PubMed Health⌕ Search

Biomedical subjects

C Bush

Publications and source records attributed to C Bush.

At least 19 recordsLinked to original sources
PubMed1998

Comparison between pulsed-field gel electrophoresis and the comet assay as predictive assays for radiosensitivity in fibroblasts.

The radiosensitivity of skin fibroblasts derived from patients as measured in vitro by a clonogenic survival assay appears to correlate with the risk of developing severe late reactions to radiation. Unfortunately, these assays are clinically impractical as a predictive test for radiosensitivity. The purpose of this study was to assess the utility of two possible surrogate assays for radiosensitivity, pulsed-field gel electrophoresis (PFGE) and single-cell gel electrophoresis (comet assay), both of which can be used to measure DNA double-strand breaks. Twenty-three nontransformed human fibroblast cell lines exhibiting a range of radiosensitivities were studied with both of these assays. The results were correlated with measurements of radiosensitivity obtained as part of a larger study examining the correlation between cellular radiosensitivity and clinical response. [2-(14)C]Thymidine-labeled confluent cultures were irradiated at 1.0 Gy/min with doses of 0 to 150 Gy. After allowing 4 h for repair at 37 degrees C, cells were trypsinized and aliquots were used for preparing slides for the comet assay. After neutral lysis and electrophoresis, the slides were stained with ethidium bromide and 50 comet moments were measured for each dose. The remainder of the cells were formed into agarose plugs and, after neutral lysis, were subjected to PFGE. The fraction of activity released (FAR) from the well was measured by scintillation counting of appropriate segments of each gel lane. Cellular radiosensitivity was measured with a standard clonogenic assay at a low dose rate of 1.2 cGy/min, and the dose that resulted in a surviving fraction of 0.01 (D0.01) was calculated. The slope of the plot of comet moment as a function of dose for each cell line did not correlate with D0.01 (R = 0.36, P > 0.1). In contrast, the slope of the FAR as a function of dose had a weak inverse correlation with D0.01 (R = 0.43 and P = 0.05) such that the more radiosensitive cell lines exhibited a steeper dose response for FAR. Although the correlation between the slope of the dose response for FAR and D0.01 was weak, refinement of the PFGE technique may provide a potentially useful predictive assay for radiosensitivity.

Breast↗
PubMed1997

Screening for cognitive impairment in the elderly.

OBJECTIVE: To evaluate the extent and type of screening for cognitive impairment primary care physicians use for their elderly patients, to identify perceived barriers to screening, and to explore whether physicians would be willing to use the clock drawing test as a cognitive screening tool. DESIGN: Mailed questionnaire. SETTING: Primary care practices in the Ottawa-Carleton region. PARTICIPANTS: Family physicians and general practitioners culled from the Yellow Pages and Canadian Medical Directory; 368 of 568 questionnaires were returned for a response rate of 70%. Six respondents had fewer than 30 patients weekly and two responded too late to be included in the analysis; 360 cases were included in the analysis. MAIN OUTCOME MEASURES: Responses to 10 questions on cognitive screening and five on demographics and the nature of respondents' practices. RESULTS: About 80% of respondents reported doing at least one mental status examination during the past year. Only 24% routinely screened patients, although 82% believed screening was needed. Major barriers to cognitive screening were lack of time, risk of offending patients, and possible negative consequences of follow up. Clock drawing was perceived as an acceptable method of screening, if it were proven effective. CONCLUSIONS: Most primary care physicians believe cognitive screening is needed, but few routinely screen their elderly patients. Lack of time is the most important perceived barrier to screening. Primary care physicians are receptive to using the clock drawing test, and, because it is not time-consuming, are less likely to consider lack of time a barrier to testing. The clock test might help bridge the gap between perceived need for screening and actual screening.

Adult↗
PubMed1995

DNA strand break rejoining defect in xrs-6 is complemented by transfection with the human Ku80 gene.

The radiosensitive mutant xrs-6, derived from Chinese hamster ovary cell line CHO-K1, has been demonstrated to be defective in DNA double-strand break repair and also in its proficiency to undergo V(D)J recombination. Recent work has provided both genetic and biochemical evidence that the M(r) 80,000 subunit of the Ku protein is able to complement the radiosensitivity and the V(D)J recombination defect in the xrs-6 mutant. We demonstrate here that complementation of the radiosensitive phenotype in xrs-6 cells by the introduction of Ku80 cDNA is accompanied by the concomitant restoration of DNA double-strand break rejoining proficiency to almost that of the parental CHO-K1 cells, as measured both by neutral single-cell microgel electrophoresis (Comet) technique and by pulsed-field gel electrophoresis. These results provide further biochemical evidence for the involvement of the Ku protein in the repair of DNA double-strand breaks.

Animals↗
PubMed1994

Relationship between chromosome aberrations, micronuclei and cell kill in two human tumour cell lines of widely differing radiosensitivity.

The relationship between chromosome aberration frequency, micronucleus (MN) formation and cell kill was investigated in two human tumour cell lines, RT112, a radioresistant bladder carcinoma cell line, and HX142, a radiosensitive neuroblastoma cell line. As MN are generally accepted to result from acentric chromosome fragments that are lost at nuclear division and all unstable aberrations result in an acentric fragment, a 1:1 correlation between aberrations and MN might be expected. There was a good correlation between cell kill and aberration frequency in the two cell lines, however the relationship between cell kill and MN formation in the lines was very different. RT112 showed 0.22 aberrations and 0.21 MN per Gy whilst HX142 showed 0.61 aberrations and 0.078 MN per Gy. Possible reasons for the discrepancy observed in HX142 are discussed.

Cell Survival↗
PubMed1994

Dose-rate effect for DNA damage induced by ionizing radiation in human tumor cells.

The effect of dose rate on clonogenic cell survival and DNA double-strand breaks (DSBs) has been examined in a human bladder carcinoma cell line, RT112, treated with ionizing radiation. Cell survival changed markedly over the range of dose rates used (0.01-1.28 Gy/min) with the curves becoming shallower and straighter as the dose rate was lowered. Similarly, the number of DSBs measured by pulsed-field gel electrophoresis (PFGE) immediately after irradiation varied with dose rate. Fewer DSBs were detectable after low-dose-rate irradiation. However, when a 4-h repair period was allowed after irradiation, cells treated at all dose rates exhibited approximately the same amount of damage. The final level of unrejoined DSBs, as detected by PFGE, therefore does not correlate with cell survival at different dose rates.

Cell Survival↗
PubMed1993

The anatomy of missed breast cancers.

Missed breast cancer continues to account for the highest percentage of medical malpractice cases in the United States. A retrospective, computer-aided study was performed to investigate the mechanisms of missed breast carcinomas, missed either by mammography or by clinical exam. In a consecutive series of 509 breast cancers found in patients registered at a University Comprehensive Breast Cancer Clinic, no tumour that was 5 mm or less in maximal diameter was clinically palpable. This subgroup consisted of seven in situ and 32 invasive carcinomas. The incidence of palpable tumours in 5 mm increments increased so that when a tumour was between 11 and 15 mm in size, 48% of the lesions were palpable, and with tumours greater than 20 mm in size, 84% were palpable. There was a good correlation between size of the tumour as judged by mammography and the eventual size determined by histologic examination. Smaller breast cancers were detected by mammography than by physical examination. In a separate analysis of 553 consecutive cases of breast cancer examined by mammography, there were 50 (9%) cases in which the cancer was not read from the mammogram. In retrospect, 10 of these mammograms were abnormal for a misinterpretation rate of 1.8%. Cancers associated with false negative mammograms occurred more often in younger women and in dense breast parenchyma than cancers detected by mammography. Cancers missed by mammography were smaller than palpable cancers detected by mammography, more often had negative nodes and presented with a lower stage of disease. Breast augmentation implants were associated more frequently with missed breast cancers, with 5/8 clinically detected breast carcinomas being undetected by mammography. An asymmetric mass was more often associated with cancers missed by mammography, accounting for the sole sign of malignancy in 3% of all cancers, but was the source of 14% of false negative exams. Architectural distortion, ill-defined or well circumscribed masses or calcifications as mammographic signs of malignancy were not associated with an increased frequency of missed cancers. Three 'interval' breast cancers occurred in this series and are included in the false negative mammograms. It is concluded that the threshold of clinically detected breast cancers is 6 mm and experienced clinicians do not detect the majority of breast cancers until the lesions are greater than 16 mm. Mammography has a defined misinterpretation and false negative rate. Likewise, asymmetric mammographic densities that are greater than 16 mm and are not palpable may be followed, since most breast cancers are palpable in this range.

Adult↗
PubMed1993

Micronucleus formation in human tumour cells: lack of correlation with radiosensitivity.

The micronucleus (MN) test has been carefully characterized in four human tumour cell lines of widely differing radiosensitivity. Two radioresistant bladder carcinoma cell lines (MGH-U1 and RT112), one sensitive medulloblastoma cell line (D283MED) and a sensitive neuroblastoma cell line (HX142) were used. The number of MN per Gy of ionising radiation was 0.13 for HX142, 0.17 for D283MED, 0.21 for RT112 and 0.26 for MGH-U1. This does not rank the cell lines in the same order of radiosensitivity as clonogenic cell survival where the surviving fraction at 2 Gy (SF2) was 0.11 for HX142, 0.2 for D283MED, 0.62 for RT112 and 0.53 for MGH-U1. This discrepancy between MN formation and cell death leaves doubt as to the potential usefulness of the MN test as a rapid assay of radiosensitivity but it has potential implications for the mechanistic basis of radiosensitivity in these cells.

Cell Death↗
PubMed1991

Evaluation of cell attachment matrix (CAM) coated plates for primary culture of human tumour biopsies.

Baker et al. [Cancer Res. 46: 1263-1274, 1986] developed an adhesive tumour cell culture system (ATCCS) using a culture surface coated with a cell attachment matrix (CAM). The ability of CAM-coated plates to support the growth of cells from human tumour biopsies has been evaluated. Successful growth was obtained in 9/22 samples (41%), but fibroblasts, rather than tumour cells, grew in the majority. Comparison of CAM with other surfaces showed that CAM was no better for establishing tumour cell growth than the presence of feeder cells or an alternative attachment factor vitronectin.

Animals↗
PubMed1991

Proliferation in human bladder carcinoma measured by Ki-67 antibody labelling: its potential clinical importance.

Ki-67 is a monoclonal antibody which recognises a human nuclear antigen expressed in proliferating cells. The antibody was used to assess proliferation in primary human bladder tumours from 64 patients. Ki-67 index (the number of Ki-67 positive tumour cells divided by the total number of tumour cells %) was derived from 59 tumours. A wide range of Ki-67 indices were recorded, range 3.0-65.8%, mean 20.2%. The Ki-67 index correlated with known prognostic factors: T stage (P = 0.002) and histological grade (P less than 0.001), early stage disease and more differentiated tumours having lower Ki-67 indices. Patients with invasive disease (21 patients) had significantly higher Ki-67 indices than those with non-invasive disease (P = 0.01). Patients with metastatic disease at presentation (four cases) all had a Ki-67 index of greater than or equal to 29%. Ki-67 antibody staining is a simple technique for assessing the proliferation fraction than can be performed on a small amount of tissue taken at routine biopsy without prior injection of thymidine analogues.

Aged↗
PubMed1991

Cell proliferation in human tumour xenografts: measurement using antibody labelling against bromodeoxyuridine and Ki-67.

Cell proliferation was investigated in human tumour xenografts using bromodeoxyuridine (BrdUrd) labelling, evaluated either by flow cytometry or in tissue sections, and also using the proliferation marker Ki-67. BrdUrd labelling was found to increase when cryostat tumour sections were digested with an enzymic solution. This yielded a labelling index up to four times higher than that obtained using the flow cytometer. Ki-67 indices were found to be higher than those reported for human tumour biopsies, as may be expected due to the enhanced growth rate of the xenografts. Significant heterogeneity was observed in the results for cervix, breast and bladder tumours, and the results of the three methods were poorly correlated. However, three of the four tumour types showed that the tumour with the lowest Ki-67 index also had the longest potential doubling time. Since the measurement of Ki-67 index was found technically easier to perform, and also adequately reflects relative tumour cell proliferation, it is preferred over the other techniques.

Animals↗
PubMed1988

Growth and chemotherapy of a human germ-cell tumour line (GCT 27).

The human germ-cell tumour cell line GCT 27 growing as subcutaneous xenograft tumours in male nude mice was used in the 4th and 5th passage to study chemotherapeutic drug responses. Recipient mice received 5 Gy whole body irradiation immediately before tumour transplantation. The median take rate was 62% (range 39-73%) and the median volume doubling time 14 days (range 7-28 days). For bleomycin, cisplatin and carboplatin a clear dose response for growth delay was observed. Bleomycin caused substantial weight loss at doses above 75 mg/kg whereas good response to cisplatin was obtained without serious toxic effects. Vinblastine and etoposide exerted no effect when given in non-toxic doses. The response to etoposide was not improved either by fractionated treatment or by combination with verapamil. However, the combination of 20 mg/kg etoposide and 2 mg/kg cisplatin, which when given alone were ineffective, led to a growth delay that was equal to that observed following the administration of higher cisplatin doses. This effect may be explained by the fact that etoposide, as an inhibitor of DNA-topoisomerase II, may interfere with the repair of DNA interstrand cross-links caused by cisplatin.

Animals↗
PubMed1988

In situ detection of human immunodeficiency virus (HIV) nucleic acid in H9 cells using nonradioactive DNA probes and an image cytophotometry system.

Rapid and sensitive nonradioactive methods to detect human immunodeficiency virus (HIV)-infected cells are needed in clinical medicine. We developed an in situ hybridization test using 2-acetylaminofluorene (AAF)-labeled HIV DNA as a hybridization probe. Hybridized probe was detected using rabbit anti-AAF antibody, followed by alkaline phosphatase-conjugated goat anti-rabbit, and the bromochloroindolyl phosphate-nitroblue tetrazolium reaction. An image cytophotometry system was used to quantitate the percentage of HIV-infected cells. These methods were used to determine the percentage of H9 cells infected with HIV. HIV was detected in 0% of cells on day 1 post infection, 7% on day 4, 41% on day 8, and 5% on day 15. These results paralleled those of the reverse transcriptase assay and an antigen capture ELISA assay for HIV antigen. Thus the AAF modified HIV DNA probe detected HIV nucleic acid in infected H9 cells and the image cytophotometry system improved the sensitivity and objectivity of detection.

2-Acetylaminofluorene↗
PubMed1988

Systemic-pulmonary polytetrafluoroethylene shunts in palliative operations for congenital heart disease. Revival of the central shunt.

The concept of central shunting in smaller children with the Waterston shunt was initially well accepted. It has been abandoned because of the difficult estimation of lumen size, preferential flow to the right side, and difficulty in the take-down of the shunt. We have replaced the Waterston shunt with a short segment of polytetrafluoroethylene between the ascending aorta and the main pulmonary artery. From January 1979 to December 1986, 190 shunt operations were performed in 157 patients, with the use of 26 classic Blalock-Taussig shunts (13.7%), six Waterston shunts (3.1%), nine Glenn shunts (4.7%), 80 central aortopulmonary polytetrafluoroethylene shunts (42.2%), and 69 modified Blalock-Taussig shunts (36.3%). Polytetrafluoroethylene grafts were used for 149 of the 190 (78.4%) shunts. Overall mortality was 15.2%, with nine early deaths (4.7%) and 20 late deaths (10.5%). Deaths were due to the complex nature of the congenital anomaly or definitive surgical repair. The patients weighed from 1.6 to 48 kg and ages ranged from 1 day to 22 years. We have modified our technique so that (1) graft length is less than 0.5 cm and both ends are beveled, (2) the aortotomy is fashioned with a punch, (3) the center of the polytetrafluoroethylene graft is never clamped, (4) heparin is given during the construction of the shunt, and (5) aspirin (10 mg/kg/day) is administered daily. Patency ranges from 1 to 4 years. We conclude that the polytetrafluoroethylene shunt provides excellent palliation and that the central shunt, in the smaller child and infant, offers the benefits of shunting without distortion of the peripheral pulmonary arteries.

Adolescent↗