Poloxamine micellar solubilization of α-tocopherol for topical ocular treatment

Novel drug delivery systems for the management of dry eye

Dry eye disease (DED) is a frequently observed eye complaint, which has recently attracted considerable research interest. Conventional therapy for DED involves the use of artificial tear products, cyclosporin, corticosteroids, mucin secretagogues, antibiotics and nonsteroidal anti-inflammatory drugs. In addition, ocular drug delivery systems based on nanotechnology are currently the focus of significant research effort and several nanotherapeutics, such as nanoemulsions, nanosuspensions, microemulsions, liposomes and nanomicelles, are in clinical trials and some have FDA approval as novel treatments for DED. Thus, there has been remarkable progress in the design of nanotechnology-based approaches to overcome the limitations of ophthalmic formulations for the management of anterior eye diseases. This review presents research results on diagnostic methods for DED, current treatment options, and promising pharmaceuticals as future therapeutics, as well as new ocular drug delivery systems.

Reported evidence of vitamin E protection against cataract and glaucoma

Cataract and glaucoma are the major causes of severe visual loss and blindness in older adults. This review article describes the currently available basic and clinical evidence regarding vitamin E protection against these eye diseases in the chronologic order of the publications. Experimental evidence has suggested both that oxidative stress due to the accumulation of free radicals plays a role in the pathogenesis of cataracts and glaucoma and that the process can be prevented or ameliorated by vitamin E. The results of observational studies have been inconsistent regarding the association between blood vitamin E levels and the risk of age-related cataract or glaucoma. Despite the encouraging effects of vitamin E from case series, case-control studies, and cross-sectional studies in humans, the effects on cataract formation and/or progression have not been consistent among prospective and randomized control studies; few randomized control studies have tested the effects of supplemental vitamin E on glaucoma development or progression. Given the high prevalence of cataract and glaucoma in the elderly population, even a modest reduction in the risk for these eye diseases would potentially have a substantial public health impact; however, the potential benefits of vitamin E on cataract or glaucoma remain inconclusive and need to be carefully considered.

Micellar buccal film for safe and effective control of seizures: Preparation, in vitro characterization, ex vivo permeation studies and in vivo assessment

The current research article focused on formulating an easily applied, water-based buccal film loaded with the antiepileptic drug, lamotrigine (LTG). The designed film can be comfortably administered by epileptic patients to ensure a controllable therapeutic efficacy against seizures. The solubility of LTG in water was significantly improved by micellar solubilization. Upon testing several surfactants, three of them (Synperonic PE/P84, Brij L23, and Brij 78) achieved maximum possible solubility for LTG and were characterized for their micellar size, cloud point, and % transmittance. Selected micellar systems were incorporated within a buccal film prepared using solvent casting method based on either gelatin or polyvinylpyrrolidone (3%w/v) with 1.5%w/v propylene glycol as a plasticizer. Different micellar films were characterized for their physicochemical characteristics, swelling index, folding endurance, drug content uniformity, and in vitro LTG release. From the tested formulations, one formulation; LTG-BF1 (in which Brij 78 was used for the micellar solubilization and gelatin as the matrix former), was selected as the optimum and extensively studied for mucoadhesion, ex vivo permeation studies by Franz diffusion cells and confocal laser scanning microscopy. Results showed superior enhanced permeation of micellar film. LTG-BF1 was evaluated for the in vivo performance using rats. Status epilepticus was induced in rats by injecting Pentylenetetrazol (PTZ) i.p. at an initial dose of 30 mg/kg, followed by 10 mg/kg every10 min till 60 min. A group of rats receiving the designed buccal formulation (20 mg/kg) was compared with a group receiving the same dose of the oral market product and the normal control and PTZ groups. Rats receiving LTG-BF1 recorded reduced seizure scores at all stages, longer latency time, and higher threshold PTZ dose compared to PTZ and market product groups. In addition, LTG-BF1 reduced brain concentrations of TNF-α and TGF-β with an elevation of EAAT2 and GABA brain contents compared to PTZ and market product groups and ameliorated neuronal damage. In conclusion, LTG-loaded buccal micellar film proved a superior antiepileptic effect in PTZ induced acute epileptic model.

Effects of eye drops containing a mixture of 3% diquafosol sodium and tocopherol acetate (vitamin E) on the ocular surface of murine dry eye

PURPOSE

To investigate the efficacy of topical application of 3% diquafosol sodium (DQS) and tocopherol (TCP) acetate mixtures in a mouse model of experimental dry eye (EDE).

METHODS

After exposure to desiccating stress for 5 days, eye drops consisting of 3% DQS alone, 0.01% TCP alone, or 3% DQS and 0.005% or 0.01% TCP mixture were applied for the treatment of EDE. Tear volume, tear film break-up time (TBUT), corneal fluorescein staining scores (CFSS), and tear film lipid layer grades (TFLLG) were measured at 0, 5 and 10 days after treatment. The 2',7'-dichlorodihydrofluorescein diacetate assay (DCFDA) for reactive oxygen species (ROS) production, enzyme-linked immunosorbent assay (ELISA) for malondialdehyde (MDA), and flow cytometry for CD4 + interferon (IFN)-γ+ T cells were evaluated on the ocular surface at 10 days after treatment. In addition, levels of tumour necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and chemokine CC motif ligand 4 (CCL4) in the conjunctiva were measured using a multiplex immunobead assay, and conjunctival goblet cells were counted by periodic acid-Schiff staining at 10 days after treatment.

RESULTS

Both the TCP mixture groups indicated a significant improvement in TBUT, ROS production, and MDA concentrations compared to those in the DQS alone group. Furthermore, the 0.01% TCP mixture group also showed higher tear film lipid layer grades and conjunctival goblet cell density and lower corneal fluorescein staining scores, number of CD4 + IFN-γ+ T cells, and levels of TNF-α, IL-1β, and CCL4 than the DQS alone group (P < 0.05).

CONCLUSIONS

Application of eye drops containing the mixture of DQS and TCP could stabilize the tear film lipid layer, improve TBUT and corneal epithelial damages, decrease ROS production, inflammatory molecules, and T cells, and increase conjunctival goblet cell density on the ocular surface. Topical DQS and TCP mixtures may have a greater therapeutic effect on clinical signs, oxidative damage, and inflammation of dry eye than DQS eye drops.

Prodrugs and nanomicelles to overcome ocular barriers for drug penetration

INTRODUCTION

Ocular barriers hinder drug delivery and reduce drug bioavailability. This article focuses on enhancing drug absorption across the corneal and conjunctival epithelium. Both, transporter targeted prodrug formulations and nanomicellar strategy is proven to enhance the drug permeation of therapeutic agents across various ocular barriers. These strategies can increase aqueous drug solubility and stability of many hydrophobic drugs for topical ophthalmic formulations.

AREAS COVERED

The article discusses various ocular barriers, ocular influx, and efflux transporters. It elaborates various prodrug strategies used for enhancing drug absorption. Along with this, the article also describes nanomicellar formulation, its characteristic and advantages, and applications in for anterior and posterior segment drug delivery.

EXPERT OPINION

Prodrugs and nanomicellar formulations provide an effective strategy for improving drug absorption and drug bioavailability across various ocular barriers. It will be exciting to see the efficacy of nanomicelles for treating back of the eye disorders after their topical application. This is considered as a holy grail of ocular drug delivery due to the dynamic and static ocular barriers, restricting posterior entry of topically applied drug formulations.

The Role of Nano-ophthalmology in Treating Dry Eye Disease

Dry eye disease (DED) is a common multifactorial disease linked to the tears/ocular surface leading to eye discomfort, ocular surface damage, and visual disturbance. Antiinflammatory agents (steroids and cyclosporine A), hormonal therapy, antibiotics, nerve growth factors, essential fatty acids are used as treatment options of DED. Current therapies attempt to reduce the ocular discomfort by producing lubrication and stimulating gland/nerve(s) associated with tear production, without providing a permanent cure for dry eye. Nanocarrier systems show a great promise to revolutionize drug delivery in DED, offering many advantages such as site specific and sustained delivery of therapeutic agents. This review presents an overview, pathophysiology, prevalence and etiology of DED, with an emphasis on preclinical and clinical studies involving the use of nanocarrier systems in treating DED. Lay Summary: Dry eye disease (DED) is a multifactorial disease associated with tear deficiency or excessive tear evaporation. There are several review articles that summarize DED, disease symptoms, causes and treatment approaches. Nanocarrier systems show a great promise to revolutionize drug delivery in DED, offering many advantages such as site specific and sustained delivery of therapeutic agents. Very few review articles summarize the findings on the use of nanotherapeutics in DED. In this review, we have exclusively discussed the preclinical and clinical studies of nanotherapeutics in DED therapy. This information will be attractive to both academic and pharmaceutical industry researchers working in DED therapeutics.

Cytosine-functionalized bioinspired hydrogels for ocular delivery of antioxidant transferulic acid

Contact lenses (CLs) are being pointed out as feasible platforms for controlled delivery of ophthalmic drugs. Bioinspired strategies may endow CLs with affinity for a given drug by mimicking its physiological receptor using adequate functional monomers and tuning their conformation in the space through the molecular imprinting technology. However, there are some active substances, such as efficient antioxidant agents, that cannot be used as templates because they degrade during polymerization or even hinder the polymerization itself. Therefore, the development of CLs able to sustain the release of antioxidants for the prevention and/or treatment of several age-related and light-induced eye diseases has not been explored yet. Searching for an alternative bioinspired strategy, the present work relies on the fact that some drugs owe their therapeutic action to their ability to interact with nucleotides that build up DNA and RNA. Thus, the aim of this work was to design hydrogels functionalized with the nitrogenous base cytosine for the controlled uptake and release of transferulic acid (TA) having a complementary chemical structure in terms of hydrogen bonding and π-π stacking ability. Hydrogels were prepared from mixtures of 2-hydroxyethyl methacrylate (HEMA), glycidyl methacrylate (GMA) and ethyleneglycolphenylether methacrylate (EGPEM). GMA was used as a bridge to immobilize cytosine after hydrogel synthesis, while EGPEM was added to reinforce hydrophobic interactions with TA. The hydrogels were characterized in terms of suitability to be used as CLs (swelling, light transmission, mechanical properties, biocompatibility) and capability to host TA and sustain its release in lachrymal fluid while maintaining the antioxidant activity. Relevantly, the bioinspired CLs favored TA accumulation in cornea and sclera tissues.

Topical application of polymeric nanomicelles in ophthalmology: a review on research efforts for the noninvasive delivery of ocular therapeutics

INTRODUCTION

Polymeric micelles represent nowadays an interesting formulative approach for ocular drug delivery, as they act as solubility enhancers of poorly soluble drugs and promote drug transport across cornea and sclera. In particular, in the last 5 years polymeric nanomicelles have been increasingly investigated to overcome some of the important challenges of the topical treatment of ocular diseases.

AREAS COVERED

The aim of this review was to gather up-to-date information on the different roles that polymeric micelles (commonly in the nanosize scale) can play in ocular delivery. Thus, after a general description of ocular barriers and micelles features, the attention is focused on those properties that are relevant for ophthalmic application. Finally, their efficacy in improving the ocular delivery of different classes of therapeutics (anti-inflammatory, immunosuppressant, antiglaucoma, antifungal, and antiviral drugs) are reported.

EXPERT OPINION

Although still a few, in vivo experiments have clearly demonstrated the capability of polymeric nanomicelles to overcome a variety of hurdles associated to ocular therapy, notably increasing drug bioavailability. However, there are still some very important issues to be solved, such as tolerability and stability; additionally, the role of micelles in drug uptake by the ocular tissues and their potential for the treatment of posterior eye diseases still need to be clarified/verified.

Polymeric micelles as cutaneous drug delivery system in normal skin and dermatological disorders

The easy accessibility of skin made dermal application, one of the approaches for local drug therapy. Effectiveness of topical drug application is depended on different parameters such as skin barrier properties, physicochemical properties of drug and vehicle, and interaction between drug and its vehicle with the skin layers. In this review, an overview of skin structure and feature of polymeric micelles as topical nanocarriers is provided. We also summarized the research studies dealing with the application of polymeric micelles for cutaneous delivery. In the past decades, numerous types of nanocarriers have been widely investigated as a novel delivery approach to improve skin penetration and localization of drugs in normal skin and dermatological diseases. Polymeric micelles are one of them, with their specific ability to encapsulate hydrophilic drugs. These carriers can enhance the therapeutic efficacy and minimize the systemic side effects of the drugs. Polymeric micelles could enhance the deposition of drugs in targeted sites of the skin in the normal and dermatological diseases such as psoriasis and acne. Nevertheless, still there is a need to investigate the mechanism of action of these carriers and the fate of polymeric micelles in skin.

Mixed micelles for encapsulation of doxorubicin with enhanced in vitro cytotoxicity on breast and ovarian cancer cell lines versus Doxil®

Doxorubicin (DOX) is used as a "first-line" antineoplastic drug in ovarian and metastatic breast cancer. However, serious side effects, such as cardiotoxicity have been reported after DOX intravenous administration. Hence, we investigated different micelle-former biomaterials, as Soluplus^®, Pluronic F127, Tetronic T1107 and d-α-tocopheryl polyethylene glycol 1000 succinate (TPGS) to develop a potential mixed micellar nanocarrier for DOX delivery. Since DOX hydrochloride is a poor candidate to be encapsulated inside the hydrophobic core of the mixed micelles, we assayed a hydrophobic complex between DOX and sodium deoxycholate (NaDC) as an excellent candidate to be encapsulated within polymeric micelles. The combination of T1107:TPGS (1:3, weight ratio) demonstrated the best physicochemical properties together with a high DL capacity (6.43% w/v). Particularly, DOX in vitro release was higher at acidic tumour microenvironment pH value (5.5) than at physiological counterpart (7.4). The hydrodynamic diameter of the DOX/NaDC-loaded mixed micellar system was 10.7nm (PDI=0.239). The in vitro cytotoxicity of the mixed micellar formulation resulted significantly (p<0.05) higher than Doxil^® against ovarian (SKOV-3) and triple-negative breast cancer cells (MDA-MB- 231). Further, the in vitro cellular uptake assays demonstrated a significant increment (p<0.05) of the DOX intracellular content for the mixed micelles versus Doxil^® for both, SKOV-3 (at 2, 4 and 6h of incubation) and MDA-MB-231 (at 4h of incubation) cells. These findings suggest that T1107:TPGS (1:3) mixed micelles could be employed as a potential nanotechnological platform for drug delivery of DOX.

Tri-block co-polymer nanocarriers for enhancement of oral delivery of felodipine: preparation, in vitro characterization and ex vivo permeation

This study aimed to prepare, optimize and characterize novel felodipine-loaded polymeric nanomicelles, using a pluronic mixture of F127 and P123. Thin-film hydration method was adopted for the preparation of different polymeric nanomicelles (T1-T12) according to a 4¹.3¹ full factorial design. Factors studied were: Pluronic®:drug ratio (P:D ratio) (10, 20, 30 and 40 w/w) and percent of hydrophilic polymer (F127%) (33.33%, 50% and 66.67% w/w). Optimization criteria were to maximize transmittance percent (T%) and entrapment efficiency percent (EE%) and to minimize particle size (PS) and polydispersity index (PDI). The optimized formulation was further characterized by DSC, FTIR and ¹H NMR studies. It was also subjected to stability testing and ex vivo permeation using rabbit intestines. Spherical nanomicelles of particle size ranging from 26.18 to 87.54 nm were successfully obtained. The optimized formulation was found to be the already prepared formulation T12 (P:D ratio of 40 and 66.67% F127) with suitable T% and EE% of 95.12% and 91.75%, respectively. DSC, FTIR and ¹H NMR studies revealed felodipine (FLD) incorporation within T12 nanomicelles. T12 enhanced the ex vivo intestinal permeation of FLD when compared to a drug suspension and showed good stability. Therefore, pluronic nanomicelles could be promising for improved oral delivery of FLD.

Polymeric micelles for ocular drug delivery: From structural frameworks to recent preclinical studies

Effective intraocular drug delivery poses a major challenge due to the presence of various elimination mechanisms and physiological barriers that result in low ocular bioavailability after topical application. Over the past decades, polymeric micelles have emerged as one of the most promising drug delivery platforms for the management of ocular diseases affecting the anterior (dry eye syndrome) and posterior (age-related macular degeneration, diabetic retinopathy and glaucoma) segments of the eye. Promising preclinical efficacy results from both in-vitro and in-vivo animal studies have led to their steady progression through clinical trials. The mucoadhesive nature of these polymeric micelles results in enhanced contact with the ocular surface while their small size allows better tissue penetration. Most importantly, being highly water soluble, these polymeric micelles generate clear aqueous solutions which allows easy application in the form of eye drops without any vision interference. Enhanced stability, larger cargo capacity, non-toxicity, ease of surface modification and controlled drug release are additional advantages with polymeric micelles. Finally, simple and cost effective fabrication techniques render their industrial acceptance relatively high. This review summarizes structural frameworks, methods of preparation, physicochemical properties, patented inventions and recent advances of these micelles as effective carriers for ocular drug delivery highlighting their performance in preclinical studies.

Encapsulation of Antioxidant Gallate Derivatives in Biocompatible Poly(ε-caprolactone)-b-Pluronic-b-Poly(ε-caprolactone) Micelles

Formulation of antioxidant agents is still a challenge that limits their application in the biomedical field. Pentablock copolymers obtained through modification of two common PEO-PPO-PEO copolymers (Pluronic F127 and F68) with poly(ε-carprolactone) (PCL) were evaluated regarding their capability to form nanocarriers suitable for gallic acid, methyl gallate, and ethyl gallate. Applying a dialysis method, PCL/F127/PCL and PCL/F68/PCL self-assembled into spherical micelles in 0.9% NaCl aqueous solution but notably differed in critical micellar concentration (CMC), micelle core hydrophobicity, and micelle size, as evidenced by pyrene fluorescence, transmission electron microscopy, and dynamic light scattering. Cytotoxicity studies showed that the copolymers were safe at concentrations well above the CMC. Transfer of gallic acid and derivatives from aqueous medium to the micelle phase was characterized in terms of distribution constant and free energy of transference, which were shown to be strongly dependent on the hydrophobicity of the gallate derivatives and the length of PCL in the pentablock copolymer. Antioxidant activity of gallates was challenged against DPPH previously loaded in PCL/F127/PCL and PCL/F68/PCL micelles. The more the hydrophobicity of the gallate derivative, the greater the capability to enter in the micelle and to consume free radicals. In vitro release studies of gallic acid, methyl gallate, and ethyl gallate from the pentablock copolymer micelles also evidenced the influence of the hydrophobicity of both the gallate derivative and the micelle core on release rate, recording a variety of release patterns. Overall, PCL/F127/PCL and PCL/F68/PCL appear as suitable nanocarriers of potent antioxidant agents in a wide range of polarities, which may be useful for diverse therapeutic applications.

Tri/tetra-block co-polymeric nanocarriers as a potential ocular delivery system of lornoxicam: in-vitro characterization, and in-vivo estimation of corneal permeation

Polymeric micelles that can deliver drug to intended sites of the eye have attracted much scientific attention recently. The aim of this study was to evaluate the aqueous-based formulation of drug-loaded polymeric micelles that hold significant promise for ophthalmic drug delivery. This study investigated the synergistic performance of mixed polymeric micelles made of linear and branched poly(ethylene oxide)-poly(propylene oxide) for the more effective encapsulation of lornoxicam (LX) as a hydrophobic model drug. The co-micellization process of 10% binary systems combining different weight ratios of the highly hydrophilic poloxamers; Synperonic(®) PE/P84, and Synperonic(®) PE/F127 and the hydrophobic poloxamine counterpart (Tetronic(®) T701) was investigated by means of photon correlation spectroscopy and cloud point. The drug-loaded micelles were tested for their solubilizing capacity towards LX. Results showed a sharp solubility increase from 0.0318 mg/mL up to more than 2.34 mg/mL, representing about 73-fold increase. Optimized formulation was selected to achieve maximum drug solubilizing power and clarity with lowest possible particle size, and was characterized by (1)HNMR analysis which revealed complete encapsulation of the drug within the micelles. Further investigations by histopathological and confocal laser studies revealed the non-irritant nature and good corneal penetrating power of the proposed nano-formulation.

Evaluation of gatifloxacin pluronic micelles and development of its formulation for ocular delivery

The purpose of the present study was to enhance the solubility of gatifloxacin by developing self-assembling pluronic micelles of gatifloxacin for ocular delivery, to overcome the problem of poor bioavailability and therefore lesser therapeutic response exhibited by conventional ophthalmic solutions of the drug. Gatifloxacin was loaded in micelles by solid dispersion method using Pluronic F127 and evaluated for particle size, drug loading, loading efficiency, in vitro transcorneal permeation study, in vitro drug release, solubility studies, microbiological studies, ex vivo mucoadhesive strength, and ocular safety studies. The drug loading and drug loading efficiency studies revealed that gatifloxacin/Pluronic F127 ratio of 0.25/2.52 g offered good drug loading (9.96 %), high loading efficiency (90 %), and acceptable particle size of 176 nm (polydispersity index 0.345). Hen's egg test chorioallantoic membrane (HET-CAM) assay with 0 score in 8 h and ocular safety test with score of 2 indicate the nonirritant property of the developed pluronic micelles. In vitro transcorneal permeation studies through excised goat cornea indicated increase in ocular availability with no corneal damage. In vitro drug release data of optimized formulation provided sustained release over a period of 8 h. Optimized formulation was found to possess acceptable transcorneal permeation and antimicrobial efficacy when compared to marketed eye drops. The solubility studies of gatifloxacin from these lyophilized pluronic micelles revealed 18.67-fold increase in comparison to gatifloxacin suspension in water. The pluronic micelles could enhance ocular bioavailability of gatifloxacin, prolong its residence time in the eyes, and may lead to reduced instillation frequency, thereby resulting in better patient compliance.

Controlled ocular drug delivery with nanomicelles

Many vision threatening ocular diseases such as age-related macular degeneration (AMD), diabetic retinopathy, glaucoma, and proliferative vitreoretinopathy may result in blindness. Ocular drug delivery specifically to the intraocular tissues remains a challenging task due to the presence of various physiological barriers. Nonetheless, recent advancements in the field of nanomicelle-based novel drug delivery system could fulfil these unmet needs. Nanomicelles consists of amphiphilic molecules that self-assemble in aqueous media to form organized supramolecular structures. Micelles can be prepared in various sizes (10-1000 nm) and shapes depending on the molecular weights of the core and corona forming blocks. Nanomicelles have been an attractive carrier for their potential to solubilize hydrophobic molecules in aqueous solution. In addition, small size in nanometer range and highly modifiable surface properties have been reported to be advantageous in ocular drug delivery. In this review, various factors influencing rationale design of nanomicelles formulation and disposition are discussed along with case studies. Despite the progress in the field, influence of various properties of nanomicelles such as size, shape, surface charge, rigidity of structure on ocular disposition need to be studied in further details to develop an efficient nanocarrier system.

Soft contact lenses for controlled ocular delivery: 50 years in the making

The use of contact lenses as ocular bandages for drug delivery was envisioned nearly 50 years ago by Wichterle and co-workers. Despite the therapeutic advantages that can be obtained, this application has to face up to the poor affinity shown by commercially available contact lenses for most ophthalmic drugs, resulting in small amounts of drug being loaded and short time of therapeutic levels in the eye structures. Novel strategies that appeared in the beginning of 21st century, for example coating lenses with vitamin E, incorporation of drug nanocarriers or application of molecular imprinting technology, are becoming relevant tools for development of true drug/contact lens combination products that may be available for ocular therapy in the foreseeable future.