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Biomedical subjects

D M Brown

Publications and source records attributed to D M Brown.

At least 109 records · Page 6Linked to original sources
PubMed1995

Free radical detoxification in Giardia duodenalis.

Non-denaturing polyacrylamide gels were used to analyse superoxide dismutase (SOD), catalase, peroxidase, NADH oxidase and NADH peroxidase in the microaerophilic protozoan parasite Giardia duodenalis. A cytosolic H2O-producing NADH oxidase and membrane-associated NADH peroxidase were readily detected from G. duodenalis. In all Giardia strains investigated the NADH oxidase was present in high levels (1.2-2 U (mg protein)-1). Using the same technique, NADH oxidase activity was also detected in the microaerophilic protozoan parasites Tritrichomonas foetus, Trichomonas vaginalis and Entamoeba histolytica and in the bacterium Escherichia coli. The conventional enzymes of oxidative stress management (superoxide dismutase, catalase and peroxidase) were not detected in particulate or cytosolic extracts from recent and established strains of Giardia assayed in situ. Spectrophotometric assays also yielded negative results. The same methodology readily detected one or more of these enzyme activities in T. foetus, T. vaginalis and E. coli. Superoxide dismutase activity was not detected in lines of Giardia resistant to high levels of metronidazole or furazolidone. Furthermore, the agents 1,10 phenanthroline, diamide, MnCl2 and KNO3, which induce SOD in anaerobically cultured E. coli, did not induce SOD in Giardia. 1,10 phenanthroline has also been shown to induce iron-containing (Fe-) SOD in Entamoeba. Neither peroxidase nor catalase activities were detected in a peroxide-resistant line of Giardia. Viable trophozoites from parent lines were able to decompose H2O2 at a significant rate. It appears that the conventional SOD, catalase and peroxidase utilised in aerobic metabolism have been substituted in Giardia by NADH oxidase and NADH peroxidase, similar to anaerobic bacteria. The O2-scavenging NADH oxidase explains the previously observed futile 'respiration' in Giardia.

Animals↗
PubMed1995

Acute myocardial and vascular responses to specific angiotensin II antagonism in the spontaneously hypertensive rat.

As the AT1 receptor is the primary angiotensin II receptor in the myocardium and vasculature, we assessed the acute myocardial and vascular response to the AT1 angiotensin II antagonist losartan in the spontaneously hypertensive rat (SHR) to determine the contribution of angiotensin II in this genetic form of hypertension. In a preliminary dose response study, which evaluated losartan at 1.0, 3.0, and 10 mg/kg, 10 mg/kg uniformly lowered blood pressure. In a second group of experiments, 10 mg/kg also completely attenuated the pressor effects of angiotensin II administration. In nine adult SHR, intravenous losartan, 10 mg/kg, was given, with hemodynamics measured immediately and at steady-state intervals to delineate the hemodynamic response to angiotensin II antagonism. Losartan significantly lowered systolic, diastolic, and mean blood pressures, yet heart rate was unchanged. Cardiac function, as assessed by cardiac output and blood flow acceleration, demonstrated only transient increases which were not sustained during steady-state blood pressure reduction. Significant increases of peak blood flow and pulse pressure were sustained throughout the blood pressure response. At immediate and steady-state determinations, system vascular resistance and characteristic aortic impedance were significantly reduced with losartan (both P < .01). In addition, concomitant reduction of the wave reflectance index also occurred, achieving significance at steady state (P < .05). These changes demonstrate that the AT1 angiotensin II receptor contributes to both central and peripheral vasoconstriction in the spontaneously hypertensive rat. Absence of sustained increase of cardiac output and blood flow acceleration are consistent with inhibition of the previously reported positive inotropic effect of angiotensin II.

Angiotensin II↗
PubMed1995

Intralesional sustained-release chemotherapy with therapeutic implants for treatment of canine sun-induced squamous cell carcinoma.

Squamous cell carcinoma (SCC) is the most frequently reported malignant epithelial tumour in dogs. Canine sun-induced SCC represents a useful animal model to evaluate new therapeutic modalities for possible human applications. We evaluated the safety and efficacy of treating sun-induced SCC in dogs with intralesional sustained-released chemotherapeutic gel implants that contained collagen, epinephrine (epi), and either 5-fluorouracil (5-FU) or cisplatin (CDDP). Dogs with large, single SCC or fields of multiple SCC were treated with 5-FU/epi gel for a minimum of three weekly injections. Dogs without a complete response were then treated with CDDP/epi gel for a minimum of three weekly treatments. We treated from one to 11 primary, recurrent, or refractory SCC per dog (tumour size 0.2-92.4 cm2; mean cumulative tumour area of 40.7 cm2 per dog). All dogs had at least 50% reduction in cumulative tumour area after treatment with 5-FU/epi gel. More than half (seven of 13) had complete resolution of SCC after treatment with 5-FU/epi gel or CDDP/epi gel. Minimal local tissue reactions were noted; no systemic toxicity occurred. Sustained-release chemotherapy using intralesional 5-FU/epi gel and CDDP/epi gel therapeutic implants is effective in treating canine sun-induced SCC of the skin.

Animals↗
PubMed1995

Coordinated activation of corneal wound response genes in vivo as observed by in situ hybridization.

We used subtractive screening of a cDNA library prepared from corneoscleral rims after cauterizing rat corneas. We identified 76 clones whose corresponding mRNA increased during the wound healing process in an in vivo model of injury which damages the corneal epithelium, stroma, and endothelium. Of these clones, 31 sequences encode known proteins. Another 45 clones are novel sequences based on comparison with the GenBank/EMBL databases. Changes in the level of expression of the novel genes, and a selected number of the known genes, were examined by in situ hybridization 22 and 72 hr after corneal injury. The majority produced a 'wound pattern' of expression such that the mRNAs were highly induced in all cell types adjacent to the wound site at 22 hr post injury. This signal decreased in intensity with distance from the wound site. In a subset of corneoslceral rims examined by in situ hybridization, the mRNAs for these genes were also highly induced in the limbal epithelium, where the progenitor corneal epithelial stem cells reside. By 72 hr, when acute tissue damage had been repaired, the induced mRNA was only faintly present in the thickened epithelium. Our results provide a useful framework for further studies defining the pathophysiological roles of the known and novel proteins encoded by the isolated cDNA clones.

Animals↗
PubMed1995

Bromo-deoxyuridine (BRDU) uptake in the lungs of rats inhaling amosite asbestos or vitreous fibres at equal airborne fibre concentrations.

Rats were exposed, by inhalation, to target airborne fibre concentrations of 1000 f/ml (PCOM fibres by WHO criteria) of a long amosite asbestos sample and a vitreous fibre sample; the target was closely attained for both fibre samples. The size distributions of the two fibre samples was closely similar. Rats were placed in the chambers for 7 hours and then, following a further 16 hours in room air, were injected with bromo-deoxyuridine (BRDU). The presence of BRDU-positive cells in terminal bronchioles/alveolar ducts was assessed in blocks taken from various parts of the left lung, from apex to base. There were significant differences in the proliferative responses between animals but there were also significant differences between the treatments. Lungs from rats exposed to vitreous fibres showed no greater response than the controls, but there was a markedly greater proliferative response in the lungs of rats inhaling long amosite. There was a decreasing gradient of proliferative response from the apex of the lung to the base with all treatments. This could be explained by different degrees of deposition in different areas of the lung. Similar amounts of fibre accumulated in the lungs of rats exposed to the two fibre types and it is unlikely that dissolution could be important over the timescale used here. We conclude that, when amosite asbestos deposits in the lungs of rats it stimulates a proliferative response and that deposition of an equal number of similar-sized vitreous fibres has no effect.

Air Pollutants↗
PubMed1995

Isolation and structural elucidation of pentacyclic triterpenoids from Maprounea africana.

Pentacyclic triterpenoids based on the taraxer-14-ene skeleton with a C-28 attached carboxylic acid group have been isolated from the roots of Maprounea africana. These compounds were identified as 1 beta,2 alpha-dihydroxyaleuritolic acid 2,3-bis-p-hydroxybenzoate [1], 2 alpha-hydroxyaleuritolic acid 3-p-hydroxybenzoate [2], 2 alpha-hydroxyaleuritolic acid 2,3-bis-p-hydroxybenzoate [4], aleuritolic acid 3-p-hydroxybenzoate [5], aleuritolic acid [6], and aleuritolic acid 3-acetate [7]. Compounds 1 and 2 are new triterpene esters. Compound 3 was previously reported as 7 beta-hydroxymaprounic acid 3-p-hydroxybenzoate [13]. However, based on detailed nmr studies, its structure has been revised.

Magnetic Resonance Spectroscopy↗
PubMed1995

Gummiferol, a cytotoxic polyacetylene from the leaves of Adenia gummifera.

A new polyacetylenic diepoxide compound, gummiferol [1] was isolated from the leaves of Adenia gummifera by KB cytotoxicity-guided fractionation. Compound 1 exhibited significant activity against the KB human cell line and a broad cytotoxic spectrum against other human cancer cell lines. The structure of 1 was established primarily on the basis of its spectral data.

Acetates↗
PubMed1995

Isolation and structure identification of an active DNA strand-scission agent, (+)-3,4-di-hydroxy-8,9-methylenedioxypterocarpan.

A new pterocarpan, (+)-3,4-dihydroxy-8,9-methylenedioxypterocarpan [1], was isolated from the flowers of Petalostemon purpureus by a DNA strand-scission assay-guided fractionation procedure. Compound 1 demonstrated activity in a standard in vitro DNA strand-scission assay, and cytotoxicity toward a KB tumor cell line. Two other related pterocarpans [2, 3] isolated from same plant were found to be moderately active for KB cells, but were inactive in the DNA strand-scission assay. (+)-4-Hydroxy-3-methoxy-8,9-methylenedioxypterocarpan [2] has not been reported previously as a natural product, while (+)-maackiain [3] has been isolated only as an optically inactive racemate along with its optical antipode, the (-)-isomer.

Antineoplastic Agents↗
PubMed1995

A genetic linkage map of the laboratory rat, Rattus norvegicus.

We report the construction of the first complete genetic linkage map of the laboratory rat. By testing 1171 simple sequence length polymorphisms (SSLPs), we have identified 432 markers that show polymorphisms between the SHR and BN rat strains and mapped them in a single (SHR x BN) F2 intercross. The loci define 21 large linkage groups corresponding to the 21 rat chromosomes, together with a pair of nearby markers on chromosome 9 that are not linked to the rest of the map. Because 99.5% of the markers fall into one of the 21 large linkage groups, the maps appear to cover the vast majority of the rat genome. The availability of the map should facilitate whole genome scans for genes underlying qualitative and quantitative traits relevant to mammalian physiology and pathobiology.

Animals↗
PubMed1995

Discovery of betulinic acid as a selective inhibitor of human melanoma that functions by induction of apoptosis.

As a result of bioassay-guided fractionation, betulinic acid, a pentacyclic triterpene, was identified as a melanoma-specific cytotoxic agent. In follow-up studies conducted with athymic mice carrying human melanomas, tumour growth was completely inhibited without toxicity. As judged by a variety of cellular responses, antitumour activity was mediated by the induction of apoptosis. Betulinic acid is inexpensive and available in abundant supply from common natural sources, notably the bark of white birch trees. The compound is currently undergoing preclinical development for the treatment or prevention of malignant melanoma.

Animals↗
PubMed1995

Topical tissue factor pathway inhibitor improves free-flap survival in a model simulating free-flap errors.

Free flap failure is frequently due to tension, twisting, kinking, or compression of the vascular pedicle after the anastomosis is completed. A rabbit model simulating these errors was used to evaluate the capacity of topically-applied tissue factor pathway inhibitor (TFPI) to prevent microvascular thrombosis. The rabbit ear was isolated on the central artery and vein. The artery was transected, shortened, repaired, and twisted 360 degrees around the vein. Immediately following the anastomosis. TFPI in concentrations of 1, 4, 10, or 40 micrograms/ml was irrigated across the lumen. Topically-applied control buffer and heparin (50 U/ml) were compared to TFPI. Treatment with control buffer resulted in a 20 percent survival rate. Topically-applied heparin improved the survival rate to 60 percent (p < 0.05). In contrast, TFPI in concentrations of 4, 10, and 40 micrograms/ml yielded survival rates of 89, 100, and 97 percent, respectively. This was significantly greater than the heparin-treated ears (p < 0.05). TFPI in a concentration of 40 micrograms/ml was effective in preventing arterial thrombosis when applied for as little as 30 sec; 4 micrograms/ml was effective in preventing thrombosis when applied for 10 min. These results support the use of TFPI as a topical irrigation solution to help prevent microvascular arterial thrombosis in free-flap surgery.

Administration, Topical↗
PubMed1995

Detection of surface free radical activity of respirable industrial fibres using supercoiled phi X174 RF1 plasmid DNA.

The ability of a number of respirable industrial fibres, amosite and crocidolite asbestos, refractory ceramic fibres (RCFs) and man-made vitreous fibres (MMVFs) to cause free radical injury to plasmid phi X174 RFI DNA was assessed. The oxidative DNA damage was observed as depletion of supercoiled DNA after fibre treatment was quantified by scanning laser densitometry. The mechanism of fibre-mediated damage was determined by the use of the specific hydroxyl radical scavenger mannitol and the iron chelator desferrioxamine-B. The amosite and crocidolite asbestos caused substantial damage to DNA that was dose-related. The free radicals responsible for the asbestos-mediated DNA damage were hydroxyl radicals, as determined by inhibition with mannitol. Asbestos fibre-mediated damage to DNA was completely ameliorated by the chelation of fibre-associated iron with desferrioxamine-B. The amount of Fe(II) and Fe(III) released by equal numbers of the different fibre types at equal fibre number was determined. The fibres released very small amounts of Fe(II) and there were no significant differences between the fibre types. The fibres released substantial amounts of Fe(III); MMVF 21 released significantly more Fe(III) than any of the other fibres and short fibre amosite also released more Fe(III) than three of the MMVFs and two of the RCFs. When ability to release Fe(II) and Fe(III) was compared with ability to cause DNA damage there was not a good correlation, because only the long amosite and crocidolite caused substantial free radical injury to DNA; this contrasts with MMVF 21 and short amosite being the two fibres that released the greatest amounts of iron. The loss of ability to damage DNA in DSF-B-treated asbestos fibres shows that iron at the surface of asbestos fibres definitely has a role in generating hydroxyl radicals. However, it is clear that some fibres, such as short amosite and MMVF 21, release large quantities of iron without causing free radical damage, whilst neither long amosite nor crocidolite released more iron than the other fibres. The exact role of iron in fibre reactivity therefore remains unresolved, but fibre-bound iron not released from the surface of asbestos could be important. Further research is under way to investigate this possibility.

Air Pollutants, Occupational↗
PubMed1995

Intratumoral chemotherapy with a sustained-release drug delivery system inhibits growth of human pancreatic cancer xenografts.

This study provides the first evidence that treatment of human pancreatic adenocarcinoma is markedly improved by the intratumoral administration of chemotherapeutic agents in a novel drug delivery system. The effect of chemotherapeutic agents delivered in a sustained-release, protein-based, injectable gel was evaluated on the growth of human pancreatic adenocarcinoma cell line, BxPC-3. In vitro chemosensitivity of BxPC-3 cells exposed for 24 or 72 h to fluorouracil (0.01-5 mM), cisplatin or doxorubicin (0.1-50 microM) and floxuridine, vinblastine, mitomycin or paclitaxel (1.0-100 microM) was compared with that of untreated cells. In vitro chemosensitivity was also studied with fluorouracil and mitomycin in the poorly differentiated PANC-1, human pancreatic cancer cell line. Survival was determined after 7-10 days. All drugs decreased cell growth in a dose-dependent fashion. The efficacy of fluorouracil, cisplatin and doxorubicin increased with prolonged exposure, rendering these drugs most appropriate for a sustained-release preparation. For in vivo studies, athymic nude mice bearing BxPC-3 xenografts were treated either with fluorouracil, cisplatin or doxorubicin in the therapeutic injectable gel containing epinephrine or with vehicle alone administered intratumorally on days 1 and 4. After 28 days, the mice were sacrificed and tumors dissected and weighed. Tumors in mice treated with the injectable gel decreased in size by 72-79% compared with tumors in untreated controls and tumors treated with vehicle alone. Intratumoral injection of drug solution and intraperitoneal injection of drug in the injectable gel did not change tumor size compared with controls. In a drug-retention study, mice were injected intratumorally with [3H]fluorouracil either in the injectable gel or in solution. Sustained radioactivity was observed in tumors injected with the gel, and, conversely, greater radioactivity was detected in the liver and kidneys in mice receiving the radiolabeled solution. These results suggest that the therapeutic injectable gel chemotherapy, when given intratumorally, may improve tumor response with less systemic toxicity in comparison with conventional systemic chemotherapy.

Adenocarcinoma↗
PubMed1995

Neutrophil sequestration in rat lungs.

BACKGROUND: The transit of neutrophils through the pulmonary microvasculature is prolonged compared with red blood cells and is increased further during cigarette smoking and in exacerbations of chronic obstructive pulmonary disease. The increased residence time (sequestration) of neutrophils in the pulmonary capillaries in these conditions may be the first step leading to the accumulation of cells within the lung interstitium and in the bronchoalveolar space, so potentiating lung damage. A rat model has been developed to investigate the factors which may influence neutrophil transit through the lung microvasculature. METHODS: Intratracheal instillation of the heat killed organism Corynebacterium parvum was used to induce an acute neutrophil alveolitis. Neutrophils and red blood cells were isolated from donor rats, labelled with two distinct radioisotopes, and then reinjected into recipient rats to assess their transit through the pulmonary circulation. To ascertain whether peripheral blood neutrophils were minimally altered by the isolation procedure their functional status in vitro was compared with that of inflammatory neutrophils in a number of assays commonly used as descriptors of neutrophil activation. The influence of neutrophil activation on the accumulation of cells in the lungs was assessed by comparing the lung sequestration of control neutrophils, isolated from peripheral blood, with that of inflammatory neutrophils obtained from bronchoalveolar lavage of inflamed rat lungs. Lung sequestration of neutrophils was defined as the fold increase in the ratio of neutrophils labelled with chromium-51 to red blood cells labelled with technetium-99m in lung tissue compared with the same ratio in peripheral blood. RESULTS: Sequestration of peripheral blood neutrophils occurred in control rat lungs as shown by a 17.5 (2.1) fold increase in the ratio of neutrophils to red blood cells in the pulmonary circulation compared with the ratio of these cells in the peripheral circulation. When inflammatory neutrophils, obtained by bronchoalveolar lavage from C parvum-treated animals, were injected into control rats, the increase was 90.6 (11.0) fold. Induction of an inflammatory response in the lung tissue of the recipient rat also caused an increase in the sequestration of control neutrophils compared with the same cells in control rat lungs which was, however, less marked than when inflammatory neutrophils were used (34.7 (4.7) fold). The mean (SE) pressure developed on filtration of inflammatory neutrophils in vitro through a millipore filter (7.53 (0.2) cm H2O) was greater than that of peripheral blood neutrophils (1.18 (0.2) cm H2O). Increased filtration pressure indicates a decrease in cell deformability and suggests that this may be a contributory factor to the increased sequestration of inflammatory neutrophils in the pulmonary vasculature. CONCLUSIONS: This study shows that there is sequestration of neutrophils in the pulmonary vasculature in normal rat lungs which increases in acute lung inflammation and when inflammatory neutrophils are injected into control animals. In this model changes in the neutrophil, such as cell deformability, may have a more important role in inducing increased neutrophil sequestration than the inflammatory response in the lungs.

Animals↗
PubMed1995

Cloning, characterization, and genetic mapping of the rat type 2 angiotensin II receptor gene.

The renin-angiotensin system plays an important role in blood pressure homeostasis, but the contribution of the type 2 angiotensin II receptor (AT2R) is still unclear. The reports that the AT2R gene has been mapped to the X chromosome in human and rat and the previous report of a gene, Bp3, on the X chromosome responsible for an increase in blood pressure have suggested that the rat AT2R gene (Agtr2) could be this gene. To elucidate whether Agtr2 is Bp3, Agtr2 was cloned. A simple sequence repeat in the 3'-flanking region of this gene was identified and used as a genetic marker to map Agtr2 to the X chromosome at 18.1 cM distal to the androgen receptor locus. This map position is outside the confidence interval reported for Bp3, demonstrating that Agtr2 cannot be Bp3. However, these data will enhance the research into the AT2R biology as well as the study of the X chromosome.

Alleles↗
PubMed1995

Deformability and CD11/CD18 expression of sequestered neutrophils in normal and inflamed lungs.

Neutrophil (PMN) sequestration in the pulmonary microvasculature precedes the migration of these cells into the airspaces in inflamed lungs. Intratracheal instillation of the heat-killed organism Corynebacterium parvum in the rat induces an alveolitis in which PMN constitute 70 to 80% of the total cell count in the bronchoalveolar lavage (BAL). This acute alveolitis results in increased sequestration in the pulmonary microvasculature of 51Cr-labeled PMN when compared with control lungs. The aims of this study were to confirm this increased pulmonary PMN sequestration using unlabeled cells and to assess the function and adhesion molecule expression of such sequestered PMN. We counted the number of PMN and erythrocytes obtained by pulmonary vascular lavage (PVL) and compared the ratio of these two cell types in PVL and peripheral blood (PB) as a measure of the sequestration of PMN in the pulmonary vasculature. Compared with control animals, PVL in C. parvum-treated rats had higher PMN counts, which could not be accounted for by the PB leukocytosis. Sequestration of PMN in the pulmonary microvasculature depends on several factors, including the upregulation of adhesion molecules on both PMN and endothelial surfaces and the ability of the cells to deform when passing through the microcirculation. Cells obtained from the PVL were less deformable than PB cells in control but not in C. parvum-treated animals. The expression of the CD18 integrin on PMN obtained from the PVL of C. parvum-treated animals was increased compared with cells from control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Sensory interaction and descriptions of fabric hand.

82 subjects who viewed and felt fabrics (sensory interaction group) used different categories of terms to describe fabric hand than did 38 subjects who only felt the fabrics. Therefore, the methods used to measure fabric hand that isolate the senses may not accurately assess the way in which subjects describe fabric hand in nonlaboratory settings.

Adult↗