A mutation in the hepatitis E virus might contribute to ribavirin treatment failure in transplant recipients with chronic HEV infection, according to a small study published in the November issue of Gastroenterology.
The study is the first to find in vitro evidence for a virulence mutation in HEV, said Dr. Yannick Debing at the University of Leuven in Belgium, Dr. Annett Gisa at the Hanover Medical School in Germany, and their associates.
Courtesy: American Gastroenterological Association
The researchers studied 15 solid-organ transplant recipients who received ribavirin monotherapy for chronic HEV infection. Thirteen patients were successfully treated, but two with genotype 3c infections failed therapy. Viral RNA levels in both of these patients initially dropped and then rose, suggesting emerging resistance to ribavirin therapy, the investigators said (Gastroenterology 2014 Aug. 30 [doi: 10.1053/j.gastro.2014.08.040]).
When the researchers sequenced HEV genomes from the nonresponders, they found a G1634R mutation in HEV viral polymerase that conferred greater replication capacity compared with wild-type HEV, even after in vitro ribavirin treatment, they reported. “It may be interesting to assess the possible use of position 1634 as a prognostic marker, and accordingly to adjust the dose and duration of ribavirin therapy based on the presence of the G1634R variant,” Dr. Debing and his associates said.
The mutation consisted of a G-to-A nucleotide substitution in the C-terminal region of viral polymerase, the investigators said. By comparing HEV sequences in GenBank (an open-access collection of publicly available nucleotide sequences and their proteins), they found that G1634 was the most common amino acid sequence in genotype 3 HEV, while the K1634 sequence predominated in genotypes 1 and 4.
A subgenomic replicon of genotype 3 HEV with the 1634R mutation showed no increase in ribavirin sensitivity, compared with the wild-type replicon (50% effective concentration [EC50] values, 5.1 ± 4.1 mcM and 5.1 ± 3.7 mcM, respectively), the investigators said. But when they tested the 1634R variant in human hepatoma cells, they observed a 3.4-fold increase in luminescence signaling, compared with cells transfected with capped replicon RNA from wild-type HEV (P = .04). Greater luminescence indicated that the 1634R mutation increased viral replication, they said.
In addition, an HEV replicon with the K1634 mutation showed 2.7 times more luminescence compared with cells transfected with wild-type viral RNA (P = .07), the researchers reported.
The investigators next studied the effects of the 1634 R/K mutations on the full-length HEV genome. They introduced HEV with the two variants into human hepatoma cells, measured the amounts of viral RNA released, and found that both variants replicated at higher levels than did wild-type virus. When they treated these cells with 10- or 25-mcM ribavirin, replication levels dropped for the 1634 R/K variants and for wild-type virus, but remained at least twice as high for the variants, they said.
“The increased replication capacity of the mutant may have contributed to the persistent disease courses despite [ribavirin] treatment, although other patient- and virus-related factors could have contributed as well,” the investigators said.
The research was supported by the Research Foundation–Flanders, KU Leuven University, the Robert Koch Institute, Geconcerteerde Onderzoeksactie, the German Federal Ministry for Education and Research, and EU FP7 project SILVER. The authors reported having no conflicts of interest.