title: Effect of different organic acids (citric, malic and ascorbic) on intragastric urease activity.
abstract: BACKGROUND
  The mechanism of citric acid-enhanced Helicobacter pylori urease activity remains unclear.
  
  
  OBJECTIVE
  To compare ascorbic, citric and malic acid given at the same concentration and pH on intragastric urease activity.
  
  
  METHODS
  Volunteers received 40 mg of famotidine the evening prior to breath testing. After an overnight fast volunteers were randomized to receive 100 mL of water or 100 mm citric, malic, or ascorbic acid, pH 2.3 containing 75 mg of 13C-urea. At 15 min a second 100 mL solution of one of the test solutions was taken without added urea.
  
  
  RESULTS
  Twelve volunteers were studied (eight men, four women, age 19-57, median 50.7) in a randomized-crossover study. The mean breath test result at 30 min with ascorbic (17.5 +/- 5), malic (25.8 +/- 5) and citric acid (29.5 +/- 5) were all significantly greater than with water (9.5 +/- 3). Citric and malic acid were similar (P = 0.699) and significantly greater than ascorbic acid (P < 0.02). When the ascorbic acid was followed by citric acid, the result was similar to that with citrate alone (25.8 +/- 4) and greater than with ascorbic then ascorbic (P = 0.026).
  
  
  CONCLUSIONS
  Enhancement of H. pylori urease activity is not strictly a function of the pH. We propose the effect is related to differential effects of the availability of nickel, which is required for urease activity. Citric acid and malic acid were essentially equivalent such that malic acid could substitute for citric acid in the UBT; ascorbic acid would be a poor choice.
authors.affiliation: Department of Medicine, Michael E. DeBakey VA Medical Center and Baylor College of Medicine, Houston, TX 77030, USA.
authors.forename: A
authors.initials: A
authors.lastname: Agha
authors.forename: A R
authors.initials: AR
authors.lastname: Opekun
authors.forename: S
authors.initials: S
authors.lastname: Abudayyeh
authors.forename: D Y
authors.initials: DY
authors.lastname: Graham
mesh_terms: D000328:Adult; D001205:Ascorbic Acid / Q000494:pharmacology*; D019343:Citric Acid / Q000494:pharmacology*; D005260:Female; D016481:Helicobacter Infections / Q000201:enzymology; D016480:Helicobacter pylori / Q000201:enzymology; D006801:Humans; D008293:Malates / Q000494:pharmacology*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013272:Stomach Diseases / Q000201:enzymology* / Q000382:microbiology; D014510:Urease / Q000378:metabolism*
chemical_list: D008293:Malates; D019343:Citric Acid; C030298:malic acid; D014510:Urease; D001205:Ascorbic Acid