Simultaneous determination of eight beta-blockers by gradient high-performance liquid chromatography with combined ultraviolet and fluorescence detection in corneal permeability studies in vitro

A multi-walled carbon nanotube-based magnetic molecularly imprinted polymer as a highly selective sorbent for ultrasonic-assisted dispersive solid-phase microextraction of sotalol in biological fluids

A modified multiwalled carbon nanotube-based magnetic molecularly imprinted polymer (MWCNT-MMIP) was synthesized and applied for selective extraction and preconcentration of sotalol (SOT) in biological fluid samples by using ultrasonic-assisted dispersive solid-phase microextraction (UA-DSPME).

Development of SPME-LC-MS method for screening of eight beta-blockers and bronchodilators in plasma and urine samples

The current work describes the development and validation of a simple, efficient, and fast method using solid phase microextraction coupled to liquid chromatography-tandem mass spectrometry (SPME-LC-MS/MS) for the concomitant measurement of eight beta-blockers and bronchodilators in plasma and urine. The presented assay enables quantitative determination of acebutolol, atenolol, fenoterol, nadolol, pindolol, procaterol, sotalol, and timolol. In this work, samples were prepared on a high-throughput platform using the 96-well plate format of the thin film solid phase microextraction (TFME) system, and a biocompatible extraction phase made of hydrophilic-lipophilic balance particles. Analytes were separated on a pentafluorophenyl column (100mm×2.1mm, 3μm) by gradient elution using an UPLC Nexera coupled with an LCMS-8060 mass spectrometer. The mobile phase consisted of water-acetonitrile (0.1% formic acid) at a flow rate of 0.4mLmin(-1). The linearity of the method was checked within therapeutic blood-plasma concentrations, and shown to adequately reflect typically expected concentrations of future study samples. Post-extraction addition experiments showed that the matrix effect ranged in plasma from 98% for procaterol to 115% for nadolol, and in urine, from 85% for nadolol and pindolol to 119% for atenolol. The method was successfully validated using Food and Drug Administration (FDA) guidelines, and met all acceptance criteria for bioanalytical assays at five concentration levels for all selected drugs. The final protocol can be successfully applied for monitoring concentrations of the selected drugs in both plasma and urine matrices obtained from patients or athletes.

Comprehensive evaluation of formulation factors for ocular penetration of fluoroquinolones in rabbits using cassette dosing technique

OBJECTIVE

Corneal permeability of drugs is an important factor used to assess the efficacy of topical preparations. Transcorneal penetration of drugs from aqueous formulation is governed by various physiological, physiochemical, and formulation factors. In the present study, we investigated the effect of formulation factors like concentration, pH, and volume of instillation across the cornea using cassette dosing technique for ophthalmic fluoroquinolones (FQs).

MATERIALS AND METHODS

Sterile cocktail formulations were prepared using four congeneric ophthalmic FQs (ofloxacin, sparfloxacin, pefloxacin mesylate, and gatifloxacin) at concentrations of 0.025%, 0.5%, and 0.1%. Each formulation was adjusted to different pH ranges (4.5, 7.0, and 8.0) and assessed for transcorneal penetration in vivo in rabbit's cornea (n=4 eyes) at three different volumes (12.5, 25, and 50 μL). Aqueous humor was aspirated through paracentesis after applying local anesthesia at 0, 5, 15, 30, 60, 120, and 240 minutes postdosing. The biosamples collected from a total of 27 groups were analyzed using liquid chromatography-tandem mass spectroscopy to determine transcorneal permeability of all four FQs individually.

RESULTS

Increase in concentration showed an increase in penetration up to 0.05%; thereafter, the effect of concentration was found to be dependent on volume of instillation as we observed a decrease in transcorneal penetration. The highest transcorneal penetration of all FQs was observed at pH 7.0 at concentration 0.05% followed by 0.025% at pH 4.5. Lastly, increasing the volume of instillation from 12.5 to 50 μL showed a significant fall in transcorneal penetration.

CONCLUSION

The study concludes that formulation factors showed discernible effect on transcorneal permeation; therefore, due emphasis should be given on drug development and design of ophthalmic formulation.

A validated RP-HPLC method for simultaneous determination of propranolol and valsartan in bulk drug and gel formulation

Objective:

A simple, precise, and stability indicating high performance liquid chromatography (HPLC) method was developed and validated for the simultaneous determination of propranolol hydrochloride and valsartan in pharmaceutical dosage form.

Materials and Methods:

The method involves the use of easily available inexpensive laboratory reagents. The separation was achieved on Hypersil ODS C-18 column (250*4.6 mm, i.d., 5 μm particle size) with isocratic flow with UV detector. The mobile phase at a flow rate of 1.0 mL/min consisted of acetonitrile, methanol, and 0.01 M disodium hydrogen phosphate (pH 3.5) in the ratio of 50:35:15 v/v.

Results:

A linear response was observed over the concentration range 5-50 μg/mL of propranolol and the concentration range 4-32 μg/mL of valsartan. Limit of detection and limit of quantitation for propranolol were 0.27 μg/mL and 0.85 μg/mL, and for valsartan were 0.45 μg/mL and 1.39 μg/mL, respectively. The method was successfully validated in accordance to ICH guidelines acceptance criteria for linearity, accuracy, precision, specificity, robustness.

Conclusion:

The analysis concluded that the method was selective for simultaneous estimation of propranolol and valsartan can be potentially used for the estimation of these drugs in combined dosage form.

Transport of organic cationic drugs: effect of ion-pair formation with bile salts on the biliary excretion and pharmacokinetics

More than 40% of clinically used drugs are organic cations (OCs), which are positively charged at a physiologic pH, and recent reports have established that these drugs are substrates of membrane transporters. The transport of OCs via membrane transporters may play important roles in gastrointestinal absorption, distribution to target sites, and biliary and/or renal elimination of various OC drugs. Almost 40 years ago, a molecular weight (Mw) threshold of 200 was reported to exist in rats for monoquaternary ammonium (mono QA) compounds to be substantially (e.g., >10% of iv dose) excreted to bile. It is well known that some OCs interact with appropriate endogenous organic anions in the body (e.g., bile salts) to form lipophilic ion-pair complexes. The ion-pair formation may influence the affinity or binding of OCs to membrane transporters that are relevant to biliary excretion. In that sense, the association of the ion-pair formation with the existence of the Mw threshold appears to be worthy of examination. It assumes the ion-pair formation of high Mw mono QA compounds (i.e., >200) in the presence of bile salts in the liver, followed by accelerated transport of the ion-pair complexes via relevant bile canalicular transporter(s). In this article, therefore, the transport of OC drugs will be reviewed with a special focus on the ion-pair formation hypothesis. Such information will deepen the understanding of the pharmacokinetics of OC drugs as well as the physiological roles of endogenous bile salts in the detoxification or phase II metabolism of high Mw QA drugs.

Development of novel in silico model to predict corneal permeability for congeneric drugs: a QSPR approach

This study was undertaken to determine in vivo permeability coefficients for fluoroquinolones and to assess its correlation with the permeability derived using reported models in the literature. Further, the aim was to develop novel QSPR model to predict corneal permeability for fluoroquinolones and test its suitability on other training sets. The in vivo permeability coefficient was determined using cassette dosing (N-in-One) approach for nine fluoroquinolones (norfloxacin, ciprofloxacin, lomefloxacin, ofloxacin, levofloxacin, sparfloxacin, pefloxacin, gatifloxacin, and moxifloxacin) in rabbits. The correlation between corneal permeability derived using in vivo studies with that derived from reported models was determined. Novel QSPR-based model was developed using in vivo corneal permeability along with other molecular descriptors. The suitability of developed model was tested on β-blockers (n = 15). The model showed better prediction of corneal permeability for fluoroquinolones (r(2) > 0.9) as well as β-blockers (r(2) > 0.6). The newly developed QSPR model based upon in vivo generated data was found suitable to predict corneal permeability for fluoroquinolones as well as other sets of compounds.

Simple and rapid HPLC method for simultaneous determination of atenolol and chlorthalidone in spiked human plasma

A simple, sensitive and rapid chromatographic method was developed and validated for the simultaneous quantification of atenolol and chlorthalidone in human plasma using hydrochlorothiazide as internal standard (IS). The method utilized proteins precipitation with acetonitril as the only sample preparation involved prior to reverse phase-HPLC. The analytes were chromatographed on Shim-pack cyanopropyl column with isocratic elution with 10 mM KH2PO4 (pH 6.0) - methanol (70:30, v/v) at ambient temperature with flow rate of 1 mL min(-1) and UV detection at 225 nm. The chromatographic run time was less than 10 min for the mixture. The calibration curves were linear over the range of 0.1-10 μg mL(-1). The method was validated in terms of accuracy, precision, absolute recovery, freeze-thaw stability, bench-top stability and re-injection reproducibility. The within- and between-day accuracy and precision were found to be within acceptable limits <15%. The analytes were stable after three freeze-thaw cycles (deviation <15%). The proposed method was specific for the simultaneous determination of atenolol and chlorthalidone in human plasma where there was no interference from endogenous biological substances.

Fibers with polypyrrole and polythiophene phases for isolation and determination of adrenolytic drugs from human plasma by SPME-HPLC

In this study, polypyrrole (PPy) and polythiophene (PTh) SPME coatings and their ability to extract selected adrenolytic drugs with different physico-chemical properties from standard solutions and human plasma samples were evaluated. In measurements metoprolol, oxprenolol, mexiletine, propranolol, and propaphenon were investigated. The main parameters such as extraction time, desorption conditions and pH influence were examined. Inter-day precisions were in range 0.1-2.0%, 1.1-2.9%, 1.3-2.6%, 0.1-2.6% and 0.3-2.1% for metoprolol, oxprenolol, mexiletine, propranolol and propaphenon, respectively. Accuracies were less than 15%, which was evaluated by analyzing preparation samples of five replicates. The method was successfully applied to human plasma samples spiked with selected adrenolytic drugs. The method was linear in the concentration range from 1 to 10microg/ml for all of studied adrenolytic drugs using human plasma samples. The PTh-SPME coating displayed higher extraction efficiency towards the target analytes in comparison to PPy-SPME. The reproducibility of the extraction using polypyrrole and polythiophene fibers was confirmed by variation coefficients lower than 8% and 3%, respectively.

Filter-cultured ARPE-19 cells as outer blood-retinal barrier model

Retinal pigment epithelium (RPE) regulates drug transfer between posterior eye segment and blood circulation, but there is no established RPE cell model for drug delivery studies. We evaluated ARPE-19 filter culture model for this purpose. Passive permeability of 6-carboxyfluorescein, betaxolol and FITC-dextran (40kDa) and active transport of 6-carboxyfluorescein, sodium fluorescein, rhodamine 123, cyclosporine A and digoxin in ARPE-19 model were investigated and compared with isolated bovine RPE-choroid tissue. In addition, barrier properties, and mRNA expression of RPE-specific and melanogenesis-related genes (RPE65, VMD2, CRALBP, OTX-2, MITF-A, TRP-1, tyrosinase) were measured in various culture conditions. The filter grown ARPE-19 cell model showed reasonable barrier properties (TER close to 100Omegacm(2)), but its permeability was slightly higher than that of isolated bovine RPE/choroid specimens. In active transport studies the ARPE-19 model mimics qualitatively the permeability profile of bovine RPE-choroid, but ARPE-19 model underestimates the importance of active transport relative to passive diffusion. Long-term filter-cultured ARPE-19 cells expressed various RPE-specific and melanogenesis-related genes at higher levels than the ARPE-19 cells cultured short-term in flasks. ARPE-19 model can be used to study drug permeation processes in the RPE.

Detection and quantitation of β-blockers in plasma and urine

β-blockers are a class of antihypertensive drugs that are used for the management of cardiac arrhythmias, cardioprotection after myocardial infarction (heart attack) and hypertension. They have revolutionized the medical management of angina pectoris and are recommended as first-line agents by national and international guidelines. Although β-blockers are still the cornerstone for the treatment of heart failure, some of the drugs in this category are prohibited in several sports requiring vehicle control and bodily movements as they reduce heart rate and tremors, and improve performance. As a result, urine analysis of β-blockers is mandatory in doping control and toxicological screening. The determination of plasma levels of β-blockers helps to ensure noncompliance in patients with persistent hypertonia to confirm the diagnosis of β-blocker poisoning and for therapeutic drug monitoring. This review provides a comprehensive account of various analytical methods developed for detection and quantitation of β-blockers in plasma and urine.

Feasibility Evaluation of 3 Automated Cellular Drug Screening Assays on a Robotic Workstation

This study presents the implementation and optimization of 3 cell-based assays on a TECAN Genesis workstation—the Caspase-Glo® 3/7 and sulforhodamine B (SRB) screening assays and the mechanistic Caco-2 permeability protocol—and evaluates their feasibility for automation. During implementation, the dispensing speed to add drug solutions and fixative trichloroacetic acid and the aspiration speed to remove the supernatant immediately after fixation were optimized. Decontamination steps for cleaning the tips and pipetting tubing were also added. The automated Caspase-Glo® 3/7 screen was successfully optimized with Caco-2 cells (Z′ 0.7, signal-to-base ratio [S/B] 1.7) but not with DU-145 cells. In contrast, the automated SRB screen was successfully optimized with the DU-145 cells (Z′ 0.8, S/B 2.4) but not with the Caco-2 cells (Z′ —0.8, S/B 1.4). The automated bidirectional Caco-2 permeability experiments separated successfully low- and high-permeability compounds (Z′ 0.8, S/B 84.2) and passive drug permeation from efflux-mediated transport (Z′ 0.5, S/B 8.6). Of the assays, the homogeneous Caspase-Glo® 3/7 assay benefits the most from automation, but also the heterogeneous SRB assay and Caco-2 permeability experiments gain advantages from automation.

Cassette analysis of eight beta-blockers in bovine eye sclera, choroid-RPE, retina, and vitreous by liquid chromatography-tandem mass spectrometry

A simple, selective, and sensitive LC-MS/MS method was developed for the simultaneous extraction and determination of eight beta-blockers (atenolol, sotalol, nadolol, pindolol, timolol, metoprolol, betaxolol and propranolol) in various bovine eye tissues including sclera, choroid-RPE, retina, and vitreous. The analytes were extracted by liquid-liquid extraction after samples were alkalinized with 2% NaOH solution in water. The chromatographic separation was performed on a Hypersil-ODS C18 column (100 mm x 2.1 mm, 3.9 microm) using a gradient mixture of (A) 5 mM ammonium formate in water (pH 3.5 adjusted with formic acid) and (B) acetonitrile:methanol (75:25) containing 0.02% triethyl amine (pH 4.0; adjusted with formic acid) as mobile phase at a flow rate of 0.4 ml/min. The compounds were ionized in the positive electrospray ionization (ESI) mode and detected in the multiple reaction monitoring (MRM) mode. The average recoveries in all four eye tissues for all beta-blockers were >82%, except for sotalol (>51%). The matrix effect for beta-blockers ranged from 81 to 110% in the four eye tissues. This analytical method was validated and applied successfully for simultaneous quantification of the beta-blockers in sclera after tissue exposure using cassette dosing method. The calibration curve was linear in the range of 10-2000 ng/ml for all analytes, with the correlation coefficient >0.996. Intra-day and inter-day precision (% CV) was less than 15%, and accuracy ranged from 85 to 110% for all analytes. Scleral uptake was the lowest for sotalol and atenolol, two hydrophilic beta-blockers, and the highest for propranolol, a lipophilic beta-blocker.

Liquid chromatography tandem mass spectrometry method for simultaneous determination of metoprolol tartrate and ramipril in human plasma

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of metoprolol tartrate (MT) and ramipril, in human plasma. Both the drugs were extracted by liquid-liquid extraction with diethyl ether-dichloromethane (70:30, v/v). The chromatographic separation was performed on a reversed-phase C8 column with a mobile phase of 10 mM ammonium formate-methanol (3:97, v/v). The protonated analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The method was validated over the concentration range of 5-500 ng/ml for metoprolol and ramipril in human plasma. The precursor to product ion transitions of m/z 268.0-103.10 and m/z 417.20-117.20 were used to measure metoprolol and ramipril, respectively.

Biopharmaceutics classification of selected beta-blockers: solubility and permeability class membership

The purpose of this study was to determine the permeability and solubility of seven beta-blockers (acebutolol, atenolol, labetalol, metoprolol, nadolol, sotalol, and timolol) and to classify them according to the Biopharmaceutics Classification System (BCS). Apparent permeability coefficients (Papp) were measured using the Caco-2 cell line, and the solubility was determined at 37 degrees C over a pH range of 1.0-7.5. The permeability coefficients ranged from 1.0x10(-7) to 4.8x10(-5) cm/s. On the basis of the in vitro permeability and solubility data observed in the study, labetolol, metoprolol, and timolol can be categorized as BCS Class I drugs, whereas acebutolol, atenolol, and nadolol belong to BCS Class III. The permeability coefficients in Caco-2 cells were consistent with the reported extent of intestinal absorption in humans for all drugs except sotalol. Sotalol displayed low permeability in the Caco-2 cell line, but the extent of intestinal absorption in humans is over 90%. The low permeability through the Caco-2 monolayers might be largely related to its low lipophilicity. In addition, the difference between the tightness of the intercellular junction in vivo and in vitro may partially contribute to this disparity in the sotalol permeability of in vivo and in vitro.

Binding of betaxolol, metoprolol and oligonucleotides to synthetic and bovine ocular melanin, and prediction of drug binding to melanin in human choroid-retinal pigment epithelium

PURPOSE

To characterize the binding of betaxolol, metoprolol and oligonucleotides to synthetic and bovine ocular melanin, and to predict the binding to melanin in human choroid-retinal pigment epithelium (RPE).

MATERIALS AND METHODS

The shape, size and specific surface area of synthetic melanin and isolated melanin granules from bovine choroid-retinal pigment epithelium (RPE) were characterized by SEM, laser diffractometry and BET. The binding of betaxolol, metoprolol, fluorescein isothiocyanate (FITC)-labeled phosphodiesther oligonucleotides and 6-carboxyfluorescein (6-CF) to melanin was determined. The binding of beta-blockers to melanin in human choroid-RPE was estimated based on binding parameters and the melanin content in human choroid-RPE.

RESULTS

Bovine melanin granules were round or oval with a mean diameter of ca. 1 mum. Synthetic granules were slightly smaller and irregular and had a two times higher specific surface area than bovine melanin. Synthetic melanin bound more betaxolol and metoprolol than bovine melanin and both melanin types showed a high affinity and a low affinity binding sites. The human choroid-RPE was predicted to contain 3-19 times more melanin bound drug than unbound drug at typical therapeutic concentrations (1-1,000 ng/ml). FITC-labeled oligonucleotides and 6-CF did not bind to melanin.

CONCLUSIONS

The binding of lipophilic drugs to biological melanin differs from that of synthetic melanin. Lipophilic beta-blockers are expected to bind significantly to melanin in human choroid-RPE: only a small fraction of the drug being in active free form. In contrast, phosphodiesther oligonucleotides do not seem to bind to melanin.

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.

Determination of atenolol by the micelle-stabilized room-temperature phosphorescence methodology

A micellar-stabilized room-temperature phosphorescence (MS-RTP) method for the determination of atenolol has been developed in micellar solutions of sodium dodecylsulphate (SDS) in the presence of thallium(I) as a heavy atom and sodium sulphite as an oxygen scavenger. The effects of thallium(I) nitrate, SDS and sodium sulphite concentrations on atenolol MS-RTP intensity were studied. Optimized conditions to obtain maximum sensitivity were 0.015 mol/L thallium(I) nitrate, 0.1 mol/L SDS and 0.0075 mol/L sodium sulphite. The maximum phosphorescence signal was completely developed in 10 min and the intensity was measured at lambda(ex) = 272 nm and lambda(em) = 412 nm. The linear range of application obtained was 2.01-16.00 microg/mL. The detection limit estimated from the least-squares regression analysis was 0.86 microg/mL and the relative standard deviation of 10 replicates was 1.7%. The proposed method was applied to the determination of atenolol in a pharmaceutical formulation. The quantitation was carried out by means of standard calibration, standard-additions calibration and Youden calibration. These three experiments were necessary to evaluate the presence of constant and proportional errors due to the matrix.

Evaluation of contactless conductivity detection for the determination of UV absorbing and non-UV absorbing species in reversed-phase high-performance liquid chromatography

A capacitively coupled contactless conductivity detector (C(4)D) was used for the determination of three groups of ionizable species in reversed-phase HPLC with isocratic elution. These were non-steroidal anti-inflammatory drugs which are arylpropionic acid derivatives and represent anionic analytes, beta-blockers which are amines and therefore cationic, and zwitterionic amino acids. Optimization of the eluents led to detection limits in the order of 1 microM for all species. The precision in peak areas was typically between 0.2 and 2.1% and calibration curves were linear up to 500 microM. The determination of ibuprofen, acetylsalicylic acid and atenolol in real samples was also demonstrated by direct injection of dissolved pharmaceutical formulations into the HPLC-C(4)D system.

Cell culture models of the ocular barriers

The presence of tight barriers, which regulate the environment of ocular tissues in the anterior and posterior part of the eye, is essential for normal visual function. The development of strategies to overcome these barriers for the targeted ocular delivery of drugs, e.g. to the retina, remains a major challenge. During the last years numerous cell culture models of the ocular barriers (cornea, conjunctiva, blood-retinal barrier) have been established. They are considered to be promising tools for studying the drug transport into ocular tissues, and for numerous other purposes, such as the investigation of pathological ocular conditions, and the toxicological screening of compounds as alternative to in vivo toxicity tests. The further development of these in vitro models will require more detailed investigations of the barrier properties of both the cell culture models and the in vivo ocular barriers. It is the aim of this review to describe the current status in the development of cell culture models of the ocular barriers, and to discuss the applicability of these models in pharmaceutical research.

Hydrophilic interaction liquid chromatographic tandem mass spectrometric determination of atenolol in human plasma

A hydrophilic interaction liquid chromatographic method with tandem mass spectrometry for the determination of atenolol, a beta-blocking agent, in human plasma has been developed and validated over the curve range of 10--2000 ng/mL. The assay was based on protein precipitation followed by evaporation of the extraction solvent, reconstitution with acetonitrile, and chromatography on an Hypersil silica column (50 x 4.6 mm) using a low aqueous--high organic mobile phase. The mobile phase consists of 85% acetonitrile, 15% water, 0.5% acetic acid and 0.04% trifluoroacetic acid and runs isocratically at a flow rate of 2.0 mL/min. The column ef fluent was split so that 50% of it was transferred into the LC-MS/MS interface operated in positive electrospray ionization mode. The chromatographic run time was 2.0 min per injection. Atenolol and the internal standard, atenolol-d(7), showed a retention time of 1.0 min. The inter-day and intra-day precision and accuracy of the quality control samples were <5.3% relative standard deviation and <8.0% relative error, respectively. To explore the application of the current method for the analysis of other beta-blocking agents, propranolol and metoprolol were tested under the same chromatographic conditions with retention times of 0.68 and 0.75 min, respectively. The present method could be used for therapeutic drug monitoring, pharmacokinetic and drug--drug interaction studies of beta-blocking agents.

Ocular pharmacokinetic modeling using corneal absorption and desorption rates from in vitro permeation experiments with cultured corneal epithelial cells

PURPOSE

To determine corneal absorption and desorption rate constants in a corneal epithelial cell culture model and to apply them to predict ocular pharmacokinetics after topical ocular drug application.

METHOD

In vitro permeation experiments were performed with a mixture of six beta-blockers using an immortalized human corneal epithelial cell culture model. Disappearance of the compounds from the apical donor solution and their appearance in the basolateral receiver solution were determined and used to calculate the corneal absorption and desorption rate constants. An ocular pharmacokinetic simulation model was constructed for timolol with the Stella program using the absorption and desorption rate constants and previously published in vivo pharmacokinetic parameters.

RESULTS

The corneal absorption rates of beta-blockers increased significantly with the lipophilicity of the compounds. The pharmacokinetic simulation model gave a realistic mean residence time for timolol in the cornea (57 min) and the aqueous humor (90 min). The simulated timolol concentration in the aqueous humor was about 1.8 times higher than the previously published experimental values.

CONCLUSIONS

The simulation model gave a reasonable estimate of the aqueous humor concentration profile of timolol. This was the first attempt to combine cell culture methods and pharmacokinetic modeling for prediction of ocular pharmacokinetics. The wider applicability of this approach remains to be seen.

Paracellular and passive transcellular permeability in immortalized human corneal epithelial cell culture model

A cell culture model of human corneal epithelium (HCE-model) was recently introduced [Invest. Ophthalmol. Vis. Sci. 42 (2001) 2942] as a tool for ocular drug permeation studies. In this study, passive permeability and esterase activity of the HCE-model were characterised. Immortalised human corneal epithelial cells were grown on collagen coated filters under air-lift. The sensitivity of transcellular permeability to lipophilicity was tested in studies using nine beta-blockers. The size selectivity of the paracellular route was investigated using 16 polyethylene glycol oligomers (PEG). An effusion-like approach was used to estimate porosity and pore sizes of the paracellular space in HCE membrane. Permeability and degradation of fluorescein diacetate to fluorescein in HCE-cells was used to probe the esterase activity of the HCE-model. Drug concentrations were analyzed using HPLC (beta-blockers), LC-MS (PEGs), and fluorometry (fluorescein). Permeabilities were compared to those in the excised rabbit cornea. Penetration of beta-blockers increased with lipophilicity according to a sigmoidal relationship. This was almost similar to the profile in excised cornea. No apical to basolateral directionality was seen in the permeation of beta-blockers. Paracellular permeability of the HCE-model was generally slightly higher than that of the excised rabbit cornea. The HCE-model has larger paracellular pores, but lower pore density than the excised cornea, but the overall paracellular space was fairly similar in both models. The HCE-model shows significant esterase activity (i.e. fluorescein diacetate was converted to free fluorescein). These data on permeability of 27 compounds demonstrate that the barrier of the HCE-model closely resembles that of the excised rabbit cornea. Therefore, the HCE-model is a promising alternative corneal substitute for ocular drug delivery studies.