Significance of Ammonia in the Genesis of Gastric Epithelial Lesions Induced by <i>Helicobacter pylori:</i> An in vitro Study with Different Bacterial Strains and Urea Concentrations

Abstract

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 acid (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.

Common themes and unique proteins for the uptake and trafficking of nickel, a metal essential for the virulence of Helicobacter pylori

“…In addition to its role in acid resistance, urease fuels H. pylori with ammonium for nitrogen assimilation (Williams et al, 1996). The produced ammonia is cytotoxic either alone or in conjunction with neutrophil metabolites (Sommi et al, 1996). Urease activity is also important for survival into macrophages, evasion from phagocytosis, and complement-mediated opsonisation.…”

Helicobacter pylori vacuolating toxin accumulates within the endosomal-vacuolar compartment of cultured gastric cells and potentiates the vacuolating activity of ammonia

“…Bacteria were then removed by centrifugation and the supernatants were sterilized by passage through a 0·22 m cellulose acetate filter (Nalge Co., Rochester, NY, U.S.A.) to obtain the broth culture filtrates (BCFs). 25,26 Uninoculated broth filtrate served as a control. To remove the ammonia content, control and BCFs were dialysed against Hanks's balanced salt solution (HBSS) for 36 h in dialysis tubing with a 12 kD molecular mass cut-off (Sigma, St Louis, MO, U.S.A.).…”

Staying alive overdosed: How does control urease activity?

“…Indeed, recycling of the nitrogenous waste product, urea, is the principal function of many other bacterial ureases. Urease has also been implicated in the damage of host cells through the production of ammonia known to be cytotoxic either alone or in conjunction with neutrophil metabolites (Sommi et al, 1996). Moreover, the urease ARTICLE IN PRESS Fig.…”