Sustained reduction of intraocular pressure by supraciliary delivery of brimonidine-loaded poly(lactic acid) microspheres for the treatment of glaucoma

Co-instillation of nano-solid magnesium hydroxide enhances corneal permeability of dissolved timolol

We prepared magnesium hydroxide (MH) nanoparticles by a bead mill method, and investigated whether the co-instillation of MH nanoparticles improves the low transcorneal penetration of water-soluble drugs, such as the anti-glaucoma eye drug timolol maleate (TM). MH particle size was decreased by the bead mill treatment to a mean particle size of 71 nm. In addition, the MH nanoparticles were highly stable. Next, we demonstrated the effect of MH nanoparticles on the corneal surface. MH shows only slight solubility in lacrimal fluid, and the instillation of MH nanoparticles for 14 days did not affect the behavior (balance of secretion and excretion) of the lacrimal fluid in rabbit corneas. Moreover, there was no observable corneal toxicity of MH nanoparticles, and treatment with MH nanoparticles enhanced the intercellular space ratio in the eyes of rats. MH alone did not permeate into the cornea; however, the co-instillation of MH nanoparticles and dissolved TM (nMTFC) enhanced the corneal penetration of TM. In addition, the intraocular pressure (IOP)-reducing effect of nMTFC was significantly higher than those of the TM solution or the co-instillation of MH microparticles and TM. In conclusion, we found that MH nanoparticles enhance the corneal penetration of dissolved TM with no observable corneal stimulation or obstruction of the nasolacrimal duct by the MH nanoparticles. It is possible that the co-instillation of MH nanoparticles may provide a useful way to improve the bioavailability of water-soluble drugs in the ophthalmic field. These findings provide significant information that can be used to design further studies aimed at developing anti-glaucoma eye drugs.

[Possibilities and limitations of eye drops for glaucoma therapy]

BACKGROUND

In Germany, chronic open-angle glaucoma is mostly treated by daily eye drop application. The possibilities and limitations of this form of therapy are presented. Reasons for the change in the selection of the preferred substances over time are also discussed and the limits of local drug therapy are described.

OBJECTIVES

What effects can be expected of the available drugs?

MATERIALS AND METHODS

The article provides a review of the literature from PubMed and clinical experience.

RESULTS

In chronic open-angle glaucoma, eye drops containing a single agent can achieve an intraocular pressure decrease of 15-35 % compared to the initial pressure level. This is dependent on the substance and is achievable when used as directed. Difficulties in administration are often observed in older patients where regular use over extended periods of time is required. In addition, there are limits in the achievable pressure reduction by combining several active ingredients. Novel systems are being developed for future applications. The idea is to achieve a continuous slow release of the active substance by surgical application of a biodegradable carrier.

CONCLUSION

A treatment regimen which is individually tailored to the individual patient's needs should be developed by the attending physician and the achievement of the set objectives should be monitored at regular intervals. However, restrictions induced by patients due to inadequate adherence or by the drug due to limited efficacy of the drug have to be considered. Therefore, eye drop therapy in open-angle glaucoma is not always sufficient. It should be supplemented in due time by laser or filtering surgery before the affected patients and their optic nerves suffer advanced glaucomatous damage.

Long Term Glaucoma Drug Delivery Using a Topically Retained Gel/Microsphere Eye Drop

The purpose of this study was to characterize and determine the efficacy of a long-term, non-invasive gel/microsphere (GMS) eye drop for glaucoma. This novel drug delivery system is comprised of a thermoresponsive hydrogel carrier and drug-loaded polymer microspheres. In vitro release of brimonidine from the GMS drops and gel properties were quantified. A single brimonidine-loaded GMS drop was administered to 5 normotensive rabbits and intraocular pressure (IOP) was monitored for 28 days. Here we report that IOP reduction in rabbits receiving a single brimonidine GMS drop was comparable to that of rabbits receiving twice daily, standard brimonidine drops. GMS drops were retained in the inferior fornix in all animals for the length of the study. Our results suggest in vivo efficacy over 28 days from a single GMS drop and a potential decrease in systemic absorption, based on a lack of substantial IOP effects on the fellow untreated eye, compared to brimonidine twice-daily eye drops. To our knowledge, this represents the first long-term, drug-releasing depot that can be administered as a traditional eye drop.

Non-invasive strategies for targeting the posterior segment of eye

The safe and effective treatment of eye diseases has been remained a global myth. Several advancements have been done and various drug delivery and treatment techniques have been suggested. The Posterior segment disorders are the leading cause of visual impairments and blindness. Targeting the therapeutic agents to the anterior and posterior segments of the eye has attracted extensive attention from the scientific community. Significant key factors in the success of ocular therapy are the development of safe, effective, economic and non-invasive novel drug delivery systems. These specialized non-invasive ocular drug delivery systems revolutionized the drug delivery strategies by overcoming the limitations, provided targeted delivery to the ocular tissues by avoiding larger doses, and reducing the toxicity encountered by the conventional approaches. These non-invasive systems are fabricated by ingredients encompassing biodegradability, biocompatibility, mucoadhesion, solubility and permeability enhancement and stimuli responsiveness. The variety of routes are utilized to provide minimally invasive drug delivery to the patients without any discomfort and pain. This review is focused on the brief introduction, types, significance, preparation techniques, components and mechanism of drug release of non-invasive systems, including in situ gelling systems, microspheres, iontophoresis, nanoparticles, nanosuspensions and specialized novel emulsions.

Clearance Kinetics and Clearance Routes of Molecules From the Suprachoroidal Space After Microneedle Injection

Purpose

To determine clearance kinetics and routes of clearance of molecules from the suprachoroidal space (SCS) of live New Zealand White rabbits.

Methods

Suprachoroidal space collapse rate and pressure changes after microneedle injection into SCS were determined. Fluorescent fundus images were acquired to determine clearance rates of molecules ranging in size from 332 Da to 2 MDa. Microneedle injections of fluorescein were performed, and samples were taken from various sites over time to determine amount of fluorescein exiting the eye. Clearance transport was modeled theoretically and compared with experimental data.

Results

After injection, pressures in SCS and vitreous humor spiked and returned to baseline within 20 minutes; there was no difference between these two pressures. Suprachoroidal space collapse occurred within 40 minutes. One hour after fluorescein injection, 46% of fluorescein was still present in the eye, 15% had transported across sclera, 6% had been cleared by choroidal vasculature, and 4% had exited via leakage pathways. Characteristic clearance time increased in proportion with molecular radius, but total clearance of 2 MDa FITC-dextran was significantly slower (21 days) than smaller molecules. These data generally agreed with predictions from a theoretical model of molecular transport.

Conclusions

Guided by experimental data in the context of model predictions, molecular clearance from SCS occurred in three regimes: (1) on a time scale of approximately 10 minutes, fluid and molecules exited SCS by diffusion into sclera and choroid, and by pressure-driven reflux via transscleral leakage sites; (2) in approximately 1 hour, molecules cleared from choroid by blood flow; and (3) in 1 to 10 hours, molecules cleared from sclera by diffusion and convection.

Thickness and Closure Kinetics of the Suprachoroidal Space Following Microneedle Injection of Liquid Formulations

Purpose

To determine the effect of injection volume and formulation of a microneedle injection into the suprachoroidal space (SCS) on SCS thickness and closure kinetics.

Methods

Microneedle injections containing 25 to 150 μL Hanks' balanced salt solution (HBSS) were performed in the rabbit SCS ex vivo. Distribution of SCS thickness was measured by ultrasonography and three-dimensional (3D) cryo-reconstruction. Microneedle injections were performed in the rabbit SCS in vivo using HBSS, Discovisc, and 1% to 5% carboxymethyl cellulose (CMC) in HBSS. Ultrasonography was used to track SCS thickness over time.

Results

Increasing HBSS injection volume increased the area of expanded SCS, but did not increase SCS thickness ex vivo. With SCS injections in vivo, the SCS initially expanded to thicknesses of 0.43 ± 0.06 mm with HBSS, 1.5 ± 0.4 mm with Discovisc, and 0.69 to 2.1 mm with 1% to 5% CMC. After injection with HBSS, Discovisc, and 1% CMC solution, the SCS collapsed to baseline with time constants of 19 minutes, 6 hours, and 2.4 days, respectively. In contrast, injections with 3% to 5% CMC solution resulted in SCS expansion to 2.3 to 2.8 mm over the course of 2.8 to 9.1 hours, after which the SCS collapsed to baseline with time constants of 4.5 to 9.2 days.

Conclusions

With low-viscosity formulations, SCS expands to a thickness that remains roughly constant, independent of the volume of fluid injected. Increasing injection fluid viscosity significantly increased SCS thickness. Expansion of the SCS is hypothesized to be controlled by a balance between the viscous forces of the liquid formulation and the resistive biomechanical forces of the tissue.

Biocompatibility and Pharmacokinetic Analysis of an Intracameral Polycaprolactone Drug Delivery Implant for Glaucoma

Purpose

We developed polycaprolactone (PCL) implants that achieve zero-order release of a proprietary ocular hypotensive agent (DE-117) over 6 months.

Methods

The release rates of DE-117–loaded PCL devices were tuned based on an established predictive model and confirmed by in vitro release studies. Devices containing DE-117 and empty devices were implanted intracamerally in normotensive rabbits for up to 8 weeks' duration. Devices were retrieved after rabbits were euthanized and evaluated for tissue adherence. The drug remaining in each device was analyzed by high performance liquid chromatography. Drug distribution in ocular tissues was measured by liquid chromatography coupled with a tandem mass spectrometry (LC/MS/MS).

Results

In vitro release of DE-117 showed zero-order release with a release rate of 0.5 μg/day over 6 months. Implantation in rabbit eyes demonstrated that the devices were well tolerated in the intracameral space. Quantification of DE-117 and hDE-117 (the hydrolyzed active form of DE-117) in ocular tissues (cornea, iris-ciliary body, aqueous humor, and vitreous humor) indicated sustained release of DE-117 and its conversion to hDE-117 when released from the device. Analysis of drug remaining in the device found that concentration of hDE-117 was below the limit of detection, indicating the encapsulated drug was protected from hydrolysis in the device.

Conclusions

Proof-of-concept PCL drug delivery devices containing DE-117 show promise as a long-term glaucoma treatment based on their zero-order drug release profile in vitro, biocompatibility in vivo, and effective distribution of released drug in relevant ocular tissues.

Sustained drug delivery for glaucoma: current data and future trends

PURPOSE OF REVIEW

Sustained drug delivery has been recognized as a need for patients with ocular hypertension or glaucomatous optic neuropathy. Several sustained drug delivery systems and devices are currently on the horizon. This review aims to summarize initial results with these platforms, as reported in the literature, and also provide insight into their possible role in the glaucoma treatment paradigm.

RECENT FINDINGS

Sustained drug delivery systems currently on the horizon include the topical bimatoprost ocular insert, travoprost and latanoprost punctal plugs, latanoprost-eluting contact lenses, bimatoprost and travoprost intraocular implants, as well as several other therapies in earlier stages of development. Delivery strategies differ with respect to ocular site of implantation, ocular hypotensive agent, and duration of efficacy. Efficacy and safety outcomes with these devices are favorable thus far.

SUMMARY

The glaucoma treatment paradigm is currently in a state of flux as sustained drug delivery systems bring promise to individuals suffering from ocular hypertension or glaucoma. Several options will likely become available in the near future to ease the burden of daily administration of chronic therapy with intraocular pressure-lowering agents.

Sustained Release of Brimonidine from a New Composite Drug Delivery System for Treatment of Glaucoma

A novel layered double hydroxide (LDH) nanoparticle/thermogel composite drug delivery system (DDS) for sustained release of brimonidine (Bri) has been designed, prepared, and characterized in this study for treatment of severe glaucoma. Brimonidine is first loaded onto LDH (Bri@LDH) nanoparticles, which are then dispersed in the thermogel consisting of plenty of micelles based on poly(dl-lactic acid-co-coglycolic acid)-polyethylene glycol-poly(dl-lactic acid-co-coglycolic acid) (PLGA-PEG-PLGA) copolymer. The Bri@LDH/Thermogel DDS containing 125.0 μg/g of brimonidine has been found to sustainably release the drug for up to 144 h, significantly extending the drug release period compared to that from Bri@LDH nanoparticles. The Bri@LDH/Thermogel DDS is not cytotoxic to human corneal epithelial cells and shows good biocompatibility. In vivo drug release from the special contact lens made of Bri@LDH/Thermogel DDS has been sustained for at least 7 days, which more effectively modulates the relief of intraocular pressure (IOP). Thus, the Bri@LDH/Thermogel DDS is a promising drug delivery alternative that can be used for treatment of severe glaucoma.

The Pathway From Genes to Gene Therapy in Glaucoma: A Review of Possibilities for Using Genes as Glaucoma Drugs

Treatment of diseases with gene therapy is advancing rapidly. The use of gene therapy has expanded from the original concept of re-placing the mutated gene causing the disease to the use of genes to con-trol nonphysiological levels of expression or to modify pathways known to affect the disease. Genes offer numerous advantages over conventional drugs. They have longer duration of action and are more specific. Genes can be delivered to the target site by naked DNA, cells, nonviral, and viral vectors. The enormous progress of the past decade in molecular bi-ology and delivery systems has provided ways for targeting genes to the intended cell/tissue and safe, long-term vectors. The eye is an ideal organ for gene therapy. It is easily accessible and it is an immune-privileged site. Currently, there are clinical trials for diseases affecting practically every tissue of the eye, including those to restore vision in patients with Leber congenital amaurosis. However, the number of eye trials compared with those for systemic diseases is quite low (1.8%). Nevertheless, judg-ing by the vast amount of ongoing preclinical studies, it is expected that such number will increase considerably in the near future. One area of great need for eye gene therapy is glaucoma, where a long-term gene drug would eliminate daily applications and compliance issues. Here, we review the current state of gene therapy for glaucoma and the possibilities for treating the trabecular meshwork to lower intraocular pressure and the retinal ganglion cells to protect them from neurodegeneration.

Distribution of particles, small molecules and polymeric formulation excipients in the suprachoroidal space after microneedle injection

The purpose of this work was to determine the effect of injection volume, formulation composition, and time on circumferential spread of particles, small molecules, and polymeric formulation excipients in the suprachoroidal space (SCS) after microneedle injection into New Zealand White rabbit eyes ex vivo and in vivo. Microneedle injections of 25-150 μL Hank's Balanced Salt Solution (HBSS) containing 0.2 μm red-fluorescent particles and a model small molecule (fluorescein) were performed in rabbit eyes ex vivo, and visualized via flat mount. Particles with diameters of 0.02-2 μm were co-injected into SCS in vivo with fluorescein or a polymeric formulation excipient: fluorescein isothiocyanate (FITC)-labeled Discovisc or FITC-labeled carboxymethyl cellulose (CMC). Fluorescent fundus images were acquired over time to determine area of particle, fluorescein, and polymeric formulation excipient spread, as well as their co-localization. We found that fluorescein covered a significantly larger area than co-injected particles when suspended in HBSS, and that this difference was present from 3 min post-injection onwards. We further showed that there was no difference in initial area covered by FITC-Discovisc and particles; the transport time (i.e., the time until the FITC-Discovisc and particle area began dissociating) was 2 d. There was also no difference in initial area covered by FITC-CMC and particles; the transport time in FITC-CMC was 4 d. We also found that particle size (20 nm-2 μm) had no effect on spreading area when delivered in HBSS or Discovisc. We conclude that (i) the area of particle spread in SCS during injection generally increased with increasing injection volume, was unaffected by particle size, and was significantly less than the area of fluorescein spread, (ii) particles suspended in low-viscosity HBSS formulation were entrapped in the SCS after injection, whereas fluorescein was not and (iii) particles co-injected with viscous polymeric formulation excipients co-localized near the site of injection in the SCS, continued to co-localize while spreading over larger areas for 2-4 days, and then no longer co-localized as the polymeric formulation excipients were cleared within 1-3 weeks and the particles remained largely in place. These data suggest that particles encounter greater barriers to flow in SCS compared to molecules and that co-localization of particles and polymeric formulation excipients allows spreading over larger areas of the SCS until the particles and excipients dissociate.