The complement system and age-related macular degeneration

Geographic atrophy in Asia

PURPOSE

Geographic atrophy (GA) is a late-stage manifestation of age-related macular degeneration associated with vision loss. Differences between Asian and non-Asian populations with GA have been reported. It is essential to understand these differences because they may reflect variations in the natural history of the disease and its underlying pathophysiology, impacting resultant future treatment strategies and clinical trial designs.

METHODS

A non-systematic search for articles published up to November 22, 2023 was performed using PubMed. Reference lists from included articles were reviewed and relevant articles manually selected and included, as well as read for background information about the topic. Only articles in English were considered for inclusion in this narrative review.

RESULTS

Although the overall prevalence of GA appears to be low across Asia and shows a male predominance, regional variability is evident. Compared with White and other non-Asian populations, Asian populations typically have more distinct but fewer drusen overall (regardless of type), smaller GA lesion size at presentation, a thicker choroid, and lower rates of bilaterality. In both Asian and non-Asian populations, certain characteristics of GA may be associated with an increased risk of fast disease progression.

CONCLUSION

The characteristics of GA in Asian populations show some similarities as well as relevant differences compared with those in White and other non-Asian populations. A better understanding of the characteristics associated with GA subphenotypes and predictors of progression will help to optimize management strategies for Asian patients with GA and improve study designs for future interventional trials.

CRISPR targeting of SNPs associated with age-related macular degeneration in ARPE-19 cells: a potential model for manipulating the complement system

Age-related Macular degeneration (AMD) is a major cause of vision loss and is linked to several predisposing single nucleotide polymorphisms (SNPs). CRISPR-mediated genome editing offers the potential to target negatively associated SNPs in an allele-specific manner, necessitating the need for a relevant cell model. The ARPE-19 cell line, with its stable monolayer growth and retinal pigment epithelium (RPE) characteristics, serves as an ideal model for AMD studies. Chronic inflammation and complement system dysregulation are implicated in AMD pathogenesis. Most genetic variations associated with AMD are in complement genes, suggesting their regulatory role. In this study, we conducted targeted PCRs to identify AMD-related SNPs in ARPE-19 cells and used CRISPR constructs to assess allele-specific activity. Guide RNA sequences were cloned into an EF-1-driven SpCas9 vector and packaged into lentivirus. Targeting efficiencies were evaluated with TIDE analysis, and allele-specificity was measured with NGS analysis 30 days post-transduction. Our results showed varying targeting efficiencies depending on guide RNA efficacy. For example, TIDE analysis of CFH SNPs rs1061170 and rs1410996 revealed efficiencies of 35.5% and 33.8%, respectively. CFB SNP rs4541862 showed efficiencies from 3% to 36.7%, and rs641153 ranged from 3.4% to 23.8%. Additionally, allele-specific targeting of AMD-related SNPs rs1061170, rs1410996, rs4541862, and rs641153 ranged from 48% to 52% in heterozygous differentiated ARPE-19 cells. These findings demonstrate the potential to manipulate the complement system in an AMD model by targeting disease-associated SNPs in an allele-specific manner, offering a promising therapeutic approach.

Predict and Protect: Evaluating the Double-Layer Sign in Age-Related Macular Degeneration

INTRODUCTION

Advanced age-related macular degeneration (AMD) is a major cause of vision loss. Therefore, there is interest in precursor lesions that may predict or prevent the onset of advanced AMD. One such lesion is a shallow separation of the retinal pigment epithelium (RPE) and Bruch's membrane (BM), which is described by various terms, including double-layer sign (DLS).

METHODS

In this article, we aim to examine and clarify the different terms referring to shallow separation of the RPE and BM. We also review current evidence on the outcomes associated with DLS: firstly, whether DLS is predictive of exudative neovascular AMD; and secondly, whether DLS has potential protective properties against geographic atrophy.

RESULTS

The range of terms used to describe a shallow separation of the RPE and BM reflects that DLS can present with different characteristics. While vascularised DLS appears to protect against atrophy but can progress to exudation, non-vascularised DLS is associated with an increased risk of atrophy. Optical coherence tomography (OCT) angiography (OCTA) is the principal method for identifying and differentiating various forms of DLS. If OCTA is unavailable or not practically possible, simplified classification of DLS as thick or thin, using OCT, enables the likelihood of vascularisation to be approximated. Research is ongoing to automate DLS detection by applying deep-learning algorithms to OCT scans.

CONCLUSIONS

The term DLS remains applicable for describing shallow separation of the RPE and BM. Detection and classification of this feature provides valuable information regarding the risk of progression to advanced AMD. However, the appearance of DLS and its value in predicting AMD progression can vary between patients. With further research, individualised risks can be confirmed to inform appropriate treatment.

A comprehensive genetic map of cytokine responses in Lyme borreliosis

The incidence of Lyme borreliosis has risen, accompanied by persistent symptoms. The innate immune system and related cytokines are crucial in the host response and symptom development. We characterized cytokine production capacity before and after antibiotic treatment in 1,060 Lyme borreliosis patients. We observed a negative correlation between antibody production and IL-10 responses, as well as increased IL-1Ra responses in patients with disseminated disease. Genome-wide mapping the cytokine production allowed us to identify 34 cytokine quantitative trait loci (cQTLs), with 31 novel ones. We pinpointed the causal variant at the TLR1-6-10 locus and validated the regulation of IL-1Ra responses at transcritpome level using an independent cohort. We found that cQTLs contribute to Lyme borreliosis susceptibility and are relevant to other immune-mediated diseases. Our findings improve the understanding of cytokine responses in Lyme borreliosis and provide a genetic map of immune function as an expanded resource.

The Role of Complement Dysregulation in Glaucoma

Glaucoma is a progressive neurodegenerative disease characterized by damage to the optic nerve that results in irreversible vision loss. While the exact pathology of glaucoma is not well understood, emerging evidence suggests that dysregulation of the complement system, a key component of innate immunity, plays a crucial role. In glaucoma, dysregulation of the complement cascade and impaired regulation of complement factors contribute to chronic inflammation and neurodegeneration. Complement components such as C1Q, C3, and the membrane attack complex have been implicated in glaucomatous neuroinflammation and retinal ganglion cell death. This review will provide a summary of human and experimental studies that document the dysregulation of the complement system observed in glaucoma patients and animal models of glaucoma driving chronic inflammation and neurodegeneration. Understanding how complement-mediated damage contributes to glaucoma will provide opportunities for new therapies.

Biomarkers for the Progression of Intermediate Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of severe vision loss worldwide, with a global prevalence that is predicted to substantially increase. Identifying early biomarkers indicative of progression risk will improve our ability to assess which patients are at greatest risk of progressing from intermediate AMD (iAMD) to vision-threatening late-stage AMD. This is key to ensuring individualized management and timely intervention before substantial structural damage. Some structural biomarkers suggestive of AMD progression risk are well established, such as changes seen on color fundus photography and more recently optical coherence tomography (drusen volume, pigmentary abnormalities). Emerging biomarkers identified through multimodal imaging, including reticular pseudodrusen, hyperreflective foci, and drusen sub-phenotypes, are being intensively explored as risk factors for progression towards late-stage disease. Other structural biomarkers merit further research, such as ellipsoid zone reflectivity and choriocapillaris flow features. The measures of visual function that best detect change in iAMD and correlate with risk of progression remain under intense investigation, with tests such as dark adaptometry and cone-specific contrast tests being explored. Evidence on blood and plasma markers is preliminary, but there are indications that changes in levels of C-reactive protein and high-density lipoprotein cholesterol may be used to stratify patients and predict risk. With further research, some of these biomarkers may be used to monitor progression. Emerging artificial intelligence methods may help evaluate and validate these biomarkers; however, until we have large and well-curated longitudinal data sets, using artificial intelligence effectively to inform clinical trial design and detect outcomes will remain challenging. This is an exciting area of intense research, and further work is needed to establish the most promising biomarkers for disease progression and their use in clinical care and future trials. Ultimately, a multimodal approach may yield the most accurate means of monitoring and predicting future progression towards vision-threatening, late-stage AMD.

Treating patients with geographic atrophy: are we there yet?

Geographic atrophy (GA) is a progressive degenerative disease that significantly contributes to visual impairment in individuals aged 50 years and older. The development of GA is influenced by various modifiable and non-modifiable risk factors, including age, smoking, and specific genetic variants, particularly those related to the complement system regulators. Given the multifactorial and complex nature of GA, several treatment approaches have been explored, such as complement inhibition, gene therapy, and cell therapy. The recent approval by the Food and Drug Administration of pegcetacoplan, a complement C3 inhibitor, marks a significant breakthrough as the first approved treatment for GA. Furthermore, numerous interventions are currently in phase II or III trials, alongside this groundbreaking development. In light of these advancements, this review provides a comprehensive overview of GA, encompassing risk factors, prevalence, genetic associations, and imaging characteristics. Additionally, it delves into the current landscape of GA treatment, emphasizing the latest progress and future considerations. The goal of starting this discussion is to ultimately identify the most suitable candidates for each therapy, highlight the importance of tailoring treatments to individual cases, and continue monitoring the long-term implications of these emerging interventions.

Ocular Delivery of Therapeutic Agents by Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are short peptides with the ability to translocate through the cell membrane to facilitate their cellular uptake. CPPs can be used as drug-delivery systems for molecules that are difficult to uptake. Ocular drug delivery is challenging due to the structural and physiological complexity of the eye. CPPs may be tailored to overcome this challenge, facilitating cellular uptake and delivery to the targeted area. Retinal diseases occur at the posterior pole of the eye; thus, intravitreal injections are needed to deliver drugs at an effective concentration in situ. However, frequent injections have risks of causing vision-threatening complications. Recent investigations have focused on developing long-acting drugs and drug delivery systems to reduce the frequency of injections. In fact, conjugation with CPP could deliver FDA-approved drugs to the back of the eye, as seen by topical application in animal models. This review summarizes recent advances in CPPs, protein/peptide-based drugs for eye diseases, and the use of CPPs for drug delivery based on systematic searches in PubMed and clinical trials. We highlight targeted therapies and explore the potential of CPPs and peptide-based drugs for eye diseases.

Salivary Exosomes in Health and Disease: Future Prospects in the Eye

Exosomes are a group of vesicles that package and transport DNA, RNA, proteins, and lipids to recipient cells. They can be derived from blood, saliva, urine, and/or other biological tissues. Their impact on several diseases, such as neurodegenerative, autoimmune, and ocular diseases, have been reported, but not fully unraveled. The exosomes that are derived from saliva are less studied, but offer significant advantages over exosomes from other sources, due to their accessibility and ease of collection. Thus, their role in the pathophysiology of diseases is largely unknown. In the context of ocular diseases, salivary exosomes have been under-utilized, thus creating an enormous gap in the literature. The current review discusses the state of exosomes research on systemic and ocular diseases and highlights the role and potential of salivary exosomes as future ocular therapeutic vehicles.

Phenome-wide Mendelian randomisation analysis identifies causal factors for age-related macular degeneration

Background

Age-related macular degeneration (AMD) is a leading cause of blindness in the industrialised world and is projected to affect >280 million people worldwide by 2040. Aiming to identify causal factors and potential therapeutic targets for this common condition, we designed and undertook a phenome-wide Mendelian randomisation (MR) study.

Methods

We evaluated the effect of 4591 exposure traits on early AMD using univariable MR. Statistically significant results were explored further using: validation in an advanced AMD cohort; MR Bayesian model averaging (MR-BMA); and multivariable MR.

Results

Overall, 44 traits were found to be putatively causal for early AMD in univariable analysis. Serum proteins that were found to have significant relationships with AMD included S100-A5 (odds ratio [OR] = 1.07, p-value = 6.80E-06), cathepsin F (OR = 1.10, p-value = 7.16E-05), and serine palmitoyltransferase 2 (OR = 0.86, p-value = 1.00E-03). Univariable MR analysis also supported roles for complement and immune cell traits. Although numerous lipid traits were found to be significantly related to AMD, MR-BMA suggested a driving causal role for serum sphingomyelin (marginal inclusion probability [MIP] = 0.76; model-averaged causal estimate [MACE] = 0.29).

Conclusions

The results of this MR study support several putative causal factors for AMD and highlight avenues for future translational research.

Funding

This project was funded by the Wellcome Trust (224643/Z/21/Z; 200990/Z/16/Z); the University of Manchester's Wellcome Institutional Strategic Support Fund (Wellcome ISSF) grant (204796/Z/16/Z); the UK National Institute for Health Research (NIHR) Academic Clinical Fellow and Clinical Lecturer Programmes; Retina UK and Fight for Sight (GR586); the Australian National Health and Medical Research Council (NHMRC) (1150144).

DeepLUCIA: predicting tissue-specific chromatin loops using Deep Learning-based Universal Chromatin Interaction Annotator

MOTIVATION

The importance of chromatin loops in gene regulation is broadly accepted. There are mainly two approaches to predict chromatin loops: transcription factor (TF) binding-dependent approach and genomic variation-based approach. However, neither of these approaches provides an adequate understanding of gene regulation in human tissues. To address this issue, we developed a deep learning-based chromatin loop prediction model called DeepLUCIA (Deep Learning-based Universal Chromatin Interaction Annotator).

RESULTS

Although DeepLUCIA does not use TF binding profile data which previous TF binding-dependent methods critically rely on, its prediction accuracies are comparable to those of the previous TF binding-dependent methods. More importantly, DeepLUCIA enables the tissue-specific chromatin loop predictions from tissue-specific epigenomes that cannot be handled by genomic variation-based approach. We demonstrated the utility of the DeepLUCIA by predicting several novel target genes of SNPs identified in genome-wide association studies targeting Brugada syndrome, COVID-19 severity, and age-related macular degeneration.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Genetically Predicted Circulating Concentrations of Micronutrients and COVID-19 Susceptibility and Severity: A Mendelian Randomization Study

Background

Coronavirus disease 2019 (COVID-19) is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) which since 2019 has caused over 5 million deaths to date. The pathogenicity of the virus is highly variable ranging from asymptomatic to fatal. Evidence from experimental and observational studies suggests that circulating micronutrients may affect COVID-19 outcomes.

Objectives

To complement and inform observational studies, we investigated the associations of genetically predicted concentrations of 12 micronutrients (β-carotene, calcium, copper, folate, iron, magnesium, phosphorus, selenium, vitamin B-6, vitamin B-12, vitamin D, and zinc) with SARS-CoV-2 infection risk and COVID-19 severity using Mendelian randomization (MR).

Methods

Two-sample MR was conducted using 87,870 individuals of European descent with a COVID-19 diagnosis and 2,210,804 controls from the COVID-19 host genetics initiative. Inverse variance-weighted MR analyses were performed with sensitivity analyses to assess the impact of potential violations of MR assumptions.

Results

Compared to the general population, nominally significant associations were noted for higher genetically predicted vitamin B-6 (Odds ratio per standard deviation [OR_SD]: 1.06; 95% confidence interval [CI]: 1.00, 1.13; p-value = 0.036) and lower magnesium concentrations (OR_SD: 0.33; 95%CI: 0.11, 0.96; P = 0.042) with COVID-19 infection risk. However, the association for magnesium was not consistent in some sensitivity analyses, and sensitivity analyses could not be performed for vitamin B-6 as only two genetic instruments were available. Genetically predicted levels of calcium, folate, β-carotene, copper, iron, vitamin B-12, vitamin D, selenium, phosphorus, or zinc were not associated with the outcomes from COVID-19 disease.

Conclusion

These results, though based only on genetically predicated circulating micronutrient concentrations, provide scant evidence for possible associations of micronutrients with COVID-19 outcomes.

The Development of Macular Atrophy in Patients with Wet Age-Related Macular Degeneration Receiving Anti-VEGF Treatment

Age-related macular degeneration (AMD) is a leading cause of blindness. Late AMD can be classified into exudative (commonly known as wet AMD [wAMD]) or dry AMD, both of which may progress to macular atrophy (MA). MA causes irreversible vision loss and currently has no approved pharmacological treatment. The standard of care for wAMD is treatment with anti-vascular endothelial growth factors (VEGF). However, recent evidence suggests that anti-VEGF treatment may play a role in the development of MA. Therefore, it is important to identify risk factors for the development of MA in patients with wAMD. For example, excessive blockade of VEGF through intense use of anti-VEGF agents may accelerate the development of MA. Patients with type III macular neovascularisation (retinal angiomatous proliferation) have a particularly high risk of MA. These patients are characterised as having a pre-existing thin choroid (age-related choroidopathy), suggesting that the choroidal circulation is unable to respond to increased VEGF expression. Evidence suggests that subretinal fluid (possibly indicative of residual VEGF activity) may play a protective role. Patients receiving anti-VEGF agents must be assessed for overall risk of MA and there is an unmet medical need to prevent the development of MA without undertreating wAMD.

RNA Therapeutics - Research and Clinical Advancements

RNA therapeutics involve the use of coding RNA such as mRNA as well as non-coding RNAs such as small interfering RNAs (siRNA), antisense oligonucleotides (ASO) to target mRNA, aptamers, ribozymes, and clustered regularly interspaced short palindromic repeats-CRISPR-associated (CRISPR/Cas) endonuclease to target proteins and DNA. Due to their diverse targeting ability and research in RNA modification and delivery systems, RNA-based formulations have emerged as suitable treatment options for many diseases. Therefore, in this article, we have summarized different RNA therapeutics, their targeting strategies, and clinical progress for various diseases as well as limitations; so that it might help researchers formulate new and advanced RNA therapeutics for various diseases. Additionally, U.S. Food and Drug Administration (USFDA)-approved RNA-based therapeutics have also been discussed.

Oxidative Stress and Mitochondrial Damage in Dry Age-Related Macular Degeneration Like NFE2L2/PGC-1α -/- Mouse Model Evoke Complement Component C5a Independent of C3

Aging-associated chronic oxidative stress and inflammation are known to be involved in various diseases, e.g., age-related macular degeneration (AMD). Previously, we reported the presence of dry AMD-like signs, such as elevated oxidative stress, dysfunctional mitophagy and the accumulation of detrimental oxidized materials in the retinal pigment epithelial (RPE) cells of nuclear factor erythroid 2-related factor 2, and a peroxisome proliferator-activated receptor gamma coactivator 1-alpha (NFE2L2/PGC1α) double knockout (dKO) mouse model. Here, we investigated the dynamics of inflammatory markers in one-year-old NFE2L2/PGC1α dKO mice. Immunohistochemical analysis revealed an increase in levels of Toll-like receptors 3 and 9, while those of NOD-like receptor 3 were decreased in NFE2L2/PGC1α dKO retinal specimens as compared to wild type animals. Further analysis showed a trend towards an increase in complement component C5a independent of component C3, observed to be tightly regulated by complement factor H. Interestingly, we found that thrombin, a serine protease enzyme, was involved in enhancing the terminal pathway producing C5a, independent of C3. We also detected an increase in primary acute phase C-reactive protein and receptor for advanced glycation end products in NFE2L2/PGC1α dKO retina. Our main data show C5 and thrombin upregulation together with decreased C3 levels in this dry AMD-like model. In general, the retina strives to mount an orchestrated inflammatory response while attempting to maintain tissue homeostasis and resolve inflammation.

HDL Cholesterol and Non-Cardiovascular Disease: A Narrative Review

High density lipoprotein (HDL) cholesterol has traditionally been considered the “good cholesterol”, and most of the research regarding HDL cholesterol has for decades revolved around the possible role of HDL in atherosclerosis and its therapeutic potential within atherosclerotic cardiovascular disease. Randomized trials aiming at increasing HDL cholesterol have, however, failed and left questions to what role HDL cholesterol plays in human health and disease. Recent observational studies involving non-cardiovascular diseases have shown that high levels of HDL cholesterol are not necessarily associated with beneficial outcomes as observed for age-related macular degeneration, type II diabetes, dementia, infection, and mortality. In this narrative review, we discuss these interesting associations between HDL cholesterol and non-cardiovascular diseases, covering observational studies, human genetics, and plausible mechanisms.

Nucleoside reverse transcriptase inhibitors and Kamuvudines inhibit amyloid-β induced retinal pigmented epithelium degeneration

Nonfibrillar amyloid-β oligomers (AβOs) are a major component of drusen, the sub-retinal pigmented epithelium (RPE) extracellular deposits characteristic of age-related macular degeneration (AMD), a common cause of global blindness. We report that AβOs induce RPE degeneration, a clinical hallmark of geographic atrophy (GA), a vision-threatening late stage of AMD that is currently untreatable. We demonstrate that AβOs induce activation of the NLRP3 inflammasome in the mouse RPE in vivo and that RPE expression of the purinergic ATP receptor P2RX7, an upstream mediator of NLRP3 inflammasome activation, is required for AβO-induced RPE degeneration. Two classes of small molecule inflammasome inhibitors—nucleoside reverse transcriptase inhibitors (NRTIs) and their antiretrovirally inert modified analog Kamuvudines—both inhibit AβOs-induced RPE degeneration. These findings crystallize the importance of P2RX7 and NLRP3 in a disease-relevant model of AMD and identify inflammasome inhibitors as potential treatments for GA.

Potential Therapeutic Benefit of NAD+ Supplementation for Glaucoma and Age-Related Macular Degeneration

Glaucoma and age-related macular degeneration are leading causes of irreversible blindness worldwide with significant health and societal burdens. To date, no clinical cures are available and treatments target only the manageable symptoms and risk factors (but do not remediate the underlying pathology of the disease). Both diseases are neurodegenerative in their pathology of the retina and as such many of the events that trigger cell dysfunction, degeneration, and eventual loss are due to mitochondrial dysfunction, inflammation, and oxidative stress. Here, we critically review how a decreased bioavailability of nicotinamide adenine dinucleotide (NAD; a crucial metabolite in healthy and disease states) may underpin many of these aberrant mechanisms. We propose how exogenous sources of NAD may become a therapeutic standard for the treatment of these conditions.

C-reactive protein and complement factor H polymorphism interaction in advanced exudative age-related macular degeneration

PURPOSE

To determine the association of C-reactive protein (CRP) and complement factor H (CFH) gene with exudative age-related macular degeneration (AMD) and any possible interaction among these factors.

METHODS

In this case-control study, 139 unrelated patients with exudative AMD and 123 non-AMD controls were recruited. Blood sample was taken for analysis of the CRP levels and DNA testing. DNA fragments of CFH gene variants containing 4 single nucleotide polymorphisms including rs800292, rs1061170, rs2274700, and rs3753395 were assessed. A CRP level of ≥3 mg/L was considered as elevated. The association of elevated CRP and CFH gene variants polymorphism with exudative AMD was compared between the groups.

RESULTS

Mean age was 72.6 ± 6.4 for controls and 74.9 ± 7.4 for case group (P = 0.006). The difference between CRP levels in cases and controls was not statistically significant (P = 0.055). However, Y402H variant of CFH in both homozygous and heterozygous carriers C allele was significantly more frequent among exudative AMD patients than controls, 32.1 versus 6.5 % (P < 0.001). Evaluating various CRP levels in patients with CC and non-CC genotypes disclosed that in CC genotype group, higher CRP level (>3 mg/L) was associated with higher risk of developing exudative AMD (OR = 12.0, CI: 1.5-98.8) compared with the control group.

CONCLUSION

This study disclosed no difference in CRP levels per se between exudative AMD patients with control group. However, higher levels of CRP in the presence of C allele of Y402H might confer more risk for the development of exudative AMD.

Retinal disease in the C3 glomerulopathies and the risk of impaired vision

BACKGROUND

Dense deposit disease and atypical hemolytic uremic syndrome are often caused by Complement Factor H (CFH) mutations. This study describes the retinal abnormalities in dense deposit disease and, for the first time, atypical haemolytic uremic syndrome. It also reviews our understanding of drusen pathogenesis and their relevance for glomerular disease.

METHODS

Six individuals with dense deposit disease and one with atypical haemolytic uremic syndrome were studied from 2 to 40 years after presentation. Five had renal transplants. All four who had genetic testing had CFH mutations. Individuals underwent ophthalmological review and retinal photography, and in some cases, optical coherence tomography, and further tests of retinal function.

RESULTS

All subjects with dense deposit disease had impaired night vision and retinal drusen or whitish-yellow deposits. Retinal atrophy, pigmentation, and hemorrhage were common. In late disease, peripheral vision was restricted, central vision was distorted, and there were scotoma from sub-retinal choroidal neovascular membranes and atypical serous retinopathy. Drusen were present but less prominent in the young person with atypical uremic syndrome due to a heterozygous CFH mutation.

CONCLUSIONS

Drusen are common in forms of C3 glomerulopathy caused by compound heterozygous or heterozygous CFH mutations. They are useful diagnostically but also impair vision. Drusen have an identical composition to glomerular deposits. They are also identical to the drusen of age-related macular degeneration, and may respond to the same treatments. Individuals with a C3 glomerulopathy should be assessed ophthalmologically at diagnosis, and monitored regularly for vision-threatening complications.

Investigating the choriocapillaris and choroidal vasculature with new optical coherence tomography technologies

The body of knowledge of in vivo investigation of the choroid has been markedly enhanced by recent technological advances in optical coherence tomography (OCT). New insights elucidating the morphological features of the choriocapillaris and choroidal vasculature, in both physiological and pathological conditions, indicate that the choroid plays a pivotal role in many posterior segment diseases. In this article, a review of the histological characteristics of the choroid, which must be considered for the proper interpretation of in vivo imaging, is followed by a comprehensive discussion of fundamental principles of the current state-of-the-art in OCT, including cross-sectional OCT, en face OCT, and OCT angiography using both spectral domain OCT and swept source OCT technologies. A detailed review of the tomographic features of the choroid in the normal eye is followed by relevant findings in prevalent chorioretinal diseases, focusing on major causes of vision loss such as typical early and advanced age-related macular degeneration, polypoidal choroidal vasculopathy, central serous chorioretinopathy, pachychoroid spectrum disorders, diabetic choroidopathy, and myopia.

Complement Factor H Expressed by Retinal Pigment Epithelium Cells Can Suppress Neovascularization of Human Umbilical Vein Endothelial Cells: An in vitro Study

Complement factor H (CFH) is one of the most important soluble complement regulatory proteins and is closely associated with age-related macular degeneration (AMD), the leading cause of irreversible central vision loss in the elderly population in developed countries. Our study searches to investigate whether CFH expression is changed in oxidative damaged retinal pigment epithelium (RPE) cells and the role of CFH in the in vitro neovascularization. First, it was confirmed by immunofluorescence staining that CFH was expressed by ARPE-19 cells. CFH mRNA and protein in oxidative (H₂O₂) damaged ARPE-19 cells were both reduced, as determined by Real-time PCR and Western blotting analysis. Enzyme-linked immunosorbent assay (ELISA) also showed that ARPE-19 cells treated with H₂O₂ caused an increase in C3a content, which indicates complement activation. Then, wound assays were performed to show that CFH expression suppression promoted human umbilical vein endothelial cell (HUVECs) migration. Thereafter, ARPE-19 cells were transfected with CFH-specific siRNA and CFH knockdown was confirmed with the aid of Real-time PCR, immunofluorescence staining and Western blotting. The ELISA results showed that specific CFH knockdown in ARPE-19 cells activated the complement system. Finally, in vitro matrigel tube formation assay was performed to determine whether change of CFH expression in RPE would affect tube formation by HUVECs. More tubes were formed by HUVECs co-cultured with ARPE-19 cells transfected with CFH specific-siRNA when compared with controls. Our results suggested that RPE cells might be the local CFH source, and RPE cell injuries (such as oxidative stress) may cause CFH expression suppression, which in turn may lead to complement activation and promotion of tube formation by HUVECs. This finding is of importance in elucidating the role of complement in the pathogenesis of ocular neovascularization including choroidal neovascularization.

Intravitreal inhibition of complement C5a reduces choroidal neovascularization in mice

PURPOSE

To investigate the influence of complement component C5a inhibition on laser-induced choroidal neovascularization (CNV) in mice using a C5a specific L-aptamer.

METHODS

In C57BL/6 J mice CNV was induced by argon-laser, C5a-inhibitor (NOX-D20) was intravitreally injected in three concentrations: 0.3, 3.0, and 30 mg/ml. The unPEGylated derivate (NOX-D20001) was applied at 3.0 mg/ml; the vehicle (5 % glucose) was injected in controls. Vascular leakage was evaluated using fluorescence angiography, CNV area was examined immunohistochemically. Activated immune cells surrounding the CNV lesion and potential cytotoxicity were analyzed.

RESULTS

Compared to controls, CNV areas were significantly reduced after NOX-D20 injection at a concentration of 0.3 and 3.0 mg/ml (p = 0.042; p = 0.016). NOX-D20001 significantly decreased CNV leakage but not the area (p = 0.007; p = 0.276). At a concentration of 30 mg/ml, NOX-D20 did not reveal significant effects on vascular leakage or CNV area (p = 0.624; p = 0.121). The amount of CD11b positive cells was significantly reduced after treatment with 0.3 and 3.0 mg/ml NOX-D20 (p = 0.027; p = 0.002). No adverse glial cell proliferation or increased apoptosis were observed at effective dosages.

CONCLUSIONS

Our findings demonstrate that the targeted inhibition of complement component C5a reduces vascular leakage and neovascular area in laser-induced CNV in mice. NOX-D20 was proven to be an effective and safe agent that might be considered as a therapeutic candidate for CNV treatment. The deficiency of activated immune cells highlights promising new aspects in the pathology of choroidal neovascularization, and warrants further investigations.

Recent developments in the management of dry age-related macular degeneration

Dry age-related macular degeneration (AMD), also called geographic atrophy, is characterized by the atrophy of outer retinal layers and retinal pigment epithelium (RPE) cells. Dry AMD accounts for 80% of all intermediate and advanced forms of the disease. Although vision loss is mainly due to the neovascular form (75%), dry AMD remains a challenge for ophthalmologists because of the lack of effective therapies. Actual management consists of lifestyle modification, vitamin supplements, and supportive measures in the advanced stages. The Age-Related Eye Disease Study demonstrated a statistically significant protective effect of dietary supplementation of antioxidants (vitamin C, vitamin E, beta-carotene, zinc, and copper) on dry AMD progression rate. It was also stated that the consumption of omega-3 polyunsaturated fatty acids, such as docosahexaenoic acid and eicosapentaenoic acid, has protective effects. Other antioxidants, vitamins, and minerals (such as crocetin, curcumin, and vitamins B9, B12, and B6) are under evaluation, but the results are still uncertain. New strategies aim to 1) reduce or block drusen formation, 2) reduce or eliminate inflammation, 3) lower the accumulation of toxic by-products from the visual cycle, 4) reduce or eliminate retinal oxidative stress, 5) improve choroidal perfusion, 6) replace/repair or regenerate lost RPE cells and photoreceptors with stem cell therapy, and 7) develop a target gene therapy.

Activated complement classical pathway in a murine model of oxygen-induced retinopathy

AIM

To investigate whether the complement system is involved in a murine model of oxygen-induced retinopathy (OIR).

METHODS

Forty C57BL/6J newborn mice were divided randomly into OIR group and control group. OIR was induced by exposing mice to 75%±2% oxygen from postnatal 7d (P7) to P12 and then recovered in room air. For the control group, the litters were raised in room air. At the postnatal 17d (P17), gene expressions of the complement components of the classical pathway (CP), the mannose-binding lectin (MBL) pathway and the alternative pathway (AP) in the retina were determined by quantitative real-time polymerase chain reaction (RT-PCR). Retinal protein expressions of the key components in the CP were examined by Western blotting.

RESULTS

Whole mounted retina in the OIR mice showed area of central hypoperfusion in both superficial and deep layers and neovascular tufts in the periphery. The expressions of C1qb and C4b genes in the OIR retina were significantly higher than those of the controls. The expression of retinal complement factor B (CFB) gene in OIR mice was significantly lower than those of the controls. However, the expressions of C3 and complement factor H (CFH) genes were higher. The protein synthesis of the key components involved in the CP (C1q, C4 and C3) were also significantly higher in OIR mouse retina. Although MBL-associated serine protease 1 (MASP1) and MASP2 were detected in both the OIR and the control groups, the expressions were weak and the difference between the two groups was not significant.

CONCLUSION

Our data suggest that the complement system CP is activated during the pathogenesis of murine model of OIR.

Lutein and Factor D: two intriguing players in the field of age-related macular degeneration

Age-related macular degeneration (AMD) is a progressive eye disease that impairs central vision among elderly populations in Western, industrialized countries. In this review we will focus on the role of factor D (FD) and lutein in AMD. FD is a rate-limiting enzyme of the alternative complement activation pathway that may play an important role in the development of AMD. Several independent studies have shown a significant increase in the level of a number of complement factors of the alternative pathway, including factor D in the blood of AMD patients as compared to healthy individuals, which suggests a systemic involvement in the pathogenesis of AMD. FD, also called adipsin, is mainly produced by adipose tissue. Besides playing a role in the activation of the alternative pathway, FD is also known to regulate the immune system. Of interest is our preliminary finding that lutein supplementation of early AMD cases was shown to lower the level of systemic FD. If confirmed, these findings provide further support for the application of anti-factor D intervention as a new approach to control the development of this disease.

Aptamer-based therapeutics of the past, present and future: from the perspective of eye-related diseases

Aptamers have emerged as a novel and powerful class of biomolecules with an immense untapped potential. The ability to synthesise highly specific aptamers against any molecular target make them a vital cog in the design of effective therapeutics for the future. However, only a minutia of the enormous potential of this dynamic class of molecule has been exploited. Several aptamers have been studied for the treatment of eye-related disorders, and one such strategy has been successful in therapy. This review gives an account of several eye diseases and their regulatory biomolecules where other nucleic acid therapeutics have been attempted with limited success and how aptamers, with their exceptional flexibility to chemical modifications, can overcome those inherent shortcomings.

Complement inhibitors for age-related macular degeneration

BACKGROUND

Given the relatively high prevalence of age-related macular degeneration (AMD) and the increased incidence of AMD as populations age, the results of trials of novel treatments are awaited with much anticipation. The complement cascade describes a series of proteolytic reactions occurring throughout the body that generate proteins with a variety of roles including the initiation and promotion of immune reactions against foreign materials or micro-organisms. The complement cascade is normally tightly regulated, but much evidence implicates complement overactivity in AMD and so it is a logical therapeutic target in the treatment of AMD.

OBJECTIVES

To assess the effects and safety of complement inhibitors in the prevention or treatment of advanced AMD.

SEARCH METHODS

We searched CENTRAL (which contains the Cochrane Eyes and Vision Group Trials Register) (The Cochrane Library 2013, Issue 11), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to November 2013), EMBASE (January 1980 to November 2013), Allied and Complementary Medicine Database (AMED) (January 1985 to November 2013), Latin American and Caribbean Literature on Health Sciences (LILACS) (January 1982 to November 2013), OpenGrey (System for Information on Grey Literature in Europe) (www.opengrey.eu/), Web of Science Conference Proceedings Citation Index - Science (CPCI-S) (January 1990 to November 2013), the metaRegister of Controlled Trials (mRCT) (www.controlled-trials.com), ClinicalTrials.gov (www.clinicaltrials.gov) and the WHO International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 21 November 2013. We also performed handsearching of proceedings, from 2012 onwards, of meetings and conferences of specific professional organisations.

SELECTION CRITERIA

We planned to include randomised controlled trials (RCTs) with parallel treatment groups which investigated either the prevention or treatment of advanced AMD by inhibition of the complement cascade.

DATA COLLECTION AND ANALYSIS

Two authors (MW and GMcK) independently evaluated all the titles and abstracts resulting from the searches. We contacted companies running clinical trials which had not yet reported results to request information. Since no trials met our inclusion criteria, we undertook no assessment of quality or meta-analysis.

MAIN RESULTS

We identified and screened 317 references but there were no published RCTs that met the inclusion criteria. We identified two ongoing studies: one phase I study and one phase II study.

AUTHORS' CONCLUSIONS

There is insufficient information at present to generate evidence-based recommendations on the potential safety and efficacy of complement inhibitors for prevention or treatment of AMD. However we anticipate the results of ongoing trials.

Pharmacogenetics of antiangiogenic and antineovascular therapies of age-related macular degeneration

Age-related macular degeneration (AMD), the most common age-related disease causing irreversible visual loss in industrialized countries, is a complex and multifactorial illness. Researchers have found components of the complement alternative pathway inside drusen and Bruch's membrane of AMD patients, underlying a possible important role of complement factor H in the pathogenesis of AMD. The neovascular (wet) AMD is the most destructive form and it is characterized by invasion of new blood vessels into subretinal spaces with subsequent exudation and bleeding, resulting in scarring of the macular region and loss of the central vision. The hallmark of the neovascular form is the choroidal neovascularization, where VEGF-A has an important role in the pathogenesis of the disease. SNPs of these genes have recently been investigated as potential pharmacogenetic markers of the antiangiogenic and antineovascular therapy of AMD, which includes verteporfin photodynamic therapy and anti-VEGF-A drugs, such as pegaptanib, bevacizumab and ranibizumab. The CFH rs1061170 CT and TT genotypes have been associated with an improvement of visual acuity in bevacizumab or ranibizumab treated patients, whereas patients harboring VEGF-A rs699946 G allele responded better to bevacizumab-based therapy if compared with patients carrying the A allele. In conclusion, the discovery of pharmacogenetic markers for the personalization of the antiangiogenic and/or antineovascular therapy could be, in the future, a key issue in ophthalmology to obtain a personalization of the therapy and to avoid unnecessary costs and adverse drug reactions.

Implication of CD21, CD35, and CD55 in the pathogenesis of age-related macular degeneration

PURPOSE

To determine a possible implication of CD21, CD35, and CD55 in the pathogenesis of age-related macular degeneration (AMD) by assessing the difference in expression rates of these factors on AMD patients and a control group.

DESIGN

Case-control study.

METHODS

Fifty unrelated AMD patients and 48 unrelated sex- and age-matched control subjects participated in this case-control study. Samples of fresh EDTA-blood were stained and flow cytometry was chosen to measure fluorescence emissions. The association between exudative AMD and CD21, CD35, and CD55 was evaluated from all patients who completed the study.

RESULTS

Our study shows CD35 to be expressed in a significantly higher frequency in AMD patients on monocytes (P = .00586), lymphocytes (P = .000605), and granulocytes (P < .000033). In contrast, the expression rate of CD21 (P > .05) and CD55 (P > .05) are similar in both groups.

CONCLUSION

More regulative factors of the complement system are involved in pathogenesis of AMD. Our study underlines the key role of the complement system in AMD and shows the involvement of the whole immune system through more regulative factors.

Age related macular degeneration and drusen: neuroinflammation in the retina

Inflammation protects from dangerous stimuli, restoring normal tissue homeostasis. Inflammatory response in the nervous system ("neuroinflammation") has distinct features, which are shared in several diseases. The retina is an immune-privileged site, and the tight balance of immune reaction can be disrupted and lead to age-related macular disease (AMD) and to its peculiar sign, the druse. Excessive activation of inflammatory and immunological cascade with subsequent induction of damage, persistent activation of resident immune cells, accumulation of byproducts that exceeds the normal capacity of clearance giving origin to a chronic local inflammation, alterations in the activation of the complement system, infiltration of macrophages, T-lymphocytes and mast-cells from the bloodstream, participate in the mechanisms which originate the drusen. In addition, aging of the retina and AMD involve also para-inflammation, by which immune cells react to persistent stressful stimuli generating low-grade inflammation, aimed at restoring function and maintaining tissue homeostasis by varying the set point in relation to the new altered conditions. This mechanism is also seen in the normal aging retina, but, in the presence of noxious stimuli as in AMD, it can become chronic and have an adverse outcome. Finally, autophagy may provide new insights to understand AMD pathology, due to its contribution in the removal of defective proteins. Therefore, the AMD retina can represent a valuable model to study neuroinflammation, its mechanisms and therapy in a restricted and controllable environment. Targeting these pathways could represent a new way to treat and prevent both exudative and dry forms of AMD.

A review and meta-analysis of the association between C-reactive protein and age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in people over 60 in western countries. Inflammatory markers have been implicated in the development and progression of AMD. C-reactive protein (CRP) is an inflammatory marker known to be associated with cardiovascular disease, and a link between AMD and CRP has been suggested. In this systematic review we summarize the currently available evidence from clinic-based and population-based studies investigating this association. A meta-analysis of evidence from eleven studies (41,690 study participants) shows that high serum levels (>3 mg/L) of CRP are associated with a two-fold likelihood of late onset AMD, compared to low levels (<1mg/L). Sub-group meta-analyses show a higher association in studies using ophthalmoscopic examination, compared to those using photographic grading (pooled odds ratio 3.83 vs 1.36), to determine AMD status, or in clinic-based samples compared to population-based studies.

C20-D3-vitamin A slows lipofuscin accumulation and electrophysiological retinal degeneration in a mouse model of Stargardt disease

Stargardt disease, also known as juvenile macular degeneration, occurs in approximately one in 10,000 people and results from genetic defects in the ABCA4 gene. The disease is characterized by premature accumulation of lipofuscin in the retinal pigment epithelium (RPE) of the eye and by vision loss. No cure or treatment is available. Although lipofuscin is considered a hallmark of Stargardt disease, its mechanism of formation and its role in disease pathogenesis are poorly understood. In this work we investigated the effects of long-term administration of deuterium-enriched vitamin A, C20-D(3)-vitamin A, on RPE lipofuscin deposition and eye function in a mouse model of Stargardt's disease. Results support the notion that lipofuscin forms partly as a result of the aberrant reactivity of vitamin A through the formation of vitamin A dimers, provide evidence that preventing vitamin A dimerization may slow disease related, retinal physiological changes and perhaps vision loss and suggest that administration of C20-D(3)-vitamin A may be a potential clinical strategy to ameliorate clinical symptoms resulting from ABCA4 genetic defects.

Complement component C5a activates ICAM-1 expression on human choroidal endothelial cells

PURPOSE

The complement system plays a crucial role in the progression of age-related macular degeneration (AMD). In this study, the authors sought to evaluate the pathophysiologic roles of complement components C3a and C5a in the human choroid in AMD.

METHODS

Human RPE/choroid was assayed for the presence of C3a and C5a receptors (C3aR and C5aR) using RT-PCR and immunohistochemistry. Choroidal endothelial cell migration and proliferation were evaluated in the presence of C5a. Organ cultures of human choroid were incubated in C5a or bovine serum albumin (BSA) followed by quantitative immunohistochemistry and quantitative PCR for ICAM-1. AMD patients and controls were genotyped at SNPs in the C5R1 and C3AR1 genes.

RESULTS

C5aR, but not C3aR, was detected in human choroid. C5a did not promote endothelial cell migration or proliferation. However, choriocapillaris endothelial cells in organ culture responded to C5a by increasing ICAM-1 mRNA and protein. No significant association of SNP genotypes was detected in AMD patients at the C3AR1 and C5R1 genes.

CONCLUSIONS

The generation of C5a peptides may lead to activation of choriocapillaris endothelial cells in AMD. Activation of the choroidal endothelium may affect the progression of AMD by recruitment of monocytes, leading to additional sequelae of AMD pathogenesis.

The molecular basis of human retinal and vitreoretinal diseases

During the last two to three decades, a large body of work has revealed the molecular basis of many human disorders, including retinal and vitreoretinal degenerations and dysfunctions. Although belonging to the group of orphan diseases, they affect probably more than two million people worldwide. Most excitingly, treatment of a particular form of congenital retinal degeneration is now possible. A major advantage for treatment is the unique structure and accessibility of the eye and its different components, including the vitreous and retina. Knowledge of the many different eye diseases affecting retinal structure and function (night and colour blindness, retinitis pigmentosa, cone and cone rod dystrophies, photoreceptor dysfunctions, as well as vitreoretinal traits) is critical for future therapeutic development. We have attempted to present a comprehensive picture of these disorders, including biological, clinical, genetic and molecular information. The structural organization of the review leads the reader through non-syndromic and syndromic forms of (i) rod dominated diseases, (ii) cone dominated diseases, (iii) generalized retinal degenerations and (iv) vitreoretinal disorders, caused by mutations in more than 165 genes. Clinical variability and genetic heterogeneity have an important impact on genetic testing and counselling of affected families. As phenotypes do not always correlate with the respective genotypes, it is of utmost importance that clinicians, geneticists, counsellors, diagnostic laboratories and basic researchers understand the relationships between phenotypic manifestations and specific genes, as well as mutations and pathophysiologic mechanisms. We discuss future perspectives.

Genetic basis of inherited macular dystrophies and implications for stem cell therapy

Untreatable hereditary macular dystrophy (HMD) presents a major burden to society in terms of the resulting patient disability and the cost to the healthcare provision system. HMD results in central vision loss in humans sufficiently severe for blind registration, and key issues in the development of therapeutic strategies to target these conditions are greater understanding of the causes of photoreceptor loss and the development of restorative procedures. More effective and precise analytical techniques coupled to the development of transgenic models of disease have led to a prolific growth in the identification and our understanding of the genetic mutations that underly HMD. Recent successes in driving differentiation of pluripotent cells towards specific somatic lineages have led to the development of more efficient protocols that can yield enriched populations of a desired phenotype. Retinal pigmented epithelial cells and photoreceptors derived from these are some of the most promising cells that may soon be used in the treatment of specific HMD, especially since rapid developments in the field of induced pluripotency have now set the stage for the production of patient-derived stem cells that overcome the ethical and methodological issues surrounding the use of embryonic derivatives. In this review we highlight a selection of HMD which appear suitable candidates for combinatorial restorative therapy, focusing specifically on where those photoreceptor loss occurs. This technology, along with increased genetic screening, opens up an entirely new pathway to restore vision in patients affected by HMD.

Complement-associated deposits in the human retina

PURPOSE

The purpose of this study was to investigate complement activation and associated inflammatory mechanisms in normal, aged human retina.

METHODS

Evidence of complement activation and associated mechanisms was assessed in normal human retina (n = 52) using a panel of antibodies directed against membrane attack complex (C5b-9), microglia (CD11b), amyloid precursor protein (APP), scavenger receptor (CD36), and a phytolectin (RCA-I). Fifty-two eyes, categorized into two age groups, were used. Nineteen "younger" eyes (<56 years) and 33 "older" eyes (>69 years) with no history of ocular disease were processed between 4 and 22 hours, with a median delay of 14 hours postmortem.

RESULTS

Age-dependent expression was evident in C5b-9, APP, CD11b, and RCA-I, but not CD36, immunoreactivity. Immunoreactivity for C5b-9 was robust in Bruch membrane (BM) and the intercapillary pillars of Bruch. Immunoreactivity for APP was robust in the basal cytoplasm of the retinal pigment epithelium. Immunoreactivity for CD11b was robust on the surface of the retinal pigment epithelial cell, in the choriocapillaris, and in BM. Lectin binding of RCA-I was strong throughout the neuroretina.

CONCLUSIONS

Robust immunostaining for APP in older donor eyes suggested that amyloid beta peptides may be one of the triggers of complement activation during the normal aging process. Microglial markers CD11b and RCA-I also increase with age, suggesting a concomitant inflammatory response to C5b-9 deposits in the retinal pigment epithelium, BM, and CC. Immunoreactivity for CD36 was strong in both age groups; the lack of age dependence in this candidate receptor for amyloid beta suggested that complement activation may arise from interactions of amyloid beta with other candidate receptors in normal human retina.

The role of complement system in ocular diseases including uveitis and macular degeneration

In the normal eye, the complement system is continuously activated at low levels and both membrane-bound and soluble intraocular complement regulatory proteins tightly regulate this spontaneous complement activation. This allows protection against pathogens without causing any damage to self-tissue and vision loss. The complement system and complement regulatory proteins control the intraocular inflammation in autoimmune uveitis and play an important role in the development of corneal inflammation, age-related macular degeneration and diabetic retinopathy. The evidence derived from both animal models and patient studies support the concept that complement inhibition is a relevant therapeutic target in the treatment of various ocular diseases. Currently, several clinical trials using complement inhibitors are going on. It is possible that, in the near future, complement inhibitors might be used as therapeutic agents in eye clinics.

Age-related macular degeneration: a perspective on genetic studies

AIM

Age-related macular degeneration (AMD) is a common macular disease in the developed world and recent studies have shown that specific genes may be associated with it and may contribute to a higher risk of developing AMD.

OBJECTIVE

Our objective was to review systematically recent publications related to the genetics of AMD and provide relevant information that would help both scientists and clinicians in advising patients.

METHOD

A systematic search was performed on PubMed, Medline, and National Library of Medicine as well as ARVO abstracts using key words relevant to the genetic associations of AMD.

RESULTS

The most important genetic associations in AMD involved the complement factor H (CFH) gene, which showed that possession of the variant Y402H polymorphism significantly increases the risk for AMD. Protective genes have also been identified such as those on either factor B (BFor complement factor B (CFB)) or complement component 2 (C2) genes. The genes involved in inherited macular dystrophies such as ATP-binding cassette, subfamily A (ABC1), member 4 (ABCA4), vitelliform macular dystrophy (VMD2), tissue inhibitor of matrix metalloproteinase-3 (TIMP3), and EFEMP1have yielded some important information but further confirmatory work has yet to establish a clear association with AMD.

CONCLUSION

Patients with AMD possess specific genetic variants of the CFHgene, which put them at a higher risk of developing the disease. Other unaffected individuals may possess certain protective genetic variants, which could prevent them from developing AMD. Further research will no doubt shed light on other such mechanisms and these will be useful in identifying possible direct targets for drugs or indirectly through modulation of the genes responsible for disease presentation.

New therapeutic targets in atrophic age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in developed countries. There is no effective treatment for the most prevalent atrophic (dry) form of AMD. Atrophic AMD is triggered by abnormalities in the retinal pigment epithelium (RPE) that lies beneath the photoreceptor cells and normally provides critical metabolic support to these light-sensing cells. Secondary to RPE dysfunction, macular rods and cones degenerate leading to the irreversible loss of vision. Oxidative stress, formation of drusen, accumulation of lipofuscin, local inflammation and reactive gliosis represent the pathologic processes implicated in pathogenesis of atrophic AMD. This review discusses potential target areas for small-molecule and biologic intervention, which may lead to development of new therapeutic treatments for atrophic AMD.

Age-related decline in VIP-positive parasympathetic nerve fibers in the human submacular choroid

PURPOSE

An age-related decline in macular choroidal blood flow (ChBF) occurs in humans. Vasodilatory nerve fibers containing vasoactive intestinal polypeptide (VIP) innervate choroidal blood vessels. The current study was conducted to examine the possibility that an age-related loss of these fibers might occur in the submacular choroid in humans, and thus contribute to a decline in ChBF.

METHODS

Macular choroid punches were collected from 35 healthy human donors ranging from 21 to 93 years of age. Choroidal samples were immunolabeled using anti-VIP and the peroxidase-antiperoxidase

METHOD

VIP-positive nerve fiber abundance was quantified in up to 12 fields per punch. Fifty macular punches were analyzed, and results for eye pairs were averaged. Choroidal vessel diameter (ChVD) was measured for these same fields. The relationship between age and vessel diameter or VIP-positive fiber abundance was analyzed. Multivariate statistical models were generated correcting for gender, variables related to the tissue specimens, and potential procedural sources of variability.

RESULTS

The fully adjusted multivariate models showed a significant age-related reduction in both the VIP-positive fiber abundance (P = 0.0003, adjusted R(2) = 0.51) and ChVD (P < 0.0001, adjusted R(2) = 0.63), with slopes of -0.45 and -0.19, respectively. Adjusting for the same variables, VIP-positive fiber abundance showed a significant direct correlation with ChVD.

CONCLUSIONS

The results indicate a significant age-related decline in VIP-positive nerve fibers and vessel diameter in the submacular choroid in disease-free human donor eyes. These findings suggest that a decline in the neural control of ChBF and vessel diameter may explain the reductions in ChBF and its adaptive control observed clinically with aging.

Systematic review and meta-analysis of the association between complement factor H Y402H polymorphisms and age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world and complement factor H (CFH) polymorphism has been found to associated with the AMD. We performed a meta-analysis to estimate the magnitude of the gene effect and the possible mode of action. A meta-analysis of eight studies assessing association between the CFH Y402H polymorphism and AMD was performed. Data extraction and study quality assessment were performed in duplicate, and heterogeneity and publication bias were explored. There was strong evidence for association between CFH and AMD, with those having CC and TC genotypes being roughly six and 2.5 times more likely to have AMD than patients with TT genotype, suggesting a co-dominant, multiplicative genetic model. The population attributable risk for the CC/TC genotype is 58.9%, i.e. the CFH polymorphism is involved in over half of all AMD. This meta-analysis summarizes the strong evidence for an association between CFH and AMD and indicates a multiplicative model with each C allele increasing the odds of AMD by approximately 2.5-fold. This result is at least as important at the population level as ApoE4 and Alzheimer's disease, playing a role in almost 60% of AMD at the population level.

Extended haplotypes in the complement factor H (CFH) and CFH-related (CFHR) family of genes protect against age-related macular degeneration: Characterization, ethnic distribution and evolutionary implications

BACKGROUND

Variants in the complement factor H gene (CFH) are associated with age-related macular degeneration (AMD). CFH and five CFH-related genes (CFHR1-5) lie within the regulators of complement activation (RCA) locus on chromosome 1q32.

AIMS AND METHODS

In this study, the structural and evolutionary relationships between these genes and AMD was refined using a combined genetic, molecular and immunohistochemical approach.

RESULTS

We identify and characterize a large, common deletion that encompasses both the CFHR1 and CFHR3 genes. CFHR1, an abundant serum protein, is absent in subjects homozygous for the deletion. Genotyping analyses of AMD cases and controls from two cohorts demonstrates that deletion homozygotes comprise 1.1% of cases and 5.7% of the controls (chi-square = 32.8; P = 1.6 E-09). CFHR1 and CFHR3 transcripts are abundant in liver, but undetectable in the ocular retinal pigmented epithelium/choroid complex. AMD-associated CFH/CFHR1/CFHR3 haplotypes are widespread in human populations.

CONCLUSION

The absence of CFHR1 and/or CFHR3 may account for the protective effects conferred by some CFH haplotypes. Moreover, the high frequencies of the 402H allele and the delCFHR1/CFHR3 alleles in African populations suggest an ancient origin for these alleles. The considerable diversity accumulated at this locus may be due to selection, which is consistent with an important role for the CFHR genes in innate immunity.