The β-Adrenergic Receptor Antagonist Metipranolol Blunts Zinc-Induced Photoreceptor and RPE Apoptosis

Effects of systemic drugs on the development and progression of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe loss of central vision among people over 50. The pathophysiology of the disease is multifactorial and can be attributed to genetics, aging, inflammation, environmental factors, and lifestyle factors including smoking, diet, obesity, and alcohol consumption. While there is no treatment for dry AMD, the current standard treatment for wet AMD is an intraocular injection of anti-vascular endothelial growth factor-an effective, yet expensive, therapy that requires ongoing treatment. As the aging population continues to grow, and AMD diagnoses continue to rise, new treatments should be explored to reduce vision complications and decrease treatment burdens. Many systemic conditions have progressive pathological changes that may affect AMD, particularly those affecting systemic vasculature like diabetes and cardiovascular status. Consequently, systemic drugs used to treat coexistent systemic diseases may influence some of the pathogenic mechanisms of AMD and lead its progression or delay. In this review we explore the current literature to summarize the findings of the reported effects of antihypertensive, immunosuppressants, cholesterol lowering agents, nonsteroidal anti-inflammatory drugs, dopamine precursors, hypoglycemic agents, and anticoagulants on AMD.

SYSTEMIC BETA-BLOCKERS AND RISK OF PROGRESSION TO NEOVASCULAR AGE-RELATED MACULAR DEGENERATION

PURPOSE

To determine whether oral beta-blockers (BBs) are associated with the development of neovascular age-related macular degeneration (nAMD).

METHODS

Retrospective cohort study of patients from 2000 to 2014 using data from a large national U.S. insurer's administrative medical claims database. Patients with nonexudative AMD who initiated (index date) BB, a calcium channel blocker (CCB), an angiotensin-converting enzyme/angiotensin receptor blocker, or a diuretic. Patients were excluded for <2 years in the plan before the index date, any history of nAMD or diagnosis, or treatment for an ocular disease that could be confused with nAMD. Hazard of developing of nAMD was the main outcome measure. Primary analysis compared BB with CCB patients with BB versus the other classes as secondary analyses. In addition, a sensitivity analysis was performed between BB and CCB cohorts using 1:1 propensity score matching. Cox proportional hazard regression was performed to estimate the hazard ratio (HR) of developing nAMD at 90, 180, and 365 days for BB. Covariates of interest included demographic information, year of index date, number of antihypertensive medications, and other comorbid systemic conditions.

RESULTS

Eighteen thousand seven hundred and fifty-four BB patients and 12,784 CCB patients met criteria for inclusion. After controlling for covariates, patients on BB had a lower hazard for nAMD at both 90 and 180 days than patients on CCB (HRs: 0.67-0.71; P < 0.01 for both) and diuretics (HRs: 0.55-0.62; P < 0.01). Patients on BB versus angiotensin-converting enzyme/angiotensin receptor blocker at all time points and BB versus CCB and diuretics at 365 days did not have a significantly lower association with nAMD (HR: 0.73-0.85; P > 0.06 for all comparisons). A sensitivity analysis using propensity score matching yielded similar results with patients on BB significantly less likely to develop nAMD at 90 and 180 days (HR: 0.70-0.76; P < 0.049 for both) but not at 365 days (HR: 0.88; P = 0.30) compared with patients on CCB.

CONCLUSION

No evidence was found that BB usage increased the hazard for nAMD relative to other antihypertensive medications.

A pilot study to evaluate the levels of aqueous humor trace elements in open-angle glaucoma

BACKGROUND

Primary open angle glaucoma (POAG) is the most common form of chronic, progressive optic neuropathies characterized by slow degeneration of the retinal ganglion cells and their axons, resulting in visual field loss. Risk factors for this disease are elevated intraocular pressure (IOP), increased age, European and African ethnicity, family history, myopia and decreased corneal thickness. In addition, studies indicated that levels of trace elements are also significantly related to the POAG.

METHOD

The association between toxic and essential elements and POAG was explored in a population-based case-control study in the Sardinia Island (Italy). The aqueous humor levels of Al, Cd, Cu, Fe, Hg, Mn, Ni, Pb and Zn were measured in 25 POAG patients compared to 20 age- and gender-matched healthy controls by sector field inductively coupled mass spectrometry. Risk factors as gender, age and increased IOP were also explored.

RESULTS

The concentrations of Fe, Hg and Zn were significantly higher in POAG patients than in control subjects, showing these elements as possible determinants in POAG development or degeneration. Other findings were the increased Cu and Fe levels in glaucomatous patients with age less than 70 years. Levels of Ni were found elevated in POAG females. Mercury accumulated more in POAG females, in patients over 70 years and in those with higher levels of IOP in the left eye. Moreover, the positive associations CuFe and Mn-Zn may indicate synergistic effects of elements.

CONCLUSIONS

Altogether, these findings suggested a multifactorial role in the risk for POAG disease. The present study documented the levels of trace elements in aqueous humor of Sardinian POAG patients for the first time.

The effects of zinc supplementation on primary human retinal pigment epithelium

Population-based and interventional studies have shown that elevated zinc levels can reduce the progression to advanced age-related macular degeneration. The objective of this study was to assess whether elevated extracellular zinc has a direct effect on retinal pigment epithelial cells (RPE), by examining the phenotype and molecular characteristics of increased extracellular zinc on human primary RPE cells. Monolayers of human foetal primary RPE cells were grown on culture inserts and maintained in medium supplemented with increasing total concentrations of zinc (0, 75, 100, 125 and 150 μM) for up to 4 weeks. Changes in cell viability and differentiation as well as expression and secretion of proteins were investigated. RPE cells developed a confluent monolayer with cobblestone morphology and transepithelial resistance (TER) >200 Ω*cm² within 4 weeks. There was a zinc concentration-dependent increase in TER and pigmentation, with the largest effects being achieved by the addition of 125 μM zinc to the culture medium, corresponding to 3.4 nM available (free) zinc levels. The cells responded to addition of zinc by significantly increasing the expression of Retinoid Isomerohydrolase (RPE65) gene; cell pigmentation; Premelanosome Protein (PMEL17) immunoreactivity; and secretion of proteins including Apolipoprotein E (APOE), Complement Factor H (CFH), and High-Temperature Requirement A Serine Peptidase 1 (HTRA1) without an effect on cell viability. This study shows that elevated extracellular zinc levels have a significant and direct effect on differentiation and function of the RPE cells in culture, which may explain, at least in part, the positive effects seen in clinical settings. The results also highlight that determining and controlling of available, as opposed to total added, zinc will be essential to be able to compare results obtained in different laboratories.

Cellular responses following retinal injuries and therapeutic approaches for neurodegenerative diseases

Retinal neurodegenerative diseases like age-related macular degeneration, glaucoma, diabetic retinopathy and retinitis pigmentosa each have a different etiology and pathogenesis. However, at the cellular and molecular level, the response to retinal injury is similar in all of them, and results in morphological and functional impairment of retinal cells. This retinal degeneration may be triggered by gene defects, increased intraocular pressure, high levels of blood glucose, other types of stress or aging, but they all frequently induce a set of cell signals that lead to well-established and similar morphological and functional changes, including controlled cell death and retinal remodeling. Interestingly, an inflammatory response, oxidative stress and activation of apoptotic pathways are common features in all these diseases. Furthermore, it is important to note the relevant role of glial cells, including astrocytes, Müller cells and microglia, because their response to injury is decisive for maintaining the health of the retina or its degeneration. Several therapeutic approaches have been developed to preserve retinal function or restore eyesight in pathological conditions. In this context, neuroprotective compounds, gene therapy, cell transplantation or artificial devices should be applied at the appropriate stage of retinal degeneration to obtain successful results. This review provides an overview of the common and distinctive features of retinal neurodegenerative diseases, including the molecular, anatomical and functional changes caused by the cellular response to damage, in order to establish appropriate treatments for these pathologies.

Stable overexpression of human metallothionein-IIA in a heart-derived cell line confers oxidative protection

Metallothionein (MT) is a metal binding protein and cardioprotective. In order to understand the molecular mechanisms underlying the role of MT in the heart, in the current study we established a stable MT-IIA over-expressing cardiac cell line, and evaluated its anti-oxidative property. Rat heart-derived H9c2 cell line was stably transfected with a vector in which the human MT-IIA gene was placed under the control of the constitutively active beta-actin promoter. The transfected cell line (H9c2MT7) exhibited similar growth kinetics and morphology. Western blotting analysis showed that H9c2MT7 had a remarkable increased MT protein level compared with the parent cell line H9c2. Addition of 25 microM ZnSO(4) had an undetectable effect on the induction of endogenous MT, but it likely stabilized the MT protein that is expressed only in H9c2MT7 cells. H9c2MT7 cells showed marked reduction in reactive oxygen species production when exposed to hydrogen peroxide or subjected to hypoxia/reoxygenation challenge evaluated by dihydroethidium staining. In addition, transfection of MT conferred cellular resistance to cadmium toxicity. In summary, we have established a stable human MT-IIA over-expressing cardiac cell line; and this cell line showed a markedly increased oxidative protection and would be useful for dissection of the mechanisms of MT in the cardiac protection.

[Post-traumatic inflammation with an intraocular foreign body]

BACKGROUND

To report on the diagnosis and management of a"firecracker" injury presenting with a post-traumatic intraocular inflammation.

CASE REPORT

A 10-year-old boy sustained a penetrating 16-mm cornea-sclera blast injury to his left eye with uveal prolapse and hemophthalmus and doubtful light perception. The cranial computed tomography revealed a metallic intraocular foreign body (IOFB), retinal detachment, and subretinal and subchoroidal hemorrhage. After primary wound closure and antibiotic treatment for 1 week, increasing cell infiltration and amaurosis developed, and a lensectomy, pars plana vitrectomy, and extraction of the 17x7x7-mm encapsulated IOFB via a scleral tunnel was indicated.

RESULTS

A vitreous specimen did not reveal microbial growth; however, plenty of polymorphonuclear cells, macrophages, and lymphocytes were observed. Spectroscopy of the IOFB showed copper, zinc, silicon, lead, and other metals. A diagnosis of noninfectious inflammation due to heavy metals, primarily copper (=chalcosis), was made. The postoperative course was unremarkable, the intraocular lens in place, fundus CDR 0.2, retina and macula attached, intraocular pressure 9 mmHg. Three weeks after surgery, the flash VEP showed absent potentials.

CONCLUSIONS

Large projectiles or parts should be removed from the eye immediately in order to prevent complications from toxic metallosis and early fibrotic reactions.

A suprachoroidal electrical retinal stimulator design for long-term animal experiments and in vivo assessment of its feasibility and biocompatibility in rabbits

This article reports on a retinal stimulation system for long-term use in animal electrical stimulation experiments. The presented system consisted of an implantable stimulator which provided continuous electrical stimulation, and an external component which provided preset stimulation patterns and power to the implanted stimulator via a paired radio frequency (RF) coil. A rechargeable internal battery and a parameter memory component were introduced to the implanted retinal stimulator. As a result, the external component was not necessary during the stimulation mode. The inductive coil pair was used to pass the parameter data and to recharge the battery. A switch circuit was used to separate the stimulation mode from the battery recharging mode. The implantable stimulator was implemented with IC chips and the electronics, except for the stimulation electrodes, were hermetically packaged in a biocompatible metal case. A polyimide-based gold electrode array was used. Surgical implantation into rabbits was performed to verify the functionality and safety of this newly designed system. The electrodes were implanted in the suprachoroidal space. Evoked cortical potentials were recorded during electrical stimulation of the retina. Long-term follow-up using OCT showed no chorioretinal abnormality after implantation of the electrodes.

UV-A induced oxidative stress is more prominent in naturally pigmented aged human RPE cells compared to non-pigmented human RPE cells independent of zinc treatment

To investigate the effects of zinc supplementation on human amelanotic (ARPE-19) and native pigmented retinal pigment epithelial cells (hRPE) under normal light conditions and after ultraviolet A light exposure. hRPE cells, containing both melanin and lipofuscin granules, were prepared from human donor eyes of 60-70 year old patients. Cells of the amelanotic ARPE-19 cell line and pigmented hRPE cells were treated with zinc chloride and subjected to oxidative stress by UV-A irradiation. Intracellular H(2)O(2) formation was measured using a fluorescence oxidation assay. Additionally, apoptosis and viability assays were performed. Control cells were treated identically except for irradiation and zinc supplementation. Under normal light conditions, zinc treated hRPE cells produced less H(2)O(2) than unsupplemented hRPE cells. Viability and apoptosis events did not change. After UV-A irradiation, ARPE and hRPE cells were greatly impaired in all tests performed compared to the non-irradiated controls. No differences were found after zinc supplementation. hRPE cells showed a higher apoptosis and mortality rate than non-pigmented cells when stressed by UV-A light. ARPE cells never showed any zinc related effects. In contrast, without irradiation, zinc supplementation reduced H(2)O(2) production in pigmented hRPE cells slightly. We did not find any zinc effect in irradiated hRPE cells. After UV light exposure, pigmented cells showed a higher apoptosis and mortality than cells lacking any pigmentation. We conclude that cells with pigmentation consisting of melanin and lipofuscin granules have more prooxidative than antioxidative capacity when stressed by UV light exposure compared to cells lacking any pigmentation.

Flupirtine attenuates sodium nitroprusside-induced damage to retinal photoreceptors, in situ

Flupirtine has been shown to function as a neuroprotectant and is presently used in man to treat a number of conditions. The aim of this study was to investigate the specific antioxidant properties of flupirtine in relation to oxidant-induced damage to retinal photoreceptors. Initial in vitro studies on brain membranes showed that flupirtine was approximately 20 times more potent than trolox (vitamin E analogue) and 8 times more potent than metipranolol at attenuating lipid peroxidation caused by the nitric oxide donor, sodium nitroprusside (SNP). Subsequent immunohistochemical studies revealed that following an intraocular injection of SNP, retinal photoreceptors are the only retinal cell types that appear to be clearly affected. This was supported by electroretinogram (ERG) recordings which showed both the a- and b-wave amplitudes to be significantly reduced. Western blotting techniques showed that SNP caused a significant decrease in photoreceptor-specific markers (RET-P1, rhodopsin kinase), an increase in cleaved caspase-3, Bcl-2, and cleaved PARP proteins that are associated with apoptosis and no change in the ganglion cell specific marker, neurofilament (NF-L). This was supported by RT-PCR data where rhodopsin (photoreceptor specific) mRNA was reduced while Thy-1 and NF-L (ganglion cell specific) mRNAs were unaffected. In addition SNP caused an elevation of glial cell response mRNAs primarily associated with Müller cells (GFAP, CNTF, bFGF) as well as caspase-3 and Bcl-2. Importantly, when flupirtine was co-injected, the effects to the retina caused by SNP on retinal proteins and mRNAs were in most cases significantly blunted. The conclusion reached from this study is that flupirtine is a powerful antioxidant and when injected into the eye with SNP attenuates the detrimental influence of SNP to retinal photoreceptors. Since oxidative stress has been implicated in retinal diseases like age-related macular degeneration (AMD) this study provides "proof of principle" for the idea that flupirtine may help individuals suffering from such retinal diseases.

Oxidative-induced retinal degeneration is attenuated by epigallocatechin gallate

The aim of this investigation was to determine whether an ingredient of green tea, epigallocatechin gallate (EGCG) could attenuate oxidative stress-induced degeneration of the retina as occurs in age-related macular degeneration (AMD) and glaucoma. Initial in vitro studies on brain membranes showed that EGCG was approximately 10 times more potent than trolox (vitamin E analogue) at attenuating lipid peroxidation caused by the nitric oxide donor, sodium nitroprusside (SNP). Subsequent immunohistochemical studies revealed that following an intraocular injection of SNP retinal photoreceptors are affected. This was supported by electroretinogram (ERG) recordings which showed both the a- and b-wave amplitudes to be significantly reduced. RT-PCR and Western blotting techniques showed that SNP caused a significant decrease in photoreceptor-specific markers (RET-P1, rhodopsin kinase), an increase in the cell death marker caspase-3, and no change in the ganglion cell specific markers, neurofilament (NF-L) and Thy-1. Importantly, when EGCG was co-injected, the detrimental effects to the retina caused by SNP were significantly blunted. The conclusion reached from this study is that EGCG is a powerful antioxidant and when injected into the eye with SNP attenuated the detrimental influence of SNP to retinal photoreceptors. Since oxidative stress has been implicated in retinal diseases like AMD and glaucoma this study provides "proof of principle" for the idea that daily intake of EGCG may help individuals suffering from retinal diseases where oxidative stress is implicated.