Drug delivery in ocular diseases: Barriers and strategies

Formulation and characterization of transfersomes for ocular delivery of tonabersat

Transfersomes (TFS) are deformable vesicles, known for their ability to enhance transdermal drug penetration. This study aimed to evaluate whether TFS can also enhance ocular delivery of poorly soluble tonabersat. TFS were prepared using Phospholipon® 90G with Tween® 80 as the edge activator. The effect of formulation parameters (edge activator and cryoprotectant concentrations) on TFS characteristics were evaluated using a full factorial design. The optimized TFS eyedrop was characterized for particle size, zeta potential, deformability, entrapment efficiency (EE), drug content, pH, osmolality and TFS stability over 3 months at different storage conditions. Furthermore, drug penetration into the cornea, conjunctiva, eyelid, and sclera-choroid after topical application was studied ex vivo using a tonabersat solution in medium chain triglycerides as the control. The optimized TFS formed spherical unilamellar vesicles with a mean diameter <130 nm, EE >80%, and were stable at -20 and 5 ± 3 °C for up to 3 months. The TFS eyedrop resulted in significantly greater ocular penetration than the control without affecting the barrier properties of the tested tissues. Drug penetration into different ocular tissues was compared, shedding light on the penetration mechanism of TFS. Overall, this study demonstrates that TFS provide a promising alternative for the ocular delivery of tonabersat.

Evaluation of ocular tolerability and bioavailability of tonabersat transfersomes ex vivo

While transfersomes (TFS) have extensively been investigated as carriers for topical drug delivery to the skin, their application in ocular drug delivery remains largely unexplored. This study aimed to evaluate the tolerability, contact angle, and ocular penetration of tonabersat-loaded TFS using ex vivo models, with a focus on comparing drug distribution in different ocular tissues. A solution of tonabersat in medium chain triglycerides (MCT) was used as the control. Conjunctival tolerability was evaluated using the Hen's Egg Test on Chorioallantoic Membrane (HET-CAM), while the Bovine Corneal Opacity and Permeability (BCOP) assay was used to establish corneal tolerability. Drop contact angle on freshly excised bovine corneas was measured using a goniometer. Drug penetration into the cornea, conjunctiva, eyelid and sclera-choroid was evaluated using an ex vivo porcine whole eye model under simulated tear flow, 0.25, 0.5, 1, and 2 h after eyedrop application. Both the TFS and MCT formulations exhibited good conjunctival and corneal tolerability with the TFS contact angle on the corneal surface being lower than that of MCT. Significantly greater drug concentrations were achieved in all ocular tissues with the TFS eyedrop, with the Cmax from TFS being at least 16-fold higher than that achieved with the MCT solution in the conjunctiva, eyelid and sclera-choroid, with the difference being greatest in the latter. Meanwhile, the corneal Cmax was 6-fold greater with TFS. Interestingly, despite simulated tear flow, the Tmax was observed at a later timepoint with TFS in all ocular tissues. Overall, this study demonstrates that TFS are well tolerated on the ocular surface and have the potential for sustained and targeted drug delivery to ocular tissues. Thus, they present a promising alternative for safe and effective ocular drug delivery.

Transfersomes: a next-generation drug delivery system for topical ocular drug delivery

INTRODUCTION

The eye is a complex organ with several anatomical and physiological barriers that make ocular drug delivery an ongoing challenge. Transfersomes (TFS) are deformable vesicles that have been extensively applied to enhance transdermal drug delivery. However, their application in ocular drug delivery remains largely unexplored.

AREAS COVERED

This review highlights the challenges typically associated with ocular drug delivery and emphasizes the inherent properties of TFS that enable them to overcome these challenges. The influence of excipients and critical process parameters on TFS characteristics have been discussed in detail with an emphasis on the fabrication and characterization techniques typically employed for TFS development and optimization. Furthermore, recent studies evaluating the application of TFS in ocular drug delivery have been discussed in depth.

EXPERT OPINION

The unique stress-responsive and deformable nature of TFS makes them promising carriers for ocular drug delivery. However, further research in this direction is needed to understand their penetration mechanism and elucidate their potential for sustained and targeted drug delivery to ocular tissues. Moreover, further research is needed to optimize the stability and scalability of TFS to encourage their translation to the market.

Advanced Technologies of Drug Delivery to the Posterior Eye Segment Targeting Angiogenesis and Ocular Cancer

Retinoblastoma (RB), a childhood retinal cancer is caused due to RB1 gene mutation which affects the child below 5 years of age. Angiogenesis has been proven its role in RB metastasis due to the presence of vascular endothelial growth factor (VEGF) in RB cells. Therefore, exploring angiogenic pathway by inhibiting VEGF in treating RB would pave the way for future treatment. In preclinical studies, anti-VEGF molecule have shown their efficacy in treating RB. However, treatment requires recurrent intra-vitreal injections causing various side effects along with patient nonadherence. As a result, delivery of anti-VEGF agent to retina requires an ocular delivery system that can transport it in a non-invasive manner to achieve patient compliance. Moreover, development of these type of systems are challenging due to the complicated physiological barriers of eye. Adopting a non-invasive or minimally invasive approach for delivery of anti-VEGF agents would not only address the bioavailability issues but also improve patient adherence to therapy overcoming the side effects associated with invasive approach. The present review focuses on the eye cancer, angiogenesis and various novel ocular drug delivery systems that can facilitate inhibition of VEGF in the posterior eye segment by overcoming the eye barriers.

Alternatives to Topical Glaucoma Medication for Glaucoma Management

Topical glaucoma medications have favorable safety and efficacy, but their use is limited by factors such as side effects, nonadherence, costs, ocular surface disease, intraocular pressure fluctuations, diminished quality of life, and the inherent difficulty of penetrating the corneal surface. Although traditionally these limitations have been accepted as an inevitable part of glaucoma treatment, a rapidly-evolving arena of minimally invasive surgical and laser interventions has initiated the beginnings of a reevaluation of the glaucoma treatment paradigm. This reevaluation encompasses an overall shift away from the reactive, topical-medication-first default and a shift toward earlier intervention with laser or surgical therapies such as selective laser trabeculoplasty, sustained-release drug delivery, and micro-invasive glaucoma surgery. Aside from favorable safety, these interventions may have clinically important attributes such as consistent IOP control, cost-effectiveness, independence from patient adherence, prevention of disease progression, and improved quality of life.

Recent Progress of Solid Lipid Nanoparticles and Nanostructured Lipid Carriers as Ocular Drug Delivery Platforms

Sufficient ocular bioavailability is often considered a challenge by the researchers, due to the complex structure of the eye and its protective physiological mechanisms. In addition, the low viscosity of the eye drops and the resulting short ocular residence time further contribute to the observed low drug concentration at the target site. Therefore, various drug delivery platforms are being developed to enhance ocular bioavailability, provide controlled and sustained drug release, reduce the number of applications, and maximize therapy outcomes. Solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) exhibit all these benefits, in addition to being biocompatible, biodegradable, and susceptible to sterilization and scale-up. Furthermore, their successive surface modification contributes to prolonged ocular residence time (by adding cationic compounds), enhanced penetration, and improved performance. The review highlights the salient characteristics of SLNs and NLCs concerning ocular drug delivery, and updates the research progress in this area.

Advantages and Disadvantages of Using Magnetic Nanoparticles for the Treatment of Complicated Ocular Disorders

Nanomaterials provide enormous opportunities to overcome the limitations of conventional ocular delivery systems, such as low therapeutic efficacy, side effects due to the systemic exposure, or invasive surgery. Apart from the more common ocular disorders, there are some genetic diseases, such as cystic fibrosis, that develop ocular disorders as secondary effects as long as the disease progresses. These patients are more difficult to be pharmacologically treated using conventional drug routes (topically, systemic), since specific pharmacological formulations can be incompatible, display increased toxicity, or their therapeutic efficacy decreases with the administration of different kind of chemical molecules. Magnetic nanoparticles can be used as potent drug carriers and magnetic hyperthermia agents due to their response to an external magnetic field. Drugs can be concentrated in the target point, limiting the damage to other tissues. The other advantage of these magnetic nanoparticles is that they can act as magnetic resonance imaging agents, allowing the detection of the exact location of the disease. However, there are some drawbacks related to their use in drug delivery, such as the limitation to maintain efficacy in the target organ once the magnetic field is removed from outside. Another disadvantage is the difficulty in maintaining the therapeutic action in three dimensions inside the human body. This review summarizes all the application possibilities related to magnetic nanoparticles in ocular diseases.

Novel corneal targeting cell penetrating peptide as an efficient nanocarrier with an effective antimicrobial activity

Delivery of therapeutics to the ocular tissues is challenging due to various anatomical and physiological barriers imposed. Cell penetrating peptides (CPPs) have emerged as potent drug nanocarriers that have been shown to overcome these barriers and enhance bioavailability of therapeutic macromolecules in deep ocular tissues. In the present study, an ocular targeting CPP has been designed by exploring potential targets of anterior ocular tissues in particular receptors, transporters and glycosaminoglycans (GAGs). The novel 11 mer peptide sequence, Corneal Targeting Sequence 1 (CorTS 1), has been developed by modifying leucine rich repeat (LRR) motif ensuring that it interacts with small leucine rich proteoglycans and collagen present in the corneal stroma. CorTS 1 exhibited dose dependent cellular translocation from 5 μM in Human Corneal Epithelial cell line (HCE) with no cytotoxicity. CorTS 1 was also found to deliver protein cargo inside HCE cells. Ex vivo tissue penetration study of CorTS 1 demonstrated in goat eyes revealed an augmented accumulation of peptide in the stromal region of cornea than in aqueous humor. Interestingly, CorTS 1 showed an antimicrobial activity against MRSA and Fusarium dimerum. Therefore, CorTS 1 can be a promising candidate with dual traits of antimicrobial agent and nanocarrier for ocular drugs.

Formulation development, optimization, and in vitro assessment of thermoresponsive ophthalmic pluronic F127-chitosan in situ tacrolimus gel

To overcome problems associated with topical delivery of tacrolimus (TCS), a thermoresponsive in situ gel system containing pluronic F127 (PL), and chitosan (CS) was developed, to enhance the precorneal retention, and to sustain the release of the drug. The PL-CS in situ gel was optimized using a 2-factor-3-level central composite experimental design by selecting the concentration of PL and CS as independent variables while gelation time, gelation temperature, and spreadability as dependent variables. The optimized formulation was developed using 22.5 g PL and 0.3 g CS, gels at 33.6 °C, in 22.93 s, and showed the spreadability of 6.2 cm. In vitro studies conducted for the optimized gel revealed the sustained release of TCS (81.73% in 4 h) and improved corneal permeation (74.13% in 4 h), compared with TCS solution. The mechanism of release of TCS followed the Higuchi model with Fickian diffusion transport. Further, histopathology and HET-CAM studies revealed that the developed gel was non-irritating and safe for ocular administration.

Preparation and Evaluation of Cubosomes/Cubosomal Gels for Ocular Delivery of Beclomethasone Dipropionate for Management of Uveitis

PURPOSE

Topical corticosteroids administration is commonly used for management of various ocular conditions especially those affecting the anterior segment of the eye. Poor solubility and limited pre-corneal residence time result in insufficient drug penetration to the outer (cornea and conjunctival-scleral) coats of the eye. This study aimed to prepare and evaluate cubosomes for prolonging residence time and enhancing ocular bioavailability of BDP.

METHODS

GMO-cubosomes were prepared using the top-down technique. Two stabilizers were investigated: poloxamer 407 and solulan C24. Particle size, EE %, polarized-light microscopy, TEM, in vitro release, transcorneal permeation, BCOP, histopathology and in vivo evaluation for treatment of uveitis in a rabbits' model were studied.

RESULTS

The prepared cubosomes were of nano-sizes (100 nm - 278 nm); EE% was around 94%. The cubosomes were confirmed by visualizing the "Maltese crosses" textures. Transcorneal permeation was significantly (p < 0.05) improved, compared to BDP-suspension (the control formulation). The optimized cubosomes F1P was incorporated in CMC gel (Cubo-gel). The prepared Cubo-gel formulations showed better rheological characteristics and high ocular tolerability. Superior anti-inflammatory properties were recorded for the Cubo-gel for treatment of endotoxin-induced uveitis in the rabbit model when compared to the control BDP-suspension.

CONCLUSIONS

Transcorneal permeation parameters P_app and flux and AUC_0-10h markedly enhanced by up to 4-, 5.8-and 5.5-fold respectively, compared to the control BDP-suspension formulation. This study suggested that cubosomes/Cubo-gel could be an auspicious ocular delivery system for BDP that was able to effectively treat uveitis (a disease of the posterior segment of the eye).

Nanocarriers for ocular drug delivery: current status and translational opportunity

Ocular diseases have a significant effect on vision and quality of life. Drug delivery to ocular tissues is a challenge to formulation scientists. The major barriers to delivering drugs to the anterior and posterior segments include physiological barriers (nasolacrimal drainage, blinking), anatomical barriers (static and dynamic), efflux pumps and metabolic barriers. The static barriers comprise the different layers of the cornea, sclera, and blood-aqueous barriers whereas dynamic barriers involve conjunctival blood flow, lymphatic clearance and tear drainage. The tight junctions of the blood-retinal barrier (BRB) restrict systemically administered drugs from entering the retina. Nanocarriers have been found to be effective at overcoming the issues associated with conventional ophthalmic dosage forms. Various nanocarriers, including nanodispersion systems, nanomicelles, lipidic nanocarriers, polymeric nanoparticles, liposomes, niosomes, and dendrimers, have been investigated for improved permeation and effective targeted drug delivery to various ophthalmic sites. In this review, various nanomedicines and their application for ophthalmic delivery of therapeutics are discussed. Additionally, scale-up and clinical status are also addressed to understand the current scenario for ophthalmic drug delivery.