Treatment with isotretinoin inhibits lipofuscin accumulation in a mouse model of recessive Stargardt's macular degeneration

Intravitreal Delivery of PEGylated-ECO Plasmid DNA Nanoparticles for Gene Therapy of Stargardt Disease

OBJECTIVE

Current gene therapy of inherited retinal diseases is achieved mainly by subretinal injection, which is invasive with severe adverse effects. Intravitreal injection is a minimally invasive alternative for gene therapy of inherited retinal diseases. This work explores the efficacy of intravitreal delivery of PEGylated ECO (a multifunctional pH-sensitive amphiphilic amino lipid) plasmid DNA (pGRK1-ABCA4-S/MAR) nanoparticles (PEG-ELNP) for gene therapy of Stargardt disease.

METHODS

Pigmented Abca4-/- knockout mice received 1 µL of PEG-ELNP solution (200 ng/uL, pDNA concentration) by intravitreal injections at an interval of 1.5 months. The expression of ABCA4 in the retina was determined by RT-PCR and immunohistochemistry at 6 months after the second injection. A2E levels in the treated eyes and untreated controls were determined by HPLC. The safety of treatment was monitored by scanning laser ophthalmoscopy and electroretinogram (ERG).

RESULTS

PEG-ELNP resulted in significant ABCA4 expression at both mRNA level and protein level at]6 months after 2 intravitreal injections, and a 40% A2E accumulation reduction compared with non-treated controls. The PEG-ELNP also demonstrated excellent safety as shown by scanning laser ophthalmoscopy, and the eye function evaluation from electroretinogram.

CONCLUSIONS

Intravitreal delivery of the PEG-ELNP of pGRK1-ABCA4-S/MAR is a promising approach for gene therapy of Stargardt Disease, which can also be a delivery platform for gene therapy of other inherited retinal diseases.

Current Insights into Targeting Strategies for the Effective Therapy of Diseases of the Posterior Eye Segment

The eye is one a unique sophisticated human sense organ with a complex anatomical structure. It is encased by variety of protective barriers as responsible for vision. There has been a paradigm shift in the prevalence of several major vision threatening ocular conditions with enhanced reliance on computer-based technologies in our workaday life and work-from-home modalities although aging, pollution, injury, harmful chemicals, lifestyle changes will always remain the root cause. Treating posterior eye diseases is a challenge faced by clinicians worldwide. The clinical use of conventional drug delivery systems for posterior eye targeting is restricted by the ocular barriers. Indeed, for overcoming various ocular barriers for efficient delivery of the therapeutic moiety and prolonged therapeutic effect requires prudent and target-specific approaches. Therefore, for efficient drug delivery to the posterior ocular segment, advancements in the development of sustained release and nanotechnology-based ocular drug delivery systems have gained immense importance. Therapeutic efficacy and patient compliance are of paramount importance in clinical translation of these investigative drug delivery systems. This review provides an insight into the various strategies employed for improving the treatment efficacies of the posterior eye diseases. Various drug delivery systems such as systemic and intraocular injections, implants have demonstrated promising outcomes, along with that they have also exhibited side-effects, limitations and strategies employed to overcome them are discussed in this review. The application of artificial intelligence-based technologies along with an appreciation of disease, delivery systems, and patient-specific outcomes will likely enable more effective therapy for targeting the posterior eye segment.

Gene Therapy for Inherited Retinal Diseases: From Laboratory Bench to Patient Bedside and Beyond

This comprehensive review provides a thorough examination of inherited retinal diseases (IRDs), encompassing their classification, genetic underpinnings, and the promising landscape of gene therapy trials. IRDs, a diverse group of genetic conditions causing vision loss through photoreceptor cell death, are explored through various angles, including inheritance patterns, gene involvement, and associated systemic disorders. The focal point is gene therapy, which offers hope for halting or even reversing the progression of IRDs. The review highlights ongoing clinical trials spanning retinal cell replacement, neuroprotection, pharmacological interventions, and optogenetics. While these therapies hold tremendous potential, they face challenges like timing optimization, standardized assessment criteria, inflammation management, vector refinement, and raising awareness among vision scientists. Additionally, translating gene therapy success into widespread adoption and addressing cost-effectiveness are crucial challenges to address. Continued research and clinical trials are essential to fully harness gene therapy's potential in treating IRDs and enhancing the lives of affected individuals.

Lipofuscin, Its Origin, Properties, and Contribution to Retinal Fluorescence as a Potential Biomarker of Oxidative Damage to the Retina

Lipofuscin accumulates with age as intracellular fluorescent granules originating from incomplete lysosomal digestion of phagocytosed and autophagocytosed material. The purpose of this review is to provide an update on the current understanding of the role of oxidative stress and/or lysosomal dysfunction in lipofuscin accumulation and its consequences, particularly for retinal pigment epithelium (RPE). Next, the fluorescence of lipofuscin, spectral changes induced by oxidation, and its contribution to retinal fluorescence are discussed. This is followed by reviewing recent developments in fluorescence imaging of the retina and the current evidence on the prognostic value of retinal fluorescence for the progression of age-related macular degeneration (AMD), the major blinding disease affecting elderly people in developed countries. The evidence of lipofuscin oxidation in vivo and the evidence of increased oxidative damage in AMD retina ex vivo lead to the conclusion that imaging of spectral characteristics of lipofuscin fluorescence may serve as a useful biomarker of oxidative damage, which can be helpful in assessing the efficacy of potential antioxidant therapies in retinal degenerations associated with accumulation of lipofuscin and increased oxidative stress. Finally, amendments to currently used fluorescence imaging instruments are suggested to be more sensitive and specific for imaging spectral characteristics of lipofuscin fluorescence.

Neuronal Senescence in the Aged Brain

Cellular senescence is a highly complicated cellular state that occurs throughout the lifespan of an organism. It has been well-defined in mitotic cells by various senescent features. Neurons are long-lived post-mitotic cells with special structures and functions. With age, neurons display morphological and functional changes, accompanying alterations in proteostasis, redox balance, and Ca2+ dynamics; however, it is ambiguous whether these neuronal changes belong to the features of neuronal senescence. In this review, we strive to identify and classify changes that are relatively specific to neurons in the aging brain and define them as features of neuronal senescence through comparisons with common senescent features. We also associate them with the functional decline of multiple cellular homeostasis systems, proposing the possibility that these systems are the main drivers of neuronal senescence. We hope this summary will serve as a steppingstone for further inputs on a comprehensive but relatively specific list of phenotypes for neuronal senescence and in particular their underlying molecular events during aging. This will in turn shine light on the association between neuronal senescence and neurodegeneration and lead to the development of strategies to perturb the processes.

Polymer- and lipid-based nanocarriers for ocular drug delivery: Current status and future perspectives

Ocular diseases seriously affect patients' vision and life quality, with a global morbidity of over 43 million blindness. However, efficient drug delivery to treat ocular diseases, particularly intraocular disorders, remains a huge challenge due to multiple ocular barriers that significantly affect the ultimate therapeutic efficacy of drugs. Recent advances in nanocarrier technology offer a promising opportunity to overcome these barriers by providing enhanced penetration, increased retention, improved solubility, reduced toxicity, prolonged release, and targeted delivery of the loaded drug to the eyes. This review primarily provides an overview of the progress and contemporary applications of nanocarriers, mainly polymer- and lipid-based nanocarriers, in treating various eye diseases, highlighting their value in achieving efficient ocular drug delivery. Additionally, the review covers the ocular barriers and administration routes, as well as the prospective future developments and challenges in the field of nanocarriers for treating ocular diseases.

Towards a New Biomarker for Diabetic Retinopathy: Exploring RBP3 Structure and Retinoids Binding for Functional Imaging of Eyes In Vivo

Diabetic retinopathy (DR) is a severe disease with a growing number of afflicted patients, which places a heavy burden on society, both socially and financially. While there are treatments available, they are not always effective and are usually administered when the disease is already at a developed stage with visible clinical manifestation. However, homeostasis at a molecular level is disrupted before visible signs of the disease are evident. Thus, there has been a constant search for effective biomarkers that could signal the onset of DR. There is evidence that early detection and prompt disease control are effective in preventing or slowing DR progression. Here, we review some of the molecular changes that occur before clinical manifestations are observable. As a possible new biomarker, we focus on retinol binding protein 3 (RBP3). We argue that it displays unique features that make it a very good biomarker for non-invasive, early-stage DR detection. Linking chemistry to biological function and focusing on new developments in eye imaging and two-photon technology, we describe a new potential diagnostic tool that would allow rapid and effective quantification of RBP3 in the retina. Moreover, this tool would also be useful in the future to monitor therapeutic effectiveness if levels of RBP3 are elevated by DR treatments.

Human retinal dark adaptation tracked in vivo with the electroretinogram: insights into processes underlying recovery of cone- and rod-mediated vision

The substantial time taken for regaining visual sensitivity (dark adaptation) following bleaching exposures has been investigated for over a century. Psychophysical studies yielded the classic biphasic curve representing recovery of cone-driven and rod-driven vision. The electroretinogram (ERG) permits direct assessment of recovery at the level of the retina (photoreceptors, bipolar cells), with the first report over 70 years ago. Over the last two decades, ERG studies of dark adaptation have generated insights into underlying physiological processes. After large bleaches, rod photoreceptor circulating current, estimated from the rod-isolated bright-flash ERG a-wave, takes 30 min to recover, indicating that products of bleaching, thought to be free opsin (unbound to 11-cis-retinal), continue to activate phototransduction, shutting off rod circulating current. In contrast, cone current, assessed with cone-driven bright-flash ERG a-waves, recovers within 100 ms following similar exposures, suggesting that free opsin is less able to shut off cone current. The cone-driven dim-flash a-wave can be used to track recovery of cone photopigment, showing regeneration is 'rate-limited' rather than first order. Recoveries of the dim-flash ERG b-wave are consistent also with rate-limited rod photopigment regeneration (where free opsin, desensitising the visual system as an 'equivalent background', is removed by rate-limited delivery of 11-cis-retinal). These findings agree with psychophysical and retinal densitometry studies, although there are unexplained points of divergence. Post-bleach ERG recovery has been explored in age-related macular degeneration and in trials of visual cycle inhibitors for retinal diseases. ERG tracking of dark adaptation may prove useful in future clinical contexts.

The novel visual cycle inhibitor (±)-RPE65-61 protects retinal photoreceptors from light-induced degeneration

The visual cycle refers to a series of biochemical reactions of retinoids in ocular tissues and supports the vision in vertebrates. The visual cycle regenerates visual pigments chromophore, 11-cis-retinal, and eliminates its toxic byproducts from the retina, supporting visual function and retinal neuron survival. Unfortunately, during the visual cycle, when 11-cis-retinal is being regenerated in the retina, toxic byproducts, such as all-trans-retinal and bis-retinoid is N-retinylidene-N-retinylethanolamine (A2E), are produced, which are proposed to contribute to the pathogenesis of the dry form of age-related macular degeneration (AMD). The primary biochemical defect in Stargardt disease (STGD1) is the accelerated synthesis of cytotoxic lipofuscin bisretinoids, such as A2E, in the retinal pigment epithelium (RPE) due to mutations in the ABCA4 gene. To prevent all-trans-retinal-and bisretinoid-mediated retinal degeneration, slowing down the retinoid flow by modulating the visual cycle with a small molecule has been proposed as a therapeutic strategy. The present study describes RPE65-61, a novel, non-retinoid compound, as an inhibitor of RPE65 (a key enzyme in the visual cycle), intended to modulate the excessive activity of the visual cycle to protect the retina from harm degenerative diseases. Our data demonstrated that (±)-RPE65-61 selectively inhibited retinoid isomerase activity of RPE65, with an IC50 of 80 nM. Furthermore, (±)-RPE65-61 inhibited RPE65 via an uncompetitive mechanism. Systemic administration of (±)-RPE65-61 in mice resulted in slower chromophore regeneration after light bleach, confirming in vivo target engagement and visual cycle modulation. Concomitant protection of the mouse retina from high-intensity light damage was also observed. Furthermore, RPE65-61 down-regulated the cyclic GMP-AMP synthase stimulator of interferon genes (cGAS-STING) pathway, decreased the inflammatory factor, and attenuated retinal apoptosis caused by light-induced retinal damage (LIRD), which led to the preservation of the retinal function. Taken together, (±)-RPE65-61 is a potent visual cycle modulator that may provide a neuroprotective therapeutic benefit for patients with STGD and AMD.

A Rare Occurrence of Stargardt Disease in a Quadragenarian Adult

The retina is the light-sensitive layer of the human eye. The macula forms the central part of the retina. The character of light responsiveness is attributed to the presence of photoreceptor cells here. Stargardt's disease is the most common cause of hereditary macular dystrophy. It is linked to disease-causing sequence variations/mutations in the ABCA4 gene on chromosome 1p21-p13, which destroys rod and cone cells within the retina. The disc membranes of rod and cone outer segments include an ATP-binding cassette transport protein encoded by the ABCA4 gene. All trans-retinal conjugates are transported across disc membranes by the ABCA4 protein. Abnormally high amounts of lipofuscin pigments build up in the retinal pigment epithelium (RPE) due to mutations in the ABCA4 gene, leading to RPE cell loss and secondary photoreceptor cell degeneration. As a result of this disease, the central or detailed vision becomes blurred, and the patient may find it challenging to discern colours. The retina presents with a distinctive "beaten-bronze" appearance due to the presence of prominent yellow dots. The phenotypic form of Stargardt disease, known as fundus flavimaculatus, is characterized by the widespread distribution of flecks throughout the fundus, including the periphery. In the given case report, we present a 46-year-old male patient who presented with complaints of persistence of a blind spot in central vision, difficulty in identifying faces, distortion of letters while reading, decreased visual acuity and difficulty in adapting from light to dark settings as symptoms. The stepwise assessment of the patient led to the diagnosis of Stargardt's disease. The case report reflects the disease history, pathogenesis, manifestations, prognosis, differential diagnosis and treatment options for this rare presentation.

Effective gene therapy of Stargardt disease with PEG-ECO/pGRK1-ABCA4-S/MAR nanoparticles

Stargardt disease (STGD) is the most common form of inherited retinal genetic disorders and is often caused by mutations in ABCA4. Gene therapy has the promise to effectively treat monogenic retinal disorders. However, clinically approved adeno-associated virus (AAV) vectors do not have a loading capacity for large genes, such as ABCA4. Self-assembly nanoparticles composed of (1-aminoethyl)iminobis[N-(oleoylcysteinyl-1-amino-ethyl)propionamide (ECO; a multifunctional pH-sensitive/ionizable amino lipid) and plasmid DNA produce gene transfection comparable with or better than the AAV2 capsid. Stable PEG-ECO/pGRK1-ABCA4-S/MAR nanoparticles produce specific and prolonged expression of ABCA4 in the photoreceptors of Abca4 -/- mice and significantly inhibit accumulation of toxic A2E in the eye. Multiple subretinal injections enhance gene expression and therapeutic efficacy with an approximately 69% reduction in A2E accumulation in Abca4 -/- mice after 3 doses. Very mild inflammation was observed after multiple injections of the nanoparticles. PEG-ECO/pGRK1-ABCA4-S/MAR nanoparticles are a promising non-viral mediated gene therapy modality for STGD type 1 (STGD1).

Vitamin A aldehyde-taurine adducts function in photoreceptor cells

To facilitate the movement of retinoids through the visual cycle and to limit nonspecific chemical reaction, multiple mechanisms are utilized to handle these molecules when not contained within the binding pocket of opsin. Vitamin A aldehyde is sequestered by reversible Schiff base formation with phosphatidylethanolamine (PE) and subsequently undergoes NADPH-dependent reduction. Otherwise inefficient handling of retinaldehyde can lead to the formation of fluorescent di-retinal compounds within the outer segments of photoreceptor cells. These bisretinoid fluorophores initiate photooxidative processes having adverse consequences for retina. Various carrier proteins confer water solubility and maintain the 11-cis-retinoid configuration. Mechanisms for sequestration of retinoid include the formation of a reversible Schiff base between retinaldehyde and taurine (A1-taurine, A1T), the most abundant amino acid in photoreceptor cells. Here we have undertaken to examine the effects of taurine depletion using the transport inhibitors guanidinoethyl sulfonate (GES) and β-alanine. Oral treatment of BALB/cJ mice with β-alanine reduced ocular A1T and the mice exhibited significantly lower scotopic and photopic a-wave amplitudes. As a secondary effect of retinal degeneration, A1T was not detected and taurine was significantly reduced in mice carrying a P23H opsin mutation. The thinning of ONL that is indicative of reduced photoreceptor cell viability in albino Abca4^-/- mice was more pronounced in β-alanine treated mice. Treatment of agouti and albino Abca4^-/- mice with β-alanine and GES was associated with reduced bisretinoid measured chromatographically. Consistent with a reduction in carbonyl scavenging activity by taurine, methylglyoxal-adducts were also increased in the presence of β-alanine. Taken together these findings support the postulate that A1T serves as a reservoir of vitamin A aldehyde, with diminished A1T explaining reduced photoreceptor light-sensitivity, accentuated ONL thinning in Abca4^-/- mice and attenuated bisretinoid formation.

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.

Cross-sectional assessment of the ellipsoid zone and the retinal pigment epithelium-Bruch membrane complex after systemic isotretinotin use

PURPOSE

To evaluate the cross-sectional areas of the retinal pigment epithelium-Bruch membrane complex (RPE-B) and ellipsoid zon (EZ) and the thickness of the macula, retinal nerve fibre layer (RNFL), and ganglion cell-inner plexiform layer (GC-IPL) in patients using short-term systemic isotretinoin.

METHOD

A total of 43 right eyes of 43 patients treated with systemic isotretinoin for acne vulgaris were included in this prospective study. Macula, GC-IPL, RNFL thicknesses and central cross-sectional EZ and RPE-B areas were evaluated with optical coherence tomography (Zeiss, Cirrus HD OCT 5000) prior to treatment and in first, second and third months after the onset of isotretinoin treatment. For the measurement of EZ and RPE-B area, foveal EDI-OCT scans were binarized by using the public domain software ImageJ 1.51 s.

RESULTS

Mean duration of isotretinoin treatment was 77 ± 15 days and mean dose was 2228 ± 574 milligrams. There was a statistically significant increment in central cross-sectional EZ and RPE-B areas in each follow-up examination, when analysed by repeated measurement analysis (p:0.002 and p:0.006, respectively). There was no correlation between total isotretinoin dose and the difference between final and basal EZ and RPE-B areas (p > 0.05, for both). When repeated measurements in follow-up examinations were compared, GC-IPL thicknesses except the superotemporal region (p:0.040) and RNFL thicknesses did not show a significant difference (p > 0.05). There was not any significant relation between total isotretinoin dose and 3rd month and basal measurement differences in macula, GC-IPL and RNFL thicknesses in any area (p > 0.05, for all).

CONCLUSION

There has been an increase in the area of RPE-B and EZ with short-term use of isotretinoin therapy. Future studies examining the relationship between functional tests and the RPE-B and EZ areas may provide more in-depth information on the effects of isotretinoin in the eye.

Structure and function of ABCA4 and its role in the visual cycle and Stargardt macular degeneration

ABCA4 is a member of the superfamily of ATP-binding cassette (ABC) transporters that is preferentially localized along the rim region of rod and cone photoreceptor outer segment disc membranes. It uses the energy from ATP binding and hydrolysis to transport N-retinylidene-phosphatidylethanolamine (N-Ret-PE), the Schiff base adduct of retinal and phosphatidylethanolamine, from the lumen to the cytoplasmic leaflet of disc membranes. This ensures that all-trans-retinal and excess 11-cis-retinal are efficiently cleared from photoreceptor cells thereby preventing the accumulation of toxic retinoid compounds. Loss-of-function mutations in the gene encoding ABCA4 cause autosomal recessive Stargardt macular degeneration, also known as Stargardt disease (STGD1), and related autosomal recessive retinopathies characterized by impaired central vision and an accumulation of lipofuscin and bis-retinoid compounds. High resolution structures of ABCA4 in its substrate and nucleotide free state and containing bound N-Ret-PE or ATP have been determined by cryo-electron microscopy providing insight into the molecular architecture of ABCA4 and mechanisms underlying substrate recognition and conformational changes induced by ATP binding. The expression and functional characterization of a large number of disease-causing missense ABCA4 variants have been determined. These studies have shed light into the molecular mechanisms underlying Stargardt disease and a classification that reliably predicts the effect of a specific missense mutation on the severity of the disease. They also provide a framework for developing rational therapeutic treatments for ABCA4-associated diseases.

Stargardt disease and progress in therapeutic strategies

Background: Stargardt disease (STGD1) is an autosomal recessive retinal dystrophy due to mutations in ABCA4, characterized by subretinal deposition of lipofuscin-like substances and bilateral centrifugal vision loss. Despite the tremendous progress made in the understanding of STGD1, there are no approved treatments to date. This review examines the challenges in the development of an effective STGD1 therapy.Materials and Methods: A literature review was performed through to June 2021 summarizing the spectrum of retinal phenotypes in STGD1, the molecular biology of ABCA4 protein, the in vivo and in vitro models used to investigate the mechanisms of ABCA4 mutations and current clinical trials.Results: STGD1 phenotypic variability remains an challenge for clinical trial design and patient selection. Pre-clinical development of therapeutic options has been limited by the lack of animal models reflecting the diverse phenotypic spectrum of STDG1. Patient-derived cell lines have facilitated the characterization of splice mutations but the clinical presentation is not always predicted by the effect of specific mutations on retinoid metabolism in cellular models. Current therapies primarily aim to delay vision loss whilst strategies to restore vision are less well developed.Conclusions: STGD1 therapy development can be accelerated by a deeper understanding of genotype-phenotype correlations.

An Overview of the Genetics of ABCA4 Retinopathies, an Evolving Story

Stargardt disease (STGD1) and ABCA4 retinopathies (ABCA4R) are caused by pathogenic variants in the ABCA4 gene inherited in an autosomal recessive manner. The gene encodes an importer flippase protein that prevents the build-up of vitamin A derivatives that are toxic to the RPE. Diagnosing ABCA4R is complex due to its phenotypic variability and the presence of other inherited retinal dystrophy phenocopies. ABCA4 is a large gene, comprising 50 exons; to date > 2000 variants have been described. These include missense, nonsense, splicing, structural, and deep intronic variants. Missense variants account for the majority of variants in ABCA4. However, in a significant proportion of patients with an ABCA4R phenotype, a second variant in ABCA4 is not identified. This could be due to the presence of yet unknown variants, or hypomorphic alleles being incorrectly classified as benign, or the possibility that the disease is caused by a variant in another gene. This underlines the importance of accurate genetic testing. The pathogenicity of novel variants can be predicted using in silico programs, but these rely on databases that are not ethnically diverse, thus highlighting the need for studies in differing populations. Functional studies in vitro are useful towards assessing protein function but do not directly measure the flippase activity. Obtaining an accurate molecular diagnosis is becoming increasingly more important as targeted therapeutic options become available; these include pharmacological, gene-based, and cell replacement-based therapies. The aim of this review is to provide an update on the current status of genotyping in ABCA4 and the status of the therapeutic approaches being investigated.

Formulation and efficacy of ECO/pRHO-ABCA4-SV40 nanoparticles for nonviral gene therapy of Stargardt disease in a mouse model

It is still a challenge to develop gene replacement therapy for retinal disorders caused by mutations in large genes, such as Stargardt disease (STGD). STGD is caused by mutations in ABCA4 gene. Previously, we have developed an effective non-viral gene therapy using self-assembled nanoparticles of a multifunctional pH-sensitive amino lipid ECO and a therapeutic ABCA4 plasmid containing rhodopsin promoter (pRHO-ABCA4). In this study, we modified the ABCA4 plasmid with simian virus 40 enhancer (SV40, pRHO-ABCA4-SV40) for enhanced gene expression. We also prepared and assessed the formulations of ECO/pDNA nanoparticles using sucrose or sorbitol as a stablilizer to develop consistent and stable formulations. Results demonstrated that ECO formed stable nanoparticles with pRHO-ABCA4-SV40 in the presence of sucrose, but not with sorbitol. The transfection efficiency in vitro increased significantly after introduction of SV40 enhancer for plasmid pCMV-ABCA4-SV40 with a CMV promoter. Sucrose didn't affect the transfection efficiency, while sorbitol resulted in a fluctuation of the in vitro transfection efficiency. Subretinal gene therapy in Abca4-/- mice using ECO/pRHO-ABCA4 and ECO/pRHO-ABCA4-SV40 nanoparticles induced 36% and 29% reduction in A2E accumulation respectively. Therefore, the ECO/pABCA4 based nanoparticles are promising for non-viral gene therapy for Stargardt disease and can be expended for applications in a variety of visual dystrophies with mutated large genes.

Bisretinoid phospholipid and vitamin A aldehyde: shining a light

Vitamin A aldehyde covalently bound to opsin protein is embedded in a phospholipid-rich membrane that supports photon absorption and phototransduction in photoreceptor cell outer segments. Following absorption of a photon, the 11-cis-retinal chromophore of visual pigment in photoreceptor cells isomerizes to all-trans-retinal. To maintain photosensitivity 11-cis-retinal must be replaced. At the same time, however, all-trans-retinal has to be handled so as to prevent nonspecific aldehyde activity. Some molecules of retinaldehyde upon release from opsin are efficiently reduced to retinol. Other molecules are released into the lipid phase of the disc membrane where they form a conjugate [N-retinylidene-PE (NRPE)] through a Schiff base linkage with PE. The reversible formation of NRPE serves as a transient sink for retinaldehyde that is intended to return retinaldehyde to the visual cycle. However, if instead of hydrolyzing to PE and retinaldehyde, NRPE reacts with a second molecule of retinaldehyde, a synthetic pathway is initiated that leads to the formation of multiple species of unwanted bisretinoid fluorophores. We report on recently identified members of the bisretinoid family, some of which differ with respect to the acyl chains associated with the glycerol backbone. We discuss processing of the lipid moieties of these fluorophores in lysosomes of retinal pigment epithelial cells, their fluorescence characters, and new findings related to light- and iron-associated oxidation of bisretinoids.

A vicious cycle of bisretinoid formation and oxidation relevant to recessive Stargardt disease

The ability of iron to transfer electrons enables the contribution of this metal to a variety of cellular activities even as the redox properties of iron are also responsible for the generation of hydroxyl radicals (^•OH), the most destructive of the reactive oxygen species. We previously showed that iron can promote the oxidation of bisretinoid by generating highly reactive hydroxyl radical (^•OH). Now we report that preservation of iron regulation in the retina is not sufficient to prevent iron-induced bisretinoid oxidative degradation when blood iron levels are elevated in liver-specific hepcidin knockout mice. We obtained evidence for the perpetuation of Fenton reactions in the presence of the bisretinoid A2E and visible light. On the other hand, iron chelation by deferiprone was not associated with changes in postbleaching recovery of 11-cis-retinal or dark-adapted ERG b-wave amplitudes indicating that the activity of Rpe65, a rate-determining visual cycle protein that carries an iron-binding domain, is not affected. Notably, iron levels were elevated in the neural retina and retinal pigment epithelial (RPE) cells of Abca4^−/− mice. Consistent with higher iron content, ferritin-L immunostaining was elevated in RPE of a patient diagnosed with ABCA4-associated disease and in RPE and photoreceptor cells of Abca4^−/− mice. In neural retina of the mutant mice, reduced Tfrc mRNA was also an indicator of retinal iron overload. Thus iron chelation may defend retina when bisretinoid toxicity is implicated in disease processes.

The role of multimodal imaging and vision function testing in ABCA4-related retinopathies and their relevance to future therapeutic interventions

The aim of this review article is to describe the specific features of Stargardt disease and ABCA4 retinopathies (ABCA4R) using multimodal imaging and functional testing and to highlight their relevance to potential therapeutic interventions. Standardised measures of tissue loss, tissue function and rate of change over time using formal structured deep phenotyping in Stargardt disease and ABCA4R are key in diagnosis, and prognosis as well as when selecting cohorts for therapeutic intervention. In addition, a meticulous documentation of natural history will be invaluable in the future to compare treated with untreated retinas. Despite the familiarity with the term Stargardt disease, this eponymous classification alone is unhelpful when evaluating ABCA4R, as the ABCA4 gene is associated with a number of phenotypes, and a range of severity. Multimodal imaging, psychophysical and electrophysiologic measurements are necessary in diagnosing and characterising these differing retinopathies. A wide range of retinal dystrophy phenotypes are seen in association with ABCA4 mutations. In this article, these will be referred to as ABCA4R. These different phenotypes and the existence of phenocopies present a significant challenge to the clinician. Careful phenotypic characterisation coupled with the genotype enables the clinician to provide an accurate diagnosis, associated inheritance pattern and information regarding prognosis and management. This is particularly relevant now for recruiting to therapeutic trials, and in the future when therapies become available. The importance of accurate genotype-phenotype correlation studies cannot be overemphasised. This approach together with segregation studies can be vital in the identification of causal mutations when variants in more than one gene are being considered as possible. In this article, we give an overview of the current imaging, psychophysical and electrophysiological investigations, as well as current therapeutic research trials for retinopathies associated with the ABCA4 gene.

Interphotoreceptor Retinoid-Binding Protein (IRBP) in Retinal Health and Disease

Interphotoreceptor retinoid-binding protein (IRBP), also known as retinol binding protein 3 (RBP3), is a lipophilic glycoprotein specifically secreted by photoreceptors. Enriched in the interphotoreceptor matrix (IPM) and recycled by the retinal pigment epithelium (RPE), IRBP is essential for the vision of all vertebrates as it facilitates the transfer of retinoids in the visual cycle. It also helps to transport lipids between the RPE and photoreceptors. The thiol-dependent antioxidant activity of IRBP maintains the delicate redox balance in the normal retina. Thus, its dysfunction is suspected to play a role in many retinal diseases. We have reviewed here the latest research on IRBP in both retinal health and disease, including the function and regulation of IRBP under retinal stress in both animal models and the human retina. We have also explored the therapeutic potential of targeting IRBP in retinal diseases. Although some technical barriers remain, it is possible that manipulating the expression of IRBP in the retina will rescue or prevent photoreceptor degeneration in many retinal diseases.

Penetration, distribution, and elimination of remofuscin/soraprazan in Stargardt mouse eyes following a single intravitreal injection using pharmacokinetics and transmission electron microscopic autoradiography: Implication for the local treatment of Stargardt's disease and dry age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of blindness in older people in the developed world while Stargardt's disease (SD) is a juvenile macular degeneration and an orphan disease. Both diseases are untreatable and are marked by accumulation of lipofuscin advancing to progressive deterioration of the retinal pigment epithelium (RPE) and retina and subsequent vision loss till blindness. We discovered that a small molecule belonging to the tetrahydropyridoether class of compounds, soraprazan renamed remofuscin, is able to remove existing lipofuscin from the RPE. This study investigated the drug penetration, distribution, and elimination into the eyes of a mouse model for increased lipofuscinogenesis, following a single intravitreal injection. We measured the time course of concentrations of remofuscin in different eye tissues using high-performance liquid chromatography combined with mass spectroscopy (HPLC-MS). We also visualized the penetration and distribution of 3 H-remofuscin in eye sections up to 20 weeks post-injection using transmission electron microscopic (TEM) autoradiography. The distribution of silver grains revealed that remofuscin accumulated specifically in the RPE by binding to the RPE pigments (melanin, lipofuscin and melanolipofuscin) and that it was still detected after 20 weeks. Importantly, the melanosomes in choroidal melanocytes only rarely bind remofuscin emphasizing its potential to serve as an active ingredient in the RPE for the treatment of SD and dry AMD. In addition, our study highlights the importance of electron microscopic autoradiography as it is the only method able to show drug binding with a high intracellular resolution.

Retinoid analogs and polyphenols as potential therapeutics for age-related macular degeneration

IMPACT STATEMENT

Age-related macular degeneration (AMD) is a devastating retinal degenerative disease. Epidemiological reports showed an expected increasing prevalence of AMD in the near future. The only one existing FDA-approved pharmacological treatment involves an anti-vascular endothelial growth factor (VEGF) therapy with serious disadvantages. This limitation emphasizes an alarming need to develop new therapeutic approaches to prevent and treat AMD. In this review, we summarize scientific data unraveling the therapeutic potential of the specific retinoid and natural compounds. The experimental results reported by us and other research groups demonstrated that retinoid analogs and compounds with natural product scaffolds could serve as lead compounds for the development of new therapeutic agents with potential to prevent or slow down the pathogenesis of AMD.

A Ketogenic & Low-Protein Diet Slows Retinal Degeneration in rd10 Mice

Purpose

Treatments that delay retinal cell death regardless of genetic causation are needed for inherited retinal degeneration (IRD) patients. The ketogenic diet is a high-fat, low-carbohydrate diet, used to treat epilepsy, and has beneficial effects for neurodegenerative diseases. This study aimed to determine whether the ketogenic diet could slow retinal degeneration.

Methods

Early weaned, rd10 and wild-type (WT) mice were placed on either standard chow, a ketogenic diet, or a ketogenic & low-protein diet. From postnatal day (PD) 23 to PD50, weight and blood β-hydroxybutyrate levels were recorded. Retinal thickness, retinal function, and visual performance were measured via optical coherence tomography, electroretinography (ERG), and optokinetic tracking (OKT). At PD40, serum albumin, rhodopsin protein, and phototransduction gene expression were measured.

Results

Both ketogenic diets elicited a systemic induction of ketosis. However, rd10 mice on the ketogenic & low-protein diet had significant increases in photoreceptor thickness, ERG amplitudes, and OKT thresholds, whereas rd10 mice on the ketogenic diet showed no photoreceptor preservation. In both rd10 and WT mice, the ketogenic & low-protein diet was associated with abnormal weight gain and decreases in serum albumin levels, 27% and 56%, respectively. In WT mice, the ketogenic & low-protein diet was also associated with an ∼20% to 30% reduction in ERG amplitudes.

Conclusions

The ketogenic & low-protein diet slowed retinal degeneration in a clinically relevant IRD model. In WT mice, the ketogenic & low-protein diet was associated with a decrease in phototransduction and serum albumin, which could serve as a protective mechanism in the rd10 model. Although ketosis was associated with protection, its role remains unclear.

Translational Relevance

Neuroprotective mechanisms associated with the ketogenic & low-protein diet have potential to slow retinal degeneration.

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.

Suppressive Effect of Arctium Lappa L. Leaves on Retinal Damage Against A2E-Induced ARPE-19 Cells and Mice

Age-related macular degeneration (AMD) is a major cause of irreversible loss of vision with 80–90% of patients demonstrating dry type AMD. Dry AMD could possibly be prevented by polyphenol-rich medicinal foods by the inhibition of N-retinylidene-N-retinylethanolamine (A2E)-induced oxidative stress and cell damage. Arctium lappa L. (AL) leaves are medicinal and have antioxidant activity. The purpose of this study was to elucidate the protective effects of the extract of AL leaves (ALE) on dry AMD models, including in vitro A2E-induced damage in ARPE-19 cells, a human retinal pigment epithelial cell line, and in vivo light-induced retinal damage in BALB/c mice. According to the total phenolic contents (TPCs), total flavonoid contents (TFCs) and antioxidant activities, ALE was rich in polyphenols and had antioxidant efficacies on 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and 2′,7′-dichlorofluorescin diacetate (DCFDA) assays. The effects of ALE on A2E accumulation and A2E-induced cell death were also monitored. Despite continued exposure to A2E (10 μM), ALE attenuated A2E accumulation in APRE-19 cells with levels similar to lutein. A2E-induced cell death at high concentration (25 μM) was also suppressed by ALE by inhibiting the apoptotic signaling pathway. Furthermore, ALE could protect the outer nuclear layer (ONL) in the retina from light-induced AMD in BALB/c mice. In conclusion, ALE could be considered a potentially valuable medicinal food for dry AMD.

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.

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.

Impacts of deletion and ichthyosis prematurity syndrome-associated mutations in fatty acid transport protein 4 on the function of RPE65

The retinal pigment epithelium-specific 65 kDa (RPE65) isomerase plays a pivotal role in photoreceptor survival and function. RPE65-catalyzed synthesis of 11-cis-retinol from all-trans-retinyl esters in the visual cycle is negatively regulated, through a heretofore unknown mechanism, by the fatty acid transport protein FATP4, mutations in which are associated with ichthyosis prematurity syndrome (IPS). Here, we analyzed the interaction between deletion mutants of FATP4 and RPE65 and the impacts of IPS-associated FATP4 mutations on RPE65 expression, 11-cis-retinol synthesis, and all-trans-retinyl ester synthesis. Our results suggest that the interaction between FATP4 and RPE65 contributes to the inhibition of RPE65 function and that IPS-associated nonsense and missense mutations in FATP4 have different effects on the visual cycle.

Non-viral Gene Therapy for Stargardt Disease with ECO/pRHO-ABCA4 Self-Assembled Nanoparticles

Stargardt disease (STGD) is an autosomal recessive retinal disorder caused by a monogenic ABCA4 mutation. Currently, there is no effective therapy to cure Stargardt disease. The replacement of mutated ABCA4 with a functional gene remains an attractive strategy. In this study, we have developed a non-viral gene therapy using nanoparticles self-assembled by a multifunctional pH-sensitive amino lipid ECO and a therapeutic ABCA4 plasmid. The nanoparticles mediated efficient intracellular gene transduction in wild-type (WT) and Abca4^-/- mice. Specific ABCA4 expression in the outer segment of photoreceptors was achieved by incorporating a rhodopsin promoter into the plasmids. The ECO/pRHO-ABCA4 nanoparticles induced substantial and specific ABCA4 expression for at least 8 months, 35% reduction in A2E accumulation on average, and a delayed Stargardt disease progression for at least 6 months in Abca4^-/- mice. ECO/plasmid nanoparticles constitute a promising non-viral gene therapy platform for Stargardt disease and other visual dystrophies.

Omega-3 Fatty Acids Supplementation: Therapeutic Potential in a Mouse Model of Stargardt Disease

Purpose

To evaluate the therapeutic effects of omega-3 (ω3) fatty acids on retinal degeneration in the ABCA4-/- model of Stargardt disease when the blood level of arachidonic acid (AA)/eicosapentaenoic acid (EPA) ratio is between 1 and 1.5.

Methods

Eight-month-old mice were allocated to three groups: wild type (129S1), ABCA4-/- untreated, and ABCA4-/- ω3 treated. ω3 treatment lasted 3 months and comprised daily gavage administration of EPA and docosahexaenoic acid (DHA). Blood and retinal fatty acid analysis was performed using gas chromatography to adjust the blood AA/EPA ∼1 to 1.5. Eyecups were histologically examined using transmission electron microscopy and confocal microscopy to evaluate lipofuscin granules and the photoreceptor layer. Retinal N-retinylidene-N-retinylethanolamine (A2E), a major component of retinal pigment epithelium lipofuscin, was quantified using liquid chromatography and tandem mass spectrometry, in addition to retinal proteomic analysis to determine changes in inflammatory proteins.

Results

EPA levels increased and AA levels decreased in the blood and retinas of the treatment group. Significantly less A2E and lipofuscin granules were observed in the treatment group. The thickness of the outer nuclear layer was significantly greater in the treatment group (75.66 ± 4.80 μm) than in the wild-type (61.40 ± 1.84 μm) or untreated ABCA4-/- (56.50 ± 3.24 μm) groups. Proteomic analysis indicated lower levels of complement component 3 (C3) in the treatment group, indicative of lower complement-induced inflammatory response.

Conclusions

Three months of ω3 supplementation (AA/EPA ∼1-1.5) reduces A2E levels, lipofuscin granules, and C3 levels in the ABCA4-/- mouse model of Stargardt disease, consistent with slowing of the disease.

Monitoring and Management of the Patient with Stargardt Disease

Stargardt disease (STGD1) represents one of the major common causes of inherited irreversible visual loss. Due to its high phenotypic and genotypic heterogeneity, STGD1 is a complex disease to understand. Non-invasive imaging, biochemical, and genetic advances have led to substantial improvements in unveiling the disease processes and novel promising therapeutic landscapes have been proposed. This review recapitulates the modalities for monitoring patients with STGD1 and the therapeutic options currently under investigation for the different stages of the disease.

Stemming retinal regeneration with pluripotent stem cells

Cell replacement therapy is a promising treatment for irreversible retinal cell death in diverse diseases, such as age-related macular degeneration (AMD), Stargardt's disease, retinitis pigmentosa (RP) and glaucoma. These diseases are all characterized by the degeneration of one or two retinal cell types that cannot regenerate spontaneously in humans. Aberrant retinal pigment epithelial (RPE) cells can be observed through optical coherence tomography (OCT) in AMD patients. In RP patients, the morphological and functional abnormalities of RPE and photoreceptor layers are caused by a genetic abnormality. Stargardt's disease or juvenile macular degeneration, which is characterized by the loss of the RPE and photoreceptors in the macular area, causes central vision loss at an early age. Loss of retinal ganglion cells (RGCs) can be observed in patients with glaucoma. Once the retinal cell degeneration is triggered, no treatments can reverse it. Transplantation-based approaches have been proposed as a universal therapy to target patients with various concomitant diseases. Both the replacement of dead cells and neuroprotection are strategies used to rescue visual function in animal models of retinal degeneration. Diverse retinal cell types derived from pluripotent stem cells, including RPE cells, photoreceptors, RGCs and even retinal organoids with a layered structure, provide unlimited cell sources for transplantation. In addition, mesenchymal stem cells (MSCs) are multifunctional and protect degenerating retinal cells. The aim of this review is to summarize current findings from preclinical and clinical studies. We begin with a brief introduction to retinal degenerative diseases and cell death in diverse diseases, followed by methods for retinal cell generation. Preclinical and clinical studies are discussed, and future concerns about efficacy, safety and immunorejection are also addressed.

Functional trade-offs and environmental variation shaped ancient trajectories in the evolution of dim-light vision

Trade-offs between protein stability and activity can restrict access to evolutionary trajectories, but widespread epistasis may facilitate indirect routes to adaptation. This may be enhanced by natural environmental variation, but in multicellular organisms this process is poorly understood. We investigated a paradoxical trajectory taken during the evolution of tetrapod dim-light vision, where in the rod visual pigment rhodopsin, E122 was fixed 350 million years ago, a residue associated with increased active-state (MII) stability but greatly diminished rod photosensitivity. Here, we demonstrate that high MII stability could have likely evolved without E122, but instead, selection appears to have entrenched E122 in tetrapods via epistatic interactions with nearby coevolving sites. In fishes by contrast, selection may have exploited these epistatic effects to explore alternative trajectories, but via indirect routes with low MII stability. Our results suggest that within tetrapods, E122 and high MII stability cannot be sacrificed-not even for improvements to rod photosensitivity.

Stargardt macular dystrophy and evolving therapies

INTRODUCTION

Stargardt macular dystrophy (STGD1) is a hereditary retinal degeneration that lacks effective treatment options. Gene therapy, stem cell therapy, and pharmacotherapy with visual cycle modulators (VCMs) and complement inhibitors are discussed as potential treatments.

AREAS COVERED

Investigational therapies for STGD1 aim to reduce toxic bisretinoids and lipofuscin in the retina and retinal pigment epithelium (RPE). These agents include C20-D3-vitamin A (ALK-001), isotretinoin, VM200, emixustat, and A1120. Avacincaptad pegol is a C5 complement inhibitor that may reduce inflammation-related RPE damage. Animal models of STGD1 show promising data for these treatments, though proof of efficacy in humans is lacking. Fenretinide and emixustat are VCMs for dry AMD and STGD1 that failed to halt geographic atrophy progression or improve vision in trials for AMD. A1120 prevents retinol transport into RPE and may spare side effects typically seen with VCMs (nyctalopia and chromatopsia). Stem cell transplantation suggests potential biologic plausibility in a phase I/II trial. Gene therapy aims to augment the mutated ABCA4 gene, though results of a phase I/II trial are pending.

EXPERT OPINION

Stem cell transplantation, ABCA4 gene therapy, VCMs, and complement inhibitors offer biologically plausible treatment mechanisms for treatment of STGD1. Further trials are warranted to assess efficacy and safety in humans.

Supplementation with Qter® and Creatine improves functional performance in COPD patients on long term oxygen therapy

BACKGROUND

Skeletal muscle dysfunction and poor functional capacity are important extra-pulmonary manifestations of chronic obstructive pulmonary disease (COPD), especially in COPD patients on long-term O₂ therapy (LTOT). Beside the role of pulmonary rehabilitation, the effect of nutritional interventions is still controversial, and there are knowledge gaps on the effective role of nutraceutical supplementation on hard endpoints. The aim of this study was to investigate the effects of nutritional supplementation with Coenzyme Q10 (QTer^®) - a powerful antioxidant with the potential to reduce oxidative stress and improve mitochondrial function - and Creatine on functional, nutritional, and metabolomic profile in COPD patients on long-term O₂ therapy.

METHODS

One-hundred and eight patients with COPD from 9 Italian hospitals were enrolled in this double-blinded randomized placebo-controlled clinical study. At baseline and after 2 months of therapy, the patients underwent spirometry, 6-minute walk test (6MWT), bioelectrical impedance analysis, and activities of daily living questionnaire (ADL). Also, dyspnea scores and BODE index were calculated. At both time points, plasma concentration of CoQ10 and metabolomic profiling were measured.

FINDINGS

Ninety patients, who randomly received supplementation with QTer^® and Creatine or placebo, completed the study. Compared with placebo, supplemented patients showed improvements in 6MWT (51 ± 69 versus 15 ± 91 m, p < 0.05), body cell mass and phase angle, sodium/potassium ratio, dyspnea indices and ADL score. The CoQ10 plasma concentration increased in the supplementation group whereas it did not change in the placebo group. The metabolomics profile also differed between groups. Adverse events were similar in both groups.

INTERPRETATION

These results show that in patients with COPD, dietary supplementation with CoQ10 and Creatine improves functional performance, body composition and perception of dyspnea. A systemic increase in some anti-inflammatory metabolites supports a pathobiological mechanism as a reason for these benefits. Further trials should help clarifying the role of QTer^® and Creatine supplementation in patients with COPD.

A non-retinoid antagonist of retinol-binding protein 4 rescues phenotype in a model of Stargardt disease without inhibiting the visual cycle

A primary pathological defect in the heritable eye disorder Stargardt disease is excessive accumulation of cytotoxic lipofuscin bisretinoids in the retina. Age-dependent accumulation of lipofuscin in the retinal pigment epithelium (RPE) matches the age-dependent increase in the incidence of the atrophic (dry) form of age-related macular degeneration (AMD) and therefore may be one of several pathogenic factors contributing to AMD progression. Lipofuscin bisretinoid synthesis in the retina depends on the influx of serum retinol from the circulation into the RPE. Formation of the tertiary retinol-binding protein 4 (RBP4)-transthyretin-retinol complex in the serum is required for this influx. Herein, we report the pharmacological effects of the non-retinoid RBP4 antagonist, BPN-14136. BPN-14136 dosing in the Abca4^-/- mouse model of increased lipofuscinogenesis significantly reduced serum RBP4 levels and inhibited bisretinoid synthesis, and this inhibition correlated with a partial reduction in visual cycle retinoids such as retinaldehydes serving as bisretinoid precursors. BPN-14136 administration at doses inducing maximal serum RBP4 reduction did not produce changes in the rate of the visual cycle, consistent with minimal changes in dark adaptation. Abca4^-/- mice exhibited dysregulation of the complement system in the retina, and BPN-14136 administration normalized the retinal levels of proinflammatory complement cascade components such as complement factors D and H, C-reactive protein, and C3. We conclude that BPN-14136 has several beneficial characteristics, combining inhibition of bisretinoid synthesis and reduction in retinaldehydes with normalization of the retinal complement system. BPN-14136, or a similar compound, may be a promising drug candidate to manage Stargardt disease and dry AMD.

A novel RPE65 inhibitor CU239 suppresses visual cycle and prevents retinal degeneration

The retinoid visual cycle is an ocular retinoid metabolism specifically dedicated to support vertebrate vision. The visual cycle serves not only to generate light-sensitive visual chromophore 11-cis-retinal, but also to clear toxic byproducts of normal visual cycle (i.e. all-trans-retinal and its condensation products) from the retina, ensuring both the visual function and the retinal health. Unfortunately, various conditions including genetic predisposition, environment and aging may attribute to a functional decline of the all-trans-retinal clearance. To combat all-trans-retinal mediated retinal degeneration, we sought to slow down the retinoid influx from the RPE by inhibiting the visual cycle with a small molecule. The present study describes identification of CU239, a novel non-retinoid inhibitor of RPE65, a key enzyme in the visual cycle. Our data demonstrated that CU239 selectively inhibited isomerase activity of RPE65, with IC₅₀ of 6 μM. Further, our results indicated that CU239 inhibited RPE65 via competition with its substrate all-trans-retinyl ester. Mice with systemic injection of CU239 exhibited delayed chromophore regeneration after light bleach, and conferred a partial protection of the retina against injury from high intensity light. Taken together, CU239 is a potent visual cycle modulator and may have a therapeutic potential for retinal degeneration.

Statistically strong label-free quantitative identification of native fluorophores in a biological sample

Bioimaging using endogenous cell fluorescence, without any external biomarkers makes it possible to explore cells and tissues in their original native state, also in vivo. In order to be informative, this label-free method requires careful multispectral or hyperspectral recording of autofluorescence images followed by unsupervised extraction (unmixing) of biochemical signatures. The unmixing is difficult due to the scarcity of biochemically pure regions in cells and also because autofluorescence is weak compared with signals from labelled cells, typically leading to low signal to noise ratio. Here, we solve the problem of unsupervised hyperspectral unmixing of cellular autofluorescence by introducing the Robust Dependent Component Analysis (RoDECA). This approach provides sophisticated and statistically robust quantitative biochemical analysis of cellular autofluorescence images. We validate our method on artificial images, where the addition of varying known level of noise has allowed us to quantify the accuracy of our RoDECA analysis in a way that can be applied to real biological datasets. The same unsupervised statistical minimisation is then applied to imaging of mouse retinal photoreceptor cells where we establish the identity of key endogenous fluorophores (free NADH, FAD and lipofuscin) and derive the corresponding molecular abundance maps. The pre-processing methodology of image datasets is also presented, which is essential for the spectral unmixing analysis, but mostly overlooked in the previous studies.

Juvenile Macular Degenerations

In this article, we review the following 3 common juvenile macular degenerations: Stargardt disease, X-linked retinoschisis, and Best vitelliform macular dystrophy. These are inherited disorders that typically present during childhood, when vision is still developing. They are sufficiently common that they should be included in the differential diagnosis of visual loss in pediatric patients. Diagnosis is secured by a combination of clinical findings, optical coherence tomography imaging, and genetic testing. Early diagnosis promotes optimal management. Although there is currently no definitive cure for these conditions, therapeutic modalities under investigation include pharmacologic treatment, gene therapy, and stem cell transplantation.

Highly sensitive measurements of disease progression in rare disorders: Developing and validating a multimodal model of retinal degeneration in Stargardt disease

Background

Each inherited retinal disorder is rare, but together, they affect millions of people worldwide. No treatment is currently available for these blinding diseases, but promising new options—including gene therapy—are emerging. Arguably, the most prevalent retinal dystrophy is Stargardt disease. In each case, the specific combination of ABCA4 variants (> 900 identified to date) and modifying factors is virtually unique. It accounts for the vast phenotypic heterogeneity including variable rates of functional and structural progression, thereby potentially limiting the ability of phase I/II clinical trials to assess efficacy of novel therapies with few patients. To accommodate this problem, we developed and validated a sensitive and reliable composite clinical trial endpoint for disease progression based on structural measurements of retinal degeneration.

Methods and findings

We used longitudinal data from early-onset Stargardt patients from the Netherlands (development cohort, n = 14) and the United Kingdom (external validation cohort, n = 18). The composite endpoint was derived from best-corrected visual acuity, fundus autofluorescence, and spectral-domain optical coherence tomography. Weighting optimization techniques excluded visual acuity from the composite endpoint. After optimization, the endpoint outperformed each univariable outcome, and showed an average progression of 0.41° retinal eccentricity per year (95% confidence interval, 0.30–0.52). Comparing with actual longitudinal values, the model accurately predicted progression (R², 0.904). These properties were largely preserved in the validation cohort (0.43°/year [0.33–0.53]; prediction: R², 0.872). We subsequently ran a two-year trial simulation with the composite endpoint, which detected a 25% decrease in disease progression with 80% statistical power using only 14 patients.

Conclusions

These results suggest that a multimodal endpoint, reflecting structural macular changes, provides a sensitive measurement of disease progression in Stargardt disease. It can be very useful in the evaluation of novel therapeutic modalities in rare disorders.

Complement modulation in the retinal pigment epithelium rescues photoreceptor degeneration in a mouse model of Stargardt disease

Recessive Stargardt macular degeneration (STGD1) is caused by mutations in the gene for the ABCA4 transporter in photoreceptor outer segments. STGD1 patients and Abca4^-/- (STGD1) mice exhibit buildup of bisretinoid-containing lipofuscin pigments in the retinal pigment epithelium (RPE), increased oxidative stress, augmented complement activation and slow degeneration of photoreceptors. A reduction in complement negative regulatory proteins (CRPs), possibly owing to bisretinoid accumulation, may be responsible for the increased complement activation seen on the RPE of STGD1 mice. CRPs prevent attack on host cells by the complement system, and complement receptor 1-like protein y (CRRY) is an important CRP in mice. Here we attempted to rescue the phenotype in STGD1 mice by increasing expression of CRRY in the RPE using a gene therapy approach. We injected recombinant adeno-associated virus containing the CRRY coding sequence (AAV-CRRY) into the subretinal space of 4-wk-old Abca4^-/- mice. This resulted in sustained, several-fold increased expression of CRRY in the RPE, which significantly reduced the complement factors C3/C3b in the RPE. Unexpectedly, AAV-CRRY-treated STGD1 mice also showed reduced accumulation of bisretinoids compared with sham-injected STGD1 control mice. Furthermore, we observed slower photoreceptor degeneration and increased visual chromophore in 1-y-old AAV-CRRY-treated STGD1 mice. Rescue of the STGD1 phenotype by AAV-CRRY gene therapy suggests that complement attack on the RPE is an important etiologic factor in STGD1. Modulation of the complement system by locally increasing CRP expression using targeted gene therapy represents a potential treatment strategy for STGD1 and other retinopathies associated with complement dysregulation.

Norbixin Protects Retinal Pigmented Epithelium Cells and Photoreceptors against A2E-Mediated Phototoxicity In Vitro and In Vivo

The accumulation of N-retinylidene-N-retinylethanolamine (A2E, a toxic by-product of the visual pigment cycle) in the retinal pigment epithelium (RPE) is a major cause of visual impairment in the elderly. Photooxidation of A2E results in retinal pigment epithelium degeneration followed by that of associated photoreceptors. Present treatments rely on nutrient supplementation with antioxidants. 9’-cis-Norbixin (a natural diapocarotenoid, 97% purity) was prepared from Bixa orellana seeds. It was first evaluated in primary cultures of porcine retinal pigment epithelium cells challenged with A2E and illuminated with blue light, and it provided an improved photo-protection as compared with lutein or zeaxanthin. In Abca4^-/-Rdh8^-/- mice (a model of dry AMD), intravitreally-injected norbixin maintained the electroretinogram and protected photoreceptors against light damage. In a standard rat blue-light model of photodamage, norbixin was at least equally as active as phenyl-N-tert-butylnitrone, a free radical spin-trap. Chronic experiments performed with Abca4^-/-Rdh8^-/- mice treated orally for 3 months with norbixin showed a reduced A2E accumulation in the retina. Norbixin appears promising for developing an oral treatment of macular degeneration. A drug candidate (BIO201) with 9’-cis-norbixin as the active principle ingredient is under development, and its potential will be assessed in a forthcoming clinical trial.

Retinol Dehydrogenases Regulate Vitamin A Metabolism for Visual Function

The visual system produces visual chromophore, 11-cis-retinal from dietary vitamin A, all-trans-retinol making this vitamin essential for retinal health and function. These metabolic events are mediated by a sequential biochemical process called the visual cycle. Retinol dehydrogenases (RDHs) are responsible for two reactions in the visual cycle performed in retinal pigmented epithelial (RPE) cells, photoreceptor cells and Müller cells in the retina. RDHs in the RPE function as 11-cis-RDHs, which oxidize 11-cis-retinol to 11-cis-retinal in vivo. RDHs in rod photoreceptor cells in the retina work as all-trans-RDHs, which reduce all-trans-retinal to all-trans-retinol. Dysfunction of RDHs can cause inherited retinal diseases in humans. To facilitate further understanding of human diseases, mouse models of RDHs-related diseases have been carefully examined and have revealed the physiological contribution of specific RDHs to visual cycle function and overall retinal health. Herein we describe the function of RDHs in the RPE and the retina, particularly in rod photoreceptor cells, their regulatory properties for retinoid homeostasis and future therapeutic strategy for treatment of retinal diseases.

Protective effects of resveratrol and its analogs on age-related macular degeneration in vitro

Damage of retinal pigment epithelial (RPE) cells by A2E may be critical for age-related macular degeneration (AMD) management. Accumulation and photooxidation of A2E are known to be one of the critical causes in AMD. Here, we evaluated the protective effect of resveratrol (RES), piceatannol (PIC) and RES glycones on blue-light-induced RPE cell death caused by A2E photooxidation. A2E treatment followed by blue light exposure caused significant damages on human RPE cells (ARPE-19). But the damages were attenuated by post- and pre-treatment of RES and PIC in our in vitro models. The results of cell free system and FAB-MS analysis clearly showed that the reduction of A2E by blue light exposure was significantly rescued, and that oxidized forms of A2E were significantly reduced by RES or PIC treatment. Besides, RES or PIC inhibited the intracellular accumulation of A2E. Not only RES and PIC but RES glycones showed protection of ARPE-19 cells against A2E and blue-light-induced photo-damage. These findings demonstrate that RES and its analogs may have protective effects against A2E and blue-light-induced ARPE-19 cell death through regulation of A2E accumulation as well as photooxidation of A2E. Thus RES and its analogs may be beneficial for AMD treatment.