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Biomedical subjects

J A O'Brien

Publications and source records attributed to J A O'Brien.

At least 73 records · Page 4Linked to original sources
PubMed1991

Pyridinone derivatives: specific human immunodeficiency virus type 1 reverse transcriptase inhibitors with antiviral activity.

Derivatives of pyridinones were found to inhibit human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT) activity and prevent the spread of HIV-1 infection in cell culture without an appreciable effect on other retroviral or cellular polymerases. 3-[( (4,7-Dimethyl-1,3-benzoxazol-2-yl) methyl]amino ]-5-ethyl-6-methylpyridin-2(1H)-one (L-697,639) and 3-[[ (4,7-dichloro-1,3-benzoxazol-2-yl) methyl]amino]-5-ethyl-6-methylpyridin-2(1H)-one (L-697,661), two compounds within this series, had HIV-1 RT IC50 values in the range of 20-800 nM, depending upon the template-primer used. The most potent inhibition was obtained with rC.dG and dA.dT as template--primers. With rC.dG, reversible slow-binding non-competitive inhibition was observed. [3H]L-697,639 bound preferentially to enzyme-template-primer complexes. This binding was magnesium-dependent and saturable with a stoichiometry of 1 mol of [3H]L-697,639 per mol of RT heterodimer. Displacement of [3H]L-697,639 was seen with phosphonoformate. In human T-lymphoid-cell culture, L-697,639 and L-697,661 inhibited the spread of HIV-1 infection by at least 95% at concentrations of 12-200 nM. Synergism between 3'-azido-3'-deoxythymidine or dideoxyinosine and either of these compounds was also demonstrated in cell culture. Based upon their specificity for HIV-1 RT activity, template-primer dependence on potency and ability to displace [3H]L-697,639; a tetrahydroimidazo [4,5,1-jk] [1,4]-benzodiazepin-2(1H)-thione derivative R82150 and the dipyridodiazepinone BI-RG-587 appear to inhibit RT activity by the same mechanism as the pyridinones.

Antiviral Agents↗
PubMed1991

Primary cultures of guinea-pig gall-bladder epithelial cells suitable for patch-clamp studies.

Cells derived from explants of guinea-pig gall-bladder maintained in culture for up to 14 days, exhibit a network of cytoskeletal filaments that are labelled by an anti-cytokeratin antibody, but not by an anti-desmin antibody, suggesting that they are of epithelial origin. These cells proved suitable for patch-clamp studies and by using this method channels selective for K+ and Cl- were observed.

Animals↗
PubMed1991

Viral resistance to human immunodeficiency virus type 1-specific pyridinone reverse transcriptase inhibitors.

Human immunodeficiency virus type 1 (HIV-1)-specific pyridinone reverse transcriptase (RT) inhibitors prevent HIV-1 replication in cell culture (M. E. Goldman, J. H. Nunberg, J. A. O'Brien, J.C. Quintero, W. A. Schleif, K. F. Freund, S. L. Gaul, W. S. Saari, J. S. Wai, J. M. Hoffman, P. S. Anderson, D. J. Hupe, E. A. Emini, and A. M. Stern, Proc. Natl. Acad. Sci. USA 88:6863-6867, 1991). In contrast to nucleoside analog inhibitors, such as AZT, which need to be converted to triphosphates by host cells, these compounds act directly to inhibit RT via a mechanism which is noncompetitive with respect to deoxynucleoside triphosphates. As one approach to define the mechanism of action of pyridinone inhibitors, we isolated resistant mutants of HIV-1 in cell culture. Serial passage in the presence of inhibitor yielded virus which was 1,000-fold resistant to compounds of this class. Bacterially expressed RTs molecularly cloned from resistant viruses were also resistant. The resistant RT genes encoded two amino acid changes, K-103 to N and Y-181 to C, each of which contributed partial resistance. The mutation at amino acid 181 lies adjacent to the conserved YG/MDD motif found in most DNA and RNA polymerases. The mutation at amino acid 103 lies within a region of RT which may be involved in PPi binding. The resistant viruses, although sensitive to nucleoside analogs, were cross-resistant to the structurally unrelated RT inhibitors TIBO R82150 (R. Pauwels, K. Andries, J. Desmyter, D. Schols, M. J. Kukla, H. J. Breslin, A. Raeymaeckers, J. Van Gelder, R. Woestenborghs, J. Heykanti, K. Schellekens, M. A. C. Janssen, E. De Clercq, and P. A. J. Janssen, Nature [London] 343:470-474, 1990) and BI-RG-587 (V. J. Merluzzi, K. D. Hargrave, M. Labadia, K. Grozinger, M. Skoog, J. C. Wu, C.-K. Shih, K. Eckner, S. Hattox, J. Adams, A. S. Rosenthal, R. Faanes, R. J. Eckner, R. A. Koup, and J. L. Sullivan, Science 250:1411-1413, 1990). Thus, these nonnucleoside analog inhibitors may share a common binding site on RT and may all make up a single pharmacologic class of RT inhibitor. This observation may have important implications for the clinical development of these compounds.

Amino Acid Sequence↗
PubMed1990

Lung cancer at Groote Schuur Hospital--a local perspective.

Over a 1-year period (1 January 1987-31 December 1987) 401 patients at Groote Schuur Hospital with newly diagnosed lung cancer were evaluated prospectively. The mean age of the patients was 59 years (range 31-87 years); 251 were coloured (62%), 100 white (25%), 47 black (12%) and 3 Asian (1%), and 280 were men (70%). Smokers numbered 378 (95%). The median delay between the onset of symptoms and presentation was 13 weeks (range 0-65 weeks). The commonest cell type was squamous--127 patients (34%), followed by adenocarcinoma 84 (23%), undifferentiated 78 (21%), small-cell 48 (13%), large-cell 29 (8%) and other types in 5 (1%). At the time of diagnosis 228 patients (57%) had evidence of metastases. Forty-six patients (11%) underwent surgery, 46 (11%) received chemotherapy, 141 (35%) radiotherapy and 168 (42%) symptomatic treatment as initial management. The overall 1- and 2-year survival rates were 18% and 8% respectively.

Adult↗
PubMed1989

Uptake of the 35 kDa major surfactant apoprotein (SP-A) by neonatal rabbit lung tissue.

Secreted surfactant is made up of both phospholipid and protein components. Therefore, we investigated the possibility that surfactant apoproteins might be taken up by the alveolar type II cell in a manner similar to the uptake of surfactant phosphatidylcholines. Day 2 neonatal rabbits were infused via the trachea with a solution of carrier surfactant and 125I-labelled surfactant apoprotein (SP-A, Mr approx. 35,000). Most of the 125I-SP-A remained within the alveolus; however, a fraction of the 125I-SP-A was taken up by the lung tissue from the alveolus in a time-dependent manner. The small amount of radiolabeled material detected in blood, liver or kidney tissues of 125I-SP-A-infused animals was not trichloroacetic acid (TCA) precipitable, i.e., probably represented degradation products. In contrast, the proportion of TCA-precipitable 125I-SP-A in lung tissue or lavage samples did not change as function of time after tracheal administration. Two-dimensional gel electrophoresis of the 125I-SP-A present in the lavage samples or associated with lung tissue was used to show that a small proportion of the 125I-SP-A was partially degraded in the lung tissue and alveolus. These data are suggestive that the SP-A is taken up by lung tissue, perhaps in a manner similar to the uptake of surfactant phospholipid by the alveolar type II cell.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1988

Activation of basolateral membrane K+ permeability by bradykinin in MDCK cells.

We study bradykinin-stimulated K+ efflux in Madin-Darby canine kidney (MDCK) cells using 86Rb as an isotopic tracer. Bradykinin brings about a rapid increase in the permeability of MDCK cells to K+, the effect is dose-dependent with a plateau at 10(-6) M. The effect seems to be mediated by Ca2+-activated K+ channels, localised at the basolateral aspect of the epithelium. Unlike alpha-receptors, which mediate a similar effect of adrenalin in these cells, bradykinin receptors seem to be present at both sides of the epithelium. Bradykinin increases the labelling of IP3, and bradykinin-stimulated K+ efflux persists even in cells which are bathed in Ca2+-free medium, suggesting that the effects seen in the present work are probably due to Ca2+ release from intracellular stores. Some extracellular Ca2+ also might be involved in the bradykinin effect, consistent with the kinin-increasing membrane permeability to Ca2+.

Animals↗
PubMed1988

An investigation of the effectiveness of certain antioxidants in preserving the motility of reactivated bull sperm models.

Bull sperm that had been disrupted by freezing and thawing were reactivated with 1 mM Mg-adenosine 5'-triphosphate. The antioxidants superoxide dismutase, catalase, dithiothreitol, and reduced glutathione (GSH) were tested for their ability to prolong the motility of the reactivated sperm. GSH was employed both by itself and as part of a reducing system that maintained the tripeptide in the reduced form. Three of the test agents were found to increase the duration of motility in the sperm preparations; these were reduced glutathione, dithiothreitol, and superoxide dismutase. Glutathione was the most effective protective agent, yielding reactivated preparations with a half-life for the decay of motility of 2.5 h. While dithiothreitol (DTT) is widely employed as an antioxidant, we found that DTT is measurably less effective than glutathione (half-life of 1.5 h). In spite of glutathione's effectiveness in preserving motility, we have found, by direct assay, that mature bull sperm do not contain detectable amounts of this common biological antioxidant. Our results support the hypothesis that oxidative damage contributes to the loss of motility in reactivated sperm and suggest that oxidation could be a factor in motility loss in living sperm.

Adenosine Triphosphate↗
PubMed1988

The concentration of the 35-kDa surfactant apoprotein in amniotic fluid from normal and diabetic pregnancies.

A specific, enzyme-linked immunoabsorbent assay was used to determine the concentration of the 35,000 mol wt surfactant apoprotein (SP-A) in samples of amniotic fluid obtained from nondiabetic (n = 358) and diabetic (n = 29) women. The enzyme-linked immunoabsorbent assay was performed with rabbit antibodies directed against SP-A present in lavage fluid from a patient with alveolar proteinosis. Amniotic fluid SP-A concentrations increased as a function of gestational age, from less than 3 micrograms/ml at 30-31 wk to 24 micrograms/ml at 40-41 wk, and were positively correlated with the lecithin to sphingomyelin ratio (p less than 0.01). SP-A concentrations also increased as a function of gestational age in shake test positive samples (p less than 0.05), but were unchanged in shake test-negative samples. There was no difference in the surfactant apoprotein concentration of male compared with female fetuses at any gestational age. In amniotic fluid obtained from 20 diabetic women, SP-A levels were significantly less than in nondiabetic pregnancies that were matched for gestational age and sex of the fetus (p less than 0.05). The SP-A concentrations in amniotic fluids obtained from nine women who were diabetic and hypertensive and from 10 hypertensive women were not different from matched controls. The relationships described above were valid whether the SP-A concentration was expressed per mg protein or per ml amniotic fluid. These data are suggestive that the concentration of amniotic fluid SP-A is decreased in diabetic pregnancies.

Amniotic Fluid↗