Fenofibrate-Loaded Biodegradable Nanoparticles for the Treatment of Experimental Diabetic Retinopathy and Neovascular Age-Related Macular Degeneration

Advances in ophthalmic therapeutic delivery: A comprehensive overview of present and future directions

Ophthalmic treatment demands precision and consistency in delivering therapeutic agents over extended periods to address many conditions, from common eye disorders to complex diseases. This diversity necessitates a range of delivery strategies, each tailored to specific needs. We delve into various delivery cargos that are pivotal in ophthalmic care. These cargos encompass biodegradable implants that gradually release medication, nonbiodegradable implants for sustained drug delivery, refillable tools allowing flexibility in treatment, hydrogels capable of retaining substances while maintaining ocular comfort, and advanced nanotechnology devices that precisely target eye tissues. Within each cargo category, we explore cutting-edge research-level approaches and FDA-approved methods, providing a thorough overview of the current state of ophthalmic drug delivery. In particular, our focus on nanotechnology reveals the promising potential for gene delivery, cell therapy administration, and the implantation of active devices directly into the retina. These advancements hold the key to more effective, personalized, and minimally- invasive ophthalmic treatments, revolutionizing the field of eye care.

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.

Multifunctional nano-in-micro delivery systems for targeted therapy in fundus neovascularization diseases

Fundus neovascularization diseases are a series of blinding eye diseases that seriously impair vision worldwide. Currently, the means of treating these diseases in clinical practice are continuously evolving and have rapidly revolutionized treatment opinions. However, key issues such as inadequate treatment effectiveness, high rates of recurrence, and poor patient compliance still need to be urgently addressed. Multifunctional nanomedicine can specifically respond to both endogenous and exogenous microenvironments, effectively deliver drugs to specific targets and participate in activities such as biological imaging and the detection of small molecules. Nano-in-micro (NIM) delivery systems such as metal, metal oxide and up-conversion nanoparticles (NPs), quantum dots, and carbon materials, have shown certain advantages in overcoming the presence of physiological barriers within the eyeball and are widely used in the treatment of ophthalmic diseases. Few studies, however, have evaluated the efficacy of NIM delivery systems in treating fundus neovascular diseases (FNDs). The present study describes the main clinical treatment strategies and the adverse events associated with the treatment of FNDs with NIM delivery systems and summarizes the anatomical obstacles that must be overcome. In this review, we wish to highlight the principle of intraocular microenvironment normalization, aiming to provide a more rational approach for designing new NIM delivery systems to treat specific FNDs.

Therapeutic Effects of Anti-Inflammatory and Anti-Oxidant Nutritional Supplementation in Retinal Ischemic Diseases

Appropriate nutrients are essential for cellular function. Dietary components can alter the risk of systemic metabolic diseases, including cardiovascular diseases, cancer, diabetes, and obesity, and can also affect retinal diseases, including age-related macular degeneration, diabetic retinopathy, and glaucoma. Dietary nutrients have been assessed for the prevention or treatment of retinal ischemic diseases and the diseases of aging. In this article, we review clinical and experimental evidence concerning the potential of some nutritional supplements to prevent or treat retinal ischemic diseases and provide further insights into the therapeutic effects of nutritional supplementation on retinopathies. We will review the roles of nutrients in preventing or protecting against retinal ischemic diseases.

Multi-physics simulations for investigating the effect of electrode conditions on transscleral ocular iontophoresis for particulate drug delivery into ocular tissues

Purpose

Transscleral ocular iontophoresis has been proposed to deliver charged particulate drugs to ocular tissues effectively by transmitting a weak electrical current through the sclera. The electric fields formed are influenced by the electrode conditions, thus affecting the amount of particulate drugs delivered to the ocular tissues via iontophoresis. Computational simulation is widely used to simulate drug concentrations in the eye; therefore, reflecting the characteristics of the drugs in living tissues to the simulations is important for a more precise estimation of drug concentration. In this study, we investigated the effect of electrode conditions (location and size) on the efficacy of transscleral iontophoresis.

Methods

We first determined the simulation parameters based on the comparison of the amount of drug in the sclera in the simulation and in vivo experimental results. The injection of the negatively charged nanoparticles into the cul-de-sac of the lower eyelid was simulated. The active electrode (cathode) was attached to the skin immediately above the injection site, while the return electrode (anode) was placed over the eyebrow. The drug concentration distribution in the eye, based on either the location or size of each electrode, was evaluated using the finite element method with the estimated simulation parameters.

Results

Our results indicate that drug permeability varies depending on the location and the size of the electrodes.

Conclusion

Our findings demonstrate that the determination of optimal electrode conditions is necessary to enhance the effectiveness of transscleral iontophoresis.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-024-00359-2.

An update on the latest strategies in retinal drug delivery

INTRODUCTION

Retinal drug delivery has witnessed significant advancements in recent years, mainly driven by the prevalence of retinal diseases and the need for more efficient and patient-friendly treatment strategies.

AREAS COVERED

Advancements in nanotechnology have introduced novel drug delivery platforms to improve bioavailability and provide controlled/targeted delivery to specific retinal layers. This review highlights various treatment options for retinal diseases. Additionally, diverse strategies aimed at enhancing delivery of small molecules and antibodies to the posterior segment such as implants, polymeric nanoparticles, liposomes, niosomes, microneedles, iontophoresis and mixed micelles were emphasized. A comprehensive overview of the special technologies currently under clinical trials or already in the clinic was provided.

EXPERT OPINION

Ideally, drug delivery system for treating retinal diseases should be less invasive in nature and exhibit sustained release up to several months. Though topical administration in the form of eye drops offers better patient compliance, its clinical utility is limited by nature of the drug. There is a wide range of delivery platforms available, however, it is not easy to modify any single platform to accommodate all types of drugs. Coordinated efforts between ophthalmologists and drug delivery scientists are necessary while developing therapeutic compounds, right from their inception.

Comprehensive Ocular and Systemic Safety Evaluation of Polysialic Acid-Decorated Immune Modulating Therapeutic Nanoparticles (PolySia-NPs) to Support Entry into First-in-Human Clinical Trials

An inflammation-resolving polysialic acid-decorated PLGA nanoparticle (PolySia-NP) has been developed to treat geographic atrophy/age-related macular degeneration and other conditions caused by macrophage and complement over-activation. While PolySia-NPs have demonstrated pre-clinical efficacy, this study evaluated its systemic and intraocular safety. PolySia-NPs were evaluated in vitro for mutagenic activity using Salmonella strains and E. coli, with and without metabolic activation; cytotoxicity was evaluated based on its interference with normal mitosis. PolySia-NPs were administered intravenously in CD-1 mice and Sprague Dawley rats and assessed for survival and toxicity. Intravitreal (IVT) administration in Dutch Belted rabbits and non-human primates was assessed for ocular or systemic toxicity. In vitro results indicate that PolySia-NPs did not induce mutagenicity or cytotoxicity. Intravenous administration did not show clastogenic activity, effects on survival, or toxicity. A single intravitreal (IVT) injection and two elevated repeat IVT doses of PolySia-NPs separated by 7 days in rabbits showed no signs of systemic or ocular toxicity. A single IVT inoculation of PolySia-NPs in non-human primates demonstrated no adverse clinical or ophthalmological effects. The demonstration of systemic and ocular safety of PolySia-NPs supports its advancement into human clinical trials as a promising therapeutic approach for systemic and retinal degenerative diseases caused by chronic immune activation.

Next generation therapeutics for retinal neurodegenerative diseases

Neurodegenerative diseases affecting the visual system encompass glaucoma, macular degeneration, retinopathies, and inherited genetic disorders such as retinitis pigmentosa. These ocular pathologies pose a serious burden of visual impairment and blindness worldwide. Current treatment modalities include small molecule drugs, biologics, or gene therapies, most of which are administered topically as eye drops or as injectables. However, the topical route of administration faces challenges in effectively reaching the posterior segment and achieving desired concentrations at the target site, while injections and implants risk severe complications, such as retinal detachment and endophthalmitis. This necessitates the development of innovative therapeutic strategies that can prolong drug release, deliver effective concentrations to the back of the eye with minimal systemic exposure, and improve patient compliance and safety. In this review, we introduce retinal degenerative diseases, followed by a discussion of the existing clinical standard of care. We then delve into detail about drug and gene delivery systems currently in preclinical and clinical development, including formulation and delivery advantages/drawbacks, with a special emphasis on potential for clinical translation.

Role of fenofibrate in multiple sclerosis

Multiple sclerosis (MS) is the most frequent inflammatory and demyelinating disease of the central nervous system (CNS). The underlying pathophysiology of MS is the destruction of myelin sheath by immune cells. The formation of myelin plaques, inflammation, and injury of neuronal myelin sheath characterizes its neuropathology. MS plaques are multiple focal regions of demyelination disseminated in the brain's white matter, spinal cords, deep grey matter, and cerebral cortex. Fenofibrate is a peroxisome proliferative activated receptor alpha (PPAR-α) that attenuates the inflammatory reactions in MS. Fenofibrate inhibits differentiation of Th17 by inhibiting the expression of pro-inflammatory signaling. According to these findings, this review intended to illuminate the mechanistic immunoinflammatory role of fenofibrate in mitigating MS neuropathology. In conclusion, fenofibrate can attenuate MS neuropathology by modulating different pathways, including oxidative stress, autophagy, mitochondrial dysfunction, inflammatory-signaling pathways, and neuroinflammation.

Applications of nanomaterials in anti-VEGF treatment for ophthalmic diseases

Angiogenesis has been determined to be essential in the occurrence and metastasis of diabetic retinopathy (DR), age-related macular degeneration (AMD), retinal vein occlusion (RVO), choroidal neovascularization (CNV), retinopathy of prematurity (ROP), tumor, etc. However, the clinical use of anti-vascular endothelial growth factors (VEGF) drugs is currently limited due to its high cost, potential side effects, and need for repeated injections. In recent years, nanotechnology has shown promising results in inhibiting neovascularization and reducing reactive oxygen species (ROS) or inflammatory factors. Some nanomaterials can also act as vehicles for drug delivery, such as lipid nanoparticles and PLGA. The process of angiogenesis and its molecular mechanism are discussed in this article. At the same time, this study aims to systematically review the research progress of nanotechnology and offer more treatment options for neovascularization-related diseases in clinical ophthalmology.

Development of uniform fenofibrate-loaded biodegradable microparticle by membrane emulsification

Fenofibrate has shown therapeutic effects on diabetic retinopathy. However, fenofibrate can be rapidly cleared from the eye after a single intravitreal injection. Here, we aim to develop fenofibrate loaded PLGA microparticles (Feno-MP) with high drug loading and sustained in vitro release up to 6 months suitable for intravitreal injection. First, orthogonal array experimental design was applied for formulation optimization. The selected formulation parameters were used to formulate Feno-MP using homogenization method and direct membrane emulsification method. Both methods generated Feno-MP with high drug loading and sustained in vitro drug release more than 140 days. Unlike the polydisperse Feno-MP prepared using homogenization method, membrane emulsification method generated Feno-MP with uniform size distribution. By controlling the membrane pore size, 1.5 µm, 8 µm and 16 µm Feno-MP were formulated and we found that larger Feno-MP demonstrated higher drug loading, more sustained drug release in vitro with less burst drug release than the smaller Feno-MP. In conclusion, we developed Feno-MP with high drug loading and sustained release profile, and elucidated that changing the particle size could have notable impacts on drug loading and release kinetics. Formulating Feno-MP with uniform size distribution by membrane emulsification method would benefit the batch-to-batch repeatability.

Recent Updates on Nanocarriers for Drug Delivery in Posterior Segment Diseases with Emphasis on Diabetic Retinopathy

In recent years, various conventional formulations have been used for the treatment and/or management of ocular medical conditions. Diabetic retinopathy, a microvascular disease of the retina, remains the leading cause of visual disability in patients with diabetes. Currently, for treating diabetic retinopathy, only intraocular, intravitreal, periocular injections, and laser photocoagulation are widely used. Frequent administration of these drugs by injections may lead to serious complications, including retinal detachment and endophthalmitis. Although conventional ophthalmic formulations like eye drops, ointments, and suspensions are available globally, these formulations fail to achieve optimum drug therapeutic profile due to immediate nasolacrimal drainage, rapid tearing, and systemic tearing toxicity of the drugs. To achieve better therapeutic outcomes with prolonged release of the therapeutic agents, nano-drug delivery materials have been investigated. These nanocarriers include nanoparticles, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), dendrimers, nanofibers, in-situ gel, vesicular carriers, niosomes, and mucoadhesive systems, among others. The nanocarriers carry the potential benefits of site-specific delivery and controlled and sustained drug release profile. In the present article, various nanomaterials explored for treating diabetic retinopathy are reviewed.

Preclinical study of diabetic foot ulcers: From pathogenesis to vivo/vitro models and clinical therapeutic transformation

Diabetic foot ulcer (DFU), a common intractable chronic complication of diabetes mellitus (DM), has a prevalence of up to 25%, with more than 17% of the affected patients at risk of amputation or even death. Vascular risk factors, including vascular stenosis or occlusion, dyslipidemia, impaired neurosensory and motor function, and skin infection caused by trauma, all increase the risk of DFU in patients with diabetes. Therefore, diabetic foot is not a single pathogenesis. Preclinical studies have contributed greatly to the pathogenesis determination and efficacy evaluation of DFU. Many therapeutic tools are currently being investigated using DFU animal models for effective clinical translation. However, preclinical animal models that completely mimic the pathogenesis of DFU remain unexplored. Therefore, in this review, the preparation methods and evaluation criteria of DFU animal models with three major pathological mechanisms: neuropathy, angiopathy and DFU infection were discussed in detail. And the advantages and disadvantages of various DFU animal models for clinical sign simulation. Furthermore, the current status of vitro models of DFU and some preclinical studies have been transformed into clinical treatment programs, such as medical dressings, growth factor therapy, 3D bioprinting and pre-vascularization, Traditional Chinese Medicine treatment. However, because of the complexity of the pathological mechanism of DFU, the clinical transformation of DFU model still faces many challenges. We need to further optimize the existing preclinical studies of DFU to provide an effective animal platform for the future study of pathophysiology and clinical treatment of DFU.

An insight on ophthalmic drug delivery systems: Focus on polymeric biomaterials-based carriers

Presently, different types of eye diseases, such as glaucoma, myopia, infection, and dry eyes are treated with topical eye drops. However, due to ocular surface barriers, eye drops require multiple administrations, which may cause several risks, thereby necessitating additional strategies. Some of the key characteristics of an ideal ocular drug delivery system are as follows: (a) good penetration into cornea, (b) high drug retention in the ocular tissues, (c) targetability to the desired regions of the eye, and (d) good bioavailability. It is worthy to note that the corneal epithelial tight junctions hinder the permeation of therapeutics through the cornea. Therefore, it is necessary to design nanocarriers that can overcome these barriers and enhance drug penetration into the inner parts of the eye. Moreover, intelligent multifunctional nanocarriers can be designed to include cavities, which may help encapsulate sufficient amount of the drug. In addition, nanocarriers can be modified with the targeting moieties. Different types of nanocarriers have been developed for ocular drug delivery applications, including emulsions, liposomes, micelles, and nanoparticles. However, these formulations may be rapidly cleared from the eye. The therapeutic use of the nanoparticles (NPs) is also hindered by the non-specific adsorption of proteins on NPs, which may limit their interaction with the cellular moieties or other targeted biological factors. Functional drug delivery systems (DDS), which can offer targeted ocular drug delivery while avoiding the non-specific protein adsorption could exhibit great potential. This could be further realized by the on-demand DDS, which can respond to the stimuli in a spatio-temporal fashion. The cell-mediated DDS offer another valuable platform for ophthalmological drug delivery.

A review on PLGA particles as a sustained drug-delivery system and its effect on the retina

In this review, the designs and recent developments of polymer-based drug delivery of Poly(lactic-co-glycolic acid) (PLGA) will be discussed for the possible treatment of age-related macular degeneration (AMD). PLGA is a versatile co-polymer that consists of synthetic lactic acid and glycolic acid monomers that are constructed to produce nanoparticles, microparticles, and scaffolds for the intraocular delivery of various drugs. As an FDA-approved polymer, PLGA has historically been well-suited for systemic slow-sustained release therapies due to its performance in biodegradability and biocompatibility. This review will examine recent in vitro and in vivo studies that provide evidence for PLGA-based particles as a therapeutic drug carrier for the treatment of AMD. Anti-angiogenic and antiproliferative effects of small peptides, small molecules, RNA molecules, and proteins within PLGA particles are briefly discussed. AMD is a leading cause of central vision loss in people over 55 years and the number of those afflicted will rise as the aging population increases. AMD has two forms that are often sequential. Dry AMD and wet AMD account for 85-90% and 10-15% of cases, respectively. The distinct categories of PLGA-based drug delivery vehicles are important for dispensing novel small molecules, RNA molecules, peptides, and proteins as a long-term effective treatment of AMD.

Eco-friendly chitosan-based nanostructures in diabetes mellitus therapy: Promising bioplatforms with versatile therapeutic perspectives

Nature-derived polymers, or biopolymers, are among the most employed materials for the development of nanocarriers. Chitosan (CS) is derived from the acetylation of chitin, and this biopolymer displays features such as biocompatibility, biodegradability, low toxicity, and ease of modification. CS-based nano-scale delivery systems have been demonstrated to be promising carriers for drug and gene delivery, and they can provide site-specific delivery of cargo. Owing to the high biocompatibility of CS-based nanocarriers, they can be used in the future in clinical trials. On the other hand, diabetes mellitus (DM) is a chronic disease that can develop due to a lack of insulin secretion or insulin sensitivity. Recently, CS-based nanocarriers have been extensively applied for DM therapy. Oral delivery of insulin is the most common use of CS nanoparticles in DM therapy, and they improve the pharmacological bioavailability of insulin. Moreover, CS-based nanostructures with mucoadhesive features can improve oral bioavailability of insulin. CS-based hydrogels have been developed for the sustained release of drugs and the treatment of DM complications such as wound healing. Furthermore, CS-based nanoparticles can mediate delivery of phytochemicals and other therapeutic agents in DM therapy, and they are promising compounds for the treatment of DM complications, including nephropathy, neuropathy, and cardiovascular diseases, among others. The surface modification of nanostructures with CS can improve their properties in terms of drug delivery and release, biocompatibility, and others, causing high attention to these nanocarriers in DM therapy.

Recent Advances of Ocular Drug Delivery Systems: Prominence of Ocular Implants for Chronic Eye Diseases

Chronic ocular diseases can seriously impact the eyes and could potentially result in blindness or serious vision loss. According to the most recent data from the WHO, there are more than 2 billion visually impaired people in the world. Therefore, it is pivotal to develop more sophisticated, long-acting drug delivery systems/devices to treat chronic eye conditions. This review covers several drug delivery nanocarriers that can control chronic eye disorders non-invasively. However, most of the developed nanocarriers are still in preclinical or clinical stages. Long-acting drug delivery systems, such as inserts and implants, constitute the majority of the clinically used methods for the treatment of chronic eye diseases due to their steady state release, persistent therapeutic activity, and ability to bypass most ocular barriers. However, implants are considered invasive drug delivery technologies, especially those that are nonbiodegradable. Furthermore, in vitro characterization approaches, although useful, are limited in mimicking or truly representing the in vivo environment. This review focuses on long-acting drug delivery systems (LADDS), particularly implantable drug delivery systems (IDDS), their formulation, methods of characterization, and clinical application for the treatment of eye diseases.

Maillard Reaction Crosslinked Alginate-Albumin Scaffolds for Enhanced Fenofibrate Delivery to the Retina: A Promising Strategy to Treat RPE-Related Dysfunction

There are limited treatments currently available for retinal diseases such as age-related macular degeneration (AMD). Cell-based therapy holds great promise in treating these degenerative diseases. Three-dimensional (3D) polymeric scaffolds have gained attention for tissue restoration by mimicking the native extracellular matrix (ECM). The scaffolds can deliver therapeutic agents to the retina, potentially overcoming current treatment limitations and minimizing secondary complications. In the present study, 3D scaffolds made up of alginate and bovine serum albumin (BSA) containing fenofibrate (FNB) were prepared by freeze-drying technique. The incorporation of BSA enhanced the scaffold porosity due to its foamability, and the Maillard reaction increased crosslinking degree between ALG with BSA resulting in a robust scaffold with thicker pore walls with a compression modulus of 13.08 KPa suitable for retinal regeneration. Compared with ALG and ALG-BSA physical mixture scaffolds, ALG-BSA conjugated scaffolds had higher FNB loading capacity, slower release of FNB in the simulated vitreous humour and less swelling in water and buffers, and better cell viability and distribution when tested with ARPE-19 cells. These results suggest that ALG-BSA MR conjugate scaffolds may be a promising option for implantable scaffolds for drug delivery and retinal disease treatment.

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.

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.

Transient receptor potential channel 6 knockdown prevents high glucose-induced Müller cell pyroptosis

BACKGROUND

Transient receptor potential channel 6 (TRPC6) is reported to be involved in the pathogenesis of diabetic complications, but its role in diabetic retinopathy (DR) remains unknown. The aim of our study was to determine the role and mechanism of TRPC6 in DR.

METHODS

High glucose was used to construct a DR cell model using rat retinal Müller cells (rMC-1). Intracellular Ca²⁺, reactive oxygen species (ROS) and cell pyroptosis were evaluated by flow cytometry. Protein levels of NLRP3, pro-caspase-1, active caspase-1, gasdermin D (GSDMD), GSDMD-N, TRPC6 and H3K27ac were detected by Western blot. mRNA levels of EP300 and TRPC6 were analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR). Levels of IL-1β and IL-18 were estimated by enzyme linked immunosorbent assay (ELISA). The interaction between EP300 and TRPC6 was validated by a chromatin immunoprecipitation assay.

RESULTS

The knockdown of TRPC6 reduced inflammation and cell pyroptosis in HG induced rMC-1 cells, whereas overexpression of TRPC6 had the opposite effects. The inhibition of ROS and NLRP3 reversed TRPC6-mediated cell pyroptosis in the DR cell model. In addition, EP300 increased the expression of H3K27ac and TRPC6 to promote cell pyroptosis, which was suppressed by the knockdown of TRPC6.

CONCLUSIONS

Our study revealed a novel EP300/H3K27ac/TRPC6 signaling pathway that may contribute to HG induced Müller cell pyroptosis. TRPC6 played a novel role in Müller cell pyroptosis triggered by HG, and may be a potential target for DR treatment in the future.

Effects of systemic drugs on the development and progression of age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of severe loss of central vision among people over 50. The pathophysiology of the disease is multifactorial and can be attributed to genetics, aging, inflammation, environmental factors, and lifestyle factors including smoking, diet, obesity, and alcohol consumption. While there is no treatment for dry AMD, the current standard treatment for wet AMD is an intraocular injection of anti-vascular endothelial growth factor-an effective, yet expensive, therapy that requires ongoing treatment. As the aging population continues to grow, and AMD diagnoses continue to rise, new treatments should be explored to reduce vision complications and decrease treatment burdens. Many systemic conditions have progressive pathological changes that may affect AMD, particularly those affecting systemic vasculature like diabetes and cardiovascular status. Consequently, systemic drugs used to treat coexistent systemic diseases may influence some of the pathogenic mechanisms of AMD and lead its progression or delay. In this review we explore the current literature to summarize the findings of the reported effects of antihypertensive, immunosuppressants, cholesterol lowering agents, nonsteroidal anti-inflammatory drugs, dopamine precursors, hypoglycemic agents, and anticoagulants on AMD.

Environmental Light Has an Essential Effect on the Disease Expression in a Dominant RPE65 Mutation

The retina pigmented epithelium 65 kDa protein (RPE65) is an essential enzyme in the visual cycle that regenerates the 11-cis-retinal chromophore obligatory for vision. Mutations in RPE65 are associated with blinding diseases. D477G (C.1430G > A) is the only known RPE65 variant to cause autosomal dominant retinitis pigmentosa (adRP). Previously, we reported that the heterozygous D477G knock-in (WT/KI) mice exposed to dim light intensity demonstrated delayed chromophore regeneration rates and slowed recovery of photoreceptor sensitivity following photobleaching. However, visual function and retinal architecture were indistinguishable from the wild-type (WT) mice. In this study, when maintained under the physiological day-light intensity (2 K lux), the WT/KI heterozygous mice displayed retina degeneration and reduced electroretinography (ERG) amplitude, recapitulating that observed in human patients. Our findings indicated the importance of the light environment in the mechanism of RPE65 D477G pathogenicity.

A Trojan horse biomimetic delivery system using mesenchymal stem cells for HIF-1α siRNA-loaded nanoparticles on retinal pigment epithelial cells under hypoxia environment

AIM

To demonstrate the feasibility of mesenchymal stem cell (MSC)-mediated nano drug delivery, which was characterized by the "Trojan horse"-like transport of hypoxia-inducible factor-1α small interfering RNA (HIF-1α siRNA) between MSCs and retinal pigment epithelial cells (RPE) under hypoxia environment.

METHODS

Plasmid and lentivirus targeting the human HIF-1α gene were designed and constructed. HIF-1α siRNA was encapsulated into poly(lactic-co-glycolic acid) nanoparticles (PLGA-NPs) through the water-in-oil-in-water (w/o/w) multiple emulsion technique. The effect of PLGA-NPs uptake on the expression of HIF-1α mRNA was tested in RPE cells by real-time quantitative polymerase chain reaction (qPCR) and additional transfected conditions were used as control, including lentivirus group, nude plasmid group and blank PLGA group. MSCs were transfected with the NPs and the transfection efficacy was evaluated by flow cytometry. Transwell co-culture system of transfected MSCs and RPE cells was constructed under hypoxia environment. The effects of MSC-loaded HIF-1α siRNA PLGA-NPs on proliferation, apoptosis, and migration of RPE cells were then evaluated. The effect of transfected MSCs on HIF-1α expression of RPE cells was analyzed by using qPCR at the time points 24h, 3d, and 7d.

RESULTS

The average diameter of PLGA-NPs loaded with HIF siRNA was 314.1 nm and the zeta potential was -0.36 mV. The transfection efficiency of PLGA-NPs was 67.3%±5.2% into MSCs by using flow cytometry. Compared with the lentivirus group, the PLGA-NPs loaded with HIF-1α siRNA can effectively reduce the expression of HIF-1α mRNA up to 7d in RPE (0.63±0.05 at 7d, P<0.001). In the Transwell co-culture system of transfected MSCs and RPE, the abilities of proliferation (2.34±0.17, 2.40±0.28, 2.47±0.24 at 48h, F=0.23, P=0.80), apoptosis (14.83%±2.43%, 12.94%±2.19%, 12.39%±3.21%; F=0.70, P=0.53) and migration (124.5±7.78, 119.5±5.32, 130±9.89, F=1.33, P=0.33) of the RPE cells had no differences between MSC-loaded HIF-1α siRNA PLGA-NPs and other groups. The inhibition of PLGA on the HIF-1α mRNA expression in RPE cells could continue until the 7^th day, the level of HIF-1α mRNA was lower than that of other groups (F=171.98, P<0.001).

CONCLUSION

The delivery of PLGA-NPs loaded with HIF-1α siRNA carried by MSCs is found to be beneficial temporally for HIF-1α mRNA inhibition in RPE cells under hypoxia environment. The MSC-based bio-mimetic delivery of HIF-1α siRNA nanoparticles is a potential method for therapy against choroidal neovascularization.

Effective treatment of intractable diseases using nanoparticles to interfere with vascular supply and angiogenic process

Angiogenesis is a vital biological process involving blood vessels forming from pre-existing vascular systems. This process contributes to various physiological activities, including embryonic development, hair growth, ovulation, menstruation, and the repair and regeneration of damaged tissue. On the other hand, it is essential in treating a wide range of pathological diseases, such as cardiovascular and ischemic diseases, rheumatoid arthritis, malignancies, ophthalmic and retinal diseases, and other chronic conditions. These diseases and disorders are frequently treated by regulating angiogenesis by utilizing a variety of pro-angiogenic or anti-angiogenic agents or molecules by stimulating or suppressing this complicated process, respectively. Nevertheless, many traditional angiogenic therapy techniques suffer from a lack of ability to achieve the intended therapeutic impact because of various constraints. These disadvantages include limited bioavailability, drug resistance, fast elimination, increased price, nonspecificity, and adverse effects. As a result, it is an excellent time for developing various pro- and anti-angiogenic substances that might circumvent the abovementioned restrictions, followed by their efficient use in treating disorders associated with angiogenesis. In recent years, significant progress has been made in different fields of medicine and biology, including therapeutic angiogenesis. Around the world, a multitude of research groups investigated several inorganic or organic nanoparticles (NPs) that had the potential to effectively modify the angiogenesis processes by either enhancing or suppressing the process. Many studies into the processes behind NP-mediated angiogenesis are well described. In this article, we also cover the application of NPs to encourage tissue vascularization as well as their angiogenic and anti-angiogenic effects in the treatment of several disorders, including bone regeneration, peripheral vascular disease, diabetic retinopathy, ischemic stroke, rheumatoid arthritis, post-ischemic cardiovascular injury, age-related macular degeneration, diabetic retinopathy, gene delivery-based angiogenic therapy, protein delivery-based angiogenic therapy, stem cell angiogenic therapy, and diabetic retinopathy, cancer that may benefit from the behavior of the nanostructures in the vascular system throughout the body. In addition, the accompanying difficulties and potential future applications of NPs in treating angiogenesis-related diseases and antiangiogenic therapies are discussed.

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.

Penetrating-peptide-mediated non-invasive Axitinib delivery for anti-neovascularisation

The unique physiological makeup of the eye limits the use of small-molecule drugs for treating the posterior segment of the eye. Nevertheless, transmembrane-peptide-mediated non-invasive drug delivery can serve as an ideal treatment strategy, as it is capable of delivering small-molecule drugs across the membrane in the form of eye drops, thereby achieving the effective treatment of neovascularisation in the posterior cavity. In this study, we screened and compared the posterior segment distribution of two poly(ethylene glycol)-distearoylphosphatidylethanolamine carriers modified using targeting-peptides. Thereafter, a transmembrane peptide (i.e., PENE) with a greater ability of transmembrane delivery was selected for delivering the anti-vascular drug (i.e., Axitinib) to the posterior segment of the eye. Using two different mouse models with fundus neovascular diseases, the complete non-invasive delivery of Axitinib to the posterior segment of the eye was confirmed using the targeted system; the designed eye drops (i.e., PENE-nanoparticles) could achieve drug distribution to the retina and veins of the eye as well as good drug permeability for renewal. Moreover, using the eye-drop treatment, neovascularisation was substantially reduced, demonstrating the high efficacy of this drug delivery system. This study, which combines nanodrug-loading technology and the transmembrane delivery of penetrating-peptides to achieve the goal of the non-invasive delivery of small-molecule drugs through the dense blood vessels of the sclera, shows wide applicability and considerably expands the use of ocular drugs. Thus, this study is expected to help develop a more acceptable drug administration strategy for the drug treatment of the posterior segment of the eye.

Lipids, hyperreflective crystalline deposits and diabetic retinopathy: potential systemic and retinal-specific effect of lipid-lowering therapies

The metabolically active retina obtains essential lipids by endogenous biosynthesis and from the systemic circulation. Clinical studies provide limited and sometimes conflicting evidence as to the relationships between circulating lipid levels and the development and progression of diabetic retinopathy in people with diabetes. Cardiovascular-system-focused clinical trials that also evaluated some retinal outcomes demonstrate the potential protective power of lipid-lowering therapies in diabetic retinopathy and some trials with ocular primary endpoints are in progress. Although triacylglycerol-lowering therapies with fibrates afforded some protection against diabetic retinopathy, the effect was independent of changes in traditional blood lipid classes. While systemic LDL-cholesterol lowering with statins did not afford protection against diabetic retinopathy in most clinical trials, and none of the trials focused on retinopathy as the main outcome, data from very large database studies suggest the possible effectiveness of statins. Potential challenges in these studies are discussed, including lipid-independent effects of fibrates and statins, modified lipoproteins and retinal-specific effects of lipid-lowering drugs. Dysregulation of retinal-specific cholesterol metabolism leading to retinal cholesterol accumulation and potential formation of cholesterol crystals are also addressed.

Pathogenic Role of Diabetes-Induced Overexpression of Kallistatin in Corneal Wound Healing Deficiency Through Inhibition of Canonical Wnt Signaling

It was reported previously that circulation levels of kallistatin, an endogenous Wnt signaling inhibitor, are increased in patients with diabetes. The current study was conducted to determine the role of kallistatin in delayed wound healing in diabetic corneas. Immunostaining and Western blot analysis showed kallistatin levels were upregulated in corneas from humans and rodents with diabetes. In murine corneal wound healing models, the canonical Wnt signaling was activated in nondiabetic corneas and suppressed in diabetic corneas, correlating with delayed wound healing. Transgenic expression of kallistatin suppressed the activation of Wnt signaling in the cornea and delayed wound healing. Local inhibition of Wnt signaling in the cornea by kallistatin, an LRP6-blocking antibody, or the soluble VLDL receptor ectodomain (an endogenous Wnt signaling inhibitor) delayed wound healing. In contrast, ablation of the VLDL receptor resulted in overactivation of Wnt/β-catenin signaling and accelerated corneal wound healing. Activation of Wnt signaling in the cornea accelerated wound healing. Activation of Wnt signaling promoted human corneal epithelial cell migration and proliferation, which was attenuated by kallistatin. Our findings suggested that diabetes-induced overexpression of kallistatin contributes to delayed corneal wound healing by inhibiting the canonical Wnt signaling. Thus, kallistatin and Wnt/β-catenin signaling in the cornea could be potential therapeutic targets for diabetic corneal complications.

Structure-Function Relationships in the Rodent Streptozotocin-Induced Model for Diabetic Retinopathy: A Systematic Review

The streptozotocin (STZ)-induced rodent model is one of the most commonly employed models in preclinical drug discovery for diabetic retinopathy (DR). However, standardization and validation of experimental readouts are largely lacking. The aim of this systematic review was to identify and compare the most useful readouts of STZ-induced DR and provide recommendations for future study design based on our findings. We performed a systematic search using 2 major databases, PubMed and EMBASE. Only articles describing STZ-induced DR describing both functional and structural readouts were selected. We also assessed the risk of bias and analyzed qualitative data in the selected studies. We identified 21 studies that met our inclusion/exclusion criteria, using either rats or mice and study periods of 2 to 24 weeks. Glucose level thresholds used to define hyperglycemia were inconsistent between studies, however, most studies used either 250 or 300.6 mg/dL as a defining criterion for hyperglycemia. All included studies performed electroretinography (ERG) and reported a reduction in a-, b-, or c-wave and/or oscillatory potential amplitudes. Spectral-domain optical coherence tomography and fluorescein angiography, as well as immunohistochemical and histopathological analyses showed reductions in retinal thickness, vascular changes, and presence of inflammation. Risk of bias assessment showed that all studies had a high risk of bias due to lack of reporting or correctly following procedures. Our systematic review highlights that ERG represents the most consistent functional readout in the STZ model. However, due to the high risk of bias, caution must be used when interpreting these studies.

The interplay of environmental luminance and genetics in the retinal dystrophy induced by the dominant RPE65 mutation

SignificanceIn humans, genetic mutations in the retinal pigment epithelium (RPE) 65 are associated with blinding diseases, for which there is no effective therapy alleviating progressive retinal degeneration in affected patients. Our findings uncovered that the increased free opsin caused by enhancing the ambient light intensity increased retinal activation, and when compounded with the RPE visual cycle dysfunction caused by the heterozygous D477G mutation and aggregation, led to the onset of retinal degeneration.

Annexin A1 promotes reparative angiogenesis and ameliorates neuronal injury in ischemic retinopathy

PURPOSE

Retinal ischemia is the main reason for vision threatening. Inflammation and aberrant angiogenesis play an important role in the pathogenesis of ischemia. Annexin A1 is an endogenous protein modulating anti-inflammatory processes, and its therapeutic potential has been reported in a range of inflammatory diseases. However, the effect of annexin A1 on ischemic retinal injury has not been examined.

METHODS

Expression of annexin A1 was assessed by real time PCR and western blotting, and location of annexin A1 was evaluated by immunofluorescence staining in retina of OIR. The activation of annexin A1 were assayed in HRECs after hypoxia stimuli. The effect of annexin A1 on vascularization of OIR mouse through quantification vaso-obliteration and neovascularization, as well as expression of relevant angiogenic factors and inflammatory cytokines was compared between wild type and annexin A1 deficiency mice. We also investigated the effect of annexin A1 on retinal neuronal degeneration as measured by ERG and OCT.

RESULTS

In retinas of OIR, the expression of annexin A1 significantly increased and located in inner retinal layers. Annexin A1 was induced in HRECs after hypoxic stimuli. Furthermore, annexin A1 deficiency increased pro-angiogenic and pro-inflammatory cytokines. Ablation of annexin A1 suppressed aortic outgrowth and retinal reparative revascularization and promoted pathological neovascularization to exacerbate retinal dysfunction after ischemia injury.

CONCLUSION

Annexin A1 inhibits angiogenic and inhibits pro-inflammatory cytokines and promotes reparative angiogenesis, thus exhibits neuronal protective function in ischemic retinopathy.

Therapeutic Effects of Fenofibrate Nano-Emulsion Eye Drops on Retinal Vascular Leakage and Neovascularization

Macular edema caused by retinal vascular leakage and ocular neovascularization are the leading causes of severe vision loss in diabetic retinopathy (DR) and age-related macular degeneration (AMD) patients. Oral administration of fenofibrate, a PPARα agonist, has shown therapeutic effects on macular edema and retinal neovascularization in diabetic patients. To improve the drug delivery to the retina and its efficacy, we have developed a nano-emulsion-based fenofibrate eye drop formulation that delivered significantly higher amounts of the drug to the retina compared to the systemic administration, as measured by liquid chromatography-mass spectrometer (LC-MS). The fenofibrate eye drop decreased leukocytes adherent to retinal vasculature and attenuated overexpression of multiple inflammatory factors in the retina of very low-density lipoprotein receptor knockout (Vldlr^-/-) mice, a model manifesting AMD phenotypes, and streptozotocin-induced diabetic rats. The fenofibrate eye drop also reduced retinal vascular leakage in these models. The laser-induced choroidal neovascularization was also alleviated by the fenofibrate eye drop. There were no detectable ocular toxicities associated with the fenofibrate eye drop treatment. These findings suggest that fenofibrate can be delivered efficiently to the retina through topical administration of the nano-emulsion eye drop, which has therapeutic potential for macular edema and neovascularization.

Sirolimus loaded chitosan functionalized poly (lactic-co-glycolic acid) (PLGA) nanoparticles for potential treatment of age-related macular degeneration

The usefulness of sirolimus (SIR) in the treatment of diseases that involve retinal degeneration like age-related macular degeneration (AMD) has been well documented. However, the problem still remains probably owing to the peculiar environment of the eye and/or unfavourable physiochemical profile of SIR. In the present work, we aimed to fabricate sirolimus loaded PLGA nanoparticles (SIR-PLGA-NP) and chitosan decorated PLGA nanoparticles (SIR-CH-PLGA-NP) to be administered via non-invasive subconjunctival route. Both the nanoparticles were characterized in terms of size, zeta potential, DSC, FTIR and XRD analysis. Quality by Design (QbD) approach was employed during the preparation of nanoparticles and the presence of chitosan coating was confirmed through thermogravimetric analysis and contact angle studies. Cationic polymer modification showed sustained in-vitro SIR release and enhanced ex-vivo scleral permeation and penetration. Further, SIR-CH-PLGA-NP revealed enhanced cellular uptake and thus, reduced lipopolysaccharide (LPS)-induced free-radicals generation by RAW 264.7 cells. The prepared nanoparticles were devoid of residual solvent and were found to be safe in HET-CAM analysis, RBCs damage analysis and histopathology studies. Moreover, high anti-angiogenic potential was observed in SIR-CH-PLGA-NP compared with SIR-PLGA-NP in chorioallantoic membrane (CAM) test. Overall, the current work opens up an avenue for further investigation of CH-PLGA-NP as SIR nanocarrier in the treatment of AMD.

Soluble very low-density lipoprotein receptor (sVLDLR) inhibits fibrosis in neovascular age-related macular degeneration

Subretinal fibrosis is a key pathological feature in neovascular age‐related macular degeneration (nAMD). Previously, we identified soluble very low‐density lipoprotein receptor (sVLDLR) as an endogenous Wnt signaling inhibitor. This study investigates whether sVLDLR plays an anti‐fibrogenic role in nAMD models, including Vldlr^−/− mice and laser‐induced choroidal neovascularization (CNV). We found that fibrosis factors including P‐Smad2/3, α‐SMA, and CTGF were upregulated in the subretinal area of Vldlr^−/− mice and the laser‐induced CNV model. The antibody blocking Wnt co‐receptor LRP6 significantly attenuated the overexpression of fibrotic factors in these two models. Moreover, there was a significant reduction of sVLDLR in the interphotoreceptor matrix (IPM) in the laser‐induced CNV model. A transgenic strain (sVLDLR‐Tg) with sVLDLR overexpression in the IPM was generated. Overexpression of sVLDLR ameliorated the profibrotic changes in the subretinal area of the laser‐induced CNV model. In addition, Wnt and TGF‐β signaling synergistically promoted fibrogenesis in human primary retinal pigment epithelium (RPE) cells. CRISPR/Cas9‐mediated LRP6 gene knockout (KO) attenuated this synergistic effect. The disruption of VLDLR expression promoted, while the overexpression of sVLDLR inhibited TGF‐β‐induced fibrosis. These findings suggest that overactivated Wnt signaling enhances the TGF‐β pathway in subretinal fibrosis. sVLDLR confers an antifibrotic effect, at least partially, through the inhibition of Wnt signaling and thus, has therapeutic potential for fibrosis.

Therapeutic approaches targeting molecular signaling pathways common to diabetes, lung diseases and cancer

Diabetes mellitus (DM), is the most common metabolic disease and is characterized by sustained hyperglycemia. Accumulating evidences supports a strong association between DM and numerous lung diseases including chronic obstructive pulmonary disease (COPD), fibrosis, and lung cancer (LC). The global incidence of DM-associated lung disorders is rising and several ongoing studies, including clinical trials, aim to elucidate the molecular mechanisms linking DM with lung disorders, in particular LC. Several potential mechanisms, including hyperglycemia, hyperinsulinemia, glycation, inflammation, and hypoxia, are cited as plausible links between DM and LC. In addition, studies also propose a connection between the use of anti-diabetic medications and reduction in the incidence of LC. However, the exact cause for DM associated lung diseases especially LC is not clear and is an area under intense investigation. Herein, we review the biological links reported between DM and lung disorders with an emphasis on LC. Furthermore, we report common signaling pathways (eg: TGF-β, IL-6, HIF-1, PDGF) and miRNAs that are dysregulated in DM and LC and serve as molecular targets for therapy. Finally, we propose a nanomedicine based approach for delivering therapeutics (eg: IL-24 plasmid DNA, HuR siRNA) to disrupt signaling pathways common to DM and LC and thus potentially treat DM-associated LC. Finally, we conclude that the effective modulation of commonly regulated signaling pathways would help design novel therapeutic protocols for treating DM patients diagnosed with LC.

Pyroptosis in the Retinal Neurovascular Unit: New Insights Into Diabetic Retinopathy

Diabetic retinopathy (DR) is prevalent among people with long-term diabetes mellitus (DM) and remains the leading cause of visual impairment in working-aged people. DR is related to chronic low-level inflammatory reactions. Pyroptosis is an emerging type of inflammatory cell death mediated by gasdermin D (GSDMD), NOD-like receptors and inflammatory caspases that promote interleukin-1β (IL-1β) and IL-18 release. In addition, the retinal neurovascular unit (NVU) is the functional basis of the retina. Recent studies have shown that pyroptosis may participate in the destruction of retinal NVU cells in simulated hyperglycemic DR environments. In this review, we will clarify the importance of pyroptosis in the retinal NVU during the development of DR.

Therapeutic potential of PGC-1α in age-related macular degeneration (AMD) - the involvement of mitochondrial quality control, autophagy, and antioxidant response

INTRODUCTION

Age-related macular degeneration (AMD) is the leading, cause of sight loss in the elderly in the Western world. Most patients remain still without any treatment options. The targeting of Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), a transcription co-factor, is a putative therapy against AMD.

AREAS COVERED

The characteristics of AMD and their possible connection with PGC-1α as well as the transcriptional and post-transcriptional control of PGC-1α are discussed. The PGC-1α-driven control of mitochondrial functions, and its involvement in autophagy and antioxidant responses are also examined. Therapeutic possibilities via drugs and epigenetic approaches to enhance PGC-1α expression are discussed. Authors conducted a search of literature mainly from the recent decade from the PubMed database.

EXPERT OPINION

Therapy options in AMD could include PGC-1α activation or stabilization. This could be achieved by a direct elevation of PGC-1α activity, a stabilization or modification of its upstream activators and inhibitors by chemical compounds, like 5-Aminoimidazole-4-carboxamide riboside, metformin, and resveratrol. Furthermore, manipulations with epigenetic modifiers of PGC-1α expression, including miRNAs, e.g. miR-204, are considered. A therapy aimed at PGC-1α up-regulation may be possible in other disorders besides AMD, if they are associated with disturbances in the mitochondria-antioxidant response-autophagy axis.

Nanotechnology: revolutionizing the delivery of drugs to treat age-related macular degeneration

Introduction: Age-related macular degeneration (AMD) is a progressive retinal disease that degrades the eye's ability to grasp visual acuity. The antivascular endothelial growth factor (VEGF) therapies have made significant strides in improving the quality of life, and there is a continued opportunity to improve delivery, outcomes, and patient convenience and compliance. The treatments available could gain better clinical outcome from novel therapeutics through nanotechnology application.Areas covered: This review summarizes AMD biology and the pathophysiology of the disease along with the successes and limitations of available therapies. It further discusses the promising nanotechnology modalities that could become the cornerstone of future AMD research for improving delivery and reducing frequency of administration thus, enabling development of novel therapeutics.Expert opinion: The robust translation from preclinical work to clinical outcome for AMD remains an unmet need. Continuing to investigate in deeper understanding of biology and advancing high-quality targets into the clinic in combination with the application of advanced nanotechnology to design patient-centric offerings for both dry and wet AMD is needed. Because of the lack of regulatory precedence, and challenging manufacturing and supply chain need, the future of nano-enabled technologies is challenging but presents exciting treatment options for AMD.

Emerging innovations in nano-enabled therapy against age-related macular degeneration: A paradigm shift

Age-related macular degeneration (AMD), a degenerative eye disease, is the major cause of irreversible loss of vision among individuals aged 50 and older. Both genetic and environmental factors are responsible for the progressive damage to central vision. It is a multifactorial retinal disease with features such as drusen, hypopigmentation and/or hyperpigmentation of the retinal pigment epithelium, and even choroidal neovascularization in certain patients. AMD is of two major forms: exudative (wet) and atrophic (dry) with changes affecting the macula leading to impaired vision. Although the retina remains an accessible portion for delivering drugs, there are no current options to cure or treat AMD. The existing expensive therapeutics are unable to treat the underlying pathology but display several side effects. However, recent innovations in nanotherapeutics provide an optimal alternative of drug delivery to treat the neovascular condition. These new-age technologies in the nanometer scale would enhance bioactivity and improve the bioavailability of drugs at the site of action to treat AMD. The nanomedicine also provides sustained release of the drug with prolonged retention after penetrating across the ocular tissues. In this review, the insights into the cellular and molecular mechanisms associated with the pathophysiology of AMD are provided. It also serves to review the current progress in nanoparticle-based drug delivery systems that offer feasible treatments in AMD.

Pathogenic role of human C-reactive protein in diabetic retinopathy

PURPOSE

Elevated blood levels of C-reactive protein (CRP) are associated with both type 1 and type 2 diabetes and diabetic complications, such as diabetic retinopathy (DR). However, its pathogenic role in DR remains unknown. The present study aims to investigate the potential role of CRP in DR pathogenesis and explore its underlying mechanism.

MATERIALS AND METHODS

Human CRP transgenic (hCRP-Tg) rats were employed for streptozotocin (STZ)-induced diabetic and oxygen-induced retinopathy (OIR) models. The retina function was monitored by electroretinography (ERG) and retinal thickness was measured by optical coherence tomography (OCT). TUNEL and cell death ELISA were performed to measure the apoptosis. Oxidative stress was detected by the measurement of reactive oxygen species (ROS) in cells and 3-Nitrotyrosine staining in tissue sections.

RESULTS

In non-diabetic condition, hCRP-Tg with elevated hCRP levels in the retinas demonstrated declined ERG responses and decreased retinal thickness. In STZ-induced diabetic condition, overexpression of hCRP deteriorated retinal neurodegeneration as shown by ERG and apoptosis assays. hCRP also exacerbated retinal leukostasis and acellular capillary formation induced by diabetes. In the OIR model, overexpression of hCRP exacerbated retinal neovascularization (NV). In retinal cell lines, hCRP treatment induced cell death and over-production of ROS. Furthermore, hCRP-induced overexpression of pro-inflammatory, pro-oxidative, and pro-angiogenic factors was associated with up-regulation of CD32 and the NF-κB signaling in the retinas.

CONCLUSIONS

Elevated hCRP levels play a pathogenic role in DR. Targeting the hCRP-CD32-NF-κB pathway may represent a novel therapeutic strategy for DR.

A review of nanocarrier-mediated drug delivery systems for posterior segment eye disease: challenges analysis and recent advances

Posterior segment eye disease is a leading cause of irreversible vision impairment and blindness. As the unique organ for vision, eyes are protected by various protective barriers. The existence of physiological barriers and elimination mechanisms makes it challenging to treat the posterior segment eye diseases. To achieve efficient drug delivery to the posterior segment of eyes, different drug delivery systems have been proposed. Due to their abilities to enhance ocular tissue permeability, make controlled drug release and target retina, nanocarriers, such as lipid nanoparticles, liposomes and polymeric nanomicelles, have been widely studied for posterior segment drug delivery. However, clinical applications of nanocarrier mediated drug delivery systems as non-invasive ocular drops is still not ready. The delivery of nanocarrier-mediated drug for posterior segment disease still faces the choice of being more effective or more invasive for long-term treatment. Therefore, it is necessary to have a clear understanding of the barriers and the routes of ocular drug delivery while developing the delivery systems. In this review, types of ocular barriers and drug administration routes are categorised in a more intuitive way. Recent advances in nanocarrier mediated drug delivery systems with focus on posterior segment are reviewed with illustrative examples.

Ocular Drug Delivery to the Retina: Current Innovations and Future Perspectives

Treatment options for retinal diseases, such as neovascular age-related macular degeneration, diabetic retinopathy, and retinal vascular disorders, have markedly expanded following the development of anti-vascular endothelial growth factor intravitreal injection methods. However, because intravitreal treatment requires monthly or bimonthly repeat injections to achieve optimal efficacy, recent investigations have focused on extended drug delivery systems to lengthen the treatment intervals in the long term. Dose escalation and increasing molecular weight of drugs, intravitreal implants and nanoparticles, hydrogels, combined systems, and port delivery systems are presently under preclinical and clinical investigations. In addition, less invasive techniques rather than intravitreal administration routes, such as topical, subconjunctival, suprachoroidal, subretinal, and trans-scleral, have been evaluated to reduce the treatment burden. Despite the latest advancements in the field of ophthalmic pharmacology, enhancing drug efficacy with high ocular bioavailability while avoiding systemic and local adverse effects is quite challenging. Consequently, despite the performance of numerous in vitro studies, only a few techniques have translated to clinical trials. This review discusses the recent developments in ocular drug delivery to the retina, the pharmacokinetics of intravitreal drugs, efforts to extend drug efficacy in the intraocular space, minimally invasive techniques for drug delivery to the retina, and future perspectives in this field.

Recent advances in intraocular and novel drug delivery systems for the treatment of diabetic retinopathy

Introduction: Diabetic retinopathy (DR) is associated with damage to the retinal blood vessels that lead eventually to vision loss. The existing treatments of DR are invasive, expensive, and cumbersome. To overcome challenges associated with existing therapies, various intraocular sustained release and novel drug delivery systems (NDDS) have been explored.Areas covered: The review discusses recently developed intraocular devices for sustained release of drugs as well as novel noninvasive drug delivery systems that have met a varying degree of success in local delivery of drugs to retinal circulation.Expert opinion: The intraocular devices have got very good success in providing sustained release of drugs in patients. The development of NDDS and their application through the ocular route has certainly provided an edge to treat DR over existing therapies such as anti-VEGF administration but their success rate is quite low. Moreover, most of them have proved to be effective only in animal models. In addition, the extent of targeting the drug to the retina still remains variable and unpredictable. The toxicity aspect of the NDDS has generally been neglected. In order to have successful commercialization of nanotechnology-based innovations well-designed clinical research studies need to be conducted to evaluate their clinical superiority over that of the existing formulations.

Biotechnology and Biomaterial-Based Therapeutic Strategies for Age-Related Macular Degeneration. Part I: Biomaterials-Based Drug Delivery Devices

Age-related Macular Degeneration (AMD) is an up-to-date untreatable chronic neurodegenerative eye disease of multifactorial origin, and the main causes of blindness in over 65 years old people. It is characterized by a slow progression and the presence of a multitude of factors, highlighting those related to diet, genetic heritage and environmental conditions, present throughout each of the stages of the illness. Current therapeutic approaches, mainly consisting of intraocular drug delivery, are only used for symptoms relief and/or to decelerate the progression of the disease. Furthermore, they are overly simplistic and ignore the complexity of the disease and the enormous differences in the symptomatology between patients. Due to the wide impact of the AMD and the up-to-date absence of clinical solutions, the development of biomaterials-based approaches for a personalized and controlled delivery of therapeutic drugs and biomolecules represents the main challenge for the defeat of this neurodegenerative disease. Here we present a critical review of the available and under development AMD therapeutic approaches, from a biomaterials and biotechnological point of view. We highlight benefits and limitations and we forecast forthcoming alternatives based on novel biomaterials and biotechnology methods. In the first part we expose the physiological and clinical aspects of the disease, focusing on the multiple factors that give origin to the disorder and highlighting the contribution of these factors to the triggering of each step of the disease. Then we analyze available and under development biomaterials-based drug-delivery devices (DDD), taking into account the anatomical and functional characteristics of the healthy and ill retinal tissue.

Fenofibrate prevents iron induced activation of canonical Wnt/β-catenin and oxidative stress signaling in the retina

Accumulating evidence strongly implicates iron in the pathogenesis of aging and disease. Iron levels have been found to increase with age in both the human and mouse retinas. We and others have shown that retinal diseases such as age-related macular degeneration and diabetic retinopathy are associated with disrupted iron homeostasis, resulting in retinal iron accumulation. In addition, hereditary disorders due to mutation in one of the iron regulatory genes lead to age dependent retinal iron overload and degeneration. However, our knowledge on whether iron toxicity contributes to the retinopathy is limited. Recently, we reported that iron accumulation is associated with the upregulation of retinal and renal renin-angiotensin system (RAS). Evidences indicate that multiple genes/components of the RAS are targets of Wnt/β-catenin signaling. Interestingly, aberrant activation of Wnt/β-catenin signaling is observed in several degenerative diseases. In the present study, we explored whether iron accumulation regulates canonical Wnt signaling in the retina. We found that in vitro and in vivo iron treatment resulted in the upregulation of Wnt/β-catenin signaling and its downstream target genes including renin-angiotensin system in the retina. We confirmed further that iron activates canonical Wnt signaling in the retina using TOPFlash T-cell factor/lymphoid enhancer factor promoter assay and Axin2-LacZ reporter mouse. The presence of an iron chelator or an antioxidant reversed the iron-mediated upregulation of Wnt/β-catenin signaling in retinal pigment epithelial (RPE) cells. In addition, treatment of RPE cells with peroxisome proliferator-activated receptor (PPAR) α-agonist fenofibrate prevented iron-induced activation of oxidative stress and Wnt/β-catenin signaling by chelating the iron. The role of fenofibrate, an FDA-approved drug for hyperlipidemia, as an iron chelator has potentially significant therapeutic impact on iron associated degenerative diseases.

Polymeric Nanoparticles: Production, Characterization, Toxicology and Ecotoxicology

Polymeric nanoparticles (NPs) are particles within the size range from 1 to 1000 nm and can be loaded with active compounds entrapped within or surface-adsorbed onto the polymeric core. The term "nanoparticle" stands for both nanocapsules and nanospheres, which are distinguished by the morphological structure. Polymeric NPs have shown great potential for targeted delivery of drugs for the treatment of several diseases. In this review, we discuss the most commonly used methods for the production and characterization of polymeric NPs, the association efficiency of the active compound to the polymeric core, and the in vitro release mechanisms. As the safety of nanoparticles is a high priority, we also discuss the toxicology and ecotoxicology of nanoparticles to humans and to the environment.

Recent theranostic paradigms for the management of Age-related macular degeneration

Degenerative diseases of eye like Age-related macular degeneration (AMD), that affects the central portion of the retina (macula), is one of the leading causes of blindness worldwide especially in the elderly population. It is classified mainly as wet and dry form. With expanding knowledge about the underlying pathophysiology of the disease, various treatment strategies are being employed to halt the course of the disease progression. Hitherto, there is no ideal therapy which can cure the disease completely, and targeting the posterior segment of the eye is yet another challenge. The purpose of this review is to summarize the recent advances in the management and treatment stratagems (therapies, delivery systems and diagnostic tools) pertaining to AMD viz. molecular targeting, stem cell therapy, nanotechnology and exosomes with special reference to newer technologies like artificial intelligence and 3D printing. Furthermore, the role of diet and nutritional supplements in the prevention and treatment of the disease has also been highlighted. The alarming increase in the said disorder around the globe demands exhaustive research and investigations in the treatment zone. This review thus additionally directs the attention towards the challenges and future perspectives of different treatment approaches for AMD.

Polymeric Nanoparticles for Drug Delivery: Recent Developments and Future Prospects

The complexity of some diseases—as well as the inherent toxicity of certain drugs—has led to an increasing interest in the development and optimization of drug-delivery systems. Polymeric nanoparticles stand out as a key tool to improve drug bioavailability or specific delivery at the site of action. The versatility of polymers makes them potentially ideal for fulfilling the requirements of each particular drug-delivery system. In this review, a summary of the state-of-the-art panorama of polymeric nanoparticles as drug-delivery systems has been conducted, focusing mainly on those applications in which the corresponding disease involves an important morbidity, a considerable reduction in the life quality of patients—or even a high mortality. A revision of the use of polymeric nanoparticles for ocular drug delivery, for cancer diagnosis and treatment, as well as nutraceutical delivery, was carried out, and a short discussion about future prospects of these systems is included.