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Biomedical subjects

K Brown

Publications and source records attributed to K Brown.

At least 145 records · Page 8Linked to original sources
PubMed1999

Further characterization of the DNA adducts formed in rat liver after the administration of tamoxifen, N-desmethyltamoxifen or N, N-didesmethyltamoxifen.

The present study compares the formation of DNA adducts, determined by (32)P-postlabelling, in the livers of rats given tamoxifen and the N-demethylated metabolites N-desmethyltamoxifen and N, N-didesmethyltamoxifen. Results show that after 4 days treatment (0.11 mmol/kg i.p.), similar levels of DNA damage were seen after treatment with either tamoxifen or N-desmethyltamoxifen [109 +/- 40 (n = 3) and 100 +/- 33 (n = 4) adducts/10(8) nucleotides, respectively], even though the concentration of tamoxifen in the livers of tamoxifen-treated rats was about half that of N-desmethyltamoxifen in the N-desmethyltamoxifen-treated animals (51 +/- 16 and 100 +/- 8 nmol/g, respectively). Administration of N, N-didesmethyltamoxifen to rats resulted in a 5-fold lower level of damage (19 adducts/10(8) nucleotides, n = 2). Following (32)P-postlabelling and HPLC, hepatic DNA from rats treated with tamoxifen and its metabolites showed distinctive patterns of adducts. Treatment of rats with N,N-didesmethyltamoxifen gave a major product that co-eluted with one of the minor adduct peaks seen in the livers of rats given tamoxifen. Following dosing with N-desmethyltamoxifen, the major product co-eluted with one of the main peaks seen following treatment of rats with tamoxifen. This suggests that tamoxifen can be metabolically converted to N-desmethyltamoxifen prior to activation. However, analysis of the (32)P-postlabelled products from the reaction between alpha-acetoxytamoxifen and calf thymus DNA showed two main peaks, the smaller one of which ( approximately 15% of the total) also co-eluted with that attributed to N-desmethyltamoxifen. This indicates that N-desmethyltamoxifen and N,N-didesmethyltamoxifen are activated in a similar manner to tamoxifen leading to a complex mixture of adducts. Since an HPLC system does not exist that can fully separate all these (32)P-postlabelled adducts, care has to be taken when interpreting results and determining the relative importance of individual adducts and the metabolites they are derived from in the carcinogenic process.

Animals↗
PubMed1999

Pharmacodynamic activity and antithrombotic efficacy of RPR120844, a novel inhibitor of coagulation factor Xa.

These studies were designed to examine the pharmacodynamic profile and antithrombotic efficacy of RPR120844, a competitive inhibitor of coagulation factor Xa, with a K(i) of 7 nM against human factor Xa. In vitro, RPR120844 doubled activated partial thromboplastin time (APTT) at concentrations of 1.54, 1.48, and 0.74 microM in plasma obtained from humans, dogs, and rats, respectively. Intravenous bolus administration of RPR 120844 at 0.3, 1, and 3 mg/kg to rats resulted in maximal increases in APTT of 1.8-, 2.6-, and 8.4-fold over baseline, respectively. The effect on prothrombin time (PT) was less pronounced, resulting in a 4.4-fold increase at 3 mg/kg. These effects were rapidly reversible; APTT and PT returned to control values by 30 min after dosing. Intragastric administration to rats at 50, 100, and 200 mg/kg resulted in modest increases in APTT and PT of 1.5- and 1.3-fold over baseline at the highest dose. Plasma levels were estimated by anti-Xa activity by using an amidolytic, chromogenic assay. Plasma levels were 0.65, 1.29, and 2.45 microM at 30 min after dosing at 50, 100, and 200 mg/kg, respectively. Intravenous administration to dogs at 0.1 and 0.3 mg/kg produced maximal increases in APTT of 1.7- and 2.4-fold over baseline, respectively. Intragastric administration to dogs at 50 mg/kg resulted in maximal increases in APTT and PT of 1.7- and 1.1-fold over baseline, with peak plasma levels of 3.9 microM observed at 15 min after dosing. In a rat model of FeCl2-induced carotid artery thrombosis, RPR120844 (3 mg/kg, i.v. bolus + 300 microg/kg/min constant infusion; n = 4) significantly increased time-to-occlusion from 18+/-1 min (vehicle, n = 4) to 60 min (maximal observation time) and reduced thrombus mass from 5.5 +/- 0.2 mg (vehicle) to 1.4 +/- 0.2 mg. These results indicate that RPR120844 is a potent, selective inhibitor of Xa that exhibits oral activity and is efficacious in a standard model of arterial thrombosis.

Animals↗
PubMed1999

Cyclosporine plasma unbound fraction in heart and lung transplantation recipients.

To investigate the variability in the unbound fraction (fu) of cyclosporine in recipients of heart, heart-lung, and lung transplantation, cyclosporine fu was determined ex vivo in plasma by equilibrium dialysis. In a retrospective study, 260 samples of plasma (one to seven per patient) were obtained from 89 heart (86%), lung (9%), and heart-lung (5%) transplant patients. The unbound fraction (x100) of cyclosporine ranged from 0.52% to 3.94%, with an overall mean of 1.53%+/-0.375% (SD). The mean percentage unbound for individual patients ranged from 0.71% to 1.98%, giving a 2.8-fold interpatient variation. In heart transplant recipients (66 patients), the values of fu were significantly lower (p < 0.01) during more severe rejection episodes, which required antirejection treatment (endomycardial biopsy result of grade 3a and higher) than in the absence of rejection (grade 0) or during grade la rejections. The value of fu did not vary with organ transplanted (p = 0.35) or etiology of organ failure (p = 0.32). Cyclosporine fu was negatively correlated with the age of the patient (r = -0.18, p < 0.05). Correlations were not observed between fu and blood biochemical and cytologic indices. However, fu was significantly lower (p < 0.01) in hypercholesterolemic transplant recipients (1.37+/-0.52%) than in normocholesterolemic patients (1.60+/-0.63%). Administration of simvastatin resulted in a significant increase in the mean fu from 1.40+/-0.09%) to 1.82+/-0.13% (paired t test, n = 13; p < 0.01). In patients who received ketoconazole, fu was not different from controls. These findings suggest that the level of cyclosporine fu may be an important determinant of immunosuppressive activity of cyclosporine. Moreover, the variation in fu could be strongly related to the concentration of serum lipoproteins; interpretation of the results of cyclosporine monitoring thus requires consideration of the lipidemic status of the patient.

Adolescent↗
PubMed1999

Use of a concurrent operants paradigm to evaluate positive reinforcers during treatment of food refusal.

The authors evaluated the responsiveness of 4 preschool-aged children to positive reinforcers within a concurrent operants paradigm during mealtimes. The children were presented with two identical, concurrently available sets of food. Each set differed in quantity and quality of positive reinforcement paired with acceptance of each bite of food or in the number of bites of food required to obtain positive reinforcement. Experiment 1 evaluated 1 child's responsiveness to positive reinforcement while permitting escape from bite offers. Experiment 2 evaluated 2 children's responsiveness to positive reinforcement when escape extinction occurred. Results from these experiments suggested that the children were responsive to positive reinforcers and chose more often the bites paired with the greater quantity and/or quality of reinforcement. Experiment 3 evaluated 1 child's responsiveness to positive reinforcement both without and with escape extinction. Results suggested that positive reinforcement affected choice behavior and that escape extinction affected amount of food consumed.

Behavior Therapy↗
PubMed1999

Antioxidant intake and adult-onset wheeze: a case-control study. Aberdeen WHEASE Study Group.

An increase in prevalence of wheezing illness in the UK has coincided with a reduction in the consumption of natural antioxidants, which may modulate the lung's response to oxidant stress, limiting the expression of airway inflammation and respiratory symptoms. The hypothesis that intakes and plasma levels of natural antioxidants would be determinants of adult-onset wheezing illness was tested. A nested case-control study was conducted in 94 cases with adult-onset wheeze and 203 controls aged 39-45 yrs identified in a 30-yr follow-up survey. Antioxidant intake was measured by a food frequency questionnaire, and plasma and red cell measurements of antioxidant status were obtained. Outcome measures were onset of wheeze since age 15 yrs (ever wheeze) and wheeze occurring in the past 12 months (current wheeze). After adjusting for the effects of smoking, socioeconomic status, atopy, family history of atopic disease and total energy intake, intakes of vitamin E (odds ratio (OR) = 4.02 for low compared to high tertile of intake) and plasma levels of ascorbate (OR = 0.98 per unit) and alpha-tocopherol:triglyceride ratio (OR = 0.34 per log(e) unit) were inversely related to adult-onset wheeze. In analyses stratified by social class and smoking, intakes of vitamin C and E and plasma levels of ascorbate and alpha-tocopherol:triglyceride ratio were inversely related to current wheeze in the manual social class and among current smokers. No independent associations of vitamin A, beta-carotene or total plasma antioxidant capacity were found. The results support the hypothesis that deficiencies of vitamins C and E are associated with wheezing symptoms. Smokers in the manual social class are particularly susceptible to these effects.

Adolescent↗
PubMed1999

New corn technology: scientists are all eyes and ears.

Corn and other crops contaminated with the fungus Aspergillus flavus give off a carcinogenic by-product called aflatoxin, which is blamed for high rates of liver cancer in Asia and Africa, where rice and corn are food staples. In the United States, aflatoxin's major threat is to farm animals, which can get sick or even die from consuming too much of the toxin. Scientists are working on ways to keep the deadly toxin out of the food supply. Two techniques under development identify aflatoxin-tainted corn by using infrared light to elicit telltale sounds and light from contaminated kernels. Other scientists hope to protect corn from A. flavus in the first place by designing genetically engineered aflatoxin-resistant grain species and by working with drugs such as oltipraz that reportedly detoxify aflatoxin already in the body.

Aspergillus flavus↗
PubMed1999

Effect of inhibitors on the biotransformation of tamoxifen by female rat and mouse liver slices and homogenates.

The metabolism of tamoxifen was studied in female Sprague-Dawley rat and mouse liver slices and homogenates, and the three principal tamoxifen metabolites, 4-hydroxytamoxifen, N-desmethyl-tamoxifen and tamoxifen N-oxide, were identified by HPLC using authentic standards. It was not possible to identify any of the minor metabolites such as the epoxides using this technique. The N-oxide metabolite only appeared when NADPH was added to the system; this is because the production of tamoxifen N-oxide is primarily mediated by microsomal flavin monooxygenase (FMO) which is NADPH dependent. However, this metabolite did appear in incubations with mouse liver slices only, because they are rich in flavin monooxygenases (FMOs). It did not appear in female rat or mouse liver homogenates, because the NADPH present is destroyed during homogenisation, therefore it was necessary to add NADPH to the system to produce the N-oxide metabolite. The purpose of this study was to investigate the effect of inhibitors on the biotransformation of tamoxifen by female rat and mouse liver slices and homogenates. Female rat liver slices and homogenates were incubated with the following inhibitors (1 mM): cimetidine, ascorbate, sodium azide and reduced glutathione. Cimetidine, a general P-450 inhibitor, inhibited the production of the N-desmethyl metabolite by about 80%; this is in agreement with the action of the other inhibitors. Reduced glutathione, ascorbate and sodium azide are mainly peroxidase inhibitors, so therefore from these novel and interesting results it was possible to suggest that peroxidases play a role in the metabolism of tamoxifen. This observation was also strengthened when the production of the N-desmethyl metabolite increased when horseradish peroxidase was added to the incubate. The production of 4-hydroxytamoxifen was reduced and the N-oxide metabolite was completely inhibited in the presence of peroxidase inhibitors. When rat liver homogenates was incubated with superoxide dismutase (SOD) and catalase, it was observed that the N-desmethyl metabolite disappeared completely at 60 min and the N-oxide and 4-hydroxy metabolites were completely inhibited. However, this phenomenon was only observed when SOD and catalase were preincubated for 30 min with the rat liver homogenate at 37 degrees C; without preincubation the production of these metabolites was unaffected. Finally, the effect of long incubation periods (300 min) on the production of metabolites was examined. It was found that there was a reduction in the concentration of metabolite produced after 60 min which was due to enzyme and co-factor degradation.

Animals↗
PubMed1999

Nuclear structure, gene expression and development.

This article considers the extent to which features of nuclear structure are involved in the regulation of genome function. The recent renaissance in imaging technology has inspired a new determination to assign specific functions to nuclear domains or structures, many of which have been described as "factories" to express the idea that they coordinate nuclear processes in an efficient way. Visual data have been combined with genetic and biochemical information to support the idea that nuclear organization has functional significance. Particular DNA sequences or chromatin structures may nucleate domains that are permissive or restrictive of transcription, to which active or inactive loci could be recruited. Associations within the nucleus, as well as many nuclear structures, are transient and change dynamically during cell cycle progression and development. Despite this complexity, elucidation of the possible structural basis of epigenetic phenomena, such as the inheritance of a "cellular memory" of gene expression status, is an important goal for cell biology. Topics for discussion include the regulatory effect of chromatin structure on gene expression, putative "nuclear addresses" for genes and proteins, the functional significance of nuclear bodies, and the role of the nuclear matrix in nuclear compartmentalization.

Animals↗
PubMed1999

Error estimates in novice and expert raters for the KT-1000 arthrometer.

STUDY DESIGN: Single group repeated measures with multiple raters. OBJECTIVES: To determine the inter-rater reliability of KT-1000 measurements of novice and experienced raters and to provide error estimates for these raters. BACKGROUND: The KT-1000 arthrometer is often used clinically to quantify anterior tibial displacement. Few data have been documented, however, about the relative reliability of KT-1000 measurements obtained by novice compared with experienced users. METHODS AND MEASURES: Two novice and two experienced KT-1000 users performed measurements on 29 knees of 25 patients after anterior cruciate ligament (ACL) reconstruction or with a diagnosis of ACL deficiency. Measurements were performed at 131 N. Interrater and intertrial reliability coefficients (interclass correlation coefficient; ICC) and the standard error of measurement were calculated for expert and novice raters. RESULTS: The interrater ICC for novices was 0.65 and the interrate error was +/- 3.52 mm (90% confidence interval [CI]). The interrater ICC for experts was 0.79 and the interrater error was +/- 2.94 mm (90% CI). CONCLUSIONS: These results suggest that experience in using the KT-1000 is related to the interrater error of measurements and that training is an important consideration when using the KT-1000 arthrometer.

Adolescent↗
PubMed1999

Adaptive responses to environmental chemicals.

Adaption to chemical agents in the environment is a fundamental part of the evolutionary process and a large number of genes have evolved to specifically detoxify potentially harmful chemical agents. These genes can act at various levels within cells and determine circulating chemical or toxin concentrations, and uptake and efflux rates as well as intracellular detoxification enzymes, such as the cytochrome P-450-dependent mono-oxygenases and glutathione S-transferases. These multigene families of proteins play a central role in chemical and drug detoxification and their polymorphic expression may well be a factor in disease susceptibility.

Adaptation, Physiological↗
PubMed1999

Risk of venous thromboembolism associated with the common hereditary haemochromatosis Hfe gene (C282Y) mutation.

A high prevalence of a common mutation in the Hfe gene (C282Y) has recently been reported in patients with the factor V Leiden mutation and a history of thrombosis. The aim of this study was to estimate the relative risk of venous thromboembolism in a large case-control study. 56/481 patients (11.6%) and 57/497 controls (11.5%) were heterozygous for the C282Y allele giving an odds ratio of 1.02 (95%CI 0.69-1.51). 12/81 patients with the factor V Leiden mutation were heterozygous for the C282Y allele compared to 1/13 controls, odds ratio 2.09 (95%CI 0.25-17.6). An analysis of a further group of patients and controls selected for the factor V Leiden mutation did not indicate a higher prevalence of the C282Y allele in symptomatic patients, odds ratio 0.17 (95%CI 0.34-0.81). This study does not support the hypothesis that the C282Y allele is an additional risk factor for venous thrombosis in patients with the factor V Leiden mutation.

Adolescent↗
PubMed1999

RPR120844, a novel, specific inhibitor of coagulation factor Xa inhibits venous thrombosis in the rabbit.

The in vivo antithrombotic activity of RPR 20844, a novel synthetic coagulation factor Xa (fXa) inhibitor (Ki = 7 nM), was assessed by its ability to inhibit thrombus formation in a damaged segment of the rabbit jugular vein. Intravenous dose-response studies were performed and thrombus mass (TM), activated partial thromboplastin time (APTT), prothrombin time (PT), inhibition of ex vivo fXa activity and plasma drug levels (PDL) were determined. TM, measured at the end of a 50 min infusion, was significantly reduced (p<0.05 vs. saline-treated animals) by RPR120844 at 30 and 100 microg/kg/min. At doses of 10, 30 and 100 microg/kg/min, APTT was prolonged by 2.1, 4.2 and 6.1-fold, and PT was prolonged by 1.4, 2.2 and 3.5-fold, respectively. PDL were determined by measuring anti-fXa activity using an amidolytic assay. Peak PDL were 0.8+/-0.3, 1.5+/-0.9 and 2.4+/-0.6 microM, respectively. The drug effect was reversible with APTT, PT and PDL returning toward pretreatment values 30 min after termination of treatment. The results suggest that RPR 120844, or similar compounds, may provide an efficacious, yet easily reversible, means of inhibiting thrombus formation.

Animals↗
PubMed1999

Gravity, stress, calcium and gene expression.

Cytoplasmic calcium is a major regulator of plant metabolism and its levels are under strict control, but it increases rapidly and transiently after stress treatments such as cold and touch (Trewavas 1999). Gravity is also thought to affect Ca2+ levels, although one report, using fluorescence microscopy of Ca(2+)-binding dyes, showed no changes (Legue et al. 1997). However, in these studies Ca2+ could not be visualized for at least 1 min after gravistimulation and thus changes could have occurred more rapidly. In order to circumvent problems associated with the delay in taking readings imposed by the fluorescence microscopy techniques, we chose a different method using plants transgenic for the Ca(2+)-binding, light-emitting jellyfish protein aequorin (Knight & Knight 1995). We subjected Arabidopsis and tomato plants to heat-wounding, vibration and gravity stimulation and measured cytoplasmic Ca2+ levels. We also measured the levels of several transcripts after heat-wound and gravity stimulation to determine whether both treatments evoked the same changes.

Aequorin↗
PubMed1998

Kinetics and interaction studies between cytochrome c3 and Fe-only hydrogenase from Desulfovibrio vulgaris Hildenborough.

Hydrogenases from Desulfovibrio are found to catalyze hydrogen uptake with low potential multiheme cytochromes, such as cytochrome c3, acting as acceptors. The production of Fe-only hydrogenase from Desulfovibrio vulgaris Hildenborough was improved with respect to the growth phase and media to determine the best large-scale bacteria growth conditions. The interaction and electron transfer from Fe-only hydrogenase to multiheme cytochrome has been studied in detail by both BLAcore and steady-state measurements. The electron transfer between [Fe] hydrogenase and cytochrome c3 appears to be a cooperative phenomenon (h = 1.37). This behavior could be related to the conductivity properties of multihemic cytochromes. An apparent dissociation constant was determined (2 x 10(-7) M). The importance of the cooperativity for contrasting models proposed to describe the functional role of the hydrogenase/cytochrome c3 complex is discussed. Presently, the only determined structure is from [NiFe] hydrogenase and there are no obvious similarities between [NiFe] and [Fe] hydrogenase. Furthermore, no crystallographic data are available concerning [Fe] hydrogenase. The first results on crystallization and X-ray crystallography are reported.

Biosensing Techniques↗
PubMed1998

Mechanism of Cdc42-induced actin polymerization in neutrophil extracts.

Cdc42, activated with GTPgammaS, induces actin polymerization in supernatants of lysed neutrophils. This polymerization, like that induced by agonists, requires elongation at filament barbed ends. To determine if creation of free barbed ends was sufficient to induce actin polymerization, free barbed ends in the form of spectrin-actin seeds or sheared F-actin filaments were added to cell supernatants. Neither induced polymerization. Furthermore, the presence of spectrin-actin seeds did not increase the rate of Cdc42-induced polymerization, suggesting that the presence of Cdc42 did not facilitate polymerization from spectrin-actin seeds such as might have been the case if Cdc42 inhibited capping or released G-actin from a sequestered pool. Electron microscopy revealed that Cdc42-induced filaments elongated rapidly, achieving a mean length greater than 1 micron in 15 s. The mean length of filaments formed from spectrin-actin seeds was <0.4 micron. Had spectrin-actin seeds elongated at comparable rates before they were capped, they would have induced longer filaments. There was little change in mean length of Cdc42-induced filaments between 15 s and 5 min, suggesting that the increase in F-actin over this time was due to an increase in filament number. These data suggest that Cdc42 induction of actin polymerization requires both creation of free barbed ends and facilitated elongation at these ends.

Actin Cytoskeleton↗