The Wilson laboratory is focused on gastrointestinal mucosal inflammation and carcinogenesis. We study the host immune response to the gastric pathogen Helicobacter pylori that causes peptic ulcer disease and gastric cancer. This includes the innate immune response in macrophages and the identification of ways that this response is ineffective. We have also elucidated mechanisms whereby epithelial responses are inappropriate, leading to risk for cancer development. We study novel mechanisms for inflammation and cellular/DNA damage, which leads to increased cancer risk.
We have reported that H. pylori induces the enzyme spermine oxidase (SMOX), originally known as polyamine oxidase 1, which utilizes the polyamine spermine as substrate. Generation of H2O2 by SMOX results in mitochondrial membrane depolarization, cytochrome c release, and apoptosis. Spermine itself contributes to the inadequacy of the host response, by blocking translation of inducible nitric oxide (NO) synthase (iNOS) and hence NO production that is needed for the killing of H. pylori. Upregulation of SMOX causes oxidative stress in gastric epithelial cells that leads to both apoptosis and DNA damage. Induction of ornithine decarboxylase (ODC) that generates polyamines also leads to apoptosis of macrophages, contributing to loss of host innate immunity to H. pylori. We have shown that induction of the transcription factor c-Myc by H. pylori enhances ODC transcription and has a causal role in macrophage apoptosis. We have also implicated formation of a specific AP-1 complex in the activation of c-Myc.
We are utilizing clinical material from a large cohort of human subjects from Colombia, South America where H. pylori infection prevalence is very high, but gastric cancer risk is 25-fold higher in the Andean mountains when compared to the coastal region. We have found that SMOX-dependent oxidative stress is increased in gastric epithelial cells in vivo in the subjects at high risk for gastric cancer and that H. pylori clinical strains from these subjects induce more SMOX and oxidative DNA damage both in vitro and in vivo in a gerbil model. Furthermore, inhibition of ODC or SMOX reduces gastric cancer in the gerbil model. Studies are ongoing to pursue the mechanisms involved in the differential induction of SMOX and DNA damage.
We are also pursuing studies on immune dysregulation in inflammatory bowel disease. This includes work on arginine availability/transport, polyamines, and nitric oxide. We have reported that levels of the amino acid L-arginine are increased in the serum of humans with ulcerative colitis. Because L-arginine is important in regulation of epithelial integrity and immune function a defect in the utilization of L-arginine could contribute to the disease pathogenesis. Consistent with this, we have shown that treatment with L-arginine improves colitis in mouse models and that mice lacking an inducible L-arginine transporter have increased disease activity.
Our funded studies are focused on:
1) Mechanisms of H. pylori induced DNA damage and immune dysregulation, with an emphasis on the effects of polyamines and their oxidation (PI, R01 grant)
2) The role oxidative and nitrosative stress in the development of gastric cancer in Colombia, and the importance of H. pylori strains from regions of low and high gastric cancer risk in modulation of host responses (PI, P01 grant)
3) Importance of arginine metabolism in the immune response to H. pylori (PI, VA Merit Review Grant)
4) Role of EGFR signaling and polyamines in epithelial dysfunction in H. pylori infection and carcinogenesis (PI, project on P01)
5) Inhibition of polyamine synthesis with difluoromethylornithine in human subjects in Colombia and Honduras with precancerous gastric lesions (PI, R01 grant).
6) Arginine and other amino acids as immunomodulatory agents and potential therapies in colitis and colitis-associated cancer (PI, R01 grant)
7) Clinical study on amino acids in ulcerative colitis (PI- R01 supplement; funding completed, analysis ongoing)