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Biomedical subjects

A M George

Publications and source records attributed to A M George.

At least 19 recordsLinked to original sources
PubMed1998

Co-migration of RAPD-PCR amplicons from Aeromonas hydrophila.

Random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) uses arbitrary primers and low stringency annealing conditions to amplify anonymous DNA fragments which are then depicted in agarose gels. RAPD-PCR fingerprints have been used for typing and differentiation of bacteria and, increasingly, for the study of genetic relationships between strains and species of microorganisms, plants and animals. The analysis of such fingerprints is based upon the assumption that co-migration of amplicons does not occur and that any given band contains a single amplicon. This report shows that co-migration of fragments of nearly identical size, but different nucleotide sequences, occurs between different isolates and within single RAPD-PCR bands from Aeromonas hydrophila. The possibility of the same phenomenon occurring for other prokaryotic or eukaryotic genomes argues for caution in the interpretation of RAPD-PCR fingerprints.

Aeromonas hydrophila↗
PubMed1997

The XRCC2 DNA repair gene: identification of a positional candidate.

The human XRCC2 gene, complementing a hamster cell line (irs1) hypersensitive to DNA-damaging agents, was previously mapped to chromosome 7q36.1. Following radiation reduction of human/hamster hybrids, the gene was found to be associated with the marker D7S483. Yeast artificial chromosomes (YACs) carrying D7S483 were fused to the irs1 cell line to identify a YAC that complemented the sensitivity defect. Transcribed sequences were isolated by direct cDNA selection using the complementing YAC, and these were mapped back to the YAC and hybrids to define a 400-kb region carrying XRCC2. Sequencing of cDNAs led to the identification of both known and novel gene sequences, including a candidate for XRCC2 with homology to the yeast RAD51 gene involved in the recombinational repair of DNA damage. Strong support for the candidacy of this gene was obtained from its refined map position and by the full complementation of irs1 sensitivity with a 40-kb cosmid carrying the gene.

Animals↗
PubMed1997

23Na chemical shifts and local structure in crystalline, glassy, and molten sodium borates and germanates.

A simple correlation between average Na-O bond length and 23Na isotropic chemical shift in crystalline germanates and borates has been established, similar to existing correlations for sodium in silicates and carbonates. This empirical trend is discussed in terms of a decreasing paramagnetic contribution to the chemical shift with increasing average bond length. The correlation is then applied to data for sodium borate and germanate glasses and melts from room temperature to 1200 degrees C, where both structural and compositional effects on the chemical shift are apparent.

Borates↗
PubMed1996

Functional expression of the human MDR1 gene in Escherichia coli.

In this preliminary study, we report the cloning of the human MDR1 cDNA into a prokaryotic expression vector and the consequent functional expression of heterologous P-glycoprotein in Escherichia coli. We demonstrate increased resistance to the P-glycoprotein substrates TPA+, TPP+, and puromycin; reduced accumulation of TPP+ and tetracycline by resistant cells; and the expression of a full-length immunoreactive P-glycoprotein molecule in the membrane fraction of resistant cells. The obvious structural and functional similarities of P-gp to prokaryotic ABC transporters and other efflux transporters argues for a more complete study of the consequences pertaining to the expression of human P-glycoprotein in E. coli.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Multidrug resistance in enteric and other gram-negative bacteria.

In Gram-negative bacteria, multidrug resistance is a term that is used to describe mechanisms of resistance by chromosomal genes that are activated by induction or mutation caused by the stress of exposure to antibiotics in natural and clinical environments. Unlike plasmid-borne resistance genes, there is no alteration or degradation of drugs or need for genetic transfer. Exposure to a single drug leads to cross-resistance to many other structurally and functionally unrelated drugs. The only mechanism identified for multidrug resistance in bacteria is drug efflux by membrane transporters, even though many of these transporters remain to be identified. The enteric bacteria exhibit mostly complex multidrug resistance systems which are often regulated by operons or regulons. The purpose of this review is to survey molecular mechanisms of multidrug resistance in enteric and other Gram-negative bacteria, and to speculate on the origins and natural physiological functions of the genes involved.

Drug Resistance, Microbial↗
PubMed1994

Analysis of Mnk, the murine homologue of the locus for Menkes disease, in normal and mottled (Mo) mice.

Menkes disease (MNK) lies immediately proximal to pphosphoglycerate kinase (PGK1) in Xq13 in human. Phenotypic similarities between MNK patients and murine mottled (Mo) mutants strongly suggest that both defects are caused by mutations at the same locus. Human MNK cDNA clones and a genomic subclone derived from a 40-kb YAC clone that includes Pgk1 have been used to position the murine homologue of Menkes disease (MNK, Mnk) immediately proximal to, and within 150-200 kb of, phosphoglycerate kinase (Pgk1) on the mouse X chromosome using interspecific backcross analysis and pulsed-field gel electrophoresis. A related autosomal locus has been mapped to mouse chromosome 18. RFLVs at Mnk between inbred strains of mice that show a strong association with the presence of the Mo phenotype have been detected. Hybridization of 4.1 kb of the 4.5-kb MNK coding sequence failed to reveal any deletions or alterations to restriction fragments containing exons of the Mnk locus in 9 Mo mutants. Furthermore, no genomic deletions or alterations > 20 kb were detected in 10 independently derived Mo mutants using pulsed-field gel electrophoresis. As no deletions or alterations at the Mnk gene were found, we suggest that any mutations in Mnk that cause the Mo phenotype are likely to be due to small changes at the nucleotide level and/or small deletions (< 20 kb) that lie outside the coding sequence.

Animals↗
PubMed1994

Active efflux of chloramphenicol in susceptible Escherichia coli strains and in multiple-antibiotic-resistant (Mar) mutants.

The multiple-antibiotic resistance (mar) locus (min 34) regulates a resistance to chloramphenicol in Escherichia coli that does not involve acetyltransferase. Transport studies showed that wild-type cells had an apparent endogenous active efflux of chloramphenicol which depended on the proton motive force. This efflux was not altered by a 39-kb chromosomal deletion which included the mar locus. Nevertheless, mutations at the mar locus led to a stronger net chloramphenicol efflux. Therefore, a gene encoding the putative efflux system cannot be at the mar locus but may be positively influenced by that locus.

Cell Membrane↗
PubMed1990

The IL-1 alpha and beta genes are closely linked (less than 70 kb) on mouse chromosome 2.

The murine IL-1 alpha and IL-1 beta genes encode structurally and evolutionarily related cytokines that exert a regulatory role in numerous physiological processes including hemopoiesis. Previous studies have shown these genes to be closely linked in the F region of mouse chromosome 2. Here we show, using pulsed-field gel electrophoresis, that the IL-1 alpha and beta genes of the CBA/H mouse are very closely linked and contained within a SmaI genomic fragment of approximately 70 kb. From conventional and PFGE analyses we suggest that IL-1 beta lies 5' to IL-1 alpha and that the two genes are in the same orientation and separated by approximately 50 kb. The apparent clustering of such hemopoietic genes is discussed in relation to evolutionary tandem gene duplication and possible associations with chromosomal fragile sites and leukemogenesis.

Animals↗
PubMed1990

The epidemiology of AIDS.

By 31 July 1989 172,143 cases of AIDS have been notified to the WHO from 150 countries worldwide. This review on epidemiology of AIDS shows that there are 3 distinct patterns of distribution of the disease. According to the different epidemiology in the different regions different initiatives should be taken by the health authorities. Extrapolating the available data to the future the urgent necessity for this initiative is stressed.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Validated HPLC procedures for the analysis of MBY-28090 in human plasma and urine.

The compound BMY-28090 (elsamicin A) is a new fermentation product with antitumor properties, which has the same aglycone as chartreusin but contains two novel sugars. To define the disposition of BMY-28090 during phase I trials, HPLC procedures were developed and validated for the quantitation of the drug in human plasma and urine. To 1.0 ml plasma were added 0.5 ml 0.2 M phosphate buffer (pH 8.0), 125 ng 1-naphthol (internal standard) in 25 microliters MeOH and 5 ml ethyl acetate. After mixing and centrifugation, 4 ml ethyl acetate layer was removed, evaporated to dryness, and the residue was dissolved in 250 microliters mobile phase and injected (200 microliters). To 1.0 ml urine were added 100 microliters MeOH and 1.0 ml 0.5 M succinate buffer (pH 4.0). After mixing (30 s) and sonication (1 min), the solution was filtered in an Amicon Centrifree micropartition unit and injected (30 microliters). An IBM C-8 column 5-microns and fluorescence detection (excitation at 254 mm, 418 nm emission filter) were used for both analyses. The mobile phases for plasma (2 ml/min) and urine (1.3 ml/min) were H2O/CH3CN (7:3 v/v) and H2O/CH3CN/MeOH (6:3:1 (v/v), respectively, with 1.5 ml 85% H3PO4 and 1.5 ml triethylamine/l. BMY-28090 eluted at 8-10 min and 1-naphthol, at 10-11 min. The standard curves were linear from 1 to 50 ng/ml plasma and from 10 to 1000 ng/ml urine. The within- and between-day precision was less than 3% for plasma and less than 5% for urine. Accuracies were within 6% of the nominal value and recoveries were 75% and 90% for plasma and urine, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoglycosides↗
PubMed1988

The disposition of carboplatin in the beagle dog.

Carboplatin was administered i.v. to four groups of three male beagle dogs at doses of 3, 6, 12, and 24 mg/kg (60-580 mg/m2). Plasma samples were obtained at appropriate times and protein-free plasma ultrafiltrates (PU) were generated with Amicon Centrifree micropartition systems. Urine was collected at 24-h intervals for 96 h. PU and urine samples were analyzed for carboplatin by HPLC and for total platinum by atomic absorption spectrophotometry. Carboplatin accounted for about 90% of the free platinum in plasma. The Cmax and AUCinf values for carboplatin and for free platinum increased linearly with dose. The terminal elimination half-life and mean residence times for carboplatin and free platinum were each about 1 h. Total-body clearances for carboplatin (5.6 l/h per m2) and free platinum (5.1 l/h per m2) were constant over the dose range studied, as were the respective volumes of distribution (5.7 and 5.0 l/m2). A mean of 46% of the dose was excreted as carboplatin in 24-h urine; and by 72 h, 70% of the platinum administered was excreted in the urine. Free platinum was cleared by both renal and non-renal processes. These results show that a dose of carboplatin is rapidly excreted in the urine and that carboplatin and plasma-free platinum exhibit linear pharmacokinetics in the beagle dog.

Animals↗
PubMed1988

The disposition of carboplatin in ovarian cancer patients.

Carboplatin was given as a 30-min infusion to 11 ovarian cancer patients at doses of 170-500 mg/m2. The ages, weights, and creatinine clearances (Clcr) ranged from 44 to 75 years, from 44 to 74 kg, and from 32 to 101 ml/min, respectively. Plasma, plasma ultrafiltrate (PU), and urine samples were obtained at appropriate times for 96 h and were analyzed for platinum. The PU and urine were also analyzed for the parent compound by HPLC. In patients with a Clcr of about 60 ml/min or greater, carboplatin decayed biexponentially with a mean t1/2 alpha of 1.6 h and a t1/2 beta of 3.0 h. The mean (+/- SD) residence time, total body clearance, and apparent volume of distribution were 3.5 +/- 0.4 h, 4.4 +/- 0.85 l/h, and 16 +/- 3 l, respectively. Cmax and AUCinf values increased linearly with dose, and the latter values correlated better with the dose in mg than in mg/m2. No significant quantities of free, ultrafilterable, platinum-containing species other than the parent compound were found in plasma, but platinum from carboplatin became protein-bound and was slowly eliminated with a minimal t1/2 of 5 days. The major route of elimination was excretion via the kidneys. Patients with a Clcr of 60 ml/min or greater excreted 70% of the dose as the parent compound in the urine, with most of this occurring within 12-16 h. All of the platinum in 24-h urine was carboplatin, and only 2%-3% of the dosed platinum was excreted from 48 to 96 h. Patients with a Clcr of less than about 60 ml/min exhibited dose-disproportional increases in AUCinf and MRT values. The latter were inversely related to Clcr (r = -0.98). Over a dose range of 300-500 mg/m2, carboplatin exhibited linear, dose-independent pharmacokinetics in patients with a Clcr of about 60 ml/min or greater, but dose reductions are necessary for patients with mild renal failure.

Adult↗
PubMed1987

In vitro stability, plasma protein binding and blood cell partitioning of 14C-carboplatin.

Radiochemically pure 14C-labeled carboplatin, cis-diammine [1,1-cyclobutane (1-14C) dicarboxylato (2-)-0,0'] platinum (II), was added to fresh human, dog and rat plasma, at concentrations ranging from 1 to 100 micrograms 14C-carboplatin/ml. After 10 min incubation at ambient temperature, the plasma was ultrafiltered in Amicon Centrifree micropartition units to generate protein-free plasma ultrafiltrate (PU). Total radioactivity was determined by liquid scintillation counting. A mean (+/- SD) of 102% +/- 2.0%, 99.5% +/- 1.9%, and 99.0% +/- 1.0% of the 14C-carboplatin added to fresh human, dog, and rat plasma respectively was recovered in the PU. 14C-carboplatin was incubated at 37 degrees C with fresh plasma (60 micrograms/ml) and urine (200 micrograms/ml) from humans and dogs for 120 h, and samples were removed at appropriate times for analysis of carboplatin, 1,1-cyclobutane dicarboxylic acid and cyclobutane carboxylic acid. The latter were separated by HPLC on a C-18 column with a mobile phase of H2O/CH3CN/0.3 M tetrabutylammonium phosphate (880:50:20 v/v/v), and the column eluants at the retention time of each compound were collected and counted for total radioactivity. Carboplatin degraded in each of the matrices with a corresponding release of 1,1-cyclobutane dicarboxylic acid. 14C-carboplatin (50 micrograms/ml) was incubated at 37 degrees C with fresh human, dog and rat blood and the distribution of radioactivity into the cellular fraction was determined. Radioactivity did not distribute into the blood cells of humans or dogs, but after 5 h, 44% of the radioactivity in rat blood was associated with the cellular fraction. These results show that carboplatin, at physiological concentrations, does not bind instantaneously and reversibly to the plasma proteins of rat, dog or human, and that the molecule slowly degrades in plasma and urine in vitro with the release of 1,1-cyclobutane dicarboxylic acid. The remaining diammine platinum (II) portion of the molecule therefore accounts for the essentially irreversible protein binding of the platinum from carboplatin.

Animals↗
PubMed1987

DNA quaternary structure in the radiation sensitivity of human lymphocytes--a proposed role of copper.

On challenging with 2M NaCl, the nuclei of human lymphocytes yield an aggregate of DNA-protein material. The density of the material is less when isolated from irradiated cells than when isolated from unirradiated cells. The density of this material, designated histone-free-DNA (HF-DNA), from irradiated cells returns to that from unirradiated cells if the irradiated cells are allowed time at 37 degrees C in nutrient conditions. Lymphocyte HF-DNA from patients who have exhibited hypersensitivity to radiotherapy exhibit slower repair characteristics than lymphocyte HF-DNA from the average normal subjects. Neutrons are more effective than X-rays in producing density changes. Misonidazole and the ADPRT inhibitor 3-AAB substantially inhibit return to unirradiated densities. The oer for the initial effect is between 2 and 3. These properties of this DNA material from human lymphocytes suggest that alterations in the configuration of such material by the loss and re-establishment of relatively weak cellular bonds are closely related to the well-known changes observed in classical cell survival experiments. Where the proliferation of human lymphocytes has been observed by concanavalin A stimulation, oer, RBE and chemical modification has been of the same order as the measured density changes. Additionally, we have found that the density of HF-DNA is heavily dependent upon Cu content. This has led us to propose that cell killing or malfunction at the nuclear level caused by ionizing radiation is caused by the conversion CuII----CuI and also by specific .OH attack on DNA or proteins at a Cu site.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Survival↗