Lamivudine is used for the treatment of chronic hepatitis B (CH-B), and exhibits excellent antiviral activity. However, longterm administration increases the likelihood of the emergence of resistant viruses, with an accompanying relapse of hepatitis. However, recent studies have reported lamivudine-resistant viruses in patients with CH-B before such treatment. The aim of this study was to investigate whether YMDD mutants occur in nature.
The existence of lamivudine-resistant viruses was examined in 20 asymptomatic carriers of hepatitis B virus (ASC), 10 patients who lost hepatitis B surface antigen (HBsAg) during follow-up and in 20 lamivudine-treated patients with and without breakthrough hepatitis. Both polymerase chain reaction (PCR) restriction fragment length polymorphism and SMITEST hepatitis B virus (HBV)-YMDD mutation detection methods were used to detect resistant viruses.
No YMDD mutants were detected in the sera of the 20 ASC at the initial and final medical examinations, nor were YMDD mutants detected in sera collected at the initial medical examination, about 6 months before, or immediately after the loss of HBsAg in the 10 patients. In the 20 patients treated with lamivudine, YMDD mutants were not detected in any of them before treatment, whereas mutants were detected in the sera of 10 patients during treatment.
Our results suggest that lamivudine-resistant YMDD mutant viruses were present in a few patients with HBV infection before they have been treated with lamivudine.
"However, among five patients after 12 months lamivudine treatment , M552I mutations in two patients with HBV DNA rebounding were detected. In fact, YMDD mutations are found in nature, but it is difficult to explain significant distinction between few YMDD mutations detected in nature (Matsuda et al., 2004; Chen et al., 2004) and high mutational rate during long-term lamivudine treatment. The resistant mutations occur in 14.0–32.0% of patients after 1 year of treatment (Lai et al., 1998; Ono-Nita et al., 1999) increasing to 38.0% and 49.0% after 2 and 3 years of treatment, respectively (Liaw et al., 2000; Leung et al., 2001).Yao et al. (2004) has even detected the YMDD mutations in 70.5% of patients at year 3. Like HIV, HBV utilizes a reverse transcription step in replicating the viral genome. "
[Show abstract][Hide abstract] ABSTRACT: The mutation of YMDD motif of hepatitis B virus (HBV) polymerase gene is the most frequent cause in HBV resistant to lamivudine. The aim of the study was to investigate variation features of HBV polymerase gene in chronic hepatitis B (CHB) patients before and after lamivudine treatment. From the serum samples of five CHB patients before and after 12 months of lamivudine treatment, HBV polymerase gene was amplificated and positive DNA fragments were cloned into JM105 competent cell. Twenty positive clones of every sample were checked with mismatched polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and YMDD variants were sequenced. Among five patients after 12 months of lamivudine treatment, M552I mutations in two patients with HBV DNA rebounding and D553G mutation in one non-responder were detected except two patients with negative HBV DNA consecutively. In summary, D553G mutation is probably one of the reasons that caused non-responders during lamivudine treatment. The mutations of YMDD motif occurred after lamivudine treatment are caused by the induction of lamivudine.
Microbiological Research 02/2008; 163(4):487-92. DOI:10.1016/j.micres.2006.11.004 · 2.56 Impact Factor
"However, lamivudine-resistant isolates would eventually be expected to circulate in the environment as a result of contact with chronic hepatitis B patients undergoing lamivudine antiviral therapy, allowing healthy individuals, including blood donors, to become exposed to a primary infection with an HBV mutant strain. The presence of lamivudine-resistant isolates could also be related to previously reports of HBV isolates with a YMDD motif mutation in chronic hepatitis B patients not treated with lamivudine [50,51]. "
[Show abstract][Hide abstract] ABSTRACT: Hepatitis B virus (HBV) isolates have been classified in eight genotypes, A to H, which exhibit distinct geographical distributions. Genotypes A, D and F are predominant in Brazil, a country formed by a miscegenated population, where the proportion of individuals from Caucasian, Amerindian and African origins varies by region. Genotype F, which is the most divergent, is considered indigenous to the Americas. A systematic molecular characterization of HBV isolates from different parts of the world would be invaluable in establishing HBV evolutionary origins and dispersion patterns. A large-scale study is needed to map the region-by-region distribution of the HBV genotypes in Brazil.
Genotyping by PCR-RFLP of 303 HBV isolates from HBsAg-positive blood donors showed that at least two of the three genotypes, A, D, and F, co-circulate in each of the five geographic regions of Brazil. No other genotypes were identified. Overall, genotype A was most prevalent (48.5%), and most of these isolates were classified as subgenotype A1 (138/153; 90.2%). Genotype D was the most common genotype in the South (84.2%) and Central (47.6%) regions. The prevalence of genotype F was low (13%) countrywide. Nucleotide sequencing of the S gene and a phylogenetic analysis of 32 HBV genotype F isolates showed that a great majority (28/32; 87.5%) belonged to subgenotype F2, cluster II. The deduced serotype of 31 of 32 F isolates was adw4. The remaining isolate showed a leucine-to-isoleucine substitution at position 127.
The presence of genotypes A, D and F, and the absence of other genotypes in a large cohort of HBV infected individuals may reflect the ethnic origins of the Brazilian population. The high prevalence of isolates from subgenotype A1 (of African origin) indicates that the African influx during the colonial slavery period had a major impact on the circulation of HBV genotype A currently found in Brazil. Although most genotype F isolates belonged to cluster II, the presence of some isolates belonging to clusters I (subgroup Ib) and IV suggests the existence of two or more founder viral populations of genotype F in Brazil.
[Show abstract][Hide abstract] ABSTRACT: Hepatitis B virus (HBV) mutants with mutations in the YMDD motif of viral DNA polymerase/reverse transcriptase are described in patients infected with HBV who have not received lamivudine therapy, but their pathogenetic potential is not clear. These mutants were detected by the polymerase chain reaction with peptide nucleic acid clamping in pretreatment sera from two patients who later received lamivudine. One patient developed acute exacerbation with hepatic encephalopathy and received lamivudine along with plasma exchange, which were effective on his illness. YIDD mutants were detected in all three pretreatment sera and both posttreatment sera from him. HBV DNA clones from pretreatment and posttreatment sera, however, did not have the same amino acid sequence. In the other patient who developed severe breakthrough hepatitis after receiving lamivudine, YIDD mutants were detected in two pretreatment and two posttreatment sera. When amino acid sequences of HBV DNA clones with the YIDD mutation were compared before and after he received lamivudine, however, they were not in accord. Hence, YIDD mutants in both patients with chronic hepatitis B before treatment were not selected by lamivudine after they had been placed on it. Numerous amino acid conversions were detected in HBV DNA clones with YIDD mutations, and some of them created stop codons in the overlapping S gene sequence. In Conclusion, HBV mutants with mutations in the YMDD motif in patients before treatment would not be selected by lamivudine or induce breakthrough hepatitis, and some of these would not be replication-competent due to stop codons in the S gene.
Journal of Medical Virology 10/2004; 74(2):361-6. DOI:10.1002/jmv.20185 · 2.35 Impact Factor
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