Hepatitis C virus E1 recruits high-density lipoprotein to support infectivity and evade antibody recognition.

Hepatitis C virus (HCV) is a member of the Flaviviridae family; however, unlike other family members, the HCV virion has an unusually high lipid content. HCV has two envelope glycoproteins, E1 and E2. E2 contributes to receptor binding, cell membrane attachment, and immune evasion. In contrast, the functions of E1 are poorly characterized due, in part, to challenges in producing the protein. This manuscript describes the expression and purification of a soluble E1 ectodomain (eE1) that is recognized by conformational, human monoclonal antibodies. eE1 forms a complex with apolipoproteins AI and AII, cholesterol, and phospholipids by recruiting high-density lipoprotein (HDL) from the extracellular media. We show that HDL binding is a function specific to eE1 and HDL hinders recognition of E1 by a neutralizing monoclonal antibody. Either low-density lipoprotein or HDL increases the production and infectivity of cell culture-produced HCV, but E1 preferentially selects HDL, influencing both viral life cycle and antibody evasion.IMPORTANCEHepatitis C virus (HCV) infection is a significant burden on human health, but vaccine candidates have yet to provide broad protection against this infection. We have developed a method to produce high quantities of soluble E1 or E2, the viral proteins located on the surface of HCV. HCV has an unusually high lipid content due to the recruitment of apolipoproteins. We found that E1 (and not E2) preferentially recruits host high-density lipoprotein (HDL) extracellularly. This recruitment of HDL by E1 prevents binding of E1 by a neutralizing antibody and furthermore prevents antibody-mediated neutralization of the virus. By comparison, low-density lipoprotein does not protect the virus from antibody-mediated neutralization. Our findings provide mechanistic insight into apolipoprotein recruitment, which may be critical for vaccine development.

Asthmatic patients with high serum amyloid A have proinflammatory HDL: Implications for augmented systemic and airway inflammation.

RATIONALE: Serum amyloid A (SAA) is bound to high-density lipoproteins (HDL) in blood. Although SAA is increased in the blood of patients with asthma, it is not known whether this modifies asthma severity. OBJECTIVE: We sought to define the clinical characteristics of patients with asthma who have high SAA levels and assess whether HDL from SAA-high patients with asthma is proinflammatory. METHODS: SAA levels in serum from subjects with and without asthma were quantified by ELISA. HDLs isolated from subjects with asthma and high SAA levels were used to stimulate human monocytes and were intravenously administered to BALB/c mice. RESULTS: An SAA level greater than or equal to 108.8 µg/mL was defined as the threshold to identify 11% of an asthmatic cohort (n = 146) as being SAA-high. SAA-high patients with asthma were characterized by increased serum C-reactive protein, IL-6, and TNF-α; older age; and an increased prevalence of obesity and severe asthma. HDL isolated from SAA-high patients with asthma (SAA-high HDL) had an increased content of SAA as compared with HDL from SAA-low patients with asthma and induced the secretion of IL-6, IL-1ß, and TNF-α from human monocytes via a formyl peptide receptor 2/ATP/P2X purinoceptor 7 axis. Intravenous administration to mice of SAA-high HDL, but not normal HDL, induced systemic inflammation and amplified allergen-induced neutrophilic airway inflammation and goblet cell metaplasia. CONCLUSIONS: SAA-high patients with asthma are characterized by systemic inflammation, older age, and an increased prevalence of obesity and severe asthma. HDL from SAA-high patients with asthma is proinflammatory and, when intravenously administered to mice, induces systemic inflammation, and amplifies allergen-induced neutrophilic airway inflammation. This suggests that systemic inflammation induced by SAA-high HDL may augment disease severity in asthma.

Flipped C-Terminal Ends of APOA1 Promote ABCA1-Dependent Cholesterol Efflux by Small HDLs.

BACKGROUND: Cholesterol efflux capacity (CEC) predicts cardiovascular disease independently of high-density lipoprotein (HDL) cholesterol levels. Isolated small HDL particles are potent promoters of macrophage CEC by the ABCA1 (ATP-binding cassette transporter A1) pathway, but the underlying mechanisms are unclear. METHODS: We used model system studies of reconstituted HDL and plasma from control and lecithin-cholesterol acyltransferase (LCAT)-deficient subjects to investigate the relationships among the sizes of HDL particles, the structure of APOA1 (apolipoprotein A1) in the different particles, and the CECs of plasma and isolated HDLs. RESULTS: We quantified macrophage and ABCA1 CEC of 4 distinct sizes of reconstituted HDL. CEC increased as particle size decreased. Tandem mass spectrometric analysis of chemically cross-linked peptides and molecular dynamics simulations of APOA1, the major protein of HDL, indicated that the mobility of C-terminus of that protein was markedly higher and flipped off the surface in the smallest particles. To explore the physiological relevance of the model system studies, we isolated HDL from LCAT-deficient subjects, whose small HDLs (like reconstituted HDLs) are discoidal and composed of APOA1, cholesterol, and phospholipid. Despite their very low plasma levels of HDL particles, these subjects had normal CEC. In both the LCAT-deficient subjects and control subjects, the CEC of isolated extra-small HDL (a mixture of extra-small and small HDL by calibrated ion mobility analysis) was 3- to 5-fold greater than that of the larger sizes of isolated HDL. Incubating LCAT-deficient plasma and control plasma with human LCAT converted extra-small and small HDL particles into larger particles, and it markedly inhibited CEC. CONCLUSIONS: We present a mechanism for the enhanced CEC of small HDLs. In smaller particles, the C-termini of the 2 antiparallel molecules of APOA1 are "flipped" off the lipid surface of HDL. This extended conformation allows them to engage with ABCA1. In contrast, the C-termini of larger HDLs are unable to interact productively with ABCA1 because they form a helical bundle that strongly adheres to the lipid on the particle. Enhanced CEC, as seen with the smaller particles, predicts decreased cardiovascular disease risk. Thus, extra-small and small HDLs may be key mediators and indicators of the cardioprotective effects of HDL.

Dietary fish oil enriched in very-long-chain polyunsaturated fatty acid reduces cardiometabolic risk factors and improves retinal function.

Very-long-chain polyunsaturated fatty acids (VLCPUFAs; C24-38) constitute a unique class of PUFA that have important biological roles, but the lack of a suitable dietary source has limited research in this field. We produced an n-3 C24-28-rich VLCPUFA-oil concentrated from fish oil to study its bioavailability and physiological functions in C57BL/6J mice. The serum and retinal C24:5 levels increased significantly compared to control after a single-dose gavage, and VLCPUFAs were incorporated into the liver, brain, and eyes after 8-week supplementation. Dietary VLCPUFAs resulted in favorable cardiometabolic changes, and improved electroretinography responses and visual performance. VLCPUFA supplementation changed the expression of genes involved in PPAR signaling pathways. Further in vitro studies demonstrated that the VLCPUFA-oil and chemically synthesized C24:5 are potent agonists for PPARs. The multiple potential beneficial effects of fish oil-derived VLCPUFAs on cardiometabolic risk and eye health in mice support future efforts to develop VLCPUFA-oil into a supplemental therapy.

Structural flexibility of apolipoprotein E-derived arginine-rich peptides improves their cell penetration capability.

Amphipathic arginine-rich peptide, A2-17, exhibits moderate perturbation of lipid membranes and the highest cell penetration among its structural isomers. We investigated the direct cell-membrane penetration mechanism of the A2-17 peptide while focusing on structural flexibility. We designed conformationally constrained versions of A2-17, stapled (StpA2-17) and stitched (StchA2-17), whose α-helical conformations were stabilized by chemical crosslinking. Circular dichroism confirmed that StpA2-17 and StchA2-17 had higher α-helix content than A2-17 in aqueous solution. Upon liposome binding, only A2-17 exhibited a coil-to-helix transition. Confocal microscopy revealed that A2-17 had higher cell penetration efficiency than StpA2-17, whereas StchA2-17 remained on the cell membrane without cell penetration. Although the tryptophan fluorescence analysis suggested that A2-17 and its analogs had similar membrane-insertion positions between the interface and hydrophobic core, StchA2-17 exhibited a higher membrane affinity than A2-17 or StpA2-17. Atomic force microscopy demonstrated that A2-17 reduced the mechanical rigidity of liposomes to a greater extent than StpA2-17 and StchA2-17. Finally, electrophysiological analysis showed that A2-17 induced a higher charge influx through transient pores in a planer lipid bilayer than StpA2-17 and StchA2-17. These findings indicate that structural flexibility, which enables diverse conformations of A2-17, leads to a membrane perturbation mode that contributes to cell membrane penetration.

Cell-free, high-density lipoprotein-specific phospholipid efflux assay predicts incident cardiovascular disease.

BACKGROUNDCellular cholesterol efflux capacity (CEC) is a better predictor of cardiovascular disease (CVD) events than HDL-cholesterol (HDL-C) but is not suitable as a routine clinical assay.METHODSWe developed an HDL-specific phospholipid efflux (HDL-SPE) assay to assess HDL functionality based on whole plasma HDL apolipoprotein-mediated solubilization of fluorescent phosphatidylethanolamine from artificial lipid donor particles. We first assessed the association of HDL-SPE with prevalent coronary artery disease (CAD): study I included NIH severe-CAD (n = 50) and non-CAD (n = 50) participants, who were frequency matched for sex, BMI, type 2 diabetes mellitus, and smoking; study II included Japanese CAD (n = 70) and non-CAD (n = 154) participants. We also examined the association of HDL-SPE with incident CVD events in the Prevention of Renal and Vascular End-stage Disease (PREVEND) study comparing 340 patients with 340 controls individually matched for age, sex, smoking, and HDL-C levels.RESULTSReceiver operating characteristic curves revealed stronger associations of HDL-SPE with prevalent CAD. The AUCs in study I were as follows: HDL-SPE, 0.68; apolipoprotein A-I (apoA-I), 0.62; HDL-C, 0.63; and CEC, 0.52. The AUCs in study II were as follows: HDL-SPE, 0.83; apoA-I, 0.64; and HDL-C, 0.53. Also longitudinally, HDL-SPE was significantly associated with incident CVD events independent of traditional risk factors with ORs below 0.2 per SD increment in the PREVEND study (P < 0.001).CONCLUSIONHDL-SPE could serve as a routine clinical assay for improving CVD risk assessment and drug discovery.TRIAL REGISTRATIONClinicalTrials.gov NCT01621594.FUNDINGNHLBI Intramural Research Program, NIH (HL006095-06).

Association of Lipoprotein Subfractions With Presence and Severity of Coronary Artery Disease in Patients Referred for Coronary Angiography.

Lipoprotein subfractions (LS) can be used for better risk stratification in subjects deemed not at high risk for coronary artery disease (CAD). In this study, we evaluated the correlation between LS with CAD presence and severity. This is a prospective case-control study of 157 patients referred for coronary angiography who were not on lipid-lowering therapy and had LS measured by nuclear magnetic resonance spectroscopy. Synergy between PCI with Taxus and Cardiac Surgery (SYNTAX) scores were calculated to estimate CAD severity. Univariate and multivariable regression analysis was performed to determine correlation of LS with CAD presence and severity and acute coronary syndrome (ACS). There was significant association of certain LS (positive for total low-density lipoprotein particle [LDL-P], small LDL-P and apolipoprotein B, negative for large high-density lipoprotein particle [HDL-P] and apolipoprotein A1 [ApoA1]) with the presence of obstructive CAD and CAD severity. Small LDL-P and HDL-P were still predictive for obstructive CAD after adjusting for traditional risk factors, 10-year atherosclerotic cardiovascular disease risk score and in those with low-density lipoprotein cholesterol <100 mg/100 ml. Total LDL-P and ApoA1 were predictive of CAD severity on multivariable analysis. Higher small LDL-P and lower large HDL-P were associated with ACS presence, although only large HDL-P had a significant inverse correlation with ACS on adjusted analysis (odds ratio 0.74 95% confidence interval 0.58, 0.95) In conclusion, in our cohort of patients referred for coronary angiography, total LDL-P, small LDL-P, and apolipoprotein B had significant direct correlation, and large HDL-P and ApoA1 had significant inverse correlation with obstructive CAD and CAD severity.

Variability in Lipid Levels and Risk for Cardiovascular Disease: An Electronic Health Record-Based Population Cohort Study.

Background Larger within-patient variability of lipid levels has been associated with increased risk of cardiovascular disease (CVD); however, measures of lipid variability require ≥3 measurements and are not currently used clinically. We investigated the feasibility of calculating lipid variability within a large electronic health record-based population cohort and assessed associations with incident CVD. Methods and Results We identified all individuals ≥40 years of age who resided in Olmsted County, MN, on January 1, 2006 (index date), without prior CVD, defined as myocardial infarction, coronary artery bypass graft surgery, percutaneous coronary intervention, or CVD death. Patients with ≥3 measurements of total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, or triglycerides during the 5 years before the index date were retained. Lipid variability was calculated using variability independent of the mean. Patients were followed through December 31, 2020 for incident CVD. We identified 19 652 individuals (mean age 61 years; 55% female), who were CVD-free and had variability independent of the mean calculated for at least 1 lipid type. After adjustment, those with highest total cholesterol variability had a 20% increased risk of CVD (Q5 versus Q1 hazard ratio, 1.20 [95% CI, 1.06-1.37]). Results were similar for low-density lipoprotein cholesterol and high-density lipoprotein cholesterol. Conclusions In a large electronic health record-based population cohort, high variability in total cholesterol, high-density lipoprotein cholesterol, and low-density lipoprotein cholesterol was associated with an increased risk of CVD, independent of traditional risk factors, suggesting it may be a possible risk marker and target for intervention. Lipid variability can be calculated in the electronic health record environment, but more research is needed to determine its clinical utility.

Systematic evaluation of the effect of different apolipoprotein A-I mimetic peptides on the performance of synthetic high-density lipoproteins in vitro and in vivo.

Synthetic high-density lipoproteins nanomedicine (sHDL) composed of apolipoprotein A-I (ApoA-I) mimetic peptides and lipids have shown very promising results for the treatment of various cardiovascular diseases. Numerous efforts have also been made to design different ApoA-I mimetic peptides to improve the potency of sHDL, especially the efficiency of reverse cholesterol transport. However, the way in which ApoA-I mimetic peptides affect the properties of sHDL, including stability, cholesterol efflux, cholesterol esterification, elimination in vivo, and the relationship of these properties, is still poorly understood. Revealing the effect of these factors on the potency of sHDL is important for the design of better ApoA-I mimetic peptides. In this study, three widely used ApoA-I mimetic peptides with different sequences, lengths, LCAT activation and lipid binding affinities were used for the preparation of sHDL and were evaluated in terms of physical/chemical properties, cholesterol efflux, cholesterol esterification, remodeling, and pharmacokinetics/pharmacodynamics. Our results showed that ApoA-I mimetic peptides with the highest cholesterol efflux and cholesterol esterification in vitro did not exhibit the highest cholesterol mobilization in vivo. Further analysis indicated that other factors, such as pharmacokinetics and remodeling of sHDL, need to be considered in order to predict the efficiency of cholesterol mobilization in vivo. Thus, our study highlights the importance of using the overall performance, rather than in vitro results alone, as the blueprint for the design and optimization of ApoA-I mimetic peptides.

High-density lipoprotein revisited: biological functions and clinical relevance.

Previous interest in high-density lipoproteins (HDLs) focused on their possible protective role in atherosclerotic cardiovascular disease (ASCVD). Evidence from genetic studies and randomized trials, however, questioned that the inverse association of HDL-cholesterol (HDL-C) is causal. This review aims to provide an update on the role of HDL in health and disease, also beyond ASCVD. Through evolution from invertebrates, HDLs are the principal lipoproteins, while apolipoprotein B-containing lipoproteins first developed in vertebrates. HDLs transport cholesterol and other lipids between different cells like a reusable ferry, but serve many other functions including communication with cells and the inactivation of biohazards like bacterial lipopolysaccharides. These functions are exerted by entire HDL particles or distinct proteins or lipids carried by HDL rather than by its cholesterol cargo measured as HDL-C. Neither does HDL-C measurement reflect the efficiency of reverse cholesterol transport. Recent studies indicate that functional measures of HDL, notably cholesterol efflux capacity, numbers of HDL particles, or distinct HDL proteins are better predictors of ASCVD events than HDL-C. Low HDL-C levels are related observationally, but also genetically, to increased risks of infectious diseases, death during sepsis, diabetes mellitus, and chronic kidney disease. Additional, but only observational, data indicate associations of low HDL-C with various autoimmune diseases, and cancers, as well as all-cause mortality. Conversely, extremely high HDL-C levels are associated with an increased risk of age-related macular degeneration (also genetically), infectious disease, and all-cause mortality. HDL encompasses dynamic multimolecular and multifunctional lipoproteins that likely emerged during evolution to serve several physiological roles and prevent or heal pathologies beyond ASCVD. For any clinical exploitation of HDL, the indirect marker HDL-C must be replaced by direct biomarkers reflecting the causal role of HDL in the respective disease.

The ApoA-I mimetic peptide 5A enhances remyelination by promoting clearance and degradation of myelin debris.

The progressive nature of demyelinating diseases lies in the inability of the central nervous system (CNS) to induce proper remyelination. Recently, we and others demonstrated that a dysregulated innate immune response partially underlies failure of CNS remyelination. Extensive accumulation of myelin-derived lipids and an inability to process these lipids was found to induce a disease-promoting phagocyte phenotype. Hence, restoring the ability of these phagocytes to metabolize and efflux myelin-derived lipids represents a promising strategy to promote remyelination. Here, we show that ApoA-I mimetic peptide 5A, a molecule well known to promote activity of the lipid efflux transporter ABCA1, markedly enhances remyelination. Mechanistically, we find that the repair-inducing properties of 5A are attributable to increased clearance and metabolism of remyelination-inhibiting myelin debris via the fatty acid translocase protein CD36, which is transcriptionally controlled by the ABCA1-JAK2-STAT3 signaling pathway. Altogether, our findings indicate that 5A promotes remyelination by stimulating clearance and degradation of myelin debris.

A New Structural Model of Apolipoprotein B100 Based on Computational Modeling and Cross Linking.

ApoB-100 is a member of a large lipid transfer protein superfamily and is one of the main apolipoproteins found on low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) particles. Despite its clinical significance for the development of cardiovascular disease, there is limited information on apoB-100 structure. We have developed a novel method based on the "divide and conquer" algorithm, using PSIPRED software, by dividing apoB-100 into five subunits and 11 domains. Models of each domain were prepared using I-TASSER, DEMO, RoseTTAFold, Phyre2, and MODELLER. Subsequently, we used disuccinimidyl sulfoxide (DSSO), a new mass spectrometry cleavable cross-linker, and the known position of disulfide bonds to experimentally validate each model. We obtained 65 unique DSSO cross-links, of which 87.5% were within a 26 Å threshold in the final model. We also evaluated the positions of cysteine residues involved in the eight known disulfide bonds in apoB-100, and each pair was measured within the expected 5.6 Å constraint. Finally, multiple domains were combined by applying constraints based on detected long-range DSSO cross-links to generate five subunits, which were subsequently merged to achieve an uninterrupted architecture for apoB-100 around a lipoprotein particle. Moreover, the dynamics of apoB-100 during particle size transitions was examined by comparing VLDL and LDL computational models and using experimental cross-linking data. In addition, the proposed model of receptor ligand binding of apoB-100 provides new insights into some of its functions.

Differential Effect of Dietary Supplementation with a Soybean Oil Enriched in Oleic Acid versus Linoleic Acid on Plasma Lipids and Atherosclerosis in LDLR-Deficient Mice.

Both monounsaturated fatty acids (MUFAs) and polyunsaturated fatty acids (PUFAs) play important roles in lipid metabolism, and diets enriched with either of these two fatty acids are associated with decreased cardiovascular risk. Conventional soybean oil (CSO), a common food ingredient, predominantly contains linoleic acid (LA; C18:2), a n-6 PUFA. Recently, a modified soybean oil (MSO) enriched in oleic acid (C18:1), a n-9 MUFA, has been developed, because of its improved chemical stability to oxidation. However, the effect of the different dietary soybean oils on cardiovascular disease remains unknown. To test whether diets rich in CSO versus MSO would attenuate atherosclerosis development, LDL receptor knock-out (LDLR-KO) mice were fed a Western diet enriched in saturated fatty acids (control), or a Western diet supplemented with 5% (w/w) LA-rich CSO or high-oleic MSO for 12 weeks. Both soybean oils contained a similar amount of linolenic acid (C18:3 n-3). The CSO diet decreased plasma lipid levels and the cholesterol content of VLDL and LDL by approximately 18% (p < 0.05), likely from increased hepatic levels of PUFA, which favorably regulated genes involved in cholesterol metabolism. The MSO diet, but not the CSO diet, suppressed atherosclerotic plaque size compared to the Western control diet (Control Western diet: 6.5 ± 0.9%; CSO diet: 6.4 ± 0.7%; MSO diet: 4.0 ± 0.5%) (p < 0.05), independent of plasma lipid level changes. The MSO diet also decreased the ratio of n-6/n-3 PUFA in the liver (Control Western diet: 4.5 ± 0.2; CSO diet: 6.1 ± 0.2; MSO diet: 2.9 ± 0.2) (p < 0.05), which correlated with favorable hepatic gene expression changes in lipid metabolism and markers of systemic inflammation. In conclusion, supplementation of the Western diet with MSO, but not CSO, reduced atherosclerosis development in LDLR-KO mice independent of changes in plasma lipids.

Estimated Atherosclerotic Cardiovascular Disease Risk Score: An Automated Decision Aid for Statin Therapy.

BACKGROUND: Estimation of atherosclerotic cardiovascular disease (ASCVD) risk is a key step in cardiovascular disease (CVD) prevention, but it requires entering additional risk factor information into a computer. We developed a simplified ASCVD risk score that can be automatically calculated by the clinical laboratory when a fasting standard lipid panel is reported. METHODS: Equations for an estimated ASCVD (eASCVD) risk score were developed for 4 race/sex groups (non-Hispanic White/Black, men/women), using the following variables: total cholesterol, high-density lipoprotein cholesterol, triglycerides, and age. The eASCVD score was derived using regression analysis to yield similar risk estimates as the standard ASCVD risk equations for non-diabetic individuals not on lipid-lowering therapy in the National Health and Nutrition Examination Survey (NHANES) (n = 6027). RESULTS: At a cutpoint of 7.5%/10-year, the eASCVD risk score had an overall sensitivity of 69.1% and a specificity of 97.5% for identifying statin-eligible patients with at least intermediate risk based on the standard risk score. By using the sum of other risk factors present (systolic blood pressure >130 mmHg, blood pressure medication use, and cigarette use), the overall sensitivity of the eASCVD score improved to 93.7%, with a specificity of 92.3%. Furthermore, it showed 90% concordance with the standard risk score in predicting cardiovascular events in the Atherosclerosis Risk in Communities (ARIC) study (n = 14 742). CONCLUSIONS: Because the automated eASCVD risk score can be computed for all patients with a fasting standard lipid panel, it could be used as an adjunctive tool for the primary prevention of ASCVD and as a decision aid for statin therapy.

High-density lipoproteins: A promising tool against cancer.

High-density lipoproteins (HDL) are well known for their protective role against the development and progression of atherosclerosis. Atheroprotection is mainly due to the key role of HDL within the reverse cholesterol transport, and to their ability to exert a series of antioxidant and anti-inflammatory activities. Through the same mechanisms HDL could also affect cancer cell proliferation and tumor progression. Many types of cancers share common alterations of cellular metabolism, including lipid metabolism. In this context, not only fatty acids but also cholesterol and its metabolites play a key role. HDL were shown to reduce cancer cell content of cholesterol, overall rewiring cholesterol homeostasis. In addition, HDL reduce oxidative stress and the levels of pro-inflammatory molecules in cancer cells and in the tumor microenvironment (TME). Here, HDL can also help in reverting tumor immune escape and in inhibiting angiogenesis. Interestingly, HDL are good candidates for drug delivery, targeting antineoplastic agents to the tumor mass mainly through their binding to the scavenger receptor BI. Since they could affect cancer development and progression per se, HDL-based drug delivery systems may render cancer cells more sensitive to antitumor agents and reduce the development of drug resistance.

Mitochondrial C5aR1 activity in macrophages controls IL-1ß production underlying sterile inflammation.

While serum-circulating complement destroys invading pathogens, intracellularly active complement, termed the "complosome," functions as a vital orchestrator of cell-metabolic events underlying T cell effector responses. Whether intracellular complement is also nonredundant for the activity of myeloid immune cells is currently unknown. Here, we show that monocytes and macrophages constitutively express complement component (C) 5 and generate autocrine C5a via formation of an intracellular C5 convertase. Cholesterol crystal sensing by macrophages induced C5aR1 signaling on mitochondrial membranes, which shifted ATP production via reverse electron chain flux toward reactive oxygen species generation and anaerobic glycolysis to favor IL-1ß production, both at the transcriptional level and processing of pro­IL-1ß. Consequently, atherosclerosis-prone mice lacking macrophage-specific C5ar1 had ameliorated cardiovascular disease on a high-cholesterol diet. Conversely, inflammatory gene signatures and IL-1ß produced by cells in unstable atherosclerotic plaques of patients were normalized by a specific cell-permeable C5aR1 antagonist. Deficiency of the macrophage cell-autonomous C5 system also protected mice from crystal nephropathy mediated by folic acid. These data demonstrate the unexpected intracellular formation of a C5 convertase and identify C5aR1 as a direct modulator of mitochondrial function and inflammatory output from myeloid cells. Together, these findings suggest that the complosome is a contributor to the biologic processes underlying sterile inflammation and indicate that targeting this system could be beneficial in macrophage-dependent diseases, such as atherosclerosis.

Serum levels of small HDL particles are negatively correlated with death or lung transplantation in an observational study of idiopathic pulmonary fibrosis.

BACKGROUND: Serum lipoproteins, such as high-density lipoproteins (HDL), may influence disease severity in idiopathic pulmonary fibrosis (IPF). Here, we investigated associations between serum lipids and lipoproteins and clinical end-points in IPF. METHODS: Clinical data and serum lipids were analysed from a discovery cohort (59 IPF subjects, 56 healthy volunteers) and validated using an independent, multicentre cohort (207 IPF subjects) from the Pulmonary Fibrosis Foundation registry. Associations between lipids and clinical end-points (forced vital capacity, 6-min walk distance, gender age physiology (GAP) index, death or lung transplantation) were examined using Pearson's correlation and multivariable analyses. RESULTS: Serum concentrations of small HDL particles measured using nuclear magnetic resonance spectroscopy (S-HDLPNMR) correlated negatively with the GAP index in the discovery cohort of IPF subjects. The negative correlation of S-HDLPNMR with GAP index was confirmed in the validation cohort of IPF subjects. Higher levels of S-HDLPNMR were associated with lower odds of death or its competing outcome, lung transplantation (OR 0.9 for each 1-µmol·L-1 increase in S-HDLPNMR, p<0.05), at 1, 2 and 3 years from study entry in a combined cohort of all IPF subjects. CONCLUSIONS: Higher serum levels of S-HDLPNMR are negatively correlated with the GAP index, as well as with lower observed mortality or lung transplantation in IPF subjects. These findings support the hypothesis that S-HDLPNMR may modify mortality risk in patients with IPF.

HDL in the 21st Century: A Multifunctional Roadmap for Future HDL Research.

Low high-density lipoprotein cholesterol (HDL-C) characterizes an atherogenic dyslipidemia that reflects adverse lifestyle choices, impaired metabolism, and increased cardiovascular risk. Low HDL-C is also associated with increased risk of inflammatory disorders, malignancy, diabetes, and other diseases. This epidemiologic evidence has not translated to raising HDL-C as a viable therapeutic target, partly because HDL-C does not reflect high-density lipoprotein (HDL) function. Mendelian randomization analyses that have found no evidence of a causal relationship between HDL-C levels and cardiovascular risk have decreased interest in increasing HDL-C levels as a therapeutic target. HDLs comprise distinct subpopulations of particles of varying size, charge, and composition that have several dynamic and context-dependent functions, especially with respect to acute and chronic inflammatory states. These functions include reverse cholesterol transport, inhibition of inflammation and oxidation, and antidiabetic properties. HDLs can be anti-inflammatory (which may protect against atherosclerosis and diabetes) and proinflammatory (which may help clear pathogens in sepsis). The molecular regulation of HDLs is complex, as evidenced by their association with multiple proteins, as well as bioactive lipids and noncoding RNAs. Clinical investigations of HDL biomarkers (HDL-C, HDL particle number, and apolipoprotein A through I) have revealed nonlinear relationships with cardiovascular outcomes, differential relationships by sex and ethnicity, and differential patterns with coronary versus noncoronary events. Novel HDL markers may also have relevance for heart failure, cancer, and diabetes. HDL function markers (namely, cholesterol efflux capacity) are associated with coronary disease, but they remain research tools. Therapeutics that manipulate aspects of HDL metabolism remain the holy grail. None has proven to be successful, but most have targeted HDL-C, not metrics of HDL function. Future therapeutic strategies should focus on optimizing HDL function in the right patients at the optimal time in their disease course. We provide a framework to help the research and clinical communities, as well as funding agencies and stakeholders, obtain insights into current thinking on these topics, and what we predict will be an exciting future for research and development on HDLs.

Apolipoprotein Mimetic Peptides: Potential New Therapies for Cardiovascular Diseases.

Since the seminal breakthrough of treating diabetic patients with insulin in the 1920s, there has been great interest in developing other proteins and their peptide mimetics as therapies for a wide variety of other medical disorders. Currently, there are at least 60 different peptides that have been approved for human use and over 150 peptides that are in various stages of clinical development. Peptides mimetic of the major proteins on lipoproteins, namely apolipoproteins, have also been developed first as tools for understanding apolipoprotein structure and more recently as potential therapeutics. In this review, we discuss the biochemistry, peptide mimetics design and clinical trials for peptides based on apoA-I, apoE and apoC-II. We primarily focus on applications of peptide mimetics related to cardiovascular diseases. We conclude with a discussion on the limitations of peptides as therapeutic agents and the challenges that need to be overcome before apolipoprotein mimetic peptides can be developed into new drugs.