Transscleral drug delivery to the posterior eye: prospects of pharmacokinetic modeling

'Nanotechnology-based implants: recent advances and future prospects for a range of diseases'

This is the goal of bio-implant engineering, which seeks to develop sophisticated biomaterials that can replace or augment lost or impaired tissue, and most importantly, replace the function of failed organs. Novel developments in nanotechnology have brought nanomaterials that mimic natural tissues, especially in terms of wettability, topographical, and energy states to act as a complementary substitute to the native tissues for biomedical implants. Theses nanomaterials, such as functional nanocoatings and nanostructured surfaces, enhance implant integration by offering highly effective antibacterial properties; and stimulating cell attachment, differentiation and proliferation. Its use in orthopedic biomaterials impacts on crucial issues of the existent implants which include corrosion and bacterial adhesion while smart biomaterials, porosity and three-dimensional are about personalized, and stimuli-responsive implants. This review covers recent advances in nanotechnology-based implant systems, designed and investigated for orthopedic and tissue engineering applications. Future prospects are also studied and critical concerns related to commcercialization of nanomaterial-based bio-implants, including cost, quality, pain management and implant lifespan are also touched.

Topical Administration of Mucoadhesive Liposomes-Epoetin-β for Targeting the Ocular Posterior Segment

Delivering drugs to the posterior eye segment is a complex task, particularly for treating retinal diseases. Neuroprotective approaches to maintain neuronal integrity have garnered significant attention in recent research. Here, we developed a mucoadhesive nanoparticulate system based on thiolated hyaluronic acid-modified cationic liposomes (HA-SH@liposomes) for topical administration. To fabricate these liposomes, we utilized microfluidic technology with a toroidal mixer to ensure consistent size and stability. Cationic liposomes were prepared by using the microfluidic method, and Epoetin-β (EPOβ), a neuroprotective agent, was loaded into the liposomes. Following this, HA-SH was conjugated to the EPOβ/HA-SH@liposomes using a postmicrofluidics conjugation method, wherein HA-SH was added dropwise to facilitate electrostatic interactions between the cationic liposomes and the anionic polymer. The resulting liposomes exhibited a mean size of 144 ± 1.3 nm and a polydispersity index (PDI) of 0.09 ± 0.01, indicating their uniformity. We evaluated the biocompatibility of the EPOβ/HA-SH@liposomes in vitro using live/dead and MTS assays on the RGC-5 cell line, demonstrating no notable cytotoxicity compared to the controls. To assess the in vivo performance, we conducted extensive ophthalmological examinations in C57/BL6 mice, including immunofluorescence staining to track the distribution of EPOβ and EPOβ/HA-SH@liposomes within the eyeball. Additionally, we quantified EPOβ levels in the retina using an enzyme-linked immunosorbent assay (ELISA) kit after the topical application of free EPOβ and the EPOβ/HA-SH@liposome formulation. The immunofluorescence staining revealed efficient delivery of EPOβ into the retina and choroid via the transcorneal route when administered as EPOβ/HA-SH@liposomes. ELISA results showed that the liposomal formulation achieved approximately 1.9× greater penetration efficiency than free EPOβ. Furthermore, optokinetic response (OKR) assays indicated that animals treated with EPOβ/HA-SH@liposomes exhibited slightly improved visual acuity compared with those treated with free EPOβ, though the difference was not statistically significant. In conclusion, the topical ocular administration of EPOβ/HA-SH@liposomes facilitated the efficient delivery of EPOβ to the retina, promoting retinal recovery and confirming its neuroprotective properties. This preclinical study provides a foundation for innovative strategies in the topical delivery of neuroprotective agents in ocular therapy.

A Model of the Mechanisms Underpinning Unconventional Aqueous Humor Outflow

Purpose

To develop a mathematical model of the unconventional outflow pathway.

Methods

The unconventional pathway is modeled as having two key components: the uveo-vortex and the trans-scleral pathways. The uveo-vortex pathway is modeled using Starling's law and the trans-scleral flow using predominately hydrostatic forces. We include transcytosis from the choriocapillaris (CC) and collapsibility of the suprachoroidal space (SCS) as particular features. There is considerable uncertainty in a number of model parameter values, and we identify the most significant ones using sensitivity analysis.

Results

The model successfully generates a fluid flow from anterior to posterior in the choroidal tissue and the SCS, which also demonstrates many of the known physiological features, including the insensitivity of the unconventional flow to fluctuations in the IOP, albumin removal by the trans-scleral flow, and the CC as a net absorber of fluid from, and supplier of albumin to, the choroidal tissue. The model supports the two previously proposed mechanisms of the action of prostaglandin F2α analogues.

Conclusions

We have developed a theoretical model of the unconventional aqueous outflow pathway that successfully captures its physiological features and elucidates the actions of prostaglandin F2α analogues and other drugs.

Sustained release of RNA nanoparticles from reservoir implant for ocular delivery

Previous studies of RNA nanoparticles have demonstrated the potential of these nanoparticles in ocular delivery via the subconjunctival route. Sustained ocular delivery is beneficial for chronic eye disease treatment, and utilizing a reservoir implant in the periocular space (e.g., episcleral implant) can prolong ocular delivery of these nanoparticles. The objectives of the present study were to (a) demonstrate the fabrication of the reservoir implants, (b) evaluate the performance of the implants with model permeants and RNA nanoparticles in vitro, and (c) investigate the applicability of hindered transport theory for the release kinetics from the implants. In vitro release testing was performed with the implants to determine the release kinetics and implant membrane permeability. In addition to RNA nanoparticles, model permeants fluorescein-isothiocyanate (FITC) labeled dextrans (10, 40, and 150 kDa) were examined. The results indicated that the rates of permeant release from the implants were a function of the (a) size and structure of the permeant/nanoparticle and (b) type and pore size of the implant membrane. The model analyses provided insights into implant membrane transport and ocular pharmacokinetics of the nanoparticles for transscleral delivery. The results suggested the potential of prolonged delivery of the RNA nanoparticles with the episcleral implant approach.

Nanocarrier-Based, ocular drug delivery: Challenges, prospects, and the therapeutic landscape in the United Arab Emirates

Human eyes have the most complex and advanced physiological defense barriers. Due to these barriers, efficient delivery of ocular drugs is a major challenge in the treatment of eye diseases and disorders. Posterior eye diseases such as retinopathy are the leading causes of impaired vision and blindness globally. The topical and systemic administration of drugs such as eye drops, ointments, intravitreal injections, intraocular implants, contact lenses, and emulsions are the perennial approaches employed to treat ocular diseases. However, these modalities are inefficient due to the low bioavailability of the active drug and the potential for drug-related cytotoxicity to the ocular tissue. In this review, the conventional approaches in ocular drug delivery systems (DDSs) are explored and the limitations associated with each technique are elucidated. A comparison between the different DDSs is presented, showing the most effective treatment techniques available to date. In addition, this review presents recent advances in the field of nanocarriers and microcarriers used in ocular drug delivery systems such as nanoparticles, nano-suspensions, nanofibers, nanogels, nano-liposomes, nano micelles, dendrimers, contact lens, microneedle, and implants. Further, this review identifies the utility of nano-carriers in enabling the development of new-generation ocular DDSs with low toxicity, high efficiency, and high stability of targeted drug delivery systems to overcome the limitations observed with conventional ocular DDSs. In addition, this manuscript sheds light on the incidence and unique landscape of ocular diseases in the United Arab Emirates (UAE), and the potential for employing novel ocular DDSs for targeted treatment of conditions such as diabetic retinopathy in the UAE. It also discusses the putative role genetic variants of the VEGF gene may play in predisposing the local population in the UAE to developing posterior eye segment diseases such as retinopathy.

Microneedles: A minimally invasive delivery system for ocular treatment

This review article delves into the extensive use of microneedles in ocular therapy, emphasizing their efficacy in delivering drug substances to the posterior region of the eye. The conventional methods of drug delivery, while widely employed, are marred by inherent drawbacks such as neovascularization, abrasion, and infiltration. To address these limitations, the review explores various approaches to microneedle fabrication, shedding light on the diverse materials employed in the process. Furthermore, the article meticulously examines the delivered drug substances using distinct microneedle approaches and their applications in ocular therapy. By critically evaluating the drawbacks associated with conventional ophthalmic drug delivery, the review seeks to pave the way for a paradigm shift. It advocates for a novel approach centered around minimally invasive microneedles, presenting them as a promising solution to overcome the limitations of current drug delivery methods. The comprehensive discussion within this article not only offers insights into the fabrication techniques and materials used for microneedles but also provides a nuanced understanding of the applications and advantages associated with this innovative approach. As the exploration of microneedle technology continues to evolve, this review serves as a valuable resource for researchers, clinicians, and pharmaceutical professionals seeking to enhance ocular therapy by embracing the potential of minimally invasive microneedles.

Posterior eye delivery of angiogenesis-inhibiting RNA nanoparticles via subconjunctival injection

Neovascularization contributes to various posterior eye segment diseases such as age-related macular degeneration and diabetic retinopathy. RNA nanoparticles were demonstrated previously to enter the corneal and retinal cells after subconjunctival injection for ocular delivery. In the present study, antiangiogenic aptamers (anti-vascular endothelial growth factor (VEGF) and anti-angiopoietin-2 (Ang2) aptamers) were conjugated to RNA nanoparticles. The objectives were to investigate the clearance and distribution of these angiogenesis-inhibiting RNA nanoparticles after subconjunctival injection in vivo and their antiangiogenic effects for inhibiting ocular neovascularization in vitro. The results in the whole-body fluorescence imaging study showed that the clearance of RNA nanoparticles was size-dependent with no significant differences between RNA nanoparticles with and without the aptamers except for pRNA-3WJ. The distribution study of RNA nanoparticles by confocal microscopy of the dissected eye tissues in vivo indicated cell internalization of the larger RNA nanoparticles in the retina and retinal pigment epithelium after subconjunctival injection, and the larger nanoparticles with aptamers showed higher levels of cell internalization than those without. In the cell proliferation assay in vitro, RNA nanoparticles with multiple aptamers had higher antiangiogenic effects. With both longer retention time and high antiangiogenic effect, SQR-VEGF-Ang2 could be a promising RNA nanoparticle for posterior eye delivery.

Encapsulated cell technology: Delivering cytokines to treat posterior ocular diseases

Encapsulated cell technology (ECT) is a targeted delivery method that uses the genetically engineered cells in semipermeable polymer capsules to deliver cytokines. Thus far, ECT has been extensively utilized in pharmacologic research, and shows enormous potentials in the treatment of posterior segment diseases. Due to the biological barriers within the eyeball, it is difficult to attain effective therapeutic concentration in the posterior segment through topical administration of drug molecules. Encouragingly, therapeutic cytokines provided by ECT can cross these biological barriers and achieve sustained release at the desired location. The encapsulation system uses permeable materials that allow growth factors and cytokines to diffuse efficiently into retinal tissue. Moreover, the ECT based treatment can be terminated timely when we need to retrieve the implant, which makes the therapy reversible and provides a safer alternative for intraocular gene therapy. Meanwhile, we also place special emphasis on optimizing encapsulation materials and enhancing preservation techniques to achieve the stable release of growth factors and cytokines in the eyeball. This technology holds great promise for the treatment of patients with dry AMD, RP, glaucoma and MacTel. These findings would enrich our understandings of ECT and promote its future applications in treatment of degenerative retinopathy. This review comprises articles evaluating the exactness of artificial intelligence-based formulas published from 2000 to March 2024. The papers were identified by a literature search of various databases (PubMed/MEDLINE, Google Scholar, Cochrane Library and Web of Science).

Comprehensive ocular and systemic pharmacokinetics of dexamethasone after subconjunctival and intravenous injections in rabbits

Even though subconjunctival injections are used in clinics, their quantitative pharmacokinetics has not been studied systematically. For this purpose, we evaluated the ocular and plasma pharmacokinetics of subconjunctival dexamethasone in rabbits. Intravenous injection was also given to enable a better understanding of the systemic pharmacokinetics. Dexamethasone concentrations in plasma (after subconjunctival and intravenous injections) and four ocular tissues (iris-ciliary body, aqueous humour, neural retina and vitreous) were analysed using LC-MS/MS. Population pharmacokinetic modelling for plasma data from both injection routes were used, and for first time the constant rate of absorption of dexamethasone from the subconjunctival space into plasma was estimated (ka,plasma = 0.043 min-1, i.e. absorption half-life of 17.3 min). Non-compartmental analysis was used for the ocular data analysis and resulting in ocular drug exposure of iris-ciliary body (AUC0-∞= 41984 min·ng/g) > neural retina (AUC0-∞= 25511 min·ng/g) > vitreous (AUC0-∞= 7319 min·ng/mL) > aqueous humour (AUC0-∞= 6146 min·ng/mL). The absolute bioavailability values after subconjunctival injection, reported for the first time, were 0.74 % in aqueous humour (comparable to topical dexamethasone suspensions), and 0.30 % in vitreous humour (estimated to be higher than in topical administration). These novel and comprehensive pharmacokinetic data provide valuable information on the potential for exploiting this route in ocular drug development for treating both, anterior and posterior segment ocular diseases. Moreover, the new generated dexamethasone-parameters are a step-forward in building predictive pharmacokinetic models to support the design of new subconjunctival dexamethasone formulations, which may sustain drug effect for longer period of time.

Drug-like properties of tyrosine kinase inhibitors in ophthalmology: Formulation and topical availability

Tyrosine kinase inhibitors (TKIs) can inhibit edema and neovascularization, such as in age-related macular degeneration and diabetic retinopathy. However, their topical administration in ophthalmology is limited by their toxicity and poor aqueous solubility. There are multiple types of TKIs, and each TKI has an affinity to more than one type of receptor. Studies have shown that ocular toxicity can be addressed by selecting TKIs that have a high affinity for specific vascular endothelial growth factor receptors (VEGFRs) but a low affinity for epidermal growth factor receptors (EGFRs). Drugs permeate from the aqueous tear fluid into the eye via passive diffusion. Thus, a sustained high concentration of the dissolved drug in the aqueous tear fluid is essential for a successful delivery to posterior tissues such as the retina. Unfortunately, the aqueous solubility of the TKIs that have the most favorable VEGFR/EGFR affinity ratio, that is, axitinib and cabozantinib, is well below 1 µg/mL, making their topical delivery very challenging. This is a review of the drug-like properties of TKIs that are currently being evaluated or have been evaluated as ophthalmic drugs. These properties include their solubilization, cyclodextrin complexation, and ability to permeate from the aqueous tear fluid to the posterior eye segment.

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

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

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.

Clinical Correlation of Retinal Fluid Fluctuation Represented by Fluctuation Index in Wet Age-Related Macular Degeneration: TOWER Study Report 2

Purpose

To explore outcomes and biomarkers associated with retinal fluid instability represented by a new parameter in neovascular age-related macular degeneration (nAMD).

Methods

Patients with treatment-naïve nAMD receiving anti-vascular endothelial growth factor (VEGF) injections for a duration of 1 to 3 years were consecutively reviewed. Fluctuation Index (FI) of each eye, calculated by averaging the sum of differences in 1-mm central subfield thickness between each follow-up from months 3 to 24, was arranged into ascending order from the lowest to the highest and split equally into low, moderate, and high fluctuation groups. Outcomes were analyzed at 24 months.

Results

Of 558 eyes, FI values showed a negative correlation with a degree-response gradient with 24-month visual improvement. After controlling for baseline best-corrected visual acuity and potential confounders, eyes with low fluctuation gained more Early Treatment Diabetic Retinopathy Study letters than those in the moderate and high fluctuation group (Δ, 10.1 and 14.0 letters, respectively). Significant best-corrected visual acuity improvement from baseline to month 24 (11.8 letters) was observed exclusively in the low fluctuation group despite the indifference in the number of injections and types of anti-VEGF drug used among groups. Patients presenting with central subfield thickness of ≥405 µm or intraretinal fluid coinciding with subretinal fluid showed a significant association with foveal thickness instability during the maintenance phase.

Conclusions

Apart from the central subfield thickness values, unstable macular thickening represented by the FI was associated with some baseline features and may contribute to substandard visual outcomes.

Translational Relevance

FI may be a valuable tool for assessing therapeutic adequacy in the treatment of nAMD.

Challenges and strategies for ocular posterior diseases therapy via non-invasive advanced drug delivery

Posterior segment diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) are vital factor that seriously threatens human vision health and quality of life, the treatment of which poses a great challenge to ophthalmologists and ophthalmic scientists. In particular, ocular posterior drug delivery in a non-invasive manner is highly desired but still faces many difficulties such as rapid drug clearance, limited permeability and low drug accumulation at the target site. At present, many novel non-invasive topical ocular drug delivery systems are under development aiming to improve drug delivery efficiency and biocompatibility for better therapy of posterior segment oculopathy. The purpose of this review is to present the challenges in the noninvasive treatment of posterior segment diseases, and to propose strategies to tackle these bottlenecks. First of all, barriers to ocular administration were introduced based on ocular physiological structure and behavior, including analysis and discussion on the influence of ocular structures on noninvasive posterior segment delivery. Thereafter, various routes of posterior drug delivery, both invasive and noninvasive, were illustrated, along with the respective anatomical obstacles that need to be overcome. The widespread and risky application of invasive drug delivery, and the need to develop non-invasive local drug delivery with alternative to injectable therapy were described. Absorption routes through topical administration and strategies to enhance ocular posterior drug delivery were then discussed. As a follow-up, an up-to-date research advances in non-invasive delivery systems for the therapy of ocular fundus lesions were presented, including different nanocarriers, contact lenses, and several other carriers. In conclusion, it seems feasible and promising to treat posterior oculopathy via non-invasive local preparations or in combination with appropriate devices.

Alternative application of an iTrack microcatheter and canaloplasty: case report and literature review

INTRODUCTION

Glaucoma is the leading cause of irreversible blindness worldwide. Schlemm's canal surgery using an iTrack flexible microcatheter has become popular because of its high quality-of-life issues and the growing demand for less invasive but effective procedures. The unique design of the microcatheter makes it a multimodal tool, which can be used not only in the field of antiglaucoma surgery but also as a drug delivery system to treat various conditions.

AREAS COVERED

This review presents an update on the selected aspects of a drug delivery system using the iTrack microcatheter, including glaucoma gene therapy and posterior-segment diseases, both in animal models and human patients. The authors also report the case of a patient with branch retinal vein occlusion treated with suprachoroidal bevacizumab in the submacular region administered with the iTrack catheter.

EXPERT OPINION

The findings presented in this study may indicate that the application of a microcatheter in open-angle glaucoma gene therapy is reasonable and can be combined with full or partial surgical canaloplasty procedures. Translation of this potential into a treatment modality would require overcoming multiple barriers.

Real-Time Monitoring Platform for Ocular Drug Delivery

Real-time measurement is important in modern dissolution testing to aid in parallel drug characterisation and quality control (QC). The development of a real-time monitoring platform (microfluidic system, a novel eye movement platform with temperature sensors and accelerometers and a concentration probe setup) in conjunction with an in vitro model of the human eye (PK-Eye™) is reported. The importance of surface membrane permeability when modelling the PK-Eye™ was determined with a "pursing model" (a simplified setup of the hyaloid membrane). Parallel microfluidic control of PK-Eye™ models from a single source of pressure was performed with a ratio of 1:6 (pressure source:models) demonstrating scalability and reproducibility of pressure-flow data. Pore size and exposed surface area helped obtain a physiological range of intraocular pressure (IOP) within the models, demonstrating the need to reproduce in vitro dimensions as closely as possible to the real eye. Variation of aqueous humour flow rate throughout the day was demonstrated with a developed circadian rhythm program. Capabilities of different eye movements were programmed and achieved with an in-house eye movement platform. A concentration probe recorded the real-time concentration monitoring of injected albumin-conjugated Alexa Fluor 488 (Alexa albumin), which displayed constant release profiles. These results demonstrate the possibility of real-time monitoring of a pharmaceutical model for preclinical testing of ocular formulations.

How can machine learning and multiscale modeling benefit ocular drug development?

The eyes possess sophisticated physiological structures, diverse disease targets, limited drug delivery space, distinctive barriers, and complicated biomechanical processes, requiring a more in-depth understanding of the interactions between drug delivery systems and biological systems for ocular formulation development. However, the tiny size of the eyes makes sampling difficult and invasive studies costly and ethically constrained. Developing ocular formulations following conventional trial-and-error formulation and manufacturing process screening procedures is inefficient. Along with the popularity of computational pharmaceutics, non-invasive in silico modeling & simulation offer new opportunities for the paradigm shift of ocular formulation development. The current work first systematically reviews the theoretical underpinnings, advanced applications, and unique advantages of data-driven machine learning and multiscale simulation approaches represented by molecular simulation, mathematical modeling, and pharmacokinetic (PK)/pharmacodynamic (PD) modeling for ocular drug development. Following this, a new computer-driven framework for rational pharmaceutical formulation design is proposed, inspired by the potential of in silico explorations in understanding drug delivery details and facilitating drug formulation design. Lastly, to promote the paradigm shift, integrated in silico methodologies were highlighted, and discussions on data challenges, model practicality, personalized modeling, regulatory science, interdisciplinary collaboration, and talent training were conducted in detail with a view to achieving more efficient objective-oriented pharmaceutical formulation design.

A comparative study between a transscleral sustained-release device and eyedrops on intraocular distribution of carteolol hydrochloride

The objectives of this study were to develop a sustained-release device for carteolol hydrochloride (CH) and investigate any potential difference in the intraocular distribution of this agent between the transscleral administration of the device and treatment with eyedrops. The device was formulated with photocurable resin, poly (ethyleneglycol) dimethacrylate, to fit within the curve of the rabbit eyeball. In vitro study showed that CH was released in a sustained-release manner for 2 weeks. The concentration of CH in the retina, choroid/retinal pigment epithelium, sclera, iris, and aqueous humor was determined by high-performance liquid chromatography. Transscleral administration was able to deliver CH to the posterior segment (i.e., retina and choroid/retinal pigment epithelium) rather than the anterior segment (i.e., aqueous humor), while eyedrops delivered CH only to the anterior segment. Transscleral administration could deliver CH to aqueous humor at half the concentration versus treatment with eyedrops and reduced intraocular pressure (IOP) at 1 day after implantation; however, the IOP-lowering effect was not sustained thereafter. In conclusion, transscleral drug delivery may be a useful method for the reduction of IOP. Notably, the aqueous concentration must be equal to that delivered by the eyedrops, and this approach might be preferable for drug delivery to the posterior segment of the eye.

Topical ocular delivery of nanoparticles with epoetin beta in Wistar Hannover rats

Topical instillation of drugs targeting the posterior ocular segment is an expanding area of research. Chitosan and hyaluronic acid have remarkable mucoadhesive properties and potentially enhance pre-corneal retention time after topical instillation. Bearing this in mind, we explored the possibility of delivering epoetin beta (EPOβ) to the posterior segment of the eye in a chitosan-hyaluronic acid (CS/HA-EPOβ) nanoparticulate system using the topical route of administration. Complete ophthalmological examinations, electroretinography and microhematocrit evaluations were performed in Wistar Hannover (WH) rats, before and after topical administration of nanoparticles. The right eye received CS/HA-EPOβ and the left eye received only empty nanocarriers (control). Animals were split into 6 groups and at designated timepoints, all animals from each group (n = 3) were euthanized and both eyes enucleated. Retinal morphology and EPOβ ocular distribution were assessed, respectively, through hematoxylin and eosin (HE) and immunofluorescence staining. After topical administration, no adverse ocular signs were noted and no significant changes either in microhematocrits nor in electroretinographies were detected. During the study, intraocular pressure (IOP) was always kept within physiological range bilaterally. No histological changes were detected in any of the ocular globes. Immunofluorescence enabled the identification of EPOβ in the retina 12 h after the administration, its presence still being detectable at day 21. In conclusion, CS/HA nanoparticles could efficiently deliver EPOβ to the retina of WH rats after topical instillation, being considered biologically safe. Topical administration of this nanoformulation could be a valuable tool for retinal neuroprotection, decreasing risks associated with more invasive routes of administration, being cost effective and also increasing long-term patients' compliance.

Targeted Nanotherapies for the Posterior Segment of the Eye: An Integrative Review on Recent Advancements and Challenges

The eye is a one-of-a-kind sensory organ with intricate anatomy and physiology. It is protected by a variety of barriers, ranging from static barriers to dynamic barriers. Although these barriers are very effective at protecting the eye from exogenous substances and external stress, they are highly compromised by various vision-impairing diseases of both the anterior and the posterior segment of the eye. Due to ocular elimination systems and intricate obstacles that selectively limit drug entry into the eye, effective drug delivery to the posterior segment of the eye (PSE) continues to be a challenge in ophthalmology. Since more than half of the most debilitating eye illnesses are thought to originate in the posterior segment (PS), understanding the physiology and clearance mechanism of the eye could help design improved formulations that could be noninvasive and intended for targeted posterior segment therapeutics. Moreover, the major drawback associated with the conventional drug delivery system to PSE is minimal therapeutic drug concentration in the desired ocular tissue and life-threatening ophthalmic complications. One possible approach that can be implemented to overcome these ocular barriers for efficient ocular therapy, non-invasive and targeted drug action to the posterior tissues is by designing nanomedicines. This review summarizes the recent non-invasive and patient compliant advances in designing nanomedicines targeting PSE. The various routes and pathways of drug administration to the ocular tissue are also summarized.

Recent achievements in nano-based technologies for ocular disease diagnosis and treatment, review and update

Ocular drug delivery is one of the most challenging endeavors among the various available drug delivery systems. Despite having suitable drugs for the treatment of ophthalmic disease, we have not yet succeeded in achieving a proper drug delivery approach with the least adverse effects. Nanotechnology offers great opportunities to overwhelm the restrictions of common ocular delivery systems, including low therapeutic effects and adverse effects because of invasive surgery or systemic exposure. The present review is dedicated to highlighting and updating the recent achievements of nano-based technologies for ocular disease diagnosis and treatment. While further effort remains, the progress illustrated here might pave the way to new and very useful ocular nanomedicines.

Nanosuspension-loaded dissolving bilayer microneedles for hydrophobic drug delivery to the posterior segment of the eye

Intravitreal injections (IVT) are regarded as the gold standard for effective delivery of hydrophobic drugs to the back of the eye. However, as a highly invasive procedure, the injection itself may lead to poor patient compliance and severe complications. In this research work, a hybrid system of nanosuspensions (NS) and dissolving microneedles (MNs) was developed as an alternative to conventional hypodermic needles used in IVT for minimally invasive transscleral delivery of hydrophobic drugs. NS of a hydrophobic drug, triamcinolone acetonide (TA), were fabricated using a wet milling technique. TA NS optimised by central composite factorial design had a proven diameter of 246.65 ± 8.55 nm. After optimisation, TA NS were incorporated into MN arrays to form a bilayer structure by high-speed centrifugation. TA NS-loaded MNs were robust enough to pierce excised porcine sclera with insertion depth higher than 80% of the needle height and showed rapid dissolution (<3 min). In contrast, the plain TA-loaded MNs exhibited poor mechanical and insertion performances and took more than 8 min to be fully dissolved in the scleral tissue. Importantly, transscleral deposition studies showed that 56.46 ± 7.76 μg/mm² of TA was deposited into the sclera after 5 min of NS-loaded MN application, which was 4.5-fold higher than plain drug-loaded MNs (12.56 ± 2.59 μg/mm²). An ex vivo distribution study revealed that MN arrays could promote the transscleral penetration of hydrophobic molecules with higher drug concentrations observed in the deep layer of the sclera. Moreover, the developed TA NS-loaded MN array was biocompatible with ocular tissues, as demonstrated using the hens egg-chorioallantoic membrane assay and cytotoxicity test. The results presented here demonstrate that the hybrid system of NS and dissolving MNs can provide a novel and promising technology to alleviate retinal diseases in a therapeutically effective and minimally invasive manner.

Lab-on-a-Contact Lens: Recent Advances and Future Opportunities in Diagnostics and Therapeutics

The eye is one of the most complex organs in the human body, containing rich and critical physiological information (e.g., intraocular pressure, corneal temperature, and pH) as well as a library of metabolite biomarkers (e.g., glucose, proteins, and specific ions). Smart contact lenses (SCLs) can serve as a wearable intelligent ocular prosthetic device capable of noninvasive and continuous monitoring of various essential physical/biochemical parameters and drug loading/delivery for the treatment of ocular diseases. Advances in SCL technologies and the growing public interest in personalized health are accelerating SCL research more than ever before. Here, the current status and potential of SCL development through a comprehensive review from fabrication to applications to commercialization are discussed. First, the material, fabrication, and platform designs of the SCLs for the diagnostic and therapeutic applications are discussed. Then, the latest advances in diagnostic and therapeutic SCLs for clinical translation are reviewed. Later, the established techniques for wearable power transfer and wireless data transmission applied to current SCL devices are summarized. An outlook, future opportunities, and challenges for developing next-generation SCL devices are also provided. With the rise in interest of SCL development, this comprehensive and essential review can serve as a new paradigm for the SCL devices.

Novel Eye Drop Delivery Systems: Advance on Formulation Design Strategies Targeting Anterior and Posterior Segments of the Eye

Eye drops are the most common and convenient route of topical administration and the first choice of treatment for many ocular diseases. However, the ocular bioavailability of traditional eye drops (i.e., solutions, suspensions, and ointments) is very low because of ophthalmic physiology and barriers, which greatly limits their therapeutic effect. Over the past few decades, many novel eye drop delivery systems, such as prodrugs, cyclodextrins, in situ gels, and nanoparticles, have been developed to improve ophthalmic bioavailability. These novel eye drop delivery systems have good biocompatibility, adhesion, and propermeation properties and have shown superior performance and efficacy over traditional eye drops. Therefore, the purpose of this review was to systematically present the research progress on novel eye drop delivery systems and provide a reference for the development of dosage form, clinical application, and commercial transformation of eye drops.

Chitosan and Hyaluronic Acid Nanoparticles as Vehicles of Epoetin Beta for Subconjunctival Ocular Delivery

Neuroprotection in glaucoma using epoetin beta (EPOβ) has yielded promising results. Our team has developed chitosan-hyaluronic acid nanoparticles (CS/HA) designed to carry EPOβ into the ocular globe, improving the drug’s mucoadhesion and retention time on the ocular surface to increase its bioavailability. In the present in vivo study, we explored the possibility of delivering EPOβ to the eye through subconjunctival administration of chitosan-hyaluronic acid-EPOβ (CS/HA-EPOβ) nanoparticles. Healthy Wistar Hannover rats (n = 21) were split into 7 groups and underwent complete ophthalmological examinations, including electroretinography and microhematocrit evaluations before and after the subconjunctival administrations. CS/HA-EPOβ nanoparticles were administered to the right eye (OD), and the contralateral eye (OS) served as control. At selected timepoints, animals from each group (n = 3) were euthanized, and both eyes were enucleated for histological evaluation (immunofluorescence and HE). No adverse ocular signs, no changes in the microhematocrits (≈45%), and no deviations in the electroretinographies in both photopic and scotopic exams were observed after the administrations (p < 0.05). Intraocular pressure remained in the physiological range during the assays (11–22 mmHg). EPOβ was detected in the retina by immunofluorescence 12 h after the subconjunctival administration and remained detectable until day 21. We concluded that CS/HA nanoparticles could efficiently deliver EPOβ into the retina, and this alternative was considered biologically safe. This nanoformulation could be a promising tool for treating retinopathies, namely optic nerve degeneration associated with glaucoma.

Untethered Microrobots for Active Drug Delivery: From Rational Design to Clinical Settings

Recent advances of untethered microrobots, which navigate the complex regions in vivo for therapeutics, have presented promising multiple applications on future healthcare. Microrobots used for active drug delivery system (DDS) have been demonstrated for advanced targeting distribution, improved delivery efficiency, and reduced systemic side effects. In this review, the therapeutic benefits of active DDS are presented compared to the traditional passive DDS, which illustrate the historical reasons for choosing active DDS. An integrated 5D radar chart analysis model containing the core capabilities of the active DDS is innovatively proposed. It would be a practical tool for measurement and mapping of the field of active delivery, followed by the evolutions and bottlenecks of each technical module. The comprehensive consideration of microrobots before clinical application is also discussed from the aspects of robot ethics, dosage, quality control and stability control in actual production. Gastrointestinal and blood administration, as two major clinical scenes of drug delivery, are discussed in detail as examples of the potential bedside applications of active DDS. Finally, combined with the reported analysis model, the current status and future outlook from the translation prospect to the clinical scenes of microrobots are provided.

Topical drug delivery to the retina: obstacles and routes to success

INTRODUCTION

Retinal diseases are one of the main reasons for vision loss where all available drug treatments are based on invasive drug administration such as intravitreal injections. Despite huge efforts and some promising results in animal models, almost all delivery technologies tested have failed in human trials. There are however examples of clinically effective topical delivery systems such as fast dissolving aqueous eye drop suspensions.

AREAS COVERED

Six obstacles to topical drug delivery to the eye have been identified and discussed in some details. These obstacles consist of static membrane barriers to drug permeation into the eye, dynamic barriers such as the lacrimal drainage and physiochemical barriers such as low thermodynamic activity. It is explained how and why these obstacles hamper drug permeation and how different technologies, both those that are applied in marketed drug products and those that are under investigation, have addressed these obstacles.

EXPERT OPINION

The reason that most topical drug delivery systems have failed to deliver therapeutic drug concentrations to the retina is that they do not address physiochemical barriers such as the thermodynamic activity of the permeating drug molecules. Topical drug delivery to the retina has only been successful when the static, dynamic, and physiochemical barriers are addressed simultaneously.

Ocular Fluid Mechanics and Drug Delivery: A Review of Mathematical and Computational Models

The human eye is a complex biomechanical structure with a range of biomechanical processes involved in various physiological as well as pathological conditions. Fluid flow inside different domains of the eye is one of the most significant biomechanical processes that tend to perform a wide variety of functions and when combined with other biophysical processes play a crucial role in ocular drug delivery. However, it is quite difficult to comprehend the effect of these processes on drug transport and associated treatment experimentally because of ethical constraints and economic feasibility. Computational modeling on the other hand is an excellent means to understand the associated complexity between these aforementioned processes and drug delivery. A wide range of computational models specific to different types of fluids present in different domains of the eye as well as varying drug delivery modes has been established to understand the fluid flow behavior and drug transport phenomenon in an insilico manner. These computational models have been used as a non-invasive tool to aid ophthalmologists in identifying the challenges associated with a particular drug delivery mode while treating particular eye diseases and to advance the understanding of the biomechanical behavior of the eye. In this regard, the author attempts to summarize the existing computational and mathematical approaches proposed in the last two decades for understanding the fluid mechanics and drug transport associated with different domains of the eye, together with their application to modify the existing treatment processes.

Emerging era of microneedle array for pharmaceutical and biomedical applications: recent advances and toxicological perspectives

Background

Microneedles (MNs) are the utmost unique, efficient, and minimally invasive inventions in the pharmaceutical field. Over the past decades, many scientists around the globe have reported MNs cautious because of their superb future in distinct areas. Concerning the wise use of MNs herein, we deal in depth with the present applications of MNs in drug delivery.

Main text

The present review comprises various fabrication materials and methods used for MN synthesis. The article also noted the distinctive advantages of these MNs, which holds huge potential for pharmaceutical and biomedical applications. The role of MNs in serving as a platform to treat various ailments has been explained accompanied by unusual approaches. The review also inculcates the pharmacokinetics of MNs, which includes permeation, absorption, and bioavailability enhancement. Besides this, the in vitro/in vivo toxicity, biosafety, and marketed product of MNs have been reviewed. We have also discussed the clinical trials and patents on the pharmaceutical applications of MNs in brief.

Conclusion

To sum up, this article gives insight into the MNs and provides a recent advancement in MNs, which pave the pathway for future pharmaceutical and biomedical applications.

Graphical abstract

Pharmaceutical and biomedical applications of MNs

RETRACTED: Sustained delivery of epalrestat to the retina using PEGylated solid lipid nanoparticles laden contact lens

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Significant similarities were noticed post-publication between this article and an article submitted to the Journal of Drug Delivery Science and Technology on the same day, by an apparently unrelated research group: Tong Zhang, Tianhui Zhu, Fanyin Wang, Ling Peng and Mingying Lai 60 (2020) 101949 https://doi.org/10.1016/j.jddst.2020.101949 Moreover, the authors did not respond to the journal request to comment on these similarities and to provide the raw data, and the Editor-in-Chief decided to retract the article. One of the conditions of submission of a paper for publication is that authors declare explicitly that their work is original and genuine. As such this article represents a severe abuse of the scientific publishing system.

Ex-Vivo Trans-Corneal and Trans-Scleral Diffusion Studies with Ocular Formulations of Glutathione as an Antioxidant Treatment for Ocular Diseases

Exposure to sunlight and contact with atmospheric oxygen makes the eye particularly susceptible to oxidative stress, which can potentially produce cellular damage. In physiological conditions, there are several antioxidant defense mechanisms within the eye. Glutathione (GSH) is the most important antioxidant in the eye; GSH deficit has been linked to several ocular pathologies. The aim of this study was to explore the potential for newly developed formulations allowing controlled delivery of antioxidants such as GSH and vitamin C (Vit C) directly to the eye. We have investigated the stability of antioxidants in aqueous solution and assessed ex-vivo the diffusion of GSH through two ocular membranes, namely cornea and sclera, either in solution or included in a semisolid insert. We have also carried out the hen’s egg-chlorioallantoic membrane test (HET-CAM) to evaluate the ocular irritancy of the different antioxidant solutions. Our results showed that GSH is stable for up to 30 days at 4 °C in darkness and it is not an irritant to the eye. The diffusion studies revealed that the manufactured formulation, a semisolid insert containing GSH, could deliver this tripeptide directly to the eye in a sustained manner.

A drug delivery analysis of large molecules in ocular vitreous chamber: Dependency on saccadic movements after intravitreal injection

The purpose of this study is to investigate the effect of vitreous sloshing induced by saccades on the intravitreal delivery of large molecule drugs. The vitreous body was considered in its age-related liquefaction condition. Fluid dynamics and large molecule distribution were described by the coupling of mass conservation's and Fick's laws with continuity and momentum equations for a Newtonian incompressible fluid in a 3D unsteady analysis. Two injection sites were analyzed, in both the mixing effect of a 50° periodic saccade leads to uniform drug distribution in 30 s of simulation, the initial bolus site being left after 3 s of simulation. In absence of saccadic movements, the dominant transport contribution is the diffusive one and large molecules hardly reach their uniform distribution inside the vitreous cavity. A model describing the intravitreal distribution of large molecules in presence of saccades was developed, improving the understanding of drug transport mechanism after an intravitreal injection and highlighting how advection contribution enhances its distribution in the vitreous chamber.

Characterization of Antineovascularization Activity and Ocular Pharmacokinetics of Phosphoinositide 3-Kinase/Mammalian Target of Rapamycin Inhibitor GNE-947

The objectives of the present study were to characterize GNE-947 for its phosphoinositide 3-kinase (PI3K) and mammalian target of rapamycin (mTOR) inhibitory activities, in vitro anti-cell migration activity in human umbilical vein endothelial cells (HUVECs), in vivo antineovascularization activity in laser-induced rat choroidal neovascular (CNV) eyes, pharmacokinetics in rabbit plasma and eyes, and ocular distribution using matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) and autoradioluminography. Its PI3K and mTOR K i were 0.0005 and 0.045 µM, respectively, and its HUVEC IC50 was 0.093 µM. GNE-947 prevented neovascularization in the rat CNV model at 50 or 100 µg per eye with repeat dosing. After a single intravenous injection at 2.5 and 500 μg/kg in rabbits, its plasma terminal half-lives (t 1/2) were 9.11 and 9.59 hours, respectively. After a single intravitreal injection of a solution at 2.5 μg per eye in rabbits, its apparent t 1/2 values were 14.4, 16.3, and 23.2 hours in the plasma, vitreous humor, and aqueous humor, respectively. After a single intravitreal injection of a suspension at 33.5, 100, 200 μg per eye in rabbits, the t 1/2 were 29, 74, and 219 days in the plasma and 46, 143, and 191 days in the eyes, respectively. MALDI-IMS and autoradioluminography images show that GNE-947 did not homogenously distribute in the vitreous humor and aggregated at the injection sites after injection of the suspension, which was responsible for the long t 1/2 of the suspension because of the slow dissolution process. This hypothesis was supported by pharmacokinetic modeling analyses. In conclusion, the PI3K/mTOR inhibitor GNE-947 prevented neovascularization in a rat CNV model, with t 1/2 up to approximately 6 months after a single intravitreal injection of the suspension in rabbit eyes. SIGNIFICANCE STATEMENT: GNE-947 is a potent phosphoinositide 3-kinase/mammalian target of rapamycin inhibitor and exhibits anti-choroidal neovascular activity in rat eyes. The duration of GNE-947 in the rabbit eyes after intravitreal injection in a solution is short, with a half-life (t 1/2) of less than a day. However, the duration after intravitreal dose of a suspension is long, with t 1/2 up to 6 months due to low solubility and slow dissolution. These results indicate that intravitreal injection of a suspension for low-solubility drugs can be used to achieve long-term drug exposure.

A 3D Printed Self-Sustainable Cell-Encapsulation Drug Delivery Device for Periocular Transplant-Based Treatment of Retinal Degenerative Diseases

Self-sustainable release of brain-derived neurotrophic factor (BDNF) to the retina using minimally invasive cell-encapsulation devices is a promising approach to treat retinal degenerative diseases (RDD). Herein, we describe such a self-sustainable drug delivery device with human retinal pigment epithelial (ARPE-19) cells (cultured on collagen coated polystyrene (PS) sheets) enclosed inside a 3D printed semi-porous capsule. The capsule was 3D printed with two photo curable polymers: triethylene glycol dimethacrylate (TEGDM) and polyethylene glycol dimethylacrylate (PEGDM). The capsule's semi-porous membrane (PEGDM) could serve three functions: protecting the cells from body's immune system by limiting diffusion (5.97 ± 0.11%) of large molecules like immunoglobin G (IgG)(150 kDa); helping the cells to survive inside the capsule by allowing diffusion (43.20 ± 2.16%) of small molecules (40 kDa) like oxygen and necessary nutrients; and helping in the treatment of RDD by allowing diffusion of cell-secreted BDNF to the outside environment. In vitro results showed a continuous BDNF secretion from the device for at least 16 days, demonstrating future potential of the cell-encapsulation device for the treatment of RDD in a minimally invasive and self-sustainable way through a periocular transplant.

Pharmacokinetics after Periocular Methylprednisolone Sodium Succinate Injection in Rabbit Eyes

The present study aimed to determine the pharmacokinetics and distribution of methylprednisolone sodium succinate (MPSS) and its metabolic product methylprednisolone (MP) in plasma and ocular tissues after periocular injection of MPSS in rabbit eyes. Forty-eight healthy New Zealand white rabbits were randomly divided into 12 groups, including the control group and 11 MPSS-treated groups sampling at different time points. Rabbits in the MPSS-treated groups underwent left eye periocular injection of MPSS (10 mg). The pharmacokinetics of MPSS and MP in plasma and ocular tissues (including aqueous humor, vitreous, iris, lens, sclera, optic nerve, and choroid and retina) were investigated by liquid chromatography tandem mass spectrometry (LC-MS/MS). After periocular injection, the time of maximum concentration (T_max) of MPSS ranged from 0.25 h to 1 h in ocular tissues and was 0.25 h in plasma. T_max of MP in ocular tissues ranged from 0.5 h to 6 h, and T_max of MP in plasma was 0.5 h. The maximum concentration (C_max) of MPSS and MP and the area under the curve (AUC_0-t) in ocular tissues from high to low was sclera, optic nerve, choroid and retina, iris, and lens. Especially, the concentrations of MPSS and MP in the lens were much lower when compared with the other ocular tissues. After periocular administration, MPSS could be rapidly metabolized to its active constituent MP in the ocular tissues. Also, the MPSS can be delivered effectively into the posterior segment of the eye (choroid and retina), while not easily be absorbed by the lens.

Drug Delivery to the Posterior Segment of the Eye: Biopharmaceutic and Pharmacokinetic Considerations

The treatment of the posterior-segment ocular diseases, such as age-related eye diseases (AMD) or diabetic retinopathy (DR), present a challenge for ophthalmologists due to the complex anatomy and physiology of the eye. This specialized organ is composed of various static and dynamic barriers that restrict drug delivery into the target site of action. Despite numerous efforts, effective intraocular drug delivery remains unresolved and, therefore, it is highly desirable to improve the current treatments of diseases affecting the posterior cavity. This review article gives an overview of pharmacokinetic and biopharmaceutics aspects for the most commonly-used ocular administration routes (intravitreal, topical, systemic, and periocular), including information of the absorption, distribution, and elimination, as well as the benefits and limitations of each one. This article also encompasses different conventional and novel drug delivery systems designed and developed to improve drug pharmacokinetics intended for the posterior ocular segment treatment.

Ex Vivo Conjunctival Retention and Transconjunctival Transport of Poorly Soluble Drugs Using Polymeric Micelles

This paper addresses the problem of ocular delivery of lipophilic drugs. The aim of the paper is the evaluation of polymeric micelles, prepared using TPGS (d-α-Tocopheryl polyethylene glycol 1000 succinate), a water-soluble derivative of Vitamin E and/or poloxamer 407, as a vehicle for the ocular delivery of dexamethasone, cyclosporine, and econazole nitrate. The research steps were: (1) characterize polymeric micelles by dynamic light scattering (DLS) and X-ray scattering; (2) evaluate the solubility increase of the three drugs; (3) measure the in vitro transport and conjunctiva retention, in comparison to conventional vehicles; (4) investigate the mechanisms of enhancement, by studying drug release from the micelles and transconjunctival permeation of TPGS; and (5) study the effect of micelles application on the histology of conjunctiva. The data obtained demonstrate the application potential of polymeric micelles in ocular delivery, due to their ability to increase the solubility of lipophilic drugs and enhance transport in and across the conjunctival epithelium. The best-performing formulation was the one made of TPGS alone (micelles size ≈ 12 nm), probably because of the higher mobility of these micelles, an enhanced interaction with the conjunctival epithelium, and, possibly, the penetration of intact micelles.

Transscleral sustained ranibizumab delivery using an episcleral implantable device: Suppression of laser-induced choroidal neovascularization in rats

Successful treatment of age-related macular diseases requires an effective controlled drug release system with less invasive route of administration in the eye to reduce the burden of frequent intravitreal injections for patients. In this study, we developed an episcleral implantable device for sustained release of ranibizumab, and evaluated its efficacy on suppression of laser-induced choroidal neovascularization (CNV) in rats. We tested both biodegradable and non-biodegradable sheet-type devices consisting of crosslinked gelatin/chitosan (Gel/CS) and photopolymerized poly(ethyleneglycol) dimethacrylate that incorporated collagen microparticles (PEGDM/COL). In vitro release studies of FITC-labeled albumin showed a constant release from PEGDM/COL sheets compared to Gel/CS sheets. The Gel/CS sheets gradually biodegraded in the sclera during the 24-week implantation; however, the PEGDM/COL sheets did not degrade. FITC-albumin was detected in the retina during 18 weeks implantation in the PEGDM/COL sheet-treated group, and was detected in the Gel/CS sheet-treated group during 6 weeks implantation. CNV was suppressed 18 weeks after application of ranibizumab-loaded PEGDM/COL sheets compared to a placebo PEGDM/COL sheet-treated group, and to the intravitreal ranibizumab-injected group. In conclusion, the PEGDM/COL sheet device suppressed CNV via a transscleral administration route for 18 weeks, indicating that prolonged sustained ranibizumab release could reduce the burden of repeated intravitreal injections.

Controlled non-invasive iontophoretic delivery of triamcinolone acetonide amino acid ester prodrugs into the posterior segment of the eye

This study investigated short duration transscleral iontophoretic delivery of four triamcinolone acetonide (TA) amino acid ester prodrugs (TA-AA) (alanine, Ala; arginine, Arg; isoleucine, Ile and lysine, Lys) using whole porcine eyes globes in vitro. Post-iontophoretic biodistribution of TA was quantified by UHPLC-MS/MS in the different ocular compartments (cornea, aqueous humor, sclera, ciliary body, choroid and retinal pigmented epithelium (RPE), neural retina and vitreous humor). Transscleral iontophoresis (3 mA/cm² for 10 min) increased total drug delivery of the TA-AA prodrugs by 14-30-fold as compared to passive diffusion. The TA-AA prodrugs had distinct biodistribution profiles - the penetration depth achieved was dependent on their physicochemical properties (e.g. lipophilicity for TA-Ile) and susceptibility to hydrolysis (e.g. TA-Arg). Intraocular drug distribution was also influenced by prodrug binding to melanin (TA-Lys). Interestingly, under conditions of equivalent charge (6 mA/cm² for 5 min vs. 1.5 mA/cm² for 20 min, i.e. 1.44 C respectively) the longer duration (20 min) at lower current density resulted in ∼6 times more TA delivery into the vitreous humor. Overall, the study provided further evidence of the potential of transscleral iontophoresis for the non-invasive treatment of posterior segment inflammatory diseases.

Functional and Structural Effects of Erythropoietin Subconjunctival Administration in Glaucomatous Animals

Purpose

The present study aimed to assess functional and structural benefits of erythropoietin (EPO) when administered subconjunctivally in the retina of glaucomatous rats using electroretinography (ERG) and retinal thickness (RT) measurements.

Methods

Glaucoma was experimentally induced in 26 Wistar Hannover albino rats. Animals were divided into 2 groups of 13 animals each: a treated group receiving a unique subconjunctival injection of 1,000 IU of EPO and a control group receiving a saline solution. In each group, 7 animals were used for retinal function evaluation (ERG) and 6 animals were used for retinal structural evaluation (histology). RT was measured, dorsally and ventrally, at 500 μm (RT1) and at 1,500 μm (RT2) from the optic nerve.

Results

Retinal function evaluation: for both scotopic and photopic conditions, ERG wave amplitudes increased in the treated group. This increase was statistically significant (p < 0.05) in photopic conditions. Structural evaluation: for both locations RT1 and RT2, the retinas were significantly (p < 0.05) thicker in the treated group.

Conclusion

Subconjunctival EPO administration showed beneficial effects both on retinal structure and on retinal function in induced glaucoma in albino rats. This neuroprotective effect should be applied in other animal species.

Drug delivery devices for retinal diseases

Retinal degenerative diseases are a leading cause of irreversible blindness and visual impairment, affecting millions of people worldwide. Although intravitreal injection can directly deliver drugs to the posterior segment of the eye, it is invasive and associated with serious side effects. The design of drug delivery systems targeting the posterior segment of the eye in a less invasive manner has still been challenging because of various anatomical and physiological barriers. In this review, we provide an overview of the current implant device-based approaches used for treating retinal degenerative diseases. We then offer our perspectives on future directions and challenges that remain for developing more effective device-based therapies for retinal diseases.

Ocular translational science: A review of development steps and paths

Developing successful drug delivery methods is challenging for any tissue, and the eye is no exception. Translating initial concepts into advanced technologies treating diseases in preclinical models and finally into functional and marketable products for humans can be particularly daunting. While referring to specific ophthalmic companies and products, this review considers key exchanges that lead to successful translation. By building on basic science discoveries in the academic setting, applied science can perform proof-of-concept work with simple, benchtop experiments. Eventually, simple models need to be translated to more robust ones where cells, tissues, and entire organisms are incorporated. Successful translation also includes performing due diligence of the intellectual property, understanding the market needs, undertaking clinical development, meeting regulatory requirements, and eventually scale up manufacturing. Different stages of the translation can occur in different environments, including moving from academia to industry, from one company to another, or between veterinary and human applications. The translation process may also rely on contract organizations to move through the complex landscape. While the path to a commercial, marketable product may not look the same each time, it is important to design a development plan with clear goals and milestones to keep on track.

Principles of pharmacology in the eye

The eye is a highly specialized organ that is subject to a huge range of pathology. Both local and systemic disease may affect different anatomical regions of the eye. The least invasive routes for ocular drug administration are topical (e.g. eye drops) and systemic (e.g. tablets) formulations. Barriers that subserve as protection against pathogen entry also restrict drug permeation. Topically administered drugs often display limited bioavailability due to many physical and biochemical barriers including the pre-corneal tear film, the structure and biophysiological properties of the cornea, the limited volume that can be accommodated by the cul-de-sac, the lacrimal drainage system and reflex tearing. The tissue layers of the cornea and conjunctiva are further key factors that act to restrict drug delivery. Using carriers that enhance viscosity or bind to the ocular surface increases bioavailability. Matching the pH and polarity of drug molecules to the tissue layers allows greater penetration. Drug delivery to the posterior segment is a greater challenge and, currently, the standard route is via intravitreal injection, notwithstanding the risks of endophthalmitis and retinal detachment with frequent injections. Intraocular implants that allow sustained drug release are at different stages of development. Novel exciting therapeutic approaches include methods for promoting transscleral delivery, sustained release devices, nanotechnology and gene therapy.

Research on the comparison of the demethylvancomycin's diffusion-deposition characteristics in the ocular solid tissues of sustained subtenon drug delivery with subconjunctival injection

PURPOSE

To compare the demethylvancomycin's diffusion-deposition characteristics in the ocular solid tissues of sustained subtenon drug delivery with subconjunctival injection.

METHOD

Sixty adult white rabbits were randomly assigned to the subtenon drug delivery group and the subconjunctival injection group. The subtenon drug delivery group was continuously infused demethylvancomycin to the subtenon of rabbits. The subconjunctival injection group was injected demethylvancomycin to the subconjunctival of rabbits. Cornea, iris and sclera were collected for high-performance liquid chromatography analyses to determine drug concentrations at one hour, three hours, six hours, 12 h and 24 h of drug administration. WinNonlin 6.3 was used to calculate the parameters of cumulative area under the curve (AUCcum) of demethylvancomycin.

RESULTS

The peak levels of demethylvancomycin concentration of the subtenon drug delivery group and the subconjunctival injection group were 92.406 ± 21.555 and 51.778 ± 14.001 μg/g in cornea, 28.451 ± 10.229 μg/g and 42.271 ± 27.291 μg/g in iris, 153.166 ± 51.738 μg/g and 57.423 ± 18.480 μg/g in sclera. The differences of concentrations between the two groups in cornea and sclera were statistically significant (F = 487.775, p < 0.001; F = 132.748, p < 0.001). The difference in iris was not statistically significant (F = 4.848, p = 0.064). The maximum of AUCcum of the subtenon drug delivery group and the subconjunctival injection group was 1808.23 h * μg/g and 273.73 h * μg/g in cornea, 489.12 h * μg/g and 216.16 h * μg/g in iris and 2166.34 h * μg/g and 392.57 h * μg/g in sclera at 24 h of drug administration.

CONCLUSION

The sustained subtenon drug delivery had a better drug permeability and accumulation in the intraocular solid tissue compared to subconjunctival injection, which demonstrated it was probably a promising and effective approach for treating posterior segment diseases and endophthalmitis.

Preliminary study of a controllable device for subtenon drug infusion in a rabbit model

BACKGROUND AND OBJECTIVE

Conventional methods to treat intraocular diseases are invasive or associated with adverse effects. A minimally invasive means of sustained-release drug delivery to the vitreous is required. This study evaluated a novel device for subtenon drug delivery to the vitreous, relative to a single subconjunctival injection.

METHODS

Sixty adult New Zealand White rabbits were randomly assigned to receive demethylvancomycin (DMV) by continuous subtenon delivery with the flow rate of 0.1 ml/hr for 24 hr, or as a single 0.3 ml subconjunctival injection in the right eyes. Rabbits were killed in subgroups of six at 1, 3, 6, 12 and 24 hr. The DMV concentration of the vitreous humour of the right eye was analysed by high-performance liquid chromatography.

RESULTS

Overall, the vitreous DMV concentration of the subtenon group was significantly higher than that of the subconjunctival group (F = 25.928, p = 0.001). The DMV concentration of the subtenon group was also significantly higher than that of the subconjunctival group at 3, 6, 12 and 24 hr (t = 2.457, 5.064, 3.085, 4.207; p = 0.04, 0.01, 0.018, 0.004, respectively). In the subtenon group, the DMV concentration reached maximum (2.41 ± 0.67 μg/ml) at 6 hr, and at 24 hr was 2.37 ± 1.23 μg/ml. In the subconjunctival group, the DMV concentration reached maximum (0.48 ± 0.27 μg/ml) at 1 hr and declined to 0.09 ± 0.05 μg/ml at 24 hr.

CONCLUSION

Subtenon application with this novel minimally invasive design is an effective method for delivering an appropriate drug to the vitreous in a sustained and controllable amount.

Ocular Drug Distribution After Topical Administration: Population Pharmacokinetic Model in Rabbits

BACKGROUND AND OBJECTIVE

When eye diseases are treated by topical administration, the success of treatment lies in the effective drug concentration in the target tissue. This is why the drug's pharmacokinetic, in the different substructures of the eye, needs to be explored more accurately during drug development. The aim of the present analysis was to describe by rabbit model, the distribution of a drug after ocular instillation in the selected eye tissues and fluids.

METHODS

By a top-down population approach, we developed and validated a population pharmacokinetics (PopPK) model, using tissue concentrations (tear, naso-lacrymal duct, cornea and aqueous humor) of a new src tyrosine kinase inhibitor (FV-60165) in each anterior segment's tissue and fluid of the rabbit eye. Inter-individual variability was estimated and the impact of the formulation (solution or nanosuspension) was evaluated.

RESULTS

The model structure selected for the eye is a 4-compartment model with the formulation as a significant covariate on the first-order rate constant between tears and the naso-lacrymal duct. The model showed a good predictive performance and may be used to estimate the concentration-time profiles after single or repeated administration, in each substructure of the eye for each animal included in the analysis.

CONCLUSIONS

This analysis allowed describing the distribution of a drug in the different selected tissues and fluids in the rabbit's eyes after instillation of the prodrug as a solution or nanosuspension.