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Biomedical subjects

R Ball

Publications and source records attributed to R Ball.

At least 73 records · Page 4Linked to original sources
PubMed1995

Evidence for the role of protein kinase C in astrocyte-induced proliferation of rat cerebromicrovascular endothelial cells.

The proliferation of cerebral endothelial cells is a crucial step in neural angiogenesis and is a process responsive to changes in the surrounding environment. Serum-free medium conditioned by rat cortical astrocytes was found to accelerate DNA synthesis, induce transient activation of protein kinase C (PKC), and increase the endogenous phosphorylation of the PKC-specific substrate, the 85 kDa MARCKS protein, in rat cerebromicrovascular endothelial cells (RCEC). The stimulatory factor(s) in astrocyte conditioned media (ACM) were heat- and trypsin-sensitive and found to have an apparent molecular weight greater than 10 kDa. The potent PKC activator, 12-O-tetradecanoyl phorbol 13-acetate (TPA), also stimulated RCEC proliferation, whereas the inhibition of PKC by staurosporine caused a concomitant loss in ACM-induced PKC translocation, MARCKS protein phosphorylation and DNA synthesis. These findings implicate PKC activation as a critical early event in cerebral endothelial cell proliferation triggered by astrocyte-derived mitogen(s).

Animals↗
PubMed1995

The role of intracellular calcium and protein kinase C in endothelin-stimulated proliferation of rat type I astrocytes.

The increased expression of immunoreactive endothelin-1 (ET-1) in reactive astrocytes and its mitogenic effects on astrocytes and glioma cell lines, have implicated endothelins in the development of reactive gliosis. In this study, an increase in DNA synthesis in rat type I astrocytes was observed after cultures were transiently exposed to ET-1 for 15 min, suggesting that early signal transduction events are essential and sufficient for the propagation of the ET-1-induced mitogenic signal. Prompt increases in inositol triphosphate (IP3) formation and [Ca2+]i were observed upon the addition of ET-1 to these cells. The ET-1-evoked increase in [Ca2+]i consisted of an initial peak which was preserved in Ca(2+)-free medium, and a sustained phase which was abolished in Ca(2+)-free medium and partly attenuated by nifedipine. ET-1 also increased the activity of membrane-associated protein kinase C (PKC) and induced the in vivo phosphorylation of the 85 kD MARCKS protein, an endogenous PKC-specific substrate. The ET-1-evoked increases in DNA synthesis, IP3, [Ca2+]i, membrane PKC, and 85 kD MARCKS protein phosphorylation in rat cortical astrocytes were prevented by either the selective endothelin ETA receptor antagonist, BQ-123, or the phospholipase C (PLC)-specific inhibitor, U-73122. However, the inhibition of PKC activity did not affect ET-1-induced DNA synthesis in rat cortical astrocytes. These results suggest that ET-1-induced IP3 and/or [CA2+]i responses, but not the activation of PKC, are essential for the growth-factor like actions of ET-1 in rat cortical astrocytes.

Animals↗
PubMed1995

Baculovirus expression and purification of the second messenger enzyme phospholipase C-gamma 1, a tyrosine kinase substrate.

A rat cDNA encoding phospholipase C-gamma 1 (PLC-gamma 1) was expressed as a histidine-tagged fusion protein in insect cells utilizing the expression vector pBlueBacHis. The fusion protein was purified by Ni(2+)-agarose affinity chromatography to apparent homogeneity as defined by SDS-PAGE and Coomassie staining. Using a Triton X-100/PIP2 mixed micelle assay, (His6)-PLC-gamma 1 exhibited a calcium-dependent specific enzyme activity of 3 mumol/min/mg, a value similar to that reported for purified bovine brain PLC-gamma 1. Also similar to bovine brain PLC-gamma 1, (His6)-PLC-gamma 1 activity was stimulated by phosphatidic acid and inhibited by adenosine 5'monophosphate. (His6)-PLC-gamma 1 interacted directly with two known PLC-gamma 1 binding proteins, dynamin and the activated EGF receptor. Also, purified (His6)-PLC-gamma 1 was a tyrosine phosphorylation substrate for purified EGF receptor. These results suggest that (His6)-PLC-gamma 1 can be overexpressed as a functional enzyme in baculovirus-infected insect cells and purified by a one-step metal affinity chromatography procedure.

Animals↗
PubMed1995

Free radical-induced endothelial membrane dysfunction at the site of blood-brain barrier: relationship between lipid peroxidation, Na,K-ATPase activity, and 51Cr release.

Na,K-ATPase activity, membrane lipid peroxidation (TBARM), and membrane 'leakiness' for small molecules were examined in rat cerebromicrovascular endothelial cells (RCEC) following exposure to hydrogen peroxide and xanthine/xanthine oxidase. Whereas short-term (15-30 min) exposure to either oxidant decreased ouabain-sensitive 86Rb uptake and increased TBARM in a concentration-dependent fashion, significant release of 51Cr (30-40%) from cells was observed only after one hour exposure to the oxidants. By comparison, much longer exposure times (i.e., 4 hours) were needed to induce significant lactate dehydrogenase release from oxidant-treated cells. The oxidant-evoked decrease in Na,K-ATPase activity and increases in TBARM and RCEC 'permeability' were abolished in the presence of the steroid antioxidants U-74500A and U-74389G (5-20 microM). Reduced glutathione (4 mM) partially attenuated oxidant-induced changes, whereas ascorbic acid (2 mM) and the disulfide bond-protecting agent, dithiothreitol (1 mM), were ineffective. These results suggest that the oxidant-induced loss of Na,K-ATPase activity in RCEC results primarily from changes in membrane lipids, and implicate both the inhibition of Na,K-ATPase and membrane lipid peroxidation in the mechanism responsible for the delayed free radical-induced increase in RCEC membrane 'permeability'.

Animals↗
PubMed1995

Evaluation of Ki-67 reactivity in neuroblastoma using paraffin embedded tissue.

AIMS: To examine the pattern of reactivity of Ki-67 in neuroblastoma and correlate this with a) clinical prognostic criteria and b) cell cycle statistics (using flow cytometry). METHODS: Four micron sections of paraffin embedded (PE) tissue from 55 patients (25 pre chemotherapy and 30 post) were placed on to aminosialinised slides, dewaxed and rehydrated. Slides were pretreated in a microwave oven, endogenous peroxidase activity blocked using 3% hydrogen peroxide and Ki-67 reactivity investigated using a streptavidin/biotin/peroxidase technique. DNA ploidy was also performed from an immediately adjacent section on the same block using a FACScan and Cellfit software. RESULTS: Ki-67 reactivity was well defined and highly reproducible. Eighteen out of 30 post chemotherapy samples were totally negative, despite evidence of proliferation on flow cytometry and all subsequently died of disease. As interpretation post chemotherapy was therefore deemed unreliable, this group was excluded from analysis. Reactivity in pretreatment samples ranged from 0% to 67%; staining was restricted to the nucleus with a distinct pattern noted in the nucleolus. Ki-67 positivity was lower in aneuploid compared with diploid tumours (mean 26% vs 36%, NS). Among diploid tumours, a lower percentage positivity was noted in those patients with better clinical prognostic parameters. Correlation however between Ki-67 and SG2M phases of cell cycle was poor (RS = 0.39, NS). CONCLUSION: Assessment of proliferation in neuroblastoma by Ki-67 reactivity in paraffin embedded tissue is reliable in pretreatment samples and can be incorporated into routine immunohistochemical evaluation. Larger multicentre studies are required to further evaluate Ki-67 reactivity as a prognostic indicator.

Biomarkers, Tumor↗
PubMed1995

Somatic genetic changes in lung cancer and precancerous lesions.

BACKGROUND: Morphological abnormalities of the bronchial epithelium are associated with lung cancer development and are considered likely to represent the preneoplastic stage of the disease. The association of these lesions with different histological types of lung cancer was reviewed in a series of 97 samples. Lesions associated with squamous cell carcinomas provided the best samples for further study. The objective of this study was to describe the somatic genetic changes which occur in these preinvasive lesions. Among the various candidate somatic genetic changes, loss of heterozygosity on chromosome 3 and changes to the p53 gene were selected as being the most informative. It was demonstrated that these genetic changes, characteristic of fully invasive lung tumours, also occur at the premalignant stage of the disease. In an attempt to take a less directed approach to the comparison of invasive and preinvasive lesions, karyotype analysis was performed on short-term cultures of bronchial cells adjacent to the bronchial margin obtained from patients undergoing lung tumour resection. One such karyotype had a deletion to chromosome 3 (del 3p13-14) as the single abnormality. CONCLUSION: It was concluded that genetic damage to p53 and chromosome 3 is involved in the preinvasive stage of lung cancer, and that damage to chromosome 3 is a particularly early event.

Bronchi↗
PubMed1995

Does the time course of bubble evolution explain decompression sickness risk?

A probabilistic model of decompression sickness (DCS) risk based on linear-exponential (LE) kinetics has given the best fit of the human air and nitrox DCS database. To test the hypothesis that its success may be due to the formation of a gas phase during decompression, we developed a physiologically based bubble evolution model using a numerical solution of a partial differential equation system. Because of the computational intensity of this method, it could not be used to fully explore our hypothesis. Consequently, we compared the solution with that of a computationally simpler approximation that was previously published by Van Liew and found the two approaches gave similar results. Using the simpler model, assuming bubble densities of 1 and 1,000 bubbles/cm3, we found a tissue time constant of at least 80 min (equivalent to perfusion of 1/80 ml.g-1.min-1) was required to achieve a delay in bubble dissolution comparable to the prolonged risk of DCS predicted by the LE model. We suggest that the persistence of single bubbles in a uniformly perfused homogeneous tissue alone is unlikely to explain persistent DCS risk.

Blood Flow Velocity↗
PubMed1994

Drug and alcohol abuse by doctors.

OBJECTIVE: To determine whether doctors who abuse substances differ from controls in terms of their physical and psychological well-being, and their marital and occupational functioning. DESIGN AND PARTICIPANTS: The 44 doctors concerned in all cases of substance abuse which came before the Medical Board of Victoria between 1984 and 1990 were invited to complete a demographic questionnaire, psychological tests and a semi-structured interview. A control group of 42 doctors, obtained from the Medical Register, was also invited, and the groups were compared. SETTING: The study was carried out at St Vincent's Hospital, Melbourne, under the auspices of the Medical Board of Victoria. RESULTS: Questionnaires were returned by 70% of the drug-dependent doctors and 83% of the controls. However, interviews were given by only 20% of the drug-dependent doctors. The groups differed significantly in terms of marital status (P < 0.002), overall health (P < 0.003), general wellbeing (P < 0.0009), and having experienced physical illness (P < 0.02) and psychiatric illness (P < 0.006) since graduation. No differences were found on the standardised questionnaires; this may reflect successful treatment. CONCLUSION: Substance abuse in medical practitioners is a major problem and is associated with considerable morbidity. Prevention and early intervention are crucial.

Adult↗
PubMed1994

CMATRIX: software for physiologically based pharmacokinetic modeling using a symbolic matrix representation system.

Physiologically based pharmacokinetic (PBPK) modeling is based on an understanding of the physical and biological factors governing drug distribution. It is a procedure requiring composition of differential equations describing the distribution of drugs among physiologically defined compartments. CMATRIX is a program that facilitates development of PBPK models. In CMATRIX, the model is represented as a matrix of transfer parameters; the program generates a corresponding system of differential equations, and solves them numerically. This system dramatically improves the ease with which PBPK models can be developed, allowing the freedom to construct subcompartments down to the receptor level.

Body Fluid Compartments↗
PubMed1993

Ploidy changes between diagnosis and relapse in childhood renal tumours.

Ploidy patterns, analysed by flow cytometry (FCM) and image analysis (IA), were investigated at relapse in a group of six children with renal tumours [five Wilms' tumour (WT) and one bone metastasizing renal tumour of childhood (BMRTC)] and results compared with diagnostic profiles. IA detected one or more aneuploid populations in five of 12 tumours which were diploid on FCM. Patterns in three of six patients [two with unfavourable histology (UH) and one with favourable histology (FH)] were aneuploid at diagnosis and relapse, two patients (one FH, one BMRTC) developed aneuploid features at relapse and one patient with a tetraploid tumour was diploid at relapse. Histology patterns were similar at diagnosis and relapse in all patients. Three of six patients (two UH, one BMRTC) have died of disease. This report highlights (1) the superiority of IA over FCM in detecting aneuploid populations and (2) changes in ploidy status which have not previously been reported in these tumours. Overinterpretation of DNA status at relapse may prove misleading.

Aneuploidy↗
PubMed1993

Effect of severity, time to recompression with oxygen, and re-treatment on outcome in forty-nine cases of spinal cord decompression sickness.

For systematic study of the effects of clinical severity, time to recompression with oxygen, and re-treatment on outcome from spinal cord DCS, case records from the recompression chamber at the U.S. Naval Station Subic Bay were reviewed. Forty-nine cases of spinal cord DCS were classified using a numerical severity index and time to recompression with oxygen. Cases were divided by initial severity into mild, moderate, and severe groups and by time to recompression with oxygen into less than 12-h, 12-24-h, and greater than 24-h groups. Re-treatment effect was analyzed by severity after the first treatment and by the depth of the re-treatment table used. Severity after all treatment is strongly correlated with initial severity (r = 0.88) and moderately correlated with time to recompression with oxygen (r = 0.58). Response to treatment is significantly different among initial severity groups (P < 0.001). Delay to treatment worsens outcome for severely injured divers (P = 0.008). Residual severity after all treatments is highly correlated with severity after the first treatment (r = 0.97). There is no difference in re-treatment outcome by groups defined by severity after the first treatment or by 60- or 45-ft re-treatment tables.

Adult↗
PubMed1992

Staff-patient relationships in the care of the long-term adult mentally ill. A content analysis of Expressed Emotion interviews.

Analysis of the content of 61 interviews with keyworkers supporting chronically disabled patients in long-term care settings revealed a range of EE ratings and associated characteristics. Low-EE interviews were prevalent (n = 46), a finding not unlikely given the experience and training of the staff group sampled. High-EE (n = 15) relationships were characterised by less tolerance, inappropriate expectations of patient progress and frustration in the key worker. Criticism in both high- and low-EE interviews was most frequently focused on socially embarrassing or difficult behaviour and, to a slightly lesser extent, the clinical poverty syndrome. It was rarely directed at positive symptomatology. High levels of criticism were significantly related to regarding the patient's difficulties as within their control and having negative rather than positive expectations of their ability to manage on their own. The factors identified by the EE interview that influence the nature of the staff-patient relationship are discussed, and the clinical implications of the findings briefly considered.

Adult↗
PubMed1992

DNA quantitation of Wilms' tumour (nephroblastoma) using flow cytometry and image analysis.

AIMS: To compare flow cytometry (FCM) with image analysis (IA) in the DNA quantitation of Wilms' tumour (WT) and to correlate data so obtained with recognised clinical and pathological prognostic parameters. METHODS: Thirty six patients with histologically proved WT diagnosed between 1980-89 were investigated. Fifteen patients had stage I disease, 10 stage II, six stage III, two stage IV and three stage V. Suspension of nuclei obtained by pepsin digestion of paraffin wax embedded tumour tissue was analysed using a FAC-Scan flow cytometer, and a CAS-100 image analyser. RESULTS: Tumours were concordant in most instances, however, IA identified aneuploidy in two tumour samples which were diploid by FCM. Aneuploidy was detected in 5/33 tumours with favourable histology and 3/3 with unfavourable histology. Three of 28 patients with Stage I, II and V disease and 5/8 patients with stage III and IV had aneuploid tumours. All patients with unfavourable histology died of disease. In the group with favourable histology, 4/5 patients with aneuploid tumours developed recurrent disease compared with 1/27 diploid tumours (p less than 0.0001). CONCLUSIONS: Ploidy may be a useful additional prognostic indicator in Wilms' tumour with favourable histology. Larger scale studies are needed to confirm the relation of ploidy to survival in early stage WT.

Child↗
PubMed1992

Effects of a simulated microgravity model on cell structure and function in rat testis and epididymis.

A tail-suspension (TS) rat model used to simulate microgravity was tested for its effects on the anatomy, cell structure, and function of the testis and epididymis in sexually mature male rats. Rats suspended for 7 days without inguinal canal ligation exhibited a significant (P less than or equal to 0.05) reduction in testis weight compared with controls (1.55 +/- 0.04 to 1.1 +/- 0.02 g). Except for the liver, epididymis, and adrenals of TS rats and TS rats allowed to recover for 7 days, no significant (P less than or equal to 0.05) change was observed in the weight of other body and accessory sex organs. A histological examination of the testes and epididymides of model animals revealed disorganized seminiferous tubules and accumulation of large multinucleated cells and spermatids in the lumen of the epididymis. A significant (P less than or equal to 0.05) increase in serum luteinizing hormone (53.1 +/- 6.7 to 66.2 +/- 10.1 ng/ml) and follicle-stimulating hormone (257 +/- 25 to 305 +/- 38 ng/ml) was observed in TS nonligated rats, whereas serum prolactin and testosterone levels were observed to decline from 8.3 +/- 1.3 to 5.1 +/- 0.29 and 7.1 +/- 1.3 to 3.8 +/- 0.25 ng/ml, respectively. Decreases in testis protein content and testosterone levels of the testis, interstitial fluid, and epididymis were also observed in model animals. These data demonstrate that the suspension procedure used in the National Aeronautics and Space Administration TS model results in the testis and epididymis translocating into the abdominal cavity, causing cellular degeneration and organ dysfunction.

Animals↗
PubMed1992

Reactivity of P-glycoprotein monoclonal antibodies in childhood cancers.

P-Glycoprotein (P-gp), the product of the mdr-1 gene, is implicated in the development of chemoresistance in a variety of, mostly adult, cancers. Its role in paediatric tumours, most of which are non-epithelial in origin, has yet to be fully elucidated. A study was undertaken to investigate reactivity of two P-gp monoclonal antibodies (MAbs), JBS-1 and MRK16, recognising cytoplasmic and surface epitopes, respectively, of the P-gp molecule, in a variety of newly diagnosed and relapsed childhood cancers. P-gp was not expressed in any of 36 tumours examined (neuroblastoma 13, nephroblastoma 12, rhabdomyosarcoma 6, lymphoma 3, teratoma 1, Ewings 1), 14 of whom had chemoresistant disease. Reactivity to both MAbs was also investigated in patients with acute leukaemia. Out of 10 diagnostic acute lymphoblastic leukaemia (ALL) samples, a positive reaction with JSB-1 was observed in 1 patient who failed to remit on standard induction therapy and in 3 of 6 patients in ALL relapse, only 1 of whom showed low grade positivity with MRK16. Both MAbs reacted positively in 1 patient with acute non-lymphocytic leukaemia (ANLL) at diagnosis who achieved remission with teniposide and cytosine arabinoside, but relapsed 7 months later and was again positive with both Mabs. JSB-1 also showed varying degrees of positivity in 4 out of 4 other patients in ANLL relapse. It would therefore appear that P-gp is unlikely to mediate chemoresistance in most solid tumours of childhood, but may well play a major role in the development of chemoresistance in acute leukaemia.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

L-696,474, a novel cytochalasin as an inhibitor of HIV-1 protease. II. Isolation and structure.

A novel HIV-1 protease inhibitor, L-696,474 (C30H39NO4, 477), was isolated from the fermentations of the fungus Hypoxylon fragiforme (ATCC 20995, MF5511) and purified by silica gel chromatography followed by crystallization. Spectroscopic studies have shown the competitive inhibitor L-696,474 to be a novel cytochalasin. Two related novel cytochalasins were also isolated and had no effect on the enzyme.

Ascomycota↗