Ocular tolerance of preservatives on the murine cornea

Long-term Effects of Latanoprost with Different Excipient Compositions on Intraocular Pressure, Hyperemia and Discomfort

Purpose: To compare the long-term effects of two preservative-free 0.005% latanoprost ophthalmic solutions with different excipient compositions on intraocular pressure (IOP), conjunctival hyperemia, and subjective ocular discomfort.Methods: The medical records of patients newly diagnosed with normal tension glaucoma or primary open angle glaucoma who started treatment using Xalost S® or Monoprost® were reviewed. IOP was measured with Goldmann applanation tonometry. Conjunctival hyperemia was measured with a Keratograph® 5M and subjective ocular discomfort was surveyed using a visual analog scale. Routine examinations were scheduled 1 week and 1, 3, 6, and 12 months after treatment. A generalized estimating equation was used to evaluate the changes of these parameters with time.Results: Xalost S® was used in 31 patients (60 eyes) and Monoprost® in 27 patients (50 eyes). The baseline characteristics were generally similar in the two groups with no significant differences. In the Xalost S® group, the IOP difference from baseline was significant at all time points (p < 0.001). However, in the Monoprost® group, after 1 month of treatment, the IOP difference decreased significantly (p = 0.054 at 1 week; p = 0.005 at 1 month; p < 0.001 after 1 month). Conjunctival hyperemia and subjective ocular discomfort did not differ significantly from baseline in either group.Conclusions: There was no significant difference in the frequency of side effects between the two drugs. The effect on the IOP drop was similar over time, but the initial IOP drop was greater in the Xalost S® group. This difference is presumed to be due to the different excipient compositions of the two drugs.

Corneal sensitivity is required for orientation in free-flying migratory bats

The exact anatomical location for an iron particle-based magnetic sense remains enigmatic in vertebrates. For mammals, findings from a cornea anaesthesia experiment in mole rats suggest that it carries the primary sensors for magnetoreception. Yet, this has never been tested in a free-ranging mammal. Here, we investigated whether intact corneal sensation is crucial for navigation in migrating Nathusius' bats, Pipistrellus nathusii, translocated from their migratory corridor. We found that bats treated with corneal anaesthesia in both eyes flew in random directions after translocation and release, contrasting bats with a single eye treated, and the control group, which both oriented in the seasonally appropriate direction. Using a Y-maze test, we confirmed that light detection remained unaffected by topical anaesthesia. Therefore our results suggest the cornea as a possible site of magnetoreception in bats, although other conceivable effects of the anaesthetic are also explored. Furthermore, we demonstrate that the corneal based sense is of bilateral nature but can function in a single eye if necessary.

Stability, safety, and transcorneal mechanistic studies of ophthalmic lyophilized cyclosporine-loaded polymeric micelles

Introduction

Cyclosporine-A (CsA) is generally used as an immunosuppressant and is also prescribed for some ophthalmic applications such as vernal keratoconjunctivitis and dry eye. However, it is limited clinically due to its low aqueous solubility and ocular bioavailability.

Methods

In this work, lyophilized methoxy poly(ethylene glycol)-poly(lactide) (mPEG-PLA) polymer micelles were prepared for ophthalmic formulations as a promising nanocarrier for hydrophobic drugs like CsA. A mPEG-PLA diblock polymer was synthesized by ring opening polymerization and CsA was loaded into mPEG-PLA micelles by a simple film dispersion method. A uniform design of experiments was utilized to optimize the final formulation. The obtained formulation was characterized for diameter (57.0±3.2 nm), entrapment efficiency % (98.51±1.4), and in vitro release. Moreover, incorporating the stabilizer mPEG2000 could increase the in vitro stability of the lyophilized CsA-loaded mPEG-PLA micelles.

Results

Results showed a sustained release of CsA from the micelles. Drug concentration and time-dependent cytotoxicity of human corneal epithelial-2 cells was observed. Additionally, the transcorneal mechanism of mPEG-PLA micelles was studied and the results showed that the mPEG-PLA micelles mainly absorbed by a paracellular pathway via corneal epithelial cells.

Conclusion

Taken together, the results proved that this mPEG-PLA diblock polymer can be potentially used as a nanoscopic carrier to deliver hydrophobic drugs in a controlled manner to the ocular region and, thus, deserves further attention.

Improving the topical ocular pharmacokinetics of lyophilized cyclosporine A-loaded micelles: formulation, in vitro and in vivo studies

Dry eye syndrome (DES) is one of the most common disorders of the eye for which combined treatment includes modification of the ocular environment and pathogenic therapies. Cyclosporine A (CsA), a immunosuppressive agent, has been demonstrated to be effective for the treatment of DES but is limited clinically by its low ocular bioavailability due to poor water solubility. In this paper, methoxy poly (ethylene glycol)-poly (lactide) polymer (mPEG-PLA) micelles were investigated as alternative vehicles for the solubilization and delivery of CsA to the eye. The in vitro stability indicated that CsA-loaded micellar lyophilized powder was stable for at least 3 months and the release profile showed a sustained release manner of CsA from micelles physically. In vivo ocular distribution studies demonstrated that the micellar formulations exhibited a 4.5-fold increase in retention effect at eyes compared with 0.05% CsA emulsion. In addition, the in vivo pharmacokinetics profile showed that the CsA-loaded micelles could enhance the retention time, achieving longer effect toward the DES. These studies proposed an effective micelle formulation as a novel ocular drug delivery system to improve solubility and bioavailability of ophthalmic CsA-controlled delivery.

Ocular Symptoms and Signs with Preserved and Preservative-Free Glaucoma Medications

PURPOSE

To compare the prevalence of side effects between eyedrops with or without preservatives, in terms of subjective symptoms and objective signs in patients with open-angle glaucoma.

METHODS

In a multicenter cross-sectional epidemiologic survey in four European countries, ophthalmologists in private practice enrolled 9658 nonconsecutive patients using preservative (P) or preservative-free (PF) beta-blocking eyedrops between June 1997 and December 2003. Subjective symptoms, conjunctival and palpebral signs, and superficial punctate keratitis were explored before and after a change in therapy. For statistical analysis, a Chi-square test was used to calculate the differences in the prevalence of symptoms and signs with or without preservatives.

RESULTS

A total of 74% of the patients used P, 12% PF, 10% a P-PF combination, and in 4% the type of medication was unknown. Each recorded symptom and all the palpebral, conjunctival, and corneal signs were significantly more frequent (p<0.0001) in the P-group than in the PF-group, such as pain or discomfort during instillation (48 vs 19%), foreign body sensation (42 vs 15%), stinging or burning (48 vs 20%), and dry eye sensation (35 vs 16%). A total of 68% of the patients had a sec-ond visit performed, of whom 63% (6083) had been evaluated on treatment difference. A significant decrease (p<0.0001) of all ocular symptoms and signs was observed in patients in whom the preserved eyedrops were diminished in number or altered into preservative free drops.

CONCLUSIONS

Compared to preserved eyedrops, preservative free eyedrops are significantly less associated with ocular symptoms and signs of irritation.

An overview on dry eye treatment: approaches for cyclosporin a delivery

Dry eye syndrome (DES, Keratoconjunctivitis sicca) is a common disorder of the tear film caused by decreased tear production or increased evaporation. Changes in tear composition also promote inflammation on the ocular surface by various mechanisms. Artificial tear drops, tear retention treatment, stimulation of tear secretion, or anti-inflammatory drugs may be used for dry eye treatment according to the severity of the disease. For untreated patients, the risk of ocular infection increases at considerable level and clinical course of the disease may proceed up to infection, corneal ulcer, and blindness. Artificial tears and/or punctual occlusions are used for tear replacement or preservation. New treatment approaches are designed to modify the underlying disease process. For the treatment of severe dry eye disease, cyclosporin A (CsA), the first one of the new generation immunomodulatory drugs, which has an anti-inflammatory effect, is frequently used. CsA has immunosuppressive effects following systemic application. Following local administration of CsA, it is expected to obtain effective drug concentration at the target area and to avoid the various side effects associated with systemic delivery. Microspheres, implants, and liposomes have been developed for administration of CsA subconjunctivally in order to enhance its efficiency.

In vitro cytotoxic effects of benzalkonium chloride on adenovirus

OBJECTIVE

To investigate the in vitro effects of benzalkonium chloride (BAK) at various concentrations and dosing schedules on adenoviral infection.

METHODS

Adenovirus was placed in Refeed media and at 30 min after infection, various concentrations and doses of BAK were placed into the 1 mL solution. All assays were incubated at 37 degrees C. Dosing of BAK was performed for 3 days and qualitative viral immunofluorescence was compared with that of controls.

RESULTS

BAK at multiple concentrations lysed the epithelial cell lines to varying degrees as did viral infection. Further, adenoviral infection was halted with many concentrations as well.

CONCLUSIONS

Adenoviral infection was inhibited in vitro by different concentrations of BAK.

CLINICAL RELEVANCE

Zymar solution which contains BAK could potentially have a role in the treatment of adenoviral ocular infection in humans.

Detrimental effect of preservatives in eyedrops: implications for the treatment of glaucoma

Antiglaucoma medications are often associated with ocular adverse reactions such as dry eye, and burning or stinging sensations. These undesirable effects may lead to treatment discontinuation and reduced quality of life in patients with glaucoma. Antiglaucoma medications usually contain benzalkonium chloride (BAK) as a preservative. Animal studies, in vitro studies and in vivo experiments have demonstrated various adverse effects of BAK. Clinical studies have also shown an increased incidence of adverse events with BAK and have demonstrated that the withdrawal of preservatives reduces these effects. Collectively, these data suggest that preservative-free antiglaucoma treatments have clinically relevant benefits for patients.

Disease, destination, dose and delivery aspects of ciclosporin: the state of the art

Since its discovery in 1971, ciclosporin has revolutionized organ transplantation and the treatment of autoimmune disorders. The wide array of applications resulting from its clinical efficacy warrant unique administration strategies and varying doses, times of exposure and extents of distribution, depending on target tissue. The poor biopharmaceutical characteristics of low solubility and permeability makes this uphill task even more challenging for the drug delivery scientist. Efforts underway have explored various body routes employing approaches like emulsions, microspheres, nanoparticles, liposomes, iontophoresis and penetration enhancers. This review attempts a brief holistic view of the "four Ds" (disease, destination, dose and delivery) surrounding this immunomodulator drug.

Cytotoxicity Evaluation of Soft Contact Lens Care Solutions on Human Conjunctival Fibroblasts

PURPOSE

To determine whether different contact lens care solutions for soft lenses cause damage to human conjunctival cells.

METHODS

Primary cultured human conjunctival fibroblasts were incubated with various concentrations of four different commercially available soft contact lens care solutions (OptiFree, Renu, SoloCare, Titmus) at concentrations of 5, 10 and 50 microl/ml medium. Toxicity was examined by determination of (1) the cell viability and mitochondrial activity with the colorimetric MTT test, and (2) the number of living cells with a cell analysis system (CASY 1) as compared with untreated cells.

RESULTS

For all four soft contact lens care solutions at a concentration of 5 mul/ml medium, no significant decrease in mitochondrial activity of the human conjunctival fibroblasts was found by the MTT test. At 10 microl/ml, only OptiFree and Titmus reduced mitochondrial viability significantly. The greatest reduction in mitochondrial activity occurred with all of the four soft contact lens care solutions at a concentration of 50 microl/ml. No significant decrease in the number of living conjunctival fibroblasts was observed by CASY 1 even at higher concentrations of the four solutions investigated.

CONCLUSION

This in vitro study demonstrates that the examined soft contact lens care solutions induce changes in mitochondria of human conjunctival cells only at higher doses as observed by the MTT test. However, this damage to the mitochondria did not lead to cell death as shown by the cell analysis system.

Cyclosporine A delivery to the eye: a pharmaceutical challenge

Systemic administration of cyclosporine A (CsA) is commonly used in the treatment of local ophthalmic conditions involving cytokines, such as corneal graft rejection, autoimmune uveitis and dry eye syndrome. Local administration is expected to avoid the various side effects associated with systemic delivery. However, the currently available systems using oils to deliver CsA topically are poorly tolerated and provide a low bioavailability. These difficulties may be overcome through formulations aimed at improving CsA water solubility (e.g. cyclodextrins), or those designed to facilitate tissue drug penetration using penetration enhancers. The use of colloidal carriers (micelles, emulsions, liposomes and nanoparticles) as well as the approach using hydrosoluble prodrugs of CsA have shown promising results. Solid devices such as shields and particles of collagen have been investigated to enhance retention time on the eye surface. Some of these topical formulations have shown efficacy in the treatment of extraocular diseases but were inefficient at reaching intraocular targets. Microspheres, implants and liposomes have been developed to be directly administered subconjunctivally or intravitreally in order to enhance CsA concentration in the vitreous. Although progress has been made, there is still room for improvement in CsA ocular application, as none of these formulations is ideal.

New surface-active polymers for ophthalmic formulations: evaluation of ocular tolerance

Two n-octenylsuccinate starch (AS) types of unknown molecular weights were assessed for ocular tolerance. Irritation potential of different solutions (containing 2 and 15% (w/w) AS) and AS stabilized emulsions (containing 15% (w/w) AS) was evaluated in vivo in rabbit eyes, using a confocal laser scanning microscope, and in vitro on treated excised pig corneas by light microscopy of histological cross sections. Both AS types were previously characterized by viscosity, osmolality and surface tension measurements. All tested solutions and emulsions showed good eye tolerance regardless of concentration and emulsifying properties suggesting AS to be a good alternative to commonly used solubilizing or emulsifying agents in ophthalmic formulations.

Evaluation of various compounds to inhibit activity of matrix metalloproteinases in the tear film of horses with ulcerative keratitis

OBJECTIVE

To examine in vitro effects of various antiproteolytic compounds on activity of matrix metalloproteinase (MMP)-2 and -9 in the tear film of horses with active corneal ulcers.

SAMPLE POPULATION

Samples of tear film obtained from the eyes of 34 horses with active ulcerative keratitis.

PROCEDURE

Horses were sedated, and tear samples were collected from the lower fornix of 34 ulcerated eyes by use of capillary tubes. The protease inhibitors 0.2% EDTA, 0.1% doxycycline, 10% N-acetylcysteine (NAC), 0.1% solution of a modified dipeptide that contains hydroxamic acid (ie, ilomostat), 0.1% alpha1-proteinase inhibitor (PI), 0.5% alpha1-PI, and 100% fresh equine serum (ES) were used to treat pooled samples. Amount of latent and active MMP-2 and -9 was measured by optical density scanning of gelatin zymograms of treated and untreated tear samples.

RESULTS

Pooled tear samples obtained from ulcerated eyes contained the latent and active forms of MMP-2 and -9. Compared with MMP activity in untreated samples, total MMP activity (sum of all bands detected) observed on the gelatin zymogram gels was reduced by 99.4% by EDTA, 96.3% by doxycycline, 98.8% by NAC, 98.9% by ilomostat, 52.4% by 0.1% alpha1-PI, 93.6% by 0.5% alpha1-PI, and 90.0% by ES.

CONCLUSIONS AND CLINICAL RELEVANCE

We documented that EDTA, doxycycline, NAC, ilomostat, alpha1PI, and ES inhibited MMP activity in vitro. Because these compounds use different mechanisms to inhibit various families of proteases in the tear film of horses, a combination of these protease inhibitors may be beneficial for treatment of corneal ulcers in horses.

Influence of n-octenylsuccinate starch on in vitro permeation of sodium diclofenac across excised porcine cornea in comparison to Voltaren ophtha

The influence of different n-octenylsuccinate starch (AS) formulations, i.e. AS solutions and an AS stabilized emulsion system, on the in vitro corneal permeation behaviour of sodium diclofenac (DfNa) was investigated and compared to the commercial product Voltaren ophtha (VO). Although saturation concentrations of DfNa achieved with polyoxethylene-35-castor oil (POC), which is the solubilizing additive in VO, are higher than those achieved with AS at varying pH values, it was found that AS solutions yield higher DfNa permeation rates than VO or a POC solution. However, permeation is extremely reduced with rising AS concentrations or AS emulsions. Neither pH value (6.5 or 7.4) nor presence of preservative seem to have an impact on permeation activity. In order to assess possible cytotoxic effects of the preparations investigated, red blood cell haemolysis studies were performed with different preparations containing DfNa. None of the tested AS formulations showed significantly high haemolytic data. On the other hand the high in vitro haemolysis obtained with VO is primarily based on an osmotic effect caused by boric acid.

Evaluation of the health aspects of methyl paraben: a review of the published literature

Methyl paraben (CAS No. 99-76-3) is a methyl ester of p-hydroxybenzoic acid. It is a stable, non-volatile compound used as an antimicrobial preservative in foods, drugs and cosmetics for over 50 years. Methyl paraben is readily and completely absorbed through the skin and from the gastrointestinal tract. It is hydrolyzed to p-hydroxybenzoic acid, conjugated, and the conjugates are rapidly excreted in the urine. There is no evidence of accumulation. Acute toxicity studies in animals indicate that methyl paraben is practically non-toxic by both oral and parenteral routes. In a population with normal skin, methyl paraben is practically non-irritating and non-sensitizing. In chronic administration studies, no-observed-effect levels (NOEL) as high as 1050 mg/kg have been reported and a no-observed-adverse-effect level (NOAEL) in the rat of 5700 mg/kg is posited. Methyl paraben is not carcinogenic or mutagenic. It is not teratogenic or embryotoxic and is negative in the uterotrophic assay. The mechanism of cytotoxic action of parabens may be linked to mitochondrial failure dependent on induction of membrane permeability transition accompanied by the mitochondrial depolarization and depletion of cellular ATP through uncoupling of oxidative phosphorylation. Parabens are reported to cause contact dermatitis reactions in some individuals on cutaneous exposure. Parabens have been implicated in numerous cases of contact sensitivity associated with cutaneous exposure; however, the mechanism of this sensitivity is unknown. Sensitization has occurred when medications containing parabens have been applied to damaged or broken skin. Allergic reactions to ingested parabens have been reported, although rigorous evidence of the allergenicity of ingested paraben is lacking.

Ocular tolerance of preservatives and alternatives

Eye drops are multiple dosage forms protected against microbial contamination by means of preservatives. However, the ocular tolerance of these chemicals can vary and this may result in adverse toxic or allergic reactions. This overview presents the pharmacopoeial requirements for the preservation of eye drops, the factors affecting ocular tolerance as well as the adverse external ocular effects induced by preservatives. The alternatives to the use of preservatives are also discussed, including the recent progress in eye drops packaging.

Increased corneal hydration induced by potential ocular penetration enhancers: assessment by differential scanning calorimetry (DSC) and by desiccation

The corneal toxicity of some surfactants of possible use as ocular penetration enhancers was investigated by measuring their effect on hydration of rabbit corneas 'in vitro'. The tested substances were benzalkonium chloride (BAC), cetylpyridinium chloride (CPC), ethylenediaminetetraacetic acid disodium salt (EDTA), polyoxyethylene-20-stearyl ether (Brij 78, PSE), polyethoxylated castor oil (Cremophor EL, PCO) and sodium deoxycholate (DC). Freshly excised corneas, mounted in perfusion cells, were kept in contact for 1 h with solutions of these agents; corneal hydration was then evaluated by measuring: (a) their total (free+bound) water content by desiccation (gravimetric analysis); and (b) their free water content by differential scanning calorimetry (DSC). The DSC measurements also provided a rough quantitative estimate of corneal solutes. All tested agents significantly influenced corneal hydration, evidently as a consequence of alteration of the corneal epithelium. Although a brief contact with the precorneal tissues 'in vivo' may not prove harmful, the use of these compounds as potential ocular permeation enhancers or otherwise as ingredients of topical ocular formulations for long-term use should be considered with caution.