Stability of chosen beta-adrenolytic drugs of different polarity in basic environment

The stability of atenolol, acebutolol, and propranolol was investigated in sodium hydroxide solutions at concentrations of 0.1, 0.3, 0.5, and 1 M at 3 temperatures ranging from 37 to 95 degrees C. The degradation processes that occurred in drugs under investigation were described with kinetic parameters (k, t0.1, and t0.5) and energy of activation (Ea). It was found that the stability of the drugs increased toward lipophilic propranolol in the assumed experimental model. The rate constants k decreased, contrary to t0.1, t0.5, and Ea, which varied comparably to log P (partition coefficient), thus increasing from the most hydrophilic atenolol, through acebutolol of lower polarity, to the most lipophilic propranolol. The identification of degradation products was performed with the application of proton nuclear magnetic resonance spectrometry and thin-layer chromatography-densitometry and data from the literature.

Free radical destruction of beta-blockers in aqueous solution

Many pharmaceutical compounds and metabolites are currently found in surface and ground waters which indicates their ineffective removal by conventional water treatment technologies. Advanced oxidation/reduction processes (AO/ RPs) are alternatives to traditional water treatment, which utilize free radical reactions to directly degrade chemical contaminants. This study reports the absolute rate constants for reaction of three beta-blockers (atenolol, metoprolol, and propranolol) with the two major AO/RP radicals; the hydroxyl radical (*OH) and hydrated electron ((e-)aq). The bimolecular reaction rate constants for *OH are (7.05 +/- 0.27) x 10(9), (8.39 +/- 0.06) x 10(9), and (1.07 +/- 0.02) x 10(10), and for (e-)aq they are (5.91 +/- 0.21) x 10(8), (1.73 +/- 0.03) x 10(8), and (1.26 +/- 0.02) x 10(10), respectively. Transient spectra were observed for the intermediate radicals produced by hydroxyl radical reactions. In addition, preliminary degradation mechanisms and major products were elucidated using 60Co gamma-irradiation and LC-MS. These data are required for both evaluating the potential use of AO/RPs for the destruction of these compounds and for studies of their fate and transport in surface waters where radical chemistry may be important in assessing their lifetime.

S-Propranolol imprinted polymer nanoparticle-on-microsphere composite porous cellulose membrane for the enantioselectively controlled delivery of racemic propranolol

Molecularly imprinted polymer (MIP) nanoparticle-on-microspheres (NOM) selective for S-propranolol were successfully prepared using suspension polymerization involving agitation of the reaction mixture at high speed. The integration of the MIP-NOM into a self-assembled porous cellulose membrane allowed a controlled distribution and availability of the molecule recognition sites within a porous structure. The nature of the membrane-included microparticles determined the degree of porosity whilst the adherent nanoparticles provided an increased surface area enabling the composite membrane to be employed efficiently for the trans-membrane transport of the imprinted molecule. The MIP-NOM within the membrane were easily accessible for binding of the imprinted molecule and appeared to maintain high selectivity, indicating that the composite membranes may potentially provide valuable affinity matrices. In this study, the application for MIP-NOM composite cellulose membranes were investigated for their potential to act as transdermal drug delivery systems for the S-enantiomers from racemic propranolol, its ester prodrugs (cyclopropanoyl- and valeryl-propranolol) or other beta-blockers (pindolol and oxprenolol). The enantioselective release of the fluorescently active 1-pyrene-butyryl ester prodrug of S-propranolol from MIP-NOM composite membranes and its diffusion and transit across excised rat skin was monitored by confocal laser scanning microscopy. The mechanism underlying the release of S-propranolol from the MIP-NOM composite membrane was found to involve specific adsorption and mobility of this enantiomer at the binding site in the MIP-NOM as the latter undergo a transition from the dry to wet state. The proposed MIP-NOM composite membrane controlled release system may be applicable for fabrication of novel membranes with self-controllable permeability responding to the presence of target solutes.

Use of the X-ray structure of the Beta2-adrenergic receptor for drug discovery

The recently reported X-ray structure of the Beta2-adrenergic receptor, the first reported crystal structure of a ligand-mediated GPCR, is used to explore its utility in computer-aided drug design. Validations were conducted with known beta blockers. This was followed by high-throughput docking studies with proprietary and commercial databases to further validate the X-ray structure's usefulness as a design tool and to explore the potential for discovery of novel chemical classes acting as Beta2 inhibitors. Our results include the finding of ligands with traditional beta-blocker motifs as well as new motifs, thereby serving to both validate the approach and project its usefulness in the finding and design of novel compounds.

Supramolecular systems-based HPLC for chiral separation of beta-adrenergics and beta-adrenolytics in drug discovery schemes

Increasing amount of data considering polymorphism, splice variants and various affinity states of beta-adrenoceptors has resulted in a new range of opportunities for enantiopure beta-adrenergic and beta-adrenolytic drug discovery and continuous development of reliable high-throughput screening procedures enabling tissue specific pharmacological evaluation of these drugs. Design and fast pharmacological profiling of single enantiomeric molecules combining beta-adrenoceptor affinity with other pharmacophores is also still challenging ability. As the use of chiral stationary phases in HPLC has particularly benefited from results of supramolecular chemistry, this review summarises recent achievements provided by this technique in deciphering of enatiorecognition phenomena affecting pharmacological selectivity of beta-adrenergics and beta-adrenolytics and modifying the efficiency of currently proposed beta-adrenoceptor-targeted therapies. Detailed characteristic of chiral separation performance of these drugs in the range of available supramolecular HPLC systems has also been presented.

Effect of formulation parameters on the release characteristics of propranolol from asymmetric membrane coated tablets

Controlled delivery of drugs has been achieved successfully by use of asymmetric membranes. In our study, we have evaluated the influence of various preparation parameters such as concentration of the polymer, concentration of the pore former and temperature of the precipitation bath on the permeability and the release characteristics of propranolol. Propranolol tablets were prepared by direct compression and were coated with varying concentrations of cellulose acetate and glycerin. The coat was precipitated in water, maintained at various temperatures, followed by air drying of the coat. Scanning Electron Microscopy (SEM) was used to characterize the asymmetric structure of the membrane. The influence of various preparation parameters on the release of propranolol from asymmetric coated tablets was evaluated. SEM confirmed the asymmetric nature of the membrane. A zero order release of propranolol was obtained from the coated tablets of propranolol. Various preparation parameters studied significantly affected (p<0.05) the release of propranolol hydrochloride from the asymmetric membrane coated tablets and the release was independent of the pH and the rate of agitation of the dissolution medium (p>0.05). Asymmetric membranes can be successfully utilized in the controlled delivery of highly water soluble drugs like propranolol and by modifying preparation parameters like polymer concentration, pore former concentration and temperature of the precipitation bath, desired release rates can be obtained.

Stereoisomer analysis of wastewater-derived β-blockers, selective serotonin re-uptake inhibitors, and salbutamol by high-performance liquid chromatography–tandem mass spectrometry

A reversed-phase enantioselective liquid chromatography-tandem mass spectrometry (HPLC-MS-MS) method was developed to measure enantiomer fractions (EF) and concentrations of pharmaceuticals in wastewater. Enantiomer resolution of six beta-blockers (atenolol, metoprolol, nadolol, pindolol, propranolol, and sotalol) along with two selective serotonin re-uptake inhibitors (citalopram, fluoxetine) and one beta(2)-agonist (salbutamol) was achieved with the Chirobiotic V stationary phase. Analyte recovery averaged 86% in influent and 78% in effluent with limits of detection ranging from 0.2 to 7.5 ng/L. These results represent an improvement in wastewater EF measurement for atenolol, metoprolol and propranolol as well as the first EF measurements of citalopram, fluoxetine, nadolol, pindolol, salbutamol and sotalol in wastewaters. Changes in EF through treatment indicate biologically mediated stereoselective processes were likely occurring during wastewater treatment.

Role of chemical structure in stereoselective recognition of beta-blockers by cyclodextrins in capillary zone electrophoresis

Most of the beta-blocking drugs for treating diseases of the cardiovascular system are chiral aryloxy-propanolamine derivatives. Tipically, the S(-) enantiomers are more active than the R(+) enantiomers. Only some of them (for example timolol) are used as single enantiomers, the others are employed as racemates. For the determination of the enantiomeric purity of timolol European Pharmacopoeia prescribes an HPLC method using chiral stationary phase. However, the use of chiral capillary zone electrophoresis for the determination of the enantiomeric purity is of pharmaceutical interest. This study describes the application of various cyclodextrin derivatives, hydroxypropyl-beta-cyclodextrin, randomly methylated beta-cyclodextrin, sulphated beta-cyclodextrin and sulphated alpha-cyclodextrin for the stereoselective analyses of beta-blockers. Baseline separation was obtained for bopindolol, carvedilol, mepindolol, pindolol and alprenolol, while only partial separation was observed for sotalol, propranolol, oxprenolol, atenolol, bisoprolol, bupranolol, and metoprolol. The uneven molecular recognition of the enantiomers of the beta-blockers, especially of the optical isomers of labetalol and nadolol, showed the importance of the chemical nature of the separators and the analytes.

Application of Direct Crystallization for Racemic Compound Propranolol Hydrochloride

The application of direct crystallization integrating with chromatography to the resolution of a racemic compound propranolol hydrochloride was studied and the crystallization progression was clearly illustrated in terms of the diagram of solubility and metastable zone widths with different enantiomeric compositions. The solubility and metastable zone widths of propranolol hydrochloride in the mixture of methanol and isopropanol were determined using an in situ Lasentec Focused Beam Reflectance Measurement (FBRM) probe. The direct crystallizations were carried out in an automatic lab reactor (Mettler Toledo LabMax) system. The optical purity of final product crystals was examined using differential scanning calorimetry (DSC), HPLC and PXRD. The crystal size distribution and morphology were analyzed using Malvern Mastersizer and Jeol SEM. It was found that optically pure crystal product could be obtained within certain safe supersaturation limit and there was no evidence of polymorph or solvate/hydrate transformation during the crystallization process. There was no selectivity of crystal growth or nucleation between the pure enantiomer and its racemate when the solution reaches the temperature lower than saturation temperature of the racemate. Hence, the critical supersaturation control of a solution was essential to obtain pure enantiomers from a partially resolved racemate.

Estimation of carvedilol in human plasma by using HPLC-fluorescence detector and its application to pharmacokinetic study

A simple, precise and sensitive high performance liquid chromatography procedure has been developed for determination of carvedilol in human plasma. The method was developed on Lichrosphere R CN column using a mobile phase of acetonitrile/20 mM ammonium acetate buffer with 0.1% triethylamine (pH adjusted to 4.5) (40/60, v/v). The peaks were detected by using fluorescence detector (excitation wavelength 282 nm and emission wavelength 340 nm). Carvedilol and domperidone (internal standard) were extracted by liquid-liquid extraction procedure using dichloromethane. This method was specific and had a linearity range of 1-128 ng/ml with intra- and inter-day precision (%C.V.) less than 15%. The accuracy ranges from 87.3 to 100.88% and the recovery of carvedilol was 69.90%. The stability studies showed that carvedilol in human plasma was stable during short-term period for sample preparation and analysis. This method was used to assay the carvedilol in human plasma samples obtained from subjects who had been given an oral tablet of 12.5 mg carvedilol.

Are [O-methyl-11C]derivatives of ICI 89,406 beta1-adrenoceptor selective radioligands suitable for PET?

PURPOSE

Radioligand binding studies show that beta(1)-adrenoceptor (beta(1)-AR) density may be reduced in heart disease without down regulation of beta(2)-ARs. Radioligands are available for measuring total beta-AR density non-invasively with clinical positron emission tomography (PET) but none are selective for beta(1)- or beta(2)-ARs. The aim was to evaluate ICI 89,406, a beta(1)-AR-selective antagonist amenable to labelling with positron emitters, for PET.

METHODS

The S-enantiomer of an [O-methyl-(11)C] derivative of ICI 89,406 ((S)-[(11)C]ICI-OMe) was synthesised. Tissue radioactivity after i.v. injection of (S)-[(11)C]ICI-OMe (< 2 nmol x kg(-1)) into adult Wistar rats was assessed by small animal PET and post mortem dissection. Metabolism was assessed by HPLC of extracts prepared from plasma and tissues and by measuring [(11)C]CO(2) in exhaled air.

RESULTS

The heart was visualised by PET after injection of (S)-[(11)C]ICI-OMe but neither unlabelled (S)-ICI-OMe nor propranolol (non-selective beta-AR antagonist) injected 15 min after (S)-[(11)C]ICI-OMe affected myocardial radioactivity. Ex vivo dissection showed that injecting unlabelled (S)-ICI-OMe, propranolol or CGP 20712A (beta(1)-selective AR antagonist) at high dose (> 2 mumol x kg(-1)) before (S)-[(11)C]ICI-OMe had a small effect on myocardial radioactivity. HPLC demonstrated that radioactivity in myocardium was due to unmetabolised (S)-[(11)C]ICI-OMe although (11)C-labelled metabolites rapidly appeared in plasma and liver and [(11)C]CO(2) was detected in exhaled air.

CONCLUSION

Myocardial uptake of (S)-[(11)C]ICI-OMe after i.v. injection was low, possibly due to rapid metabolism in other tissues. Injection of unlabelled ligand or beta-AR antagonists had little effect indicating that binding was mainly to non-specific myocardial sites, thus precluding the use of (S)-[(11)C]ICI-OMe to assess beta(1)-ARs with PET.

Combined effect of solvent content, temperature and pH on the chromatographic behaviour of ionisable compounds

The organic solvent content and the pH in the mobile phase are the usual main factors in reversed-phase liquid chromatographic separations, owing to their strong effects on retention and/or selectivity. Temperature is often neglected. However, even in cases where the impact of this factor on selectivity is minor, the reduction in analysis time is still an interesting reason to consider it. In addition, ionisable compounds may exhibit selectivity changes, owing to the interaction of organic solvent and/or temperature with pH. The separation of ionisable compounds (nine diuretics: bendroflumethiazide, benzthiazide, bumetanide, chlorthalidone, furosemide, piretanide, probenecid, trichloromethiazide and xipamide, and two beta-blockers: oxprenolol and propranolol) exhibiting different acid-base behaviour was studied. The compounds were tested in a Zorbax SB C18 column under a wide range of conditions: 25-45% (v/v) acetonitrile, pH 3-7 and 20-50 degrees C. Models considering two factors (organic solvent/pH and temperature/pH), and three factors (organic solvent/temperature/pH) were developed from a previously reported equation, which considers the polarity contributions of solute, stationary and mobile phases. This allowed a comprehensive method to predict the retention of the 11 compounds, the modification of their acid-base behaviour (i.e. determination of protonation constants and shifts of the retention versus pH curves), and the selectivity changes within the studied factor ranges.

Adsorption of beta blockers to environmental surfaces

Beta-adrenergic blocking agents (beta blockers) are widely used pharmaceuticals which have been detected in the environment. Predicting the transport and ultimate fate of beta blockers in the environment requires understanding their adsorption to soils and sediments, something for which little information is currently available. The objective of this work was to examine the adsorption of three beta blockers, propranolol, metoprolol and nadolol, to a natural alluvial material, as well as to six minerals present as components of the alluvial material. Batch adsorption experiments indicate that, for most of the minerals studied, compound hydrophobicity is an important predictor of adsorption, with propranolol,the most hydrophobic compound studied, adsorbing to the greatest extent. Results further suggest that, for the minerals studied, electrostatic effects are not a good predictor of adsorption; adsorption extent was not well-predicted by either surface zeta potential or by the difference between experiment pH and point of zero charge, despite the cationic nature af the three beta blockers at experiment pH values. Experiments were conducted to examine the effect of an anionic surfactant, sodium dodecyl benzene sulfonate (SDBS), on adsorption. Results indicate that SDBS significantly increases the adsorption of propranolol to two different sorbents. This result is potentially important because surfactants such as SDBS are likely to be present in wastewater effluents with beta blockers and could influence their mobility in the environment.

Support vector machine for SAR/QSAR of phenethyl-amines

AIM

To discriminate 32 phenethyl-amines between antagonists and agonists, and predict the activities of these compounds.

METHODS

The support vector machine (SVM) is employed to investigate the structure-activity relationship (SAR)/quantitative structure-activity relationship (QSAR) of phenethyl-amines based on molecular descriptors.

RESULTS

By using the leave-one-out cross-validation (LOOCV) test, 1 optimal SAR and 2 optimal QSAR models for agonists and antagonists were attained. The accuracy of prediction for the classification of phenethyl-amines by using the LOOCV test is 91.67%, and the accuracy of prediction for the classification of phenethyl-amines by using the independent test is 100%; the results are better than those of the Fisher, the artificial neural network (ANN), and the K-nearest neighbor models for this real world data. The RMSE (root mean square error) of antagonists' QSAR model is 0.5881, and the RMSE of agonists' QSAR model is 0.4779, which are better than those of the multiple linear regression, partial least squares, and ANN models for this real world data.

CONCLUSION

The SVM can be used to investigate the SAR and QSAR of phenethylamines and could be a promising tool in the field of SAR/QSAR research.

Biotransformation of metoprolol by the fungus Cunninghamella blakesleeana

AIM

To investigate the biotransformation of metoprolol, a beta1-cardioselective adrenoceptor antagonist, by filamentous fungus, and to compare the parallels between microbial transformation and mammalian metabolism.

METHODS

Five strains of Cunninghamella (C elegans AS 3.156, C elegans AS 3.2028, C echinulata AS 3.2004, C blakesleeana AS 3.153 and AS 3.910) were screened for the ability to transform metoprolol. The metabolites of metoprolol produced by C blakesleeana AS 3.153 were separated and assayed by liquid chromatography-tandem mass spectrometry (LC/MS(n)). The major metabolites were isolated by semipreparative HPLC and the structures were identified by a combination of LC/MS(n) and nuclear magnetic resonance analysis.

RESULTS

Metoprolol was transformed to 7 metabolites; 2 were identified as new metabolites and 5 were known metabolites in mammals.

CONCLUSION

The microbial transformation of metoprolol was similar to the metabolism in mammals. The fungi belonging to Cunninghamella species could be used as complementary models for predicting in vivo metabolism and producing quantities of metabolite references for drugs like metoprolol.

Development, validation and stability study of pediatric atenolol syrup

Atenolol [4-(2-hydroxy-isopropylaminopropoxy)-phenylacetamide], is a cardioselective beta1-adrenergic receptor blocking agent prescribed for treatment of hypertension, angina pectoris and cardiac arrhythmias. However, most of these medicines are not formulated for easy or accurate administration to children. Atenolol is unstable in solutions and therefore the development of a liquid dosage form is a significant challenge. Studies showed that the degradation rate of atenolol is dependent on the temperature, indicating higher stability at 4 degrees C. Atenolol syrup is stable for 9 days, with acceptable apearance. A second order model adequately described atenolol decomposition when stored as syrup. A stability-indicating method was developed and validated in order to evaluate these studies.

Tuneable Peak Deformations in Chiral Liquid Chromatography

Modern chiral stationary phases are often combined with eluents comprising a mixture of organic solvents and polar additives. The latter may cause extreme deformations of the eluted enantiomer bands in both analytical and preparative separations. In this work, we give a theoretical background for these deformations. As an experimental verification, we separate the enantiomers of different beta-blockers on a teicoplanin stationary phase (Chirobiotic T) in the presence of triethylamine/acetic acid. We show that it is possible to tune the peak shapes of the two enantiomers by varying the organic solvent composition. An advantageous situation occurs when the first eluted peak is transformed to an anti-Langmuirian shape while keeping the second enantiomer in a normal Langmuirian shape. In this situation, the two peaks tail in opposite directions with their sharp sides pointing closely to each other. It is then possible to obtain baseline resolution at higher load than when both enantiomer peaks tail in the same direction. Adsorption isotherm parameters were determined using the inverse method; no other method could be used due to the system complexity. Computer simulations, based on these parameters, agreed very well with the observed deformations, thus confirming our hypothesis of their origin.

Development and in vitro evaluation of buccoadhesive carvedilol tablets

Buccoadhesive tablets of carvedilol were prepared using HPMC K4M, HPMC K15M and Carbopol 934 as mucoadhesive polymers. Fifteen formulations were developed with varying concentrations of polymers. Formulations of the BC or BD series were composed of HPMC K4M or HPMC K15M in ratios of 1:1 to 1:5 whereas in the BE series Carbopol 934 was used (1:0.25 to 1:1.50). The formulations were tested for in vitro drug release, in vitro bioadhesion, moisture absorption and in vitro drug permeation through porcine buccal mucosa. Formulation BC3 showed maximum release of the drug (88.7 +/- 0.4%) with the Higuchi model release profile and permeated 21.5 +/- 2.9% of the drug (flux 8.35 +/- 0.291 microg h(-1)cm(-2)) permeation coefficient 1.34 +/- 0.05 cm h(-1)) through porcine buccal membrane. BC3 formulation showed 1.62 +/- 0.15 N of peak detachment force and 0.24 +/- 0.11 mJ of work of adhesion. FTIR results showed no evidence of interaction between the drug and polymers. XRD study revealed that the drug is in crystalline form in the polymer matrix. The results indicate that suitable bioadhesive buccal tablets with desired permeability could be prepared.

In vitro enantioselective displacement of propranolol from protein binding sites by acetyl salicylic acid and salicylic acid

The influences of acetyl salicylic acid (ASA) and salicylic acid (SA) on the enantioselective binding of propranolol (PL) and its enantiomers to plasma proteins and human serum albumin (HSA) were investigated. The equilibrium dialysis was employed for protein binding studies. We observed statistically significant displacement of racemic-PL, (+)-(R)-PL, and (-)-(S)-PL (0.1-10 microM) from their protein binding sites by ASA (200 microg/ml) and SA (100 microg/ml). ASA and SA displaced PL stereoselectivly from its binding sites. We concluded that ASA and its metabolite SA could change R/S ratio of PL unbound fractions and they might affect pharmacokinetic properties of PL.

Process Analytical Technology: Chemometric Analysis of Raman and Near Infra-Red Spectroscopic Data for Predicting Physical Properties of Extended Release Matrix Tablets

The purpose of this work was to develop a correlation between pharmaceutical properties such as hardness, porosity, and content with prediction models employed using Raman and near infra-red (NIR) spectroscopic methods. Metoprolol tartrate tablets were prepared by direct compression and wet granulation methods. NIR spectroscopy and chemical imaging, and Raman spectra were collected, and hardness, porosity, and dissolution were measured. The NIR PLS model showed a validated correlation coefficient of >0.90 for the predicted versus measured porosity, hardness, and amount of drug with raw and second derivative NIR spectra. Raman spectra correlated porosity of the tablets using raw data for directly compressed tablets and wet granulated tablets (r(2) > 0.90). A very close root-mean square error of calibration (RMSEC) and root-mean square error of prediction (RMSEP) values were found in all the cases indicating validity of the calibration models. Raman spectroscopy was used for the first time to predict physical quality attribute such as porosity successfully. Chemical imaging utilizing NIR detector also demonstrated to show physical changes due to compression differences. In conclusion, sensor technologies can be potentially used to predict physical parameters of the matrix tablets.

Determination of β-blockers and β2-agonists in sewage by solid-phase extraction and liquid chromatography–tandem mass spectrometry

A method using solid-phase extraction (SPE) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed for the determination of 12 beta-blockers and beta(2)-agonists in wastewater samples. Extraction of the drugs was effected by an Oasis MCX cartridge with a strong cation resin adsorbent. Matrix coextractives were removed from the SPE cartridge by methanol prior to the elution of the drugs with a mixture of dichloromethane, 2-propranol, and ammonium hydroxide. The extract was analyzed by LC-MS/MS with electrospray ionization operating in the positive mode. Recovery of the 12 compounds was in most cases better than 85% at the fortification levels of 500 and 50 ng/L, with standard deviations between 3 and 7%. Based on a concentration factor of 250, the method detection limits ranged from 6 to 11 ng/L for the target compounds. No degradation of these drugs in spiked sewage effluent samples was observed over a storage period of 7 days at 4 degrees C in the dark. Many beta-blockers were detected in the 14 wastewater samples collected from seven Canadian sewage treatment plants; those occurring at the highest concentrations were atenolol, acebutolol, sotalol, and metroprolol, with overall median concentrations of 1370, 339, 282, and 257 ng/L, respectively. However, there was only a small decrease in the median concentrations of these beta-blockers between the primary and final effluent, suggesting that these drugs are not easily removed by the sewage treatment processes. As a result of selective extraction and effective removal of coextractives, no matrix effect was observed for the samples during LC-MS/MS analyses.

Application of liquid chromatography-tandem mass spectrometry method for the analysis of new nonselective beta-adrenergic blocker 1-(1-H-indol-4-yloxy)-3-{[2-(2-methoxy phenoxy)ethylo]amino}propan-2-ol (2F109) in rat plasma

A sensitive and specific liquid chromatography electrospray ionization-tandem mass spectrometry method for the enantioselective determination of the novel beta-adrenolytic compound, 1-(1-H-indol-4-yloxy)-3-{[2-(2-methoxyphenoxy)ethylo]amino} propan-2-ol, in rat plasma has been developed and validated. Chromatography was performed on a reversed-phase Chiralcel OD-RH analytical column (150x4.6 mm, 5 microm, Daicel Chemical Industries, Tokyo, Japan) with isocratic elution using a mobile phase containing acetonitrile and water with 0.01% formic acid. Detection was achieved by an Applied Biosystems MDS Sciex (Concord, Ontario, Canada) API 2000 triple quadrupole mass spectrometer. Electrospray ionization (ESI) was used for ion production. The limit of detection in the MRM mode was found to be 1.25 ng/ml. The limit of quantification of both enantiomers was 2.5 ng/ml. The precision and accuracy for both intra- and inter-day determination of 2F109 enantiomers ranged from 2.6 to 12% and from 89.1 to 107.1%. This analytical method allowed us to carry out pharmacokinetic studies in rats. Our findings demonstrate that 2F109 shows stereoselective disposition in rat plasma after i.v. administration. The terminal half-lives of (+)-(R)-2F109 and (-)-(S)-2F109 were 33.5 and 42.6 min, respectively. The AUC0-inf of (+)-(R)-2F109 exceeded that of (-)-(S)-2F109.

Timolol Metabolism in Human Liver Microsomes Is Mediated Principally by CYP2D6

Timolol has mainly been used topically for the treatment of glaucoma. It has been suggested that the drug is metabolized by cytochrome P450 CYP2D6. The matter has not, however, been extensively studied. The aim here was to tentatively identify timolol metabolites and to determine the P450-associated metabolic and interaction properties of timolol in vitro. Four metabolites were identified, the most abundant being a hydroxy metabolite, M1. The K(m) value for the formation of M1 was 23.8 microM in human liver microsomes. Metabolism of timolol with recombinant P450s and correlation analysis have confirmed the conception that the drug is metabolized principally by CYP2D6, CYP2C19 being only a minor contributor (<10%) to the intrinsic microsomal clearance. The CYP2D6 inhibitor quinidine proved a potent competitive inhibitor of timolol metabolism, with an in vitro K(i) value of 0.08 microM. Fluvoxamine, an inhibitor of CYP2C19, inhibited timolol metabolism to a lesser extent, confirming its minor contribution. Timolol itself did not inhibit CYP2D6-catalyzed dextromethorphan O-demethylation. Judging from the disappearance of timolol in human liver homogenate, the in vivo half-life was extrapolated to be about 3 h, an estimate close to the half-life of about 2 to 5 h observed in vivo. In conclusion, the inhibition of timolol metabolism by quinidine should be taken into account when patients are treated with timolol. However, when plasma timolol concentrations in patients remain low (< or = 0.2 microg/l), it is suggested that such interaction is of minor clinical relevance.

iTRAQ-coupled 2D LC-MS/MS analysis on protein profile in vascular smooth muscle cells incubated with S- and R-enantiomers of propranolol: possible role of metabolic enzymes involved in cellular anabolism and antioxidant activity

Propranolol is a nonselective beta-blocker of the beta-adrenergic receptors, and the S-enantiomer is more active compared with the R-enantiomer. Clinically, it has been shown to be effective in hypermetabolic burn patients by decreasing cardiac work, protein catabolism, and lipolysis. While gene expression profiles have recently been reported in children receiving propranolol treatment, variations from one individual to another may have influenced the data analysis. Using iTRAQ-coupled 2D LC-MS/MS analysis, we report here the first study of protein profile in vascular smooth muscle cells incubated separately with the two enantiomers of propranolol. Four types of cellular proteins including metabolic enzymes, signaling molecules, cytoskeletal proteins, and those involved in DNA synthesis/protein translation displayed changes. The higher protein level of a number of enzymes involved in cellular anabolism and antioxidant activity in cells incubated with the S-enantiomer, as revealed by LC-MS/MS, was further supported by real-time PCR and Western blot analyses. Significantly, the increase in the anabolic activity associated with the higher level of metabolic enzymes was also supported by the higher intracellular concentration of the metabolic cofactor NAD+ which was a result of an increased oxidation of NADH. Our findings therefore provide molecular evidence on metabolic effect associated with propranolol treatment. The metabolic enzymes identified in our study may in turn be useful targets for future pharmaceutical interventions to reduce clinical side effects following propranolol treatment.

Effect of dl-nebivolol, its enantiomers and metabolites on the intracellular production of superoxide and nitric oxide in human endothelial cells

Nebivolol, a third generation selective beta(1)-adrenoceptor (beta(1)-AR) antagonist, has been reported to reduce intracellular oxidative stress and to induce the release of nitric oxide (NO) from the endothelium. Nebivolol is also subjected to a complex metabolic process where glucuronidation, aromatic and alicyclic hydroxylation are the major pathways leading to several metabolites. We have studied the effect of nebivolol, its enantiomers and metabolites on intracellular oxidative stress and NO availability in human umbilical vein endothelial cells (HUVECs). Furthermore, since the receptors involved in this endothelial effect of nebivolol remain controversial, we have studied this matter by the use of antagonists of beta-AR. dl-Nebivolol, d-nebivolol and l-nebivolol significantly reduced the formation of reactive oxygen species (ROS) and superoxide induced by oxidized-low density lipoprotein (ox-LDL), although the racemic and l-form were significantly more active than d-nebivolol in this activity. A marked decrease in the availability of intracellular NO was found in HUVECs exposed to ox-LDL and this parameter was normalized by the prior incubation with dl-nebivolol, d-nebivolol and l-nebivolol; the effect of racemate was mainly mimicked by its l-enantiomer. eNOS activity significantly increased by a 5-min contact of HUVECs with dl-nebivolol and l-nebivolol, but not with d-nebivolol, and a similar pattern was observed when the intracellular calcium increase was measured. The metabolites A2, A3', A12 and A14 but not A1, A3 and R 81,928, derived from different metabolic pathways, retained the antioxidant activity of the parent racemic compound dl-nebivolol, reducing the intracellular formation of ROS and superoxide. The effects of dl-nebivolol on intracellular formation of NO, eNOS activity and intracellular Ca(2+) were partially antagonized by the antagonists of beta(1-2)-AR nadolol or by the beta(3)-AR antagonist SR59230A and further antagonized by their combination or by (beta(1-2-3)-AR antagonist bupranolol. In conclusion, this study shows that the NO releasing effect of nebivolol is mainly due to its l-enantiomer; the racemate and its enantiomers possess a remarkable antioxidant activity that contributes to its effect on the cellular NO metabolism and the activation of beta(3)-AR through a calcium dependent pathway is involved in the mechanisms leading to the NO release.