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D Weeks

Publications and source records attributed to D Weeks.

At least 19 recordsLinked to original sources
PubMed1998

Influence of pH on metabolism and urease activity of Helicobacter pylori.

BACKGROUND & AIMS: The metabolic and urease responses of Helicobacter pylori to variations in gastric acidity are unknown. The aim of this study was to determine effects of changes of environmental pH on metabolism, urease activity, and survival of H. pylori in an unbuffered environment. METHODS: Bacterial metabolism and urease activity were determined by measuring pH changes in perfused microphysiometer chambers over a pH range from 2.5 to 9.0 with or without urea and survival by restoration of metabolism at pH 7.4. RESULTS: Glucose metabolism by acid-adapted H. pylori occurred at a perfusion pH between 3.5 and 8.6 and was highest between 7.4 and 8.2. Metabolism was irreversibly inhibited at pH <3.5 or >8.6. In the presence of 2.5 mmol/L urea, the chamber pH increased to about 6.2 during perfusion between pH 5.5 and 4.0. At pH 4.0 and below, urease activity increased several-fold without change of chamber pH. Urea in the perfusate enabled retention of metabolism after acid exposure but was toxic at pH 7.4. CONCLUSIONS: The metabolic range of acid-adapted H. pylori is between an environmental pH of 3.5 and 8.6. Extracellular pH-regulated internal urease activity allows metabolism in the pH range between 4.0 and 2. 5 by maintaining periplasmic pH at 6.2. The organism is an acid-tolerant neutralophile due to internal urease activity.

Ammonium Chloride↗
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↗
PubMed1998

Phospholipase A of Yersinia enterocolitica contributes to pathogenesis in a mouse model.

Some isolates of Yersinia enterocolitica exhibit phospholipase activity, which has been linked to lecithin-dependent hemolysis (M. Tsubokura, K. Otsoki, I. Shimohira, and H. Yamamoto, Infect. Immun. 25:939-942, 1979). A gene encoding Y. enterocolitica phospholipase was identified, and analysis of the nucleotide sequence revealed two tandemly transcribed open reading frames. The first, yplA, has 74% identity and 85% similarity to the phospholipase A found in Serratia liquefaciens. Though the other, yplB, was less similar to the downstream accessory protein found in S. liquefaciens, the organization in both species is similar. Subsequently, a yplA-null Y. enterocolitica strain, YEDS10, was constructed and demonstrated to be phospholipase negative by plate and spectrophotometric assays. To ascertain whether the phospholipase has a role in pathogenesis, YEDS10 was tested in the mouse model. In experiments with perorally infected BALB/c mice, fewer YEDS10 organisms were recovered from the mesenteric lymph nodes and Peyer's patches (PP) than the parental strain at 3 or 5 days postinfection. Furthermore, bowel tissue and PP infected with YEDS10 appeared to be less inflamed than those infected with the parental strain. When extremely high doses of both the parental and YEDS10 strains were given, similar numbers of viable bacteria were recovered from the PP and mesenteric lymph nodes on day 3. However, the numbers of foci and the extent of inflammation and necrosis within them were noticeably less for YEDS10 compared to the parental strain. Together these findings suggest that Y. enterocolitica produces a phospholipase A which has a role in pathogenesis.

Amino Acid Sequence↗
PubMed1998

The life and death of Helicobacter pylori.

The ability of Helicobacter pylori to survive in the varying acidity of the stomach is considered to be linked to its ability to maintain a tolerable pH in its periplasmic space by acid dependent activation of internal urease activity. Whereas survival of H pylori can occur between a periplasmic pH of 4.0 to 8.0, growth can only occur between a periplasmic pH of 6.0 to 8.0. When urease activity is only able to elevate periplasmic pH to between 4.0 and 6.0, the organisms will survive but not divide. In the absence of division, antibiotics such as clarithromycin and amoxycillin are ineffective. Proton pump inhibitors, by elevating gastric pH, would increase the population of dividing organisms and hence synergise with these antibiotics.

Adenosine Triphosphate↗
PubMed1997

Identification of membrane insertion sequences of the rabbit gastric cholecystokinin-A receptor by in vitro translation.

To determine which amino acid sequences account for transmembrane folding of G7 receptors, the membrane domain of the rabbit cholecystokinin-A (CCK-A) G-protein-coupled receptor has been investigated by in vitro transcription/translation of two types of fusion vectors containing sequences that include putative transmembrane segments. First, the seven putative transmembrane domains of the CCK-A receptor were inserted individually into pGEM vectors beginning with the cDNA encoding the first 101 (HK-M0) or 139 (HK-M1) amino acids of the alpha subunit of the gastric H, K-ATPase. These were separated by the cDNA for the inserted transmembrane domains from the cDNA encoding the last 177 amino acids of the beta subunit of the H,K-ATPase containing five N-linked glycosylation consensus sequences (Bamberg, K., and Sachs, G. (1994) J. Biol. Chem. 269, 16909-16919). Transcription/translation of these fusion vectors in rabbit reticulocyte lysate +/- dog pancreatic microsomes followed by SDS-polyacrylamide gel electrophoresis defined the presence of signal anchor sequences in HK-M0 by glycosylation and stop transfer sequences in HK-M1 by inhibition of glycosylation. Six out of the seven putative transmembrane domains had membrane insertion signals, but no membrane insertion activity was found for the H3 segment in these vectors. To test the effect of specific upstream and downstream sequences on membrane insertion, vectors were also made starting with the cDNA encoding the N terminus of the CCK-A receptor separated from the last 177 amino acids of the H,K-ATPase beta subunit by cDNA encoding CCK-A receptor sequences of different lengths. In addition to transcription/translation, endoglycosidase H treatment was used to verify glycosylation when multiple bands were found in the presence of microsomes. The four positive charges in the loop between H1 and H2 were required for the correct orientation of the first transmembrane domain. The H3 segment acted as a stop transfer sequence only when the whole N terminus and H3 were followed by the positive charges in the cytoplasmic loop between H3 and H4. The activity of H6 as a signal anchor sequence depended on preceding positive charges. These translation data using two types of fusion vectors establish a seven-transmembrane folding model using only in vitro translation for the CCK-A receptor beginning with two signal anchor sequences and then alternating stop transfer and signal anchor insertions. Positive charges between H1 and H2, H3 and H4, and H5 and H6 function as cytoplasmic anchors in the membrane folding of this receptor.

Amino Acid Sequence↗
PubMed1997

Perforated duodenal ulcer presenting with shock in a child.

Presentation of peptic ulcer disease in children covers a broad spectrum ranging from subtle, and thus overlooked and underdiagnosed, to catastrophic, as in this case. It is important for the emergency physician to realize the potential morbidity and mortality of this disease and be aware of the spectrum of presentation for primary and secondary pediatric ulcer disease.

Abdomen, Acute↗
PubMed1996

Safety of antioxidant vitamins.

As a result of the many scientific and popular press reports of the benefits of antioxidant vitamins (vitamin A, beta-carotene, vitamin E, and ascorbic acid), it is estimated that 40% of the US population is consuming vitamin supplements. The efficacy of these supplements is not yet proved, and some have questioned their safety. Approximately 10 to 15 cases of vitamin A toxic reactions are reported per year in the United States, usually at doses greater than 100,000 IU/d. No adverse effects have been reported for beta-carotene. The frequency of vitamin E toxic reactions is not well delineated, but case reports are few at dosages less than 3200 mg/d. Ascorbic acid toxic reactions are rare at dosages less than 4 g/d. Despite a lack of clinical trial data, it seems that antioxidant vitamins are safe, although prudence might dictate their avoidance by women of childbearing potential, persons with liver disease or renal dysfunction, and those taking certain medications or undergoing specific laboratory tests.

Antioxidants↗
PubMed1995

The membrane topology of the rat sarcoplasmic and endoplasmic reticulum calcium ATPases by in vitro translation scanning.

The membrane topology of the rat endoplasmic reticulum (ER) and sarcoplasmic reticulum (SR) Ca2+ ATPases were investigated using in vitro transcription/translation of fusion vectors containing DNA sequences encoding putative membrane-spanning domains. The sequences of these Ca2+ ATPases are identical except for the COOH-terminal end, which contains an additional predicted transmembrane segment in the ER ATPase. The M0 and M1 fusion vectors (Bamberg, K., and Sachs, G. (1994) J. Biol. Chem. 269, 16909-16919) encode the NH2-terminal 101 (M0 vector) or 139 (M1 vector) amino acids of the H,K-ATPase alpha subunit followed by a linker region for insertion of putative transmembrane sequences and, finally, the COOH-terminal 177 amino acids of the H,K-ATPase beta subunit containing five N-linked glycosylation consensus sequences. The linker region was replaced by the putative transmembrane domains of the Ca2+ ATPases, either individually or in pairs. Transcription and translation were performed using [35S]methionine in a reticulocyte lysate system in the absence or presence of canine pancreatic microsomes. The translated fusion protein was identified by autoradiography following separation using SDS-polyacrylamide gel electrophoresis. When testing single transmembrane segments, this method detects signal anchor activity with M0 or stop transfer activity with M1. The first four predicted SERCA transmembrane domains acted as both signal anchor and stop transfer sequences. A construct containing the fifth predicted transmembrane segment was able to act only as a stop transfer sequence. The sixth transmembrane segment did not insert cotranslationally into the membrane. The seventh was able to act as both a signal anchor and stop transfer sequence, and the eighth showed stop transfer ability in the M1 vector. The ninth transmembrane segment had both signal anchor and stop transfer capacity, whereas the tenth transmembrane segment showed only stop transfer sequence properties. The eleventh transmembrane sequence, unique to the ER Ca2+ ATPase, had both signal anchor and stop transfer properties. These translation data provide direct experimental evidence for 8 or 9 of the 10 or 11 predicted transmembrane sequences in the current topological models for the SR or ER Ca2+ ATPases, respectively.

Amino Acid Sequence↗
PubMed1993

Experimental otitis media with effusion induced by platelet activating factor.

This study tested the hypothesis that platelet activating factor (PAF) in the middle ear can induce otitis media with effusion (OME) and that PAF antagonists can prevent PAF-induced OME. An initial trial of 16 micrograms of PAF was injected into chinchilla bullae, and all ears developed middle ear effusion (MEE) within 48 hours. Subsequent trials were performed to test dose dependency. Interestingly, 1 or 16 micrograms of PAF caused more MEE and inflammation than did 4 or 8 micrograms. A dose of 0.5 micrograms PAF did not cause MEE. Middle ear effusion from injected bullae contained the full spectrum of lipoxygenase and cyclooxygenase products; additionally, more PAF was detected than was injected. Finally, a PAF antagonist (WEB 2170) injected intraperitoneally prevented PAF-induced OME. This study demonstrates that PAF injected into the middle ear can induce OME and that PAF antagonists effectively prevent PAF-induced OME. These findings suggest that PAF plays an important role in the pathogenesis of OME.

Animals↗
PubMed1992

Effect of the radioprotector WR2721 on irradiation-induced injury to ciliated cells of eustachian tube.

Our previous studies revealed that injury to the ciliated cells of the eustachian tube may be the primary cause of irradiation-induced serous otitis media. The purpose of this study was to investigate the effects of the radioprotector WR2721 on irradiation-induced injury to ciliated cells of the eustachian tube (ET) in chinchillas. Twelve chinchillas were divided into two groups: the control group and the experimental group, which was pretreated with a single intraperitoneal dose of the radioprotector S-2-[3-aminopropylamino]ethylphosphorothioic acid (WR2721) 400 mg/kg. The two groups were exposed to 30 Gy of 13-MeV electrons in a single fraction to the area of the bullae and nasopharynx. Ciliary dysfunction was tested and ciliated cells of the ET were examined by scanning and transmission electron microscopy. Pretreatment with WR2721 was found to protect ciliated cells of the ET from irradiation injury.

Amifostine↗
PubMed1991

Washing the blood.

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Education, Nursing, Continuing↗
PubMed1990

Effect of prostaglandin, leukotriene, and arachidonic acid on experimental otitis media with effusion in chinchillas.

Although previous studies have shown that prostaglandins (PGs), leukotrienes (LTs), and other arachidonic acid (AA) metabolites play an important role in the pathogenesis of otitis media with effusion (OME), the exact role of each AA metabolite in OME is still unknown. The purpose of this study was to examine the effect of several individual AA metabolites alone or in combination and AA itself on experimental otitis media in chinchillas. Normal chinchillas were inoculated daily with normal saline, PGE2, LTC4, LTC4 + PGE2, and AA through the superior bullae over 7 days. Animals were followed by otoscopy and tympanometry, samples of middle ear effusion were collected for biochemical assay, and temporal bones were processed for histopathology. The highest number of ears that developed OME was in the group inoculated with PGE2 + LTC4. The degree of inflammatory change was more pronounced in groups injected with LTC4 than any other group. The findings of this study suggest that eicosanoids PGE2, LTC4, and AA alone or in combination inoculated into the middle ear can induce OME.

6-Ketoprostaglandin F1 alpha↗
PubMed1990

B-adrenergic receptor stimulation increases anti-DNA antibody production in MRL/1 pr mice.

To gain insight into a role for excessive B-adrenergic receptor stimulation in the pathogenesis of autoimmune diseases, MRL/1 pr mice were chronically injected with isoproterenol. The mean change of serum antibody levels after one month of treatment was higher in the isoproterenol treated mice than in controls (anti-ssDNA, p less than 0.05; anti-nDNA, p less than 0.04; and antiguanosine antibodies, p less than 0.03) without significant differences in serum IgG levels. Additionally, mean serum creatinine levels were higher and glomerulonephritis more severe in the isoproterenol treated group. Our findings provide the first evidence linking aberrant B-adrenergic receptor activities, serum anti-DNA antibodies, and end-organ pathology in an animal model of lupus nephritis.

Animals↗
PubMed1980

ECT: II: patients who complain.

Twenty-six subjects who complained of permanent unwanted effects following ECT were compared with two groups of control subjects on a battery of 19 cognitive tests. Many statistically significant differences were found in cognitive functioning, mostly attributable to the level of depression or medication in the complainers. However, after analysis of variance/co-variance some differences still remained, indicating impaired cognitive functioning in the ECT complaining group.

Adult↗
PubMed1980

ECT: III: Enduring cognitive deficits?

Cognitive function was compared in carefully matched groups of ECT and non-ECT treated depressives and in matched normal volunteer controls on admission, at 4 months and at 7 months. ECT caused little impairment at 4 months and no impairment at 7 months on a comprehensive cognitive test battery. Severity of depression had a marked effect on cognitive function. Within the ECT group bilateral ECT caused more impairment than unilateral ECT one week after a course but 3 months later the differences had disappeared. They were equally antidepressant.

Adolescent↗