Investigating the Unbinding of Muscarinic Antagonists from the Muscarinic 3 Receptor

Patient symptom relief is often heavily influenced by the residence time of the inhibitor-target complex. For the human muscarinic receptor 3 (hMR3), tiotropium is a long-acting bronchodilator used in conditions such as asthma or chronic obstructive pulmonary disease (COPD). The mechanistic insights into this inhibitor remain unclear; specifically, the elucidation of the main factors determining the unbinding rates could help develop the next generation of antimuscarinic agents. Using our novel unbinding algorithm, we were able to investigate ligand dissociation from hMR3. The unbinding paths of tiotropium and two of its analogues, N-methylscopolamin and homatropine methylbromide, show a consistent qualitative mechanism and allow us to identify the structural bottleneck of the process. Furthermore, our machine learning-based analysis identified key roles of the ECL2/TM5 junction involved in the transition state. Additionally, our results point to relevant changes at the intracellular end of the TM6 helix leading to the ICL3 kinase domain, highlighting the closest residue L482. This residue is located right between two main protein binding sites involved in signal transduction for hMR3's activation and regulation. We also highlight key pharmacophores of tiotropium that play determining roles in the unbinding kinetics and could aid toward drug design and lead optimization.

Validating Whole-Airway CFD Predictions of DPI Aerosol Deposition at Multiple Flow Rates

BACKGROUND

The objective of this study was to compare aerosol deposition predictions of a new whole-airway CFD model with available in vivo data for a dry powder inhaler (DPI) considered across multiple inhalation waveforms, which affect both the particle size distribution (PSD) and particle deposition.

METHODS

The Novolizer DPI with a budesonide formulation was selected based on the availability of 2D gamma scintigraphy data in humans for three different well-defined inhalation waveforms. Initial in vitro cascade impaction experiments were conducted at multiple constant (square-wave) particle sizing flow rates to characterize PSDs. The whole-airway CFD modeling approach implemented the experimentally determined PSDs at the point of aerosol formation in the inhaler. Complete characteristic airway geometries for an adult were evaluated through the lobar bronchi, followed by stochastic individual pathway (SIP) approximations through the tracheobronchial region and new acinar moving wall models of the alveolar region.

RESULTS

It was determined that the PSD used for each inhalation waveform should be based on a constant particle sizing flow rate equal to the average of the inhalation waveform's peak inspiratory flow rate (PIFR) and mean flow rate [i.e., AVG(PIFR, Mean)]. Using this technique, agreement with the in vivo data was acceptable with <15% relative differences averaged across the three regions considered for all inhalation waveforms. Defining a peripheral to central deposition ratio (P/C) based on alveolar and tracheobronchial compartments, respectively, large flow-rate-dependent differences were observed, which were not evident in the original 2D in vivo data.

CONCLUSIONS

The agreement between the CFD predictions and in vivo data was dependent on accurate initial estimates of the PSD, emphasizing the need for a combination in vitro-in silico approach. Furthermore, use of the AVG(PIFR, Mean) value was identified as a potentially useful method for characterizing a DPI aerosol at a constant flow rate.

Binding studies of terbutaline sulfate to calf thymus DNA using multispectroscopic and molecular docking techniques

The interaction of terbutaline sulfate (TS) with calf thymus DNA (ctDNA) were investigated by fluorescence quenching, UV-vis absorption, viscosity measurements, ionic strength effect, DNA melting experiments and molecular docking. The binding constants (Ka) of TS to ctDNA were determined as 4.92×10(4), 1.26×10(4) and 1.16×10(4) L mol(-1) at 17, 27 and 37 °C, respectively. Stern-Volmer plots suggested that the quenching of fluorescence of TS by ctDNA was a static quenching. The absorption spectra of TS with ctDNA revealed a slight blue shift and hyperchromic effect. The relative viscosity ctDNA was hardly changed by TS, and melting temperature varied slightly. For the system of TS-ctDNA, the intensity of fluorescence decreased with the increase of ionic strength. Also, the Ka for TS-double stranded DNA (dsDNA) was clearly weaker than that for TS-single stranded DNA (ssDNA). All these results revealed that the binding mode of TS with ctDNA should be groove binding. The enthalpy change and entropy change suggested that van der Waals force or hydrogen bonds was a main binding force between TS and ctDNA. Furthermore, the quantum yield of TS was measured by comparing with the standard solution. Based on the Förster energy transference theory (FRET), the binding distance between the acceptor and donor was calculated. Molecular docking showed that TS was a minor groove binder of ctDNA and preferentially bound to A-T rich regions.

Is the cellular uptake of respiratory aerosols delivered from different devices equivalent?

The study focuses on the application of a cell integrated modified Andersen Cascade Impactor (ACI) as an in vitro lung model for the evaluation of aerosols' behaviour of different formulation devices, containing the same active drug, specifically nebuliser, pressurised metered dose inhaler (pMDI) and dry powder inhaler (DPI). Deposition and transport profiles of the three different inhaled salbutamol sulphate (SS) formulations with clinically relevant doses were evaluated using a modified ACI coupled with the air interface Calu-3 bronchial cell model. Reproducible amounts of SS were deposited on Snapwells for the different formulations, with no significant difference in SS deposition found between the standard ACI plate and modified plate. The transport of SS aerosols produced from pMDI formulation had similar transport kinetics to nebulised SS but significantly higher compared to the DPI, which could have led to the differences in clinical outcomes. Furthermore, drug absorption of different inhaled formulation devices of the same aerodynamic fraction was found not to be equivalent due to their physical chemical properties upon aerosolisation. This study has established an in vitro platform for the evaluation of the different inhaled formulations in physiologically relevant pulmonary conditions.

Salbutamol: how does it enter smooth muscle cells?

Polyspecific organic cation transporters (OCTs) in human cell membranes are involved in the uptake, distribution and excretion of cationic compounds. Although their relevance to drug disposition in the liver, small intestine and kidney has been investigated previously, less is known about the influence of these transporters on the pharmacokinetics and pharmacodynamics of inhaled drugs. Drugs that are commonly administered by inhalation for the treatment of respiratory diseases, such as glucocorticoids and cationic β(2)-agonists, might interact with several of these transporters, which are strongly expressed on the surfaces of airway epithelial cells. We evaluated the expression of OCT3 and measured the in vitro uptake of the short-acting β(2)-agonist salbutamol (SALB), alone or in combination with corticosterone (CS) and beclomethasone dipropionate (BDP), by bronchial smooth muscle cells. Our results showed that these cells express the OCT3 transporter and that SALB enters the cell in a transporter-independent fashion. Moreover, CS and BDP have different activities on SALB transport inside the cell. CS increases SALB transport and BDP decreases SALB transport, although neither of these effects are statistically significant. A better understanding of these mechanisms might lead to the improved treatment of airway diseases.

The influence of fatty acids on theophylline binding to human serum albumin. Comparative fluorescence study

Theophylline, popular diuretic, is used to treat asthma and bronchospasm. In blood it forms complexes with albumin, which is also the main transporter of fatty acids. The aim of the present study was to describe the influence of fatty acids (FA) on binding of theophylline (Th) to human serum albumin (HSA) in the high affinity binding sites. Binding parameters have been obtained on the basis of the fluorescence analysis. The data obtained for the complex of Th and natural human serum albumin (nHSA) obtained from blood of obese patients qualified for surgical removal of stomach was compared with our previous studies on the influence of FA on the complex of Th and commercially available defatted human serum albumin (dHSA).

Vibrating-mesh nebulization of liposomes generated using an ethanol-based proliposome technology

This is the first study that evaluates the influence of the compartmental design of the micropump Aeroneb Go nebulizer and the viscosity of a proliposome hydration medium on vibrating-mesh aerosolization of liposomes. Ethanol-based proliposomes comprising soya phosphatidylcholine and cholesterol (1:1 mole ratio) were hydrated by using isotonic NaCl (0.9%) or sucrose (9.25%) solutions to generate liposomes that entrapped approximately 61% of the hydrophilic drug, salbutamol sulphate. Liposomes were aerosolized by the nebulizer to a two-stage impinger. For both formulations, the aerosol mass output was higher than the phospholipid output, indicating some accumulation of large liposomes or liposome aggregate within the nebulizer. Using NaCl (0.9%) solution as the dispersion medium, aerosol droplet size was much smaller and aerosol mass and phospholipid outputs were higher. This was attributed to the lower viscosity of the NaCl solution, resulting in a reduced retention of the aerosols in the "trap" of the nebulizer. For the entrapped salbutamol sulphate, although the "fine particle fraction" was relatively high (57.44%), size reduction of the liposomes during nebulization caused marked losses of the drug originally entrapped. Overall, liposomes generated from proliposomes when using this nebulizer showed high nebulization output and small droplet size. However, further work is required to reduce the losses of the originally entrapped drug from liposomes.

Emerging molecular targets for the treatment of asthma

Current therapeutic approaches for the treatment of asthma have limitations in their ability to target all the features of the disease. Indeed, existing pharmacological asthma therapies are based on decades old strategies that were developed prior to the rapid growth in knowledge stemming from cell and molecular biology in the past decade. Thus, there is an unmet need for developing new drugs to target these features along with improved efficacy and safety. In the present review, the limitations of prevalent pharmacological asthma therapy are discussed briefly, and some explanations are suggested as to why new therapeutic targets are required to treat asthma, and finally directions for novel asthma therapies are proposed.

Molecular mechanisms for the persistent bronchodilatory effect of the beta 2-adrenoceptor agonist salmeterol

BACKGROUND

Beta(2)-adrenoceptor agonists are effective bronchodilators. In vitro studies demonstrated long-lasting airway smooth muscle relaxation by salmeterol after washout, the quick disappearance of this effect in presence of antagonists and its recovery after antagonist removal. Current explanations invoke salmeterol accumulation in the membrane ('diffusion microkinetic' model) or the existence of salmeterol-binding 'exosites'. An alternative model based on 'rebinding' of a dissociated ligand to the receptor molecules also produces an apparent decrease in the ligand's dissociation rate in the absence of competing ligands. PURPOSE AND APPROACH: Computer-assisted simulations were performed to follow the receptor-occupation by a salmeterol-like ligand and a competing ligand as a function of time. The aptness of the models to describe the above in vitro findings was evaluated.

KEY RESULTS

The 'diffusion microkinetic' model is sufficient to explain a long-lasting beta(2)-adrenoceptor stimulation and reassertion as long as the membrane harbors a high concentration of the agonist. At lower concentration, 'rebinding' and, in second place, 'exosite' binding are likely to become operational.

CONCLUSIONS AND IMPLICATIONS

The 'rebinding' and 'exosite' binding mechanisms take place at a sub-cellular/molecular scale. Pending their demonstration by experiments on appropriate, simple models such as intact cells or membranes thereof, these mechanisms remain hypothetical in the case of salmeterol. Airway smooth muscle contraction could also be governed by additional mechanisms that are particular to this macroscopic approach.

Elevated exhaled nitric oxide (NO) in asymptomatic asthmatics taking bronchodilators on demand with controlled body composition

OBJECTIVE

Fractional Exhaled Nitric Oxide (FENO) is a recently introduced non invasive marker to measure inflammation and oxidative stress in the lung. This study aimed to measure FENO in Saudi asthmatic adult patients who had mild to moderate persistent asthma, on inhaled short-acting? 2 agonists and compared them to healthy individuals matched for body composition without any evidence of obstructive airway disease.

METHODS

As per selection criteria 61 subjects were selected. 30 subjects were known asthmatic and 31 were healthy individuals matched for age, height, weight, BMI and body composition. Forced expiratory volume in 1 s (FEV1), FVC, FEV1/ FVC, PEF, FEF25, FEF50 and FEF75 were measured by standard methods. FENO measurements were performed according to the ATS (American Thoracic Society) recommendations.

RESULTS

Ventillatory function parameters FEV1 (p = 0.0020), FVC (p = 0.0030), PEF (p = 0.0121), FEF25 (p = 0.0241), FEF50 (p = 0.0240) and FEF75 (p = 0.1824) were significantly lower in asthmatic subjects compared to matched healthy control group. FENO was significantly higher (82.51 +/- 39.26) in asthmatic subjects compared to control group (23.03 +/- 8.56) p < 0.0000)

CONCLUSION

FENO levels are increased in patients with bronchial asthma with mild to moderate symptoms taking bronchodilators on demand only. It may be suggestive of the need for more accurate evaluation and early intervention with anti inflammatory drugs in a significant proportion of these patients.

Structural evaluation of the glucuronides of morphine and formoterol using chemical derivatization with 1,2-dimethylimidazole-4-sulfonyl chloride and liquid chromatography/ion trap mass spectrometry

For the first time chemical derivatization of isomeric drug glucuronides with 1,2-dimethylimidazole-4-sulfonyl chloride (DMISC) has been successfully applied as a tool for determining the site of conjugation. This provides a way to differentiate between glucuronide isomers containing aliphatic and phenolic hydroxyl groups. The analyses were performed with liquid chromatography/electrospray ion trap mass spectrometry (LC/ESI-MSn). DMISC has previously been shown to react selectively with phenols in estrogens, thus improving sensitivity in ESI-MS. The model compounds selected for this study were commercially available standards of formoterol, morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G). Formoterol glucuronides were produced with an enzymatic method in house. Both formoterol and morphine possess one phenolic and one aliphatic hydroxyl group where glucuronidation could take place. The product ion mass spectra of the native morphine glucuronides were indistinguishable due to the initial neutral loss of monodehydrated glucuronic acid (176 u). However, a significant difference between the isomers was observed with DMISC derivatization, as only the form with a free phenol, M6G, gave a detectable reaction product. Formoterol formed two detectable glucuronide isomers in the enzymatic reaction. Their respective sites of conjugation could not be directly determined from the product ion spectra. Reaction with DMISC, however, gave a detectable product with only one of the isomers. Based on previous experience of the preferred DMISC reactions with phenols, and interpretation of the fragmentation pattern of the derivative, it was concluded that the reactive isomer had a free phenol, and was thus conjugated on the aliphatic chain.

An insilico approach to high altitude pulmonary edema - Molecular modeling of human beta2 adrenergic receptor and its interaction with Salmeterol & Nifedipine

Knowledge of the three-dimensional structures of protein targets from genomic data has the potential to accelerate researches pertaining to drug discovery. Human beta(2) adrenergic receptor is a G-protein-coupled receptor with seven transmembrane helices, and is important in pharmaceutical targeting on pulmonary and cardiovascular diseases. The human beta(2) adrenergic receptor has been found to play a very important role in the pathogenesis of high altitude pulmonary edema (HAPE). In the present study, a high quality of protein 3D structure has been predicted for the human beta(2) adrenergic receptor sequence with primary accession number P07550. Homologous template protein sequence with known 3D structure was identified and the template-query protein sequence validation was done by multiple sequence alignment method. The homology model was performed through Modeller and depended on the quality of the sequence alignment by BLAST, template structure and the consolidated result performed by Gene silico meta-server. The statistical verification of the generated model was evaluated by PROCHECK which revealed that the structure modeled through Modeller to be of good quality with 84.1% of residues in the most favored region. Docking studies were carried out after modeling with two well known ligands namely Salmeterol and Nifedipine, and the fitness score revealed that Salmeterol has a higher fitness score than Nifedipine. Estimation of binding affinity by X-Score revealed that Salmeterol had -10.40 binding affinity while Nifedipine showed -9.62 binding affinity. From the present study, it can be concluded that the generated model of human beta(2) adrenergic receptor can be used for further studies related to this receptor and Salmeterol was found to have a high binding affinity with human beta(2) adrenergic receptor.

[Role of measurement of nitric oxide in respiratory diseases]

Nitric oxide (NO) is a molecule with a homeostatic role in a number of physiological processes. Concerning respiratory diseases, exhaled nitric oxide (FE(NO)) is a marker of airway inflammation, and its measurement can be easily performed. To date, a large number of publications defined the performances of FE(NO). Studies on asthma attributed to FE(NO) an important role in diagnosis and especially in monitoring the effects of anti-inflammatory treatment, which label it as an "inflammometer" to be used as a guide in therapy algorithms. Less consistent results were thus far obtained in chronic obstructive lung disease, in which FE(NO) levels seem usually higher than in healthy subjects but lower than in asthma, unless an eosinophil inflammation is present, and in rhinosinusitis, where the levels of nasal NO (nNO) are low, probably because of a reduced NO flow into the nose due to mucosal swelling, while they increase after an effective treatment. Among other respiratory disorders, such as cystic fibrosis and primary ciliary dyskinesia, nNO levels are particularly low in the latter (possibly for the trapping and altered NO metabolism caused by dense secretions, and by decreased NO synthase activity) and suggest nNO as a good screening tool for such disease.

Hydrogen sulfide causes relaxation in mouse bronchial smooth muscle

We investigated the effects of NaHS, a hydrogen sulfide (H(2)S) donor, on the tension of isolated mouse and guinea-pig bronchial rings. NaHS at 0.01 - 10 mM had no effect on the tone of those preparations without precontraction. When the preparation was precontracted with carbachol, NaHS at 0.1 - 3 mM strongly relaxed the mouse rings, but produced only slight relaxation in the guinea-pig rings. The NaHS-induced relaxation in the mouse bronchus was resistant to inhibitors of ATP-sensitive K(+) channels, soluble guanylyl cyclase, cyclooxygenase (COX)-1 or COX-2, and antagonists of tachykinin receptors. Thus, NaHS evokes bronchodilation in mice, suggesting a possible role for H(2)S in the respiratory system.

[New insight into nitric oxide involvement in regulation of airways smooth muscle tone]

All three isoforms of NO synthases (NOS) were localised in the lung and are involved in regulation of airways and pulmonary vessels smooth muscle tone and inflammatory response. The participation of nitric oxide in the regulation of airways smooth muscle has not been understood yet.

MATERIAL AND METHOD

We studied age-related variation of NO secretion on three lots of bronchi rats: young (4-6 weeks), adults (2-3 months), old (12-14 months). The implied of NO synthesis on airways smooth muscle tone was indirectly investigated by blocking NOS with N(omega)-nitro-L-arginine methyl ester (L-NAME).

RESULTS

Pre-treatment of isolated bronchi rings with 0.1 mM L-NAME amplified both tonic contractions induced by cumulative doses of acetylcholine (0.1 nM - 1mM) and various doses of angiotensin II (10 nM - 10 eM). L-NAME actions were lower on old than young rats: at least two times for ACh and three times for Ang II. These results suggest that NO actions decrease with age. Decrease of NO activity on airways was described in pathological states like asthma.

CONCLUSIONS

Decrease of NO activity would generate increase of airway smooth muscle tone and would explain partially aging changes on airway reactivity.

Solid lipid microparticles as a sustained release system for pulmonary drug delivery

The controlled release of drugs for pulmonary delivery is a research field which has been so far rather unexploited but is currently becoming increasingly attractive. The introduction part of this research article first details the potential advantages of solid lipid microparticles (SLMs) as drug carrier compared to liposomes and polymeric microspheres. The aim of this work is to use SLMs to impart a sustained release profile to a model drug, salbutamol acetonide (SA). SA was synthesized from salbutamol in order to increase the lipophilicity of this molecule and thereby to increase its incorporation efficiency into SLMs. SA-loaded SLMs were then produced by a hot emulsion technique followed by high-shear homogenisation and the manufacturing parameters were optimized using the experimental design methodology in order to reach a suitable particle size for pulmonary administration. Scanning electron micrographs showed that SLMs are spherical, have a smooth surface and that SA crystallizes outside of the particles when the drug loading is higher than 20%. This was confirmed by X-ray diffraction. SA in vitro release study from SLMs showed that the release rate increased with SA loading but remained in every case lower than the dissolution rate of pure SA.

CYP2A13 metabolizes the substrates of human CYP1A2, phenacetin, and theophylline

Human cytochrome CYP2A13 shows overlapping substrate specificity with CYP2A6, catalyzing the metabolism of coumarin, nicotine, cotinine, and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone. Recently, it was found that CYP2A13 could catalyze the metabolic activations of 4-aminobiphenyl and aflatoxin B(1), which are known to be catalyzed by human CYP1A2. In the present study, we investigated the substrate specificity of CYP2A13. It was shown that CYP2A13 could catalyze ethoxyresorufin O-deethylation, methoxyresorufin O-demethylation, and phenacetin O-deethylation, which are used as marker activities for human CYP1A2. Although the intrinsic clearances (V(max)/K(m)) of the two former reactions by CYP2A13 were much lower than that of CYP1A2, the value of the last reaction by CYP2A13 was 2-fold higher than that of CYP1A2. Of particular interest was that CYP2A13 has higher affinity toward phenacetin than CYP1A2. In contrast, CYP2A6 hardly catalyzed these reactions, although the amino acid identity with CYP2A13 is as high as 93.5%. Furthermore, we found that CYP2A13 can catalyze theophylline 8-hydroxylation and 3-demethylation, which are known to be mainly catalyzed by human CYP1A2, although the intrinsic clearances were approximately one-tenth that of CYP1A2. CYP2A13 would not contribute to the systemic clearance of these drugs because CYP2A13 is hardly expressed in human liver. However, it may play a role in metabolism in local tissues such as lung or trachea. In conclusion, the results of the present study could extend our understanding of the substrate specificity of CYP2A13.

Pharmacogenomics of beta2-agonist: key focus on signaling pathways

Asthma is one of the most common respiratory diseases, where inhalation and exhalation are obstructed due to narrowing of the airways by broncho-constriction or by inflammation. Among all the available anti-asthma therapies, beta2-agonists are the most effective bronchodilators available, and give rapid relief of asthma symptoms. Evidence suggests that the degree of beta2-agonist response varies greatly between patients and genetic factors have a major role in it. Despite several studies on the beta2-agonist pharmacogenetics, significant gaps in knowledge still remain and need to be resolved before the pharmacotyping of beta2-agonist responsiveness comes to clinical practice. As we know, beta2-agonists show their influence by targeting beta2-adrenergic receptors, leading to the activation of beta2-adrenergic receptors and its downstream cascade. Signaling through beta2-adrenergic receptors mediates numerous airway functions by regulating broncho-constriction and dilation pathways. Therefore, it is an important prerequisite to understand these pathways, which will assist in defining the variability in therapeutic responses for beta2-agonists. Owing to the complexity of the action of a beta2-agonist and its therapeutic response, a broader genomics approach will help in optimizing therapy for the individual patient. This might be achieved by considering and focusing on receptor/s at which the drug binds directly, signal transduction cascades or downstream proteins and proteins involved in the relaxation and constriction of the airway smooth muscle. Considering that a drug response may involve a large number of proteins, it seems unlikely that a single polymorphism or haplotype in a single gene would explain a high degree of drug response variability in a consistent fashion. Thus, it shows that a polygenic approach will be more appropriate. In order to follow this, the mode of action of the beta2-agonist and its downstream signaling cascade should essentially be assessed to resolve the beta2-agonist enigma.

Variation in the Pulmonary Hypertensive Responsiveness of Broilers to Lipopolysaccharide and Innate Variation in Nitric Oxide Production by Mononuclear Cells

Variability among broilers in their pulmonary hypertensive (PH) responsiveness to lipopolysaccharide (LPS) appears to reflect innate variation in the types or proportions of vasodilators and vasoconstrictors released by leukocytes and endothelial cells. Two experiments were designed to evaluate possible correlations between the PH responsiveness to LPS in vivo and the quantities of nitric oxide (NO; a potent pulmonary vasodilator) produced by mononuclear cells in vitro. In Experiment 1, blood samples were collected from male broilers from a base population (control group) and from survivors of a 60% lethal dose i.v. injection of cellulose microparticles (MP survivor group). In Experiment 2, blood samples were collected from male broilers from a relaxed line and from lines known to be susceptible or resistant to pulmonary hypertension syndrome. Peripheral mononuclear cells (PMNC) from each blood sample were cultured at 2 million cells per well, remained unstimulated, or were stimulated with LPS to elicit the expression of inducible NO synthase, and the 24-h production of NO was measured. In both experiments, unstimulated PMNC cultures did not produce consistently detectable levels of NO, whereas LPS-stimulated cultures produced quantities of NO that varied widely among individuals. Nitric oxide production by cultured PMNC also was evaluated by flow cytometry, demonstrating that LPS-stimulated PMNC produced substantially more NO than did unstimulated cells in all of the groups evaluated. Moreover, NO-producing PMNC were identified to be monocytes. The same broilers from which PMNC had been isolated were catheterized subsequently to record pulmonary arterial pressure, LPS was injected i.v. to assess the amplitudes of peak and postpeak PH responses, then N(omega)-nitro-L-arginine methyl ester was injected to inhibit ongoing NO production. In Experiment 1, the amplitude of the peak and postpeak PH responses to LPS were correlated with the quantity of NO produced by LPS-stimulated cultured PMNC from broilers in the control group but not for MP survivors. In Experiment 2, the postpeak PH response to LPS was correlated with the quantity of NO produced by LPS-stimulated PMNC from broilers in the relaxed line, but not in the susceptible or resistant lines. In all groups, N(omega)-nitro-L-arginine methyl ester injections triggered substantial increases in pulmonary arterial pressure (> or = 8 mm Hg), thereby revealing a significant ongoing modulation by NO of the PH response to LPS. We concluded that most of the modulatory NO generated in vivo during the acute PH response to LPS (within 60 min postinjection) likely is produced by constitutive NO synthase in the vascular endothelium. In addition, the NO produced by inducible NO synthase in PMNC appeared to have modulated the LPS-stimulated PH responses of unselected broilers having the broadest range of pulmonary vascular capacities (control broilers and relaxed line), but not in broilers whose pulmonary vascular capacities had been selected to represent the higher (MP survivors, resistant line) or lower (susceptible line) extremes of the population.

Novel concepts of neuropeptide-based drug therapy: vasoactive intestinal polypeptide and its receptors

Chronic inflammatory airway diseases such as bronchial asthma or chronic obstructive pulmonary disease (COPD) are major contributors to the global burden of disease. Although inflammatory cells play the central role in the pathogenesis of the diseases, recent observations indicate that also resident respiratory cells represent important targets for pulmonary drug development. Especially targeting airway neuromediators offers a possible mechanism by which respiratory diseases may be treated in the future. Among numerous peptide mediators such as tachykinins, calcitonin gene-related peptide, neurotrophins or opioids, vasoactive intestinal polypeptide (VIP) is one of the most abundant molecules found in the respiratory tract. In human airways, it influences many respiratory functions via the receptors VPAC1, VPAC2 and PAC1. VIP-expressing nerve fibers are present in the tracheobronchial smooth muscle layer, submucosal glands and in the walls of pulmonary and bronchial arteries and veins. Next to its strong bronchodilator effects, VIP potently relaxes pulmonary vessels, and plays a pivotal role in the mediation of immune mechanisms. A therapy utilizing the respiratory effects of VIP would offer potential benefits in the treatment of obstructive and inflammatory diseases and long acting VIP-based synthetic non-peptide compounds may represent a novel target for drug development.

Synthesis and biological evaluation of 1,2,4-triazinylphenylalkylthiazolecarboxylic acid esters as cytokine-inhibiting antedrugs with strong bronchodilating effects in an animal model of asthma

The influx of leukocytes (eosinophils, lymphocytes, and monocytes) into the airways and their production of proinflammatory cytokines contribute to the severity of allergic asthma. We describe here the synthesis and pharmacological evaluation of a series of triazinylphenylalkylthiazolecarboxylic acid esters that were designed to act as lung-specific antedrugs and inhibitors of the production of interleukin (IL)-5, a primary eosinophil-activating and proinflammatory cytokine. Closer examination of the hydroxypropyl ester, 15, indicated its high metabolic stability (t(1/2) > 240 min) in human lung S9 fraction but rapid conversion (t(1/2) = 15 min) into the pharmacologically inactive carboxylic acid by human liver preparations. In stimulated human whole blood cultures, 15 reduced not only the production of IL-5 (IC(50) = 78 nM) but also the biosynthesis of the monocyte chemotactic proteins MCP-1 (IC(50) = 220 nM), MCP-2 (IC(50) = 580 nM), and MCP-3 (IC(50) = 80 nM). In vivo, intratracheal administration of 15 (6 mg/animal) to allergic sheep, either before (-4 h) or after (+1.5 h) the pulmonary allergen challenge, completely abrogated the late-phase airway response and reduced the bronchial hyperreactivity to inhaled carbachol.

New drugs for asthma

Asthma is a major and increasing global health problem and, despite major advances in therapy, many patients' symptoms are not adequately controlled. Treatment with combination inhalers, which contain a corticosteroid and long-acting beta(2) adrenoceptor agonist, is the most effective current therapy. There is therefore a search for new therapies, particularly safe and effective oral treatments and those that are more efficacious in severe asthma. New therapies in development include mediator antagonists and inhibitors of cytokines, although these therapies might be too specific to be very effective. New anti-inflammatory therapies include corticosteroids and inhibitors of phosphodiesterase-4, p38 mitogen-activated protein kinase and nuclear factor-kappaB. The prospects for a curative treatment are on the horizon.

Inhaled budesonide induced Cushing's syndrome in cystic fibrosis patients, due to drug inhibition of cytochrome P450

Two CF patients developed Cushing's syndrome during administration of inhaled budesonide (400 microg/d) with oral itraconazole in one and with clarithromycin in the other patient. Clinical features appeared respectively after 2 and 6 weeks of drug co-administration, with prolonged adrenal suppression, and a slow recovery after ceasing the drugs. Inhibitors of the cytochrome P450 interfere with the metabolism of corticosteroids. Combination of these drugs even with moderate doses of budesonide should be closely monitored.

Effects of inhaled fluticasone propionate in children less than 2 years old with recurrent wheezing

Our objective was to evaluate the efficacy and safety of two doses of fluticasone propionate (FP) in young children with recurrent wheezing and risk factors for asthma. Our study design was a randomized, double-blind, placebo-controlled comparison of inhaled FP 50 mcg twice daily (FP 100) and 125 mcg twice daily (FP 250), for 6 months. Outcome measures included number of wheezing episodes, days on albuterol, height standard deviation score (height SDS), osteocalcin (OC), bone alkaline phosphatase fraction (AKP), insulin-like growth factor-binding protein 3 (IGFBP-3), and serum levels of cortisol (SC). Our subjects were 30 patients, aged 7-24 months. Mean wheezing episodes were 6.0 +/- 1.9, 1.9 +/- 1.9, and 2.8 +/- 1.2; mean days of albuterol use were 24.3 +/- 1.3, 6.5 +/- 0.8, and 9.1 +/- 0.8, per patient for placebo, FP100, and FP250 groups, respectively. There was a significant reduction in clinical outcome in the two FP groups compared to placebo (P < 0.01). No significant correlations were found between FP dosage and height SDS, OC, AKP, IGFBP-3, and SC. In conclusion, in young children with asthmatic symptoms, FP at 50 and 125 mcg b.i.d. for 6 months significantly improved respiratory symptoms without causing significant side effects on growth and bone metabolism.

Budesonide fatty-acid esterification: a novel mechanism prolonging binding to airway tissue. Review of available data

AIMS

Evidence is accumulating that budesonide (BUD) forms intracellular esters in airways. which may affect both duration of action and therapeutic ratio of this drug. The aim of the present paper is to review the preclinical and human experimental evidence supporting the esterification of BUD, and to discuss the clinical implications this may have on asthma and rhinitis treatment.

RESULTS

After inhalation, intact BUD binds primarily to available steroid receptors, and mainly excess (unbound) BUD is esterified. Esterification of BUD is a rapid process: within 20 minutes of inhalation in the rat of radiolabeled BUD, approximately 80% of radioactivity within the trachea and main bronchi was associated with BUD esters, primarily BUD oleate. After 4 hours, the proportion of BUD esters/total cellular BUD was typically 40 to 50% for lung, 70 to 90% for trachea, and only 10 to 15% for peripheral muscle. Comparative in vitro and in vivo studies have shown that esterification prolongs BUD's anti-inflammatory activity longer than that of corticosteroids that can not form esters. Clinical studies have confirmed the prolonged presence of BUD esters, as well as intact BUD, in human airway tissues: 6 hours postdosing, nasal biopsy concentrations of intact BUD were >10-fold greater than those of fluticasone propionate and at 24 hours BUD was detectable in threefold more biopsies than fluticasone propionate. The impact of esterification on airway selectivity of BUD has also been demonstrated in vivo and using pharmacokinetic/pharmacodynamic models.

CONCLUSIONS

BUD is retained in airways as esters, a novel kinetic mechanism for synthetic glucocorticoids. In preclinical studies this esterification is correlated to a prolonged local tissue binding and efficacy, which is not found when the esterification is inhibited by an esterification blocker. Because less esters are formed in the systemic compartment than in airways/lung, the local benefit:systemic risk ratio may also be improved by this mechanism. BUD possesses favorable clinical properties, including its approved once-daily efficacy in asthma, which is probably in part attributable to esterification. However, a direct proof of the latter in patients requires effective and safe inhibitors of the esterification, which are not yet available. Therefore, evidence to support the therapeutic impact of esterification is still circumstantial.

Clinical pharmacokinetics of salmeterol

Salmeterol is an inhaled long-acting selective beta(2)-adrenoceptor agonist that is commercially available as the xinafoate (1-hydroxy-2-naphthoic acid) salt of the racemic mixture of the two optical isomers, (R)- and (S)-, of salmeterol. It acts locally in the lung through action on beta2 receptors. Limited data have been published on the pharmacokinetics of salmeterol. Moreover, there are no data on the extent to which inhaled salmeterol undergoes first-pass metabolism. This lack of information is most likely due to the very low plasma concentrations reached after inhalation of therapeutic doses of salmeterol and the problems in developing an analytical method that is sensitive enough to determine these concentrations. When salmeterol is inhaled, plasma concentrations of the drug often cannot be detected, even at 30 minutes after administration of therapeutic doses. Larger inhaled doses give approximately proportionally increased blood concentrations. Plasma salmeterol concentrations of 0.1 to 0.2 and 1 to 2 microg/L have been attained in healthy volunteers about 5 to 15 minutes after inhalation of a single dose of 50 and 400 microg, respectively. In patients who inhaled salmeterol 50microg twice daily for 10 months, a second peak concentration of 0.07 to 0.2 microg/L occurred 45 to 90 minutes after inhalation, probably because of the gastrointestinal absorption of the swallowed drug. Salmeterol xinafoate dissociates in solution to salmeterol and 1-hydroxy-2-naphthoic acid. These two compounds are then absorbed, distributed, metabolised and excreted independently. The xinafoate moiety has no apparent pharmacological activity, is highly protein bound (>99%), largely to albumin, and has a long elimination half-life of about 12 to 15 days in healthy individuals. For this reason, it accumulates in plasma during repeated administration, with steady-state concentrations reaching about 80 to 90 microg/L in patients treated with salmeterol 50microg twice daily for several months. The cytochrome P450 (CYP) isoform 3A4 is responsible for aliphatic oxidation of salmeterol base, which is extensively metabolised by hydroxylation with the major metabolite being alpha-hydroxysalmeterol, with subsequent elimination predominantly in the faeces. It has been demonstrated that 57.4% of administered radioactivity is recovered in the faeces and 23% in the urine; most is recovered between 24 and 72 hours after administration. Unchanged salmeterol accounts for <5% of the excreted dose in the urine. Since the therapeutic dose of salmeterol is very low, it is unlikely that any clinically relevant interactions will be observed as a consequence of the coadministration of salmeterol and other drugs, such as fluticasone propionate, that are metabolised by CYP3A. All the available data clearly show that at the recommended doses of salmeterol, systemic concentrations are low or even undetectable. This is an important point, because it has been demonstrated that the systemic effects of salmeterol are more likely to occur with higher doses, which lead to approximately proportionally increased blood concentrations.

Development status of second generation PDE4 inhibitors for asthma and COPD: the story so far

The beginning of the 1990s saw the synthesis and evaluation of orally-active, second generation phosphodiesterase (PDE) inhibitors that have high specificity for the PDE4 subtype. In vitro and in vivo studies established that this class of compounds suppresses the activity of many pro-inflammatory and immune cells indicating that they may be effective in the treatment of airway inflammatory diseases. In this article we review the development status of the most advanced and extensively studied PDE4 inhibitors for asthma and chronic obstructive pulmonary disease.

Differential adrenomedullin release and endothelin receptor expression in distinct subpopulations of human airway smooth-muscle cells

Although adrenomedullin (ADM) is implicated in the control of airway tone, regulation of ADM release from airway smooth-muscle cells (ASMCs) has not been explored. Preliminary experiments have indicated that human ASMC populations were heterogeneous in their rate of ADM release and expression of endothelin (ET)(A) and ET(B) receptors. We isolated these phenotypically distinct ASMCs from explants derived from the same airway segment. ASMCs possessing exclusively ET(A) receptors appeared smaller and proliferated faster than ET(A)/ET(B) isolates. Macroautoradiographic analysis confirmed the presence of both receptors in human bronchi. ADM release and messenger RNA expression was greater in ET(A)/ET(B) isolates compared with ET(A) isolates. No measurable ET release was detected from ASMCs. Exogenous ET-1 (1 to 100 nM) more potently stimulated the release of ADM from ET(A)/ET(B) compared with ET(A) isolates. In addition, ET-3 (1 to 100 nM) stimulated ADM release only from ET(A)/ET(B) isolates, implicating the ET(B) receptor in this response. Exogenous ET-1 potentiated platelet- derived growth factor-stimulated [3H]thymidine uptake in ET(A)/ ET(B) but not ET(A) isolates. ET-3 did not affect [3H]thymidine uptake in either cell type. Possession of ET(A)/ET(B) receptors is associated with higher rates of ADM release and slower proliferation, but a capacity for ET-1 stimulated DNA synthesis via ET(A) receptors. These results support a paracrine role for the regulation of ADM release predominantly via the ET(B) receptor in human ASMCs.

Cilomilast: a second generation phosphodiesterase 4 inhibitor for asthma and chronic obstructive pulmonary disease

Cilomilast (Ariflo, SB-207499) is an orally-active, second generation phosphodiesterase (PDE) inhibitor that may be effective in the treatment of asthma and chronic obstructive pulmonary disease (COPD). It has high selectivity for the cyclic AMP-specific, or PDE4, isoenzyme that predominates in pro-inflammatory and immune cells and is ten-fold more selective for PDE4D than for PDE4A, B and C. In vitro, cilomilast suppresses the activity of many pro-inflammatory and immune cells that have been implicated in the pathogenesis of asthma and COPD and is highly active in animal models of these diseases. Cilomilast demonstrates a markedly improved side effect profile over the archetypal PDE4 inhibitor, rolipram, which has been attributed to its inability to discriminate between the high affinity rolipram binding site and the catalytic domain of the enzyme, and the fact that it is negatively charged which at physiological pH should limit its penetration in to the CNS. In humans cilomilast is rapidly absorbed after oral administration, providing dose-proportional systemic exposure up to 4 mg, completely bioavailable, has a half-life of approximately 7 h and is subject to negligible first pass hepatic metabolism. Cilomilast is extensively metabolised with decyclopentylation, acyl glucuronidation and 3-hydroxylation of the cyclopentyl ring representing the principal routes. Most of the drug is excreted in the urine (approximately 90%) and faeces (6 - 7%) with unchanged cilomilast accounting for less than 1% of the administered dose. Cilomilast has been evaluated in Phase I, Phase II and Phase III trials and dose-response experiments have demonstrated a clinically significant increase in lung function and a perceived improvement in quality of life in patients with COPD. Trials of cilomilast in asthma have been less impressive although a trend towards improved lung function has been reported. Cilomilast is safe and well-tolerated at doses up to 15 mg in both short- and long-term dosing trials with a low incidence of adverse effects. No evidence for drug-drug interactions with commonly prescribed medications for COPD and asthma such as digoxin, corticosteroids, salbutamol, theophylline or warfarin has been found. Moreover, the pharmacokinetics of cilomilast are essentially the same in smokers and non-smokers, indicating that no dose adjustments of cilomilast will be required in patients with COPD. Thus, cilomilast displays a promising clinical profile in the treatment of inflammatory airway diseases, in particular COPD and the results of further Phase III trials are awaited with interest.

[Bioequivalence of bambuteral and its metabolites terbutaline after oral bambuteral tablet in healthy volunteers by HPLC/MS]

AIM

To study bioequivalence of bambuteral and its metablites terbutaline in 20 healthy male volunteers.

METHODS

A single oral dose of domestic or imported bambuteral tablet was given according to a randomized 2-way cross-over design. The plasma bambuteral and terbutaline concentrations were determined by HPLC/MS.

RESULTS

The pharmacokinetic parameters of domestic and imported bambuteral: AUC0-t were (52 +/- 21) microgram.h.L-1 and (51 +/- 20) microgram.h.L-1, Tmax were (2.9 +/- 0.9) h and (2.6 +/- 0.7) h, Cmax were (6.0 +/- 2.6) microgram.L-1 and (6.2 +/- 2.9) microgram.L-1, T1/2Ke were (11.2 +/- 2.3) h and (11.2 +/- 1.9) h, respectively; terbutaline: AUC0-t were (191 +/- 30) microgram.h.L-1 and (197 +/- 37) microgram.h.L-1; Tmax were (4.2 +/- 1.0) h and (4.2 +/- 1.0) h; Cmax were (10 +/- 5) microgram.L-1 and (10 +/- 4) microgram.L-1; T1/2Ke were (20 +/- 3) h and (21 +/- 4) h, respectively. The bioavaiability of the domestics was 102% +/- 8% (bambuteral) and 100% +/- 12% (terbutaline).

CONCLUSION

The results demonstrate that the two forms of bambuteral and terbutaline were bioequivalent by analysis of variance, two-one sided test and 90% confidential limit.

Tiotropium (Spiriva): mechanistical considerations and clinical profile in obstructive lung disease

Inhaled antimuscarinics, often called anticholinergics in clinical medicine, are established as first line bronchodilators in COPD. Tiotropium has been developed as a new generation antimuscarinic following ipratropium. Tiotropium is a specific, highly potent antimuscarinic, demonstrating very slow dissociation from muscarinic receptors. Dissociation from M2-receptors is faster than from M3 or M1, which in functional in vitro studies, appeared as kinetic receptor subtype selectivity of M3 and M1 over M2. The high potency and slow receptor dissociation found its clinical correlate in significant and long lasting bronchodilatation and bronchoprotection in patients with COPD and asthma. In asthma, protection against methacholine challenge exceeded the study period of 48 hours. In COPD, bronchodilatation of about 80% of the plateau was demonstrated after the first dose. Following chronic once daily inhalation for 28 days, the improvement in pulmonary function was sustained and there was a further increase in peak effects, but more importantly a rising baseline, achieving steady state within 2 weeks. Tiotropium achieves very stable long lasting effects with comparatively low variation of bronchodilatation between peak and trough (the level before the next administration). Stable 24 hour effectiveness profiles the compound as the first once daily bronchodilator. Clinical correlates of kinetic receptor subtype selective blockade remain to be shown. Plasma levels of tiotropium at trough are in the low pg/ml range and are unlikely to explain the sustained effectiveness in the airways. Slow dissociation from muscarinic receptors is likely to be responsible for the long duration of action.

A potent, long-acting, orally active (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamide: novel muscarinic M(3) receptor antagonist with high selectivity for M(3) over M(2) receptors

A novel series of (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamides was designed and synthesized based on the structure and biological profiles of an active metabolite 2 of our prototype muscarinic M(3) receptor selective antagonist 1, to develop a potent, long-acting, orally active M(3) antagonist for the treatment of urinary tract disorders, irritable bowel syndrome, and respiratory disorders. Investigation of (2R)-2-[(1R)-3, 3-difluorocyclopentyl]-2-hydroxy-2-phenylacetamides containing a phenyl or heterocyclic ring as the piperidinyl side chain in place of the 4-methyl-3-pentenyl moiety of 15a revealed that this acid moiety was a versatile template for improving the selectivity for M(3) over M(2) receptors in comparison with the corresponding cyclopentylphenylacetic acid group. However, since the in vitro metabolic stability of these analogues was insufficient compared with that of 2, further derivatization was performed by introducing an appropriate hydrophilic group into the phenyl or 2-pyridyl ring. Thus, the 1-(6-aminopyridin-2-ylmethyl)piperidine analogue 15y exhibiting 190-fold selectivity for M(3) receptors (K(i) = 2.8 nM) over M(2) receptors (K(i) = 530 nM) in a human binding assay and good in vitro metabolic stability in dog and human hepatic microsomes was identified. This compound has excellent oral activity at 4 h after oral dosing (1 mg/kg), inhibiting methacholine-induced bronchoconstriction in dogs, and may be useful in clinical situations in which M(3) over M(2) selectivity is desirable.

Effect of dissolution fluid and presence of hog intestinal barrier on the dissolution of theophylline from bioadhesive granules

The effect of dissolution fluid and the presence of a natural barrier (hog intestine) on the release of theophylline from some bioadhesive granules is presented. A higher quantity of the drug was released in simulated intestinal fluid (SIF) than O. IN HCl. When a hog intestine was used as the diffusion barrier, the availability of the drug through the barrier into the sink solution was low, ranging from 20-35%.

Molecular interactions and metal binding in the theophylline-binding core of an RNA aptamer

An RNA aptamer containing a 15-nt binding site shows high affinity and specificity for the bronchodilator theophylline. A variety of base modifications or 2' deoxyribose substitutions in binding-site residues were tested for theophyllinebinding affinity and the results were compared with the previously determined three-dimensional structure of the RNA-theophylline complex. The RNA-theophylline complex contains a U6-A28-U23 base triple, and disruption of this A28-U23 Hoogsteen-pair by a 7-deaza, 2'-deoxy A28 mutant reduces theophylline binding >45-fold at 25 degrees C. U24 is part of a U-turn in the core of the RNA, and disruption of this U-turn motif by a 2'-deoxy substitution of U24 also reduces theophylline binding by >90-fold. Several mutations outside the "conserved core" of the RNA aptamer showed reduced binding affinity, and these effects could be rationalized by comparison with the three-dimensional structure of the complex. Divalent ions are absolutely required for high-affinity theophylline binding. High-affinity binding was observed with 5 mM Mg2+, Mn2+, or Co2+ ions, whereas little or no significant binding was observed for other divalent or lanthanide ions. A metal-binding site in the core of the complex was revealed by paramagnetic Mn2+-induced broadening of specific RNA resonances in the NMR spectra. When caffeine is added to the aptamer in tenfold excess, the NMR spectra show no evidence for binding in the conserved core and instead the drug stacks on the terminal helix. The lack of interaction between caffeine and the theophylline-binding site emphasizes the extreme molecular discrimination of this RNA aptamer.

Higher incidence of elevated body temperature or increased C-reactive protein level in asthmatic children showing transient reduction of theophylline metabolism

The authors investigated whether theophylline metabolism is decreased in asthmatic patients and what condition may be related to its reduction. Fifty-two children with asthma were given 15 mg/kg/day aminophylline intravenously at a constant rate. Blood and spot urine samples were collected at 24 hours, 48 hours, and 72 hours after beginning infusion. The ratio of plasma theophylline concentration at 72 hours to that at 24 hours (C72h/C24h) varied from 0.42 to 1.51 (average 0.894). Plasma theophylline concentration of patients with lower C72h/C24h than average reduced significantly, while the concentration of those with higher C72h/C24h remained unchanged. The urinary ratio of the sum of the metabolites to theophylline was significantly increased in the patients with the lower ratio. Among the demographic characteristics examined, significant difference was found only in the incidence of patients with C-reactive protein (CRP) of 0.5 mg/dl or greater or patients with a fever of 37.5 degrees C or greater when admitted. Acute febrile illness accompanied by increased CRP level may affect theophylline metabolism.

Prodrug to probe solution HFA pMDI formulation and pulmonary esterase activity

A novel salbutamol prodrug was synthesised. Solubility in HFA-134a and susceptibility to rat lung homogenate, blood and plasma esterase enzymes were investigated. Whereas salbutamol had a very low solubility in HFA-134a, the prodrug was found to be miscible in all proportions. In lung homogenate, the prodrug hydrolysed with a half-life of 45 min, re-generating approximately 17% of expected salbutamol after 8 h incubation. The use of a solution pMDI for pulmonary delivery of the salbutamol prodrug is predicted to result in liberation of salbutamol in the lungs following in vivo hydrolysis by lung esterases.

Enhanced theophylline metabolism in patients with bronchial asthma at age 4 and under

The plasma levels of theophylline (TP) and its metabolites were measured in patients with bronchial asthma who were treated with a slow-release preparation of TP. The ratios of the plasma levels of these metabolites to TP levels in the group aged 1-4 years were larger than those in the group aged 5 years and older, suggesting enhanced activity of drug-metabolizing enzymes during infancy.

J-104129, a novel muscarinic M3 receptor antagonist with high selectivity for M3 over M2 receptors

A new class of 4-acetamidopiperidine derivatives has been synthesized and investigated for human muscarinic receptor subtype selectivity. Introduction of a hydrocarbon chain of appropriate length into the piperidine nitrogen of the racemic N-(piperidin-4-yl)-2-cyclobutyl-2-hydroxy-2-phenylacetamide platform conferred up to 70-fold selectivity for human muscarinic M3 receptors over M2 receptors. Subsequent synthetic derivatizations resulted in highly potent M3 receptor antagonists with selectivity greater than two orders of magnitude for M3 over M2 receptors, from which the analogue 4r was selected. Preparation of both enantiomers of 4r led to the identification of (2R)-N-[1-(4-methyl-3-pentenyl)piperidin-4-yl]-2-cyclopentyl-2-hyd roxy-2-phenylacetamide (J-104129, (R)-4r), which exhibited 120-fold selectivity for M3 receptors (Ki = 4.2 nM) over M2 receptors (Ki = 490 nM). In isolated rat trachea, (R)-4r potently and specifically antagonized acetylcholine (ACh)-induced responses with a K(B) value of 3.3 nM. The highly subtype-selective profile was also seen in isolated rat tissue assays (50-fold) and in anesthetized rats (> 250-fold). Oral administration of J-104129 ((R)-4r) antagonized ACh-induced bronchoconstriction with an ED50 value of 0.58 mg/kg in rats. Thus, J-104129 ((R)-4r) may effectively facilitate bronchodilation in the treatment of obstructive airway disease.

Contrasting properties of albuterol stereoisomers

Racemic albuterol is composed of an equimolar mixture of stereoisomers. For asthma therapy, (R)-albuterol is the eutomer and (S)-albuterol is the distomer. By interacting with beta(2 )-adrenoceptors, (R)-albuterol has bronchodilator, bronchoprotective, anti-edematous properties and inhibits activation of mast cells and eosinophils. (S)-albuterol does not activate beta(2 )-adrenoceptors and does not modify activation of beta(2 )-adrenoceptors by (R)-albuterol so that for many years it was presumed to be biologically inert. Recently, it has been established that regular and excessive use of racemic albuterol induces paradoxical reactions in some subjects with asthma. Because such effects cannot be accounted for by activation of beta(2 )-adrenoceptors, the pharmacologic profile of (S)-albuterol has been more carefully defined. (S)-albuterol has distinctive pharmacologic properties that are unrelated to activation of beta(2 )-adrenoceptors. Thus, (S)-albuterol intensifies bronchoconstrictor responses of sensitized guinea pigs and induces hypersensitivity of asthmatic airways; it also promotes the activation of human eosinophils in vitro. These actions of (S)-albuterol may explain why racemic albuterol can intensify allergic bronchospasm and promote eosinophil activation in asthmatic airways. The capacity of (S)-albuterol to elevate intracellular Ca(2+) would account for the paradox because this action will oppose, or even nullify, the consequences of adenylyl cyclase activation by (R)-albuterol. Because (S)-albuterol is metabolized more slowly than (R)-albuterol and is retained preferentially within the airways, paradoxical effects become more prominent during regular and excessive use of racemic albuterol. Because (S)-albuterol has detrimental effects in asthmatic airways, levalbuterol [homochiral (R)-albuterol] should have advantages over racemic albuterol in therapy for asthma.

Tiotropium bromide (Ba 679 BR), a novel long-acting muscarinic antagonist for the treatment of obstructive airways disease

Tiotropium bromide (Ba 679 BR) is a novel potent and long-lasting muscarinic antagonist that has been developed for the treatment of chronic obstructive airways disease (COPD). Binding studies with [3H]tiotropium bromide in human lung have confirmed that this is a potent muscarinic antagonist with equal affinity for M1-, M2- and M3-receptors and is approximately 10-fold more potent than ipratropium bromide. Tiotropium bromide dissociates very slowly from lung muscarinic receptors compared with ipratropium bromide. In vitro tiotropium bromide has a potent inhibitory effect against cholinergic nerve-induced contraction of guinea-pig and human airways, that has a slower onset than atropine or ipratropium bromide. After washout, however, tiotropium bromide dissociates extremely slowly compared with the dissociation of atropine and ipratropium bromide. Measurement of acetylcholine (ACh) release from guinea-pig trachea shows that tiotropium bromide, ipratropium bromide and atropine all increase ACh release on neural stimulation and that this effect is washed out equally quickly for the three antagonists. This confirms binding studies to transfected human muscarinic receptors which suggested that tiotropium bromide dissociates slowly from M3-receptors (on airway smooth muscle) but rapidly from M2 autoreceptors (on cholinergic nerve terminals). Clinical studies with inhaled tiotropium bromide confirm that it is a potent and long-lasting bronchodilator in COPD and asthma. Furthermore, it protects against cholinergic bronchoconstriction for > 24 h. This suggests that tiotropium bromide will be a useful bronchodilator, particularly in patients with COPD, and may be suitable for daily dosing. The selectivity for M3- over M2-receptors may also confer a clinical advantage.

Nasal nitric oxide does not control basal nasal patency or acute congestion following allergen challenge in allergic rhinitis

Nasal nitric oxide (NO), a powerful vasodilator, could control the filling of nasal capacitance vessels, thus determining nasal patency and mediating the acute congestion accompanying allergen challenge. We examined the effect of topical N-nitro-L-arginine-methyl-ester (L-NAME; 100 to 200 mg), an NO synthase inhibitor, on nasal NO and on nasal patency assessed by acoustic rhinometry in 7 subjects with nasal allergy, and in 4 subjects we examined the effects of nasal allergen challenge on nasal NO before and after a short course of nasal steroid. After L-NAME, nasal NO fell to 42.1%+/-15.7% of baseline (p < .0001) with no significant change in minimal cross-sectional area. After allergen challenge, acute congestion was associated with a significant fall in nasal NO, which returned to baseline by 4 hours, when the congestion resolved. Repeat challenge after 2 weeks of nasal corticosteroid yielded similar findings. A role for NO in modulating vascular tone was not supported by the present study.

Nitrogen dioxide formation during inhaled nitric oxide therapy

BACKGROUND

Nitrogen dioxide (NO2) is a toxic by-product of inhalation therapy with nitric oxide (NO). The rate of NO2 formation during NO therapy is controversial.

METHODS

The formation of NO2 was studied under dynamic flows emulating a base case NO ventilator mixture containing 80 ppm NO in a 90% oxygen matrix. The difficulty in measuring NO2 concentrations below 2 ppm accurately was overcome by the use of tunable diode laser absorption spectroscopy.

RESULTS

Using a second-order model, the rate constant, k, for NO2 formation was determined to be (1.19 +/- 0.11) x 10(-11) ppm-2s-1, which is in basic agreement with evaluated data from atmospheric literature.

CONCLUSIONS

Inhaled NO can be delivered safely in a well-designed, continuous flow neonatal ventilatory circuit, and NO2 formation can be calculated reliably using the rate constant and circuit dwell time.

Airway synthesis of 20-hydroxyeicosatetraenoic acid: metabolism by cyclooxygenase to a bronchodilator

Rabbit airway tissue is a particularly rich source of cytochrome P-4504A protein, but very little information regarding the effect(s) of 20-hydroxyeicosatetraenoic acid (20-HETE) on bronchial tone is available. Our studies examined the response of rabbit bronchial rings to 20-HETE and the metabolism of arachidonic acid and 20-HETE from airway microsomes. 20-HETE (10(-8) to 10(-6) M) produced a concentration-dependent relaxation of bronchial rings precontracted with KCl or histamine but not with carbachol. Relaxation to 20-HETE was blocked by indomethacin or epithelium removal, consistent with the conversion of 20-HETE to a bronchial relaxant by epithelial cyclooxygenase. A cyclooxygenase product of 20-HETE also elicited relaxation of bronchial rings. [14C]arachidonic acid was converted by airway microsomes to products that comigrated with authentic 20-HETE (confirmed by gas chromatography-mass spectrometry as 19- and 20-HETE) and to unidentified polar metabolites. [3H]20-HETE was metabolized to indomethacin-inhibitable products. These data suggest that 20-HETE is an endogenous product of rabbit airway tissue and may modulate airway resistance in a cyclooxygenase-dependent manner.

Relationship between exhaled nitric oxide and childhood asthma

The purpose of the study was to determine if exhaled nitric oxide levels in children varied according to their asthmatic and atopic status. Exhaled nitric oxide was measured in a sample of 93 children attending the North West Lung Centre, Manchester, United Kingdom, for the clinical evaluation of a respiratory questionnaire being developed as a screening tool in general practice. The clinical assessment included full lung function, skin prick testing, and exercise challenge. Children were said to be asthmatic either by consensus decision of three independent consultant pediatricians, who reviewed all the clinical results except the nitric oxide measurements, or by positive exercise test. Atopic asthmatic children had higher geometric mean exhaled nitric oxide levels (consensus decision, 12.5 ppb [parts per billion] 95% CI, 8.3 to 18. 8; positive exercise test, 12.2 ppb 95% CI, 7.6 to 19.7) than did nonatopic asthmatic children (3.2 ppb 95% CI, 2.3 to 4.6; 3.2 ppb 95% CI, 2.0 to 5.0), atopic nonasthmatic children (3.8 ppb 95% CI, 2. 7 to 5.5; 5.7 ppb 95% CI, 4.1 to 8.0), or nonatopic nonasthmatic children (3.4 ppb 95% CI, 2.8 to 4.1; 3.5 ppb 95% CI, 3.0 to 4.1). Thus, exhaled nitric oxide was raised in atopic asthmatics but not in nonatopic asthmatics, and these nonatopic asthmatics had levels of exhaled nitric oxide similar to those of the nonasthmatics whether atopic or not.

Pharmacokinetics of theophylline metabolites in 8 Chinese patients

AIM

To study theophylline metabolites pharmacokinetics in patients after a therapeutic dose.

METHODS

Eight adult patients with mild bronchial asthma and normal liver function were infused aminophylline intravenously (6.6 mumol.kg-1). The plasma concentrations of theophylline and its 4 metabolites: 1,3-dimethyluric acid (DMUA), 3-methylxanthine (3-MX), 1-methyluric acid (MUA), and the intermediate 1-methylxanthine (1-MX) were monitored by HPLC throughout 24 h.

RESULTS

The plasma concentration of DMUA was the highest one among the 4 metabolites. 3-MX showed the slowest elimination rate. The plasma concentration of 1-MX throughout a 24-h period showed that there was a picking up of 1-MX (from 0.04 mumol.L-1 to 1.05 mumol.L-1) in the next morning.

CONCLUSION

The formation of DMUA was the main metabolites. During night there was an accumulation of 1-MX.