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Biomedical subjects

D Stone

Publications and source records attributed to D Stone.

At least 109 records · Page 6Linked to original sources
PubMed1989

Activity of bleomycin in iron- and copper-deficient cells.

Three models were used to examine the requirement of bleomycin (Blm) for iron (Fe) to carry out its antitumor or cytotoxic activity. Mice were made iron deficient by dietary means. Animals with depressed iron stores in liver and low plasma and ascites fluid iron supported Ehrlich tumor growth as well as mice maintained on a control diet. Bleomycin was equally effective against this tumor in iron-deficient mice as it was against the tumor in iron-sufficient controls. Likewise, nutrient copper deficiency did not change the efficacy of the drug. Ehrlich cells in culture were treated with a non-growth inhibiting concentration of the chelating agent, 1,10-phenanthroline before or during their exposure to bleomycin. Again, the treated cells were as sensitive to drug as controls, despite the fact that this ligand reduces cellular iron and zinc and can extract iron from Fe(II)Blm. Lastly, it was demonstrated that iron-depleted Euglena gracilis cells growing at reduced rates were as sensitive to growth inhibition by bleomycin as control cells.

Animals↗
PubMed1989

Hypoxia-reoxygenation induced increase in cellular Ca2+ in myocytes and perfused hearts: the role of mitochondria.

Reoxygenation of isolated rat cardiac myocytes following a period of hypoxia and substrate deprivation resulted in a 1.5-2-fold increase in the total Ca2+ content which could be inhibited by 1 microM antimycin A or ruthenium red (50% inhibition at 2.5 microM). This increase in Ca2+ content was not accompanied by any release of creatine kinase into the medium. Treatment of reoxygenated cells with digitonin also resulted in an antimycin A-sensitive increase in Ca2+ but this was inhibited by a lower concentration of ruthenium red (50% inhibition at 0.25 microM) and was associated with a substantial release of creatine kinase from the cells. It is concluded that the reoxygenation-stimulated increase in Ca2+ is dependent on functioning mitochondria and does not occur as a result of physical damage to the sarcolemma. In a parallel series of experiments, the effects of antimycin A and ruthenium red on the reoxygenation-induced increase in Ca2+ and release of cytosolic contents in the perfused heart (the oxygen paradox) were also investigated. As was observed with the isolated myocytes, each of the compounds significantly reduced the magnitude of the Ca2+ increase that occurred on reoxygenation: the compounds also reduced the extent of release of cell contents in the perfused heart. The implications of these results for the series of events occurring on reoxygenation of the hypoxic myocardium are discussed.

Animals↗
PubMed1989

Epidemiologic characteristics of scabies in the Israel Defense Force.

Scabies is not a notifiable disease in most countries. As a result the data on its epidemiologic characteristics are limited. In the Israel Defense Force, compulsory reporting of individual cases has been required for years, and in this study the epidemiology of the disease is examined for the years 1968-1988. A moderate epidemic occurred between 1969 and 1973, and was followed by a return to the previous low incidence. In 1982 a massive outbreak began, and peaked from 1985-1986. From 1987 to 1988, the incidence of infestation has markedly declined. A seasonal pattern of morbidity was evident during epidemic periods only; maximum incidence occurred during the winter months. These data are compared with those described in other countries and provide a more complete picture of the epidemiology of scabies based on individually reported cases.

Adolescent↗
PubMed1989

Switching of Candida albicans during successive episodes of recurrent vaginitis.

Strain relatedness and switching were monitored in Candida albicans strains isolated from different body locations through three episodes of recurrent vulvovaginal candidiasis separated by two treatment-latency periods in a single patient. Strain relatedness was assessed by comparing Southern blot hybridization patterns with the relatively immobile mid-repeat sequence Ca3. The following conclusions are demonstrated. (i) Three different strains of C. albicans colonized the mouth, the area under the breasts, and the vulvovaginal, anal, and rectal regions, respectively, at the time of the first infection. (ii) The same strain of C. albicans was responsible for the three vaginal infections. (iii) Switching of colony phenotype occurred with each new vaginal infection. (iv) Enrichment of drug-resistant switch phenotypes (assessed in vitro) was unlikely the basis for the changes in the switch phenotypes of the strain found in the vulvovaginal, anal, and rectal areas after treatment of the first infection with clotrimazole. (v) The same strain of C. albicans was responsible for the recurrent increases in mouth colonization and was distinct from the recurrent vaginal strain. The results of this case study demonstrate the need for further detailed analyses of full-body mycofloras, strain relatedness, switching repertoires, and changes in drug susceptibility during successive episodes of recurrent vulvovaginal candidiasis.

Antifungal Agents↗
PubMed1989

The glutathione status of perfused rat hearts subjected to hypoxia and reoxygenation: the oxygen paradox.

Langendorff perfused rat hearts were subjected to 30 min hypoxia followed by 20 min reoxygenation and the levels of the oxidised and reduced forms of glutathione measured. No change in the concentration of oxidised glutathione was detected in reoxygenated hearts when compared to normoxic controls. In contrast hearts exposed to oxidative stress in the form of H2O2 showed elevated levels of both oxidised glutathione (GSSG) and the glutathione-protein mixed disulphide. These results suggest that if oxidants do contribute to cell damage on reoxygenation of the hypoxic myocardium then their action is local and not through overwhelming of the cells antioxidant defences.

Animals↗
PubMed1989

Oxygen and reperfusion damage: an overview.

The ischaemic myocardium shows a number of distinct oxygen dependent responses to reperfusion. In the case of myocardial stunning and reperfusion arrhythmias there appears to be a beneficial effect of scavenging radicals in the extracellular space. This result is supported by the finding that free radicals can be detected extracellularly after reperfusion. The source of these oxidants and site of action is as yet unclear. In contrast hypoxic myocytes shown an oxygen dependent Ca2+ uptake on reoxygenation which is not affected by externally applied antioxidants. This Ca2+ uptake may in turn lead to the cell lysis characteristic of the oxygen paradox in the perfused heart. As yet there is no compelling evidence to suggest that this aspect of reperfusion damage is due to oxidative stress. It appears more likely that mitochondrial electron transport and ion movement play a central role. In the open chested dog model of ischaemia reperfusion, in which the volume of infarcted tissue is measured, considerable evidence suggests that oxidants derived from activated neutrophils contribute to cell death. This is not however the sole mechanism for cell damage in this model since an inhibitor of mitochondrial Ca2+ uptake, ruthenium red, can improve recovery after reperfusion. We conclude that a number of mechanisms may contribute to the observed oxygen dependent dysfunctions which occur on reperfusion of ischaemic tissue.

Animals↗
PubMed1988

A comparative study of the cardiovascular and biochemical actions of the imidazo [4,5b] pyridine sulmazole and an imidazo [4,5c] pyridine analogue, BW A746C.

1. BW A746C is a chemical analogue of the imidazo [4,5b] pyridine, sulmazole (AR-L115 BS). Like sulmazole, BW A746C possesses positive inotropic and vasodilator activity in vivo. 2. In anaesthetized guinea-pigs, dogs and primates, a bolus i.v. injection of BW A746C, (0.001-1.0 mg kg-1) caused a significant, dose-related increase in ventricular dP/dt, and reduction in diastolic blood pressure, with small increases in heart rate. In these species, a significantly higher dose of BW A746C was required to lower blood pressure by 30% from basal, than was needed to raise ventricular dP/dt by 50% over basal. 3. In anaesthetized guinea-pigs and dogs, bolus i.v. injections of sulmazole (0.1-10.0 mg kg-1) caused similar effects to those observed with BW A746C. In these species, however, there was no significant difference between the dose of sulmazole required to lower blood pressure by 30% from basal and that required to raise ventricular dP/dt by 50%. 4. In conscious dogs, i.v. infusion of BW A746C (to a total dose of 0.3 mg kg-1) caused a significant increase in ventricular dP/dt, but no significant change in either diastolic blood pressure or heart rate. 5. In cell-free biochemical assays, there were no clear differences between the observed activities of BW A746C and sulmazole. Both compounds are cyclic nucleotide phosphodiesterase inhibitors with similar potencies and selectivities for the Type III enzyme (IC50 BW A746C = 3.0 +/- 0.5 X 10(-5) M, sulmazole 5.0 +/- 1.9 X 10(-5) M). The compounds had little or no effects on sarcolemmal Na+/K+-ATPase, Ca2+ ATPase or Na+/Ca2+ exchange, and sulmazole, but not BW A746C, had a small, stimulatory effect on myofibrillar ATPase. 6. In anaesthetized guinea-pigs and dogs, BW A746C was significantly more potent as a positive inotrope than sulmazole. In contrast with sulmazole, BW A746C produced its inotropic effects at significantly lower doses than those required to reduce diastolic blood pressure. This was also apparent from the results obtained in the anaesthetised primates and the conscious dogs. It was therefore concluded that the inotropic/vasodilator profile of BW A746C favours its positive inotrope activity. This profile cannot be explained on the basis of any biochemical differences from sulmazole.

Animals↗
PubMed1988

Reciprocal regulation of antral gastrin and somatostatin gene expression by omeprazole-induced achlorhydria.

Gastric acid exerts a feedback inhibition on the secretion of gastrin from antral G cells. This study examines whether gastrin gene expression is also regulated by changes in gastric pH. Achlorhydria was induced in rats by the gastric H+/K+ ATPase inhibitor, omeprazole (100 mumol/kg). This resulted in fourfold increases in both serum gastrin (within 2 h) and gastrin mRNA levels (after 24 h). Antral somatostatin D cells probably act as chemoreceptors for gastric acid to mediate a paracrine inhibition on gastrin secretion from adjacent G cells. Omeprazole-induced achlorhydria reduced D-cell activity as shown by a threefold decrease in antral somatostatin mRNA levels that began after 24 h. Exogenous administration of the somatostatin analogue SMS 201-995 (10 micrograms/kg) prevented both the hypergastrinemia and the increase in gastrin mRNA levels caused by omeprazole-induced achlorhydria. Exogenous somatostatin, however, did not influence the decrease in antral somatostatin mRNA levels seen with achlorhydria. These data, therefore, support the hypothesis that antral D cells act as chemoreceptors for changes in gastric pH, and modulates somatostatin secretion and synthesis to mediate a paracrine inhibition on gastrin gene expression in adjacent G cells.

Achlorhydria↗
PubMed1987

Epidemiology of intraocular pressure in a population screened for glaucoma.

This study evaluated the association between intraocular pressure and various sociodemographic characteristics, ocular findings, and cardiovascular risk factors in a population screened for glaucoma. A total of 2594 subjects older than 40 years residing in three urban areas of southern Israel participated. Of those screened 6.1% had a raised intraocular pressure (IOP greater than or equal to 21). The mean IOP increased with age, was higher among persons born in Africa or Asia than those born in Europe or America, higher among myopes than hypermetropes and among those with an enlarged cup-disc ratio (CDR). Analysis of variance tests indicated that refractive status, CDR, age, country of birth, and diabetes were each independently associated with IOP. In addition, associations between raised intraocular pressure and age, country of birth, myopia, CDR, diabetes, and glaucoma in the family were found.

Adult↗
PubMed1986

The impact of prenatal care on the outcome of pregnancy.

In a 12-months' prospective project all women delivering at the Soroka Medical Center, Beer-Sheba, Israel, were studied with regard to the type of prenatal care (P.C.) and the outcome of pregnancy. The Soroka Medical Center is the sole medical facility providing obstetric and neonatal services to the 300,000 inhabitants of the region. Prenatal care is delivered by a uniform network of 70 community-based stations. The availability, type and quality of services were uniform for all women and were not altered throughout the study period. The project encompassed 7308 deliveries. 2154 Bedouin women were excluded in order to avoid possible bias due to cultural and genetic characteristics. Data regarding 5154 Jewish women were analysed. Perinatal mortality was inversely proportional to the number of prenatal contacts. The uncorrected mortality rates were 12.7% in women entirely lacking P.C. and 6.2%, 1.9% and 1.0% in patients who had 1-6, 7-10 and 11 or more prenatal contacts respectively. The low-birthweight rate was significantly increased in women lacking prenatal care (22.8%) or having rudimentary care (17.4%) as compared to those who had 11 or more prenatal contacts with medical personnel (5.9%). Prenatal care reduced neonatal morbidity as expressed by the length of hospitalization, the frequency of infants with multiple diagnoses and the incidence of specific pathologies such as respiratory distress syndrome, light for dates and asphyxia. The incidence of some complications of pregnancy (abruptio placentae, premature labor, PROM) was significantly increased in women lacking P.C. or having inadequate P.C. (1-6 prenatal contacts). Moreover, lack of prenatal care was clearly connected with high-risk delivery, thus increasing the danger to the baby. It is suggested that many adverse effects of various socio-economic, genetic and general health factors may be diminished by proper prenatal care coupled with adequate obstetric and neonatal services.

Adult↗
PubMed1984

Characterization and amino acid sequence of Neisseria gonorrhoeae dihydrofolate reductase.

Dihydrofolate reductase has been purified from a trimethoprim-resistant strain of Neisseria gonorrhoeae. The enzyme showed a single component on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Mr = 18,000) and on isoelectric focusing in 5 M urea (pI = 6.8). Although gel electrophoresis under nondenaturing conditions resolved the preparation into two enzymatically active proteins (called form 1 and form 2), they were not genetically determined isozymes. Both had a similar dihydrofolate Km (2 microM), NADPH Km (10 microM), and trimethoprim Ki (20 nM), and form 2 (the slower migrating species) was shown to be generated from form 1 by the electrophoresis conditions. The complete covalent structure of the enzyme has also been determined. It is a single polypeptide composed of 162 residues and containing 4 cysteines. The gonococcal dihydrofolate reductase shares a 35% homology with the chicken liver enzyme and a 40% homology with the Escherichia coli enzyme. Most of these identities are residues that have been implicated in the binding of NADPH and methotrexate to the E. coli and Lactobacillus casei reductases.

Amino Acid Sequence↗
PubMed1984

Species-specific irreversible inhibition of Neisseria gonorrhoeae dihydrofolate reductase by a substituted 2,4-diamino-5-benzylpyrimidine.

Neisseria gonorrhoeae dihydrofolate reductase undergoes a time-dependent, irreversible inactivation by 2,4-diamino-5-[3,5-dimethoxy-4-(p-bromoacetamidophenoxy)benzyl] pyrimidine. The kinetics of inactivation are consistent with the reversible formation of an enzyme-inhibitor complex followed by covalent binding to the enzyme. The reversible component is competitive with dihydrofolate and has an inhibitor binding constant of 10 nM. Irreversible inactivation proceeds as a pseudo first-order process with a minimum inactivation half-time of 20 min and a Ki of 28 nM. Using radiolabeled inhibitor, it was shown that approximately 1 mol of ligand was covalently bound to the enzyme/mol of methotrexate binding site when the enzyme was completely inhibited. Radiolabeled inhibitor remained associated with the enzyme following denaturation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cyanogen bromide cleavage of the 14C-labeled enzyme-inhibitor complex yielded only one radioactive polypeptide, and sequence determinations showed that His-25 was modified by covalent attachment of the inhibitor. When dihydrofolate reductases from Lactobacillus casei, Streptococcus faecium, Escherichia coli, SR-1 rodent lymphoma, and chicken liver were tested with the affinity label, only the L. casei enzyme showed a time-dependent increase in inhibition. These data, along with comparisons of known amino acid sequences and x-ray crystal structures, were used to make predictions concerning the three-dimensional conformation of the gonococcal enzyme.

Folic Acid Antagonists↗
PubMed1984

Characterization of an R-plasmid dihydrofolate reductase with a monomeric structure.

A plasmid-encoded dihydrofolate reductase that originated in a clinical isolate of Salmonella typhimurium (phage type 179) moderately resistant to trimethoprim has been isolated and characterized. The dihydrofolate reductase (called type III) was purified to homogeneity using a combination of gel filtration, hydrophobic chromatography, and methotrexate affinity chromatography. Polyacrylamide gel electrophoresis under denaturing and nondenaturing conditions indicated that the enzyme is a 16,900 molecular weight monomeric protein. Kinetic analyses showed that trimethoprim is a relatively tight binding inhibitor (Ki = 19 nM) competitive with dihydrofolate. The enzyme is also extremely sensitive to methotrexate inhibition (Ki = 9 pM) and has a high affinity for dihydrofolate (Km = 0.4 microM). The sequence of the first 20 NH2-terminal residues of the protein shows 50% homology with the trimethoprim-sensitive chromosomal Escherichia coli dihydrofolate reductase and suggests that the two enzymes may be closely related. This is the first example of a plasmid encoding for a monomeric dihydrofolate reductase only moderately resistant to trimethoprim, and a resistance mechanism, dependent in part on the high dihydrofolate affinity of the type III enzyme, is proposed.

Amino Acid Sequence↗
PubMed1983

R plasmid dihydrofolate reductase with a dimeric subunit structure.

Dihydrofolate reductase specified by plasmid R483 from a trimethoprim-resistant strain of Escherichia coli has been purified 2,000-fold to homogeneity using dye-ligand chromatography, gel filtration, and polyacrylamide gel electrophoresis. The protein migrated as a single band on nondenaturing polyacrylamide gel electrophoresis and had a specific activity of 250 mumol/mg min(-1). The molecular weight was estimated to be 32,000 by gel filtration and 39,000 by Ferguson analysis of polyacrylamide gel electrophoresis. When subjected to electrophoresis in the presence of sodium dodecyl sulfate, the protein migrated as a single 19,000-molecular weight species, a fact that suggests that the native enzyme is a dimer of similar or identical subunits. Antibody specific for R483-encoded dihydrofolate reductase did not cross-react with dihydrofolate reductase encoded by plasmid R67, T4 phage, E. coli RT500, or mouse L1210 leukemia cells. The amino acid sequence of the first 34 NH2-terminal residues suggests that the R483 plasmid dihydrofolate reductase is more closely related to the chromosomal dihydrofolate reductase than is the enzyme coded by plasmid R67.

Amino Acid Sequence↗