Preparation and in vitro/in vivo evaluations of novel ocular micelle formulations of hesperetin with glycyrrhizin as a nanocarrier

Formulation, Preparation, and Evaluation of Bifunctional Micelle with Glycyrrhizic Acid Containing Emodin for Toxicity Attenuation Application

OBJECTIVE

To prepare GA-Emo micelles and investigate the feasibility of using GA as both a bifunctional drug and carrier.

METHODS

The preparation of GA-Emo micelles was accomplished via the thin-film dispersion method with GA as the carrier. Size distribution, entrapment efficiency, and drug loading were used to evaluate the characteristics of micelles. The absorption and transport properties of the micelles in Caco-2 cells were investigated, while their pharmacodynamics in mice were preliminarily studied.

RESULTS

The optimal formulation featured a GA/Emo in weight ratio of 2:1 and an encapsulation efficiency of 23.68%. The optimized GA/Emo was characterized as small uniform spheres with an average micellar size of 168.64 ± 5.69 nm, a polydispersity index of 0.17 ± 0.01, and an electrically negative surface (-35.33 ± 0.94 mV). Absorption and transport experiments with Caco-2 cells showed that the absorption of GA-Emo micelles in small intestines was mainly passive transport, amid their transport volume being significantly higher than that of Emo monomer. The intestinal wall thickness of the GAEmo micelles group was significantly lower than that of the Emo group, which meant that the colonic toxicity of the micelles was lower than unincorporated Emo.

CONCLUSION

The advantages of GA as a bifunctional micelle carrier in formulation characters, drug release, and toxicity attenuation provide a new idea for the application of the GA of natural medicine in drug delivery for toxicity reduction.

The potential benefits of polyphenols for corneal diseases

The cornea functions as the primary barrier of the ocular surface, regulating temperature and humidity while providing protection against oxidative stress, harmful stimuli and pathogenic microorganisms. Corneal diseases can affect the biomechanical and optical properties of the eye, resulting in visual impairment or even blindness. Due to their diverse origins and potent biological activities, plant secondary metabolites known as polyphenols offer potential advantages for treating corneal diseases owing to their anti-inflammatory, antioxidant, and antibacterial properties. Various polyphenols and their derivatives have demonstrated diverse mechanisms of action in vitro and in vivo, exhibiting efficacy against a range of corneal diseases including repair of tissue damage, treatment of keratitis, inhibition of neovascularization, alleviation of dry eye syndrome, among others. Therefore, this article presents a concise overview of corneal and related diseases, along with an update on the research progress of natural polyphenols in safeguarding corneal health. A more comprehensive understanding of natural polyphenols provides a novel perspective for secure treatment of corneal diseases.

Nanotechnology based drug delivery systems for the treatment of anterior segment eye diseases

Diseases affecting the anterior segment of the eye are the primary causes of vision impairment and blindness globally. Drug administration through the topical ocular route is widely accepted because of its user/patient friendliness - ease of administration and convenience. However, it remains a significant challenge to efficiently deliver drugs to the eye through this route because of various structural and physiological constraints that restrict the distribution of therapeutic molecules into the ocular tissues. The bioavailability of topically applied ocular medications such as eye drops is typically less than 5%. Developing novel delivery systems to increase the retention time on the ocular surfaces and permeation through the cornea is one of the approaches adopted to boost the bioavailability of topically administered medications. Drug delivery systems based on nanotechnology such as micelles, nanosuspensions, nanoparticles, nanoemulsions, liposomes, dendrimers, niosomes, cubosomes and nanowafers have been investigated as effective alternatives to conventional ocular delivery systems in treating diseases of the anterior segment of the eye. This review discussed different nanotechnology-based delivery systems that are currently investigated for treating and managing diseases affecting the anterior ocular tissues. We also looked at the challenges in translating these systems into clinical use and the prospects of nanocarriers as a vehicle for the delivery of phytoactive compounds to the anterior segment of the eye.

Nanoparticles in ocular applications and their potential toxicity

Nanotechnology has been developed rapidly in recent decades and widely applied in ocular disease therapy. Nano-drug delivery systems overcome the bottlenecks of current ophthalmic drug delivery and are characterized with strong biocompatibility, stability, efficiency, sustainability, controllability, and few side effects. Nanoparticles have been identified as a promising and generally safe ophthalmic drug-delivery system based on the toxicity assessment in animals. Previous studies have found that common nanoparticles can be toxic to the cornea, conjunctiva, and retina under certain conditions. Because of the species differences between humans and animals, advanced in vitro cell culture techniques, such as human organoids, can mimic the human organism to a certain extent, bringing nanoparticle toxicity assessment to a new stage. This review summarizes the advanced application of nanoparticles in ocular drug delivery and the potential toxicity, as well as some of the current challenges and future opportunities in nanotoxicological evaluation.

A novel osmoprotective liposomal formulation from synthetic phospholipids to reduce in vitro hyperosmolar stress in dry eye treatments

Dry eye disease (DED) is a worldwide, multifactorial disease mainly caused by a deficit in tear production or increased tear evaporation with an increase in tear osmolarity and inflammation. This causes discomfort and there is a therapeutic need to restore the homeostasis of the ocular surface. The aim of the present work was to develop a biodegradable and biocompatible liposomal formulation from the synthetic phospholipids 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) that is able to reduce the effects of hypertonic stress by helping to restore the lipid layer of the tear film. Liposomes were made using the lipid film hydration method with synthetic phospholipids (10 mg/mL) with and without 0.2% HPMC. They were characterised in terms of size, osmolarity, pH, surface tension, and viscosity. Additionally, the in vitro toxicity of the formulation at 1 and 4 h in human corneal epithelial cells (hTERT-HCECs) and human conjunctival cells (IM-HConEpiC) was determined. Furthermore, osmoprotective activity was tested in a corneal model of hyperosmolar stress. In vivo acute tolerance testing was also carried out in albino New Zealand rabbits by topical application of the ophthalmic formulations every 30 min for 6 h. All the assayed formulations showed suitable physicochemical characteristics for ocular surface administration. The liposomal formulations were well-tolerated in cell cultures and showed osmoprotective activity in a hyperosmolar model. No alterations or discomfort were reported when they were topically administered in rabbits. According to the results, the osmoprotective liposomal formulations developed in this work are promising candidates for the treatment of DED.

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.

Ocular Effects of Glycyrrhizin at Acidic and Neutral pH

Purpose

To test the effects of acidic vs. neutral pH glycyrrhizin (GLY) on the unwounded and wounded normal mouse cornea and after infection with Pseudomonas aeruginosa isolates KEI 1025 and multidrug-resistant MDR9.

Methods

Acidic or neutral GLY vs. phosphate-buffered saline (PBS) was topically applied to normal or wounded corneas of C57BL/6 mice. In unwounded corneas, goblet cells and corneal nerves were stained and quantitated. After wounding, corneas were fluorescein stained and photographed using a slit lamp. Mice also were infected with KEI 1025 or MDR9 and the protective effects of GLY pH evaluated comparatively.

Results

In the unwounded cornea, application of acidic or neutral GLY vs. PBS reduced the number of bulbar conjunctival goblet cells but did not alter corneal nerve density. Similar application of GLY to scarified corneas delayed wound closure. After KEI 1025 infection, none of the GLY vs. PBS-treated corneas perforated; GLY treatment also decreased plate count (neutral pH more effective) and reduced MPO and several cytokines. Similarly, for MDR9, GLY at either pH was protective and also enhanced the effects of moxifloxacin to which MDR9 is resistant.

Conclusion

Acidic or neutral pH GLY decreased goblet cell number but had no effect on nerve density. After corneal wounding, GLY at either pH (1) delayed wound closure and, (2) after infection, decreased keratitis when used alone or in combination with moxifloxacin. Neutral pH did not alter the therapeutic effect of GLY and would be preferred if used clinically.

Micelles based on polyvinylpyrrolidone VA64: A potential nanoplatform for the ocular delivery of apocynin

Purpose of this work was to determine the feasibility of a nano-ophthalmic solution consisting of the nanocarrier polyvinylpyrrolidone VA64 (VA64) and encapsulated apocynin (APO) as treatment for ocular inflammatory diseases. Results showed the solution, termed APO-VA64 ophthalmic solution, could be fabricated via a simple process. This solution was clear, colorless, and possessed valuable characteristics, such as small micelle size (14.12 ± 1.24 nm), narrow micelle size distribution, and high APO encapsulation efficiency. Encapsulated APO was also found to have high aqueous solubility and in vitro release and antioxidant activities. APO-VA64 ophthalmic solution showed good ocular tolerance and demonstrated improved corneal permeation ability in mouse eyes. In an in vivo mice model, topically administered APO-VA64 ophthalmic solution was found to be significantly more effective against benzalkonium chloride-induced ocular damage than APO, VA64, and a mix of APO and VA64. Blockage of high mobility group box 1 signaling and its related proinflammatory cytokines were involved in this therapeutic effect. In conclusion, these in vitro and in vivo findings demonstrate that VA64 micelles are a potential nanoplatform for ocular drug delivery, and that the nanoformulation APO-VA64 ophthalmic solution may be a promising candidate for the efficacious treatment of ocular inflammatory diseases.

A nano-phytochemical ophthalmic solution for marked improvement of corneal wound healing in healthy or diabetic mice

Aim: To formulate a novel nano-phytochemical ophthalmic solution to promote corneal wound healing. Methods: Dipotassium glycyrrhizinate (DG) and palmatine (PAL) were used to formulate this formulation marked as DG-PAL, and its efficacy and mechanisms for promoting corneal wound healing were evaluated in mice. Results: DG-PAL was easily fabricated with excellent physical profiles. In in vivo efficiency evaluations, DG-PAL demonstrated an excellent promoting effect on corneal epithelial/nerve wound healing in both healthy and diabetic mice. These effects were involved in the DG-PAL-induced decreased expression levels of HMGB1 and its signaling-related factors in the corneas and trigeminal neurons of the healthy or diabetic mice. Conclusion: DG-PAL possibly represents a promising ophthalmic solution for promoting corneal wound healing.

Strengthened rebamipide ocular nanoformulation to effectively treat corneal alkali burns in mice through the HMGB1 signaling pathway

Corneal alkali burns are a major ophthalmic emergency, as current therapeutic treatments are limited. Novel treatment targets and new potential agents are required to combat this severe ocular injury. Glycyrrhizin and rebamipide (RBM) are both FDA-approved drugs with potential effects against corneal alkali burns, but RBM is limited by its low aqueous solubility and low bioavailability. This study aimed to utilize dipotassium glycyrrhizinate (DG, a dipotassium salt of glycyrrhizin) as a nanocarrier encapsulating RBM to formulate an ophthalmic solution (marked DG-RBM) with strengthened activities to treat corneal alkali burns. Results showed that an easy DG-RBM preparative process generated particles with high encapsulation efficacy and ultra-small micellar size. The solubility of RBM in DG-RBM in aqueous solution was 3.1 × 10⁵-fold enhanced than its free solution. DG-RBM exhibited excellent storage stability. In vitro cytotoxicity, ex vivo conjunctival responses, and rabbit eye tolerance tests showed that DG-RBM possessed good ocular safety profiles. DG-RBM exhibited improved in vivo corneal permeation profiles and demonstrated a strong effect against H₂O₂-induced oxidative damage, with a significant effect on promoting epithelial wound healing in corneal cells in vitro. As expected, in a mouse model of corneal alkali burns, the topical administration of DG-RBM achieved a strengthened efficacy against alkali burn damages. The mechanism of this therapeutic effect involved regulating high-mobility group box 1 (HMGB1) signaling and its related angiogenic and proinflammatory cytokines. These findings demonstrate the ease of preparing DG-RBM and its great potential as a novel ocular topical formulation to treat corneal alkali burns by regulating HMGB1 signaling.

Recent advances in ophthalmic preparations: Ocular barriers, dosage forms and routes of administration

The human eye is a complex organ with unique anatomy and physiology that restricts the delivery of drugs to target ocular tissues/sites. Recent advances in the field of pharmacy, biotechnology and material science have led to development of novel ophthalmic dosage forms which can provide sustained drug delivery, reduce dosing frequency and improve the ocular bioavailability of drugs. This review highlights the different anatomical and physiological factors which affect ocular bioavailability of drugs and explores advancements from 2016 to 2020 in various ophthalmic preparations. Different routes of drug administration such as topical, intravitreal, intraocular, juxtascleral, subconjunctival, intracameral and retrobulbar are discussed with their advances and limitations.