Association between Hepatitis C Virus and Very-Low-Density Lipoprotein (VLDL)/LDL Analyzed in Iodixanol Density Gradients

Abstract

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, <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.

High plasma level of nucleocapsid-free envelope glycoprotein-positive lipoproteins in hepatitis C patients

“…The association of apoB with LVPs that resists to detergent treatment further rejects this possibility. 33 Fig . 3.…”

Entry and replication of recombinant hepatitis C viruses in cell culture

“…In particular, hepatocytes secrete lipoproteins and are the only cells capable to pack and release in the bloodstream lipids within very-low-density lipoproteins (VLDL) [20]. It seems that HCV can hijack this function for its own assembly as it circulates in patient serum in association with lipoproteins [22,23]. Moreover, host factors crucial for production of VLDL like apolipoprotein E, apolipoprotein B and microsomal triglyceride transfer protein have been found to be important for production and release of infectious HCV particles [24][25][26][27][28][29].…”

“…It might also contribute to protect the virus from the host humoral immune response. It seems moreover that a fraction of patient-derived HCV is attached to immunoglobulins or to molecules of the complement [22]. Finally, the intrinsically high error-rate of HCV RNA polymerase, combined with a high level of viral replication and under 4 pressure of the host immune response, is responsible for the high virus variability.…”

HCV and lipoproteins: Is oxLDL an Achilles' heel of the Trojan horse?

“…First, the efficacy of the virus to establish productive infection of primary hepatocytes or hepatoma cell lines is very low; second, the availability of primary hepatocytes and of well-characterized native HCV populations is significantly restricted; third, purification of plasma-derived HCV may alter the properties of the viral particles and/or their association with lipoproteins. 4 A significant number of model systems of HCV particles have been developed in an attempt to overcome these severe limitations associated with the study of HCV structure and cell entry. 6 They include (1) non-infectious HCV-like particles (HCV-LP), 7 (2) "infectious" HCV pseudo-particles derived from vesicular stomatitis virus (VSV) 8 or from retroviruses (HCVpp), 9,10 (3) cell culturegrown authentic HCV (HCVcc) that produces infectious virus particles.…”

“…In the blood of infected patients, HCV presents itself either in "free" forms, complexed with immunogobulins, associated with high-, low-or very low-density lipoproteins, or "encrusted" in ␤-lipoproteins as so called lipo-viro-particles (LVPs). [1][2][3][4][5] Indirect evidence suggests that low-density HCV (i.e., LVPs or other lipoprotein-associated HCV forms) are more infectious than the lipoprotein-free viral forms of higher densities. 2,3 This could be due to neutralization of the viral forms of high densities by immunoglobulins, to protection of low-density HCV against neutralizing antibodies, and/or to lipoprotein-association that stimulates HCV infection.…”