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Biomedical subjects

J A Bogan

Publications and source records attributed to J A Bogan.

At least 19 recordsLinked to original sources
PubMed1996

mioC transcription, initiation of replication, and the eclipse in Escherichia coli.

The potential role of mioC transcription as a negative regulator of initiation of chromosome replication in Escherichia coli was evaluated. When initiation was aligned by a shift of dnaC2(Ts) mutants to nonpermissive temperature (40 degrees C), mioC transcript levels measured at the 5' end or reading through oriC disappeared within one mass doubling. Upon return to permissive temperature (30 degrees C), the transcripts reappeared coordinately about 15 min after the first synchronized initiation and then declined sharply again 10 min later, just before the second initiation. Although these observations were consistent with the idea that mioC transcription might have to be terminated prior to initiation, it was found that the interval between initiations at permissive temperature, i.e., the eclipse period, was not influenced by the time required to shut down mioC transcription, since the eclipse was the same for chromosomes and minichromosomes which lacked mioC transcription. This finding did not, in itself, rule out the possibility that mioC transcription must be terminated prior to initiation of replication, since it might normally be shut off before initiation, and never be limiting, even during the eclipse. Therefore, experiments were performed to determine whether the continued presence of mioC transcription during the process of initiation altered the timing of initiation. It was found that minichromosomes possessing a deletion in the DnaA box upstream of the promoter transcribed mioC continuously and replicated with the same timing as those that either shut down expression prior to initiation or lacked expression entirely. It was further shown that mioC transcription was present throughout the induction of initiation by addition of chloramphenicol to a dnaA5(Ts) mutant growing at a semipermissive temperature. Thus, transcription through oriC emanating from the mioC gene promoter is normally inhibited prior to initiation of replication by the binding of DnaA protein, but replication can initiate with the proper timing even when transcription is not shut down; i.e., mioC does not serve as a negative regulator of initiation. It is proposed, however, that the reappearance and subsequent disappearance of mioC transcription during a 10-min interval at the end of the eclipse serves as an index of the minimum time required for the establishment of active protein-DNA complexes at the DnaA boxes in the fully methylated origin region of the chromosome. On this basis, the eclipse constitutes the time for methylation of the newly formed DNA strands (15 to 20 min at 30 degrees C) followed by the time for DnaA protein to bind and activate oriC for replication (10 min).

Bacterial Proteins↗
PubMed1993

Correlation of gene transcription with the time of initiation of chromosome replication in Escherichia coli.

Transcriptional levels of the Escherichia coli mioC and gidA genes, which flank the chromosomal origin of replication (oriC) and the dnaA gene, were correlated with the time of initiation of chromosome replication. The transcripts were measured either in dnaC2(ts) mutants that had been aligned for initiation of chromosome replication by a temperature shift or in synchronous cultures of cells obtained using the baby machine technique. In both types of experiments, mioC transcription was inhibited prior to initiation of chromosome replication and resumed several minutes after initiation. Conversely, gidA and dnaA transcription were both inhibited after initiation of replication, coincident with the period of hemimethylation of oriC DNA. It is proposed that mioC transcription prevents initiation of chromosome replication, and must terminate before replication can begin. It is further proposed that the eclipse period between rounds of replication, i.e. the minimum interval between successive initiations, encompasses the time required to methylate GATC sequences in newly replicated oriC plus the time required to terminate mioC transcription. Conversely, the active transcription of gidA and dnaA prior to initiation is consistent with their positive effects on initiation, and their shutdown after initiation could serve to limit premature reinitiation.

Algal Proteins↗
PubMed1993

Environmental regulation of the fim switch controlling type 1 fimbrial phase variation in Escherichia coli K-12: effects of temperature and media.

Expression of type 1 fimbriae in Escherichia coli K-12 is phase variable and associated with the inversion of a short DNA element (switch). The fim switch requires either fimB (on-to-off or off-to-on switching) or fimE (on-to-off switching only) and is affected by the global regulators leucine-responsive regulatory protein (Lrp), integration host factor (IHF), and H-NS. Here it is shown that switching frequencies are regulated by both temperature and media and that these effects appear to be independent. fimE-promoted on-to-off switching occurs far more rapidly than previously estimated (0.3 per cell per generation in defined rich medium at 37 degrees C) and faster at lower than at higher temperatures. In direct contrast, fimB-promoted switching increases with temperature, with optima between 37 and 41 degrees C. Switching promoted by both fimB and fimE is stimulated by aliphatic amino acids (alanine, isoleucine, leucine, and valine), and this stimulation requires lrp. Furthermore, lrp appears to differentially regulate fimB- and fimE-promoted switching in different media.

Agar↗
PubMed1992

The gene-protein database of Escherichia coli: edition 5.

The gene-protein database of Escherichia coli is both an index relating a gene to its protein product on two-dimensional gels, and a catalog of information about the function, regulation, and genetics of individual proteins obtained from two-dimensional gel analysis or collated from the literature. Edition 5 has 102 new entries--a 15% increase in the number of annotated two-dimensional gel spots. The large increase in this edition was accomplished in part by the use of a new method for expression analysis of ordered segments of the E. coli genome, which has resulted in linking 50 gel spots to their genes (or open reading frames) and another 45 to specific regions of the chromosome awaiting the availability of DNA sequence information. Communication of information from the scientific community resulted in additional identifications and regulatory information. To increase accessibility of the database it has been placed in the repository at the National Center for Biotechnology Information (NCBI) at the National Library of Medicine under the name ECO2DBASE. It will be updated twice yearly. This edition of the gene-protein database is estimated to contain entries for one-sixth of the protein-encoding genes of E. coli.

Bacterial Proteins↗
PubMed1991

Pharmacokinetic, biochemical and tolerance studies on carprofen in the horse.

Carprofen, a non-steroidal anti-inflammatory drug (NSAID) was administered to three Thoroughbred geldings and three Shetland ponies to determine its plasma disposition and tolerance. The main pharmacokinetic characteristics of carprofen in horses and ponies were a volume of distribution of 0.08 to 0.32 litres/kg (mean +/- se = 0.23 +/- 0.04) a systemic clearance of 26.4 to 78.5 ml/min (mean +/- se = 44.9 +/- 8.0) and a plasma elimination half-life of 14.5 to 31.4 h (mean +/- se = 21.9 +/- 2.3). There was no evidence of any accumulation of carprofen in plasma when the drug was given orally at a dose rate of 0.7 mg/kg for 14 consecutive days. Carprofen was well tolerated following intravenous (iv) and oral administration. Intramuscular (im) administration resulted in elevated levels of plasma creatine kinase suggesting muscle cell damage. According to the results of this study carprofen can be regarded as a long-acting NSAID in horses from a pharmacokinetic point of view. Either iv, im or the oral route of administration could be used to achieve high carprofen plasma concentrations.

Administration, Oral↗
PubMed1990

Effect of meclofenamic acid on the response of parasite-naive lambs and adult sheep to Ostertagia circumcincta.

Meclofenamic acid was used to inhibit prostaglandin synthesis in lambs challenged with Ostertagia circumcincta. It lowered the number of parasites which established in treated animals but not significantly. In treated animals plasma pepsinogen values were elevated at the time of parasite emergence but had dropped below the values achieved in control lambs towards the end of the experiment when parasites were at the adult, lumenal dwelling stage. Meclofenamic acid administered to adult immune ewes during challenge with third stage O circumcincta larvae did not significantly affect the establishment of the parasites, nor did it affect the rise in pepsinogen concentration associated with the challenge.

Abomasum↗
PubMed1989

Flunixin pharmacokinetics and serum thromboxane inhibition in the dog.

Flunixin meglumine administered orally to beagle dogs at doses of 0.55, 1.10 or 1.65 mg/kg bodyweight was rapidly absorbed to produce maximum mean plasma concentrations of 2.40 +/- 0.70, 4.57 +/- 1.12 and 7.42 +/- 2.07 micrograms/ml, respectively. Thereafter, the plasma concentrations of flunixin fell rapidly to values less than 0.10 micrograms/ml from 24 hours after drug administration at all dosage levels. The maximum mean inhibition of serum thromboxane B2 was 91.5 per cent after the lowest dose of flunixin and 98.8 per cent for both the intermediate and high dose rates. At plasma concentrations of flunixin above 2 micrograms/ml there was more than 90 per cent inhibition of thromboxane.

Administration, Oral↗
PubMed1989

Level of benzimidazole resistance in a strain of Ostertagia circumcincta studied over several infections in lambs.

A benzimidazole-resistant strain of Ostertagia circumcincta (HFRO) was used experimentally to infect lambs. The level of resistance, measured by an egg hatch assay, was studied throughout each infection and also after treatment of the lambs with fenbendazole. The HFRO strain was highly resistant to benzimidazoles. There was day-to-day variation in the level of resistance throughout a single infection with a high level of resistance in the early part of the infection, around Day 27 post-inoculation of infective larvae, falling to a lower level later in the infection. Egg hatch assays on the 3 days immediately post-treatment with fenbendazole showed the resistance level was high then resistance fell to the pre-treatment level after 7 days. Selection for benzimidazole resistance using fenbendazole treatment at the normal dose rate of 5 mg kg-1 over five passages of the HFRO strain in lambs failed to increase the resistance level. Storage of larvae over a 5-month period at 4 degrees C, prior to infection of lambs, did not produce any alteration in the resistance level. The possible reasons for the variations in resistance found with the HFRO strain are discussed along with the implications for sheep parasite control and further development of benzimidazole resistance.

Albendazole↗
PubMed1989

Relay bioavailability and toxicity of isometamidium residues: a model for human risk assessment.

The bioavailability and potential toxicity of the residues of the antitrypanosomal drug isometamidium (ISMM) in bovine tissues were investigated in male Sprague-Dawley rats. They were allowed to feed for 7 and 21 days on a standard diet, to which were added lyophilized tissues from a calf treated im with a combination of 45 mg 14C-ISMM and 73 mg unlabelled ISMM (1 mg/kg bodyweight). Cumulative excretion of radioactivity of the residues in feces of the rats was on average 90% of the dose. No radioactivity was detectable in the tissues examined, including the kidney, liver, spleen, muscle, stomach and small intestine. No clinical effects were seen in any of the rats, and both gross and histopathological examinations did not reveal any lesions. In rats given 14C-ISMM (2.245 mg/kg bodyweight) by oral gavage, cumulative excretion of radioactivity in feces after 48 hr amounted to about 93% of the dose, and no radioactivity was detectable in tissues. Similarly, none of the rats showed any clinical effects and no gross lesions were seen at necropsy. This study shows that ISMM residues are not significantly bioavailable and exhibit no subchronic toxicity.

Animals↗
PubMed1988

Development of a radioimmunoassay for isometamidium.

A radioimmunoassay for the trypanocidal drug isometamidium (ISMM) has been developed using antibodies produced in sheep immunized against the drug cross-linked to human serum albumin. With 14C-ISMM as a radioligand, cross-reactivity of the antibodies was determined and found to be less than 3% with pyrithidium, diminazene and quinapyramine and about 13% with homidium. The limit of detection of ISMM in serum without prior extraction was 5.8 pmol/tube and within-assay and between-assay coefficients of variation were four and 14% respectively.

Animals↗
PubMed1988

Pharmacokinetics and efficacy of triclabendazole in goats with induced fascioliasis.

The pharmacokinetics of triclabendazole were evaluated in normal goats and in goats artificially infected with Fasciola hepatica. Triclabendazole and its metabolites were determined using a novel high performance liquid chromatographic method with fluorimetric detection after solid-phase extraction. In normal goats triclabendazole given orally was metabolized rapidly to its sulphoxide and sulphone derivatives. The maximum plasma concentrations for the sulphoxide and sulphone were similar ranging from 9 to 19 micrograms/ml and these were attained at an average 12.8 and 25.6 h, respectively, after administration. Both metabolites were eliminated slowly from plasma with elimination half-lives of 22.4 h for the sulphoxide and 19.4 h for the sulphone. They persisted at measurable concentrations in plasma for up to seven days. In milk, the two metabolites occurred in low concentrations and none of them was detectable (sulphoxide less than 0.04 microgram/ml, sulphone less than 0.02 microgram/ml) after seven days. The pharmacokinetic behaviour of triclabendazole was not altered in animals with fascioliasis. Efficacy of the drug against immature (six-week) F. hepatica was 100%.

Animals↗
PubMed1988

The pharmacodynamics of ivermectin in sheep and cattle.

The concentrations of ivermectin in the gastrointestinal tract of sheep and cattle were determined after subcutaneous administration of ivermectin. Ivermectin was not detected (limit of detection 1 ng/ml) in abomasal and ruminal fluids either after a normal therapeutic dose of 200 micrograms/kg or even at an increased dose of 2000 micrograms/kg. It was also not detected in abomasal and ruminal fluids of a sheep infected with the abomasal parasite Ostertagia circumcincta. However, ivermectin was detectable at similar concentrations in abomasal mucus and in small intestinal mucus. Excretion of ivermectin was high in bile but the concentrations in small intestinal mucus, distal and proximal to the bile duct opening, were similar. It is hypothesized that the low efficacy of ivermectin against small intestinal nematodes compared with abomasal nematodes is not due to differences in ivermectin concentrations in the predilection sites but is probably due to tachyphylaxis in the nematodes allowing the small intestinal nematodes to re-establish before they have left their predilection site. Ivermectin was excreted in the milk of ewes at concentrations similar to those in plasma. Lambs suckling ivermectin-treated ewes received about 4% of a normal therapeutic dose (200 micrograms/kg) via the milk.

Animals↗
PubMed1988

Parvaquone and buparvaquone: HPLC analysis and comparative pharmacokinetics in cattle.

A high performance liquid chromatographic (HPLC) method for the determination of the antitheilerial drugs parvaquone and buparvaquone in plasma was developed. Both compounds were extracted from plasma with ether. After evaporating the extracts to dryness the residue was dissolved in methanol and an aliquot was injected onto a column (10 cm X 5 mm, i.d.) of ODS-Hypersil (5 mu) with a mobile phase of 0.05 M-Na acetate buffer (pH 3.6)-methanol (15:85, v/v). Detection was at 252 nm. The mean recovery for both compounds was about 92%. This method was used to elucidate their pharmacokinetics in 6 calves after intramuscular administration. The maximum plasma concentration for parvaquone was 6.36 +/- 0.58 micrograms/ml after 0.84 +/- 0.08 h. The corresponding values for buparvaquone were 0.102 +/- 0.030 microgram/ml and 3.17 +/- 0.39 h, respectively. The decay in plasma concentrations for the two drugs was biexponential and the terminal elimination half lives were 11.12 +/- 1.63 h and 26.44 +/- 2.81 h for parvaquone and buparvaquone, respectively.

Animals↗
PubMed1988

Solid-phase extraction and ion-pair reversed-phase HPLC of isometamidium in bovine serum and tissues.

An analytical method has been developed for the determination of isometamidium in bovine serum and tissues. Samples were enzymatically hydrolysed and cleaned up on a solid-phase system (C8 Bond Elut column). The drug was chromatographed by an ion-pair reversed-phase technique using heptane sulphonate as a pairing-ion and triethylamine as a counter-ion reagent. Detection was by fluorescence at 593 nm (excitation = 380 nm). The method is more sensitive and specific than existing methods and it is currently being used in evaluating the pharmacokinetics of isometamidium in cattle.

Animals↗