Polydopamine nanoparticles attenuate retina ganglion cell degeneration and restore visual function after optic nerve injury.

BACKGROUND: Oxidative stress contributes to retina ganglion cells (RGCs) loss in variety of ocular diseases, including ocular trauma, ocular vein occlusion, and glaucoma. Scavenging the excessed reactive oxygen species (ROS) in retinal neurovascular unit could be beneficial to RGCs survival. In this study, a polydopamine (PDA)-based nanoplatform is developed to protect RGCs. RESULTS: The PDA nanoparticles efficiently eliminate multi-types of ROS, protect endothelia and neuronal cells from oxidative damage, and inhibit microglia activation in retinas. In an optic nerve crush (ONC) model, single intravitreal injection of PDA nanoparticles could significantly attenuate RGCs loss via eliminating ROS in retinas, reducing the inflammatory response and maintaining barrier function of retinal vascular endothelia. Comparative transcriptome analysis of the retina implied that PDA nanoparticles improve RGCs survival probably by altering the expression of genes involved in inflammation and ROS production. Importantly, as a versatile drug carrier, PDA nanoparticles could deliver brimonidine (a neuroprotection drug) to synergistically attenuate RGCs loss and promote axon regeneration, thus restore visual function. CONCLUSIONS: The PDA nanoparticle-based therapeutic nanoplatform displayed excellent performance in ROS elimination, providing a promising probability for treating retinal degeneration diseases.

Improved Treatment Options for Glaucoma with Brimonidine-Loaded Lipid DNA Nanoparticles.

Glaucoma is the second leading cause of irreversible blindness worldwide. Among others, elevated intraocular pressure (IOP) is one of the hallmarks of the disease. Antiglaucoma drugs such as brimonidine can lower the IOP but their adherence to the ocular surface is low, leading to a low drug uptake. This results in a frequent dropping regime causing low compliance by the patients. Lipid DNA nanoparticles (NPs) have the intrinsic ability to bind to the ocular surface and can be loaded with different drugs. Here, we report DNA NPs functionalized for loading of brimonidine through specific aptamers and via hydrophobic interactions with double stranded micelles. Both NP systems exhibited improved affinity toward the cornea and retained release of the drug as compared to controls both in vitro and in vivo. Both NP types were able to lower the IOP in living animals significantly more than pristine brimonidine. Importantly, the brimonidine-loaded NPs showed no toxicity and improved efficacy and hence should improve compliance. In conclusion, this drug-delivery system offers high chances of an improved treatment for glaucoma and thus preserving vision in the aging population.

Brimonidine-montmorillonite hybrid formulation for topical drug delivery to the eye.

Brimonidine (BMD) is often prescribed as an eye drop to reduce the intraocular pressure (IOP) for glaucoma treatment. However, eye drops are limited by rapid clearance from the preocular surface, and hence a low ocular drug bioavailability. Therefore, in this study, we propose montmorillonite (MMT), as a delivery carrier, hybridized with BMD (BMD-MMT) for topical drug delivery to the eye. The BMD-MMT hybrid was prepared by intercalating the BMD molecules in the interlayer space of the MMT lattice via ion-exchange reaction; it was then formulated with polyvinyl alcohol (PVA) to produce a dry tablet (i.e., BMD-MMT@PVA). The BMD-MMT@PVA hybrid drug released BMD in a sustained manner for more than 5 h under in vitro conditions. When the hybrid drug was administered to rabbit eyes in vivo, 43% and 18.5% BMD-MMT still remained on the preocular surface for 10 and 60 min after administration, respectively. Thus, the BMD-MMT@PVA hybrid drug exhibited a prolonged decrease in IOP, that is, for 12 h, which was approximately two times longer than that observed with the commercially available BMD eye drop, Alphagan® P.

MOF-Based Polymeric Nanocomposite Films as Potential Materials for Drug Delivery Devices in Ocular Therapeutics.

Novel MOF-based polymer nanocomposite films were successfully prepared using Zr-based UiO-67 as a metal-organic framework (MOF) and polyurethane (PU) as a polymeric matrix. Synchrotron X-ray powder diffraction (SXRPD) analysis confirms the improved stability of the UiO-67 embedded nanocrystals, and scanning electron microscopy images confirm their homogeneous distribution (average crystal size ∼100-200 nm) within the 50 µm thick film. Accessibility to the inner porous structure of the embedded MOFs was completely suppressed for N2 at cryogenic temperatures. However, ethylene adsorption measurements at 25 °C confirm that at least 45% of the MOF crystals are fully accessible for gas-phase adsorption of nonpolar molecules. Although this partial blockage limits the adsorption performance of the embedded MOFs for ocular drugs (e.g., brimonidine tartrate) compared to the pure MOF, an almost 60-fold improvement in the adsorption capacity was observed for the PU matrix after incorporation of the UiO-67 nanocrystals. The UiO-67@PU nanocomposite exhibits a prolonged release of brimonidine (up to 14 days were quantified). Finally, the combined use of SXRPD, thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR) analyses confirmed the presence of the drug in the nanocomposite film, the stability of the MOF framework and the drug upon loading, and the presence of brimonidine in an amorphous phase once adsorbed. These results open the gate toward the application of these polymeric nanocomposite films for drug delivery in ocular therapeutics, either as a component of a contact lens, in the composition of lacrimal stoppers (e.g., punctal plugs), or in subtenon inserts.

Co-Delivery of Timolol and Brimonidine with a Polymer Thin-Film Intraocular Device.

PURPOSE: We developed a polycaprolactone (PCL) co-delivery implant that achieves zero-order release of 2 ocular hypotensive agents, timolol maleate and brimonidine tartrate. We also demonstrate intraocular pressure (IOP)-lowering effects of the implant for 3 months in vivo. METHODS: Two PCL thin-film compartments were attached to form a V-shaped co-delivery device using film thicknesses of ∼40 and 20 µm for timolol and brimonidine compartments, respectively. In vitro release kinetics were measured in pH- and temperature-controlled fluid chambers. Empty or drug-loaded devices were implanted intracamerally in normotensive rabbits for up to 13 weeks with weekly measurements of IOP. For ocular concentrations, rabbits were euthanized at 4, 8, or 13 weeks, aqueous fluid was collected, and ocular tissues were dissected. Drug concentrations were measured by liquid chromatography-tandem mass spectrometry. RESULTS: In vitro studies show zero-order release kinetics for both timolol (1.75 µg/day) and brimonidine (0.48 µg/day) for up to 60 days. In rabbit eyes, the device achieved an average aqueous fluid concentration of 98.1 ± 68.3 ng/mL for timolol and 5.5 ± 3.6 ng/mL for brimonidine. Over 13 weeks, the drug-loaded co-delivery device resulted in a statistically significant cumulative reduction in IOP compared to untreated eyes (P < 0.05) and empty-device eyes (P < 0.05). CONCLUSIONS: The co-delivery device demonstrated a zero-order release profile in vitro for 2 hypotensive agents over 60 days. In vivo, the device led to significant cumulative IOP reduction of 3.4 ± 1.6 mmHg over 13 weeks. Acceptable ocular tolerance was seen, and systemic drug levels were unmeasurable.

Metal-Organic Frameworks as Drug Delivery Platforms for Ocular Therapeutics.

Metal-organic frameworks (MOFs) have been evaluated as potential nanocarriers for intraocular incorporation of brimonidine tartrate to treat chronic glaucoma. Experimental results show that UiO-67 and MIL-100 (Fe) exhibit the highest loading capacity with values up to 50-60 wt %, whereas the performance is quite limited for MOFs with narrow cavities (below 0.8 nm, for example, UiO-66 and HKUST-1). The large loading capacity in UiO-67 is accompanied by an irreversible structural amorphization in aqueous and physiological media that promotes extended release kinetics above 12 days. Compared to the traditional drawbacks associated with the sudden release of the commercial drugs (e.g., ALPHAGAN), these results anticipate UiO-67 as a potential nanocarrier for drug delivery in intraocular therapeutics. These promising results are further supported by cytotoxicity tests using retinal photoreceptor cells (661W). Toxicity of these structures (including the metal nodes and organic ligands) for retinal cells is rather low for all samples evaluated, except for HKUST-1.

Impact of Ocular Compatible Lipoids and Castor Oil in Fabrication of Brimonidine Tartrate Nanoemulsions by 33 Full Factorial Design.

BACKGROUND: Brimonidine Tartrate (BRT) is used in the treatment of glaucoma. Brimonidine tartrate nanoemulsion was fabricated in this research work to enhance the permeability through barriers and faster onset of action and therapeutic effect. OBJECTIVE: To fabricate an ocular compatible nanoemulsion of brimonidine tartrate by using surfactant and co-surfactants. METHODS: The experimental work involved compatibility studies by using FTIR, DSC and crystallinity study by XRD. The prepared nanoemulsion was studied by photon correlation spectroscopy by Malvern S90 for the particle size analysis and characterized for Z average value (d.nm.) and PDI. Further studies were conducted by laser light scattering technique by delsanano common and TEM. RESULTS: The study demonstrated that the formulations BN2, BN3, BN10 demonstrated the z average value of 19.48, 22.14,26.50 d.nm. With 0.337, 0.270, 0.289 PDI respectively, the formulae BN2, BN3, BN10 demonstrated the distribution average diameter (nm) of 376.8 + 258.4, 542.8 + 494.4, 398.8 + 263.9 with the diameter of 267.5, 298.5, 272.7, respectively. The zeta potential of BN10 was -21.26 mV and other parameters such as TEM and drug release studies were also reported. CONCLUSION: The nanoemulsion of brimonidine tartrate was prepared successfully by using castor oil, Lipoid S75 (Fat free soybean phospholipids with 70% phosphatidylcholine), Lipoid E80 (Egg phospholipids with 80% phosphatidylcholine) and PF- 68. The optimised formula demonstrated the lower droplet size, satisfactory zeta potential, and high drug loading and reproducible drug release profile. Brimonididne taratarate is reported in various recent patents for various applications and is the potential candidate for future therapy. Nanoemulsion is widely explored as potential alternatives for conventional ophthalmic formulation based approaches. It enhances the ocular bioavailability by reducing the drug protein binding, increasing the corneal resident time, enhancing the drug permeability and providing a sustained drug release.It reported a significant increase in therapeutic efficacy for various chronic ocular disease states of both the anterior and posterior ocular segments.

Nanostructured lipid carriers for intraocular brimonidine localisation: development, in-vitro and in-vivo evaluation.

Brimonidine ocular hypotensive effect can be enhanced by increasing residence time and corneal penetration. The current work aimed to formulate, evaluate and compare nanostructured lipid carriers (NLCs) to solid lipid nanoparticles (SLNs) and commercial eye drops for controlled brimonidine delivery. NLCs prepared by modified high shear homogenisation were spherical with a mean size of 151.97 ± 1.98 nm, negative zeta potential (ZP) of -44.2 ± 7.81 mV, % entrapment efficiency (EE) of 83.631 ± 0.495% and low crystallinity index (CI) (17.12%), indicating a better drug incorporation. Moreover, they kept stable during storage at 4 °C for 3 months. Permeability coefficient of NLCs was 1.227 folds higher than that of SLNs. Histological examination revealed localisation of NLCs in the anterior ocular chamber. NLCs revealed the most sustained and highest intraocular pressure (IOP) lowering activity (-13.14 ± 1.28 mmHg) in rabbits. In conclusion, NLCs is a promising approach for IOP reduction compared to eye drops and SLNs.

Increasing efficacy and reducing systemic absorption of brimonidine tartrate ophthalmic gels in rabbits.

Systemic absorption of ocularly administered Brimonidine Tartrate has been reported to give rise to several side-effects. Hence, it has become crucial to develop a delivery system that could increase efficacy and reduce systemic absorption. Therefore, the present work aims to develop Brimonidine Tartrate gels with different concentrations (0.05%, 0.1%, and 0.2% w/v, respectively) using Carbopol 974 P and HPMC E4M, and compare the therapeutic efficacy and systemic absorption with that of eye drop (0.2%, w/v) by UPLC-MS/MS. The result of histological analysis did not show any morphological or structural changes after the administration of formulations. In vitro residence time studies demonstrated that the gels exhibited a better precorneal residence time as compared with the eye drop. The gels with lower concentrations of the drug (0.05% and 0.1%, w/v) could significantly decrease intraocular pressure (IOP) in both normal and water-loaded rabbits as compared to the eye drop. Finally, the values of the ratio of AUC(0→∞) in comparison to eye drop showed the gels with lower concentrations of Brimonidine Tartrate could decrease the systemic absorption. From the result, it can be concluded the 0.1% ophthalmic gel has a potential to improve therapeutic efficacy and reduce the potential toxicity caused by systemic absorption.

Formulation and ex vivo-in vivo evaluation of pH-triggered brimonidine tartrate in situ gel for the glaucoma treatment using application of 32 factorial design.

CONTEXT: Short residence time, poor bioavailability and poor permeability are the major problems for conventional eye drops treatment. OBJECTIVE: The aim of this article is to develop, optimize and ex vivo-in vivo investigation of brimonidine tartrate in situ gel as compared to marketed eye drops for the treatment of glaucoma. MATERIALS AND METHODS: The effect of independent variables, namely concentrations of polymers, on various dependent variables like viscosity at physiological pH and in vitro drug release were studied by using 32 factorial design. Further the optimized formulation was characterized for ex vivo and in vivo study. RESULTS AND DISCUSSION: Experimental data demonstrated that optimized in situ gel formulation (F8) showed in vitro-ex vivo sustained release profile with polymer composites carbopol 974P and HPMC K4M. After 5 h of ex vivo transcorneal permeation study, the amount recovered from the corneal surface on the donor chamber 12.40% (124 ug) and the amount collected from the receptor chamber 76.8% (760 ug) of the initial dose 1 mg. The total amount recovered from the permeation experiment was 89.2%. Bioadhesive carbopol 974P and viscosity HPMC K4M composites optimized formulation (F 8) produce greater influence on the duration of drug action and improved intraocular pressure reduction activity as compared to marketed eye drop solution in in vivo study. CONCLUSION: The developed in situ gelling system as a promising ophthalmic formulation to prolong the drug lowering effect on the intraocular pressure.

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.

Long-Term Subconjunctival Delivery of Brimonidine Tartrate for Glaucoma Treatment Using a Microspheres/Carrier System.

Core-shell polymer microspheres with poly(d,l-lactic-co-glycolic acid) core and poly(l-lactic acid) (PLLA) shell are developed for the long-term subconjunctival release of brimonidine tartrate (BT) in order to reduce intraocular pressure (IOP) in the treatment of glaucoma. The PLLA-rich shell acts as a diffusion barrier, enabling linear release of BT over an extended period of 40 d. The microspheres are encased in a porous non-degradable methacrylate-based carrier for ease of subconjunctival implantation in a glaucoma-induced rabbit model. In vivo release of BT from the microspheres/carrier system has enabled a significant, immediate IOP reduction of 20 mmHg, which is sustained for 55 d. Long-term IOP reduction may be maintained by periodic replacement of the microspheres/carrier system.

Thermosensitive hexanoyl glycol chitosan-based ocular delivery system for glaucoma therapy.

UNLABELLED: Conventional eye drops quickly move away from the surface of the eye; as a result, ocular bioavailability is very limited. To overcome this issue, we developed a thermosensitive hexanoyl glycol chitosan (HGC) as a carrier for topical drug delivery to the eye. Here, we modulated the degree of N-hexanoylation to control the thermogelling behavior and prepared a new ocular formulation of HGC for glaucoma therapy. The viscosity of the aqueous formulation sharply and significantly increases at body temperature. The results from cytotoxicity evaluation showed that HGC is non-toxic at up to 1.25wt.%. In vivo experiments demonstrated that HGC is maintained on the preocular surface for a comparatively longer period of time due to its enhanced viscosity at body temperature. As a result, when brimonidine was loaded, the formulation exhibited attractive bioavailability properties as well as more prolonged period of lowered intra-ocular pressure (14h) compared with Alphagan P, the marketed medication for brimonidine treatment. STATEMENT OF SIGNIFICANCE: In this manuscript, hexanoyl glycol chitosan (HGC) was synthesized by the N-hexanoylation of glycol chitosan. We have observed that an aqueous solution of HGC exhibited a dramatic increase in viscosity as the temperature increased. The HGC-based formulation showed prolonged retention on the preocular surface and enhanced drug availability and efficacy.

Effect of sterilization on the physical stability of brimonidine-loaded solid lipid nanoparticles and nanostructured lipid carriers.

Nanoparticulate delivery systems have recently been under consideration for topical ophthalmic drug delivery. Brimonidine base-loaded solid lipid nanoparticles and nanostructured lipid carrier formulations were prepared using glyceryl monostearate as solid lipid and were evaluated for their physical stability following sterilization by autoclaving at 121°C for 15min. The objective of this work was to evaluate the effect of autoclaving on the physical appearance, particle size, polydispersity index, zeta potential, entrapment efficiency and particle morphology of the prepared formulations, compared to non-autoclaved ones. Results showed that, autoclaving at 121°C for 15min allowed the production of physically stable formulations in nanometric range, below 500nm suitable for ophthalmic application. Moreover, the autoclaved samples appeared to be superior to non-autoclaved ones, due to their increased zeta potential values, indicating a better physical stability. As well as, increased amount of brimonidine base entrapped in the tested formulations.

Mucoadhesive microparticles with a nanostructured surface for enhanced bioavailability of glaucoma drug.

Topical drug administration to the eye is limited by low drug bioavailability due to its rapid clearance from the preocular surface. Thus, multiple daily administrations are often needed, but patient compliance is low, hence a high chance of unsatisfactory treatment of ocular diseases. To resolve this, we propose mucoadhesive microparticles with a nanostructured surface as potential carriers for delivery of brimonidine, an ocular drug for glaucoma treatment. For sustained drug delivery, the microparticles were composed mainly of a diffusion-wall material, poly(lactic-co-glycolic acid) and a mucoadhesive polymer, polyethylene glycol, was used as an additive. Due to their nanostructured surface, the microparticles with a mucoadhesive material exhibited a 13-fold increase in specific surface area and could thus adhere better to the mucous layer on the eye, as compared with the conventional spherical microparticles. When loaded with brimonidine, the mucoadhesive microparticles with a nanostructured surface increased both drug bioavailability and its activity period by a factor of more than 2 over Alphagan P, a marketed eye drop of brimonidine.

Validated spectrofluorimetric and spectrophotometric methods for the determination of brimonidine tartrate in ophthalmic solutions via derivatization with NBD-Cl. Application to stability study.

Two simple, selective and accurate methods were developed and validated for the determination of brimonidine tartrate (BT) in pure state and pharmaceutical formulations. Both methods are based on the coupling of the drug with 4-chloro-7-nitro-2,1,3-benzoxadiazole in borate buffer (pH 8.5) at 70 °C and measurement of the reaction product spectrophotometrically at 407 nm (method I) or spectrofluorimetrically at 528 nm upon excitation at 460 nm (method II). The calibration graphs were rectilinear over the concentration ranges of 1.0-16.0 and 0.1-4.0 µg/mL with lower detection limits of 0.21 and 0.03, and lower quantification limits of 0.65 and 0.09 µg/mL for methods I and II, respectively. Both methods were successfully applied to the analysis of commercial ophthalmic solution with mean recovery of 99.50 ± 1.00 and 100.13 ± 0.71%, respectively. Statistical analysis of the results obtained by the proposed methods revealed good agreement with those obtained using a comparison method. The proposed spectrofluorimetric method was extended to a stability study of BT under different ICH-outlined conditions such as alkaline, acidic, oxidative and photolytic degradation. Furthermore, the kinetics of oxidative degradation of the drug was investigated and the apparent first-order reaction rate constants, half-life times and Arrhenius equation were estimated. The proposed methods are practical and valuable for routine applications in quality control laboratories for the analysis of BT.

Development and Evaluation of Novel Polymeric Nanoparticles of Brimonidine Tartrate.

Micro and nanoparticulate carriers have been in focus in ophthalmic drug delivery with the objective of improving bioavailability, drug targeting and reducing pulse entry of the drug in ocular cul de sac. Polymeric nanoparticles for ocular purpose have potential in reducing the pulse entry and frequency of dosing, thus improving patient compliance. In the present study, mucoadhesive sodium alginate nanoparticles were developed for Brimonidine Tartrate (BT) as a model antiglaucoma drug by controlled ionic gelation technique. These nanoparticles would not only prolong drugs residence time but also reduce pulse entry in cul de sac. Nanoparticles were evaluated for morphology, surface characteristics, drug polymer interactions, particle size, polydispersibility index, zeta potential, entrapment efficiency, in vitro release profile and in vivo efficacy. The effect of various stabilizers on stabilization of blank and drug loaded nanoparticles was investigated. Irregular shape and loss of crystallinity for BT loaded sodium alginate nanoparticles was observed by TEM and SEM images respectively. IR spectra and DSC thermograms revealed the physicochemical interaction was involved during sodium alginate nanoparticle formation and entrapment of BT. The developed nanoparticles have average particle size of 450nm with PI 0.65, the entrapment efficiency ranged from 4-18 % and zeta potential values ranged from -27.5 mV to -24.1 mV. In vitro release profile showed a gradual drug release over the period of 3 hrs. In-vivo experiments showed that it was possible to prolong the drug release over a period of 8 hr, on topical instillation of BT loaded nanoparticles to albino rabbits, hence reducing the dosage frequency.