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Biomedical subjects

W D Cook

Publications and source records attributed to W D Cook.

At least 19 recordsLinked to original sources
PubMed1999

A simple method for the measurement of polymerization shrinkage in dental composites.

OBJECTIVE: In this study a simple non-contact method was developed to measure the polymerization shrinkage of dental composites. METHODS: A gas pycnometer was used to determine the volumes of specimens prior to and after photopolymerization and from which the total volumetric shrinkage could be determined. RESULTS: Four commercial composites were studied and were found to have polymerization shrinkages varying from 1.6 to 2.5%. The method was found to be labour efficient and produced reproducible results with a standard deviation of approximately 10%. SIGNIFICANCE: This method is appropriate for shrinkage measurements where only the total amount shrinkage is required and in particular for the measurement of shrinkage of photocured materials which are sensitive to water absorption.

Composite Resins↗
PubMed1998

Phenotypic effect correlating with loss of a novel tumor suppressor gene: towards cloning by complementation.

We intend to use a gene complementation approach to clone a tumor suppressor gene on mouse chromosome 2, the loss of which contributes to myeloid leukemia. An in vitro model system has been generated using a clonal cell line, in which tumorigenic chromosomal lesions have been selected along with myeloid differentiation. Among these lesions are deletions of chromosome 2. Comparison of subclones with deleted vs intact chromosomes 2 has allowed the identification of a growth related phenotypic pattern which correlates with the deletion, viz the retention of a marker of immature cells, resistance to inhibition by lipopolysaccharide (LPS), even in the presence of markers of mature myeloid cells, such as resistance to killing by apoptosis-inducing agents. The phenotype is shared by chromosome 2-deleted cell lines derived from conventional tumors. We have begun to investigate the mechanism of the phenotype. The LPS resistance does not correlate with lack of mRNA for CD14, a known cell surface receptor for this agent, or with failure to induce TNF alpha or nitric oxide synthase in response to its binding. The system should allow cloning of the gene using complementation of this phenotype in transfected cell lines.

Animals↗
PubMed1995

Fracture toughness of water-aged resin composite restorative materials.

OBJECTIVES: The purpose of this study was to assess the effects of aging experimental dimethacrylate resin composites in water at 37 degrees C for periods up to 6 wk by measuring the variations in fracture toughness (K(c)), elastic modulus (E), fracture energy (G(c)), and water sorption. METHODS: Six experimental resins were formulated from dimethacrylate resins, and were filled to 86 wt% (ca. 70 vol%) with treated inorganic filler to form six experimental composites. The fracture toughness was determined using a double torsion technique, the elastic modulus was measured in flexure, and the fracture energy was calculated from the fracture toughness and elastic modulus. RESULTS: As a result of aging in water, K(c) and the G(c) increased, and the elastic modulus decreased, but all values approached a plateau near 6 wk. Water sorption also occurred during this period, mainly during the first 2 wk. SIGNIFICANCE: Variations in the mechanical properties are interpreted as being due to plasticization of the resin matrix by water, which appears to lower the yield stress and increase in the size of the plastic zone ahead of the crack, thereby causing the observed increase in G(c) and K(c). After approximately 6 wk, no further changes in properties occurred.

Absorption↗
PubMed1995

Gene deletion explains both in vivo and in vitro generated chromosome 2 aberrations associated with murine myeloid leukemia.

Ninety-five percent of radiation-induced murine myeloid leukemias contain chromosome 2 aberrations. A dominant molecular defect has not yet been identified: both deletions and breakpoint-specific events have been postulated. We have generated a model in which chromosome 2 lesions have been generated in vitro in a clonal tumor cell line. In this study cytogenetic and molecular comparisons are made between two of these in vitro generated lesions and eight derived in vivo: seven by the conventional radiation protocol, and one by infection with Moloney leukemia virus. All 10 lines consistently exhibited hemizygous loss of an 18 cM region between Hoxd-4 and II-1 alpha, with variable breakpoints at both ends. These results are consistent with deletion of a gene in common rather than breakpoint-specific events, for lesions resulting from all three protocols. This will allow a novel approach to the identification of a putative tumor suppressor gene, ie to describe the biological effect of the in vitro generated deletion, and to clone the gene by complementation. In preparation for this approach, we have further narrowed the region to approximately 6.5 cM by microsatellite mapping of 22 radiation-induced F1 tumors. In addition, we have eliminated the possibility that imprinting ablates expression from the remaining undeleted chromosome.

Animals↗
PubMed1994

Mechanical properties of some polymer materials used for tooth positioners.

The chemical composition, thermal behaviour and mechanical properties of three tooth positioner materials, Urethane P1 (P1), White Rubber (WR) and Elastocryl (EL) were investigated. Infra-red spectrophotometry indicated the P1 polyurethane material to be of the polyether type, and EL to be a blend of poly(ethyl methacrylate) and poly(methyl methacrylate) while WR appeared to be filled cis-poly (isoprene) (natural rubber). The glass transition temperature (Tg) for EL was determined as approximately 10 degrees C, and for both P1 and WR the Tg was less than -50 degrees C. The stress relaxation behaviour was assessed in compression by measuring the stress variation with time. The results for all three materials conformed to the superelastic theory of rubber elasticity. EL exhibited both a more rapid rate and higher degree of stress relaxation than did P1 and WR. Recovery from deformation was assessed by compressing cylinders for given periods of time and then measuring the level of reduced residual strain of the material with time. All three materials exhibited significant residual strain (epsilon(t)) over 'clinically relevant' time periods, and the reduced residual strain (epsilon(t)/epsilon(O)) following deformation was greater for EL than P1 or WR. There was some indication that the three materials have some permanent set following deformation. It was concluded that, in considering desirable mechanical properties of tooth positioner materials, EL is the least suitable of the three examined, with none of the materials being ideal.

Butadienes↗
PubMed1993

SCL, the gene implicated in human T-cell leukaemia, is oncogenic in a murine T-lymphocyte cell line.

SCL (TAL-1) is implicated in the generation of human T-cell acute lymphoblastic leukaemia. To directly examine the role of this putative oncogene, an SCL retrovirus was constructed and used to infect a v-ABL transformed T-lymphocyte cell line. Thirteen independent SCL-infected and four control cell lines were established and injected subcutaneously into syngeneic mice. Mice injected with SCL-infected clonal cell lines died significantly more rapidly than control animals. By day 200 46% (40/87) of animals injected with SCL-infected cell lines had died due to disseminated transplantable lymphoid tumours. In contrast only 22% of control mice were dead by day 200 (P < 0.0015). Of possible relevance to the enhanced tumourigenesis, some SCL-infected cell lines displayed increased clonogenicity in agar. Increased cell growth was even more striking when ex-vivo tumour-derived cell lines were studied. Thus, SCL can co-operate with v-ABL to hasten T-cell tumourigenesis. This is the first direct evidence demonstrating that SCL can behave as an oncogene.

Amino Acid Sequence↗
PubMed1992

Tumor-associated karyotypic lesions coselected with in vitro macrophage differentiation.

Several cytogenetic lesions in chromosomes 2, 5, 12, and 16 have been repeatedly coselected with in vitro macrophage differentiation in a clonal murine thymic tumor cell line. Parental-type subclones, which show an extremely immature hemopoietic phenotype, do not carry the aberrations. The frequency of the stable differentiated variants is elevated by 5-azacytidine and bromodeoxyuridine, consistent with chromosome breakage being responsible for the phenotype. The frequency is also raised by dexamethasone. Since variants are 300-3,000-fold more resistant to dexamethasone than parental clones, we interpret this to be largely due to selection. Three of the lesions, on chromosome 2, match those previously described as associated specifically with in vivo-generated murine myeloid tumors, induced by X irradiation and corticosteroid treatment. Several implications follow from these observations. (1) In vitro differentiation in clonal tumor cell lines can be used to select for tumor-associated lesions. This should allow genetic and molecular analysis of the chromosome 2 lesions and of others that may pinpoint genes critical to macrophage differentiation and transformation. (2) Myeloid and lymphoid tumors that occur in response to X irradiation may diverge from a common initiating tumor. (3) The hemopoietic lineage switch phenomenon, previously described by several authors, may be caused by similar or identical chromosome aberrations.

Abelson murine leukemia virus↗
PubMed1990

Separate elements control DJ and VDJ rearrangement in a transgenic recombination substrate.

We describe transgenic mice that carry an antigen receptor gene minilocus comprised of germline T cell receptor (TCR) beta variable gene elements (V, D and J) linked to an immunoglobulin (Ig) C mu constant region gene with or without a DNA segment containing the Ig heavy chain transcriptional enhancer (E mu). Transgenic constructs lacking the E mu-containing segment did not undergo detectable rearrangement in any tissue of six independent transgenic lines. In contrast, transgenic constructs containing this DNA segment underwent rearrangement at high frequency in lymphoid tissues, but not other tissues, of four independent lines. Analyses of purified B and T cells, as well as B and T cell lines, from transgenic animals demonstrated that the E mu-containing segment within the construct allowed partial TCR gene assembly (D to J) in both B and T cells. However, complete TCR gene rearrangement within the construct (V to DJ) occurred only in T cells. Therefore, we have demonstrated elements that can control two separate aspects of TCR beta VDJ rearrangement within this construct. One lies within the E mu-containing DNA segment and represents a dominant, cis-acting element that initiates lymphoid cell-specific D beta to J beta rearrangement; various considerations suggest this activity may be related to that of the E mu element. The second element provides T cell-specific control of complete (V beta to DJ beta) variable region gene assembly; it correlates in activity with expression of the unrearranged V beta segment.

Animals↗
PubMed1990

Influence of chemical structure on the fracture behaviour of dimethacrylate composite resins.

Previous studies have shown that the fracture resistance of dimethacrylate-based dental composite resins is enhanced by post-curing the matrix. Here, the influence of the chemical nature of the resin matrix is examined by a study of the fracture properties of composite resins formulated from 15 homologous dimethacrylate monomers and filled to 75 wt% with treated silica. The fracture toughness was determined via the double torsion technique and the elastic modulus and flexural strength were measured in flexure. The fracture energy calculated from the fracture toughness and elastic modulus, varied between 60 and 300 J/m2 while the fracture toughness ranged from 0.2 to 2.0 MN/m3/2 and the flexural strength varied from 17 to 111 MPa. The use of a blend of monomers was found to have a synergistic effect on the fracture resistance. Increasing the length of flexible spacer units (methylene or oxyethylene) between the methacrylate groups initially improved the fracture properties; however, beyond a certain length, these properties were impaired.

Acrylates↗
PubMed1987

The influence of postcuring on the fracture properties of photo-cured dimethacrylate based dental composite resin.

The dependence of the fracture behavior of photocured dimethacrylate-based composite resins on the matrix crosslink density (varied by postcuring at various temperatures) was investigated. In general, the fracture toughness (KIc) was increased by postcuring as has been observed for epoxy-amine networks. The flexural and diametral tensile strength was also raised by postcuring. Calculation of the inherent flaw size (ao) from these properties produced conflicting dependencies on the state of cure. It is suggested that improved wear resistance and incisal edge strength of dental composite resin restoratives may be achieved by increased degree of cure.

Acrylates↗
PubMed1987

Isolation and sequence of a cDNA corresponding to a src-related gene expressed in murine hemopoietic cells.

We have isolated a murine cDNA that shares extensive homology with genes encoding the src (Rous sarcoma virus oncogene)-related family of protein-tyrosine kinases. The cDNA includes an open reading frame of 1509 base pairs, and conceptual translation predicts a protein of 56 kDa. Blot-hybridization analysis indicates that this src-related gene is expressed in normal macrophages and in cell lines representing both the myeloid and lymphoid B-cell lineages and, accordingly, is designated "bmk" (B cell/myeloid kinase). In addition, bmk mRNA levels increase following the induced differentiation of the murine myelomonocytic leukemic cell line WEHI-3B.

Amino Acid Sequence↗
PubMed1987

T-cell receptor and immunoglobulin genes are rearranged together in Abelson virus-transformed pre-B and pre-T cells.

We have assessed the state of rearrangement and expression of B- and T-cell antigen receptor genes in cells of Abelson murine leukemia virus-transformed thymomas and other tumors. We found that unrearranged TcR gamma genes are expressed, as are unrearranged C mu genes, in pre-T, pre-B, and myeloid cells. We also found TcR gamma genes rearranged and expressed in putative pre-T cells and in cells apparently committed to the B-cell lineage. This is in contrast to the data from more mature T- and B-cell tumors. We conclude that in immature lymphoid cells both immunoglobulin and TcR gamma genes are accessible for rearrangement. We discuss the implications of these observations for an understanding of the B-T lymphoid differentiation event.

Abelson murine leukemia virus↗
PubMed1987

Abelson virus transformation of an interleukin 2-dependent antigen-specific T-cell line.

Abelson murine leukemia virus (A-MuLV) carries the gene v-abl, one of a group of oncogenes with structural and functional (tyrosine kinase) homology to three growth factor receptors. Work in this and other laboratories has shown that A-MuLV infection can render myeloid and lymphoid cells independent of the growth factors interleukin 3 and granulocyte-macrophage colony-stimulating factor. We have now shown that v-abl can also relieve interleukin 2 (IL-2) dependence in T cells. We infected a cloned IL-2-dependent antigen-specific cell line. Transformed cells were generated which were factor independent and tumorigenic. The transformants each bore unique v-abl DNA inserts and expressed v-abl mRNA. No elevation of expression of either IL-2 or its receptor could be detected in these cells. Thus, A-MuLV can short-circuit the dependence of hematopoietic cells on IL-2, IL-3, and possibly granulocyte-macrophage colony-stimulating factor, none of whose receptors are known to be of the tyrosine kinase type.

Abelson murine leukemia virus↗