Effect of diabetes on transscleral delivery of celecoxib

Role of Polymeric Micelles in Ocular Drug Delivery: An Overview of Decades of Research

Local drug delivery to the eye through conventional means has faced many challenges due to three essential barriers: (a) the complex structure of the cornea limiting drug absorption, (b) the capacity of ocular absorptive cells in drug metabolism, and (c) the washing effect of eye tears. Polymeric micelles (PMs) have been the focus of much interest for ocular drug delivery due to several advantages they provide for this application, including the capacity for the solubilization of hydrophobic drugs, nonirritability, nanoscopic diameter, and the clarity of their aqueous solution not interfering with vision. The potential to increase the release and residence time of incorporated medication at the site of absorption is also a bonus advantage for these delivery systems. This Review covers research conducted on single or mixed micelles prepared from small amphiphilic molecules, copolymers (diblock, triblock, and graft), and gel systems containing micelles. The purpose of this review is to provide an update on the status of micellar ocular delivery systems for different indications, with a focus on preclinical and clinical drug development. In this context, we are discussing the anatomy of the eye, various ocular barriers, different micellar formulations, and their benefits in ocular drug delivery, as well as the role of PMs in the management of ocular diseases both in preclinical models and in clinic. The encouraging preclinical effectiveness findings from experiments conducted in both laboratory settings and live animals have paved the way for the advancement of micellar systems in clinical trials for ocular administration and the first nanomicallar formulation approved for clinical use by the United States Food and Drug Administration (marketed as Cequa by Sun Pharmaceuticals).

Melatonin exerts protective effects on diabetic retinopathy via inhibition of Wnt/β-catenin pathway as revealed by quantitative proteomics

Diabetic retinopathy (DR), the most common ocular complication resulting from diabetes in working-age adults, causes vision impairment and even blindness because of microvascular damage to the retina. Melatonin is an endogenous neurohormone possessing various biological properties, including the regulation of oxidative stress, inflammation, autophagy, and angiogenesis functions. To evaluate the effects of melatonin on DR, we first investigated the role of melatonin in retinal angiogenesis and inner blood-retina barrier (iBRB) under high glucose conditions in vitro and in vivo. Melatonin administration ameliorated high glucose-induced iBRB disruption, cell proliferation, cell migration, invasion and tube formation, and decreased the expression levels of VEGF, MMP-2, and MMP-9. Furthermore, melatonin treatment increased the level of autophagy but decreased the expression levels of inflammation-related factors under high glucose conditions. To further explore the underlying mechanism, we evaluated human retinal microvascular endothelial cells (HRMECs) via tandem mass tags (TMT)-labeled quantitative proteomics under high-glucose conditions with or without melatonin. Bioinformatics analysis results revealed that the main enrichment pathway of differentially expressed proteins (DEPs) was the Wnt pathway. We found that melatonin inhibited the activation of Wnt/β-catenin pathway following DR. These abovementioned protective effects of melatonin under hyperglycemia were blocked by lithium chloride (LiCl; activator of the Wnt/β-catenin signaling pathway). In summary, melatonin exerts protective effects on experimental DR via inhibiting Wnt/β-catenin pathway by, at least partially, alleviating autophagic dysfunction and inflammatory activation.

Ocular Pharmacokinetics

Although the fundamental concepts of pharmacokinetics remain the same, ocular pharmacokinetics has its own challenges due to the uniqueness of barrier properties posed by various ocular tissues and its growing complexity with different routes of ocular administration. A thorough understanding of the barrier nature will aid in tailoring a drug or its carrier's physicochemical properties to its advantage. In order to deliver the right payload of a drug at the target site, various approaches can be taken to leverage the pharmacokinetics that includes molecular design based on desirable physicochemical properties, formulation approaches, and alternative routes of administration. In this chapter, a brief overview of the barrier properties with respect to various routes of administration is presented along with the physicochemical properties that influence the pharmacokinetics of ocular drugs. Recent advances in ocular pharmacokinetics are discussed in addition to new perspectives in interpreting existing data.

Nanomedicines for back of the eye drug delivery, gene delivery, and imaging

Treatment and management of diseases of the posterior segment of the eye such as diabetic retinopathy, retinoblastoma, retinitis pigmentosa, and choroidal neovascularization is a challenging task due to the anatomy and physiology of ocular barriers. For instance, traditional routes of drug delivery for therapeutic treatment are hindered by poor intraocular penetration and/or rapid ocular elimination. One possible approach to improve ocular therapy is to employ nanotechnology. Nanomedicines, products of nanotechnology, having at least one dimension in the nanoscale include nanoparticles, micelles, nanotubes, and dendrimers, with and without targeting ligands. Nanomedicines are making a significant impact in the fields of ocular drug delivery, gene delivery, and imaging, the focus of this review. Key applications of nanotechnology discussed in this review include a) bioadhesive nanomedicines; b) functionalized nanomedicines that enhance target recognition and/or cell entry; c) nanomedicines capable of controlled release of the payload; d) nanomedicines capable of enhancing gene transfection and duration of transfection; f) nanomedicines responsive to stimuli including light, heat, ultrasound, electrical signals, pH, and oxidative stress; g) diversely sized and colored nanoparticles for imaging, and h) nanowires for retinal prostheses. Additionally, nanofabricated delivery systems including implants, films, microparticles, and nanoparticles are described. Although the above nanomedicines may be administered by various routes including topical, intravitreal, intravenous, transscleral, suprachoroidal, and subretinal routes, each nanomedicine should be tailored for the disease, drug, and site of administration. In addition to the nature of materials used in nanomedicine design, depending on the site of nanomedicine administration, clearance and toxicity are expected to differ.

RETRACTED: Influence of choroidal neovascularization and biodegradable polymeric particle size on transscleral sustained delivery of triamcinolone acetonide

PURPOSE

One objective of this study was to determine whether polymeric nanoparticles and/or microparticles sustain transscleral choroidal and retinal delivery of triamcinolone acetonide (TA) for two months in therapeutically effective concentrations after single periocular administration. Another objective of this study was to assess the influence of choroidal neovascularization on transscleral delivery of TA.

METHODS

Polymeric nano- and micro-particles of TA were prepared by o/w emulsion-solvent evaporation method using poly-l-lactide (PLA). Particles were characterized for drug loading, size, surface morphology, and the in vitro drug release profile. Choroidal neovascularization (CNV) was induced in brown Norway (BN) rats using a 532 nm diode argon laser and the CNV induction was assessed using fluorescein angiography. In vivo delivery was assessed in control and CNV induced rats at 2 months after periocular injection of TA loaded nano- or micro-particle suspension, or plain TA suspension in PBS (pH 7.4). Ocular tissue levels of TA were estimated using LC-MS/MS following liquid-liquid extraction of drug from tissue samples. Nile red loaded microparticles entrapped in periocular tissue at the end of the study was visualized using scanning electron microscopy and confocal microscopy. Inhibitory effect of TA on VEGF secretion was evaluated in ARPE-19 cells.

RESULTS

Triamcinolone acetonide-PLA nano- (551 nm) and micro-particles (2090 nm), with 14.7 and 29.5% drug loading, respectively, sustained in vitro TA release for about 45 and 120 days. After subconjunctival injection, microparticles were able to sustain the delivery in all intraocular tissues for 2 months; whereas no drug levels were detected for TA loaded nanoparticles and plain suspension of TA. Intraocular delivery of TA from microparticles was higher in CNV induced rats when compared to control rats. Significant amount of microparticles remained in periocular tissue at 2 months after injection, and maintained spherical shape. TA decreased VEGF secretion by 50% at 0.07 μM. At the end of the in vivo study, choroid-RPE and retina TA levels in CNV induced rats were 16- and 5-fold higher than the IC(50) for VEGF secretion.

CONCLUSIONS

Single periocular injection of polymeric microparticles but not nanoparticles sustained effective levels of TA in choroid-RPE and retina for 2 months, with the TA delivery being greater in CNV induced rats than the control rats.

Recent advances in ophthalmic drug delivery

Topical ocular drug bioavailability is notoriously poor, in the order of 5% or less. This is a consequence of effective multiple barriers to drug entry, comprising nasolacrimal drainage, epithelial drug transport barriers and clearance from the vasculature in the conjunctiva. While sustained drug delivery to the back of the eye is now feasible with intravitreal implants such as Vitrasert (-6 months), Retisert (-3 years) and Iluvien (-3 years), currently there are no marketed delivery systems for long-term drug delivery to the anterior segment of the eye. The purpose of this article is to summarize the resurgence in interest to prolong and improve drug entry from topical administration. These approaches include mucoadhesives, viscous polymer vehicles, transporter-targeted prodrug design, receptor-targeted functionalized nanoparticles, iontophoresis, punctal plug and contact lens delivery systems. A few of these delivery systems might be useful in treating diseases affecting the back of the eye. Their effectiveness will be compared against intravitreal implants (upper bound of effectiveness) and trans-scleral systems (lower bound of effectiveness). Refining the animal model by incorporating the latest advances in microdialysis and imaging technology is key to expanding the knowledge central to the design, testing and evaluation of the next generation of innovative ocular drug delivery systems.

Pazopanib, a multitargeted tyrosine kinase inhibitor, reduces diabetic retinal vascular leukostasis and leakage

OBJECTIVE

To determine the efficacy of pazopanib eye drops in the streptozotocin induced diabetic retinopathy rat model.

METHODS

A 0.5% w/v pazopanib suspension was prepared in phosphate buffered saline (PBS, pH 7.4) in the presence of 0.5% w/v sodium carboxymethyl cellulose. Brown Norway rats were divided into three groups (n=4) - (1) healthy, (2) diabetic, and (3) diabetic with treatment. The drug suspension was administered twice daily as eye drops to group 3 for 30 days. Efficacy parameters including the number of adherent leukocytes in the retinal vasculature (leukostasis), blood-retinal FITC-dextran leakage, and vitreous-to-plasma protein ratio were measured.

RESULTS

Pazopanib suspension in the form of eye drops significantly reduced leukostasis (32%), FITC-dextran leakage (39%), and the vitreous-to-plasma protein ratio (64%) in diabetic animals compared to untreated diabetic group.

CONCLUSION

Pazopanib eye drops can alleviate retinal complications of diabetic retinopathy.

Delivery of celecoxib for treating diseases of the eye: influence of pigment and diabetes

IMPORTANCE OF THE FIELD

Age-related macular degeneration (AMD) and diabetic retinopathy (DR) are two major causes of blindness. In these disorders, growth factors such as vascular endothelial growth factor (VEGF) are upregulated, leading to either enhanced vascular permeability or proliferation of endothelium. While corticosteroid therapies available at present suffer from side effects including cataracts and elevated intraocular pressure, anti-VEGF antibody therapies require frequent intravitreal injections, a procedure that can potentially lead to retinal detachment or endophthalmitis. Thus, there is a need to develop safe, sustained release therapeutic approaches for treating AMD and DR.

AREAS COVERED IN THIS REVIEW

This review discusses the pharmacological basis for using celecoxib, an anti-inflammatory drug capable of selectively inhibiting cycloxygenase 2, in treating AMD and DR. In addition, this article discusses the safety, delivery advantage and efficacy of celecoxib by transscleral retinal delivery, a periocular delivery approach that is less invasive to the globe compared with intravitreal injections.

WHAT THE READER WILL GAIN

The reader will gain insights into the development of a pharmacological agent and a sustained release delivery system for treating DR and AMD. Further, the reader will gain insights into the influence of eye physiology including pigmentation and disease states such as DR on retinal drug delivery.

TAKE HOME MESSAGE

Transscleral sustained delivery of anti-inflammatory agents is a viable option for treating retinal disorders.

Ocular drug delivery

Ocular drug delivery has been a major challenge to pharmacologists and drug delivery scientists due to its unique anatomy and physiology. Static barriers (different layers of cornea, sclera, and retina including blood aqueous and blood-retinal barriers), dynamic barriers (choroidal and conjunctival blood flow, lymphatic clearance, and tear dilution), and efflux pumps in conjunction pose a significant challenge for delivery of a drug alone or in a dosage form, especially to the posterior segment. Identification of influx transporters on various ocular tissues and designing a transporter-targeted delivery of a parent drug has gathered momentum in recent years. Parallelly, colloidal dosage forms such as nanoparticles, nanomicelles, liposomes, and microemulsions have been widely explored to overcome various static and dynamic barriers. Novel drug delivery strategies such as bioadhesive gels and fibrin sealant-based approaches were developed to sustain drug levels at the target site. Designing noninvasive sustained drug delivery systems and exploring the feasibility of topical application to deliver drugs to the posterior segment may drastically improve drug delivery in the years to come. Current developments in the field of ophthalmic drug delivery promise a significant improvement in overcoming the challenges posed by various anterior and posterior segment diseases.