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

P. Sommi, V. Ricci, R. Fiocca, M. Romano, K. J. Ivey, E. Cova, Enrico Solcia, U. Ventura

Research output: Contribution to journalArticle

18 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)299-304
Number of pages6
JournalDigestion
Volume57
Issue number5
Publication statusPublished - 1996

Fingerprint

Urease
Ammonia
Helicobacter pylori
Urea
Stomach
In Vitro Techniques
Gastric Mucosa
Culture Media
acetohydroxamic acid

Keywords

  • Acetohydroxamic acid
  • Ammonia
  • Cell vacuolation
  • Cultured gastric cells
  • Helicobacter pylori
  • Urea
  • Urease
  • VacA

ASJC Scopus subject areas

  • Gastroenterology

Cite this

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. / Sommi, P.; Ricci, V.; Fiocca, R.; Romano, M.; Ivey, K. J.; Cova, E.; Solcia, Enrico; Ventura, U.

In: Digestion, Vol. 57, No. 5, 1996, p. 299-304.

Research output: Contribution to journalArticle

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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.",
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AU - Ricci, V.

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AU - Romano, M.

AU - Ivey, K. J.

AU - Cova, E.

AU - Solcia, Enrico

AU - Ventura, U.

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