Hepatitis C virus (HCV) particles are of lowest density and most infectious early in the course of infection, based on findings from a study of chimeric mice.
Over time, however, viral density became more heterogeneous and infectivity fell, reported Ursula Andreo, PhD, of Rockefeller University, New York, with her coinvestigators. A diet of 10% sucrose, which in rats induces hepatic secretion of very-low-density lipoprotein (VLDL), caused HCV particles to become slightly lower density and more infectious in the mice, the researchers reported. Although the shift was “minor,” it “correlated with a trend toward enhanced triglyceride and cholesterol levels in the same fractions,” they wrote. They recommended studying high-fat diets to determine whether altering the VLDL secretion pathway affects the biophysical properties of HCV. “A high-fat diet might have a more significant impact on the lipoprotein profile in this humanized mouse model,” they wrote in Cellular and Molecular Gastroenterology and Hepatology ().
Because HCV tends to associate with lipoproteins, it shows a range of buoyant densities in the blood of infected patients. The “entry, replication, and assembly [of the virion] are linked closely to host lipid and lipoprotein metabolism,” wroteand her colleagues.
They created an in vivo model to study the buoyant density and infectivity of HCV particles, as well as their interaction with lipoproteins, by grafting human hepatocytes into the livers of immunodeficient mice that were homozygous recessive for fumarylacetoacetate hydrolase. Next, they infected 13 of these chimeric mice with J6-JFH1, anthat can establish long-term infections in mice that have human liver grafts ( ). The human liver xenograft reconstituted the FAH gene, restoring triglycerides to normal levels in the chimeric mice and creating a suitable “humanlike” model of lipoprotein metabolism, the investigators wrote.
Density fractionation of infectious mouse serum revealed higher infectivity in the low-density fractions soon after infection, which also has been observed in a human liver chimeric mouse model of severe combined immunodeficiency disease, they added. In the HCV model, the human liver grafts were conserved 5 weeks after infection, and the mice had a lower proportion of lighter, infectious HCV particles.
The researchers lacked sufficient material to directly study the composition of virions or detect viral proteins in the various density fractions. However, they determined that apolipoprotein C1 was the lightest fraction and that apolipoprotein E was mainly found in the five lightest fractions. Both these apolipoproteins are “essential factors of HCV infectivity,” and neither redistributed over time, they said. They suggested using immunoelectron microscopy or mass spectrometry to study the nature and infectivity of viral particles further.
In humans, ingesting a high-fat milkshake increases detectable HCV RNA in the VLDL fraction, the researchers noted. In rodents, a sucrose diet also has been found to increase VLDL lipidation and secretion, so they gave five of the infected chimeric mice drinking water containing 10% sucrose. After 5 weeks, these mice had increased infectivity and higher levels of triglycerides and cholesterol, but the effect was small and disappeared after the sucrose was withdrawn.
HCV “circulates as a population of particles of light, as well as dense, buoyant densities, and both are infectious,” the researchers concluded. “Changes in diet, as well as conditions such as fasting and feeding, affect the distribution of HCV buoyant density gradients.”
Funders included the National Institutes of Health and the American Association for the Study of Liver Diseases. The investigators disclosed no conflicts.