Triamcinolone Acetonide-Loaded PEGylated Microemulsion for the Posterior Segment of Eye

Fostering the unleashing potential of nanocarriers-mediated delivery of ocular therapeutics

Ocular delivery is the most challenging aspect in the field of pharmaceutical research. The major hurdle for the controlled delivery of drugs to the eye includes the physiological static barriers such as the complex layers of the cornea, sclera and retina which restrict the drug from permeating into the anterior and posterior segments of the eye. Recent years have witnessed inventions in the field of conventional and nanocarrier drug delivery which have shown considerable enhancement in delivering small to large molecules across the eye. The dynamic challenges associated with conventional systems include limited drug contact time and inadequate ocular bioavailability resulting from solution drainage, tear turnover, and dilution or lacrimation. To this end, various bioactive-based nanosized carriers including liposomes, ethosomes, niosomes, dendrimer, nanogel, nanofibers, contact lenses, nanoprobes, selenium nanobells, nanosponge, polymeric micelles, silver nanoparticles, and gold nanoparticles among others have been developed to circumvent the limitations associated with the conventional dosage forms. These nanocarriers have been shown to achieve enhanced drug permeation or retention and prolong drug release in the ocular tissue due to their better tissue adherence. The surface charge and the size of nanocarriers (10-1000 nm) are the important key factors to overcome ocular barriers. Various nanocarriers have been shown to deliver active therapeutic molecules including timolol maleate, ampicillin, natamycin, voriconazole, cyclosporine A, dexamethasone, moxifloxacin, and fluconazole among others for the treatment of anterior and posterior eye diseases. Taken together, in a nutshell, this extensive review provides a comprehensive perspective on the numerous facets of ocular drug delivery with a special focus on bioactive nanocarrier-based approaches, including the difficulties and constraints involved in the fabrication of nanocarriers. This also provides the detailed invention, applications, biodistribution and safety-toxicity of nanocarriers-based therapeutcis for the ophthalmic delivery.

Long-Acting Ocular Injectables: Are We Looking In The Right Direction?

The complex anatomy and physiological barriers of the eye make delivering ocular therapeutics challenging. Generally, effective drug delivery to the eye is hindered by rapid clearance and limited drug bioavailability. Biomaterial-based approaches have emerged to enhance drug delivery to ocular tissues and overcome existing limitations. In this review, some of the most promising long-acting injectables (LAIs) in ocular drug delivery are explored, focusing on novel design strategies to improve therapeutic outcomes. LAIs are designed to enable sustained therapeutic effects, thereby extending local drug residence time and facilitating controlled and targeted drug delivery. Moreover, LAIs can be engineered to enhance drug targeting and penetration across ocular physiological barriers.

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.

Nanostructured Lipid Carriers Mediated Drug Delivery to Posterior Segment of Eye and their In-vivo Successes

BACKGROUND

The disease of the posterior segment of the eye is a major concern worldwide, and it affects more than 300 million people and leads to serious visual deterioration. The current treatment available is invasive and leads to serious eye complications. These shortcomings and patient discomfort lead to poor patient compliance. In the last decade, Nanostructured lipid carriers (NLC) have established a remarkable milestone in the delivery of drug substances to the posterior segment of the eye. Additionally, NLC can reduce the clearance due to adhesive properties which are imparted due to nano-metric size. This attribute might reduce the adverse effects associated with intravitreal therapy and thus enhance therapeutic efficacy, eventually raising patient adherence to therapy. The current review provides an inclusive account of NLC as a carrier to target diseases of the posterior segment of the eye.

OBJECTIVE

The review focuses on the various barrier encountered in the delivery of drugs to the posterior segment of the eye and the detail about the physicochemical property of drug substances that are considered to be suitable candidates for encapsulation to lipid carriers. Therefore, a plethora of literature has been included in this review. The review is an attempt to describe methods adopted for assessing the in-vivo behavior that strengthens the potential of NLC to treat the disease of the posterior segment of the eye.

CONCLUSION

These NLC-based systems have proven to be a promising alternative in place of invasive intravitreal injections with improved patient compliance.

Nanotechnology-based ocular drug delivery systems: recent advances and future prospects

Ocular drug delivery has constantly challenged ophthalmologists and drug delivery scientists due to various anatomical and physiological barriers. Static and dynamic ocular barriers prevent the entry of exogenous substances and impede therapeutic agents' active absorption. This review elaborates on the anatomy of the eye and the associated constraints. Followed by an illustration of some common ocular diseases, including glaucoma and their current clinical therapies, emphasizing the significance of drug therapy in treating ocular diseases. Subsequently, advances in ocular drug delivery modalities, especially nanotechnology-based ocular drug delivery systems, are recommended, and some typical research is highlighted. Based on the related research, systematic and comprehensive characterizations of the nanocarriers are summarized, hoping to assist with future research. Besides, we summarize the nanotechnology-based ophthalmic drugs currently on the market or still in clinical trials and the recent patents of nanocarriers. Finally, inspired by current trends and therapeutic concepts, we provide an insight into the challenges faced by novel ocular drug delivery systems and further put forward directions for future research. We hope this review can provide inspiration and motivation for better design and development of novel ophthalmic formulations.

Next-Generation Nanomedicine Approaches for the Management of Retinal Diseases

Retinal diseases are one of the leading causes of blindness globally. The mainstay treatments for these blinding diseases are laser photocoagulation, vitrectomy, and repeated intravitreal injections of anti-vascular endothelial growth factor (VEGF) or steroids. Unfortunately, these therapies are associated with ocular complications like inflammation, elevated intraocular pressure, retinal detachment, endophthalmitis, and vitreous hemorrhage. Recent advances in nanomedicine seek to curtail these limitations, overcoming ocular barriers by developing non-invasive or minimally invasive delivery modalities. These modalities include delivering therapeutics to specific cellular targets in the retina, providing sustained delivery of drugs to avoid repeated intravitreal injections, and acting as a scaffold for neural tissue regeneration. These next-generation nanomedicine approaches could potentially revolutionize the treatment landscape of retinal diseases. This review describes the availability and limitations of current treatment strategies and highlights insights into the advancement of future approaches using next-generation nanomedicines to manage retinal diseases.

Bibliometric and visualized analysis of ocular drug delivery from 2001 to 2020

OBJECTIVE

To perform a bibliometric analysis in the field of ocular drug delivery research to characterize the current international trends and to present visual representations of the past and emerging trends on ocular drug delivery research over the past decade.

METHOD

In this cross-sectional study, a bibliometric analysis of data retrieved and extracted from the Web of Science Core Collection (WoSCC) database was performed to analyze evolution and theme trends on ocular drug delivery research from January 1, 2001, to December 31, 2020. A total of 4334 articles on ocular drug delivery were evaluated for specific characteristics, such as publication year, journals, authors, institutions, countries/regions, references, and keywords. Co-authorship analysis, co-occurrence analysis, co-citation analysis, and network visualization were constructed by VOSviewer. Some important subtopics identified by bibliometric characterization were further discussed and reviewed.

RESULTS

From 2001 to 2020, the annual global publications increased by 746.15%, from 52 to 440. International Journal of Pharmaceutics published the most manuscripts (250 publications) and produced the highest citations (9509 citations), followed by Investigative Ophthalmology & Visual Science (202 publications) and Journal of Ocular Pharmacology and Therapeutics (136 publications). The United States (1289 publications, 31,512 citations), the University of Florida (82 publications, 2986 citations), and Chauhan, Anuj (52 publications, 2354 citations) were the most productive and impactful institution, country, and author respectively. The co-occurrence cluster analysis of the top 100 keywords form five clusters: (1) micro/nano ocular drug delivery systems; (2) the treatment of inflammation and posterior diseases; (3) macroscopic ocular drug delivery systems/devices; (4) the characteristics of drug delivery systems; (5) and the ocular drug delivery for glaucoma treatment. Diabetic macular edema, anti-VEGF, ranibizumab, bevacizumab, micelles and latanoprost, were the latest high-frequency keywords, indicating the emerging frontiers of ocular drug delivery. Further discussions into the subtopics were provided to assist researchers to determine the range of research topics and plan research direction.

CONCLUSIONS

Over the last two decades there has been a progressive increase in the number of publications and citations on research related to ocular drug delivery across many countries, institutions, and authors. The present study sheds light on current trends, global collaboration patterns, basic knowledge, research hotspots, and emerging frontiers of ocular drug delivery. Novel solutions for ocular drug delivery and the treatment of inflammation and posterior diseases were the major themes over the last 20 years.

Drug Delivery Challenges and Current Progress in Nanocarrier-Based Ocular Therapeutic System

Drug instillation via a topical route is preferred since it is desirable and convenient due to the noninvasive and easy drug access to different segments of the eye for the treatment of ocular ailments. The low dose, rapid onset of action, low or no toxicity to the local tissues, and constrained systemic outreach are more prevalent in this route. The majority of ophthalmic preparations in the market are available as conventional eye drops, which rendered <5% of a drug instilled in the eye. The poor drug availability in ocular tissue may be attributed to the physiological barriers associated with the cornea, conjunctiva, lachrymal drainage, tear turnover, blood–retinal barrier, enzymatic drug degradation, and reflex action, thus impeding deeper drug penetration in the ocular cavity, including the posterior segment. The static barriers in the eye are composed of the sclera, cornea, retina, and blood–retinal barrier, whereas the dynamic barriers, referred to as the conjunctival and choroidal blood flow, tear dilution, and lymphatic clearance, critically impact the bioavailability of drugs. To circumvent such barriers, the rational design of the ocular therapeutic system indeed required enriching the drug holding time and the deeper permeation of the drug, which overall improve the bioavailability of the drug in the ocular tissue. This review provides a brief insight into the structural components of the eye as well as the therapeutic challenges and current developments in the arena of the ocular therapeutic system, based on novel drug delivery systems such as nanomicelles, nanoparticles (NPs), nanosuspensions, liposomes, in situ gel, dendrimers, contact lenses, implants, and microneedles. These nanotechnology platforms generously evolved to overwhelm the troubles associated with the physiological barriers in the ocular route. The controlled-drug-formulation-based strategic approach has considerable potential to enrich drug concentration in a specific area of the eye.

Self-Assembling Tacrolimus Nanomicelles for Retinal Drug Delivery

Neovascular age-related macular degeneration (AMD) is characterized by an increase in reactive oxygen species (ROS) and pro-inflammatory cytokines in the retinal pigment epithelium cells. The primary purpose of this study was the development of a clear, tacrolimus nanomicellar formulation (TAC-NMF) for AMD. The optimized formulation had a mean diameter of 15.41 nm, a zeta potential of 0.5 mV, and an entrapment efficiency of 97.13%. In-vitro cytotoxicity studies revealed the dose-dependent cytotoxicity of TAC-NMF on various ocular cell lines, such as human retinal pigment epithelium (D407), monkey retinal choroidal endothelial (RF/6A) cells, and human corneal epithelium (CCL 20.2) cells. Cellular uptake and in-vitro distribution studies using flow cytometry and confocal microscopy, respectively, indicated an elevated uptake of TAC-NMF in a time-dependent manner. Biocompatibility assay using macrophage RAW 264.7 cell line resulted in low production of inflammatory cytokines such as IL-6, IL-1β and TNF-α after treatment with TAC-NMF. There was a decrease in ROS in D407 cells pre-treated with sodium iodate (ROS inducing agent) after treating with TAC-NMF and tacrolimus drug. Similarly, there was a reduction in the pro-inflammatory cytokines and VEGF-A in D407 cells pretreated with sodium iodate. This indicates that TAC-NMF could lower pro-inflammatory cytokines and ROS commonly seen in AMD.