Oculotoxicities of systemically administered drugs

Drug-induced uveitis: A review

Uveitis maybe induced by the use of various medications known as drug-induced uveitis (DIU), though rare it is an important cause of uveitis which one needs to be aware of. The drugs may be administered through any route including systemic, topical, and intravitreal. Ocular inflammation can be in the form of anterior, intermediate, posterior or pan uveitis, and rarely may present as episcleritis and scleritis. Identification of drug as the offending agent of uveitis is important as many a times stopping the drug may help recover the uveitis or the concomitant use of corticosteroids. An extensive literature review was done using the Pubmed. An overview of DIU is provided as it is important for us to be aware of this clinical entity.

Association between use of benzodiazepines and occurrence of acute angle-closure glaucoma in the elderly: A population-based study

OBJECTIVE

Because benzodiazepines (BZDs) can affect pupillae muscles, their use could be a risk factor for acute angle-closure glaucoma (AACG), which is an ophthalmic emergency. However, there is no research evidence for the association between BZDs and AACG, except two case reports. We aimed to investigate whether BZDs increase the risk of AACG in a geriatric population.

METHODS

We performed a case-control study using a geriatric cohort from the National Health Insurance database (2002-2013) in Korea. Case subjects (n = 1117) were patients diagnosed with AACG. Controls, people who have not been diagnosed with AACG, were randomly matched with the case according to age, sex, and index year (n = 4468). To examine the risk of BZD use for AACG, we performed conditional logistic regression analyses with potential confounders including comorbidities and concomitant medication.

RESULTS

The use of BZD within 30 days was not significantly associated with AACG risk (adjusted odds ratio [aOR] = 1.14, 95% confidence interval [CI] = 0.94-1.37). Further analyses showed that, compared with non-use of BZD, new BZD use had a significantly increased risk for the development of AACG (aOR = 1.62, 95% CI = 1.09-2.37). The risk was higher in the new BZD users exposed within 7 days (aOR = 3.09, 95% CI = 1.58-5.88).

CONCLUSION

We found that BZDs increase the risk of AACG at the beginning of its use among the Korean elderly. Clinicians should monitor visual disturbance in the elderly during the early period after prescription of BZD.

An Investigation into Retigabine (Ezogabine) Associated Dyspigmentation in Rat Eyes by MALDI Imaging Mass Spectrometry

Retigabine (RTG) is an antiepileptic drug approved as an adjunctive treatment for refractory partial-onset seizures in adults. In April 2013, the Food and Drug Administration issued a warning that RTG could cause changes in retinal pigmentation and discoloration of skin, resulting in a blue appearance. As part of a larger preclinical effort to gain a mechanistic understanding as to the origins of retinal pigment changes associated with RTG, we conducted a long-term repeat dosing study in rats. Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) was used to determine the distribution of RTG and its metabolites in the rat eye following 13 and 39 weeks of dosing. IMS revealed the presence of RTG, a previously characterized N-acetyl metabolite of RTG (NAMR), and several species structurally related through the dimerization of RTG and NAMR. These species were highly localized to the melanin-containing layers of the uveal tract of the rat eye including the choroid, ciliary body, and iris, suggesting that the formation of these dimers occurs from melanin bound RTG and NAMR. Furthermore, several of the RTG-related dimers have UV absorbance which give them a purple color in solution. We propose that the melanin binding of RTG and NAMR effectively concentrates the two compounds to enable mixed condensation reactions to occur when the binding provides the proper geometry in the redox environment of the uveal tissues. High lateral resolution images illustrate that the blood-retinal barrier effectively restricts retinal access to RTG-related compounds. The spatial information provided by MALDI IMS was critical in contextualizing the homogenate concentrations of key RTG-related compounds and helped provide a basis for the mechanism of dimer formation.

Ocular Side Effects of Systemic Drugs Used in Dermatology

Some systemically used drugs in managing dermatologic disorders have associated severe side effects, of which eye involvement is very significant. There are various mechanisms for these drugs to cause damage to the eye. The damage to the eye can be acute as in Stevens–Johnson syndrome or chronic as with chloroquine and hydroxychloroquine toxicity. Knowledge about these drugs and information about the mechanisms and types of damage to the eye are essential. It is also important to understand the monitoring mechanisms to diagnose early and limit the damage. Newer investigative tools, especially the imaging techniques help us to diagnose the adverse effects at an early stage. All these issues are discussed in brief here.

Comparison between albino and pigmented rabbit ERGs

BACKGROUND

Pigmented and albino rabbits are commonly used in visual research; however, the lack of pigment in the eyes may affect retinal responses. Here, we compare and describe the differences of retinal function between pigmented (English Butterfly) and albino (New Zealand) rabbits.

METHODS

Electroretinograms were recorded in pigmented and albino rabbits in the dark-adapted eye, in the light-adapted eye and for four temporal frequencies in the light-adapted eye. The implicit time and amplitude of the a- and b-waves were analyzed, as well as the amplitude and phase of the first harmonic component of the photopic flicker response.

RESULTS

Albino rabbits presented significantly larger amplitudes for both a- and b-waves at all intensities and frequencies. The intensity-response function of the scotopic b-wave also showed that the albino retina is more sensitive than the pigmented retina and the larger flicker amplitudes found in the albino group also revealed post-receptoral changes specifically related to cone pathways.

CONCLUSIONS

The larger amplitude of albino receptoral and post-receptoral activities might be attributed to greater availability of light due to scatter and reflection at the retinal layer, and as the differences in response amplitudes between the groups increase with flicker frequency, we suggest that ON bipolar cells recover faster in the albino group, suggesting that this might be a mechanism to explain the higher temporal resolution for albinos compared to the pigmented group.

Implications of melanin binding in ocular drug delivery

Pigmented ocular tissues contain melanin within the intracellular melanosomes. Drugs bind to melanin at varying extent that ranges from no binding to extensive binding. Binding may lead to drug accumulation to the pigmented tissues and prolonged drug retention in the melanin containing cells. Therefore, melanin binding is an important feature that affects ocular drug delivery and biodistribution, but this topic has not been reviewed since 1998. In this review, we present current knowledge on ocular melanin, melanosomes and binding of drugs to pigmented cells and tissues. In vitro, in vivo and in silico methods in the field were critically evaluated, because the literature in this field can be confusing if the reader does not properly understand the methodological aspects. Literature analysis includes a comprehensive table of literature data on melanin binding of drugs. Furthermore, we aimed to give some insights beyond the current literature by making a chemical structure based classification model for melanin binding of drugs and kinetic simulations that revealed significant interplay between melanin binding and drug permeability across the melanosomal and plasma membranes. Overall, more mechanistic and systematic research is needed before the impact of melanin binding on ocular drug delivery can be properly understood and predicted.

Elvitegravir/cobicistat-associated toxic optical neuropathy in an HIV-infected patient: a call for caution?

Ocular toxicity may not only be caused by medication overdoses and drug-drug interactions, but also by chronic administration of medications at recommended doses. We describe a case of an HIV-infected patient who experienced significant and sustained bilateral visual loss 2 months after starting treatment with elvitegravir/cobicistat/tenofovir/emtricitabine. Given the absence of any evidence of tenofovir- or emtricitabine-induced optical neuropathy after several years of clinical use, the antiretroviral therapy was promptly changed to tenofovir/emtricitabine plus atazanavir/ritonavir, which led to a progressive improvement in visual acuity. However, visual evoked potentials never returned to normal amplitudes. This is the first report of toxic optical neuropathy associated with the use of elvitegravir/cobicistat. It is imperative to recognize any signs of possible eye toxicity as rapidly as possible, and refer affected patients to an ophthalmologist promptly because early detection and the withdrawal of the offending agent are crucial in reversing this adverse ocular event.

The acceptability and visual impact of 0.01% atropine in a Caucasian population

BACKGROUND

Myopia is a condition of enormous public health concern, affecting up to 2.5 billion people worldwide. The most effective treatment to prevent myopia progression is atropine but at the cost of accommodative paresis and mydriasis, necessitating the use of bifocal glasses. Low-dose atropine (0.01%) has been found to be almost as effective with significantly reduced side effects. Since there are well-recognised differences in the effect of atropine between heavily pigmented Asian eyes and Caucasian eyes, this study aimed to determine the acceptability and tolerability of 0.01% atropine (by measuring visual performance and quality of life) as a treatment for myopia control in a Caucasian population exhibiting light irides.

METHODS

14 university students aged 18-27 were recruited to the study. Participants received one drop of 0.01% atropine daily into each eye over 5 days. A range of physiological, functional and quality of life measures were assessed at baseline, day 3 and day 5.

RESULTS

The effect of atropine was statistically significant for pupil size (p=0.04) and responsiveness (p<0.01). While amplitude of accommodation reduced, the change was not statistically significant. Visual acuity (distance and near) and reading speed were not adversely affected. While there was a slight increase in symptoms such as glare, overall there was no quality of life impact associated with the use of low-dose atropine.

CONCLUSIONS

Overall, 0.01% of atropine was generally well tolerated bilaterally and no serious adverse effects were observed. Therefore this dose appears to provide a viable therapeutic option for myopia control among Caucasian eyes.

An improved method for the isolation and culture of retinal pigment epithelial cells from adult rats

PURPOSE

Since adult rats are used in pre-clinical studies, and due to the necessity of investigating the side-effects of drugs on RPE cells in vitro, there is a great need for primary RPE cells from these animals. The aim of this study was to develop a reproducible and quantifiable method of isolation, culture, and maintenance of adult rat RPE cells. Moreover, potential differences between RPE cells from albino versus pigmented rats were also investigated.

METHODS

A total of 180 pigmented rats and 340 albino rats aged 6-14 weeks were used. RPE cells were isolated and cultured for several weeks by using three different methods: 1) growing directly on flat mounts, 2) after enzymatic isolation, and 3) after they spontaneously detached from the flat mounts and continued to grow on the plastic. Yield, cell survival, and morphological characteristics were investigated using light and electron microscopy as well as immunohistochemistry.

RESULTS

After 0 weeks, the yield of the first method was 30,000 cells/eye; after 2 weeks 18,000 cells/eye; and after 4 weeks 11,000 cells/eye. The yield of RPE cells was very low after enzymatic isolation in method 2 (0 weeks, 13.000 cells/eye; 2 weeks, 30,000 cells/eye; 4 weeks 38,000 cells/eye), whereas it was higher when the RPE cells spontaneously detached from the flat mounts and then continued to grow on the plastic in method three. (0 weeks, 30,000 cells/eye; 2 weeks, 314,000 cells/eye; 4 weeks, 659,000 cells/eye). The second method often showed contamination with fibroblasts, whereas the two other methods showed pure RPE cultures. The RPE cells were able to proliferate when using the second and the third method, but not when they were cultivated directly on the flat mounts (first method).

CONCLUSION

The qualitative and quantitative best method for isolating adult rat RPE cells is the culture of RPE cells which spontaneously detach from flat mounts. No differences were observed between albino and pigmented RPE cells.

Drug-induced uveitis

INTRODUCTION

Drug-induced uveitis is a well described but often overlooked and/or misdiagnosed adverse reaction to medication. There are an increasing number of medications that have been related to the onset of intraocular inflammation. Identification of these inciting agents may decisively help the diagnostic algorithm involving new cases of uveitis.

AREAS COVERED

This review intends to be an updated comprehensive, practical guide for practitioners regarding the main drugs that have been associated with uveitis. A classification proposed by Naranjo et al. in 1981 for establishing potential causality is applied examining possible mechanisms of action. A guide for clinicians about the rationale of these observations when dealing with patients with uveitis is provided.

EXPERT OPINION

Several agents with different routes of administration (systemic, topical and/or intraocular) may cause intraocular inflammation. The mechanism behind ocular inflammation is frequently unknown. Clinicians should be aware of the potential drug effect to optimize diagnosis and management of such patients.

Ophthalmic evaluations in clinical studies of fingolimod (FTY720) in multiple sclerosis

PURPOSE

To report outcomes of ophthalmic evaluations in clinical studies of patients receiving fingolimod (Gilenya; Novartis Pharma AG, Basel, Switzerland) for multiple sclerosis (MS).

DESIGN

Analysis done on pooled safety data (N = 2615, all studies group) from 3 double-masked, randomized, parallel-group clinical trials (phase 2 core and extension >5 years, and phase 3 FREEDOMS and TRANSFORMS core and extension studies).

PARTICIPANTS

Patients aged 18 to 55 years (18-60 years in phase 2 study) diagnosed with relapsing-remitting MS were included. Patients with diabetes mellitus or macular edema (ME) at screening were excluded.

INTERVENTION

Participants received fingolimod (0.5/1.25 mg), placebo, or interferon beta for the respective study durations. Ophthalmic examination included detailed eye history (at screening), visual acuity (VA) assessment, dilated ophthalmoscopy, optical coherence tomography (OCT), and fluorescein angiography (FA).

MAIN OUTCOME MEASURES

Extensive ophthalmic monitoring was performed for all patients. While being studied, patients with abnormal findings on dilated ophthalmoscopy and OCT compatible with ME were further studied by FA. All locally diagnosed ME cases were centrally reviewed by the retina specialist (M.A.Z.) on the Data and Safety Monitoring Board.

RESULTS

Among 2615 patients assessed, 19 confirmed ME cases were observed in fingolimod-treated groups (0.5 mg: n = 4, 0.3%; 1.25 mg: n = 15, 1.2%). Most patients (n = 13, 68%) presented with blurred vision, decreased VA, or eye pain. Macular edema was diagnosed within 3 to 4 months of treatment initiation in most cases (n = 13, 68%); 2 patients had late onset (>12 months) ME. Of the 19 patients with ME, 5 (26%), all treated with fingolimod 1.25 mg, had a history of uveitis compared with 26 (1%) in the all studies group. In most cases (n = 16, 84%), ME resolved after discontinuing the study drug. Eleven patients required topical anti-inflammatory medications. No patient had further vision deterioration.

CONCLUSIONS

Fingolimod 0.5 mg is associated with a low incidence of ME in MS studies. Patients with a history of uveitis may be at an increased risk of developing ME. An ophthalmic examination before initiating fingolimod therapy and regular follow-up eye examinations during fingolimod therapy are recommended.

An overview on the toxic morphological changes in the retinal pigment epithelium after systemic compound administration

Many medications that are administered systemically for nonocular conditions may evoke ocular toxicological complications. Therefore, the eye is routinely investigated histopathologically in preclinical in vivo toxicity studies. The retinal pigment epithelium is a likely target for systemically administered compounds, since the underlying choroid is highly vascularized. The specialized pigment epithelium has numerous functions that all maintain the integrity and function of photoreceptors. Consequently, toxic effects on the pigment epithelium will eventually affect the neural retina. The potential of pigment epithelial cells to respond to toxic injury is limited, but a standardized terminology to describe its morphological changes does not exist in the scientific literature. Detailed morphologic analysis, however, might allow early detection of retinotoxicity and may provide evidence on the underlying pathomechanism. We here review toxic effects on the pigment epithelium focusing in particular on the morphology of toxic cell injury. Morphological changes comprise hypertrophy, intracytoplasmic accumulation of cellular components, loss of cell polarity, degeneration, metaplasia, and formation of subretinal membranes. Some of these changes are reversible whereas others are permanent, leading to impaired function of the pigment epithelium and eventually to photoreceptor loss and retinal atrophy.

Transplantation of the RPE in AMD

The retinal pigment epithelium (RPE) maintains retinal function as the metabolic gatekeeper between photoreceptors (PRs) and the choriocapillaries. The RPE and Bruch's membrane (BM) suffer cumulative damage over lifetime, which is thought to induce age-related macular degeneration (AMD) in susceptible individuals. Unlike palliative pharmacologic treatments, replacement of the RPE has a curative potential for AMD. This article reviews mechanisms leading to RPE dysfunction in aging and AMD, laboratory studies on RPE transplantation, and surgical techniques used in AMD patients. Future strategies using ex vivo steps prior to transplantation, BM prosthetics, and stem cell applications are discussed. The functional peculiarity of the macular region, epigenetic phenomena leading to an age-related shift in protein expression, along with the accumulation of lipofuscin may affect the metabolism in the central RPE. Thickening of BM with age decreases its hydraulic conductivity. Drusen are deposits of extracellular material and formed in part by activation of the alternative complement pathway in individuals carrying a mutant allele of complement factor H. AMD likely represents an umbrella term for a disease entity with multifactorial etiology and manifestations. Presently, a slow progressing (dry) non-neovascular atrophic form and a rapidly blinding neovascular (wet) form are discerned. No therapy is currently available for the former, while RPE transplantation and promising (albeit non-causal) anti-angiogenic therapies are available for the latter. The potential of RPE transplantation was demonstrated in animal models. Rejection of allogeneic homologous transplants in patients focused further studies on autologous sources. In vitro studies elucidated cell adhesion and wound healing mechanisms on aged human BM. Currently, autologous RPE, harvested from the midperiphery, is being transplanted as a cell suspension or a patch of RPE and choroid in AMD patients. These techniques have been evaluated from several groups. Autologous RPE transplants may have the disadvantage of carrying the same genetic information that may have led to AMD manifestation. An intermittent culturing step would allow for in vitro therapy of the RPE, its rejuvenation and prosthesis of BM to improve the success RPE transplants. Recent advances in stem cell biology when combined with lessons learned from studies of RPE transplantation are intriguing future therapeutic modalities for AMD patients.

Heavy metal concentrations in human eyes

PURPOSE

To measure the concentration of toxic heavy metals in the fluids and tissues of human eyes.

DESIGN

Laboratory investigation.

METHODS

Thirty autopsy eyes of 16 subjects were dissected to obtain the aqueous, vitreous, lens, ciliary body, retina, and retinal pigment epithelium/choroid. Concentrations of lead, cadmium, mercury, and thallium in ocular tissues, ocular fluids, and blood were determined using an inductively coupled plasma-mass spectrometer and expressed as ng/g. Heavy metal concentrations in ocular tissues were compared using a paired t test.

RESULTS

Lead and cadmium were found in all of the pigmented ocular tissues studied, concentrating to the greatest extent in the retinal pigment epithelium/choroid (mean, 432 +/- 485 ng/g and 2,358 +/- 1,522 ng/g). Cadmium was found in the retina in all eyes (mean, 1,072 +/- 489 ng/g) whereas lead was found in the retina in 9 (30%) of 30 eyes (mean, 53 +/- 54 ng/g). Trace concentrations of lead and cadmium were detected in the vitreous (mean, 0.5 +/- 1.0 ng/dl and 19 +/- 29 ng/dl), lens (mean, 13 +/- 18 ng/g and 20 +/- 18 ng/g), and blood (mean, 0.5 +/- 1.2 mug/dl and 3.1 +/- 4.1 mug/l) but were not detected in the aqueous. Mercury and thallium were not detected in any ocular tissues or fluids or in the blood.

CONCLUSIONS

Lead and cadmium accumulate in human ocular tissues, particularly in the retinal pigment epithelium and choroid. The potential ocular toxicity of these heavy metals and their possible role in eye disease requires further study.

Cataract formation and prevention

Cataract, a leading cause of blindness worldwide, is a multifactorial eye disease. In developing countries the incidence of cataract among young generations is not uncommon due to malnutrition, excess exposure to ultraviolet radiation and so on. In developed countries, age-related cataract affecting the population over 65 years of age is a major concern. Oxidative stress was suggested to inflict damage to the lens and induce opacification, and a variety of antioxidant nutrients were tested for the prevention or delay of cataract development. Although promising results were obtained in animal studies of various antioxidants, epidemiological studies on human populations do not seem to support their protective effects unequivocally. It is unlikely that age-related cataract in man, similar to the ageing process itself, will be prevented or delayed by therapeutic drugs in the foreseeable future. At present, keeping a health-conscious life style (i.e., no smoking) may be the most effective and least expensive strategy to prevent the onset of age-related cataract.

METABOLISM, PHARMACOKINETICS, TISSUE DISTRIBUTION, AND EXCRETION OF [14C]CP-424391 IN RATS

CP-424391, 2-amino-N-[3aR-benzyl-2-methyl-3-oxo-2,3,3a,4,6,7-hexahydro-pyrazolo[4,3-c]pyridin-5-yl)-1R-benzyloxymethyl-2-oxoethyl]-isobutyramide, is an orally active growth hormone secretagogue currently being developed. In this study, we investigated the metabolic fate and disposition of radiolabeled CP-424391 in rats. Following 15 mg/kg single oral administration to Sprague-Dawley rats, 91% of the radiolabeled dose was recovered. Feces was the major route of excretion: 77% of the dose recovered in feces of the female rat and 84% in the male. Excretion in the urine was 15% in the female rat compared with 7% in the male. Both fecal and urinary metabolic profiles were consistent in both genders. The metabolic pathways of CP-424391 were oxidation at the benzyl group of the O-benzylserine moiety, N-demethylation of pyrazolidine, and/or O-debenzylation. In circulation, CP-424391 was absorbed within the first hour to an average apparent C(max) of 1.44 microg/ml. CP-424391 accounts for about 40% of radioactivity area under the plasma concentration-time curve and C(max) in circulation. The plasma terminal elimination half-life of CP-424391 was 2.4 h and for total radioactivity was 2.8 h. The radioactivity was widely distributed in all tissues except for the central nervous system. [(14)C]CP-424391 radioactivity was eliminated from most tissues by 9 h with the exception of liver, skin, and uvea. By 168 h, [(14)C]CP-424391 radioactivity remained localized only in the uvea.

Binding characteristics of fluoroquinolones to synthetic levodopa melanin

To define the binding characteristics of fluoroquinolones to synthetic levodopa melanin, the binding of various drugs, including levofloxacin and ofloxacin, and positive controls (timolol and chloroquine), was investigated in-vitro. The affinity and capacity of the drug binding were calculated by Langmuir's adsorption isotherm. The affinity constant (K) and the binding capacity (r(max)) of levofloxacin were similar to those of timolol and much lower than those of chloroquine. Racemic ofloxacin and its enantiomers showed similar K and r(max), suggesting that the binding lacked stereoselectivity. The binding experiment with levofloxacin derivatives indicated that the basic nitrogen atom at position 7 of the quinolone ring, but not carboxyl group at position 3, would play a critical role in the interaction of fluoroquinolones with melanin. The melanin-drug complexes of levofloxacin and chloroquine were washed with neutral phosphate buffer, ethanol and 1 M HCl solution to explain the nature of the interaction of melanin with the drugs. Electrostatic forces mainly participate in the formation of the chloroquine-melanin complex, whereas van der Waals' and hydrophobic interactions are involved in the levofloxacin-melanin complex in addition to electrostatic forces. The interactions of various fluoroquinolones such as norfloxacin, enoxacin, sparfloxacin, ciprofloxacin and lomefloxacin with melanin were also studied. The results showed that the relative K value was: chloroquine approximately ciprofloxacin, sparfloxacin >/= lomefloxacin > timolol, levofloxacin approximately enoxacin, norfloxacin, and that the relative r(max) value was: norfloxacin, enoxacin >/= chloroquine, sparfloxacin > levofloxacin, ciprofloxacin, timolol, lomefloxacin. The fluoroquinolones vary in their affinity and capacity to bind with melanin, and ciprofloxacin and sparfloxacin showed a stronger interaction with melanin than the other fluoroquinolones studied.

Naphthoquinone-Induced cataract in mice: possible involvement of Ca2+ release and calpain activation

N-acetyl-p-benzoquinone imine (NAPQI), a semiquinone metabolite of acetaminophen, produces cataract in mice. Naphthalene is biotransformed to the cataractogenic metabolite 1,2-naphthoquinone (NQ). Intracameral injection of NAPQI elicits a rapid increase in free intracellular Ca2+ in the lens epithelium and calpain activation before lens opacification begins. In order to test whether the cellular response is a common feature of quinone-induced cataracts, we injected in this work 1,2-naphthoquinone (NA) in the anterior chamber of mouse eye and followed cellular responses in the lens prior to opacity development. A marked rise in free intracellular Ca2+ in the lens epithelium and concurrent activation of calpain were observed within 1 hr after NQ injection preceding lens opacity development. These results support the suggestion that Ca2+ release and calpain activation are involved in the mechanism of quinone-induced cataractogenesis.

Ocular toxicity associated with systemic drug therapy

Systemic drug-induced ocular side effects are increasing because of the vast numbers of new drugs being introduced. Reports of drug-induced ocular toxicity must be well documented, and other causes of these side effects must be ruled out to help establish causality. We reviewed the most recent reports of the most commonly used and newest systemic drugs that have been implicated in ocular toxicity. Using toxicologic criteria needed to establish causality, data from reports of ocular toxicity associated with systemic cidofovir (Vistide), sildenafil (Viagra), vigabatrin (Sabril), tamoxifen (Nolvadex), hydroxychloroquine (Plaquenil)/chloroquine (Aralen), amiodarone (Cordarone), and lovastatin (Mevacor)/simvastatin (Zocor) were evaluated and summarized. The probability for causality was determined to be high for all these drugs except for vigabatrin and lovastatin/simvastatin. Methods for detecting, preventing, and treating ocular toxic reactions were then reviewed for each drug.

Current understanding on the role of retinal pigment epithelium and its pigmentation

Retinal pigment epithelium (RPE) is a monolayer of cuboidal cells that is strategically placed between the rod and cone photoreceptors and the vascular bed of the choriocapillaris. It has many important functions, such as phagocytic uptake and breakdown of the shedded photoreceptor membranes, uptake, processing, transport and release of vitamin A (retinol), setting up the ion gradients within the interphotoreceptor matrix, building up the blood-retina barrier, and providing all transport from blood to the retina and back. This short review focuses on the role of the pigment granules in RPE. Although the biology of the pigment granules has been neglected in the past, they do seem to be involved in many important functions, such as protection from oxidative stress, detoxification of peroxides, and binding of zinc and drugs, and, therefore, serve as a versatile partner of the RPE cell. Melanin plays a role in the development of the fovea and routing of optic nerves. New findings show that the melanin granules are connected to the lysosomal degradation pathway. Most of these functions are not yet understood. Deficit of melanin pigment is associated with age-related macula degeneration, the leading cause of blindness.

Binding of drugs to eye melanin is not predictive of ocular toxicity

Ocular melanin is found in the uveal tract and in the pigmented epithelial layer of the retina. Many structurally and pharmacologically unrelated drugs from different therapeutic classes bind to melanin. Examples include numerous drugs acting on the central nervous system, beta-blockers, beta-agonists, antimalarial drugs, sympathomimetic amines, and antibiotics. The critical factors are the acid/base status and the lipophilicity of the molecule. In all cases, there are no direct consequences of drug-melanin binding. Drug-related toxic effects on the retina described in humans and animals are unrelated to melanin binding: melanin binding and retinal toxicity are two separate entities, the latter being related to the intrinsic toxicity of the compound rather than its ability to bind. Chloroquine and phenothiazines are often used as examples of drugs with retinal toxicity linked to melanin binding. In both cases however, experimental data show that the toxic mechanism is unrelated to binding. Melanin binding has also been found to be protective against the ocular toxicity of some drugs. In conclusion, we believe that potential ocular toxicity of future drugs can be assessed adequately by conducting well-designed toxicology studies, and using nonpigmented rodents in addition to pigmented nonrodent species remains fully justified. Binding of drugs to eye melanin is not predictive of ocular toxicity.

Drug-induced uveitis

Uveitis has been reported in association with a variety of topical, intraocular, periocular, and systemic medications. To establish causality of adverse events by drugs, in 1981, Naranjo and associates proposed seven criteria, which are related to the frequency and documentation of the event; circumstances of occurrence, recovery, and recurrence; and coexistence of other factors or medications. Rarely does a drug meet all seven criteria. The authors review reports of drug-associated uveitis, applying the seven criteria and examining possible mechanisms. Only systemically administered biphosphonates and, perhaps, topical metipranolol meet all seven criteria. Systemic sulfonamides, rifabutin, and topical glucocorticoids fulfill at least five criteria.

Acetaminophen cytotoxicity in mouse eye: mitochondria in anterior tissues are the primary target

Acetaminophen (APAP) injected into C57BL/6 mice (cytochrome P450 inducer-responsive strain) that had been pretreated with b-naphthoflavone (BNF) produced ocular tissue damage, including cataract. Our previous histocytochemical studies showed that tissue damage spread in association with the flow of the aqueous humor and appeared first in the ciliary epithelium, followed by the iris and corneal endothelium and, finally, the lens. The neural retina, retinal pigmented epithelium and choroid remained unaffected. A close examination of the affected tissues indicated that mitochondria are the primary target of APAP cytotoxicity. In order to investigate whether the respiratory capacity of mitochondria is more sensitive to APAP cytotoxicity than mitochondrial morphology, we determined in this work the oxygen uptake by eye tissues dissected from BNF-pretreated and APAP-injected C57BL/6 mice. Oxygen uptake by the ciliary body/iris decreased about 60% at 90 min and 85% at 120 min after APAP administration. The oxygen uptake was inhibited about 50% by 10 microM rotenone. Since the earliest sign of mitochondrial damage was noted at 120 min, the result indicates that mitochondrial energy dysfunction precedes morphological alterations. It was also observed that oxygen uptake by the retina remained unaffected at least for 120 min after APAP administration; therefore, it is evident that the retina and, possibly, other posterior tissues as well are resistant to APAP cytotoxicity, not only in their morphology but, also, in their capacity of mitochondrial energy metabolism.