Ophthalmic applications of lipid-based drug nanocarriers: an update of research and patenting activity

Recent Advances in Nanotechnology for the Treatment of Dry Eye Disease

Dry eye disease (DED) incidence is continuously growing, positioning it to become an emergent health issue over the next few years. Several topical treatments are commonly used to treat DED; however, reports indicate that only a minor proportion of drug bioavailability is achieved by the majority of eye drops available on the market. In this context, enhancing drug ability to overcome ocular barriers and prolonging its residence time on the ocular surface represent a new challenge in the field of ocular carrier systems. Therefore, research has focused on the development of multi-functional nanosystems, such as nanoemulsions, liposomes, dendrimers, hydrogels, and other nanosized carriers. These systems are designed to improve topical drug bioavailability and efficacy and, at the same time, require fewer daily administrations, with potentially reduced side effects. This review summarizes the different nanotechnologies developed, their role in DED, and the nanotechnology-based eyedrops currently approved for DED treatment.

Lipid Nanoparticles Traverse Non-Corneal Path to Reach the Posterior Eye Segment: In Vivo Evidence

Lipid-based nanocarriers (LNs) have made it possible to prolong corneal residence time and improve the ocular bioavailability of ophthalmic drugs. In order to investigate how the LNs interact with the ocular mucosa and reach the posterior eye segment, we have formulated lipid nanocarriers that were designed to bear a traceable fluorescent probe in the present work. The chosen fluorescent probe was obtained by a conjugation reaction between fluoresceinamine and the solid lipid excipient stearic acid, forming a chemically synthesized adduct (ODAF, N-(3′,6′-dihydroxy-3-oxospiro [isobenzofuran-1(3H),9′-[9H] xanthen]-5-yl)-octadecanamide). The novel formulation (LN-ODAF) has been formulated and characterized in terms of its technological parameters (polydispersity index, mean particle size and zeta potential), while an in vivo study was carried out to assess the ability of LN-ODAF to diffuse through different ocular compartments. LN-ODAF were in nanometric range (112.7 nm ± 0.4), showing a good homogeneity and long-term stability. A TEM (transmission electron microscopy) study corroborated these results of characterization. In vivo results pointed out that after ocular instillation, LN ODAF were concentrated in the cornea (two hours), while at a longer time (from the second hour to the eighth hour), the fluorescent signals extended gradually towards the back of the eye. From the results obtained, LN-ODAF demonstrated a potential use of lipid-based nanoparticles as efficient carriers of an active pharmaceutical ingredient (API) involved in the management of retinal diseases.

The prominence of the dosage form design to treat ocular diseases

The eye is susceptible to various diseases commonly difficult to treat. To overcome the barriers imposed by this organ for required drugs penetration, technological strategies have been implemented to ocular formulations. Among them are the use of temperature or electric stimuli and the development of nanoparticles. The objective of this review is to present the main barriers to ocular drug delivery and to discuss strategies used in the development of ocular dosage forms, primarily for topical delivery, to increase the local bioavailability of drugs, target their delivery and increase patient compliance. Results obtained in the last years related to the topical administration of liposomes, dendrimers, iontophoresis, among other nanoparticulate systems focused on ophthalmic delivery, will be addressed. Finally, some clinical trials and marketed formulations that use nanotechnology to topically treat eye diseases will be presented.

Evolving nanotechnological trends in the management of mycotic keratitis

The alarming increase in global burden of various corneal diseases in general and mycotic keratitis in particular has raised up a major concern for its treatment. Mycotic keratitis is one of the most serious infections among the various ocular diseases. The proper diagnosis and effective treatment strategies remain a great challenge for ophthalmologists. The inefficacy and failure of conventional treatments have generated need to develop alternative approaches for the treatment of mycotic keratitis. Considering the promising applications of nanotechnology in biomedical area, it is believed that various nanomaterials can be effectively used in the management of mycotic keratitis. This review focuses on worldwide burden of various corneal diseases including mycotic keratitis and the role of nanotechnology in its treatment. In addition, safety and toxicological issues are also discussed.

A Method for Efficient Loading of Ciprofloxacin Hydrochloride in Cationic Solid Lipid Nanoparticles: Formulation and Microbiological Evaluation

The aim of the study was the production of solid lipid nanoparticles (SLN) loaded with ciprofloxacin (CIP) through two different production techniques, quasi-emulsion solvent diffusion (QESD) and solvent injection (SI). In order to efficaciously entrap the commercial salt form (hydrochloride) of the antibiotic in these lipid systems, a conversion of CIP hydrochloride to the free base was realized in situ, through the addition of triethylamine. To ensure physical stability to the carriers over time and ameliorate the interaction with bacterial cell membranes, positively charged SLN were produced by addition of the cationic lipid didecyldimethylammonium bromide (DDAB). Homogeneous SLN populations with a mean particle sizes of 250–350 nm were produced by both methods; drug encapsulation was over 85% for most samples. The SLN were physically stable for up to nine months both at 4 °C and 25 °C, although the former condition appears more suitable to guarantee the maintenance of the initial particle size distribution. As expected, CIP encapsulation efficiency underwent a slight reduction after nine months of storage, although the initial high drug content values would ensure a residual concentration of the antibiotic in the SLN still appropriate to exert an acceptable antibacterial activity. Selected SLN formulations were subjected to an in vitro microbiological assay against different bacterial strains, to verify the effect of nanoencapsulation on the cell growth inhibitory activity of CIP. In general, CIP-SLN produced without DDAB showed MIC values for CIP comparable to those of the free drug. Conversely, addition of increasing percentages of the cationic lipid, reflected by a progressive increase of the positive value of the Zeta potential, showed a variety of MIC values against the various bacterial strains, but with values 2–4 order of dilution lower than free CIP. An hypothesis of the effect of the cationic lipid upon the increased antibacterial activity of CIP in the nanocarriers is also formulated.

Relevance of Lipid-Based Products in the Management of Dry Eye Disease

Components of the ocular surface synergistically contribute to maintaining and protecting a smooth refractive layer to facilitate the optimal transmission of light. At the air-water interface, the tear film lipid layer (TFLL), a mixture of lipids and proteins, plays a key role in tear surface tension and is important for the physiological hydration of the ocular surface and for ocular homeostasis. Alterations in tear fluid rheology, differences in lipid composition, or downregulation of specific tear proteins are found in most types of ocular surface disease, including dry eye disease (DED). Artificial tears have long been a first line of treatment in DED and aim to replace or supplement tears. More recently, lipid-containing eye drops have been developed to more closely mimic the combination of aqueous and lipid layers of the TFLL. Over the last 2 decades, our understanding of the nature and importance of lipids in the tear film in health and disease has increased substantially. The aim of this article is to provide a brief overview of our current understanding of tear film properties and review the effectiveness of lipid-based products in the treatment of DED. Liposome lid sprays, emulsion eye drops, and other lipid-containing formulations are discussed.

Recent perspectives on the delivery of biologics to back of the eye

INTRODUCTION

Biologics are generally macromolecules, large in size with poor stability in biological environments. Delivery of biologics to tissues at the back of the eye remains a challenge. To overcome these challenges and treat posterior ocular diseases, several novel approaches have been developed. Nanotechnology-based delivery systems, like drug encapsulation technology, macromolecule implants and gene delivery are under investigation. We provide an overview of emerging technologies for biologics delivery to back of the eye tissues. Moreover, new biologic drugs currently in clinical trials for ocular neovascular diseases have been discussed. Areas covered: Anatomy of the eye, posterior segment disease and diagnosis, barriers to biologic delivery, ocular pharmacokinetic, novel biologic delivery system Expert opinion: Anti-VEGF therapy represents a significant advance in developing biologics for the treatment of ocular neovascular diseases. Various strategies for biologic delivery to posterior ocular tissues are under development with some in early or late stages of clinical trials. Despite significant progress in the delivery of biologics, there is unmet need to develop sustained delivery of biologics with nearly zero-order release kinetics to the back of the eye tissues. In addition, elevated intraocular pressure associated with frequent intravitreal injections of macromolecules is another concern that needs to be addressed.

Application of lipid nanoparticles to ocular drug delivery

INTRODUCTION

Although eye drops are widely used as drug delivery systems for the anterior segment of the eye, they are also associated with poor drug bioavailability due to transient contact time and rapid washout by tearing. Moreover, effective drug delivery to the posterior segment of the eye is challenging, and alternative routes of administration (periocular and intravitreal) are generally needed, the blood-retinal barrier being the major obstacle to systemic drug delivery. Areas covered: Nanotechnology, and especially lipid nanoparticles, can improve the therapeutic efficiency, compliance and safety of ocular drugs, administered via different routes, to both the anterior and posterior segment of the eye. This review highlights the main ocular barriers to drug delivery, as well as the most common eye diseases suitable for pharmacological treatment in which lipid nanoparticles have proved efficacious as alternative delivery systems. Expert opinion: Lipid-based nanocarriers are among the most biocompatible and versatile means for ocular delivery. Mucoadhesion with consequent increase in pre-corneal retention time, and enhanced permeation due to cellular uptake by corneal epithelial cells, are the essential goals for topical lipid nanoparticle delivery. Gene delivery to the retina has shown very promising results after intravitreal administration of lipid nanoparticles as non-viral vectors.

Innovative hybrid vs polymeric nanocapsules: The influence of the cationic lipid coating on the "4S"

Polymeric and hybrid aqueous-core nanocapsules were prepared using a low energy organic-solvent free procedure as innovative nanodevices for the ophthalmic delivery of melatonin. In order to evaluate how different cationic lipids could affect the main properties of the nanodevices, we focused our attention on mean particles size, surface charge, shape and stability (the "4S"). The results of our study confirmed the hypothesis that the coating material differently affects the overall nanoparticles properties, above all in terms of morphology: in particular, the cationic lipid dimethyldioctadecylammonium bromide allows the formation of very stable well-defined nanocapsules with non-spherical shape with sustained and prolonged drug release, thus representing a great advantage in ophthalmic application.