Effect of Cyclodextrins on Morphology and Barrier Characteristics of Isolated Rabbit Corneas (original) (raw)
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European Journal of Pharmaceutics and Biopharmaceutics, 2005
Transcorneal in vitro permeation studies of ophthalmic drugs are normally performed with either excised animal corneas or latterly corneal cell culture models. A good correlation between these models and excised animal corneas regarding permeation behaviour of drugs has already been shown. However, comparisons between corneal in vitro models containing human cells and excised human corneas do not exist yet. Therefore in the present study the transcorneal permeation of six different model drugs (pilocarpine hydrochloride, befunolol hydrochloride, hydrocortisone, diclofenac sodium, clindamycin hydrochloride and timolol maleate) across our previously described three-dimensional organotypic human cornea construct (HCC) was tested using Franz diffusion cells and compared with permeation data obtained from human donor corneas. The HCC showed a similar permeation behaviour compared with human donor cornea for all substances. The permeabilities (permeation coefficients P) of the human cornea equivalent versus the human donor cornea were the same in the case of diclofenac, clindamycin, timolol, but marginally decreased for hydrocortisone and slightly increased for pilocarpine and befunolol. These small differences of permeation coefficients were expressed as factors and only varied from 0.8 to 1.4. The results indicate that the HCC may be an alternative for in vitro permeation studies and appropriate for predicting drug absorption into the human eye.
Journal of Pharmaceutical Sciences, 1999
The purpose of this study was to evaluate the permeability characteristics of a previously reported in vitro corneal model that utilizes SIRC rabbbit corneal cells and to investigate the permeability of three novel esters of phenylephrone chemical delivery systems (CDS) under different pH conditions using this in vitro model. The SIRC rabbit corneal cell line was grown on transwell polycarbonate membranes, and the barrier properties were assessed by measuring transepithelial electrical resistance (TEER) using a voltohmmeter. The permeabilities of esters of phenylephrone CDS across the SIRC cell layers were measured over a pH range 4.0−7.4. The esters tested include phenylacetyl (1), isovaleryl (2), and pivalyl (3). The SIRC rabbit corneal cell line, when grown on permeable filters, formed tight monolayers of high electrical resistance with TEER values increasing from 71.6 ± 20.8 Ω‚cm 2 at day 3 in culture to 2233.42 ± 15.2 Ω‚cm 2 at day 8 in culture and remained constant through day 14 in culture. The transepithelial permeability coefficients (P app) at pH 7.4 ranged from 0.58 × 10-6 cm/s for the hydrophilic marker, mannitol, to 43.5 × 10-6 cm/s for the most lipophilic molecule, testosterone. The P app at pH 7.4 for phenylephrine was 4.21 × 10-6 cm/s. The P app values and the lag times of the three esters of phenylephrone were pH dependent. The P app for 1, 2, and 3 at pH 7.4 were 14.76 × 10-6 , 13.19 × 10-6 , and 12.86 × 10-6 cm/s, respectively and the permeabilities decreased at conditions below pH 7.4. The lag times at pH 7.4 were 0.10, 0.17, and 0.12 h for 1, 2, and 3, respectively, and the values increased at lower pH conditions. The TEER values of SIRC cell line observed at day 8 to day 14 in the present investigation are similar to the resistance value reported for rabbit cornea (2 kΩ‚cm 2). All the esters showed significantly (p < 0.05) higher permeabilities than phenylephrine at pH 7.4. The rate and extent of transport of the drugs across the cell layers were influenced by the fraction of ionized and un-ionized species and the intrinsic partition coefficient of the drug. The results indicate that the permeability of ophthalmic drugs through ocular membranes may be predicted by measuring the permeability through the new in vitro cell culture model.
Comparative Permeability of Human and Rabbit Corneas to Cyclosporin and Tritiated Water
Journal of Ocular Pharmacology and Therapeutics, 2002
Diffusion of cyclosporin A (CsA) and water through fresh and frozen (liquid nitrogen, 285°C) human and rabbit corneas was compared to establish the appropriateness of using the latter tissue as a model for its human counterpart for in vitro permeability studies. Permeation of CsA in the presence of three penetration enhancers, 0.01% benzalkonium chloride (BZCl), 20% dimethylsulfoxide (DMSO), 10% and 20% Cremophor-EL was also studied. Permeability was determined using a flow-through diffusion apparatus (20°C, 24 hours). ANOVA, Duncan's multiple range test, and an unpaired t-test were used to determine steady state kinetics and flux differences over time intervals. No statistically significant differences in flux values of CsA and water could be detected between fresh and frozen/thawed human and rabbit corneas. The diffusion of water was significantly lower across frozen/thawed rabbit cornea than across the same human tissue. CsA flux rates across frozen/thawed rabbit cornea in the presence of all three enhancers increased significantly when compared to the same tissues without enhancer, except in the presence of 20% Cremophor-EL after 18 hours. The rabbit cornea appears to be an appropriate in vitro model for studying human transcorneal penetration of drugs. Smaller M w substances, however, may have higher diffusion rates across frozen/thawed human corneal tissue.
Effects of calcium chelating agents on corneal permeability
Investigative ophthalmology & visual science, 1985
Corneal penetration studies have been conducted in unanesthetized albino rabbits using various organic compounds representing both polar and nonpolar species. In the presence of calcium chelating agents, polar compounds generally demonstrate an increase in corneal penetration. Evidence that this corneal effect is reversible is presented. Concomitant with an increase in both corneal and aqueous humor drug levels was a decrease in drug concentration in both iris and conjunctival tissues tentatively attributed to chelation effects on vascular permeability of these tissues. EDTA, a known calcium chelator, was shown to penetrate the cornea, conjunctiva, and iris/ciliary body from a topically applied dose. The implications of this observation pertain to both toxicity effects, when EDTA is incorporated into ocular drug products for stability purposes, and novel strategems for improving ocular bioavailability of topically applied drugs.
Effects of Three Penetration Enhancers on Transcorneal Permeation of Cyclosporine
Cornea, 2001
Purpose. To investigate the permeation of cyclosporin A (CsA) through fresh and frozen human corneas in the presence and absence of three penetration enhancers: benzalkonium chloride (BZCl), dimethylsulfoxide (DMSO), and Cremophor-EL. Methods. Human corneas, unsuitable for transplantation, were either freshly used for permeability experiments or snap-frozen in liquid nitrogen and stored at −85°C. CsA permeation through either fresh or thawed frozen corneal tissue was determined using a flowthrough diffusion apparatus (20°C for 24 hours). Flux rates for CsA were determined in the presence and absence of the penetration enhancers 0.01% BZCl, 20% DMSO, and Cremophor-EL (10% and 20%). Analysis of variance and Duncan's multiple-range test were used to test for steady state, and an unpaired Student t test with Welch's correction was used to test for differences between the mean flux values at each time point. A significance level of 5% was used for all of the statistical tests. Results. No statistically significant differences in flux values of CsA could be detected between fresh and frozen corneas. In the presence of Cremophor-EL (10% and 20%) and 0.01% BZCl, statistically significant increases in flux values of CsA before 16 hours and after 16 hours, respectively, could be observed. In the presence of 20% DMSO, no statistically significant increases in flux values could be detected. Conclusions. The permeation of CsA through human corneas appeared to be enhanced by the presence of BZCl and Cremophor-EL. Additionally, it was shown that the flux rate of CsA across fresh and frozen corneas was not significantly different.
Mechanisms of corneal drug penetration I: In vivo and in vitro kinetics
1988
Abstreict D Corneal penetration studies were conducted in unanesthetized albino rabbits using various organic compounds representing both polar and rionpolar species. Very low molecular weight compounds demonstrate rapid uptake into the aqueous humor despite the lipid-like ba'rier imposed by the corneal epithelium Evidence that these compounds may have access to a diffusional channel fce corneal trarsport is presented. In vitro permeability studies were also conducted in an effort to quantitate the corneal diffusion of compounds covering a range of molecular weights and partition coefficients; the results corresponded well with the results of in vivo experiments. Calculations of energies of activation, taken from Arrhenius plots, indicate that the diffusion of drug across the cornea may be by two different mechanisms that depend on the physical-chemical characteristics of the pertusant. One mechanism appears similar to drug rnovement in an aqueous environment and is characterized by an activation energy similar to that for diffusion in water. The other relates to the expected partitioning of a compound across cellular membranes represented by a relatively high activation energy for diffusion. For hyrdophilit compounds, the epitheliurn appears to be rate limiting to drug movement, whereas for hydrophobic compounds, the stroma is rate limiting. In the presence of calcium-chelating agents, glycerol demonstrated an increase in corneal penetration in vivo. This effect appears to be reversible at specific concentrations of chelator I n contrast. divalent cations reduced corneal penetration of glycerol. The known calcium cheator EOTA was shown to penetrate the cornea, conjunctiva, and ins/ciliary body from a topically applied dose. The implications of this observation pertain to toxicity effects when EOTA is incorporated into ocular drug products for stability purposes, or novel stratagems for improving ocular bioavailabifity of topically applied drugs are employed. The addition of calcium-chelatiog agents to in vivo mounted corneas demonstrated increases in permeability of the cornea to glycerol which were directly related to the concentration of chelating agent used These results paralleled the findings of smilar in vivo studies. The resdlis of these studies are consistent with a currently proposed 'pore' model for the penetration of drugs through the cornea which demonstrates both a partition coefficient and molecular weight dependency on the permeability of the cornea to transported compounds.
Journal of Pharmaceutical Sciences, 1988
0 Ultrastructure analysis was conducted in an effort to augment the results of classical kinetic studies. Scanning electron microscopy (SEM) allowed visual Inspection of cellular junctions on corneal epithelium and endothelium. The addition of calcium-chelating agents to in vivo and in vitro mounted corneas demonstrated a concentration-dependent progressive expansion of the intercellular spaces of epithelium and endothelium, as seen by SEM. The expansion of these cellular Junctions correlates with increases in permeability of the cornea to glycerol under similar conditions. The size of the intercellular space was estimated by transmission electron microscopy. Use of lanthanum as a marker of aqueous diffusional pathways demonstrated that the epithelial surface 1s not a totally occlusive barrier to transport of small hydrophilic compounds. Development of a method whereby an administered drug could be visualized in its actual pathway of movement through the cornea was undertaken, involving precipitation of specific compounds in the tissue with osmium tetroxide vapor. Results suggest that separate pathways of drug movement exist in the cornea for hydrophilic and hydrophobic compounds. Hydrophilic compounds were preferentially located in intercellular spaces, whereas hydrophobic compounds were associated with the lipid structures of the tissue. The results of these studies are consistent with a currently proposed 'pore' model for the penetration of drugs through the cornea. the eye or mounting ring with a scalpel, placed back into fixative for another 30 min, and then rinsed for 1 h in cacodylate buffer (0.2 M,
2013
The present work focuses to evaluate the effect of formulation factors transcorneal permeation of aqueous drop of esmolol HCL through freshly excised goat, sheep, and buffalo corneas. Effect of concentration of esmolol HCl in aqueous solution on permeation of drug through excised goat, sheep, and buffalo corneas was study. Esmolol HCL ophthalmic solutions of different concentrations (pH 7.2) or 0.5% (w/v) solutions of different pH or 0.5% solutions (pH 7.2) containing different preservatives were made. Franz diffusion was used for measuring the drug permeated in the receptor by spectrophotometry at 280 nm, after 120 minutes. Compared with control formulation, esmolol HCL 0.5 %( w/v) solution at pH 7.2 containing benzalkonium chloride (0.01% w/v) in the formulation increased permeation to the maximum with all the corneas and the apparent permeability coefficient was found to be maximum 9.85±0.4 on goat cornea. The results of the ophthalmic aqueous drop optimized formulation containin...
Journal of Pharmaceutical Sciences, 1984
0 Current understanding of the mechanism of corneal penetration by organic molecules proposes the epithelial layer as the rate-limiting membrane for water-soluble compounds and the stromal layer as rate limiting for lipid-soluble compounds. This suggests that the relationship between corneal permeability and the logarithm of oil/water partition coefficients, for a series of drugs, should not be the typical, single, continuous, parabolic-shaped curve. Corneal penetration studies have been conducted in unanesthetized albino rabbits using various organic compounds, representing five orders of magnitude in partition coefficient, at a constant concentration of 4 X I o-s M dispensed in either a 1-or 90-centipoise (cps) solution. It has been shown that for non-ionizable compounds, a pair of bell-shaped curves were generated, one for lipid-soluble and one for water-soluble compounds. Small water-soluble species demonstrate very high apparent permeabilities, which may relate to the presence of aqueous pores or other paracellular drug movement. Penetration of ionizable compounds does not appear to correlate well with the structural relationships invoked for un-ionized compounds. Consistent with the proposed mechanisms of corneal penetration, oil-soluble drug substances show no improvement in drug bioavailability when dosed from a 90-cps solution, and water-soluble drugs show a modest improvement in ocular drug bioavailability. Small water-soluble substances demonstrate no improvement due to their already high bioavailability. The importance of nonproductive absorption and precorneal drainage on bioavailability is addressed.