title: Arginine and polyamines in Helicobacter pylori-induced immune dysregulation and gastric carcinogenesis.
abstract: L-arginine (L-Arg) is metabolized by nitric oxide synthase and arginase enzymes. The gastric pathogen Helicobacter pylori causes peptic ulcer disease and gastric cancer. We have shown that alterations in L-Arg availability and metabolism into polyamines contribute significantly to the dysregulation of the host immune response to this infection. Nitric oxide (NO) derived from inducible NO synthase (iNOS) can kill H. pylori. There are multiple mechanisms leading to failure of this process, including competition for L-Arg substrate by H. pylori arginase, and induction of host macrophage arginase II (Arg2) and ornithine decarboxylase (ODC). Generation of spermine by ODC inhibits iNOS translation and NO-mediated H. pylori killing. Expression of ODC is dependent on formation of a unique AP-1 complex, leading to upregulation of c-Myc as a transcriptional enhancer. Macrophage apoptosis is mediated by oxidation of spermine via the enzyme spermine oxidase (SMO) that generates hydrogen peroxide (H(2)O(2)), and thus oxidative stress-induced mitochondrial membrane polarization. Our studies have demonstrated that apoptosis occurs through a pERK → pc-Fos/c-Jun → c-Myc → ODC → SMO pathway. In gastric epithelial cells, activation of oxidative stress by H. pylori is dependent on SMO induction and results in both apoptosis and DNA damage, such that inhibition or knockdown of SMO markedly attenuates these events. In summary, L-Arg metabolism by the arginase-ODC pathway and the activation of SMO leads to H. pylori-induced DNA damage and immune dysregulation through polyamine-mediated oxidative stress and impairment of antimicrobial NO synthesis. Our studies indicate novel targets for therapeutic intervention in H. pylori-associated diseases, including gastritis, ulcer disease, and gastric cancer.
authors.affiliation: Division of Gastroenterology, Department of Medicine, Vanderbilt University School of Medicine, 1030C MRBIV, 2215 Garland Avenue, Nashville, TN 37232, USA.
authors.forename: Rupesh
authors.initials: R
authors.lastname: Chaturvedi
authors.forename: Thibaut
authors.initials: T
authors.lastname: de Sablet
authors.forename: Lori A
authors.initials: LA
authors.lastname: Coburn
authors.forename: Alain P
authors.initials: AP
authors.lastname: Gobert
authors.forename: Keith T
authors.initials: KT
authors.lastname: Wilson
mesh_terms: D001120:Arginine / Q000378:metabolism*; D015317:Biogenic Polyamines / Q000096:biosynthesis / Q000378:metabolism*; D002471:Cell Transformation, Neoplastic; D004249:DNA Damage; D006801:Humans; D009569:Nitric Oxide; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D018384:Oxidative Stress; D013274:Stomach Neoplasms / Q000276:immunology / Q000378:metabolism* / Q000473:pathology
chemical_list: D015317:Biogenic Polyamines; D009569:Nitric Oxide; D001120:Arginine; D052247:Nitric Oxide Synthase Type II