Glutamate uptake is inhibited by tamoxifen and toremifene in cultured retinal pigment epithelial cells

Tamoxifen related chorioretinal structural changes

PURPOSE

To evaluate the vascular structure of the choroid and each retinal layer in patients with breast cancer on tamoxifen therapy and compare them with healthy subjects.

MATERIALS AND METHODS

124 eyes of 62 patients with breast cancer who were on tamoxifen therapy (group 1) and 80 eyes of 40 healthy controls (group 2) were included in this prospective cohort study. The structure of the choroid was evaluated using enhanced depth imaging spectral-domain optical coherence tomography (EDI-OCT) and choroidal binarisation. Spectral-domain OCT (SD-OCT) was performed to analyse the peripapillary nerve fibre layer thickness (pRNFL) and each retinal layer thickness. A subgroup analysis was performed based on chemotherapy history in Group 1. All parameters were compared between Group 1 and the healthy controls and between the subgroups of Group 1.

RESULTS

The subfoveal choroidal thickness and temporal and nasal directions were increased in Group 1 when compared with Group 2 (p < 0.05, each comparison). Choroidal vascularity index was significantly decreased in Group 1 compared with Group 2 (63.15 ± 3.11% and 65.37 ± 4.63%, p < 0.001). There were no significant differences in each retinal layer, pRNFL thickness, and choroid structural parameters between the subgroups of Group 1.

CONCLUSIONS

Increased choroidal thickness may be the initial finding of subclinical tamoxifen-induced retinopathy. Patients with breast cancer undergoing tamoxifen therapy may be screened prior to tamoxifen therapy and followed during treatment by SD-OCT.

Etiology of Idiopathic Macular Holes in the Light of Estrogen Hormone

The aim of this review was to identify a new potential explanation for the development of macular holes in relation to the female sex and to explain the possible underlying pathways. This approach was based on the evaluation of anatomical, physiological, and morphological analyses currently available in the literature. The findings showed that estrogen exerts a protective effect on the neuroretina and may influence Müller and cone cells. Both cell types are responsible for the building of the fovea structure. However, this protection may be lost due to the sudden decrease in estrogen levels during menopause. In conclusion, the fovea cones, through its sensitivity to estrogen and high energy consumption, may be very vulnerable to damage caused by a sudden changes in the concentration of estrogen in menopausal females. Such changes may result in cone degeneration, and thus a destroyed structure of the fovea, and may lead to the development of a hole in the fovea, as in the case of macular holes. This review revealed that under the decreasing influence of estrogen may cones play a key role with regard to the etiology of the development of macular holes. This aspect may be of strategic importance in prophylactic therapy for the prevention of the development of macular holes in premenopausal females or after ocular trauma.

The Impact of Systemic Medications on Retinal Function

This study will provide a thorough review of systemic (and select intravitreal) medications, along with illicit drugs that are capable of causing various patterns of retinal toxicity. The diagnosis is established by taking a thorough medication and drug history, and then by pattern recognition of the clinical retinal changes and multimodal imaging features. Examples of all of these types of toxicity will be thoroughly reviewed, including agents that cause retinal pigment epithelial disruption (hydroxychloroquine, thioridazine, pentosan polysulfate sodium, dideoxyinosine), retinal vascular occlusion (quinine, oral contraceptives), cystoid macular edema/retinal edema (nicotinic acid, sulfa-containing medications, taxels, glitazones), crystalline deposition (tamoxifen, canthaxanthin, methoxyflurane), uveitis, miscellaneous, and subjective visual symptoms (digoxin, sildenafil). The impact of newer chemotherapeutics and immunotherapeutics (tyrosine kinase inhibitor, mitogen-activated protein kinase kinase, checkpoint, anaplastic lymphoma kinase, extracellular signal-regulated kinase inhibitors, and others), will also be thoroughly reviewed. The mechanism of action will be explored in detail when known. When applicable, preventive measures will be discussed, and treatment will be reviewed. Illicit drugs (cannabinoids, cocaine, heroin, methamphetamine, alkyl nitrite), will also be reviewed in terms of the potential impact on retinal function.

One-year follow-up of optical coherence tomography angiography microvascular findings: macular telangiectasia type 2 versus tamoxifen retinopathy

PURPOSE

To compare microstructural and microvascular changes in eyes with macular telangiectasia type 2 (MacTel2) and in those with tamoxifen retinopathy (TR) at baseline and at the 1-year follow-up using optical coherence tomography (OCT) and OCT angiography (OCTA).

METHODS

We followed up patients diagnosed with MacTel2 or TR for at least 1 year. We included 17 patients with MacTel2 (31 eyes) and 15 with TR (25 eyes) who discontinued tamoxifen use after a TR diagnosis. We performed OCT and OCTA at baseline and after 1 year.

RESULTS

Patients with MacTel2 and TR showed intraretinal cavitation, ellipsoid zone (EZ) loss, and capillary telangiectasia in the superficial and deep plexuses. EZ disruption predominantly affected the temporal region in MacTel2 (32%) and was limited to the foveal center in TR (24%). Vascular density (VD) was significantly reduced within the deep temporal parafovea and superficial fovea in MacTel2 and TR eyes, respectively. After 1 year, the MacTel2 eyes showed enlarged EZ loss, proliferative vascular invasion, and increased VD (p = 0.021) in the temporal deep plexus compared with TR eyes.

CONCLUSIONS

After 1-year follow-up, the MacTel2 eyes showed proliferative vascular remodeling, particularly in the temporal parafovea of the deep plexus with EZ loss progression, whereas the TR eyes maintained their baseline capillary rarefaction.

Retinal toxicities of systemic anticancer drugs

Newer anticancer drugs have revolutionized cancer treatment in the last decade, but conventional chemotherapy still occupies a central position in many cancers, with combination therapy and newer methods of delivery increasing their efficacy while minimizing toxicities. We discuss the retinal toxicities of anticancer drugs with an emphasis on the mechanism of toxicity. Uveitis is seen with the use of v-raf murine sarcoma viral oncogene homolog B editing anticancer inhibitors as well as immunotherapy. Most of the cases are mild with only anterior uveitis, but severe cases of posterior uveitis, panuveitis, and Vogt-Koyanagi-Harada-like disease may also occur. In the retina, a transient neurosensory detachment is observed in almost all patients on mitogen-activated protein kinase kinase (MEK) inhibitors. Microvasculopathy is often seen with interferon α, but vascular occlusion is a more serious toxicity caused by interferon α and MEK inhibitors. Crystalline retinopathy with or without macular edema may occur with tamoxifen; however, even asymptomatic patients may develop cavitatory spaces seen on optical coherence tomography. A unique macular edema with angiographic silence is characteristic of taxanes. Delayed dark adaptation has been observed with fenretinide. Interestingly, this drug is finding potential application in Stargardt disease and age-related macular degeneration.

Subretinal Rather Than Intravitreal Adeno-Associated Virus-Mediated Delivery of a Complement Alternative Pathway Inhibitor Is Effective in a Mouse Model of RPE Damage

Purpose

The risk for age-related macular degeneration has been tied to an overactive complement system. Despite combined attempts by academia and industry to develop therapeutics that modulate the complement response, particularly in the late geographic atrophy form of advanced AMD, to date, there is no effective treatment. We have previously demonstrated that pathology in the smoke-induced ocular pathology (SIOP) model, a model with similarities to dry AMD, is dependent on activation of the alternative complement pathway and that a novel complement activation site targeted inhibitor of the alternative pathway can be delivered to ocular tissues via an adeno-associated virus (AAV).

Methods

Two different viral vectors for specific tissue targeting were compared: AAV5-VMD2-CR2-fH for delivery to the retinal pigment epithelium (RPE) and AAV2YF-smCBA-CR2-fH for delivery to retinal ganglion cells (RGCs). Efficacy was tested in SIOP (6 months of passive smoke inhalation), assessing visual function (optokinetic responses), retinal structure (optical coherence tomography), and integrity of the RPE and Bruch's membrane (electron microscopy). Protein chemistry was used to assess complement activation, CR2-fH tissue distribution, and CR2-fH transport across the RPE.

Results

RPE- but not RGC-mediated secretion of CR2-fH was found to reduce SIOP and complement activation in RPE/choroid. Bioavailability of CR2-fH in RPE/choroid could be confirmed only after AAV5-VMD2-CR2-fH treatment, and inefficient, adenosine triphosphate-dependent transport of CR2-fH across the RPE was identified.

Conclusions

Our results suggest that complement inhibition for AMD-like pathology is required basal to the RPE and argues in favor of AAV vector delivery to the RPE or outside the blood-retina barrier.

Macular Abnormalities Associated With 5α-Reductase Inhibitor

Importance

The neuroprotective action of sex hormones has been described. Data on the association between 5α-reductase inhibitor (5-ARI), a male sex hormone antagonist, and macular abnormalities are lacking to date.

Objective

To assess the association between the use of 5-ARI for treatment of benign prostate hypertrophy and/or androgenic alopecia in men and macular abnormalities on optical coherence tomography imaging.

Design, Setting, and Participants

This retrospective case-control, cross-sectional study included electronic health record data from 31 male patients who showed foveal cavitation on spectral-domain optical coherence tomography imaging from January 1, 2016, to June 30, 2019.

Exposures

Receipt of 5-ARI for at least 2 years as treatment of benign prostate hypertrophy and/or androgenic alopecia.

Main Outcomes and Measures

Clinical data and multimodal imaging findings and the proportion of 5-ARI users.

Results

Among 31 male patients with foveal cavitation, 5-ARI was used for 10 of 14 patients (71.4%) with macular abnormalities of unknown origin and for 2 of 17 patients (11.8%) with macular abnormalities of well-known specific origin (P = .001). The mean age of these 14 patients was 74.7 years (range, 60.1-88.0 years). In the 15 eyes of 10 patients who had received 5-ARI for macular abnormalities of unknown origin, mean (SD) age was 72.8 (7.5) years, mean (SD) length of time receiving 5-ARI was 72.3 (39.2) months, and mean (SD) logMAR visual acuity was 0.08 (0.10) (Snellen equivalents, 20/24 [20/25]). Optical coherence tomography imaging showed a disease spectrum ranging from tiny foveal cavitation to an impending macular hole. Of the total male patients, 80.0% (8 of 10) had no symptoms.

Conclusions and Relevance

The findings suggest that macular abnormalities associated with 5-ARI are characterized by cystoid abnormalities and foveal cavitation in male patients, which may progress to outer foveal defect and macular hole. These macular abnormalities associated with a male sex hormone antagonist suggested by this investigation warrant further corroboration.

SEX STEROIDS AND MACULAR TELANGIECTASIA TYPE 2

PURPOSE

To investigate the relationship between macular telangiectasia Type 2 and systemic levels of sex steroids or their antagonization.

METHODS

In a prospective single-center study, 90 patients with macular telangiectasia Type 2 were investigated. Female patients were evaluated for previous surgical (e.g., ovariectomy) and/or pharmacological (e.g., aromatase inhibitors, tamoxifen) therapy resulting in reduced action of sex steroids. In males, free serum testosterone levels were assessed in patients and controls.

RESULTS

Fourteen of 49 (29%) female patients had a history of pharmacological suppression of sex steroids and/or ovariectomy. These patients were younger at disease onset when compared with those without such medical history (mean ± SD: 47.1 ± 7.8, range: 38-59, versus 60.1 ± 7.6, range: 45-76; P < 0.0001). Male patients showed significantly lower free serum testosterone levels compared with controls at younger age (P < 0.0001 and 0.04 in the first and second age quartiles, respectively), as opposed to nonsignificant differences in older patients. In men ≤ 60 years of age, a biochemical hypogonadism (free serum testosterone < 0.05 ng/mL) was present in 53% (8/15) and 4% (2/49) of patients and controls, respectively (P < 0.0001).

CONCLUSION

The results indicate that steroidal sex hormones might be involved in the presumably multifactorial pathophysiology of macular telangiectasia Type 2.

Tamoxifen Use in a Patient with Idiopathic Macular Telangiectasia Type 2

Crystalline deposits and neurosensory retinal cavitary changes can develop in both tamoxifen retinopathy and nonproliferative idiopathic macular telangiectasia type 2 (MacTel2). MacTel2 is typically differentiated from tamoxifen retinopathy based on the presence of late leakage and mid-phase telangiectatic vessels on fluorescein angiography (FA) and the presence of hyperautofluorescence. Unlike MacTel2, tamoxifen retinopathy is known to be a progressive disease and the cessation of tamoxifen results in resolution of retinopathy. We report a unique case of nonproliferative MacTel2 in a 36-year-old Hispanic woman with tamoxifen use and the vision outcome 30 months after cessation of tamoxifen. The FA and optical coherence tomography angiography findings of this patient support the diagnosis of MacTel2, but her cessation of tamoxifen led to partial reversal of the topographic findings and improvement in visual acuity. This patient is also unique in the unusually young age of presentation for MacTel2. Our case supports that there are common pathways in the pathogenesis of tamoxifen retinopathy and MacTel2, and tamoxifen use could potentially accelerate foveal atrophy in patients with MacTel2.

Cell models to study regulation of cell transformation in pathologies of retinal pigment epithelium

The retinal pigment epithelium (RPE) plays a key role in the development of many eye diseases leading to visual impairment and even blindness. Cell culture models of pathological changes in the RPE make it possible to study factors responsible for these changes and signaling pathways coordinating cellular and molecular mechanisms of cell interactions under pathological conditions. Moreover, they give an opportunity to reveal target cells and develop effective specific treatment for degenerative and dystrophic diseases of the retina. In this review, data are presented on RPE cell sources for culture models, approaches to RPE cell culturing, phenotypic changes of RPE cells in vitro, the role of signal pathways, and possibilities for their regulation in pathological processes.

Pseudocystic foveal cavitation in tamoxifen retinopathy

PURPOSE

To present 3 cases of tamoxifen-induced foveal cavitation and review previous prospective and cross-sectional studies.

DESIGN

Observational case series.

METHODS

Retrospective analysis of patients presenting to a single institution with evidence of tamoxifen-induced maculopathy.

RESULTS

Three patients presented with pseudocystic foveal cavitation similar in appearance to macular telangiectasia type 2 on spectral-domain optical coherence tomography (SD OCT) imaging.

CONCLUSIONS

Tamoxifen maculopathy is characterized by cavitation in the central macula with or without typical cystoid macular edema. Pathogenesis involves toxicity to retinal Müller cells. It can occur with low daily and cumulative doses of the drug, and in the absence of subjective visual complaints or crystalline retinopathy. Prospective research with SD OCT imaging will be required to gain a more accurate estimate of the incidence of tamoxifen retinopathy.

Functional and molecular aspects of biotin uptake via SMVT in human corneal epithelial (HCEC) and retinal pigment epithelial (D407) cells

Sodium-dependent multivitamin transporter (SMVT) is a vital transmembrane protein responsible for translocating biotin and other essential cofactors such as pantothenate and lipoate. Unlike primary cultures of corneal and retinal pigment epithelial (RPE) cells, immortalized cells can be subcultured many times, yet maintain their physiological properties. Hence, the purpose of this study was to delineate the functional and molecular aspects of biotin uptake via SMVT on immortalized human corneal epithelial (HCEC) and RPE (D407) cells. Functional aspects of [(3)H] biotin uptake were studied in the presence of different concentrations of unlabeled biotin, pH, temperature, metabolic inhibitors, ions, substrates, structural analogs and biotinylated prodrug (Biotin-Acyclovir (B-ACV)). Molecular identity of SMVT was examined with reverse transcription-polymerase chain reaction. Biotin uptake was found to be saturable in HCEC and D407 cells with K (m) of 296.2 ± 25.9 and 863.8 ± 66.9 μM and V (max) of 77.2 ± 2.2 and 308.3 ± 10.7 pmol/mg protein/min, respectively. Uptake was found to be pH, temperature, energy, and sodium-dependent. Inhibition of biotin uptake was observed in the presence of structural analogs and specific substrates. Further, uptake was lowered in the presence of B-ACV indicating the translocation of biotinylated prodrug by SMVT. A distinct band at 774 bp confirmed the molecular existence of SMVT in both the cells. This study shows for the first time the functional and molecular presence of SMVT in HCEC and D407 cells. Therefore, these cell lines may be utilized as in vitro models to study the cellular translocation of biotin-conjugated prodrugs.

Imaging tamoxifen retinopathy using spectral-domain optical coherence tomography

A case of tamoxifen retinopathy examined with spectral-domain optical coherence tomography (SD-OCT) is presented. The typical refractile deposits are located between ganglion cell layer and inner plexiform layer in SD-OCT. A defect on the outer retinal layer with disruption of the photoreceptor layer with sharp edges is seen. The still attached posterior hyaloids gives evidence of other pathomechanism involved in the outer retinal defect than that of macular hole, as suggested in the literature.

Cannabis and Amyotrophic Lateral Sclerosis: Hypothetical and Practical Applications, and a Call for Clinical Trials

Significant advances have increased our understanding of the molecular mechanisms of amyotrophic lateral sclerosis (ALS), yet this has not translated into any greatly effective therapies. It appears that a number of abnormal physiological processes occur simultaneously in this devastating disease. Ideally, a multidrug regimen, including glutamate antagonists, antioxidants, a centrally acting anti-inflammatory agent, microglial cell modulators (including tumor necrosis factor alpha [TNF-α] inhibitors), an antiapoptotic agent, 1 or more neurotrophic growth factors, and a mitochondrial function-enhancing agent would be required to comprehensively address the known pathophysiology of ALS. Remarkably, cannabis appears to have activity in all of those areas. Preclinical data indicate that cannabis has powerful antioxidative, anti-inflammatory, and neuroprotective effects. In the G93A-SOD1 ALS mouse, this has translated to prolonged neuronal cell survival, delayed onset, and slower progression of the disease. Cannabis also has properties applicable to symptom management of ALS, including analgesia, muscle relaxation, bronchodilation, saliva reduction, appetite stimulation, and sleep induction. With respect to the treatment of ALS, from both a disease modifying and symptom management viewpoint, clinical trials with cannabis are the next logical step. Based on the currently available scientific data, it is reasonable to think that cannabis might significantly slow the progression of ALS, potentially extending life expectancy and substantially reducing the overall burden of the disease.

Expression of glutamate transporter subtypes in cultured retinal pigment epithelial and retinoblastoma cells

PURPOSE

Glutamate is the major excitatory neurotransmitter in the retina and glutamate uptake is essential for normal glutamate signalling. Retinal diseases may induce neurochemical changes which affect retinal cells including retinal pigment epithelium (RPE). The aim of the study was to investigate the expression of glutamate transporter subtypes in RPE and retinoblastoma cells and to clarify the effect of proliferation modulators on the levels of the expressed transporter in the RPE cell line.

METHODS

Cultured pig RPE cells and two human RPE cell lines, D407 and ARPE-19, as well as the human retinoblastoma cell line Y79 were used. Glutamate transporter expression was evaluated with Western blot analysis and immunocytochemistry.

RESULTS

The study revealed unexpected expression of neuronal glutamate transporter/chloride channel EAAT4 in these three cell lines, but not in cultured pig RPE cells, whereas another glutamate carrier, EAAC1, was present in all cell types utilized. Other transporter subtypes, GLT1, GLAST and EAAT5 were not found. Neither tamoxifen, known to inhibit both proliferation and glutamate uptake in RPE cells, nor retinoic acid nor insulin, also known to affect cell proliferation rates, were capable of changing the total levels of EAAT4 in APRE-19 cells.

CONCLUSIONS

Neuronal glutamate transporter EAAC1 is expressed in RPE cells. The robust expression of EAAT4 in cell lines may reflect a role of EAAT4 in cell proliferation and migration. Unaltered steady-state expression of this carrier and chloride-channel protein hints at posttranslational mechanisms of regulation of EAAT4.

Bradykinin stimulates glutamate uptake via both B1R and B2R activation in a human retinal pigment epithelial cells

AIMS

We were to examine the effect of bradykinin (BK) in the regulation of glutamate transporter and its related signaling molecules in a human retinal pigment epithelial (ARPE) cells, which are important cells to support retina.

MAIN METHODS

d-[2,3-(3)H]-aspartate uptake, western immunoblotting, reverse transcription polymerase chain reaction, [(3)H]-arachidonic acid release, and siRNA transfection techniques were used.

KEY FINDINGS

BK stimulated glutamate uptake as well as the mRNA expression of excitatory amino acid transporter 4 (EAAT4) and excitatory amino acid carrier 1 (EAAC1), which was blocked by treatment with bradykinin 1 receptor (B1R) and bradykinin 2 receptor (B2R) siRNA, suggesting the role of B1R and B2R in this process. The BK-induced stimulation of glutamate uptake was also blocked by [des-Arg(10)]-HOE 140, a B1R antagonist, and HOE 140, a B2R antagonist, as well as by the tyrosine kinase inhibitors genistein and herbimycin A. In addition, the BK-induced stimulation of glutamate uptake was blocked by treatment with the phospholipase A(2) inhibitors mepacrine and AACOCF(3), the cyclooxygenase (COX) inhibitor indomethacin, and the COX-2 inhibitor Dup 697. Furthermore, the BK-induced increase in COX-2 expression was blocked by the PI-3 kinase inhibitors wortmannin and LY294002, Akt inhibitor, and the protein kinase C (PKC) inhibitors staurosporine and bisindolylmaleimide I, suggesting the role of PI-3 kinase and PKC in this process. BK stimulated Akt activation and the translocation of PKC activation via the activation of B1R and B2R.

SIGNIFICANCE

BK stimulates glutamate uptake through a PKC-Akt-COX-2 signaling cascade in ARPE cells.

Drug transport in corneal epithelium and blood-retina barrier: emerging role of transporters in ocular pharmacokinetics

Corneal epithelium and blood-retina barrier (i.e. retinal capillaries and retinal pigment epithelium (RPE)) are the key membranes that regulate the access of xenobiotics into the ocular tissues. Corneal epithelium limits drug absorption from the lacrimal fluid into the anterior chamber after eyedrop administration, whereas blood-retina barrier restricts the entry of drugs from systemic circulation to the posterior eye segment. Like in general pharmacokinetics, the role of transporters has been considered to be quite limited as compared to the passive diffusion of drugs across the membranes. As the functional role of transporters is being revealed it has become evident that the transporters are widely important in pharmacokinetics. This review updates the current knowledge about the transporters in the corneal epithelium and blood-retina barrier and demonstrates that the information is far from complete. We also show that quite many ocular drugs are known to interact with transporters, but the studies about the expression and function of those transporters in the eye are still sparse. Therefore, the transporters probably have greater role in ocular pharmacokinetics than we currently realise.

Glutamate acts at NMDA receptors on fresh bovine and on cultured human retinal pigment epithelial cells to trigger release of ATP

The photoreceptors lie between the inner retina and the retinal pigment epithelium (RPE). The release of glutamate by the phototoreceptors can signal changes in light levels to inner retinal neurons, but the role of glutamate in communicating with the RPE is unknown. Since RPE cells are known to release ATP, we asked whether glutamate could trigger ATP release from RPE cells and whether this altered cell signalling. Stimulation of the apical face of fresh bovine RPE eyecups with 100 mum NMDA increased ATP levels more than threefold, indicating that both receptors for NMDA and release of ATP occurred across the apical membrane of fresh RPE cells. NMDA increased ATP levels bathing cultured human ARPE-19 cells more than twofold, with NMDA receptor inhibitors MK-801 and d-AP5 preventing this release. Blocking the glycine site of the NMDA receptor with 5,7-dichlorokynurenic acid prevented ATP release from ARPE-19 cells. Release was also blocked by channel blocker NPPB and Ca(2+) chelator BAPTA, but not by cystic fibrosis transmembrane conductance regulator (CFTR) blocker glibenclamide or vesicular release inhibitor brefeldin A. Glutamate produced a dose-dependent release of ATP from ARPE-19 cells that was substantially inhibited by MK-801. NMDA triggered a rise in cell Ca(2+) that was blocked by MK-801, by the ATPase apyrase, by the P2Y(1) receptor antagonist MRS2179 and by depletion of intracellular Ca(2+) stores with thapsigargin. These results suggest that glutamate stimulates NMDA receptors on the apical membrane of RPE cells to release ATP. This secondary release can amplify the glutaminergic signal by increasing Ca(2+) inside RPE cells, and might activate Ca(2+)-dependent conductances. The interplay between glutaminergic and purinergic systems may thus be important for light-dependent interactions between photoreceptors and the RPE.

Optical coherence tomography in tamoxifen retinopathy

Optical coherence tomography (OCT) is a non-invasive, transpupillary imaging technology that allows detailed analysis of the retinal structures. In a recent article, Gualino et al. reported that OCT revealed a foveolar cystoid space with focal disruption of the photoreceptors line that explains the irreversible loss of central vision in tamoxifen retinopathy. In addition to providing a better understanding of the pathogenesis of tamoxifen retinopathy, OCT screening is advisable in patients treated with tamoxifen over long periods in order to detect and prevent drug-induced retinal damage.

Amyotrophic lateral sclerosis: recent advances and future therapies

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis is a rare but fatal motoneuron disorder. Despite intensive research riluzole remains the only available therapy, with only marginal effects on survival. Here we review some of the recent advances in the search for a disease-modifying therapy for amyotrophic lateral sclerosis.

RECENT FINDINGS

A number of established agents have recently been re-investigated for their potential as neuroprotective agents, including beta-lactam antibiotics and minocycline. Progress has also been made in exploiting growth factors for the treatment of amyotrophic lateral sclerosis, partly due to advances in developing effective delivery systems to the central nervous system. A number of new therapies have also been identified, including a novel class of compounds, heat-shock protein co-inducers, which upregulate cell stress responses thereby mediating neuroprotection. Non-drug-based therapies are also under development, with progress in gene-silencing and stem cell therapies.

SUMMARY

In the past few years, significant advances have been made in both our understanding of amyotrophic lateral sclerosis pathogenesis and the development of new therapeutic approaches. However, caution must be exercised in view of the long-standing failure to successfully transfer therapeutic compounds to the clinic. A deeper awareness in the research community of the need for clinically relevant preclinical studies, coupled with a better understanding of the issues surrounding clinical trial design for amyotrophic lateral sclerosis, offers hope that the growing list of validated preclinical therapeutics can finally yield an effective disease-modifying treatment.

Optical coherence tomography findings in tamoxifen retinopathy

PURPOSE

To describe optical coherence tomography (OCT) findings in two cases of typical tamoxifen retinopathy.

DESIGN

Observational cases report.

METHODS

Two patients with tamoxifen retinopathy were imaged with fluorescein angiography and OCT 3.

RESULTS

Fluorescein angiography showed foveolar hyperfluorescence. OCT revealed a foveolar cystoid space with focal disruption of the photoreceptor line. There was no evidence of macular edema or thickening.

CONCLUSIONS

In both cases, OCT findings are not consistent with previous descriptions of tamoxifen retinopathy, based on fundus examination and fluorescein angiography, which include a description of macular edema. This new imaging suggests that tamoxifen maculopathy may include a foveolar cystoid space different from macular edema.

Release of L-aspartate by reversal of glutamate transporters

Aspartate is released in the brain during metabolic inhibition and can activate NMDA receptors. We compared the characteristics of aspartate and glutamate release mediated by reversed operation of GLAST glutamate transporters in salamander retinal glial cells, when high [K(+)](o) solution was applied to mimic the ionic conditions of stroke or glaucoma. In the absence of Cl(-), to isolate the transport-associated current of the transporters, reversed uptake of aspartate and glutamate had similar characteristics. Both were increased strongly by depolarisation, inhibited by the transport inhibitor TBOA (DL-threo-beta-benzyloxyaspartate), and activated in a first order manner by intracellular amino acid (in the presence of 20mM [Na(+)](i)) with an EC(50) of 0.8mM for aspartate and 2.3mM for glutamate. In stroke the extracellular pH shifts acid by around a pH unit: this reduced the release of aspartate and glutamate by reversed uptake by a factor of 8-20. The external Cl(-) concentration had only a small effect on the current associated with reversed uptake of aspartate and glutamate. Tamoxifen, which reduces amino acid release through swelling-activated anion channels in glial cells, was found to inhibit reversed uptake with an IC(50) which was >100 microM. Part of the activation of NMDA receptors which occurs in ischaemia is likely to reflect the release of aspartate by reversed uptake.

Laser treatment of cultured retinal pigment epithelial cells-evaluation of the cellular damage in vitro

PURPOSE

Evaluation of the effects of laser photocoagulation on cultured primary retinal pigment epithelial cells.

METHODS

Cells were treated by a diode laser (678 nm) with 800 and 1600 mW for 0.186 second. Cell toxicity was tested by the WST-1 assay, and the uptakes of glutamate and gamma-aminobutyric acid (GABA) were measured.

RESULTS

Laser photocoagulation (1600 mW) caused cell damage and the mitochondrial enzyme activity evaluated by a WST-1 test significantly decreased by 20%-30%. Laser treatment caused a dose-dependent decrease in glutamate uptake but increased GABA uptake.

CONCLUSIONS

Laser treatment and the laser-induced increase in temperature influence transport processes in retinal pigment epithelial cells and may cause cell damage in the posterior part of the retina.

Iron alters glutamate secretion by regulating cytosolic aconitase activity

Glutamate has many important physiological functions, including its role as a neurotransmitter in the retina and the central nervous system. We have made the novel observations that retinal pigment epithelial cells underlying and intimately interacting with the retina secrete glutamate and that this secretion is significantly affected by iron. In addition, iron increased secretion of glutamate in cultured lens and neuronal cells, indicating that this may be a common mechanism for the regulation of glutamate production in many cell types. The activity of the iron-dependent enzyme cytosolic aconitase (c-aconitase) is increased by iron. The conversion of citrate to isocitrate by c-aconitase is the first step in a three-step process leading to glutamate formation. In the present study, iron increased c-aconitase activity, and this increase was associated with an increase in glutamate secretion. Inhibition of c-aconitase by oxalomalate decreased glutamate secretion and completely inhibited the iron-induced increase in glutamate secretion. Derangements in both glutamate secretion and iron metabolism have been noted in neurological diseases and retinal degeneration. Our results are the first to provide a functional link between these two physiologically important substances by demonstrating a significant role for iron in the regulation of glutamate production and secretion in mammalian cells resulting from iron regulation of aconitase activity. Glutamatergic systems are found in many nonneuronal tissues. We provide the first evidence that, in addition to secreting glutamate, retinal pigment epithelial cells express the vesicular glutamate transporter VGLUT1 and that regulated vesicular release of glutamate from these cells can be inhibited by riluzole.

Toxicity of selected cationic drugs in retinoblastomal cultures and in cocultures of retinoblastomal and retinal pigment epithelial cell lines

Tamoxifen and toremifene are antiestrogenic drugs successfully used in the therapy of breast cancer. Rheumatoid arthritis and malaria have been treated with chloroquine for decades. Unfortunately, tamoxifen and chloroquine are reported to induce retinal changes as a side effect. We now studied the effects of tamoxifen, toremifene, and chloroquine on the viability of the human retinoblastomal cell line Y79, using the WST-1 test or measurement of the cellular ATP content. The studies were made on Y79 cell cultures and on cocultures of Y79 cells and retinal pigment epithelial cell line ARPE-19. The cocultures were used to clarify the effect of retinal pigment epithelium on toxicity to Y79 cells. In the coculture, the drugs were applied to ARPE-19 cells growing in the culture inserts on top of Y79 cells and the viability of ARPE-19 and Y79 cells was assessed separately. Tamoxifen, toremifene, and chloroquine reduced dose-dependently the viability of Y79 cells after 24-h exposure. The ARPE-19 cells proved to be protective after chloroquine exposure in the coculture. The results shed light on the toxicity of tamoxifen and chloroquine in Y79 cells in vitro. With the coculture we were able to simulate the in vivo route of chloroquine to the retina via the retinal pigment epithelium.

Current pharmacological management of amyotrophic [corrected] lateral sclerosis and a role for rational polypharmacy

Amyotrophic [corrected] lateral sclerosis (ALS) is a progressive degenerative condition of motor neurons that is ultimately fatal. Even though scientific discovery over the past few decades has led to a greater understanding of the pathogenic mechanisms of ALS, effective pharmacotherapy intended to slow, arrest or reverse the disease progression remains difficult to obtain. Riluzole, a drug that has only modest benefit in extending survival, is still the only medication approved by the FDA for the treatment of ALS. However, a number of pharmacological agents are currently being investigated as potential therapy for ALS. This paper will review the pathophysiology of ALS and current pharmacological management of the disease and recent directions in research and clinical trials. Based on the available data, it is our opinion that combination drug therapies should be considered for future clinical trials.

Surveillance ophtalmologique de la prise des antipaludéens de synthèse au long cours : mise au point et conduite à tenir à partir de 2003

The early detection of macular toxicity linked to long-term antimalarial treatment requires regular ophthalmological screening based on patients'classification based on their results compared to successive controls. Patients are classified as "low risk" with screening every 18 months if all of the following criteria are met: age under 65 years, no associated renal, hepatic or retinal disease, treatment for less than 5 years, dose less than or equal to 6,5mg/kg/d for hydroxychloroquine and 3mg/kg/d for chloroquine (for a lean patient's weight); "at risk, without fundus findings" with screening every 12 months if one of the following criteria is met: age over 65 years (at the start of or during treatment), antimalarial treatment for more than 5 years, daily dose higher than recommended, presence of renal and/or hepatic disease; "at risk, with fundus findings" with screening every 6 months if a retinal dysfunction has been detected and even if treatment is established or followed. Screening consists of an in-depth clinical examination and at least two complementary tests of macular function: color vision (desaturated-Panel-D15 test) and/or static macular perimetry (central 10 degrees) and/or macular electroretinography (pattern ERG/multifocal ERG). If any changes or anomalies are found between two successive check-ups, the state of the retina can be assessed by angiography and global retinal function by full-field-ERG and electro-oculogram (EOG). The progression from one check-up to the next decides whether a course of treatment will be followed.

Kinetics of Inhibition of Glutamate Uptake by Antioestrogens

The antioestrogens, tamoxifen and its more recent homologue toremifene, are used in the therapy of breast cancer. Tamoxifen has been reported to cause retinal changes as side effects. Both compounds inhibited glutamate uptake in retinal pigment epithelial cells, and the present study was conducted to clarify the mechanism of this inhibition. Retinal pigment epithelial cells are part of the blood-retina barrier, and their glutamate transporters are essential for retinal glutamate homeostasis. Glutamate uptake was investigated in human retinal pigment epithelial cell line D407 and in cultured pig retinal pigment epithelial cells using L-[3H]glutamate as a tracer. The cells were exposed to 7.5 microM tamoxifen and toremifene. beta-Hydroxyaspartate, a transportable inhibitor of glutamate transport, was used as a reference compound. In kinetic analyses, beta-hydroxyaspartate increased the Km constant for glutamate transport. Tamoxifen and toremifene exhibited the same effect, which indicates that inhibition evoked by them is also competitive in nature. Both drugs were more effective in the human retinal pigment epithelial cell line than in the pig retinal pigment epithelial cells. The results show for the first time that the antioestrogens tamoxifen and toremifene could possibly hamper glutamate transport by replacing glutamate as the substrate.

Refining In Vitro Neurotoxicity Testing — The Development of Blood–Brain Barrier Models

The purpose of this paper is to review the current state of development of advanced in vitro blood–brain barrier (BBB) models. The BBB is a special capillary bed that separates the blood from the central nervous system (CNS) parenchyma. Astrocytes maintain the integrity of the BBB, and, without astrocytic contacts, isolated brain capillary endothelial cells in culture lose their barrier characteristics. Therefore, when developing in vitro BBB models, it is important to add astrocytic factors into the culture system. Recently, novel filter techniques and co-culture methods have made it possible to develop models which resemble the in vivo functions of the BBB in an effective way. With a BBB model, kinetic factors can be added into the in vitro batteries used for evaluating the neurotoxic potential of chemicals. The in vitro BBB model also represents a useful tool for the in vitro prediction of the BBB permeability of drugs, and offers the possibility to scan a large number of drugs for their potential to enter the CNS. Cultured monolayers of brain endothelial cell lines or selected epithelial cell lines, combined with astrocyte and neuron cultures, form a novel three-dimensional technique for the screening of neurotoxic compounds.