COVALENTLY CLOSED CIRCULAR DNA (cccDNA)
Intrahepatic levels in chronic HBV infection. HBV covalently closed circular DNA (cccDNA) is a key intermediate in HBV replication and serves as the template for transcription of viral RNA. Intracellular cccDNA is the reservoir responsible for the persistence of chronic HBV infection and for reactivation of hepatitis B after stopping therapy. Technical constraints have hampered the direct study of cccDNA maintenance and clearance mechanisms in patients with chronic hepatitis B. The Invader assay, a signal amplification assay, was used by Danny Wong et al. to quantify HBV cccDNA in liver biopsies. They measured total HBV DNA and cccDNA using the Invader assay in DNA extracted from liver biopsies and in serum collected from 16 HBeAg(+) and 36 anti-HBe(+) chronic HBV patients. The median intrahepatic levels of total HBV DNA and cccDNA were significantly lower in anti-HBe(+) patients than HBeAg(+) patients. The absolute level of intrahepatic cccDNA correlated positively with the total intrahepatic HBV DNA level; however, the proportion of intrahepatic HBV DNA in the form of cccDNA was inversely related to the amount of total intrahepatic HBV DNA. It was also found that serum HBV DNA levels correlated positively with intrahepatic HBV DNA and cccDNA levels. These findings indicate that cccDNA becomes the predominant form of intrahepatic HBV DNA as total HBV DNA levels decrease during progression from the HBeAg(+) to the anti-HBe(+) phase of HBV infection. In a second study, Bettina Werle-Lapostolle and colleagues measured intrahepatic cccDNA in 98 liver biopsy samples from patients in different phases of the natural history of HBV infection. In addition, paired samples from 32 HBV patients receiving adefovir dipivoxil therapy were analyzed. Similar to Wong et al., they found intrahepatic cccDNA levels were strongly correlated with serum and intrahepatic HBV DNA levels. Intrahepatic cccDNA was detected in patients in all phases of HBV infection. Furthermore, 48 weeks of adefovir treatment was associated with a significant decrease in cccDNA copies/cell. The decrease in intrahepatic cccDNA correlated with a similar reduction in serum HBsAg titer; however, the number of HBV antigen-positive cells was not observed to decrease. These data demonstrate that cccDNA persists throughout the natural history of HBV infection and that long-term adefovir treatment can decrease, but not eradicate, intrahepatic cccDNA levels. (Wong DK-H, et al. Hepatology 2004; 40: 727-737 and Werle-Lapostolle B, et al., Gastroenterology 2004;126:1750-1758) | 
发表于 2005-2-1 10:18
