The effect of epinephrine and benzalkonium chloride on cultured corneal endothelial and trabecular meshwork cells

Differential Effects of Benzalkonium Chloride on Human Trabecular Meshwork Cells Not Treated or Treated with Transforming Growth Factor-β2 or Dexamethasone

Purpose: The objective of the present study was to evaluate the effects of low concentrations of benzalkonium chloride (BAC) (10-7%, 10-6%, or 10-5%) on healthy and glaucomatous human trabecular meshwork (HTM) cells. For this purpose, we used in vitro models replicating a healthy HTM and HTM with primary open-angle glaucoma (POAG) or steroid-induced glaucoma (SG) using two-dimensional (2D) cultures of HTM cells not treated or treated with a 5 ng/mL solution of transforming growth factor-β2 or 250 nM dexamethasone (DEX). Methods: Analyses were carried out for (1) the intercellular affinity function of 2D HTM monolayers, as determined by transepithelial electrical resistance (TEER) measurements; (2) cell viability; (3) cellular metabolism by using a Seahorse bioanalyzer; and (4) expression of extracellular matrix (ECM) molecules, an ECM modulator, and cell junction-related molecules. Results: In the absence and presence of BAC (10-7% or 10-5%), intercellular affinity function determined by TEER and cellular metabolic activities were significantly and dose dependently affected in both healthy and glaucomatous HTM cells despite the fact that there was no significant decrease in cell viabilities. However, the effects based on TEER values were significantly greater in the healthy HTM. The mRNA expression of several molecules that were tested was not substantially modulated by these concentrations of BAC. Conclusions: The findings reported herein suggest that low concentrations of BAC may have unfavorable adverse effects on cellular metabolic capacity by inducing increases in the intercellular affinity properties of the HTM, but those effects of BAC were different in healthy and glaucomatous HTM cells.

Sympathetic activation leads to Schlemm's canal expansion via increasing vasoactive intestinal polypeptide secretion from trabecular meshwork

We previously demonstrated vasoactive intestinal polypeptide (VIP) eyedrops reduce intraocular pressure (IOP) and stabilize cytoskeleton of the Schlemm's canal (SC) endothelium in a chronic ocular hypertension rat model. Here we determine if the trabecular meshwork (TM) releases endogenous VIP and affect SC in paracrine manner, and whether this cellular interaction via VIP is strengthened under stimulated sympathetic activity. A rat model of moderate-intensity exercise was established to stimulate sympathetic activation. IOP post exercise was measured by a rebound tonometer. Sympathetic nerve activity at the TM was immunofluorescence-stained with DβH and PGP9.5. Morphological changes of TM and SC were quantitatively measured by hematoxylin-eosin (HE) staining. Further, epinephrine was applied to mimic sympathetic excitation on primary rat TM cells, and ELISA to measure VIP levels in the medium. The cytoskeleton protective effect of VIP in the epinephrine-stimulated conditioned medium (Epi-CM) was evaluated in oxidative stressed human umbilical vein endothelial cells (HUVECs). Elevated sympathetic nerve activity was found at TM post exercise. Changes accompanying the sympathetic excitation included thinned TM, expanded SC and decreased IOP, which were consistent with epinephrine treatment. Epinephrine decreased TM cell size, enhanced VIP expression and release in the medium in vitro. Epi-CM restored linear F-actin and cell junction integrity in H₂O₂ treated HUVECs. Blockage of VIP receptor by PG99-465 attenuated the protective capability of Epi-CM. VIP expression was upregulated at TM and the inner wall of SC post exercise in vivo. PG99-465 significantly attenuated exercise-induced SC expansion and IOP reduction. Thus, the sympathetic activation promoted VIP release from TM cells and subsequently expanded SC via stabilizing cytoskeleton, which resulted in IOP reduction.

The trabecular meshwork in glaucoma: An inflammatory trabeculopathy?

Glaucoma is an optic neuropathy in which the primary risk factor is increased intraocular pressure (IOP), attributed to increased resistance to trabecular outflow of aqueous humor (AH). This resistance is believed to result from trabecular degeneration secondary to chronic oxidative stress and cellular senescence but may also involve inflammatory mechanisms whose roles are little known. In fact, inflammatory processes play a major role in the pathophysiology of glaucoma to varying degrees, affecting all structures of the eye, including the ocular surface, the anterior and posterior segments, and even the visual pathways of the brain. These processes are thought to result from dysfunction of a regulatory, protective para-inflammation, becoming chronic and harmful in glaucoma. While the mechanisms of the retinal inflammation which accelerates the degeneration of retinal ganglion cells (RGCs) as well as the inflammation of the ocular surface aggravated by long-term use of preserved glaucoma eye drops have been described for several years, very little is known about the pathophysiology of trabecular inflammation in glaucoma. The objective of this literature review is to provide a synthesis of knowledge on the roles and mechanisms of inflammation in both the healthy and glaucomatous trabecular meshwork, as well as its role in the pathophysiology of glaucoma. Therefore, after a review of the mechanisms of cellular senescence and oxidative stress - sources of trabecular inflammation, we will approach the study of the expression and roles of the main inflammatory mediators within the trabecular meshwork. Finally, we will discuss current knowledge on the toxicity of glaucoma eye drops and their preservatives on the ocular surface and trabecular meshwork as well as their role in trabecular inflammation.

Preservative-Free Prostaglandin Analogs and Prostaglandin/Timolol Fixed Combinations in the Treatment of Glaucoma: Efficacy, Safety and Potential Advantages

Glaucoma therapy-related ocular surface disease (OSD) is a serious pathology with a broad spectrum of insidious clinical presentations and complex pathogenesis that undermines long-term glaucoma care. Preservatives, especially benzalkonium chloride (BAK), contained in topical intraocular pressure-lowering medications frequently cause or aggravate OSD in glaucoma. Management of these patients is challenging, and to date often empirical due to the scarcity of controlled long-term clinical trials. Most of the available data are extracted from case series and retrospective analysis. Preservative-free prostaglandins and prostaglandin/timolol fixed combinations are novel options developed to remove the harmful impact of preservatives, especially BAK, upon ocular tissues. Based on what is currently known on the value of preservative-free antiglaucoma therapies it is tempting to speculate how these new therapies may affect the future medical management of all glaucoma patients. This article provides a comprehensive and critical review of the current literature on preservative-free prostaglandins and preservative-free prostaglandin/timolol fixed combinations.

Preservatives in glaucoma medication

Preservatives continue to be in widespread use in ophthalmic medications due to the convenience they provide, regulatory requirements and the higher cost of alternatives. Benzalkonium chloride (BAK) remains the most commonly used preservative but there is a trend towards the use of preservative-free (PF) drops for glaucoma, although at a higher price. An extensive body of literature explores BAK toxicity on ocular structures in animal and laboratory studies (in vitro and in vivo). Non-randomised controlled studies have provided some supporting evidence of its toxicity in patients, especially in those with pre-existing ocular surface disease (OSD) or on multiple medications. However, there have been very few randomised controlled trials that compare the same medication with and without BAK preservative. Several of these trials have never been published in any peer reviewed journals. Notwithstanding, those that have been published, have not demonstrated any clear benefits of the BAK-free formulations. Short duration and exclusion of those with OSD are limitations of these studies. There is a lack of evidence of clinically significant harm from a small number of BAK preserved drops in patients without OSD. This means that generally more expensive PF glaucoma medications should only be recommended for those on poly pharmacy or those with OSD but are not necessarily required for all patients.

Glaucoma therapy: preservative-free for all?

Preservatives used in topical glaucoma medications have a plethora of well-described toxic effects on the ocular surface. Such ocular toxicity is manifest clinically as ocular surface disease (OSD) and has been confirmed in epidemiologic, prospective clinical trials and studies in which patients are switched from preservative-added to preservative-free topical therapy. Such toxicity has implications not only for tolerability, but also for adherence and persistence with therapy that is known to be poor in glaucoma. Glaucoma medication is now widely available in preservative-free formulations, and the question arises as to which patients should receive preservative-free glaucoma therapy in preference to preservative-added medication. A case can be made for several subpopulations of patients who might particularly benefit from preservative-free medication: patients with existing OSD, older patients, younger adult patients, female patients, pediatric and juvenile patients, patients who work in air-conditioned environments or who use electronic screens frequently, patients with medical risk factors for OSD, patients in whom trabecular surgery may become indicated in the future, contact lens users, perhaps patients with Asian ethnicity and patients with severe or treatment-refractory glaucoma. Whilst arguments could be made for selecting patients for preservative-free medication on the basis of their existing risk of OSD, collectively, these patients form a significant proportion of the glaucoma patient population as a whole and, in the absence of any cost premium or positive indication for preservative-added medication, preservative-free glaucoma medication for all patients seems an appropriate strategy.

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.

Switch from BAK-preserved to preservative-free latanoprost decreases anterior chamber flare in POAG patients

PURPOSE

To validate the hypothesis that BAK induces low-grade inflammation in the anterior chamber, we designed a study to investigate whether switching from BAK-preserved to preservative-free latanoprost in patients with primary open-angle glaucoma (POAG) would reduce the flare levels.

PATIENTS

Forty-one eyes of twenty-two patients with primary open-angle glaucoma treated with BAK-preserved latanoprost for at least 6 months as monotherapy were included. Exclusion criteria included any use of topical eye drops other than latanoprost, pseudoexfoliation and pigment dispersion glaucoma, wearing of contact lenses and intraocular surgery in the past year.

METHODS

At the start of the study, we measured baseline flare values. We then switched all patients to preservative-free latanoprost. After 1, 2, and 3 months, a routine ophthalmological examination was performed and flare measurement repeated.

RESULTS

Thirty-three eyes were followed up throughout the entire 3-month period. One month after the switch to preservative-free latanoprost, a statistically significant mean drop in flare of - 0.96 ph/ms (P = 0.025) was observed. Mean flare decreased further by - 1.31 ph/ms (P = 0.0027) after 2 months and by - 1.25 ph/ms (P = 0.0041) after 3 months.

CONCLUSION

The switch from BAK-preserved to preservative-free latanoprost induced a statistically significant reduction in mean flare value. Whereas our previous study showed an increase in flare when initiating treatment with BAK-preserved eye drops, this study shows a decrease in flare upon cessation of BAK-preserved drugs. The combined evidence from the two studies strongly suggests that in humans BAK exerts its effects not only on the ocular surface, but also at the level of the anterior chamber.

Exciting directions in glaucoma

Glaucoma is a complex, life-long disease that requires an individualized, multifaceted approach to treatment. Most patients will be started on topical ocular hypotensive eyedrop therapy, and over time multiple classes of drugs will be needed to control their intraocular pressure. The search for drugs with novel mechanisms of action, to treat those who do not achieve adequate intraocular pressure control with, or become refractory to, current therapeutics, is ongoing, as is the search for more efficient, targeted drug delivery methods. Gene-transfer and stem-cell applications for glaucoma therapeutics are moving forward. Advances in imaging technologies improve our understanding of glaucoma pathophysiology and enable more refined patient evaluation and monitoring, improving patient outcomes.

Effects of benzalkonium chloride on the blood-aqueous and blood-retinal barriers of pseudophakic eyes

PURPOSE

To evaluate the effects of benzalkonium chloride (BAK) on the blood-aqueous (BAB) and blood-retinal barriers (BRB) of pseudophakic eyes.

METHODS

Prospective, randomized, investigator-masked, comparative study. Patients were randomly assigned to preservative-free artificial tears or BAK-preserved artificial tears. One drop of artificial tears was instilled 4 times a day in the study eye, starting the day after randomization for 30 days. Anterior chamber flare was assessed by a laser flare meter (LFM) and macular thickness measurements were obtained with optical coherence tomography, before, 15, and 30 days after randomization.

RESULTS

A total of 44 healthy eyes of 44 pseudophakic volunteers were recruited. There were no significant differences regarding demographics (age, gender, and race distributions) and clinical characteristics (eye, mean intraocular pressure, and mean best-corrected visual acuity) between the 2 groups (P>0.05). No significant differences in baseline mean LFM values were observed (P=0.262). However, we detected a statistically significant increase in mean LFM measurements in the BAK-preserved group (11.4 ± 5.1 ph/ms) (P=0.017) after 15 days. After 30 days, the BAK-preserved group maintained significantly higher flare values (11.9 ± 5.9 ph/ms) compared with baseline (P=0.043). On the other hand, the preservative-free group showed mean flare values of 8.4 ± 2.5 ph/ms, not significantly different from those obtained at baseline (P=1.00). We observed no statistically significant change in macular thickness measurements at days 15 and 30 in either group (P>0.05). Cystoid macular edema was not detected in this series.

CONCLUSIONS

Our results suggest that a short-term exposure to BAK can cause disruption of the BAB, without altering the BRB in pseudophakic eyes.

Benzalkonium chloride and glaucoma

Glaucoma patients routinely take multiple medications, with multiple daily doses, for years or even decades. Benzalkonium chloride (BAK) is the most common preservative in glaucoma medications. BAK has been detected in the trabecular meshwork (TM), corneal endothelium, lens, and retina after topical drop installation and may accumulate in those tissues. There is evidence that BAK causes corneal and conjunctival toxicity, including cell loss, disruption of tight junctions, apoptosis and preapoptosis, cytoskeleton changes, and immunoinflammatory reactions. These same effects have been reported in cultured human TM cells exposed to concentrations of BAK found in common glaucoma drugs and in the TM of primary open-angle glaucoma donor eyes. It is possible that a relationship exists between chronic exposure to BAK and glaucoma. The hypothesis that BAK causes/worsens glaucoma is being tested experimentally in an animal model that closely reflects human physiology.

Cell viability score (CVS) as a good indicator of critical concentration of benzalkonium chloride for toxicity in cultured ocular surface cell lines

Cytotoxicity of benzalkonium chloride (BAK) is a major factor affecting drug cytotoxicity. This study aimed to determine the critical concentration of BAK for cultured ocular cells, using SIRC (rabbit corneal epithelium), BCE C/D-1b (bovine corneal epithelial cells), RC-1 (rabbit corneal epithelium), and Chang (human conjunctival cells). Cell viability was determined following the exposure of cells to 11 concentrations of BAK for 10, 30, or 60 min using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and neutral red assays, and the cell viability score (CVS) was used to evaluate comprehensively the toxicity of BAK. The CVS system consists of two values. The CVS50 was determined by the number of measurements for viability ≥50% of control. The CVS40/80 was calculated as follows: CVS40/80=(number of measurements for viability values >80%)-(number of measurements for viability values <40%). Both %CVS50 and %CVS40/80 decreased with concentrations of BAK. When BAK concentrations were 0.01% or higher, %CVS50 and %CVS40/80 became 0 and less than -90, respectively. Meanwhile, when BAK concentrations were 0.001% or lower, %CVS50 became 100. In the case of %CVS40/80, when the BAK concentrations were 0.002% or lower, the values reached 75 or more, and when 0.0005% or lower, the %CVS40/80 value reached 100. Accordingly, BAK induced very low cytotoxicity in the cultured ocular cell lines at concentrations of 0.002% or lower. The concentration-dependency confirmed that the CVS score is useful for expressing drug cytotoxicity in a simple and comprehensive manner.

Controversy: Is Benzalkonium Chloride Necessary in Antiglaucoma Drops?

Medical therapy is the first-line option in glaucoma management, with benzalkonium chloride (BAC) being the most frequently used preservative in antiglaucoma medications. Its use is however, known to be associated with deleterious effects on the ocular surface. This review is an attempt to critically evaluate whether BAC really is indispensable for better bioavailability of antiglaucoma drugs and consequently, better IOP control.

How to cite this article: Louati Y, Shaarawy T. Controversy: Is Benzalkonium Chloride Necessary in Antiglaucoma Drops? J Current Glau Prac 2012;6(3):104-107.

Differential pharmacology and clinical utility of preservative-free tafluprost in the treatment of ocular hypertension and glaucoma

Glaucoma is a chronic disease requiring lifelong treatment. Discomfort due to medications may affect patients’ quality of life and may cause poor compliance, which leads to poor intraocular pressure control. To minimize the side effects of long-term treatment, preparations with lower benzalkonium chloride concentrations, preservative-free preparations and alternative preservatives have been developed and reported to have a lower rate of side effects. Tafluprost, launched on the ophthalmic market in 2008, is a new 16-phenoxy analogue of prostaglandin F_2α, clinically used as an ocular hypotensive agent for the treatment of glaucoma and ocular hypertension. The safety and intraocular pressure-lowering efficacy of tafluprost has been demonstrated in various preclinical and clinical studies.

Benzalkonium chloride induces anterior chamber inflammation in previously untreated patients with ocular hypertension as measured by flare meter: a randomized clinical trial

PURPOSE

The deleterious effects of benzalkonium chloride (BAK) on the ocular surface are well known. However, few clinical data are available to prove a toxic effect at the level of the anterior chamber. The laser flare meter is a reliable tool to detect low levels of inflammation in the anterior chamber. We wanted to know whether instillation of BAK-preserved timolol in one eye would result in higher laser flare values than the instillation of preservative-free timolol in the fellow eye.

METHODS

Randomized prospective, single-masked clinical trial. Twenty-eight untreated patients with ocular hypertension were recruited. After obtaining baseline flare values, we randomly assigned one eye to BAK-preserved timolol and the fellow eye to preservative-free timolol. After 1 month, flare measurements were repeated.

RESULTS

There was a significant increase in the flare values in the two treatment regimens, but the increase in the BAK-treated eyes was higher than in the preservative-free treated eyes, and this difference in increase was statistically significant.

CONCLUSION

This is the first study to show that short-term BAK administration produces inflammation in the anterior segment of previously untreated patients whose blood-aqueous barrier was not affected by recent intraocular surgery.

Preservative use in topical glaucoma medications

Benzalkonium chloride (BAK) is the principal preservative employed in topical ocular hypotensive medications, although alternative compounds recently have begun to be employed or examined. Individual clinical trials have shown that exposure to BAK concentrations contained in ophthalmic solutions does not produce adverse sequelae in the majority of glaucoma patients, but concerns continue with regard to its long-term use. These concerns have resulted from an extensive research effort, including preclinical studies with in vitro and in vivo models, as well as recent clinical investigations dedicated specifically to this issue. The aim of this systematic literature review of both preclinical and clinical data was to determine the relevance of these findings to clinical practice. Most preclinical studies reported negative effects of BAK exposure, but with few exceptions, BAK concentrations and exposure times greatly exceeded those likely to be experienced by patients, given the normal physiological dilution by the tear film. In addition, consistent evidence of BAK-related toxicity did not emerge from our review of dedicated clinical investigations. Thus, taken together, current evidence supports the safety of BAK for most glaucoma patients, although subpopulations with abnormal tearing may benefit from alternative preservative compounds or preservative-free formulations. Further studies to identify these populations are needed.

[Ocular toxicity of benzalkonium]

In order to meet the requirements of the pharmacopeia, ophthalmic preparations have to be manufactured in conditions that can secure their sterility before use and can prevent the development of micro-organisms after opening of the vial. The addition of an appropriate preservative is a way to meet this requirement. However, in addition to their lack of efficacy in certain conditions, they can be problematic in terms of formulation, stability and interaction with the packagings. Furthermore, their daily and repeated use in chronic pathologies such as glaucoma, dry eye or allergy has revealed their nuisance. Moreover, the recognition of certain parameters such as life quality and therapeutic observance has strengthened the proofs that have already been clinically shown. The review of the experimental and clinical data already published about the toxicity of the preservatives shows that almost every ocular structure is affected to various extents. From the first assumption data to preclinical and clinical proofs, this article highlights the evolution of the understanding process towards the toxic role of preservatives.

Toxicity of antiglaucoma drugs with and without benzalkonium chloride to cultured human corneal endothelial cells

Purpose

The toxicity of antiglaucoma medications to ocular surface cells has been evaluated extensively; however, the toxicity to corneal endothelial cells (CECs) remains elusive. Our aim is to evaluate the toxicity of antiglaucoma medications to CECs using an in vitro toxicity assay.

Methods

Primary cultures of human (H) CECs derived from eye bank specimens were established. Following exposure of HCECs to test solutions for 10, 30, or 60 minutes, or 48 hours, we measured cell viability using a WST-1 assay. Test solutions were diluted in culture media and included 0.5% Timoptol^®, preservative-free 0.5% timolol maleate, 1% Trusopt^®, preservative-free 1% dorzolamide, Travatan^®, Travatan Z^®, Xalatan^®, and benzalkonium chloride (BAK). To assess cell viability, the value of the test culture well after treatment was expressed as a percentage of that of the control well. Toxicity of each solution was compared using the cell viability score (CVS).

Results

After exposure to 10-fold dilutions of test solutions for 48 hours, HCEC viabilities were 48.5% for 0.5% Timoptol, 80.9% for preservative-free 0.5% timolol maleate, 47.0% for 1% Trusopt, 71.7% for preservative-free 1% dorzolamide, 55.5% for Travatan, 88.5% for Travatan Z, and 52.5% for Xalatan. Exposure to test solutions diluted 100-fold or more resulted in HCEC viabilities >80%, with the exception of preservative-free 1% dorzolamide, which resulted in a viability of 72.0% at a dilution of 100-fold. Based on CVS, the order of cell viability was Travatan Z ≥ preservative-free timolol maleate = preservative-free dorzolamide > 0.5% Timoptol = 1% Trusopt > Travatan ≥ Xalatan. Assessment of the combined effect of drug and BAK revealed that latanoprost reduced the toxicity of BAK.

Conclusion

Antiglaucoma eye drops produced HCEC toxicity that appeared to depend on the presence of BAK. Because dilution of the antiglaucoma solutions resulted in markedly lower HCEC toxicity, HCEC damage due to antiglaucoma medication may occur only in rare cases. The CVS was useful for comparison of the toxicity of the drugs.

Preservatives in eyedrops: the good, the bad and the ugly

There is a large body of evidence from experimental and clinical studies showing that the long-term use of topical drugs may induce ocular surface changes, causing ocular discomfort, tear film instability, conjunctival inflammation, subconjunctival fibrosis, epithelial apoptosis, corneal surface impairment, and the potential risk of failure for further glaucoma surgery. Subclinical inflammation has also been described in patients receiving antiglaucoma treatments for long periods of time. However, the mechanisms involved, i.e., allergic, toxic, or inflammatory, as well as the respective roles of the active compound and the preservative in inducing the toxic and/or proinflammatory effects of ophthalmic solutions, is still being debated. The most frequently used preservative, benzalkonium chloride (BAK), has consistently demonstrated its toxic effects in laboratory, experimental, and clinical studies. As a quaternary ammonium, this compound has been shown to cause tear film instability, loss of goblet cells, conjunctival squamous metaplasia and apoptosis, disruption of the corneal epithelium barrier, and damage to deeper ocular tissues. The mechanisms causing these effects have not been fully elucidated, although the involvement of immunoinflammatory reactions with the release of proinflammatory cytokines, apoptosis, oxidative stress, as well as direct interactions with the lipid components of the tear film and cell membranes have been well established. Preservative-induced adverse effects are therefore far from being restricted to only allergic reactions, and side effects are often very difficult to identify because they mostly occur in a delayed or poorly specific manner. Care should therefore be taken to avoid the long-term use of preservatives, otherwise a less toxic alternative to BAK should be developed, as this weakly allergenic but highly toxic compound exerts dose- and time-dependent effects. On the basis of all these experimental and clinical reports, it would be advisable to use benzalkonium-free solutions whenever possible, especially in patients with the greatest exposure to high doses or prolonged treatments, in those suffering from preexisting or concomitant ocular surface diseases, and those experiencing side effects related to the ocular surface. Indeed, mild symptoms should not be underestimated, neglected, or denied, because they may very well be the apparent manifestations of more severe, potentially threatening subclinical reactions that may later cause major concerns.

Ocular preservatives: associated risks and newer options

Presence of a preservative in an ocular medication has often been considered a culprit in damaging the epithelium. However, the inclusion of a preservative is equally necessary, especially in multiple-dose containers, in order to protect against dangerous organisms accidentally gaining access during instillation. Benzalkonium chloride (BAK), chlorobutanol, chlorhexidine acetate (CHA), and phenylmercuric nitrate or acetate are some commonly used preservatives in eye preparations. New preservatives with a wide range of activity and good safety profiles have been introduced in the market, such as stabilized oxychloro complex (SOC), sofZia, and sodium perborate. In the present review, we discuss various conventional and newly proposed and patented preservative molecules for ocular use. Reasons for discontinuing traditional preservatives and the need for less-toxic molecules are discussed at length, along with newer options coming up in this area.

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.

Cellular cytotoxicity of antiglaucoma drugs in cultured corneal endothelial cells

In this study, the various antiglaucoma drugs including betaxolol, timolol, levobunolol, carteolol, brimonidine, dipivefrin, dorzolamide, brinzolamide, latanoprost, unoprostone, and pilocarpine were used to investigate the effects of cellular cytotoxicity in cultured bovine corneal endothelial cells. After exposure to the drugs in three dilutions, 1/100, 1/1,000, and 1/10,000, for 100 minutes, cells were estimated based on the release assay of lactate dehydrogenase (LDH) enzyme. It was found that cellular LDH was significantly released in the medium only at 1/100th dilution of betaxolol, brimonidine, dorzolamide, dipivefrin, latanoprost and unoprostone to 130%, 123%, 145%, 157%, 128% and 237%, respectively, compared with controls upon exposure to drugs for 100 minutes. Moreover, benzalkonium chloride preservative at the concentrations ranging from 0.001 to 0.00001 mg/mL did not affect cellular LDH release in bovine corneal endothelial cells. These results indicate that high concentrations of antiglaucoma drugs may induce cytotoxicity in corneal endothelial cells.

The effect of drop vehicle on the efficacy and side effects of topical glaucoma therapy: a review

PURPOSE OF REVIEW

Topically applied medications are frequently used in ophthalmology to treat acute and chronic conditions, and are considered to be safer than their systemically applied counterparts, due to the reduced rate of systemic side effects.

RECENT FINDINGS

Many experimental and clinical studies have reported that the long-term use of topical medications in chronic ophthalmic conditions, such as glaucoma, may adversely affect the ocular surface. Preservatives play a pivotal role in almost all multidose ophthalmic preparations, inhibiting microbial growth and preserving the active drug. Consequently, preservatives are partially responsible for ocular side effects, although the exact mechanism of these side effects is not known.

SUMMARY

The role of preservatives in the efficacy and side effects of antiglaucoma drugs is reviewed. The recent advances in preservative technologies and their role in decreasing the side effects associated with antiglaucoma drugs are also discussed.

Comparison of Toxicological Profiles of Benzalkonium Chloride and Polyquaternium-1: An Experimental Study

PURPOSE

The aim of this study was to compare, in vivo on a rat model, two different preservatives- benzalkonium chloride (BAC) and polyquaternium-1 (PQ-1)-using new experimental approaches.

METHODS

Thirty (30) eyes of 15 male Lewis rats were used in this study. Rats were randomly divided into five groups instilled twice a day for 11 days with eye drops containing different concentrations of preservatives, 0.1% BAC, 0.5% BAC, 0.1% PQ-1, 0.5% PQ-1, and balanced salt solution (BSS) as a control. The ocular surface toxicity of these two preservatives was investigated using new in vivo experimental approaches. Slit-lamp examination, the fluorescein test, the red phenol test, impression cytology, and in vivo corneal confocal microscopy were used to evaluate the rat ocular surface after preservative instillation. Histology sections and immunohistochemistry were also examined to confirm these results.

RESULTS

Compared to PQ-1, BAC consistently and dramatically altered the corneoconjunctival surface as evaluated by slit-lamp examination, the fluorescein test, impression cytology, in vivo confocal microscopy, and histology. The 0.5% BAC solution also significantly decreased tear production compared to the control. Although 0.5% PQ-1 significantly decreased goblet cell density in comparison to the control, and some abnormalities were observed with in vivo confocal microscopy, no statistically significant differences were observed between these two groups using the tear production test, slit-lamp and fluorescein evaluation, or histology.

CONCLUSION

Using an acute rat model of ocular toxicity by comparing preservatives at high concentrations, we demonstrated in vivo that high doses of PQ-1 were much less toxic than BAC. In vivo confocal microscopy and impression cytology are new promising experimental approaches to studying the rat corneoconjunctival surface, particularly in the field of ocular surface toxicity.

Effects of intraocular epinephrine on the corneal endothelium of rabbits

Epinephrine is frequently used in the phacoemulsification to dilate pupils. To determine the effects of different concentration of epinephrine on the corneal endothelial cells, twenty-eight rabbit eyes were equally divided into four groups. Solutions, which contained normal saline, 1:1000 epinephrine, 1:5000 epinephrine and 1:10000 epinephrine respectively, were injected into the anterior chambers of the eyes of four groups of rabbits. In vivo morphological changes of corneal endothelium and changes of thickness were checked with specular microscopy. In vitro morphological evaluation of corneal endothelium was observed in excised corneal buttons stained with alizarin red with trypan blue, and with scanning electron microscopy. Our results showed that there was no significant difference in cell density and corneal thickness among the four groups. Alizarin red with trypan blue stain and SEM exam revealed smooth and distinct cell borders of endothelial cells in each group. Intracameral injection of epinephrine does not produce toxic effect on corneal endothelial cells in rabbits.

Confocal microscopic examination of trabecular meshwork removed during ab externo trabeculectomy

AIMS

The aim of the ab externo trabeculectomy (AET) is to remove the external portion of the trabecular meshwork (ETM) responsible for the main aqueous outflow resistance in glaucoma patients, with no opening of the anterior chamber. ETM characteristics were evaluated with a confocal microscope.

METHODS

A prospective comparative observational case series was performed in 60 consecutive medically treated patients with primary open angle glaucoma and eight postmortem normal donors' eyes that underwent AET. Once deroofing the Schlemm' s canal (SC), a deeper dissection led to removal of a coherent membrane (ETM) which allowed satisfactory aqueous egress through the remaining intact internal trabecular meshwork (TM) layers. After fixation with acetone and immunostaining with anti-vimentin antibody, ETM were analysed with a confocal microscope.

RESULTS

Glaucomatous ETM (mean thickness: 29.5 (7.6) micro m) were characterised by a severe paucicellularity compared with the controls (respectively 37.3 (9.7) cells/area and 167.5 (24.9) cells/area, p<10(-4)). ETM analysis showed involvement of both cribriform and corneoscleral layers. ETM cell density was significantly decreased in case of preoperative fluorometholone instillation.

CONCLUSION

Paucicellularity of glaucomatous TM is confirmed by this original technique. Structural characteristics of the ETM, whose removal allows satisfactory aqueous egress, suggest that aqueous outflow resistance not only involves inner wall of SC and juxtacanalicular meshwork but also corneoscleral trabecular layers.

Corneal toxicity secondary to inadvertent use of benzalkonium chloride preserved viscoelastic material in cataract surgery

AIMS

To study the long term toxic effects of intraocular benzalkonium chloride (BAC).

METHODS

19 patients exposed to intraocular BAC preserved viscoelastic during cataract surgery in February 1999 developed severe striate keratopathy immediately postoperatively. 16 patients, including two who underwent penetrating keratoplasty, were studied in the period April to June 2000. Ocular symptoms, visual acuity, biomicroscopy, intraocular pressure, dilated funduscopy, specular endothelial microscopy, and corneal pachymetry findings were recorded. The corneal and iris specimens of the two patients who underwent keratoplasty were studied by light, transmission, and scanning electron microscopy.

RESULTS

Six males and 10 females, aged 64-98 years, were studied 14-16 months postoperatively. All patients were symptomatic. 12 patients had best corrected visual acuity of 6/12 or better and four patients of between 6/18 and 6/60. Five patients had corneal epithelial oedema and 11 had Descemet's membrane folds. The central corneal thickness, 620 (SD 71) microm, in affected eyes was significantly higher (p<0.005, two tailed paired t test) than that of the contralateral eyes, 563 (SD 48) microm. The endothelial cell density was significantly lower (p<0.0001, two tailed paired t test) in affected eyes: 830 (SD 280) cells/mm2 v 2017 (SD 446) cells/mm2. The mean average cell area was significantly higher in the BAC treated eyes: 1317 (SD 385) microm2 v 521 (SD 132) microm2. There was no significant difference in the coefficient of variation of cell size between the two eyes (p=0.3, two tailed paired t test). Two corneal specimens displayed morphological features of bullous keratopathy and other non-specific abnormalities. Extracellular melanosomes were present in a portion of the iris of one case.

CONCLUSION

BAC is toxic to the corneal endothelium when used intraocularly, leading to severe striate keratopathy. This cleared in most cases but left varying degrees of residual stromal thickening in all eyes. If penetrating keratoplasty is required the results are excellent.

Effects of pilocarpine and other antiglaucoma drugs on cultured human Tenon's fibroblast cells

It has been found that long-term therapy with topical antiglaucoma drugs may decrease the success of glaucoma filtering surgery. In this study, various antiglaucoma drugs, including carteolol, betaxolol, levobunolol, pilocarpine, and timolol, were investigated for their proliferative effect on cultured human Tenon's fibroblast cells. It was found that the 3H-thymidine uptake of cultured fibroblast cells was inhibited by commercial antiglaucoma drugs, including carteolol of 0.1% concentration (13%), 0.01% (50%) and 0.001% (53%), betaxolol of 0.05% concentration (14%), 0.005% (42%) and 0.0005% (62%), levobunolol of 0.05% concentration (2%), 0.005% (32%) and 0.0005% (55%), and timolol of 0.025% concentration (4%), 0.0025% (47%) and 0.00025% (55%), whereas the 3H-thymidine uptake was increased by commercial pilocarpine eyedrop from 103% (0.2% of concentration), 170% (0.02% of concentration) to 171% (0.002% of concentration), when cells were treated with commercial drugs for 100 min. Meanwhile, the proliferations of cultured fibroblast cells were stimulated by simultaneously combining 0.2%, 0.02% and 0.002% concentrations of pilocarpine eyedrops with other antiglaucoma drugs, such as carteolol of 0.1% concentration (50%), 0.01% (113%) and 0.001% (138%), betaxolol of 0.05% concentration (24%), 0.005% (128%) and 0.0005% (142%), levobunolol of 0.05% concentration (32%), 0.005% (87%) and 0.0005% (119%), and timolol of 0.025% concentration (15%), 0.0025% (94%) and 0.00025% (118%). Following incubation with pure pilocarpine, the proliferation of Tenon's fibroblast cells was inhibited for 84% (0.2% concentration), 84% (0.02% concentration) and 90% (0.002% concentration). When fibroblast cells were treated with commercial pilocarpine eyedrops for 24 hours, the 3H-thymidine uptake was increased to 160% (0.02% concentration) and 172% (0.002% concentration). This result shows that the commercial pilocarpine may play a crucial role for the proliferation of cultured human Tenon's fibroblast cells.

Pilot study on the effect of topical adrenergic medications on human Tenon's capsule fibroblasts in tissue culture

Recent publications have suggested that the long term use of topical antiglaucoma medications may be detrimental to the outcome of trabeculectomy. In order to investigate this further, the effect of several adrenergic agents and a preservative on the proliferation and viability of human Tenon's capsule fibroblasts in tissue culture were examined. The following compounds were tested: adrenaline (Eppy 1% and pure adrenaline base 1%, Smith & Nephew Pharmaceuticals Ltd); dipivefrine hydrochloride (Propine 0.1% and pure dipivefrine hydrochloride 0.1% Allergan Ltd and Allergan Pharmaceuticals (Ireland) Ltd); benzalkonium chloride (pure benzalkonium chloride 0.01%, Sigma Chemical Company Ltd); the two adrenaline based preparations were also tested in the presence of an antioxidant. None of the tested compounds stimulated the proliferation of fibroblasts. The commercial products tested, their pure compounds, and the preservative all inhibited proliferation and had toxic effects on the cells. In the presence of antioxidant, commercial Eppy and pure adrenaline base appeared to have less effect on proliferation and toxicity. These findings are discussed with reference to the outcome of trabeculectomy.

The use of cultured epithelial and endothelial cells for drug transport and metabolism studies

In an effort to develop novel strategies for delivery of drug candidates arising from rational drug design and recombinant DNA technology, pharmaceutical scientists have begun to employ the techniques of cell culture to study drug transport and metabolism at specific biological barriers. This review describes some of the general factors that should be considered in developing a cell culture model for transport studies and metabolism studies. In addition, we review in detail the recent progress that has been made in establishing, validating, and using cell cultures of epithelial barriers (e.g., cells that constitute the intestinal, rectal, buccal, sublingual, nasal, and ophthalmic mucosa as well as the epidermis of the skin) and the endothelial barriers (e.g., brain microvessel endothelial cells).