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Biomedical subjects

W A Gregory

Publications and source records attributed to W A Gregory.

At least 19 recordsLinked to original sources
PubMed1992

Antibacterials. synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 4. Multiply-substituted aryl derivatives.

The synthesis and structure-activity relationship (SAR) studies of the effect of different polysubstitution patterns in the aromatic ring of 5-(acetamidomethyl)oxazolidinone antibacterials (I) on antibacterial activity are presented. Compounds I were prepared by the six-step synthesis described previously (Gregory, W. A.; et al. J. Med. Chem. [formula: see text] 1989, 32, 1673), electrophilic aromatic substitution reactions of 3-substituted compounds, and functional-group interchange reactions of 3,4-disubstituted compounds. Antibacterial evaluation of compounds I against Staphylococcus aureus and Enterococcus faecalis gave the following results. The 2,4- and 2,5-disubstituted derivatives have weak or no antibacterial activity. Antibacterial activities of 3,4-disubstituted compounds are comparable to those of the 4-monosubstituted analogues for small 3-substituents (smaller than Br), but decline rapidly for larger 3-substituents. 3,4-Annulated derivatives are comparable in activity to their open-chain analogues. 3,5-Disubstituted and 3,4,5- and 2,4,6-trisubstituted derivatives are devoid of antibacterial activity.

Anti-Bacterial Agents↗
PubMed1992

Physical properties and repair bond strength of direct and indirect composite resins.

Use of composite resins now includes indirect curing methods. Surface chemistry, repair bond strength, plus location of failure and five physical properties of two direct and three indirect composite resins were determined. There were statistically significant differences in flexural strength of materials and in hardness values. Repair bond strength failures were not significantly different; failures occurred primarily at the interface. Multiple internal reflection spectroscopy confirmed the presence of unpolymerized material after cure in all products. Indirect cure of the direct composite resin increased the degree of cure.

Absorption↗
PubMed1992

Effect of slow-release chlorhexidine mouthguards on the levels of selected salivary bacteria.

This study evaluated the effect of an alternate delivery system for chlorhexidine on salivary levels of mutans streptococci (MS) and other selected oral bacteria. On the basis of salivary MS levels > or = 10(4) CFU/ml, 22 subjects were enrolled. All caries lesions were restored prior to treatment. Two pretreatment paraffin-stimulated saliva samples were obtained for culturing at least 1 week apart. Complete-arch vacuum-adapted mouthguards were individually fabricated and coated internally with a 3% w/v chlorhexidine varnish. Mouthguards were worn for an average of 7 h/night for 7 nights. Saliva samples were obtained immediately after treatment and 1 and 3 months later. There was no significant change in levels of any of the monitored bacteria between the two pretreatment samples. A significant and specific reduction in salivary MS levels was observed in the three after-treatment samples as compared with baseline values (p < 0.001, p < 0.001, p < 0.05, respectively). The levels of Actinomyces viscosus were also measured, and there was a significant reduction immediately after treatment (p < 0.05), a return to baseline values at 1 month, and a significant increase above baseline values at 3 months, (p < 0.001). There was no significant change in saliva volume, in total numbers of facultatively anaerobic bacteria, or in levels of lactobacilli or Streptococcus sanguis. This treatment system is capable of significant and specific suppression of MS levels for up to 3 months without retreatment.

Actinomyces viscosus↗
PubMed1991

Phthalocyanine photodynamic therapy of experimental iris neovascularization.

Photodynamic therapy using chloroaluminum sulfonated phthalocyanine (CASPc) effectively closed experimental iris neovascularization induced in 6 eyes of cynomolgus monkeys by argon laser retinal vein occlusion. Neovascularization was followed by iris photography, fluorescein angiography, and histopathologic examination by light and electron microscopy. Intravenous injection of CASPc followed by irradiation with 675 nm light damaged endothelial cells and pericytes, leading to exposure of the basal lamina and thrombotic occlusion of the blood vessels. Surrounding tissue appeared preserved without evidence of thermal damage. Resorption of occluded vessels by macrophages began 2 to 3 days after photodynamic therapy. Neovascularization reappeared 7 days after photodynamic therapy, probably representing growth of new vessels. Photodynamic therapy with CASPc may be a useful adjunct in the treatment of iris neovascularization. The model is useful in elucidating the ultrastructural changes observed after photodynamic therapy using phthalocyanines.

Aluminum↗
PubMed1991

Effects of intra-core mechanical interlocks and cement type on full crown retention.

This study compared the retention of full cast crowns over cores of amalgam or a Bis-GMA composite resin when cemented with a Bis-GMA composite resin cement or a zinc phosphate cement. The surfaces of two groups of Bis-GMA composite cores were mechanically altered with a groove or dimples to provide physical retention; two other groups were either etched with 1.23% acidulated phosphate fluoride (APF) or exposed to a zinc oxide-eugenol interim luting agent before crown cementation. Control groups of unaltered composite or amalgam core served as comparison standards. The zinc phosphate cement provided significantly greater retention with the amalgam core than with any of the composite cores. The APF-treated composite cores had the least retention of any of the zinc phosphate cementations. Cementation failure over the composite cores was at the core surface. Crown retention over the control and dimpled-surface composite core with the resin cement was twice that with zinc phosphate, and significantly greater than retention of castings cemented with the resin cement over amalgam cores. Retention over amalgam cores was significantly greater with zinc phosphate cement than with the composite resin cement.

Bisphenol A-Glycidyl Methacrylate↗
PubMed1990

Bond strengths of chemically dissimilar repaired composite resins.

Expanded use of composite resins has necessitated repair of fractured, discolored, and former restorations. Laboratory investigations have demonstrated that new composite resin can be bonded to cured composite resin of the same chemistry. The surface chemistry of three composite resins of dissimilar matrix formulae were examined by infrared spectroscopy and the tensile bond strengths of heterogeneous repairs and the site of repair failures were determined.

Analysis of Variance↗
PubMed1990

Antibacterials. Synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 2. The "A" group.

The synthesis and structure-activity relationship (SAR) studies of the effect of varying the "A" group in a series of 5-(acetamidomethyl)oxazolidonone antibacterials (2) are described. Compounds 2 were principally prepared either by the six-step synthesis described previously (J. Med. Chem. 1989, 32, 1673) or by elaboration of the synthetic intermediate 2 (A = H) via electrophilic aromatic substitution or elaboration of the intermediate 2 (A = I) by transition metal catalyzed carbon-carbon bond-forming reactions. Antibacterial evaluation of compounds 2 with A = alkyl, ethenyl, ethynyl, hydroxyalkyl, aldo and keto, oximinoakyl, carboalkoxy, nitro, amino, halo and psi-halo, alkylthio, alkylsulfinyl, and alkysulfonyl against Staphylococcus aureus and Enterococcus faecalis led to the identification of several SAR trends. In several series of homologues (alkyl, ketyl, aximinoalkyl, amino, halo and psi-halo, and alkythio), antibacterial activity increased with increasing lipophilicity. But in series with where A is a substituent with a trior tetrasubstituted (substituent larger than H) quaternary atom attached directly to the aromatic ring (hydroxyalkyl, alkylsulfinyl, alkylsufonyl), the activity peaked at the member of the series with the "tert-butyl" connectivity pattern. Conjugated electron-withdrawing substituents also had increased activity relative to nonconjugated analogues of comparable lipophilicity.

Anti-Bacterial Agents↗
PubMed1990

Interim luting agents, composite core surface hardness and retention of interim and final restorations.

This study compared the effects of ZOE interim cement on the retention of interim acrylic and final cast crowns (cemented with zinc phosphate) over cores of current conventional and hybrid composite resin formulae, and a non-eugenol interim cement (NOG) and a calcium hydroxide liner (CaOH2) on interim and final retention values over hybrid cores. Results were compared to retention of cast crowns over amalgam cores. Retention was measured with an Instron Testing Machine. Location of cement failure during separation was recorded. Surface hardness of each group was compared. Retention of cast crowns cemented with zinc phosphate over amalgam cores was significantly higher than that of any of the resin core groups (ANOVA, P less than 0.05, Sheffe Contrast). There was no significant difference in final casting retention cemented over hybrid or conventional resin cores exposed to ZOE (13.625 vs 14.125 Kg). Final casting retention differences were not significant between the three interim cement groups. Final retention of all groups exposed to an interim luting agent were significantly less than the composite control groups. The use of CaOH, as an interim luting agent for acrylic crowns over hybrid cores compared to ZOE or NOG, should afford significantly greater retention with no adverse effect on the retention of the final casting. While the surface hardness of both types of composite resin was adversely affected by exposure to interim luting agents as compared to controls, there was no correlation between final casting retention values and surface hardness of polished composite. The interim cements invariably failed at the interim acrylic crown interface while the zinc phosphate cement failed at the core interface.

Acrylic Resins↗
PubMed1989

Antibacterials. Synthesis and structure-activity studies of 3-aryl-2-oxooxazolidines. 1. The "B" group.

The synthesis and structure/activity studies of the effect of varying the "B" group in a series of oxazolidinone antibacterials (I) are described. Two synthetic routes were used: (1) alkylation of aniline with glycidol followed by dialkyl carbonate heterocyclization to afford I (A = H, B = OH), whose arene ring was further elaborated by using electrophilic aromatic substitution methodology; (2) cycloaddition of substituted aryl isocyanates with epoxides to give A and B with a variety of values. I with B = OH or Br were converted to other "B" functionalities by using SN2 methodology. Antibacterial evaluation of compounds I with A = acetyl, isopropyl, methylthio, methylsulfinyl, methylsulfonyl, and sulfonamido and a variety of different "B" groups against Staphylococcus aureus and Enterococcus faecalis concluded that the compounds with B = aminoacyl, and particularly acetamido, were the most active of those examined in each A series, possessing MICs in the range of 0.5-4 micrograms/mL for the most active compounds described.

Anti-Bacterial Agents↗
PubMed1989

cAMP delays disappearance of gap junctions between pairs of rat hepatocytes in primary culture.

Freshly isolated adult rat hepatocytes were found to be coupled through gap junctions, but coupling decreased abruptly 5-8 h after plating the cells on plastic culture dishes in physiological saline containing insulin and fetal calf serum. Loss of intercellular coupling was associated with disappearance of 27-kDa gap junction protein and of gap junctions seen by electron microscopy or immunocytochemistry. This disappearance of coupling was delayed approximately 8 h by treatment of the cultures with membrane permeant adenosine 3',5'-cyclic monophosphate (cAMP) [but not guanosine 3',5'-cyclic monophosphate (cGMP)] derivatives. Levels of gap junction protein and anatomically identified junctions were also maintained by 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP). Level of mRNA encoding the gap junction protein was maintained longer in cells treated with 8-BrcAMP than in untreated cells, but 8-BrcAMP did not detectably increase the transcription rate. Thus prolongation of coupling must result at least partially from extension of the lifetime of gap junction mRNA, allowing translation of message and assembly of channels for a longer period after plating. Treatment of cells with mRNA or protein synthesis inhibitors (alpha-amanitin and cycloheximide) prolonged coupling to a similar extent as did treatment with 8-BrcAMP. alpha-Amanitin blocked transcription of gap junction mRNA, but levels of cytoplasmic mRNA encoding the 27-kDa gap junction protein were maintained, presumably by block of transcription of an mRNA degrading factor. The factor is probably a protein, since a similar effect on mRNA level was produced in cycloheximide-treated cells. Cells cultured in control medium were also observed to flatten as they became uncoupled, whereas cells cultured for as long as 16 h in elevated 8-BrcAMP remained round and well coupled. The correlation between shape and coupling strength was not obtained after treatment with the microtubule stabilizing agent, taxol, which maintained the spherical shape of the cells but did not delay the disappearance of dye coupling. Nocodazole, which blocks microtubule formation, also maintained the spherical shape of the cells but delayed the disappearance of dye coupling. In addition to gating by covalent modification or other mechanisms, hormones and drugs that alter the intracellular cAMP concentration may affect intercellular communication by changing the lifetime of the mRNA encoding the main gap junction protein, thereby decreasing or increasing its synthesis. In addition, cAMP may act by decreasing removal of junctions from appositional membranes.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1989

Quantitative evaluation of approximal contacts in Class 2 composite resin restorations: a clinical study.

The purpose of this study was to develop an accurate and reproducible intraoral method of measuring the distance between two teeth, and to conduct a clinical pilot study of the effect of placement of a class 2 posterior resin restoration upon this intertooth dimension. A Kaman Sciences KD-2611 noncontact displacement measuring system with a 1U unshielding sensor, based upon the variable resistance of eddy current, was used for the intraoral measurement. Seven patients requiring conservative interproximal restorations (initial placements or replacements) on the premolars were selected. Addition silicone impressions were taken of the posterior quadrants from which low-fusing metal (Cerrolow-136) casts were made. Composite resin copings constructed on modified rubber dam clamps were fabricated for the restoration and adjacent teeth upon these metal casts. Aluminum targets and Plexiglas holders for the sensor were attached to the bow of the rubber dam clamp with light-activated composite resin. Quantitative measurements of intertooth distance were made preoperatively, postoperatively, and at one-week and 4 1/2-month recalls after placement of class 2 composite resin restorations for 11 teeth. Four unrestored premolars served as a control. The data were tabulated and analyzed using one-way analysis of variance. The results indicated that the mean postoperative intercoping distance for restored teeth increased after a multiple wedging technique had been applied during restorative procedure. At the one-week recall, these distances had decreased. The 4 1/2-month measurements showed a further decrease with an average loss of 15 microns from the preoperative baseline.

Analysis of Variance↗
PubMed1988

Satellite glial cells penetrate neurosecretory cells to perinuclear position in the goldfish preoptic area.

Some goldfish neurosecretory cells have plasma membrane invaginations filled by processes of surrounding satellite glial cells (SCs) that produce trophospongium-like multicellular neuron-glial aggregates. Some penetrating SC processes approach the neuronal nucleus, reaching to within approximately 40 nm of the outer nuclear membrane. Gap junctions were found in one freeze-fracture replica through an apparent neuronal-glial aggregate, suggesting that neuron-glial gap junctions may be present. The extensive covering and penetration of these neurons by SCs suggests trophic relationships and communication by undetermined modalities between neurons and glia. The common close proximity of invaginated SC processes to the neuronal nucleus may indicate that information is transmitted between SCs and the nucleus. Some SCs abut against the basal lamina of large blood vessels and contain dense vesicles, either secretory or lysosomal.

Animals↗
PubMed1988

Neuronal and glial gap junctions in the goldfish preoptic area, a thin section and freeze-fracture study.

In freeze-fracture, both large macular gap junctions and long thin gap junctions surrounded by a strand of tight junction were found on neurosecretory cells. Preoptic neurons show large areas of soma-to-soma apposition, but thin section showed no evidence for gap junctions between neuronal somata. Neurosecretory cell neurites formed parallel bundles in neuropil lateral to the nucleus, and gap junctions were found between the neurites. These junctions apparently correspond to macular junctions seen on neurosecretory elements in freeze-fracture. Some large macular gap junctions found in freeze-fracture presumably correspond to junctions seen between glial cells in thin section. However, glial membranes lacked characteristics distinguishing them from neuronal membranes. In one instance, a large apparent glial sheet process formed both macular and long thin gap junctions on different surfaces. The long thin gap junctions that were surrounded by a strand of tight junction were formed with a large neurosecretory cell soma. Extensive pinocytosis was observed at some membranes forming gap junctions.

Animals↗
PubMed1988

Gap junctions in goldfish preoptic ependyma: regional variation in cellular differentiation.

Ependyma adjacent to the goldfish preoptic neurosecretory nucleus was examined with transmission electron microscopy. Ependymal cells adjoining the rostroventral end of the nucleus were spindle-shaped with their long axes perpendicular to the ventricular surface. Gap junctions and desmosomes were common near the apical (ventricular) ends of these cells, and less frequent laterally in the ependymal layer. Ependymal cells in more caudodorsal preoptic regions (adjacent to large neurosecretory cells) were progressively more pleomorphic. The frequent occurrence of apparently internalized gap junctions and of gap junction fragments enclosed within lysosome-like organelles indicated extensive turnover of these junctions, or uncoupling. Ependymal cells in the caudodorsal region formed gap junctions on their lateral and basal (abluminal) surfaces with glial processes containing bundles of intermediate filaments. Subependymally, these processes (presumptive radial glia) were parallel to one another and coupled together by gap junctions. Neurites containing dense core vesicles occasionally invaginated into ependymal cells in the caudal region, but did not appear to form gap junctions. Previous observations indicate continuing maturation and growth of the goldfish preoptic area with neurosecretory cell formation rostroventrally and a rostroventral to caudodorsal gradient of maturation. The present findings suggest a parallel and related gradient in preoptic ependyma. Ependymal cell differentiation possibly involves loss of gap junctions, and radial migration or differentiation into underlying neurons and glia.

Animals↗