- NIH/National Institute of Diabetes and Digestive and
- Contact - Marcia Vital
- Scientists Replicate Hepatitis C Virus In Laboratory
- New in vitro model system will allow study of therapeutics
and virus life cycle
- For the first time, scientists have replicated hepatitis
C virus (HCV) in the laboratory. The ability to replicate HCV in cell culture
will allow researchers to better study the life cycle and biology of this
virus and to test potential antiviral compounds, which may lead to new
therapies for the liver disease that results from infection with HCV. Scientists
at the National Institute of Diabetes and Digestive and Kidney Diseases
(NIDDK), one of the National Institutes of Health (NIH), conducted the
study, which appears in the Feb. 15, 2005 issue of Proceedings of the National
Academy of Sciences (PNAS).
- "Until recently, research on this infectious disease
has suffered from the lack of a robust in vitro model system," says
T. Jake Liang, M.D., Chief of the Liver Diseases Branch of the NIDDK and
co-author of the study. "Our model system produced viral particles
that have all the properties of the whole virus. This evidence together
with an analysis of the replicated viral RNA supports a conclusion of viral
replication and production."
- The NIDDK group used a strain of HCV that would have
applications to the greatest number of people genotype 1, the major type
of HCV of human infections worldwide and the type most resistant to current
therapies. They constructed an HCV replica using a DNA copy of the original
HCV single-strand RNA genome. They placed the DNA copy between two ribozymes,
RNA molecules that have enzymatic function and can cleave RNA sequence
at specific locations. These two ribozymes were designed to generate the
correct ends of the HCV genome and to act as start and stop buttons to
gene activity. The construct was "naked," meaning that it contained
only nucleic acids, the genetic material of the virus, and did not have
the HCV viral envelope, a protective shell of lipids and proteins that
surrounds the viral RNA in fully-formed HCV. The naked HCV construct was
then placed into human liver cells in a cell culture medium.
- The NIDDK scientists found evidence of HCV proteins and
HCV RNA within the human liver cells in the culture. Electron microscopy
showed evidence of high levels of viral particles resembling fully-formed
HCV outside of the human liver cells in the culture medium. The researchers
believe that the HCV construct contained within the human liver cells behaved
like a true HCV infection by producing fully formed copies of the virus
and releasing them from the host cell into the culture medium. Further
testing is needed before the researchers can determine if the viral particles
produced in this system are in fact infectious. Also, this system only
represents the tail end of the viral life cycle viral replication, assembly
and release from host cells. Another HCV model system is needed to show
the beginning stages of the viral life cycle viral entry into host cells
and viral activity in the host cell before replication.
- "With this cell-based system, we can screen compounds
with a cell-based assay to look for inhibitors of virus replication,"
says Liang. "We can also apply this technique to develop model systems
for other similar viruses."
- HCV is a small, enveloped, single-stranded RNA virus
in the family Flaviviridae. HCV is a major cause of liver disease in the
United States and the world. One in a series of hepatitis viruses, HCV
accounts for about 15 percent of acute hepatitis cases, 60 to 70 percent
of chronic hepatitis cases, and up to 50 percent of cases of cirrhosis,
end-stage liver disease, and liver cancer. Almost 4 million Americans,
or 1.8 percent of the U.S. population, have antibodies to HCV indicating
ongoing or previous infection with the virus. Approximately 10,000 to 12,000
deaths each year in the United States are due to HCV.
- Heller, Theo; Jonathan Auerbach; Tarice Williams; Tzivia
Rachel Moreen; Allison Jazwinski; Brian Cruz; Neha Jeurkar; Ronda Sapp;
Guangxiang Luo; and T. Jake Liang. "An in vitro model of hepatitis
C virion production." Proceedings of the National Academy of Sciences,
Vol. 102, No. 7, pp. 2579-2583.
- Patricia A. Doyle, PhD
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