Understanding age-related macular degeneration (AMD): relationships between the photoreceptor/retinal pigment epithelium/Bruch's membrane/choriocapillaris complex

Preliminary study on electrophysiological changes after cellular autograft in age-related macular degeneration

Evolving atrophic macular degeneration represents at least 80% of all macular degenerations and is currently without a standardized care. Autologous fat transplantation efficacy was demonstrated by several studies, as these cells are able to produce growth factors. The aim of the work was to demonstrate possible therapeutic effect of the joined suprachoroidal graft of adipocytes, adipose-derived stem cells (ADSCs) in stromal vascular fractions (SVFs) of adipose tissue, and platelet-rich plasma (PRP). Twelve eyes in 12 dry age-related macular degeneration (AMD) patients, aged 71.25 (SD ± 6.8) between 62 and 80 years, were analyzed. A complete ocular evaluation was performed using best corrected visual acuity (BCVA), retinographic analysis, spectral-domain optical coherence tomography, microperimetry, computerized visual field, and standard electroretinogram (ERG). Each eye received a cell in graft between choroid and sclera of mature fat cells and ADSCs in SVF enriched with PRP by means of the variant second Limoli (Limoli retinal restoration technique [LRRT]). In order to test if the differences pre- and post-treatment were significant, the Wilcoxon signed-rank test has been performed. Adverse effects were not reported in the patients. After surgery with LRRT, the most significant increase in the ERG values was recorded by scotopic rod-ERG (answer coming from the rods), from 41.26 to 60.83 μV with an average increase of 47.44% highly significant (P < 0.05). Moderately significant was the one recorded by scotopic maximal ERG (answer coming from the rods and cones), from 112.22 to 129.68 μV with an average increase of 15.56% (P < 0.1). Cell-mediated therapy based on growth factors used appears interesting because it can improve the retinal functionality responses in the short term. The ERG could, therefore, be used to monitor the effect of cell-mediated regenerative therapies.

Activation of endogenously expressed ion channels by active complement in the retinal pigment epithelium

Defective regulation of the alternative pathway of the complement system is believed to contribute to damage of retinal pigment epithelial (RPE) cells in age-related macular degeneration. Thus we investigated the effect of complement activation on the RPE cell membrane by analyzing changes in membrane conductance via patch-clamp techniques and Ca(2+) imaging. Exposure of human ARPE-19 cells to complement-sufficient normal human serum (NHS) (25 %) resulted in a biphasic increase in intracellular free Ca(2+) ([Ca(2+)]i); an initial peak followed by sustained Ca(2+) increase. C5- or C7-depleted sera did not fully reproduce the signal generated by NHS. The initial peak of the Ca(2+) response was reduced by sarcoplasmic Ca(2+)-ATPase inhibitor thapsigargin, L-type channel blockers (R)-(+)-BayK8644 and isradipine, transient-receptor-potential (TRP) channel blocker ruthenium-red and ryanodine receptor blocker dantrolene. The sustained phase was carried by CaV1.3 L-type channels via tyrosine-phosphorylation. Changes in [Ca(2+)]I were accompanied by an abrupt hyperpolarization, resulting from a transient increase in membrane conductance, which was absent under extracellular Ca(2+)- or K(+)-free conditions and blocked by (R)-(+)-BayK8644 or paxilline, a maxiK channel inhibitor. Single-channel recordings confirmed the contribution of maxiK channels. Primary porcine RPE cells responded to NHS in a comparable manner. Pre-incubation with NHS reduced H2O2-induced cell death. In summary, in a concerted manner, C3a, C5a and sC5b-9 increased [Ca(2+)]i by ryanodine-receptor-dependent activation of L-type channels in addition to maxi-K channels and TRP channels absent from any insertion of a lytic pore.

Ultrahigh-speed swept-source OCT angiography in exudative AMD

BACKGROUND AND OBJECTIVE

To investigate the potential of ultrahigh-speed swept-source optical coherence tomography angiography (OCTA) to visualize retinal and choroidal vascular changes in patients with exudative age-related macular degeneration (AMD).

PATIENTS AND METHODS

Observational, prospective cross-sectional study. An ultrahigh-speed swept-source prototype was used to perform OCTA of the retinal and choriocapillaris microvasculature in 63 eyes of 32 healthy controls and 19 eyes of 15 patients with exudative AMD.

MAIN OUTCOME MEASURE

qualitative comparison of the retinal and choriocapillaris microvasculature in the two groups.

RESULTS

Choroidal neovascularization (CNV) was clearly visualized in 16 of the 19 eyes with exudative AMD, located above regions of severe choriocapillaris alteration. In 14 of these eyes, the CNV lesions were surrounded by regions of choriocapillaris alteration.

CONCLUSION

OCTA may offer noninvasive monitoring of the retinal and choriocapillaris microvasculature in patients with CNV, which may assist in diagnosis and monitoring.

Metallothioneins (MTs) in the human eye: a perspective article on the zinc-MT redox cycle

Metallothioneins (MTs) are zinc-ion-binding proteins with a wide range of functions, among which are neuroprotection, maintenance of cellular zinc homeostasis, and defense against oxidative damage and inflammation. The human eye is enriched in MTs, and multiple isoforms may contribute to distinct antioxidant defense mechanisms in various ocular tissues. Zinc is a main regulator of MT gene and protein expression, and we recently applied bioanalytical techniques to address key questions on its relationship with MTs, including the stoichiometry of zinc-MT, the fate of zinc tracers ((nat)Zn and (68)Zn) in MTs during activation by exogenous zinc and cytokines, and the concentration of MTs in human ocular cells. We found that exogenously introduced zinc induced a potent de novo synthesis of MTs as well as a strong inhibition of pro-inflammatory cytokines. Zinc and cytokines also promote a stoichiometric transition of the MT complex from Zn6Cu1-MT to Zn7-MT, suggesting that MTs may interact more effectively with reactive oxygen species to decrease potential oxidative damage. Levels of MTs decrease with aging and disease, which may result in zinc release that is potentially cytotoxic. This state is also observed with increased oxidative stress and inflammation, suggesting that the antioxidant function of MTs has been impaired. In this review we propose a working model of the "zinc-metallothionein redox cycle" to regenerate and enhance the antioxidant function of MTs with the aim of combating the progression of these disease states.

Color vision deficits in intermediate age-related macular degeneration

PURPOSE

To assess the effect of intermediate age-related macular degeneration (AMD) on foveal cone-contrast thresholds.

METHODS

We measured L-M and S-cone-contrast thresholds in subjects with intermediate AMD (n = 10) and age-matched control subjects (n = 10). Monocular, foveal 3-degree Gaussian blobs (600-millisecond raised cosine) were presented at 16 cone ratios throughout L-, M-, and S-cone space, and threshold contours were modeled with probability summation between two independent detection mechanisms. The role that preretinal absorption plays in aging was also evaluated by simulation with FG15 and neutral-density filters.

RESULTS

Aging results in loss of neural sensitivity, not explained by lens changes. On average, intermediate AMD was associated with reduced sensitivity in both color and luminance channels (p < 0.05) that appeared to indicate greater involvement of S-cones. When data were normalized to age-expected values, the changes to cone sensitivity were shown to be consistent (∼200% loss) across L-M, M-L, and S-cone mechanisms. In comparison, the luminance (L + M) mechanism showed relative sparing (155% loss, p < 0.05).

CONCLUSIONS

Eyes with the same phenotype of intermediate AMD can have varying degrees of color threshold loss. Functional markers enhance the clinical definition of disease expression in AMD.

The membrane attack complex in aging human choriocapillaris: relationship to macular degeneration and choroidal thinning

Age-related macular degeneration (AMD) is a common disease that can result in severe visual impairment. Abnormal regulation of the complement system has been implicated in its pathogenesis, and CFH polymorphisms contribute substantially to risk. How these polymorphisms exert their effects is poorly understood. We performed enzyme-linked immunosorbent assay (ELISA) analysis on young, aged, and AMD choroids to determine the abundance of the membrane attack complex (MAC) and performed immunofluorescence studies on eyes from 117 donors to evaluate the MAC in aging, early AMD, and advanced AMD. Morphometric studies were performed on eyes with high- or low-risk CFH genotypes. ELISA confirmed that MAC increases significantly with aging and with AMD. MAC was localized to Bruch's membrane and the choriocapillaris and was detectable at low levels as early as 5 years of age. Hard drusen were labeled with anti-MAC antibody, but large or confluent drusen and basal deposits were generally unlabeled. Labeling of retinal pigment epithelium was observed in some cases of advanced AMD, but not in early disease. Eyes homozygous for the high-risk CFH genotype had thinner choroids than low-risk homozygotes (P < 0.05). These findings suggest that increased complement activation in AMD and in high-risk genotypes can lead to loss of endothelial cells in early AMD. Treatments to protect the choriocapillaris in early AMD are needed.

Complement system in pathogenesis of AMD: dual player in degeneration and protection of retinal tissue

Age-related macular degeneration (AMD) is the most common cause of blindness among the elderly, especially in Western countries. Although the prevalence, risk factors, and clinical course of the disease are well described, its pathogenesis is not entirely elucidated. AMD is associated with a variety of biochemical abnormalities, including complement components deposition in the retinal pigment epithelium-Bruch's membrane-choriocapillaris complex. Although the complement system (CS) is increasingly recognized as mediating important roles in retinal biology, its particular role in AMD pathogenesis has not been precisely defined. Unrestricted activation of the CS following injury may directly damage retinal tissue and recruit immune cells to the vicinity of active complement cascades, therefore detrimentally causing bystander damage to surrounding cells and tissues. On the other hand, recent evidence supports the notion that an active complement pathway is a necessity for the normal maintenance of the neurosensory retina. In this scenario, complement activation appears to have beneficial effect as it promotes cell survival and tissue remodeling by facilitating the rapid removal of dying cells and resulting cellular debris, thus demonstrating anti-inflammatory and neuroprotective activities. In this review, we discuss both the beneficial and detrimental roles of CS in degenerative retina, focusing on the diverse aspects of CS functions that may promote or inhibit macular disease.

Emerging roles for nuclear receptors in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in the elderly in the Western world. Over the last 30 years, our understanding of the pathogenesis of the disease has grown exponentially thanks to the results of countless epidemiology, genetic, histological, and biochemical studies. This information, in turn, has led to the identification of multiple biologic pathways potentially involved in development and progression of AMD, including but not limited to inflammation, lipid and extracellular matrix dysregulation, and angiogenesis. Nuclear receptors are a superfamily of transcription factors that have been shown to regulate many of the pathogenic pathways linked with AMD and as such they are emerging as promising targets for therapeutic intervention. In this review, we will present the fundamental phenotypic features of AMD and discuss our current understanding of the pathobiological disease mechanisms. We will introduce the nuclear receptor superfamily and discuss the current literature on their effects on AMD-related pathophysiology.

Age-related macular degeneration in the aspect of chronic low-grade inflammation (pathophysiological parainflammation)

The products of oxidative stress trigger chronic low-grade inflammation (pathophysiological parainflammation) process in AMD patients. In early AMD, soft drusen contain many mediators of chronic low-grade inflammation such as C-reactive protein, adducts of the carboxyethylpyrrole protein, immunoglobulins, and acute phase molecules, as well as the complement-related proteins C3a, C5a, C5, C5b-9, CFH, CD35, and CD46. The complement system, mainly alternative pathway, mediates chronic autologous pathophysiological parainflammation in dry and exudative AMD, especially in the Y402H gene polymorphism, which causes hypofunction/lack of the protective complement factor H (CFH) and facilitates chronic inflammation mediated by C-reactive protein (CRP). Microglial activation induces photoreceptor cells injury and leads to the development of dry AMD. Many autoantibodies (antibodies against alpha beta crystallin, alpha-actinin, amyloid, C1q, chondroitin, collagen I, collagen III, collagen IV, elastin, fibronectin, heparan sulfate, histone H2A, histone H2B, hyaluronic acid, laminin, proteoglycan, vimentin, vitronectin, and aldolase C and pyruvate kinase M2) and overexpression of Fcc receptors play role in immune-mediated inflammation in AMD patients and in animal model. Macrophages infiltration of retinal/choroidal interface acts as protective factor in early AMD (M2 phenotype macrophages); however it acts as proinflammatory and proangiogenic factor in advanced AMD (M1 and M2 phenotype macrophages).

Choroid, Haller's, and Sattler's layer thickness in intermediate age-related macular degeneration with and without fellow neovascular eyes

PURPOSE

To analyze choroidal, Sattler's, and Haller's layer thickness maps in age-related macular degeneration (AMD) patients having eyes with bilateral large drusen and pigment changes (intermediate AMD), in patients having intermediate AMD eyes with neovascular fellow eyes (nAMD), and in healthy subjects using three-dimensional (3D) 1060-nm optical coherence tomography (OCT).

METHODS

Automatically generated choroidal thickness (ChT), retinal thickness, and Sattler's and Haller's layer thickness maps were statistically analyzed in 67 subjects consisting of intermediate AMD (n = 21), intermediate AMD (n = 22) with fellow nAMD eyes (n = 22), and healthy eyes (n = 24) with no age and axial eye length difference between groups of eyes (P > 0.05, ANOVA). Eyes were imaged by a prototype high-speed (60,000 A-scans/s) spectral-domain 3D 1060-nm OCT over a 36° × 36° field of view.

RESULTS

The mean ± SD (μm) subfoveal ChT for healthy subjects and for bilateral intermediate AMD, unilateral intermediate AMD, and their nAMD fellow eyes was 259 ± 95 and 222 ± 98, 149 ± 60, and 171 ± 78, respectively. Choroidal thickness maps demonstrated significant submacular thinning in unilateral intermediate AMD in comparison to healthy and bilateral intermediate AMD eyes (P < 0.001, ANOVA, post hoc P < 0.001 and P < 0.05, respectively). Sattler's and Haller's layers were thinnest in intermediate AMDs that presented with nAMD fellow eyes (Kruskal-Wallis test P < 0.01). For the choroid and its sublayers, there was no difference between the intermediate AMD eyes and their fellow nAMD eyes (paired testing, P < 0.05).

CONCLUSIONS

The 3D 1060-nm OCT choroidal imaging visualized significant changes in choroidal, Sattler's, and Haller's layer thickness in relation to the progression of AMD. This may be important for understanding the choroidopathy in the pathophysiology of AMD.

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.

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.

Choroidal changes associated with Bruch membrane pathology in pseudoxanthoma elasticum

PURPOSE

To investigate the impact of Bruch membrane pathology on the choroid in pseudoxanthoma elasticum (PXE).

DESIGN

Monocenter cross-sectional prospective case series.

METHODS

The study included 61 eyes of 51 patients with PXE and 54 eyes of 54 normal subjects. The diagnosis of PXE was based on skin biopsy, genetic analysis or both. Eyes with PXE were subdivided into 3 groups: eyes without choroidal neovascularization (CNV) or chorioretinal atrophy (Group 1); eyes with active or fibrotic CNV (Group 2); and eyes with chorioretinal atrophy only (Group 3). Choroidal thickness was measured using enhanced-depth imaging optical coherence tomography (EDI-OCT).

RESULTS

Compared to controls (331 μm ± 24; mean ± 95% CI), mean subfoveal choroidal thickness in eyes of patients with PXE was significantly reduced within all 3 groups (Group 1: 243 μm ± 29; Group 2: 184 μm ± 28; Group 3: 104 μm ± 28; P < 0.001). Associated structural changes included apparent loss of small choroidal vessels. The difference of PXE compared to control eyes was largest close to the optic disc and approximated the level of controls toward the periphery. Within the PXE subgroups, eyes without CNV or chorioretinal atrophy (Group 1) showed the least reduction of choroidal thickness, while it was most pronounced in Group 3.

CONCLUSIONS

The results indicate that changes of Bruch membrane can be associated with choroidal alterations, which are most pronounced in the presence of advanced disease. A role of Bruch membrane in choroidal homeostasis may reflect a possible contribution of Bruch membrane alterations to CNV and geographic atrophy development in age-related macular degeneration.

In vivo optical coherence tomography of light-driven melanosome translocation in retinal pigment epithelium

Optical coherence tomography (OCT) may revolutionize fundamental investigation and clinical management of age-related macular degeneration and other eye diseases. However, quantitative OCT interpretation is hampered due to uncertain sub-cellular correlates of reflectivity in the retinal pigment epithelium (RPE) and photoreceptor. The purpose of this study was twofold: 1) to test OCT correlates in the RPE, and 2) to demonstrate the feasibility of longitudinal OCT monitoring of sub-cellular RPE dynamics. A high resolution OCT was constructed to achieve dynamic imaging of frog eyes, in which light-driven translocation of RPE melanosomes occurred within the RPE cell body and apical processes. Comparative histological examination of dark- and light-adapted eyes indicated that the RPE melanin granule, i.e., melanosome, was a primary OCT correlate. In vivo OCT imaging of RPE melanosomes opens the opportunity for quantitative assessment of RPE abnormalities associated with disease, and enables longitudinal investigation of RPE kinetics correlated with visual function.

Estrogen signalling in the pathogenesis of age-related macular degeneration

Age-related macular degeneration (AMD) is a multifactorial eye disease that is associated with aging, family history, smoking, obesity, cataract surgery, arteriosclerosis, hypertension, hypercholesterolemia and unhealthy diet. Gender has commonly been classified as a weak or inconsistent risk factor for AMD. This disease is characterized by degeneration of retinal pigment epithelial (RPE) cells, Bruch's membrane, and choriocapillaris, which secondarily lead to damage and death of photoreceptor cells and central visual loss. Pathogenesis of AMD involves constant oxidative stress, chronic inflammation, and increased accumulation of lipofuscin and drusen. Estrogen has both anti-oxidative and anti-inflammatory capacity and it regulates signaling pathways that are involved in the pathogenesis of AMD. In this review, we discuss potential cellular signaling targets of estrogen in retinal cells and AMD pathology.

Platelet-derived growth factor (PDGF)-C inhibits neuroretinal apoptosis in a murine model of focal retinal degeneration

Platelet-derived growth factor (PDGF)-C is a member of the PDGF family and is critical for neuronal survival in the central nervous system. We studied the possible survival and antiapoptotic effects of PDGF-C on focal retinal lesions in Ccl2(-/-)/Cx3cr1(-/-) on C57BL/6N [Crb1(rd8)] (DKO rd8) background mice, a model for progressive and focal retinal degeneration. We found no difference in transcript and protein expression of PDGF-C in the retina between DKO rd8 mice and wild type (WT, C57BL/6N). Recombinant PDGF-CC protein (500 ng/eye) was injected intravitreally into the right eye of DKO rd8 mice with phosphate-buffered saline as controls into the left eye. The retinal effects of PDGF-C were assessed by fundoscopy, ocular histopathology, A2E levels, apoptotic molecule analysis, and direct flat mount retinal vascular labeling. We found that the PDGF-CC-treated eyes showed slower progression or attenuation of the focal retinal lesions, lesser photoreceptor and retinal pigment epithelial degeneration resulting in better-preserved photoreceptor structure. Lower expression of apoptotic molecules was detected in the PDGF-CC-treated eyes than in controls. In addition, no retinal neovascularization was observed after PDGF-CC treatment. Our results demonstrate that PDGF-C potently ameliorates photoreceptor degeneration via the suppression of apoptotic pathways without inducing retinal angiogenesis. The protective effects of PDGF-C suggest a novel alternative approach for potential age-related retinal degeneration treatment.

Detecting a weak association by testing its multiple perturbations: a data mining approach

Many risk factors/interventions in epidemiologic/biomedical studies are of minuscule effects. To detect such weak associations, one needs a study with a very large sample size (the number of subjects, n). The n of a study can be increased but unfortunately only to an extent. Here, we propose a novel method which hinges on increasing sample size in a different direction–the total number of variables (p). We construct a p-based ‘multiple perturbation test', and conduct power calculations and computer simulations to show that it can achieve a very high power to detect weak associations when p can be made very large. As a demonstration, we apply the method to analyze a genome-wide association study on age-related macular degeneration and identify two novel genetic variants that are significantly associated with the disease. The p-based method may set a stage for a new paradigm of statistical tests.

Deletion of hemojuvelin, an iron-regulatory protein, in mice results in abnormal angiogenesis and vasculogenesis in retina along with reactive gliosis

PURPOSE

Loss-of-function mutations in hemojuvelin (HJV) cause juvenile hemochromatosis, an iron-overload disease. Deletion of Hjv in mice results in excessive iron accumulation and morphologic changes in the retina. Here, we studied the retinal vasculature in Hjv(-/-) mice.

METHODS

Age-matched wild-type and Hjv(-/-) mice were used for fluorescein angiography and preparation of retinal cryosections, flat-mounts, and trypsin-digested blood vessels. Retinal angiogenesis was monitored by immunofluorescent detection of isolectin-B4, endoglin, and VEGF. Retinal vasculogenesis was monitored by immunofluorescent detection of collagen IV. Reactive gliosis was assessed based on the expression of glial fibrillary acidic protein and vimentin and CD11b/c as markers for Müller cells and microglia.

RESULTS

Between 18 and 24 months of age, retinas of Hjv(-/-) mice displayed marked disruptions in angiogenesis and vasculogenesis. Blood vessels in Hjv(-/-) mice were tortuous and dilated, with a decrease in the tight-junction protein occludin. There was also evidence of neovascularization in Hjv(-/-) mice with blood vessels appearing in the vitreous, which were leaky. There was reactive gliosis in these mice involving both Müller cells and microglia. Such changes were not detected at 2 weeks of age. Even at the age of 4 months, retinas of Hjv(-/-) mice were almost normal with changes just beginning to appear. Thus, the vascular changes in Hjv(-/-) mouse retinas represent an age-dependent phenomenon.

CONCLUSIONS

Deletion of Hjv in mice leads to abnormal retinal angiogenesis/vasculogenesis, with proliferation of new, leaky blood vessels in the vitreous. These changes are accompanied with reactive gliosis involving Müller cells and microglia.

Resveratrol Suppresses Expression of VEGF by Human Retinal Pigment Epithelial Cells: Potential Nutraceutical for Age-related Macular Degeneration

Age-related macular degeneration (AMD) is a sight threating retinal eye disease that affects millions of aging individuals world-wide. Choroid-retinal pigment epithelium (RPE)-neuroretina axis in the posterior compartment of the eye is the primary site of AMD pathology. There are compelling evidence to indicate association of vascular endothelial growth factors (VEGF) to AMD. Here, we report the inhibitory actions of resveratrol (RSV) on inflammatory cytokine, TGF-β and hypoxia induced VEGF secretion by human retinal pigment epithelial cells (HRPE). HRPE cultures prepared from aged human donor eyes were used for the studies in this report. HRPE secreted both VEGF-A and VEGF-C in small quantities constitutively. Stimulation with a mixture of inflammatory cytokines (IFN-γ, TNF-α, IL-1β), significantly increased the secretion of both VEGF-A and VEGF-C. RSV, in a dose dependent (10-50 uM) manner, suppressed VEGF-A and VEGF-C secretion induced by inflammatory cytokines significantly. RT-PCR analysis indicated that effects of RSV on VEGF secretion were possibly due to decreased mRNA levels. TGF-β and cobalt chloride (hypoxia mimic) also upregulated HRPE cell production of VEGF-A, and this was inhibited by RSV. In contrast, RSV had no effect on anti-angiogenic molecules, endostatin and pigment epithelial derived factor secretion. Studies using an in vitro scratch assay revealed that wound closure was also inhibited by RSV. These results demonstrate that RSV can suppress VEGF secretion induced by inflammatory cytokines, TGF-β and hypoxia. Under pathological conditions, over expression of VEGF is known to worsen AMD. Therefore, RSV may be useful as nutraceutical in controlling pathological choroidal neovascularization processes in AMD.

AAV-mediated expression of human PRELP inhibits complement activation, choroidal neovascularization and deposition of membrane attack complex in mice

Age-related macular degeneration (AMD) is the leading cause of blindness among the elderly. Approximately 50% of AMD patients have a polymorphism in the negative regulator of complement known as Factor H. Individuals homozygous for a Y402H polymorphism in Factor H have elevated levels of membrane attack complex (MAC) in their choroid and retinal pigment epithelium relative to individuals homozygous for the wild-type allele. An inability to form MAC due to a polymorphism in C9 is protective against the formation of choroidal neovascularization (CNV) in AMD patients. Hence, blocking MAC in AMD patients may be protective against CNV. Here we investigate the potential of human proline/arginine-rich end leucine-rich repeat protein (PRELP) as an inhibitor of complement-mediated damage when delivered via the subretinal route using an AAV2/8 vector. In a fluorescence-activated cell sorting (FACS) lysis assay, PRELP inhibited normal human serum-mediated lysis of Hepa-1c1c7 cells by 18.7%. Unexpectedly, PRELP enhanced the formation of tubes by human umbilical vein endothelial cells (HUVECs) by approximately 240%, but, when delivered via an AAV vector to the retina of mice, PRELP inhibited laser-induced CNV by 60%. PRELP reduced deposition of MAC in vivo by 25.5%. Our results have implications for the development of complement inhibitors as a therapy for AMD.

Vascular associations and dynamic process motility in perivascular myeloid cells of the mouse choroid: implications for function and senescent change

PURPOSE

Immune and vascular alterations in the choroid are implicated in age-related macular degeneration (AMD). As choroidal immune cells are incompletely understood with regard to their physiology and interactions with choroidal vessels, we examined the associations between myeloid and vascular components of the choroid in young and aged mice.

METHODS

Albino CX3CR1(GFP/+) transgenic mice, whose choroidal myeloid cells possess green fluorescence, were perfused intraluminally with the vital dye DiI to label choroidal vessels. The distribution, morphology, behavior, and vascular associations of resident myeloid cells were examined using time-lapse live confocal imaging and immunohistochemical analysis.

RESULTS

Dendritiform myeloid cells, comprising most of the resident immune cell population in the choroid, were widely distributed across the choroid and demonstrated close associations with choroidal vessels that varied with their position in the vascular tree. Notably, myeloid cells associated with choroidal arteries and arterioles appeared as elongated cells flanking the long axes of vessels, whereas those associated with the choriocapillaris were distributed as a layer of stellate cells on the scleral but not vitreal choriocapillaris surface. While stationary in position, dendritiform myeloid cells demonstrated the rapid process dynamism well suited to comprehensive immunosurveillance of the perivascular space. Myeloid cells also increased in density as a function of aging, correlating locally with greater choroidal vascular attenuation.

CONCLUSIONS

Resident myeloid cells demonstrated close but dynamic physical interactions with choroidal vessels, indicative of constitutive immune-vascular interactions in the normal choroid. These interactions may alter progressively with aging, providing a basis for understanding age-related choroidal dysfunction underlying AMD.

Prediction of passive drug permeability across the blood-retinal barrier

PURPOSE

The purpose of this study is to develop a computational model of the physical barrier function of the outer blood-retinal barrier (BRB), which is vital for normal retinal function. To our best knowledge no comprehensive models of BRB has been reported.

METHODS

The model construction is based on the three-layered structure of the BRB: retinal pigment epithelium (RPE), Bruch's membrane and choriocapillaris endothelium. Their permeabilities were calculated based on the physical theories and experimental material and permeability studies in the literature, which were used to describe diffusional hindrance in specific environments.

RESULTS

Our compartmental BRB model predicts permeabilities with magnitudes similar to the experimental values in the literature. However, due to the small number and varying experimental conditions there is a large variability in the available experimental data, rendering validation of the model difficult. The model suggests that the paracellular pathway of the RPE largely defines the total BRB permeability.

CONCLUSIONS

Our model is the first BRB model of its level and combines the present knowledge of the BRB barrier function. Furthermore, the model forms a platform for the future model development to be used for the design of new drugs and drug administration systems.

Novel endogenous glycan therapy for retinal diseases: safety, in vitro stability, ocular pharmacokinetic modeling, and biodistribution

Asialo, tri-antennary oligosaccharide (NA3 glycan) is an endogenous compound, which supports proper folding of outer segment membranes, promotes normal ultrastructure, and maintains protein expression patterns of photoreceptors and Müller cells in the absence of retinal pigment epithelium support. It is a potential new therapeutic for atrophic age-related macular degeneration (AMD) and other retinal degenerative disorders. Herein, we evaluate the safety, in vitro stability, ocular pharmacokinetics and biodistribution of NA3. NA3 was injected into the vitreous of New Zealand white rabbits at two concentrations viz. 1 nM (minimum effective concentration (MEC)) and 100 nM (100XMEC) at three time points. Safety was evaluated using routine clinical and laboratory tests. Ocular pharmacokinetics and biodistribution of [(3)H]NA3 were estimated using scintillation counting in various parts of the eye, multiple peripheral organs, and plasma. Pharmacokinetic parameters were estimated by non-compartmental modeling. A 2-aminobenzamide labeling and hydrophilic interaction liquid interaction chromatography were used to assess plasma and vitreous stability. NA3 was well tolerated by the eye. The concentration of NA3 in eye tissues was in the order: vitreous > retina > sclera/choroid > aqueous humor > cornea > lens. Area under the curve (0 to infinity) (AUC∞) was the highest in the vitreous thereby providing a positive concentration gradient for NA3 to reach the retina. Half-lives in critical eye tissues ranged between 40 and 60 h. NA3 concentrations were negligible in peripheral organs. Radioactivity from [(3)H]NA3 was excreted via urine and feces. NA3 was stable at 37°C in vitreous over a minimum of 6 days, while it degraded rapidly in plasma. Collectively, these results document that NA3 shows a good safety profile and favorable ocular pharmacokinetics.

OCT minimum intensity as a predictor of geographic atrophy enlargement

PURPOSE

We determined whether the minimum intensity (MI) of the optical coherence tomography (OCT) A-scans within the retina can predict locations of growth at the margin of geographic atrophy (GA) and the growth rate outside the margin.

METHODS

The OCT scans were analyzed at baseline and 52 weeks. Expert graders manually segmented OCT images of GA. The 52-week follow-up scans were registered to the baseline scan coordinates for comparison. The OCT MI values were studied within a 180-μm margin around the boundary of GA at baseline. Baseline MI values were compared in areas of progression and nonprogression of the GA, and sensitivity and specificity were assessed for prediction of growth at the margin. Average MI values in the margins were compared to overall growth rates to evaluate the prediction of growth outside the margins.

RESULTS

A statistically significant increase in MI (P < 0.05) was seen in areas of growth in 21/24 cases (88%), and 22/24 cases (92%) when the foveal subfield was excluded. Locations of growth within the margins at 52 weeks were predicted with 61% sensitivity and 61% specificity. The MI values correlated significantly with overall growth rate, and high and low growth rate subjects were identified with 80% sensitivity and 64% specificity.

CONCLUSIONS

The MI may be increased at the margins of GA lesions before enlargement, which may indicate disruption or atrophy of the photoreceptors in these areas before GA becomes apparent. Increased MI may help predict areas of enlargement of GA, and may relate to overall growth rate and be a useful screening tool for GA. (ClinicalTrials.gov number, NCT00935883.).

Oxidative stress, polyunsaturated fatty acids-derived oxidation products and bisretinoids as potential inducers of CNS diseases: focus on age-related macular degeneration

Many pathologies of the central nervous system (CNS) originate from excess of reactive free radicals, notably reactive oxygen species (ROS), and oxidative stress. A phenomenon which usually runs in parallel with oxidative stress is unsaturated lipid peroxidation, which, via a chain reaction, contributes to the progression of disbalanced redox homeostasis. Among long-chain (LC) polyunsaturated fatty acids (PUFAs) abundantly occurring in the CNS, docosahexaenoic acid (DHA), a member of ω-3 LC-PUFAs, deserves special attention, as it is avidly retained and uniquely concentrated in the nervous system, particularly in retinal photoreceptors and synaptic membranes; owing to the presence of the six double bonds between carbon atoms in its polyene chain (C=C), DHA is exquisitely sensitive to oxidative damage. In addition to oxidative stress and LC-PUFAs peroxidation, other stress-related mechanisms may also contribute to the development of various CNS malfunctions, and a good example of such mechanisms is the process of lipofuscin formation occurring particularly in the retina, an integral part of the CNS. The retinal lipofuscin is formed and accumulated by the retinal pigment epithelial (RPE) cells as a consequence of both visual process taking place in photoreceptor-RPE functional complex and metabolic insufficiency of RPE lysosomal compartment. Among various retinal lipofuscin constituents, bisretinoids, originating from all-trans retinal substrate--a photometabolite of visual pigment cofactor 11-cis-retinal (responsible for photon capturing), are endowed with cytotoxic and complement-activating potential which increases upon illumination and oxidation. This survey deals with oxidative stress, PUFAs (especially DHA) peroxidation products of carboxyalkylpyrrole type and bisretinoids as potential inducers of the CNS pathology. A focus is put on vision-threatening disease, i.e., age-related macular degeneration (AMD), as an example of the CNS disorder whose pathogenesis has strong background in both oxidative stress and lipid peroxidation products.

Stem cell-based treatment in geographic atrophy: promises and pitfalls

Geographic atrophy is a common and untreatable form of advanced age-related macular degeneration. The degeneration primarily affects the retinal pigment epithelium and photoreceptors of the retina and their restoration by cell transplantation seems attractive. Recently, a patient with geographic atrophy was the first human to receive cells derived from human embryonic stem cells. In this short review, the rationale, potential and obstacles for stem cell-derived therapy in geographic atrophy are discussed.

Antioxidant drug therapy approaches for neuroprotection in chronic diseases of the retina

The molecular pathways contributing to visual signal transduction in the retina generate a high energy demand that has functional and structural consequences such as vascularization and high metabolic rates contributing to oxidative stress. Multiple signaling cascades are involved to actively regulate the redox state of the retina. Age-related processes increase the oxidative load, resulting in chronically elevated levels of oxidative stress and reactive oxygen species, which in the retina ultimately result in pathologies such as glaucoma or age-related macular degeneration, as well as the neuropathic complications of diabetes in the eye. Specifically, oxidative stress results in deleterious changes to the retina through dysregulation of its intracellular physiology, ultimately leading to neurodegenerative and potentially also vascular dysfunction. Herein we will review the evidence for oxidative stress-induced contributions to each of the three major ocular pathologies, glaucoma, age-related macular degeneration, and diabetic retinopathy. The premise for neuroprotective strategies for these ocular disorders will be discussed in the context of recent clinical and preclinical research pursuing novel therapy development approaches.

Fcγ receptor upregulation is associated with immune complex inflammation in the mouse retina and early age-related macular degeneration

PURPOSE

Several lines of evidence suggest the involvement of antibodies and immune complex inflammation in AMD, a blinding disease with a strong inflammatory component. To examine this further, we developed a novel experimental mouse model of retinal inflammation and evaluated whether inflammation associated with immune complex formation was present in eyes of AMD donors.

METHODS

A localized immune complex-mediated reaction was induced in the retina of wild-type (WT), Fc receptor γ chain-deficient (γ(-/-)), and C1q-deficient (C1q(-/-)) mice, and donor eyes were obtained after death from donors with early or wet AMD and from healthy control subjects. The presence of immune complexes, Fcγ receptors (FcγRs), and markers of macrophage/microglia activation was investigated by immunohistochemistry.

RESULTS

In WT and C1q(-/-) mice, immune complex deposition in the retina led to a robust inflammatory response with activation of microglia, recruitment of myeloid cells, and increased expression of FcγRI through FcγRIV and major histocompatibility complex class II. This response was not observed in γ(-/-) mice lacking activating FcγRs. We found that early AMD was associated with deposition of IgG, C1q, and membrane attack complex in the choriocapillaris and with increased numbers of CD45+ cells expressing FcγRIIa and FcγRIIb. Furthermore, FcγRIIa and FcγRIIb were observed in eyes of donors with wet AMD.

CONCLUSIONS

Our studies suggest that immune complexes may contribute to AMD pathogenesis through interaction of IgG with FcγRs and might inform about possible adverse effects associated with therapeutic antibodies.

Choroidal thickness in retinal pigment epithelial tear as measured by spectral domain optical coherence tomography

PURPOSE

To evaluate the choroidal thickness with spectral domain optical coherence tomography in subjects with retinal pigment epithelial (RPE) tear compared with the choroidal thickness of their fellow eye.

METHODS

For this cross-sectional investigation, seven eyes of seven patients with neovascular age-related macular degeneration and RPE tear in one eye imaged with spectral domain optical coherence tomography were identified. Choroidal thickness was measured from the posterior edge of the retinal pigment epithelium to the choroid/sclera junction at 500 μm intervals up to 2,500 μm temporal and nasal to the fovea in both the eye with the RPE tear and the eye with intact RPE. All measurements were performed by two independent observers and averaged for the purpose of the analysis. Measurements were compared using paired t-test.

RESULTS

The average age of patients was 79 years (range, 66-88 years). All subjects had dome-shaped pigment epithelial detachments before RPE tear and no dome-shaped pigment epithelial detachments in the unaffected eye. Average subfoveal choroidal thickness in the eye with the RPE tear was 154.9 ± 10.1 µm. Average subfoveal choroidal thickness in the eye with intact RPE was 212.9 ± 10.6 µm (P = 0.035).

CONCLUSION

There is a significant decrease in subfoveal choroidal thickness in the subjects with RPE tear compared with their fellow eye with intact RPE. It is unclear if this thinning is a consequence of or precedes the RPE tear. Further studies are necessary to prospectively follow choroidal thickness in subjects with dome-shaped pigment epithelial detachments.

Is age-related macular degeneration a microvascular disease?

Age-related macular degeneration (AMD) is a common, degenerative disease of the central retina affecting millions of elderly in the USA alone and many more worldwide. A better understanding of the pathophysiology of AMD will be essential for developing new treatments. In this review, we discuss the potential impact of complement complex deposition at the choriocapillaris of aging eyes and the relationship between choriocapillaris loss and drusen formation. We further propose a model that integrates genetic and anatomical findings in AMD and suggest the implications of these findings for future therapies.

Choriocapillaris and choroidal microvasculature imaging with ultrahigh speed OCT angiography

We demonstrate in vivo choriocapillaris and choroidal microvasculature imaging in normal human subjects using optical coherence tomography (OCT). An ultrahigh speed swept source OCT prototype at 1060 nm wavelengths with a 400 kHz A-scan rate is developed for three-dimensional ultrahigh speed imaging of the posterior eye. OCT angiography is used to image three-dimensional vascular structure without the need for exogenous fluorophores by detecting erythrocyte motion contrast between OCT intensity cross-sectional images acquired rapidly and repeatedly from the same location on the retina. En face OCT angiograms of the choriocapillaris and choroidal vasculature are visualized by acquiring cross-sectional OCT angiograms volumetrically via raster scanning and segmenting the three-dimensional angiographic data at multiple depths below the retinal pigment epithelium (RPE). Fine microvasculature of the choriocapillaris, as well as tightly packed networks of feeding arterioles and draining venules, can be visualized at different en face depths. Panoramic ultra-wide field stitched OCT angiograms of the choriocapillaris spanning ∼32 mm on the retina show distinct vascular structures at different fundus locations. Isolated smaller fields at the central fovea and ∼6 mm nasal to the fovea at the depths of the choriocapillaris and Sattler's layer show vasculature structures consistent with established architectural morphology from histological and electron micrograph corrosion casting studies. Choriocapillaris imaging was performed in eight healthy volunteers with OCT angiograms successfully acquired from all subjects. These results demonstrate the feasibility of ultrahigh speed OCT for in vivo dye-free choriocapillaris and choroidal vasculature imaging, in addition to conventional structural imaging.

Aging is not a disease: distinguishing age-related macular degeneration from aging

Age-related macular degeneration (AMD) is a disease of the outer retina, characterized most significantly by atrophy of photoreceptors and retinal pigment epithelium accompanied with or without choroidal neovascularization. Development of AMD has been recognized as contingent on environmental and genetic risk factors, the strongest being advanced age. In this review, we highlight pathogenic changes that destabilize ocular homeostasis and promote AMD development. With normal aging, photoreceptors are steadily lost, Bruch's membrane thickens, the choroid thins, and hard drusen may form in the periphery. In AMD, many of these changes are exacerbated in addition to the development of disease-specific factors such as soft macular drusen. Para-inflammation, which can be thought of as an intermediate between basal and robust levels of inflammation, develops within the retina in an attempt to maintain ocular homeostasis, reflected by increased expression of the anti-inflammatory cytokine IL-10 coupled with shifts in macrophage plasticity from the pro-inflammatory M1 to the anti-inflammatory M2 polarization. In AMD, imbalances in the M1 and M2 populations together with activation of retinal microglia are observed and potentially contribute to tissue degeneration. Nonetheless, the retina persists in a state of chronic inflammation and increased expression of certain cytokines and inflammasomes is observed. Since not everyone develops AMD, the vital question to ask is how the body establishes a balance between normal age-related changes and the pathological phenotypes in AMD.

Aurintricarboxylic acid inhibits complement activation, membrane attack complex, and choroidal neovascularization in a model of macular degeneration

PURPOSE

Immunocytochemical and genetic data implicate a significant role for the activation of complement in the pathology of AMD. Individuals homozygous for a Y402H polymorphism in Factor H have elevated levels of membrane attack complex (MAC) in their choroidal blood vessels and RPE relative to individuals homozygous for the wild-type allele. An R95X polymorphism in C9, a protein necessary for the final assembly of MAC, is partially protective against the formation of choroidal neovascularization (CNV) in AMD patients. Aurintricarboxylic Acid (ATA) is a small molecule inhibitor of MAC. Our hypothesis was that attenuation of the formation of MAC on ocular tissues by ATA may protect mice against laser-induced CNV.

METHODS

The ability of ATA to inhibit human complement-mediated cell lysis, inhibit formation of human MAC, and inhibit formation of tubes by endothelial cells was examined in vitro. Subsequently, the Bruch's membrane of adult mice was damaged using an argon laser, followed by intravitreal injection of ATA. One week later, choroidal flat mounts from these mice were stained for the presence of MAC, endothelial cells, and macrophages.

RESULTS

ATA protects cells from human complement-mediated lysis, attenuates assembly of the MAC, and inhibits tube formation by endothelial cells in vitro. ATA also attenuates CNV, MAC deposition, and macrophage infiltration in a murine model of exudative AMD.

CONCLUSIONS

ATA warrants further study as a potential drug for the treatment of exudative and nonexudative AMD.

Phase-variance optical coherence tomography: a technique for noninvasive angiography

PURPOSE

Phase-variance optical coherence tomography (PV-OCT) provides volumetric imaging of the retinal vasculature without the need for intravenous injection of a fluorophore. We compare images from PV-OCT and fluorescein angiography (FA) for normal individuals and patients with age-related macular degeneration (AMD) and diabetic retinopathy.

DESIGN

This is an evaluation of a diagnostic technology.

PARTICIPANTS

Four patients underwent comparative retinovascular imaging using FA and PV-OCT. Imaging was performed on 1 normal individual, 1 patient with dry AMD, 1 patient with exudative AMD, and 1 patient with nonproliferative diabetic retinopathy.

METHODS

Fluorescein angiography imaging was performed using a Topcon Corp (Tokyo, Japan) (TRC-50IX) camera with a resolution of 1280 (H) × 1024 (V) pixels. The PV-OCT images were generated by software data processing of the entire cross-sectional image from consecutively acquired B-scans. Bulk axial motion was calculated and corrected for each transverse location, reducing the phase noise introduced from eye motion. Phase variance was calculated through the variance of the motion-corrected phase changes acquired within multiple B-scans at the same position. Repeating these calculations over the entire volumetric scan produced a 3-dimensional PV-OCT representation of the vasculature.

MAIN OUTCOME MEASURES

Feasibility of rendering retinal and choroidal microvasculature using PV-OCT was compared qualitatively with FA, the current gold standard for retinovascular imaging.

RESULTS

Phase-variance OCT noninvasively rendered a 2-dimensional depth color-coded vasculature map of the retinal and choroidal vasculature. The choriocapillaris was imaged with better resolution of microvascular detail using PV-OCT. Areas of geographic atrophy and choroidal neovascularization imaged by FA were depicted by PV-OCT. Regions of capillary nonperfusion from diabetic retinopathy were shown by both imaging techniques; there was not complete correspondence between microaneurysms shown on FA and PV-OCT images.

CONCLUSIONS

Phase-variance OCT yields high-resolution imaging of the retinal and choroidal microvasculature that compares favorably with FA.

Topical application of PPADS inhibits complement activation and choroidal neovascularization in a model of age-related macular degeneration

Age-related macular degeneration (AMD) is the most common cause of blindness among the elderly. AMD patients have elevated levels of membrane attack complex (MAC) in their choroidal blood vessels and retinal pigment epithelium (RPE). MAC forms pores in cell membranes. Low levels of MAC result in an elevation of cytokine release such as vascular endothelial growth factor (VEGF) that promotes the formation of choroidal neovascularization (CNV). High levels of MAC result in cell lysis and RPE degeneration is a hallmark of advanced AMD. The current standard of care for CNV associated with wet AMD is intravitreal injection of anti-VEGF molecules every 4 to 12 weeks. Such injections have significant side effects. Recently, it has been found that membrane pore-forming proteins such as α-haemolysin can mediate their toxic effects through auto- and paracrine signaling and that complement-induced lysis is amplified through ATP release followed by P2X receptor activation. We hypothesized that attenuation of P2X receptor activation may lead to a reduction in MAC deposition and consequent formation of CNV. Hence, in this study we investigated topical application of the purinergic P2X antagonist Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) as a potential treatment for AMD. We found that 4.17 µM PPADS inhibited formation of HUVEC master junctions and master segments by 74.7%. In a human complement mediated cell lysis assay, 104 µM PPADS enabled almost complete protection of Hepa1c1c7 cells from 1% normal human serum mediated cell lysis. Daily topical application of 4.17 mM PPADS for 3 days attenuated the progression of laser induced CNV in mice by 41.8% and attenuated the deposition of MAC at the site of the laser injury by 19.7%. Our data have implications for the future treatment of AMD and potentially other ocular disorders involving CNV such as angioid streaks, choroidal rupture and high myopia.

Role of antioxidant enzymes and small molecular weight antioxidants in the pathogenesis of age-related macular degeneration (AMD)

Cells in aerobic condition are constantly exposed to reactive oxygen species (ROS), which may induce damage to biomolecules, including proteins, nucleic acids and lipids. In normal circumstances, the amount of ROS is counterbalanced by cellular antioxidant defence, with its main components—antioxidant enzymes, DNA repair and small molecular weight antioxidants. An imbalance between the production and neutralization of ROS by antioxidant defence is associated with oxidative stress, which plays an important role in the pathogenesis of many age-related and degenerative diseases, including age-related macular degeneration (AMD), affecting the macula—the central part of the retina. The retina is especially prone to oxidative stress due to high oxygen pressure and exposure to UV and blue light promoting ROS generation. Because oxidative stress has an established role in AMD pathogenesis, proper functioning of antioxidant defence may be crucial for the occurrence and progression of this disease. Antioxidant enzymes play a major role in ROS scavenging and changes of their expression or/and activity are reported to be associated with AMD. Therefore, the enzymes in the retina along with their genes may constitute a perspective target in AMD prevention and therapy.

Choroid sprouting assay: an ex vivo model of microvascular angiogenesis

Angiogenesis of the microvasculature is central to the etiology of many diseases including proliferative retinopathy, age-related macular degeneration and cancer. A mouse model of microvascular angiogenesis would be very valuable and enable access to a wide range of genetically manipulated tissues that closely approximate small blood vessel growth in vivo. Vascular endothelial cells cultured in vitro are widely used, however, isolating pure vascular murine endothelial cells is technically challenging. A microvascular mouse explant model that is robust, quantitative and can be reproduced without difficulty would overcome these limitations. Here we characterized and optimized for reproducibility an organotypic microvascular angiogenesis mouse and rat model from the choroid, a microvascular bed in the posterior of eye. The choroidal tissues from C57BL/6J and 129S6/SvEvTac mice and Sprague Dawley rats were isolated and incubated in Matrigel. Vascular sprouting was comparable between choroid samples obtained from different animals of the same genetic background. The sprouting area, normalized to controls, was highly reproducible between independent experiments. We developed a semi-automated macro in ImageJ software to allow for more efficient quantification of sprouting area. Isolated choroid explants responded to manipulation of the external environment while maintaining the local interactions of endothelial cells with neighboring cells, including pericytes and macrophages as evidenced by immunohistochemistry and fluorescence-activated cell sorting (FACS) analysis. This reproducible ex vivo angiogenesis assay can be used to evaluate angiogenic potential of pharmacologic compounds on microvessels and can take advantage of genetically manipulated mouse tissue for microvascular disease research.

Multimodal assessment of microscopic morphology and retinal function in patients with geographic atrophy

PURPOSE

To correlate retinal function and visual sensitivity with retinal morphology revealed by ultrahigh-resolution imaging with adaptive optics-optical coherence tomography (AO-OCT), on patients with geographic atrophy.

METHODS

Five eyes from five subjects were tested (four with geographic atrophy [66.3 ± 6.4 years, mean ± 1 SD] and one normal [61 years]). Photopic and scotopic multifocal electroretinograms (mfERGs) were recorded. Visual fields were assessed with microperimetry (mP) combined with a scanning laser ophthalmoscope for high-resolution confocal retinal fundus imaging. The eye tracker of the microperimeter identified the preferred retinal locus that was then used as a reference for precise targeting of areas for advanced retinal imaging. Images were obtained with purpose-built, in-house, ultrahigh resolution AO-OCT. Fundus autofluorescence (FAF) and color fundus (CF) photographs were also acquired.

RESULTS

The AO-OCT imaging provided detailed cross-sectional structural representation of the retina. Up to 12 retinal layers were identified in the normal subject while many severe retinal abnormalities (i.e., calcified drusen, drusenoid pigment epithelium detachment, outer retinal tubulation) were identified in the retinae of the GA patients. The functional tests showed preservation of sensitivities, although somewhat compromised, at the border of the GA.

CONCLUSIONS

The images provided here advance our knowledge of the morphology of retinal layers in GA patients. While there was a strong correlation between altered retinal structure and reduction in visual function, there were a number of examples in which the photoreceptor inner/outer segment (IS/OS) junctions lost reflectivity at the margins of GA, while visual function was still demonstrated. This was shown to be due to changes in photoreceptor orientation near the GA border.

Hypoxia-inducible factor-1 (HIF-1): a potential target for intervention in ocular neovascular diseases

Constant oxygen supply is essential for proper tissue development, homeostasis and function of all eukaryotic organisms. Cellular response to reduced oxygen levels is mediated by the transcriptional regulator hypoxia-inducible factor-1 (HIF-1). It is a heterodimeric complex protein consisting of an oxygen dependent subunit (HIF-1α) and a constitutively expressed nuclear subunit (HIF-1β). In normoxic conditions, de novo synthesized cytoplasmic HIF-1α is degraded by 26S proteasome. Under hypoxic conditions, HIF-1α is stabilized, binds with HIF-1β and activates transcription of various target genes. These genes play a key role in regulating angiogenesis, cell survival, proliferation, chemotherapy, radiation resistance, invasion, metastasis, genetic instability, immortalization, immune evasion, metabolism and stem cell maintenance. This review highlights the importance of hypoxia signaling in development and progression of various vision threatening pathologies such as diabetic retinopathy, retinopathy of prematurity, age-related macular degeneration and glaucoma. Further, various inhibitors of HIF-1 pathway that may have a viable potential in the treatment of oxygen-dependent ocular diseases are also discussed.

The role of the immune response in age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries; with the aging population, the negative health impacts and costs of the disease will increase dramatically over the next decade. Although the exact cause of AMD is unknown, genetic studies have implicated the complement system as well as other immune responses in disease pathogenesis and severity. Furthermore, histologic studies have shown the presence of macrophages, lymphocytes, and mast cells, as well as fibroblasts, in both atrophic lesions and with retinal neovascularization. This review summarizes discussions from the fifth annual conference of the Arnold and Mabel Beckman Initiative for Macular Research by the Inflammation and Immune Response Task Force. These deliberations focused on the role of inflammatory immune responses, including complement, inflammasomes, adaptive immune responses, and para-inflammation, unanswered questions and studies to address these questions, and potential immune-related therapeutic targets for AMD.

Cellular and molecular mechanisms of age-related macular degeneration: from impaired autophagy to neovascularization

Age-related macular degeneration (AMD) is a complex, degenerative and progressive disease involving multiple genetic and environmental factors. It can result in severe visual loss e.g. AMD is the leading cause of blindness in the elderly in the western countries. Although age, genetics, diet, smoking, and many cardiovascular factors are known to be linked with this disease there is increasing evidence that long-term oxidative stress, impaired autophagy clearance and inflammasome mediated inflammation are involved in the pathogenesis. Under certain conditions these may trigger detrimental processes e.g. release of vascular endothelial growth factor (VEGF), causing choroidal neovascularization e.g. in wet AMD. This review ties together these crucial pathological threads in AMD.