Deferoxamine mesylate is toxic for retinal pigment epithelium cellsin vitro, and its toxicity is mediated by p38

A systematic review of the cell death mechanisms in retinal pigment epithelium cells and photoreceptors after subretinal hemorrhage - Implications for treatment options

Humans rely on vision as their most important sense. This is accomplished by photoreceptors (PRs) in the retina that detect light but cannot function without the support and maintenance of the retinal pigment epithelium (RPE). In subretinal hemorrhage (SRH), blood accumulates between the neurosensory retina and the RPE or between the RPE and the choroid. Blood breakdown products subsequently damage PRs and the RPE and lead to poor vision and blindness. Hence, there is a high need for options to preserve the retina and visual functions. We conducted a systematic review of the literature in accordance with the PRISMA guidelines to identify the cell death mechanisms in RPE and PRs after SRH to deepen our understanding of the pathways involved. After screening 736 publications published until November 8, 2022, we identified 19 records that assessed cell death in PRs and/or RPE in experimental models of SRH. Among the different cell death mechanisms, apoptosis was the most widely investigated mechanism (11 records), followed by ferroptosis (4), whereas necroptosis, pyroptosis, and lysosome-dependent cell death were only assessed in one study each. We discuss different therapeutic options that were assessed in these studies, including the removal of the hematoma/iron chelation, cytoprotection, anti-inflammatory agents, and antioxidants. Further systematic investigations will be necessary to determine the exact cell death mechanisms after SRH with respect to different blood breakdown components, cell types, and time courses. This will form the basis for the development of novel treatment options for SRH.

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.

Challenges and Opportunities of Metal Chelation Therapy in Trace Metals Overload-Induced Alzheimer's Disease

Essential trace metals like zinc (Zn), iron (Fe), and copper (Cu) play an important physiological role in the metabolomics and healthy functioning of body organs, including the brain. However, abnormal accumulation of trace metals in the brain and dyshomeostasis in the different regions of the brain have emerged as contributing factors in neuronal degeneration, Aβ aggregation, and Tau formation. The link between these essential trace metal ions and the risk of AD has been widely studied, although the conclusions have been ambiguous. Despite the absence of evidence for any clinical benefit, therapeutic chelation is still hypothesized to be a therapeutic option for AD. Furthermore, the parameters like bioavailability, ability to cross the BBB, and chelation specificity must be taken into consideration while selecting a suitable chelation therapy. The data in this review summarizes that the primary intervention in AD is brain metal homeostasis along with brain metal scavenging. This review evaluates the impact of different trace metals (Cu, Zn, Fe) on normal brain functioning and their association with neurodegeneration in AD. Also, it investigates the therapeutic potential of metal chelators in the management of AD. An extensive literature search was carried out on the "Web of Science, PubMed, Science Direct, and Google Scholar" to investigate the effect of trace elements in neurological impairment and the role of metal chelators in AD. In addition, the current review highlights the advantages and limitations of chelation therapies and the difficulties involved in developing selective metal chelation therapy in AD patients.

Effects of medications on hypoxia-inducible factor in the retina: A review

Hypoxia-inducible factor (HIF) plays a critical role in the mechanisms that allow cells to adapt to various oxygen levels in the environment. Specifically, HIF-1⍺ has shown to be widely involved in cellular repair, survival, and energy metabolism. HIF-1⍺ has also been found in increased levels in cancer cells, highlighting the importance of balance in the hypoxic response. Promoting HIF-1⍺ activity as a potential therapy for degenerative diseases and inhibiting HIF-1⍺ as a therapy for pathologies with overactive cell proliferation are actively being explored. Digoxin and metformin, HIF-1⍺ inhibitors, and deferoxamine and ⍺-ketoglutarate analogues, HIF-1⍺ activators, are being studied for application in age-related macular degeneration, diabetic retinopathy, and retinitis pigmentosa. However, these same medications have retinal toxicities that must be assessed before implementation of therapeutic care. Herein, we highlight the duality of therapeutic and toxic potential of HIF-1⍺ that must be carefully assessed prior to its clinical application in retinal disorders.

Desferrioxamine-Related Pseudo-Vitelliform Dystrophy and the Effect of Anti-Vascular Endothelial Growth Factor

We report a case of a 72-year-old female who developed bilateral pseudo-vitelliform dystrophy after taking desferrioxamine for the treatment of chronic iron overload. The patient then developed a right superior hemiretinal vein occlusion associated with intraretinal fluid in the right eye and was treated with monthly intravitreal aflibercept injections for 3 months followed by as required treatment. In addition to the intraretinal fluid responding to anti-VEGF treatment, there was a reduction in the size of the pseudo-vitelliform subfoveal deposit height, which was not seen in the untreated eye. Our case of an uncommon presentation of desferrioxamine-related maculopathy associated with a vein occlusion and the changes associated with intravitreal anti-VEGF treatment may help with the potential hypotheses of the pathophysiology of desferrioxamine-related pseudo-vitelliform retinal lesions and help with the potential future treatments of the condition.

Air pollutants disrupt iron homeostasis to impact oxidant generation, biological effects, and tissue injury

Air pollutants cause changes in iron homeostasis through: 1) a capacity of the pollutant, or a metabolite(s), to complex/chelate iron from pivotal sites in the cell or 2) an ability of the pollutant to displace iron from pivotal sites in the cell. Through either pathway of disruption in iron homeostasis, metal previously employed in essential cell processes is sequestered after air pollutant exposure. An absolute or functional cell iron deficiency results. If enough iron is lost or is otherwise not available within the cell, cell death ensues. However, prior to death, exposed cells will attempt to reverse the loss of requisite metal. This response of the cell includes increased expression of metal importers (e.g. divalent metal transporter 1). Oxidant generation after exposure to air pollutants includes superoxide production which functions in ferrireduction necessary for cell iron import. Activation of kinases and phosphatases and transcription factors and increased release of pro-inflammatory mediators also result from a cell iron deficiency, absolute or functional, after exposure to air pollutants. Finally, air pollutant exposure culminates in the development of inflammation and fibrosis which is a tissue response to the iron deficiency challenging cell survival. Following the response of increased expression of importers and ferrireduction, activation of kinases and phosphatases and transcription factors, release of pro-inflammatory mediators, and inflammation and fibrosis, cell iron is altered, and a new metal homeostasis is established. This new metal homeostasis includes increased total iron concentrations in cells with metal now at levels sufficient to meet requirements for continued function.

Sickle cell retinopathy. A focused review

PURPOSE

To provide a focused review of sickle cell retinopathy in the light of recent advances in the pathogenesis, multimodal retinal imaging, management of the condition, and migration trends, which may lead to increased prevalence of the condition in the Western world.

METHODS

Non-systematic focused literature review.

RESULTS

Sickle retinopathy results from aggregation of abnormal hemoglobin in the red blood cells in the retinal microcirculation, leading to reduced deformability of the red blood cells, stagnant blood flow in the retinal precapillary arterioles, thrombosis, and ischemia. This may be precipitated by hypoxia, acidosis, and hyperosmolarity. Sickle retinopathy may result in sight threatening complications, such as paracentral middle maculopathy or sequelae of proliferative retinopathy, such as vitreous hemorrhage and retinal detachment. New imaging modalities, such as wide-field imaging and optical coherence tomography angiography, have revealed the microstructural features of sickle retinopathy, enabling earlier diagnosis. The vascular growth factor ANGPTL-4 has recently been identified as a potential mediator of progression to proliferative retinopathy and may represent a possible therapeutic target. Laser therapy should be considered for proliferative retinopathy in order to prevent visual loss; however, the evidence is not very strong. With recent development of wide-field imaging, targeted laser to ischemic retina may prove to be beneficial. Exact control of intraoperative intraocular pressure, including valved trocar vitrectomy systems, may improve the outcomes of vitreoretinal surgery for complications, such as vitreous hemorrhage and retinal detachment. Stem cell transplantation and gene therapy are potentially curative treatments, which may prevent retinopathy.

CONCLUSIONS

There is lack of evidence regarding the optimal management of sickle retinopathy. Further study is needed to determine if recent progress in the understanding of the pathophysiology and diagnosis of sickle retinopathy may translate into improved management and outcome.

Involvement of NYD-SP15 in growth and oxidative-stress responses of ARPE-19

The aim of this study was to investigate the role of NYD-SP15 in the growth and oxidative-stress responses of ARPE-19 cells. ARPE-19 cell lines overexpressing wild type or RNA interference against NYD-SP15 were established via lentivirus transfection. Cell growth and proliferation, migration, apoptosis, and cell cycle progression were monitored using the Cell Counting Kit-8 assay, the wound scratch assay, and flow cytometry, respectively. Caspase-3/8/9 activity was examined using the caspase-3/8/9 assay kit. An hydrogen peroxide (H ₂ O ₂ )-induced oxidative-stress damage model was used to study the effect of NYD-SP15 knockdown by examining the activity of reactive oxygen species (ROS). Expressions of Kelch-like ECH-associated protein 1 (Keap-1)/heme oxygenase-1 (HO-1)/nuclear factor erythroid 2-related factor 2 (Nrf2), mitogen-activated protein kinase (MAPK), and Akt were detected by Western blot analysis. The mRNA chip of NYD-SP15 overexpressed ARPE-19 cells as well as controls were performed by one array plus process. Overexpression (OE) of NYD-SP15 inhibited the proliferation and migration of ARPE-19 cells, and led to apoptosis and caspase-3/9 activation. OE of NYD-SP15 inhibited MAPKs and Akt signaling. Downregulation of NYD-SP15 had no effect on the growth of normally cultured ARP19 cells with 10% fetal bovine serum, but promoted the growth of ARP19 cells in the presence of starvation challenge. Gene chip showed that OE of NYD-SP15 led to downregulation of 254 genes and upregulation of 57 genes. Downregulation of NYD-SP15 also exerted a protective effect on H ₂ O ₂ -induced cell apoptosis and ROS. NYD-SP15 downregulation led to increments in the expression of Nrf2, Keap-1, and HO-1 in response to 200 μM H ₂ O ₂ . NYD-SP15 might inhibit the growth, proliferation, and migration and promote apoptosis of ARPE-19 cells via MAPK and Akt signaling. Downregulation of NYD-SP15 could protect ARPE-19 cells from H ₂ O ₂ -induced oxidative damage by active Keap-1/HO-1/Nrf2, Akt, and MAPK signaling.

Pattern dystrophies in patients treated with deferoxamine: report of two cases and review of the literature

Background

Deferoxamine (DFO) is one of the most commonly used chelation treatments for transfusional hemosiderosis. Pattern dystrophies constitute a distinct entity of retinal disorders that has been occasionally identified in association with deferoxamine.

Case presentation

We report two cases of bilateral macular pattern dystrophy in transfusion dependent patients undergoing chronic chelation therapy with deferoxamine due to thalassemias. Our patients were evaluated with multimodal imaging and the results are presented. Both patients had normal cone and rod responses in the full-field electroretinogram and continued the prescribed chelation therapy, after hematology consult. The patients were followed up every 3 months for 2 and 4 years respectively for possible deterioration. Their best corrected visual acuity remained stable with no anatomic change on Optical Coherence Tomography findings.

Conclusion

Multimodal imaging of our patients allowed a better evaluation and possibly earlier detection of the DFO-related changes. Screening and close follow up of patients under chronic chelating therapy is important in order to promptly diagnose and manage possible toxicity either with discontinuation of the offending agent or dose modification.

Deferoxamine-induced electronegative ERG responses

PURPOSE

To report a case of deferoxamine-induced retinopathy characterized by electroretinography (ERG), optical coherence tomography angiography (OCT-A), and other multimodal imaging.

METHODS

This is an observational case report of one patient. Full-field ERG was performed. OCT-A, spectral-domain optical coherence tomography (SD-OCT), color fundus photography, and fundus autofluorescence were used to characterize the retinopathy induced by deferoxamine use.

RESULTS

A 64-year-old man with a history of β-thalassemia intermedia presented with worsening visual acuity, nyctalopia, and electronegative ERG. OCT-A revealed atrophy of the choriocapillaris in areas of hypoautofluorescence, corresponding to regions of retinal atrophy. SD-OCT showed disruption of the ellipsoid zone, granular hyperreflective deposits within the retinal pigment epithelium, thinning of the retinal layers, and extensive choroidal sclerosis and atrophy of the retinal pigment epithelium.

CONCLUSION

Deferoxamine-induced retinopathy can manifest with electronegative maximal ERG responses, and OCT-A can be used to detect deferoxamine toxicity.

Pseudovitelliform maculopathy associated with deferoxamine toxicity: multimodal imaging and electrophysiology of a rare entity

Deferoxamine is a commonly used chelating agent for secondary hemochromatosis. We report a rare retinal manifestation of deferoxamine toxicity in a 68-year-old man and provide supporting multimodal imaging and electrophysiology. The patient had iron overload related to transfusion-dependent myelodysplastic syndrome and developed a pseudovitelliform macular lesion related to deferoxamine toxicity. We also describe for the first time the worsening of this maculopathy on deferasirox, an alternative chelating agent. Macular pseudovitelliform lesion is a unique manifestation of deferoxamine toxicity that can be mistaken for pattern dystrophy. It is important to recognize this manifestation, because discontinuation of the offending agent may halt or reverse the toxicity.

Wnt5a is a key target for the pro-osteogenic effects of iron chelation on osteoblast progenitors

Iron overload due to hemochromatosis or chronic blood transfusions has been associated with the development of osteoporosis. However, the impact of changes in iron homeostasis on osteoblast functions and the underlying mechanisms are poorly defined. Since Wnt signaling is a critical regulator of bone remodeling, we aimed to analyze the effects of iron overload and iron deficiency on osteoblast function, and further define the role of Wnt signaling in these processes. Therefore, bone marrow stromal cells were isolated from wild-type mice and differentiated towards osteoblasts. Exposure of the cells to iron dose-dependently attenuated osteoblast differentiation in terms of mineralization and osteogenic gene expression, whereas iron chelation with deferoxamine promoted osteogenic differentiation in a time- and dose-dependent manner up to 3-fold. Similar results were obtained for human bone marrow stromal cells. To elucidate whether the pro-osteogenic effect of deferoxamine is mediated via Wnt signaling, we performed a Wnt profiler array of deferoxamine-treated osteoblasts. Wnt5a was amongst the most highly induced genes. Further analysis revealed a time- and dose-dependent induction of Wnt5a being up-regulated 2-fold after 48 h at 50 μM deferoxamine. Pathway analysis using specific inhibitors revealed that deferoxamine utilized the phosphatidylinositol-3-kinase and nuclear factor of activated T cell pathways to induce Wnt5a expression. Finally, we confirmed the requirement of Wnt5a in the deferoxamine-mediated osteoblast-promoting effects by analyzing the matrix mineralization of Wnt5a-deficient cells. The promoting effect of deferoxamine on matrix mineralization in wild-type cells was completely abolished in Wnt5a^-/- cells. Thus, these data demonstrate that Wnt5a is critical for the pro-osteogenic effects of iron chelation using deferoxamine.

Air pollution particles and iron homeostasis

BACKGROUND

The mechanism underlying biological effects, including pro-inflammatory outcomes, of particles deposited in the lung has not been defined.

MAJOR CONCLUSIONS

A disruption in iron homeostasis follows exposure of cells to all particulate matter including air pollution particles. Following endocytosis, functional groups at the surface of retained particle complex iron available in the cell. In response to a reduction in concentrations of requisite iron, a functional deficiency can result intracellularly. Superoxide production by the cell exposed to a particle increases ferrireduction which facilitates import of iron with the objective being the reversal of the metal deficiency. Failure to resolve the functional iron deficiency following cell exposure to particles activates kinases and transcription factors resulting in a release of inflammatory mediators and inflammation. Tissue injury is the end product of this disruption in iron homeostasis initiated by the particle exposure. Elevation of available iron to the cell precludes deficiency of the metal and either diminishes or eliminates biological effects.

GENERAL SIGNIFICANCE

Recognition of the pathway for biological effects after particle exposure to involve a functional deficiency of iron suggests novel therapies such as metal supplementation (e.g. inhaled and oral). In addition, the demonstration of a shared mechanism of biological effects allows understanding the common clinical, physiological, and pathological presentation following exposure to disparate particles. This article is part of a Special Issue entitled Air Pollution, edited by Wenjun Ding, Andrew J. Ghio and Weidong Wu.

Clinical applications of fundus autofluorescence in retinal disease

Fundus autofluorescence (FAF) is a non-invasive retinal imaging modality used in clinical practice to provide a density map of lipofuscin, the predominant ocular fluorophore, in the retinal pigment epithelium. Multiple commercially available imaging systems, including the fundus camera, the confocal scanning laser ophthalmoscope, and the ultra-widefield imaging device, are available to the clinician. Each offers unique advantages for evaluating various retinal diseases. The clinical applications of FAF continue to expand. It is now an essential tool for evaluating age related macular degeneration, macular dystrophies, retinitis pigmentosa, white dot syndromes, retinal drug toxicities, and various other retinal disorders. FAF may detect abnormalities beyond those detected on funduscopic exam, fluorescein angiography, or optical coherence tomography, and can be used to elucidate disease pathogenesis, form genotype-phenotype correlations, diagnose and monitor disease, and evaluate novel therapies. Given its ease of use, non-invasive nature, and value in characterizing retinal disease, FAF enjoys increasing clinical relevance. This review summarizes common ocular fluorophores, imaging modalities, and FAF findings for a wide spectrum of retinal disorders.

Functional and Structural Abnormalities in Deferoxamine Retinopathy: A Review of the Literature

Deferoxamine mesylate (DFO) is the most commonly used iron-chelating agent to treat transfusion-related hemosiderosis. Despite the clear advantages for the use of DFO, numerous DFO-related systemic toxicities have been reported in the literature, as well as sight-threatening ocular toxicity involving the retinal pigment epithelium (RPE). The damage to the RPE can lead to visual field defects, color-vision defects, abnormal electrophysiological tests, and permanent visual deterioration. The purpose of this review is to provide an updated summary of the ocular findings, including both functional and structural abnormalities, in DFO-treated patients. In particular, we pay particular attention to analyzing results of multimodal technologies for retinal imaging, which help ophthalmologists in the early diagnosis and correct management of DFO retinopathy. Fundus autofluorescence, for example, is not only useful for screening patients at high-risk of DFO retinopathy, but is also a prerequisite for identify specific high-risk patterns of RPE changes that are relevant for the prognosis of the disease. In addition, optical coherence tomography may have a clinical usefulness in detecting extent and location of different retinal changes in DFO retinopathy. Finally, this review wants to underline the need for universally approved guidelines for screening and followup of this particular disease.

The growth and aggressive behavior of human osteosarcoma is regulated by a CaMKII-controlled autocrine VEGF signaling mechanism

Osteosarcoma (OS) is a hyperproliferative malignant tumor that requires a high vascular density to maintain its large volume. Vascular Endothelial Growth Factor (VEGF) plays a crucial role in angiogenesis and acts as a paracrine and autocrine agent affecting both endothelial and tumor cells. The alpha-Ca²⁺/Calmodulin kinase two (α-CaMKII) protein is an important regulator of OS growth. Here, we investigate the role of α-CaMKII-induced VEGF in the growth and tumorigenicity of OS. We show that the pharmacologic and genetic inhibition of α-CaMKII results in decreases in VEGF gene expression (50%) and protein secretion (55%), while α- CaMKII overexpression increases VEGF gene expression (250%) and protein secretion (1,200%). We show that aggressive OS cells (143B) express high levels of VEGF receptor 2 (VEGFR-2) and respond to exogenous VEGF (100nm) by increasing intracellular calcium (30%). This response is ameliorated by the VEGFR inhibitor CBO-P11, suggesting that secreted VEGF results in autocrine stimulated α-CaMKII activation. Furthermore, we show that VEGF and α-CaMKII inhibition decreases the transactivation of the HIF-1α and AP-1 reporter constructs. Additionally, chromatin immunoprecipitation assay shows significantly decreased binding of HIF-1α and AP-1 to their responsive elements in the VEGF promoter. These data suggest that α-CaMKII regulates VEGF transcription by controlling HIF-1α and AP-1 transcriptional activities. Finally, CBO-P11, KN-93 (CaMKII inhibitor) and combination therapy significantly reduced tumor burden in vivo. Our results suggest that VEGF-induced OS tumor growth is controlled by CaMKII and dual therapy by CaMKII and VEGF inhibitors could be a promising therapy against this devastating adolescent disease.

Oxidative Stress Induces Biphasic ERK1/2 Activation in the RPE with Distinct Effects on Cell Survival at Early and Late Activation

PURPOSE

Oxidative stress is considered a major factor in the deterioration of retinal pigment epithelium (RPE) cells in dry age-related macular degeneration (AMD). The MAPK ERK1/2 can be activated by oxidative stress, may exert both pro- and anti-apoptotic functions, and has recently been proposed as a major factor in RPE degeneration in atrophic changes. Nrf2 is a master regulator of oxidative stress defense and ERK1/2 is an upstream activator of Nrf2. In this study, we investigate the participation of ERK1/2 in oxidative stress pathways in connection with Nrf2.

METHODS

Nrf2 knock-out and wild-type primary RPE cells were prepared from mouse eyes. Oxidative stress was induced by different concentrations of t-butylhydroperoxide. Mitogen-activated protein kinases (MAPKs) were blocked by commercially available inhibitors (SB203580, U0126, SP600125). Cell viability was determined by MTT assay. ERK1/2 expression and activation were assessed by Western blotting.

RESULTS

Oxidative stress induced concentration dependent cell death, which occurred at lower concentrations in Nrf2 knock-out RPE. Western blot analysis displayed a biphasic activation of ERK1/2 in murine wild-type RPE and the inhibition of late, but not early activation of ERK1/2 exerted protection in wild-type murine RPE cells. The biphasic activation of ERK1/2 is lost in Nrf2 knock-out mice, and inhibition of ERK1/2 was generally protective. The inhibition of MAPK JNK or p38 exerted no protection, irrespective of Nrf2.

CONCLUSION

RPE cells display a biphasic activation of ERK1/2 after oxidative insult, of which the late activation is pro-apoptotic. The biphasic activation is lost in Nrf2 knock-outs, suggesting that early ERK1/2 activation may be connected to Nrf2 signaling. In addition, ERK1/2 activation in Nrf2 knock-outs mediates oxidative stress-induced cell death.

Hyperthermia-induced upregulation of vascular endothelial growth factor in retinal pigment epithelial cells is regulated by mitogen-activated protein kinases

PURPOSE

Localized application of hyperthermia is a potential treatment for retinal diseases. Vascular endothelial growth factor (VEGF) derived from the retinal pigment epithelium (RPE) is implicated in a variety of retinal pathologies. As it has been recently shown that hyperthermia may induce VEGF in the RPE, the aim of this study was to investigate hyperthermia-induced VEGF secretion and the pathways of hyperthermal VEGF upregulation in the RPE.

MATERIAL AND METHODS

The human RPE cell line (Arpe-19) was exposed to 40°, 42°, 45° and 50 °C for one, five and 15 min. Cell viability was evaluated using a trypan blue exclusion assay, VEGF secretion was evaluated by an enzyme-linked immunosorbent assay ELISA) and VEGF expression was investigated using a Western blot. Involvement of mitogen-activated protein kinase (MAPK) pathways (ERK1/2, JNK, p38) and transient receptor potential vanilloid (TRPV) channels on VEGF induction was investigated using commercially available inhibitors (U0126, SB203580, SP600125, ruthenium red). Expression and phosphorylation of MAPKs was investigated using a Western blot.

RESULTS

Hyperthermia induces time- and temperature-dependent cell death in human RPE cells. VEGF expression and secretion is induced by hyperthermia in a time- and temperature-dependent manner mediated by p38 and to a lesser degree by JNK. TRPV channels seem to play a minor role in regulation of hyperthermia-induced VEGF secretion.

CONCLUSIONS

Hyperthermia induces temperature-dependent secretion of VEGF in the RPE, which is mediated by p38 and, to a lesser extent, JNK. This may lead to undesired effects from hyperthermal treatment of retinal diseases.

Effects of aflibercept on primary RPE cells: toxicity, wound healing, uptake and phagocytosis

BACKGROUND/AIM

Anti-VEGF treatment is the therapy of choice in age-related macular degeneration, and is also applied in diabetic macular oedema or retinal vein occlusion. Recently, the fusion protein, aflibercept, has been approved for therapeutic use. In this study, we investigate the effects of aflibercept on primary RPE cells.

METHODS

Primary RPE cells were prepared from freshly slaughtered pigs' eyes. The impact of aflibercept on cell viability was investigated with MTT and trypan blue exclusion assay. The influence of aflibercept on wound healing was assessed with a scratch assay. Intracellular uptake of aflibercept was investigated in immunohistochemistry and its influence on phagocytosis with a phagocytosis assay using opsonised latex beads.

RESULTS

Aflibercept displays no cytotoxicity on RPE cells but impairs its wound healing ability. It is taken up into RPE cells and can be intracellularly detected for at least 7 days. Intracellular aflibercept impairs the phagocytic capacity of RPE cells.

CONCLUSIONS

Aflibercept interferes with the physiology of RPE cells, as it is taken up into RPE cells, which is accompanied by a reduction of the phagocytic ability. Additionally, it impairs the wound healing capacity of RPE cells. These effects on the physiology of RPE cells may indicate possible side effects.

Fucoidan reduces secretion and expression of vascular endothelial growth factor in the retinal pigment epithelium and reduces angiogenesis in vitro

Fucoidan is a polysaccharide isolated from brown algae which is of current interest for anti-tumor therapy. In this study, we investigated the effect of fucoidan on the retinal pigment epithelium (RPE), looking at physiology, vascular endothelial growth factor (VEGF) secretion, and angiogenesis, thus investigating a potential use of fucoidan for the treatment of exudative age-related macular degeneration. For this study, human RPE cell line ARPE-19 and primary porcine RPE cells were used, as well as RPE/choroid perfusion organ cultures. The effect of fucoidan on RPE cells was investigated with methyl thiazolyl tetrazolium--assay, trypan blue exclusion assay, phagocytosis assay and a wound healing assay. VEGF expression was evaluated in immunocytochemistry and Western blot, VEGF secretion was evaluated in ELISA. The effect of fucoidan on angiogenesis was tested in a Matrigel assay using calcein-AM vital staining, evaluated by confocal laser scanning microcopy and quantitative image analysis. Fucoidan displays no toxicity and does not diminish proliferation or phagocytosis, but reduces wound healing in RPE cells. Fucoidan decreases VEGF secretion in RPE/choroid explants and RPE cells. Furthermore, it diminishes VEGF expression in RPE cells even when co-applied with bevacizumab. Furthermore, fucoidan reduces RPE-supernatant- and VEGF-induced angiogenesis of peripheral endothelial cells. In conclusion, fucoidan is a non-toxic agent that reduces VEGF expression and angiogenesis in vitro and may be of interest for further studies as a potential therapy against exudative age-related macular degeneration.

Sequestration of mitochondrial iron by silica particle initiates a biological effect

Inhalation of particulate matter has presented a challenge to human health for thousands of years. The underlying mechanism for biological effect following particle exposure is incompletely understood. We tested the postulate that particle sequestration of cell and mitochondrial iron is a pivotal event mediating oxidant generation and biological effect. In vitro exposure of human bronchial epithelial cells to silica reduced intracellular iron, which resulted in increases in both the importer divalent metal transporter 1 expression and metal uptake. Diminished mitochondrial 57Fe concentrations following silica exposure confirmed particle sequestration of cell iron. Preincubation of cells with excess ferric ammonium citrate increased cell, nuclear, and mitochondrial metal concentrations and prevented significant iron loss from mitochondria following silica exposure. Cell and mitochondrial oxidant generation increased after silica incubation, but pretreatment with iron diminished this generation of reactive oxygen species. Silica exposure activated MAP kinases (ERK and p38) and altered the expression of transcription factors (nF-κB and NF-E2-related factor 2), proinflammatory cytokines (interleukin-8 and -6), and apoptotic proteins. All of these changes in indexes of biological effect were either diminished or inhibited by cell pretreatment with iron. Finally, percentage of neutrophils and total protein concentrations in an animal model instilled with silica were decreased by concurrent exposure to iron. We conclude that an initiating event in the response to particulate matter is a sequestration of cell and mitochondrial iron by endocytosed particle. The resultant oxidative stress and biological response after particle exposure are either diminished or inhibited by increasing the cell iron concentration.

Toll-like receptor 3 activation in retinal pigment epithelium cells - Mitogen-activated protein kinase pathways of cell death and vascular endothelial growth factor secretion

PURPOSE

Toll-like receptor 3 (TLR3) is a receptor of the innate immune system, recognizing double-stranded RNA. TLR3 can lead to cytokine release or apoptosis and has recently been associated with the development of geographical atrophy via cytotoxic effects on the retinal pigment epithelium (RPE). The current study was conducted to elucidate the underlying pathways of TLR3 effects in the RPE.

METHODS

TLR3 activation via polyinosinic acid/polycytidylic acid (Poly I:C) was investigated in primary porcine RPE cells, focussing on cell death and vascular endothelial growth factor (VEGF) secretion. Primary cells were stimulated with different concentrations of Poly I:C. Cell death was investigated in trypan blue exclusion assay and cell death detection ELISA. VEGF and IFN-ß secretion were also detected in ELISA. As Mitogen-activated protein kinases (MAPK) play an important part in TLR3-mediated signal transduction, we investigated the influence of JNK, ERK1/2 and p38 on cell death and VEGF secretion, using commercially available inhibitors.

RESULTS

Activation of TLR3 by Poly I:C induced concentration-dependent cell death, partly mediated by JNK. ERK1/2 was activated and exerted some protection. Furthermore, higher concentrations of Poly I:C increased VEGF secretion after 4 and 24 hr, which was independent of MAPK.

CONCLUSION

The induction of cell death in RPE cells by TLR3 activation confirms possible involvement of TLR3 activation in GA. As cell death is partly mediated by JNK, more studies should be conducted investigating the role of JNK in RPE cell death to evaluate whether its inhibition might be a new therapeutic opportunity for the treatment of geographical atrophy. Additionally, effects on VEGF secretion can be found.

Retinal and cochlear toxicity of drugs: new insights into mechanisms and detection

PURPOSE OF REVIEW

Various medications can modify the physiology of retinal and cochlear neurons and lead to major, sometime permanent, sensory loss. A better knowledge of pathogenic mechanisms and the establishment of relevant monitoring protocols are necessary to prevent permanent sensory impairment. In this article, we review main systemic medications associated with direct neuronal toxicity on the retina and cochlea, their putative pathogenic mechanisms, when identified, as well as current recommendations, when available, for monitoring protocols.

RECENT FINDINGS

Pathogenic mechanisms and cellular target of retinotoxic drugs are often not well characterized but a better knowledge of the course of visual defect has recently helped in defining more relevant monitoring protocols especially for antimalarials and vigabatrin. Mechanisms of ototoxicity have recently been better defined, from inner ear entry with the use of fluorescent tracers to evidence for the role of oxidative stress and program cell death pathways.

SUMMARY

Experimental and clinical studies have elucidated some of the pathogenic mechanisms, courses and risk factors of retinal toxicity and ototoxicity, which have led to establishment of relevant monitoring protocols. Further studies are, however, warranted to better understand cellular pathways leading to degeneration. These would help to build more efficient preventive intervention and may also contribute to understanding of other degenerative processes such as genetic disorders.

Correlation of fundus autofluorescence, spectral-domain optical coherence tomography, and microperimetry in late deferoxamine maculopathy

PURPOSE

To describe long-term functional and morphologic retinal changes by deferoxamine, a chelating agent used to treat systemic iron overload.

METHODS

Ophthalmologic examination of acute deferoxamine maculopathy and follow-up of 5 years, using ophthalmologic examination, fluorescence angiography, electrophysiology, color vision testing, fundus image-correlated microperimetry, time-domain and spectral-domain optical coherence tomographies. The patient is a 53-year old woman who presented with acute visual deterioration to 20/50 in the right eye, 20/60 in the left eye, and reduced color vision. She had been treated with deferoxamine for 6 months. The diagnosis of deferoxamine maculopathy was made, and the drug discontinued immediately.

RESULTS

After 5 months, visual acuity was 20/25 bilaterally, but mottling of the retinal pigment epithelium (RPE) had developed. Five years later, visual acuity was 20/20 in both eyes. Fundus autofluorescence showed progressively clumped hyper- and hypofluorescence with larger areas of total RPE atrophy in the left eye. Spectral-domain optical coherence tomography visualized areas of RPE thickening, photoreceptor outer segment elongation, outer retinal tubulation, and outer retinal and RPE atrophy. Fundus image-correlated microperimetry showed relative central scotomas at the beginning, some of which recovered to normal light sensitivity, while others deteriorated to absolute scotomas.

CONCLUSION

Although visual acuity had recovered after cessation of deferoxamine, functional and morphologic residues remained, which included disturbed color vision, central microscotomas, and progressive RPE and outer retinal degeneration.