Lipoviral Particles Research Articles

The Apolipoprotein E neutralizing antibody inhibits SARS-CoV-2 infection by blocking cellular entry of lipoviral particles.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causal agent for coronavirus disease 2019 (COVID-19). Although vaccines have helped to prevent uncontrolled viral spreading, our understanding of the fundamental biology of SARS-CoV-2 infection remains insufficient, which hinders effective therapeutic development. Here, we found that Apolipoprotein E (ApoE), a lipid binding protein, is hijacked by SARS-CoV-2 for infection. Preincubation of SARS-CoV-2 with a neutralizing antibody specific to ApoE led to inhibition of SARS-CoV-2 infection. The ApoE neutralizing antibody efficiently blocked SARS-CoV-2 infection of human iPSC-derived astrocytes and air-liquid interface organoid models in addition to human ACE2-expressing HEK293T cells and Calu-3 lung cells. ApoE mediates SARS-CoV-2 entry through binding to its cellular receptors such as the low density lipoprotein receptor (LDLR). LDLR knockout or ApoE mutations at the receptor binding domain or an ApoE mimetic peptide reduced SARS-CoV-2 infection. Furthermore, we detected strong membrane LDLR expression on SARS-CoV-2 Spike-positive cells in human lung tissues, whereas no or low ACE2 expression was detected. This study provides a new paradigm for SARS-CoV-2 cellular entry through binding of ApoE on the lipoviral particles to host cell receptor(s). Moreover, this study suggests that ApoE neutralizing antibodies are promising antiviral therapies for COVID-19 by blocking entry of both parental virus and variants of concern.

Differentiated Cells in Prolonged Hypoxia Produce Highly Infectious Native-Like Hepatitis C Virus Particles.

Standard hepatitis C virus (HCV) cell-culture models present an altered lipid metabolism and thus produce lipid-poor lipoviral particles (LVPs). These models are thereby weakly adapted to explore the complete natural viral life cycle. To overcome these limitations, we used an HCV cell-culture model based on both cellular differentiation and sustained hypoxia to better mimic the host-cell environment. The long-term exposure of Huh7.5 cells to DMSO and hypoxia (1% O2 ) significantly enhanced the expression of major differentiation markers and the cellular hypoxia adaptive response by contrast with undifferentiated and normoxic (21% O2 ) standard conditions. Because hepatocyte-like differentiation and hypoxia are key regulators of intracellular lipid metabolism, we characterized the distribution of lipid droplets (LDs) and demonstrated that experimental cells significantly accumulate larger and more numerous LDs relative to standard cell-culture conditions. An immunocapture (IC) and transmission electron microscopy (TEM) method showed that differentiated and hypoxic Huh7.5 cells produced lipoproteins significantly larger than those produced by standard Huh7.5 cell cultures. The experimental cell culture model is permissive to HCV-Japanese fulminant hepatitis (JFH1) infection and produces very-low-buoyant-density LVPs that are 6-fold more infectious than LVPs formed by standard JFH1-infected Huh7.5 cells. Finally, the IC-TEM approach and antibody-neutralization experiments revealed that LVPs were highly lipidated, had a global ultrastructure and a conformation of the envelope glycoprotein complex E1E2 close to that of the ones circulating in infected individuals. This relevant HCV cell culture model thus mimics the complete native intracellular HCV life cycle and, by extension, can be proposed as a model of choice for studies of other hepatotropic viruses.

FRI-395 - Autoantibody to apolipoprotein A-1 in hepatitis C virus infection: a role in atherosclerosis?

One to three per cent of the world’s population has hepatitis C virus (HCV) infection, which is not only a major cause of liver disease and cancer but also associated with an increased risk of atherosclerosis, despite an ostensibly favourable lipid profile. Autoantibodies are frequent in HCV infection and emerging evidence shows that autoantibodies could be valuable for cardiovascular disease (CVD) risk stratification. This study investigated a novel independent biomarker of CVD, autoantibodies to apolipoprotein A-1 (anti-apoA-1 IgG) and lipids in patients with chronic HCV before, during and after direct-acting anti-viral (DAA) therapy. Eighty-nine blinded serum samples from 27 patients with advanced chronic HCV were assayed for lipids and anti-apoA-1 IgG by ELISA. Pre-treatment HCV viral load correlated with high-density lipoprotein cholesterol (HDL-C, r = 0.417; p = 0.042) and negatively with apolipoprotein (apo)B (r = − 0.497; p = 0.013) and markers of CVD risk, the apoB/apoA-1 ratio (r = − 0.490; p = 0.015) and triglyceride level (TG)/HDL-C ratio (r = − 0.450; p = 0.031). Fourteen (52%) of 27 patients had detectable anti-apoA-1 IgG autoantibodies pre-treatment; only two became undetectable with virological cure. Autoantibody-positive sera had lower apoA-1 (p = 0.012), HDL-C (p = 0.009) and total cholesterol (p = 0.006) levels. This is the first report of the presence of an emerging biomarker for atherosclerosis, anti-apoA-1 IgG, in some patients with HCV infection. It may be induced by apoA-1 on the surface of HCV lipoviral particles. The autoantibodies inversely correlate with apoA-1 and HDL levels and may render HDL dysfunctional. Whether these hypothesis-generating findings have clinical implications in HCV patients requires further study.

Autoantibody to apolipoprotein A-1 in hepatitis C virus infection: a role in atherosclerosis?

Background/purposeOne to three per cent of the world’s population has hepatitis C virus (HCV) infection, which is not only a major cause of liver disease and cancer but also associated with an increased risk of atherosclerosis, despite an ostensibly favourable lipid profile. Autoantibodies are frequent in HCV infection and emerging evidence shows that autoantibodies could be valuable for cardiovascular disease (CVD) risk stratification. This study investigated a novel independent biomarker of CVD, autoantibodies to apolipoprotein A-1 (anti-apoA-1 IgG) and lipids in patients with chronic HCV before, during and after direct-acting anti-viral (DAA) therapy.MethodsEighty-nine blinded serum samples from 27 patients with advanced chronic HCV were assayed for lipids and anti-apoA-1 IgG by ELISA.ResultsPre-treatment HCV viral load correlated with high-density lipoprotein cholesterol (HDL-C, r = 0.417; p = 0.042) and negatively with apolipoprotein (apo)B (r = − 0.497; p = 0.013) and markers of CVD risk, the apoB/apoA-1 ratio (r = − 0.490; p = 0.015) and triglyceride level (TG)/HDL-C ratio (r = − 0.450; p = 0.031). Fourteen (52%) of 27 patients had detectable anti-apoA-1 IgG autoantibodies pre-treatment; only two became undetectable with virological cure. Autoantibody-positive sera had lower apoA-1 (p = 0.012), HDL-C (p = 0.009) and total cholesterol (p = 0.006) levels.ConclusionsThis is the first report of the presence of an emerging biomarker for atherosclerosis, anti-apoA-1 IgG, in some patients with HCV infection. It may be induced by apoA-1 on the surface of HCV lipoviral particles. The autoantibodies inversely correlate with apoA-1 and HDL levels and may render HDL dysfunctional. Whether these hypothesis-generating findings have clinical implications in HCV patients requires further study.

Recent Advances in the Pathogenesis of Hepatitis C Virus-Related Non-Alcoholic Fatty Liver Disease and Its Impact on Patients Cured of Hepatitis C

Patients with chronic hepatitis C infection frequently develop non-alcoholic fatty liver disease (NAFLD), which confers a risk of hepatocellular carcinoma (HCC). Although direct-acting antivirals allow the majority of patients to achieve a sustained virologic response (SVR), post-SVR patients still carry a non-negligible risk of HCC. This review summarizes recent findings regarding the pathogenesis of hepatitis C virus (HCV)-related NAFLD and its impact on post-SVR patients. The recently discovered HCV-induced steatosis mechanisms include the upregulation of microRNA-27 expression and the formation of HCV-lipoviral particles, which suppress β-oxidation and triglyceride hydrolysis, respectively. Recent studies also revealed the incidence of NAFLD even among post-SVR patients, as well as an association of steatosis with hepatic inflammation and hepatocarcinogenesis. HCV induces changes in microRNA expression and lipoviral particles to directly promote the development of steatosis. In post-SVR patients, NAFLD is an important pathological condition related to hepatic inflammation and hepatocarcinogenesis.

Role of ApoB-516C/T promoter gene polymorphism in the risk of Hepatitis C virus infection in Egyptian patients and in gender susceptibility.

At least 1 in 10 of the Egyptian population aged 15-59 is burdened with hepatitis C virus (HCV) infection, stamping Egypt the highest country harboring HCV worldwide. Considerable evidence supported the involvement of host genetic factors in the pathogenesis of HCV and the possibility of implementation in target therapies. ApoB gene polymorphisms are postulated to affect the susceptibility of HCV infection. Hence, we aimed to evaluate the relationship between ApoB-516C/T promoter gene polymorphism and HCV infection in a cohort of Egyptian patients and to explore whether higher levels of low-density lipoprotein (LDL) might compete with lipoviral particles (LVP) in the binding to LDL receptor (LDLR), thus escaping infection. Ninety-seven HCV patients and 96 matched controls were enrolled in this study. We genotyped ApoB-516C/T using PCR-RFLP method. ApoB concentrations were measured by immunoturbidimetric assay. The genotype and the allele frequencies of ApoB-516C/T promoter gene polymorphism in cases were statistically insignificant compared with healthy individuals (P = 0.109, 0.125, respectively). Sex stratification showed significantly lower counts of C/T genotype in female patients compared with female controls (P = 0.011, OR = 0.132, 95% CI = 0.026-0.657). Significantly higher levels of LDL and ApoB were detected in the control group (P < 0.001). This study shows that the ApoB-516C/T promoter gene polymorphism has no impact on the risk of HCV infection. However, the C/T genotype may be a protective factor for our female cohort. Further studies with larger samples are needed to verify this genetic gender diversity. Additionally, high levels of LDL and ApoB might prevent HCV infection.

Hepatitis C virus and atherosclerosis: A legacy after virologic cure?

Hepatitis C virus (HCV) is a major pathogen with approximately 3% of the world's population (over 170 million) infected. Epidemiological studies have shown HCV is associated with an increased risk of cardiovascular and cerebrovascular mortality as well as peripheral arterial disease. This is despite HCV inducing an ostensibly favourable lipid profile with accompanying low classical risk score for atherosclerosis (AS). We discuss possible factors involved in the aetiopathogenesis of atherosclerosis in chronic HCV and hypothesise that an important mechanism underlying the development of AS is the presence of circulating low-density immune complexes that induce an inflammatory response. We suggest that HCV particles may be inducing an antibody response to lipoproteins present in the lipoviral particles and sub-viral particles - a concept similar to the more general 'autoantibody' response to modified LDL. After virologic cure some AS risk factors will recede but an increase in serum cholesterol could result in progression of early atherosclerotic lesions, leaving a legacy from persistent HCV infection that has clinical and therapeutic implications.

Neglected but Important Role of Apolipoprotein E Exchange in Hepatitis C Virus Infection

In this study, a neglected but important role of apoE exchange in HCV LVP infectivity after virus assembly and release was identified. The data indicated that apoE expression level in uninfected cells is important for high permissiveness to HCV infection. Secreted apoE-associated lipoprotein specifically enhances infection of HCV LVPs. apoE exchange between HCV LVP and lipoproteins is important to maintain an adequate apoE level on LVPs for their efficient attachment to cell surface. These data defined for the first time an extracellular role of exchangeable apoE in HCV infection and suggested that exchangeable apolipoproteins reach a natural equilibrium between HCV LVPs and lipoprotein particles, which provides a new perspective to the understanding of the heterogeneity of HCV LVPs in composition.

Maximum levels of hepatitis C virus lipoviral particles are associated with early and persistent infection.

Hepatitis C virus (HCV) is bound to plasma lipoproteins and circulates as an infectious lipoviral particle (LVP). Experimental evidence indicates that LVPs have decreased susceptibility to antibody-mediated neutralisation and higher infectivity. This study tested the hypothesis that LVPs are required to establish persistent infection, and conversely, low levels of LVP in recent HCV infection increase the probability of spontaneous HCV clearance. LVP in non-fasting plasma was measured using the concentration of HCV RNA bound to large >100 nm sized lipoproteins after ex vivo addition of a lipid emulsion, that represented the maximum concentration of LVP (maxi-LVP). This method correlated with LVP in fasting plasma measured using iodixanol density gradient ultracentrifugation. Maxi-LVP was measured in a cohort of 180 HCV participants with recent HCV infection and detectable HCV RNA from the Australian Trial in Acute Hepatitis C (ATAHC) and Hepatitis C Incidence and Transmission Study in prison (HITS-p) cohorts. Spontaneous clearance occurred in 15% (27 of 180) of individuals. In adjusted analyses, low plasma maxi-LVP level was independently associated with spontaneous HCV clearance (≤827 IU/ml; adjusted odds ratio 3.98, 95% CI: 1.02, 15.51, P = 0.047), after adjusting for interferon lambda-3 rs8099917 genotype, estimated duration of HCV infection and total HCV RNA level. Maxi-LVP is a biomarker for the maximum concentration of LVP in non-fasting samples. Low maxi-LVP level is an independent predictor of spontaneous clearance of acute HCV.

P0725 : Lipidomics analysis of fasting serum identifies novel lipid biomarkers specific for HCV genotype 3 and genotype 1 chronic hepatitis C virus infection

Background and Aims: HCV genotype 3 (G3) is now considered the most difficult to treat genotype in the era of new oral direct acting antiviral (DAAs) drugs, particularly in those with advanced liver disease. HCV-G3 is also associated with more rapid progression to cirrhosis. Evidence suggests that HCV-G3 has different effects on lipid metabolism compared to HCV-G1, associated with hepatic steatosis, low LDL cholesterol and distinct interactions in the formation of lipoviral particles. A lipidomic analysis was performed to identify lipid species differentially regulated in HCV-G3 compared to HCV-G1, to gain further insight into genotype-specific metabolic pathways. Methods: Lipidomic analysis was performed on fasting sera [N = 112 (73 G1, 39 G3); 25% cirrhosis] using a UPLC system coupled to a QToF mass spectrometer. Profiles were acquired in positive and negative ion modes. System suitability and stability was confirmed by injection of a quality control (QC) sample at regular intervals throughout the analytical run, prepared by combining equal aliquots of all the study samples. Data was pre-processed (alignment, noise filtering, normalisation) using XCMS and inhouse developed scripts, and subjected to multivariate statistical analysis using Simca-P. Principal component analysis (PCA) and orthogonal projection on latent structures-discriminant analysis (OPLS-DA) were performed on all data after pareto scaling. Results: Spectra were explored by PCA for initial visualisation to detect inherent trends and outliers. Samples clustered based on the differences between the HCV-G1 and HCV-G3. Pairwise analysis using OPLS-DA allowed establishing the lipids with the strongest contribution to the genotype separation in positive ion mode. Preliminary assignment based on mass, fragmentation pattern and retention time of lipid species upregulated in HCV-G3 included Cholesteryl linoleate [M+NH4] 666.621 m/z @ 15.47 min. Other lipid species were specifically increased in HCV genotype 1 [M+H] 784.588 m/z @ 6.29 min PC (36:30). In negative ion mode, additional novel lipid species were found to be differentially unregulated in HCV-G1. The novel lipid species are currently being identified and evaluated in an independent validation cohort. Conclusions: UPLC MS lipidomics methods identify novel lipid species differentially regulated in HCV-G3 compared to HCV-G1. Understanding of the lipidome in HCV-G3 may help identify factors associated with DAA relapse.

PCSK9, apolipoprotein E and lipoviral particles in chronic hepatitis C genotype 3: Evidence for genotype-specific regulation of lipoprotein metabolism

Hepatitis C virus (HCV) associates with lipoproteins to form "lipoviral particles" (LVPs) that can facilitate viral entry into hepatocytes. Initial attachment occurs via heparan sulphate proteoglycans and low-density lipoprotein receptor (LDLR); CD81 then mediates a post-attachment event. Proprotein convertase subtilisin kexin type 9 (PCSK9) enhances the degradation of the LDLR and modulates liver CD81 levels. We measured LVP and PCSK9 in patients chronically infected with HCV genotype (G)3. PCSK9 concentrations were also measured in HCV-G1 to indirectly examine the role of LDLR in LVP clearance. HCV RNA, LVP (d<1.07g/ml) and non-LVP (d>1.07g/ml) fractions, were quantified in patients with HCV-G3 (n=39) by real time RT-PCR and LVP ratios (LVPr; LVP/(LVP+non-LVP)) were calculated. Insulin resistance (IR) was assessed using the homeostasis model assessment of IR (HOMA-IR). Plasma PCSK9 concentrations were measured by ELISA in HCV-G3 and HCV-G1 (n=51). In HCV-G3 LVP load correlated inversely with HDL-C (r=-0.421; p=0.008), and apoE (r=-0.428; p=0.013). The LVPr varied more than 35-fold (median 0.286; range 0.027 to 0.969); PCSK9 was the strongest negative predictor of LVPr (R(2)=16.2%; p=0.012). HOMA-IR was not associated with LVP load or LVPr. PCSK9 concentrations were significantly lower in HCV-G3 compared to HCV-G1 (p<0.001). PCSK9 did not correlate with LDL-C in HCV-G3 or G1. The inverse correlation of LVP with apoE in HCV-G3, compared to the reverse in HCV-G1 suggests HCV genotype-specific differences in apoE mediated viral entry. Lower PCSK9 and LDL concentrations imply upregulated LDLR activity in HCV-G3.

The Association of Hepatitis C Virus Glycoproteins with Apolipoproteins E and B Early in Assembly Is Conserved in Lipoviral Particles

In patients chronically infected with hepatitis C virus and in the HCV cell culture system (HCVcc), it is known that highly infectious virus particles have low to very low buoyant densities. These low densities have been attributed to the association of HCV with lipoprotein components, which occur during the viral morphogenesis. The resulting hybrid particles are known as lipoviral particles (LVP); however, very little is known about how these particles are created. In our study, we used Huh7.5 cells to investigate the intracellular association between envelope proteins and apolipoproteins B and E (ApoB and ApoE, respectively). In particular, we were interested in the role of this association in initiating LVP morphogenesis. Co-immunoprecipitation assays revealed that ApoB, ApoE, and HCV glycoproteins formed a protein complex early in the HCV lifecycle. Confocal analyses of naïve, E1E2-transduced and HCVcc-infected cells showed that HCV glycoproteins, ApoB and ApoE were found strongly colocalized only in the endoplasmic reticulum. We also found that HCV glycoproteins, ApoB and ApoE were already associated with intracellular infectious viral particles and, furthermore, that the protein complex was conserved in the infectious viral particles present in the supernatant of infected Huh7.5 cells. The association of HCV glycoproteins with ApoE was also evidenced in the HCVpp system, using the non-hepatic HEK293T cell line. We suggest that the complex formed by HCV E1E2, ApoB, and ApoE may initiate lipoviral particle morphogenesis.

Hepatitis C virus infection mediates cholesteryl ester synthesis to facilitate infectious particle production.

Cholesterol is a critical component of the hepatitis C virus (HCV) life cycle, as demonstrated by its accumulation within infected hepatocytes and lipoviral particles. To cope with excess cholesterol, hepatic enzymes ACAT1 and ACAT2 produce cholesteryl esters (CEs), which are destined for storage in lipid droplets or for secretion as apolipoproteins. Here we demonstrate in vitro that cholesterol accumulation following HCV infection induces upregulation of the ACAT genes and increases CE synthesis. Analysis of human liver biopsy tissue showed increased ACAT2 mRNA expression in liver infected with HCV genotype 3, compared with genotype 1. Inhibiting cholesterol esterification using the potent ACAT inhibitor TMP-153 significantly reduced production of infectious virus, but did not inhibit virus RNA replication. Density gradient analysis showed that TMP-153 treatment caused a significant increase in lipoviral particle density, suggesting reduced lipidation. These data suggest that cholesterol accumulation following HCV infection stimulates the production of CE, a major component of lipoviral particles. Inhibition of CE synthesis reduces HCV particle density and infectivity, suggesting that CEs are required for optimal infection of hepatocytes.

Syndecan 4 is involved in mediating HCV entry through interaction with lipoviral particle-associated apolipoprotein E.

Hepatitis C virus (HCV) is a major cause of liver disease worldwide and HCV infection represents a major health problem. HCV associates with host lipoproteins forming host/viral hybrid complexes termed lipoviral particles. Apolipoprotein E (apoE) is a lipoprotein component that interacts with heparan sulfate proteoglycans (HSPG) to mediate hepatic lipoprotein uptake, and may likewise mediate HCV entry. We sought to define the functional regions of apoE with an aim to identify critical apoE binding partners involved in HCV infection. Using adenoviral vectors and siRNA to modulate apoE expression we show a direct correlation of apoE expression and HCV infectivity, whereas no correlation exists with viral protein expression. Mutating the HSPG binding domain (HSPG-BD) of apoE revealed key residues that are critical for mediating HCV infection. Furthermore, a novel synthetic peptide that mimics apoE’s HSPG-BD directly and competitively inhibits HCV infection. Genetic knockdown of the HSPG proteins syndecan (SDC) 1 and 4 revealed that SDC4 principally mediates HCV entry. Our data demonstrate that HCV uses apoE-SDC4 interactions to enter hepatoma cells and establish infection. Targeting apoE-SDC interactions could be an alternative strategy for blocking HCV entry, a critical step in maintaining chronic HCV infection.

Omega‐3 fatty acids and/or fluvastatin in hepatitis C prior non‐responders to combination antiviral therapy – a pilot randomised clinical trial

Hepatitis C virus (HCV) utilises cholesterol and lipoprotein metabolism for replication and infectivity. Statins and omega-3 (n-3) polyunsaturated fatty acids (PUFA) have been shown to have antiviral properties in vitro. This open label pilot study evaluated the efficacy of fluvastatin (Lescol(®) 40-80 mg) and n-3 PUFA (Omacor(®) 1 g and 2-4 g) on HCV-RNA and lipoviral particles (LVP) in difficult to treat prior non-responders. Patients (n = 60) were randomly allocated in a factorial design to: no active drug; low-dose n-3 PUFA; high-dose n-3 PUFA; fluvastatin; low-dose n-3 PUFA + fluvastatin; or high-dose n-3 PUFA + fluvastatin. 50/60 completed study drugs for 12 weeks and followed up to week 24. Comparison was made between fluvastatin (n = 24) vs no fluvastatin (n = 26) and n-3 PUFA high-dose (n = 17) vs low-dose (n = 17) vs none (n = 16). The primary outcomes were change in total HCV-RNA, LVP and ALT at week 12 compared with baseline. Secondary outcome was change in interferon-gamma-inducible protein-10 (IP10) as a measure of interferon activation. 35% had compensated cirrhosis and 45% were prior null responders. There was no significant change in total HCV RNA, LVP, non-LVP or LVP ratio in patients receiving fluvastatin or n-3 PUFAs. ALT was not significantly different in those treated with fluvastatin or n-3 PUFAs. 12 weeks of low-dose n-3 PUFA decreased median IP10 concentration by -39 pg/ml (-111, 7.0 pg/ml Q1-Q3). Fluvastatin and n-3 PUFAs have no effect on plasma HCV-RNA or LVP. The effect of low-dose n-3 PUFA on IP10 warrants further prospective evaluation as a supplemental therapy to enhance interferon sensitivity.

Hepatitis C Virus, Cholesterol and Lipoproteins — Impact for the Viral Life Cycle and Pathogenesis of Liver Disease

Hepatitis C virus (HCV) is a leading cause of chronic liver disease, including chronic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Hepatitis C infection associates with lipid and lipoprotein metabolism disorders such as hepatic steatosis, hypobetalipoproteinemia, and hypocholesterolemia. Furthermore, virus production is dependent on hepatic very-low-density lipoprotein (VLDL) assembly, and circulating virions are physically associated with lipoproteins in complexes termed lipoviral particles. Evidence has indicated several functional roles for the formation of these complexes, including co-opting of lipoprotein receptors for attachment and entry, concealing epitopes to facilitate immune escape, and hijacking host factors for HCV maturation and secretion. Here, we review the evidence surrounding pathogenesis of the hepatitis C infection regarding lipoprotein engagement, cholesterol and triglyceride regulation, and the molecular mechanisms underlying these effects.

493 METABOLIC SYNDROME AND INSULIN RESISTANCE ARE ASSOCIATED WITH MAXIMUM HEPATITIS C LIPOVIRAL PARTICLES IN GENOTYPE 1 INFECTION

Background and Aims: HCV has a direct role in the pathogenesis of insulin resistance. Patients with chronic HCV and insulin resistance are less likely to respond to antiviral therapy and are at risk for more rapid fibrosis progression. Insulin resistance is most strongly associated with HCV genotype (G)1. Infectious HCV particles have a low density due to association with triglyceride rich lipoproteins (TRLs) as lipoviral particles (LVP). We have reported that LVP levels are dynamic and can increase to a maximum level postprandially by transfer onto TRLs including chylomicrons, VLDL and lipid emulsions both in vivo and ex vivo [1]. We aimed to evaluate the relationships between the maximum amount of LVP in vivo and clinical and metabolic parameters. Methods: 53 chronic HCV G1 patients provided fasting blood samples. The maximum LVP ratio (LVPr-max) was measured by incubating fasting plasma with a lipid emulsion prior to separation using a size filter. HCV RNA was quantitated from the filtrate and retentate and LVPr-max was calculated (retentate/retentate + filtrate). Results: The median LVPr-max was 0.28 but varied widely from 0.07 to 0.86. LVPr-max was significantly correlated with HOMAIR (r = 0.362, p = 0.008). LVPr-max was significantly increased in patients with co-existing metabolic syndrome (median LVPr-max 0.49, n = 11) compared to those without metabolic syndrome (median 0.23), p = 0.001. LVPr-max did not correlate with plasma apoE concentration. There was no association of LVPr-max with IL28B or PNPLA3 genotypes. Conclusions: This study provides some mechanistic insights into the interaction of HCV with metabolic syndrome and insulin resistance, suggesting an association with increased amounts of post-prandial infectious HCV particles.

Lipids and HCV

Chronic hepatitis C virus (HCV) infection is associated with an increase in hepatic steatosis and a decrease in serum levels of total cholesterol, low-density lipoprotein cholesterol (LDL) and apolipoprotein B (apoB), the main protein constituent of LDL and very low-density lipoprotein (VLDL). These changes are more marked in HCV genotype 3 infection, and effective treatment results in their reversal. Low lipid levels in HCV infection correlate not only with steatosis and more advanced liver fibrosis but also with non-response to interferon-based therapy. The clinical relevance of disrupted lipid metabolism reflects the fact that lipids play a crucial role in the life cycle of hepatitis C virus. HCV assembly and maturation in hepatocytes depend on microsomal triglyceride transfer protein and apoB in a manner that parallels the formation of VLDL. VLDL production from the liver occurs throughout the day with an estimated 10(18) particles produced every 24 h whilst the estimated hepatitis C virion production rate is 10(12) virions per day. HCV particles in the serum exist as a mixture of complete low-density infectious lipo-viral particles (LVP) and a vast excess of apoB-associated empty nucleocapsid-free sub-viral particles that are complexed with anti-HCV envelope antibodies. Apolipoprotein E (apoE) is also involved in HCV particle morphogenesis and is an essential apolipoprotein for HCV infectivity. ApoE is a critical ligand for the receptor-mediated removal of triglyceride rich lipoprotein (TRL) remnants by the liver. The dynamics of apoB-associated lipoproteins, including HCV-LVP, change post-prandially with an increase in large TRL remnants and very low density HCV-LVP which are rapidly cleared by the liver (at least three HCV receptors are cellular receptors for uptake of TRL remnants). In summary, HCV utilises triglyceride-rich lipoprotein pathways within the liver and the circulation to its advantage.

Modified lipoproteins provide lipids that modulate dendritic cell immune function

Both physiological and pathological situations can result in biochemical changes of low-density lipoproteins (LDL). Because they can deliver signals to dendritic cells (DC), these modified lipoproteins now appear as regulators of the immune response. Among these modified lipoproteins, oxidized LDL (oxLDL) that accumulate during inflammatory conditions have been extensively studied. Numerous studies have shown that oxLDL induce the maturation of DC, enhancing their ability to activate IFNγ secretion by T cells. LDL treated by secreted phospholipase A(2) also promote DC maturation. Among the bioactive lipids generated by oxidation or phospholipase treatment of LDL, lysophosphatidylcholine (LPC) and some saturated fatty acids induce DC maturation whereas some unsaturated fatty acids or oxidized derivatives have opposite effects. Among other factors, the nuclear receptor peroxisome-proliferator activated receptor γ (PPARγ) plays a crucial role in this regulation. Non-modified lipoproteins also contribute to the regulation of DC function, suggesting that the balance between native and modified lipoproteins, as well as the biochemical nature of the LDL modifications, can regulate the activation threshold of DC. Here we discuss two pathological situations in which the impact of LDL modifications on inflammation and immunity could play an important role. During atherosclerosis, modified LDL accumulating in the arterial intima may interfere with DC maturation and function, promoting a Th1 immune response and a local inflammation favoring the development of the pathology. In patients chronically infected, the hepatitis C virus (HCV) interferes with lipoprotein metabolism resulting in the production of infectious modified lipoproteins. These lipo-viral-particles (LVP) are modified low-density lipoproteins containing viral material that can alter DC maturation and affect specific toll-like receptor signaling. In conclusion, lipoprotein modifications play an important role in the regulation of immunity by delivering signals of danger to DC and modulating their function.

Hepatitis C as a metabolic disease

Before liver cirrhosis and hepatocellula carcinoma can develop, the early and long lasting features of hepatitis C are host metabolism modifications with a specific and so far unique metabolic syndrome that may associate insulin resistance, liver steatosis and hypo-betalipoproteinemia. These metabolic perturbations are directly induced by heptatitis C virus (HCV) replication and regress after viral suppression. Symmetrically HCV depends on glucose and lipid metabolism for its replication. HCV induced insulin resistance is both hepatic and peripheral. The insulin receptor pathway is impacted at several steps by viral proteins with probable functional consequences. Mechanism of peripheral insulin resistance remains obscure and the viral signals send to adipose tissue or muscles have to be identified. One major IR metabolic consequence might contribute to the mobilization of free fatty acids from periphery to the liver and to the constitution of liver steatosis. Importantly, HCV modifies with genotype-specific differences, the synthesis, degradation and secretion of lipid in a coordinated fashion to promote the accumulation of neutral lipids. The lipid droplets (LD) that are the lipid storage organelles are mandatory platforms for the assembly of infectious viral particles. In particular localization of core protein and NS5A on LD and mobilization of the LD are essential steps that control viral infectivity. Interestingly, the efficiency of HCV to the LD disposal and use correlates to viral production and may influences the extent of hepatic accumulation of lipids. The most striking association of HCV with lipid metabolism resides in the coincidence of the betalipoproteins and viral particles pathways with the formation of unique hybrid viral particles. Indeed HCV depends on a functional very low density lipoproteins (VLDL) assembly and secretion process to be secreted. HCV also modifies at different degree the VLDL composition forming sub viral particles, which are minimally modified VLDL that bear the viral envelop glycoproteins, or hybrid viral particles known as lipo-viral-particles (LVP), which contain all the viral and VLDL components that are highly infectious. Functions of these hybrid particles on the disease features and progression as well as therapeutic targets remain to be fully characterized. Thus, HCV appears to have developed an original and so far unique way with major clinical consequences to modify and use the lipid metabolism to persist in the host.