In vivo dynamics and pathogenicity of wild-type and resistant Hepatitis B virus during long-term lamivudine monotherapy - a clinical note

Inflammation Pharmacological Reaction and YMDD Mutational Patterns in Lamivudine Therapeutics Hepatitis B Virus

Background/Aims: Emergence of tyrosine-methionine-aspartate-aspartate (YMDD) motif in reverse transcriptase is a serious problem in chronic hepatitis B(CHB) patients after Lamivudine (LAM) therapy. However, the relationship between inflammation pharmacological reaction and YMDD mutational patterns of CHB has not been well-characterized. The aim of this study was to investigate the inflammation pharmacological reaction and different YMDD mutants patterns of CHB patients. Methods: We investigated the inflammation pharmacological reaction and YMDD mutational patterns through biochemical, serological and virological detection among 83 CHB patients, including 25 YMDD mutants, 25 under detection, and 33 control patients without YMDD mutants. Results: Prevalence of YMDD mutation patterns is different. Among 25 YMDD mutants patients, YIDD was the dominant mutation (72%), followed YVDD (16%) and the hybrid YIDD + YVDD (12%). The time course during the YMDD mutations was also different. 52.4% patients developed the mutation less than 12 months after the LAM therapy. Serum hepatitis B virus (HBV) DNA level in patients with YMDD mutants were significantly higher than that in control and negative groups. Serum HbsAg and HbeAg in patients with YMDD mutants were also higher than those in control and negative groups, despite no significant difference was found forserum HbeAb. ALT and AST levels were also significantly higher in mutants group. Conclusions: Illuminating inflammation pharmacological reaction and YMDD mutational patterns of CHB during pathological process may have implications for future therapy in YMDD mutation patients. This may have impact on the choice of treatment strategies for lamivudine-resistant HBV.

Differences of YMDD mutational patterns, precore/core promoter mutations, serum HBV DNA levels in lamivudine-resistant hepatitis B genotypes B and C

The aims of this study were to investigate the viral differences among lamivudine-resistant hepatitis B virus (HBV) genotypes B and C in vivo. Fifty-three patients carrying lamivudine-resistant HBV were enrolled in this study. HBV genotypes, Levels of alanine aminotransferase (ALT), HBV DNA levels were monitored during therapy. The polymerase and precore/core promoter genes were amplified by polymerase chain reaction and their products were sequenced directly. Among 53 patients resistant HBV genotypes B and C accounted for 41.50% and 58.50%, respectively. The occurrence of reverse transcriptase rt204I mutants was lower in genotype B (36.36%) than that in genotype C (87.10%), whereas rt204V mutants was higher in genotype B (63.64%) than that in genotype C (12.90%). The occurrence of precore mutation (nt1896A) was higher in genotype B (77.27%) than that in genotype C (32.26%). Serum HBV DNA levels after emergence of lamivudine resistance were higher in genotype C (7.71 +/- 0.80 Log copies/mL) compared with genotype B (6.97 +/- 0.77 Log copies/mL). Multivariate analysis identified pretreatment HBV DNA levels, HBeAg status and HBV genotype as independent factors associated with a shorter time to lamivudine resistance(P = 0.035, P = 0.006 and P = 0.001, respectively). Multivariate analysis showed that HBV genotype (P = 0.004) and pretreatment ALT levels (P = 0.01) was independently associated with YMDD mutational patterns. The results showed that the YMDD mutational patterns, precore mutation and serum HBV DNA levels differ between lamivudine-resistant HBV genotypes B and C in vivo. It is valuable for treatment of lamivudine-resistant HBV in clinic.

Clinical and virological features of non-breakthrough and severe exacerbation due to lamivudine-resistant hepatitis B virus mutants

Patients who develop YMDD mutant during lamivudine therapy for hepatitis B virus (HBV) infection exhibit various clinical courses. Some patients show normal ALT levels, whereas others develop severe hepatitis exacerbations (SHEs) due to YMDD mutants. We studied 136 patients with YMDD mutant among 362 Japanese adult patients on lamivudine therapy. Clinical and virological features of patients without elevated HBV DNA after emergence of YMDD mutant (non-elevated group) were investigated. Moreover, virological analysis was also performed in patients with SHE due to YMDD mutants. Patients in the non-elevated group were characterized by HBeAg-negative pretreatment, HBeAg loss during therapy, a longer duration from commencement of therapy until emergence of YMDD mutant, and no mixed-type YMDD mutants. Patients with SHE had more substitutions in the reverse transcriptase (rt) region within the polymerase gene at the time of exacerbation than those without SHE, although no specific substitutions were noted. Sequence analysis of full-length HBV genome showed more substitutions in X, rt, and surface proteins in patients with SHE than in those without elevated HBV DNA level. In conclusion, negativity for HBeAg at commencement of therapy or before emergence of YMDD mutant was an important factor among non-elevated group. More substitutions in the rt region and the other proteins may be related to the emergence of severe hepatitis caused by lamivudine-resistant virus.

Complete hepatitis B virus genome analysis in chronically infected children before and during lamivudine treatment

It is well established that during lamivudine treatment, mutations emerge within the polymerase gene but there is little information about the selection of other mutations in the whole hepatitis B virus (HBV) genome. The aim of this study was to investigate whether mutations outside this region are selected during lamivudine treatment. The complete HBV genomes of six HBsAg positive chronically infected children were isolated from the children's sera before, at the beginning and during lamivudine treatment, amplified and sequenced directly. A change in the mutation rate and type in periods with and without treatment for one and the same patient were examined longitudinally because blood samples were taken long before treatment started. During the testing period before treatment, 12 mutations occurred within 11.7 +/- 8.1 months in all genomes, resulting in a mutation rate of 1.1 x 10(-3) substitutions per site per year. During treatment with lamivudine, 20 mutations occurred in all patients within an average period of 7.6 +/- 1.2 months, giving an average mutation rate of 1.8 x 10(-3) substitutions per site per year. The 20 mutations observed during the treatment period occurred in only 4 of the patients and only 3 patients experienced nonsense mutations during lamivudine treatment. The mutations were spread across the entire genome with a non-significant cluster during treatment in the P-ORF (18 mutations vs. 7, P = 0.073) and S-ORF (11 vs. 2, P = 0.063). Mutations causing drug resistance did not emerge. This study describes the changes in the complete HBV genome in the spontaneous course of infection and during lamivudine treatment. An increased mutation rate and the occurrence of specific mutations could not be proven for the early phase of lamivudine treatment.

Viral features of lamivudine resistant hepatitis B genotypes A and D

Viral differences among lamivudine resistant hepatitis B (HBV) genotypes have not been yet investigated. Therefore, we analyzed the characteristics of these viral strains in vivo. Forty-one patients carrying lamivudine resistant HBV were enrolled. Twenty-six patients (63%) carried resistant HBV genotype A (group A) and 15 patients (37%) carried resistant HBV genotype D (group D). The rate of reverse transcriptase 204I mutants was significantly higher in group D (67%) compared with group A (19%), whereas rt204V mutants (81% in group A vs 33% in group D; P =.006) and rt180M mutants (81% in group A vs 40% in group D, P =.015) prevailed in group A. The median time of shift from rt204I to rt204V mutants was significantly shorter in group A (4 months in group A, >12 months in group D, P <.001). Additional resistance associated mutations were detected exclusively in group D (P =.004). In a multivariate analysis, HBV genotype (P =.039) and pretreatment serum HBV DNA (P =.001) were independently associated with emerging rt204I or rt204V mutants, respectively. Serum HBV copy numbers after emergence of resistance were higher in group A (mean log(10) 6.99 copies/ml; range 3-9) compared with group D (mean log(10) 6.1 copies/ml; range 3.3-8; P =.04). There was no difference between both groups regarding core promoter/precore mutations, viral turnover, and number of flares or disease progression during follow-up. In conclusion, the mutational pattern during selection of lamivudine resistant HBV strains differs between genotypes A and D. This may have consequences for a salvage regimen initiated for treatment of lamivudine resistant HBV.

Clinical outcome and virologic profiles of severe hepatitis B exacerbation due to YMDD mutations

BACKGROUND/AIMS

To study the outcome and the virologic profiles of severe hepatitis exacerbations due to YMDD mutants in lamivudine-treated patients.

METHODS

Eighteen lamivudine-treated patients with severe hepatitis exacerbations due to YMDD mutants were recruited. Laboratory and clinical parameters were monitored. Viral genotypes and YMDD mutations were determined.

RESULTS

None of the 18 patients had YMDD wild-type during exacerbations. Three (17%) and 15 (83%) patients had genotypes B and C, respectively. Elevated bilirubin levels and prolonged prothrombin time were found in 11 (61%) and six patients (33%) respectively. Three patients (17%) had adverse outcome with the development of ascites and/or encephalopathy. One of these patients required liver transplantation and one died. Both patients had evidence of cirrhosis before treatment and hepatitis B e antigen (HBeAg) seroreversion from anti-HBe positivity. The remaining 16 patients (89%) have no evidence of pre-existing cirrhosis. Thirty seven percent of patients had normal alanine aminotransferase levels at the last follow-up. The median HBV DNA level at the last follow-up was significantly lower than the pre-treatment level (P=0.009).

CONCLUSIONS

Though the majority of patients with severe hepatitis exacerbations due to YMDD mutants had uneventful course, early liver transplantation should be considered in patients with pre-existing cirrhosis and HBeAg seroreversion.

Dynamics of hepatitis B virus infection

Mathematical models of the dynamics of HIV and hepatitis C virus infection have proven to be of great utility in understanding pathogenesis and designing better treatments. Here, we review the state of the art in modeling and interpreting data obtained from hepatitis B virus infected patients treated with antiviral agents.

Kinetic analysis of wild-type and YMDD mutant hepatitis B virus polymerases and effects of deoxyribonucleotide concentrations on polymerase activity

Mutations in the YMDD motif of the hepatitis B virus (HBV) DNA polymerase result in reduced susceptibility of HBV to inhibition by lamivudine, at a cost in replication fitness. The mechanisms underlying the effects of YMDD mutations on replication fitness were investigated using both a cell-based viral replication system and an in vitro enzyme assay to examine wild-type (wt) and YMDD-mutant polymerases. We calculated the affinities of wt and YMDD-mutant polymerases for each natural deoxyribonucleoside triphosphate (dNTP) and determined the intracellular concentrations of each dNTP in HepG2 cells under conditions that support HBV replication. In addition, inhibition constants for lamivudine triphosphate were determined for wt and YMDD-mutant polymerases. Relative to wt HBV polymerase, each of the YMDD-mutant polymerases showed increased apparent K(m) values for the natural dNTP substrates, indicating decreased affinities for these substrates, as well as increased K(i) values for lamivudine triphosphate, indicating decreased affinity for the drug. The effect of the differences in apparent K(m) values between YMDD-mutant polymerase and wt HBV polymerase could be masked by high levels of dNTP substrates (>20 microM). However, assays using dNTP concentrations equivalent to those measured in HepG2 cells under physiological conditions showed decreased enzymatic activity of YMDD-mutant polymerases relative to wt polymerase. Therefore, the decrease in replication fitness of YMDD-mutant HBV strains results from the lower affinities (increased K(m) values) of the YMDD-mutant polymerases for the natural dNTP substrates and physiological intracellular concentrations of dNTPs that are limiting for the replication of YMDD-mutant HBV strains.

20-fold increase in risk of lamivudine resistance in hepatitis B virus subtype adw

We investigated subtype-dependent development of lamivudine resistance in hepatitis B virus (HBV) longitudinally in 26 consecutive patients (13 adw and 13 ayw carriers) during antiviral treatment of chronic hepatitis B. Lamivudine resistance developed in seven adw carriers and one ayw carrier. Risk of lamivudine resistance was significantly higher for adw carriers than for ayw carriers (p=0.03). We believe that the adw subtype of HBV is associated with a high risk of lamivudine resistance, which might be linked to simultaneous changes of the HBsAg that occurs with the emergence of resistance.