Effect of different organic acids (citric, malic and ascorbic) on intragastric urease activity

Background: The mechanism of citric acid-enhanced Helicobacter pylori urease activity remains unclear. Aim: 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 m<smallcapitals>m</smallcapitals> citric, malic, or ascorbic acid, pH 2.3 containing 75 mg of C-13-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.