Inhibition of ceramide biosynthesis preserves photoreceptor structure and function in a mouse model of retinitis pigmentosa

Dihydroceramide desaturase modulates autolysosome maturation and ameliorates CRB1 retinopathy

Variants in the CRB1 gene cause retinal degeneration and subsequent vision impairment in patients of retinitis pigmentosa (RP). No treatments are currently available to cure or impede the progression of CRB1-associated retinopathy. Previous studies have revealed alterations in the endolysosomal systems and autophagy in the absence of CRB1, but their roles in the pathogenesis of CRB1 retinopathy are unclear. Here, we examined the disease mechanism of CRB1 retinopathy using loss-of-function mutants of crumbs (crb), the Drosophila homolog of CRB1. We found that the loss of crb results in overactivation of autophagy in the eye. We also discovered that dihydroceramide desaturase encoded by infertile crescent (ifc), was up-regulated in crb mutants. Overexpression of ifc inhibited autolysosomes and alleviated Atg1-induced autophagic cell death. Mechanistically, ifc enhanced the binding of Rac1 to Atg8 and increased the autophagosomal localization of active Rac1, thus inhibiting autophagy. Importantly, autophagy inhibitions achieved through ifc overexpression, chloroquine treatment, or Beclin-1 RNAi all ameliorated the neurodegeneration of crb mutant eyes. Together, these findings highlight the mechanism of dihydroceramide desaturase in modulating autolysosome functions in crb mutants, providing new insights for developing treatments against CRB1 retinopathy.

Gene therapy for age-related macular degeneration: a promising frontier in vision preservation

Age-related macular degeneration (AMD) is a leading cause of central vision loss, progressively impairing the retina and affecting millions worldwide. By 2040, global cases of AMD are projected to reach 300 million, posing a significant public health challenge. While early AMD may only cause mild visual impairment, advanced stages, particularly neovascular (wet) and non-neovascular (dry) AMD, can lead to severe vision loss or legal blindness, substantially affecting daily life. The introduction of anti-angiogenic therapies has revolutionized wet AMD treatment, offering a high probability of preserving or improving vision. However, these therapies do not halt AMD progression, and no definitive treatments exist for dry AMD. The limitations of current therapies, such as frequent injections and treatment resistance, underscore the urgent need for novel strategies. Gene therapy, which has shown success in treating other hereditary retinal diseases, offers a promising long-term solution for AMD by targeting retinal cells to produce therapeutic proteins. This review explores the potential of gene therapy for AMD, examining recent clinical trials and future treatment directions.

Elevated Very-Long-Chain Ceramides in the Vitreous Humor of Patients With Proliferative Diabetic Retinopathy

Purpose

To quantitate the levels of various ceramide species in the vitreous of patients with proliferative diabetic retinopathy (PDR) and to investigate the role of vitreal ceramides in the pathogenesis of PDR.

Study Design

A case control study.

Methods

We collected vitreous samples from 25 type 2 diabetes patients with PDR and 25 age- and sex-matched nondiabetic controls undergoing vitrectomy. The levels of ceramide species (C16:0, 18:0, 20:0, 22:0, 24:1, and 24:0) were measured by ultra-high-performance liquid chromatography-tandem mass spectrometry with positive electrospray ionization mode. The correlation of baseline characteristics, blood test data, and clinical manifestation of PDR were analyzed with vitreal ceramides levels.

Results

The total level of ceramides was substantially higher in the PDR group than the control group (18.626 ± 19.264 versus 3.524 ± 2.456 pmol/mg protein; P < 0.001). Among ceramides of various acyl chain lengths, the increases of very-long-chain (VLC) ceramides (C22-C24) were more drastic than those of long-chain ceramides (C16-C20). In the PDR group, VLC ceramide species accounted for 76.1%, whereas in the control group, C16 ceramide predominated at 40.5%. Based on the multivariate linear regression analysis, diagnosis of diabetes (β = 14.5751; P = 0.0327) and lower body mass index (β = -2.1396; P = 0.0173) were significantly associated with higher level of VLC ceramides. Intravitreal injection of anti-VEGF leads to insignificant reduction of VLC ceramides (P = 0.068).

Conclusions

Vitreal ceramide levels were elevated in diabetic subjects, especially the VLC species, which may contribute to the pathogenesis of diabetic retinopathy.

Nanotherapy for Neural Retinal Regeneration

Retinal diseases can severely impair vision and even lead to blindness, posing significant threats to both physical and mental health. Physical retinal regenerative therapies are poised to revolutionize the treatment of various disorders associated with blindness. However, these therapies must overcome the challenges posed by the protective inner and outer blood‒retinal barriers. Nanotechnology applications in ophthalmology have shown great potential in addressing the issue of drug delivery to the eye. Moreover, nanotechnology-based therapeutics can have profound clinical impacts on retinopathy, particularly retinal regeneration, thereby improving patient outcomes. Continuous advancements in nanotechnology are being applied to regenerate lost or damaged eye tissues and to treat vision loss and blindness caused by various retinal degenerative diseases. These approaches can be categorized into three main strategies: i) nanoparticles for delivering drugs, genes, and other essential substances; ii) nanoscaffolds for providing biocompatible support; and iii) nanocomposites for enhancing the functionality of primary or stem cells. The aim of this comprehensive review is to present the current understanding of nanotechnology-based therapeutics for retinal regeneration, with a focus on the perspective functions of nanomaterials.

Inhibiting De Novo Biosynthesis of Ceramide by L-Cycloserine Can Prevent Light-Induced Retinal Degeneration in Albino BALB/c Mice

Retinal degenerative diseases lead to irreversible vision loss due to photoreceptor cell death, driven by complex genetic and environmental factors. Ceramide, a sphingolipid metabolite, emerges as a critical mediator in the apoptotic cascade associated with retinal degeneration. Our previous work demonstrated L-Cycloserine's ability to protect photoreceptor-derived cells from oxidative stress by inhibiting the de novo ceramide pathway and thus prompting further investigation on its effect in the in vivo retina. This study investigates the potential of L-Cycloserine to protect albino BALB/c mice against light-induced retinal degeneration (LIRD). L-Cycloserine, in an optimal dose, administered systemically 30 min before LIRD, was found to prevent photoreceptor cell death significantly from light-induced degeneration. We further determined the retinal bioavailability and pharmacokinetic behavior of L-Cycloserine, its effect on sphingolipid profile, expression of sphingolipid biosynthetic, and cell death-promoting genes and proteins from the retina to understand the underlying mechanisms. This study lays the groundwork for further preclinical and clinical investigations into L-Cycloserine's potential as a novel therapeutic in treating retinal degenerative diseases.

Macular telangiectasia type 2 in a patient with Down syndrome: A possible association

Purpose

Down syndrome (DS) is one of the most prevalent genetic diseases associated with a variety of ophthalmic disorders, including reported retinal abnormalities. Macular telangiectasia type 2 (MacTel 2) is a late-onset neurodegenerative retinal disease with a substantial genetic component. We hereby describe a case of a female with DS who presented with MacTel 2, and we discuss the possible pathways associating both entities.

Observation

We report the case of a 49-year-old female with a medical history of DS and hydroxychloroquine (HCQ) intake. She was referred for HCQ retinal toxicity screening. The multimodal imaging revealed a temporal perifoveal gray area with crystal deposits on multicolor fundoscopy with parafoveal outer retinal atrophy and ellipsoid zone loss with inner retinal cavitations in both eyes on the optical Coherence Tomography (OCT) B scan. The corresponding swept-source OCT angiography confirmed the presence of bilateral macular telangiectasia.

Conclusion and importance

Metabolic pathways including serine/glycine and sphingolipids are incriminated in both entities' pathogenesis suggesting a possible association, hence, the importance of raising awareness of this association. More cases are likely to be found since DS patients currently have a nearly normal lifespan. Additional retinal examination of DS adults is then necessary to look for signs of MacTel 2.

Use of Myriocin as co-adjuvant in glaucoma surgery: An in vitro study

Mitomycin C as well as other antiproliferative drugs are off-label agents widely used to prevent the failure of glaucoma surgery due to activation of Tenon's fibroblasts and the ensuing excessive subconjunctival scarring. Though efficacious, these treatments are associated with some severe long-term complications, so it is crucial to investigate less cytotoxic compounds as adjuvant therapy in glaucoma surgery. The aim of this study was to evaluate the effect and potential cytotoxicity of Myriocin, a natural sphingolipid synthesis inhibitor, on TGF-β1-induced myofibroblasts transformation of human dermal fibroblasts. We found that myriocin significantly attenuated the transcript levels of αSMA, CTGF, and MMP9 which are involved in the fibrosis process. Mitomycin C poorly affects the same pro-fibrotic markers while reducing fibroblasts motility as much as myriocin. At similar doses, five minutes of mitomycin C treatment consistently affects human dermal fibroblast viability and proliferation compared to prolonged myriocin application, strengthening already published data on the good tolerability of this natural compound. Our results draw attention to the use of myriocin as an adjuvant in glaucoma surgery due to the effectiveness in reducing fibroblasts to myofibroblasts transformation and the low cytotoxicity.

Mutant mice with rod-specific VPS35 deletion exhibit retinal α-synuclein pathology-associated degeneration

Vacuolar protein sorting 35 (VPS35), the core component of the retromer complex which regulates endosomal trafficking, is genetically linked with Parkinson's disease (PD). Impaired vision is a common non-motor manifestation of PD. Here, we show mouse retinas with VPS35-deficient rods exhibit synapse loss and visual deficit, followed by progressive degeneration concomitant with the emergence of Lewy body-like inclusions and phospho-α-synuclein (P-αSyn) aggregation. Ultrastructural analyses reveal VPS35-deficient rods accumulate aggregates in late endosomes, deposited as lipofuscins bound to P-αSyn. Mechanistically, we uncover a protein network of VPS35 and its interaction with HSC70. VPS35 deficiency promotes sequestration of HSC70 and P-αSyn aggregation in late endosomes. Microglia which engulf lipofuscins and P-αSyn aggregates are activated, displaying autofluorescence, observed as bright dots in fundus imaging of live animals, coinciding with pathology onset and progression. The Rod∆Vps35 mouse line is a valuable tool for further mechanistic investigation of αSyn lesions and retinal degenerative diseases.

Recent Advances in Nanomedicine for Ocular Fundus Neovascularization Disease Management

As an indispensable part of the human sensory system, visual acuity may be impaired and even develop into irreversible blindness due to various ocular pathologies. Among ocular diseases, fundus neovascularization diseases (FNDs) are prominent etiologies of visual impairment worldwide. Intravitreal injection of anti-vascular endothelial growth factor drugs remains the primary therapy but is hurdled by common complications and incomplete potency. To renovate the current therapeutic modalities, nanomedicine emerged as the times required, which is endowed with advanced capabilities, able to fulfill the effective ocular fundus drug delivery and achieve precise drug release control, thus further improving the therapeutic effect. This review provides a comprehensive summary of advances in nanomedicine for FND management from state-of-the-art studies. First, the current therapeutic modalities for FNDs are thoroughly introduced, focusing on the key challenges of ocular fundus drug delivery. Second, nanocarriers are comprehensively reviewed for ocular posterior drug delivery based on the nanostructures: polymer-based nanocarriers, lipid-based nanocarriers, and inorganic nanoparticles. Thirdly, the characteristics of the fundus microenvironment, their pathological changes during FNDs, and corresponding strategies for constructing smart nanocarriers are elaborated. Furthermore, the challenges and prospects of nanomedicine for FND management are thoroughly discussed.

Sphingolipid biosynthetic inhibitor L-Cycloserine prevents oxidative-stress-mediated death in an in vitro model of photoreceptor-derived 661W cells

Oxidative stress plays a pivotal role in the pathogenesis of several neurodegenerative diseases. Retinal degeneration causes irreversible death of photoreceptor cells, ultimately leading to vision loss. Under oxidative stress, the synthesis of bioactive sphingolipid ceramide increases, triggering apoptosis in photoreceptor cells and leading to their death. This study investigates the effect of L-Cycloserine, a small molecule inhibitor of ceramide biosynthesis, on sphingolipid metabolism and the protection of photoreceptor-derived 661W cells from oxidative stress. The results demonstrate that treatment with L-Cycloserine, an inhibitor of Serine palmitoyl transferase (SPT), markedly decreases bioactive ceramide and associated sphingolipids in 661W cells. A nontoxic dose of L-Cycloserine can provide substantial protection of 661W cells against H2O2-induced oxidative stress by reversing the increase in ceramide level observed under oxidative stress conditions. Analysis of various antioxidant, apoptotic and sphingolipid pathway genes and proteins also confirms the ability of L-Cycloserine to modulate these pathways. Our findings elucidate the generation of sphingolipid mediators of cell death in retinal cells under oxidative stress and the potential of L-Cycloserine as a therapeutic candidate for targeting ceramide-induced degenerative diseases by inhibiting SPT. The promising therapeutic prospect identified in our findings lays the groundwork for further validation in in-vivo and preclinical models of retinal degeneration.

Navigating the future of retinitis pigmentosa treatments: A comprehensive analysis of therapeutic approaches in rd10 mice

Retinitis pigmentosa (RP) is a degenerative disease, caused by genetic mutations that lead to a loss in photoreceptors. For research on RP, rd10 mice, which carry mutations in the phosphodiesterase (PDE) gene, exhibit degenerative patterns comparable to those of patients with RP, making them an ideal model for investigating potential treatments. Although numerous studies have reported the potential of biochemical drugs, gene correction, and stem cell transplantation in decelerating rd10 retinal degeneration, a comprehensive review of these studies has yet to be conducted. Therefore, here, a comparative analysis of rd10 mouse treatment research over the past decade was performed. Our findings suggest that biochemical drugs capable of inhibiting the inflammatory response may be promising therapeutics. Additionally, significant progress has been made in the field of gene therapy; nevertheless, challenges such as strict delivery requirements, bystander editing, and off-target effects still need to be resolved. Nevertheless, secretory function is the only unequivocal protective effect of stem cell transplantation. In summary, this review presents a comprehensive analysis and synthesis of the treatment approaches employing rd10 mice as experimental subjects, describing a clear pathway for future RP treatment research and identifies potential clinical interventions.

Untargeted and temporal analysis of retinal lipidome in bacterial endophthalmitis

Bacterial endophthalmitis is a blinding infectious disease typically acquired during ocular surgery. We previously reported significant alterations in retinal metabolism during Staphylococcus (S) aureus endophthalmitis. However, the changes in retinal lipid composition during endophthalmitis are unknown. Here, using a mouse model of S. aureus endophthalmitis and an untargeted lipidomic approach, we comprehensively analyzed temporal alterations in total lipids and oxylipin in retina. Our data showed a time-dependent increase in the levels of lipid classes, sphingolipids, glycerolipids, sterols, and non-esterified fatty acids, whereas levels of phospholipids decreased. Among lipid subclasses, phosphatidylcholine decreased over time. The oxylipin analysis revealed increased prostaglandin-E2, hydroxyeicosatetraenoic acids, docosahexaenoic acid, eicosapentaenoic acid, and α-linolenic acid. In-vitro studies using mouse bone marrow-derived macrophages showed increased lipid droplets and lipid-peroxide formation in response to S. aureus infection. Collectively, these findings suggest that S. aureus-infection alters the retinal lipid profile, which may contribute to the pathogenesis of bacterial endophthalmitis.

Distinct mouse models of Stargardt disease display differences in pharmacological targeting of ceramides and inflammatory responses

Mutations in many visual cycle enzymes in photoreceptors and retinal pigment epithelium (RPE) cells can lead to the chronic accumulation of toxic retinoid byproducts, which poison photoreceptors and the underlying RPE if left unchecked. Without a functional ATP-binding cassette, sub-family A, member 4 (ABCA4), there is an elevation of all-trans-retinal and prolonged buildup of all-trans-retinal adducts, resulting in a retinal degenerative disease known as Stargardt-1 disease. Even in this monogenic disorder, there is significant heterogeneity in the time to onset of symptoms among patients. Using a combination of molecular techniques, we studied Abca4 knockout (simulating human noncoding disease variants) and Abca4 knock-in mice (simulating human misfolded, catalytically inactive protein variants), which serve as models for Stargardt-1 disease. We compared the two strains to ascertain whether they exhibit differential responses to agents that affect cytokine signaling and/or ceramide metabolism, as alterations in either of these pathways can exacerbate retinal degenerative phenotypes. We found different degrees of responsiveness to maraviroc, a known immunomodulatory CCR5 antagonist, and to the ceramide-lowering agent AdipoRon, an agonist of the ADIPOR1 and ADIPOR2 receptors. The two strains also display different degrees of transcriptional deviation from matched WT controls. Our phenotypic comparison of the two distinct Abca4 mutant-mouse models sheds light on potential therapeutic avenues previously unexplored in the treatment of Stargardt disease and provides a surrogate assay for assessing the effectiveness for genome editing.

AAV-mediated base-editing therapy ameliorates the disease phenotypes in a mouse model of retinitis pigmentosa

Base editing technology is an ideal solution for treating pathogenic single-nucleotide variations (SNVs). No gene editing therapy has yet been approved for eye diseases, such as retinitis pigmentosa (RP). Here, we show, in the rd10 mouse model, which carries an SNV identified as an RP-causing mutation in human patients, that subretinal delivery of an optimized dual adeno-associated virus system containing the adenine base editor corrects the pathogenic SNV in the neuroretina with up to 49% efficiency. Light microscopy showed that a thick and robust outer nuclear layer (photoreceptors) was preserved in the treated area compared with the thin, degenerated outer nuclear layer without treatment. Substantial electroretinogram signals were detected in treated rd10 eyes, whereas control treated eyes showed minimal signals. The water maze experiment showed that the treatment substantially improved vision-guided behavior. Together, we construct and validate a translational therapeutic solution for the treatment of RP in humans. Our findings might accelerate the development of base-editing based gene therapies.

Recent advances and prospects for lipid-based nanoparticles as drug carriers in the treatment of human retinal diseases

The delivery of cures for retinal diseases remains problematic. There are four main challenges: passing through multiple barriers of the eye, the delivery to particular retinal cell types, the capability to carry different forms of therapeutic cargo and long-term therapeutic efficacy. Lipid-based nanoparticles (LBNPs) are potent to overcome these challenges due to their unique merits: amphiphilic nanoarchitectures to pass biological barriers, vary modifications with specific affinity to target cell types, flexible capacity for large and mixed types of cargos and slow-release formulations for long-term treatment. We have reviewed the latest research on the applications of LBNPs for treating retinal diseases and categorized them by different payloads. Furthermore, we identified technical barriers and discussed possible future development for LBNPs to expand the therapeutic potential in treating retinal diseases.

Improved Protocol for Reproducible Human Cortical Organoids Reveals Early Alterations in Metabolism with MAPT Mutations

Cerebral cortical-enriched organoids derived from human pluripotent stem cells (hPSCs) are valuable models for studying neurodevelopment, disease mechanisms, and therapeutic development. However, recognized limitations include the high variability of organoids across hPSC donor lines and experimental replicates. We report a 96-slitwell method for efficient, scalable, reproducible cortical organoid production. When hPSCs were cultured with controlled-release FGF2 and an SB431542 concentration appropriate for their TGFBR1 / ALK5 expression level, organoid cortical patterning and reproducibility were significantly improved. Well-patterned organoids included 16 neuronal and glial subtypes by single cell RNA sequencing (scRNA-seq), frequent neural progenitor rosettes and robust BCL11B+ and TBR1+ deep layer cortical neurons at 2 months by immunohistochemistry. In contrast, poorly-patterned organoids contain mesendoderm-related cells, identifiable by negative QC markers including COL1A2 . Using this improved protocol, we demonstrate increased sensitivity to study the impact of different MAPT mutations from patients with frontotemporal dementia (FTD), revealing early changes in key metabolic pathways.

Ceramide compensation by ceramide synthases preserves retinal function and structure in a retinal dystrophy mouse model

Increasing evidence has supported the role of ceramide as a mediator of photoreceptor dysfunction or cell death in ceramide accumulation and deficiency contexts. TLCD3B, a non-canonical ceramide synthase, was previously identified in addition to the six canonical ceramide synthases (CerSs), and the Tlcd3b-/- mouse model exhibited both retinal dysfunction and degeneration. As previous canonical CerS-deficient mouse models failed to display retinal degeneration, the mechanisms of how TLCD3B interacts with CerSs have not been investigated. Additionally, as the ceramide profile of each CerS is distinct, it is unclear whether the overall level or the homeostasis of different ceramide species plays a critical role in photoreceptor degeneration. Interactions between TLCD3B with canonical CerSs expressed in the retina were examined by subretinally injecting recombinant adeno-associated virus 8 vectors containing the Cers2 (rAAV8-CerS2), Cers4 (rAAV8-CerS4) and Cers5 (rAAV8-CerS5) genes. Injection of all three rAAV8-CerS vectors restored retinal functions as indicated by improved electroretinogram responses, but only rAAV8-CerS5 successfully retained retinal morphology in Tlcd3b-/- mice. CerSs and TLCD3B played partially redundant roles. Additionally, rather than acting as an integral entity, different ceramide species had different impacts on retinal cells, suggesting that the maintenance of the overall ceramide profile is critical for retinal function.

Overcoming Treatment Challenges in Posterior Segment Diseases with Biodegradable Nano-Based Drug Delivery Systems

Posterior segment eye diseases present a challenge in treatment due to the complex structures in the eye that serve as robust static and dynamic barriers, limiting the penetration, residence time, and bioavailability of topical and intraocular medications. This hinders effective treatment and requires frequent dosing, such as the regular use of eye drops or visits to the ophthalmologist for intravitreal injections, to manage the disease. Moreover, the drugs must be biodegradable to minimize toxicity and adverse reactions, as well as small enough to not affect the visual axis. The development of biodegradable nano-based drug delivery systems (DDSs) can be the solution to these challenges. First, they can stay in ocular tissues for longer periods of time, reducing the frequency of drug administration. Second, they can pass through ocular barriers, offering higher bioavailability to targeted tissues that are otherwise inaccessible. Third, they can be made up of polymers that are biodegradable and nanosized. Hence, therapeutic innovations in biodegradable nanosized DDS have been widely explored for ophthalmic drug delivery applications. In this review, we will present a concise overview of DDSs utilized in the treatment of ocular diseases. We will then examine the current therapeutic challenges faced in the management of posterior segment diseases and explore how various types of biodegradable nanocarriers can enhance our therapeutic arsenal. A literature review of the pre-clinical and clinical studies published between 2017 and 2023 was conducted. Through the advances in biodegradable materials, combined with a better understanding of ocular pharmacology, the nano-based DDSs have rapidly evolved, showing great promise to overcome challenges currently encountered by clinicians.

Genetic modifiers of synucleinopathies-lessons from experimental models

α-Synuclein is a pleiotropic protein underlying a group of progressive neurodegenerative diseases, including Parkinson's disease and dementia with Lewy bodies. Together, these are known as synucleinopathies. Like all neurological diseases, understanding of disease mechanisms is hampered by the lack of access to biopsy tissues, precluding a real-time view of disease progression in the human body. This has driven researchers to devise various experimental models ranging from yeast to flies to human brain organoids, aiming to recapitulate aspects of synucleinopathies. Studies of these models have uncovered numerous genetic modifiers of α-synuclein, most of which are evolutionarily conserved. This review discusses what we have learned about disease mechanisms from these modifiers, and ways in which the study of modifiers have supported ongoing efforts to engineer disease-modifying interventions for synucleinopathies.

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.

Solid Lipid Nanoparticles: Multitasking Nano-Carriers for Cancer Treatment

Despite all the advances seen in recent years, the severe adverse effects and low specificity of conventional chemotherapy are still challenging problems regarding cancer treatment. Nanotechnology has helped to address these questions, making important contributions in the oncological field. The use of nanoparticles has allowed the improvement of the therapeutic index of several conventional drugs and facilitates the tumoral accumulation and intracellular delivery of complex biomolecules, such as genetic material. Among the wide range of nanotechnology-based drug delivery systems (nanoDDS), solid lipid nanoparticles (SLNs) have emerged as promising systems for delivering different types of cargo. Their solid lipid core, at room and body temperature, provides SLNs with higher stability than other formulations. Moreover, SLNs offer other important features, namely the possibility to perform active targeting, sustained and controlled release, and multifunctional therapy. Furthermore, with the possibility to use biocompatible and physiologic materials and easy scale-up and low-cost production methods, SLNs meet the principal requirements of an ideal nanoDDS. The present work aims to summarize the main aspects related to SLNs, including composition, production methods, and administration routes, as well as to show the most recent studies about the use of SLNs for cancer treatment.

The Role of Ceramide in Inherited Retinal Disease Pathology

Ceramide (Cer) plays an essential role in photoreceptor cell death in the retina. On the one hand, Cer accumulation emerges as a common feature during retina neurodegeneration, leading to the death of photoreceptors. On the other hand, Cer deficiency has also recently been associated with retinal dysfunction and degeneration. Although more and more evidence supports the importance of maintaining Cer homeostasis in the retina, mechanistic explanations of the observed phenotypes, especially in the context of Cer deficiency, are still lacking. An enhanced understanding of Cer's role in the retina will help us explore the underlying molecular basis for clinical phenotypes of retinal dystrophies and provide us with potential therapeutic targets.

rAAV-mediated over-expression of acid ceramidase prevents retinopathy in a mouse model of Farber lipogranulomatosis

Farber disease (FD) is a rare monogenic lysosomal storage disorder caused by mutations in ASAH1 that results in a deficiency of acid ceramidase (ACDase) activity and the abnormal systemic accumulation of ceramide species, leading to multi-system organ failure involving neurological decline and retinopathy. Here we describe the effects of rAAV-mediated ASAH1 over-expression on the progression of retinopathy in a mouse model of FD (Asah1^P361R/P361R) and its littermate controls (Asah1^+/+ and Asah1^+/P361R). Using a combination of non-invasive multimodal imaging, electrophysiology, post-mortem histology and mass spectrometry we demonstrate that ASAH1 over-expression significantly reduces central retinal thickening, ceramide accumulation, macrophage activation and limits fundus hyper-reflectivity and auto-fluorescence in FD mice, indicating rAAV-mediated over-expression of biologically active ACDase protein is able to rescue the anatomical retinal phenotype of Farber disease. Unexpectedly, ACDase over-expression in Asah1^+/+ and Asah1^+/P361R control eyes was observed to induce abnormal fundus hyper-reflectivity, auto-fluorescence and retinal thickening that closely resembles a FD phenotype. This study represents the first evidence of a gene therapy for Farber disease-related retinopathy. Importantly, the described gene therapy approach could be used to preserve vision in FD patients synergistically with broader enzyme replacement strategies aimed at preserving life.

Hydroxychloroquine Causes Early Inner Retinal Toxicity and Affects Autophagosome-Lysosomal Pathway and Sphingolipid Metabolism in the Retina

Hydroxychloroquine (HCQ) is an anti-malarial drug but also widely used to treat autoimmune diseases like arthritis and lupus. Although there have been multiple reports of the adverse effect of prolonged HCQ usage on the outer retina, leading to bull's-eye maculopathy, the effect of HCQ toxicity on the inner retina as well as on overall visual functions has not been explored in detail. Furthermore, lack of an established animal model of HCQ toxicity hinders our understanding of the underlying molecular mechanisms. Here, using a small clinical study, we confirmed the effect of HCQ toxicity on the inner retina, in particular the reduction in central inner retinal thickness, and established a mouse model of chronic HCQ toxicity that recapitulates the effects observed in human retina. Using the mouse model, we demonstrated that chronic HCQ toxicity results in loss of inner retinal neurons and retinal ganglion cells (RGC) and compromises visual functions. We further established that HCQ treatment prevents autophagosome-lysosome fusion and alters the sphingolipid homeostasis in mouse retina. Our results affirm the notion that HCQ treatment causes early damage to the inner retina and affects visual functions before leading to characteristic toxicity in the macular region of the outer retina, 'bull's-eye maculopathy.' We also provide insights into the underlying molecular mechanisms of HCQ retinal toxicity that may involve autophagy-lysosomal defects and alterations in sphingolipid metabolism.

AAV8-Mediated Gene Therapy Rescues Retinal Degeneration Phenotype in a Tlcd3b Knockout Mouse Model

Purpose

The purpose of this study was to assess the therapeutic efficacy of rAAV8-hGRK1-Tlcd3b in a Tlcd3b-/- mouse model of retinal generation and validate TLCD3B's role as a ceramide synthase in vivo.

Methods

Using Tlcd3b-/- mice as an inherited retinal disease animal model, we performed subretinal injection of rAAV8-hGRK1-Tlcd3b and evaluated the efficacy of gene replacement therapy. Tlcd3b-/- mice were treated at two time points: postnatal day 21 (P21) and postnatal day 120 (P120) with various dosages.

Results

Tlcd3b overexpression rescued retinal degeneration in the mutant mice, as indicated by significantly improved photoreceptor function and preservation of photoreceptor cells over the course of 1 year. Although Tlcd3b is expressed in all cell types in the retina, photoreceptor cell-specific expression of Tlcd3b is sufficient to rescue the phenotype, indicating the primary function of TLCD3B is in photoreceptors. Consistent with the idea that TLCD3B is a ceramide synthase, mass spectrometry analyses of the mutant retina indicate the reduction of C16-, C18-, and C20-ceramides in the retina, which are restored with Tlcd3b overexpression.

Conclusions

Our findings demonstrated the therapeutic efficacy of gene therapy in treating Tlcd3b mutant retina, laying the foundation for developing future therapy for TLCD3B retinopathy.

Inhibition of ceramide accumulation in AdipoR1-/- mice increases photoreceptor survival and improves vision

Adiponectin receptor 1 (ADIPOR1) is a lipid and glucose metabolism regulator that possesses intrinsic ceramidase activity. Mutations of the ADIPOR1 gene have been associated with nonsyndromic and syndromic retinitis pigmentosa. Here, we show that the absence of AdipoR1 in mice leads to progressive photoreceptor degeneration, significant reduction of electroretinogram amplitudes, decreased retinoid content in the retina, and reduced cone opsin expression. Single-cell RNA-Seq results indicate that ADIPOR1 encoded the most abundantly expressed ceramidase in mice and one of the 2 most highly expressed ceramidases in the human retina, next to acid ceramidase ASAH1. We discovered an accumulation of ceramides in the AdipoR1^–/– retina, likely due to insufficient ceramidase activity for healthy retina function, resulting in photoreceptor death. Combined treatment with desipramine/L-cycloserine (DC) lowered ceramide levels and exerted a protective effect on photoreceptors in AdipoR1^–/– mice. Moreover, we observed improvement in cone-mediated retinal function in the DC-treated animals. Lastly, we found that prolonged DC treatment corrected the electrical responses of the primary visual cortex to visual stimuli, approaching near-normal levels for some parameters. These results highlight the importance of ADIPOR1 ceramidase in the retina and show that pharmacological inhibition of ceramide generation can provide a therapeutic strategy for ADIPOR1-related retinopathy.

Compritol solid lipid nanoparticle formulations enhance the protective effect of betulinic acid derivatives in human Müller cells against oxidative injury

Müller cells maintain homeostatic functions in the retina. Their dysfunction leads to irreversible retinal diseases. Oxidative injury is a leading cause of retinal cytotoxicity. Our previous studies reported several betulinic acid (BA) derivatives can protect Müller cells from oxidative injury but achieving pharmacologically effective concentrations in the Müller cells could be a limitation. To optimise cellular delivery, we encapsulated the BA analogues H3, H5 and H7 into the clinically approved Compritol 888 and HD5 ATO solid lipid nanoparticles (SLNs) using the micro-emulsion method. The cytoprotective effects of these SLN-formulations were determined in human MIO-M1 cells. We found cytoprotection by H3 and H5 SLN-formulations was significantly enhanced, which was evident at concentrations much lower than those required with the free agents. Both SLN-formulations prolonged the duration of action of these agents. The most effective agent H5 delivered in 888 ATO SLNs attenuated glutamate-induced ROS formation and the associated necrosis in MIO-M1 cells. Overall, SLNs have emerged as promising delivery carriers for BA derivatives enhancing their protective effects against oxidative injury in human Müller cells. Our study is the first to show SLNs can be a viable route to delivery agents with improved efficacy and stability into human Müller cells favoring the treatment/prevention of retinal diseases.

Evidence for ceramide induced cytotoxicity in retinal ganglion cells

Ceramides are bioactive compounds that play important roles in regulating cellular responses to extracellular stimuli and stress. Previous studies have shown that ceramides contribute to retinal degeneration associated with ischemic and ocular hypertensive stress. Acid sphingomyelinase (ASMase) is one of the major enzymes responsible for the stress-induced generation of ceramides. The goals of this study are to investigate the effects of ceramides on retinal ganglion cells (RGCs) and of ASMase inhibition in ocular hypertensive mice. Induced pluripotent stem cell (iPSC)-derived RGCs and primary cultures of human optic nerve head astrocytes were used to characterize the response to C2-ceramide. Microbead-induced ocular hypertension in the ASMase heterozygote mouse model was used to confirm the physiological relevance of in vitro studies. In mice, RGC function and morphology were assessed with pattern ERG (pERG) and immunofluorescence. The addition of C2-ceramide to iPSC-derived RGCs produced a significant concentration- and time-dependent reduction in cell numbers when compared to control cultures. While the addition of C2-ceramide to astrocytes did not affect viability, it resulted in a 2.6-fold increase in TNF-α secretion. The addition of TNF-α or conditioned media from C2-ceramide-treated astrocytes to RGC cultures significantly reduced cell numbers by 56.1 ± 8.4% and 24.7 ± 4.8%, respectively. This cytotoxic response to astrocyte-conditioned media was blocked by TNF-α antibody. In ASMase heterozygote mice, functional and morphological analyses of ocular hypertensive eyes reveal significantly less RGC degeneration when compared with hypertensive eyes from wild-type mice. These results provide evidence that ceramides can induce RGC cell death by acting directly, as well as indirectly via the secretion of TNF-α from optic nerve head astrocytes. In vivo studies in mice provide evidence that ceramides derived through the activity of ASMase contribute to ocular hypertensive injury. Together these results support the importance of ceramides in the pathogenesis of ocular hypertensive injury to the retina.

Updates on sphingolipids: Spotlight on retinopathy

The sphingolipids ceramide (Cer), ceramide-1-phosphate (C1P), sphingosine (Sph), and sphingosine-1-phosphate (S1P)) are key signaling molecules that regulate many patho-biological processes. During the last decade, they have gained increasing attention since they may participate in important and numerous retinal processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Cer for instance has emerged as a key mediator of inflammation and death of neuronal and retinal pigment epithelium cells in experimental models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. S1P may have opposite biological actions, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1- phosphate may also contribute to uveitis. Furthermore, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), have been shown to preserve neuronal viability and retinal function. Collectively, the expanding role for these sphingolipids in the modulation of vital processes in retina cell types and in their dysregulation in retinal degenerations makes them attractive therapeutic targets.

Visual Cortex Engagement in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a family of inherited disorders caused by the progressive degeneration of retinal photoreceptors. There is no cure for RP, but recent research advances have provided promising results from many clinical trials. All these therapeutic strategies are focused on preserving existing photoreceptors or substituting light-responsive elements. Vision recovery, however, strongly relies on the anatomical and functional integrity of the visual system beyond photoreceptors. Although the retinal structure and optic pathway are substantially preserved at least in early stages of RP, studies describing the visual cortex status are missing. Using a well-established mouse model of RP, we analyzed the response of visual cortical circuits to the progressive degeneration of photoreceptors. We demonstrated that the visual cortex goes through a transient and previously undescribed alteration in the local excitation/inhibition balance, with a net shift towards increased intracortical inhibition leading to improved filtering and decoding of corrupted visual inputs. These results suggest a compensatory action of the visual cortex that increases the range of residual visual sensitivity in RP.

Inhibition of Ceramide Synthesis Reduces α-Synuclein Proteinopathy in a Cellular Model of Parkinson's Disease

Parkinson’s disease (PD) is a proteinopathy associated with the aggregation of α-synuclein and the formation of lipid–protein cellular inclusions, named Lewy bodies (LBs). LB formation results in impaired neurotransmitter release and uptake, which involve membrane traffic and require lipid synthesis and metabolism. Lipids, particularly ceramides, are accumulated in postmortem PD brains and altered in the plasma of PD patients. Autophagy is impaired in PD, reducing the ability of neurons to clear protein aggregates, thus worsening stress conditions and inducing neuronal death. The inhibition of ceramide synthesis by myriocin (Myr) in SH-SY5Y neuronal cells treated with preformed α-synuclein fibrils reduced intracellular aggregates, favoring their sequestration into lysosomes. This was associated with TFEB activation, increased expression of TFEB and LAMP2, and the cytosolic accumulation of LC3II, indicating that Myr promotes autophagy. Myr significantly reduces the fibril-related production of inflammatory mediators and lipid peroxidation and activates NRF2, which is downregulated in PD. Finally, Myr enhances the expression of genes that control neurotransmitter transport (SNARE complex, VMAT2, and DAT), whose progressive deficiency occurs in PD neurodegeneration. The present study suggests that counteracting the accumulation of inflammatory lipids could represent a possible therapeutic strategy for PD.

Sphingolipids as critical players in retinal physiology and pathology

Sphingolipids have emerged as bioactive lipids involved in the regulation of many physiological and pathological processes. In the retina, they have been established to participate in numerous processes, such as neuronal survival and death, proliferation and migration of neuronal and vascular cells, inflammation, and neovascularization. Dysregulation of sphingolipids is therefore crucial in the onset and progression of retinal diseases. This review examines the involvement of sphingolipids in retinal physiology and diseases. Ceramide (Cer) has emerged as a common mediator of inflammation and death of neuronal and retinal pigment epithelium cells in animal models of retinopathies such as glaucoma, age-related macular degeneration (AMD), and retinitis pigmentosa. Sphingosine-1-phosphate (S1P) has opposite roles, preventing photoreceptor and ganglion cell degeneration but also promoting inflammation, fibrosis, and neovascularization in AMD, glaucoma, and pro-fibrotic disorders. Alterations in Cer, S1P, and ceramide 1-phosphate may also contribute to uveitis. Notably, use of inhibitors that either prevent Cer increase or modulate S1P signaling, such as Myriocin, desipramine, and Fingolimod (FTY720), preserves neuronal viability and retinal function. These findings underscore the relevance of alterations in the sphingolipid metabolic network in the etiology of multiple retinopathies and highlight the potential of modulating their metabolism for the design of novel therapeutic approaches.

Suppression of cGMP-Dependent Photoreceptor Cytotoxicity With Mycophenolate Is Neuroprotective in Murine Models of Retinitis Pigmentosa

Purpose

To determine the effect of mycophenolate mofetil (MMF) on retinal degeneration on two mouse models of retinitis pigmentosa.

Methods

Intraperitoneal injections of MMF were administered daily in rd10 and c57 mice starting at postoperative day 12 (P12) and rd1 mice starting at P8. The effect of MMF was assessed with optical coherence tomography, immunohistochemistry, electroretinography, and OptoMotry. Whole retinal cyclic guanosine monophosphate (cGMP) and mycophenolic acid levels were quantified with mass spectrometry. Photoreceptor cGMP cytotoxicity was evaluated with cell counts of cGMP immunostaining.

Results

MMF treatment significantly delays the onset of retinal degeneration and cGMP-dependent photoreceptor cytotoxicity in rd10 and rd1 mice, albeit a more modest effect in the latter. In rd10 mice, treatment with MMF showed robust preservation of the photoreceptors up to P22 with associated suppression of cGMP immunostaining and microglial activation; The neuroprotective effect diminished after P22, but outer retinal thickness was still significantly thicker by P35 and OptoMotry response was significantly better up to P60. Whereas cGMP immunostaining of the photoreceptors were present in rd10 and rd1 mice, hyperphysiological whole retinal cGMP levels were observed only in rd1 mice.

Conclusions

Early treatment with MMF confers potent neuroprotection in two animal models of RP by suppressing the cGMP-dependent common pathway for photoreceptor cell death. The neuroprotective effect of MMF on cGMP-dependent cytotoxicity occurs independently of the presence of hyperphysiological whole retinal cGMP levels. Thus our data suggest that MMF may be an important new class of neuroprotective agent that could be useful in the treatment of patients with RP.

Preservation of Visual Cortex Plasticity in Retinitis Pigmentosa

Retinitis Pigmentosa (RP) is a class of inherited disorders caused by the progressive death of photoreceptors in the retina. RP is still orphan of an effective treatment, with increasing optimism deriving from research aimed at arresting neurodegeneration or replacing light-responsive elements. All these therapeutic strategies rely on the functional integrity of the visual system downstream of photoreceptors. Whereas the inner retinal structure and optic radiation are known to be considerably preserved at least in early stages of RP, very little is known about the visual cortex. Remarkably, it remains completely unclear whether visual cortex plasticity is still present in RP. Using a well-established murine model of RP, the rd10 mouse, we report that visual cortical circuits retain high levels of plasticity, preserving their capability of input-dependent remodelling even at a late stage of retinal degeneration.

Neuroplasticity of the visual cortex: in sickness and in health

Brain plasticity refers to the ability of synaptic connections to adapt their function and structure in response to experience, including environmental changes, sensory deprivation and injuries. Plasticity is a distinctive, but not exclusive, property of the developing nervous system. This review introduces the concept of neuroplasticity and describes classic paradigms to illustrate cellular and molecular mechanisms underlying synapse modifiability. Then, we summarize a growing number of studies showing that the adult cerebral cortex retains a significant degree of plasticity highlighting how the identification of strategies to enhance the plastic potential of the adult brain could pave the way for the development of novel therapeutic approaches aimed at treating amblyopia and other neurodevelopmental disorders. Finally, we analyze how the visual system adjusts to neurodegenerative conditions leading to blindness and we discuss the crucial role of spared plasticity in the visual system for sight recovery.

Ceramide synthase TLCD3B is a novel gene associated with human recessive retinal dystrophy

Purpose

Previous studies suggest that ceramide is a proapoptotic lipid as high levels of ceramides can lead to apoptosis of neuronal cells, including photoreceptors. However, no pathogenic variant in ceramide synthases has been identified in human patients and knockout of various ceramide synthases in mice has not led to photoreceptor degeneration.

Methods

Exome sequencing was used to identify candidate disease genes in patients with vision loss as confirmed by standard evaluation methods, including electroretinography (ERG) and optical coherence tomography. The vision loss phenotype in mice was evaluated by ERG and histological analyses.

Results

Here we have identified four patients with cone-rod dystrophy or maculopathy from three families carrying pathogenic variants in TLCD3B. Consistent with the phenotype observed in patients, the Tlcd3b^KO/KO mice exhibited a significant reduction of the cone photoreceptor light responses, thinning of the outer nuclear layer, and loss of cone photoreceptors across the retina.

Conclusion

Our results provide the first link between loss-of-function variants in a ceramide synthase gene and human retinal dystrophy. Establishment of the Tlcd3b knockout murine model, the first in vivo photoreceptor cell degeneration model due to loss of a ceramide synthase, will provide a unique opportunity in probing the role of ceramide in survival and function of photoreceptor cells.

Cyclooxygenase-1 mediates neuroinflammation and neurotoxicity in a mouse model of retinitis pigmentosa

Background

Retinitis pigmentosa (RP) is a group of inherited eye disorders with progressive degeneration of photoreceptors in the retina, ultimately leading to partial or complete blindness. The mechanisms underlying photoreceptor degeneration are not yet completely understood. Neuroinflammation is reported to play a pathological role in RP. However, the mechanisms that trigger neuroinflammation remain largely unknown. To address this question, we investigated the role of cyclooxygenase-1 (COX-1), a key enzyme in the conversion of arachidonic acid to proinflammatory prostaglandins, in the rd10 mouse model of RP.

Methods

We backcrossed COX-1 knockout mice (COX-1^−/−) onto the rd10 mouse model of RP and investigated the impact of COX-1 deletion on neuroinflammation in the resulting COX-1^−/−/rd10 mouse line, using a combination of immunocytochemistry, flow cytometry, qPCR, ELISA, and a series of simple visual tests.

Results

We found that genetic ablation or pharmacological inhibition of COX-1 alleviated neuroinflammation and subsequently preserved retinal photoreceptor and function and visual performance in rd10 mice. Moreover, we observed that the pharmacological inhibition of the prostaglandin E2 (PGE2) EP2 receptors largely replicated the beneficial effects of COX-1 deletion, suggesting that EP2 receptor was a critical downstream effector of COX-1-mediated neurotoxicity in rd10 mice.

Conclusion

Our data suggest that the COX-1/PGE2/EP2 signaling pathway was partly responsible for significantly increased neuroinflammation and disease progression in rd10 mice, and that EP2 receptor could be targeted therapeutically to block the pathological activity of COX-1 without inducing any potential side effects in treating RP patients.

Supplementary information

The online version contains supplementary material available at 10.1186/s12974-020-01993-0.

Antioxidant and Biological Properties of Mesenchymal Cells Used for Therapy in Retinitis Pigmentosa

Both tissue repair and regeneration are a priority in regenerative medicine. Retinitis pigmentosa (RP), a complex retinal disease characterized by the progressive loss of impaired photoreceptors, is currently lacking effective therapies: this represents one of the greatest challenges in the field of ophthalmological research. Although this inherited retinal dystrophy is still an incurable genetic disease, the oxidative damage is an important pathogenetic element that may represent a viable target of therapy. In this review, we summarize the current neuroscientific evidence regarding the effectiveness of cell therapies in RP, especially those based on mesenchymal cells, and we focus on their therapeutic action: limitation of both oxidative stress and apoptotic processes triggered by the disease and promotion of cell survival. Cell therapy could therefore represent a feasible therapeutic option in RP.

Diabetic photoreceptors: Mechanisms underlying changes in structure and function

Based on clinical findings, diabetic retinopathy (DR) has traditionally been defined as a retinal microvasculopathy. Retinal neuronal dysfunction is now recognized as an early event in the diabetic retina before development of overt DR. While detrimental effects of diabetes on the survival and function of inner retinal cells, such as retinal ganglion cells and amacrine cells, are widely recognized, evidence that photoreceptors in the outer retina undergo early alterations in diabetes has emerged more recently. We review data from preclinical and clinical studies demonstrating a conserved reduction of electrophysiological function in diabetic retinas, as well as evidence for photoreceptor loss. Complementing in vivo studies, we discuss the ex vivo electroretinography technique as a useful method to investigate photoreceptor function in isolated retinas from diabetic animal models. Finally, we consider the possibility that early photoreceptor pathology contributes to the progression of DR, and discuss possible mechanisms of photoreceptor damage in the diabetic retina, such as enhanced production of reactive oxygen species and other inflammatory factors whose detrimental effects may be augmented by phototransduction.

Complement activation, lipid metabolism, and mitochondrial injury: Converging pathways in age-related macular degeneration

The retinal pigment epithelium (RPE) is the primary site of injury in non-neovascular age-related macular degeneration or dry AMD. Polymorphisms in genes that regulate complement activation and cholesterol metabolism are strongly associated with AMD, but the biology underlying disease-associated variants is not well understood. Here, we highlight recent studies that have used molecular, biochemical, and live-cell imaging methods to elucidate mechanisms by which aging-associated insults conspire with AMD genetic risk variants to tip the balance towards disease. We discuss how critical functions including lipid metabolism, autophagy, complement regulation, and mitochondrial dynamics are compromised in the RPE, and how a deeper understanding of these mechanisms has helped identify promising therapeutic targets to preserve RPE homeostasis in AMD.

Systemic lipid dysregulation is a risk factor for macular neurodegenerative disease

Macular Telangiectasia type 2 (MacTel) is an uncommon bilateral retinal disease, in which glial cell and photoreceptor degeneration leads to central vision loss. The causative disease mechanism is largely unknown, and no treatment is currently available. A previous study found variants in genes associated with glycine-serine metabolism (PSPH, PHGDH and CPS1) to be associated with MacTel, and showed low levels of glycine and serine in the serum of MacTel patients. Recently, a causative role of deoxysphingolipids in MacTel disease has been established. However, little is known about possible other metabolic dysregulation. Here we used a global metabolomics platform in a case-control study to comprehensively profile serum from 60 MacTel patients and 58 controls. Analysis of the data, using innovative computational approaches, revealed a detailed, disease-associated metabolic profile with broad changes in multiple metabolic pathways. This included alterations in the levels of several metabolites that are directly or indirectly linked to glycine-serine metabolism, further validating our previous genetic findings. We also found changes unrelated to PSPH, PHGDH and CPS1 activity. Most pronounced, levels of several lipid groups were altered, with increased phosphatidylethanolamines being the most affected lipid group. Assessing correlations between different metabolites across our samples revealed putative functional connections. Correlations between phosphatidylethanolamines and sphingomyelin, and glycine-serine and sphingomyelin, observed in controls, were reduced in MacTel patients, suggesting metabolic re-wiring of sphingomyelin metabolism in MacTel patients. Our findings provide novel insights into metabolic changes associated with MacTel and implicate altered lipid metabolism as a contributor to this retinal neurodegenerative disease.

Myriocin Effect on Tvrm4 Retina, an Autosomal Dominant Pattern of Retinitis Pigmentosa

Tvrm4 mice, a model of autosomal dominant retinitis pigmentosa (RP), carry a mutation of Rhodopsin gene that can be activated by brief exposure to very intense light. Here, we test the possibility of an anatomical, metabolic, and functional recovery by delivering to degenerating Tvrm4 animals, Myriocin, an inhibitor of ceramide de novo synthesis previously shown to effectively slow down retinal degeneration in rd10 mutants (Strettoi et al., 2010; Piano et al., 2013). Different routes and durations of Myriocin administration were attempted by using either single intravitreal (i.v.) or long-term, repeated intraperitoneal (i.p.) injections. The retinal function of treated and control animals was tested by ERG recordings. Retinas from ERG-recorded animals were studied histologically to reveal the extent of photoreceptor death. A correlation was observed between Myriocin administration, lowering of retinal ceramides, and preservation of ERG responses in i.v. injected cases. Noticeably, the i.p. treatment with Myriocin decreased the extension of the retinal-degenerating area, preserved the ERG response, and correlated with decreased levels of biochemical indicators of retinal oxidative damage. The results obtained in this study confirm the efficacy of Myriocin in slowing down retinal degeneration in genetic models of RP independently of the underlying mutation responsible for the disease, likely targeting ceramide-dependent, downstream pathways. Alleviation of retinal oxidative stress upon Myriocin treatment suggests that this molecule, or yet unidentified metabolites, act on cellular detoxification systems supporting cell survival. Altogether, the pharmacological approach chosen here meets the necessary pre-requisites for translation into human therapy to slow down RP.

Transcriptome Analyses of lncRNAs in A2E-Stressed Retinal Epithelial Cells Unveil Advanced Links between Metabolic Impairments Related to Oxidative Stress and Retinitis Pigmentosa

: Long non-coding RNAs (lncRNAs) are untranslated transcripts which regulate many biological processes. Changes in lncRNA expression pattern are well-known related to various human disorders, such as ocular diseases. Among them, retinitis pigmentosa, one of the most heterogeneous inherited disorder, is strictly related to oxidative stress. However, little is known about regulative aspects able to link oxidative stress to etiopathogenesis of retinitis. Thus, we realized a total RNA-Seq experiment, analyzing human retinal pigment epithelium cells treated by the oxidant agent N-retinylidene-N-retinylethanolamine (A2E), considering three independent experimental groups (untreated control cells, cells treated for 3 h and cells treated for 6 h). Differentially expressed lncRNAs were filtered out, explored with specific tools and databases, and finally subjected to pathway analysis. We detected 3,3'-overlapping ncRNAs, 107 antisense, 24 sense-intronic, four sense-overlapping and 227 lincRNAs very differentially expressed throughout all considered time points. Analyzed lncRNAs could be involved in several biochemical pathways related to compromised response to oxidative stress, carbohydrate and lipid metabolism impairment, melanin biosynthetic process alteration, deficiency in cellular response to amino acid starvation, unbalanced regulation of cofactor metabolic process, all leading to retinal cell death. The explored lncRNAs could play a relevant role in retinitis pigmentosa etiopathogenesis, and seem to be the ideal candidate for novel molecular markers and therapeutic strategies.

Rhodopsin signaling mediates light-induced photoreceptor cell death in rd10 mice through a transducin-independent mechanism

Retinitis pigmentosa (RP) is a debilitating blinding disease affecting over 1.5 million people worldwide, but the mechanisms underlying this disease are not well understood. One of the common models used to study RP is the retinal degeneration-10 (rd10) mouse, which has a mutation in Phosphodiesterase-6b (Pde6b) that causes a phenotype mimicking the human disease. In rd10 mice, photoreceptor cell death occurs with exposure to normal light conditions, but as demonstrated in this study, rearing these mice in dark preserves their retinal function. We found that inactivating rhodopsin signaling protected photoreceptors from degeneration suggesting that the pathway activated by this G-protein-coupled receptor is causing light-induced photoreceptor cell death in rd10 mice. However, inhibition of transducin signaling did not prevent the loss of photoreceptors in rd10 mice reared under normal light conditions implying that the degeneration caused by rhodopsin signaling is not mediated through its canonical G-protein transducin. Inexplicably, loss of transducin in rd10 mice also led to photoreceptor cell death in darkness. Furthermore, we found that the rd10 mutation in Pde6b led to a reduction in the assembled PDE6αβγ2 complex, which was corroborated by our data showing mislocalization of the γ subunit. Based on our findings and previous studies, we propose a model where light activates a non-canonical pathway mediated by rhodopsin but independent of transducin that sensitizes cyclic nucleotide gated channels to cGMP and causes photoreceptor cell death. These results generate exciting possibilities for treatment of RP patients without affecting their vision or the canonical phototransduction cascade.

Novel ophthalmic formulation of myriocin: implications in retinitis pigmentosa

Myriocin is an antibiotic derived from Mycelia sterilia, and is a potent inhibitor of serine palmitoyltransferase, the enzyme involved in the first step of sphingosine synthesis. Myriocin, inhibiting ceramide synthesis, has a great potential for treatment of diseases characterized by high ceramide levels in affected tissues, such as retinitis pigmentosa (RP). Drug delivery to the retina is a challenging task, which is generally by-passed through intravitreal injection, that represents a risky invasive procedure. We, therefore, developed and characterized an ophthalmic topical nanotechnological formulation based on a nanostructured lipid carrier (NLC) and containing myriocin. The ocular distribution of myriocin in the back of the eye was assessed both in rabbits and mice using LC-MS/MS. Moreover, rabbit retinal sphingolipid and ceramides levels, after myriocin-NLC (Myr-NLC) eye drops treatment, were assessed. The results demonstrated that Myr-NLC formulation is well tolerated and provided effective levels of myriocin in the back of the eye both in rabbits and mice. We found that Myr-NLC eye drops treatment was able to significantly decrease retinal sphingolipid levels. In conclusion, these data suggest that the Myr-NLC ophthalmic formulation is suitable for pharmaceutical development and warrants further clinical evaluation of this eye drops for the treatment of RP.

Longitudinal OCT and OCTA monitoring reveals accelerated regression of hyaloid vessels in retinal degeneration 10 (rd10) mice

The hyaloid vascular system (HVS) is known to have an important role in eye development. However, physiological mechanisms of HVS regression and their correlation with developmental eye disorders remain unclear due to technical limitations of conventional ending point examination with fixed tissues. Here, we report comparative optical coherence tomography (OCT) and OCT angiography (OCTA) monitoring of HVS regression in wild-type and retinal degeneration 10 (rd10) mice. Longitudinal OCTA monitoring revealed accelerated regression of hyaloid vessels correlated with retinal degeneration in rd10. Quantitative OCT measurement disclosed significant distortions of both retinal thickness and the vitreous chamber in rd10 compared to WT mice. These OCT/OCTA observations confirmed the close relationship between HVS physiology and retinal neurovascular development. The distorted HVS regression might result from retinal hyperoxia or dopamine abnormality due to retinal remodeling in rd10 retina. By providing a noninvasive imaging platform for longitudinal monitoring of HVS regression, further OCT/OCTA study may lead to in-depth understanding of the physiological mechanisms of HVS regression in normal and diseased eyes, which is not only important for advanced study of the nature of the visual system but also may provide insights into the development of better treatment protocols of congenital eye disorders.

Lipid Nanoparticles and Active Natural Compounds: A Perfect Combination for Pharmaceutical Applications

Phytochemicals represent an important class of bioactive compounds characterized by significant health benefits. Notwithstanding these important features, their potential therapeutic properties suffer from poor water solubility and membrane permeability limiting their approach to nutraceutical and pharmaceutical applications. Lipid nanoparticles are well known carrier systems endowed with high biodegradation and an extraordinary biocompatible chemical nature, successfully used as platform for advanced delivery of many active compounds, including the oral, topical and systemic routes. This article is aimed at reviewing the last ten years of studies about the application of lipid nanoparticles in active natural compounds reporting examples and advantages of these colloidal carrier systems.