Enhancement in Corneal Permeability of Dissolved Carteolol by Its Combination with Magnesium Hydroxide Nanoparticles

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

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

Trans-corneal drug delivery strategies in the treatment of ocular diseases

The cornea is a remarkable tissue that possesses specialized structures designed to safeguard the eye against foreign objects. However, its unique properties also make it challenging to deliver drugs in a non-invasive manner. This review highlights recent advancements in achieving highly efficient drug transport across the cornea, focusing on nanomaterials. We have classified these strategies into three main categories based on their mechanisms and have analyzed their success and limitations in a systematic manner. The purpose of this review is to examine potential general principles that could improve drug penetration through the cornea and other natural barriers in the eye. We hope it will inspire the development of more effective drug delivery systems that can better treat ocular diseases.

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.

Magnesium Hydroxide Nanoparticles Improve the Ocular Hypotensive Effect of Twice Daily Topical Timolol Maleate in Healthy Dogs

Timolol maleate (TM), a beta-adrenergic receptor antagonist, is widely used for canine antiglaucoma eye drops; however, its bioavailability is <5%. Our previous study revealed that magnesium hydroxide nanoparticles (nMH) have potency in improving the bioavailability of fixed-combined TM in rodent models. This study aimed to investigate whether the fixed combination with nMH improves the ocular hypotensive effect of TM and affects pupil size (PS), heart rate (HR), and mean arterial pressure (MAP) in clinically healthy dogs. Five clinically healthy dogs were administered topical saline, commercial 0.5% TM, and a 0.01% or 0.1% nMH–0.5% TM fixed combination (0.01% or 0.1% nMH–TM) twice daily in one eye for 7 days with at least a 28-day interval. The changes from baseline were calculated and were statistically analyzed for each drug. IOP was significantly reduced in both 0.01% and 0.1% nMH–TM-treated-dogs compared with saline- and TM-treated dogs. Meanwhile, 0.01% and 0.1% nMH did not exacerbate the side effects of TM. From these results, nMH improved the ocular hypotensive effect of TM without enhancing side effects. Topical nMH–TM is potentially more effective for canine ocular hypotensive eye drops than TM.

Fixed-Combination Eye Drops Based on Fluorometholone Nanoparticles and Bromfenac/Levofloxacin Solution Improve Drug Corneal Penetration

Purpose

The multi-instillation of three commercially available (CA) eye drops [fluorometholone (FL)-, bromfenac (BF)- and levofloxacin (LV)-eye drops] has been used to manage pain and inflammation post-intraocular surgery. However, the multi-instillation of these three eye drops causes corneal damage, and the FL drops have the disadvantage of low ocular bioavailability. To overcome these problems, we prepared fixed-combination eye drops based on FL nanoparticles (FL-NPs) and BF/LV solution (nFBL-FC), and evaluated the corneal toxicity and transcorneal penetration of the nFBL-FC eye drops.

Methods

FL powder was mixed in 2-hydroxypropyl-β-cyclodextrin solution containing benzalkonium chloride, mannitol and methylcellulose, and milled with a Bead Smash 12 (5500 rpm for 30 s×30 times). The BF/LV solution was then added to the milled-dispersions to be used as nFBL-FC. The FL, BF and LV concentrations were measured by HPLC methods, and transcorneal penetration was evaluated in rabbits.

Results

The FL particle size in nFBL-FC was 40–150 nm, with only 0.0018% in liquid form. No aggregation of FL particles in the nFBL-FC was observed for 1 month. The viability of human corneal epithelial cells treated with nFBL-FC was remarkably higher than that of cells subjected to the multi-instillation of the corresponding three CA-eye drops. In addition, the corneal penetrations (AUC) of the FL, BF and LV in nFBL-FC were 4.9-, 1.8-, and 7.1-fold those of the corresponding CA-eye drops, respectively. Moreover, the caveolae-dependent endocytosis (CavME) inhibitor (nystatin) significantly prevented the transcorneal penetration of these drugs.

Conclusion

We prepared fixed-combination eye drops based on FL-NPs and BF/LV solution (nFBL-FC), and show that high levels of FL-NPs and dissolved BF/LV (liquid drugs) can be delivered into the aqueous humor by the instillation of nFBL-FC. Further, we show that CavME is mainly related to the enhancement of transcorneal penetration of both the solid (NPs) and liquid drugs.

Nanomedicines for the treatment of glaucoma: Current status and future perspectives

Glaucoma is the global leading cause of irreversible blindness. It is a chronic progressive disorder and, therefore, often requires long-term management with drugs on patients' discretion. However, there is a shortage of antiglaucoma drugs in the current market due to their low bioavailability. This is because there are multiple biological barriers of the human eyes, thereby leading to increased demands for frequent dosage regimen per day of these drugs, which could result in concomitant side effects and eventually reduced patient compliance. Recently, nanomedicines have become optimized alternatives to conventional ophthalmic formulations due to advantages of improved barrier permeability, sustained drug release, tissue targeting, and lowered systemic absorption of instilled medications. These merits provide the active ingredients in these nanomedicines an effective manner to reach the ideal concentrations at sites of damaged nerves, offering a promising platform for neuroprotective treatment of these conditions. In this study, nanomedicines and nanomedicine-based novel strategies for pharmacotherapy of glaucoma were reviewed, including liposomes, niosomes, nanoparticles, and dendrimers. This article intends to offer a comprehensive review of frontier progresses as well as hotspots and issues that appeared in the field of nanomedicines, which may enable a practical flourish in the future. STATEMENT OF SIGNIFICANCE: Recent novel pharmaceutical strategies toward glaucoma, a chronic blinding ocular disease that currently requires frequent daily dosage regimen, based on nanomedicines and nanomaterials have been comprehensively reviewed in this manuscript. The collection of field hotspots and issues in the late years should offer a quick grasp of the general concept and up-to-date threads upon the refinement of existing treatment patterns for glaucoma. Meanwhile, the Conclusion and Future Perspective section given at the end of the text brings out the possible shortages and opinions in terms of ideal research direction, which hopefully could facilitate a future practical flourish in the area.

Dose- and Time-Dependent Cytotoxicity of Carteolol in Corneal Endothelial Cells and the Underlying Mechanisms

Carteolol is a non-selective β-adrenoceptor antagonist used for the treatment of glaucoma, and its abuse might be cytotoxic to the cornea. However, its cytotoxicity and underlying mechanisms need to be elucidated. Herein, we used an in vivo model of feline corneas and an in vitro model of human corneal endothelial cells (HCECs), respectively. In vivo results displayed that 2% carteolol (clinical dosage) could induce monolayer density decline and breaking away of feline corneal endothelial (FCE) cells. An in vitro model of HCECs that were treated dose-dependently (0.015625–2%) with carteolol for 2–28 h, resulted in morphological abnormalities, declining in cell viability and elevating plasma membrane (PM) permeability in a dose- and time- dependent manner. High-dose (0.5–2%) carteolol treatment induced necrotic characteristics with uneven distribution of chromatin, marginalization and dispersed DNA degradation, inactivated caspase-2/-8, and increased RIPK1, RIPK3, MLKL, and pMLKL expression. The results suggested that high-dose carteolol could induce necroptosis via the RIPK/MLKL pathway. While low-dose (0.015625–0.25%) carteolol induced apoptotic characteristics with chromatin condensation, typical intranucleosomal DNA laddering patterns, G₁ cell-cycle arrest, phosphatidylserine (PS) externalization, and apoptotic body formation in HCECs. Meanwhile, 0.25% carteolol treatment resulted in activated caspase-2, -3, -8, and -9, downregulation of Bcl-2 and Bcl-xL, upregulation of Bax and Bad, ΔΨm disruption, and release of cytoplasmic cytochrome c (Cyt.c) and AIF into the cytoplasm. These observations suggested that low-dose carteolol could induce apoptosis via a caspase activated and mitochondrial-dependent pathway. These results suggested that carteolol should be used carefully, as low as 0.015625% cartelol caused apoptotic cell death in HCECs in vitro.

Therapeutic Potential of a Combination of Magnesium Hydroxide Nanoparticles and Sericin for Epithelial Corneal Wound Healing

We previously found the instillation of sericin to be useful as therapy for keratopathy with or without diabetes mellitus. In this study, we investigated whether a combination of solid magnesium hydroxide nanoparticles (MHN) enhances epithelial corneal wound healing by sericin using rabbits, normal rats and type 2 diabetes mellitus rats with debrided corneal epithelium (ex vivo and in vivo studies). Ophthalmic formulations containing sericin and MHN (N-Ser) were prepared using a bead mill method. The mean particle size of the N-Ser was 110.3 nm at the time of preparation, and 148.1 nm one month later. The instillation of N-Ser had no effect on the amount of lacrimal fluid in normal rabbits (in vivo), but the MHN in N-Ser was found to expand the intercellular space in ex vivo rat corneas. In addition, the instillation of N-Ser increased the phosphorylation of Extracellular Signal-regulated Kinase (ERK)1/2, a factor involved in cell adhesion and cell proliferation in the corneal epithelium, in comparison with the instillation of sericin alone. The combination with MHN enhanced epithelial corneal wound healing by sericin in rat debrided corneal epithelium (in vivo). This study provides significant information to prepare potent drugs to cure severe keratopathy, such as diabetic keratopathy.