THURSDAY, March 18, 2004 (HealthDayNews) -- Swiss researchers have found that an enzyme can block reproduction of the hepatitis B vaccine, a discovery they say could lead to a new treatment for this dangerous liver infection.
Their theory is that if the enzyme can block the genetically engineered hepatitis B proteins found in the vaccine, it might also work against the virus itself.
More than 250 million people worldwide are infected with hepatitis B, which can cause cirrhosis and liver cancer. About 300,000 Americans contract the infection each year. In about 90 percent of such cases, the virus disappears after several months. But an estimated 1 million Americans are chronically infected.
Hepatitis B is spread by infected blood and other body fluids, such as semen, so drug users who share needles and people who have unprotected sex are vulnerable to the infection. There is a vaccine that can be effective if given immediately after infection. Chronic infections are treated by injections of interferon and by two relatively new antiviral drugs, which are not completely effective. Chronic infection carries the risk of potentially fatal liver conditions.
Now the researchers from the University of Geneva report in the March 19 issue of Science that an enzyme designated as APOBEC3G (understandably abbreviated to A3G) has blocked reproduction of the hepatitis B vaccine in laboratory-grown cell lines.
The discovery is something of a surprise because A3G until now has been identified only as a molecule that defends against retroviruses that have RNA as their genetic material. The best-known retrovirus is HIV, which causes AIDS and is spread in the same way as hepatitis B, by infected blood and sexual contact.
This is the first study to show that A3G can act against a DNA-containing virus such as hepatitis B, according to study author Dr. Didier Trono, chairman of microbiology and molecular medicine at Geneva.
But, he adds, making medical use of that discovery requires a lot of work and some imagination.
"In a wild scheme, one could imagine using gene therapy to express A3G in the liver of chronically infected people," Trono says. "But one could also learn how to activate the expression of this or related genes by pharmacological means."
"We do not know precisely" what A3G does to prevent reproduction of hepatitis B, Trono acknowledges. It is a complicated subject because hepatitis B is "a retrovirus in disguise," using RNA in its reproductive cycle, he explains.
"Perhaps A3G blocks the assembly of the complex necessary for its reproduction," Trono says.
Research on how and why A3G acts as it does will continue, he adds.
More information
Facts about hepatitis B and its treatment are given by the U.S. Centers for Disease Control and Prevention and the Hepatitis B Foundation.
