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B Gilbert

Publications and source records attributed to B Gilbert.

At least 37 records · Page 2Linked to original sources
PubMed2000

Regulation of expression of methane monooxygenases by copper ions.

Many methanotrophs contain both a soluble and a particulate methane monooxygenase. A unique metabolic switch, mediated by copper ions, regulates the expression of these enzymes. When the copper-to-biomass ratio of the cell is low, the soluble enzyme is expressed, and when the copper-to-biomass ratio is high, the particulate enzyme is expressed. A model for the mechanism of this switch is proposed.

Base Sequence↗
PubMed2000

Analysis and quantitation of rotenoids and flavonoids in Derris (Lonchocarpus urucu) by high-temperature high-resolution gas chromatography.

A glass capillary column coated with PS-086 (15% phenyl-80% methylpolysiloxane, 15 m x 0.30-mm i.d., 0.1-microm film thickness) is used to analyze extracts from Lonchocarpus urucu (Derris urucu). Several secondary metabolites (8 flavonoids, 10 rotenoids) are characterized without derivatization, and the rotenoids are quantitated by high-temperature high-resolution gas chromatography (HTHRGC) and HTHRGC coupled with mass spectrometry (HTHRGC-MS). The limit of detection in flame ionization detection of rotenone is approximately 0.5 microg/mL, and the limit of quantitation was 2 microg/mL. Derris urucu bark is an excellent source of rotenone isomers (80 mg/g), deguelin (30 mg/g), and rotenolone (26 mg/g). Single solvent extractions (hexane, methylene dichloride, acetone, or methanol) are not able to fully extract the flavonoids and rotenoids. Complete extraction is achieved using a mixture of methanol-methylene dichloride (1:1), indicating a complex association of these compounds with the plant tissue. HTHRGC and HTHRGC-MS are shown to be quick and informative tools for the rapid analysis of crude extracts without the need for prior derivatization and fractionation.

Chromatography, Gas↗
PubMed2000

Spectromicroscopy of boron in human glioblastomas following administration of Na2B12H11SH.

Boron neutron capture therapy (BNCT) is an experimental, binary treatment for brain cancer which requires as the first step that tumor tissue is targeted with a boron-10 containing compound. Subsequent exposure to a thermal neutron flux results in destructive, short range nuclear reaction within 10 microm of the boron compound. The success of the therapy requires than the BNCT agents be well localized in tumor, rather than healthy tissue. The MEPHISTO spectromicroscope, which performs microchemical analysis by x-ray absorption near edge structure (XANES) spectroscopy from microscopic areas, has been used to study the distribution of trace quantities of boron in human brain cancer tissues surgically removed from patients first administered with the compound Na2B12H11SH (BSH). The interpretation of XANES spectra is complicated by interference from physiologically present sulfur and phosphorus, which contribute structure in the same energy range as boron. We addressed this problem with the present extensive set of spectra from S, B, and P in relevant compounds. We demonstrate that a linear combination of sulfate, phosphate and BSH XANES can be used to reproduce the spectra acquired on boron-treated human brain tumor tissues. We analyzed human glioblastoma tissue from two patients administered and one not administered with BSH. As well as weak signals attributed to BSH, x-ray absorption spectra acquired from tissue samples detected boron in a reduced chemical state with respect to boron in BSH. This chemical state was characterized by a sharp absorption peak at 188.3 eV. Complementary studies on BSH reference samples were not able to reproduce this chemical state of boron, indicating that it is not an artifact produced during sample preparation or x-ray exposure. These data demonstrate that the chemical state of BSH may be altered by in vivo metabolism.

Borohydrides↗
PubMed2000

Molecular analysis of the pmo (particulate methane monooxygenase) operons from two type II methanotrophs.

The particulate methane monooxygenase gene clusters, pmoCAB, from two representative type II methanotrophs of the alpha-Proteobacteria, Methylosinus trichosporium OB3b and Methylocystis sp. strain M, have been cloned and sequenced. Primer extension experiments revealed that the pmo cluster is probably transcribed from a single transcriptional start site located 300 bp upstream of the start of the first gene, pmoC, for Methylocystis sp. strain M. Immediately upstream of the putative start site, consensus sequences for sigma(70) promoters were identified, suggesting that these pmo genes are recognized by sigma(70) and negatively regulated under low-copper conditions. The pmo genes were cloned in several overlapping fragments, since parts of these genes appeared to be toxic to the Escherichia coli host. Methanotrophs contain two virtually identical copies of pmo genes, and it was necessary to use Southern blotting and probing with pmo gene fragments in order to differentiate between the two pmoCAB clusters in both methanotrophs. The complete DNA sequence of one copy of pmo genes from each organism is reported here. The gene sequences are 84% similar to each other and 75% similar to that of a type I methanotroph of the gamma-Proteobacteria, Methylococcus capsulatus Bath. The derived proteins PmoC and PmoA are predicted to be highly hydrophobic and consist mainly of transmembrane-spanning regions, whereas PmoB has only two putative transmembrane-spanning helices. Hybridization experiments showed that there are two copies of pmoC in both M. trichosporium OB3b and Methylocystis sp. strain M, and not three copies as found in M. capsulatus Bath.

Alphaproteobacteria↗
PubMed2000

Exclusion of chromosome 9 helps to identify mild variants of acromesomelic dysplasia Maroteaux type.

Acromesomelic dysplasia Maroteaux type (AMDM) is an autosomal recessive disorder belonging to the group of acromesomelic dysplasias. AMDM is characterised by severe dwarfism with shortening of the middle and distal segments of the limbs. An AMDM gene has recently been mapped to human chromosome 9p13-q12 by homozygosity mapping in four consanguineous families. Here, we show linkage of the disease gene to chromosome 9p13-q12 in four of five consanguineous AMDM families and its exclusion in a fifth family with two children affected with a mild form of the disease. This study suggests that genetic heterogeneity accounts for the variable clinical and radiological severity of AMDM.

Arm↗
PubMed1999

Cell ashing for trace element analysis: A new approach based on ultraviolet/ozone.

We studied a new approach to cell ashing based on illuminating the specimens with a low-pressure mercury discharge lamp. We analyzed with synchrotron spectromicroscopy its effects on different physiological elements in neurobiological specimens. Our results demonstrate that carbon is removed, whereas phosphorus, calcium, potassium, and sulfur are retained and their relative concentrations are enhanced. Applied to trace elements, this technique will enhance their practical detectability.

Animals↗
PubMed1999

Aerosol delivery of liposomal all-trans-retinoic acid to the lungs.

PURPOSE: To optimize the delivery of all-trans-retinoic acid (ATRA) to lung tissue, we determined the potential of vehiculating the drug in liposomes (L-ATRA) and delivering it via aerosol. Liposomes may provide a means to prevent local irritation of lung tissue and reduce pulmonary toxicity, prolong therapeutic levels and generate high drug concentrations at the tumor sites. Cumulatively, this would result in reduced systemic toxicity and enhanced drug efficacy. METHODS: Previous studies have shown that liposomes can serve as excellent carriers for otherwise poorly soluble ATRA. Delivery of ATRA to the lung tissue of mice was accomplished by nebulization of L-ATRA. The liposomes in the aerosol were relatively uniform (309 +/- 138 nm), stable, and retained the drug well. RESULTS: The drug was effectively delivered at high concentrations (10 +/- 2 microg/g of tissue) to the lungs of mice and was retained for at least up to 96 h after a single exposure to L-ATRA aerosol. No appreciable levels of ATRA were detected in the blood or the liver of treated mice. The aerosol-delivered ATRA was biologically active as demonstrated by its ability to induce the expression of tissue-type transglutaminase. CONCLUSION: Aerosol delivery of L-ATRA offers an effective way to deliver high levels of ATRA to the lung without apparent pulmonary toxic effects.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1999

Activities of the Pharmaceutical Technology Institute of the Oswaldo Cruz Foundation with medicinal, insecticidal and insect repellent plants.

In addition to original research, Far-Manguinhos, the Pharmaceutical Division of the Brazilian Ministry of Health's Oswaldo Cruz Foundation (FIOCRUZ), devotes major attention to the finalising of products for use in public health campaigns or, under contract, for private industrial development. Emphasis is on standardisation, adequate supply, safety in use and efficacy. Among the products discussed in this summary of some of its activities in the chemical and pharmaceutical fields are medicinal plants Bidens pilosa, Cymbopogon citratus, Copaifera species, Mentha crispa, Phyllanthus tenellus Roxb. and other Phyllanthus species, insecticidal plants, Lonchocarpus urucu and Quassia amara, and the insect antifeedant plants Carapa guianensis and Pterodon emarginatus.

Academies and Institutes↗
PubMed1998

High sensitivity quantitative analysis of cobalt uptake in rat cerebellar granule cells with and without excitatory amino acids.

We quantified the effect of the excitatory amino acids kainate and glutamate on the uptake of cobalt in primary rat cerebellar granule neurons, by using inductively coupled plasma-atomic emission spectroscopy (ICP-AES). We quantitatively demonstrated that Co2+ uptake, although enhanced by glutamate and kainate also takes place in the absence of excitatory amino acids. We also found that cobalt uptake is not significantly altered by the presence of glutamate receptor competitive or noncompetitive antagonists, indicating that cobalt uptake in granule neurons does not require glutamate receptor stimulation. Our results suggest, therefore, that Co2+ may enter the cell by passive diffusion through the plasma membrane.

Animals↗