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Biomedical subjects

W J O'Brien

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

At least 37 records · Page 2Linked to original sources
PubMed1995

Comparison of scleral tensile strength after transscleral retinal cryopexy, diathermy, and diode laser photocoagulation.

OBJECTIVES: To determine the effect of transscleral diode photocoagulation on the tensile strength of sclera in an experimental rabbit model and to compare it with that of transscleral cryotherapy and diathermy. METHODS: Twenty-four Dutch-belted rabbits received one of the following three treatment modalities in one eye: (1) transscleral cryotherapy, (2) transscleral diathermy, or (3) transscleral diode laser photocoagulation. The opposite eye served as a paired control. Tensile strength measurements of scleral strips excised from areas of treatment were obtained 6 weeks later. RESULTS: No statistically significant difference in mean tensile strength was observed between eyes receiving transscleral cryopexy (n = 7) or transscleral diode photocoagulation (n = 8) and their corresponding, paired, control eyes. In contrast, transscleral diathermy reduced mean scleral tensile strength to 26% of that of the paired control eyes (n = 8, P = .0001). CONCLUSIONS: In this rabbit model, scleral weakening is significant following transscleral diathermy while transscleral cryopexy or transscleral diode photocoagulation produces no significant weakening relative to paired, untreated controls.

Animals↗
PubMed1995

2',5'-oligoadenylate synthetase in interferon-alpha- and acyclovir-treated herpes simplex virus-infected cells.

The 2',5'-oligoadenylate (2-5A) synthetase pathway, induced by interferon-alpha (IFN-alpha), has been shown to be responsible for the antiviral action of IFN-alpha against some viruses. Studies were done to determine the role of this pathway in the anti-herpes simplex virus (HSV) action of IFN-alpha alone or in combination with acyclovir (ACV), a combination that leads to synergistic anti-HSV activity. Treatment of human corneal cells or Vero cells with 100 IU/ml of IFN-alpha induced expression of 2-5A synthetase mRNA and a 10-fold increase in 2-5A synthetase production compared with untreated cells. HSV infection alone did not induce 2-5A synthetase production, but when IFN-alpha-treated cells were infected with HSV, enzyme level was significantly increased (p < 0.05) compared with that in IFN-alpha-treated, uninfected cells. HSV infection actually decreased the level of 2-5A synthetase mRNA in IFN-alpha-treated cells. Although IFN-alpha treatment induced high levels of 2-5A synthetase with or without HSV infection, no activation of the latent endonuclease was detected by specific cleavage of ribosomal RNA. Treatment of infected cells with 5 microM ACV alone or combined with IFN-alpha did not increase 2-5A synthetase or endonuclease activities above those detected in cells not treated with ACV. The data indicate that the 2-5A synthetase pathway was inducible in corneal cells and Vero cells but did not appear to contribute to the anti-HSV activity of IFN-alpha alone or the synergistic activity of IFN-alpha combined with ACV.

2',5'-Oligoadenylate Synthetase↗
PubMed1995

Effect of interferon-alpha on the steady-state levels of thymine, thymidine, guanine, and guanosine metabolites in herpes simplex virus-type 1-infected cells.

Interferon-alpha (IFN-alpha) combined with acyclic guanine analogs synergistically inhibits replication of herpes simplex virus type 1. IFN-alpha treatment influenced the metabolism of exogenously supplied nucleobases and nucleosides in a manner expected to contribute to synergistic activity. IFN-alpha treatment of infected human cornea stromal cells or Vero cells significantly reduced steady-state levels of acid soluble metabolites of thymine, as well as thymidine, that accumulate early during virus replication but did not affect metabolism of thymine and thymidine in uninfected cells. IFN-alpha treatment significantly reduced the ability of uninfected cells to accumulate acid-soluble metabolites from guanine, but not guanosine. The effects of IFN-alpha on nucleobase/nucleoside metabolism could contribute to synergistic antiviral activity by reducing the accumulation of thymidine/thymine metabolites and decreasing the guanine taken into cells.

Acyclovir↗
PubMed1994

Thermal shock resistance of core reinforced all-ceramic crown systems.

The coefficient of thermal expansion of core and veneer porcelains for all ceramic crowns must be compatible to prevent formation of stresses during the firing cycles. The purpose of this study was to use a thermal shock test to evaluate the crazing resistance of six all-ceramic crown systems. The systems tested were: Vita In-Ceram, Vita Hi-Ceram, Dicor veneered with Vitadur N, magnesia core veneered with Ceramco II, magnesia core veneered with Silhouette, and magnesia core veneered with Vita VMK 68. A maxillary central incisor was prepared with 1.0 mm axial and 1.5 mm incisal reduction. Refractory dies were prepared and crowns were fabricated using the manufacturers' recommendations. Six specimens of each system were placed inside a beaker in a furnace at 90 degrees C. After 15 min heat soak, ice water was poured into the beaker through a funnel. The samples were dried in air, reheated, and inspected for crazing using light microscopy. If crazing was observed, this would constitute a failure at a temperature difference (delta T) of 90 degrees C. If no failure occurred, the test was repeated at increasing temperature increments of 10 degrees C until failure. The crazing resistance of each system, expressed as the mean delta T, was: > 200 (Hi-Ceram), 163 +/- 14 (In-Ceram), 152 +/- 19 (Dicor/Vitadur N), 143 +/- 5 (magnesia core/Vita VMK 68), 122 +/- 21 (magnesia core/Silhouette), and 118 +/- 10 (magnesia core/Ceramco II) degrees C. All systems tested resisted crazing due to quenching in ice cold water from 100 degrees C. Systems with lower coefficients of expansion showed significantly greater resistance to thermal shock using ANOVA.

Ceramics↗
PubMed1994

Leucite content of selected dental porcelains.

Leucite is a major crystalline component of dental porcelains. The presence of tetragonal leucite in dental porcelains increases their coefficients of thermal expansion due to its high coefficient of thermal expansion (20-25 x 10(-6)/degrees C). This is particularly useful for those porcelains designed for bonding to precious metals and nickel alloys. The purpose of this study was to determine the leucite content of selected commercial dental porcelains in relation to their coefficient of thermal expansion values. The weight fraction of leucite was determined with quantitative x-ray diffraction using copper as an internal standard. Coefficient of thermal expansion values were determined using a thermal dilatometric analyzer. Five commercial body porcelains were studied. Leucite was not detected in samples of Vitadur N and Duceram LFC. An ANOVA showed that there was a significant difference in the weight fraction of leucite for Silhouette, Ceramco II, and Optec HSP porcelains. Linear regression revealed a correlation (R = 0.91) between weight fraction of leucite and the coefficient of thermal expansion for those samples containing leucite. Duceram LFC, which is recommended by the manufacturer for use with metals and leucite-containing porcelains, had no detectable leucite although the coefficient of thermal expansion was found to be 13.2 +/- 0.4 x 10(-6)/degrees C at 25-472 degrees C. A low glass transition temperature contributed to the high average coefficient of thermal expansion value.

Aluminum Silicates↗
PubMed1994

Ouabain binding kinetics of the rat alpha two and alpha three isoforms of the sodium-potassium adenosine triphosphate.

The Na,K-ATPase has three alpha isoforms which differ in cardiac glycoside sensitivity and tissue distribution. The rodent alpha 1 isoform is relatively resistant to cardiac glycosides, while the alpha 2 and alpha 3 isoforms are quite sensitive. Because both the alpha 2 and alpha 3 isoforms are generally expressed in the same tissue, it has been difficult to differentiate and accurately determine the kinetics of ouabain binding to these isoforms. To more fully understand the interactions of the alpha 2 and alpha 3 isoforms with cardiac glycosides, the association and dissociation rates of ouabain binding were measured in transfected cell lines. cDNA's coding for the rat alpha 2 and alpha 3 isoforms were transfected into NIH 3T3 cells and characterized by Na,K-ATPase activity and [3H]ouabain binding. By individually expressing the alpha 2 and alpha 3 isoforms in ouabain-insensitive NIH 3T3 cells, the ouabain-binding characteristics of each isoform could be accurately determined. The association rate constants of the alpha 2 and alpha 3 isoforms were similar while the dissociation rate constant was 33 times slower for the alpha 3 isoform than the alpha 2 isoform. Calculation of the dissociation constant (Kd) from these rate constants yielded values of 115 and 1.6 nM for rat alpha 2 and alpha 3 isoforms, respectively. Scatchard analysis of the rat alpha 2 isoform produced a similar value for Kd of 37 +/- 9 nM. Inhibition of Na,K-ATPase activity indicates the rodent alpha 1 isoform has an IC50 1000-fold higher than the alpha 2 or alpha 3 isoform at 4.8 x 10(-5) M. The results are consistent with the hypothesis that the order of ouabain affinity between the rat alpha isoforms of the Na,K-ATPase is alpha 3 > alpha 2 >> alpha 1.

3T3 Cells↗
PubMed1994

Traumatic delivery: a risk factor for bleeding during ECMO?

Traumatic delivery is associated with orthopedic, nervous, and soft tissue injuries. Anticoagulation for extracorporeal membrane oxygenation (ECMO) support may predispose to hemorrhage from these birth injuries. A case of delayed hemoperitoneum secondary to hepatic laceration after delivery and ECMO, not previously reported, is detailed herein.

Birth Injuries↗
PubMed1994

Catheter-induced urinary bladder rupture presenting with pneumoperitoneum.

Neonatal bladder injury is rare and usually associated with umbilical artery catherization. Patients may present with apparent renal failure, abdominal distension, and respiratory distress. Treatment involves operative closure of the perforation and bladder drainage. A case of Foley catheter-induced bladder rupture in a premature infant, not previously reported in the literature, is detailed.

Female↗
PubMed1994

Evaluation of some properties of an opaque porcelain fired simultaneously with the body porcelain.

Recently, a porcelain-fused-to-metal opaque porcelain was introduced that does not require a separate firing before application of the body porcelain. The objective of this study was to determine the properties of this new opaque porcelain and its ability to bond to metal. The properties studied included flexural strength, linear firing shrinkage, coefficient of thermal expansion, powder particle size, and ability to bond to body porcelain and dental alloys. Sintering of this opaque porcelain was complete when fired at 1760 degrees F (960 degrees C) with a linear firing shrinkage of 13.1% +/- 0.2%. No boundary between the opaque and body porcelains could be found with a scanning electron microscope after firing at 1760 degrees F (960 degrees C). The mean flexural strengths were 99 +/- 7 and 101 +/- 8 MPa respectively, for this opaque porcelain and a conventional opaque porcelain, and were not significantly different as assessed with Student's t-test (p = 0.548). The coefficients of thermal expansion for this opaque porcelain was 13.3 +/- 0.2 x 10(-6)/degrees C. Particle size analysis showed a 63% increase in the particles below 5 microns for this opaque porcelain and bonding to two alloys was adequate as indicated by its cohesive failure. Simultaneous firing of this special opaque porcelain and body porcelain produced satisfactory sintering, strength, and bonding to metal.

Chemical Phenomena↗
PubMed1994

Evaluation of anterior segment tolerance to short-term intravitreal perfluoron.

PURPOSE: A study was performed to evaluate corneal and anterior segment toxicity from short-term (24-hour) intravitreal use of perfluoro-n-octane. METHODS: Forty aphakic, vitrectomized eyes of pigmented rabbits underwent intravitreal injection of either 0.5 ml of perfluoro-n-octane (Perfluoron; Infinitech, St. Louis, MO; treated) or 0.5 ml balanced saline solution (control). Perfluoron was allowed to remain in the vitreous cavity for 24 hours. Serial measurements of corneal pachymetry and pneumotonometry were performed at 1, 4, 12, and 24 hours after injection. After 24 hours, endothelial cell morphology and barrier function were evaluated. RESULTS: No significant differences in corneal thickness or intraocular pressure were noted between the two groups at any of the time points studied, and no differences in endothelial cell density/hexagonality or endothelial cell barrier function were observed 24 hours after injection. CONCLUSIONS: In the absence of sustained corneal contact, no evidence of significant acute corneal or anterior segment toxicity was observed in response to short-term intravitreal perfluoro-n-octane in aphakic, vitrectomized rabbit eyes.

Animals↗
PubMed1994

Regulation of herpes simplex virus thymidine kinase in cells treated with a synergistic antiviral combination of alpha interferon and acyclovir.

Alpha interferon (IFN-alpha) and acyclovir (ACV) are synergistic in their anti-herpes simplex virus activities. IFN-alpha treatment reduced the herpes simplex virus thymidine kinase (TK) activity present in cells 6 h postinfection, while steady-state levels of TK mRNA remained at or above the amount in infected, untreated cells. The inhibition of TK production by IFN-alpha treatment appeared to be transient and translational, not transcriptional.

Acyclovir↗
PubMed1994

Novel, ultrasensitive, Q-beta replicase-amplified hybridization assay for detection of Chlamydia trachomatis.

A sensitive, nonisotopic hybridization assay termed "dual capture" is described. The assay rapidly and specifically detects very low levels of target nucleic acids and organisms. The assay is based on the principles of sandwich hybridization, reversible target capture, and Q-Beta replicase amplification. The assay can be completed in less than 4 h, and in the described model format, it detects Chlamydia trachomatis rRNA or rDNA. Up to 96 samples can be analyzed simultaneously. The assay employs two types of probes: a test-specific capture probe, which mediates the cycling of the target probe complex on and off derivatized magnetic beads, and a replicatable RNA detector molecule containing a sequence complementary to and adjacent to the capture probe site on the target. Following reversible target capture, detection of the signal is accomplished by replication of the detector molecule by Q-Beta replicase in the presence of propidium iodide. A specific assay signal can be detected from as few as 1,000 molecules above the background. In a limited study of 94 urogenital samples the assay detected five of the six culture-positive samples and did not detect the C. trachomatis target in 85 of the 88 culture-negative samples.

Base Sequence↗
PubMed1994

Corneal ablations produced by the neodymium doped yttrium-lithium-fluoride picosecond laser.

This study examines corneal ablations produced by the neodymium doped yttrium-lithium-fluoride (Nd:YLF) picosecond laser. The laser delivers a 1-KHz, 40-ps pulsed, 1,053-nm wavelength beam (with energy measured in microjoules) to a 15-microns diameter spot size. The ablation mechanism is by plasma formation, which generates acoustic shock waves. Using enucleated rabbit (n = 25) and human donor eyes (n = 29), corneas were examined after tissue ablation at energies ranging from 40 to 300 microJ per pulse with various programmed ablation depths and patterns. The histologic data were collected using light microscopy and transmission electron microscopy. The tissue effects and Nd:YLF laser functions studied were ablation thresholds, cutting ability, programmed ablation depth accuracy, and acute endothelial effects. Our study showed histologic ablation thresholds for the following human corneal layers: epithelium = 7.15 +/- 0.05 x 10(11) W/cm2 (34.1 +/- 8.1 J/cm2 per pulse, 50 microJ per pulse); Bowman's layer = 1.33 +/- 0.29 x 10(12) W/cm2 (58.5 +/- 3.3 J/cm2 per pulse, 100-110 microJ per pulse); stroma and endothelium = 7.10 x 10(11) W/cm2 (28.4 J/cm2 per pulse, 50 microJ per pulse). Depth of corneal ablation was found to be directly related to energy and independent of programmed ablation depth. This study shows the endothelial loss in rabbit corneas by energy beams (50 microJ per pulse) focused 100 microns from this layer.

Animals↗
PubMed1994

The mechanism of ablation of corneal tissue by the neodymium doped yttrium-lithium-fluoride picosecond laser.

This study examines the structural changes in cornea resulting from plasma formation and propagated acoustic shock waves produced by the neodymium doped yttrium-lithium-fluoride (Nd:YLF) picosecond laser. Human donor eyes and enucleated rabbit eyes were subjected to various ablation patterns at energies ranging from 40 to 300 microJ per pulse. Two distinctly different patterns were produced depending on the location of initial plasma formation. Plasmas initiated at the corneal surface produced smooth, straight-edged ablations of corneal tissue that consisted of collagen fibril fragmentation, fibril organizational disruption, and possible thermal effect observed along the lateral borders and wound apex. The extent of lateral damage was directly related to the energy applied. The range of acute collagen disorganization observed at the ablation edge in rabbit corneas at various pulsed energies was as follows: 50 microJ = 1.0-12 microns, 150 microJ = 3.8-12.5 microns, 250 microJ = 6.2-23.7 microns, and 300 microJ = 7.5-45.0 microns. Plasma formation initiated within the stroma at or above threshold energies (50-150 microJ per pulse) produced an inter- or intralamellar separation effect with little evidence of ablation or collagen fibril fragmentation. Intrastromal plasmas generated from higher energies (200-300 microJ per pulse) produced tissue ablation, along with ablation or disruption of tissue anterior to the intrastromal target area.

Animals↗
PubMed1993

Amino acid residues of the Na,K-ATPase involved in ouabain sensitivity do not bind the sugar moiety of cardiac glycosides.

The identification of amino acid substitutions in the alpha subunit of the Na,K-ATPase that alter cardiac glycoside sensitivity provides a unique opportunity to examine the role these residues play in binding to the structural domains of these drugs. Substitution of a residue(s) involved in binding to the sugar moiety of cardiac glycosides would be expected to yield similar affinities for ouabain and its aglycone, ouabagenin. Sheep Na,K-ATPase alpha 1 subunit amino acid substitutions previously shown to influence ouabain sensitivity were tested for activity in the presence of ouabain and ouabagenin. These substitutions included both transmembrane and extracellular regions: C104F, D121E, N122D, Q111K, N122K, and Q111R, A112S. Na,K-ATPase activity versus drug concentration curves yielded I50 values over a 1000-fold range for wild type HeLa and HeLa transfectants. Interestingly, the I50 ratio for ouabagenin to ouabain in all mutants tested indicated a 19-24-fold lower affinity of the Na,K-ATPase for ouabagenin. This constant ratio among all mutations tested implies that the first transmembrane region and the first extracellular loop (H1-H2) do not participate in the binding of the sugar moiety of cardiac glycosides.

Amino Acid Sequence↗
PubMed1993

The strengthening mechanism of a magnesia core ceramic.

A high-expansion core material containing magnesia and forsterite may be used to make all-ceramic dental crowns with porcelain-fused-to-metal body porcelains. The purpose of this study was to investigate the strengthening mechanism for the magnesia core material. Six batches of the magnesia core material were made by reacting magnesia with a silica glass with holding times ranging from 17 to 120 min. The flexural strength was measured using three-point loading according to the ISO specification for dental ceramics. The forsterite content was measured using quantitative x-ray diffraction. A statistically significant correlation was found between the forsterite content and flexural strength. The proposed mechanism for strengthening is the precipitation of fine forsterite crystals in the glass matrix surrounding unreacted magnesia. Longer reaction times produced more dissolution of magnesia and subsequent precipitation of forsterite. This method results in a new strengthening mechanism for dental ceramics which have previously relied on the incorporation of alumina, leucite or ceramic whiskers.

Analysis of Variance↗
PubMed1992

Infection with a plasmid-free variant Chlamydia related to Chlamydia trachomatis identified by using multiple assays for nucleic acid detection.

Clinical samples in transport media from 40 patients exhibiting pathologies potentially caused by Chlamydia trachomatis infection were analyzed for chlamydial nucleic acid, and the results were compared with those of culture. Chlamydial culture was performed by a shell vial centrifugation method with HeLa 229 host cells. Polymerase chain reaction (PCR) assays were used to detect either regions on a 7.5-kb plasmid characteristic of C. trachomatis (plasmid-PCR) or a segment of the 16S rRNA genes (rRNA-PCR). All PCR results were confirmed by hybridization with probes for the specific amplified products in either a Southern or a dot blot format. An RNase protection (RNP) assay was used to detect genus-specific chlamydial 16S rRNA directly from the clinical samples. The PCR assays detected C. trachomatis but not other bacteria, including Chlamydia spp. C. trachomatis was isolated from six samples which were positive by the rDNA-PCR and plasmid-PCR assays. Five of the culture-positive specimens were positive by the RNP assay. Twenty-two samples were negative by all criteria. Surprisingly, nine samples were positive by rRNA-PCR and RNP assays only. Nucleic acid sequencing of the rRNA-PCR-amplified products indicated a close relationship between the variants and C. trachomatis. The data may indicate an unrecognized process in C. trachomatis infection or that these patients were infected by a variant strain of C. trachomatis which lacks the C. trachomatis-specific plasmid.

Animals↗