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Biomedical subjects

T L Walker

Publications and source records attributed to T L Walker.

At least 19 recordsLinked to original sources
PubMed2004

Characterisation of the Dunaliella tertiolecta RbcS genes and their promoter activity in Chlamydomonas reinhardtii.

The availability of highly active homologous promoters and terminators is critical in the development of a transformation system for the unicellular microalga Dunaliella tertiolecta. To facilitate transformation of this species, we isolated and characterised two native ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit genes (RbcS) including flanking sequences. The two non-allelic cDNA sequences share approximately 80% identity and have approximately 60% identity to the RbcS genes of Chlamydomonas reinhardtii. The D. tertiolecta RbcS promoter and 3' untranslated regions were shown to drive expression of the bleomycin resistance gene (ble) in C. reinhardtii. This is the first demonstration of a heterologous algal promoter being used to drive transgene expression in C. reinhardtii. In addition, promoter deletions were shown to further increase transformation efficiency.

Amino Acid Sequence↗
PubMed2001

Varus derotation osteotomy for the treatment of hip subluxation and dislocation in cerebral palsy: statistical analysis in 73 hips.

The purpose of this study is to review the results of varus osteotomy in patients with cerebral palsy and to determine factors that influence the rates of residual hip displacement. A retrospective chart review of 65 patients who underwent 79 varus osteotomies was performed. Preoperative, postoperative and follow-up radiographs were analyzed for routine radiographic measurements, pelvic obliquity, osteonecrosis (avascular necrosis), joint incongruity or degenerative joint disease. The average follow-up was 5.2 years (range, 1.1-18.4 years). At follow-up, 3 hips were dislocated, 19 were subluxated and 57 were stable (72%). Age at surgery and the degree of preoperative hip displacement had significant effects on outcome. The average age at surgery for initially subluxated hips, which were located at follow-up, was 7.2 years. This was significantly younger (P = 0.008) than initially subluxated hips, which were displaced (10 years of age). Subluxated hips at surgery were also more likely to be located at follow-up than dislocated hips.

Adolescent↗
PubMed2000

Comparison of nickel-titanium and stainless-steel spreader penetration and accessory cone fit in curved canals.

The purpose of this study was to compare nickel-titanium and stainless-steel spreader penetration in curved canals. Twenty prepared plastic blocks with a 30 degrees curvature were used for each part of the study. In part 1, the force required to insert each spreader to within 1 mm of working length in an empty canal was measured. In part 2, the force required to insert each spreader to within 3 mm of working length was measured in a canal containing a master cone. In part 3, the depth of penetration of each spreader with a master cone in place using a 1.5 kg force was measured. Additionally, in part 3, the depth of penetration of the first accessory cone was measured. The results from part 1 showed that a nickel-titanium spreader required significantly less force than a stainless-steel spreader (0.30 kg vs. 0.59 kg). In part 2, a nickel-titanium spreader required significantly less force than a stainless-steel spreader (1.56 kg vs. 2.42 kg). In part 3, a nickel-titanium spreader penetrated significantly deeper than a stainless-steel spreader (15.0 mm vs. 14.0 mm). There was no significant difference in the depth of penetration of the first accessory cone used after either spreader (0.8 mm vs. 0.7 mm). Therefore, the potential for vertical root fracture in curved canals during lateral condensation may be minimized by using nickel-titanium spreaders.

Dental Instruments↗
PubMed1999

Comparison of the cleaning efficacy of passive sonic activation and passive ultrasonic activation after hand instrumentation in molar root canals.

The purpose of this study was to compare the cleaning efficacy of passive ultrasonic activation with that of passive sonic activation after hand instrumentation. Sixty curved molar canals were hand-instrumented to size 35 and divided into three groups. Group 1 received no further treatment. Group 2 received 3 min of passive sonic activation. Group 3 received 3 min of passive ultrasonic activation. The roots were split and photomicrographs (x20) were made of the apical 6 mm of canal. A transparent grid was placed over projected images, and the total number of squares covering the apical 6 mm of canal space and the number of squares containing debris were counted. A debris score was calculated for each specimen by dividing the number of squares with debris by the total number of squares. The mean debris scores were 31.6% for hand instrumentation only, 15.1% for the sonic group, and 16.7% for the ultrasonic group. The debris scores for the sonic and ultrasonic activation groups were significantly lower than that for the hand instrumentation only group (p < 0.01); however, there was no significant difference between the sonic and ultrasonic activation groups. Passive sonics after hand instrumentation produces a cleaner canal than hand instrumentation alone and is comparable with that of passive ultrasonics.

Analysis of Variance↗
PubMed1997

Bronchoalveolar lavage: comparison of nucleopore filters and direct smear preparations.

To determine whether cytopreparation affects the diagnostic yield of bronchoalveolar lavage specimens, we compared 50 lavage samples by using two methods. One nucleopore filter preparation and four direct slides were prepared on each sample submitted. All slides were stained by the Papanicolaou method. Assessment of cellularity, cellular preservation, and an independent diagnosis were rendered on each sample for both preparatory methods. Statistical analysis showed no difference in cellularity between the two methods (P = .06). The degree of nuclear and cytoplasmic preservation was higher using the direct method, although this did not appear to affect diagnosis in this study. One major discrepancy in diagnosis was observed between the two methods. By prospectively comparing nucleopore filter and direct preparation of bronchoalveolar lavages, we found that there was minimal affect on either cellularity or diagnosis. We conclude that either method delivers reliable cytologic results.

Bronchoalveolar Lavage↗
PubMed1997

The efficacy of doxorubicin microspheres for hepatic micrometastases in a rat tumour model.

The use of sustained-release microspheres is of potential benefit as an adjuvant treatment for patients with occult hepatic micrometastases. This study investigates the response of a model of implantable adenocarcinoma micrometastases in the livers of DA rats following the intraportal injection of doxorubicin-incorporated ion-exchange microspheres compared to free drug bolus administration. A point-counting technique was used to determine the percentage of liver consisting of tumour 13 days after treatment. This was used as an indicator of tumour response, as was the derived tumour mass. There was a significantly higher tumour response in animals treated with the microspheres compared to animals treated with free drug delivered at the same concentration. This effect, however, was shown to decrease with a delay in the time of treatment. The tumour response of the sustained-release microspheres was achieved in the absence of any detectable local or systemic toxicity. This study demonstrates the potential of sustained-release microspheres in the treatment of patients with hepatic micrometastases.

Animals↗
PubMed1997

Enhanced anticancer therapy mediated by specialized liposomes.

It has been a central aim of experimental and clinical therapeutics to deliver therapeutic agents as close as possible to, or if possible within, a diseased cell. Such targeting achieves two major aims of drug delivery, the maximum dose of therapeutic agent to the diseased cell and avoidance of uptake by and, usually, accompanying side-effects to normal, healthy cells. Conventional liposomes, originally used for studies in membrane biophysics and biochemistry, have been used in therapy for the past two decades. However, when applied to deliver drugs into cells, conventional liposomes proved inefficient and so novel unconventional or specialized liposomes are constantly being prepared to enhance cell-specific delivery in-vivo. One possible way of achieving better targeting is combination of the positive attributes of more than one specialized type of liposome into one vesicle. Although a limited number of studies has examined the combined effect of such dual-specialty liposomes, more studies are warranted using appropriate models. Liposomes are composed of one, a few, or many concentric bilayer membranes which alternate with aqueous spaces. The drugs are encapsulated within the aqueous internal volume if they are hydrophilic or in the lipid bilayers if they are hydrophobic (Kim 1993). Liposomes range in size from 25 nm to more than 20 microns (Sugarman & Perez-Soler 1992). Depending on their solubility and method of formulation antimicrobial, cytotoxic and other conventional drugs, hormones, antigens, enzymes, genetic material, viruses and bacteria can be incorporated in either the aqueous or hydrophobic phase. This review discusses the types and characteristics of non-conventional liposomes used in various modes of cancer therapy, mainly chemotherapy and gene therapy. It concludes with suggestions on improving these novel liposomal to effect better targeting to cancer cells.

Animals↗
PubMed1997

Evaluation of a human corneal epithelial cell line as an in vitro model for assessing ocular irritation.

A human corneal epithelial cell line, 10.014 pRSV-T (HCR-T cells), has been used to develop a three-dimensional in vitro model of the human corneal epithelium (HCE-T model). HCE-T cells form a stratified culture when grown at the air-liquid interface on a collagen membrane in serum-free medium. This model served as the basis for assays which supported the ocular irritancy assessment of water-soluble test substances. Cellular alterations in the HCE-T model were measured following 5-min topical exposures to 20 chemicals [listed in the European Center for Ecotoxicology and Toxicology of Chemicals (ECETOC) Reference Chemicals Data Bank] and 25 surfactant-based product formulations [utilized in the Cosmetic, Toiletry, and Fragrance Association (CTFA) Alternatives Program Phase III]. In vitro assays used were transepithelial permeability to sodium fluorescein (TEP) and transepithelial electrical resistance (TER). These measured alterations in the barrier function of this corneal epithelial equivalent. Barrier function is a well-developed property in the HCE-T model that supports the mechanistic relevance of these assays. In vitro data, averaged from replicate assays, were compared to respective Draize rabbit eye irritation data from the publicly available ECETOC and CTFA databases using linear regression with Pearson's correlation analysis. For chemicals, Pearson's correlation coefficients, r, from comparisons of Draize maximum average scores (MAS) to TEP and TER data were 0.71 and 0.55, respectively. For product formulations, Pearson's correlation coefficients from comparisons of Draize MAS to TEP and TER data were 0.86 and 0.80, respectively. Data indicated that barrier function alterations in the HCE-T model correlated with ocular irritancy and corneal toxicity. While the irritancy of the chemicals tested was effectively assessed only by the TEP assay, that for the surfactant-based product formulations was effectively assessed by both the TEP and TER assays. Results also suggested that the HCE-T TEP and TER assays vary in their effectiveness for evaluating specific classes of test materials.

Animals↗
PubMed1996

Tumour cells surviving in vivo cisplatin chemotherapy display elevated c-myc expression.

The c-myc oncogene has been extensively implicated in cell proliferation, cell differentiation and programmed cell death. Aberrant expression of the c-myc gene product has been observed in a range of tumours and has also been implicated in cisplatin (cis-dichlorodiammineplatinum)-mediated chemoresistance. A solid transplantable tumour model in syngeneic DA rats was subjected to treatment with cisplatin to determine the impact of such therapy on endogenous c-myc gene expression. Serially transplanted tumours were intravenously treated with a single cisplatin dose (1 mg/kg) and c-myc expression analysed 2 and 7 days after treatment. The surviving tumour cells display a significant 2-fold elevation in c-myc expression at 48 h and 7 days after treatment. Primary cell cultures have been derived from untreated in vivo tumours of the same model and subjected to treatment with a c-myc phosphorothioate antisense oligomer. Administration of 5 microM c-myc antisense oligomer directed at the initiation codon and first four codons of c-myc mRNA results in total inhibition of c-myc expression and coincident suspension of cell growth for a period of 4 days in culture. Antisense therapies directed at the c-myc gene may well prove an effective tool for treating tumours in conjunction with cisplatin as these findings show that tumour cells surviving cisplatin chemotherapy display elevated c-myc expression.

Animals↗
PubMed1996

The basis for somatic gene therapy of cancer.

A decade of advances in understanding of the molecular basis of sporadic and familial cancers has combined with developments in mammalian gene transfer technology to stimulate intensive research into the potential applications of somatic gene therapy for cancer. Somatic gene immunotherapy is already in progress to stimulate and direct the natural targeting capabilities of the immune system against the threat of disseminated residual disease. The association of a plethora of mutated tumor suppressor genes (p53, p16 BRCA1, BRCA2) with diverse cancers has also highlighted the potential of somatic gene therapy with wild-type versions of suppressor genes as an anti-cancer therapeutic modality either in its own right or in synergistic association with traditional anti-cancer therapies. The methodologies for gene transfer technology range from direct intravenous injection of naked modified DNAs to intravenous injection of liposome-encapsulated DNAs or microsphere-bound DNAs. Recombinant retroviral and adenoviral vectors have natural transfection capabilities and display tropism for particular tissues that are of selective advantage against particular cancers. Liposomes display very high efficiencies of gene transfer with the advantages of successful transfer to a wide range of tissue types but their widespread systemic distribution offers problems in relation to selective targeting of tumor cells. The challenges to current gene transfer processes are much the same as that of other anti-cancer therapies: achieving selective targeting of cancer cells whilst optimizing dosages and minimizing the risk of collateral damage to healthy tissues.

Animals↗
PubMed1995

Phosphorylation of dense-plaque proteins talin and paxillin during tracheal smooth muscle contraction.

Reorganization of cytoskeletal-membrane interactions during contractile stimulation may contribute to the regulation of airway smooth muscle contraction. We investigated the effect of contractile stimulation on the phosphorylation of the actin-membrane attachment proteins talin, vinculin, and paxillin. Stimulation of 32P-labeled canine tracheal smooth muscle strips with acetylcholine (ACh; 10(-3) M) resulted in a rapid 2.6-fold increase in phosphorylation of serine and/or threonine residues, compared with resting levels of 0.22 mol PO4(3-)/mol talin. After stimulation with ACh, phosphorylation of tyrosine residues on paxillin increased approximately threefold. Two-dimensional phosphopeptide mapping of in vivo labeled talin and paxillin indicated phosphorylation on a limited number of sites. Vinculin phosphorylation was undetectable in either resting or ACh-stimulated muscle. We conclude that phosphorylation of talin and paxillin occurs during ACh-stimulated contraction of tracheal smooth muscle and that distinct signaling pathways activate a serine/threonine kinase that phosphorylates talin and a tyrosine kinase that phosphorylates paxillin. The pharmacological activation of airway smooth muscle cells might involve the anchoring of contractile filaments to the membrane.

Acetylcholine↗
PubMed1991

Management of vertebral column fractures in dogs and cats: 211 cases (1977-1985).

Hospital records and radiographs of 211 dogs and cats with vertebral column fractures or luxations evaluated at the University of Tennessee Veterinary Teaching Hospital between April 1977 and September 1985 were reviewed. After neurologic examination, status of the animal was graded on a scale of 1 to 8. Decision to treat each animal either medically or surgically was based on the extent and type of injury, neurologic signs, veterinarian's experience, and owner's wishes. After treatment, neurologic status was evaluated on the aforementioned scale and differences in the outcome of treatment were determined between surgically and medically treated groups, relative to initial neurologic status and location of the fracture. Surgically treated animals had pretreatment mean (+/- SD) neurologic status (3.71 +/- 1.35) that was slightly worse (P = 0.0079) than that of medically managed cases (5.16 +/- 1.48). Animals of the surgically treated group improved significantly (P = 0.0122) more than did those of the medically treated group but after treatment, significant differences in neurologic status were not evident between surgically (6.67 +/- 1.49) and medically (7.07 +/- 1.24) treated animals. Medically treated animals required substantially longer to reach optimal neurologic status, but the average hospital stay was nearly twice as long for the surgically treated animals (13.5 days), compared with those treated medically (7.1 days). Animals with thoracic vertebral fractures had mean neurologic status that was worse than that in animals with cervical vertebral fractures (P = 0.0109). After either medical or surgical treatment, neurologic status did not differ among animals with cervical, thoracic, or lumbar vertebral fractures.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Histological evaluation of ultrasonic debridement comparing sodium hypochlorite and water.

Twenty extracted human mandibular first and second molars with mesial canal curvatures of 18 to 35 degrees were randomly divided into two groups. Following routine endodontic access and canal length determination one of the mesial root canals was ultrasonically instrumented, using tap water in the first group or 2.6% sodium hypochlorite irrigation in the other. In both groups the other mesial canal was used as a control. The mesial roots were decalcified, serially sectioned, and stained with hematoxylin and eosin. Wall planing and soft tissue debridement were blindly evaluated using the light microscope. Mean canal wall planing and soft tissue debridement scores were compared by multiple t tests. Sodium hypochlorite, in conjunction with ultrasonic instrumentation, was more effective than tap water in wall planing when the entire root length was considered. Sodium hypochlorite, in conjunction with ultrasonic instrumentation, was more effective than tap water in soft tissue debridement in the middle third of the canal. Both irrigants were ineffective in conjunction with ultrasonic instrumentation in removing soft tissue from the main canal, the isthmus between canals, the canal fins, and the multiple branches or deltas often encountered in the apical one-third of the canal.

Humans↗
PubMed1989

Histological evaluation of ultrasonic and sonic instrumentation of curved root canals.

Fifty extracted human mandibular first and second molars with mesial canal curvatures of 18 to 35 degrees were randomly divided into five groups. After routine endodontic access and canal length determination, one of the mesial root canals was instrumented using tap water and one of the following instrumentation methods: (a) hand instrumentation; (b) ultrasonic instrumentation with the Cavi-Endo unit; (c) ultrasonic instrumentation with the Enac unit; (d) sonic instrumentation with the Medidenta unit; and (e) sonic instrumentation with the Endostar 5 unit. The other mesial canal was used as a control. The mesial roots were decalcified, serially sectioned, stained with hematoxylin and eosin, and blindly evaluated using the light microscope. The mean canal wall planing and soft tissue debridement scores were compared by analysis of variance. There was no statistically significant difference among the groups for wall planing or soft tissue debridement.

Humans↗
PubMed1988

Blastomycosis in cats: five cases (1979-1986).

Medical records of 5 cats with blastomycosis examined at the University of Tennessee Veterinary Teaching Hospital from 1979 to 1986 were reviewed. Clinical signs of blastomycosis varies depending on the organ(s) affected, but respiratory tract disease was most common, followed by CNS signs and ocular problems. A definitive diagnosis was made by identification of characteristic fungal organisms in biopsy or necropsy specimens. Two cats treated with amphotericin B did not respond to treatment and died or were euthanatized. The lungs, brain, eyes, and lymph nodes commonly were affected, but one cat had only cutaneous and regional lymph node involvement. The respiratory tract appeared to be a common primary site of infection, with dissemination to other organ systems. The typical host response was a pyogranulomatous cellular infiltrate with numerous fungal organisms evident.

Animals↗