Search PubMed⌕ Search

Biomedical subjects

A J Smith

Publications and source records attributed to A J Smith.

At least 109 records · Page 6Linked to original sources
PubMed2000

Oxidation-reduction properties of disulfide-containing proteins of the Rhodobacter capsulatus cytochrome c biogenesis system.

Oxidation-reduction titrations for the active-site disulfide/dithiol couples of the helX- and ccl2-encoded proteins involved in cytochrome c biogenesis in the purple non-sulfur bacterium Rhodobacter capsulatus have been carried out. The R. capsulatus HelX and Ccl2 proteins are predicted to function as part of a dithiol/disulfide cascade that reduces a disulfide on the apocytochromes c so that two cysteine thiols are available to form thioether linkages between the heme prosthetic group and the protein. Oxidation-reduction midpoint potential (E(m)) values, at pH 7.0, of -300 +/- 10 and -210 +/- 10 mV were measured for the HelX and Ccl2 (a soluble, truncated form of Ccl2) R. capsulatus proteins, respectively. Titrations of the disulfide/dithiol couple of a peptide designed to serve as a model for R. capsulatus apocytochrome c(2) have also been carried out, and an E(m) value of -170 +/- 10 mV was measured for the model peptide at pH 7.0. E(m) versus pH plots for HelX, Ccl2, and the apocytochrome c(2) model peptide were all linear over the pH range from 5.0 to 8.0, with the -59 mV/pH unit slope expected for a reaction in which two protons are taken up for each disulfide that is reduced. These results provide thermodynamic support for the proposal that HelX reduces Ccl2 and that reduced Ccl2, in turn, serves as the reductant for the production of the two thiols of the CysXxxYyyCysHis heme-binding motif of the apocytochromes.

Bacterial Proteins↗
PubMed2000

MDR3 P-glycoprotein, a phosphatidylcholine translocase, transports several cytotoxic drugs and directly interacts with drugs as judged by interference with nucleotide trapping.

The human MDR3 gene is a member of the multidrug resistance (MDR) gene family. The MDR3 P-glycoprotein is a transmembrane protein that translocates phosphatidylcholine. The MDR1 P-glycoprotein related transports cytotoxic drugs. Its overexpression can make cells resistant to a variety of drugs. Attempts to show that MDR3 P-glycoprotein can cause MDR have been unsuccessful thus far. Here, we report an increased directional transport of several MDR1 P-glycoprotein substrates, such as digoxin, paclitaxel, and vinblastine, through polarized monolayers of MDR3-transfected cells. Transport of other good MDR1 P-glycoprotein substrates, including cyclosporin A and dexamethasone, was not detectably increased. MDR3 P-glycoprotein-dependent transport of a short-chain phosphatidylcholine analog and drugs was inhibited by several MDR reversal agents and other drugs, indicating an interaction between these compounds and MDR3 P-gp. Insect cell membranes from Sf9 cells overexpressing MDR3 showed specific MgATP binding and a vanadate-dependent, N-ethylmaleimide-sensitive nucleotide trapping activity, visualized by covalent binding with [alpha-(32)P]8-azido-ATP. Nucleotide trapping was (nearly) abolished by paclitaxel, vinblastine, and the MDR reversal agents verapamil, cyclosporin A, and PSC 833. We conclude that MDR3 P-glycoprotein can bind and transport a subset of MDR1 P-glycoprotein substrates. The rate of MDR3 P-glycoprotein-mediated transport is low for most drugs, explaining why this protein is not detectably involved in multidrug resistance. It remains possible, however, that drug binding to MDR3 P-glycoprotein could adversely affect phospholipid or toxin secretion under conditions of stress (e.g. in pregnant heterozygotes with one MDR3 null allele).

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2000

Endoglin, an ancillary TGFbeta receptor, is required for extraembryonic angiogenesis and plays a key role in heart development.

Endoglin (CD105) is expressed on the surface of endothelial and haematopoietic cells in mammals and binds TGFbeta isoforms 1 and 3 in combination with the signaling complex of TGFbeta receptors types I and II. Endoglin expression increases during angiogenesis, wound healing, and inflammation, all of which are associated with TGFbeta signaling and alterations in vascular structure. The importance of endoglin for normal vascular architecture is further indicated by the association of mutations in the endoglin gene with the inherited disorder Hereditary Haemorrhagic Telangiectasia Type 1 (HHT1), a disease characterised by bleeding from vascular malformations. In order to study the role of endoglin in vivo in more detail and to work toward developing an animal model of HHT1, we have derived mice that carry a targeted nonsense mutation in the endoglin gene. Studies on these mice have revealed that endoglin is essential for early development. Embryos homozygous for the endoglin mutation fail to progress beyond 10.5 days postcoitum and fail to form mature blood vessels in the yolk sac. This phenotype is remarkably similar to that of the TGFbeta1 and the TGFbeta receptor II knockout mice, indicating that endoglin is needed in vivo for TGFbeta1 signaling during extraembryonic vascular development. In addition, we have observed cardiac defects in homozygous endoglin-deficient embryos, suggesting endoglin also plays a role in cardiogenesis. We anticipate that heterozygous mice will ultimately serve as a useful disease model for HHT1, as some individuals have dilated and fragile blood vessels similar to vascular malformations seen in HHT patients.

Animals↗
PubMed2000

Prokinetic effect of erythromycin after colorectal surgery: randomized, placebo-controlled, double-blind study.

PURPOSE: Nausea and vomiting three to seven days after an elective operation on the colon and rectum remain a persistent clinical problem. Erythromycin, a safe, inexpensive drug that stimulates intestinal motilin receptors, has previously been shown to accelerate gastric emptying significantly after upper gastrointestinal surgery. We aimed to evaluate the effect of postoperative intravenous erythromycin on postoperative ileus in patients undergoing elective surgery for primary colorectal cancer. METHODS: Between May 1998 and April 1999, 150 patients undergoing primary resection of colon or rectal cancer were enrolled in this prospective, randomized, placebo-controlled trial. One hundred thirty-four patients completed the study. Patients were excluded if they had extensive metastatic disease, were taking medications known to interact with erythromycin, or if they required an ileostomy. Patients received either 200 mg of intravenous erythromycin or placebo every six hours. Clinical endpoints were recorded and continuous end-points are presented as mean +/- standard deviation. RESULTS: There were no significant complications related to erythromycin. The erythromycin (n = 65) and placebo (n = 69) groups were comparable regarding demographic and operative factors. The erythromycin group had a slightly shorter length of time to passage of flatus (4.1 +/- 1.3 vs. 4.4 +/- 1.1 days; P = 0.03). There was no significant difference between erythromycin and placebo in time to first solid food (5.6 +/- 1.9 vs. 5.4 +/- 1.8 days), time to first bowel movement (5.2 +/- 1.9 vs. 5.4 +/- 1.3 days), or time to discharge from hospital (7.5 +/- 2.0 vs. 7.6 +/- 2.8 days). There was no difference in the rate of clinically significant nausea (26 vs. 26 percent; P = 0.99), vomiting (17 vs. 16 percent; P = 0.88), or nasogastric tube placement (9 vs. 7 percent; P = 0.68). CONCLUSIONS: Erythromycin does not seem to alter clinically important outcomes related to postoperative ileus in patients undergoing resection for colorectal cancer.

Aged↗
PubMed2000

Angiogenic growth factors in human dentine matrix.

The importance of growth factors in mediating the cellular responses to injury in the dentine-pulp complex is well recognized and several growth factors are reportedly sequestered in dentine matrix from where they may be released during repair processes. Local angiogenesis at the injury site appears to be critical for successful pulpal repair. Here, soluble and insoluble matrix fractions were isolated from human dentine and the amounts of several important angiogenic growth factors in these fractions measured by enzyme-linked immunosorbent assay (ELISA). The EDTA-soluble matrix fraction contained high concentrations of platelet-derived growth factor (PDGF-AB), lower concentrations of vascular endothelial growth factor (VEGF), placenta growth factor (PlGF) and fibroblast growth factor (FGF2), and very low concentrations of epidermal growth factor (EGF). No FGF2 or PlGF could be detected in the insoluble matrix fractions, but these fractions contained some VEGF, lower concentrations of PDGF-AB and very low concentrations of EGF. It was concluded that dentine matrix contains angiogenic growth factors and that their release from the matrix after injury could make an important contribution to the overall reparative response of the dentine-pulp complex.

Angiogenesis Inducing Agents↗
PubMed2000

Stimulation of the rat dentine-pulp complex by bone morphogenetic protein-7 in vitro.

Human recombinant bone morphogenetic protein-7 (BMP-7), when applied to freshly cut dentine in monkey teeth, stimulated tertiary dentine formation, but it is unclear whether this response involved upregulation of the synthetic and secretory activity of existing odontoblasts or the induction of differentiation of new odontoblast-like cells. Using a recently developed organ-culture system for whole tooth slices, the aim here was to examine the effects of BMP-7 on the stimulation and modulation of existing odontoblasts in the absence of tissue injury. Agarose beads were soaked in a 500 ng/ml or 100 ng/ml solution of BMP-7 in culture medium and placed on the odontoblast area of the dentine pulp complex of rat tooth slices. The slices were embedded in a semisolid agar-based medium and cultured at the liquid gas interface for 7 days. Results showed that beads soaked in 500 ng/ml BMP-7 stimulated a localized increase in extracellular matrix secretion by odontoblasts at the site of application, with greater stimulatory effects than from the lower concentration. These effects may be important in the reparative processes after tissue injury within the dentine-pulp complex and may be useful in the therapeutic induction of tertiary dentinogenesis.

Animals↗
PubMed2000

Tooth slice organ culture for cytotoxicity assessment of dental materials.

The purpose of this work was to develop a tooth slice organ culture method to assess the response of the cells of the dental pulp to commonly used dental materials and products. Wistar rat tooth slices were grown in culture for two and ten days in the presence of dental materials. After culture, the tooth tissues were processed and the responses of the pulpal cells were analysed histomorphometrically. Cytotoxic cell destruction was observed following the direct application of test materials to tooth slices (n = 298) after 10 days in culture (MANOVA, P = 0.0001), whilst the restoration of prepared deep dentine cavities (n = 30), with test products, did not result in a significant amount of pulpal injury (MANOVA, P = 0.287). In rank order of causing pulpal injury, the test materials from the most to the least cell destructive, was; Salicylic acid. Calcium hydroxide, Kalzinol zinc oxide eugenol, high-mercury Amalgam, Prime & Bond, Dycal, Barium sulphate, Hypocal, Scotchbond, Calasept, Life and One-step. Tooth slice organ culture, provided a cytotoxicity screening method for dental materials, bearing a closer physiological resemblance to the clinical situation than cell culture screening methods. Tooth slice culturing may have the potential to replace some types of in vivo animal experimentation, as there is a clear need to reduce this form of testing.

Animals↗
PubMed2000

Designing new treatment strategies in vital pulp therapy.

OBJECTIVES: The development of strategies in vital pulp therapy, which aim to maintain vitality and function of the dentine-pulp complex, represents a major focus of attention. Recent progress in understanding the molecular and cellular changes during tooth development and how they are mimicked during dental tissue repair offers the opportunity to now assess whether this knowledge can be exploited to design new treatment strategies in vital pulp therapy. DATA SOURCES AND STUDY SELECTION: Current literature on the molecular and cellular basis of tooth development and dental tissue repair has been reviewed in the context of stimulating dentinogenic responses in the tooth together with pertinent published abstracts of relevant conferences and personal communications. Tissue events of direct relevance to clinical application for vital pulp therapy are discussed. CONCLUSIONS: The involvement of growth factors and extracellular matrix molecules in signalling and regulating dentinogenic events during tooth development has been identified. During dental tissue repair, many of the processes are mimicked leading to responses of focal deposition of tertiary dentine at injury sites. The nature and specificity of these responses are determined in part by the extent of tissue injury. Traditional clinical strategies are capable of exploiting endogenous signalling molecules in the tissues to develop more effective treatment modalities. Application of exogenous signalling molecules offers opportunities for development of new therapies, although a number of delivery considerations must be addressed before these can be introduced into clinical practice.

Cell Differentiation↗
PubMed2000

Human odontoblast cell numbers after dental injury.

OBJECTIVES: The purpose of this study was to measure the changes in odontoblast cell numbers in response to cavity restoration variables and patient factors, and the effect these factors have on dental repair by tertiary dentinogenesis. The number of vital odontoblasts is a critical factor for pulpal repair following restorative surgery, and yet little information is available on these cell numbers. METHODS: Class V non-exposed cavities were prepared in the buccal surface of intact first or second premolar teeth of 27 patients, between 9 and 17 years of age. Following tooth extraction (28-163 days) the area of reactionary dentine and the area of the odontoblasts were measured histomorphometrically. RESULTS: Patient factors, as well as cavity preparation and restoration variables, had little effect on the numbers of odontoblasts per pulpal unit area. However, the age of the patient did appear to have an effect on the reactionary dentine secretory capacity of odontoblasts per unit area, and on the relative number of odontoblasts beneath cut dentinal tubules. CONCLUSIONS: Odontoblast cell numbers were maintained following the preparation of cavities cut into dentine with a 0.5mm residual dentine thickness. The repair capacity of the pulp-dentine complex would appear to be age dependent, this may explain differences in the success of various restorative treatments between patients.

Adolescent↗
PubMed2000

Transforming growth factor-beta isoform expression in mature human healthy and carious molar teeth.

Transforming growth factor (TGF)-beta isoforms have been implicated in cellular signalling during tooth development and repair, but little is known of their cellular localisation or distribution within the dental tissues in the mature tooth. This study investigated the presence of TGF-beta1, beta2 and beta3 isoforms in tissues of sound and carious human molar teeth, to understand better the expression of TGF-betas during health and disease. In healthy tissues, odontoblasts, cells of the cell rich layer, pulpal fibroblasts and endothelial cells were stained to varying degrees for all isoforms, with TGF-beta3 showing the greatest intensity and TGF-beta1 the weakest intensity. Similar patterns of staining were observed in carious teeth; however, TGF-beta1 showed significantly increased staining intensity within odontoblasts and pulpal cells of carious teeth (p < 0.001). Biochemical analysis showed greater amounts of TGF-beta1 in tertiary dentine than in primary dentine samples. The expression of TGF-betas in odontoblasts and the increased presence of TGF-beta1 in tertiary dentine suggest that these isoforms may be important in odontoblast behaviour and the modulation of the tissue response to injury.

Edetic Acid↗
PubMed2000

Ultrastructural localisation of TGF-beta exposure in dentine by chemical treatment.

Transforming growth factor-beta (TGF-beta) sequestered in dentine matrix has an important role in dental tissue repair after injury and its exposure at sites of injury may stimulate tertiary dentinogenesis. This study aimed to investigate the expression of TGF-beta isoforms in mature human dentine matrix and the ability of chemical treatments to expose TGF-beta on the cut surface of dentine using gold immunolabelling and subsequent scanning electron microscopy examination. TGF-beta1 was the only isoform that could be detected in human dentine and the nature of the chemical treatment of the tissue influenced its detection. EDTA treatment provided good exposure of TGF-beta1 on the dentine surface, whilst citric acid and sodium hypochlorite treatments revealed lesser amounts of this isoform. Only minimal staining for TGF-beta1 was observed in samples treated with phosphate-buffered saline. TGF-beta2 and -beta3 could not be detected in the specimens with any of the treatments. This study suggests that TGF-beta1 is the only TGF-beta isoform expressed by human odontoblasts to be sequestered in dentine implying that differences in isoform-extracellular matrix interactions may exist. Information on chemical treatment of tissue specimens for immunostaining may provide a useful basis for selection of tissue preparation techniques for clinical restorative treatment procedures to facilitate TGF-beta mediated reparative processes at sites of dental injury.

Citric Acid↗
PubMed2000

Development and evaluation of a stand-alone web-based CAL program. A case study.

The use of web browser technology allows the construction of computer-aided learning programs which will have a familiar interface to dentists. This paper reports on the evaluation of a web-based CAL program which covered the topic of tooth wear with an emphasis on the rôle of erosion in its aetiology. Evaluation of the software was made by 50 dentists contacted by an electronic mailing list. They completed a questionnaire which evaluated aspects of the functionality of the program educational objectives. The average age of the dentists was 39 years (range 24-70) and 82% were male. The average time of use was 1 h 10 min (range 15 min to 3 h). A significant change in their knowledge of tooth wear before and after using the program was recorded. Both the use of patient cases and leaflets scored highly with other aspects such as treatment planning and patient advice receiving high marks. All dentists commented that they had gained greater knowledge with particular reference to treatment and advice of tooth wear problems. 34 dentists (68%) found the web interface easy to use. Negative comments were mainly attributed to the quality of the pictures (4/50) which were corrected in the final release version. Respondents were asked to compare the program to other educational media on the same subject. 80% rated this CAL program as better than video, and 14% claimed it was as good as video. 84% rated it better than books, and 14% said it was as good as books. 98% preferred it to audio tapes and 86% preferred it to journals. The average amount that they would pay for a CAL package such as "tooth wear" would be 42 ECU. It is concluded that web browser software is a suitable medium for the use of a CAL program and this is reflected in its ease of use by dentists.

Adult↗
PubMed2000

The influence of sample dimensions on hydroxyl ion release from calcium hydroxide products.

The purpose of this study was to compare the rate of hydroxyl ion release from commercially available setting and non-setting calcium hydroxide products. The rate of hydroxyl ion release is important, as this has been suggested to be the main factor in the therapeutic activity of these products. In total, hydroxyl ion release was measured from 1104 samples of Dycal, Life, Calasept and Hypocal in solution using in vitro titration. The rate of hydroxyl ion release was measured for up to 14 days, using two sizes of sample surface area. The dimensions of the exposed sample surface area was found to be an important physical constraint to the hydroxyl ion release from non-setting calcium hydroxide products, whereas this was not found to be the case with setting products. The range in hydroxide activity between products was found to be 298%. In rank order of hydroxide ion release, from the most to the least active was: Hypocal, Calasept, Life and Dycal. The differences in the rate of hydroxyl ion release from these products may have some implications for their clinical applications. It is suggested that in cases where the oral healing responses have been poorer than expected, the size and seal of prepared cavities could have negatively influenced the therapeutic release of hydroxyl ions from non-setting calcium hydroxide products.

Analysis of Variance↗