The rtL229 substitutions in the reverse transcriptase region of hepatitis B virus (HBV) polymerase are potentially associated with lamivudine resistance as a compensatory mutation.

BACKGROUND: It remains unclear whether hepatitis B virus (HBV) reverse-transcriptase (RT) rtL229 substitutions influence HBV drug resistance.
OBJECTIVE: The study was to investigate the association of HBV rtL229 substitutions with viral resistance to lamivudine (LAM). STUDY
DESIGN: Entire HBV RT genes were amplified by nested PCR and sequenced from sera of 6000 nucleos(t)ide analog-experienced patients with chronic HBV infection. The incidence and clinic relevance of rtL229 substitutions were analyzed. Replication-competent viral amplicons which harbored HBV genomes of wild-type, rtM204I, or rtM204I in conjunction with various rtL229 substitutions (rtL229F/W/M/V) were constructed. The amplicons were transfected into HepG2 cells for phenotyping of replication capacity and susceptibility to nucleos(t)ide analogs.
RESULTS: The rtL229 substitutions were detected in 6.57% (394/6000) of patients. Individual substitution incidences were 2.77%, 0.97%, 0.83% and 0.55% for rtL229V, rtL229F, rtL229M and rtL229W, respectively. The incidence of rtL229 substitutions was significantly higher in LAM-experienced patients (341/4220, 8.1%) than in LAM-naïve patients (53/1780, 3.0%), and were independently associated with genotypic LAM resistance (77.9% vs. 21.2%, OR 8.806, 95%CI 6.345-12.223) and low viral replication (HBV DNA <1000IU/mL) (4.60% vs. 24.2%, OR 0.478, 95%CI 0.254-0.898). Representative cases follow-up showed that rtL229F developed subsequent to rtM204I emergence during LAM treatment and regressed with rtM204I after LAM withdrawal. Functionally, rtL229F did not confer reduced susceptibility to LAM, but could restore replication capacity of rtM204I strain.
CONCLUSION: The rtL229 substitutions were potentially associated with LAM resistance in Chinese patients and rtL229F had characteristics of a compensatory mutation of rtM204I mutant.