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

BACKGROUND & AIMS: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

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

BACKGROUND & AIMS: 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. METHODS: 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). RESULTS: 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. CONCLUSIONS: 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.

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

BACKGROUND & AIMS: 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. METHODS: 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. RESULTS: 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). CONCLUSIONS: 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.

Apolipoprotein-E and hepatitis C lipoviral particles in genotype 1 infection: evidence for an association with interferon sensitivity.

BACKGROUND & AIMS: Hepatitis C virus (HCV) interacts with apolipoproteins B (apoB) and E (apoE) to form infectious lipoviral particles (LVP). Response to peginterferon is influenced by interferon-stimulated genes (ISGs) and IL28B genotype. LDL cholesterol (LDL-C) also predicts interferon response, therefore we hypothesised that LVP may also be associated with interferon sensitivity. METHODS: LVP (HCV RNA density ≤1.07 g/ml) and 'non-LVP' (d >1.07 g/ml) were measured in 72 fasted HCV-G1 patients by iodixanol density gradient ultracentrifugation and the LVP ratio (LVP/LVP+non-LVP) was calculated. Fasting lipid profiles and apolipoproteins B and E were measured. Interferon-gamma-inducible protein 10 kDa (IP10), a marker of ISGs, was measured by ELISA. RESULTS: Complete early virological response (EVR) was associated with lower apoE (23.9±7.7 vs. 36.1±15.3 mg/L, p=0.013), higher LDL-C (p=0.039) and lower LVP ratios (p=0.022) compared to null responders. In multivariate linear regression analysis, apoE was independently associated with LVP (R(2) 19.5%, p=0.003) and LVP ratio (p=0.042), and negatively with LDL-C (p<0.001). IP10 was significantly associated with ApoB (p=0.001) and liver stiffness (p=0.032). IL28B rs12979860 CC was associated with complete EVR (p=0.044), low apoE (CC 28±11 vs. CT/TT 35±13 mg/L, p=0.048) and higher non-LVP (p=0.008). Logistic regression analysis indicated that patients with high LVP ratios were less likely to have EVR (odds ratio 0.01, p=0.018). CONCLUSIONS: In HCV-G1, interferon sensitivity is characterised by low LVP ratios and low apoE levels in addition to higher LDL-C and IL28B rs12979860 CC. Null-response is associated with increased LVP ratio. The association of apoE and LVP with peginterferon treatment response suggests that lipid modulation is a potential target to modify interferon sensitivity.

Insulin resistance and low-density apolipoprotein B-associated lipoviral particles in hepatitis C virus genotype 1 infection.

BACKGROUND: The density of hepatitis C virus (HCV) in plasma is heterogeneous but the factors which influence this are poorly understood. Evidence from animal models and cell culture suggest that low-density apolipoprotein B (apoB)-associated HCV lipoviral particles (LVP) are more infectious than high-density HCV. Objective To measure LVP in patients with chronic hepatitis C genotype 1 (CHC-G1) and examine metabolic determinants of LVP load. Patients 51 patients with CHC-G1 infection. METHODS: Fasting lipid profiles and homeostasis model assessment of insulin resistance (HOMA-IR) were determined in 51 patients with CHC-G1. LVP and non-LVP viral load were measured by real-time PCR of plasma at density <1.07 g/ml and >1.07 g/ml, respectively, following iodixanol density gradient ultracentrifugation. The LVP ratio was calculated using the formula: LVP/(LVP + non-LVP). RESULTS: The mean LVP ratio was 0.241 but varied 25-fold (from 0.029 to 0.74). Univariate analysis showed that the LVP ratio correlated with HOMA-IR (p=0.004) and the triglyceride/high-density lipoprotein cholesterol (TG/HDL-C) ratio (p = 0.004), but not with apoB. In multivariate analysis, HOMA-IR was the main determinant of LVP load (log10IU/ml) (R²=16.6%; p = 0.037) but the TG/HDL-C ratio was the strongest predictor of the LVP ratio (R² = 24.4%; p = 0.019). Higher LVP ratios were associated with non-response to antiviral therapy (p = 0.037) and with greater liver stiffness (p = 0.001). CONCLUSION: IR and associated dyslipidaemia are the major determinants of low-density apoB-associated LVP in fasting plasma. This provides a possible mechanism to explain why IR is associated with more rapidly progressive liver disease and poorer treatment outcomes.

Infection with the hepatitis C virus causes viral genotype-specific differences in cholesterol metabolism and hepatic steatosis.

Lipids play essential roles in the hepatitis C virus (HCV) life cycle and patients with chronic HCV infection display disordered lipid metabolism which resolves following successful anti-viral therapy. It has been proposed that HCV genotype 3 (HCV-G3) infection is an independent risk factor for hepatocellular carcinoma and evidence suggests lipogenic proteins are involved in hepatocarcinogenesis. We aimed to characterise variation in host lipid metabolism between participants chronically infected with HCV genotype 1 (HCV-G1) and HCV-G3 to identify likely genotype-specific differences in lipid metabolism. We combined several lipidomic approaches: analysis was performed between participants infected with HCV-G1 and HCV-G3, both in the fasting and non-fasting states, and after sustained virological response (SVR) to treatment. Sera were obtained from 112 fasting patients (25% with cirrhosis). Serum lipids were measured using standard enzymatic methods. Lathosterol and desmosterol were measured by gas-chromatography mass spectrometry (MS). For further metabolic insight on lipid metabolism, ultra-performance liquid chromatography MS was performed on all samples. A subgroup of 13 participants had whole body fat distribution determined using in vivo magnetic resonance imaging and spectroscopy. A second cohort of (non-fasting) sera were obtained from HCV Research UK for comparative analyses: 150 treatment naïve patients and 100 non-viraemic patients post-SVR. HCV-G3 patients had significantly decreased serum apoB, non-HDL cholesterol concentrations, and more hepatic steatosis than those with HCV-G1. HCV-G3 patients also had significantly decreased serum levels of lathosterol, without significant reductions in desmosterol. Lipidomic analysis showed lipid species associated with reverse cholesterol transport pathway in HCV-G3. We demonstrated that compared to HCV-G1, HCV-G3 infection is characterised by low LDL cholesterol levels, with preferential suppression of cholesterol synthesis via lathosterol, associated with increasing hepatic steatosis. The genotype-specific lipid disturbances may shed light on genotypic variations in liver disease progression and promotion of hepatocellular cancer in HCV-G3.

HCV and the hepatic lipid pathway as a potential treatment target.

Atherosclerosis has been described as a liver disease of the heart [1]. The liver is the central regulatory organ of lipid pathways but since dyslipidaemias are major contributors to cardiovascular disease and type 2 diabetes rather than liver disease, research in this area has not been a major focus for hepatologists. Virus-host interaction is a continuous co-evolutionary process [2] involving the host immune system and viral escape mechanisms [3]. One of the strategies HCV has adopted to escape immune clearance and establish persistent infection is to make use of hepatic lipid pathways. This review aims to: • update the hepatologist on lipid metabolism • review the evidence that HCV exploits hepatic lipid pathways to its advantage • discuss approaches to targeting host lipid pathways as adjunctive therapy.

Intravascular transfer contributes to postprandial increase in numbers of very-low-density hepatitis C virus particles.

BACKGROUND & AIMS: The physical association of hepatitis C virus (HCV) particles with lipoproteins in plasma results in distribution of HCV in a broad range of buoyant densities. This association is thought to increase virion infectivity by mediating cell entry via lipoprotein receptors. We sought to determine if factors that affect triglyceride-rich lipoprotein (TRL) metabolism alter the density and dynamics of HCV particles in the plasma of patients with chronic HCV infection. METHODS: Fasting patients (n = 10) consumed a high-fat milkshake; plasma was collected and fractionated by density gradients. HCV- RNA was measured in the very-low-density fraction (VLDF, d < 1.025 g/mL) before and at 7 serial time points postprandially. RESULTS: The amount of HCV RNA in the VLDF (HCV(VLDF)) increased a mean of 26-fold, peaking 180 minutes after the meal (P < .01). Quantification of HCV RNA throughout the density gradient fractions revealed that HCV(VLDF) rapidly disappeared, rather than migrating into the adjacent density fraction. Immuno-affinity separation of the VLDF, using antibodies that recognize apolipoprotein B-100 and not apolipoprotein B-48, showed that HCV(VLDF) is composed of chylomicron- and VLDL-associated HCV particles; peaking 120 and 180 minutes after the meal, respectively. Plasma from fasting HCV-infected patients mixed with uninfected plasma increased the quantity of HCV(VLDF), compared with that mixed with phosphate-buffered saline, showing extracellular assembly of HCV(VLDF). CONCLUSIONS: Dietary triglyceride alters the density and dynamics of HCV in plasma. The rapid clearance rate of HCV(VLDF) indicates that association with TRL is important for HCV infectivity. HCV particles, such as exchangeable apolipoproteins, appear to reassociate with TRLs in the vascular compartment.

Revisiting the Elusive Hepatitis C Vaccine.

The impactful discovery and subsequent characterisation of hepatitis C virus (HCV), an RNA virus of the flavivirus family, led to the awarding of the 2020 Nobel Prize in Physiology or Medicine to Harvey J. Alter, Michael Houghton and Charles M. Rice [...].

Relapse of polymyalgia rheumatica following adjuvanted influenza vaccine: A case-based review.

Polymyalgia rheumatica (PMR) is the most common inflammatory rheumatological condition affecting individuals aged >50 years. There have been rare reports of PMR and other vasculitides developing within 3 months of influenza vaccination. Influenza is a major public health issue associated with seasonal increased mortality and intensified health care service use. Annual vaccination is the most effective intervention to prevent influenza, especially in elderly individuals. We report a severe "flare" of PMR in a 70-year-old patient after receiving the adjuvanted trivalent influenza vaccine, as recommended by the Joint Committee on Vaccination and Immunisations for this age group in the UK National Health Service in 2018-2019. The adverse event (AE) could be interpreted as the newly described autoimmune/inflammatory syndrome induced by adjuvants (ASIA syndrome) as both PMR and ASIA display hyperactive immune responses. Caution is warranted in the use of vaccine adjuvants in patients with PMR with pre-existing imbalance of B and T cell homeostasis. Rare AEs are important to individuals, and personalized medicine means we should move away from "one size fits all" for vaccines, as well as for therapeutics.

COVID-19 and comorbidities: A role for dipeptidyl peptidase 4 (DPP4) in disease severity?

The coronavirus disease 2019 (COVID-19) pandemic is caused by a novel betacoronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), similar to SARS-CoV and Middle East respiratory syndrome (MERS-CoV), which cause acute respiratory distress syndrome and case fatalities. COVID-19 disease severity is worse in older obese patients with comorbidities such as diabetes, hypertension, cardiovascular disease, and chronic lung disease. Cell binding and entry of betacoronaviruses is via their surface spike glycoprotein; SARS-CoV binds to the metalloprotease angiotensin-converting enzyme 2 (ACE2), MERS-CoV utilizes dipeptidyl peptidase 4 (DPP4), and recent modeling of the structure of SARS-CoV-2 spike glycoprotein predicts that it can interact with human DPP4 in addition to ACE2. DPP4 is a ubiquitous membrane-bound aminopeptidase that circulates in plasma; it is multifunctional with roles in nutrition, metabolism, and immune and endocrine systems. DPP4 activity differentially regulates glucose homeostasis and inflammation via its enzymatic activity and nonenzymatic immunomodulatory effects. The importance of DPP4 for the medical community has been highlighted by the approval of DPP4 inhibitors, or gliptins, for the treatment of type 2 diabetes mellitus. This review discusses the dysregulation of DPP4 in COVID-19 comorbid conditions; DPP4 activity is higher in older individuals and increased plasma DPP4 is a predictor of the onset of metabolic syndrome. DPP4 upregulation may be a determinant of COVID-19 disease severity, which creates interest regarding the use of gliptins in management of COVID-19. Also, knowledge of the chemistry and biology of DPP4 could be utilized to develop novel therapies to block viral entry of some betacoronaviruses, potentially including SARS-CoV-2.

Is Alzheimer's Disease a Liver Disease of the Brain?

Clinical specialization is not only a force for progress, but it has also led to the fragmentation of medical knowledge. The focus of research in the field of Alzheimer's disease (AD) is neurobiology, while hepatologists focus on liver diseases and lipid specialists on atherosclerosis. This article on AD focuses on the role of the liver and lipid homeostasis in the development of AD. Amyloid-ß (Aß) deposits accumulate as plaques in the brain of an AD patient long before cognitive decline is evident. Aß generation is a normal physiological process; the steady-state level of Aß in the brain is determined by balance between Aß production and its clearance. We present evidence suggesting that the liver is the origin of brain Aß deposits and that it is involved in peripheral clearance of circulating Aß in the blood. Hence the liver could be targeted to decrease Aß production or increase peripheral clearance.

Identification of a residue in hepatitis C virus E2 glycoprotein that determines scavenger receptor BI and CD81 receptor dependency and sensitivity to neutralizing antibodies.

Hepatitis C virus (HCV) infection is dependent on at least three coreceptors: CD81, scavenger receptor BI (SR-BI), and claudin-1. The mechanism of how these molecules coordinate HCV entry is unknown. In this study we demonstrate that a cell culture-adapted JFH-1 mutant, with an amino acid change in E2 at position 451 (G451R), has a reduced dependency on SR-BI. This altered receptor dependency is accompanied by an increased sensitivity to neutralization by soluble CD81 and enhanced binding of recombinant E2 to cell surface-expressed and soluble CD81. Fractionation of HCV by density gradient centrifugation allows the analysis of particle-lipoprotein associations. The cell culture-adapted mutation alters the relationship between particle density and infectivity, with the peak infectivity occurring at higher density than the parental virus. No association was observed between particle density and SR-BI or CD81 coreceptor dependence. JFH-1 G451R is highly sensitive to neutralization by gp-specific antibodies, suggesting increased epitope exposure at the virion surface. Finally, an association was observed between JFH-1 particle density and sensitivity to neutralizing antibodies (NAbs), suggesting that lipoprotein association reduces the sensitivity of particles to NAbs. In summary, mutation of E2 at position 451 alters the relationship between particle density and infectivity, disrupts coreceptor dependence, and increases virion sensitivity to receptor mimics and NAbs. Our data suggest that a balanced interplay between HCV particles, lipoprotein components, and viral receptors allows the evasion of host immune responses.

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

BACKGROUND/PURPOSE: 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. METHODS: Eighty-nine blinded serum samples from 27 patients with advanced chronic HCV were assayed for lipids and anti-apoA-1 IgG by ELISA. RESULTS: 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. CONCLUSIONS: 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.

Hepatitis C virus and lipids in the era of direct acting antivirals (DAAs).

The six different HCV-genotypes have marked differences in response to therapy with pegylated interferon-α and ribavirin. The introduction of the direct acting antiviral (DAA) protease inhibitors, telaprevir and boceprevir in combination with pegylated interferon-α and ribavirin has become the new standard of care for genotype 1 infection. Several host factors associated with response to pegylated interferon-α and ribavirin are not as important in predicting response to triple therapy, and yet low-density lipoprotein cholesterol (LDLC) and statin use remain important associations of outcome with DAAs. This review focuses on the clinical associations between lipids and treatment response to interferon based antiviral treatments. We consider how understanding the interactions of HCV and host lipid metabolism remains relevant in the era of DAAs for genotype 1 infection and for treatment of non-genotype 1 chronic hepatitis C.

Binding of liver derived, low density hepatitis C virus to human hepatoma cells.

HCV recovered from low density fractions of infected blood is associated with lipid and host apo-lipoproteins in lipo-viro-particles (LVP). It has been proposed that these particles are capable of binding and entering hepatocytes by viral glycoprotein independent mechanisms utilizing uptake pathways of normal host lipoproteins after binding to cell surface glycosaminoglycans (GAG), the low density lipoprotein receptor (LDL-r) or scavenger receptor B1 (SR-B1). In this study binding to human hepatoma cells of HCV low density RNA containing particles, semi-purified from macerates of infected human liver, is compared with that of normal host low density lipoprotein (LDL). Binding of both LDL and HCV low density RNA containing particles paralleled LDL-r but not SR-B1 expression on the recipient cells. Binding of both particle types was sensitive to suramin at 0 degrees C but less so at 37 degrees C suggesting that they both bind initially to GAG but, at 37 degrees C, are internalized or transferred to a suramin resistant receptor. Suramin resistant uptake of both particles was blocked in the presence of excess LDL or oxidized LDL. However, whilst LDL uptake was blocked by anti-apoB-100, HCV low density RNA uptake was enhanced by anti-apoB100 and further enhanced by a cocktail of anti-apo-B100 and anti-apoE. Pre-incubation of HCV low density RNA containing particles with antibodies to the E2 glycoprotein had little or no effect on uptake. These data indicate that whilst liver derived HCV RNA containing particles are taken up by HepG2 cells by a virus glycoprotein independent mechanism, the mechanism differs from that of LDL uptake.

Characterization of hepatitis C RNA-containing particles from human liver by density and size.

Hepatitis C virus (HCV) particles found in vivo are heterogeneous in density and size, but their detailed characterization has been restricted by the low titre of HCV in human serum. Previously, our group has found that HCV circulates in blood in association with very-low-density lipoprotein (VLDL). Our aim in this study was to characterize HCV RNA-containing membranes and particles in human liver by both density and size and to identify the subcellular compartment(s) where the association with VLDL occurs. HCV was purified by density using iodixanol gradients and by size using gel filtration. Both positive-strand HCV RNA (present in virus particles) and negative-strand HCV RNA (an intermediate in virus replication) were found with densities below 1.08 g ml(-1). Viral structural and non-structural proteins, host proteins ApoB, ApoE and caveolin-2, as well as cholesterol, triglyceride and phospholipids were also detected in these low density fractions. After fractionation by size with Superose gel filtration, HCV RNA and viral proteins co-fractionated with endoplasmic reticulum proteins and VLDL. Fractionation on Toyopearl, which separates particles with diameters up to 200 nm, showed that 78 % of HCV RNA from liver was >100 nm in size, with a positive-/negative-strand ratio of 6 : 1. Also, 8 % of HCV RNA was found in particles with diameters between 40 nm and 70 nm and a positive-/negative-strand ratio of 45 : 1. This HCV was associated with ApoB, ApoE and viral glycoprotein E2, similar to viral particles circulating in serum. Our results indicate that the association between HCV and VLDL occurs in the liver.

Association between hepatitis C virus and very-low-density lipoprotein (VLDL)/LDL analyzed in iodixanol density gradients.

Hepatitis C virus (HCV) RNA circulates in the blood of persistently infected patients in lipoviroparticles (LVPs), which are heterogeneous in density and associated with host lipoproteins and antibodies. The variability and lability of these virus-host complexes on fractionation has hindered our understanding of the structure of LVP and determination of the physicochemical properties of the HCV virion. In this study, HCV from an antibody-negative immunodeficient patient was analyzed using three fractionation techniques, NaBr gradients, isotonic iodixanol, and sucrose gradient centrifugation. Iodixanol gradients were shown to best preserve host lipoprotein-virus complexes, and all HCV RNA was found at densities below 1.13 g/ml, with the majority at low density, < or =1.08 g/ml. Immunoprecipitation with polyclonal antibodies against human ApoB and ApoE precipitated 91.8% and 95.0% of HCV with low density, respectively, suggesting that host lipoprotein is closely associated with HCV in a particle resembling VLDL. Immunoprecipitation with antibodies against glycoprotein E2 precipitated 25% of HCV with low density, providing evidence for the presence of E2 in LVPs. Treatment of serum with 0.5% deoxycholic acid in the absence of salt produced HCV with a density of 1.12 g/ml and a sedimentation coefficient of 215S. The diameters of these particles were calculated as 54 nm. Treatment of serum with 0.18% NP-40 produced HCV with a density of 1.18 g/ml, a sedimentation coefficient of 180S, and a diameter of 42 nm. Immunoprecipitation analysis showed that ApoB remained associated with HCV after treatment of serum with deoxycholic acid or NP-40, whereas ApoE was removed from HCV with these detergents.