Conformational restriction shapes the inhibition of a multidrug efflux adaptor protein

Membrane efflux pumps play a major role in bacterial multidrug resistance. The tripartite multidrug efflux pump system from Escherichia coli, AcrAB-TolC, is a target for inhibition to lessen resistance development and restore antibiotic efficacy, with homologs in other ESKAPE pathogens. Here, we rationalize a mechanism of inhibition against the periplasmic adaptor protein, AcrA, using a combination of hydrogen/deuterium exchange mass spectrometry, cellular efflux assays, and molecular dynamics simulations. We define the structural dynamics of AcrA and find that an inhibitor can inflict long-range stabilisation across all four of its domains, whereas an interacting efflux substrate has minimal effect. Our results support a model where an inhibitor forms a molecular wedge within a cleft between the lipoyl and αβ barrel domains of AcrA, diminishing its conformational transmission of drug-evoked signals from AcrB to TolC. This work provides molecular insights into multidrug adaptor protein function which could be valuable for developing antimicrobial therapeutics.

Cycloalkane-modified amphiphilic polymers provide direct extraction of membrane proteins for CryoEM analysis

Membrane proteins are essential for cellular growth, signalling and homeostasis, making up a large proportion of therapeutic targets. However, the necessity for a solubilising agent to extract them from the membrane creates challenges in their structural and functional study. Although amphipols have been very effective for single-particle electron cryo-microscopy (cryoEM) and mass spectrometry, they rely on initial detergent extraction before exchange into the amphipol environment. Therefore, circumventing this pre-requirement would be a big advantage. Here we use an alternative type of amphipol: a cycloalkane-modified amphiphile polymer (CyclAPol) to extract Escherichia coli AcrB directly from the membrane and demonstrate that the protein can be isolated in a one-step purification with the resultant cryoEM structure achieving 3.2 Å resolution. Together this work shows that cycloalkane amphipols provide a powerful approach for the study of membrane proteins, allowing native extraction and high-resolution structure determination by cryoEM.

Distortion of the bilayer and dynamics of the BAM complex in lipid nanodiscs

The β-barrel assembly machinery (BAM) catalyses the folding and insertion of β-barrel outer membrane proteins (OMPs) into the outer membranes of Gram-negative bacteria by mechanisms that remain unclear. Here, we present an ensemble of cryoEM structures of the E. coli BamABCDE (BAM) complex in lipid nanodiscs, determined using multi-body refinement techniques. These structures, supported by single-molecule FRET measurements, describe a range of motions in the BAM complex, mostly localised within the periplasmic region of the major subunit BamA. The β-barrel domain of BamA is in a 'lateral open' conformation in all of the determined structures, suggesting that this is the most energetically favourable species in this bilayer. Strikingly, the BAM-containing lipid nanodisc is deformed, especially around BAM's lateral gate. This distortion is also captured in molecular dynamics simulations, and provides direct structural evidence for the lipid 'disruptase' activity of BAM, suggested to be an important part of its functional mechanism.

The Role of SurA PPIase Domains in Preventing Aggregation of the Outer-Membrane Proteins tOmpA and OmpT

SurA is a conserved ATP-independent periplasmic chaperone involved in the biogenesis of outer-membrane proteins (OMPs). Escherichia coli SurA has a core domain and two peptidylprolyl isomerase (PPIase) domains, the role(s) of which remain unresolved. Here we show that while SurA homologues in early proteobacteria typically contain one or no PPIase domains, the presence of two PPIase domains is common in SurA in later proteobacteria, implying an evolutionary advantage for this domain architecture. Bioinformatics analysis of >350,000 OMP sequences showed that their length, hydrophobicity and aggregation propensity are similar across the proteobacterial classes, ruling out a simple correlation between SurA domain architecture and these properties of OMP sequences. To investigate the role of the PPIase domains in SurA activity, we deleted one or both PPIase domains from E.coli SurA and investigated the ability of the resulting proteins to bind and prevent the aggregation of tOmpA (19 kDa) and OmpT (33 kDa). The results show that wild-type SurA inhibits the aggregation of both OMPs, as do the cytoplasmic OMP chaperones trigger factor and SecB. However, while the ability of SurA to bind and prevent tOmpA aggregation does not depend on its PPIase domains, deletion of even a single PPIase domain ablates the ability of SurA to prevent OmpT aggregation. The results demonstrate that the core domain of SurA endows its generic chaperone ability, while the presence of PPIase domains enhances its chaperone activity for specific OMPs, suggesting one reason for the conservation of multiple PPIase domains in SurA in proteobacteria.

Effects of Periplasmic Chaperones and Membrane Thickness on BamA-Catalyzed Outer-Membrane Protein Folding

The biogenesis of outer-membrane proteins (OMPs) in gram-negative bacteria involves delivery by periplasmic chaperones to the β-barrel assembly machinery (BAM), which catalyzes OMP insertion into the outer membrane. Here, we examine the effects of membrane thickness, the Escherichia coli periplasmic chaperones Skp and SurA, and BamA, the central subunit of the BAM complex, on the folding kinetics of a model OMP (tOmpA) using fluorescence spectroscopy, native mass spectrometry, and molecular dynamics simulations. We show that prefolded BamA promotes the release of tOmpA from Skp despite the nM affinity of the Skp:tOmpA complex. This activity is located in the BamA β-barrel domain, but is greater when full-length BamA is present, indicating that both the β-barrel and polypeptide transport-associated (POTRA) domains are required for maximal activity. By contrast, SurA is unable to release tOmpA from Skp, providing direct evidence against a sequential chaperone model. By varying lipid acyl chain length in synthetic liposomes we show that BamA has a greater catalytic effect on tOmpA folding in thicker bilayers, suggesting that BAM catalysis involves lowering of the kinetic barrier imposed by the hydrophobic thickness of the membrane. Consistent with this, molecular dynamics simulations reveal that increases in membrane thinning/disorder by the transmembrane domain of BamA is greatest in thicker bilayers. Finally, we demonstrate that cross-linking of the BamA barrel does not affect tOmpA folding kinetics in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes, suggesting that lateral gating of the BamA barrel and/or hybrid barrel formation is not required, at least for the assembly of a small 8-stranded OMP in vitro.

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Mechanisms of OMP periplasmic transport and folding by BAM are poorly understood.

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BamA catalyzes folding by reducing the kinetic barrier imposed by membrane thickness.

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BamA proteoliposomes promote folding of Skp-bound tOmpA.

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Lateral gating is not required for BamA-catalyzed folding of tOmpA in DMPC bilayers.

Lateral opening in the intact β-barrel assembly machinery captured by cryo-EM

The β-barrel assembly machinery (BAM) is a ∼203 kDa complex of five proteins (BamA-E), which is essential for viability in E. coli. BAM promotes the folding and insertion of β-barrel proteins into the outer membrane via a poorly understood mechanism. Several current models suggest that BAM functions through a 'lateral gating' motion of the β-barrel of BamA. Here we present a cryo-EM structure of the BamABCDE complex, at 4.9 Å resolution. The structure is in a laterally open conformation showing that gating is independent of BamB binding. We describe conformational changes throughout the complex and interactions between BamA, B, D and E, and the detergent micelle that suggest communication between BAM and the lipid bilayer. Finally, using an enhanced reconstitution protocol and functional assays, we show that for the outer membrane protein OmpT, efficient folding in vitro requires lateral gating in BAM.

Restoration of the root-filled tooth: pre-operative assessment

This is the first in a series of four papers related to the management of root canal treated teeth. When teeth compromised by extensive restorations become non-vital, suggestions have been given as to how root canal treatment can be carried out with the greatest chance of success. Once root canal treated, either by a previous dentist or by the current dentist, a review of the assessment process that should be carried out prior to placing costly indirect definitive restorations is given. It will be clear that post-retained restorations are mainly reserved for anterior or single-rooted teeth, posterior teeth rarely requiring a post for core retention. The second paper in this series describes the basic tooth preparation that should be carried out prior to placing a post. Depending on the type of post system used, further modifications to tooth preparation may be required and the cementation techniques may also have to be modified. The third paper therefore discusses the various post types, when and how they should be used for optimum results. The final paper addresses reinforcement and restoration of compromised root canals, such as those with immature, open apices, or those that have been over-prepared for previous post-retained restorations.

Therapeutic advantages of third generation antihistamines

A third generation of antihistamines is emerging for the treatment of allergic rhinitis and chronic urticaria. First generation antihistamines are among the most widely used drugs in the world, and provide symptomatic relief from allergies and the common cold to millions of patients, mainly in OTC combination preparations. Their full potential is limited by the sedation caused by their effects on histamine receptors in the brain. Second generation antihistamines (terfenadine, astemizole, loratadine and cetirizine), which block peripheral H1 receptors without penetrating the blood-brain barrier, were developed and introduced from 1981 onwards to provide comparable therapeutic benefit without the CNS side-effects. Although largely successful in this goal, terfenadine and astemizole were found to cause potentially serious arrhythmias when plasma concentrations became elevated subsequent to impaired metabolism. It was established that the cardiac toxicity was mainly due to the parent drugs. As active metabolites could account for most of the clinical benefit, the goal for the third generation of antihistamines became to develop therapeutically active metabolites that were devoid of cardiac toxicity. The first of these drugs, fexofenadine (the active metabolite of terfenadine), was approved in July 1996, after an unusually rapid development programme. Its introduction set a new standard of safety that led the FDA to request the withdrawal of terfenadine in 1997 on the grounds that a safer version of an equivalent drug was now available. Norastemizole and descarboethoxy loratadine, the metabolites of astemizole and loratadine, respectively, are also in clinical development. These offer comparable or superior clinical benefits.

Weakened anterior roots--intraradicular rehabilitation

This paper highlights the fact that many anterior teeth requiring restoration are severely weakened having wide, flared canal spaces, and thin dentinal walls that are prone to fracture. Traditionally these teeth have been restored using metal posts and are often unsuccessful because of lack of retention or root fracture. This paper describes how mineral trioxide aggregate (MTA) can be used to form an immediate apical seal rather than waiting months for apexification. Weakened roots can be reinforced using dentine bonding agents and composite resin and if insufficient coronal tooth structure is present a quartz-fibre post can be placed to retain a composite core.

Post and core systems, refinements to tooth preparation and cementation

With a plethora of post systems available, it is often difficult to decide which one to use. This is made more difficult by the fact that new posts are introduced before existing ones are fully evaluated in laboratory and clinical studies. This paper therefore describes the different post types and the main advantages and disadvantages of each. In addition, the choice of post system will influence whether further tooth preparation is required and will dictate which luting cement and core material are most appropriate. Whilst the choice of post will, for many dentists, be driven by personal preference and a history of clinical success, there are certain pit falls to avoid and these are outlined.

Tooth preparation for post-retained restorations

Failure of root canal treatment and/or post crowns can be avoided in many cases if appropriate tooth preparation is carried out. This paper discusses the rationale for the timing of post placement following root canal treatment and appropriate methods for removal of gutta-percha prior to post space preparation. The basic principles of post space preparation are described, which should reduce the risk of weakening the root unnecessarily, causing damage to the periodontium and post perforation.

Oxidant injury, nitric oxide and pulmonary vascular function: implications for the exercising horse

The athletic ability of the horse is facilitated by vital physiological adaptations to high-intensity exercise, including a thin (but strong) pulmonary blood-gas barrier, a large pulmonary functional reserve capacity and a consequent maximum oxygen uptake (VO2max) far higher than in other species. A high pulmonary artery pressure also serves to enhance pulmonary function, although stress failure of lung capillaries at high pulmonary transmural pressures, and the contribution of other factors which act in the exercising horse to increase pulmonary vascular tone, may lead to pathological or pathophysiological sequelae, such as exercise-induced pulmonary haemorrhage (EIPH). Reactive oxygen species (ROS) are an important component of the mammalian inflammatory response. They are released during tissue injury and form a necessary component of cellular defences against pathogens and disease processes. The effects of ROS are normally limited or neutralized by a multifactorial system of antioxidant defences, although excessive production and/or deficient antioxidant defences may expose healthy tissue to oxidant damage. In the lung, ROS can damage pulmonary structures both directly and by initiating the release of other inflammatory mediators, including proteases and eicosanoids. Vascular endothelial cells are particularly susceptible to ROS-induced oxidant injury in the lung, and both the destruction of the pulmonary blood-gas barrier and the action of vasoactive substances will increase pulmonary vascular resistance. Moreover, ROS can degrade endothelium-derived nitric oxide (NO), a major pulmonary vasodilator, thereby, with exercise, synergistically increasing the likelihood of stress failure of pulmonary capillaries, a contributing factor to EIPH. This review considers the implications for the exercising horse of oxidant injury, pulmonary vascular function and NO and the contribution of these factors to the pathogenesis of equine respiratory diseases.

First recorded outbreak of equine viral arteritis in the United Kingdom

Equine viral arteritis was diagnosed for the first time in the United Kingdom in 1993. The outbreak began on a non-thoroughbred stud in south Nottinghamshire and spread to five other premises through chilled semen used for artificial insemination and from acutely and subclinically infected mares returning home. The outbreak was contained on these six premises by means of voluntary movement restrictions. The most commonly observed clinical signs were typical: pyrexia with depression, and conjunctivitis with periorbital oedema; nasal discharge, and oedema of the distal limbs, prepuce and mammary glands were less common. The first mare to be covered by a recently imported stallion was the first animal to be affected. The mare was resident and no new mares had arrived on the stud during the previous five months. About 100 animals became infected during the outbreak, including three indigenous stallions. Equine arteritis virus was isolated from semen and heparinised blood samples and seroconversions were demonstrated by using the equine arteritis virus neutralisation test. Although the outbreak was contained, the free movement of animals within the European Union increases the possibility of infected stallions being introduced into the UK.

Inhibition of long-chain acylcarnitine accumulation during coronary artery occlusion does not alter infarct size in dogs

We tested whether inhibition of carnitine acyl-transferase-1 (CAT-1) during coronary artery occlusion can limit infarct size (IS) by suppressing accumulation of long-chain acylcarnitines (LCAs), potentially cytotoxic intermediates of fatty acid metabolism. The CAT-1 inhibitor 2-[5-(4-chlorophenyl)-pentyl]-oxirane-2-carboxylate (POCA) was administered to dogs before 90-min occlusion and 4-h reperfusion of the left anterior descending or left circumflex coronary artery (LAD, LCX). Dogs in the LAD occlusion series received 7.5 (n = 5) or 15 (n = 2) mg/kg POCA intravenously (i.v.); dogs in the LCX occlusion series received 15 mg/kg i.v. (n = 7); an equal number were treated with drug vehicle. Biopsies were obtained for determination of myocardial LCAs. The region at risk and IS were delineated by dye injection and tetrazolium staining. In vehicle-treated dogs, myocardial LCAs (in picomoles per milligram of wet weight +/- SEM) increased from 11 +/- 3 to a peak of 75 +/- 24 during LAD occlusion and from 32 +/- 10 to 192 +/- 55 during LCX occlusion. In POCA-treated dogs LCAs increased from 12 +/- 2 to only 33 +/- 13 pmol/mg wet weight during LAD occlusion (p < 0.05 vs. vehicle) and did not increase significantly during LCX occlusion; 22 +/- 8 to 27 +/- 5 pmol/mg wet weight (p < 0.005 vs. vehicle). LCX occlusion resulted in larger areas at risk and larger infarcts (as a percentage of left ventricle) than did LAD occlusion. IS as a percentage of the region at risk did not differ significantly among the experimental groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Reperfusion-induced accumulation of long-chain acylcarnitines in previously ischemic myocardium

Long-chain acylcarnitines (LCA) have been shown to accumulate during myocardial ischemia and to contribute to malignant derangements characteristic of ischemia. We detail the time course of the increase in LCA levels during both ischemia and reperfusion. Evidence indicates an additional specific reperfusion-induced increase in LCA that peaks at 2 min and decreases to basal levels by 30 min. This increase in LCA during reperfusion is observed after 2-, 10-, or 20-min ischemia and is inhibited by the presence of the carnitine palmitoyl transferase 1 (CPT1) inhibitor phenyloxirane carboxylic acid (POCA). A role for increased LCA in mediating "reperfusion damage" is not indicated, however, because POCA did not attenuate either the incidence of ventricular fibrillation (VF) during early reperfusion or the survival rate of rats undergoing 24-h reperfusion after 10-min occlusion.

Electropharmacology of dofetilide, a new class III agent, in anaesthetised dogs

In open chest anaesthetised dogs, dofetilide increased the ventricular effective refractory period over the dose range 1-100 micrograms/kg i.v. and the ventricular fibrillation threshold at doses between 3-100 micrograms/kg and was 80-1000 times more potent than sematilide, racemic sotalol, d-sotalol or quinidine. The maximal increases in ventricular fibrillation threshold induced by sematilide and quinidine were less than that induced by the other drugs. A change in the character of the induced arrhythmia from true ventricular fibrillation to a rapid ventricular flutter, with frequent spontaneous conversion, was observed following all drugs. No adverse haemodynamic effects of dofetilide, sematilide or d-sotalol were observed, but quinidine induced marked cardiac depression and racemic sotalol also impaired left ventricular contractility. All drugs reduced heart rate, though the effect of racemic sotalol was clearly greater than that of the other agents. Dofetilide is a potent class III antiarrhythmic agent with antifibrillatory properties and a favourable haemodynamic profile.

Effects of action potential prolongation via different cellular mechanisms on the electrophysiological properties of rat and guinea-pig ventricular myocardium

The effects of d-sotalol and the sea anemone toxin ATXII on the electrophysiological properties of rat and guinea-pig ventricular myocardium in vitro and on arrhythmias following coronary artery ligation in rat hearts in vivo were studied. ATXII (1-5 nM) prolonged the cardiac action potential of isolated papillary muscles and the effective refractory period of perfused hearts from both rats and guinea-pigs. In rat hearts, ATXII induced gross action potential prolongation and early afterdepolarizations at concentrations above 1 nM. In contrast, d-sotalol prolonged the action potential and effective refractory period of guinea-pig, but not of rat myocardium. Neither drug prevented arrhythmias in anaesthetized rats following coronary ligation.

Electrophysiologic properties of UK-66,914, a novel class III antiarrhythmic agent

A class III antiarrhythmic agent that preferentially increases the effective refractory period without altering conduction velocity holds considerable promise for the treatment of life-threatening cardiac arrhythmias dependent on a reentrant mechanism. In the present study, the cellular electrophysiologic effects of a novel class III antiarrhythmic agent, UK-66,914, were evaluated. UK-66,914 prolonged action potential duration and extended the effective refractory period in isolated canine ventricular muscle and Purkinje fibers in a concentration-dependent manner, beginning at a threshold concentration of 0.1 microM. Analogous effects were found in isolated rabbit atrium beginning at a threshold concentration of 2 microM. At concentrations of UK-66,914 up to 20 microM there was no effect on the maximum rate of phase 0 depolarization (Vmax) or the amplitude of the action potential. In guinea pig papillary muscles. UK-66,914 at concentrations from 0.1 to 20 microM increased the effective refractory period at stimulation frequencies of 1 or 5 Hz, but did not slow conduction velocity. Therefore, UK-66,914 exhibits high selectivity for a class III antiarrhythmic effect in normal tissue. To elucidate the mechanisms responsible for the increase in effective refractory period, voltage clamp procedures were used in guinea pig ventricular myocytes. UK-66,914 reduced the amplitude of outward tail currents following depolarizing clamp steps with little effect either on the background K+ current or calcium currents, indicating that UK-66,914 selectively blocked the time-dependent potassium current. In anesthetized dogs, UK-66,914 (10 micrograms/kg to 1 mg/kg i.v.) prolonged both atrial and ventricular effective refractory periods, but in contrast to the studies performed in vitro, the minimum effective doses required to increase the effective refractory period in atria and ventricle were the same. Therefore, UK-66,914 is a potent selective class III antiarrhythmic agent, which owes its electrophysiologic profile to blockade of the time-dependent potassium current.

Pharmacodynamics and pharmacokinetics of miloxicam in the horse

The novel non-steroidal anti-inflammatory drug (NSAID) miloxicam was administered intravenously to six New Forest ponies at a dosage rate of 0.6 mg/kg in a two-part cross-over study. In each part, three horses received miloxicam and three were given a placebo preparation. The actions of miloxicam, compared to placebo, were assessed in a carrageenan-sponge model of acute inflammation. The rise in skin temperature over the site of the acute inflammatory reaction was less in treated ponies, but differences were not statistically significant. Concentrations of the enzymes acid phosphatase (AP) and lysozyme in inflammatory exudates harvested at 4, 8, 12 and 24 h were not significantly different in drug-treated animals compared with those receiving placebo. Concentrations of protein and lactate dehydrogenase (LDH) in exudate and exudate leucocyte numbers were significantly reduced in drug-treated horses when data for all sampling times were pooled. The differences were not significant, however, at each sampling time. Exudate concentrations of the eicosanoids, bicyclic-PGE2, 6-keto-PGF1 alpha and TXB2, were reduced significantly by miloxicam at most sampling times, and serum TXB2 was also significantly reduced at 4 and 8 h but not at 12 and 24 h after drug administration. These pharmacodynamic findings correlated with the pharmacokinetic properties of miloxicam. The plasma concentration-time curve was defined by a three-compartment open model in one pony and by a two-compartment model in five ponies. Mean values for pharmacokinetic parameters for the five ponies were: t1/2 alpha 0.40 h; t1/2 beta 2.70 h; Vd area 0.158 l/kg; ClB 41.87 ml/kg/h. Exudate concentrations of miloxicam were initially similar to and eventually greater than concentrations in plasma, and this may explain the more prolonged inhibition of eicosanoid synthesis in exudate than in serum. These findings demonstrate the value of relating, in a single experimental study, drug action on a range of variables to drug fate in the body.

UK-68,798: a novel, potent and highly selective class III antiarrhythmic agent which blocks potassium channels in cardiac cells

UK-68,798 increased the duration and effective refractory period of cardiac action potentials recorded in vitro from canine ventricular muscle and Purkinje fibers in a concentration dependent manner from 5 nM to 1 microM. The resting membrane potential, amplitude and maximum upstroke velocity of action potentials were unaffected by UK-68,798, indicating the selective class III antiarrhythmic properties of this agent. UK-68,798 (5 nM-1 microM) increased the effective refractory period of isolated guinea pig papillary muscles at stimulation frequencies of 1 Hz and 5 Hz without influencing the conduction velocity, further confirming that UK-68,798 is devoid of class I antiarrhythmic activity including block of the sodium channel. Studies using single voltage clamped guinea pig ventricular myocytes indicated that UK-68,798 at concentrations of 50 nM and 2 microM blocks a time-dependent K+ current, with no appreciable effects on the time-independent K+ current or the inward calcium current. UK-68,798 is therefore a highly selective K+ channel blocking agent with class III antiarrhythmic properties, a profile that holds considerable promise for the therapy of life-threatening cardiac arrhythmias.

Comparative assessment of enprofylline and theophylline for chronic obstructive airways disease in the elderly

Enprofylline, a recently developed xanthine derivative, is a more potent bronchodilator than theophylline. This study compares the efficacy and safety of enprofylline with theophylline for chronic obstructive airways disease (COAD) in elderly subjects. The study was of a randomized double-blind parallel design and commenced with a 1-week reference period when oral bronchodilators were withdrawn. Patients were then treated with either enprofylline or theophylline 150 mg bd for 2 weeks (period 1) followed by 300 mg bd for a further 3 weeks (period 2). Patients recorded peak expiratory flow rate (PEFR) and adverse experiences, if any, in a diary, daily. Of 111 patients recruited for the study, 85 entered active treatment (theophylline, n = 44; enprofylline, n = 41). Mean age was 72 years and mean bronchodilator reversibility was 22%. Enprofylline increased mean morning PEFR by 11% (period 1) and 19% (period 2) whereas theophylline increased PEFR by 13% and 19%, respectively. From the enprofylline group 29% were withdrawn from the study due mainly to headache and nausea/vomiting and from the theophylline group 7% were withdrawn due mainly to nausea/vomiting. Mean plasma concentrations of enprofylline were 2.0 mg l-1 and 3.4 mg l-1, and with theophylline 5.4 mg l-1 and 10.0 mg l-1 at the end of periods 1 and 2, respectively. Enprofylline and theophylline produced similar improvements in lung functions and symptoms of chronic obstructive airways disease, but enprofylline was less well tolerated than theophylline.

Selective class III antiarrhythmic agents. 1 Bis(arylalkyl)amines

A series of bis(arylalkyl)amines is described and their effects on prolonging effective refractory period in isolated cardiac tissue listed. Most compounds prolonged the cardiac action potential without significantly altering the maximum rate of depolarization and may be defined as selective class III antiarrhythmic agents. It was found that a particularly advantageous structural feature was to have a methanesulfonamido moiety on both of the aryl rings. Thus, compound 16 [1-(4-methanesulfonamidophenoxy)2-[N-(4-methanesulfonamidophene thyl)-N- methylamine]ethane] was selected for further investigations. The compound is highly potent and selective class III agent which acts by blockade of cardiac potassium channels.

Breath-actuated inhalers: comparison of terbutaline Turbohaler with salbutamol Rotahaler

Two breath-actuated inhalers, the Turbohaler and the Rotahaler, were compared in 24 patients with chronic asthma using an open, cross-over study design. Patients were treated with terbutaline (500 micrograms) and salbutamol (400 micrograms) four times daily, each trial period lasting three weeks. Mean morning peak expiratory flow (PEF) values were higher during Turbohaler treatment, but were similar 15 min after inhaler use. The Turbohaler was found to be easier to use than the Rotahaler.

Breath-actuated inhalers: comparison of terbutaline Turbohaler with salbutamol Rotahaler

Two breath-actuated inhalers, the Turbohaler and the Rotahaler, were compared in 24 patients with chronic asthma using an open, cross-over study design. Patients were treated with terbutaline (500 micrograms) and salbutamol (400 micrograms) four times daily, each trial period lasting three weeks. Mean morning peak expiratory flow (PEF) values were higher during Turbohaler treatment, but were similar 15 min after inhaler use. The Turbohaler was found to be easier to use than the Rotahaler.

In vitro and in vivo binding of phenylbutazone and related drugs to equine feeds and digesta

In vitro and in vivo studies of phenylbutazone binding to equine ingesta and digesta were undertaken. In vitro binding to chopped hay and powdered pony nuts in buffer solutions at 37 degrees C was found to be time-, concentration- and pH-dependent. Percentage binding generally increased with time, decreased with concentration and varied with buffer pH in an unpredictable manner. Other non-steroidal anti-inflammatory drugs (NSAIDs) also bound to hay, the degree of binding being less for meclofenamate and least for flunixin in comparison with phenylbutazone. Phenylbutazone became bound to digesta collected from eight regions of the gastrointestinal tract when they were spiked with a concentration of 1 mg.10 g-1 digesta, the amounts ranging from 80.0 per cent (duodenum) to 99.6 per cent (stomach). Binding also occurred to equine digesta following the oral administration of phenylbutazone (4.4 mg.kg-1) to three ponies. It was concluded that drug uptake by and release from equine ingesta and digesta were probably adsorptive and desorptive processes. The clinical significance of the findings for the use of NSAIDs in equine medicine was considered.

Physiological, biochemical and haematological effects on horses of a phenylbutazone paste

Five matched pairs of horses were used to investigate the biochemical, haematological and general clinical effects of a new dosage schedule of a phenylbutazone paste administered under controlled feeding conditions. One group of horses received a loading dose (8.8 mg/kg) on day 1, followed by doses of 3.3 mg/kg daily on days 2 to 8, 10 and 12 with no treatment on days 9 and 11. The second group received equivalent doses of a placebo paste. Bodyweight, skin temperature, respiratory rate, glutamate dehydrogenase activity, packed cell volume, mean corpuscular volume and neutrophil count were altered significantly in the drug-treated but not in the placebo-treated animals. From the direction and magnitude of the changes in these variables, it was concluded that they did not reflect toxic actions of phenylbutazone. Several variables were unaffected by either treatment both during and after dosing and others were significantly altered in both groups of horses. These changes were considered to be toxicologically insignificant.

Measurement of flunixin in equine inflammatory exudate and plasma by high performance liquid chromatography

An accurate and reliable method for the separation of flunixin from, and measurement in, equine inflammatory exudate and plasma by high performance liquid chromatography has been developed. Flunixin can be detected in concentrations as low as 0.05 micrograms/ml using an ultraviolet spectrophotometric detector at 285 nm. Samples were acidified with 2M hydrochloric acid and extracted with dichloromethane. The extract was evaporated and reconstituted in acetonitrile. Iminodibenzyl was used as internal standard. The mean recovery of flunixin from plasma was 97.6 +/- 3.9 per cent. Particular advantages of the method are the short analysis time and ease of sample preparation. Data were obtained on the distribution of flunixin between plasma and acute inflammatory exudate following administration of a single intravenous dose of 1.1 mg/kg bodyweight flunixin meglumine. The drug was cleared more slowly from exudate than from plasma.

Applications of equine models of acute inflammation. The Ciba-Geigy Prize for Research in Animal Health

The development of reproducible models of acute inflammation in which inflammatory heat is easily quantified and from which inflammatory exudate is readily harvested has facilitated studies in the horse of the actions of steroids and non-steroidal anti-inflammatory drugs (NSAIDS). Blockade of the synthesis of eicosanoids and suppression of inflammatory heat by clinical dose rates of NSAIDS suggests a causal link between the two events and provides further evidence for a role of these compounds in acute equine inflammation. The tendency for enolic and carboxylic acids NSAIDS to accumulate in inflammatory exudate may account for the duration of action of these compounds in inhibiting exudate eicosanoid synthesis and the data confirm clinical experiences with these drugs. A novel NSAID which inhibits both cyclo-oxygenase and lipoxygenase pathways of arachidonic acid metabolism, BW540C, and two anti-inflammatory steroids, betamethasone and dexamethasone, have been evaluated in the models of equine inflammation with some interesting and unexpected findings. This paper emphasises the interrelationships between the inflammatory process and the actions and fate of anti-inflammatory drugs.

Inflammation: a clinical perspective. The Ciba-Geigy Prize for Research in Animal Health

The cardinal signs of acute inflammation have been recognised for almost 2000 years, but it is only in the last hundred years that significant progress has been made in understanding the underlying cellular response. Our knowledge of the chemical messengers which regulate and in some cases lead to persistence of the inflammatory process is, as yet, incomplete, but it is hoped that further research at this level will lead to the development of more effective therapeutic agents.

Development of equine models of inflammation. The Ciba-Geigy Prize for Research in Animal Health

Two experimental models of acute non-immune inflammation have been developed to enable studies of the biochemical composition and cellular content of exudates to be undertaken. Both are based on the creation of a mild, reproducible and reversible inflammatory reaction, which is free from uncontrolled incidental factors and which causes minimal distress to the experimental animals. The polyester sponge model involves the insertion of small polyester sponge strips soaked in sterile carrageenan solution into subcutaneous neck pouches and their serial removal. The tissue-cage model is based on the initial insertion of a spherical tissue-cage subcutaneously in the neck and the subsequent stimulation with carrageenan of the granulation tissue which lines and permeates the cage. The acute inflammatory exudates have been shown to contain eicosanoids with prostaglandin E2 predominant. Polymorphonuclear leucocyte numbers increased progressively in the polyester sponge model, whereas cell numbers were maximal at 12 hours in the tissue-cage model. The relationships between eicosanoid formation at the site of inflammation and leucocyte accumulation, enzyme release, total protein content of exudates and the temperature of the lesions have been investigated.

Actions of BW540C in an equine model of acute inflammation: a preliminary study

An equine model of acute non-immune inflammation has been developed to facilitate studies of the inflammatory process and the actions of novel anti-inflammatory drugs. Five polyester sponge strips soaked in sterile 2% carrageenin solution were placed in subcutaneous pouches prepared under local anaesthesia in the necks of conscious ponies. Serial removal of the strips and harvesting of the exudate enabled studies to be made of the cellular, biochemical and mediator aspects of the localised, acute inflammation, and the heat generated by the lesion was monitored by infra-red thermometry. Maximal concentrations of the eicosanoids 6-keto-prostaglandin F1 alpha, thromboxane B2 and leukotriene B4 occurred at 9 h, whereas leukocyte numbers, lactate dehydrogenase (LDH) and total protein concentrations were greatest at 24 h. Lesional skin temperature was increased by approximately 4 degrees C throughout the 24 h period. The novel anti-inflammatory agent BW540C, administered orally at a dose-rate of 20 mg/kg, did not affect leukocyte infiltration or the concentrations of protein, LDH and eicosanoids in exudate but serum thromboxane B2 levels were reduced. Skin temperature rises were greater in drug-treated animals. It is concluded that higher doses of BW540C will be required for a clinically useful anti-inflammatory action in horses.

Metabolism, excretion, pharmacokinetics and tissue residues of phenylbutazone in the horse

The pharmacokinetics, metabolism, excretion and tissue residues of phenylbutazone (PBZ) in the horse were studied following both intravenous and oral administration of the drug at a dose rate of 4.4 mg/kg. A 72-hour blood sampling schedule failed to demonstrate a third exponential phase; the plasma disposition following intravenous injection being described by a two compartment open model, with the following elimination phase parameters: beta = 0.13h-1, t1/2 beta = 5.46h, Vdarea = 0.141 1/kg and C1B = 17.9 ml/kg/h. The hydroxylated metabolites oxyphenbutazone (OPBZ) and gamma-hydroxyphenylbutazone (OHPBZ) were present in detectable concentrations in plasma for 72 and 24 h, respectively. After 36 h OPBZ concentrations exceeded plasma PBZ concentrations. In urine the principal metabolites were OPBZ and OHPBZ but smaller concentrations of another compound, probably gamma-hydroxyoxyphenbutazone (OHOPBZ), were also detected. The percentages of the administered dose recovered from urine were 30.7, 39.0 and 40.3 after 24, 48 and 72 h from the time of injection. Recovery of PBZ and its metabolites from urine was significantly reduced in the first 24 h after oral dosing when the horses had free access to hay, probably as a result of markedly delayed absorption, but this did not occur in animals deprived of food for a few hours before and after dosing. Determination of approximate values of urine/plasma (U/P) concentration ratios for PBZ and its metabolites relative to endogenous creatinine U/P concentration ratio suggested that PBZ was filtered in small amounts only because of the high degree of plasma protein binding and then excreted by diffusion trapping in the alkaline urine. Much higher U/P ratios were obtained for the hydroxylated derivatives, and one at least (OHPBZ) was secreted into urine.

The effects of ischaemia, lysophosphatidylcholine and palmitoylcarnitine on rat heart phospholipase A2 activity

Phospholipase A2 activity was studied in the isolated rat heart following coronary artery ligation. In both the homogenate and mitochondrial fractions phospholipase A2 activity was significantly depressed at 20 min post ligation in the ischaemic region only. This is at a time of peak lysophospholipid concentration and severity of arrhythmias. No such depression of activity was seen in a crude sarcolemmal fraction, possibly due to washout of inhibitory factors during isolation. Lysophosphatidylcholine and palmitoylcarnitine, two amphiphiles known to accumulate during ischaemia, were both shown to be capable of inhibiting phospholipase A2. It is suggested that lysophospholipid and palmitoylcarnitine accumulation during ischaemia may contribute to the depression of phospholipase A2 activity seen and that the decreased metabolism of lysophospholipids may be of more importance in their accumulation than increased production by phospholipase A2.

Calcium channel blocking properties of amlodipine in vascular smooth muscle and cardiac muscle in vitro: evidence for voltage modulation of vascular dihydropyridine receptors

Amlodipine was twice as potent as nifedipine at inhibiting Ca2+-induced contractions in depolarised rat aorta (IC50 1.9 nM vs. 4.1 nM) but, unlike nifedipine, displayed a very slow onset of action. Contractions induced by depolarising steps with 45 mM K+ were much less potently blocked by amlodipine (IC50 19.4 nM), whereas the potency of nifedipine was little changed (IC50 7.1 nM). This difference may be explained by a modulated receptor hypothesis, similar to that described for cardiac muscle, in which block of vascular calcium channels by dihydropyridines is enhanced at depolarized membrane potentials, such voltage-dependence only being apparent with a slow-acting drug such as amlodipine. Recovery from amlodipine block of K+-responses in rat portal vein after drug washout was also very slow. Amlodipine and nifedipine blocked phenylephrine-induced contractions of the rat aorta with potencies similar to those against depolarisation-induced responses. Negative inotropic potencies of amlodipine and nifedipine in perfused guinea pig hearts were approximately one-tenth those against Ca2+-induced contractions in rat aorta. Amlodipine caused complete block of guinea pig papillary muscle single-cell slow action potentials at a concentration (5 microM) that had no effect on upstroke velocity of normal, fast potentials but reduced the duration of the plateau phase.

Use of a novel non-steroidal anti-inflammatory drug in the horse

In a two-part cross-over experiment in six ponies, an acute inflammatory reaction was generated by injecting carrageenin solution into subcutaneously-implanted tissue-cages lined with fibrovascular granulation tissue. In each part of the cross-over, half of the ponies received a novel phenylpyrazoline anti-inflammatory agent (BW540C) orally and half received a placebo treatment. BW540C inhibited platelet cyclo-oxygenase for 24 h but the reductions in exudate eicosanoid concentrations were less pronounced. A significant suppression in the rise of surface skin temperature in BW540C-treated ponies paralleled drug-induced inhibition of thromboxane B2 bicyclic prostaglandin (PG) E2 concentrations at the inflamed site. The drug had no significant effect on 6-keto-PGF1 alpha, migrating leucocytes, lactate dehydrogenase or total protein in exudates. Maximum plasma concentrations of both compounds occurred 2 to 4 h after dosing and maximum exudate levels of drug and metabolite occurred at 12 h. Both compounds penetrated approximately three times less readily into exudate than into plasma.

Effects of a phenylbutazone paste in ponies: model of acute nonimmune inflammation

In a 12-day treatment schedule, 5 ponies were given orally a paste formulation of phenylbutazone (PBZ) and 5 matched ponies were given equivalent doses of a placebo paste. On day 12, a mild, nonimmune inflammatory reaction was induced subcutaneously in the neck of each pony by inserting sterile, polyester sponge strips soaked in a 2% carrageenan solution. Exudate was collected at 4, 8, 12, and 24 hours by serial removal of sponges. There were no significant (P less than 0.05) differences in exudate protein concentration and leukocyte numbers between the treatment groups, but the group given PBZ had significantly reduced exudate concentrations of eicosanoids 6-keto-prostaglandin F 1 alpha (the stable metabolite of prostacyclin) at 4, 8, and 12 hours; thromboxane B2 at 8, 12, and 24 hours; and bicyclic prostaglandin E2 at 8 hours. The maximal depression of eicosanoid synthesis occurred at times of peak exudate concentrations of PBZ (8 and 12 hours). Phenylbutazone was cleared more slowly from exudate than from plasma. Changes in surface skin temperature were measured by infrared thermometry. Lesional temperatures were recorded 1 cm below the base of the incision line, and mean increases were significantly (P less than 0.05) less in PBZ-treated than in placebo-treated ponies between 4 and 24 hours. The importance of the findings for the clinical efficacy of this dosage schedule is considered.

Absorption of phenylbutazone from a paste formulation administered orally to the horse

The absorption pattern of phenylbutazone was studied in five horses during administration of the drug in a paste formulation on days 1, 5, 8 and 12 of a 12-day dosing schedule. Since two or more plasma concentration peaks were usually obtained following each oral dose, it was concluded that phasic absorption was a particular feature of the oil:water formulation of the product. Possible causes of this unusual absorption pattern are discussed and the therapeutic implications of both phasic absorption and the recorded values of Cmax, tmax and AUC024 for phenylbutazone and its active metabolite oxyphenbutazone are considered.

Phenylbutazone and oxyphenbutazone distribution into tissue fluids in the horse

The clinically recommended dose rate of phenylbutazone (4.4 mg/kg) was administered intravenously as a single dose to five Welsh Mountain ponies. Distribution of phenylbutazone and its active metabolite oxyphenbutazone into body fluids was studied by measuring concentrations in plasma, tissue-cage fluid, peritoneal fluid and acute inflammatory exudate harvested from a polyester sponge model of inflammation. The ready penetration of phenylbutazone into inflammatory exudate was demonstrated by the relatively high mean value for Cmax of 12.4 micrograms/ml occurring at a time of 4.6 h and a mean AUC0-24 of 128 microgram X h/ml. A high mean exudate:plasma AUC0-24 ratio of 0.83 was recorded. Plasma:exudate concentration ratios for phenylbutazone were initially greater than and subsequently less than one; the slower clearance from exudate was indicated by approximate t1/2 beta) values of 4.8 and 24 h for plasma and exudate, respectively. These findings may help to explain the relatively long duration of action of phenylbutazone, in spite of a plasma elimination half-life of less than 5 h. Lower values of Cmax and AUC0-24 for phenylbutazone passage into peritoneal fluid (6.3 micrograms/ml and 45 micrograms X h/ml) were recorded, and a limited number of sampling times indicated a similar degree of penetration as into tissue cage fluid. Mean concentrations of oxyphenbutazone in all fluids were lower than phenylbutazone concentrations at all times, but ready penetration of the metabolite into body fluids, especially into inflammatory exudate, occurred suggesting that oxyphenbutazone may contribute to the anti-inflammatory effect. The hyperaemia of acute inflammation and the high protein levels in inflammatory exudate may both assist passage of phenylbutazone and oxyphenbutazone into exudate.