PubMed Health⌕ Search

Biomedical subjects

R M Peek

Publications and source records attributed to R M Peek.

At least 19 recordsLinked to original sources
PubMed2005

Transactivation of the epidermal growth factor receptor by cag+ Helicobacter pylori induces upregulation of the early growth response gene Egr-1 in gastric epithelial cells.

BACKGROUND AND AIMS: Helicobacter pylori, in particular cytotoxin associated gene (cag)+ strains, have been shown to enhance gastric epithelial cell proliferation in vivo, an effect that likely contributes to gastric carcinogenesis. Early growth response gene 1 (Egr-1) is a crucial regulator of cell growth, differentiation, and survival, which is known to play a role in carcinogenesis and cancer progression. The aims of this study were to: (1) examine whether H pylori could upregulate Egr-1 in gastric epithelial cell lines; (2) determine whether there was a differential response to infection with different strains; (3) examine the role of the cag pathogenicity island in this process; and (4) elucidate the molecular mechanisms leading to Egr-1 upregulation. METHODS AND RESULTS: We found that infection of AGS cells with cag+H pylori resulted in a rapid (1-2 hours) but transient increase in Egr-1 mRNA and protein levels whereas coculture with cag- isolates did not elicit this response. Furthermore, two independent cagE- isogenic mutants of H pylori also demonstrated impaired ability to upregulate Egr-1. Upregulation of Egr-1 protein was inhibited by the extracellular regulated kinase (ERK)1/2 inhibitor PD98059 and overexpression of dominant negative MEK1 downregulated Egr-1 luciferase reporter gene activity. Treatment of AGS cells with the epidermal growth factor receptor (EGFR) kinase inhibitors PD153035 and AG1478 resulted in a reduction in H pylori mediated Egr-1 upregulation, demonstrating that EGFR transactivation plays a role in this early cellular process. CONCLUSIONS: Our findings show that cag+H pylori cause rapid induction of Egr-1 in gastric epithelial cells which may contribute to H pylori mediated pathogenesis.

Antigens, Bacterial↗
PubMed2002

Polymorphisms of Helicobacter pylori HP0638 reflect geographic origin and correlate with cagA status.

Since the associations between Helicobacter pylori genotype and disease differ in Asia and the West, we investigated the correlation between HP0638, encoding an outer membrane protein, and potential markers of virulence (cagA, vacA, and iceA). For 109 strains from nine countries, the status of cagA, vacA, and iceA was determined by PCR and/or a line probe assay. We also studied 18 strains from 8 patients (parents and 6 daughters) from a Dutch family and paired strains collected on average 8 years apart from 11 patients. When the HP0638 signal sequences were amplified by PCR and DNA sequence determinations were performed, 89 (96%) of 93 cagA-positive strains had HP0638 in frame, versus none (0%) of 16 cagA-negative strains (P < 0.001). Among strains in which HP0638 was in frame, a six-CT dinucleotide repeat pattern was dominant in Western countries (23 of 33 strains [70%]), while a pattern of three CT repeats with another CT after four T's (3 + 1-CT-repeat pattern) was dominant in East Asia (31 of 46 strains [67%]); however, specific CT repeat patterns did not correlate with clinical outcome. HP0638 phylogenetic trees also showed geographic characters. The HP0638 frame status and CT dinucleotide repeat patterns were identical for 9 of 11 pairs of strains obtained on average 8 years apart from individuals and the 15 strains obtained from the mother and all six daughters. Thus, HP0638 frame status and cagA status are strongly correlated. The CT dinucleotide repeat pattern in the putative HP0638 signal sequence has geographic characters and appears stable in particular patients and families over a period of years. Analysis of HP0638 CT polymorphisms may serve as a new typing system to discriminate H. pylori isolates for epidemiological purposes.

Adult↗
PubMed2001

Helicobacter pylori genetic diversity within the gastric niche of a single human host.

Isolates of the gastric pathogen Helicobacter pylori harvested from different individuals are highly polymorphic. Strain variation also has been observed within a single host. To more fully ascertain the extent of H. pylori genetic diversity within the ecological niche of its natural host, we harvested additional isolates of the sequenced H. pylori strain J99 from its human source patient after a 6-year interval. Randomly amplified polymorphic DNA PCR and DNA sequencing of four unlinked loci indicated that these isolates were closely related to the original strain. In contrast, microarray analysis revealed differences in genetic content among all of the isolates that were not detected by randomly amplified polymorphic DNA PCR or sequence analysis. Several ORFs from loci scattered throughout the chromosome in the archival strain did not hybridize with DNA from the recent strains, including multiple ORFs within the J99 plasticity zone. In addition, DNA from the recent isolates hybridized with probes for ORFs specific for the other fully sequenced H. pylori strain 26695, including a putative traG homolog. Among the additional J99 isolates, patterns of genetic diversity were distinct both when compared with each other and to the original prototype isolate. These results indicate that within an apparently homogeneous population, as determined by macroscale comparison and nucleotide sequence analysis, remarkable genetic differences exist among single-colony isolates of H. pylori. Direct evidence that H. pylori has the capacity to lose and possibly acquire exogenous DNA is consistent with a model of continuous microevolution within its cognate host.

Chromosomes, Bacterial↗
PubMed2001

cag+ Helicobacter pylori induce transactivation of the epidermal growth factor receptor in AGS gastric epithelial cells.

The gastric pathogen Helicobacter pylori is known to activate epithelial cell signaling pathways that regulate numerous inflammatory response genes. The aim of this study was to elucidate the pathway leading to extracellular signal-regulated kinase (ERK) 1/2 phosphorylation in H. pylori-infected AGS gastric epithelial cells. We find that H. pylori, via activation of the epidermal growth factor (EGF) receptor activates the small GTP-binding protein Ras, which in turn, mediates ERK1/2 phosphorylation. cag+ strains of H. pylori are able to induce greater EGF receptor activation than cag- strains, and studies with isogenic mutants indicate that an intact type IV bacterial secretion system is required for this effect. Blockade of EGF receptor activation using tyrphostin AG1478 prevents H. pylori-mediated Ras activation, inhibits ERK1/2 phosphorylation, and substantially decreases interleukin-8 gene expression and protein production. Investigations into the mechanism of EGF receptor activation, using heparin, a metalloproteinase inhibitor and neutralizing antibodies reveal that H. pylori transactivates the EGF receptor via activation of the endogenous ligand heparin-binding EGF-like growth factor. Transactivation of gastric epithelial cell EGF receptors may be instrumental in regulating both proliferative and inflammatory responses induced by cag+ H. pylori infection.

Antigens, Bacterial↗
PubMed2001

Activation of peroxisome proliferator-activated receptor gamma suppresses nuclear factor kappa B-mediated apoptosis induced by Helicobacter pylori in gastric epithelial cells.

Helicobacter pylori colonization leads to epithelial cell hyperproliferation within inflamed mucosa, but levels of apoptosis vary, suggesting that imbalances between rates of cell production and loss may contribute to differences in gastric cancer risk among infected populations. Peroxisome proliferator-activated receptor gamma (PPARgamma) regulates inflammatory and growth responses of intestinal epithelial cells. We determined whether activation of PPARgamma modified H. pylori-induced apoptosis in gastric epithelial cells. PPARgamma was expressed and functionally active in gastric epithelial cell lines sensitive to H. pylori-induced apoptosis. PPARgamma ligands 15d-PGJ(2) and BRL-49653 significantly attenuated H. pylomicronri-induced apoptosis, effects that could be reversed by co-treatment with a specific PPARgamma antagonist. Cyclopentanone prostaglandins that do not bind and activate PPARgamma had no effects on H. pylori-induced apoptosis. The ability of H. pylori to activate nuclear factor (NF)-kappaB and increase levels of the NF-kappaB target IL-8 was blocked by co-treatment with PPARgamma agonists, and direct inhibition of NF-kappaB also abolished H. pylori-stimulated apoptosis. These results suggest that activation of the PPARgamma pathway attenuates the ability of H. pylori to induce NF-kappaB-mediated apoptosis in gastric epithelial cells. Because PPARgamma regulates a multitude of host responses, activation of this receptor may contribute to varying levels of cellular turnover as well as the diverse pathologic outcomes associated with chronic H. pylori colonization.

Apoptosis↗
PubMed2001

pathogenesis of Helicobacter pylori-induced gastric inflammation.

Helicobacter pylori causes persistent inflammation in the human stomach, yet only a minority of persons harbouring this organism develop peptic ulcer disease or gastric malignancy. An important question is why such variation exists among colonized individuals. Recent evidence has demonstrated that H. pylori isolates possess substantial phenotypic and genotypic diversity, which may engender differential host inflammatory responses that influence clinical outcome. For example, H. pylori strains that possess the cag pathogenicity island induce more severe gastritis and augment the risk for developing peptic ulcer disease and distal gastric cancer. An alternative, but not exclusive, hypothesis is that enhanced inflammation and injury is a consequence of an inappropriate host immune response to the chronic presence of H. pylori within the gastric niche. Investigations that precisely delineate the mechanisms responsible for induction of gastritis will ultimately help to define which H. pylori-colonized persons bear the highest risk for subsequent development of clinical disease, and thus, enable physicians to focus eradication therapy.

Adenocarcinoma↗
PubMed2001

Helicobacter pylori genotypes, host factors, and gastric mucosal histopathology in peptic ulcer disease.

From 183 patients undergoing upper gastrointestinal endoscopy, we used antral and corpus gastric biopsies for bacterial culture and histopathologic examination, blood samples to detect immunoglobulin G antibodies against Helicobacter pylori, and H pylori genomic DNA to analyze cytotoxin-associated gene A (cagA) and vacuolating cytotoxin (vacA) genotypes. As expected, among H pylori biopsy-positive patients, those with duodenal ulcer (DU) (n = 34) had significantly more severe chronic and acute inflammation (P <.001) and epithelial degeneration (P =.004) in the gastric antrum than in the gastric corpus. Each of those 3 parameters and H pylori density were significantly higher in the antrum of patients with DU than in patients with gastric ulcer (GU) or no ulcer. Colonization with vacA s1/cagA-positive strains of H pylori was associated with inflammation and epithelial degeneration in gastric mucosa and increased risk for peptic ulcer disease (PUD), whereas colonization with vacA s2m2/cagA-negative strains was associated with mild gastric histopathology and was not associated with any significant risk for PUD. The predominant H pylori strains in African Americans were vacA s1bm1/cagA-positive, whereas all genotypes were well represented in non-Hispanic-Caucasians. By multivariate analysis, H pylori colonization was significantly associated with DU (Adjusted odds ratio [AdjOR] = 3.2 [1.4-7.2]) and nonsteroidal anti-inflammatory drugs (NSAID) use was inversely associated (AdjOR = 0.3 [0.2-0.7]). NSAID use (AdjOR = 4.3 [1.02-18.5]) and African-American ethnicity (AdjOR = 10.9 [2.6-50]) were significantly associated with GU. Smoking and age were not significantly associated with either DU or GU. These data indicate that DU is associated with an antral-dominant gastritis, and H pylori genotype and NSAID use independently contribute to the pathogenesis of PUD. HUM PATHOL 32:264-273. This is a US Government work. There are no restrictions on its use.

Aged↗
PubMed2001

Endoscopic ablation with cyanoacrylate glue for isolated gastric variceal bleeding.

BACKGROUND: Endoscopic ablation with cyanoacrylate glue may achieve gastric variceal obliteration. A prospective evaluation of its therapeutic effects on bleeding gastric varices was conducted, focusing on endoscopic features. METHODS: Thirty-seven patients with bleeding gastric varices underwent endoscopic ablation with cyanoacrylate. RESULTS: Patients with localized-type gastric varices (n = 14) had a better clinical course in terms of recurrent bleeding, variceal eradication, and survival than those with diffuse-type gastric varices (n = 23) after endoscopic ablation with cyanoacrylate. These clinical effects were related to the vascular anatomy of the gastric varices as determined by varicography and 3-dimensional CT. Type 1 vascular anatomy (one varicose vessel without noticeable ramifications) was much more common (86%) in localized-type gastric varices, whereas type 2 vascular anatomy (multiple varicose vessels with complex connecting ramifications) was found almost exclusively (91%) in diffuse-type gastric varices. CONCLUSIONS: Endoscopic ablation with cyanoacrylate is an effective and safe procedure for patients with bleeding gastric varices. Determination of variceal anatomy may be useful for improving treatment strategies for such patients.

Adhesives↗
PubMed2001

Analysis of iceA genotypes in South African Helicobacter pylori strains and relationship to clinically significant disease.

BACKGROUND: South African Helicobacter pylori isolates are characterised by the universal presence of cagA but have differences in vacuolating cytotoxin gene (vacA) alleles which correlate with clinically significant disease. However, the candidate virulence marker gene iceA has not been investigated. AIM: To characterise the genetic organisation and heterogeneity of iceA genotypes in different South African clinical isolates. PATIENTS AND METHODS: We studied H pylori strains isolated from 86 dyspeptic patients (30 with peptic ulcer disease (PUD), 19 with distal gastric adenocarcinoma (GC), and 37 with non-erosive gastritis) for the presence of iceA1 or iceA2 genes, and for differences in the genetic organisation of iceA2 by polymerase chain reaction, Southern hybridisation analysis, and sequencing. RESULTS: Genetic analysis of iceA1 demonstrated significant homology (92-95%) with the USA type strain 26695 and probably functions as a transcriptional regulator, while a novel variant (iceA2D') of iceA2 and marked differences in predicted protein secondary structure of the iceA2 protein were defined. iceA1 was detected in 68% and iceA2 in 80% of all clinical isolates. Although approximately 40% of patients had both strains, a higher prevalence (p< 0.01) of GC patients were infected with iceA1 isolates which were invariably vacA s1/iceA1 (p< 0.005 v gastritis). Isolates from PUD patients were distinguished by the structurally altered iceA2D variant (53%; p<0.03 v gastritis) while the iceA2C variant distinguished isolates from patients with gastritis alone (67%; p< 0.005 v PUD). CONCLUSION: In this study, an association between iceA1 and GC was noted while differences in variants of iceA2 differentiated between PUD and gastritis alone. Combination analyses of iceA genotypes and vacA alleles supported these associations.

Adenocarcinoma↗
PubMed2001

IV. Helicobacter pylori strain-specific activation of signal transduction cascades related to gastric inflammation.

Helicobacter pylori strains that possess the cag pathogenicity island induce more severe gastritis and augment the risk of developing peptic ulcer disease and distal gastric cancer. A specific mechanism by which cag(+) strains may enhance gastritis is strain-selective regulation of interleukin (IL)-8 production. On contact with gastric epithelial cells, H. pylori activates multiple signal transduction cascades that regulate IL-8 secretion, including nuclear factor-kappaB and mitogen-activated protein kinases, and these events are dependent on genes within the cag island. An independent effect of cag-mediated cellular contact is translocation and phosphorylation of H. pylori proteins within the host epithelial cell. The redundancy of intracellular signaling cascades activated by H. pylori and the divergent epithelial cell responses induced by components of the cag island may contribute to the ability of this organism to persist for decades within the gastric niche.

Animals↗
PubMed2001

Helicobacter pylori strain-specific differences in genetic content, identified by microarray, influence host inflammatory responses.

Helicobacter pylori enhances the risk for ulcer disease and gastric cancer, yet only a minority of H. pylori-colonized individuals develop disease. We examined the ability of two H. pylori isolates to induce differential host responses in vivo or in vitro, and then used an H. pylori whole genome microarray to identify bacterial determinants related to pathogenesis. Gastric ulcer strain B128 induced more severe gastritis, proliferation, and apoptosis in gerbil mucosa than did duodenal ulcer strain G1.1, and gastric ulceration and atrophy occurred only in B128+ gerbils. In vitro, gerbil-passaged B128 derivatives significantly increased IL-8 secretion and apoptosis compared with G1.1 strains. DNA hybridization to the microarray identified several strain-specific differences in gene composition including a large deletion of the cag pathogenicity island in strain G1.1. Partial and complete disruption of the cag island in strain B128 attenuated induction of IL-8 in vitro and significantly decreased gastric inflammation in vivo. These results indicate that the ability of H. pylori to regulate epithelial cell responses related to inflammation depends on the presence of an intact cag pathogenicity island. Use of an H pylori whole genome microarray is an effective method to identify differences in gene content between H. pylori strains that induce distinct pathological outcomes in a rodent model of H. pylori infection.

Animals↗
PubMed2001

The biological impact of Helicobacter pylori colonization.

Helicobacterpylori causes persistent inflammation in the human stomach, yet only a minority of persons harboring this organism develop peptic ulcer disease or gastric malignancy. H. pylori isolates possess substantial phenotypic and genotypic diversity, which may engender differential host inflammatory responses that influence clinical outcome. For example, strains that possess the cag pathogenicity island induce more severe gastritis and augment the risk for developing peptic ulcer disease and distal gastric cancer. However, important geographic differences in susceptibility to disease exist as clear-cut markers for H. pylori strains that affect certain groups of colonized individuals have little or no predictive power for other populations. Recent investigations that have more precisely delineated mechanisms of H. pylori pathogenesis will ultimately help to define which colonized persons bear the highest risk for subsequent development of clinical disease, and thus enable physicians to appropriately focus diagnostic testing and eradication therapy. Although stratification of disease risk based on H. pylori strain characteristics is unlikely to completely account for differences in clinical outcomes, it is an important first step in helping to understand the biology of long-term interactions between H. pylori and its human host.

Antigens, Bacterial↗
PubMed2000

Genetic organization and heterogeneity of the iceA locus of Helicobacter pylori.

The genetic organization and sequence heterogeneity of the iceA locus of Helicobacter pylori was studied, and the existence of two distinct gene families, iceA1 and iceA2, at this locus was confirmed. iceA1 has significant sequence homology to nlaIIIR, encoding an endonuclease in Neisseria lactamica, but the similarity at the protein level is limited, due to frameshift mutations of iceA1 in most H. pylori strains. In only five of the 19 iceA1 strains studied, a full-length open reading frame (ORF), capable of encoding a 228aa protein, with 52% homology to NlaIII was observed. The region upstream of iceA2 is highly variable in length, containing up to 15 copies of 8bp tandem repeats. iceA2 can encode proteins of 24, 59, 94, or 129 amino acids, consisting of 14 and 10aa domains, conserved in all iceA2 strains, flanking 0, 1, 2, or 3 copies of a 35aa cassette. This 35aa cassette consists of domains of 13, 16 and 6aa, respectively. The 13aa and 6aa domains are highly conserved, but the 16aa domain exists in two variants. In total, five distinct iceA2 subtypes were defined. Database searches did not reveal any homologous sequences. Recombinant IceA1 and IceA2 proteins were expressed in Escherichia coli, confirming the predicted ORFs. Genotype-specific PCR primers permitted iceA genotyping in 318 (99. 1%) of a worldwide collection of 321 H. pylori strains. The conserved sizes of the amplification products confirmed the worldwide distribution of discrete variants of iceA1 and iceA2.

Amino Acid Sequence↗
PubMed2000

Helicobacter pylori alters gastric epithelial cell cycle events and gastrin secretion in Mongolian gerbils.

BACKGROUND & AIMS: Human colonization with Helicobacter pylori increases the risk for distal gastric adenocarcinoma, possibly by altering gastric epithelial cell cycle events and/or gastrin secretion. This study aimed to determine whether H. pylori virulence-related characteristics affect apoptosis, proliferation, and gastrin levels in a rodent model of gastric adenocarcinoma. METHODS: Mongolian gerbils were challenged with H. pylori wild-type or isogenic cagA(-) and vacA(-) mutants, and apoptotic and proliferating cells were identified by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and proliferating cell nuclear antigen immunohistochemistry, respectively. Serum gastrin levels were determined by radioimmunoassay. RESULTS: Gastric epithelial cell turnover was no different after infection with the wild-type, cagA(-), or vacA(-) strains. H. pylori infection significantly increased antral apoptosis 2-4 weeks after challenge, before apoptotic indices decreased to baseline. In contrast, antral proliferation rates were significantly higher 16-20 weeks after inoculation, but then decreased by 40 weeks. Antral proliferation was significantly related to serum gastrin levels, whereas antral apoptosis was inversely related to acute inflammation and lymphoid follicles. CONCLUSIONS: In H. pylori-infected gerbils, enhanced antral apoptosis is an early and transient cell cycle event. Epithelial cell proliferation peaks later and is significantly related to increased gastrin levels, suggesting that epithelial cell growth in H. pylori-colonized mucosa may be mediated by gastrin-dependent mechanisms.

Animals↗
PubMed2000

Overcoming the restriction barrier to plasmid transformation of Helicobacter pylori.

Helicobacter pylori strains demonstrate substantial variability in the efficiency of transformation by plasmids from Escherichia coli, and many strains are completely resistant to transformation. Among the barriers to transformation are numerous strain-specific restriction-modification systems in H. pylori. We have developed a method to protect plasmid DNA from restriction by in vitro site-specific methylation using cell-free extracts of H. pylori before transformation. In two cases, plasmid DNA treated with cell-free extracts in vitro acquired the restriction pattern characteristic of genomic DNA from the source strain. Among three strains examined in detail, the transformation frequency by treated plasmid shuttle and suicide vectors was significantly increased compared with mock-treated plasmid DNA. The results indicate that the restriction barrier in H. pylori can be largely overcome by specific DNA methylation in vitro. The approach described should significantly enhance the ability to manipulate gene function in H. pylori and other organisms that have substantial restriction barriers to transformation.

Bacterial Proteins↗
PubMed2000

Analysis of iceA1 transcription in Helicobacter pylori.

BACKGROUND: Transcription of the Helicobacter pylori iceA1 gene is induced following adherence of the bacterium to gastric epithelial cells in vitro, suggesting that this gene might be involved in H. pylori pathogenesis. Consequently, the current studies were undertaken to characterize iceA1 transcription and to define the structure of iceA1-containing transcripts to evaluate the potential of this gene to encode functional proteins. MATERIALS AND METHODS: Northern blots and primer extension of RNA isolated from broth-grown cultures of various H. pylori strains was done to analyze iceA1-specific gene transcription. Reverse transcriptase (RT)-PCR was used to determine the levels of iceA1 transcripts derived from readthrough transcription that was initiated upstream of iceA1 within the 5'-flanking cysE gene. RESULTS: Three major transcripts were detected and each was initiated from a common promoter, designated PI. Two of these transcripts were comprised of iceA1 sequence, while a third transcript was dicistronic and included the downstream gene, hpyIM. In addition, 10-fold lower levels of iceA1 transcripts were initiated upstream of PI, either within or immediately downstream of cysE. CONCLUSIONS: The present analysis suggests that iceA1 does not encode a functional protein in the majority of H. pylori strains. However, transcription of hpyIM, which encodes a highly conserved DNA adenine methyltransferase, is linked to iceA1 transcription. Therefore, iceA1 may affect H. pylori virulence in vivo through transcriptional regulation of hpyIM expression levels, which may result in specific variations in DNA methylation patterns leading to alteration in the expression of genes involved in virulence or pathogenesis.

Acetyltransferases↗