Naturally occurring and bioengineered apoA-I mutations that inhibit the conversion of discoidal to spherical HDL: the abnormal HDL phenotypes can be corrected by treatment with LCAT

Precision Nutrition and Cardiovascular Disease Risk Reduction: the Promise of High-Density Lipoproteins

PURPOSE OF REVIEW

Emerging evidence supports the promise of precision nutritional approaches for cardiovascular disease (CVD) prevention. Here, we discuss current findings from precision nutrition trials and studies reporting substantial inter-individual variability in responses to diets and dietary components relevant to CVD outcomes. We highlight examples where early precision nutrition research already points to actionable intervention targets tailored to an individual's biology and lifestyle. Finally, we make the case for high-density lipoproteins (HDL) as a compelling next generation target for precision nutrition aimed at CVD prevention. HDL possesses complex structural features including diverse protein components, lipids, size distribution, extensive glycosylation, and interacts with the gut microbiome, all of which influence HDL's anti-inflammatory, antioxidant, and cholesterol efflux properties. Elucidating the nuances of HDL structure and function at an individual level may unlock personalized dietary and lifestyle strategies to optimize HDL-mediated atheroprotection and reduce CVD risk.

RECENT FINDINGS

Recent human studies have demonstrated that HDL particles are key players in the reduction of CVD risk. Our review highlights the role of HDL and the importance of personalized therapeutic approaches to improve their potential for reducing CVD risk. Factors such as diet, genetics, glycosylation, and gut microbiome interactions can modulate HDL structure and function at the individual level. We emphasize that fractionating HDL into size-based subclasses and measuring particle concentration are necessary to understand HDL biology and for developing the next generation of diagnostics and biomarkers. These discoveries underscore the need to move beyond a one-size-fits-all approach to HDL management. Precision nutrition strategies that account for personalized metabolic, genetic, and lifestyle data hold promise for optimizing HDL therapies and function to mitigate CVD risk more potently. While human studies show HDL play a key role in reducing CVD risk, recent findings indicate that factors such as diet, genetics, glycosylation, and gut microbes modulate HDL function at the individual level, underscoring the need for precision nutrition strategies that account for personalized variability to optimize HDL's potential for mitigating CVD risk.

Association of Plasma Vitamins and Carotenoids, DNA Methylation of LCAT, and Risk of Age-Related Macular Degeneration

Dysregulation of lipid metabolism has been implicated in age-related macular degeneration (AMD), the leading cause of blindness among the elderly. Lecithin cholesterol acyltransferase (LCAT) is an important enzyme responsible for lipid metabolism, which could be regulated by DNA methylation during the development of various age-related diseases. This study aimed to assess the association between LCAT DNA methylation and the risk of AMD, and to examine whether plasma vitamin and carotenoid concentrations modified this association. A total of 126 cases of AMD and 174 controls were included in the present analysis. LCAT DNA methylation was detected by quantitative real-time methylation-1specific PCR (qMSP). Circulating vitamins and carotenoids were measured using reversed-phase high-performance liquid chromatography (RP-HPLC). DNA methylation of LCAT was significantly higher in patients with AMD than those in the control subjects. After multivariable adjustment, participants in the highest tertile of LCAT DNA methylation had a 5.37-fold higher risk (95% CI: 2.56, 11.28) of AMD compared with those in the lowest tertile. Each standard deviation (SD) increment of LCAT DNA methylation was associated with a 2.23-fold (95% CI: 1.58, 3.13) increased risk of AMD. There was a J-shaped association between LCAT DNA methylation and AMD risk (P_{non-linearity} = 0.03). Higher concentrations of plasma retinol and β-cryptoxanthin were significantly associated with decreased levels of LCAT DNA methylation, with the multivariate-adjusted β coefficient being -0.05 (95% CI: -0.08, -0.01) and -0.25 (95% CI: -0.42, -0.08), respectively. In joint analyses of LCAT DNA methylation and plasma vitamin and carotenoid concentrations, the inverse association between increased LCAT DNA methylation and AMD risk was more pronounced among participants who had a lower concentration of plasma retinol and β-cryptoxanthin. These findings highlight the importance of comprehensively assessing LCAT DNA methylation and increasing vitamin and carotenoid status for the prevention of AMD.

Using adenovirus-mediated gene transfer to study the effect of myeloperoxidase on plasma lipid levels, HDL structure and functionality in mice expressing human apoA-I forms

Apolipoprotein A-I (apoA-I), the main protein component of High-Density Lipoprotein (HDL), is modified in plasma and the arterial wall by various enzymes. Myeloperoxidase (MPO), a leukocyte-derived peroxidase, is highly expressed during inflammation and associates with HDL reducing its functionality and contributing to atherosclerosis. In the present study we sought to explore further the effect of MPO on HDL structure and functionality in vivo using adenovirus-mediated gene transfer of human MPO combined with human apoA-I forms containing substitutions at MPO-sensitive sites or wild type apoA-I. We found that overexpression of MPO in mice significantly increased plasma apoA-I and HDL levels without affecting the expression of genes involved in HDL biogenesis or catabolism in the liver. Overexpression of MPO in the liver reduced the expression of pro-inflammatory genes and increased or did not affect the expression of anti-inflammatory genes suggesting that MPO had no toxic effects in this organ. In the plasma of mice overexpressing MPO, no significant alterations in HDL size or electrophoretic mobility was observed with the exception of mice expressing apoA-I (M148A) which showed enriched pre-β relative to α HDL particles, suggesting that the apoA-I (M148A) mutation may interfere with HDL remodelling. Overexpression of MPO was associated with reduced anti-oxidant capacity of HDL particles in all mice. Interestingly, HDL particles bearing apoA-I (Y192A) showed enhanced ABCA1-dependent cholesterol efflux from macrophages which was not affected by MPO and these mice had reduced levels of LDL-c. These findings provide new insights on the role of specific amino acid residues of apoA-I in HDL structure and function following modification by MPO. This knowledge may facilitate the development of novel therapies based on improved HDL forms for patients with chronic diseases that are characterized by dysfunctional HDL.

Apolipoprotein A1-Related Proteins and Reverse Cholesterol Transport in Antiatherosclerosis Therapy: Recent Progress and Future Perspectives

Hyperlipidemia characterized by abnormal deposition of cholesterol in arteries can cause atherosclerosis and coronary artery occlusion, leading to atherosclerotic coronary heart disease. The body prevents atherosclerosis by reverse cholesterol transport to mobilize and excrete cholesterol and other lipids. Apolipoprotein A1, the major component of high-density lipoprotein, plays a key role in reverse cholesterol transport. Here, we reviewed the role of apolipoprotein A1-targeting molecules in antiatherosclerosis therapy, in particular ATP-binding cassette transporter A1, lecithin-cholesterol acyltransferase, and scavenger receptor class B type 1.

Current Therapies Focused on High-Density Lipoproteins Associated with Cardiovascular Disease

High-density lipoproteins (HDL) comprise a heterogeneous family of lipoprotein particles divided into subclasses that are determined by density, size and surface charge as well as protein composition. Epidemiological studies have suggested an inverse correlation between High-density lipoprotein-cholesterol (HDL-C) levels and the risk of cardiovascular diseases and atherosclerosis. HDLs promote reverse cholesterol transport (RCT) and have several atheroprotective functions such as anti-inflammation, anti-thrombosis, and anti-oxidation. HDLs are considered to be atheroprotective because they are associated in serum with paraoxonases (PONs) which protect HDL from oxidation. Polyphenol consumption reduces the risk of chronic diseases in humans. Polyphenols increase the binding of HDL to PON1, increasing the catalytic activity of PON1. This review summarizes the evidence currently available regarding pharmacological and alternative treatments aimed at improving the functionality of HDL-C. Information on the effectiveness of the treatments has contributed to the understanding of the molecular mechanisms that regulate plasma levels of HDL-C, thereby promoting the development of more effective treatment of cardiovascular diseases. For that purpose, Scopus and Medline databases were searched to identify the publications investigating the impact of current therapies focused on high-density lipoproteins.

Role of apolipoproteins, ABCA1 and LCAT in the biogenesis of normal and aberrant high density lipoproteins

In this review, we focus on the pathway of biogenesis of HDL, the essential role of apoA-I, ATP binding cassette transporter A1 (ABCA1), and lecithin: cholesterol acyltransferase (LCAT) in the formation of plasma HDL; the generation of aberrant forms of HDL containing mutant apoA-I forms and the role of apoA-IV and apoE in the formation of distinct HDL subpopulations. The biogenesis of HDL requires functional interactions of the ABCA1 with apoA-I (and to a lesser extent with apoE and apoA-IV) and subsequent interactions of the nascent HDL species thus formed with LCAT. Mutations in apoA-I, ABCA1 and LCAT either prevent or impair the formation of HDL and may also affect the functionality of the HDL species formed. Emphasis is placed on three categories of apoA-I mutations. The first category describes a unique bio-engineered apoA-I mutation that disrupts interactions between apoA-I and ABCA1 and generates aberrant preβ HDL subpopulations that cannot be converted efficiently to α subpopulations by LCAT. The second category describes natural and bio-engineered apoA-I mutations that generate preβ and small size α4 HDL subpopulations, and are associated with low plasma HDL levels. These phenotypes can be corrected by excess LCAT. The third category describes bio-engineered apoA-I mutations that induce hypertriglyceridemia that can be corrected by excess lipoprotein lipase and also have defective maturation of HDL. The HDL phenotypes described here may serve in the future for diagnosis, prognoses and potential treatment of abnormalities that affect the biogenesis and functionality of HDL.

Structural Insights into High Density Lipoprotein: Old Models and New Facts

The physiological link between circulating high density lipoprotein (HDL) levels and cardiovascular disease is well-documented, albeit its intricacies are not well-understood. An improved appreciation of HDL function and overall role in vascular health and disease requires at its foundation a better understanding of the lipoprotein's molecular structure, its formation, and its process of maturation through interactions with various plasma enzymes and cell receptors that intervene along the pathway of reverse cholesterol transport. This review focuses on summarizing recent developments in the field of lipid free apoA-I and HDL structure, with emphasis on new insights revealed by newly published nascent and spherical HDL models constructed by combining low resolution structures obtained from small angle neutron scattering (SANS) with contrast variation and geometrical constraints derived from hydrogen-deuterium exchange (HDX), crosslinking mass spectrometry, electron microscopy, Förster resonance energy transfer, and electron spin resonance. Recently published low resolution structures of nascent and spherical HDL obtained from SANS with contrast variation and isotopic labeling of apolipoprotein A-I (apoA-I) will be critically reviewed and discussed in terms of how they accommodate existing biophysical structural data from alternative approaches. The new low resolution structures revealed and also provided some answers to long standing questions concerning lipid organization and particle maturation of lipoproteins. The review will discuss the merits of newly proposed SANS based all atom models for nascent and spherical HDL, and compare them with accepted models. Finally, naturally occurring and bioengineered mutations in apoA-I, and their impact on HDL phenotype, are reviewed and discuss together with new therapeutics employed for restoring HDL function.

The Effect of Natural LCAT Mutations on the Biogenesis of HDL

We have investigated how the natural LCAT[T147I] and LCAT[P274S] mutations affect the pathway of biogenesis of HDL. Gene transfer of WT LCAT in LCAT(-/-) mice increased 11.8-fold the plasma cholesterol, whereas the LCAT[T147I] and LCAT[P274S] mutants caused a 5.2- and 2.9-fold increase, respectively. The LCAT[P274S] and the WT LCAT caused a monophasic distribution of cholesterol in the HDL region, whereas the LCAT[T147I] caused a biphasic distribution of cholesterol in the LDL and HDL region. Fractionation of plasma showed that the expression of WT LCAT increased plasma apoE and apoA-IV levels and shifted the distribution of apoA-I to lower densities. The LCAT[T147I] and LCAT[P274S] mutants restored partially apoA-I in the HDL3 fraction and LCAT[T147I] increased apoE in the VLD/IDL/LDL fractions. The in vivo functionality of LCAT was further assessed based on is its ability to correct the aberrant HDL phenotype that was caused by the apoA-I[L159R]FIN mutation. Co-infection of apoA-I(-/-) mice with this apoA-I mutant and either of the two mutant LCAT forms restored only partially the HDL biogenesis defect that was caused by the apoA-I[L159R]FIN and generated a distinct aberrant HDL phenotype.

HDL biogenesis, remodeling, and catabolism

In this chapter, we review how HDL is generated, remodeled, and catabolized in plasma. We describe key features of the proteins that participate in these processes, emphasizing how mutations in apolipoprotein A-I (apoA-I) and the other proteins affect HDL metabolism. The biogenesis of HDL initially requires functional interaction of apoA-I with the ATP-binding cassette transporter A1 (ABCA1) and subsequently interactions of the lipidated apoA-I forms with lecithin/cholesterol acyltransferase (LCAT). Mutations in these proteins either prevent or impair the formation and possibly the functionality of HDL. Remodeling and catabolism of HDL is the result of interactions of HDL with cell receptors and other membrane and plasma proteins including hepatic lipase (HL), endothelial lipase (EL), phospholipid transfer protein (PLTP), cholesteryl ester transfer protein (CETP), apolipoprotein M (apoM), scavenger receptor class B type I (SR-BI), ATP-binding cassette transporter G1 (ABCG1), the F1 subunit of ATPase (Ecto F1-ATPase), and the cubulin/megalin receptor. Similarly to apoA-I, apolipoprotein E and apolipoprotein A-IV were shown to form discrete HDL particles containing these apolipoproteins which may have important but still unexplored functions. Furthermore, several plasma proteins were found associated with HDL and may modulate its biological functions. The effect of these proteins on the functionality of HDL is the topic of ongoing research.

apoE3[K146N/R147W] acts as a dominant negative apoE form that prevents remnant clearance and inhibits the biogenesis of HDL

The K146N/R147W substitutions in apoE3 were described in patients with a dominant form of type III hyperlipoproteinemia. The effects of these mutations on the in vivo functions of apoE were studied by adenovirus-mediated gene transfer in different mouse models. Expression of the apoE3[K146N/R147W] mutant in apoE-deficient (apoE(-/-)) or apoA-I-deficient (apoA-I(-/-))×apoE(-/-) mice exacerbated the hypercholesterolemia and increased plasma apoE and triglyceride levels. In apoE(-/-) mice, the apoE3[K146N/R147W] mutant displaced apoA-I from the VLDL/LDL/HDL region and caused the accumulation of discoidal apoE-containing HDL. The WT apoE3 cleared the cholesterol of apoE(-/-) mice without induction of hypertriglyceridemia and promoted formation of spherical HDL. A unique property of the truncated apoE3[K146N/R147W]202 mutant, compared with similarly truncated apoE forms, is that it did not correct the hypercholesterolemia. The contribution of LPL and LCAT in the induction of the dyslipidemia was studied. Treatment of apoE(-/-) mice with apoE3[K146N/R147W] and LPL corrected the hypertriglyceridemia, but did not prevent the formation of discoidal HDL. Treatment with LCAT corrected hypertriglyceridemia and generated spherical HDL. The combined data indicate that the K146N/R147W substitutions convert the full-length and the truncated apoE3[K146N/R147W] mutant into a dominant negative ligand that prevents receptor-mediated remnant clearance, exacerbates the dyslipidemia, and inhibits the biogenesis of HDL.

Significance of the hydrophobic residues 225-230 of apoA-I for the biogenesis of HDL

We studied the significance of four hydrophobic residues within the 225-230 region of apoA-I on its structure and functions and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of an apoA-I[F225A/V227A/F229A/L230A] mutant in apoA-I⁻/⁻ mice decreased plasma cholesterol, HDL cholesterol, and apoA-I levels. When expressed in apoA-I⁻/⁻ × apoE⁻/⁻ mice, approximately 40% of the mutant apoA-I as well as mouse apoA-IV and apoB-48 appeared in the VLDL/IDL/LDL. In both mouse models, the apoA-I mutant generated small spherical particles of pre-β- and α4-HDL mobility. Coexpression of the apoA-I mutant and LCAT increased and shifted the-HDL cholesterol peak toward lower densities, created normal αHDL subpopulations, and generated spherical-HDL particles. Biophysical analyses suggested that the apoA-I[225-230] mutations led to a more compact folding that may limit the conformational flexibility of the protein. The mutations also reduced the ability of apoA-I to promote ABCA1-mediated cholesterol efflux and to activate LCAT to 31% and 66%, respectively, of the WT control. Overall, the apoA-I[225-230] mutations inhibited the biogenesis of-HDL and led to the accumulation of immature pre-β- and α4-HDL particles, a phenotype that could be corrected by administration of LCAT.

Role of the hydrophobic and charged residues in the 218-226 region of apoA-I in the biogenesis of HDL

We investigated the significance of hydrophobic and charged residues 218-226 on the structure and functions of apoA-I and their contribution to the biogenesis of HDL. Adenovirus-mediated gene transfer of apoA-I[L218A/L219A/V221A/L222A] in apoA-I⁻/⁻ mice decreased plasma cholesterol and apoA-I levels to 15% of wild-type (WT) control mice and generated pre-β- and α4-HDL particles. In apoA-I⁻/⁻ × apoE⁻/⁻ mice, the same mutant formed few discoidal and pre-β-HDL particles that could not be converted to mature α-HDL particles by excess LCAT. Expression of the apoA-I[E223A/K226A] mutant in apoA-I⁻/⁻ mice caused lesser but discrete alterations in the HDL phenotype. The apoA-I[218-222] and apoA-I[E223A/K226A] mutants had 20% and normal capacity, respectively, to promote ABCA1-mediated cholesterol efflux. Both mutants had ∼65% of normal capacity to activate LCAT in vitro. Biophysical analyses suggested that both mutants affected in a distinct manner the structural integrity and plasticity of apoA-I that is necessary for normal functions. We conclude that the alteration of the hydrophobic 218-222 residues of apoA-I disrupts apoA-I/ABCA1 interactions and promotes the generation of defective pre-β particles that fail to mature into α-HDL subpopulations, thus resulting in low plasma apoA-I and HDL. Alterations of the charged 223, 226 residues caused milder but discrete changes in HDL phenotype.

HDL drug carriers for targeted therapy

Plasma concentrations of high-density lipoprotein cholesterol (HDL-C) are strongly and inversely associated with cardiovascular risk. HDL is not a simple lipid transporter, but possesses multiple anti-atherosclerosis activities because it contains special proteins, signaling lipid, and microRNAs. Natural or recombinant HDLs have emerged as potential carriers for delivering a drug to a specified target. However, HDL function also depends on enzymes that alter its structure and composition, as well as cellular receptors and membrane micro-domains that facilitate interactions with the microenvironment. In this review, four mechanisms predicted to enhance functions or targeted therapy of HDL in vivo are discussed. The first involves caveolae-mediated recruitment of HDL signal to bind their receptors. The second involves scavenger receptor class B type I (SR-BI) mediating anchoring and fluidity for signal-lipid of HDL. The third involves lecithin-cholesterol acyltransferase (LCAT) concentrating the signaling lipid at the surface of the HDL particle. The fourth involves microRNAs (miRNAs) being delivered in the blood to special targets by HDL. Exploitation of these four mechanisms will promote HDL to carry targeted drugs and increase HDL's clinical value.

Apolipoprotein A-I exerts bactericidal activity against Yersinia enterocolitica serotype O:3

Apolipoprotein A-I (apoA-I), the main protein component of high density lipoprotein (HDL), is well recognized for its antiatherogenic, antioxidant, and antiinflammatory properties. Here, we report a novel role for apoA-I as a host defense molecule that contributes to the complement-mediated killing of an important gastrointestinal pathogen, Gram-negative bacterium Yersinia enterocolitica. We specifically show that the C-terminal domain of apoA-I is the effector site providing the bactericidal activity. Although the presence of the lipopolysaccharide O-antigen on the bacterial surface is absolutely required for apoA-I to kill the bacteria, apoA-I does not interact with the bacteria directly. To the contrary, exposure of the bacteria by serum proteins triggers apoA-I deposition on the bacterial surface. As our data show that both purified lipid-free and HDL-associated apoA-I displays anti-bacterial potential, apoA-I mimetic peptides may be a promising therapeutic agent for the treatment of certain Gram-negative infections.

Alteration of negatively charged residues in the 89 to 99 domain of apoA-I affects lipid homeostasis and maturation of HDL

In this study, we investigated the role of positively and negatively charged amino acids within the 89-99 region of apolipoprotein A-I (apoA-I), which are highly conserved in mammals, on plasma lipid homeostasis and the biogenesis of HDL. We previously showed that deletion of the 89-99 region of apoA-I increased plasma cholesterol and phospholipids, but it did not affect plasma triglycerides. Functional studies using adenovirus-mediated gene transfer of two apoA-I mutants in apoA-I-deficient mice showed that apoA-I[D89A/E91A/E92A] increased plasma cholesterol and caused severe hypertriglyceridemia. HDL levels were reduced, and approximately 40% of the apoA-I was distributed in VLDL/IDL. The HDL consisted of mostly spherical and a few discoidal particles and contained preβ1 and α4-HDL subpopulations. The lipid, lipoprotein, and HDL profiles generated by the apoA-I[K94A/K96A] mutant were similar to those of wild-type (WT) apoA-I. Coexpression of apoA-I[D89A/E91A/E92A] and human lipoprotein lipase abolished hypertriglyceridemia, restored in part the α1,2,3,4 HDL subpopulations, and redistributed apoA-I in the HDL2/HDL3 regions, but it did not prevent the formation of discoidal HDL particles. Physicochemical studies showed that the apoA-I[D89A/E91A/E92A] mutant had reduced α-helical content and effective enthalpy of thermal denaturation, increased exposure of hydrophobic surfaces, and increased affinity for triglyceride-rich emulsions. We conclude that residues D89, E91, and E92 of apoA-I are important for plasma cholesterol and triglyceride homeostasis as well as for the maturation of HDL.

Carboxyl terminus of apolipoprotein A-I (ApoA-I) is necessary for the transport of lipid-free ApoA-I but not prelipidated ApoA-I particles through aortic endothelial cells

High density lipoproteins (HDL) and apolipoprotein A-I (apoA-I) must leave the circulation and pass the endothelium to exert their atheroprotective actions in the arterial wall. We previously demonstrated that the transendothelial transport of apoA-I involves ATP-binding cassette transporter (ABC) A1 and re-secretion of lipidated particles. Transendothelial transport of HDL is modulated by ABCG1 and the scavenger receptor BI (SR-BI). We hypothesize that apoA-I transport is started by the ABCA1-mediated generation of a lipidated particle which is then transported by ABCA1-independent pathways. To test this hypothesis we analyzed the endothelial binding and transport properties of initially lipid-free as well as prelipidated apoA-I mutants. Lipid-free apoA-I mutants with a defective carboxyl-terminal domain showed an 80% decreased specific binding and 90% decreased specific transport by aortic endothelial cells. After prior cell-free lipidation of the mutants, the resulting HDL-like particles were transported through endothelial cells by an ABCG1- and SR-BI-dependent process. ApoA-I mutants with deletions of either the amino terminus or both the amino and carboxyl termini showed dramatic increases in nonspecific binding but no specific binding or transport. Prior cell-free lipidation did not rescue these anomalies. Our findings of stringent structure-function relationships underline the specificity of transendothelial apoA-I transport and suggest that lipidation of initially lipid-free apoA-I is necessary but not sufficient for specific transendothelial transport. Our data also support the model of a two-step process for the transendothelial transport of apoA-I in which apoA-I is initially lipidated by ABCA1 and then further processed by ABCA1-independent mechanisms.

High pre-beta1 HDL concentrations and low lecithin: cholesterol acyltransferase activities are strong positive risk markers for ischemic heart disease and independent of HDL-cholesterol

BACKGROUND

We hypothesized that patients with high HDL-cholesterol (HDL-C) and ischemic heart disease (IHD) may have dysfunctional HDL or unrecognized nonconventional risk factors.

METHODS

Individuals with IHD (Copenhagen University Hospital) and either high HDL-C (n = 53; women >or=735 mg/L; men >or=619 mg/L) or low HDL-C (n = 42; women <or=387 mg/L; men <or=341 mg/L) were compared with individuals without IHD (Copenhagen City Heart Study) matched by age, sex, and HDL-C concentrations (n = 110). All participants had concentrations within reference intervals for LDL-C (<1600 mg/L) and triglyceride (<1500 mg/L), and none were treated with lipid-lowering medications. Pre-beta(1) HDL and phospholipid transfer protein concentrations were measured by using commercial kits and lecithin:cholesterol acyltransferase (LCAT) activity by using a proteoliposome cholesterol esterification assay.

RESULTS

Pre-beta(1) HDL concentrations were 2-fold higher in individuals with IHD vs no IHD in both the high [63 (5.7) vs 35 (2.3) mg/L; P < 0.0001] and low HDL-C [49 (5.0) vs 27 (1.5) mg/L; P = 0.001] groups. Low LCAT activity was also associated with IHD in the high [95.2 (6.7) vs 123.0 (5.3) micromol x L(-1) x h(-1); P = 0.002] and low [93.4 (8.3) vs 113.5 (4.9) micromol x L(-1) . h(-1); P = 0.03] HDL-C groups. ROC curves for pre-beta(1) HDL in the high-HDL-C groups yielded an area under the curve of 0.71 (95% CI: 0.61-0.81) for predicting IHD, which increased to 0.92 (0.87-0.97) when LCAT was included. Similar results were obtained for low HDL-C groups. An inverse correlation between LCAT activity and pre-beta(1) HDL was observed (r(2) = 0.30; P < 0.0001) in IHD participants, which was stronger in the low HDL-C group (r(2) = 0.56; P < 0.0001).

CONCLUSIONS

IHD was associated with high pre-beta(1) HDL concentrations and low LCAT levels, yielding correct classification in more than 90% of the IHD cases for which both were measured, thus making pre-beta(1) HDL concentration and LCAT activity level potentially useful diagnostic markers for cardiovascular disease.

Double superhelix model of high density lipoprotein

High density lipoprotein (HDL), the carrier of so-called "good" cholesterol, serves as the major athero-protective lipoprotein and has emerged as a key therapeutic target for cardiovascular disease. We applied small angle neutron scattering (SANS) with contrast variation and selective isotopic deuteration to the study of nascent HDL to obtain the low resolution structure in solution of the overall time-averaged conformation of apolipoprotein AI (apoA-I) versus the lipid (acyl chain) core of the particle. Remarkably, apoA-I is observed to possess an open helical shape that wraps around a central ellipsoidal lipid phase. Using the low resolution SANS shapes of the protein and lipid core as scaffolding, an all-atom computational model for the protein and lipid components of nascent HDL was developed by integrating complementary structural data from hydrogen/deuterium exchange mass spectrometry and previously published constraints from multiple biophysical techniques. Both SANS data and the new computational model, the double superhelix model, suggest an unexpected structural arrangement of protein and lipids of nascent HDL, an anti-parallel double superhelix wrapped around an ellipsoidal lipid phase. The protein and lipid organization in nascent HDL envisages a potential generalized mechanism for lipoprotein biogenesis and remodeling, biological processes critical to sterol and lipid transport, organismal energy metabolism, and innate immunity.

Activation of lecithin:cholesterol acyltransferase by HDL ApoA-I central helices

Lecithin:cholesterol acyltransferase (LCAT) is an enzyme that first hydrolyzes the sn-2 position of phospholipids, preferentially a diacylphosphocholine, and then transfers the fatty acid to cholesterol to yield a cholesteryl ester. HDL ApoA-I is the principal catalytic activator for LCAT. Activity of LCAT on nascent or lipid-poor HDL particles composed of phospholipid, cholesterol and ApoA-I allows the maturation of HDL particles into lipid-rich spherical particles that contain a core of cholesteryl ester surrounded by phospholipid and ApoA-I on the surface. This article reviews the recent progress in elucidating structural aspects of the interaction between LCAT and ApoA-I. In the last decade, there has been considerable progress in understanding the structure of ApoA-I and the central helices 5, 6, and 7 that are known to activate LCAT. However, much less information has been forthcoming describing the 3D structure and conformation of LCAT required to catalyze two separate reactions within a single monomeric peptide.

Discrete roles of apoA-I and apoE in the biogenesis of HDL species: lessons learned from gene transfer studies in different mouse models

Using adenovirus-mediated gene transfer in apolipoprotein A-I (apoA-I)-deficient mice, we have established that apoA-I mutations inhibit discrete steps in a pathway that leads to the biogenesis and remodeling of high-density lipoprotein (HDL). To this point, five discrete categories of apoA-I mutants have been characterized that may affect the interactions of apoA-I with ATP-binding cassette superfamily A, member 1 (ABCA1) or lecithin:cholesterol acyl transferase (LCAT) or may influence the plasma phospholipid transfer protein activity or may cause various forms of dyslipidemia. Biogenesis of HDL is not a unique property of apoA-I. Using adenovirus-mediated gene transfer of apoE in apoA-I- or ABCA1-deficient mice, we have established that apolipoprotein E (apoE) also participates in a novel pathway of biogenesis of apoE-containing HDL particles. This process requires the functions of the ABCA1 lipid transporter and LCAT, and it is promoted by substitution of hydrophobic residues in the 261 to 269 region of apoE by Ala. The apoE-containing HDL particles formed in the circulation may have atheroprotective properties. ApoE-containing HDL may also have important biological functions in the brain that confer protection from Alzheimer's disease.