Biomedical subjects
Richard M Peek
Publications and source records attributed to Richard M Peek.
The role of decay-accelerating factor as a receptor for Helicobacter pylori and a mediator of gastric inflammation.
Persistent gastritis induced by Helicobacter pylori is the strongest known risk factor for peptic ulcer disease and distal gastric adenocarcinoma, a process for which adherence of H. pylori to gastric epithelial cells is critical. Decay-accelerating factor (DAF), a protein that protects epithelial cells from complement-mediated lysis, also functions as a receptor for several microbial pathogens. In this study, we investigated whether H. pylori utilizes DAF as a receptor and the role of DAF within H. pylori-infected gastric mucosa. In vitro studies showed that H. pylori adhered avidly to Chinese hamster ovary cells expressing human DAF but not to vector controls. In H. pylori, disruption of the virulence factors vacA, cagA, and cagE did not alter adherence, but deletion of DAF complement control protein (CCP) domains 1-4 or the heavily O-glycosylated serine-threonine-rich COOH-terminal domain reduced binding. In cultured gastric epithelial cells, H. pylori induced transcriptional up-regulation of DAF, and genetic deficiency of DAF attenuated the development of inflammation among H. pylori-infected mice. These results indicate that DAF may regulate H. pylori-epithelial cell interactions relevant to pathogenesis.
Helicobacter infection and gastric neoplasia.
Chronic gastritis induced by Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the distal stomach, yet only a minority of people who harbour this organism ever develop cancer. H. pylori isolates possess substantial genotypic diversity, which engenders differential host inflammatory responses that influence clinical outcome. H. pylori strains that possess the cag pathogenicity island and secrete a functional cytotoxin induce more severe gastric injury and further augment the risk for developing distal gastric cancer. However, carcinogenesis is also influenced by host genetic diversity, particularly involving immune response genes such as IL-1ss and TNF-alpha. It is important to gain insight into the pathogenesis of H. pylori-induced gastritis and adenocarcinoma, not only to develop more effective treatments for gastric cancer, but also because it might serve as a paradigm for the role of chronic inflammation in the genesis of other malignancies that arise within the gastrointestinal tract.
The role of persistence in Helicobacter pylori pathogenesis.
PURPOSE OF REVIEW: Helicobacter pylori induces chronic gastritis and is the strongest known risk factor for peptic ulcer disease and distal gastric cancer, yet only a fraction of colonized individuals ever develop clinical disease. The aim of this article is to provide an overview of recent advances into mechanisms of H. pylori persistence and to incorporate these findings into our current understanding of H. pylori pathogenesis. RECENT FINDINGS: Recent studies have heightened awareness of the significance of bacterial persistence in H. pylori-associated diseases. Persistence is achieved through initial interactions between H. pylori adhesins and cellular receptors, after which H. pylori must avoid clearance by the immune system. This is accomplished by avoiding host recognition, by producing specific bacterial factors that stimulate selective expression of host genes, and by inducing an ineffective T-cell response. Further, it has become increasingly evident that the genetic diversity of H. pylori also plays a significant role in its persistence. SUMMARY: H. pylori persists in its acidic gastric niche, typically for the lifetime of the host. This persistence increases the risk of diseases such as peptic ulcer disease and gastric cancer. Delineation of mechanisms that regulate ongoing H. pylori-host interactions will not only improve targeted diagnostic and therapeutic modalities, but may also provide insights into other diseases that arise within the context of chronic pathogen infection.
Interleukin-1beta and interleukin-1 receptor antagonist gene polymorphisms and gastric cancer: a meta-analysis.
BACKGROUND: Polymorphisms of interleukin-1B (IL1B) and its receptor antagonist (IL1RN) genes have been inconsistently associated with gastric cancer risk. We examined these associations by performing meta-analyses. MATERIALS AND METHODS: Twenty-five studies testing the association between IL1B and/or IL1RN gene polymorphisms and gastric cancer were examined: 14 studies of IL1B-511, 14 studies of IL1B-31, 8 studies of IL1B+3954, and 23 studies of IL1RN. Overall and ethnicity-specific summary odds ratios and corresponding 95% confidence intervals for gastric cancer associated with these polymorphisms were estimated using fixed- and random-effects models. Heterogeneity and publication bias were evaluated. RESULTS: IL1B-511T and IL1RN*2 were associated with gastric cancer risk in Caucasians, but not in Asians. For IL1B-511T, the association in Caucasians was stronger when intestinal-subtype and noncardia gastric cancer cases were examined. A nonsignificant trend was observed between IL1B-31C and gastric cancer in Caucasians. No significant association of IL1B+3954T and gastric cancer risk was detected. Studies with better methodologic characteristics reported stronger effects. There was no evidence of publication bias. CONCLUSION: IL1B-511T is associated with gastric cancer susceptibility in Caucasians. The meta-analyses suggest that the conflicting results among studies may be explained by variation in allele frequencies among the ethnic groups and variation in tumor types, as well as by the methodologic quality of the studies.
Bacterial biota in reflux esophagitis and Barrett's esophagus.
AIM: To identify the bacterial flora in conditions such as Barrettos esophagus and reflux esophagitis to determine if they are similar to normal esophageal flora. METHODS: Using broad-range 16S rDNA PCR, esophageal biopsies were examined from 24 patients [9 with normal esophageal mucosa, 12 with gastroesophageal reflux disease (GERD), and 3 with Barrettos esophagus]. Two separate broad-range PCR reactions were performed for each patient, and the resulting products were cloned. In one patient with Barrettos esophagus, 99 PCR clones were analyzed. RESULTS: Two separate clones were recovered from each patient (total = 48), representing 24 different species, with 14 species homologous to known bacteria, 5 homologous to unidentified bacteria, and 5 were not homologous (<97% identity) to any known bacterial 16S rDNA sequences. Seventeen species were found in the reflux esophagitis patients, 5 in the Barrettos esophagus patients, and 10 in normal esophagus patients. Further analysis concentrating on a single biopsy from an individual with Barrettos esophagus revealed the presence of 21 distinct bacterial species. Members of four phyla were represented, including Bacteroidetes, Firmicutes, Proteobacteria, and Actinobacteria. Microscopic examination of each biopsy demonstrated bacteria in intimate association with the distal esophageal epithelium, suggesting that the presence of these bacteria is not transitory. CONCLUSION: These findings provide evidence for a complex, residential bacterial population in esophageal reflux-related disorders. While much of this biota is present in the normal esophagus, more detailed comparisons may help identify potential disease associations.
Interleukin-17 levels in Helicobacter pylori-infected gastric mucosa and pathologic sequelae of colonization.
AIM: To determine the role of interleukin (IL)-17 in gastric ulcerogenesis. METHODS: Thirty-six gastric ulcer (GU) patients and 29 non-ulcer (NU) patients were enrolled in this study. Mucosal biopsy samples were obtained from the gastric antrum and GU site during endoscopy. Samples were used in in situ stimulation for 48 h in the presence of 10 microg/mL phytohemagglutinin-P (PHA), histological examination, and Helicobacter pylori (H pylori) culture. IL-17 and IL-8 protein levels in culture supernatants were assayed by ELISA. IL-17 mRNA expression was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). H pylori cagA and vacA status was assessed by reverse hybridization using a line probe assay (LiPA). IL-8 levels in culture supernatants were assayed after AGS cells were co-cultured with H pylori strain 26,695 or recombinant human (rh) IL-17. RESULTS: All 36 GU patients and 15 of 29 NU patients were found to be H pylori-positive, while 14 NU patients were H pylori-negative. All 51 H pylori strains from both GU and NU patients were cagA- and vacAs1/m1-positive. Antral mucosal tissues from H pylori-positive patients contained significantly (H pylori-positive NU patients: median 467 pg/mg/protein, range 53-2,499; H pylori-negative NU patients: median 104 pg/mg/protein, range 16-312, P< 0.0005) higher levels of IL-17 than those from uninfected patients. IL-17 levels at the ulcer site were significantly (ulcer site: median 1,356 pg/mg/protein, range 121-1,3730; antrum: median 761 pg/mg/protein, range 24-7,620, P< 0.005) higher than those at distant sites in the antrum. Biopsies from H pylori-positive GU and NU patients showed IL-17 mRNA expression in all samples whereas those from the antrum of the H pylori-negative controls showed no detectable expression. A significant correlation was seen between IL-17 and IL-8 levels at each biopsy site (ulcer: r = 0.62, P< 0.0001; antrum: r = 0.61, P< 0.0001) in GU patients. RhIL-17 and H pylori strain 26,695 each stimulated IL-8 production from AGS cells. CONCLUSION: IL-17 may play an important role in the inflammatory response to H pylori colonization, and may ultimately influence the outcome of H pylori-associated diseases that arise within the context of gastritis.
Inflammation in the genesis and perpetuation of cancer: summary and recommendations from a national cancer institute-sponsored meeting.
The Inflammation and Cancer Think Tank Meeting was organized by the National Cancer Institute with the purpose of identifying research advances, gaps, and opportunities for the study and clinical application of the role of inflammation on tumorigenesis. The format of this meeting consisted of brief presentations that focused on concepts, with extensive discussion periods to allow participants to identify issues and barriers limiting progress in this area. The strong relationship between inflammation and cancer in the gastrointestinal tract prompted several presentations that were focused on carcinogenesis within this organ system; however, many of the same immune mediators that influence esophageal, gastric, and colorectal carcinoma were also shown to influence inflammation-related malignancies at other anatomic sites. This article summarizes the findings of this Think Tank Meeting, which highlight the intimate relationship between malignant cells and their inflammatory microenvironment and specifically address opportunities to manipulate the host immune response and therefore intervene at different points along the tumorigenic cascade.
Activation of beta-catenin by carcinogenic Helicobacter pylori.
Persistent gastritis induced by Helicobacter pylori is the strongest known risk factor for adenocarcinoma of the distal stomach, yet only a fraction of colonized persons ever develop gastric cancer. The H. pylori cytotoxin-associated gene (cag) pathogenicity island encodes a type IV secretion system that delivers the bacterial effector CagA into host cells after bacterial attachment, and cag+ strains augment gastric cancer risk. A host effector that is aberrantly activated in gastric cancer precursor lesions is beta-catenin, and activation of beta-catenin leads to targeted transcriptional up-regulation of genes implicated in carcinogenesis. We report that in vivo adaptation endowed an H. pylori strain with the ability to rapidly and reproducibly induce gastric dysplasia and adenocarcinoma in a rodent model of gastritis. Compared with its parental noncarcinogenic isolate, the oncogenic H. pylori strain selectively activates beta-catenin in model gastric epithelia, which is dependent on translocation of CagA into host epithelial cells. Beta-catenin nuclear accumulation is increased in gastric epithelium harvested from gerbils infected with the H. pylori carcinogenic strain as well as from persons carrying cag+ vs. cag- strains or uninfected persons. These results indicate that H. pylori-induced dysregulation of beta-catenin-dependent pathways may explain in part the augmentation in the risk of gastric cancer conferred by this pathogen.
Pathogenesis of Helicobacter pylori infection.
Helicobacter pylori induces chronic gastritis, the strongest known risk factor for peptic ulcer disease and distal gastric cancer, yet only a fraction of colonized individuals ever develop clinical disease. H. pylori isolates possess substantial genotypic diversity, which engenders differential host inflammatory responses that influence pathologic outcome. However, clinical sequelae are not completely dependent upon bacterial virulence factors, and disease is also influenced by host genetic diversity, particularly within immune response genes. The focus of this article will be to provide an understanding of mechanisms that underlie H. pylori persistence and pathogenesis as a framework for understanding disease processes that develop from chronic inflammation. Identification of mechanisms that regulate ongoing H. pylori-host interactions will not only improve targeted diagnostic and therapeutic modalities, but may also provide insights into other diseases that arise within the context of pathogen-initiated inflammatory states.
Helicobacter pylori protein HP0222 belongs to Arc/MetJ family of transcriptional regulators.
Helicobacter pylori is a widespread human bacterial pathogen responsible for inducing gastric and duodenal ulcers and gastric cancers. To date, only 16 protein structures from this organism have been determined, and more than 30% of its 1500 protein functions remain unknown. We report the biochemical characterization, the tertiary structure determined by solution nuclear magnetic resonance (NMR) methods and the putative function of the previously uncharacterized protein HP0222 (JHP0208) from H. pylori. Recombinant HP0222 behaves as a dimer in crosslinking and size exclusion chromatography experiments. The structure consists of a ribbon-helix-helix fold characteristic of transcription factors of the Arc/MetJ family, which all bind DNA as higher order oligomers. Electrophoretic mobility shift assays reveal that HP0222 binds to double-stranded DNA. Previous studies have shown significant increases in transcription levels of HP0222 in response to acid shock and adherence to gastric epithelial cells. To assess possible involvement of HP0222 in acid resistance, we constructed and assayed an H. pylori HP0222 null mutant. We propose that HP0222 is a novel transcriptional regulator in H. pylori.
Orchestration of aberrant epithelial signaling by Helicobacter pylori CagA.
Persistent colonization by Helicobacter pylori is the strongest risk factor for distal gastric adenocarcinoma, and H. pylori strains that harbor the cag pathogenicity island further augment cancer risk. The H. pylori cag island encodes a secretion system, and the product of the terminal gene in the island (CagA) is translocated into host epithelial cells after bacterial attachment, where it undergoes tyrosine phosphorylation by Src kinases and binds the eukaryotic phosphatase SHP-2. Higashi et al. now demonstrate that CagA-dependent SHP-2 activation leads to sustained activation of ERK (extracellular signal-regulated kinase), culminating in morphological changes that mimic unrestrained stimulation by growth factors. These data implicate the cag island as a key mediator of pathogenic epithelial responses that may heighten the risk for gastric cancer.
Subproteomes of soluble and structure-bound Helicobacter pylori proteins analyzed by two-dimensional gel electrophoresis and mass spectrometry.
Helicobacter pylori is one of the most common bacterial pathogens and causes a variety of diseases, such as peptic ulcer or gastric cancer. Despite intensive study of this human pathogen in the last decades, knowledge about its membrane proteins and, in particular, those which are putative components of the type IV secretion system encoded by the cag pathogenicity island (PAI) remains limited. Our aim is to establish a dynamic two-dimensional electrophoresis-polyacrylamide gel electrophoresis (2-DE-PAGE) database with multiple subproteomes of H. pylori (http://www.mpiib-berlin.mpg.de/2D-PAGE) which facilitates identification of bacterial proteins important in pathogen-host interactions. Using a proteomic approach, we investigated the protein composition of two H. pylori fractions: soluble proteins and structure-bound proteins (including membrane proteins). Both fractions differed markedly in the overall protein composition as determined by 2-DE. The 50 most abundant protein spots in each fraction were identified by peptide mass fingerprinting. We detected four cag PAI proteins, numerous outer membrane proteins (OMPs), the vacuolating cytotoxin VacA, other potential virulence factors, and few ribosomal proteins in the structure-bound fraction. In contrast, catalase (KatA), gamma-glutamyltranspeptidase (Ggt), and the neutrophil-activating protein NapA were found almost exclusively in the soluble protein fraction. The results presented here are an important complement to genome sequence data, and the established 2-D PAGE maps provide a basis for comparative studies of the H. pylori proteome. Such subproteomes in the public domain will be effective instruments for identifying new virulence factors and antigens of potential diagnostic and/or curative value against infections with this important pathogen.
Evidence for repatterning of the gastric fundic epithelium associated with Ménétrier's disease and TGFalpha overexpression.
BACKGROUND & AIMS: Increase of intramucosal transforming growth factor alpha (TGFalpha) levels in the gastric fundus leads to oxyntic atrophy and massive foveolar hyperplasia in both metallothionein (MT)-TGFalpha mice and patients with Ménétrier's disease. We have evaluated the hypothesis that increased levels of TGFalpha in the fundus induces an antral pattern of cell differentiation in fundic glands by studying Pdx1, a transcription factor whose expression normally is confined to the gastric antrum. METHODS: Induction of Pdx1 expression was evaluated in Pdx1(lacZ/+)/MT-TGFalpha bigenic mice treated with zinc. The distribution of Pdx1 in MT-TGFalpha mice and Ménétrier's disease patients was evaluated with anti-Pdx1 antibodies. Transcript levels were evaluated by quantitative polymerase chain reaction in mouse and human tissues and AGS cells. RESULTS: In Pdx1(lacZ/+) mice, Pdx1 was expressed in antral mucosal cells including gastrin cells and TFF2-expressing deep glandular mucous cells. Zinc treatment for 2 to 8 weeks in Pdx1(lacZ/+)/MT-TGFalpha transgenic mice resulted in expression of Pdx1 throughout the fundus. No ectopic fundic Pdx1 expression was observed in either H. felis-infected or DMP777-treated mice. In MT-TGFalpha mice, 8 weeks of zinc treatment elicited nuclear Pdx1 staining throughout the fundic mucosa. TGFalpha treatment in AGS cells led to increases in Pdx1 and gastrin messenger RNA expression. Fundic sections from Ménétrier's disease patients showed nuclear Pdx1 staining throughout the fundic glands. Treatment of a Ménétrier's disease patient with an anti-epidermal growth factor receptor monoclonal antibody reduced fundic expression of both Pdx1 and gastrin. CONCLUSIONS: Overexpression of TGFalpha in MT-TGFalpha mice and Ménétrier's disease patients elicits ectopic expression in the fundus of Pdx1, consistent with the phenotype of antralization.
Local and systemic immune and inflammatory responses to Helicobacter pylori strains.
Colonization with Helicobacter pylori eventuates in varied clinical outcomes, which relate to both bacterial and host factors. Here we examine the relationships between cagA status, serum and gastric juice antibody responses, and gastric inflammation in dyspeptic patients. Serum, gastric juice, and gastric biopsy specimens were obtained from 89 patients undergoing endoscopy. H. pylori colonization and cagA status were determined by histology, culture, and PCR methods, and acute inflammation and chronic inflammation in the gastric mucosa were scored by a single pathologist. Serum and gastric juice antibodies to H. pylori whole-cell and CagA antigens were determined by enzyme-linked immunosorbent assay. Relationships between variables were sequentially analyzed using univariate and multivariate statistical methods. Of the 89 subjects, 62 were colonized by H. pylori. By univariate analyses, levels of serum immunoglobulin G (IgG) and IgA and gastric juice IgA antibodies against whole-cell and CagA antigens each were significantly higher in the H. pylori-positive group than in the H. pylori-negative group (P<0.001). H. pylori and CagA sero-positivities were both significantly associated with enhanced inflammation in gastric antrum and body (P<0.02). The presence of gastric juice antibodies to H. pylori antigens was associated with more severe gastric inflammation. However, in multivariate analyses, only the presence of serum antibodies against CagA and, to a lesser extent, whole-cell antigens remained significantly associated with acute and chronic inflammation in antrum and body (P<0.05). Thus, serum antibody response to CagA correlates with severity of gastric inflammation. Furthermore, given the relationships demonstrated by multivariate analysis, determination of gastric juice antibodies may provide a better representation of serum, rather than secretory, immune response.
Genomic Comparison of cag pathogenicity island (PAI)-positive and -negative Helicobacter pylori strains: identification of novel markers for cag PAI-positive strains.
In an analysis of Helicobacter pylori genomic DNA by macroarray methodology, genomic DNA from a panel of cag pathogenicity island (PAI)-negative H. pylori clinical isolates failed to hybridize with 27 genes located outside the cag PAI in a cag PAI-positive reference strain. PCR analyses confirmed that HP0217 (encoding a lipopolysaccharide biosynthetic protein) and HP1079 (encoding a protein of unknown function) were present significantly more frequently in cagA-positive strains than in cagA-negative strains. A low G+C content of these two genes suggests they were acquired by horizontal transfer events.
Events at the host-microbial interface of the gastrointestinal tract IV. The pathogenesis of Helicobacter pylori persistence.
Long-term interactions between Helicobacter pylori and humans significantly increase the risk for peptic ulcer disease and noncardia gastric adenocarcinoma. The vast majority of infected persons remain persistently colonized unless a targeted antibiotic regimen is employed; thus regulation of inflammation by H. pylori is governed by levels of host-bacteria equilibria that are not found during cellular interactions with acute enteric pathogens. It is important to gain insight into mechanisms that regulate immune evasion by H. pylori not only to develop more effective treatments for disease, but also because such knowledge may serve as a paradigm for the role that other chronic infectious agents play in the genesis of pathological lesions that arise from inflammatory foci.
Helicobacter pylori flagellin evades toll-like receptor 5-mediated innate immunity.
Helicobacter pylori colonizes the human stomach for decades unless pharmacologically eradicated. We hypothesized that this flagellated pathogen escapes immune clearance, in part, by avoiding detection by the flagellin receptor Toll-like receptor 5 (TLR5). In contrast to other gram-negative microbes, H. pylori did not release flagellin. Furthermore, recombinant H. pylori flagellin (FlaA) was significantly less potent (1000-fold) than Salmonella typhimurium flagellin in activating TLR5-mediated interleukin (IL)-8 secretion. TLR5 can mediate flagellin-induced IL-8 secretion via p38 mitogen-activated protein kinase signaling; however, compared with potent induction by S. typhimurium flagellin, H. pylori FlaA-dependent p38 activation was substantially attenuated. In addition, disruption of H. pylori flaA decreased motility but had no effect on H. pylori-induced IL-8 secretion, which indicates that H. pylori flagellin plays no role in activating epithelial orchestration of inflammation. We conclude that H. pylori evades TLR5-mediated detection, which may contribute to its long-term persistence in individual hosts.