H. pylori remains a major public health problem, since half of the world's population is infected and the associated gastric cancer is the second leading cause of cancer deaths. We have elucidated mechanisms of immune system failure that result in persistence of the organism and sustained oxidative stress that leads to DNA damage. H. pylori induces ornithine decarboxylase (ODC), the rate limiting enzyme for polyamine synthesis, in macrophages. In both in vitro and in vivo models, ODC-derived spermine synthesis results in 1.) apoptosis;and 2.) inhibition of nitric oxide (NO) synthesis, by inhibition of L-arginine (L-Arg)-dependent inducible nitric oxide (NO) synthase (iNOS) protein translation. Inhibition of ODC with oral administration of a- difluoromethylornithine (DFMO) in mice restores L-Arg uptake, macrophage NO production, and cytokine balance, resulting in reduction in both gastritis and H. pylori colonization. H. pylori also up-regulates the enzyme spermine oxidase (SMO), thus generating H2O2, and acting as a novel mechanism for the generation of oxidative stress-associated DNA damage in gastric epithelial cells. We have also discovered another target of H. pylori, heme oxygenase (HO)-1, known for its anti-inflammatory and anti-oxidant properties. We show that H. pylori blocks NO-induced HO-1 in gastric epithelial cells, and this results in unrestrained chemokine synthesis. We hypothesize that H. pylori infection results in failure of antimicrobial and immunoregulatory NO generation and overproduction of polyamines and H2O2, leading to dysregulation of immune responses and survival of gastric epithelial cells with DNA damage. These events lead to persistence of the bacterium, chronic inflammation, and risk for neoplastic transformation.
Our Specific Aims are as follows. 1.) To determine the mechanism of persistence of H. pylori colonization and gastritis due to ODC. We will compare WT and ODC+/-, myeloid-specific ODC-/-, iNOS-/- mice, and appropriate bone marrow chimeras, each ? DFMO, and assess: A.) gastritis and colonization;B.) immune responses;C.) DNA damage and carcinogenesis by comparing WT and ODC mutant x INS-GAS mice, each ? DFMO. 2.) To determine the role of SMO in H. pylori infection, gastritis, and carcinogenesis. We will use SMO-/- mice and assess: A.) colonization, gastritis, advanced lesions, and effects on iNOS;B.) gastric epithelial cell apoptosis and DNA damage;C.) role in carcinogenesis by comparing WT and SMO-/- INS-GAS mice. 3.) To determine the role of HO-1 as a regulator of H. pylori immunopathogenesis and carcinogenesis in vivo by assessing: A.) modulation of HO-1 by polyamines and NO in ODC, SMO, and iNOS KO mice;B.) in mice with normal versus increased NO production and HO-1 expression treated with a pharmacologic inhibitor of HO-1, or in HO-1-/- and epithelial-specific HO-1-/- mice, effects on colonization, gastritis, immune responses, apoptosis, DNA damage, and carcinogenesis. The studies proposed seek new strategies for amelioration or prevention of H. pylori-induced disease by clarifying targets for intervention in the pathogenic immune response that lead to disease persistence and cancer risk.
Helicobacter pylori is a type of bacteria that infects the stomach of half of the world's human population, which can lead to the development of gastric cancer, the second leading cause of cancer death worldwide. In this project we will utilize in vitro and in vivo model systems to assess novel molecular pathways that are altered by H. pylori leading to host responses that fail to eradicate the pathogen, and cause persistent inflammation and DNA damage. The studies proposed seek to define new strategies for amelioration or prevention of H. pylori-induced disease by clarifying targets for intervention in the pathogenic immune response that lead to disease persistence and cancer risk.
|Chaturvedi, R; de Sablet, T; Asim, M et al. (2015) Increased Helicobacter pylori-associated gastric cancer risk in the Andean region of Colombia is mediated by spermine oxidase. Oncogene 34:3429-40|
|Krakowiak, M S; Noto, J M; Piazuelo, M B et al. (2015) Matrix metalloproteinase 7 restrains Helicobacter pylori-induced gastric inflammation and premalignant lesions in the stomach by altering macrophage polarization. Oncogene 34:1865-71|
|Carbo, Adria; Olivares-Villagómez, Danyvid; Hontecillas, Raquel et al. (2014) Systems modeling of the role of interleukin-21 in the maintenance of effector CD4+ T cell responses during chronic Helicobacter pylori infection. MBio 5:e01243-14|
|Shi, Chanjuan; Washington, M Kay; Chaturvedi, Rupesh et al. (2014) Fibrogenesis in pancreatic cancer is a dynamic process regulated by macrophage-stellate cell interaction. Lab Invest 94:409-21|
|Gobert, Alain P; Verriere, Thomas; Asim, Mohammad et al. (2014) Heme oxygenase-1 dysregulates macrophage polarization and the immune response to Helicobacter pylori. J Immunol 193:3013-22|
|Wang, Dingzhi; Fu, Lingchen; Ning, Wei et al. (2014) Peroxisome proliferator-activated receptor ? promotes colonic inflammation and tumor growth. Proc Natl Acad Sci U S A 111:7084-9|
|Chaturvedi, Rupesh; Asim, Mohammad; Barry, Daniel P et al. (2014) Spermine oxidase is a regulator of macrophage host response to Helicobacter pylori: enhancement of antimicrobial nitric oxide generation by depletion of spermine. Amino Acids 46:531-42|
|Kodaman, Nuri; Pazos, Alvaro; Schneider, Barbara G et al. (2014) Human and Helicobacter pylori coevolution shapes the risk of gastric disease. Proc Natl Acad Sci U S A 111:1455-60|
|Ahmad, R; Chaturvedi, R; Olivares-Villagómez, D et al. (2014) Targeted colonic claudin-2 expression renders resistance to epithelial injury, induces immune suppression, and protects from colitis. Mucosal Immunol 7:1340-53|
|Chaturvedi, Rupesh; Asim, Mohammad; Piazuelo, M Blanca et al. (2014) Activation of EGFR and ERBB2 by Helicobacter pylori results in survival of gastric epithelial cells with DNA damage. Gastroenterology 146:1739-51.e14|
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