Investigation of oral fenretinide for treatment of geographic atrophy in age-related macular degeneration

Emerging Oral Pharmaceuticals for Dry Age-Related Macular Degeneration: Mechanism of Action, Current Clinical Status, and Future Directions

Dry age-related macular degeneration (AMD) has been historically managed with lifestyle modifications, monitoring for conversion to wet AMD, and vitamins. Recently there has been a flurry of research focused on discovering new targets to prevent worsening of dry AMD. In 2023, the US Food and Drug Administration approved the first two intravitreal complement inhibitors to slow the rate of geographic atrophy progression. However, serial intravitreal injections for a chronic progressive disease are burdensome for patients and have procedural risks. Therefore, there is significant research to discover novel oral medications to manage dry AMD. Several oral medications are currently in phase 2 and 3 clinical trials for dry AMD, whereas others have had recent readouts on their clinical trials and efficacy. The purpose of this review is to describe the therapeutic pathways currently being investigated and to provide an update on the clinical status of novel oral medications for the management of dry AMD. [Ophthalmic Surg Lasers Imaging Retina 2024;55:528-534.].

Emerging Therapeutic Approaches and Genetic Insights in Stargardt Disease: A Comprehensive Review

Stargardt disease, one of the most common forms of inherited retinal diseases, affects individuals worldwide. The primary cause is mutations in the ABCA4 gene, leading to the accumulation of toxic byproducts in the retinal pigment epithelium (RPE) and subsequent photoreceptor cell degeneration. Over the past few years, research on Stargardt disease has advanced significantly, focusing on clinical and molecular genetics. Recent studies have explored various innovative therapeutic approaches, including gene therapy, stem cell therapy, and pharmacological interventions. Gene therapy has shown promise, particularly with adeno-associated viral (AAV) vectors capable of delivering the ABCA4 gene to retinal cells. However, challenges remain due to the gene's large size. Stem cell therapy aims to replace degenerated RPE and photoreceptor cells, with several clinical trials demonstrating safety and preliminary efficacy. Pharmacological approaches focus on reducing toxic byproduct accumulation and modulating the visual cycle. Precision medicine, targeting specific genetic mutations and pathways, is becoming increasingly important. Novel techniques such as clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 offer potential for directly correcting genetic defects. This review aims to synthesize recent advancements in understanding and treating Stargardt disease. By highlighting breakthroughs in genetic therapies, stem cell treatments, and novel pharmacological strategies, it provides a comprehensive overview of emerging therapeutic options.

Advancements in Imaging and Therapeutic Options for Dry Age-Related Macular Degeneration and Geographic Atrophy

Age-related macular degeneration (AMD) is a leading cause of vision loss in the elderly, with dry AMD (d-AMD) leading to geographic atrophy (GA) and significant visual impairment. Multimodal imaging plays a crucial role in d-AMD diagnosis and management, allowing for detailed classification of patient phenotypes and aiding in treatment planning and prognosis determination. Treatment approaches for d-AMD have recently witnessed profound change with the development of specific drugs targeting the complement cascade, with the first anticomplement agents recently approved for GA treatment. Additionally, emerging strategies such as gene therapy and laser treatments may offer potential benefits, though further research is needed to fully establish their efficacy. However, the lack of effective therapies capable of restoring damaged retinal cells remains a major challenge. In the future, genetic treatments aimed at preventing the progression of d-AMD may emerge as a powerful approach. Currently, however, their development is still in the early stages.

Quantitative Autofluorescence at AMD's Beginnings Highlights Retinal Topography and Grading System Differences: ALSTAR2 Baseline

INTRODUCTION

The aims of the study were to describe baseline quantitative (short-wavelength) autofluorescence (qAF) findings in a large pseudophakic cohort at age-related macular degeneration (AMD)'s beginnings and to assess qAF8 as an outcome measure and evaluate Age-Related Eye Disease Study (AREDS) and Beckman grading systems.

METHODS

In the ALSTAR2 baseline cohort (NCT04112667), 346 pseudophakic eyes of 188 persons (74.0 ± 5.5 years) were classified as normal (N = 160 by AREDS, 158 by Beckman), early AMD (eAMD) (N = 104, 66), and intermediate AMD (iAMD) (N = 82, 122). Groups were compared via mean qAF intensities in a 6°-8° annulus (qAF8) and maps of differences between observations and the overall mean, divided by standard deviation (Z-score).

RESULTS

qAF8 did not differ significantly among diagnostic groups by either stratification (p = 0.0869 AREDS; p = 0.0569 by Beckman). Notably, 45 eyes considered eAMD by AREDS became iAMD by Beckman. For AREDS-stratified eyes, Z-score maps showed higher centrally located qAF for normal, near the mean in eAMD, and lower values for iAMD. Maps deviated from this pattern for Beckman-stratified eyes.

CONCLUSIONS

In a large sample of pseudophakic eyes, qAF8 does not differ overall from normal aging to iAMD but also does not capture the earliest AMD activity in the macula lutea. AREDS classification gives results more consistent with a slow decline in histologic autofluorescence than Beckman classification.

Recent Advances on Small-Molecule Inhibitors of Lipocalin-like Proteins

Lipid transfer proteins (LTPs) are crucial players in nonvesicular lipid trafficking. LTPs sharing a lipocalin lipid transfer domain (lipocalin-like proteins) have a wide range of biological functions, such as regulating immune responses and cell proliferation, differentiation, and death as well as participating in the pathogenesis of inflammatory, metabolic, and neurological disorders and cancer. Therefore, the development of small-molecule inhibitors targeting these LTPs is important and has potential clinical applications. Herein, we summarize the structure and function of lipocalin-like proteins, mainly including retinol-binding proteins, lipocalins, and fatty acid-binding proteins and discuss the recent advances on small-molecule inhibitors for these protein families and their applications in disease treatment. The findings of our Perspective can provide guidance for the development of inhibitors of these LTPs and highlight the challenges that might be faced during the procedures.

Geographic atrophy: pathophysiology and current therapeutic strategies

Geographic atrophy (GA) is an advanced stage of age-related macular degeneration (AMD) that leads to gradual and permanent vision loss. GA is characterized by the loss of photoreceptor cells and retinal pigment epithelium (RPE), leading to distinct atrophic patches in the macula, which tends to increase with time. Patients with geographic atrophy often experience a gradual and painless loss of central vision, resulting in difficulty reading, recognizing faces, or performing activities that require detailed vision. The primary risk factor for the development of geographic atrophy is advanced age; however, other risk factors, such as family history, smoking, and certain genetic variations, are also associated with AMD. Diagnosis is usually based on a comprehensive eye examination, including imaging tests such as fundus photography, optical coherence tomography (OCT), and fluorescein angiography. Numerous clinical trials are underway, targeting identified molecular pathways associated with GA that are promising. Recent approvals of Syfovre and Izervay by the FDA for the treatment of GA provide hope to affected patients. Administration of these drugs resulted in slowing the rate of progression of the disease. Though these products provide treatment benefits to the patients, they do not offer a cure for geographic atrophy and are limited in efficacy. Considering these safety concerns and limited treatment benefits, there is still a significant need for therapeutics with improved efficacy, safety profiles, and better patient compliance. This comprehensive review discusses pathophysiology, currently approved products, their limitations, and potential future treatment strategies for GA.

Advancements in the treatment of geographic atrophy: focus on pegcetacoplan in age-related macular degeneration

Geographic atrophy (GA) is a progressive form of age-related macular degeneration characterized by the degeneration of retinal pigment epithelial cells and photoreceptor death. The dysregulation of the complement cascade has been implicated in GA progression. This review provides a comprehensive overview of the pathophysiology of age-related macular degeneration and GA, discusses current therapeutic options, and focuses on the recent breakthrough drug, pegcetacoplan (SYFOVRE). Pegcetacoplan is a complement inhibitor that selectively targets the C3 complement protein, effectively modulating complement activation. Clinical trials, including the OAKS and DERBY studies, have demonstrated the efficacy of SYFOVRE in reducing the growth of GA lesions compared to placebo. The FDA approval of SYFOVRE as the first and only definitive therapy for GA marks a significant milestone in the management of this debilitating condition. The review also explores potential future treatment strategies, including immune-modulating agents and ocular gene therapy. While SYFOVRE offers new hope for GA patients, further research is needed to evaluate its long-term benefits, safety profile, and optimal treatment regimens.

Targeting Retinol-Binding Protein 4 (RBP4) in the Management of Cardiometabolic Diseases

The ancient use of herbs for the treatment of various human diseases have been documented, with several scientific literatures supporting the use of medicinal plants. There is however a major concern about the phyto-constituents in the plants that performs the healing function and the mechanism by which it works for different ailments are still a research prospect. Cardiometabolic disease (CMD) is no doubt becoming more frequent globally and this is due to poor approach in therapy, contrary effects linked with intensive control, inept strategies with old drugs, inadequate control of some risk factors and lack of knowledge of the pathophysiological mechanisms that lead to this malaise. Retinol-binding protein 4 (RBP4) are predominantly secreted in the liver and adipose tissues and several researches have observed that elevation in serum levels of RBP4 often observed in obese experimental animals and human subjects causes CMD (obesity, insulin resistance, hyperlipidemia, etc.). RBP4 has gained special attention in the last 20 years in the field of metabolism research. This review aims to show research interaction of some medicinal plants targeting RBP4 in treating CMD and to encourage researchers, who are interested in CMD drug design, to focus on medicinal plants that inhibit the secretion of serum RBP4 in the adipose tissue for therapeutic approach to CMD. It also aims to identify the major bioactive compounds of plants that serves as a better and cheaper drug candidate for CMD and also study the signaling pathway which the plant material uses to regulate the metabolic consequences.

Biomaterials used for tissue engineering of barrier-forming cell monolayers in the eye

Cell monolayers that form a barrier between two structures play an important role for the maintenance of tissue functionality. In the anterior portion of the eye, the corneal endothelium forms a barrier that controls fluid exchange between the aqueous humor of the anterior chamber and the corneal stroma. This monolayer is central in the pathogenesis of Fuchs endothelial corneal dystrophy (FECD). FECD is a common corneal disease, in which corneal endothelial cells deposit extracellular matrix that increases the thickness of its basal membrane (Descemet's membrane), and forms excrescences (guttae). With time, there is a decrease in endothelial cell density that generates vision loss. Transplantation of a monolayer of healthy corneal endothelial cells on a Descemet membrane substitute could become an interesting alternative for the treatment of this pathology. In the back of the eye, the retinal pigment epithelium (RPE) forms the blood-retinal barrier, controlling fluid exchange between the choriocapillaris and the photoreceptors of the outer retina. In the retinal disease dry age-related macular degeneration (dry AMD), deposits (drusen) form between the RPE and its basal membrane (Bruch's membrane). These deposits hinder fluid exchange, resulting in progressive RPE cell death, which in turn generates photoreceptor cell death, and vision loss. Transplantation of a RPE monolayer on a Bruch's membrane/choroidal stromal substitute to replace the RPE before photoreceptor cell death could become a treatment alternative for this eye disease. This review will present the different biomaterials that are proposed for the engineering of a monolayer of corneal endothelium for the treatment of FECD, and a RPE monolayer for the treatment of dry AMD.

Updates on Emerging Interventions for Autosomal Recessive ABCA4-Associated Stargardt Disease

Autosomal recessive Stargardt disease (STGD1) is an inherited retinal degenerative disease associated with a mutated ATP-binding cassette, subfamily A, member 4 (ABCA4) gene. STGD1 is the most common form of juvenile macular degeneration with onset in late childhood to early or middle adulthood and causes progressive, irreversible visual impairment and blindness. No effective treatment is currently available. In the present article, we review the most recent updates in clinical trials targeting the management of STGD1, including gene therapy, small molecule therapy, and stem cell therapy. In gene therapy, dual adeno-associated virus and non-viral vectors have been successful in delivering the human ABCA4 gene in preclinical studies. For pharmaceutical therapies ALK-001, deuterated vitamin A shows promise with preliminary data for phase 2 trial, demonstrating a decreased atrophy growth rate after two years. Stem cell therapy using human pluripotent stem cell-derived retinal pigment epithelium cells demonstrated long-term safety three years after implantation and visual acuity improvements in the first two years after initiation of therapy. Many other treatment options have ongoing investigations and clinical trials. While multiple potential interventions have shown promise in attenuating disease progression, further exploration is necessary to demonstrate treatment safety and efficacy.

Analysis of Retinol Binding Protein 4 and ABCA4 Gene Variation in Non-Neovascular Age-Related Macular Degeneration

Age-related macular degeneration (AMD) may be associated with ABCA4 variants and is characterized by the accumulation of visual cycle-byproduct lipofuscin. Reducing retinol-binding protein 4 (RBP4), a retinol transporter protein, may reduce lipofuscin production. This study aims to assess the associations between plasma RBP4, the ABCA4 variation, and AMD severity. Sixty-seven participants were grouped into healthy/mild AMD (n = 32) and severe AMD (n = 35) groups. The latter group was older than the former group and had higher levels of RBP4 (36.8 ± 8.3 vs. 30.4 ± 7.0 μg/mL, p = 0.0012). The ten participants with six ABCA4 linked-variants had higher RBP4 than those without (37.8 ± 7.7 vs. 32.4 ± 7.9 μg/mL; p = 0.026), and eight of them had severe AMD. Univariate analyses showed that severe AMD was related to older age (OR, 1.26; 95% CI, 1.13-1.40; p < 0.0001) and to higher RBP4 levels (OR, 1.12; 95% CI, 1.04-1.20; p = 0.003), whereas the linked ABCA4 variants had no associations. After adjustment, however, only age remained significantly associated with severe AMD. This pilot study shows a trend of higher plasma RBP4 levels in severe AMD or the ABCA4-linked variants, and further age-matched studies are warranted.

Novel oral medications for retinal disease: an update on clinical development

PURPOSE OF REVIEW

Intravitreal and periocular injections for retinal disease provide a targeted delivery of medication to the eye. However, given risks of injections, including endophthalmitis, pain and treatment burden for both patients and retina specialists, there has been significant interest and effort in developing oral medications for the management of retinal disease. This article provides clinical and preclinical details of new oral medications in the pipeline for management of retinal disease.

RECENT FINDINGS

Several new oral medications show clinical and preclinical promise for the management of retinal disease, including macular degeneration, diabetic retinopathy and Stargardt disease.

SUMMARY

Oral medications provide promise for treating retinal disease, possibly increasing compliance, and reducing side effects of intravitreal or periocular injections. However, difficulties in this approach include systemic side effects and efficacy targeting the eye. There are multiple medications that are currently under investigation with the potential to act as stand-alone treatment or as an adjunct treatment for management of retinal diseases such as diabetic retinopathy, macular degeneration and Stargardt disease.

Quantitative Autofluorescence in Non-Neovascular Age Related Macular Degeneration

Quantitative autofluorescence (qAF8) level is a presumed surrogate marker of lipofuscin content in the retina. We investigated the changes in the qAF8 levels in non-neovascular AMD. In this prospective cohort study, Caucasians aged ≥50 years with varying severity of non-neovascular AMD in at least one eye and Snellen visual acuity ≥6/18 were recruited. The qAF8 levels were analysed in the middle eight segments of the Delori pattern (HEYEX software, Heidelberg, Germany). The AMD categories were graded using both the Beckman classification and multimodal imaging (MMI) to include the presence of subretinal drusenoid deposits (SDD). A total of 353 eyes from 231 participants were analyzed. Compared with the age-matched controls, the qAF8 values decreased in the eyes with AMD (adjusted % difference = -19.7% [95% CI -28.8%, -10.4%]; p < 0.001) and across the AMD categories, (adjusted % differences; Early, -13.1% (-24.4%, -1%), p = 0.04; intermediate AMD (iAMD), -22.9% (-32.3%, -13.1%), p < 0.001; geographic atrophy -25.2% (-38.1%, -10.4%), p = 0.002). On MMI, the qAF8 was reduced in the AMD subgroups relative to the controls, (adjusted % differences; Early, -5.8% (-18.9%, 8.3%); p = 0.40; iAMD, -26.7% (-36.2%, -15.6%); p < 0.001; SDD, -23.7% (-33.6%, -12.2%); p < 0.001; atrophy, -26.7% (-39.3%, -11.3%), p = 0.001). The qAF8 levels declined early in AMD and were not significantly different between the severity levels of non-neovascular AMD, suggesting the early and sustained loss of function of the retinal pigment epithelium in AMD.

RPE-Directed Gene Therapy Improves Mitochondrial Function in Murine Dry AMD Models

Age-related macular degeneration (AMD) is the most common cause of blindness in the aged population. However, to date there is no effective treatment for the dry form of the disease, representing 85-90% of cases. AMD is an immensely complex disease which affects, amongst others, both retinal pigment epithelium (RPE) and photoreceptor cells and leads to the progressive loss of central vision. Mitochondrial dysfunction in both RPE and photoreceptor cells is emerging as a key player in the disease. There are indications that during disease progression, the RPE is first impaired and RPE dysfunction in turn leads to subsequent photoreceptor cell degeneration; however, the exact sequence of events has not as yet been fully determined. We recently showed that AAV delivery of an optimised NADH-ubiquinone oxidoreductase (NDI1) gene, a nuclear-encoded complex 1 equivalent from S. cerevisiae, expressed from a general promoter, provided robust benefit in a variety of murine and cellular models of dry AMD; this was the first study employing a gene therapy to directly boost mitochondrial function, providing functional benefit in vivo. However, use of a restricted RPE-specific promoter to drive expression of the gene therapy enables exploration of the optimal target retinal cell type for dry AMD therapies. Furthermore, such restricted transgene expression could reduce potential off-target effects, possibly improving the safety profile of the therapy. Therefore, in the current study, we interrogate whether expression of the gene therapy from the RPE-specific promoter, Vitelliform macular dystrophy 2 (VMD2), might be sufficient to rescue dry AMD models.

Pretreatment of human retinal pigment epithelial cells with sterculic acid forestalls fenretinide-induced apoptosis

The ratio of saturated to monounsaturated fatty acids, thought to play a critical role in many cellular functions, is regulated by stearoyl-CoA desaturase (SCD), a rate-limiting enzyme in the biosynthesis of monounsaturated fatty acids. Previously, we observed a decrease in both SCD protein and enzymatic activity in apoptosis induced by fenretinide, a synthetic analog of retinoic acid, in the human retinal pigment epithelial (RPE) cell line ARPE-19. Here, we investigated the effect of pretreating ARPE-19 with sterculic acid, a cyclopropenoic fatty acid inhibitor of SCD, on preventing fenretinide-induced apoptosis, given the role of SCD in cell proliferation and apoptosis. We show that sterculic acid pretreatment prevents the effects of fenretinide-induced apoptosis shown by changes in cell morphology, viability, and caspase-3 activation. Analysis of endoplasmic reticulum (ER)-associated proteins shows that sterculic acid pretreatment reduced the fenretinide-induced upregulation of heme oxygenase-1, ATF3 and GADD153 expression that are in response to reactive oxygen species (ROS) generation. Sterculic acid is as effective as allopurinol in inhibition of xanthine oxidase (XDH), and this may play a role in reducing the potential role of XDH in fenretinide-induced ROS generation. Sterculic acid pretreatment also results in a reduction in SOD2 mRNA expression. Dihydroceramide accumulation, compared to ceramide, and ROS generation indicate that a ceramide-independent pathway mediates fenretinide-induced apoptosis, and ROS mediation is borne out by activation of the NF-κBp50 and NF-κBp65 downstream signaling cascade. Its prevention by sterculic acid pretreatment further indicates the latter's antioxidant/anti-inflammatory effect. Taken together, our results suggest that sterculic acid pretreatment can mitigate ROS-mediated fenretinide-induced apoptosis. Thus, sterculic acid may serve as a potential antioxidant and therapeutic agent. These effects may be independent of its effects on SCD activity.

Electroretinography as a Biomarker to Monitor the Progression of Stargardt Disease

The aim of the present study is to determine how electroretinographic (ERG) responses reflect age-related disease progression in the Stargardt disease (STGD1). The prospective comparative cohort study included 8 patients harboring two null ABCA4 variants (Group 1) and 34 patients with other ABCA4 genotypes (Group 2). Age at exam, age at onset, visual acuity (VA) and ERG responses were evaluated. The correlation between ERG responses and age in each patient group was determined using linear regression. A Mann-Whitney U Test was used to compare the median values between the groups. Age of onset was significantly earlier in Group 1 than in Group 2 (8 vs. 18), while disease duration was similar (13 vs. 12 years, i.e., advanced stage). Group 1 had significantly worse VA and lower ERG responses. ERG responses that significantly correlated with age in Group 1 were DA 0.01 and 3.0 ERG, which represented a retinal rod system response. The only ERG response that significantly correlated with age in Group 2 was the S-cone ERG. The observed difference was likely due to early cone loss occurring in double-null patients and slower photoreceptor loss in patients with other genotypes. The results suggest that specific ERG responses may be used to detect double-null patients at an early stage and monitor STGD1 disease progression in patients with specific genotypes.

Investigational drugs in clinical trials for macular degeneration

INTRODUCTION

Intravitreal anti-vascular endothelial growth factor (VEGF) injections for exudative age-related macular degeneration (eAMD) are effective and safe but require frequent injections and have nonresponding patients. Geographic atrophy/dry AMD (gaAMD) remains an unmet medical need . New therapies are needed to address this leading cause of blindness in the increasing aged population.

AREAS COVERED

This paper reviews the pathogenesis of macular degeneration, current and failed therapeutics, therapies undergoing clinical trials and a rationale for why certain AMD therapies may succeed or fail .

EXPERT OPINION

VEGF- inhibitors reduce both vascular leakage and neovascularization. Experimental therapies that only address neovascularization or leakage will unlikely supplant anti-VEGF therapies. The most promising future therapies for eAMD, are those that target, more potently inhibit and have a more sustained effect on the VEGF pathway such as KSI-301, RGX-314, CLS-AX, EYEP-1901, OTX-TKI.

GaAMD is a phenotype of phagocytic retinal cell loss. Inhibiting phagocytic activity of retinal microglial/macrophages at the border of GA and reducing complement derived activators of microglial/macrophage is the most promising strategy. Complement inhibitors (Pegcetacoplan and Avacincaptad pegol) will likely obtain FDA approval but will serve to pave the way for combined complement and direct phagocytic inhibitors such as AVD-104.

Recent Advances in Age-Related Macular Degeneration Therapies

Age-related macular degeneration (AMD) was described for the first time in the 1840s and is currently the leading cause of blindness for patients over 65 years in Western Countries. This disease impacts the eye’s posterior segment and damages the macula, a retina section with high levels of photoreceptor cells and responsible for the central vision. Advanced AMD stages are divided into the atrophic (dry) form and the exudative (wet) form. Atrophic AMD consists in the progressive atrophy of the retinal pigment epithelium (RPE) and the outer retinal layers, while the exudative form results in the anarchic invasion by choroidal neo-vessels of RPE and the retina. This invasion is responsible for fluid accumulation in the intra/sub-retinal spaces and for a progressive dysfunction of the photoreceptor cells. To date, the few existing anti-AMD therapies may only delay or suspend its progression, without providing cure to patients. However, in the last decade, an outstanding number of research programs targeting its different aspects have been initiated by academics and industrials. This review aims to bring together the most recent advances and insights into the mechanisms underlying AMD pathogenicity and disease evolution, and to highlight the current hypotheses towards the development of new treatments, i.e., symptomatic vs. curative. The therapeutic options and drugs proposed to tackle these mechanisms are analyzed and critically compared. A particular emphasis has been given to the therapeutic agents currently tested in clinical trials, whose results have been carefully collected and discussed whenever possible.

Neuroprotection for Age-Related Macular Degeneration

Age-related macular degeneration (AMD) is a leading cause of blindness worldwide. Early to intermediate AMD is characterized by the accumulation of lipid- and protein-rich drusen. Late stages of the disease are characterized by the development of choroidal neovascularization, termed "exudative" or "neovascular AMD," or retinal pigment epithelium (RPE) cell and photoreceptor death, termed "geographic atrophy" (GA) in advanced nonexudative AMD. Although we have effective treatments for exudative AMD in the form of anti-VEGF agents, they have no role for patients with GA. Neuroprotection strategies have emerged as a possible way to slow photoreceptor degeneration and vision loss in patients with GA. These approaches include reduction of oxidative stress, modulation of the visual cycle, reduction of toxic molecules, inhibition of pathologic protein activity, prevention of cellular apoptosis or programmed necrosis (necroptosis), inhibition of inflammation, direct activation of neurotrophic factors, delivery of umbilical tissue-derived cells, and RPE replacement. Despite active investigation in this area and significant promise based on preclinical studies, many clinical studies have not yielded successful results. We discuss selected past and current neuroprotection trials for AMD, highlight the lessons learned from these past studies, and discuss our perspective regarding remaining questions that must be answered before neuroprotection can be successfully applied in the field of AMD research.

Fenretinide in Cancer and Neurological Disease: A Two-Face Janus Molecule

Recently, several chemotherapeutic drugs have been repositioned in neurological diseases, based on common biological backgrounds and the inverse comorbidity between cancer and neurodegenerative diseases. Fenretinide (all-trans-N-(4-hydroxyphenyl) retinamide, 4-HPR) is a synthetic derivative of all-trans-retinoic acid initially proposed in anticancer therapy for its antitumor effects combined with limited toxicity. Subsequently, fenretinide has been proposed for other diseases, for which it was not intentionally designed for, due to its ability to influence different biological pathways, providing a broad spectrum of pharmacological effects. Here, we review the most relevant preclinical and clinical findings from fenretinide and discuss its therapeutic role towards cancer and neurological diseases, highlighting the hormetic behavior of this pleiotropic molecule.

Retinoid Homeostasis and Beyond: How Retinol Binding Protein 4 Contributes to Health and Disease

Retinol binding protein 4 (RBP4) is the specific transport protein of the lipophilic vitamin A, retinol, in blood. Circulating RBP4 originates from the liver. It is secreted by hepatocytes after it has been loaded with retinol and binding to transthyretin (TTR). TTR association prevents renal filtration due to the formation of a higher molecular weight complex. In the circulation, RBP4 binds to specific membrane receptors, thereby delivering retinol to target cells, rendering liver-secreted RBP4 the major mechanism to distribute hepatic vitamin A stores to extrahepatic tissues. In particular, binding of RBP4 to 'stimulated by retinoic acid 6' (STRA6) is required to balance tissue retinoid responses in a highly homeostatic manner. Consequently, defects/mutations in RBP4 can cause a variety of conditions and diseases due to dysregulated retinoid homeostasis and cover embryonic development, vision, metabolism, and cardiovascular diseases. Aside from the effects related to retinol transport, non-canonical functions of RBP4 have also been reported. In this review, we summarize the current knowledge on the regulation and function of RBP4 in health and disease derived from murine models and human mutations.

Baseline Levels of Retinol Binding Protein 4 and Vitamin A in Healthy Subjects, Stargardt Disease and Geographic Atrophy Patients

INTRODUCTION

The accumulation of lipofuscin is a hallmark in the pathogenesis of Stargardt disease (STGD1) and geographic atrophy (GA) secondary to age-related macular degeneration (AMD). Limiting lipofuscin accumulation by inhibiting the retinol binding protein 4 (RBP4) is being explored as a potential treatment target for those diseases. In this study, we aimed to establish the concentration of RBP4 in the systemic circulation in different age cohorts of healthy individuals and to check if patients with STGD1 or GA may show abnormal RBP4 levels.

METHODS

40 healthy subjects of various age groups, 15 Stargardt patients and 15 GA patients were included in the study. We measured RBP4 levels, serum retinol (SR) levels, complete blood count (CBC), and blood chemistry including liver function tests.

RESULTS

Mean RBP4 for all cohorts was 26'911.40 ± 6'198.61 ng/mL and mean SR 1.75 ± 0.36 µmol/L. Age was not found to significantly impact levels neither of RBP4 and SR nor of the RBP4-to-SR ratio. Also, the two patient groups showed similar blood levels to their age-matched controls.

DISCUSSION/CONCLUSION

Serum RBP4 and SR do not appear to be affected by age in healthy individuals and remain within normal limits in both STGD1 and GA.

Fenretinide inhibits vitamin A formation from β-carotene and regulates carotenoid levels in mice

N-[4-hydroxyphenyl]retinamide, commonly known as fenretinide, a synthetic retinoid with pleiotropic benefits for human health, is currently utilized in clinical trials for cancer, cystic fibrosis, and COVID-19. However, fenretinide reduces plasma vitamin A levels by interacting with retinol-binding protein 4 (RBP4), which often results in reversible night blindness in patients. Cell culture and in vitro studies show that fenretinide binds and inhibits the activity of β-carotene oxygenase 1 (BCO1), the enzyme responsible for endogenous vitamin A formation. Whether fenretinide inhibits vitamin A synthesis in mammals, however, remains unknown. The goal of this study was to determine if the inhibition of BCO1 by fenretinide affects vitamin A formation in mice fed β-carotene. Our results show that wild-type mice treated with fenretinide for ten days had a reduction in tissue vitamin A stores accompanied by a two-fold increase in β-carotene in plasma (P < 0.01) and several tissues. These effects persisted in RBP4-deficient mice and were independent of changes in intestinal β-carotene absorption, suggesting that fenretinide inhibits vitamin A synthesis in mice. Using Bco1-/- and Bco2-/- mice we also show that fenretinide regulates intestinal carotenoid and vitamin E uptake by activating vitamin A signaling during short-term vitamin A deficiency. This study provides a deeper understanding of the impact of fenretinide on vitamin A, carotenoid, and vitamin E homeostasis, which is crucial for the pharmacological utilization of this retinoid.

The Role of Vitamin A in Retinal Diseases

Vitamin A is an essential fat-soluble vitamin that occurs in various chemical forms. It is essential for several physiological processes. Either hyper- or hypovitaminosis can be harmful. One of the most important vitamin A functions is its involvement in visual phototransduction, where it serves as the crucial part of photopigment, the first molecule in the process of transforming photons of light into electrical signals. In this process, large quantities of vitamin A in the form of 11-cis-retinal are being isomerized to all-trans-retinal and then quickly recycled back to 11-cis-retinal. Complex machinery of transporters and enzymes is involved in this process (i.e., the visual cycle). Any fault in the machinery may not only reduce the efficiency of visual detection but also cause the accumulation of toxic chemicals in the retina. This review provides a comprehensive overview of diseases that are directly or indirectly connected with vitamin A pathways in the retina. It includes the pathophysiological background and clinical presentation of each disease and summarizes the already existing therapeutic and prospective interventions.

Retinol binding protein 4 antagonists and protein synthesis inhibitors: Potential for therapeutic development

Retinol-binding protein 4 (RBP4) is a serum protein that transports Vitamin A. RBP4 is correlated with numerous diseases and metabolic syndromes, including insulin resistance in type 2 diabetes, cardiovascular diseases, obesity, and macular degeneration. Recently, RBP4 antagonists and protein synthesis inhibitors are under development to regulate the effect of RBP4. Several RBP4 antagonists, especially BPN-14136, have demonstrated promising safety profiles and potential therapeutic benefits in animal studies. Two RBP4 antagonists, specifically tinlarebant (Belite Bio) and STG-001 (Stargazer) are currently undergoing clinical trials. Some antidiabetic drugs and nutraceuticals have been reported to reduce RBP4 expression, but more clinical data is needed to evaluate their therapeutical benefits. As regulating RBP4 levels or its activities would benefit a wide range of patients, further research is highly recommended to develop clinically useful RBP4 antagonists or protein synthesis inhibitors.

Therapy Approaches for Stargardt Disease

Despite being the most prevalent cause of inherited blindness in children, Stargardt disease is yet to achieve the same clinical trial success as has been achieved for other inherited retinal diseases. With an early age of onset and continual progression of disease over the life course of an individual, Stargardt disease appears to lend itself to therapeutic intervention. However, the aetiology provides issues not encountered with the likes of choroideremia and X-linked retinitis pigmentosa and this has led to a spectrum of treatment strategies that approach the problem from different aspects. These include therapeutics ranging from small molecules and anti-sense oligonucleotides to viral gene supplementation and cell replacement. The advancing development of CRISPR-based molecular tools is also likely to contribute to future therapies by way of genome editing. In this we review, we consider the most recent pre-clinical and clinical trial data relating to the different strategies being applied to the problem of generating a treatment for the large cohort of Stargardt disease patients worldwide.

Relative Contributions of All-Trans and 11-Cis Retinal to Formation of Lipofuscin and A2E Accumulating in Mouse Retinal Pigment Epithelium

Purpose

Bis-retinoids are a major component of lipofuscin that accumulates in the retinal pigment epithelium (RPE) in aging and age-related macular degeneration (AMD). Although bis-retinoids are known to originate from retinaldehydes required for the light response of photoreceptor cells, the relative contributions of the chromophore, 11-cis retinal, and photoisomerization product, all-trans retinal, are unknown. In photoreceptor outer segments, all-trans retinal, but not 11-cis retinal, is reduced by retinol dehydrogenase 8 (RDH8). Using Rdh8^−/− mice, we evaluated the contribution of increased all-trans retinal to the formation and stability of RPE lipofuscin.

Methods

Rdh8^−/− mice were reared in cyclic-light or darkness for up to 6 months, with selected light-reared cohorts switched to dark-rearing for the final 1 to 8 weeks. The bis-retinoid A2E was measured from chloroform-methanol extracts of RPE-choroid using HPLC-UV/VIS spectroscopy. Lipofuscin fluorescence was measured from whole flattened eyecups (excitation, 488 nm; emission, 565–725 nm).

Results

Cyclic-light-reared Rdh8^−/− mice accumulated A2E and RPE lipofuscin approximately 1.5 times and approximately 2 times faster, respectively, than dark-reared mice. Moving Rdh8^−/− mice from cyclic-light to darkness resulted in A2E levels less than expected to have accumulated before the move.

Conclusions

Our findings establish that elevated levels of all-trans retinal present in cyclic-light-reared Rdh8^−/− mice, which remain low in wild-type mice, contribute only modestly to RPE lipofuscin formation and accumulation. Furthermore, decreases in A2E levels occurring after moving cyclic-light-reared Rdh8^−/− mice to darkness are consistent with processing of A2E within the RPE and the existence of a mechanism that could be a therapeutic target for controlling A2E cytotoxicity.

Retinol-binding protein 4 in obesity and metabolic dysfunctions

Excessive increased adipose tissue mass in obesity is associated with numerous co-morbid disorders including increased risk of type 2 diabetes, fatty liver disease, hypertension, dyslipidemia, cardiovascular diseases, dementia, airway disease and some cancers. The causal mechanisms explaining these associations are not fully understood. Adipose tissue is an active endocrine organ that secretes many adipokines, cytokines and releases metabolites. These biomolecules referred to as adipocytokines play a significant role in the regulation of whole-body energy homeostasis and metabolism by influencing and altering target tissues function. Understanding the mechanisms of adipocytokine actions represents a hot topic in obesity research. Among several secreted bioactive signalling molecules from adipose tissue and liver, retinol-binding protein 4 (RBP4) has been associated with systemic insulin resistance, dyslipidemia, type 2 diabetes and other metabolic diseases. Here, we aim to review and discuss the current knowledge on RBP4 with a focus on its role in the pathogenesis of obesity comorbid diseases.

Emerging biological therapies for the treatment of age-related macular degeneration

INTRODUCTION

Age-related macular degeneration (AMD) is the leading cause of blindness in individuals over age 50 in developed countries. Current therapy for nonexudative AMD (neAMD) is aimed at modifying risk factors and vitamin supplementation to slow progression, while intravitreal anti-vascular endothelial factor (VEGF) injections are the mainstay for treatment of choroidal neovascularization in exudative AMD (eAMD).

AREAS COVERED

Over the past decade, promising therapies have emerged that aim to improve the current standard of care for both diseases. Clinical trials for neAMD are investigating targets in the complement cascade, vitamin A metabolism, metformin, and tetracycline, whereas clinical trials for eAMD are aiming to decrease treatment burden through novel port delivery systems, increasing drug half-life, and targeting new sites of the VEGF cascade. Stem cell and gene therapy are also being evaluated for treatment of neAMD and eAMD.

EXPERT OPINION

With an aging population, the need for effective, long term, low burden treatment options for AMD will be in increasingly high demand. Current investigations aim to address the shortcomings of current treatment options with breakthrough treatment approaches. Therapeutics in the pipeline hold promise for improving the treatment of AMD, and are on track for widespread use within the next decade.

Retinal toxicities of systemic anticancer drugs

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

Treatments for dry age-related macular degeneration: therapeutic avenues, clinical trials and future directions

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in the developed world. The identification of the central role of vascular endothelial growth factor (VEGF) in the pathogenesis of neovascular AMD and the introduction of anti-VEGF agents as gold-standard treatment, have drastically changed its prognosis-something yet to be seen in dry AMD. Several therapeutic avenues with a wide variability of targets are currently being investigated in dry AMD. The approaches being investigated to reduce the rate of disease progression include, (1) drugs with antioxidative properties, (2) inhibitors of the complement cascade, (3) neuroprotective agents, (4) visual cycle inhibitors, (5) gene therapy and (6) cell-based therapies. A number of early phase clinical trials have provided promising results, with many more ongoing and anticipated in the near future. In this review, we aim to provide an update of the interventional trials to date and future prospects for the treatment of dry AMD.

Protective effects of NAC and salubrinal on apoptosis of retinal pigment epithelial cells induced by all-trans retinoic acid

PURPOSE

Accumulation of endogenous all-trans retinoic acid (ATRA) plays a role in the degeneration of photoreceptor cells and retinal pigment epithelium (RPE) cells, contributing to age-related macular degeneration (AMD). This study attempted to investigate the influence of antioxidant N-acetylcysteine (NAC) and selective endoplasmic reticulum stress (ERS) inhibitor salubrinal on apoptosis of ARPE-19 cells induced by ATRA.

METHODS

The RPE cell line (ARPE-19) was treated with ATRA, ATRA+NAC, ATRA+salubrinal or ATRA+NAC+salubrinal and the control was untreated. After 24 h of cell culture, the levels of apoptosis, multicaspase and reactive oxygen species (ROS) were detected by flow cytometry. Western blot analysis was employed to detect the expression of vascular endothelial growth factor-A (VEGF-A), C/EBP homologous protein (CHOP) and cleaved caspase-3 in the groups.

RESULTS

The results of flow cytometry showed that NAC and salubrinal decreased the levels of apoptosis, ROS and multicaspase. ATRA increased VEGF-A levels associated with neovascularisation. NAC and salubrinal inhibited an increase in VEGF-A, CHOP and caspase-3 caused by ATRA in ARPE-19 cells.

CONCLUSIONS

In ARPE-19 cells, the levels of ROS and ERS can be increased by ATRA, contributing to apoptosis, which can be effectively inhibited by NAC and salubrinal. Thus, ATRA may play an important role in the prevention, diagnosis and treatment of age-related macular degeneration.

Biological Functions of RBP4 and Its Relevance for Human Diseases

Retinol binding protein 4 (RBP4) is a member of the lipocalin family and the major transport protein of the hydrophobic molecule retinol, also known as vitamin A, in the circulation. Expression of RBP4 is highest in the liver, where most of the body’s vitamin A reserves are stored as retinyl esters. For the mobilization of vitamin A from the liver, retinyl esters are hydrolyzed to retinol, which then binds to RBP4 in the hepatocyte. After associating with transthyretin (TTR), the retinol/RBP4/TTR complex is released into the bloodstream and delivers retinol to tissues via binding to specific membrane receptors. So far, two distinct RBP4 receptors have been identified that mediate the uptake of retinol across the cell membrane and, under specific conditions, bi-directional retinol transport. Although most of RBP4’s actions depend on its role in retinoid homeostasis, functions independent of retinol transport have been described. In this review, we summarize and discuss the recent findings on the structure, regulation, and functions of RBP4 and lay out the biological relevance of this lipocalin for human diseases.

Visual cycle modulators versus placebo or observation for the prevention and treatment of geographic atrophy due to age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is a highly prevalent condition in an ever-increasing elderly population. Although insidious in the early stages, advanced AMD (neovascular and atrophic forms) can cause significant visual disability and economic burden on health systems worldwide. The most common form, geographic atrophy, has no effective treatment to date, whereas neovascular AMD can be treated with intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections. Geographic atrophy has a slow disease progression and patients tend to have preserved central vision until the final stages. This tendency, coupled with the use of modern imaging modalities, provides a large window of opportunity to intervene with validated methods to assess treatment efficacy. As geographic atrophy is an increasingly common condition with no effective intervention, many treatments are under investigation, one of which is visual cycle modulators. These medications have been shown to reduce lipofuscin accumulation in pre-clinical studies that have led to several clinical trials, reviewed herein.

OBJECTIVES

To assess the efficacy and safety of visual cycle modulators for the prevention and treatment of geographic atrophy secondary to AMD.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (which contains the Cochrane Eyes and Vision Trials Register) (2020, Issue 1); MEDLINE Ovid; Embase Ovid; Web of Science Core Collection; Scopus; Association for Research in Vision and Ophthalmology (ARVO) website; ClinicalTrials.gov and the WHO ICTRP to 11 January 2020 with no language restrictions. We also searched using the reference lists of reviews and existing studies and the Cited Reference Search function in Web of Science to identify further relevant studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and quasi-randomised clinical studies (if available) that compared visual cycle modulators to placebo or no treatment (observation) in people diagnosed with AMD (early, intermediate or geographic atrophy).

DATA COLLECTION AND ANALYSIS

Two authors independently assessed risk of bias in the included studies and extracted data. Both authors entered data into RevMan 5. We resolved discrepancies through discussion. We graded the certainty of the evidence using the GRADE approach.

MAIN RESULTS

We included three RCTs from the USA; one of these had clinical sites in Germany. Two studies compared emixustat to placebo while the other compared fenretinide to placebo. All assigned one study eye per participant and, combined, have a total of 821 participants with a majority white ethnicity (97.6%). All participants were diagnosed with geographic atrophy due to AMD based on validated imaging modalities. All three studies have high risk of attrition bias mainly due to ocular adverse effects of emixustat and fenretinide. We considered only one study to be adequately conducted and reported with high risk of bias in only one domain (attrition bias). We considered the other two studies to be poorly reported and to have high risk of attrition bias and reporting bias. People with geographic atrophy treated with emixustat may not experience a clinically important change in best-corrected visual acuity (BCVA) between baseline and 24 months compared to people treated with placebo (mean difference (MD) 1.9 Early Treatment Diabetic Retinopathy Study (ETDRS) letters, 95% confidence interval (CI) -2.34 to 6.14, low-certainty evidence). Emixustat may also result in little or no difference in loss of 15 ETDRS letters or more of BCVA compared with placebo at 24 months (16.4% versus 18%) (risk ratio (RR) 0.91, 95% CI 0.59 to 1.4, low-certainty evidence). In terms of disease progression, emixustat may result in little or no difference in the annual growth rate of geographic atrophy compared with placebo (mean difference MD 0.09 mm2/year (95% CI -0.26 to 0.44, low-certainty evidence). All three studies reported adverse events of both drugs (emixustat: moderate-certainty evidence; fenretinide: low-certainty evidence). The main adverse events were ocular in nature and associated with the mechanism of action of the drugs. Delayed dark adaptation (emixustat: 54.5%; fenretinide: 39.3%) and chromatopsia (emixustat: 22.6%; fenretinide: 25.2%) were the most common adverse events reported, and were the most prevalent reasons for study dropout in emixustat trials. These effects were dose-dependent and resolved after drug cessation. No specific systemic adverse events were considered related to emixustat; only pruritus and rash were considered to be due to fenretinide. One emixustat study reported six deaths, none deemed related to the drug. None of the included RCTs reported the other pre-specified outcomes, including proportion of participants losing 10 letters or more, and mean change in macular sensitivity. We planned to investigate progression to advanced AMD (geographic atrophy or neovascular AMD) in prevention studies, including participants with early or intermediate AMD, but we identified no such studies. Two of the included studies reported an additional outcome - incidence of choroidal neovascularisation (CNV) - that was not in our published protocol. CNV onset may be reduced in those treated with emixustat but the evidence was uncertain (risk ratio (RR) 0.67, 95% CI 0.27 to 1.65, low-certainty evidence), or fenretinide (RR 0.5, 95% CI 0.26 to 0.98, low-certainty evidence) compared to placebo. A dose-dependent relationship was observed with emixustat.

AUTHORS' CONCLUSIONS

There is limited evidence to support the use of visual cycle modulators (emixustat and fenretinide) for the treatment of established geographic atrophy due to AMD. The possible reduction in the incidence of CNV observed with fenretinide, and to a lesser extent, emixustat, requires formal assessment in focused studies.

Deep learning segmentation of hyperautofluorescent fleck lesions in Stargardt disease

Stargardt disease is one of the most common forms of inherited retinal disease and leads to permanent vision loss. A diagnostic feature of the disease is retinal flecks, which appear hyperautofluorescent in fundus autofluorescence (FAF) imaging. The size and number of these flecks increase with disease progression. Manual segmentation of flecks allows monitoring of disease, but is time-consuming. Herein, we have developed and validated a deep learning approach for segmenting these Stargardt flecks (1750 training and 100 validation FAF patches from 37 eyes with Stargardt disease). Testing was done in 10 separate Stargardt FAF images and we observed a good overall agreement between manual and deep learning in both fleck count and fleck area. Longitudinal data were available in both eyes from 6 patients (average total follow-up time 4.2 years), with both manual and deep learning segmentation performed on all (n = 82) images. Both methods detected a similar upward trend in fleck number and area over time. In conclusion, we demonstrated the feasibility of utilizing deep learning to segment and quantify FAF lesions, laying the foundation for future studies using fleck parameters as a trial endpoint.

[New possibilities in the treatment of Stargardt disease]

Stargardt disease is a hereditary retinal dystrophy associated with mutations in the ABCA4 gene. Currently, no etiopathogenetic drugs nor treatment methods for Stargardt disease have completely passed clinical trials. The review summarizes experimental and clinical studies of drugs aimed at reducing the accumulation of vitamin A dimers, lipofuscin, complement inhibition and RPE regeneration by stem cell transplantation, as well as gene therapy studies with intravitreal vector injection of the ABCA4 functional gene.

Growth Rate of Geographic Atrophy Secondary to Age-Related Macular Degeneration: A Meta-Analysis of Natural History Studies and Implications for Designing Future Trials

INTRODUCTION

There is no effective treatment for geographic atrophy (GA). To help design future GA treatment trials, we conducted a meta-analysis for GA growth rate and its variability in natural history studies.

METHODS

Literatures were searched up to April 30, 2020. Data were extracted independently by 2 authors and analyzed using random-effects models.

RESULTS

The pooled mean GA growth rate was 1.66 mm2/year (SD = 1.27 mm2/year, I2 = 97.0%, p < 0.001) from 23 studies (3,078 patients) reported with growth rate in mm2/year and 0.33 mm/year (SD = 0.17 mm/year, I2 = 83.0%, p < 0.001) from 12 studies (1,808 patients) reported with growth rate in mm/year. Larger mean baseline GA area in mm2 was associated with larger mean growth rate in both mm2/year and mm/year (p < 0.001). The sample size at 85% power for detecting 15% reduction in growth rate in a 2-arm GA trial is 464 and 209 patients per arm, respectively, for using mm2/year and mm/year as the primary outcome.

DISCUSSION/CONCLUSION

GA natural history studies had a pooled mean (SD) GA growth rate of 1.66 (1.27) mm2/year or 0.33 (0.17) mm/year. Because GA growth rate using mm/year requires smaller sample size than using mm2/year, GA growth rate in mm/year is recommended as the primary outcome measure for future GA trials.

Ultra-small-size Astragaloside-IV loaded lipid nanocapsules eye drops for the effective management of dry age-related macular degeneration

Background Age-related macular degeneration (AMD) is a major cause of severe visual loss in elderly people. The treatments for dry AMD (dAMD) are severely limited so far. In this work, we aim to develop an eye drop to protect retinal functions against oxidative stress and apoptosis for improving dAMD management. Methods Astragaloside-IV (ASIV) was prepared into phospholipid complex and loaded into three sizes (20, 50 and 90 nm) of ASIV lipid nanocapsules (ASIV-LNCs). The penetration and distribution of LNCs were investigated. DAMD mice model was induced by NaIO₃, and therapeutic effect was evaluated by electroretinography (ERG), histological examination, apoptosis and ROS detection. Results The ocular penetration and pharmacokinetic studies corroborated the feasibility of the LNCs to reach the fundus, and ultra-small-size LNCs (ASIV-LNCs-20) had the best delivery effect. ASIV-LNCs-20 was able to decrease ROS production and reduce the apoptosis rate from 5.12% to 0.533%. ERG and H&E staining results confirmed ASIV-LNCs-20 had a good protective effect on the morphology and function of the retina. Conclusions These results suggest that ASIV-LNCs can be a promising therapy approach for dAMD, and this research also offers new possibilities for further applications of LNCs as a drug delivery system for other eye diseases. Abbreviations AMD: Age-related macular degeneration;AREDS Age-related eye disease study; ASIV: Astragaloside-IV;AUC: Area under the concentration-time curve; dAMD: Dry age-related macular degeneration; DHE: Dihydroethidium; DL: Drug Loading; DLS: Dynamic light scattering; DSC: Differential scanning calorimetry; EE: Entrapment efficiency; ELSD: Evaporative light scattering detector; ERG: Electroretinographic; H&E: Hematoxylin and Eosin; I.S.: Internal standard; LB: Langmuir-Blodgett; LNCs: Lipid nanocapsules; MCT: Medium-chain triacylglycerol; ONL: Outer nuclear layer; OPL: Outer plexiform layer; PDI: Polydispersity index; PR: Photoreceptor;ROS: Reactive oxygen species; RPE: Retinal pigment epithelium; TEM: Transmission electron microscope; wAMD: Wet age-related macular degeneration.

Effect of Human Central Nervous System Stem Cell Subretinal Transplantation on Progression of Geographic Atrophy Secondary to Nonneovascular Age-Related Macular Degeneration

PURPOSE

To evaluate the effect of subretinally transplanted human central nervous system stem cells (HuCNS-SC) on the progression of geographic atrophy (GA) in patients with nonneovascular age-related macular degeneration (AMD).

DESIGN

Multicenter, prospective, phase 1 open-label clinical trial.

PARTICIPANTS

Fifteen patients with bilateral GA solely the result of AMD.

METHODS

The eye with the worst best-corrected visual acuity from each patient was selected for treatment and was considered the study eye; fellow eyes served as controls. A total of 0.25 × 10⁶ or 1.0 × 10⁶ HuCNS-SCs were infused directly into the subretinal space, superotemporal to the fovea near the junctional zone, outside the area of GA. All patients underwent spectral-domain OCT and fundus autofluorescence imaging using the Spectralis HRA+OCT (Heidelberg Engineering, Inc., Heidelberg, Germany). Total GA area in both eyes was measured at baseline and month 12 by certified reading center graders using the Spectralis Region Finder software. Sectoral (clock hour) per directional radial GA progression rates with respect to the foveal center in both eyes were calculated using the polar transformation method in Image J software (National Institutes of Health, Bethesda, MD). To facilitate comparative analysis across the cohort, all eyes were transformed to a right-eye orientation.

MAIN OUTCOME MEASURES

Total GA area and sectoral per directional GA progression rates were compared in both study and control eyes.

RESULTS

No statistically significant difference was found in mean change in total GA area at month 12 between study and fellow eyes (1.07 ± 0.84 mm² vs. 2.08 ± 1.97 mm²; P = 0.08). However, the month 12 sectoral per directional radial GA growth rate for the superotemporal region (i.e., the location of HuCNS-SC transplantation) showed a significantly slower progression rate in study eyes than in fellow eyes (0.29 ± 0.58 mm vs. 1.08 ± 0.65 mm; P = 0.007). The progression rate in the superotemporal quadrant of the study eye was significantly slower than in the other 3 quadrants combined (P = 0.04).

CONCLUSIONS

In this small pilot study, HuCNS-SC transplantation seems to be associated with slower expansion of the GA lesion in the transplanted quadrant. Larger confirmatory studies are required. Sectoral or directional analysis of growth rates of GA may be a useful approach for assessing the efficacy of locally delivered therapies.

Non-photopic and photopic visual cycles differentially regulate immediate, early, and late phases of cone photoreceptor-mediated vision

Cone photoreceptors in the retina enable vision over a wide range of light intensities. However, the processes enabling cone vision in bright light (i.e. photopic vision) are not adequately understood. Chromophore regeneration of cone photopigments may require the retinal pigment epithelium (RPE) and/or retinal Müller glia. In the RPE, isomerization of all-trans-retinyl esters to 11-cis-retinol is mediated by the retinoid isomerohydrolase Rpe65. A putative alternative retinoid isomerase, dihydroceramide desaturase-1 (DES1), is expressed in RPE and Müller cells. The retinol-isomerase activities of Rpe65 and Des1 are inhibited by emixustat and fenretinide, respectively. Here, we tested the effects of these visual cycle inhibitors on immediate, early, and late phases of cone photopic vision. In zebrafish larvae raised under cyclic light conditions, fenretinide impaired late cone photopic vision, while the emixustat-treated zebrafish unexpectedly had normal vision. In contrast, emixustat-treated larvae raised under extensive dark-adaptation displayed significantly attenuated immediate photopic vision concomitant with significantly reduced 11-cis-retinaldehyde (11cRAL). Following 30 min of light, early photopic vision was recovered, despite 11cRAL levels remaining significantly reduced. Defects in immediate cone photopic vision were rescued in emixustat- or fenretinide-treated larvae following exogenous 9-cis-retinaldehyde supplementation. Genetic knockout of Des1 (degs1) or retinaldehyde-binding protein 1b (rlbp1b) did not eliminate photopic vision in zebrafish. Our findings define molecular and temporal requirements of the nonphotopic or photopic visual cycles for mediating vision in bright light.

Effects of deficiency in the RLBP1-encoded visual cycle protein CRALBP on visual dysfunction in humans and mice

Mutations in retinaldehyde-binding protein 1 (RLBP1), encoding the visual cycle protein cellular retinaldehyde-binding protein (CRALBP), cause an autosomal recessive form of retinal degeneration. By binding to 11-cis-retinoid, CRALBP augments the isomerase activity of retinoid isomerohydrolase RPE65 (RPE65) and facilitates 11-cis-retinol oxidation to 11-cis-retinal. CRALBP also maintains the 11-cis configuration and protects against unwanted retinaldehyde activity. Studying a sibling pair that is compound heterozygous for mutations in RLBP1/CRALBP, here we expand the phenotype of affected individuals, elucidate a previously unreported phenotype in RLBP1/CRALBP carriers, and demonstrate consistencies between the affected individuals and Rlbp1/Cralbp^−/− mice. In the RLBP1/CRALBP-affected individuals, nonrecordable rod-specific electroretinogram traces were recovered after prolonged dark adaptation. In ultrawide-field fundus images, we observed radially arranged puncta typical of RLBP1/CRALBP-associated disease. Spectral domain-optical coherence tomography (SD-OCT) revealed hyperreflective aberrations within photoreceptor-associated bands. In short-wavelength fundus autofluorescence (SW-AF) images, speckled hyperautofluorescence and mottling indicated macular involvement. In both the affected individuals and their asymptomatic carrier parents, reduced SW-AF intensities, measured as quantitative fundus autofluorescence (qAF), indicated chronic impairment in 11-cis-retinal availability and provided information on mutation severity. Hypertransmission of the SD-OCT signal into the choroid together with decreased near-infrared autofluorescence (NIR-AF) provided evidence for retinal pigment epithelial cell (RPE) involvement. In Rlbp1/Cralbp^−/− mice, reduced 11-cis-retinal levels, qAF and NIR-AF intensities, and photoreceptor loss were consistent with the clinical presentation of the affected siblings. These findings indicate that RLBP1 mutations are associated with progressive disease involving RPE atrophy and photoreceptor cell degeneration. In asymptomatic carriers, qAF disclosed previously undetected visual cycle deficiency.

State-of-the art pharmacotherapy for non-neovascular age-related macular degeneration

INTRODUCTION

Age-related macular degeneration (AMD) is the most common cause of blindness among the elderly in the industrialized world. While effective treatment is available for neovascular AMD, no therapy is successful for the non-neovascular form. Herein, the authors report the current knowledge on non-neovascular AMD pathogenesis and the promising research on treatments.

AREAS COVERED

In the present review, the authors summarize the most recent advances in the treatment of non-neovascular AMD and provide an update on current treatment strategies. Evidence available from preclinical and clinical studies and from a selective literature search is reported.

EXPERT OPINION

When investigating AMD, numerous pathological cascades and alterations of physiological processes have been investigated. It is well-known that AMD is a multifactorial disease, with environmental causes and genetics playing a role. Perturbations in multiple pathogenic pathways have been identified and this led to the development of several molecules directed at specific therapeutic targets. However, despite the huge research effort, the only proven approach so far is oral antioxidant supplementation. We believe that, in addition to successful advancement of promising drugs, further research should be directed at tailoring therapy to specific patient groups, eventually employing a combinational therapy strategy.

Comparative pharmacokinetics and pharmacodynamics of the advanced Retinol-Binding Protein 4 antagonist in dog and cynomolgus monkey

Accumulation of lipofuscin bisretinoids in the retina contributes to pathogenesis of macular degeneration. Retinol-Binding Protein 4 (RBP4) antagonists reduce serum retinol concentrations thus partially reducing retinol delivery to the retina which decreases bisretinoid synthesis. BPN-14136 is a novel RBP4 antagonist with good in vitro potency and selectivity and optimal rodent pharmacokinetic (PK) and pharmacodynamic (PD) characteristics. To select a non-rodent species for regulatory toxicology studies, we conducted PK and PD evaluation of BPN-14136 in dogs and non-human primates (NHP). PK properties were determined following oral and intravenous administration of BPN-14136 in beagle dogs and cynomolgus monkeys. Dynamics of plasma RBP4 reduction in response to compound administration was used as a PD marker. BPN-14136 exhibited favorable PK profile in both species. Dose-normalized exposure was significantly higher in NHP than in dog. Baseline concentrations of RBP4 were considerably lower in dog than in NHP, reflecting the atypical reliance of canids on non-RBP4 mechanisms of retinoid trafficking. Oral administration of BPN-14136 to NHP induced a strong 99% serum RBP4 reduction. Dynamics of RBP4 lowering in both species correlated with compound exposure. Despite adequate PK and PD characteristics of BPN-14136 in dog, reliance of canids on non-RBP4 mechanisms of retinoid trafficking precludes evaluation of on-target toxicities for RBP4 antagonists in this species. Strong RBP4 lowering combined with good PK attributes and high BPN-14136 exposure achieved in NHP, along with the biology of retinoid trafficking that is similar to that of humans, support the choice of NHP as a non-rodent safety species.

Efficacy of Optimized Treatment Protocol Using LAU-7b Formulation against Ovalbumin (OVA) and House Dust Mite (HDM) -Induced Allergic Asthma in Atopic Hyperresponsive A/J Mice

PURPOSE

To assess the efficacy of the novel clinical formulation of fenretinide (LAU-7b) for the treatment of allergic asthma. To study the association between LAU-7b treatment in allergic asthma and the modulation of very long chain ceramides (VLCC).

METHODS

We used two allergens (OVA and HDM) to induce asthma in mouse models and we established a treatment protocol with LAU-7b. The severity of allergic asthma reaction was quantified by measuring the airway resistance, quantifying lung inflammatory cell infiltration (Haematoxylin and eosin stain) and mucus production (Periodic acid Schiff satin). IgE levels were measured by ELISA. Immunophenotyping of T cells was done using Fluorescence-activated cell sorting (FACS) analysis. The analysis of the specific species of lipids and markers of oxidation was performed using mass spectrometry.

RESULTS

Our data demonstrate that 10 mg/kg of LAU-7b was able to protect OVA- and HDM-challenged mice against increase in airway hyperresponsiveness, influx of inflammatory cells into the airways, and mucus production without affecting IgE levels. Treatment with LAU-7b significantly increased percentage of regulatory T cells and CD4⁺ IL-10-producing T cells and significantly decreased percentage of CD4⁺ IL-4-producing T cells. Our data also demonstrate a strong association between the improvement in the lung physiology and histology parameters and the drug-induced normalization of the aberrant distribution of ceramides in allergic mice.

CONCLUSION

9 days of 10 mg/kg of LAU-7b daily treatment protects the mice against allergen-induced asthma and restores VLCC levels in the lungs and plasma.

Quantifying Retinal Pigment Epithelium Dysmorphia and Loss of Histologic Autofluorescence in Age-Related Macular Degeneration

Purpose

Lipofuscin and melanolipofuscin organelles in retinal pigment epithelium (RPE) cells are signal sources for clinical fundus autofluorescence (AF). To elucidate the subcellular basis of AF imaging, we identified, characterized, and quantified the frequency of RPE morphology and AF phenotypes in donor eyes with age-related macular degeneration (AMD).

Methods

In 25 RPE-Bruch's membrane flat mounts from 25 eyes, we analyzed 0.4-μm z-stack epifluorescence images of RPE stained with phalloidin for actin cytoskeleton. Using a custom ImageJ plugin, we classified cells selected in a systematic unbiased fashion in six phenotypes representing increasing degrees of pathology. For each cell, area, AF intensity, and number of Voronoi neighbors were compared with phenotype 1 (uniform AF, polygonal morphology) via generalized estimating equations. We also analyzed each cell's neighborhood.

Results

In 29,323 cells, compared with phenotype 1, all other phenotypes, in order of increasing pathology, had significantly larger area, reduced AF, and more variable number of neighbors. Neighborhood area and AF showed similar, but subtler, trends. Cells with highly autofluorescent granule aggregates are no more autofluorescent than others and are in fact lower overall in AF. Pre-aggregates were found in phenotype 1. Phenotype 2, which exhibited degranulation despite normal cytoskeleton, was the most numerous nonhealthy phenotype (16.23%).

Conclusions

Despite aggregation of granules that created hyperAF aggregates within cells, overall AF on a per cell basis decreased with increasing severity of dysmorphia (abnormal shape). Data motivate further development of subcellular resolution in clinical fundus AF imaging and inform an ongoing reexamination of the role of lipofuscin in AMD.

Pharmacotherapy for metabolic and cellular stress in degenerative retinal diseases

Retinal photoreceptors continually endure stresses associated with prolonged light exposure and the metabolic demands of dark adaptation. Although healthy photoreceptors are able to withstand these stresses for several decades, the disease-affected retina functions at a reduced capacity and is at an increased risk for dysfunction. To alleviate cellular and metabolic stressors in degenerative retinal diseases, a new class of drugs that modulate the metabolic activity of the retina have been developed. A clinical candidate in this class (emixustat) has been shown to reduce retinal pathology in various animal models of human retinal disease and is currently under clinical study. Here, we describe the pharmacological properties of emixustat, its mechanisms of action, and potential for use in the treatment of specific retinal diseases.

Retinal function determined by flicker ERGs before and soon after intravitreal injection of anti-VEGF agents

Background

To evaluate the retinal function before and soon after an intravitreal injection of an anti-vascular endothelial growth factor (anti-VEGF) agents.

Methods

Seventy-nine eyes of 79 patients that were treated by an intravitreal injection of an anti-VEGF agent for age-related macular degeneration (AMD), diabetic macular edema (DME), or retinal vein occlusion (RVO) with macular edema (ME) were studied. The RETeval® system was used to record 28 Hz flicker electroretinograms (ERGs) from the injected and non-injected eyes before (Phase 1, P1), within 2 h after the injection (P2), and 2 to 24 h after the injection (P3). Patients were grouped by disease or by the injected agent and compared. The significance of the changes in the implicit times and amplitudes was determined by t tests.

Results

The amplitudes were not significantly different at the three phases. The implicit time of the injected eye was 31.2 ± 3.2 msec at P1, and it was not significantly different at P2 (31.7 ± 3.1 msec) but it was significantly longer at P3 (32.2 ± 3.3 msec, P < 0.01, ANOVA for both). The implicit time in the non-injected fellow eye was 30.5 ± 3.3 msec at P1, and it was significantly longer at P2 (31.1 ± 3.2 msec) and phase 3 (31.3 ± 3.4 msec, P < 0.01, ANOVA for both).

Conclusions

The results indicate that an intravitreal anti-VEGF injection will increase the implicit times not only in the injected eye but also in the non-injected eye soon after the intravitreal injection.