Pyruvate Decarboxylase, the Target for Omeprazole in Metronidazole-Resistant and Iron-Restricted Tritrichomonas foetus

Abstract

The substituted benzimidazole omeprazole, used for the treatment of human peptic ulcer disease, inhibits the growth of the metronidazole-resistant bovine pathogen Tritrichomonas foetus in vitro (MIC at which the growth of parasite cultures is inhibited by 50%, 22 g/ml [63 M]). The antitrichomonad activity appears to be due to the inhibition of pyruvate decarboxylase (PDC), which is the key enzyme responsible for ethanol production and which is strongly upregulated in metronidazole-resistant trichomonads. PDC was purified to homogeneity from the cytosol of metronidazole-resistant strain. The tetrameric enzyme of 60-kDa subunits is inhibited by omeprazole (50% inhibitory concentration, 16 g/ml). Metronidazole-susceptible T. foetus, which expresses very little PDC, is only slightly affected. Omeprazole has the same inhibitory effect on T. foetus cells grown under iron-limited conditions. Similarly to metronidazole-resistant cells, T. foetus cells grown under iron-limited conditions have nonfunctional hydrogenosomal metabolism and rely on cytosolic PDC-mediated ethanol fermentation.Tritrichomonas foetus is a parasitic flagellate that causes sexually transmitted diseases in cattle that can lead to abortion and infertility. For decades the drugs of choice for the treatment of urogenital trichomoniasis were 5-nitroimidazoles, such as metronidazole ( Fig. 1), dimetridazole, and related derivatives, until they were subjected to regulatory actions in the United States, the European Union, and some other countries. The antitrichomonad activity of metronidazole depends upon reduction of its nitro group to short-lived free radicals, which cause multiple forms of cellular damage, including DNA breakage and subsequent cell death. Reductive activation of the drug proceeds in typical trichomonad organelles called hydrogenosomes, whose main function is a substrate-level synthesis of ATP linked to the production of molecular hydrogen. Electrons required for metronidazole reduction are generated by pyruvate:ferredoxin oxidoreductase, the key hydrogenosomal enzyme catalyzing oxidative decarboxylation of pyruvate (6,16,18).Prolonged cultivation of trichomonads with sublethal concentrations of metronidazole can result in the development of stable drug resistance accompanied by the loss of pyruvate: ferredoxin oxidoreductase activity (14, 15). Metronidazole-resistant trichomonads show an altered carbohydrate metabolism. The pyruvate-oxidizing pathway in the hydrogenosomes disappears, and the loss of ATP is compensated for by an increased rate of glycolysis in the cytosol. The dominant end product of glucose breakdown becomes ethanol, the production of which is negligible in metronidazole-susceptible trichomonads. The ethanol production depends on the activities of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (2). While the activity of the latter enzyme is not markedly changed in metronidazole-resistant strains, the activity of PDC is strongly upregulated, suggesting that PDC is the rate-limiting enzyme in the production of et...

Secondary alcohol dehydrogenase catalyzes the reduction of exogenous acetone to 2‐propanol in Trichomonas vaginalis

“…However, the source of substrates for Tv ‐S‐ADH is not clear. A related parasite T. foetus possesses a pyruvate decarboxylase to catalyze the conversion of pyruvate to acetaldehyde, a S‐ADH substrate [40]. Other anaerobic protists that produce ethanol, such as Giardia intestinalis and E. histolytica do not possess hydrogenosomes and metabolize pyruvate exclusively in the cytosol.…”

Biochemistry and Evolution of Anaerobic Energy Metabolism in Eukaryotes

“…Glycerol is produced from dihydroxyacetone phosphate via glycerol-3-phosphate dehydrogenase and glycerol-3-phosphatase (354,469). Ethanol is generated from pyruvate, as in yeast, via pyruvate decarboxylase and alcohol dehydrogenase (256,477). Lactate is produced in the cytosol by a lactate dehydrogenase (LDH) that is derived phylogenetically from the duplication and modification of a preexisting malate dehydrogenase (MDH) (563).…”

Proton pump inhibitors are associated with a reduced likelihood for sexually transmitted diseases in women in the emergency department

“…[617] The PPI omeprazole was found to kill metronidazole-resistant TF at 22 μg/mL (63 μM) in cell culture. [17] The authors suggest that omeprazole works by inhibition of pyruvate decarboxylase (PDC), which is an enzyme responsible for ethanol production. PDC was inhibited by omeprazole with an IC 50 of 16 μg/mL.…”