Therapeutic nanoemulsions in ophthalmic drug administration: Concept in formulations and characterization techniques for ocular drug delivery

Development and evaluation of methotrexate-loaded nanoemulsion formulation for topical treatment of psoriasis

Psoriasis is a chronic inflammatory disease that is becoming widespread and is associated with many kinds of additional severe diseases. The present study aimed to develop a methotrexate-loaded almond oil-based nanoemulsion formulation (MTX NE) for topical administration. The drug-loaded nanoemulsion formulation was prepared by high shear homogenization technique. The formulation's stability, as well as other physical and chemical characteristics, including entrapment effectiveness, drug release kinetics, skin permeability, skin irritation, and in vivo evaluation of the optimized formulation, was assessed. Additionally, imiquimod-induced psoriasis in rats was employed to investigate the efficacy of MTX NE against skin disorders. The MTX NE formulation was developed with a particle size of 18.74 ± 9.748 nm, a polydispersity index (PDI) of 0.198 ± 0.01, and an average entrapment efficiency of 79.65 ± 3.84%. The release kinetics model estimates 81.08% drug release at pH 5.5 after 24 h. The major layers of the skin, the epidermis, and dermis were successfully fluidized by the optimized MTX NE formulation, as shown by FTIR results, most likely enhancing drug retention and permeability. However, since Tween 80 and PEG 400 are well-known penetration enhancers, their application greatly accelerates these effects. Permeation data indicate that after 24 h, methotrexate was released from the nano-emulsion at 76.83 ± 4.98 g/cm2 with a flux rate of 2.385 ± 0.61 µg/cm2/h. The in vivo study conducted on rabbit skin showed that the enhanced skin penetration of the prepared MTX-loaded nanoemulsion formulation does not cause any structural modifications in the inter-cellular lipid layers of the stratum corneum. Rabbits used in the in vivo anti-psoriatic investigation demonstrated that MTX NE produced a 95% reduction in PASI. The pharmacokinetic profile revealed that the Cmax, Tmax, and t1/2 values were 8.63 µg/mL, 12.5 h, and 17.77 ± 2.21 h, respectively. These findings suggest that the formulation MTX NE is effective in treating psoriasis and may reduce psoriasis symptoms.

Applying Different Conditions in the OphthalMimic Device Using Polymeric and Hydrogel-Based Hybrid Membranes to Evaluate Gels and Nanostructured Ophthalmic Formulations

The OphthalMimic is a 3D-printed device that simulates human ocular conditions with artificial lacrimal flow, cul-de-sac area, moving eyelid, and a surface to interact with ophthalmic formulations. All tests with such a device have used a continuous artificial tear flow rate of 1 mL/min for 5 min. Here, we implemented protocol variations regarding the application time and simulated tear flow to increase the test's discrimination and achieve reliable performance results. The new protocols incorporated the previously evaluated 0.2% fluconazole formulations containing or not chitosan as a mucoadhesive component (PLX16CS10 and PLX16, respectively) and novel moxifloxacin 5% formulations, either in a conventional formulation and a microemulsion (CONTROL and NEMOX, respectively). The flow rate was reduced by 50%, and a pre-flow application period was also included to allow formulation interaction with the membrane. The OphthalMimic model was used with both polymeric and hydrogel-based hybrid membranes, including a simulated eyelid. Lowering the flow made it feasible to prolong the testing duration, enhancing device discrimination potential. The hydrogel membrane was adequate for testing nanostructure formulations. The OphthalMimic device demonstrated once again to be a versatile method for evaluating the performance of ophthalmic drug formulations with the potential of reducing the use of animals for experimentation.

Biodegradable microspheres come into sight: A promising biomaterial for delivering drug to the posterior segment of the eyeball

Posterior segment disease acts as a major cause of irreversible visual impairments. Successful treatment of posterior segment disease requires the efficient delivery of therapeutic substances to the targeted lesion. However, the complex ocular architecture makes the bioavailability of topically applied drugs extremely low. Invasive delivery approaches like intravitreal injection may cause adverse complications. To enhance the efficiency, several biomedical engineering systems have been developed to increase the penetration efficiency and improve the bioavailability of drugs at the posterior segments. Advantageously, biodegradable microspheres are found to deliver the therapeutic agents in a controlled fashion. The microspheres prepared from novel biomaterials can realize the prolonged release at the posterior segment with minimum side effects. Moreover, it will be degraded automatically into products that are non-toxic to the human body without the necessity of secondary operation to remove the residual polymer matrix. Additionally, biodegradable microspheres have decent thermoplasticity, adjustable hydrophilicity, controlled crystallinity, and high tensile strength, which make them suitable for intraocular delivery. In this review, we introduce the latest advancements in microsphere production technology and elaborate on the biomaterials that are used to prepare microspheres. We discuss systematically the pharmacological characteristics of biodegradable microspheres and compare their potential advantages and limitations in the treatment of posterior segment diseases. These findings would enrich our knowledge of biodegradable microspheres and cast light into the discovery of effective biomaterials for ocular drug delivery.

Advances on Delivery System of Active Ingredients of Dried Toad Skin and Toad Venom

Dried toad skin (TS) and toad venom (TV) are the dried skin of the Bufo bufo gargarizans Cantor and the Bufo melanostictus Schneider, which remove the internal organs and the white secretions of the skin and retroauricular glands. Since 2005, cinobufacini preparations have been approved by the State Food and Drug Administration for use as adjuvant therapies in the treatment of various advanced cancers. Meanwhile, bufalenolides has been identified as the main component of TS/TV, exhibiting antitumor activity, inducing apoptosis of cancer cells and inhibiting cancer cell proliferation or metastasis through a variety of signaling pathways. However, clinical agents frequently face limitations such as inherent toxicity at high concentrations and insufficient tumor targeting. Additionally, the development and utilization of these active ingredients are hindered by poor water solubility, low bioavailability, and rapid clearance from the bloodstream. To address these challenges, the design of a targeted drug delivery system (TDDS) aims to enhance drug bioavailability, improve targeting within the body, increase drug efficacy, and reduce adverse reactions. This article reviews the TDDS for TS/TV, and their active components, including passive, active, and stimuli-responsive TDDS, to provide a reference for advancing their clinical development and use.

A review on revolutionizing ophthalmic therapy: Unveiling the potential of chitosan, hyaluronic acid, cellulose, cyclodextrin, and poloxamer in eye disease treatments

Ocular disorders, encompassing both common ailments like dry eye syndrome and more severe situations for instance age-related macular degeneration, present significant challenges to effective treatment due to the intricate architecture and physiological barriers of the eye. Polysaccharides are emerging as potential solutions for drug delivery to the eyes due to their compatibility with living organisms, natural biodegradability, and adhesive properties. In this review, we explore not only the recent advancements in polysaccharide-based technologies and their transformative potential in treating ocular illnesses, offering renewed optimism for both patients and professionals but also anatomy of the eye and the significant obstacles hindering drug transportation, followed by an investigation into various drug administration methods and their ability to overcome ocular-specific challenges. Our focus lies on biological adhesive polymers, including chitosan, hyaluronic acid, cellulose, cyclodextrin, and poloxamer, known for their adhesive characteristics enhancing drug retention on ocular surfaces and increasing bioavailability. A detailed analysis of material designs used in ophthalmic formulations, such as gels, lenses, eye drops, nanofibers, microneedles, microspheres, and nanoparticles, their advantages and limitations, the potential of formulations in improving therapeutic outcomes for various eye conditions. Moreover, we underscore the discovery of novel polysaccharides and their potential uses in ocular drug delivery.

Development of ophthalmic nanoemulsions of β-caryophyllene for the treatment of Acanthamoeba keratitis

Although rare, amoebic keratitis (AK) is a disease caused by Acanthamoeba spp. that can lead to blindness. The drugs currently available for its treatment are very toxic, which has motivated the investigation for more effective and safe therapeutic options. In this study, the in vitro activity of ß-caryophyllene (BCP) was exploited taking into account its action against other protozoans as well as its well-known healing and anti-inflammatory properties (aspects relevant for the AK pathogenesis). On the other hand, high volatilization and oxidation phenomena are found for this compound, which led to its incorporation into nanoemulsions (NEs). Two emulsifying agents were tested, resulting in monodisperse systems with reduced droplet size (<265 nm) and high surface charge (positive and negative for NEs prepared with cetrimonium bromide -CTAB and Phosal® 50+, respectively). NEs prepared with CTAB were shown to be more stable after long-term storage at 4 and 25 °C than those prepared with Phosal®. Pure BCP, at the highest concentration (500 µM), resulted in a level of inhibition of Acanthamoeba trophozoites equivalent to that of reference drug (chlorhexidine). This activity was even greater after oil nanoencapsulation. The reduced droplet size could improve the interaction of the oil with the microorganism, justifying this finding. Changes in surface charge did not impact the activity. Positively charged NEs improved the interaction and retention of BCP in the cornea and thus should be prioritized for further studies.

Advancing ophthalmic delivery of flurbiprofen via synergistic chiral resolution and ion-pairing strategies

Flurbiprofen (FB), a nonsteroidal anti-inflammatory drug, is widely employed in treating ocular inflammation owing to its remarkable anti-inflammatory effects. However, the racemic nature of its commercially available formulation (Ocufen®) limits the full potential of its therapeutic activity, as the (S)-enantiomer is responsible for the desired anti-inflammatory effects. Additionally, the limited corneal permeability of FB significantly restricts its bioavailability. In this study, we successfully separated the chiral isomers of FB to obtain the highly active (S)-FB. Subsequently, utilizing ion-pairing technology, we coupled (S)-FB with various counter-ions, such as sodium, diethylamine, trimethamine (TMA), and l-arginine, to enhance its ocular bioavailability. A comprehensive evaluation encompassed balanced solubility, octanol-water partition coefficient, corneal permeability, ocular pharmacokinetics, tissue distribution, and in vivo ocular anti-inflammatory activity of each chiral isomer salt. Among the various formulations, S-FBTMA exhibited superior water solubility (about 1-12 mg/ml), lipid solubility (1< lg Pow < 3) and corneal permeability. In comparison to Ocufen®, S-FBTMA demonstrated significantly higher in vivo anti-inflammatory activity and lower ocular irritability (such as conjunctival congestion and tingling). The findings from this research highlight the potential of chiral separation and ion-pair enhanced permeation techniques in providing pharmaceutical enterprises focused on drug development with a valuable avenue for improving therapeutic outcomes.

Silk Fibroin Formed Bioadhesive Ophthalmic Gel for Dry Eye Syndrome Treatment

PURPOSE

Dry eye syndrome (DES), arising from various etiologic factors, leads to tear film instability and ocular surface damage. Given its anti-inflammatory effects, cyclosporine A (CsA) has been widely used as a short-term treatment option for DES. However, poor bioavailability and solubility of CsA in aqueous phase make the development of a cyclosporine A-based eye drop for ocular topical application a huge challenge.

METHODS

In this study, a novel strategy for preparing cyclosporine A-loaded silk fibroin nanoemulsion gel (CsA NBGs) was proposed to address these barriers. Additionally, the rheological properties, ocular irritation potential, tear elimination kinetics, and pharmacodynamics based on a rabbit dry eye model were investigated for the prepared CsA NBGs. Furthermore, the transcorneal mechanism across the ocular barrier was also investigated.

RESULTS

The pharmacodynamics and pharmacokinetics of CsA NBGs exhibited superior performance compared to cyclosporine eye drops, leading to a significant enhancement in the bioavailability of CsA NBGs. Furthermore, our investigation into the transcorneal mechanism of CsA NBGs revealed their ability to be absorbed by corneal epithelial cells via the paracellular pathway.

CONCLUSION

The CsA NBG formulation exhibits promising potential for intraocular drug delivery, enabling safe, effective, and controlled administration of hydrophobic drugs into the eye. Moreover, it enhances drug retention within the ocular tissues and improves systemic bioavailability, thereby demonstrating significant clinical translational prospects.

OCTN2- and ATB0,+-targeted nanoemulsions for improving ocular drug delivery

Traditional eye drops are administered via topical instillation. However, frequent dosing is needed due to their relatively rapid precorneal removal and low ocular bioavailability. To address these issues, stearoyl L-carnitine-modified nanoemulsions (SC-NEs) were fabricated. The physicochemical properties of SC-NEs in terms of size, morphology, zeta potential, encapsulation efficiency, and in vitro drug release behavior were characterized. The cellular uptake and mechanisms of SC-NEs were comprehensively studied in human corneal epithelial cells and the stearoyl L-carnitine ratio in SC-NEs was optimized. The optimized SC-NEs could target the novel organic cation/carnitine transporter 2 (OCTN2) and amino acid transporter B (0 +) (ATB0,+) on the corneal epithelium, which led to superior corneal permeation, ocular surface retention ability, ocular bioavailability. Furthermore, SC-NEs showed excellent in vivo anti-inflammatory efficacy in a rabbit model of endotoxin-induced uveitis. The ocular safety test indicated that the SC-NEs were biocompatible. In general, the current study demonstrated that OCTN2 and ATB0,+-targeted nanoemulsions were promising ophthalmologic drug delivery systems that can improve ocular drug bioavailability and boost the therapeutic effects of drugs for eye diseases.

Recent advances in the treatment and delivery system of diabetic retinopathy

Diabetic retinopathy (DR) is a highly tissue-specific neurovascular complication of type 1 and type 2 diabetes mellitus and is among the leading causes of blindness worldwide. Pathophysiological changes in DR encompass neurodegeneration, inflammation, and oxidative stress. Current treatments for DR, including anti-vascular endothelial growth factor, steroids, laser photocoagulation, and vitrectomy have limitations and adverse reactions, necessitating the exploration of novel treatment strategies. This review aims to summarize the current pathophysiology, therapeutic approaches, and available drug-delivery methods for treating DR, and discuss their respective development potentials. Recent research indicates the efficacy of novel receptor inhibitors and agonists, such as aldose reductase inhibitors, angiotensin-converting enzyme inhibitors, peroxisome proliferator-activated receptor alpha agonists, and novel drugs in delaying DR. Furthermore, with continuous advancements in nanotechnology, a new form of drug delivery has been developed that can address certain limitations of clinical drug therapy, such as low solubility and poor penetration. This review serves as a theoretical foundation for future research on DR treatment. While highlighting promising therapeutic targets, it underscores the need for continuous exploration to enhance our understanding of DR pathogenesis. The limitations of current treatments and the potential for future advancements emphasize the importance of ongoing research in this field.

Recent advances in nanocrystal-based technologies applied for ocular drug delivery

INTRODUCTION

The intricate physiological barriers of the eye and the limited volume of eye drops impede efficient delivery of poorly water-soluble drugs. In the last decade, nanocrystals have emerged as versatile drug delivery systems in various administration routes from bench to bedside. The unique superiorities of nanocrystals, mainly embodied in high drug-loading capacity, good mucosal adhesion and penetration, and greatly improved drug solubility, reveal a promising prospect for ocular delivery of poorly water-soluble drugs.

AREAS COVERED

This article focuses on the ophthalmic nanocrystal technologies and products that are in the literature, clinical trials, and even on the market. The recent research progress in the preparation, ocular application, and absorption of nanocrystals are highlighted, and the pros and cons of nanocrystals in overcoming the physiological barriers of the eye are also summarized.

EXPERT OPINION

Nanocrystals have demonstrated success as glucocorticoid eye drops in the treatment of anterior segment diseases. However, the thermodynamic stability of nanocrystals remains the major challenge in product development. New technologies for efficiently optimizing stabilizers and sterilization processes are still expected. Strategies to confer more diverse functions via surface modification are also worth exploration to improve the potential of nanocrystals in delivering poorly water-soluble drugs to posterior segment of the eye.

Ophthalmic wild olive (ACEBUCHE) oil nanoemulsions exert oculoprotective effects against oxidative stress induced by arterial hypertension

Oxidative stress plays a key role in several systemic and ocular diseases, including hypertensive eye diseases. In this context, we previously showed that oral administration of wild olive (acebuche, ACE) oil from Olea europaea var. sylvestris can counteract ocular damage secondary to arterial hypertension by modulating excess reactive oxygen species (ROS) produced by the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Therefore, this work describes the development of an ACE oil-based formulation for ocular administration as a local therapy to counteract hypertension-related oxidative damage. Specifically, ACE oil nanoemulsions (NEs) were successfully produced and characterized, exhibiting appropriate features for ophthalmic administration, including a nanometer size (<200 nm), moderate negative ZP, adequate osmolality and pH, and colloidal stability in biorelevant fluids. Likewise, the NEs presented a shear thinning behavior, especially convenient for ocular instillation. In vivo evaluation was performed through either intravitreal injection or topical ophthalmic administration in mice with hypertension induced via administration of Nω-nitro-L-arginine-methyl-ester (L-NAME). Both routes of administration reduced hypertensive morphological alterations and demonstrated a noticeable antioxidant effect thanks to the reduction of the activity/expression of NADPH oxidase in cornea and retina. Thus, an ACE oil ophthalmic formulation represent a promising therapy for ocular pathologies associated with arterial hypertension.

The Effect of High-Pressure Homogenization Conditions on the Physicochemical Properties and Stability of Designed Fluconazole-Loaded Ocular Nanoemulsions

The growing interest in high-energy emulsification is a result of its scalability, which is important from an industrial perspective and allows for a more reproducible and efficient production of pharmaceutical formulations. The aim of this study was to evaluate the effect of composition, mainly a fixed surfactant/cosurfactant (Smix) ratio, their concentration, and the parameters of high-pressure homogenization (HPH) processing on the quality and stability of ophthalmic fluconazole-loaded nanoemulsions. After a physicochemical analysis of nanoemulsions containing 20% w/w of oil, as optimal conditions for the HPH process, three cycles at a pressure of 1000 bar were established, obtaining formulations with an average droplet diameter size in the range of 80.63-129.68 nm and PDI values below 0.25. While it was expected that an increasing cosurfactant concentration decreased the droplet size, in the case of formulations containing Tween 20 and 10% w/w of cosurfactants, "over-processing" was observed, identified by the droplet size and polydispersity index increase. Consecutively, the selected formulations were evaluated for in vitro drug release in Franz's cell, antifungal activity, and 30-day stability using NMR spectroscopy. An antifungal activity test showed no significant difference in the antifungal activity between optimal fluconazole-loaded nanoemulsions and a 0.3% aqueous drug solution, but previously, research showed that prepared formulations were characterized by a higher viscosity and satisfactory prolonged release compared to a control. In a 30-day stability study, it was observed that higher HLB values of the used surfactants decreased the stability of the formulations in the following order: Kolliphor EL, Tween 80, Tween 20. The NMR spectra confirmed that Kolliphor EL-based formulations ensured the higher stability of the nanoemulsion composition in comparison to Tween 80 and a better stabilizing effect of propylene glycol as a cosurfactant in comparison to PEG 200. Therefore, the optimization of HPH technology should be focused on the selection of Smix and the Smix:oil ratio in order to prepare stable formulations of high quality.

PLGA Nanoparticles Containing Natural Flavanones for Ocular Inflammation

Flavanones are natural compounds that display anti-inflammatory activity. The aim of this work was to prepare PLGA nanoparticles (NPs) containing natural flavanones I ((2S)-5,7-dihydroxy-6-methyl-8-(3-methyl-2-buten-1-il)-2-phenyl-2,3-dihydro-4H-1-Benzopyran-4-one) and II (2S)-5,7-dihydroxy-2-(4'-methoxyphenyl)-6-methyl-8-(3-methyl-2-buten-1-yl)-2,3-dihydro-4H-1-Benzopyran-4-one) (NP I and NP II, respectively) so as to evaluate their potential for topical anti-inflammatory ocular therapy. An in silico study was carried out using the Molinspiration® and PASS Online web platforms before evaluating the in vitro release study and the ex vivo porcine cornea and sclera permeation. The HPLC analytical method was also established and validated. Finally, the in vitro anti-inflammatory efficacy of NPs was studied in the HCE-2 model. The flavanones I and II could be released following a kinetic hyperbolic model. Neither of the two NPs was able to permeate through the tissues. NP I and NP II were found to be respectful of any changes in the tissues' morphology, as evidenced by histological studies. In HCE-2 cells, NP I and NP II were not cytotoxic at concentrations up to 25 µM. NP I showed higher anti-inflammatory activity than NP II, being able to significantly reduce IL-8 production in LPS-treated HCE-2 cells. In summary, ocular treatment with NP I and NP II could be used as a promising therapy for the inhibition of ocular inflammation.

[Topical treatment for age-related macular degeneration: Where are we now?]

The therapeutic management of age-related macular degeneration (AMD) is a major public health issue. One of its two late forms, neovascular AMD, is currently treated by intravitreal injections of pharmaceutical active ingredients. Although it is very effective in treating pathologies of the posterior segment of the eye, the intravitreal route is not an ideal option for the long-term management of a chronic disease such as AMD. Indeed, in the literature, some authors even call it a "burden" for the practitioners, the patients and the healthcare system. Thus, consideration should be given to less invasive routes. Among the possible administration routes to reach the posterior segment of the eye, the most suitable for the patient with the least risk of systemic adverse effects is the topical route. Several research teams have attempted to formulate molecules for topical administration in the treatment of atrophic or neovascular AMD. In this review, we emphasize the importance of the pharmaceutical formulation to meet the challenge of targeting the posterior segment of the eye by a topical route.

Tacrolimus-Loaded Cationic Nanoemulsion In-Situ Gel System: In-Vitro Characterization and Performance in a Dry-Eye Rabbit Model

Dry eye disease (DED) is a highly prevalent ocular surface disease that affects life quality and reduces productivity at work. The purpose of this study is to improve the efficacy of tacrolimus (FK506) in the treatment of DED using the special eye surface retention properties of cationic nanoemulsion (CNE) modified by thermosensitive in-situ gel (ISG) (CNE-ISG). The precorneal retention of CNE-ISG containing 0.05% FK506 (50 min) was longer than that of CNE containing 0.05% FK506 (25 min) and commercial suspension containing 0.1% FK506 (Talymus®) (10 min). Successfully modeled dry-eye rabbits were treated with 0.05% CNE-ISG (twice/day), 0.05% CNE and 0.1% suspension (Talymus®) (thrice/day). Schirmer's tear secretion test showed no significant difference between the CNE-ISG group and the healthy group after 5 days of treatment (p > 0.05). The results of a tear ferning test (TFT) showed that the tear-fern-like crystal branches in the CNE-ISG group returned to normal after 5 days of treatment. Histological analysis showed that the number of goblet cells in the CNE-ISG group significantly increased. HET-CAM stimulation test showed that the CNE-ISG group had no ocular irritation. The above results indicated that CNE-ISG might be a promising delivery system and as an effective dosage form was employed for FK506 in the treatment of DED.

Overview of Recent Advances in Nano-Based Ocular Drug Delivery

Ocular diseases profoundly impact patients' vision and overall quality of life globally. However, effective ocular drug delivery presents formidable challenges within clinical pharmacology and biomaterial science, primarily due to the intricate anatomical and physiological barriers unique to the eye. In this comprehensive review, we aim to shed light on the anatomical and physiological features of the eye, emphasizing the natural barriers it presents to drug administration. Our goal is to provide a thorough overview of various characteristics inherent to each nano-based drug delivery system. These encompass nanomicelles, nanoparticles, nanosuspensions, nanoemulsions, microemulsions, nanofibers, dendrimers, liposomes, niosomes, nanowafers, contact lenses, hydrogels, microneedles, and innovative gene therapy approaches employing nano-based ocular delivery techniques. We delve into the biology and methodology of these systems, introducing their clinical applications over the past decade. Furthermore, we discuss the advantages and challenges illuminated by recent studies. While nano-based drug delivery systems for ophthalmic formulations are gaining increasing attention, further research is imperative to address potential safety and toxicity concerns.

An insight on ophthalmic drug delivery systems: Focus on polymeric biomaterials-based carriers

Presently, different types of eye diseases, such as glaucoma, myopia, infection, and dry eyes are treated with topical eye drops. However, due to ocular surface barriers, eye drops require multiple administrations, which may cause several risks, thereby necessitating additional strategies. Some of the key characteristics of an ideal ocular drug delivery system are as follows: (a) good penetration into cornea, (b) high drug retention in the ocular tissues, (c) targetability to the desired regions of the eye, and (d) good bioavailability. It is worthy to note that the corneal epithelial tight junctions hinder the permeation of therapeutics through the cornea. Therefore, it is necessary to design nanocarriers that can overcome these barriers and enhance drug penetration into the inner parts of the eye. Moreover, intelligent multifunctional nanocarriers can be designed to include cavities, which may help encapsulate sufficient amount of the drug. In addition, nanocarriers can be modified with the targeting moieties. Different types of nanocarriers have been developed for ocular drug delivery applications, including emulsions, liposomes, micelles, and nanoparticles. However, these formulations may be rapidly cleared from the eye. The therapeutic use of the nanoparticles (NPs) is also hindered by the non-specific adsorption of proteins on NPs, which may limit their interaction with the cellular moieties or other targeted biological factors. Functional drug delivery systems (DDS), which can offer targeted ocular drug delivery while avoiding the non-specific protein adsorption could exhibit great potential. This could be further realized by the on-demand DDS, which can respond to the stimuli in a spatio-temporal fashion. The cell-mediated DDS offer another valuable platform for ophthalmological drug delivery.

Gatifloxacin Loaded Nano Lipid Carriers for the Management of Bacterial Conjunctivitis

Bacterial conjunctivitis (BC) entails inflammation of the ocular mucous membrane. Early effective treatment of BC can prevent the spread of the infection to the intraocular tissues, which could lead to bacterial endophthalmitis or serious visual disability. In 2003, gatifloxacin (GTX) eyedrops were introduced as a new broad-spectrum fluoroquinolone to treat BC. Subsequently, GTX use was extended to other ocular bacterial infections. However, due to precorneal loss and poor ocular bioavailability, frequent administration of the commercial eyedrops is necessary, leading to poor patient compliance. Thus, the goal of the current investigation was to formulate GTX in a lipid-based drug delivery system to overcome the challenges with the existing marketed eyedrops and, thus, improve the management of bacterial conjunctivitis. GTX-NLCs and SLNs were formulated with a hot homogenization-probe sonication method. The lead GTX-NLC formulation was characterized and assessed for in vitro drug release, antimicrobial efficacy (against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa), and ex vivo permeation. The lead formulation exhibited desired physicochemical characteristics, an extended release of GTX over a 12 h period, and was stable over three months at the three storage conditions (refrigerated, room temperature, and accelerated). The transcorneal flux and permeability of GTX from the GTX-NLC formulation were 5.5- and 6.0-fold higher in comparison to the commercial eyedrops and exhibited a similar in vitro antibacterial activity. Therefore, GTX-NLCs could serve as an alternative drug delivery platform to improve treatment outcomes in BC.

Fabrication and Biological Activities of All-in-One Composite Nanoemulsion Based on Blumea balsamifera Oil-Tea Tree Oil

Nanoemulsion is a new multi-component drug delivery system; the selection of different oil phases can give it special physiological activity, and play the role of "medicine and pharmaceutical excipients all-in-one". In this paper, we used glycyrrhizic acid as the natural surfactant, and Blumea balsamifera oil (BB) and tea tree oil (TTO) as the mixed oil phase, to obtain a new green functional composite nanoemulsion. Using the average particle size and polydispersion index (PDI) as the evaluation criteria, the effects of the oil ratio, oil content, glycyrrhizic acid concentration, and ultrasonic time on the nanoemulsion were systematically investigated. The stability and physicochemical properties and biological activities of BB-TTO NEs prepared via the optimum formulation were characterized. The optimal prescription was BB: TTO = 1:1, 5% oil phase, 0.7% glycyrrhizic acid, and 5 min ultrasonication time. The mean particle size, PDI, and zeta potential were 160.01 nm, 0.125, and -50.94 mV, respectively. The nanoemulsion showed non-significant changes in stability after centrifugation, dilution, and 120 days storage. These nanoemulsions were found to exhibit potential antibacterial and anti-inflammatory activities. The minimal inhibitory concentration (MIC) of BB-TTO NEs against Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa is 2975 μg/mL, 2975 μg/mL, and 5950 μg/mL, respectively. A lower level of inflammatory cell infiltration and proportion of fibrosis were found in the synovial tissue of AIA rats treated with BB-TTO NEs. These findings demonstrate that the BB-TTO NEs produced in this study have significant potential for usage in antibacterial and anti-inflammatory areas.

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.

Carbohydrate polymer-based bioadhesive formulations and their potentials for the treatment of ocular diseases: A review

Eyes are directly exposed to the outer environment and susceptible to infections, leading to various ocular disorders. Local medication is preferred to treat eye diseases due to its convenience and compliance. However, the rapid clearance of the local formulations highly limits the therapeutic efficacy. In the past decades, several carbohydrate bioadhesive polymers (CBPs), such as chitosan and hyaluronic acid, have been used in ophthalmology for sustained ocular drug delivery. These CBP-based delivery systems have improved the treatment of ocular diseases to a large extent but also caused some undesired effects. Herein, we aim to summarize the applications of some typical CBPs (including chitosan, hyaluronic acid, cellulose, cyclodextrin, alginate and pectin) in treating ocular diseases from the general view of ocular physiology, pathophysiology and drug delivery, and to provide a comprehensive understanding of the design of the CBP-based formulations for ocular use. The patents and clinical trials of CBPs for ocular management are also discussed. In addition, a discussion on the concerns of CBPs in clinical use and the possible solutions is presented.

Cannabinoid-Based Ocular Therapies and Formulations

The interest in the pharmacological applications of cannabinoids is largely increasing in a wide range of medical areas. Recently, research on its potential role in eye conditions, many of which are chronic and/or disabling and in need of new alternative treatments, has intensified. However, due to cannabinoids’ unfavorable physicochemical properties and adverse systemic effects, along with ocular biological barriers to local drug administration, drug delivery systems are needed. Hence, this review focused on the following: (i) identifying eye disease conditions potentially subject to treatment with cannabinoids and their pharmacological role, with emphasis on glaucoma, uveitis, diabetic retinopathy, keratitis and the prevention of Pseudomonas aeruginosa infections; (ii) reviewing the physicochemical properties of formulations that must be controlled and/or optimized for successful ocular administration; (iii) analyzing works evaluating cannabinoid-based formulations for ocular administration, with emphasis on results and limitations; and (iv) identifying alternative cannabinoid-based formulations that could potentially be useful for ocular administration strategies. Finally, an overview of the current advances and limitations in the field, the technological challenges to overcome and the prospective further developments, is provided.

Pre-clinical safety of topically administered sunitinib-loaded lipid and polymeric nanocarriers targeting corneal neovascularization

Three different types of sunitinib-loaded (SUN-loaded) nanocarriers were compared, aiming at the topical treatment of corneal neovascularization (CNV): polymeric nanospheres (NS), liposomes (LIP), and solid lipid nanoparticles (SLN). Three out of eleven formulations prepared for an optimization study - the best SUN-loaded nanocarrier of each assessed type (NS, LIP, and SLN) - were selected, based on their size, polydispersity index (PdI), drug load (DL), and encapsulation efficiency (EE). These three optimal formulations were further characterized by nanoparticle tracking analysis (NTA), electron paramagnetic resonance (EPR) spectroscopy, and zeta potential. In vitro SUN release profiles were obtained for the optimal formulations, along with ex vivo corneal permeability/retention studies, and ocular tolerance assays, namely: the bovine corneal opacity and permeability (BCOP) assay, the HET-CAM test (hen's egg test - chorioallantoic membrane), and hemolytic potential (HP) assay. None of the optimal formulations exhibited toxicity or potential for ocular irritation. SLN showed higher surface fluidity, drug release more suitable for topical ocular applications, besides greater SUN corneal retention. Our results suggest that SLN are the best CNV-targeting SUN-loaded nanocarriers for clinical translation when compared to their NS and LIP analogues.

Nanocarriers for the Delivery of Neuroprotective Agents in the Treatment of Ocular Neurodegenerative Diseases

Retinal neurodegeneration is considered an early event in the pathogenesis of several ocular diseases, such as diabetic retinopathy, age-related macular degeneration, and glaucoma. At present, there is no definitive treatment to prevent the progression or reversal of vision loss caused by photoreceptor degeneration and the death of retinal ganglion cells. Neuroprotective approaches are being developed to increase the life expectancy of neurons by maintaining their shape/function and thus prevent the loss of vision and blindness. A successful neuroprotective approach could prolong patients' vision functioning and quality of life. Conventional pharmaceutical technologies have been investigated for delivering ocular medications; however, the distinctive structural characteristics of the eye and the physiological ocular barriers restrict the efficient delivery of drugs. Recent developments in bio-adhesive in situ gelling systems and nanotechnology-based targeted/sustained drug delivery systems are receiving a lot of attention. This review summarizes the putative mechanism, pharmacokinetics, and mode of administration of neuroprotective drugs used to treat ocular disorders. Additionally, this review focuses on cutting-edge nanocarriers that demonstrated promising results in treating ocular neurodegenerative diseases.

Towards the development of a biorelevant in vitro method for the prediction of nanoemulsion stability on the ocular surface

Ophthalmic oil-in-water nanoemulsions (NEs) are a complex technological platform, representing an advancement in the treatment of dry eye disease. In addition to enabling the incorporation of poorly soluble active pharmaceutical ingredients (APIs), NEs provide prolonged residence time of APIs and other formulation components and consequent replenishment and stabilization of the compromised tear film. Ophthalmic NEs have been on the market for over 20 years, but considering their complexity, as well as the complex nature of the ocular surface, they are still a poorly understood advanced dosage form. The objective of this study was to develop a biorelevant in vitro method that would be able to predict the behavior of ophthalmic NEs after application. With that goal, NE formulations differing in critical material attributes and critical formulation variables were employed and subjected to simulated tear turnover and blinking. By gradually increasing the complexity of the in vitro method, we were able to detect key parameters influencing NE stability. The undertaken study presents a step forward in the development of in vitro tools that are fundamental to the reliable, cost and time-effective development of innovative and generic topical ophthalmic NEs.

Updated insight into the characterization of nano-emulsions

INTRODUCTION

In most of the studies, nano-emulsion characterization is limited to their size distribution and zeta potential. In this review, we present an updated insight of the characterization methods of nano-emulsions, including new or unconventional experimental approaches to explore in depth the nano-emulsion properties.

AREA COVERED

We propose an overview of all the main techniques used to characterize nano-emulsions, including the most classical ones, up to in vitro, ex vivo and in vivo evaluation. Innovative approaches are then presented in the second part of the review that presents innovative, experimental techniques less known in the field of nano-emulsion such as the nanoparticle tracking analysis, small-angle X-ray scattering, Raman spectroscopy, and nuclear magnetic resonance. Finally, in the last part we discuss the use of lipophilic fluorescent probes and imaging techniques as an emerging tool to understand the nano-emulsion droplet stability, surface decoration, release mechanisms, and in vivo fate.

EXPERT OPINION

This review is mostly intended for a broad readership and provides key tools regarding the choice of the approach to characterize nano-emulsions. Innovative and uncommon methods will be precious to disclose the information potentially reachable behind a formulation of nano-emulsions, not always known in first intention and with conventional methods.

Tadalafil Nanoemulsion Mists for Treatment of Pediatric Pulmonary Hypertension via Nebulization

Oral tadalafil (TD) proved promising in treating pediatric pulmonary arterial hypertension (PAH). However, to ensure higher efficacy and reduce the systemic side effects, targeted delivery to the lungs through nebulization was proposed as an alternative approach. This poorly soluble drug was previously dissolved in nanoemulsions (NEs). However, the formulations could not resist aqueous dilution, which precluded its dilution with saline for nebulization. Thus, the current study aimed to modify the previous systems into dilutable TD-NEs and assess their suitability for a pulmonary application. In this regard, screening of various excipients was conducted to optimize the former systems; different formulations were selected and characterized in terms of physicochemical properties, nebulization performance, stability following sterilization, and biocompatibility. Results showed that the optimal system comprised of Capmul-MCM-EP:Labrafac-lipophile (1:1) (w/w) as oil, Labrasol:Poloxamer-407 (2:1) (w/w) as surfactant mixture (S_mix) and water. The optimum formulation P2_TD resisted aqueous dilution, exhibited reasonable drug loading (2.45 mg/mL) and globule size (25.04 nm), acceptable pH and viscosity for pulmonary administration, and could be aerosolized using a jet nebulizer. Moreover, P2_TD demonstrated stability following sterilization and a favorable safety profile confirmed by both in-vitro and in-vivo toxicity studies. These favorable findings make P2_TD promising for the treatment of pediatric PAH.

Preparation and in vitro and in vivo evaluation of an isoliquiritigenin-loaded ophthalmic nanoemulsion for the treatment of corneal neovascularization

Isoliquiritigenin (ISL), as a natural flavonoid, has been proven to have therapeutic potential for corneal neovascularization (CNV) treatment; however, its therapeutic use is restricted due to its poor aqueous solubility and limited bioavailability. To overcome these limitations, a novel ISL-loaded nanoemulsion (ISL-NE) was designed for inhibiting CNV in this study. ISL-NE formulation was composed of propylene glycol dicaprylate (PGD), Cremophor® EL (EL35), polyethylene glycol 400 (PEG 400) and adding water with sodium hyaluronate, its particle size was 34.56 ± 0.80 nm with a low polydispersity index of less than 0.05, which suggested a narrow size distribution. The results demonstrated that ISL-NE released higher and permeated more drug than ISL suspension (ISL-Susp) in in vitro drug release and ex vivo corneal permeation study. ISL-NE showed no cytotoxicity in human corneal epithelial cells toxicity study, which was consistent with the result of ocular irritation study in rabbit eyes. ISL-NE had bioavailability 5.76-fold, 7.80-fold and 2.13-fold higher than ISL-Sups in tears, cornea and aqueous humor after a single dose of ISL-NE, respectively. Furthermore, the efficacy of ISL-NE treatment (0.2% ISL) was comparable to that of dexamethasone treatment (0.025%) in the inhibition of CNV in mice model. Enzyme-linked immunosorbent assay (ELISA) showed that the expressions of corneal vascular endothelial growth factor (VEGF-A) and matrix metalloproteinase (MMP-2) were decreased. In conclusion, the ISL-NE demonstrated excellent physicochemical properties, good tolerance, and enhanced ocular bioavailability. It could be a promising, safe, and effective treatment for CNV.

Cannabidiol Loaded Topical Ophthalmic Nanoemulsion Lowers Intraocular Pressure in Normotensive Dutch-Belted Rabbits

Cannabidiol (CBD) is the major non-psychoactive and most widely studied of the cannabinoid constituents and has great therapeutic potential in a variety of diseases. However, contradictory reports in the literature with respect to CBD's effect on intraocular pressure (IOP) have raised concerns and halted research exploring its use in ocular therapeutics. Therefore, the current investigation aimed to further evaluate CBD's impact on the IOP in the rabbit model. CBD nanoemulsions, containing Carbopol® 940 NF as a mucoadhesive agent (CBD-NEC), were prepared using hot-homogenization followed by probe sonication. The stability of the formulations post-moist-heat sterilization, in terms of physical and chemical characteristics, was studied for three different storage conditions. The effect of the formulation on the intraocular pressure (IOP) profile in normotensive Dutch Belted male rabbits was then examined. The lead CBD-NEC formulation (1% w/v CBD) exhibited a globule size of 259 ± 2.0 nm, 0.27 ± 0.01 PDI, and 23.2 ± 0.4 cP viscosity, and was physically and chemically stable for one month (last time point tested) at 4 °C, 25 °C, and 40 °C. CBD-NEC significantly lowered the IOP in the treated eyes for up to 360 min, with a peak drop in IOP of 4.5 mmHg observed at the 150 min time point, post-topical application. The IOP of the contralateral eye (untreated) was also observed to be lowered significantly, but the effect lasted up to the 180 min time point only. Overall, topically administered CBD, formulated in a mucoadhesive nanoemulsion formulation, reduced the IOP in the animal model studied. The results support further exploration of CBD as a therapeutic option for various inflammation-based ocular diseases.

Aqueous Prostaglandin Eye Drop Formulations

Glaucoma is one of the leading causes of irreversible blindness worldwide. It is characterized by progressive optic neuropathy in association with damage to the optic nerve head and, subsequently, visual loss if it is left untreated. Among the drug classes used for the long-term treatment of open-angle glaucoma, prostaglandin analogues (PGAs) are the first-line treatment and are available as marketed eye drop formulations for intraocular pressure (IOP) reduction by increasing the trabecular and uveoscleral outflow. PGAs have low aqueous solubility and are very unstable (i.e., hydrolysis) in aqueous solutions, which may hamper their ocular bioavailability and decrease their chemical stability. Additionally, treatment with PGA in conventional eye drops is associated with adverse effects, such as conjunctival hyperemia and trichiasis. It has been a very challenging for formulation scientists to develop stable aqueous eye drop formulations that increase the PGAs' solubility and enhance their therapeutic efficacy while simultaneously lowering their ocular side effects. Here the physiochemical properties and chemical stabilities of the commercially available PGAs are reviewed, and the compositions of their eye drop formulations are discussed. Furthermore, the novel PGA formulations for glaucoma treatment are reviewed.

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.

Customized cationic nanoemulsions loading triamcinolone acetonide for corneal neovascularization secondary to inflammatory processes

Customized cationic oil-in-water nanoemulsions (NEs) have been produced to improve the bioavailability of poorly water-soluble drugs, such as triamcinolone acetonide (TA). TA is a synthetic glucocorticoid with anti-inflammatory and antiangiogenic therapeutic properties and it is widely used as an effective treatment in ocular disorders. In this work, TA-NEs were characterized using two different custom-made cationic surfactants, showing a high positive surface charge favouring corneal penetration and a particle size below 300 nm. Both TA-NE formulations demonstrated to be stable at 4 °C during the first months of storage. Furthermore, TA-NEs were able to produce antiangiogenic effects in chicken membranes. The TA-NEs safety profile was evaluated using in vitro and in vivo ocular tolerance tests. Out of the two formulations, the one showing no irritant effects was screened in vivo demonstrating capacity to ameliorate ocular inflammation in New Zealand rabbits significantly, specially to reduce the risk of ocular inflammation processes, with antiangiogenic activity, and can therefore be exploited as a suitable formulation to avoid inflammatory reactions upon ocular surgical procedures, such as cataracts.

Design of Topical Moxifloxacin Mucoadhesive Nanoemulsion for the Management of Ocular Bacterial Infections

Ocular bacterial infections can lead to serious visual disability without proper treatment. Moxifloxacin (MOX) has been approved by the US Food and Drug Administration as a monotherapy for ocular bacterial infections and is available commercially as an ophthalmic solution (0.5% w/v). However, precorneal retention, drainage, and low bioavailability remain the foremost challenges associated with current commercial eyedrops. With this study, we aimed to design a MOX-loaded nanoemulsion (NE; MOX-NE) with mucoadhesive agents (MOX-NEM) to sustain MOX release, as well as to overcome the potential drawbacks of the current commercial ophthalmic formulation. MOX-NE and MOX-NEM formulations were prepared by hot homogenization coupled with probe sonication technique and subsequently characterized. The lead formulations were further evaluated for in vitro release, ex vivo transcorneal permeation, sterilization, and antimicrobial efficacy studies. Commercial MOX ophthalmic solution was used as a control. The lead formulations showed the desired physicochemical properties and viscosity. All lead formulations showed sustained release profiles a period of more than 12 h. Filtered and autoclaved lead formulations were stable for one month (the last time point tested) under refrigeration and at room temperature. Ex vivo transcorneal permeation studies revealed a 2.1-fold improvement in MOX permeation of the lead MOX-NE formulation compared with Vigamox^® eyedrops. However, MOX-NEM formulations showed similar flux and permeability coefficients to those of Vigamox^® eyedrops. The lead formulations showed similar in vitro antibacterial activity as the commercial eyedrops and crude drug solution. Therefore, MOX-NE and MOX-NEM formulations could serve as effective delivery vehicles for MOX and could improve treatment outcomes in different ocular bacterial infections.

Multiphase Drug Distribution and Exchange in Oil-in-Water Nanoemulsion Revealed by High-Resolution 19F qNMR

An oil-in-water (o/w) nanoemulsion (NE), composed of oil globules, stabilized by a surfactant, and dispersed in an aqueous phase, is increasingly developed in complex drug formulation. Kinetically stable NEs are used to formulate hydrophobic drugs and typically provide higher dosage strengths and better content uniformity. However, little is known accurately about drug distribution in its multiphase solution, especially for the possible drug presence in the surfactant (s) phase, the interface layer between the dispersed oil (o) and the continuous water (w) phases. Here, high-resolution ¹⁹F quantitative NMR spectroscopy was applied directly and noninvasively on an o/w NE drug product containing difluprednate (DFPN). The well-resolved ¹⁹F peaks of DFPN depended on the shielding molecules in each phase, which revealed mass-balanced DFPN distribution in multiple phases of (w), (s), and (o) of NE globules at a quantity of 1.8 ± 0.1, 35 ± 2, and 59 ± 3% per labeled content, respectively. Furthermore, the dilution-dependent ¹⁹F peak line broadening and shift suggested a millisecond dynamic exchange between the NE and the less-noticed smaller but thermodynamically stable microemulsion (ME) globules in NE solution. The high-resolution NMR result revealed that the drug availability could be quickly achieved using an o/w NE formulation because of the drug multiphase distribution and the ME-assisted fast drug exchange among globules.

Bibliometric analysis of articles on nanoemulsion and/or in-situ gel for ocular drug delivery system published during the 2011–2021 period

The bibliometric data were extracted from the Scopus database to investigate the conceptual framework of ocular nanoemulsion and/or in-situ gel drug delivery system using “ocular” AND “nanoemulsion” OR “in-situ gel” keywords. The data were evaluated with RStudio and VOSviewer program.

The results reveal that the publication trends tend to increase continually. India is the most impactful country, and the most constructive institution is Department of Pharmaceutics and Industrial Pharmacy, Faculty of Pharmacy, Cairo University. International Journal of Pharmaceutics is the top influential source. Ali A is the most prolific author. The title of the most impactful article was In-situ gelling systems based on Pluronic F127/Pluronic F68 formulations for ocular drug delivery”. “Controlled release” is the most popular keyword.

These results provide insights for stimulating research collaborations and revealing open issues of controlled-release ocular preparation to overcome an ocular barrier and enhance patient compliance.

Current trends in pharmaceutical treatment of Dry Eye Disease: A review

Dry eye disease (DED), keratoconjunctivitis sicca or dysfunctional tear syndrome, is the most prevalent ophthalmic disease which affects a substantial segment of people worldwide with increasing frequency. It is considered a multifactorial disease of the ocular surface and tear film, characterized by a variation of signs and symptoms. The symptoms range from mild to severe itching, burning, irritation, eye fatigue, and ocular inflammation that may lead to potential damage to the cornea, conjunctiva and even vision loss. Correspondingly, depending on the different manifestations and pathophysiology, the treatment must be tailored specifically to each patient by targeting the specific mechanisms implicated in their disease. Currently, there are several medical products and techniques available or under investigation for the treatment of DED. The present article focused on the pathophysiology of DED, the new diagnostic approach and the recently developed drug delivery systems or devices reducing the progress of the disease and treating the causes.

Ferrostatin-1-loaded liposome for treatment of corneal alkali burn via targeting ferroptosis

Alkali burn is a potentially blinding corneal injury. During the progression of alkali burn-induced injury, overwhelmed oxidative stress in the cornea triggers cell damage, including oxidative changes in cellular macromolecules and lipid peroxidation in membranes, leading to impaired corneal transparency, decreased vision, or even blindness. In this study, we identified that ferroptosis, a type of lipid peroxidation-dependent cell death, mediated alkali burn-induced corneal injury. Ferroptosis-targeting therapy protected the cornea from cell damage and neovascularization. However, the specific ferroptosis inhibitor ferrostatin-1 (Fer-1) is hydrophobic and cannot be directly applied in the clinic. Therefore, we developed Fer-1-loaded liposomes (Fer-1-NPs) to improve the bioavailability of Fer-1. Our study demonstrated that Fer-1-NPs exerted remarkable curative effects regarding corneal opacity and neovascularization in vivo. The efficacy was comparable to that of dexamethasone, but without appreciable side effects. The significant suppression of ferroptosis (induced by lipid peroxidation and mitochondria disruption), inflammation, and neovascularization might be the mechanisms underlying the therapeutic effect of Fer-1-NPs. Moreover, the Fer-1-NPs treatment showed no signs of cytotoxicity, hematologic toxicity, or visceral organ damage, which further confirmed the biocompatibility. Overall, Fer-1-NPs provide a new prospect for safe and effective therapy for corneal alkali burn.

Antibiotic-loaded lipid-based nanocarrier: a promising strategy to overcome bacterial infection

According to the World Health Organization (WHO) and Centers for Disease Control and Prevention (CDC), bacterial infections are one of the greatest threats to global health, food production, and life expectancy. In this sense, the development of innovative formulations aiming at greater therapeutic efficacy, safety, and shorter treatment duration compared to conventional products is urgently needed. Lipid-based nanocarriers (LBNs) have demonstrated the potential to enhance the effectiveness of available antibiotics. Among them, liposome, nanoemulsion, solid lipid nanoparticle (SLN), and nanostructured lipid carrier (NLC) are the most promising due to their solid technical background for laboratory and industrial production. This review describes recent advances in developing antibiotic-loaded LBNs against susceptible and resistant bacterial strains and biofilm. LBNs revealed to be a promising alternative to deliver antibiotics due to their superior characteristics compared to conventional preparations, including their modified drug release, improved bioavailability, drug protection against chemical or enzymatic degradation, greater drug loading capacity, and biocompatibility. Antibiotic-loaded LBNs can improve current clinical drug therapy, bring innovative products and rescue discarded antibiotics. Thus, antibiotic-loaded LBNs have potential to open a window of opportunities to continue saving millions of lives and prevent the devastating impact of bacterial infection.

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.

Lipid Nanoparticles as a Promising Drug Delivery Carrier for Topical Ocular Therapy-An Overview on Recent Advances

Due to complicated anatomical and physical properties, targeted drug delivery to ocular tissues continues to be a key challenge for formulation scientists. Various attempts are currently being made to improve the in vivo performance of therapeutic molecules by encapsulating them in various nanocarrier systems or devices and administering them via invasive/non-invasive or minimally invasive drug administration methods. Biocompatible and biodegradable lipid nanoparticles have emerged as a potential alternative to conventional ocular drug delivery systems to overcome various ocular barriers. Lipid-based nanocarrier systems led to major technological advancements and therapeutic advantages during the last few decades of ocular therapy, such as high precorneal residence time, sustained drug release profile, minimum dosing frequency, decreased drug toxicity, targeted site delivery, and, therefore, an improvement in ocular bioavailability. In addition, such formulations can be given as fine dispersion in patient-friendly droppable preparation without causing blurred vision and ocular sensitivity reactions. The unique advantages of lipid nanoparticles, namely, solid lipid nanoparticles, nanostructured lipid carriers, nanoemulsions, and liposomes in intraocular targeted administration of various therapeutic drugs are extensively discussed. Ongoing and completed clinical trials of various liposome-based formulations and various characterization techniques designed for nanoemulsion in ocular delivery are tabulated. This review also describes diverse solid lipid nanoparticle preparation methods, procedures, advantages, and limitations. Functionalization approaches to overcome the drawbacks of lipid nanoparticles, as well as the exploration of new functional additives with the potential to improve the penetration of macromolecular pharmaceuticals, would quickly progress the challenging field of ocular drug delivery systems.

New Preservative-Free Formulation for the Enhanced Ocular Bioavailability of Prostaglandin Analogues in Glaucoma

Glaucoma is a wide-spread eye disease caused by elevated intraocular pressure. Uncontrolled, this pressure may lead to damages to the optic nerve. Prostaglandin analogues, such as latanoprost and travoprost (which are water-insoluble active substances), are the most used class of active pharmaceutical ingredient. To administer them as eye drops, preservatives, such as benzalkonium chloride, are used as solubilizers. The latter is known to cause a local inflammation when used chronically and is not recommended for patients with ocular surface disorders. In this work, we sought to use polysorbate 80 (PS80) as a solubilizing agent simultaneously with sodium hyaluronate (NaHA) as a thickener and cytoprotective agent for the corneal surface. The first part of this study assessed the compatibility of the excipients with the active substance, using physicochemical methods such as spectra fluorescence and differential scanning calorimetry (DSC), as well as the solubilization mechanism of PS80 regarding prostaglandin analogues using nuclear magnetic resonance (NMR). The second part evaluated the stability of a formula candidate, its viscosity upon instillation, and its pharmacokinetic profile in rabbits as compared to the commercially approved medicine Travatan®. The results show that sodium hyaluronate is inert with respect to travoprost, while PS80 successfully solubilizes it, meaning that benzalkonium chloride is no longer required. Moreover, the pharmacokinetic profiles of the rabbits showed that the original formula described in the present study enhanced the ocular bioavailability of the drug, making it a promising product to control intraocular pressure with a potential reduced dosage of travoprost, therefore minimizing its related side effects.

Targeted drug delivery vehicles mediated by nanocarriers and aptamers for posterior eye disease therapeutics: barriers, recent advances and potential opportunities

Nanomedicine and aptamer have excellent potential in giving play to passive and active targeting respectively, which are considered to be effective strategies in the retro-ocular drug delivery system. The presence of closely adjoined tissue structures in the eye makes it difficult to administer the drug in the posterior segment of the eye. The application of nanomedicine could represent a new avenue for the treatment, since it could improve penetration, achieve targeted release, and improve bioavailability. Additionally, a novel type of targeted molecule aptamer with identical objective was proposed. As an emerging molecule, aptamer shows the advantages of penetration, non-toxicity, and high biocompatibility, which make it suitable for ocular drug administration. The purpose of this paper is to summarize the recent studies on the effectiveness of nanoparticles as a drug delivery to the posterior segment of the eye. This paper also creatively looks forward to the possibility of the combined application of nanocarriers and aptamers as a new method of targeted drug delivery system in the field of post-ophthalmic therapy.

Nanoemulsion delivery systems for enhanced efficacy of antimicrobials and essential oils

The ever-growing threat of new and existing infectious diseases in combination with antimicrobial resistance requires the need for innovative and effective forms of drug delivery. Optimal drug delivery systems for existing and newly developed antimicrobials can enhance drug bioavailability, enable site-specific drug targeting, and overcome current limitations of drug formulations such as short elimination half-lives, poor drug solubility, and undesirable side effects. Nanoemulsions (NE) consist of nanometer-sized droplets stabilized by emulsifiers and are typically more stable and permeable due to their smaller particle sizes and higher surface area compared to conventional emulsions. NE have been identified as a promising means of antimicrobial delivery due to their intrinsic antimicrobial properties, ability to increase drug solubility, stability, bioavailability, organ and cellular targeting potentials, capability of targeting biofilms, and potential to overcome antimicrobial resistance. Herein, we discuss non-drug loaded essential oil-based NE that can confer antimicrobial actions through predominantly physical or biochemical mechanisms without drug payloads. We also describe drug-loaded NE for enhanced antimicrobial efficacy by augmenting the potency of existing antimicrobials. We highlight the versatility of NE to be administered through multiple different routes (oral, parenteral, dermal, transdermal, pulmonary, nasal, ocular, and rectal). We summarize recent advances in the clinical translation of antimicrobial NE and shed light on future development of effective antimicrobial therapy to combat infectious diseases.

Monolith/Hydrogel composites as triamcinolone acetonide carriers for curing corneal neovascularization in mice by inhibiting the fibrinolytic system

Corneal neovascularization is a serious corneal pathological change caused by various factors. The drug delivery system is of great significance for the effective treatment of corneal neovascularization. Herein, we developed and characterized a monolith/hydrogel composite as the triamcinolone acetonide (TA) carrier for curing corneal neovascularization. The composite was prepared by photo-initiated free radical polymerization of multi-methacrylate substituted dodecamine organic molecular cage and post-modified by the sequential photo-initiated free radical polymerization of acrylated gelatin. The globular morphology and structural property of as-prepared composites were evaluated by scanning electron microscopy, Fourier-transform infrared spectroscopy and solid-state cross polarization magic angle spinning carbon-13 nuclear magnetic resonance. Then swelling ratio and the TA loading capacity were investigated then. Compared with gelatin hydrogel, the composites exhibited a decreased swelling ratio and an improved loading capacity. With good biocompatibility, the composite can sustainedly release TA for up to 28 days, and effectively inhibit corneal neovascularization with an alkali burn-induced corneal neovascularization model. Additionally, tandem mass tags-labeled quantitative proteomics were performed to identify differentially expressed proteins between vascularized and devascularized corneas. The Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that the inhibition process could be primarily linked to the fibrinolytic system. These results demonstrated the potential of monolith/hydrogel composites as delivery systems in the therapy for biomedical diseases.