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L Woo

Publications and source records attributed to L Woo.

At least 19 recordsLinked to original sources
PubMed2001

The genome of the natural genetic engineer Agrobacterium tumefaciens C58.

The 5.67-megabase genome of the plant pathogen Agrobacterium tumefaciens C58 consists of a circular chromosome, a linear chromosome, and two plasmids. Extensive orthology and nucleotide colinearity between the genomes of A. tumefaciens and the plant symbiont Sinorhizobium meliloti suggest a recent evolutionary divergence. Their similarities include metabolic, transport, and regulatory systems that promote survival in the highly competitive rhizosphere; differences are apparent in their genome structure and virulence gene complement. Availability of the A. tumefaciens sequence will facilitate investigations into the molecular basis of pathogenesis and the evolutionary divergence of pathogenic and symbiotic lifestyles.

Agrobacterium tumefaciens↗
PubMed2001

New triterpenoid saponins from the sponge Erylus nobilis.

Erylosides G--J (1--4), four new triterpenoid saponins, were isolated from the sponge Erylus nobilis collected from Jaeju Island, Korea. On the basis of the results of combined chemical and spectral analyses, the structures of the aglycones were determined to be lanostane-based, modified penasterols. The oligosaccharide portions were composed of one unit each of L-arabinose, D-galactose, and 2-N-acetyl-D-glucosamine (1 and 3) or two units of L-arabinose and one unit of 2-N-acetyl-D-glucosamine (2 and 4). These compounds exhibited moderate cytotoxicty against a human leukemia cell line.

Animals↗
PubMed2001

Novel material properties via ionising radiation.

Ionising radiation is normally associated with the degradation of materials during radiation sterilisation. However, these same radiation sources can be used to create material properties that are unobtainable by other methods. This review of some novel properties that can be achieved also critically compares the relative merits and disadvantages of each radiation source.

Equipment Contamination↗
PubMed1999

The most pathogenic transthyretin variant, L55P, forms amyloid fibrils under acidic conditions and protofilaments under physiological conditions.

The L55P transthyretin (TTR) familial amyloid polyneuropathy-associated variant is distinct from the other TTR variants studied to date and the wild-type protein in that the L55P tetramer can dissociate to the monomeric amyloidogenic intermediate and form fibril precursors under physiological conditions (pH 7.0, 37 degrees C). The activation barrier associated with L55P-TTR tetramer dissociation is lower than the barrier for wild-type transthyretin dissociation, which does not form fibrils under physiological conditions. The L55P-TTR tetramer is also very sensitive to acidic conditions, readily dissociating to form the monomeric amyloidogenic intermediate between pH 5.5-5.0 where the wild-type TTR adopts a nonamyloidogenic tetrameric structure. The formation of the L55P monomeric amyloidogenic intermediate involves subtle tertiary structural changes within the beta-sheet rich subunit as discerned from Trp fluorescence, circular dichroism analysis, and ANS binding studies. The assembly of the L55P-TTR amyloidogenic intermediate at physiological pH (pH 7.5) affords protofilaments that elongate with time. TEM studies suggest that the entropic barrier associated with filament assembly (amyloid fibril formation) is high in vitro, amyloid being defined by the laterally assembled four filament structure observed by Blake upon isolation of "fibrils" from the eye of a FAP patient. The L55P-TTR protofilaments formed in vitro bind Congo red and thioflavin T (albeit more weakly than the fibrils produced at acidic pH), suggesting that the structure observed probably represents an amyloid precursor. The structural continuum from misfolded monomer through protofilaments, filaments, and ultimately fibrils must be considered as a possible source of pathology associated with these diseases.

Amyloid↗
PubMed1999

The quest for high temperature flexible polymers.

A unique set of material properties is needed to meet the special requirements of the medical market. Flexible poly(vinyl chloride), which has occupied a pre-eminent position for nearly half a century, is increasingly being challenged by newer and more advanced polymer systems. Several propylene-based elastomers with low crystallinities are promising to be the dominant medical materials of the future. This article discusses one company's actual experiences in utilizing these new materials in medical applications.

Biocompatible Materials↗
PubMed1997

Effect of weight, sex, age, clinical diagnosis, and thromboplastin reagent on steady-state intravenous heparin requirements.

BACKGROUND: There is a significant direct relationship between steady-state intravenous heparin dose requirements and total body weight. Less is known about whether sex, age, clinical diagnosis, and the thromboplastin used to measure the activated partial thromboplastin time (aPTT) affect heparin dose requirements. METHODS: Four cohorts of patients treated with intravenous heparin were gathered from 3 hospitals: 2 cohorts with deep vein thrombosis (DVT) and 2 cohorts with coronary artery disease (CAD). For each clinical diagnosis, half the patients were monitored using one aPTT reagent and the remainder were monitored using a second reagent. Heparin doses and aPTT measurements were recorded, and the dose necessary to achieve an aPTT ratio of 2.0 was calculated using a computer software program. RESULTS: We analyzed the records of 340 patients: 165 with DVT and 175 with CAD. Using analysis of variance, there was a significant difference in the steady-state heparin requirements among patients with DVT compared with patients with CAD (P < .001). For each clinical diagnosis, the use of a different thromboplastin reagent did not affect heparin dose requirements (P > .42). Linear regression modeling disclosed that the steady-state heparin dose for patients with DVT was a function of weight plus an effect modifier involving weight and age, whereas for patients with CAD there was only a weak relationship with weight. CONCLUSIONS: Steady-state heparin dose requirements were significantly different in patients with DVT compared with patients with CAD, suggesting that different dosing nomograms are needed for each condition. For patients with DVT, the accuracy of the initial heparin dose estimate may be improved by considering the patient's age and weight.

Aged↗
PubMed1990

Modification of the clonogenic assay for the detection of lymphokine activated killer cell activity.

The soft agar clonogenic assay using [3H]thymidine uptake as an endpoint was adapted for the detection of human LAK activity against the Daudi lymphoma cell line and human tumor cells obtained by biopsy. Using Daudi cells as the target population the modified agar assay was more sensitive than the conventional 4 h 51Cr release assay. Use of a single layer agar assay allowed the assessment of LAK cytotoxic/cytostatic activity against Daudi lymphoma cells after cell to cell contact, while a two layer system permitted evaluation of the role of soluble mediators in LAK/target cell interactions. This study shows that LAK cells can either kill or inhibit the proliferation of Daudi cells by two mechanisms: one which requires cell-to-cell contact, and a second via soluble mediators. As determined by the use of neutralizing antisera, the soluble factor(s) are not tumor necrosis factor and interferon-gamma. Of the nine individual human tumor samples obtained by biopsy. 89% were sensitive to allogeneic LAK cells when the two populations were admixed. Of these nine tumors 44% were inhibited by LAK-derived soluble factors. The soft agar assay system should serve as a useful tool for determining the sensitivity of human tumors to LAK cells and for studying the mechanisms of LAK anti-tumor activity.

Colony-Forming Units Assay↗
PubMed1989

Microrheological aspects of adhesion of Escherichia coli on glass.

The adhesion of both live and fixed bacteria (Escherichia coli) on glass has been studied under well-defined hydrodynamic conditions, created in an impinging jet apparatus. With this technique one can accurately measure the initial deposition rate jo on the surface, the average lifetime of a bacterium on the surface, tau esc, and the surface area blocked per deposited bacterium, normalized by its projected area, gamma. The experimental results are compared to theoretical results for equivalent spheres. It is found that near the stagnation point the deposition rate jo is mainly controlled by convective diffusive transport which, for rod-shaped Eschericia coli, with an axis ratio of about 2, is found to be equal to that for spheres. No differences in jo and tau esc were found between live and fixed bacteria at low flow rates. At high flow rates fixed bacteria adhered to the surface at a slower rate. In both systems jo was found to decrease suddenly at a distance of about 150 microns from the stagnation point, in contrast to systems of spherical particles for which jo is uniform over the surface. Most likely this is due to the rotation of the rod-shaped particles, which vary their distance to the surface periodically with time. The main difference between live and fixed bacteria, besides different deposition rates in strong flows, is that gamma is about 30% larger for fixed bacteria than for live ones, resulting in a much lower final coverage for fixed bacteria. These results imply a larger repulsion between fixed bacteria than between living ones. From detachment experiments we can conclude that not all bacteria stick to the surface with the same bond strength. The variation in the bond strength is due to the aging of the bonds between the bacteria and the surface. The average bond strength corresponds to an energy of about 13-15 kT.

Bacterial Adhesion↗
PubMed1988

Effects of bone marrow fibroblastic cells and fibroblastic conditioned medium on HL-60 and KG-1.

The in-vitro effects of bone marrow fibroblastic cells (FC) and fibroblastic conditioned medium (FCM) on the proliferation and differentiation of two human leukemic cell lines, HL-60 and KG-1 were studied. When FC were seeded onto only one-half of the culture dish an increase in colony size of HL-60 and KG-1 was observed directly above the FC. FCM had a greater effect, resulting in approximately a four-fold increase in the size of HL-60 and KG-1 colonies. In regards to colony number, FCM from normals inhibited HL-60, but FCM from other sources had no effect. FCM from both normals and ANLL in CR inhibited KG-1 colony number in contrast to the lack of effect with FCM from ANLL at diagnosis and RAEB. Neither FC nor FCM had any effect on the differentiation of either cell line. Our results indicate that FC modulate the proliferation of both HL-60 and KG-1. Furthermore, in ANLL the effects of FC are dependent upon the stage of the disease.

Bone Marrow Cells↗
PubMed1988

Variability of the thymidine labeling index in squamous cell carcinoma of the head and neck.

Tritiated thymidine (3HTdR) labeling is the standard technique for determining the kinetic activity of tumors. This method has been used to label multiple sections of tumor specimens obtained from seven patients with advanced squamous cell carcinoma of the head and neck. Considerable variability was observed in the labeling index in different sites from the same specimen. To reduce the large sampling error due to heterogeneity, we recommend that an average value be determined from multiple sections when employing this technique.

Carcinoma, Squamous Cell↗
PubMed1987

Cytogenetics of bone marrow fibroblastic cells in idiopathic chronic myelofibrosis.

To determine the nature of the fibroblastic proliferation in myelofibrosis, we studied the cytogenetic composition of a pure population of in-vitro bone marrow fibroblastic cells (FC) from a patient with idiopathic chronic myelofibrosis who had trisomy 8 in her unstimulated peripheral blood cells. This cytogenetic abnormality was absent in all the FC studied supporting the premise that in the myeloproliferative disorders the myelofibrosis represents a secondary or non-neoplastic reaction to the clonal proliferation of haematopoietic stem cells.

Aged↗
PubMed1987

Morphological evidence of an altered bone marrow microenvironment in patients with acute nonlymphoblastic leukemia and myelodysplastic disorders.

Type IV nuclear bodies are classified as true intranuclear inclusions that ultrastructurally contain numerous densely packed 20- to 30-nm osmiophilic granules surrounded by a microfibrillar cortex. In the present study, we have found statistically significant ultrastructural differences in the frequency and size of type IV nuclear bodies in the in vitro bone marrow fibroblastic cells (FC) derived from eight nonleukemic subjects and 13 patients with acute nonlymphoblastic leukemia (ANLL) and myelodysplastic disorders (MDD). Patients with ANLL, MDD, and myelofibrosis, as a group, had four times as many type IV nuclear bodies as nonleukemic subjects. The mean frequency of type IV nuclear bodies for patients with ANLL and MDD was 2.68% +/- 3.27% as compared with 0.63% +/- 1.06% for the nonleukemic subjects (p less than 0.05). The mean maximum type IV nuclear body area of the ANLL and chronic myelomonocytic leukemia (CMML) patients as a group was 2.08 +/- 1.10 micron2, compared with a mean maximum area of 0.93 +/- 0.10 micron2 from nonleukemic subjects (p less than 0.05). The FC were otherwise morphologically indistinguishable and displayed the typical ultrastructural features of fibroblasts. These findings have provided the first morphologic evidence that supports the concept of an altered bone marrow microenvironment in patients with ANLL and MDD. Since type IV nuclear bodies are found in high frequency in virally infected tissues, our quantitative ultrastructural findings raise the possibility of a local viral infection that affects the bone marrow microenvironment of patients with ANLL and some MDD disorders.

Acute Disease↗
PubMed1986

The growth of benign prostatic hypertrophy in semisolid agar culture.

Tissue samples from transurethrally resected benign prostatic hypertrophy (BPH) in 29 patients were disaggregated into single cells and cultured in semisolid media. In 15 cultured specimens not overgrown with bacteria or fungus, colony formation occurred in seven (47 per cent). The median plating efficiency was 0.036 per cent with a range of 0.0005 to 0.9 per cent. Studies of the cells forming the colonies demonstrated histochemical, immunohistologic, morphologic and ultrastructural findings characteristic of an epithelial origin. The results suggest a potential utility of colony forming assays in the study of benign as well as malignant cells. These BPH culture studies were limited by microorganism contamination and low yields from the disaggregation technique.

Agar↗
PubMed1986

Growth in semisolid agar of prostate cancer cells obtained from bone marrow aspirates.

Thirty-one bone marrow aspirations were performed on patients with prostatic carcinoma metastatic to bone. After separation over a Ficoll-Hypaque gradient viable nucleated cells were cultured in semisolid agar. Colony formation occurred in 14 of 27 (52%) nonbacterially contaminated cultures. Characterization of cells from the colonies showed them to be consistent with malignant prostate cells. After staining, these cells were periodic acid-Schiff positive, prostatic acid phosphatase positive, and prostatic specific antigen positive. Other studies demonstrated the cells to be karyotypically abnormal, ultrastructurally similar to epithelial cells, and capable of secondary colony formation. Three bone marrow aspirate specimens did not have metastatic prostatic carcinoma detected by standard methods but did demonstrate colony formation. However, colony formation was most frequently seen when a radionuclide scan was positive at the aspiration site and when tumor cells were microscopically detectable by Wright staining of a smeared aspirate. The potential utility of colony forming cultures in prostate cancer is discussed. In working with bone marrow aspirates, additional cell separation procedures may be required to calculate and maximize plating efficiencies.

Agar↗
PubMed1984

In vitro radiation response studies on bone marrow fibroblasts (CFU-F) obtained from normal and chronically irradiated dogs.

The radiation resistance of bone marrow fibroblasts as measured by their proliferative potential was evaluated in chronically irradiated dogs. Bone marrows were obtained from eight dogs that had been chronically irradiated beginning at 21 days of gestation or after birth and eight age-matched controls. Of these irradiated dogs, four were either preleukemic or exhibited frank acute nonlymphocytic leukemia. The other four were clinically normal but demonstrated abnormalities in their marrow that could be attributed to radiation effects and/or other pathologic changes. Fibroblasts from six of the irradiated dogs were significantly more radioresistant than those of their controls. Five of these six dogs subsequently succumbed to hematopathologic disease, while the two irradiated dogs with normal fibroblasts remained clinically normal, suggesting that this observed radioresistance may be linked to the disease process.

Animals↗
PubMed1984

Increased in vitro radioresistance of bone marrow fibroblastic progenitors (CFU-F) from patients with acute non-lymphocytic leukemia.

The proliferative potential following in vitro irradiation of bone marrow fibroblastic progenitors (CFU-F) derived from four patients with acute nonlymphocytic leukemia (ANLL) and seven nonleukemic subjects was compared. The CFU-F from the ANLL patients were significantly more radioresistant than the CFU-F from the nonleukemic subjects. The increased radioresistance in ANLL patients was evident in both the mean slope of the survival curve (control = -0.385, ANLL = -0.256) and in the Do values (control = 2.68 Gy, ANLL = 4.61 Gy). Thus CFU-F derived from ANLL patients differ from those derived from nonleukemics in both radioresistance and in granulopoietic effects as suggested from previous studies.

Bone Marrow↗
PubMed1981

Cytogenetics and granulopoietic effects of bone marrow fibroblastic cells in Fanconi's anaemia.

To determine if abnormalities exist in the bone marrow stroma in Fanconi's anaemia, we studied the cytogenetic composition of in vitro bone marrow fibroblastic cells (FC) from a patient with this disorder and compared it to those obtained from skin fibroblasts, peripheral blood lymphocytes, and direct bone marrow preparations. The presence of granulocytic progenitors in bone marrow and T lymphocyte colonies in peripheral blood was also determined in addition to the ability of this patient's FC to stimulate normal granulocytic progenitors. We found that the FC had far fewer chromosomal abnormalities and stimulated normally the growth of granulocyte colonies. Granulocyte progenitors were not found, but T lymphocyte colonies were abundant. These results support the concept that a defect in haematopoietic stromal elements is not responsible for the aplasia developing in the disorder.

Adolescent↗