Altered composition of HDL3 in FH subjects causing a HDL subfraction with less atheroprotective function

Capacity of HDL to Efflux Cellular Cholesterol from Lipid-Loaded Macrophages Is Reduced in Patients with Familial Hypercholesterolemia

This study aimed to evaluate the high-density lipoprotein (HDL) capacity to efflux cellular cholesterol from lipid-loaded macrophages to find a reliable and low-cost biomarker with the purpose of better evaluating the risk of premature cardiovascular (CV) events in FH patients. This case-controlled study comprised 16 homozygous (HOFH) and 18 heterozygous (HEFH) FH patients, as well as 20 healthy subjects recruited as controls. Two main subfractions of HDL (HDL2 (d = 1.063-1.125 g/mL) and HDL3 (d = 1.125-1.210 g/mL)) were isolated from the patients' serum samples using sequential ultracentrifugation. After compositional characterization, the capacity of HDL to efflux cholesterol (CEC%) from lipid-laden macrophages was measured. The HDL2 and HDL3 subfractions showed some differences in lipid and protein composition between the studied groups. In addition, both HDL subfractions (p < 0.001) revealed significantly reduced CEC% in HOFH patients (HDL2: 2.5 ± 0.1 and HDL3: 3.2 ± 0.2) in comparison with the HEFH (HDL2: 3.2 ± 0.1% and HDL3: 4.1 ± 0.2%) and healthy (HDL2: 3.3 ± 0.2% and HDL3: 4.5 ± 0.3%) subjects. Additionally, multinomial logistic regression results indicated that the CEC% of both HDL2 (OR: 0.091; 95% CI: 0.018-0.452, p < 0.01) and HDL3 (OR: 0.118; 95% CI: 0.035-0.399, p < 0.01) subfractions are strongly and inversely associated with the homozygous form of FH. A decreased capacity of HDL particles to efflux cholesterol from macrophages might identify homozygous FH patients who are at elevated risk for premature CVDs. Prospective studies with a large sample size are warranted to evaluate this hypothesis.

Familial Hypercholesterolemia: Do HDL Play a Role?

Cardiovascular disease (CVD) in heterozygous familial hypercholesterolemia (HeFH), the most frequent monogenic disorder of human metabolism, is largely driven by low-density lipoprotein (LDL) cholesterol concentrations. Since the CVD rate differs considerably in this population, beyond the lifetime LDL cholesterol vascular accumulation, other classical risk factors are involved in the high cardiovascular risk of HeFH. Among other lipoprotein disturbances, alterations in the phenotype and functionality of high-density lipoproteins (HDL) have been described in HeFH patients, contributing to the presence and severity of CVD. In fact, HDL are the first defensive barrier against the burden of high LDL cholesterol levels owing to their contribution to reverse cholesterol transport as well as their antioxidant and anti-inflammatory properties, among others. In this context, the present narrative review aimed to focus on quantitative and qualitative abnormalities in HDL particles in HeFH, encompassing metabolic, genetic and epigenetic aspects.

Characterization of immortalized human dermal microvascular endothelial cells (HMEC-1) for the study of HDL functionality

BACKGROUND

Primary cultures endothelial cells have been used as models of endothelial related diseases such atherosclerosis. Biological behavior of primary cultures is donor-dependent and data could not be easily reproducible; endothelial cell lines are emerging options, particularly, human dermal microvascular endothelial cells (HMEC-1), that should be validated to substitute primary cultures for the study of HDL functions.

METHODS

Morphology, size and granularity of cells were assessed by phase contrast microscopy and flow cytometry of HMEC-1. The adhesion molecules, ICAM-1and VCAM-1 after TNF-α stimulation, and endothelial markers CD105 endoglin, as well as HDL receptor SR-BI were determined by flow cytometry. Internalization of HDL protein was demonstrated by confocal microscopy using HDL labeled with Alexa Fluor 488. HUVECs were used as reference to compared the characteristics with HMEC-1.

RESULTS

HMEC-1 and HUVEC had similar morphologies, size and granularity. HMEC-1 expressed endothelial markers as HUVECs, as well as functional SR-B1 receptor since the cell line was able to internalize HDL particles. HMEC-1 effectively increased ICAM-1 and VCAM-1 expression after TNF-α stimulation. HUVECs showed more sensibility to TNF-α stimulus but the range of ICAM-1 and VCAM-1 expression was less homogeneous than in HMEC-1, probably due to biological variation of the former. Finally, the expression of adhesion molecules in HMEC-1 was attenuated by co-incubation with HDL.

CONCLUSION

HMEC-1 possess characteristics of endothelial cells, similar to HUVECs, being a cell line suitable to evaluate the functionality of HDL vis-à-vis the endothelium.

Protein changes in non-LDL-lipoproteins in familial hypercholesterolemia: implications in cardiovascular disease manifestation and outcome

PURPOSE OF REVIEW

Familial hypercholesterolemia, represents one of the most extreme clinical entities associated with premature coronary artery disease (CAD). However, clinical manifestation of CAD varies across cohorts and individual patients suggesting the existence of additional non-LDL factors potentially contributing to their cardiovascular burden.

RECENT FINDINGS

Changes in HDL-associated proteins appear as one of the potential additional factors contributing to the cardiovascular risk in familial hypercholesterolemia. Specifically, the content of Apo M-SP1 in HDL3 has been directly associated with cholesterol efflux capacity. In addition, a coordinated decrease in the content of Apo L1 and LCAT in HDL3 has been related to the presence of corneal arcus and to bad prognosis in familial hypercholesterolemia patients after an acute ischemic event. In fact, HDL3 particles of familial hypercholesterolemia patients have diminished antioxidant and anti-inflammatory function.

SUMMARY

The identification of the specific changes in HDL-associated proteins that contribute to the increased cardiovascular risk of familial hypercholesterolemia patients could be useful for the development of novel therapeutic targets. These novel strategies, in combination with current lipid-lowering therapies, may help to reduce the residual risk found in these patients.

Comprehensive lipid and metabolite profiling of children with and without familial hypercholesterolemia: A cross-sectional study

BACKGROUND AND AIMS

Individuals with familial hypercholesterolemia (FH) have elevated low-density lipoprotein cholesterol (LDL-C), accelerated atherosclerosis, and premature cardiovascular disease. Whereas children with lifestyle-induced dyslipidemias often present with complex lipid abnormalities, children with FH have isolated hypercholesterolemia. However, to the best of our knowledge, a comprehensive profiling of FH children is lacking. Therefore, we aimed to characterize the lipid-related and metabolic alterations associated with elevated LDL-C in children with FH and healthy children.

METHODS

We measured plasma metabolites in children with FH (n = 47) and in healthy children (n = 57) using a high-throughput nuclear magnetic resonance (NMR) spectroscopy platform, and compared the differences between FH and healthy children.

RESULTS

Both statin treated (n = 17) and non-statin treated FH children (n = 30) had higher levels of atherogenic ApoB-containing lipoproteins and lipids, and lipid fractions in lipoprotein subclasses, compared to healthy children (n = 57). FH children displayed alterations in HDL particle concentration and lipid content, compared with healthy children. Interestingly, the small HDL particles were characterized by higher content of cholesteryl esters, and lower levels of free cholesterol and phospholipids. Furthermore, plasma fatty acids were higher in non-statin treated FH children, particularly linoleic acid. Finally, acetoacetate and acetate were lower in FH children compared with healthy children.

CONCLUSIONS

Hypercholesterolemia in children associates with diverse metabolic repercussions and is more complex than previously believed. In particular, we found that hypercholesterolemia in FH children was paralleled not only by increased atherogenic ApoB-containing lipoproteins and lipid fractions, but also alterations in HDL subfractions that suggest impaired reverse cholesterol transport.

Altered leukocyte distribution under hypercholesterolemia: A cross-sectional study in children with familial hypercholesterolemia

BACKGROUND AND AIMS

Children with familial hypercholesterolemia (FH) have elevated LDL cholesterol from the first year of life, and represent a model of early-stage atherosclerosis. Data suggest that adults with FH have alterations in circulating monocyte subpopulations towards a more pro-inflammatory phenotype, but it is not known whether FH children have similar perturbations. In addition, there are no data on the distribution of lymphocyte subpopulations in FH children. The objective of the present study was to characterize the distributions of circulating monocyte and lymphocyte subpopulations in children with FH and healthy, normocholesterolemic children.

METHODS

Using flow cytometry analysis, we analyzed whole blood B- and T-cell subpopulations and monocyte subpopulations in FH (n = 23) and healthy (n = 20) children. Moreover, we measured serum markers of leukocyte and endothelial cell activation using EIA.

RESULTS

We found that FH children had monocytosis as well as a shift in the monocyte subpopulations. This shift was characterized by higher circulating pro-inflammatory and non-classical monocytes, and lower levels of classical monocytes, and seemed to be present only in FH children with low HDL cholesterol (HDL-C, below 1.3 mmol/L). Additionally, monocytes expressing CD18 and serum E-selectin were higher in FH children, in particular FH children with low HDL-C.

CONCLUSIONS

FH children with low HDL-C had monocytosis as well as a shift in monocyte subpopulations towards a more pro-inflammatory phenotype. Our results suggest activation of monocytes at a very early stage of atherosclerosis in humans.

Dysfunctional high-density lipoproteins in coronary heart disease: implications for diagnostics and therapy

Low plasma levels of high-density lipoprotein (HDL) cholesterol are associated with increased risks of coronary heart disease. HDL mediates cholesterol efflux from macrophages for reverse transport to the liver and elicits many anti-inflammatory and anti-oxidative activities which are potentially anti-atherogenic. Nevertheless, HDL has not been successfully targeted by drugs for prevention or treatment of cardiovascular diseases. One potential reason is the targeting of HDL cholesterol which does not capture the structural and functional complexity of HDL particles. Hundreds of lipid species and dozens of proteins as well as several microRNAs have been identified in HDL. This physiological heterogeneity is further increased in pathologic conditions due to additional quantitative and qualitative molecular changes of HDL components which have been associated with both loss of physiological function and gain of pathologic dysfunction. This structural and functional complexity of HDL has prevented clear assignments of molecules to the functions of normal HDL and dysfunctions of pathologic HDL. Systematic analyses of structure-function relationships of HDL-associated molecules and their modifications are needed to test the different components and functions of HDL for their relative contribution in the pathogenesis of atherosclerosis. The derived biomarkers and targets may eventually help to exploit HDL for treatment and diagnostics of cardiovascular diseases.

ApoL1 levels in high density lipoprotein and cardiovascular event presentation in patients with familial hypercholesterolemia

HDL composition rather than HDL-cholesterol (HDL-C) levels seems to be a key determinant of HDL-induced atheroprotection. Heterozygous familial hypercholesterolemia (FH) patients, with lifelong exposure to high LDL levels, show a high prevalence of premature coronary artery disease. We hypothesized that HDL of FH patients might have a modified protein composition and investigated the proteomic signature of HDL obtained from FH patients and their unaffected relatives. HDLs were characterized by 2D electrophoresis/MS in 10 families from the SAFEHEART cohort (3 individuals/family: 2 with genetic FH diagnosis and 1 non-FH relative) clinically characterized and treated as per guidelines. FH patients had lower apoA-I levels and a differential HDL distribution profile of apoL1 and apoA-IV. ELISA validation revealed decreased apoL1 serum levels in FH patients. ApoL1 levels were able to predict presentation of an ischemic cardiac event, and apoL1/HDL-C ratio was associated with the survival rate after the event. FH patients who died because of a fatal cardiac event had lower apoL1 and LCAT content in HDL3 an average of 3.5 years before the event than those who survived. Changes in HDL protein composition could affect patients' prognosis. The proteomic profile of apoL1 is modified in HDLs of high cardiovascular risk patients, and apoL1 plasma levels are significantly lower in serum and in HDL3 of patients that will suffer an adverse cardiac event within 3 years.

Small, dense high-density lipoprotein 3 particles exhibit defective antioxidative and anti-inflammatory function in familial hypercholesterolemia: Partial correction by low-density lipoprotein apheresis

BACKGROUND

Familial hypercholesterolemia (FH) features elevated oxidative stress and accelerated atherosclerosis driven by elevated levels of atherogenic lipoproteins relative to subnormal levels of atheroprotective high-density lipoprotein (HDL). Small, dense HDL3 potently protects low-density lipoprotein (LDL) against proinflammatory oxidative damage.

OBJECTIVE

To determine whether antioxidative and/or anti-inflammatory activities of HDL are defective in FH and whether such defects are corrected by LDL apheresis.

METHODS

Antioxidative and antiinflammatory activities of HDL were evaluated as protection of reference LDL from oxidative stress and capacity to prevent accumulation of proinflammatory oxidised lipids, respectively. Lipid surface rigidity of HDL was assessed using a fluorescent probe. HDL components were measured by analytical approaches. Systemic oxidative stress was characterized as plasma 8-isoprostanes.

RESULTS

Pre-LDL-apheresis, FH patients (n = 10) exhibited elevated systemic oxidative stress (3.3-fold, P < 0.001) vs. sex- and age-matched normolipidemic controls (n = 10). Both antioxidative and antiinflammatory activity of HDL3 were impaired (up to -91%, P < 0.01) in FH. Sphingomyelin and saturated fatty acid contents were elevated in FH HDL3, resulting in enhanced lipid surface rigidity. The surface lipid content (phospholipids, free cholesterol) was reduced in FH (up to -15%, P < 0.001), whereas content of core lipids (cholesteryl esters, triglycerides) was elevated (up to +17%, P < 0.001). Molar apolipoprotein A-I content of HDL3 was subnormal in FH. A single LDL-apheresis session partially corrected (by up to 76%) deficient HDL antiatherogenic activities, attenuated systemic oxidative stress and partially normalised both the lipid composition and surface rigidity of HDL particles.

CONCLUSIONS

FH features elevated oxidative stress and deficient antioxidative and anti-inflammatory activities of small, dense HDL3; such functional deficiency is intimately linked to anomalies in lipid and protein composition, which may impair the capacity of HDL to acquire and inactivate oxidized lipids.

Unraveling the complexities of the HDL lipidome

Plasma high density lipoproteins (HDL) are small, dense, protein-rich particles compared with other lipoprotein classes; roughly half of total HDL mass is accounted for by lipid components. Phospholipids predominate in the HDL lipidome, accounting for 40-60% of total lipid, with lesser proportions of cholesteryl esters (30-40%), triglycerides (5-12%), and free cholesterol (5-10%). Lipidomic approaches have provided initial insights into the HDL lipidome with identification of over 200 individual molecular lipids species in normolipidemic HDL. Plasma HDL particles, however, reveal high levels of structural, compositional, and functional heterogeneity. Establishing direct relationships between HDL structure, composition, and atheroprotective functions bears the potential to identify clinically relevant HDL subpopulations. Furthermore, development of HDL-based therapies designed to target beneficial subspecies within the circulating HDL pool can be facilitated using this approach. HDL lipidomics can equally contribute to the identification of biomarkers of both normal and deficient HDL functionality, which may prove useful as biomarkers of cardiovascular risk. However, numerous technical issues remain to be addressed in order to make such developments possible. With all technical questions resolved, quantitative analysis of the molecular components of the HDL lipidome will contribute to expand our knowledge of cardiovascular and metabolic diseases.

Antiatherogenic function of HDL particle subpopulations: focus on antioxidative activities

Oxidative stress, an emerging risk factor for premature atherosclerosis and cardiovascular disease, mediates the formation of proinflammatory, pro-atherogenic oxidized low-density lipoprotein (oxLDL) in the arterial intima. Circulating HDL particles, and particularly small, dense, protein-rich HDL3, may provide potent protection of LDL in vivo from oxidative damage by free radicals in the arterial intima, resulting in the inhibition of the generation of proinflammatory oxidized lipids, primarily lipid hydroperoxides (LOOH) but also short-chain oxidized phospholipids (oxPL). HDL-mediated inactivation of LOOH involves initial transfer of phospholipid hydroperoxides (PLOOH) from LDL to HDL3, which is governed by the rigidity of the surface monolayer of HDL, and subsequent reduction of PLOOH by redox-active Met residues of apolipoprotein A-I (apoA-I) with the formation of phospholipid hydroxides (PLOH) and methionine sulphoxides. HDL-associated enzymes may in turn contribute to the hydrolytic inactivation of short-chain oxPL. Mounting evidence suggests that the integrated antioxidative activity of HDL appear to be defective in atherogenic dyslipidaemias involving low HDL-cholesterol levels; anomalies in the proteome and lipidome of HDL particles in dyslipidaemic patients may underlie such functional deficiency. Pharmacological normalization of HDL metabolism concomitantly with correction of circulating levels, composition and biological activities of HDL particles, with enrichment in apoA-I and reduction in HDL surface rigidity, may constitute an efficacious therapeutic approach to attenuate atherosclerosis in dyslipidaemic patients at high cardiovascular risk.

The antiatherogenic function of HDL is impaired in hyperhomocysteinemic subjects

High plasma homocysteine concentrations have been associated with increased risk of cardiovascular disease, whereas plasma HDL concentration is inversely correlated to such disorders. We hypothesized that hyperhomocysteinemic subjects may have dysfunctional HDL. We therefore investigated the ability of serum from hyperhomocysteinemic male and female subjects (n = 10) and control subjects (n = 10) to induce cholesterol efflux and to inhibit release of inflammatory mediators from human umbilical vein endothelial cell. We found that serum from hyperhomocysteinemic subjects had impaired ability to induce cholesterol efflux from lipid-loaded macrophages compared with healthy controls. HDL from those with markedly raised homocysteine concentrations had a reduced antiinflammatory effect in tumor necrosis factor-alpha-activated endothelial cells with an attenuated suppressive effect on interleukin-6 growth-related oncogene-alpha release. Also, the activity of paraoxonase in serum, a multifunctional enzyme with antioxidative effects in relation to the function of HDL, was significantly reduced in hyperhomocysteinemic subjects, in particular those with markedly raised homocysteine concentration. Our findings suggest that hyperhomocysteinemic individuals have dysfunctional HDL particles with attenuated antiatherogenic activity and may represent a novel explanation for the increased risk of cardiovascular events in these individuals.

Historical milestones in measurement of HDL-cholesterol: Impact on clinical and laboratory practice

High-density lipoprotein cholesterol (HDL-C) comprises a family of particles with differing physicochemical characteristics. Continuing progress in improving HDL-C analysis has originated from two separate fields-one clinical, reflecting increased attention to HDL-C in estimating risk for coronary heart disease (CHD), and the other analytical, reflecting increased emphasis on finding more reliable and cost-effective HDL-C assays. Epidemiologic and prospective studies established the inverse association of HDL-C with CHD risk, a relationship that is consistent with protective mechanisms demonstrated in basic research and animal studies. Atheroprotective and less atheroprotective HDL subpopulations have been described. Guidelines on primary and secondary CHD prevention, which increased the workload in clinical laboratories, have led to a revolution in HDL-C assay technology. Many analytical techniques including ultracentrifugation, electrophoresis, chromatography, and polyanion precipitation methods have been developed to separate and quantify HDL-C and HDL subclasses. More recently developed homogeneous assays enable direct measurement of HDL-C on an automated analyzer, without the need for manual pretreatment to separate non-HDL. Although homogeneous assays show improved accuracy and precision in normal serum, discrepant results exist in samples with atypical lipoprotein characteristics. Hypertriglyceridemia and monoclonal paraproteins are important interfering factors. A novel approach is nuclear magnetic resonance spectroscopy that allows rapid and reliable analysis of lipoprotein subclasses, which may improve the identification of individuals at increased CHD risk. Apolipoprotein A-I, the major protein of HDL, has been proposed as an alternative cardioprotective marker avoiding the analytical limitations of HDL-C.

Triglyceride-rich HDL3 from patients with familial hypercholesterolemia are less able to inhibit cytokine release or to promote cholesterol efflux

Familial hypercholesterolemia (FH) is associated with heterogeneity of the onset and severity of coronary heart disease (CHD). In this study, we investigated different low-grade proinflammatory markers and the atheroprotective function of the HDL3 subfraction in FH-patients (n = 13) with identical LDL-receptor mutations and in age- and sex-matched healthy controls (n = 11). Compared with healthy controls, FH-patients had greater gene expressions of the proatherogenic mediators TNF-alpha and IL-8 in circulating peripheral blood mononuclear cells. In addition, they had a higher serum concentration of intercellular adhesion molecule-1 (ICAM-1) and a lower net antioxidant capacity. FH-derived HDL3 with a high level of triglycerides had a reduced capacity to inhibit the release of IL-8 from TNF-alpha-stimulated human umbilical vein endothelial cells (HUVEC) [1.864 mg/L (1.461-2.208 mg/L) vs. 1.466 mg/L (1.225-1.643 mg/L); P < 0.05; median (range)], and a reduced capacity to promote cholesterol efflux from lipid-loaded macrophages [12% (12-14%) vs. 15% (14-18%); P < 0.05; median (range)] compared with HDL3 with a lower triglyceride content. Notably, the degree of inhibition of IL-8 release from HUVEC by HDL3 was correlated with the ability of HDL3 to promote cholesterol efflux (r = -0.80, P = 0.03). In conclusion, compared with healthy controls, FH-patients are characterized by higher levels of low-grade proinflammatory markers, and FH-derived HDL3 with high triglyceride content may be more proatherogenic. These triglyceride rich-HDL3 might be partly responsible for the phenotypic variation among FH-patients with identical LDL-receptor mutations.