Background: Helicobacter pylori, which causes gastritis and peptic ulc
er, seems to be an important factor in the pathogenesis of gastric can
cer and MALT lymphoma. Thus our aim was to examine whether H. pylori i
nfluences DNA synthesis in epithelial cells in vitro. Methods: Sonicat
ed and water extracts of H. pylori (cytotoxic strains NCTC 11637, 88-2
3 and A5, and a noncytotoxic isogenic mutant of A5, A5 vac A) were dil
uted to a final concentration of 1/1,000, 1/100, 1/50 and 1/10. Water
extracts of Escherichia coli were used as reference. IEC-6 cells were
incubated during 24 h with fragments of H. pylori or extracts of the c
oncentrations described above. The cells were labeled with H-3-methylt
hymidine for 4 h and processed for autoradiography. DNA synthesis was
evaluated by the labeling index (LI). Results: The LI% of controls was
15.6 +/- 5.1%. All the water extracts and sonicated strains of H. pyl
ori increased the LI% in a dose-dependent manner (p < 0.001). The high
est concentrations of the sonicated strains tended to reduce the LI%,
although these values were still higher than those of the control grou
p. The water extracts of E. coli increased the LI% in a dose-dependent
manner (p < 0.0001). Conclusion: H. pylori stimulates DNA synthesis i
n epithelial cells in vitro, but no association was found with the pre
sence of cytotoxin production. Our results suggest that hitherto unkno
wn components of H. pylori may contribute to the increase in cell prol
iferation observed in gastritis and to the development of MALT lymphom
a and gastric cancer.