Sequence requirements of the ATP-binding site within the C-terminal nucleotide-binding domain of mouse P-glycoprotein: structure-activity relationships for flavonoid binding.

Sequence requirements of the ATP-binding site within the C-terminal nucleotide-binding domain (NBD2) of mouse P-glycoprotein were investigated by using two recombinantly expressed soluble proteins of different lengths and photoactive ATP analogues, 8-azidoadenosine triphosphate (8N(3)-ATP) and 2',3',4'-O-(2,4,6-trinitrophenyl)-8-azidoadenosine triphosphate (TNP-8N(3)-ATP). The two proteins, Thr(1044)-Thr(1224) (NBD2(short)) and Lys(1025)-Ser(1276) (NBD2(long)), both incorporated the four consensus sequences of ABC (ATP-binding cassette) transporters, Walker A and B motifs, the Q-loop, and the ABC signature, while differing in N-terminal and C-terminal extensions. Radioactive photolabeling of both proteins was characterized by hyperbolic dependence on nucleotide concentration and high-affinity binding with K(0.

Determination of residues of enrofloxacin and its metabolite ciprofloxacin in biological materials by capillary electrophoresis.

A method for the analysis of enrofloxacin and ciprofloxacin in chicken muscle using marbofloxacin as internal standard is proposed. Clean-up and pre-concentration of the samples are effected by solid-phase extraction and determination is carried out by capillary electrophoresis using a photodiode array detector. The calibration graphs are linear for enrofloxacin and ciprofloxacin from 10 to 300 microg/kg.

Prediction of electrophoretic behaviour of a series of quinolones in aqueous methanol.

Quinolones are a family of antibacterial agents used in human and veterinary clinics. The examination of protonation equilibria is essential because their antibacterial activity is pH-dependent. In this work, dissociation constants of quinolones in MeOH-water mixtures were obtained using capillary electrophoresis.

Repair of truncus arteriosus: a considered approach to right ventricular outflow tract reconstruction.

Objective: In repair of truncus arteriosus the accepted methods of establishing right ventricle (RV) to pulmonary artery (PA) continuity utilize an allograft or xenograft valved conduit. Alternatively, the PA confluence may be directly anastomosed to the RV with anterior patch augmentation, which may allow growth and delay or avoid subsequent RVOT obstruction. These methods of RVOT reconstruction were evaluated in infants undergoing truncus arteriosus repair.

Modulation of cancer cell multidrug resistance by an extract of Ficus citrifolia.

Multidrug resistance due to P-glycoprotein is a serious impediment to successful chemotherapy of cancer. Previous studies have shown that natural compounds such as prenyl flavonoids are able to modulate the multidrug resistance phenotype of P-glycoprotein-positive cancer cells. A fraction from the dichloromethane extract of a common Guadalupe Ficus, Ficus citrifolia was studied for its direct interaction with the purified C-terminal cytosolic domain of P-glycoprotein, and for its induced accumulation and cytotoxicity of vinblastine and daunomycin in two model cell lines overexpressing P-glycoprotein, namely K562/R7 and MESSA/Dx5.

Natural and synthetic benzophenones: interaction with the cytosolic binding domain of P-glycoprotein.

A benzophenone glycoside has been isolated from Davallia solida. Its structure was elucidated by chemical and spectral means as 4-O-beta-D-glucopyranosyl-2,6,4'-trihydroxybenzophenone. It bound with moderate affinity to the purified C-terminal cytosolic domain of P-glycoprotein, but the binding affinity was 6- to 10-fold increased for its aglycone derivative and other related benzophenones.

Baccatin III induces assembly of purified tubulin into long microtubules.

Baccatin III is widely considered to be an inactive derivative of Taxol. We have reexamined its effect on in vitro assembly of tubulin under a variety of conditions. We found baccatin III to be active in all circumstances in which Taxol is active: it assembled GTP-tubulin, GDP-tubulin, and microtubule protein into normal microtubules and stabilized these polymers against cold-induced disassembly.

Scapular insertion of the rabbit latissimus dorsi muscle: gross anatomy and fibre-type composition.

This paper defines the characteristics and significance of the scapular insertion of the latissimus dorsi muscle (LDM) of the rabbit. In a study of the New Zealand White species (n = 10) the scapular insertion was found to be a consistent anatomical feature of the LDM that made up 12.3% (+/-2.

Combination of preconditioning and delayed flap elevation: evidence for improved perfusion and oxygenation of the latissimus dorsi muscle for cardiomyoplasty.

Background: Atrophy and fibrosis of the distal part of the latissimus dorsi muscle (LDM) wrap is a recognized complication of cardiomyoplasty that has been attributed to ischemia. Failure of the muscle wrap contributes to the late attrition seen in clinical cardiomyoplasty. In this study we examined the role of two-staged mobilization and of preconditioning by electrical stimulation on the regional perfusion and oxygenation of the LDM.

C-Isoprenylation of flavonoids enhances binding affinity toward P-glycoprotein and modulation of cancer cell chemoresistance.

Previous studies have shown that flavones bind to P-glycoprotein (Pgp) with higher affinity than isoflavones, flavanones, and glycosylated derivatives. In the present work, a series of C- or O-substituted hydrophobic derivatives of chrysin were synthesized to further investigate structural requirements of the A ring toward Pgp modulation. Increasing hydrophobicity at either position 6, 8, or 7 increased the affinity of in vitro binding to a purified cytosolic domain of Pgp, but only benzyl and 3,3-dimethylallyl C-substitution produced a high maximal quenching of the protein intrinsic fluorescence.

Evaluation of electrophoretic method versus chromatographic, potentiometric and absorptiometric methodologies for determing pK(a) values of quinolones in hydroorganic mixtures.

The advantages of using capillary electrophoresis (CE) over other methodologies for determining pK(a) values of drugs in hydroorganic media are discussed. The focus of the discussion based upon the pK(a) values of a series of quinolones determined in acetonitrile (MeCN)--water mixtures by CE, liquid chromatography, potentiometric, and spectrophotometric methods.

High-affinity binding of silybin derivatives to the nucleotide-binding domain of a Leishmania tropica P-glycoprotein-like transporter and chemosensitization of a multidrug-resistant parasite to daunomycin.

In order to overcome the multidrug resistance mediated by P-glycoprotein-like transporters in Leishmania spp., we have studied the effects produced by derivatives of the flavanolignan silybin and related compounds lacking the monolignol unit on (i) the affinity of binding to a recombinant C-terminal nucleotide-binding domain of the L. tropica P-glycoprotein-like transporter and (ii) the sensitization to daunomycin on promastigote forms of a multidrug-resistant L.

Phenylpropanoids from Umbilicus pendulinus.

Phytochemical investigation of the leaves of Umbilicus pendulinus afforded in addition to 2-O-caffeoyl malate, isoquercitrin and Z-venusol, the new isomer E-venusol. Special NMR experiments were carried out to elucidate the configuration of the two latter compounds.

Prenylated xanthones as potential P-glycoprotein modulators.

Dimethylallyl (DMA) derivatives of a naturally occurring xanthone (decussatin 1) were prepared. Their activity as potential P-glycoprotein inhibitors was monitored by affinity of direct binding and compared to that of corresponding DMA-flavones. Both classes of compounds exhibited the same structure-activity relationships.

Video teleconferencing with realistic simulation for medical education.

This report describes how realistic patient simulation can be used with video teleconferencing to conduct long-distance clinical case discussions with realistic re-enactments of critical events. By observing what appears to be a real procedure unfolding in real time, it is intended that audience members will better learn and appreciate the lessons from conferences. A commercially available mannequin simulator and video teleconferencing technology were used in nine sessions between a free-standing simulation center and different conference sites throughout the U.

Prenyl-flavonoids as potent inhibitors of the Pdr5p multidrug ABC transporter from Saccharomyces cerevisiae.

The Pdr5p multidrug ABC ("ATP-binding cassette) transporter was highly overexpressed in plasma membranes from a yeast strain exhibiting both pdr1-3 gain-of-function mutation in the transcription factor-encoding gene PDR1 and disruption of genes encoding other plasma membrane ABC transporters. Solubilized and purified Pdr5p displayed a tryptophan-characteristic intrinsic fluorescence, whose quenching was used to monitor interactions with substrates and effectors. The transporter exhibited a magnesium-dependent binding affinity for ATP and its fluorescent analogue 2'(3')-N-methylanthraniloyl-ATP, producing a marked fluorescence resonance-energy transfer.

Microcratering within the lunar regolith--a theory and observation.

Since the Apollo 11 mission to the moon, there has been substantial analysis of the lunar rocks and soil grains, utilizing more recent advances in electron probe technologies. It is the objective of this research to revisit the theories concerning the microcratering within the lunar regolith. Recent theories have included the idea that the microcratering phenomenon was caused by meteoric impacting onto the lunar surface during early lunar history.

Influence of pH and pKa values on electrophoretic behaviour of quinolones in aqueous and hydro-organic media.

Through correct pH measurements, pKa and activity coefficient values, a model describing their effect on electrophoretic behaviour of substances is established. The suggested model uses the pH values in the acetonitrile-water mixtures used and takes into account the effect of activity coefficients. The model permits the calculation of acidity constants of analytes in hydro-organic media and also the prediction of the effect of pH on the electrophoretic mobility.

Prediction of electrophoretic mobilities in non-aqueous capillary electrophoresis. Optimal separation of quinolones in acetonitrile-water media.

A model of electrophoretic behaviour is used to predict the optimum conditions for the separation of a series of quinolones zwitterionic substances in mixtures of acetonitrile-water up to 30% (w/w) of acetonitrile. The effect of pH, pKa, the electrophoretic mobility of protonated and anionic species, and activity coefficients on the electrophoretic behaviour of quinolones is considered. The model proposed allows the resolution between substances in acetonitrile-water mixtures to be predicted from a few experimental data and thus permits one to obtain the best experimental conditions for separation methodologies.

Myocardial tissue oxygen supply and utilization during coronary artery bypass surgery: evidence of microvascular no-reflow.

The supply and utilization of oxygen by the myocardium reflect the dynamic efficiency of the microcirculation. The present study examines these parameters during coronary artery bypass surgery. We used a voltammetric microelectrode technique to assess regional variations in myocardial tissue partial pressure of oxygen (PO(2)) and myocardial tissue perfusion (MTP) in patients undergoing coronary artery bypass surgery.

The flavanolignan silybin and its hemisynthetic derivatives, a novel series of potential modulators of P-glycoprotein.

A new series of potential flavonoidic modulators of P-glycoprotein activity has been prepared. The flavanolignan silybin was first oxidised to dehydrosilybin and then C-alkylated with either prenyl or geranyl bromide. The resulting isoprenoid dehydrosilybins were shown to display high in vitro affinities for direct binding to P-glycoprotein, which ranged them among the best flavonoids ever tested.

Orthostatic intolerance and chronic fatigue syndrome associated with Ehlers-Danlos syndrome.

Objective: To report chronic fatigue syndrome (CFS) associated with both Ehlers-Danlos syndrome (EDS) and orthostatic intolerance.

Study Design: Case series of adolescents referred to a tertiary clinic for the evaluation of CFS. All subjects had 2-dimensional echocardiography, tests of orthostatic tolerance, and examinations by both a geneticist and an ophthalmologist.