Search PubMed⌕ Search

Biomedical subjects

D Bell

Publications and source records attributed to D Bell.

At least 91 records · Page 5Linked to original sources
PubMed1996

Peptidoglycan synthesis and structure in Staphylococcus haemolyticus expressing increasing levels of resistance to glycopeptide antibiotics.

The structures of cytoplasmic peptidoglycan precursor and mature peptidoglycan of an isogenic series of Staphylococcus haemolyticus strains expressing increasing levels of resistance to the glycopeptide antibiotics teicoplanin and vancomycin (MICs, 8 to 32 and 4 to 16 microg/ml, respectively) were determined. High-performance liquid chromatography, mass spectrometry, amino acid analysis, digestion by R39 D,D-carboxypeptidase, and N-terminal amino acid sequencing were utilized. UDP-muramyl-tetrapeptide-D-lactate constituted 1.7% of total cytoplasmic peptidoglycan precursors in the most resistant strain. It is not clear if this amount of depsipeptide precursor can account for the levels of resistance achieved by this strain. Detailed structural analysis of mature peptidoglycan, examined for the first time for this species, revealed that the peptidoglycan of these strains, like that of other staphylococci, is highly cross-linked and is composed of a lysine muropeptide acceptor containing a substitution at its epsilon-amino position of a glycine-containing cross bridge to the D-Ala 4 of the donor, with disaccharide-pentapeptide frequently serving as an acceptor for transpeptidation. The predominant cross bridges were found to be COOH-Gly-Gly-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Gly-Gly-NH2. Liquid chromatography-mass spectrometry analysis of the peptidoglycan of resistant strains revealed polymeric muropeptides bearing cross bridges containing an additional serine in place of glycine (probable structures, COOH-Gly-Ser-Ser-Gly-Gly-NH2 and COOH-Ala-Gly-Ser-Ser-Gly-NH2). Muropeptides bearing an additional serine in their cross bridges are estimated to account for 13.6% of peptidoglycan analyzed from resistant strains of S. haemolyticus. A soluble glycopeptide target (L-Ala-gamma-D-iso-glutamyl-L-Lys-D-Ala-D-Ala) was able to more effectively compete for vancomycin when assayed in the presence of resistant cells than when assayed in the presence of susceptible cells, suggesting that some of the resistance was directed towards the cooperativity of glycopeptide binding to its target. These results are consistent with a hypothesis that alterations at the level of the cross bridge might interfere with the binding of glycopeptide dimers and therefore with the cooperative binding of the antibiotic to its target in situ. Glycopeptide resistance in S. haemolyticus may be multifactorial.

Amino Acid Sequence↗
PubMed1996

Molecular epidemiology in environmental carcinogenesis.

Molecular epidemiology has significant potential in preventing cancer and other diseases caused by environmental exposures (related to lifestyle, occupation, or ambient pollution). This approach attempts to prevent cancer by incorporating laboratory methods to document the molecular dose and preclinical effects of carcinogens, as well as factors that increases individual susceptibility to carcinogens. Recently we have carried out validation studies of biologic markers such as carcinogen--DNA and carcinogen--protein adducts, gene and chromosomal mutations, alterations in target oncogenes or tumor suppressor genes, polymorphisms in putative susceptibility genes (individual P450s, glutathione transferase M1), and serum levels of micronutrients. This research involves adults, infants, and children exposed to varying levels of carcinogens, as well as cancer cases and controls. On a group level, dose-response relationships have frequently been seen between various biomarkers and environmental exposures such as polycyclic aromatic hydrocarbons, cigarette smoke (active and passive), and ambient indoor and workplace air pollution. However, there is significant interindividual variation in biomarkers that appears to reflect a modulating effect on biomarkers (hence potential risk) by genetic and acquired susceptibility factors. Ongoing retrospective and nested case-control studies of lung and breast cancer are examining the association between biomarkers and cancer risk. Results of these studies are encouraging; they suggest that biomarkers, once validated, can be useful in identifying populations and individuals at risk in time to intervene effectively.

Biomarkers, Tumor↗
PubMed1996

Malaria in Honiara, Solomon Islands: vector studies.

Adult and larval specimens of anopheline mosquitos were collected throughout eastern Honiara during a study into risk factors for malaria illness in adults. Species identification was by morphology, DNA probes and by PCR. Only Anopheles farauti s.s. were identified from part-night landing catches carried out from 1900 to 2200 hours. Most mosquitos attracted to humans were culicines. The majority of anophelines (85%) were captured between 1900 and 2000 hours. An. farauti s.s. larvae were most common but one An. farauti No. 7, and ten An. punctulatus larvae were also collected.

Adult↗
PubMed1995

Activity of amylin at CGRP1-preferring receptors coupled to positive contractile response in rat ventricular cardiomyocytes.

Calcitonin gene-related peptide (CGRP) exerts a positive contractile response directly in rat ventricular cardiomyocytes. This response is mediated by receptors of the CGRP1-subtype. Amylin is 46% homologous with CGRP and binds to receptors selective for CGRP in a range of tissues. The ability of amylin to influence ventricular contractility has been assessed using cardiomyocytes isolated from the ventricles of adult rats. Cardiomyocytes were subjected to biphasic electrical stimulation at 0.5 Hz. CGRP produced a concentration-dependent positive contractile response which became maximal 4 min after initial stimulation. CGRP increased the contractile amplitude maximally at 1 nM and to a value which was 23.3% greater than in the absence of peptide (EC50 value = 21 pM). Amylin increased the contractile amplitude maximally at 20 nM and to a value which was 17.3% greater than in the absence of peptide (EC50 value = 216 pM). In the presence of amylin (20 nM), the concentration-dependence of the contractile response to CGRP was shifted to the left, so that the response became maximal when CGRP was present at 50 pM. In the presence of CGRP8-37 (100 nM), a selective antagonist at CGRP1-preferring receptors, the concentration-dependence of the contractile response to CGRP was shifted to the right (dose ratio = 54). Similarly, in the presence of CGRP8-37 (100 nM), the contractile response to amylin was inhibited significantly (P < or = 0.01). Amylin8-37 (100 nM) did not inhibit the concentration-dependence of the contractile responses to CGRP and amylin significantly (dose ratios = 4.2 and 2.4, respectively). In conclusion, these data indicate that amylin exerts a contractile response directly in rat ventricular cardiomyocytes via CGRP1-preferring receptors. This effect could assume greater significance in non-insulin-dependent diabetes mellitus and in hypertensive states, in which the concentration of amylin is elevated in plasma.

Amyloid↗
PubMed1995

Further insights into the natural history and management of primary cutaneous neuroendocrine (Merkel cell) carcinoma.

PURPOSE: Primary cutaneous neuroendocrine (Merkel cell) carcinoma is a rare neoplasm with aggressive behavior but potential for response to radiotherapy and chemotherapy. Optimal treatment regimens are evolving based on reports of case series and a growing understanding of the natural history. METHODS AND MATERIALS: A retrospective analysis of 34 cases treated at two Australian Institutions over 13 years is presented, focusing on clinical features and response to therapy. RESULTS: The aggressive nature of this neoplasm is confirmed by the local recurrence rate of 22% following surgical excision, the development of regional node metastases in 76%, and of distant metastases in 70%. Overall median survival was 24 months with 65% of patients succumbing to metastatic disease. An association with B cell malignancies and immunosuppressive therapy is noted, with these patients having a poorer outcome, and one spontaneous remission was observed. Radiation therapy produced responses in 21 of 30 measurable sites (11 complete, 10 partial), and in 11 sites irradiated prophylactically there was only one infield relapse (9%). Responses to chemotherapy were observed in 8 of 20 applications (40%), particularly carboplatin and etoposide given in the setting of regional node disease. CONCLUSION: In this poor prognosis tumor, further investigation of adjuvant radiotherapy and chemotherapy is warranted, as responsiveness of recurrent disease is confirmed. Immunological factors appear important in the natural history, and their manipulation may offer additional therapeutic options.

Adult↗
PubMed1995

Hypertrophic effects of calcitonin gene-related peptide (CGRP) and amylin on adult mammalian ventricular cardiomyocytes.

Calcitonin gene-related peptide (CGRP), a neuropeptide localized in the cardiac autonomic nervous supply, shares 46% similarity in sequence of amino acids with amylin, a peptide synthesized in pancreatic beta-cells. In the present study, the question was addressed whether these peptides could exert hypertrophic effects in cardiomyocytes isolated from the ventricles of adult rats and maintained in short-term, serum-free primary culture. FCS (10% v/v), employed as a positive control, increased the incorporation of l-[14C]phenylalanine into cellular protein, total content of cellular RNA and total mass of cellular protein significantly. CGRP and amylin also increased each of these parameters significantly and in a concentration-dependent manner; maximum responses occurred at 100 pM and 10 nM for CGRP and amylin, respectively. The selective antagonist at CGRP1-receptors, CGRP8-37(100 nM), inhibited significantly the incorporation of l-[14C] phenylalanine into cellular protein in response to CGRP and amylin. The selective inhibitor of protein kinase C (PKC), bisindolylmalemide (BIM) (5 microM), reduced significantly the incorporation of l-[14C] phenylalanine into cellular protein in response to phenylephrine (1 microM), employed as a positive control, but did not inhibit the response to insulin (1 unit/ml), employed as a negative control. BIM (5 microM) reduced significantly the responses to FCS (10% v/v), amylin (10 nM) and CGRP (10 pM), but did not inhibit the response to CGRP (100 pM). The activity of protein kinase C in membranes prepared from intact myocytes pre-treated for 10 min with the phorbol ester, phorbol 12-myristate 13-acetate (PMA) (100 nM), employed as a positive control, and CGRP (10 pM) was significantly greater than in membranes prepared from cardiomyocytes not subjected to agonist stimulation. Phenylephrine (1 microM) increased significantly the specific activity of creatine kinase but not of lactate dehydrogenase in day 1 cultures of freshly isolated cardiomyocytes. Significant induction of creatine kinase, but not lactate dehydrogenase, was also stimulated by CGRP and amylin; the maximum responses occurred at 100 pM and 100 nM CGRP and amylin, respectively. In conclusion, CGRP and amylin exert hypertrophic effects directly on ventricular cardiomyocytes from the hearts of adult rats in vitro. These effects are: (1) due to de novo protein synthesis since total content of cellular RNA and incorporation of l-[14C]phenylalanine into cellular protein were also increased; (2) mediated by a common population of CGRP1-preferring receptors at which amylin binds with lower potency: (3) mediated, at least partly, by the activation of PKC; (4) may be associated with a fetal shift in gene expression, characterized by selective induction of creatine kinase.

Age Factors↗
PubMed1995

Inhibition by verapamil and diltiazem of agonist-stimulated contractile responses in mammalian ventricular cardiomyocytes.

Secretin, vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide (CGRP) each exert potent positive contractile responses directly in rat ventricular cardiomyocytes. However, the contractile-coupling mechanisms associated with these responses have not been determined. In the present study, the involvement of L-type calcium channels in the contractile responses elicited by each peptide has been investigated using the selective antagonists at L-type calcium channels, verapamil and diltiazem. Ventricular cardiomyocytes, isolated from the hearts of adult rats, were stimulated to contract at 0.5 Hz in the presence of CaCl2 (2 mM) and adenosine deaminase (5U/ml). Cardiomyocytes were pre-incubated for 3 min prior to stimulation, in the absence of L-type calcium channel antagonist, and in the presence of verapamil (< or = 1 microM) or diltiazem (< or = 1 microM). Verapamil (< or = 1 microM) and diltiazem (< or = 1 microM) inhibited the contractile responses elicited by isoprenaline (100 nM) and forskolin (40 microM), used as positive controls, significantly, and in a concentration-dependent manner, but did not inhibit significantly the contractile response elicited by phenylephrine (2 microM), which was employed as a negative control. Verapamil (< or = 1 microM) and diltiazem (< or = 1 microM) inhibited the contractile responses to secretin (20 nM) and VIP (20 nM) significantly, and in a concentration-dependent manner, but did not inhibit the contractile response to CGRP. These data indicate that the positive contractile responses to secretin and VIP in mammalian ventricular cardiomyocytes involve the influx of calcium ion via L-type calcium channels, while the positive contractile response to CGRP does not.

Animals↗
PubMed1995

Phase II study of high dose epirubicin in combination with cyclophosphamide in patients with advanced breast cancer.

BACKGROUND: Combination chemotherapy for metastatic breast cancer will palliate symptoms in the majority of patients but only a small percentage will have prolonged survival. Higher doses of doxorubicin lead to increased response rates in breast cancer and early studies have shown that epirubicin could be tolerated in higher doses with less relative toxicity than doxorubicin. AIMS: This study was initiated to assess the dose of epirubicin that could be tolerated by escalating its dose while maintaining a fixed dose of cyclophosphamide. Simultaneously tumour response rate, spectrum of toxicities, duration of response and overall survival in patients with metastatic breast cancer were assessed. METHODS: Patients with metastatic breast cancer commenced chemotherapy with a starting dose of epirubicin of 120 milligram per metre squared (mg/m2) and cyclophosphamide 600 mg/m2. The dose of epirubicin was to be escalated or reduced depending on toxicity. RESULTS: Forty female patients were entered into this study and three patients withdrew because of toxicity. Overall tumour response rate was 75% with 27.5% of patients obtaining a complete response. Median time to progressive disease was 35 weeks and median overall survival was 48 weeks, with median survival for complete responders being 103 weeks. Thirty-one (77%) patients completed five or more courses of treatment. Haematological toxicity was the main side effect and 70% of patients required a dose reduction. No patients were eligible for a dose escalation. One patient died as a consequence of neutropenic sepsis. Four (10%) patients had treatment ceased because of decrease in left ventricular ejection fraction and one patient died as a consequence of heart failure. Four patients remain alive. CONCLUSIONS: High dose epirubicin combined with cyclophosphamide is an effective treatment regimen for metastatic breast cancer obtaining higher overall response rates with increased percentage complete responses compared to conventional dose chemotherapy. Although toxicity was increased, high dose chemotherapy was well tolerated and mortality associated with treatment was not increased. No dose escalations of epirubicin were possible and a dose of 90 mg/m2 of epirubicin would be the maximum dose when used in combination with cyclophosphamide. Further trials are required to determine the influence of this high dose therapy on survival duration and whether comparable benefits can be achieved with shorter durations of therapy.

Adenocarcinoma↗
PubMed1995

Vestibular function test anomalies in patients with chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) is distinguished by the new onset of debilitating fatigue that lasts at least 6 months, concomitant with other symptoms to be described later. Many CFS patients complain of disequilibrium, yet the exact type of the balance dysfunction and its function and its location (peripheral vs. central) have not been described. Herein we report results of vestibular function testing performed on 11 CFS patients. These results revealed no predominant pattern of abnormalities. Patients typically performed below average in dynamic posturography testing, with a significant number of falls in the tests requiring subjects to depend heavily on the vestibular system. One patient had abnormal caloric testing, while 3 had abnormally low earth vertical axis rotation (EVA) gains at the higher frequencies tested. As a group, the average gain of EVA was significantly lower than normals in the 0.1 - 1.0 Hz range (p < 0.05). In earth horizontal axis rotation, the CFS group had a higher than normal bias value for the optokinetic (OKN) and eyes open in the dark conditions (p < 0.05), but had normal scores during visual vestibular reflex testing. Five of the 11 subjects had an abnormal OKN bias build up over the course of the run, equal to or actually exceeding the 60 degrees/s target velocity by as much as 14 degrees/s. Altogether, these results are more suggestive of central nervous system deficits than of peripheral vestibular disfunction.

Adult↗
PubMed1995

Effect of triazolam on responses to a cold-water immersion in humans.

Managing alertness of soldiers during sustained operations is a source of serious concern for military unit commanders. A frequently employed strategy is to induce sleep before an operation, especially operations requiring prolonged travel. Sleep-inducing drugs could have an action on thermoregulation through their effect on alertness and a possible direct effect on the brain. The goal of this study was therefore to evaluate the effect of a commonly prescribed triazolam (Halcion) on thermoregulatory responses to cold-water immersion. Eight subjects were immersed twice in 18 degrees C water for up to 90 min in the morning; once after ingesting 0.25 mg triazolam (TRZ) the prior evening, and again after placebo (PLB) treatment. There were no significant differences between trials for mean duration of the immersion, the change in rectal temperature and mean skin temperature. Total metabolic heat production was similar for both conditions: 767 +/- 107 vs. 781 +/- 105 kj.m-2 for TRZ and PLB, respectively. The results should be considered in light of a large variation among the subjects in sensitivity to TRZ, which was unrelated to biometrical characteristics such as surface area-to-mass ratio, lean body mass, % body fat, and physical fitness. Although not statistically significant, there was a trend for a smaller increase in plasma free fatty acid and glycerol concentrations after water immersion with TRZ. The results suggest that the ingestion of a single dose of triazolam 11 h prior to a cold-water immersion is not likely to accelerate the rate of onset of hypothermia. Individual sensitivity, however, may predispose some sensitive subjects to negative effects in this regard.

Adipose Tissue↗
PubMed1994

Use of the cyclic AMP antagonist, Rp-cAMPS, to distinguish between cyclic AMP-dependent and cyclic AMP-independent contractile responses in rat ventricular cardiomyocytes.

Conventional inhibitors of cyclic AMP-dependent protein kinase lack membrane-permeability or selectivity, or both. The Rp diastereomer of adenosine cyclic 3',5'-phosphorothioate, Rp-cAMPS, is a novel membrane-permeable antagonist of cyclic AMP. We have assessed the ability of this compound to distinguish between cyclic AMP-dependent and cyclic AMP-independent contractile responses elicited in ventricular cardiomyocytes isolated from the hearts of adult rats. Cardiomyocytes were stimulated to contract at 0.5 Hz in the presence of calcium ion (2 mM) and adenosine deaminase (5 units/ml). Contractile shortening was expressed as maximum shortening relative to prestimulus cell length (delta L%). In the presence of a maximally-effective concentration of isoprenaline (100 nM), which acts by a cyclic AMP-dependent mechanism, Rp-cAMPS inhibited the contractile response in a concentration-dependent and time-dependent manner. Following preincubation for 30 min with Rp-cAMPS (100 microM), the contractile response to isoprenaline (100 nM) was 14% of that elicited in the absence of this inhibitor. An incubation time of 30 min was chosen for all subsequent studies. Rp-cAMPS (< or = 200 microM) inhibited the contractile response to isoprenaline (100 nM) significantly and in a concentration-dependent manner, but failed to inhibit the contractile responses elicited by phenylephrine (2 microM) and calcium ion (7 mM) which act by cyclic AMP-independent mechanisms. In the presence of Rp-cAMPs (200 microM), the contractile response to isoprenaline (100 nM) was 24% of that in the absence of inhibitor. Rp-cAMPS was used subsequently to investigate the contractile-coupling mechanisms associated with some novel inotropic agents. Rp-cAMPS (< or = 200 microM) also inhibited the contractile responses to secretin (20 nM) and VIP (20 nM) significantly. In the presence of Rp-cAMPS (200 microM), the contractile response elicited by secretin (20 nM) was 19% of that in the absence of inhibitor, while that elicited by VIP (20 nM) was abolished completely. Rp-cAMPS (< or = 200 microM) failed to inhibit the contractile response elicited by CGRP (1 nM). In summary, Rp-cAMPS is a membrane-permeable, selective antagonist of cyclic AMP in ventricular cardiomyocytes and can be used, in conjunction with the bioassay of the intracellular accumulation of cyclic AMP, to distinguish between cyclic AMP-dependent and cyclic AMP-independent contractile coupling mechanisms in these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Deaminase↗
PubMed1994

A reproducible method for identification of human genomic DNA autonomously replicating sequences.

We demonstrate a method for the isolation of autonomously replicating sequences from pools of clones obtained from genomic DNA libraries constructed using affinity purification of cruciform DNA. The selection of autonomously replicating sequences was based on their differential ability to replicate as episomes after transfection of pools of plasmid clones into human HeLa cells. Two separate libraries containing affinity-purified cruciform DNA were used, one prepared from DNA of log phase primary human genital fibroblasts and the other prepared from DNA of log phase SW48 colon adenocarcinoma cells. Representative samples of the entire phage libraries were converted to phagemid clones by filamentous helper phage-mediated mass excision to produce pBluescript libraries in Escherichia coli. Clones were grown up individually and the bacteria pooled into groups of 48 for recovery of plasmid DNA. Plasmid pools of 48 independent clones (120 micrograms total) were then transfected by calcium phosphate coprecipitation onto log phase HeLa cells, which were allowed to grow for 3 days before recovery of plasmid by Hirt lysis. The recovery of plasmid from each transfection was estimated to range from 10 to 60 ng. DpnI digestion was then used to digest plasmids which had not been replicated and therefore retained a bacterial methylation pattern which was sensitive to digestion. We estimated from agarose electrophoresis gels that 40-200 pg of recovered plasmid DNA per transfected pool of DNA was resistant to DpnI and therefore was capable of transforming competent E. coli cells. The DpnI-resistant fraction yielded from one to seven independent clones from each pool, with genomic DNA inserts ranging in size from 0.35 to 3.4 kb.(ABSTRACT TRUNCATED AT 250 WORDS)

DNA↗