Treatment Of Posterior Segment Diseases Research Articles

The Evolution of Triamcinolone Acetonide Therapeutic Use in Retinal Diseases: From Off-Label Intravitreal Injection to Advanced Nano-Drug Delivery Systems.

Ophthalmic drug delivery to the posterior segment of the eye has been challenging due to the complex ocular anatomy. Intravitreal injection of drugs was introduced to deliver therapeutic doses in the posterior segment. Different posterior segment diseases including age-related macular degeneration, diabetic macular edema, retinal vein occlusions, uveitis, and cystoid macular edema, among others, have been historically treated with intravitreal corticosteroids injections, and more recently with intravitreal corticosteroids drug implants. Triamcinolone acetonide (TA) is the most frequently used intraocular synthetic corticosteroid. Using nanoparticle-based TA delivery systems has been proposed as an alternative to intravitreal injections in the treatment of posterior segment diseases. From these novel delivery systems, topical liposomes have been the most promising strategy. This review is oriented to exhibit triamcinolone acetonide drug evolution and its results in treating posterior segment diseases using diverse delivery platforms.

Polymeric biomaterials in the treatment of posterior segment diseases.

Polymeric biomaterials are biological or synthetic substances which can be engineered to interact with biological systems for the diagnosis or treatment of diseases. These biomaterials have immense potential for treating eyes diseases, particularly the retina-a site of many inherited and acquired diseases. Polymeric biomaterials can be engineered to function both as an endotamponade agent and to prevent intraocular scarring in retinal detachment repair surgeries. They can also be designed as a drug delivery platform for treatment of retinal diseases. Finally, they can be used as scaffolds for cellular products and provide non-viral gene delivery solutions to the retina. This perspective article explains the role of polymeric biomaterials in the treatment of retinal conditions by highlighting recent advances being translated to clinical practice. The article will also identify potential hurdles to clinical translation as future research directions in the field.

Chitosan/sulfobutylether-β-cyclodextrin based nanoparticles coated with thiolated hyaluronic acid for indomethacin ophthalmic delivery

Indomethacin (IND) is topically administered for the treatment of the anterior segment diseases such as conjunctivitis, uveitis, and inflammation prevention for post-cataract surgery, as well as posterior segment diseases as macular edema. Currently IND is available as 0.1% w/v hydroxypropyl-β-cyclodextrin-based eye drop formulation and its bioavailability is limited by several drawbacks such as the nasolacrimal duct draining, the reflex blinking and the low volume of the conjunctival sac. In this study, chitosan (CS)/sulfobutylether-β-cyclodextrin (SBE-β-CD) based nanoparticles (NPs) with a mean diameter of 340 (±7) nm, a ζ-potential value of +18.3 (±0.5) mV and coated with thiolated low molecular weight hyaluronic acid were formulated to improve both the solubility and the residential time in the conjunctival sac of the loaded drug IND. The NPs were prepared through the ionotropic gelation technique, exploiting the interaction between the positively charged amino group of CS and the negatively charged sulfonic group of SBE-β-CD. The mucoadhesive properties of the NPs were evaluated on chicken trachea and esophagus tissues using a texture analyser. The irritability effects of NPs were disclaimed with Hecam test. The developed coated NPs showed increased residential time in the conjunctival sac, displayed no irritancy or toxicity for local administration, making them an optimal and innovative drug delivery system for the treatment of anterior segment inflammation diseases. On the other hand, the uncoated NPs displayed better permeating properties since they are smaller and could be further exploited for the treatment of posterior segment diseases.

In-vivo Evaluation and Characterization of Novel In-Situ Gelling System as Controlled Delivery System Containing Ciprofloxacin for Ocular Drug Delivery

Objectives: The purpose of this research was to develop the micro emulsion-based in situ gelling systems containing Ciprofloxacin for prophylaxis and treatment of the posterior segment diseases like endophthalmitis.
 Methods: Ciprofloxacin was encapsulated in small droplets owing to form microemulsion, and then the formed droplets were dispersed in a polymer solution that converted into a gel upon triggered by the electrolyte present in the tear fluid.
 Results: The formulation approach provides better absorption, penetration, retention, and improves the bioavailability of the drug. The average concentration reached into vitreous humor from topical microemulsion in situ gelling formulation was ~0.4 µg/ml, which is far more than the concentration required for therapeutic effect (i.e. >0.047 µg/ml or >MIC90 for S. Epidermidis, a pathogen commonly responsible to cause endophthalmitis).
 Conclusion: Thus, novel micro emulsion-based in situ gelling formulation could be a potential drug delivery system for the treatment of posterior segment diseases like endophthalmitis.
 Keywords: Microemulsion, ciprofloxacin, endophthalmitis, ocular, infection, in situ

Micelles: Promising Ocular Drug Carriers for Anterior and Posterior Segment Diseases.

Micelles have been studied in the targeting of drug substances to different tissues as a nano-sized delivery system for many years. Sustained drug release, ease of production, increased solubility, and bioavailability of drugs with low water solubility are the most important superiorites of micellar carriers. These advantages paved the way for the use of micelles as a drug delivery system in the ocular tissues. The unique anatomical structure of the eye as well as its natural barriers and physiology affect ocular bioavailability of the drugs negatively. Conventional dosage forms can only reach the anterior segment of the eye and are used for the treatment of diseases of this segment. In the treatment of posterior segment diseases, conventional dosage forms are administered sclerally, via an intravitreal injection, or systemically. However, ocular irritation, low patient compliance, and high side effects are also observed. Micellar ocular drug delivery systems have significant promise for the treatment of ocular diseases. The potential of micellar systems ocular drug delivery has been demonstrated by in vivo animal experiments and clinical studies, and they are continuing extensively. In this review, the recent research studies, in which the positive outcomes of micelles for ocular targeting of drugs for both anterior and posterior segment diseases as well as glaucoma has been demonstrated by in vitro, ex vivo, or in vivo studies, are highlighted.

Transscleral Delivery of Bevacizumab-Loaded Chitosan Nanoparticles.

Purpose: The aim of this study was to synthesize bevacizumab-loaded nanoparticles and evaluate their effects on the treatment of posterior segment diseases via subtenon injections. Methods: Bevacizumab-loaded chitosan nanoparticles (BLCNs) were synthesized by the ionic gelation method, and their physicochemical characteristics and in vitro release profile were studied. The BLCNs were characterized using atomic force microscopy (AFM), FTIR spectroscopy, dynamic light scattering, and scanning electron microscopy. The BLCNs were delivered into rabbits' eyes via posterior subtenon injections. An immunohistochemical evaluation of the ocular tissues was performed, and the vitreous humor and serum bevacizumab levels were measured by ELISA. Results: Bevacizumab-loaded chitosan nanoparticles with a diameter of 80 to 380 nm were prepared and characterized. In vitro studies showed that after the first 5 days of the experiment, a significant increase in the drug release maintained the desired drug dosage for 3 weeks. Immunohistochemical in vivo studies revealed that there were BLCNs penetrating through the sclera. Furthermore, the intravitreal bevacizumab concentration reached a maximum concentration of 18 μg/ml, and it decreased to 6 μg/ml after only a week. Conclusion: The results revealed that subtenon injection of BLCNs is a promising alternative to intravitreal injections. In addition to the ELISA studies, immunohistochemical experiments confirmed that BLCNs enable transscleral bevacizumab penetration, and BLCN usage may provide the required bevacizumab levels for the treatment of posterior segment diseases.

7.1 T MRI and T2 mapping of the human and porcine vitreous body post mortem

Numerous literature reports describe the liquefaction of the vitreous body with increasing age. It must be expected that this process also influences drug distribution and elimination following intravitreal application of active pharmaceutical ingredients (APIs). To better understand the impact and extent of the liquefaction a magnetic resonance imaging (MRI) study was performed examining human donor eyes post mortem. For comparison, eyes of juvenile pigs were also examined representing a fully gelled vitreous.7.1Tesla ultra-high field MRI and T2 mapping of the vitreous body were used in this study since it must be expected that age-induced degradation processes and structural changes of the vitreous gel to a liquid state will result in changes of the T2 relaxation time of water proton spins. The vitreous bodies were imaged in 12 axial slices and within each image the T2 relaxation times of water proton spins were determined. It was found that T2 relaxation time increased with increasing age of the donor. Whilst the mean T2 relaxation time (±standard deviation) of water proton spins within the central vitreous body of a juvenile porcine eye was 210.1 ± 31.1 ms, the mean T2 relaxation time within the central vitreous body of the 88-year-old and therefore oldest human donor was 528.0 ± 79.3 ms. Within the vitreous body of a single donor, the T2 relaxation time increased from the anterior to the posterior segment, for example in the vitreous body of the oldest human donor from 388.0 ± 31.1 ms on average in the anterior to 631.7 ± 42.8 ms in the posterior segment, indicating an increase in intravitreal liquefaction respectively inhomogeneity from anterior to posterior regions. Additionally, physicochemical parameters were determined yielding averages of 7.54 ± 0.34 for pH, 1.33629 ± 0.00044 for refractive index, 368.99 ± 26.87 mosmol/kg for osmolality, 97.56 ± 0.43% for drying mass loss and 0.73 ± 0.18 mg/mL for total protein content.The aging process and the liquefaction of the vitreous body are expected to affect the pharmacokinetic profile of intravitreally injected APIs, which is of high relevance to drug release from intravitreal drug delivery systems and the therapeutic concept in the treatment of posterior segment diseases. Our data indicate that such processes are not reflected in animal models. Since there is still a need for valid pharmacokinetic data, invitro test systems for the characterization of intraocular drug delivery systems have to be improved according to the current state of knowledge about the vitreous structure and intravitreal transport phenomena.

Evaluation of the Safety and Tolerability of Conjunctival Ring for Posterior Segment of the Eye

ABSTRACTPurpose: To evaluate the safety and tolerability of conjunctival rings (CRs), a novel device for drug delivery to the posterior segment of the eye.Methods: In animal studies, CRs containing 5% dexamethasone sodium phosphate (DSP) or vehicle solution were placed on the right and left eyes of C57BL/6J mice, respectively. Contact lenses (CLs) containing vehicle solution were used as a control. Twenty-four hours after placement of the CRs, corneal fluorescein staining was graded based on the McDonald-Shadduck scoring system, ranging from 0 to 4. In humans, CRs containing vehicle solution were placed on the right eye of healthy volunteers for 9 hours. The corneal curvature, corneal thickness, intraocular pressure, visual acuity, tear production (Schirmer I test), tear film break-up time and fluorescein staining scores of the cornea (scores ranging from 0 to 3) and conjunctiva (scores ranging from 0 to 6) were assessed before and after wearing the CRs. The release characteristics of DSP from CRs were also evaluated.Results: In animal experiments, corneal fluorescein staining scores were 1 or less in all the groups, and there was no significant difference between the CR group and the CL group. In the preclinical safety evaluation of CR for humans, ophthalmic examination revealed that CR caused no significant changes in all the parameters investigated including corneal curvature (p = 0.77), corneal thickness (p = 0.96), intraocular pressure (p = 0.59), visual acuity (p = 0.14), Schirmer I test results (p = 0.76), tear film break-up time (p = 0.68), corneal fluorescein staining scores (p = 0.64), and conjunctival fluorescein staining scores (p = 0.52). The DSP release from CRs occurs within a few hours, which is similar to the drug-release property of medicated CL, as reported previously.Conclusions: The current data showed the safety and tolerability of CR as a drug delivery device for the treatment of posterior segment diseases.

Intravitreal infusion: A novel approach for intraocular drug delivery.

Intraocular injection has become an increasingly important intervention in the treatment of posterior segment diseases. However, an acute intraocular pressure (IOP) elevation after intravitreal injection is a common concern. This study aimed to evaluate the efficacy of intravitreal infusion in maintaining stable IOP in a rabbit model. Trypan blue (TB) 0.06% with an external pump was used to evaluate intravitreal infusion in rabbit eyes. Groups A (50 μL), B (100 μL), C (150 μL), and D (200 μL) were slowly infused over 30 minutes with TB. As a control, Group E underwent conventional intravitreal injection of 100 μL of TB. Group F received a bolus infusion of 100 μL of TB within 1 minute. The mean increases in IOP during infusion for each group were: Group A (7.93 ± 3.80 mmHg), B (13.97 ± 3.17 mmHg), C (19.91 ± 6.06 mmHg) and D (29.38 ± 8.97 mmHg). Immediately post-injection in group E the mean increase in IOP amounted to 34.33 ± 6.57 mmHg. The mean increase in IOP of group F after bolus infusion was 49.89 ± 1.71 mmHg. Intravitreal infusion maintains a stable IOP and provides a controlled infusion speed compared with intravitreal injection.

Circumferential flow of particles in the suprachoroidal space is impeded by the posterior ciliary arteries

Microneedle injection into the suprachoroidal space (SCS) enables targeted drug delivery for treatment of posterior segment diseases. This study sought to identify and characterize anatomical barriers to circumferential spread of particles in the SCS of rabbit and human cadaver eyes. These barriers could make targeting specific regions within the SCS challenging. A hollow microneedle (33-gauge, 750 μm long) was used to inject fluorescent particles into albino New Zealand White rabbit eyes ex vivo at six different positions around the limbus and a limited number of conditions in vivo. SCS injections were also performed in human cadaver eyes 8 mm and 2 mm from the optic nerve (ON). Eyes were dissected and particle distribution was quantified. In rabbit eyes, injections made in the superior or inferior hemispheres (even when injected temporally immediately adjacent to the long posterior ciliary artery (LPCA)) did not significantly cross into the other hemisphere, apparently due to a barrier formed by the LPCA. The vortex veins had a minor effect on particle deposition, limited to only around the vortex vein root. In human eyes, the short posterior ciliary arteries (SPCAs) prevented circumferential spread towards the macula and ON. In conclusion, the rabbit LPCA and the human SPCA were anatomical barriers to particle spread within the SCS. Therefore, design of drug delivery protocols targeting the SCS need to account for barriers formed by anatomical structures in order for injected drug to reach target tissues.

Sustained intravitreal delivery of dexamethasone using an injectable and biodegradable thermogel

Delivery of therapeutic agents to posterior segment of the eyes is challenging due to the anatomy and physiology of ocular barriers and thus long-acting implantable formulations are much desired. In this study, a thermogelling system composed of two poly(lactic acid-co-glycolic acid)–poly(ethylene glycol)–poly(lactic acid-co-glycolic acid) (PLGA–PEG–PLGA) triblock copolymers was developed as an injectable matrix for intravitreal drug delivery. The thermogel was prepared by mixing a sol and a precipitate of PLGA–PEG–PLGA triblock copolymers with different block ratios, among which a hydrophobic glucocorticoid, dexamethasone (DEX), was incorporated. The DEX-loaded thermogel was a low-viscous liquid at low temperature and formed a non-flowing gel at body temperature. The in vitro release rate of DEX from the thermogel could be conveniently modulated by varying the mixing ratio of the two copolymers. The long-lasting intraocular residence of the thermogel was demonstrated by intravitreal injection of a fluorescence-labeled thermogel to rabbits. Compared with a DEX suspension, the intravitreal retention time of DEX increased from a dozen hours to over 1week when being loaded in the thermogel. Additionally, intravitreal administration of the thermogel did not impair the morphology of retina and cornea. This study reveals that the injectable PLGA–PEG–PLGA thermogel is a biocompatible carrier for sustained delivery of bioactive agents into the eyes, and provides an alternative approach for treatment of posterior segment diseases.

Novel thermosensitive pentablock copolymers for sustained delivery of proteins in the treatment of posterior segment diseases.

Biodegradable and injectable in situ thermosensitive hydrogels were investigated for sustained delivery of pro- tein therapeutics in the treatment of ocular posterior segment neovascular diseases. A series of triblock (TB, polycaprolac- tone-polyethylene glycol-polycaprolactone (PCL-PEG-PCL), B-A-B) and pentablock copolymers (PBCs) (polylactic acid (PLA)-PCL-PEG-PCL-PLA (C-B-A-B-C) and PEG-PCL-PLA-PCL-PEG (A-B-C-B-A)) were synthesized and evaluated for their thermosensitive behavior. Effects of molecular weight, hydr ophobicity and block arrangement on polymer crys-tallinity, sol-gel transition, micelle size, viscosity and in vitro drug release were examined. Results from sol-gel transition studies demonstrated that aqueous solutions of block copolymers can immediately transform to hydrogel upon exposure to physiological temperature. PBC provide significantly longer sustained release (more than 20 days) of IgG relative to TB copolymers. Moreover, kinematic viscosity of aqueous solution at 25°C for A-B-C-B-A type of PBCs was noticeably lower than the TB (B-A-B) copolymers and other PBCs with C-B-A-B-C block arrangements suggesting desired syringe- ability. The presence of PLA blocks in PBCs (C-B-A-B-C and A-B-C-B-A) significantly reduces crystallinity. Hence, it is anticipated that PBCs will have a faster rate of degradation relative to PCL-PEG-PCL based TB c opolyme rs. PBCs also exhibited excellent cell viability and biocompatibility on ARPE-19 (human retinal pigment epithelial cell line) and RAW- 264.7 (mouse macrophage cells), likely rendering it safe for ocular applications. Owing to biodegradability, thermosensi- tivity, ease of handling and biocompatibility PBC hydrogels can be considered as promising biomaterial for sustained de- livery of protein therapeutics to the back of the eye.

Topical dexamethasone–cyclodextrin microparticle eye drops for uveitic macular oedema

Cystoid macular oedema (CME) is the main cause of visual loss in patients with uveitis (Rothova 2007). The mainstay of treatment of uveitic CME is corticosteroids and to be effective, steroid needs to be given periocularly, intravitreally or systemically. Topical steroid generally is of little benefit for the treatment of posterior segment diseases. Dexamethasone eye drops containing γ-cyclodextrin-based nanoparticles, however, have recently been shown to be effectively delivered to the posterior part of the eye to treat diabetic CME (Loftsson & Stefánsson 2002; Loftsson et al. 2007; Tanito et al. 2011). Therefore, it seems tempting to examine the effect of this dexamethasone eye drop formulation for the treatment of uveitis with posterior manifestations. We have treated three patients with uveitic CME with 1.5% dexamethasone–cyclodextrin ophthalmic solution (Oculis ehf., Reykjavik, Iceland) after obtaining informed consent from each patient. A 54-year-old female with bilateral, chronic, idiopathic intermediate uveitis and CME. Left eye was previously vitrectomized. Visual acuity was reduced to 0.4 (in decimals) on both eyes. She had pronounced CME and slight vitritis (+1) in both eyes. The CME and vitritis resolved on treatment with systemic prednisone in high dose and visual acuity increased to 0.63 in both eyes. CME on the left eye, however, recurred 3 months after tapering prednisone (Fig. 1A), and visual acuity dropped down to 0.5. The patient was then treated with 1.5% dexamethasone–cyclodextrin ophthalmic solution four times daily for 1 month in the left eye. Visual acuity increased to 0.63 and the CME resolved (Fig. 1B). As dexamethasone–cyclodextrin eye drops are not available in Denmark, she then continued treatment with commercial dexamethasone eye drops, Maxidex ® (Dexamethasone 0.1%; Alcon Inc, Fort Worth, TX, USA) 4 times daily in the left eye. After 1 month, the CME in the left eye had recurred (Fig. 1C), and she was subsequently treated with periocular triamcinolone acetonide and systemic prednisone in a low dose. A 84-year-old woman with bilateral vitritis and CME. Vitritis resolved after initating systemical treatment with mycophenolate mofetil. CME was persistent in both eyes (foveal thickness 357/332 μm). Visual acuity was 0.5 in both eyes. Right eye was treated with dexamethasone–cyclodextrin eye drops two drops four times daily tapered to one drop three times daily after 3 weeks. Left eye was treated with an intravitreal dexamethasone implant (Ozurdex; Allergan, Inc., Irvine, CA, USA). After 6 weeks of treatment, visual acuity was 0.8 in the right eye and 0.63 in the left eye, and the CME had resolved in both eyes (foveal thickness 315/317 μm). A 47-year-old woman with chronic, bilateral, posterior uveitis and CME. She was treated with Ozurdex in both eyes, but the CME recurred after 3 months. The Ozurdex implantation was repeated on the left eye. The right eye was treated with dexamethasone–cyclodextrin eye drops one drop six times daily for 1 week and then four times daily for 1 week. After 2 weeks of treatment, the CME in the right eye was increased further, and the eye received a new Ozurdex implant. The present cases indicate that topical dexamethasone–cyclodextrin nanoparticle eye drops may be effective for the treatment of uveitic CME in some patients. In the first two cases, the CME was resolved after 1 month of treatment with this topical steroid formulation and recurred 1 month after treatment with conventional steroid eye drops. It therefore seems worth to explore the potential of dexamethasone–cyclodextrin nanoparticle eye drops for the treatment of uveitis with posterior manifestations as an alternative to periocular, intravitreal and systemic treatment with steroid. Periocular and intravitreal steroid carry a potential risk of ocular complications, and treatment with systemic steroid involves a considerable risk of serious systemic side-effects. Moreover, in children, the possibility of topical steroid treatment for uveitis with posterior manifestations would be of great benefit as treatment with periocular and intravitreal steroid in these patients requires a general anaesthetic prior to administration.

Tailor-made pentablock copolymer based formulation for sustained ocular delivery of protein therapeutics.

The objective of this research article is to report the synthesis and evaluation of novel pentablock copolymers for controlled delivery of macromolecules in the treatment of posterior segment diseases. Novel biodegradable PB copolymers were synthesized by sequential ring-opening polymerization. Various ratios and molecular weights of each block (polyglycolic acid, polyethylene glycol, polylactic acid, and polycaprolactone) were selected for synthesis and to optimize release profile of FITC-BSA, IgG, and bevacizumab from nanoparticles (NPs) and thermosensitive gel. NPs were characterized for particle size, polydispersity, entrapment efficiency, and drug loading. In vitro release study of proteins from NPs alone and composite formulation (NPs suspended in thermosensitive gel) was performed. Composite formulations demonstrated no or negligible burst release with continuous near zero-order release in contrast to NPs alone. Hydrodynamic diameter of protein therapeutics and hydrophobicity of PB copolymer exhibited significant effect on entrapment efficiency and in vitro release profile. CD spectroscopy confirmed retention of structural conformation of released protein. Biological activity of released bevacizumab was confirmed by in vitro cell proliferation and cell migration assays. It can be concluded that novel PB polymers can serve a platform for sustained delivery of therapeutic proteins.

Drug Delivery to the Back of the Eye Following Topical Administration: An Update on Research and Patenting Activity

Drug delivery to the back of the eye following topical administration remains an unmet need for the scientific community. Treatment of posterior segment diseases requires localized and long-term drug delivery to the retina, choroid, and Bruch's membrane. Until the last decade, there was limited evidence from large clinical trials that demonstrated the usefulness of pharmacotherapy compared to laser therapy or other vitreoretinal surgical techniques for the treatment of retinal diseases. This paradigm has shifted in recent years, with strong evidence demonstrating superior efficacy of ophthalmic drugs compared to previous gold standards. However, ophthalmologists are left with no options other than administering the therapeutics via implants and intravitreal injections, which are highly invasive and associated with patient non-compliance. A non-invasive topical therapy would enhance patient compliance and minimize the side-effects associated with intraocular implants and intravitreal injections. In an attempt to enhance patient compliance, the focus of research has shifted to the development of novel small molecule-based eye drop formulations. This review article discusses the relevant patents and summarizes the resurgence in the treatment of posterior segment eye diseases through topical drug administration.

Progress in sustained-release drug delivery system for treatment of posterior segment eye diseases

There is an urgent requirement to find effective therapeutic procedures for the treatment of refractory eye diseases of posterior segment such as posterior uveitis, proliferative vitreoretinopathy, and macular edema associated with diabetes and retinal vein occlusion. Due to systemic side effect developed from systemic drug administration and the low efficiency of topical drug administration, implantable drug devices for the treatment of posterior segment diseases have been explored. In recent years, three different intraocular implantable devices (ganciclovir, fluocinolone acetonide and dexamethasone) have been approved by FDA and showed exciting clinical efficacy. However, these devices have surgical complications and the drug-related side effects. Recently, transscleral drug delivery to the posterior segment has been investigated. Transscleral drug delivery has advantages of large scleral surface area, better safety profile, easily drug administration and could evolve into an effective route with the use of novel biomaterials and the study of drug delivery methods.

Intravitreal Administration of Dexamethasone-Loaded PLGA-TPGS Nanoparticles for the Treatment of Posterior Segment Diseases

The purpose of this research was to investigate the possibility of dexamethasone (DEX)-loaded PLGA-TPGS nanoparticles (NPs) in rabbits after intravitreal administration for the treatment of posterior segment diseases. The DEX-loaded PLGA-TPGS NPs were fabricated and characterized in terms of surface morphology, particle size and size distribution, entrapment efficiency, and in vitro drug release. The animals were classified randomly into two groups: experimental group with thirty rabbits, and control group with eighteen rabbits. Rabbits in the experimental group received intravitreal injections of 0.1 mL of DEX-loaded PLGA-TPGS NPs suspension and the control rabbits received intravitreal injection of 0.1 mL DEX (20 g/L in saline). The DEX concentrations in plasma and the ocular tissues such as the cornea, aqueous humor, lens, iris, vitreous humor, and chorioretina were determined by HPLC. The DEX-loaded PLGA-TPGS nanoparticle suspension were transparent and maintained a sustained release of DEX for about 45 days in vitreous and provided relatively constant DEX levels for more than 30 days with a mean concentration of 3.93 mg/L. Based on the area-under-the-curve (AUC), the bioavailability of DEX in the experimental group was significantly higher than that in the control group administrated with regular DEX. These results suggest that intravitreal administration of DEX-loaded PL.3A-TPGS NPs leads to a sustained release of DEX with a high bioavailability, providing a basis for a novel approach to treat posterior segment diseases.

Intraocular administration of biodegradable microspheres to increase drug bioavailability and extend therapeutic effect

AbstractPurpose Treatment of posterior segment diseases often requires repeated intravitreal injections to achieve and maintain steady state concentrations of the active substance in the target site. However, intraocular injections are associated to adverse effects and the risk of complications increases with the number of administrations. Biodegradable microspheres (MPs) are considered an alternative to multiple injections as they are able to release the encapsulated drug over weeks or months. Copolymers of lactic and glycolic acids (PLGA) are FDA approved biodegradable biomaterials commonly used to prepare MPs. They are biocompatible and degrade to metabolic products that are easily eliminated from the body. The main advantages of these systems is that they can be injected as a conventional suspension without surgical procedures. After intravitreal administration, PLGA microspheres suffer aggregation disappearing from the site of injection after delivering the drug. Microspheres can be loaded with different active substances (small molecules and biotechnological products) useful to treat vitreoretinal diseases. Administration of microparticles can be performed by periocular, intravitreal, sub‐ retinal, or other intraocular routes to treat posterior segment disorders.Conclusion PLGA microspheres are emerging therapeutic tools for the treatment of posterior segment diseases in which steady state concentrations of the active substance is needed over an extended period of time. Acknowledgements: PANOPTES‐Peptide‐based Nanoparticles as Ocular Drug Delivery Vehicles‐ collaborative project (FP7‐NMP‐2009); Spanish Ministry of Economy MAT 2010‐18242, UCM Research Group 920415 and RETICs (RD07/0062/2002)

In Vitro Response of Retinal Pigment Epithelial Cells Exposed to Chitosan Materials Prepared with Different Cross-Linkers

The interaction between cells and biopolymers is the evaluation indicator of the biocompatibility of materials. The purpose of this work was to examine the responses of retinal pigment epithelial (RPE) cells to genipin (GP) or glutaraldehyde (GTA) cross-linked chitosan by means of cell viability assays, cytokine expression analyses, and apoptosis assays. Evaluations of non-cross-linked chitosan were conducted simultaneously for comparison. Both GP and GTA treated samples with the same extent of cross-linking (around 80%) were prepared by varying cross-linking time. Our results showed that GP cross-linking was carried out by either radical polymerization of the monomers or SN2 nucleophilic substitution reaction involving the replacement of the ester group on the monomer with a secondary amide linkage. On the other hand, GTA could react with free amino groups of chitosan, leading to the formation of either the Schiff bases or the Michael-type adducts with terminal aldehydes. The biocompatibility of non-cross-linked chitosan membranes was demonstrated by the absence of any signs of toxicity or inflammation reaction. The present study showed that the ARPE-19 cells exposed to GTA cross-linked chitosan membranes had significantly higher cytotoxicity, interleukin-6 levels, and number of TUNEL-positive nuclei than did those exposed to GP treated samples. In addition, the materials modified with GTA trigger apoptosis at an early stage and may induce toxicity in the RPE cells later. The findings suggest that while the chitosan molecules bridged by GP are satisfactorily cytocompatible, the counterparts treated by GTA do not seem to be tolerated. In terms of material safety, the GP cross-linked chitosan may be compatible with human RPE cells and may have a potential application as delivery carriers in the treatment of posterior segment diseases.

Pharmacokinetics and tolerance study of intravitreal injection of dexamethasone-loaded nanoparticles in rabbits.

The aim of the study was to investigate the tolerance and pharmacokinetics of dexamethasone (DEX)-loaded poly(lactic acid-co-glycolic acid) nanoparticles (DEX-NPs) in rabbits after intravitreal injection. The DEX-NPs were prepared and characterized in terms of morphology, particle size and size distribution, encapsulation efficiency, and in vitro release. Ophthalmic investigations were performed, including fundus observation and photography, intraocular pressure measurement, and B-scan ocular ultrasonography. There were no abnormalities up to 50 days after administration of DEX-NPs in rabbits. The DEX concentrations in plasma and the ocular tissues such as the cornea, aqueous humor, lens, iris, vitreous humor, and chorioretina were determined by high-pressure liquid chromatography. The DEX-NPs maintained a sustained release of DEX for about 50 days in vitreous and provided relatively constant DEX levels for more than 30 days with a mean concentration of 3.85 mg/L(-1). Based on the areas under the curve, the bioavailability of DEX in the experimental group was significantly higher than that in the control group injected with regular DEX. These results suggest that intravitreal injection of DEX-NPs lead to a sustained release of DEX with a high bioavailability, providing a basis for a novel approach to the treatment of posterior segment diseases.