Search PubMed⌕ Search

Biomedical subjects

P L Davis

Publications and source records attributed to P L Davis.

At least 19 recordsLinked to original sources
PubMed1999

Isolation and initial characterization of the BRCA2 promoter.

The hereditary breast cancer susceptibility gene, BRCA2, is considered to be a tumor suppressor gene that may be involved in the cellular response to DNA damage. The transcript for this gene is cell cycle regulated with mRNA levels reaching a peak just before the onset of DNA synthesis. In order to define the mechanisms by which BRCA2 is transcriptionally regulated, we have begun to study upstream regulatory sequences. In this report, we define a minimal promoter region that has strong activity in human breast epithelial cells. Deletions of this sequence narrowed the strong basal activity to a region extending from -66 to +129 with respect to the BRCA2 transcriptional start site. This sequence demonstrated cell cycle regulated activity with kinetics similar to the endogenous transcript. Examination of the sequence revealed several consensus binding sites for transcription factors including an E-box, E2F and Ets recognition motifs. Electrohoretic mobility shift assays revealed specific protein binding to two sequences upstream of the start site; the palindromic E-box and an Ets/E2F site. Site-directed mutagenesis of either of these sites reduced both the basal activity in log phase cells and the cell cycle regulated activity of the promoter. Mutational inactivation of both sites within the same construct effectively eliminated promoter activity. Antibodies to candidate transcription factors used in super shift experiments revealed specific interactions between the BRCA2 promoter and the basic region/helix - loop - helix containing USF-1 and 2 proteins and Elf-1, an Ets domain protein. Binding of these factors depended upon the presence of intact recognition sequences. The USF factors were shown to bind predominantly as a heterodimeric complex of USF-1 and 2 while Elf-1 bound the promoter when it was not occupied by USF. Co-transfection studies with USF proteins and the varicella zoster IE62 protein provide evidence for the involvement of endogenous and exogenous USF in the activation of the BRCA2 promoter. We propose that interactions between USF-1, USF-2 and Elf-1 play an important role in the transcriptional regulation of the BRCA2 gene.

BRCA2 Protein↗
PubMed1999

Chronic lung injury in preterm lambs. Disordered respiratory tract development.

The cause of chronic lung disease of early infancy, often called bronchopulmonary dysplasia (BPD), remains unclear, partly because large-animal models that reliably reproduce BPD have not been available. We developed a model of BPD in lambs that are delivered prematurely and ventilated for 3 to 4 wk after birth to determine whether the histopathology of chronic lung injury in premature lambs mimics that which occurs in preterm infants who die with BPD, and to compare two ventilation strategies to test the hypothesis that differences in tidal volume (VT) influence histopathologic outcome. The two ventilation strategies were slow, deep ventilation (20 breaths/min, 15 +/- 2 ml/kg body weight VT; n = 5) or rapid, shallow ventilation (60 breaths/min, 6 +/- 1 ml/kg body weight VT; n = 5). Lambs were delivered at 125 +/- 4 d gestation (term = 147 d), treated with surfactant, and mechanically ventilated with sufficient supplemental oxygen to maintain normal arterial oxygenation (60 to 90 mm Hg). Quantitative histologic analysis revealed lung structural abnormalities for both groups of experimental lambs compared with lungs of control term lambs that were < 1 d old (matched for developmental age; n = 5) or 3 to 4 wk old (matched for postnatal age; n = 5). Compared with control lambs, chronically ventilated preterm lambs had pulmonary histopathology characterized by nonuniform inflation patterns, impaired alveolar formation, abnormal abundance of elastin, increased muscularization of terminal bronchioles, and inflammation and edema. Slow, deep ventilation was associated with less atelectasis, less alveolar formation, and more elastin when compared with rapid, shallow ventilation. We conclude that prolonged mechanical ventilation of preterm lambs disrupts lung development and produces pulmonary histopathologic changes that are very similar to those that are seen in the lungs of preterm infants who die with BPD. This chronic lung disease is not prevented by surfactant replacement at birth, does not appear to require arterial hyperoxia, and is influenced by VT.

Animals↗
PubMed1999

Evidence-based practice and the home care nurse's bag.

How safe is the home care nurse's bag anyway? What kind of precautions and procedures should an agency and nurses adopt to ensure that contamination does not occur? This article uses the evolving theory of evidence-based practice to suggest the best approaches to these challenging questions.

Aged↗
PubMed1998

Anterior chamber metal fragments after phacoemulsification surgery.

PURPOSE: To determine whether metal fragments can be shaken loose from phaco needles during surgery and embed in the iris. SETTING: Private practice, Vernon, British Columbia, Canada, and scanning electron microscope laboratory, Mastel Precision, Rapid City, South Dakota, USA. METHODS: The surfaces and rims of new and used phaco needles and the lumens of halved new needles were examined by scanning electron microscopy (SEM). To determine whether the fragments on the phaco needles were approximately the same size as those seen in the iris, a photograph of an eye with metal fragments imbedded in the iris was projected and the image size of the metal fragments approximated by using their magnification value. The magnification scale of the SEM images was used to determine the size of the metal fragments photographed on the phaco needles. RESULTS: The SEM studies of new phaco needles revealed tiny fragments of metal firmly adherent to the interior, exterior, and rim surfaces. No fragments were detected on the surfaces of the used phaco needles. Two metal fragments in the eye photograph were calculated to be 0.20 x 0.20 mm and 0.15 x 0.20 mm. Those in the SEM photos were calculated to be 0.03 to 0.10 mm. CONCLUSION: Althogh SEM of new titanium phaco needles revealed adherent metal fragments on their lathed surfaces, no fragments were found on used phaco needles. The iris fragments calculated from a projected photograph were slightly larger than those from the SEM micrographs, supporting the conclusion that annealed metal fragments shook loose from the phaco needles. This indicates that ultrasonic activation of a new phaco needle with metal fragments annealed to its surface causes fragments to release and embed in the iris.

Alloys↗
PubMed1998

Magnetic resonance imaging in breast cancer staging.

For many solid carcinomas, high-resolution cross-sectional imaging has changed cancer staging, the evaluation of therapeutic response, the detection of recurrence, and even how therapy is selected and performed. Such imaging has not yet had similar effects on breast cancer. Evaluations of therapeutic response in breast carcinomas have been impeded by the current limited methods of evaluating breast tumor size and extent: clinical palpation, ultrasonography, and mammography. The use of magnetic resonance imaging (MRI) of the breast in the evaluation of breast tumors brings the advantages of high-resolution cross-sectional imaging to breast cancer staging and treatment evaluation and is likely to greatly enhance research efforts in this complex disease. MRI of the breast has evolved to be the most accurate noninvasive technique for local staging of breast cancer. MRI is most accurate in measuring tumor size and detecting multicentric disease. These staging characteristics affect the selection of therapy and initial determination of prognosis; therefore, MRI of the breast can change the assessment of fundamental parameters on which treatment is selected. Because clinical trials of new cancer treatments are predicated on proper and accurate characterization of the tumor, MRI also should affect how clinical trials are performed and evaluated.

Adult↗
PubMed1997

BRCA1 expression is not directly responsive to estrogen.

Expression of the breast cancer susceptibility gene, BRCA1, is induced by 17-beta estradiol (E2) in estrogen receptor containing breast cancer cell lines. Our previous studies have shown that BRCA1 transcription is also regulated with the cell cycle, reaching maximal levels just before the onset of DNA synthesis. In this study, we have examined whether the estrogen induction of BRCA1 is direct or is a result of the mitogenic activity of the hormone. Four lines of evidence lead us to conclude that E2 induces BRCA1 primarily through an increase in DNA synthesis: (1) The kinetics and magnitude of induction are different from the directly E2 inducible gene, pS2; (2) Induction of BRCA1, but not pS2, is blocked by cycloheximide indicating that de novo protein synthesis is required; (3) Other hormonal and growth factor treatments that induce DNA synthesis have a similar effect, including IGF-1, EGF and DNA synthetic flares induced by tamoxifen and retinoic acid; (4) BRCA1 genomic fragments near the 5' end of the gene containing putative estrogen response elements fail to respond to E2 when transfected into breast cancer cell lines. The most consistent explanation for these findings and other published studies is that BRCA1 transcription is induced as a result of the mitogenic activity of E2 in estrogen receptor positive cells.

BRCA1 Protein↗
PubMed1997

Sensitivity of enhanced MRI for the detection of breast cancer: new, multicentric, residual, and recurrent.

Magnetic resonance imaging (MRI) of the breast brings the advantages of high resolution cross-sectional imaging to breast cancer diagnosis, treatment and research: improved cancer detection, staging, selection of therapy, evaluation of therapeutic response in vivo, detection of recurrence, and even the development of new therapies. Until now breast cancer treatment and research has been impeded by the limited means of evaluating the breast cancer in vivo: primarily clinical palpation and mammography of the breast tumor. A review of the initial studies shows that with the use of paramagnetic contrast agents, MRI has a sensitivity of 96 % for detecting breast cancers. MRI detects multicentric disease with a sensitivity of 98 %, superior to any other modality. The ability of MRI to detect recurrent local breast cancer in the conservatively treated breast is nearly 100 %. MRI is capable of monitoring tumor response to chemotherapy and actually guiding therapeutic interventions such as interstitial laser photocoagulation.

Breast Neoplasms↗
PubMed1996

Breast cancer measurements with magnetic resonance imaging, ultrasonography, and mammography.

BACKGROUND: Accurate measurement of the size of breast cancers becomes more important as breast cancer therapy advances. This study reports the accuracy of magnetic resonance imaging (MRI), ultrasonography and mammography for measuring the largest breast cancer diameter in comparison to the pathology measurement. MATERIALS AND METHODS: Fourteen breast cancers were examined in 13 women with MRI, ultrasonography and mammography. The age range was 31-73 (mean 56). Six of the cancers were in premenopausal women. The MRI was performed with the intravenous injection of gadolinium based contrast agent and a three dimensional fast spoiled gradient echo sequence with fat suppression. The largest cancer diameter was measured with each imaging technique and compared to the largest cancer diameter measured at pathology. RESULTS: At pathological examination cancers ranged from 0.6 to 6 cm (mean 2.2) in largest diameter. MRI measurements had the highest correlation coefficient (r = 0.98) and the smallest standard error (0.34). Ultrasonography measurements had a correlation coeffient of r = 0.45 and a standard error of 0.78. Mammography measurements had a correlation coefficient of r = 0.46 and a standard error of 1.04. CONCLUSIONS: MRI was more accurate than ultrasonography and mammography in measuring the largest cancer diameters in this group of women. This was particularly evident for several larger cancers, and a postchemotherapy cancer.

Adenocarcinoma↗
PubMed1996

Cirrhosis of the liver: MR imaging with mangafodipir trisodium (Mn-DPDP).

PURPOSE: To evaluate the usefulness of manganese (II) N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis(phosphate) (Mn-DPDP) in magnetic resonance (MR) imaging of cirrhotic livers. MATERIALS AND METHODS: Fifty-eight patients (mean age, 58.8 years), 29 with and 29 without cirrhosis, underwent MR imaging before and after intravenous administration of 5 mumol/kg Mn-DPDP. Enhancement effects were assessed quantitatively and qualitatively. Histologic confirmation was obtained in 51 patients. RESULTS: Liver parenchyma in both patient groups enhanced significantly on T1-weighted spin-echo and gradient-recalled-echo (GRE) images (P < .01). However, cirrhotic livers enhanced significantly less than noncirrhotic livers on T1-weighted GRE images (P < .05). Fourteen cirrhotic livers had heterogeneous enhancement of parenchyma; enhancement was more prominent on GRE images. Decreased enhancement was seen in patients with confluent fibrosis (n = 5), diffuse fibrosis (n = 6), and siderotic regenerating nodules (n = 4). Increased enhancement was seen in patients with benign regenerating nodules (n = 4). CONCLUSION: Mn-DPDP is useful in patients with cirrhosis.

Case-Control Studies↗
PubMed1996

Hepatocellular carcinoma: MR imaging with mangafodipir trisodium (Mn-DPDP).

PURPOSE: To determine the efficacy of manganese (II) N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis(phosphate) (DPDP) at magnetic resonance (MR) imaging for evaluation of hepatocellular carcinoma (HCC). MATERIALS AND METHODS: MR imaging at 1.5 T was performed in 20 patients with 65 HCC nodules. T1- and T2-weighted spin-echo and T1-weighted gradient-recalled-echo images were obtained before and after administration of 5 mumol/kg Mn-DPDP. Readers individually evaluated the pre- and postcontrast images for detection of tumor nodules, with subsequent consensus reading for interpretation discrepancies. Quantitative measurements of tumor-liver contrast-to-noise ratio (C/N) were also performed. Enhancement characteristics were correlated with histologic tumor differentiation. RESULTS: Precontrast images depicted 50 lesions in 17 patients, and postcontrast images depicted 49 lesions in 20 patients. Combination of pre- and postcontrast images enabled detection of 53 lesions in 20 patients. Three lesions (three patients) were seen only on postcontrast images. Four lesions (three patients) were seen only on precontrast images. Reader evaluation of tumor conspicuity showed a significant preference for precontrast T2-weighted SE images (P < .01). Quantitative evaluation showed a significant increase in C/N on postcontrast T1-weighted images (P < .01). Well-differentiated lesions showed significantly greater enhancement than that of poorly differentiated lesions (P < .05). CONCLUSION: Mn-DPDP-enhanced MR imaging depicts HCC tumors not visualized with unenhanced studies. The degree of tumor enhancement correlates with histologic differentiation.

Adult↗
PubMed1996

BRCA1 expression is induced before DNA synthesis in both normal and tumor-derived breast cells.

Insight into the function of the BRCA1 tumor suppressor gene may be gained by studying its regulation. In this study, the expression of BRCA1 was examined as a function of the cell cycle in normal and tumor-derived breast epithelial cells. Cells arrested in G(zero) or early in G1 contained low levels of BRCA1 mRNA. After release, populations of cells reached maximal levels of BRCA1 in late G1 and S phase. Induction of BRCA1 was shown to occur before the onset of DNA synthesis by synchronizing cells at the G1-S boundary. Levels of the BRCA1 protein were regulated in a similar manner. No difference was observed between primary cultures of normal mammary epithelial cells and immortalized tumor-derived cell lines. These results suggest that BRCA1 may function at the G1-S checkpoint.

Adult↗
PubMed1996

Relationship between p21 expression and mutation of the p53 tumor suppressor gene in normal and malignant ovarian epithelial cells.

In many cell types, p53-mediated growth inhibition is dependent on induction of p21, which is an inhibitor of cyclin-dependent kinases that are required for cell cycle progression. Failure of mutant p53 proteins to transactivate p21 may lead to uncontrolled proliferation. Because many ovarian cancers have mutations in the p53 gene, we examined p21 levels in normal and malignant ovarian epithelial cells to determine whether p21 expression is dependent on wild-type p53. Normal ovarian epithelial cells and two ovarian cancer cell lines with wild-type p53 expressed readily detectable levels of p21, whereas in p53 null and mutant cell lines, expression of p21 was diminished strikingly. A correlation between the status of the p53 gene and p21 expression also was noted in 23 primary epithelial ovarian cancers. Normal levels of p21 RNA were seen in 4/7 (57%) cancers with wild-type p53, whereas 14/16 (88%) cancers with mutant p53 had reduced p21 expression (P < 0.05). In addition, we found that lambda-irradiation of normal and malignant ovarian epithelial cells with wild-type, but not mutant, p53 resulted in induction of p21. These data are suggestive that induction of p21 is a feature of p53-mediated growth inhibition in normal ovarian epithelial cells. Conversely, mutation of the p53 gene in ovarian cancers usually is associated with decreased p21 expression. The lack of an absolute correlation between p21 expression and the status of the p53 gene in ovarian cancers is consistent with other studies that have suggested that p21 may also be regulated by p53-independent pathways.

Blotting, Northern↗
PubMed1995

Hepatic MR imaging with ferumoxides: a multicenter clinical trial of the safety and efficacy in the detection of focal hepatic lesions.

PURPOSE: To assess the safety and diagnostic efficacy of intravenous ferumoxides, a superparamagnetic iron oxide, for depiction of focal hepatic lesions on magnetic resonance (MR) images. MATERIALS AND METHODS: This open-label study included 208 patients with known or suspected focal hepatic lesions. MR images were obtained before and 45 minutes to 4 hours after intravenous infusion of ferumoxides (10 mumol/kg). The effect of ferumoxides on signal intensity of the liver was assessed with quantitative analysis. Safety was evaluated with patient monitoring and laboratory measurements. RESULTS: Mean lesion-to-liver contrast-to-noise ratio on T2-weighted images was 9.1 on unenhanced images and 12.7 on enhanced images. Signal intensity of normal liver on enhanced images decreased to 37% of that on unenhanced images. In blinded image evaluations, additional lesions were identified on 27% of enhanced images. No serious adverse events occurred. CONCLUSION: Ferumoxides is a safe and efficacious contrast agent for the detection of focal liver lesions on T2-weighted images.

Contrast Media↗
PubMed1995

Gadoteridol-enhanced MR imaging of malignant hepatic tumors: effects of triple versus standard doses on lesion-liver contrast.

OBJECTIVE: The purpose of this study was to compare liver signal-to-noise ratio (SNR), lesion SNR, and lesion-liver contrast-to-noise-ratio (CNR) in patients with malignant liver lesions after the administration of a standard dose (0.1 mmol/kg of body weight) or a triple dose (0.3 mmol/kg) of a gadolinium chelate (gadoteridol). We hypothesized that the higher dose would produce a higher lesion-liver CNR and therefore increase the conspicuity of hepatic lesions. MATERIALS AND METHODS: A total of 85 patients with malignant hepatic masses (61 metastases, 22 hepatocellular carcinomas, and two lymphomas) proved by histologic or follow-up studies underwent MR imaging at 1.5 T. T1-weighted spin-echo imaging and gradient-echo imaging were done before and within 1 min after (gradient echo) as well as 5 (spin echo) and 15 (spin echo) min after the injection of 0.1 or 0.3 mmol of gadoteridol per kg, randomized before the start of the study (39 patients received the standard dose, and 46 received the triple dose). The signal intensities of the liver and lesions and the SD of background noise were measured by use of regions of interest to calculate the SNR of the liver and malignant lesions and the lesion-liver CNR. RESULTS: The lesion-liver CNR was increased significantly at 5 and 15 min after the administration of gadoteridol. No significant differences in the liver SNR, lesion SNR, and lesion-liver CNR (after 1 min: standard dose, -5 +/- 8, and triple dose, -4 +/- 14; after 5 min: standard dose, -1 +/- 5, and triple dose, 2 +/- 8; and after 15 min: standard dose, 1 +/- 5, and triple dose, 6 +/- 20) were found between the doses at all time points. CONCLUSION: Triple-dose gadoteridol does not improve the lesion-liver contrast of malignant hepatic lesions over that provided by the standard dose and is not warranted for liver MR imaging.

Adult↗
PubMed1995

Use of nitroxides as NMR contrast enhancing agents for joints.

NMR imaging is a well-established technology for obtaining cross-sectional anatomic pictures of organs and tissues. In addition, NMR can provide valuable information about the physiologic state of organs and tissues, especially, as a consequence of cellular injury. With this in mind, NMR in combination with gadolinium-based contrast enhancing agents has been used to assist in the detection of abnormalities to joints as well as to evaluate the status of damage resulting from an injury to this site. We describe the synthesis of a new nitroxide, which is bioresistant to the one-electron reduction mediated by superoxide in the presence of cysteine. This model mimics the reduction of nitroxides by extracellular secretion of superoxide by PMA-stimulated neutrophils. With this nitroxide, we found, in the range from 15 to 17.5 mumoles, enhancement of an NMR image in the knee joint of rabbits. Of interest is the finding that the contrast image remained for at least 90 minutes. These results demonstrate the utility of nitroxides as contrast enhancing agents for NMR imaging of joints.

Animals↗
PubMed1994

Digital radiography and conventional imaging of the chest: a comparison of observer performance.

OBJECTIVE: The purpose of this study was to compare observer performance in interpreting high-quality, digitally acquired computed radiographs of the chest displayed on either laser-printed radiographs or a workstation with observer performance in interpreting conventional chest radiographs. SUBJECTS AND METHODS: We performed a receiver-operating-characteristic study in which the presence or absence of five abnormalities was determined by nine experienced radiologists on 310 posteroanterior radiographs of the chest displayed in three forms: conventional radiographs, laser-printed films of digital radiographs, and digital radiographs on a high-resolution workstation. RESULTS: The results of our study suggest that observer performance with laser-printed films of digital radiographs obtained with high-resolution (4K x 5K), high-contrast sensitivity (12 bits) and appropriate exposure is comparable to observer performance with conventional radiographs. Observer performance with digital radiographs displayed on the workstation was found to be significantly lower for abnormalities that contained high-frequency and low-contrast information (e.g., interstitial disease and pneumothorax). CONCLUSION: Computed radiography technology can produce image quality that is adequate for interpreting posteroanterior radiographs of the chest. Observer performance is not as good when radiographs displayed on workstations are used to diagnose specific abnormalities.

Humans↗