PubMed Health⌕ Search

Biomedical subjects

D R Scott

Publications and source records attributed to D R Scott.

At least 19 recordsLinked to original sources
PubMed2003

13C urea breath test (UBT) in the diagnosis of Helicobacter pylori: why does it work better with acid test meals?

BACKGROUND: Acid test meals may improve the accuracy of the (13)C urea breath test (UBT). This has been attributed to changes in gastric emptying rather than to the effects of gastric pH on Helicobacter pylori urease. AIMS: To determine whether enhancement of (13)CO(2) excretion in the UBT in H pylori infected volunteers by acidification of a test meal is due to a delay in gastric emptying. METHODS: Urease activity in vitro was measured in intact bacteria and in bacterial homogenates. Urease activity in vivo was assessed by means of the UBT. Eleven H pylori infected subjects underwent UBTs with neutral Ensure (pH 7.0), acidified Ensure (pH 3.0), and apple juice (pH 3.0). Gastric emptying was assessed by (13)C sodium acetate breath test. RESULTS: From pH 7 to pH 3, the in vitro urease activity of intact bacteria increased sixfold. In contrast, urease activity of bacterial homogenates was inactivated by low pH. In vivo, urease activity, as measured by the UBT 20 minutes after meal ingestion, was higher with apple juice (delta (13)CO(2)=21.1; p=0.03) and acidified Ensure (delta (13)CO(2)=25.5; p=0.01) than with neutral Ensure (delta (13)CO(2)=12.5). Gastric emptying was faster with apple juice (T(max)=36.7 (8) minutes) but not with acidified Ensure (T(max)=63.3 (5) minutes; p=0.06) than with neutral Ensure (T(max)=65.0 (3) minutes; p=0.04). CONCLUSIONS: The higher UBT found with acidified compared with neutral test meals was independent of the emptying rates of the test meals but may have been due to medium acidity dependent activation of intra-bacterial urease in intact H pylori.

Adult↗
PubMed2001

Cell lysis is responsible for the appearance of extracellular urease in Helicobacter pylori.

BACKGROUND: Helicobacter pylori is a neutralophilic bacterium that colonizes the acidic human gastric surface using the neutralizing capacity of a constitutively produced urease. Urease is present both in the cytoplasm and bound to the outside surface of the bacteria. The origin of the surface urease continues to be controversial. This study provides additional evidence that the origin of surface urease is cell lysis, not secretion. METHODS: H. Pylori was transformed with a plasmid encoding green fluorescent protein (GFP), a non-native cytoplasmic protein. Cultures supplemented with beta-cyclodextrin or horse serum were collected over various time periods and spun through a ficoll cushion to gently separate whole bacteria from released protein. The pellet and supernatant fractions were analyzed by fluorimetry, SDS-PAGE and Coomassie blue or Western analysis. RESULTS: GFP fluorescence and antigenic reactivity in the supernatant increased at each time point. GFP, the non-native cytoplasmic protein, and UreB, a native cytoplasmic protein, increased over time in the supernatant and both proteins were always present in the pellet fraction. UreI, an inner membrane protein, was only present in the pellet fraction. beta-galactosidase, a protein not found in H. pylori, was used as a negative control. CONCLUSIONS: Since it is unlikely that there is an intrinsic secretion system for GFP, a non-native protein, its increasing presence over time in the supernate fraction along with UreB, and retention of UreI in the pellet fraction implies that cell lysis accounts for the presence of urease on the surface of H. pylori.

Bacteriolysis↗
PubMed2001

Cervical HPV DNA detection as a predictor of a recurrent SIL diagnosis among untreated women.

OBJECTIVES: This study was conducted to test whether patient history of untreated cervical intraepithelial neoplasia (CIN) 1 or low-grade squamous intraepithelial lesions (LGSIL) modifies the interpretation of a positive HPV DNA result with regards to subsequent squamous intraepithelial lesions (SIL). METHODS: Seventy-three women with recurrent SIL were compared to 105 controls who remain cytologically normal during follow up. Cervical samples collected at enrollment were assayed for HPV DNA in the subject and control groups. RESULTS: Women with and without a history of LGSIL who tested positive for HPV DNA were at a similarly increased risk of having (recurrent) LGSIL as compared to controls. However, in women with a history of LGSIL, HPV DNA appeared to be less predictive for high-grade squamous intraepithelial lesions (HGSIL) than in women without a history of disease. CONCLUSIONS: Past history of untreated CIN1 or LGSIL does not modify the predictive value of a positive HPV DNA test for subsequent LGSIL. The observed difference of the predictive value of a positive HPV DNA test for the risk of recurrent HSIL compared to incident HSIL should be pursued.

Journal Article↗
PubMed2000

A prospective study of human papillomavirus (HPV) type 16 DNA detection by polymerase chain reaction and its association with acquisition and persistence of other HPV types.

Human papillomavirus (HPV)-16 causes about half the cases of cervical cancer worldwide and is the focus of HPV vaccine development efforts. Systematic data are lacking as to whether the prevention of HPV-16 could affect the equilibrium of infection with other HPV types and thus alter the predicted impact of vaccination on the occurrence of cervical neoplasia. Therefore, the associations of HPV-16 detection with subsequent acquisition of other HPV types and with the persistence of concomitantly detected HPV types were examined prospectively among 1124 initially cytologically normal women. Preexisting HPV-16 was generally associated with an increased risk for subsequent acquisition of other types. HPV-16 did not affect the persistence of concomitant infections, regardless of type. These findings suggest that the prevention or removal of HPV-16 is not likely to promote the risk of infection with other types, a theoretical concern with current vaccination efforts.

Cohort Studies↗
PubMed2000

Review of the Bethesda System atlas does not improve reproducibility or accuracy in the classification of atypical squamous cells of undetermined significance smears.

BACKGROUND: The Bethesda System (TBS) and its accompanying atlas were developed to promote uniform diagnosis and reporting of cervical and vaginal cytology, especially with respect to borderline abnormal smears. The authors assessed whether group study of TBS atlas improves the reproducibility and accuracy of the cytopathologic diagnosis of equivocal Papanicolaou smears. METHODS: One hundred "atypical" smears were divided into pretest and posttest sets containing equal numbers of negative, atypical squamous cells of undetermined significance (ASCUS), and squamous intraepithelial lesion (SIL) diagnoses based on a five-member panel review. Two comparable teams of four pathologists from George Washington University Medical Center (Washington, DC) and Kaiser Permanente (Portland, OR), each comprised of two more experienced cytopathologists and two less experienced pathologists, independently reviewed the 50 pretest slides and classified the slides according to TBS as negative, ASCUS, or SIL. The teams then conducted group study sessions using TBS atlas. After the review, the pathologists independently classified the 50 posttest slides in a similar manner. RESULTS: Pretest, pair-wise interobserver agreement ranged from 30% to 66% compared with 34-62% for posttest agreement. Absolute percent agreement of reviewers' diagnoses with a previously developed consensus diagnosis based on opinions of a five-expert panel (cytopathologic certainty scale) ranged from 44% to 62% for the pretest set and from 40% to 60% for the posttest set. Comparison of the detection of oncogenic human papilloma virus (HPV) DNA by hybrid capture tube test with smears classified as negative, ASCUS, or SIL revealed that seven of eight reviewers did not demonstrate a stronger association between HPV detection and cytologic diagnosis in the posttest set. CONCLUSIONS: Review of TBS atlas by itself does not appear to improve the reproducibility or accuracy of cytologic diagnoses. The lack of improvement was similar among the pathologists involved regardless of experience level or whether they had a close working relation. Cancer (Cancer Cytopathol)

Cervix Uteri↗
PubMed2000

A H+-gated urea channel: the link between Helicobacter pylori urease and gastric colonization.

Acidic media trigger cytoplasmic urease activity of the unique human gastric pathogen Helicobacter pylori. Deletion of ureI prevents this activation of cytoplasmic urease that is essential for bacterial acid resistance. UreI is an inner membrane protein with six transmembrane segments as shown by in vitro transcription/translation and membrane separation. Expression of UreI in Xenopus oocytes results in acid-stimulated urea uptake, with a pH profile similar to activation of cytoplasmic urease. Mutation of periplasmic histidine 123 abolishes stimulation. UreI-mediated transport is urea specific, passive, nonsaturable, nonelectrogenic, and temperature independent. UreI functions as a H+-gated urea channel regulating cytoplasmic urease that is essential for gastric survival and colonization.

Amino Acid Sequence↗
PubMed2000

Contrast-enhanced immunoelectron microscopy for Helicobacter pylori.

Since a method of contrast enhancement for immunoelectron microscopy has not been available in bacteriology, the morphological localization of proteins of Helicobacter pylori is not well known. In this report, we established a method of contrast enhancement in immunoelectron microscopy in this organism. Immunostained ultrathin sections are stained with a mixture of alcian blue and osmium tetroxide prior to staining with uranyl acetate. This method of staining provided good contrast enhancement of the bacterial cell wall and membrane without any loss of immunolabeled gold particles on the ultrathin section.

Acrylic Resins↗
PubMed2000

Review article: the control of gastric acid and Helicobacter pylori eradication.

This review focuses on the gastric acid pump as a therapeutic target for the control of acid secretion in peptic ulcer and gastro-oesophageal reflux disease. The mechanism of the proton pump inhibitors is discussed as well as their clinical use. The biology of Helicobacter pylori as a gastric denizen is then discussed, with special regard to its mechanisms of acid resistance. Here the properties of the products of the urease gene clusters, ureA, B and ureI, E, F, G and H are explored in order to explain the unique location of this pathogen. The dominant requirement for acid resistance is the presence of a proton gated urea transporter, UreI, which increases access of gastric juice urea to the intrabacterial urease 300-fold. This enables rapid and continuous buffering of the bacterial periplasm to approximately pH 6.0, allowing acid resistance and growth at acidic pH in the presence of 1 mM urea. A hypothesis for the basis of combination therapy for eradication is also presented.

Gastric Acid↗
PubMed2000

Expression of the Helicobacter pylori ureI gene is required for acidic pH activation of cytoplasmic urease.

ureI encodes an integral cytoplasmic membrane protein. It is present in the urease gene cluster of Helicobacter pylori and is essential for infection and acid survival, but its role is unknown. To determine the function of UreI protein, we produced H. pylori ureI deletion mutants and measured the pH dependence of urease activity of intact and lysed bacteria and the effect of urea on the membrane potential. We also determined ureI expression, urease activity, and the effect of urea on membrane potential of several gastric and nongastric Helicobacter species. ureI was found to be present in the genome of the gastric Helicobacter species and absent in the nongastric Helicobacter species studied, as determined by PCR. Likewise, Western blot analysis confirmed that UreI was expressed only in the gastric Helicobacter species. When UreI is present, acidic medium pH activation of cytoplasmic urease is found, and urea addition increases membrane potential at acidic pH. The addition of a low concentration of detergent raised urease activity of intact bacteria at neutral pH to that of their homogenates, showing that urease activity was membrane limited. No acidic pH activation or urea induced membrane potential changes were found in the nongastric Helicobacter species. The ureI gene product is probably a pH activated urea transporter or perhaps regulates such a transporter as a function of periplasmic pH.

Bacterial Proteins↗
PubMed2000

Improved amplification of genital human papillomaviruses.

Genital human papillomaviruses (HPVs) are commonly detected from clinical samples by consensus PCR methods. Two commonly used primer systems, the MY09-MY11 (MY09/11) primers and the GP5+-GP6+ (GP5+/6+) primers, amplify a broad spectrum of HPV genotypes, but with various levels of sensitivity among the HPV types. Analysis of the primer-target sequence homology for the MY09/11 primers showed an association between inefficient amplification of HPV types and the number and position of mismatches, despite accommodation of sequence variation by inclusion of degenerate base sites. The MY09/11 primers were redesigned to increase the sensitivity of amplification across the type spectrum by using the same primer binding regions in the L1 open reading frame. Sequence heterogeneity was accommodated by designing multiple primer sequences that were combined into an upstream pool of 5 oligonucleotides (PGMY11) and a downstream pool of 13 oligonucleotides (PGMY09), thereby avoiding use of degenerate bases that yield irreproducible primer syntheses. The performance of the PGMY09-PGMY11 (PGMY09/11) primer system relative to that of the standard MY09/11 system was evaluated with a set of 262 cervicovaginal lavage specimens. There was a 91.5% overall agreement between the two systems (kappa = 0.83; P < 0.001). The PGMY09/11 system appeared to be significantly more sensitive than the MY09/11 system, detecting an additional 20 HPV-positive specimens, for a prevalence of 62.8% versus a prevalence of 55.1% with the MY09/11 system (McNemar's chi(2) = 17.2; P < 0.001). The proportion of multiple infections detected increased with the PGMY09/11 system (40. 0 versus 33.8% of positive infections). HPV types 26, 35, 42, 45, 52, 54, 55, 59, 66, 73, and MM7 were detected at least 25% more often with the PGMY09/11 system. The PGMY09/11 primer system affords an increase in type-specific amplification sensitivity over that of the standard MY09/11 primer system. This new primer system will be useful in assessing the natural history of HPV infections, particularly when the analysis requires HPV typing.

Base Sequence↗
PubMed2000

Regulation of parietal cell calcium signaling in gastric glands.

The ligands interacting with enterochromaffin-like (ECL) and parietal cells and the signaling interactions between these cells were investigated in rabbit gastric glands using confocal microscopy. Intracellular calcium concentration ([Ca(2+)](i)) changes were used to monitor cellular responses. Histamine and carbachol increased [Ca(2+)](i) in parietal cells. Gastrin (1 nM) increased [Ca(2+)](i) in ECL cells and adjacent parietal cells. Only the increase of [Ca(2+)](i) in parietal cells was inhibited by H(2) receptor antagonists (H(2)RA). Gastrin (10 nM) evoked an H(2)RA-insensitive [Ca(2+)](i) increase in parietal cells. Carbachol produced large H(2)RA- and somatostatin-insensitive signals in parietal cells. Pituitary adenylate cyclase-activating peptide (PACAP, 100 nM) elevated [Ca(2+)](i) in ECL cells and adjacent parietal cells. H(2)RAs abolished the PACAP-stimulated [Ca(2+)](i) increase in adjacent parietal cells. Somatostatin did not inhibit the increase of [Ca(2+)](i) in parietal cells stimulated with histamine, high gastrin concentrations, or carbachol but abolished ECL cell calcium responses to gastrin or PACAP. Hence, rabbit parietal cells express histaminergic, muscarinic, and CCK-B receptors coupled to calcium signaling but insensitive to somatostatin, whereas rabbit and rat ECL cells express PACAP and CCK-B calcium coupled receptors sensitive to somatostatin.

Animals↗
PubMed2000

Local pH elevation mediated by the intrabacterial urease of Helicobacter pylori cocultured with gastric cells.

Helicobacter pylori resists gastric acidity by modulating the proton-gated urea channel UreI, allowing for pH(out)-dependent regulation of urea access to intrabacterial urease. We employed pH- and Ca(2+)-sensitive fluorescent dyes and confocal microscopy to determine the location, rate, and magnitude of pH changes in an H. pylori-AGS cell coculture model, comparing wild-type bacteria with nonpolar ureI-deletion strains (ureI-ve). Addition of urea at pH 5.5 to the coculture resulted first in elevation of bacterial periplasmic pH, followed by an increase of medium pH and then pH in AGS cells. No change in periplasmic pH occurred in ureI-deletion mutants, which also induced a slower increase in the pH of the medium. Pretreatment of the mutant bacteria with the detergent C(12)E(8) before adding urea resulted in rapid elevation of bacterial cytoplasmic pH and medium pH. UreI-dependent NH(3) generation by intrabacterial urease buffers the bacterial periplasm, enabling acid resistance at the low urea concentrations found in gastric juice. Perfusion of AGS cells with urea-containing medium from coculture at pH 5.5 did not elevate pH(in) or [Ca(2+)](in), unless the conditioned medium was first neutralized to elevate the NH(3)/NH(4)(+) ratio. Therefore, cellular effects of intrabacterial ammonia generation under acidic conditions are indirect and not through a type IV secretory complex. The pH(in) and [Ca(2+)](in) elevation that causes the NH(3)/NH(4)(+) ratio to increase after neutralization of infected gastric juice may contribute to the gastritis seen with H. pylori infection.

Ammonia↗
PubMed1999

Detection of human papillomavirus DNA in cytologically normal women and subsequent cervical squamous intraepithelial lesions.

BACKGROUND: Human papillomavirus (HPV) infection has been strongly associated with cervical carcinoma and its cytologic precursors, squamous intraepithelial lesions (SIL). We investigated the risk of SIL prospectively following polymerase chain reaction (PCR)-based DNA testing for a wide range of genital HPV types in a cohort of initially cytologically normal women, to clarify the role of HPV in the etiology of SIL. METHODS: Starting in April 1989, 17,654 women who were receiving routine cytologic screening at Kaiser Permanente (Portland, OR) were followed for the development of incident SIL. During follow-up, 380 incident case patients and 1037 matched control subjects were eligible for this nested case-control study. Cervical lavages collected at enrollment and, later, at the time of case diagnosis (or the corresponding time for selection of control subjects) were tested for HPV DNA using a PCR-based method. The data were analyzed as contingency tables with two-sided P values or, for multivariable analyses, using odds ratios (ORs) with 95% confidence intervals (CIs). RESULTS: In comparison with initially HPV-negative women, women who tested positive for HPV DNA at enrollment were 3.8 times (95% CI = 2.6-5.5) more likely to have low-grade SIL subsequently diagnosed for the first time during follow-up and 12.7 times more likely (95% CI = 6.2-25.9) to develop high-grade SIL. At the time of diagnosis, the cross-sectional association of HPV DNA and SIL was extremely strong (OR = 44.4 and 95% CI = 24.2-81.5 for low-grade SIL and OR = 67.1 and 95% CI = 19.3-233.7 for high-grade SIL). HPV16 was the virus type most predictive of SIL, even low-grade SIL. CONCLUSIONS: These findings are consistent with the hypothesis that HPV infection is the primary cause of cervical neoplasia. Furthermore, they support HPV vaccine research to prevent cervical cancer and efforts to develop HPV DNA diagnostic tests.

Carcinoma, Squamous Cell↗
PubMed1999

Seroreactivity to human papillomavirus types 16, 18, 31, and 45 virus-like particles in a case-control study of cervical squamous intraepithelial lesions.

Serum IgG antibodies to human papillomavirus (HPV) types 16, 18, 31, and 45 virus-like particles were measured in a nested case-control study of cervical squamous intraepithelial lesions. HPV-16 seroreactivity was strongly associated with HPV-16 DNA detection (odds ratio, 9.0; 95% confidence interval, 4.4-19.4), and similar type specificity was observed for HPV-31 and -45. In contrast, seroreactivity to any type was associated with elevated seroreactivity to all others. Among cases and controls, HPV-16 showed the highest seroprevalence, with 23.8% of 80 cases and 10.5% of 258 controls seroreactive to HPV-16 alone, and another 27.5% and 5.4%, respectively, seroreactive to HPV-16 plus other types. Overall, 24 (30.0%) cases and 17 (6.6%) controls were seroreactive to multiple types. These data suggest that seroreactivity to a given type reflects mainly type-specific HPV infection as measured by DNA detection and may also signal past exposure to other types that are now only serologically detected.

Antibodies, Viral↗
PubMed1999

"ASCUS, rule out HSIL": cytologic features, histologic correlates, and human papillomavirus detection.

Risk factors, cytologic and histopathologic features, and human papillomavirus (HPV) detection associated with 75 cervical smears classified as atypical squamous cells of undetermined significance, rule out high-grade squamous intraepithelial lesion (ASCUS, rule out HSIL) were reviewed. Cases were identified in a pathology panel review of material collected from 1953 women participating in a 5-year prospective study of HPV infection and squamous intraepithelial lesions at Kaiser Permanente, Portland, Oregon, sponsored by the National Cancer Institute. Initial abnormal smears diagnosed as ASCUS, rule out HSIL by one panelist or diagnosed as ASCUS by one pathologist and as HSIL by another were included. The 75 ASCUS, rule out HSIL smears identified were examined again by two pathologists after the study. These cases were compared with cases of ASCUS, not otherwise specified (ASCUS, NOS) and HSIL identified in the same group of 1953 women. Findings in ASCUS, rule out HSIL included tissue fragments (21%); atypical immature metaplasia (17%); atypical mature metaplasia (15%); small atypical cells (9%); and atypical repair (4%). A final patient classification of HSIL, reflecting all available data, was assigned to 11 (24%) of 46 women with ASCUS, rule out HSIL and to 1(1%) of 80 women with ASCUS, NOS in the original review (P < .001). Detection of oncogenic HPV types at diagnosis in ASCUS, rule out HSIL; ASCUS, NOS; and HSIL was similar, but data were unavailable for many subjects. Among women not tested at diagnosis, enrollment testing (1 to 4 years earlier) revealed that HPV detection in women with ASCUS, rule out HSIL was intermediate in frequency between ASCUS, NOS and HSIL. These data suggest that ASCUS, rule out HSIL is a distinct diagnosis from ASCUS, NOS because it is more often associated with an underlying HSIL. Consequently, women with ASCUS, rule out HSIL should be referred for colposcopic examination.

Adolescent↗
PubMed1998

The role of internal urease in acid resistance of Helicobacter pylori.

BACKGROUND & AIMS: The relative role of internal urease for acid protection of Helicobacter pylori is unknown. The aim of this study was to determine the comparative importance of internal and external urease under acidic conditions. METHODS: The pH optimum and measured Michaelis constant for urea of external urease and urease in intact bacteria at different medium pH (pHout) were measured using 14CO2 release from 14C-urea. The effect of urea on membrane potential and bacterial cytoplasmic pH was measured at different fixed pHout. 35S-methionine labeling and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of labeled proteins in the organism and medium measured protein synthesis at different pHout and mechanisms of urease externalization. RESULTS: External urease had activity between pH 5.0 and 8.5 and internal urease between pHout 2.5 and 6.5, and its Michaelis constant at pHout 7.5 was 300 mmol/L but at pHout 4.5 was 0.5 mmol/L, similar to free urease. The addition of 5 mmol/L urea to bacteria at fixed pHout from 3.0 to 6.0 elevated potential to about -105 mV and periplasmic pH to about pH 6.2. Protein synthesis occurred mainly between pH 6.5 and 8.0, and urease activity resulted in increased protein synthesis at acidic pH. The labeling pattern of intrabacterial and released protein was similar. CONCLUSIONS: Intracellular urease activity is regulated by external pH, defends against gastric acidity by increasing periplasmic pH and membrane potential, and stimulates protein synthesis at acidic pH. External urease is produced mostly by cell lysis.

Gastric Acid↗