Biomedical subjects

C J Turner

Publications and source records attributed to C J Turner.

At least 19 recordsLinked to original sources

PubMed2002

The production of single strand and double strand breaks in DNA in aqueous solution by vacuum UV photons below 10 eV.

The mechanisms of break formation in fully hydrated DNA have been investigated using monochromatic photons below 10 eV. This has been achieved by developing a novel 'wet cell' for irradiating DNA in aqueous solution. Our preliminary data show that 7-10 eV photons readily induce strand breaks even though almost all of the energy is absorbed in the water. Therefore, the mechanism for the induction of single and double strand breaks (SSBs and DSBs) most likely involves indirect damage by OH radicals and is substantiated by data from studies in the presence of the OH radical scavenger Tris, which showed a substantial protective effect. The dose-effect curve for DSB induction is seen to be linear, or near-linear, indicating the involvement of 1-hit mediated induction of DSBs. These data point to single-event induction of DSBs being a significant pathway with all radiation types.

DNA↗

PubMed2001

Solution structure of an oligonucleotide containing an abasic site: evidence for an unusual deoxyribose conformation.

The antitumor antibiotic bleomycin causes two major lesions in the deoxyribose backbone of DNA: formation of 4'-keto abasic sites and formation of strand breaks with 3'-phosphoglycolate and 5'-phosphate ends. As a model for the 4'-keto abasic site, we have characterized an abasic site (X) in d(CCAAAGXACTGGG).d(CCCAGTACTTTGG) by two-dimensional NMR spectroscopy. A total of 475 NOEs and 101 dihedral angles provided the restraints for molecular modeling. Four unusual NOEs were observed between each anomer of the abasic site and the neighboring bases. In addition, four coupling constants for adjacent protons of the deoxyribose of both the alpha and beta anomers of the abasic site were observed. The modeling suggests that for both anomers the abasic site is extrahelical, without significant distortion of the backbone opposite the lesion. The coupling constants further allowed assignment of an unusual sugar pucker for each anomer. The unique position of the abasic site in our structural model for each anomer is discussed in terms of repair of such lesions in vivo.

Antibiotics, Antineoplastic↗

PubMed2001

Solution structure of Co(III)-bleomycin-OOH bound to a phosphoglycolate lesion containing oligonucleotide: implications for bleomycin-induced double-strand DNA cleavage.

Bleomycin (BLM) is an antitumor antibiotic that is used clinically. Its major cause of cytotoxicity is thought to be related to BLM's ability to cause double-strand (ds) DNA cleavage. A single molecule of BLM appears to cleave both strands of DNA in the presence of its required cofactors Fe(2+) and oxygen without dissociating from the helix. A mechanism for this process has been proposed based on a model structure of the hydroperoxide of Co(III)-BLM (CoBLM) bound sequence-specifically to an intact duplex containing a GTAC site, a hot spot for ds cleavage [Vanderwall, D. E., Lui, S. M., Wu, W., Turner, C. J., Kozarich, J. W., and Stubbe, J. (1997) Chem. Biol. 4, 373-387]. In this paper, we present a structural model for the second cleavage event. Two-dimensional NMR spectroscopy and molecular modeling were carried out to study CoBLM bound to d(CCAAAGXACTGGG).d(CCCAGTACTTTGG), where X represents a 3'-phosphoglycolate lesion next to a 5'-phosphate. Assignments of 729 NOEs, including 51 between the drug and the DNA and 126 within the BLM molecule, have been made. These NOEs in addition to 96 dihedral angle constraints have been used to obtain a well-defined structural model for this complex. The model reveals that the bithiazole tail is partially intercalated between the T19 and the A20 of the duplex and that the metal binding domain is poised for abstraction of the T19 H4' in the minor groove. The modeling further reveals that the predominant conformation of the bithiazole protons is trans. Two cis conformations of these protons are also observed, and ROESY experiments provide evidence for interconversion of all of these forms. The relationship of these observations to the model for ds cleavage is presented.

Antibiotics, Antineoplastic↗

PubMed2000

Community pharmacist outreach program directed at physicians treating congestive heart failure.

The predictive value of digoxin and furosemide treatment for identifying patients receiving treatment for congestive heart failure (CHF), the use of angiotensin-converting-enzyme (ACE) inhibitors in this population, and the ability of a pharmacist outreach program to address underutilization of ACE inhibitors were studied. All physicians and owner-managers of community pharmacies on Newfoundland's Avalon Peninsula were asked to participate in the study. Pharmacists who agreed to participate were asked to list patients of the participating physicians with prescriptions for (1) furosemide and digoxin with and without an ACE inhibitor or angiotensin II-receptor inhibitor and (2) an ACE inhibitor. Physicians were visited by a pharmacist and asked whether each of their patients receiving digoxin and furosemide was being treated for CHF and to identify further cases of CHF among their patients receiving an ACE inhibitor. Intervention-group physicians received academic detailing on the use and dosage of ACE inhibitors and angiotensin II-receptor inhibitors for CHF. Both groups were reinterviewed after three months to establish what if any changes in therapy had occurred for each patient discussed during the first visit. The positive predictive value of digoxin and furosemide treatment for identifying patients receiving treatment for CHF was 94%. Seventy-six percent of patients identified by physicians as CHF patients who were taking digoxin and furosemide were treated with an ACE inhibitor. Thirty-six percent of patients treated with an ACE inhibitor for CHF received the targeted dosage. Four physicians stated that the outreach visit influenced their prescribing, but there was no significant difference in ACE inhibitor prescribing between the intervention and control groups. A pharmacist outreach program involving the use of prescription records and academic detailing did not affect prescribing or dosages of ACE inhibitors but demonstrated value as a quality assurance tool.

Angiotensin Receptor Antagonists↗

PubMed2000

Cost analysis of a provincial drug program to guide the treatment of upper gastrointestinal disorders.

BACKGROUND: Concerned with the rising costs of its drug programs for seniors and social-assistance recipients, the government of Newfoundland and Labrador requested physicians and pharmacists at the Memorial University of Newfoundland, and members of the Newfoundland and Labrador Medical Association and the Newfoundland Pharmaceutical Association to provide guidance to the health care community for the use of drugs to treat upper gastrointestinal disorders. METHODS: Algorithms for the management of dyspepsia and gastrointestinal reflux disease were created and distributed to all physicians and pharmacists in the province in June 1996. On July 1, 1996, the provincial government implemented a program to restrict payment for proton-pump inhibitors through its drug programs to situations defined by the algorithms. Restrictions were not applied to the prescribing of cimetidine, ranitidine and prokinetic agents. The status of famotidine and nizatidine was changed from "open benefit" to "special consideration," which requires prescribers to request authorization of their use on a case-by-case basis. RESULTS: Between July 1 and Dec. 31, 1996, 973 of 1078 requests for a proton-pump inhibitor were approved (679 for gastroesophageal reflux, 186 for Helicobacter pylori eradication, 55 for ulcer treatment and 53 for other reasons). The program resulted in a sustained reduction in drug expenditures. Total drug expenditures, which had risen from $39.0 million in 1992/93 to $50.8 million in 1995/96, fell after implementation of the program to $46.4 million in 1996/97 because of a decrease of more than 80% in the use of proton-pump inhibitors. Expenditures on proton-pump inhibitors, which had increased from $0.7 million for the 6 months ending March 1993 to $1.6 million for the 6 months ending March 1996, decreased to $0.3 million for the 6 months ending March 1997. The use of H2-antagonists, but not prokinetic agents, increased concomitantly with the decline in proton-pump inhibitor use. Compared with the year preceding implementation of the program, annual combined expenditures in the subsequent 3 years for H2-antagonists, prokinetic drugs and proton-pump inhibitors were reduced by $1.6 million, $1.7 million and $1.0 million, respectively. Feedback from physicians and pharmacists was supportive for the clinical information and prescribing guidelines. Concerns were mostly limited to process issues. INTERPRETATION: The program, designed by health care professionals, approved by health care associations and implemented by the province of Newfoundland and Labrador to guide the treatment of upper gastrointestinal disorders, has achieved a substantial reduction in drug expenditures.

Algorithms↗

PubMed2000

New antimicrobial flavanones from Physena madagascariensis.

Two new flavanones (1 and 2) with antibacterial activity were isolated from the methanolic extract of the dried leaves of Physena madagascariensis using activity against Staphylococcus aureus to guide the isolation. A third flavonoid, a flavanone dimer linked by a methylene group (3) was also isolated and proved to be inactive. The structures of 1 and 2 were established primarily from NMR studies, while that of 3 required more extensive mass spectrometric analysis. All three flavanones had lavandulyl units in the limonene form. Flavanones 1 and 2 were active against several bacteria at concentrations as low as 4 microM.

Anti-Bacterial Agents↗

PubMed1999

The solution structure of the Zalpha domain of the human RNA editing enzyme ADAR1 reveals a prepositioned binding surface for Z-DNA.

Double-stranded RNA deaminase I (ADAR1) contains the Z-DNA binding domain Zalpha. Here we report the solution structure of free Zalpha and map the interaction surface with Z-DNA, confirming roles previously assigned to residues by mutagenesis. Comparison with the crystal structure of the (Zalpha)(2)/Z-DNA complex shows that most Z-DNA contacting residues in free Zalpha are prepositioned to bind Z-DNA, thus minimizing the entropic cost of binding. Comparison with homologous (alpha+beta)helix-turn-helix/B-DNA complexes suggests that binding of Zalpha to B-DNA is disfavored by steric hindrance, but does not eliminate the possibility that related domains may bind to both B- and Z-DNA.

Adenosine Deaminase↗

PubMed1999

DNA bending and sequence-dependent backbone conformation NMR and computer experiments.

Although DNA bending plays a crucial role in several biological processes, very little is known experimentally about the relationship between sugar phosphate conformation and sequence directed bending. In this paper, we determine the coupling constants for a nonself-complementary 11-mer A-tract DNA duplex from 2D NMR experiments and along each chain of the duplex, we report the sugar pucker, torsional preferences and conformational averaging about the C3'-O3', C4'-C5' and C5'-O5' bonds for each nucleotide. The A-tract exists as an equilibrium blend of canonical B-form and noncanonical B-form in which the exocyclic C4'-C5' bond is in trans conformation as in the original Watson-Crick model [Crick, F.H.C. & Watson, J.D. (1954) Proc. Roy. Soc. (London), A223, 80-96]. The trans conformation at the C4'-C5' can increase the interphosphate distance and lead to local unwinding of the duplex and rolling of the base pair into the major groove. This will create a kink or hinge. At the 3'-end of the A-tract in the purine-thymine step, the duplex is compressed by the presence of a junction between A and B forms of DNA exclusively in one strand, with consequent reduction of the phosphate-phosphate distance. The coupling constant data seriously disagree with the A-tract DNA bending model of Crothers [Koo, H.-S., Wu, H.-M. & Crothers, D.M. (1986) Nature 320, 501-506], but is in agreement with the finding of Leroy et al. [Leroy, J.-L., Charretier, E., Kochoyan, M. & Gueron, M. (1988) Biochemistry 27, 8894-8898] that the structure that drives bending in the A-tract is locally different from B-DNA. Structural distortions are extremely localized with little or no propagation. It is likely that transcription factor proteins recognize these preexisting deformations in the free DNA itself and mold it into the matrix of the protein.

Computer Simulation↗

PubMed1999

Structure-function analysis of the Z-DNA-binding domain Zalpha of dsRNA adenosine deaminase type I reveals similarity to the (alpha + beta) family of helix-turn-helix proteins.

RNA editing alters pre-mRNA through site-selective adenosine deamination, which results in codon changes that lead to the production of novel proteins. An enzyme that catalyzes this reaction, double-stranded RNA adenosine deaminase (ADAR1), contains two N-terminal Z-DNA-binding motifs, Zalpha and Zbeta, the function of which is as yet unknown. In this study, multidimensional NMR spectroscopy was used to show that the topology of Zalpha is alpha1beta1alpha2alpha3beta2beta3. Long-range NOEs indicate that beta1 and beta3 interact with each other. Site-directed mutagenesis was used to identify residues in alpha3, beta3 and the loop connecting beta2 to beta3 that affect Z-DNA binding. Also identified were 11 hydrophobic residues that are essential for protein stability. Comparison with known structures reveals some similarity between Zalpha and (alpha + beta) helix-turn-helix proteins, such as histone 5 and the family of hepatocyte nuclear factor-3 winged-helix-turn-helix transcription factors. Taken together, the structural and functional data suggest that recognition of Z-DNA by Zalpha involves residues in both the alpha3 helix and the C-terminal beta-sheet.

Adenosine Deaminase↗

PubMed1999

Artifacts in sensitivity-enhanced HSQC.

Proton-proton coupling can generate artifacts in sensitivity-enhanced HSQC spectra. These artifacts appear as cross-peaks involving remote protons. They are caused by relayed coherence transfer during the back-transfer portion of the pulse sequence. We present a product operator analysis of artifact formation and experimental results which demonstrate that the magnitude of these artifacts can exceed 10% of the main peak.

Artifacts↗

PubMed1999

Pilot study to improve health outcomes for medication-induced headache sufferers.

The objectives of this prospective cohort study were to identify and encourage individuals with symptoms consistent with medication-induced headache (MIH) to seek medical help, and to determine the health outcomes of these patients. All community pharmacists (approximately 150) on Newfoundland's Avalon Peninsula were provided with continuing education material on MIH and were asked to display a poster inviting individuals taking analgesics more than two days a week for headache to speak to their pharmacist. Pharmacists were asked to provide a patient information pamphlet to individuals with medication use and symptoms consistent with MIH, to request them to contact a study nurse and to log the number of potential MIH patients encountered. The study nurse supervised the completion of headache and quality of life questionnaires, and advised the subjects to seek help from their family physicians. Forty-six pharmacists returned logs identifying 142 potential MIH subjects: 21 contacted the study nurse, 17 completed the questionnaires and 11 were classified as MIH sufferers. MIH sufferers reported a reduction in headache frequency (P<0.02) and analgesic consumption (P<0.05) when re-interviewed after three months. A health care team approach can improve health outcomes for some MIH sufferers. Further work to evaluate strategies to encourage chronic headache sufferers to seek help is required.

Headache↗

PubMed1997

A model of the structure of HOO-Co.bleomycin bound to d(CCAGTACTGG): recognition at the d(GpT) site and implications for double-stranded DNA cleavage.

BACKGROUND: The bleomycins (BLMs) are a family of natural products used clinically as antitumor agents. In the presence of their required cofactors, iron and oxygen, BLMs bind to and mediate single-stranded and double-stranded DNA cleavage. Recently, two dimensional nuclear magnetic resonance (2D NMR) spectroscopic studies and molecular modeling have provided a picture of how the hydroperoxide form of cobalt BLM A2 (HOO-CoBLM), an analog of 'activated' iron BLM (HOO-FeBLM), binds to a d(GpC) motif and of the basis for both sequence specificity and chemical specificity of DNA cleavage. RESULTS: The solution structure of HOO-CoBLM bound to d(CCAGTACTGG) containing a 'hot spot' for double-stranded DNA cleavage at T5 and T15 is reported using constraints from 2D NMR spectroscopy. The mode of binding and basis for sequence specificity and chemical specificity of cleavage is almost identical to that of a d(GpC) motif. This structure has allowed formulation of a structural model for how a single molecule of FeBLM can mediate a double-stranded DNA cleavage event without dissociation from the DNA. CONCLUSIONS: The structural similarity of HOO-CoBLM bound to d(GpT) in d(CCAGTACTGG) compared to a d(GpC) motif suggests a general paradigm for the binding of HOO-CoBLM to DNA and, by analogy, for the binding of the biological significant entity HOO-FeBLM.

Binding Sites↗

PubMed1997

Structure of an anti-HIV-1 hammerhead ribozyme complex with a 17-mer DNA substrate analog of HIV-1 gag RNA and a mechanism for the cleavage reaction: 750 MHz NMR and computer experiments.

The structure of an anti-HIV-1 ribozyme-DNA abortive substrate complex was investigated by 750 MHz NMR and computer modeling experiments. The ribozyme was a chimeric molecule with 30 residues-18 DNA nucleotides, and 12 RNA residues in the conserved core. The DNA substrate analog had 17 residues. The chimeric ribozyme and the DNA substrate formed a shortened ribozyme-abortive substrate complex of 47 nucleotides with two DNA stems (stems I and III) and a loop consisting of the conserved core residues. Circular dichroism spectra showed that the DNA stems assume A-family conformation at the NMR concentration and a temperature of 15 degrees C, contrary to the conventional wisdom that DNA duplexes in aqueous solution populate entirely in the B-form. It is proposed that the A-family RNA residues at the core expand the A-family initiated at the core into the DNA stems because of the large free energy requirement for the formation of A/B junctions. Assignments of the base H8/H6 protons and H1' of the 47 residues were made by a NOESY walk. In addition to the methyl groups of all T's, the imino resonances of stems I and III and AH2's were assigned from appropriate NOESY walks. The extracted NMR data along with available crystallographic data, were used to derive a structural model of the complex. Stems I and III of the final model displayed a remarkable similarity to the A form of DNA; in stem III, a GC base pair was found to be moving into the floor of the minor groove defined by flanking AT pairs; data suggest the formation of a buckled rhombic structure with the adjacent pair; in addition, the base pair at the interface of stem III and the loop region displayed deformed geometry. The loop with the catalytic core, and the immediate region of the stems displayed conformational multiplicity within the NMR time scale. A catalytic mechanism for ribozyme action based on the derived structure, and consistent with biochemical data in the literature, is proposed. The complex between the anti HIV-1 gag ribozyme and its abortive DNA substrate manifests in the detection of a continuous track of A.T base pairs; this suggests that the interaction between the ribozyme and its DNA substrate is stronger than the one observed in the case of the free ribozyme where the bases in stem I and stem III regions interact strongly with the ribozyme core region (Sarma, R. H., et al. FEBS Letters 375, 317-23, 1995). The complex formation provides certain guidelines in the design of suitable therapeutic ribozymes. If the residues in the ribozyme stem regions interact with the conserved core, it may either prevent or interfere with the formation of a catalytically active tertiary structure.

Catalysis↗

PubMed1996

Prescribing practices for the management of headache in Newfoundland and Labrador.

To assess the impact of sumatriptan in clinical practice, we undertook a retrospective analysis of the government of Newfoundland and Labrador's prescription drug program data base for 35 consecutive patients prescribed sumatriptan. The number of doses of all drugs prescribed ranged from 121 to 18,874 on from 4 to 357 prescriptions per patient over 1 to 19 months. The mean number of doses of analgesic drugs prescribed before sumatriptan therapy was 56 per month and after initiation of sumatriptan was 46 per month. The prescribing of multiple analgesics was common; 79% received three or more different analgesics. Twenty-two (63%) patients were prescribed medications indicated for the prophylaxis of migraine concomitantly with drugs indicated for symptomatic treatment. Twenty-four (69%) patients were prescribed medication capable of inducing migraine. We conclude that sumatriptan did not have a major impact on the outcomes of these patients judged by their use of analgesics. The simplest explanation is that many of the patients were suffering from analgesic-induced headache rather than migraine. In addition, we conclude that there were deficiencies in prescribing practices including numbers, quantities, and choice of analgesics; the use of analgesics concomitantly with drugs indicated for migraine prophylaxis; and the use of drugs capable of inducing migraine. Further research is required to validate these findings.

Analgesics↗

PubMed1995

Health risk appraisals: the issues surrounding use in the workplace.

1. Health risk appraisals have been used effectively to measure the likelihood of individuals developing preventable or chronic diseases over time. The components of an HRA include the questionnaire, the risk estimation, and the educational messages or reports. 2. The typical uses of HRA are for needs assessment, health education, and gate-keeping/incentive programs. 3. To select the best HRA for a particular setting, obtain support from management and develop clear program objectives. The HRA has some limits, but careful planning can decrease these problems. 4. The occupational health nurse's role can include: eliciting support from management, developing objectives to achieve a comprehensive health promotion program, coordinating the program's operational aspects, generating and analyzing data, and educating clients.

Health Promotion↗

PubMed1991

Combined effects of methylmercury and ethanol on renal metallothionein and mercury residues in rats fed restricted amounts of a liquid diet.

Simultaneous treatment of rats with ethanol (EtOH) and methylmercury (MeHg) increases the frequency of lesions in the rat kidney. Therefore, it was of interest to us to study the effects of simultaneous treatment of rats with MeHg and EtOH on kidney metallothionein (MT) and mercury residues levels in kidneys of rats maintained on 70% of ad libitum diet. Treatment with MeHg alone induced kidney MT the most (twice) compared to its pair-fed control. Simultaneous treatment with MeHg and EtOH also induced kidney MT but to a lesser degree than treatment with MeHg alone (by about 30%). Ethanol by itself caused a slight increase in kidney MT although starvation resulting from pair-feeding with mercury-treated animals may have contributed to this observation. Simultaneous treatment with MeHg and 2 g/kg EtOH caused a significant reduction in inorganic mercury levels in the kidney (P less than 0.05) compared to treatment with MeHg alone or in combination with 1 g/kg EtOH. Corresponding with the decrease in kidney inorganic mercury levels was a significant increase in urine inorganic mercury levels in this group compared to treatment with 1 g/kg ethanol + MeHg.

Animals↗

PubMed1990

Effect of subchronic administration of ethanol and methylmercury in combination on the tissue distribution of mercury in rats.

The effect of oral administration for 14 weeks of 8 g.kg-1.day-1 ethanol and 0.5 mg.kg-1.day-1 methylmercuric chloride in combination to rats fed isocaloric diets has been investigated. Ethanol, in contrast to published studies, failed to influence the tissue distribution of methylmercury and its inorganic mercury metabolite in brain and kidney, and did not inhibit the increase in kidney weight induced by methylmercury. Ethanol and methylmercury, in combination and individually, reduced the renal but not the hepatic activity of gamma-glutamyltransferase, but did not affect the renal and biliary concentration of reduced glutathione. Further study is required to determine the circumstances under which ethanol can influence the tissue distribution of methylmercury and its inorganic mercury metabolite.

Animals↗

PubMed1988

Combined toxicity of ethanol and methylmercury in rat.

The hepatotoxic and nephrotoxic effects of methylmercury (CH3Hg) and ethanol (EtOH) are well known; however, their interaction in vivo is not clearly understood. In order to investigate the combined effects of these 2 substances, 4 groups of male Wistar rats with an initial weight of approximately 190 g were treated for 7 weeks. Each group consisting of 8 rats was gavaged as follows: Group 1 with 5.0 ml/kg body weight of double distilled water, Group 2 with 5.0 ml/kg body weight of 25% EtOH, Group 3 with 2.5 mg/kg of CH3Hg in water, and Group 4 with 2.5 mg/kg of CH3Hg in 25% EtOH. At the termination of the experiment the mean body weights of the rats in Group 3 (372.5 +/- 10.8 S.E.) and Group 4 (383.4 +/- 13.4) were significantly lower than that of Group 1 (433.0 +/- 7.8). Linear regression showed a positive feed conversion efficiency for Groups 1 and 2 (1.07 and 0.83, respectively), and a negative score for this parameter for Groups 3 and 4 (-1.43, -1.53). At necropsy, rat livers from Group 3 exhibited random multifocal tan spots. The relative liver weights were similar to those of controls. Semithin sections of liver revealed an increase in lipid droplets in Groups 2 and 3 compared to those in the other 2 groups while vacuolization was more striking in CH3Hg treated rats (Groups 3 and 4). Severe hepatolysis and portal canal edema were noted in the groups of rats exposed to either EtOH alone or in combination with mercury. The relative weight of left kidney in Group 3 (0.70 +/- 0.03) and Group 4 (0.51 +/- 0.04) rats was significantly greater than that of the control (0.39 +/- 0.03). In gross appearance the kidney was pale and the urine production was significantly higher (P less than 0.05) in Group 3 compared to that of Group 1. Group 4 rats had significantly more (P less than 0.05) Hg in the kidney than Group 3; however, the inorganic percentages in both groups were similar. Morphological examination of the kidney proximal tubules from CH3Hg treated rats (Groups 3 and 4) revealed an increase in lipid droplets, vacuoles, cell sloughing and tubular degeneration compared to Groups 1 and 2. These histological changes in the proximal tubules of Group 4 rats indicate an additive effect of EtOH on the kidney pathology caused by CH3Hg.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗