Significance of ammonia in the genesis of gastric epithelial lesions induced by Helicobacter pylori: an in vitro study with different bacterial strains and urea concentrations.
Two Helicobacter pylori products cause cell damage both in vivo and in vitro: ammonia, from bacterial urease activity, and a vacuolating toxin named VacA. In this in vitro study, the vacuolating effect of H. pylori broth culture filtrate from a VacA-positive/urease-positive strain is compared with that of a VacA-negative/urease-positive strain and a VacA-negative/urease-negative strain. The effect of VacA and ammonia was evaluated with and without addition of 10 mM urea, a physiological concentration for the human stomach, and with and without addition of 0.5 mg/ml acetohydroxamic and (AHA), an urease inhibitor. Our data show that: (1) both urease-positive H. pylori strains caused cell vacuolation in the absence of urea, the VacA-positive strain being approximatively twice as potent as the VacA-negative strain; (2) addition of urea to the culture medium caused an approximatively 3-fold increase in the vacuolating activity of both urease-positive strains; (3) a VacA-negative/urease-negative strain did not exert any vacuolating effect, either in the presence or in the absence of urea; (4) the ratio between cell vacuolation induced by VacA-positive and VacA-negative strains was enhanced by the presence of AHA: ratio was about 2 in the absence of AHA and about 6 in the presence of AHA, either with or without urea added. The increment of vacuolation is likely due to an interaction between AHA and VacA. In conclusion, a VacA-negative/urease-positive strain becomes highly cytotoxic when physiological levels of urea are present in the incubation medium. This finding suggests that all urease-positive H. pylori strains, both with and without VacA expression, should be considered as potentially cytotoxic for the human gastric mucosa, although VacA enhances the severity of cell damage.
Sommi
P
P
Institute of Human Physiology, University of Pavia, Italy.
Ricci
V
V
Fiocca
R
R
Romano
M
M
Ivey
K J
KJ
Cova
E
E
Solcia
E
E
Ventura
U
U
D000641:Ammonia; D001426:Bacterial Proteins / Q000032:analysis / Q000502:physiology; D001427:Bacterial Toxins / Q000032:analysis; D005753:Gastric Mucosa / Q000382:microbiology* / Q000473:pathology; D016480:Helicobacter pylori / Q000201:enzymology / Q000472:pathogenicity*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D014508:Urea / Q000032:analysis*; D014510:Urease / Q000037:antagonists & inhibitors / Q000378:metabolism; D014617:Vacuoles
D001426:Bacterial Proteins; D001427:Bacterial Toxins; D006877:Hydroxamic Acids; C074689:VacA protein, Helicobacter pylori; C006358:acetohydroxamic acid; D000641:Ammonia; D014508:Urea; D014510:Urease