of TRLs-related diseases as it mimics more complex hyperlipidemia.

Distinct Differences in Lipoprotein Particle Number Evaluation between GP-HPLC and NMR: Analysis in Dyslipidemic Patients Administered a Selective PPARα Modulator, Pemafibrate

AIM

We established a method to evaluate the lipid concentrations, size and particle numbers (PNs) of lipoprotein subclasses by gel permeation chromatography (GP-HPLC). Nuclear magnetic resonance (NMR) is widely used to analyze these parameters of lipoprotein subclasses, but differences of the two methods are unknown. Current study compared the PNs of each lipoprotein subclass measured by GP-HPLC and NMR, and assessed the effect of a selective PPARα modulator, pemafibrate.

METHODS

Lipoprotein profiles of 212 patients with dyslipidemia who participated in the phase 2 clinical trial of a selective PPARα modulator, pemafibrate, were analyzed by two methods, GP-HPLC and NMR, which were performed with LipoSEARCH (Skylight Biotech) and LipoProfile 3 (LabCorp), respectively. GP-HPLC evaluated the PNs of 18 subclasses, consisting of CM, VLDL1-5, LDL1-6, and HDL1-6. NMR evaluated the PNs of 9 subclasses, consisting of large VLDL & CM, medium VLDL, small VLDL, IDL, large LDL, small LDL, large HDL, medium HDL and small HDL.

RESULTS

Three major classes, total CM&VLDL, total LDL and total HDL were obtained by grouping of corresponding subclasses in both methods and PNs of these classes analyzed by GP-HPLC were correlated positively with those by NMR. The correlation coefficients in total CM&VLDL, total LDL and total HDL between GP-HPLC and NMR was 0.658, 0.863 and 0.798 (all p＜0.0001), respectively. The PNs of total CM&VLDL, total LDL and total HDL analyzed by GP-HPLC was 249.5±51.7nM, 1,679±359 nM and 13,273±1,564 nM, respectively, while those by NMR was 124.6±41.8 nM, 1,514±386 nM and 31,161±4,839 nM, respectively. A marked difference in the PNs between the two methods was demonstrated especially in total HDL. The number of apolipoprotein (Apo) B molecule per one ApoB-containing lipoprotein particle, total CM&VLDL plus total LDL, was 1.10±0.05 by GP-HPLC, while 1.32±0.18 by NMR. The number of ApoA-I per one HDL particle was 3.40±0.17 by GP-HPLC, but only 1.46±0.15 by NMR, much less than reported previously.From the phase 2 clinical trial, randomizing 212 patients to pemafibrate 0.025-0.2 mg BID, fenofibrate 100 mg QD, or placebo groups, pemafibrate reduced the PNs of CM, large VLDL1-VLDL3 and medium VLDL4, but not small VLDL5 by GP-HPLC. It significantly decreased the PNs of smaller LDL and larger HDL particles, but increased those of larger LDL and smaller HDL particles. In contrast, NMR showed marked variations in the effect of pemafibrate on lipoprotein PNs, and no significant size-dependent changes.

CONCLUSIONS

GP-HPLC evaluates the lipoprotein PNs more accurately than NMR and can be used for assessing the effects of lipid-lowering drugs on lipoprotein subclasses.

Hyperalphalipoproteinemia and Beyond: The Role of HDL in Cardiovascular Diseases

Hyperalphalipoproteinemia (HALP) is a lipid disorder characterized by elevated plasma high-density lipoprotein cholesterol (HDL-C) levels above the 90th percentile of the distribution of HDL-C values in the general population. Secondary non-genetic factors such as drugs, pregnancy, alcohol intake, and liver diseases might induce HDL increases. Primary forms of HALP are caused by mutations in the genes coding for cholesteryl ester transfer protein (CETP), hepatic lipase (HL), apolipoprotein C-III (apo C-III), scavenger receptor class B type I (SR-BI) and endothelial lipase (EL). However, in the last decades, genome-wide association studies (GWAS) have also suggested a polygenic inheritance of hyperalphalipoproteinemia. Epidemiological studies have suggested that HDL-C is inversely correlated with cardiovascular (CV) risk, but recent Mendelian randomization data have shown a lack of atheroprotective causal effects of HDL-C. This review will focus on primary forms of HALP, the role of polygenic inheritance on HDL-C, associated risk for cardiovascular diseases and possible treatment options.

Development and Clinical Application of an Enzyme-Linked Immunosorbent Assay for Oxidized High-Density Lipoprotein

Aims: HDL particles have various anti-atherogenic functions, whereas HDL from atherosclerotic patients was demonstrated to be dysfunctional. One possible mechanism for the formation of dysfunctional HDL is the oxidation of its components. However, oxidized HDLs (Ox-HDLs) remain to be well investigated due to lack of reliable assay systems.

Methods: We have developed a novel sandwich enzyme-linked immunosorbent assay (ELISA) for Ox-HDL by using the FOH1a/DLH3 antibody, which can specifically recognize oxidized phosphatidylcholine, a major component of HDL phospholipid (HDL-PL). We defined forced oxidation of 1 mg/L HDL-PL as 1 U/L Ox-HDL. We assessed serum Ox-HDL levels of normolipidemic healthy subjects ( n =94) and dyslipidemic patients ( n =177).

Results: The coefficients of variation of within-run and between-run assays were 12.5% and 13.5%. In healthy subjects, serum Ox-HDL levels were 28.5±5.0 (mean±SD) U/L. As Ox-HDL levels were moderately correlated with HDL-PL (r=0.59), we also evaluated the Ox-HDL/HDL-PL ratio, which represents the proportion of oxidized phospholipids in HDL particles. In dyslipidemic patients, Ox-HDL levels were highly variable and ranged from 7.2 to 62.1U/L, and were extremely high (50.4±13.3U/L) especially in patients with hyperalphalipoproteinemia due to cholesteryl ester transfer protein deficiency. Regarding patients with familial hypercholesterolemia, those treated with probucol, which is a potent anti-oxidative and anti-hyperlipidemic drug, showed significantly lower Ox-HDL (16.2±5.8 vs. 30.2±5.4, p ＜0.001) and Ox-HDL/HDL-PL ratios (0.200±0.035 vs. 0.229±0.031, p =0.015) than those without probucol.

Conclusion: We have established a novel sandwich ELISA for Ox-HDL, which might be a useful and easy strategy to evaluate HDL functionality, although the comparison study between this Ox-HDL ELISA and the assay of HDL cholesterol efflux capacity remains to be done. Our results indicated that probucol treatment may be associated with lower Ox-HDL levels.

Administration of eicosapentaenoic acid may alter lipoprotein particle heterogeneity in statin-treated patients with stable coronary artery disease: A pilot 6-month randomized study

BACKGROUND

We hypothesized that the addition of eicosapentaenoic acid (EPA) to ongoing statin therapy could change the particle heterogeneity of low-density lipoprotein (LDL) and high-density lipoprotein (HDL) particles, even in stable coronary artery disease (CAD) patients.

METHODS

We assigned CAD patients already receiving statin therapy to one of two groups: an EPA group (1800 mg/day; n = 30) and a control group (n = 30). A gel permeation high-performance liquid chromatography method was used to measure the particle concentration and number of lipoprotein subclasses.

RESULTS

In the EPA group, significant decreases of both the concentration and number of medium LDL (p = 0.0002 and 0.0001), small LDL (p = 0.0004 and 0.0005) and very small LDL (p = 0.0005 and 0.002) particles were observed. Conversely, the concentration and number of large HDL particles increased significantly (p = 0.024 and 0.048). The concentration of very large HDL particles also increased significantly (p = 0.028). Furthermore, significant correlations between the variables that showed significant changes in the LDL and HDL particle subclasses, and the EPA/arachidonic acid (AA) ratio were found. No other significant associations of lipoprotein particle heterogeneity with the serum EPA/AA ratio were noted in either the control group or the EPA group. Interestingly, univariate and multivariate regression analyses revealed that increased serum lecithin-cholesterol acyltransferase activity, a key enzyme of HDL cholesterol efflux, was a predictor for increased above-mentioned HDL particles subclasses.

CONCLUSIONS

Administration of EPA might alter both LDL and HDL particle heterogeneity, causing decreased concentration and number of smaller LDL particles and increased concentration and number of larger HDL particles. Furthermore, addition of EPA to ongoing statin therapy appears to be capable of increasing the EPA/AA ratio, which might have an anti-atherosclerotic effect on lipoprotein particle heterogeneity, even in stable CAD patients with well-controlled serum lipid levels.

CLINICAL TRIAL REGISTRATION

UMIN (http://www.umin.ac.jp/) Study ID: UMIN000010452.

Inherited metabolic disorders and dyslipidaemia

Monogenic dyslipidaemia is a diverse group of multisystem disorders. Patients may present to various specialities from early childhood to late in adult life, and it usually takes longer before the diagnosis is established. Increased awareness of these disorders among clinicians is imperative for early diagnosis. This best practice review provides an overview of primary dyslipidaemias, highlighting their clinical presentation, relevant biochemical and molecular tests. It also addresses the emerging role of genetics in the early diagnosis and prevention of these disorders.

Shotgun proteomic analysis reveals proteome alterations in HDL of patients with cholesteryl ester transfer protein deficiency

BACKGROUND

We previously reported that the patients with cholesteryl ester transfer protein (CETP) deficiency (CETP-D) show marked changes in the size and lipid compositions of high-density lipoprotein (HDL) and that they are not protected from atherosclerotic cardiovascular diseases, despite increased serum HDL-cholesterol (HDL-C) levels. HDL particles carry a variety of proteins, some of which are known to have antiatherogenic functions.

OBJECTIVE

This study aimed to investigate the protein composition of HDL particles in patients with CETP-D.

METHODS

Eight patients with complete deficiency of CETP and 8 normolipidemic healthy subjects were enrolled. We performed shotgun proteomic analysis to investigate the proteome of ultracentrifugally isolated HDL.

RESULTS

We identified 79 HDL-associated proteins involved in lipid metabolism, protease inhibition, complement regulation, and acute-phase response, including 5 potential newly identified HDL-associated proteins such as angiopoietin-like3 (ANGPTL3). Spectral counts of apolipoprotein (apo) E were increased in patients with CETP-D compared with controls (60.3 ± 6.9 vs 43.7 ± 2.5, P < .001), which is concordant with our previous report. Complement regulatory proteins such as C3, C4a, C4b, and C9 were also significantly enriched in HDL from patients with CETP-D. Furthermore, apoC-III and ANGPTL3, both of which are now known to associate with increased atherosclerotic cardiovascular diseases, were enriched in patients with CETP-D compared with normolipidemic subjects (35.9 ± 5.3 vs 27.1 ± 3.7, 2.3 ± 1.1 vs 0.4 ± 1.1, respectively; P < .01).

CONCLUSION

We have characterized HDL-associated proteins in patients with CETP-D. We identified a significant increase in the amount of apoE, apoC-III, ANGPTL3, and complement regulatory proteins. These proteomic changes might be partly responsible for the enhanced atherogenicity of patients with CETP-D.