Biomedical subjects

M F Go

Publications and source records attributed to M F Go.

At least 37 records · Page 2Linked to original sources

PubMed1999

Proinflammatory activation of neutrophils and monocytes by Helicobacter pylori is not associated with cagA, vacA or picB genotypes.

Chronic Helicobacter pylori infection is associated with mucosal inflammation. The aim of the present study was to assess human neutrophil and monocyte activation induced by H. pylori strains with different virulence genotypes. Bacterial sonicates from 12 strains were used to induce phagocyte up-regulation of adherence molecule CD11b, assessed by fluorescence flow cytometry, and oxidative burst responses, assessed by chemiluminescence. A dose-dependent induction of the expression of CD11b was observed with sonicate from all H. pylori strains on both neutrophils and monocytes. Strains negative for cagA and picB genes had the same inducing activity of upregulation of CD11b as strains positive for these genes. A vacA-S2 type strain had the same activity as vacA-S1 type strains. The induction of toxic oxygen radicals by H. pylori-activated neutrophils gave higher median values for the cagA-positive strains than for the cagA-negative strains. For the monocyte chemiluminescence response, cagA-negative strains gave higher median values compared to cagA-positive strains. We conclude that upregulation of the neutrophil and monocyte adherence molecule CD11b induced by H. pylori sonicates is not associated with the presence of cagA, picB or mosaic pattern of vacA, and that cagA, picB-negative strains and vacA-S2 strains retain their inflammatory capacity.

Adult↗

PubMed1998

The effect of galE gene inactivation on lipopolysaccharide profile of Helicobacter pylori.

The galE gene product, UDP-galactose 4-epimerase, mediates the incorporation of galactose in extracellular polysaccharide materials such as the O-side chain of lipopolysaccharide (LPS). The O-side chain in H. pylori LPS has been shown to cross-react with Lewis x and/or y blood group antigens, suggesting its potential involvement in H. pylori-linked autoimmune disease. To study its role in H. pylori LPS biosynthesis, the galE gene was cloned, sequenced, and a galE-knockout H. pylori strain was constructed. The H. pylori galE gene encoded a protein of 344 amino acids with a molecular weight of 39K. The LPS profile from the galE-knockout H. pylori strain showed a lower molecular weight than that of the parental strain, indicating the involvement of the galE gene in LPS biosynthesis of H. pylori.

Amino Acid Sequence↗

PubMed1998

REP-PCR fragments as biomarkers for differentiating gastroduodenal disease-specific Helicobacter pylori strains.

We previously identified four potential putative gastroduodenal disease fragments by using the interspersed repetitive extragenic palindromic DNA sequence based PCR (REP-PCR) technique. We investigated these fragments with regard to their disease specificity. The putative disease-specific REP-PCR fragments were cloned, mapped by restriction enzymes, cross-hybridized, and confirmed by Southern hybridization. The four fragments were also used as probes against REP-PCR amplicons from H. pylori isolates obtained from gastritis (N = 20), duodenal ulcer (N = 30), and gastric cancer patients (N = 30). Three of these fragments (1.4- and 0.76-kb for gastritis; 1.35 kb for duodenal ulcer) were amplified without any discrimination between any disease-specific H. pylori isolates. However, amplification following hybridization with the fourth 0.81-kb fragment was observed only from gastritis (60%) and duodenal ulcer (52%) but with none (0%) of gastric cancer patients. Nucleotide sequence analysis of the 0.81-kb fragment revealed that it was an open reading frame of the hypothetical protein HP0373 matched to the position of 380,966 to 383,068 nucleotides of the H. pylori complete genome sequence. Hence, the REP-PCR sequence was not a extragenic palindromic DNA sequence. The hypothetical protein was also present in all the tested isolates. The REP-PCR fingerprinting technique is useful to differentiate disease-specific H. pylori strains based on the interspersed repetitive extragenic palindromic DNA sequences; however, it may not be useful to identify disease-specific virulence determinant(s) without being confirmed by DNA sequence analysis and functional studies.

Amino Acid Sequence↗

PubMed1998

Failure to confirm association of vac A gene mosaicism with duodenal ulcer disease.

BACKGROUND: Mosaicism of the Helicobacter pylori vac A gene comprises two families of allelic variations of the signal sequence region (s1, s2) and of the mid-region (m1, m2). Initial studies suggested that peptic ulcer disease correlated with the s1 subtype of vac A. We compared the prevalence of various vac A genotypes of H. pylori isolates obtained from duodenal ulcer (DU) patients and subjects with simple gastritis. Those isolates with s1 type were further examined to determine whether the specific vac A s1 (s1a versus s1b) genotype enabled prediction of gastroduodenal disease. METHODS: H. pylori isolates were obtained from 38 patients with endoscopically documented DU and 39 individuals with asymptomatic H. pylori gastritis from Houston, Texas. The vac A genotype of each isolate was determined by polymerase chain reaction (PCR) amplification of genomic DNA for specific regions of the vac A gene. Those isolates with s1 vac A subtype were further examined to determine whether they had s1a or s1b mosaicism. RESULTS: There was no difference in frequency of the s1 genotype of isolates obtained from patients with duodenal ulcer or asymptomatic H. pylori gastritis in this sample (84% versus 79%, respectively; P = 0.77). The s1/m1 vac A genotype was detected in isolates from 16 duodenal ulcer patients versus 15 with H. pylori gastritis (P = 0.82). Detailed analysis of the s1 region failed to show a correlation of either s1a or s1b with duodenal ulcer. Both s1a and s1b genotypes were detected in 24 strains, and both m1 and m2 mid-gene PCR amplicons were seen in 16 strains. CONCLUSIONS: We were unable to use H. pylori vac A genotyping to predict type of gastroduodenal disease in our patient sample. This failure to confirm an association of vac A genotype and duodenal ulcer disease differs from samples from other regions. This most likely represents an example of differences in H. pylori strains infecting host populations in different geographic regions. This study confirms the importance of establishing statistical associations with isolates from widely separate geographic regions before concluding that disease-related associations exist.

Adult↗

PubMed1998

Frequency of vacA genotypes and cytotoxin activity in Helicobacter pylori associated with low-grade gastric mucosa-associated lymphoid tissue lymphoma.

The vacA genotypes s1,m1 and s1,m2 were detected in 44 and 30% of Helicobacter pylori isolates, respectively, from patients with gastric mucosa-associated lymphoid tissue lymphoma, compared to 26 and 56% of isolates, respectively, from individuals with gastritis. The vacA s1 genotype was significantly associated with, but not predictive of, the presence of vacuolating cytotoxin activity.

Bacterial Proteins↗

PubMed1998

Serologic detection of Helicobacter pylori infection with cagA-positive strains in duodenal ulcer, gastric cancer, and asymptomatic gastritis.

CagA has been suggested as a marker for more virulent strains of Helicobacter pylori. Studies using purified proteins and an enzyme-linked immunosorbent assay (ELISA) method for serological detection of antibodies against CagA reported considerable discordance between the results of the ELISA and molecular detection of the cagA gene, with a tendency for estimation of the prevalence of cagA-positive H. Pylori to be higher by ELISA than by colony hybridization. It is not clear whether the discordance was either due to simultaneous infections with both cagA-positive and -negative strains or because of false-positive ELISA results. We correlated the presence of cagA-positive H. pylori by Polymerase chain reaction (PCR) with the presence of serum antibodies against the CagA protein from denatured H. pylori lysates. Gastric biopsies and sera were obtained from 75 patients from Korea; 25 each with gastric carcinoma, duodenal ulcer, and simple gastritis. Seventy-four of 75 isolates (98.6%) were cagA-positive by PCR and 70 sera were CagA antibody-positive by Western blotting. The cagA gene is common in H. pylori isolates from Korea regardless of the underlying disease. The presence of cagA is almost always associated with antibody to the CagA protein as determined by Western blotting. Western blotting may be the preferred method for serological detection of infection with cagA-positive H. pylori.

Adult↗

PubMed1997

What are the host factors that place an individual at risk for Helicobacter pylori-associated disease?

Helicobacter pylori infection is associated with duodenal and gastric ulcer disease, gastric cancer, and gastric mucosa-associated lymphoid tissue lymphoma. Although more than half the world's population harbors H. pylori, only a proportion will develop clinically significant disease. The specific clinical outcome of an individual can be examined as the modulation of host factors by H. pylori infection. Host acid-secretory status and sensitivity to gastrin can be modulated by H. pylori infection. Once H. pylori has established itself in the stomach, virtually everyone develops gastritis, and variations in gastritis patterns have been associated with different gastric acid responses to H. pylori infection. The patterns of gastritis are important because they seem to determine disease outcome. Blood group antigens have been implicated in studies of ulcer disease. Receptors to Lewis antigens in gastric mucosa indicate that host mucosal factors influence H. pylori attachment. Conversely, H. pylori strains express Lewis antigen-like molecules, suggesting an autoimmune component for some H. pylori-associated diseases. HLA genotypes may influence the host response to H. pylori infection, and those of H. pylori-infected individuals have been correlated with histological features. The clinical outcome of H. pylori infection is most likely a result of complex interactions among host, bacterial, and environmental factors. The mechanisms by which these diverse factors influence the pathogenesis of different clinical outcomes remain under investigation.

Animals↗

PubMed1996

Presence of the cagA gene in the majority of Helicobacter pylori strains is independent of whether the individual has duodenal ulcer or asymptomatic gastritis.

BACKGROUND: Helicobacter pylori infection presents as many different diseases, including asymptomatic gastritis, peptic ulcer disease, and gastric cancer. Although the virulence factor(s) responsible for different H. pylori-related diseases have not been identified, several candidate genes are being investigated for such an association. The polymerase chain reaction (PCR) frequently is used to assess the presence of genetic factors associated with pathogenesis of disease; the cagA gene and its product have been postulated to have a disease-specific relationship to peptic ulcer and gastric cancer because of differential expression in these diseases compared to histological gastritis alone. MATERIALS AND METHODS: Genomic DNA was amplified by PCR, using synthetic oligonucleotide primers to the cagA gene to determine the prevalence of the cagA gene in 60 H. pylori isolates obtained from well-documented duodenal ulcer or asymptomatic gastritis patients (30 each). Results were confirmed by hybridization with a 1.4-Kb cagA probe. RESULTS: The expected PCR product was obtained in 90% of isolates from duodenal ulcer patients, compared to 70% of isolates from individuals with asymptomatic gastritis. The PCR products were polymorphic in size, suggesting cagA gene sequence differences among isolates. Evaluation for the presence of the cagA gene by hybridization with a 1.4-Kb cagA probe showed a homologous product in 29 of 30 strains [96.7%; 95% confidence interval (CI) = 83-100%] from duodenal ulcer patients versus 25 of 30 strains (83.3%; 95% CI = 65-94%) obtained from individuals with asymptomatic gastritis (p = 0.19). CONCLUSIONS: The high prevalence of the cagA gene in asymptomatic gastritis suggests that it will not prove to be a useful marker to distinguish more virulent or disease-specific H. pylori strains. The genetic heterogeneity among H. pylori strains makes PCR an unwise choice as the single method to determine prevalence of a putative virulence factor. In evaluation of the prevalence of a gene or genetic factor in a population of H. pylori, hybridization with extended probes might be important to ensure that the results are representative of the organism's genotype.

Adult↗

PubMed1996

Mutations in 23S rRNA are associated with clarithromycin resistance in Helicobacter pylori.

Twelve clarithromycin-resistant Helicobacter pylori isolates (100% of resistant isolates examined) from seven different patients each contained an A-->G transition mutation within a conserved loop of 23S rRNA. A-->G transition mutations at positions cognate with Escherichia coli 23S rRNA positions 2058 and 2059 were identified. Clarithromycin-susceptible H. pylori isolates from 14 different patients displayed no polymorphisms in a conserved loop within domain V of 23S rRNA. The study is the first to report mutations in H. pylori associated with resistance to an antimicrobial agent used in established peptic ulcer treatment regimens.

Anti-Bacterial Agents↗

PubMed1996

Population genetic analysis of Helicobacter pylori by multilocus enzyme electrophoresis: extensive allelic diversity and recombinational population structure.

Genetic diversity and relationships in 74 Helicobacter pylori isolates recovered from patients assigned to distinct clinical categories were estimated by examination of allelic variation in six genes encoding metabolic housekeeping enzymes by multilocus enzyme electrophoresis. Seventy-three distinct allele profiles, representing multilocus chromosomal genotypes, were identified. All six loci were highly polymorphic, with an average of 11.2 alleles per locus. The mean genetic diversity in the sample was 0.735, a value that exceeds the level of diversity recorded in virtually all bacterial species studied by multilocus enzyme electrophoresis. A high frequency of occurrence of null alleles (lack of enzyme activity) was identified and warrants further investigation at the molecular level. Lack of linkage disequilibrium (nonrandom association (of alleles over loci) indicates that horizontal transfer and recombination of metabolic enzyme genes have contributed to the generation of chromosomal diversity in H. pylori. In this sample of isolates, there was no statistically significant association of multilocus enzyme electrophoretic types or cluster of related chromosomal types and disease category.

Adult↗

PubMed1996

The interaction of pH, bile, and Helicobacter pylori may explain duodenal ulcer.

BACKGROUND: Inhibition of Helicobacter pylori growth by bile suggests that it should be difficult for H. pylori to colonize the duodenum and cause duodenal ulcer. To search for a common mechanism, we investigated the relationship between H. pylori strain (duodenal ulcer vs gastritis), type of bile acid conjugate, and inhibition of H. pylori growth. METHODS: H. pylori isolates from patients with duodenal ulcer and from volunteers with asymptomatic gastritis (six each) were grown in brain heart infusion broth medium containing mixtures of glycocholate, taurocholate, glycodeoxycholate, taurodeoxycholate, glycochenodeoxycholate, and taurochenodeoxycholate with and without lecithin. RESULTS: Synthetic human bile with or without lecithin inhibited H. pylori growth in a dose-dependent manner. There was no difference in inhibition between H. pylori gastritis and duodenal ulcer isolates. Glycine and mixed glycine and taurine-conjugated bile acids inhibited H. pylori more than taurine-conjugated bile acids (e.g., 51%, 67%, and 80% compared to 21%, 39%, and 46% for 1, 2, and 4 mM mixed conjugates compared with taurine conjugates, p < 0.05, respectively. CONCLUSIONS: The ability of H. pylori to grow in the presence of taurine-conjugated bile acids and the precipitation of glycine but not taurine bile acid conjugates by acid may provide one missing link among inhibition of H. pylori by bile, acid secretion, ability of antisecretory therapy to accelerate ulcer healing, and the ability of H. pylori to colonize the duodenal bulb of ulcer patients, leading to duodenal ulcer. These data also explain the disparate results of previous investigations of the effect of bile reflux in the stomach on the presence of H. pylori.

Bile↗

PubMed1996

Allelic variation in the cagA gene of Helicobacter pylori obtained from Korea compared to the United States.

OBJECTIVE: Helicobacter pylori is an important factor in the development of duodenal ulcer disease and has been implicated in the pathogenesis of gastric adenocarcinoma. It has been suggested that the cagA gene is a marker for more virulent strains of H. pylori. METHODS: We determined the prevalence of the cagA gene in 60 clinical isolates [34 from gastric carcinoma patients (CA), 26 from duodenal ulcer patients (DU)] from Korea, a country with a high incidence and mortality from gastric cancer. Genomic DNA was polymerase chain reaction-amplified by using two different primer sets for the cagA gene. The first cagA primer set amplifies a 297-bp product from the midregion of the cagA gene. The second primer set, which was previously established in a patient population from the Houston area (21 DU patients, 20 from individuals with asymptomatic gastritis) amplified a 1.4-kb region further downstream in the cagA gene. RESULTS: The expected 297 bp polymerase chain reaction amplicon for cagA was identified in 59/60 (98.3%) H. pylori isolates from Korea (33/34 CA, 26/26 DU), and in 36/41 (88%) isolates from the Houston area (20/21 DU, 16/20 asymptomatic gastritis) (NS). Using the second cagA primer set, the expected 1.4-kb product was found in only 1/60 (1.7%) H. pylori isolates from Korea (1/34 CA, 0/26 DU), and in 36/41 (88%) of isolates from the Houston area (20/21 DU, 16/20 GST) (p < 0.001). Western blot analysis showed that all Korean H. pylori isolates expressed cagA. CONCLUSIONS: The high prevalence of the cagA gene in H. pylori isolates from Korean patients with gastric adenocarcinoma or duodenal ulcers indicates that the cagA gene is common in H. pylori strains, and therefore, is not reliable as a single marker for the discrimination of H. pylori strains with respect to a specific disease. Our data further suggest that allelic variations in the genome of H. pylori strains may exist and that distinct H. pylori populations may circulate in different geographic regions.

Adenocarcinoma↗

PubMed1996

Molecular pathogenesis of H. pylori disease.

H. pylori infection is a ubiquitous infection in man; it is associated with the development of various gastroduodenal disease manifestations. Numerous investigations are now seeking to elucidate the factors important in the microorganism that directly, or in concert with host and/or environmental factors, affect disease outcome. These studies involve the physiology and genetics of both the host and its pathogen, H. pylori.

Animals↗

PubMed1996

Helicobacter pylori: its role in ulcer disease and gastric cancer and how to detect the infection.

H. pylori infection is strongly implicated in the pathogenesis of peptic ulcer disease and gastric cancer. Although the infection may be detected in over half the world's population, only a proportion will develop either ulcer disease or gastric cancer. The prevalence of the infection is very high in both diseases, but other factors combined with chronic infection must lead to specific clinical manifestations of the disease. Long-standing infection results in chronic active gastritis. In a certain subset of the H. pylori-infected population, factors such as dietary, environmental, and/or genetic factors, or specific strains of the bacterium, may result in the expression of one disease or another. There are now many investigations into these various aspects of association of the infection and disease outcome which may lead to elucidation of the actual processes in the development of specific disease in the H. pylori-infected patient. Many different tests are now available for accurate diagnosis of the infection. The non-invasive tests include the serologic tests, which include both the ELISA and the rapid-immunoassay, and the urea breath test. Invasive tests can be performed on the patient at the time of endoscopy when tissue specimens can be taken for the rapid urease test, histology, or culture.

Gastritis↗

PubMed1996