Serum Hepatitis B Virus RNA: A New Potential Biomarker for Chronic Hepatitis B Virus Infection

Abstract

Chronic hepatitis B infection is one of the major etiological causes of liver failure, cirrhosis, and hepatocellular carcinoma (HCC) worldwide. This condition cannot be completely cured by currently available drugs due to the persistent existence of hepatitis B virus (HBV) covalently closed circular DNA (cccDNA), the bona fide transcription template for HBV RNAs, in infected hepatocytes. Because quantifying cccDNA per se requires an invasive procedure, serum biomarkers reflecting intrahepatic cccDNA activity are warranted. Recently, a growing body of research suggests that the circulating HBV RNA may serve as a serum biomarker for HBV infection, treatment, and prognosis. In order to delineate the molecular and clinical characteristics of serum HBV RNA, we systematically reviewed the available literature on serum HBV RNA dating back to the early 1990s. In this review, we summarize the reported serum HBV RNA quantification methods and discuss the potential HBV RNA species in patient serum. We also compare the reported correlations of serum HBV RNA with other serological markers, including HBV DNA, hepatitis B surface antigen, e antigen, and core-related antigen, as well as their correlations with intrahepatic cccDNA, to assess their potential in clinical applications. Future directions for serum HBV RNA research are also discussed.

Figure 1.. HBV life cycle.

The major steps in HBV life cycle including entry, de-envelopment, cccDNA formation, mRNA transcription, protein translation, pgRNA encapsidation, DNA replication, viral particle assembly and secretion are shown. See text for details. (Abbreviations: NTCP: sodium taurocholate cotransporting polypeptide; rcDNA: relaxed circular DNA; cccDNA: covalently closed circular DNA; pgRNA: pregenomic RNA; ssDNA: single-stranded DNA; dslDNA: double-stranded linear DNA; pol: polymerase; L: large surface protein; M: middle surface protein; S: small surface protein; HBsAg: hepatitis B surface antigen; HBeAg: hepatitis B e antigen; HBx: hepatitis B X protein; ER: endoplasmic reticulum; MVB: multivesicular body.)

Figure 2.. Representatives of published PCR methods for detecting serum HBV RNA.

HBV ORFs are shown as horizontal arrows and their nucleotide positions are marked on the scale bar which represents the length of HBV 3.5kb mRNA (genotype B/C). The blue and brown upward arrows pointing to scale bar indicate the location of canonical polyadenylation signal TATAAA and a cryptic polyadenylation signal CATAAA, respectively. The overlapping full-length HBV mRNAs are shown in wave lines. The direct repeat (DR) sequence DR1 and DR2 are denoted on pgRNA, the vertical red and black arrows pointing to pgRNA indicate the major 5’ splicing donor sites and 3’ splicing acceptor sites of pgRNA. The red lines underneath HBV mRNAs represent the PCR amplicon in the referenced studies (denoted with reference numbers in square brackets). Multiple PCR amplicons from the same reference are numbered. The primer information is provided in the embedded table, and additional information can be found in Table 1. “RT-Primer”, FW-Primer”, and “RV-Primer” refer to reverse transcription primer, forward primer and reverse primer of PCR, respectively. (Note: ^a The HBV-specific RT-primer in reference [6] is composed of a HBV-specific sequence and a unique anchored sequence at the 5’-end. The anchored sequence is used as RV-primer in PCR cycles. ^b RT-primer in reference [32] contains a 3’-terminal sequence complementary to the HBV flRNA or trRNA sequence adjacent to polyA tail, a middle stretch of oligo(dT), and a 5’ artificial anchored sequence. The anchored sequence is same as RV-primer. ^c The sequences of RV-primers in reference [20], [21], [36], [38] and [52] are identical to RT-primers.)