Biomedical subjects

G M Brown

Publications and source records attributed to G M Brown.

At least 19 recordsLinked to original sources

PubMed1992

Mutagenic DNA repair in Escherichia coli. XXI. A stable SOS-inducing signal persisting after excision repair of ultraviolet damage.

Mutations to streptomycin resistance induced by ultraviolet light in Escherichia coli can lose their susceptibility to photoreversing light during excision repair and in the absence of chromosomal replication and protein synthesis, i.e., under conditions where SOS induction cannot occur. Using fusions of lac with sulA and umuC we have shown that after excision of UV damage in the presence of chloramphenicol there is a persisting, relatively stable signal capable of inducing SOS genes when protein synthesis is subsequently permitted. The persisting signal is formed roughly in proportion to the square of the UV dose and is about 30% photoreversible. It is suggested that the persisting SOS-inducing signal comprises a UV photoproduct (the target lesion) opposite a gap in the opposing DNA strand, and is formed by excision of one (the ancillary lesion) of a pair of closely opposed photoproducts. Calculations suggest that as few as two or three such configurations in a cell can lead to induction of sulA when protein synthesis is permitted. It is not clear whether these configurations can directly induce the SOS system because of their region of single-stranded DNA or whether the ultimate SOS-inducing signal is a more extensive single-stranded region formed when such configurations encounter a replication fork. Photoproduct/gap configurations have been previously suggested to be potentially mutagenic. UV-induced mutations to streptomycin resistance are mostly at A:T sites and are not photoreversible in fully SOS-induced bacteria in the absence of excision repair, indicating that they are not targeted at cyclobutane-type pyrimidine dimers. In SOS-induced excision-proficient bacteria there is about 39% photoreversibility which is rapidly lost after UV. This photoreversibility is attributed to many ancillary lesions being cyclobutane-type pyrimidine dimers which are excised leading to the exposure of target lesions on the opposing strand which, at these particular sites, are mostly non-photoreversible photoproducts.

Bacterial Proteins↗

PubMed1992

Characterization of 2-[125I]iodomelatonin-binding sites in quail testes at mid-light and mid-dark.

The binding and pharmacological characteristics of 2-[125I]iodomelatonin binding sites in testis membrane preparations of quails were examined. Scatchard analyses yielded an equilibrium dissociation constant (Kd) of 46.6 +/- 8.6 pmol/l and maximum binding capacity (Bmax) of 2.77 +/- 0.20 fmol/mg protein for the gonadal 2-[125I]iodomelatonin binding sites. Except for melatonin, 6-chloromelatonin, 2-iodomelatonin and N-acetylserotonin, all compounds tested elicited no significant inhibition of radioligand binding. Significant diurnal variations were detected in serum melatonin levels of 24-week-old quails while no diurnal difference was detected in the affinities or densities of the gonadal 2-[125I]iodomelatonin binding sites in quails. Results of the present study suggest possible direct gonadal action by pineal melatonin in birds.

Animals↗

PubMed1992

Immobilization of DNA for scanning probe microscopy.

Reproducible scanning tunneling microscope and atomic force microscope images of entire molecules of uncoated plasmid DNA chemically bound to surfaces are presented. The chemically mediated immobilization of DNA to surfaces and subsequent scanning tunneling microscope imaging of DNA molecules demonstrate that the problem of molecular instability to forces exerted by the probe tip, inherent with scanning probe microscopes, can be prevented.

DNA, Bacterial↗

PubMed1992

A sub-population of keratan sulphates derived from bovine articular cartilage is capped with alpha(2-6)-linked N-acetylneuraminic acid residues. Affinity chromatography using immobilized Sambucus nigra lectin and characterization using 1H n.m.r. spectroscopy.

Alkaline borohydride-reduced keratan sulphate (KS) chains derived from bovine femoral head cartilage were fractionated by lectin affinity chromatography with Sambucus nigra agglutinin (SNA) into binding and non-binding populations. Analysis of the SNA-binding and non-binding KS chains using 600 MHz 1H n.m.r. spectroscopy showed that the former population contained alpha(2-6)-N-acetylneuraminic acid residues and the latter contained primarily alpha(2-3)-N-acetylneuraminic acid residues as chain terminators. Both populations contained a similar proportion of alpha(2-3)-N-acetylneuraminic acid residues within their protein-linkage regions, and similar sulphation and fucosylation levels. Analysis of these two fractions by gel-permeation chromatography (g.p.c.) on a TSK-30 XL column showed them to have the same size distributions. It was concluded from the n.m.r. spectra and g.p.c. data that the populations differed primarily in the mode of linkage of the chain-terminating sialic acids.

Animals↗

PubMed1992

Degradation of articular cartilage keratan sulphates using hydrazinolysis and nitrous acid. Environment of fucose residues.

Alkaline borohydride-reduced keratan sulphate (KS) chains from bovine articular cartilage (6-8-year-old animals) were fragmented by an anhydrous hydrazine/nitrous acid procedure, previously used on KS by Hopwood & Elliott to isolate the major disaccharides from the poly-N-acetyl-lactosamine repeat sequence [Hopwood & Elliott (1983) Carbohydr. Res. 117, 263-274]. The resulting oligosaccharides were reduced with NaB3H4 or NaBH4 and subjected to ion-exchange chromatography on a Nucleosil 5SB column. In addition to the major disaccharides, two fucose-containing oligosaccharides were examined by high-field 1H n.m.r. spectroscopy, and shown to have the following structures (where AnManOH is 2,5-anhydro-D-mannitol): [formula: see text] It is evident that the presence of fucose protects the N-acetylglucosamine residue from de-N-acetylation, and therefore fragments are produced which preserve the immediate environment of the fucose residue. It may be of biosynthetic significance that these two oligosaccharides contain an unsulphated galactose on the non-reducing side of the fucose residue. The hydrazine/nitrous acid/NaB3H4 method followed by h.p.l.c. provides a sensitive fingerprinting technique for the assay of KS composition and sub-populations.

Animals↗

PubMed1992

Asbestos-stimulated tumour necrosis factor release from alveolar macrophages depends on fibre length and opsonization.

Fibre length has been shown to be an important factor in the ability of respirable fibres to cause lung fibrosis and cancer. We have reported that a long sample of amosite asbestos is more carcinogenic and fibrogenic than a short sample of similar diameter. These amosite asbestos samples were studied with regard to their ability to stimulate the release of the pro-inflammatory cytokine tumour necrosis factor (TNF) from rat alveolar macrophages in vitro. The long fibre sample was found to stimulate substantially greater release of the cytokine than the short sample. Furthermore, on treatment of the fibres with rat immunoglobulin G (IgG), there was an increase in the ability of both the long and the short sample to stimulate TNF secretion, although the long sample retained by far the greatest activity. Coating of the fibres with a range of other proteins had no substantial effect on their ability to stimulate TNF secretion. Quartz and titanium dioxide (TiO2) were included as control particles and the TNF-stimulating activity of quartz was notably increased by opsonization with IgG. TiO2 showed a similar low activity to that of the short fibre sample of amosite but this again could be modestly increased by opsonization with IgG. The simulation of TNF release caused by treatment with immunoglobulin-opsonized long fibre amosite could be inhibited by treatment of the macrophages with the protein kinase C-inhibitor staurosporine. The study demonstrates a fibre length-related ability to stimulate cytokine secretion by alveolar macrophages, and its enhancement by opsonization with IgG.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

Activated human peripheral blood neutrophils produce epithelial injury and fibronectin breakdown in vitro.

The ability of peripheral blood neutrophils to injure elements of the alveolar septum was assessed. Experiments consisted of activating previously isolated neutrophils (PMNs) with a soluble (phorbol myristate acetate, PMA) and a particulate (zymosan) trigger, and measuring detachment of 51Cr-labeled epithelial cells. In addition, the mechanisms of epithelial injury were investigated by including anti-proteinase and antioxidants in the system. Untriggered PMNs produced only slight detachment injury to epithelial cells at two effector-target cell ratios, this effect being dramatically increased after triggering with PMA; zymosan caused triggering but less than was produced by PMA. Alpha-1-protease inhibitor produced a decrease in detachment when both PMA- and zymosan-triggered cells were the effectors; superoxide dismutase did not significantly reduce detachment. The ability of triggered PMNs to cause proteolysis of fibronectin, as measured in a radiolabeled fibronectin matrix degradation assay, was related to their triggerability in the detachment assay, zymosan being largely ineffective in triggering enhanced proteolysis. These findings suggest that fibronectin is important in maintaining the integrity of the alveolar epithelial surfaces. Furthermore, in inflamed alveoli, activated PMNs can release proteinases, which cause degradation of this matrix component leading to compromise of the alveolar epithelial barrier.

Cell Adhesion↗

PubMed1992

Age-associated changes and sex differences in urinary 6-sulphatoxymelatonin circadian rhythm in the rat.

The circadian rhythm of 6-sulphatoxymelatonin (aMT6s) excretion has been determined in male and female rats at 3 weeks and at 2, 8, 14 and 20 months of age. All animals have a pronounced circadian pattern of aMT6s excretion under a 12 hour dark: 12 hour light cycle. A significant increase in aMT6s excretion is observed from 3 weeks to 14 months followed by a decrease at 20 months. There is a highly significant correlation between aMT6s excretion and body weight (r = 0.73 for female rats and r = 0.74 for male rats; p values are all less than 0.001). Thus, a decrease in aMT6s excretion associated with increasing age occurs when body weight is taken into consideration. aMT6s excretion is higher in males at 3 weeks and at 2 and 8 months of ages. Urinary testosterone in male rats and estradiol in female rats increase from 3 weeks to 8 months and decrease at older ages. These data suggest that increase of body weight from 3 weeks to 14 months is an important factor responsible for the age-related alteration. The sex differences in aMT6s excretion in younger rats may be associated with their sex hormonal milieu.

Age Factors↗

PubMed1992

Effect of chronic antidepressant treatment with adinazolam and desipramine on melatonin output.

Output of melatonin or its main metabolite, 6-sulphatoxy melatonin, provides an index of noradrenergic activity in the pineal gland, which is of interest in major depression and during its treatment with antidepressants. Fifteen female depressed outpatients did not differ in levels of 24-hour urinary 6-sulphatoxy melatonin compared with 13 female control subjects. However, a subgroup of the depressed patients (n = 9) who were treated with desipramine showed a significant elevation of 6-sulphatoxy melatonin levels after 1 week of treatment and a return to baseline levels after 6 weeks. There was also a significant negative correlation between 6-sulphatoxy melatonin levels and symptom severity as measured by the Hamilton Rating Scale for Depression after 3 weeks of treatment with desipramine. The other subgroup of depressed patients (n = 6) were treated with adinazolam, a benzodiazepine with antidepressant properties. Despite comparable antidepressant effects to those achieved with desipramine, adinazolam was not associated with any apparent change in 6-sulphatoxy melatonin output during 6 weeks of treatment. There was also no correlation between 6-sulphatoxy melatonin levels and symptom severity.

Adult↗

PubMed1992

Urinary catecholamines and cortisol in parasuicide.

A relationship of urinary catecholamines and of urinary free cortisol with violent suicide attempts has been reported. We have reexamined this issue in patients within 24 hours of hospital admission. Suicide attempters had significantly higher norepinephrine (NE: mean +/- SD = 58.3 +/- 27.0 micrograms/24 hours; n = 27) than did control patients with suicidal ideation (mean +/- SD = 37.1 +/- 21.3; n = 10). Among suicide attempters, those who used physical means had the highest NE levels (mean +/- SD = 69.7 +/- 21.3) and those who took overdoses of antidepressants (mean +/- SD = 51.9 +/- 17.3; n = 6), benzodiazepines (mean +/- SD = 65.1 +/- 29.7; n = 5), or miscellaneous drugs (mean +/- SD = 59.1 +/- 36.5; n = 11) had lower NE values. In contrast to NE, urinary dopamine (mean +/- SD = 402.6 +/- 392 micrograms/24 hours, epinephrine (EPI: mean +/- SD = 14.3 +/- 4.0 micrograms/24 hours), the NE/EPI ratio (mean +/- SD = 8.3 +/- 0.9), urinary free cortisol (mean +/- SD = 157.9 +/- 11.5 micrograms/24 hours) and serum cortisol (mean +/- SD = 35.0 +/- 13.1 nM/l) did not differ between groups. There were no group differences in age (mean +/- SD = 36.3 +/- 16.5 years), Beck Depression Inventory score (mean +/- SD = 26.3 +/- 12.9), Beck Hopelessness Scale score (mean +/- SD = 10.0 +/- 5.6), Beck Scale for Suicidal Ideation score (mean +/- SD = 13.6 +/- 9.3), or Hamilton Rating Scale for Depression score (mean +/- SD = 19.5 +/- 9.8). In the four parasuicide groups, there was no difference in suicide intent (mean +/- SD = 13.3 +/- 7.9). These findings indicate that there is increased NE output shortly after suicide attempts. Previous reports of a low NE/EPI ratio in suicidal patients may reflect adaptive changes rather than the acute state of the patient at the time of the attempt.

Adult↗

PubMed1992

Scanning tunneling microscopy of DNA: a novel technique using radiolabeled DNA to evaluate chemically mediated attachment of DNA to surfaces.

pBS+ plasmid deoxyribonucleic acid (DNA) was imaged by scanning tunneling microscopy (STM) after mounting microdroplets by aerosol deposition onto heated epitaxial gold surfaces. However, the instability of the adsorbate to forces exerted by the tunneling tip points out the need for more aggressive bonding of molecules to surfaces. We describe a sensitive assay for the qualitative and quantitative evaluation of chemical agents to influence binding of DNA to surfaces using 32P-labeled pBS+ plasmid DNA. We propose that such an assay can make an important contribution to immobilization techniques prior to STM imaging.

DNA↗

PubMed1992

An oral melatonin replacement regimen that re-establishes the normal circadian levels of urinary 6-sulphatoxymelatonin in functionally pinealectomized rats.

Wistar rats maintained on a 12-hr daily photoperiod (LD 12:12 cycle) exhibited a diurnal rhythm in urinary 6-sulphatoxymelatonin (aMT6s) concentrations with peak levels in the scotophase. Light-induced functional pinealectomy (FPX) abolished the nocturnal rise in aMT6s, lowering it to photophase levels. The objective of the study was to formulate an oral melatonin replacement regimen that would restore a normal rhythmic output of urinary aMT6s in functionally pinealectomised rats. Three regimens of sequential doses of melatonin were tested. Of these, the regimen with melatonin concentrations of 4 ng, 12 ng, 65 ng, and 4 ng per ml of drinking water given to rats during the 1st, 2nd, 3rd, and 4th 3-hr periods, respectively, of the 12-hr FPX phase, was found to generate a urinary aMT6s level that closely resembled the natural level and rhythm exhibited under an LD 12:12 cycle. This dose is considered appropriate to restore certain melatonin-mediated physiological functions in Wistar rats subjected to FPX.

Administration, Oral↗

PubMed1992

Day-night rhythm disturbance, pineal function and human disease.

Depression, mania and probably starvation all induce changes in pineal function. At present it is unknown what secondary effects on the endocrine and other systems are produced by these changes. Studies in rats have established an entraining effect of melatonin on locomotor activity and a feedback effect on the pineal itself. Studies of jet-lag and of sleep dysregulation in a blind subject established that melatonin treatment has a synchronizing effect in these conditions. Further investigations will be necessary to establish whether melatonin reduction in depression and other disorders leads secondarily to dysregulation of other circadian rhythms.

Animals↗

PubMed1992

Toward a brain map of auditory hallucinations.

OBJECTIVE: This study asks whether auditory hallucinations are reflected in a distinctive metabolic map of the brain. METHOD: Regional brain metabolism was measured by positron emission tomography with [18F]-fluorodeoxyglucose in 12 DSM-III schizophrenic patients who experienced auditory hallucinations during glucose uptake and 10 who did not. All patients were free of neuroleptics and 19 had never been treated with neuroleptics. Nine patients were reexamined after 1 year to assess effects of neuroleptic treatment. RESULTS: Compared with the patients who did not experience hallucinations, the patients who did experience hallucinations had significantly lower relative metabolism in auditory and Wernicke's regions and a trend toward higher metabolism in the right hemisphere homologue of Broca's region. Hallucination scores correlated positively and significantly with relative metabolism in the striatum and anterior cingulate regions. Neuroleptic treatment resulted in a significant increase in striatal metabolism and a reduced frontal-parietal ratio, which was significantly correlated with a decrease in hallucination scores. CONCLUSIONS: Auditory hallucinations involve language regions of the cortex in a pattern similar to that seen in normal subjects listening to their own voices but different in that left prefrontal regions are not activated. The striatum plays a critical role in auditory hallucinations.

Adult↗

PubMed1992

Epithelial and extracellular matrix injury in quartz-inflamed lung: role of the alveolar macrophage.

The bronchoalveolar leukocytes from quartz-inflamed lung were separated into macrophage-enriched and neutrophil-enriched populations on density gradients. Neutrophil-enriched populations showed the greatest activity in causing injury to epithelial cells and fibronectin in vitro. Inflammatory macrophage-enriched populations from quartz-exposed lung had the ability to cause fibronectin degradation but could not cause detachment injury to epithelial cells over and above that caused by control alveolar macrophages. Fibronectin damage in vivo could be an important factor in disordering the connective tissue scaffold of the lung, thereby favoring fibrosis. In vitro quartz stimulated more production of cytokines by alveolar macrophages than the inert particulate titanium dioxide. Cytokines could be important in upregulating adhesion molecules in the membranes of lung cells in vivo; this process could aid leukocyte/lung cell contact, allowing epithelial injury to be expressed, and could also be a factor leading to pathological change.

Animals↗

PubMed1992

Persistent inflammation and impaired chemotaxis of alveolar macrophages on cessation of dust exposure.

Rats were exposed by inhalation to coal mine dust, titanium dioxide, or quartz. The magnitude of the consequent inflammatory response was assessed by counting numbers and types of leukocytes in the bronchoalveolar lavage fluid. The magnitude of the inflammatory response reflected the toxicity of the dusts, with quartz eliciting the greatest recruitment of inflammatory leukocytes, coal mine dust less than quartz, and titanium dioxide eliciting no inflammation. To assess the persistence of the inflammation, groups of rats were maintained in room air for 30 or 60 days after cessation of dust exposure and then numbers of leukocytes were assessed. Bronchoalveolar leukocytes in rats exposed to coal mine dust were reduced after exposure, but in the quartz-exposed rats the numbers increased with time after exposure. The chemotactic responses of bronchoalveolar leukocytes from rats inhaling coal mine dust and quartz were reduced and remained so after a 30-day recovery period. Their reduced ability to chemotact did not fully prevent macrophages from leaving the bronchoalveolar region of dust-exposed rats. However, it is likely that the delayed removal of inflammatory leukocytes with the potential to injure the lung tissue may contribute to septal damage and so contribute to the pathogenesis of pneumoconiosis.

Animals↗

PubMed1992

Atomic force microscopy of DNA on mica and chemically modified mica.

Atomic force microscopy (AFM) was used to image circular DNA adsorbed on freshly cleaved mica and mica chemically modified with Mg(II), Co(II), La(III), and Zr(IV). Images obtained on unmodified mica show coiling of DNA due to forces involved during the drying process. The coiling or super twisting appeared to be right handed and the extent of super twisting could be controlled by the drying conditions. Images of DNA observed on chemically modified surfaces show isolated open circular DNA that is free from super twisting, presumably due to strong binding of DNA on chemically modified surfaces.

Adsorption↗

PubMed1992

Nutritional status in rheumatoid arthritis. Effects of disease activity, corticosteroid therapy and functional impairment.

Sixty-five patients with rheumatoid arthritis (RA) (mean age 37.2 years) were compared with 71 controls (mean age 33.8 years). Anthropometric measurements included body diameters and skin-fold thickness at multiple sites, while biochemical markers of nutritional status included serum albumin, thyroxine-binding pre-albumin and retinol-binding globulin levels. None of the RA subjects was outside the range that extended 2 standard deviations above and below the normal control values for lean body mass. Discriminant analysis showed that corticosteroid therapy did not significantly influence skinfold thickness in RA. A combination of bi-acromial and bi-ankle diameters had a sensitivity of 70% and a specificity of 72% in differentiating the RA group, in whom disease activity had a greater effect on body diameters than corticosteroid therapy did. Differences related to functional impairment were a manifestation of disease activity rather than a direct effect on skinfold thickness or body diameters. According to anthropometric measurements in ambulant patients, RA does not result in malnutrition in young individuals.

Adrenal Cortex Hormones↗