Diabetic eye: associated diseases, drugs in clinic, and role of self-assembled carriers in topical treatment

Oleogels for the ocular delivery of epalrestat: formulation, in vitro, in ovo, ex vivo and in vivo evaluation

The ocular administration of lipophilic and labile drugs such as epalrestat, an aldose reductase inhibitor with potential for diabetic retinopathy treatment, demands the development of topical delivery systems capable of providing sufficient ocular bioavailability. The aim of this work was to develop non-aqueous oleogels based on soybean oil and gelators from natural and sustainable sources (ethyl cellulose, beeswax and cocoa butter) and to assess their reproducibility, safety and efficiency in epalrestat release and permeation both ex vivo and in vivo. Binary combinations of gelators at 10% w/w resulted in solid oleogels (oleorods), while single gelator oleogels at 5% w/w remained liquid at room temperature, with most of the oleogels displaying shear thinning behavior. The oleorods released up to 4 µg epalrestat per mg of oleorod in a sustained or burst pattern depending on the gelator (approx. 10% dose in 24 h). The HET-CAM assay indicated that oleogel formulations did not induce ocular irritation and were safe for topical ocular administration. Corneal and scleral ex vivo assays evidenced the permeation of epalrestat from the oleorods up to 4 and 2.5 µg/cm2 after six hours, respectively. Finally, the capacity of the developed oleogels to sustain release and provide significant amounts of epalrestat to the ocular tissues was demonstrated in vivo against aqueous-based niosomes and micelles formulations loaded with the same drug concentration. Overall, the gathered information provides valuable insights into the development of oleogels for ocular drug delivery, emphasizing their safety and controlled release capabilities, which have implications for the treatment of diabetic neuropathy and other ocular conditions.

Lage E, Casas M, Concheiro A, Alvarez-Lorenzo C. Langmuir monolayer studies of non-ionic surfactants and DOTMA for the design of ophthalmic niosomes

The worldwide increase in diabetes entails a rise in associated diseases, with diabetic retinopathy on the forefront of the ocular complications. To overcome the challenges posed by ocular barriers, self-assembled nanocarriers have gathered increasing attention in recent years, with niosomes revealing themselves to be suitable for the delivery of a variety of drugs. This study investigated the mechanical properties of Langmuir monolayers comprising cholesterol, Tween 60, and 1,2-di-O-octadecenyl-3-trimethylammonium propane (DOTMA), both individually and in binary and ternary systems. The cholesterol monolayer was characterized by an L-shaped isotherm, reflecting two surface aggregation states. Tween 60 exhibited expanded conformation and progressive aggregation, transitioning through a phase change. The addition of cholesterol to Tween 60 resulted in a subtle reduction in surface compressional modulus. The compression isotherms highlighted the stabilizing effect of cholesterol on the monolayer, affecting the film's resistance to compression. The introduction of DOTMA in Tween 60 monolayers revealed concentration-dependent effects, where the compression resistance of the film was proportional to DOTMA concentration. Ternary systems of cholesterol, DOTMA and Tween 60 exhibited unique behavior, with DOTMA enhancing film stability and cholesterol modulating this effect. Temperature and subphase ionic strength variations further exacerbated the effects of DOTMA concentration. Brewster Angle Microscopy confirmed the absence of microdomains in the compressed monolayer, supporting the hypothesis of a monolayer collapse. Overall, the research provided valuable insights into the intricate interactions and mechanical behavior of these surfactant systems and the feasibility of obtaining cationic niosome-based drug delivery.

AAV-Based Strategies for Treatment of Retinal and Choroidal Vascular Diseases: Advances in Age-Related Macular Degeneration and Diabetic Retinopathy Therapies

Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are vascular diseases with high prevalence, ranking among the leading causes of blindness and vision loss worldwide. Despite being effective, current treatments for AMD and DR are burdensome for patients and clinicians, resulting in suboptimal compliance and real risk of vision loss. Thus, there is an unmet need for long-lasting alternatives with improved safety and efficacy. Adeno-associated virus (AAV) is the leading vector for ocular gene delivery, given its ability to enable long-term expression while eliciting relatively mild immune responses. Progress has been made in AAV-based gene therapies for not only inherited retinal diseases but also acquired conditions with preclinical and clinical studies of AMD and DR showing promising results. These studies have explored several pathways involved in the disease pathogenesis, as well as different strategies to optimise gene delivery. These include engineered capsids with enhanced tropism to particular cell types, and expression cassettes incorporating elements for a targeted and controlled expression. Multiple-acting constructs have also been investigated, in addition to gene silencing and editing. Here, we provide an overview of strategies employing AAV-mediated gene delivery to treat AMD and DR. We discuss preclinical efficacy studies and present the latest data from clinical trials for both diseases.

Novel Drug Delivery Methods and Approaches for the Treatment of Retinal Diseases

This review discusses emerging approaches to ocular drug delivery for retinal diseases. Intravitreal injections have proven to be an effective, safe, and commonly used drug delivery method. However, the optimal management of chronic retinal diseases requires frequent intravitreal injections over extended periods of time. Although this can be achieved in a clinical trial environment, it is difficult to replicate in routine clinical practice. In addition, frequent treatment increases the risk of complications, incurs more costs, and increases the treatment burden for patients and caregivers. Given the aging global population and diabetes pandemic, there is an urgent need for drug delivery methods that support more durable retinal therapy while maintaining the efficacy and safety of currently available intravitreal therapies. Several innovative drug delivery methods are currently being investigated. These include sustained-release implants and depots using prodrugs, microparticles, and hydrogels, surgically implanted reservoirs, gene therapy via submacular injections or suprachoroidal injections, as well as topical and systemic therapies.

Formulation and Characterization of Epalrestat-Loaded Polysorbate 60 Cationic Niosomes for Ocular Delivery

The aim of this work was to develop niosomes for the ocular delivery of epalrestat, a drug that inhibits the polyol pathway and protects diabetic eyes from damage linked to sorbitol production and accumulation. Cationic niosomes were made using polysorbate 60, cholesterol, and 1,2-di-O-octadecenyl-3-trimethylammonium propane. The niosomes were characterized using dynamic light scattering, zeta-potential, and transmission electron microscopy to determine their size (80 nm; polydispersity index 0.3 to 0.5), charge (-23 to +40 mV), and shape (spherical). The encapsulation efficiency (99.76%) and the release (75% drug release over 20 days) were measured with dialysis. The ocular irritability potential (non-irritating) was measured using the Hen's Egg Test on the Chorioallantoic Membrane model, and the blood glucose levels (on par with positive control) were measured using the gluc-HET model. The toxicity of the niosomes (non-toxic) was monitored using a zebrafish embryo model. Finally, corneal and scleral permeation was assessed with the help of Franz diffusion cells and confirmed with Raman spectroscopy. Niosomal permeation was higher than an unencapsulated drug in the sclera, and accumulation in tissues was confirmed with Raman. The prepared niosomes show promise to encapsulate and carry epalrestat through the eye to meet the need for controlled drug systems to treat the diabetic eye.

An Update on Novel Ocular Nanosystems with Possible Benefits in the Treatment of Corneal Neovascularization

Corneal neovascularization (CNV) is an ocular pathological change that results from an imbalance between angiogenic factors and antiangiogenic factors as a result of various ocular insults, including infection, inflammation, hypoxia, trauma, corneal degeneration, and corneal transplantation. Current clinical strategies for the treatment of CNV include pharmacological treatment and surgical intervention. Despite some degree of success, the current treatment strategies are restricted by limited efficacy, adverse effects, and a short duration of action. Recently, gene-based antiangiogenic therapy has become an emerging strategy that has attracted considerable interest. However, potential complications with the use of viral vectors, such as potential genotoxicity resulting from long-term expression and nonspecific targeting, cannot be ignored. The use of ocular nanosystems (ONS) based on nanotechnology has emerged as a great advantage in ocular disease treatment during the last two decades. The potential functions of ONS range from nanocarriers, which deliver drugs and genes to target sites in the eye, to therapeutic agents themselves. Various preclinical studies conducted to date have demonstrated promising results of the use of ONS in the treatment of CNV. In this review, we provide an overview of CNV and its current therapeutic strategies and summarize the properties and applications of various ONS related to the treatment of CNV reported to date. Our goal is to provide a comprehensive review of these considerable advances in ONS in the field of CNV therapy over the past two decades to fill the gaps in previous related reports. Finally, we discuss existing challenges and future perspectives of the use of ONS in CNV therapy, with the goal of providing a theoretical contribution to facilitate future practical growth in the area.

Treatment and prevention of pathological mitochondrial dysfunction in retinal degeneration and in photoreceptor injury

Pathological deterioration of mitochondrial function is increasingly linked with multiple degenerative illnesses as a mediator of a wide range of neurologic and age-related chronic diseases, including those of genetic origin. Several of these diseases are rare, typically defined in the United States as an illness affecting fewer than 200,000 people in the U.S. population, or about one in 1600 individuals. Vision impairment due to mitochondrial dysfunction in the eye is a prominent feature evident in numerous primary mitochondrial diseases and is common to the pathophysiology of many of the familiar ophthalmic disorders, including age-related macular degeneration, diabetic retinopathy, glaucoma and retinopathy of prematurity - a collection of syndromes, diseases and disorders with significant unmet medical needs. Focusing on metabolic mitochondrial pathway mechanisms, including the possible roles of cuproptosis and ferroptosis in retinal mitochondrial dysfunction, we shed light on the potential of α-lipoyl-L-carnitine in treating eye diseases. α-Lipoyl-L-carnitine is a bioavailable mitochondria-targeting lipoic acid prodrug that has shown potential in protecting against retinal degeneration and photoreceptor cell loss in ophthalmic indications.