Intravitreal controlled release of dexamethasone from engineered microparticles of porous silicon dioxide

Magnetically Controlled Intraocular Delivery of Dexamethasone Using Silica-Coated Magnetic Nanoparticles

Although the number of patients with eye diseases is increasing, efficient drug delivery to the posterior segment of the eyeball remains challenging. The reasons include the unique anatomy of the eyeball, the blood-aqueous barrier, the blood-retina barrier, and drug elimination via the anterior chamber and uveoscleral routes. Solutions to these obstacles for therapeutic delivery to the posterior segment will increase the efficacy, efficiency, and safety of ophthalmic treatment. Micro/nanorobots are promising tools to deliver therapeutics to the retina under the direction of an external magnetic field. Although many groups have evaluated potential uses of micro/nanorobots in retinal treatment, most experiments have been performed under idealized in vitro laboratory conditions and thus do not fully demonstrate the clinical feasibility of this approach. This study examined the use of magnetic nanoparticles (MNPs) to deliver dexamethasone, a drug widely used in retinal disease treatment. The MNPs allowed sustainable drug release and successful magnetic manipulation inside bovine vitreous humor and the vitreous humor of living rabbits. Therefore, controlled drug distribution via magnetic manipulation of MNPs is a promising strategy for targeted drug delivery to the retina.

Reverse engineering the Ozurdex dexamethasone intravitreal implant

Ozurdex is a biodegradable implant formulated for sustained-release delivery of the corticosteroid dexamethasone to the posterior segment of the eye. The small, rod-shaped implant is administered directly to the vitreous using a dedicated applicator, and releases drug for up to 6 months after administration. Sustained release is achieved by embedding dexamethasone in a matrix of 50:50 poly(lactic-co-glycolic acid) (PLGA). In this work, the Ozurdex implant was thoroughly characterized to enable the reverse engineering of a compositionally and structurally equivalent implant. Advanced imaging techniques such as scanning electron microscopy (SEM) and microcomputed tomography (microCT) revealed that the Ozurdex implant exhibits an irregular surface and an internal porosity of 6% due to a large number of discrete voids approximately 3 μm in diameter. Thermal and spectroscopic analyses showed limited interaction between the drug and the polymer, resulting in a two-phase system of dexamethasone crystals embedded within a PLGA matrix. Reverse-engineered implants with properties similar to Ozurdex were prepared using a two-step hot-melt extrusion process. The reverse-engineered implants exhibited a triphasic drug release profile similar to Ozurdex. This work seeks to provide insight into the manufacturing process and characterization of PLGA-based solid implants to support future generic product development.

A novel, minimally invasive implant to assist in repeated intraocular drug delivery

The standard of care for posterior segment disorders such as wet age-related macular degeneration, diabetic macular oedema and retinal vascular occlusions is pharmacotherapy by intravitreal drug delivery. Since the therapeutic effect of these drugs lasts only around 4 to 8 weeks, repeated intravitreal injections are required. Pain is experienced by the patients during injection as the needle courses through the sclera and choroid. The current work describes the design and development of a novel anodized titanium alloy implant that allows for intravitreal injections through the implant so that the needle transverses only the conjunctiva, thus minimizing discomfort to the patient. Both ex-vivo testing of the implant in enucleated goat's eye as well as in-vivo validation in rabbit eyes was carried out. The implant was placed through pars plana via a minor surgical procedure and was sutured to the sclera and covered with conjunctiva. Subsequent intravitreal injections were administered under topical anaesthesia with a 30-gauge needle through the implant thus delivering the drug into the vitreous cavity. Repeated intravitreal injections were administered every 2 weeks via the implant for 3 months in 4 rabbits. Apart from cataract in 1 rabbit, no complications were observed. There was no evidence of intra-ocular inflammation or infection at final follow-up. Histopathological analysis did not reveal any inflammation or necrosis around the area of implant. The implants were subsequently removed at 5 months and scleral wound was closed with a single suture. The sclera and overlying conjunctiva healed well and no intraocular complications were observed after removal.

Polymer based sustained drug delivery to the ocular posterior segment: barriers and future opportunities for the treatment of neovascular pathologies

There is an increasing momentum in research and pharmaceutical industry communities to design sustained, non-invasive delivery systems to treat chronic neovascular ocular diseases that affect the posterior segment of the eye including age-related macular degeneration and diabetic retinopathy. Current treatments include VEGF blockers, which have revolutionized the standard of care for patients, but their maximum therapeutic benefit is hampered by the need for recurrent and invasive administration procedures. Currently approved delivery systems intended to address these limitations exploit polymer technology to regulate drug release in a sustained manner. Here, we critically review sustained drug delivery approaches for the treatment of chronic neovascular diseases affecting the ocular posterior segment, with a special emphasis on novel and polymeric technologies spanning the spectrum of preclinical and clinical investigation, and those approved for treatment. The mechanism by which each formulation imparts sustained release, the impact of formulation characteristics on release and foreign body reaction, and special considerations related to the translation of these systems are discussed.

Mechanistic study of silica nanoparticles on the size-dependent retinal toxicity in vitro and in vivo

Background

Silica nanoparticles (SiO₂ NPs) are extensively applied in the biomedical field. The increasing medical application of SiO₂ NPs has raised concerns about their safety. However, studies on SiO₂ NP-induced retinal toxicity are lacking.

Methods

We investigated the retinal toxicity of SiO₂ NPs with different sizes (15 and 50 nm) in vitro and in vivo along with the underlying mechanisms. The cytotoxicity of SiO₂ NPs with different sizes was assessed in R28 human retinal precursor cells by determining the ATP content and LDH release. The cell morphologies and nanoparticle distributions in the cells were analyzed by phase-contrast microscopy and transmission electron microscopy, respectively. The mitochondrial membrane potential was examined by confocal laser scanning microscopy. The retinal toxicity induced by SiO₂ NPs in vivo was examined by immunohistochemical analysis. To further investigate the mechanism of retinal toxicity induced by SiO₂ NPs, reactive oxygen species (ROS) generation, glial cell activation and inflammation were monitored.

Results

The 15-nm SiO₂ NPs were found to have higher cytotoxicity than the larger NPs. Notably, the 15-nm SiO₂ NPs induced retinal toxicity in vivo, as demonstrated by increased cell death in the retina, TUNEL-stained retinal cells, retinal ganglion cell degeneration, glial cell activation, and inflammation. In addition, The SiO₂ NPs caused oxidative stress, as demonstrated by the increase in the ROS indicator H₂DCF-DA. Furthermore, the pretreatment of R28 cells with N-acetylcysteine, an ROS scavenger, attenuated the ROS production and cytotoxicity induced by SiO₂ NPs.

Conclusions

These results provide evidence that SiO₂ NPs induce size-dependent retinal toxicity and suggest that glial cell activation and ROS generation contribute to this toxicity.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01326-8.

PMMA bone cement containing long releasing silica-based chlorhexidine nanocarriers

Prosthetic joint infections (PJI) are still an extremely concerning eventuality after joint replacement surgery; growing antibiotic resistance is also limiting the prophylactic and treatment options. Chlorhexidine (a widely used topical non-antibiotic antimicrobial compound) coatings on silica nanoparticles capable of prolonged drug release have been successfully developed and characterised. Such nanocarriers were incorporated into commercial formulation PMMA bone cement (Cemex), without adversely affecting the mechanical performance. Moreover, the bone cement containing the developed nanocarriers showed superior antimicrobial activity against different bacterial species encountered in PJI, including clinical isolates already resistant to gentamicin. Cytocompatibility tests also showed non inferior performance of the bone cements containing chlorhexidine releasing silica nanocarriers to the equivalent commercial formulation.

A sustained dual drug delivery system for proliferative vitreoretinopathy

Proliferative vitreoretinopathy (PVR) is a significant threat for vision recovery from retinal detachment or ocular trauma. Currently, no approved pharmacological intervention to prevent PVR. Daunorubicin (DNR) and dexamethasone (DEX) were sequentially loaded into oxidized porous silicon (pSiO₂) particles by covalent conjugation. The DNR + DEX-loaded particles, and control particles loaded with DNR only and DEX only were incubated with RPE-populated collagen for daily gel surface quantitation. Toxicity was monitored by ophthalmic examinations and histological evaluation 21 days after injection. At 3rd week following intravitreal injection, a localized retinal detachment (RD) was created by subretinal injection of Healon in all pretreated eyes in addition to 3 non-interventional control eyes. 10 µg of bromodeoxyuridine (BrdU) was injected into the vitreous 4 h before sacrifice on day 3 after RD induction. Retinal sections were stained for glial fibrillary green protein (GFAP) and BrdU to identify activated glial cells and retinal cell proliferation. The studies demonstrated that all three pSiO₂ particle types were well tolerated in vivo. DNR alone and DNR + DEX combination formulations demonstrated equally strong suppression on gel contraction (least square mean area of the gel: control = 1.71 vs. 30DNR = 1.85 or 30/40Dual = 1.83, p < .05). Eyes pretreated with pSiO₂−DNR + DEX exhibited the least GFAP activation (least square mean intensity mm⁻²: Dual = 4.03, DNR = 7.76, Dex = 16.23, control = 29.11, p < .05) and BrdU expression (Mean number of BrdU positive cells per mm of retina: Dual = 2.77, DNR = 4.58, Dex = 4.01, control = 6.16, p < .05). The synergistic effect of a sustained release pSiO₂−DNR/DEX showed promise for the prevention of PVR development while reducing the necessary therapeutic concentration of each drug.

Dexamethasone Conjugates: Synthetic Approaches and Medical Prospects

Dexamethasone (DEX) is the most commonly prescribed glucocorticoid (GC) and has a wide spectrum of pharmacological activity. However, steroid drugs like DEX can have severe side effects on non-target organs. One strategy to reduce these side effects is to develop targeted systems with the controlled release by conjugation to polymeric carriers. This review describes the methods available for the synthesis of DEX conjugates (carbodiimide chemistry, solid-phase synthesis, reversible addition fragmentation-chain transfer [RAFT] polymerization, click reactions, and 2-iminothiolane chemistry) and perspectives for their medical application as GC drug or gene delivery systems for anti-tumor therapy. Additionally, the review focuses on the development of DEX conjugates with different physical-chemical properties as successful delivery systems in the target organs such as eye, joint, kidney, and others. Finally, polymer conjugates with improved transfection activity in which DEX is used as a vector for gene delivery in the cell nucleus have been described.

Surface functionalized mesoporous silica nanoparticles for intravitreal application of tacrolimus

Tacrolimus (TAC), a potent immunosuppressive macrolide, has been investigated for ocular diseases due to promising results in the treatment of anterior and posterior segments eye diseases. Mesoporous and functionalized silica nanoparticles show potential as TAC delivery platforms owing to their interesting characteristic as large surface area, uniform pore size distribution, high pore volume, and excellent biocompatibility. The purpose of this study was to incorporate TAC in functionalized silica nanoparticles with 3-aminopropyltriethoxysilane (MSNAPTES) and investigate the safety and biocompatibility of the systems. The MSNAPTES and MSNAPTES TAC nanoparticles were characterized. The in vitro cytotoxicity of MSNAPTES and MSNAPTES load with TAC (MSNAPTES-TAC) in retinal pigment epithelial cells (ARPE-19) was determined, chorioallantoic membrane (CAM) assay model was used to investigate the in vivo biocompatibility, and safety of intravitreal injection was evaluated using clinical examination (assessment of intraocular pressure and indirect fundus ophthalmoscopy), electroretinographic (ERG) and histologic studies in rats' eyes. The elemental analysis (CHN), thermogravimetric (TGA), photon correlation spectroscopy and Fourier transform infrared (FTIR) analysis confirmed the presence of functionalized agent and TAC in the MSNAPTES nanoparticles. TAC loading was estimated at 7% for the MSNAPTES TAC nanoparticles. MSNAPTES and MSNAPTES TAC did not present in vitro cytotoxicity. The drug delivery systems showed good biocompatibility on CAM. No retinal abnormalities, vitreous hemorrhage, neovascularization, retinal detachment, and optic nerve atrophy were observed during the in vivo study. Follow-up ERGs showed no changes in the function of the retina cells after 15 days of intravitreal injection, and histopathologic observations support these findings. In conclusion, MSNAPTES TAC was successfully synthesized, and physicochemical analyses confirmed the presence of TAC in the nanoparticles. In vitro and in vivo studies indicated that MSNAPTES TAC was safe to intravitreal administration. Taking into account the enormous potential of MSNAPTES to carry TAC, this platform could be a promising strategy for TAC ocular drug delivery in the treatment of eye diseases.

Fabrication, Optimization, and In Vitro and In Vivo Characterization of Intra-vitreal Implant of Budesonide Generally Made of PHBV

Drug delivery to vitreous in comparison with drug delivery to the other parts of the eye is complicated and challenging due to the existence of various anatomical and physiological barriers. Developing injectable intra-vitreal implant could be beneficial in this regard. Herein, poly(hydroxybutyrate-co-valerate) (PHBV) implants were fabricated and optimized using response surface method for budesonide (BZ) delivery. The acquired implants were characterized in regard to the stability of the ingredients during fabrication process, drug loading amount, and drug release pattern (in PBS-HA-A and in vitreous medium). According to this research and statistical analysis performed, first HV% (hydroxyvalerate) then molecular weight and ratio of PEG as pore former affect respectively release rate and burst strength of BZ with different coefficients. Drug release profile in rabbit eye correlated well with that of in vitro (R² = 0.9861, p ˂ 0.0001). No significant changes were seen in ERG waves, intraocular pressure, and histological studies during the in vivo part of the project. Using 8% HV, 20% PEG/PHBV, and higher molecular weight PEG (i.e., 6000), the optimum formulation was achieved. Toxicity and biocompatibility of the optimized formulation, which were evaluated in vivo, indicated the suitability of design implant for intra-vitreal BZ delivery. Grapical abstract.

Single subconjunctival injection formulation using sol-gel mesoporous silica as a controlled release system for drop-free post-cataract surgery care

PURPOSE

To develop a mesoporous silica drug delivery system and target drop-free care after cataract surgery with a single subconjunctival injection.

SETTING

Laboratory.

DESIGN

Experimental animal study.

METHODS

Ketorolac was infiltration-loaded into sol-gel mesoporous silica particles encapsulated with poly(allylamine hydrochloride) and poly(sodium 4-styrenesulfonate) using a layer-by-layer adsorption technique (SG-Ket-LBL). The formulation was subjected to an in vitro and in vivo drug release study in addition to ocular toxicology evaluation.

RESULTS

Thermogravimetric analysis revealed that the drug loading efficiency was 4.4% for the SG-Ket-LBL particles. The in vivo safety study demonstrated that the formulation was well tolerated after subconjunctival injection and aqueous humor pharmacokinetics showed sustained therapeutic drug release for the targeted time window of 6 to 8 weeks.

CONCLUSIONS

Findings indicated that sol-gel mesoporous silica could be used as a drug carrier for subconjunctival administration. The tested formulation, SG-Ket-LBL, provided therapeutic ketorolac for 6 to 8 weeks, which might be used for a single subconjunctival injection to replace nonsteroidal anti-inflammatory drug eyedrops after cataract surgery.

PEGylated microemulsion for dexamethasone delivery to posterior segment of eye

Dexamethasone (Dex) is one of the most commonly used anti-vascular endothelial growth factor (anti-VEGF) drugs being used in ocular diseases whether it is associated with anterior segment or posterior segment. For diseases of posterior segment of eye, Dex is delivered as intravitreal implant but the route used for the same is very invasive and poses several hazards on long term use. Thus, topical formulation with ability to outreach retina from ocular surface was intended. Thus, polyethylene glycolylated (PEGylated) microemulsion (ME) was attempted as it can cross the membranous barrier of eye (cornea, conjunctiva, and sclera) and remain afloat in fluidic barrier (aqueous humor, choroid, etc.) as well. Present investigation involved development of Dex-loaded PEGylated ME which was stable, non-toxic to ocular surface, capable to cross cornea and enhanced residence as well as availability of loaded drug in retina. The developed PEGylated ME had physicochemical properties like size (15.98 ± 3.05 nm), polydispersity index (0.25 ± 0.04), zeta potential (-0.04 ± 0.47 mV), percentage transmittance (99.84 ± 1.17%), and drug content (99.32 ± 3.21%). It showed sustained Dex release in in vitro conditions. It also displayed efficiency in enhancing retention of drugs in retina in in vivo pharmacokinetic study on Sprague-Dawley rats. PEGylated ME can retain the drug in retina of rats longer than simple eye drop solution via topical ocular route.

Controlling protein interactions in blood for effective liver immunosuppressive therapy by silica nanocapsules

Immunosuppression with glucocorticoids is a common treatment for autoimmune liver diseases and after liver transplant, which is however associated with severe side-effects. Targeted delivery of glucocorticoids to inflammatory cells, e.g. liver macrophages and Kupffer cells, is a promising approach for minimizing side effects. Herein, we prepare core-shell silica nanocapsules (SiO₂ NCs) via a sol-gel process confined in nanodroplets for targeted delivery of dexamethasone (DXM) for liver immunosuppressive therapy. DXM with concentrations up to 100 mg mL^-1 in olive oil are encapsulated while encapsulation efficiency remains over 95% after 15 days. Internalization of NCs by non-parenchymal murine liver cells significantly reduces the release of inflammatory cytokines, indicating an effective suppression of inflammatory response of liver macrophages. Fluorescent and magnetic labeling of the NCs allows for monitoring their intracellular trafficking and biodegradation. Controlled interaction with blood proteins and good colloidal stability in blood plasma are achieved via PEGylation of the NCs. Specific proteins responsible for stealth effect, such as apolipoprotein A-I, apolipoprotein A-IV, and clusterin, are present in large amounts on the PEGylated NCs. In vivo biodistribution investigations prove an efficient accumulation of NCs in the liver, underlining the suitability of the SiO₂ NCs as a dexamethasone carrier for treating inflammatory liver diseases.

Drug micro-carriers with a hyaluronic acid corona toward a diffusion-limited aggregation within the vitreous body

Posterior eye segment diseases are treated through monthly intravitreal injections, that evoke serious side effects. A promising approach to reduce injection frequency consists in producing biodegradable microspheres (MPs) releasing the protein in the vitreous body for long times. Moreover, a rational design of these MPs requires a discouraged diffusion/sedimentation within the intravitreal space, which are detrimental for the vision and the control over drug release kinetics. In this work, poly(lactic-co-glycolic acid) (PLGA)-based MPs encapsulating bovine serum albumin (BSA) were coated with hyaluronic acid (HA) at two molecular weights and tested for their release, diffusion and degradation features in simulated vitreous body (SVB). Results indicate that HA corona prolongs MP degradation time and BSA release. Furthermore, HA coating increased the affinity between MPs and SVB, thereby repressing device transport compared to control PLGA MPs. Results hold promise for the possible application of HA-decorated MPs for intravitreal injection of protein drugs.

The Synergistic Effects of Gold Particles and Dexamethasone on the Electrochemical and Biological Performance of PEDOT Neural Interfaces

Although neural devices have shown efficacy in the treatment of neurodegenerative diseases, their functionality is limited by the inflammatory state and glial scar formation associated with chronic implantation. The aim of this study was to investigate neural electrode performance following functionalization with an anti-inflammatory coating derived from a conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) matrix doped with dexamethasone (Dex) and decorated with Au particles. Pristine PEDOT, PEDOT-Dex and their gold-decorated analogues (PEDOT/Au and PEDOT-Dex/Au) were formulated by electrochemical deposition and characterized with respect to electrode electrochemical properties, surface morphology and biocompatibility towards primary neural cells. Through a process of gold deposition, it was possible to eliminate the initial burst release observed in PEDOT-Dex and maintain a stable, stepwise increase in Dex elution over 7 days. The released amounts of Dex exceeded the concentrations considered as therapeutic for both PEDOT-Dex and PEDOT-Dex/Au. The results clearly indicated that the presence of either Dex or Au particles facilitated the outgrowth of neurites. Finally, it was shown that the application of composite materials, such as PEDOT-Dex/Au, is an efficient way to improve the efficacy of neural interfaces in vitro.

Porous silicon based intravitreal platform for dual-drug loading and controlled release towards synergistic therapy

The number of blind and low vision persons in the US is projected to increase to 5.68 million by 2020. The eye diseases causing loss of vision are life-long, chronic, and often need protracted presence of therapeutics at the disease site to keep the disease in remission. In addition, multiple pathologies participate in the disease process and a single therapy seems insufficient to bring the disease under control and prevent vision loss. This study demonstrates the use of porous silicon (pSi) particles sequentially loaded with daunorubicin (DNR) and dexamethasone (DEX) to create a synergistic intravitreally injectable dual-drug delivery system. DEX targets chronic inflammation while DNR inhibits excessive cell proliferation as well as suppresses hypoxia-inducible factor 1 to reduce scarring. This pSi-based delivery system releases therapeutic concentrations of DNR for 100 days and DEX for over 165 days after a single dose. This intravitreal dual-drug delivery system is also well tolerated after injection into the rabbit eye model, attested by ocular biomicroscopy, ocular tonometry, electroretinography, and histology. This novel dual-drug delivery system opens an attractive modality for combination therapy to manage refractory chorioretinal diseases and further preclinical studies are warranted to evaluate its efficacy.

Evaluation of the effect of topical chamomile (Matricaria chamomilla L.) oleogel as pain relief in migraine without aura: a randomized, double-blind, placebo-controlled, crossover study

Phytotherapy is a source of finding new remedies for migraine. Traditional chamomile oil (chamomile extraction in sesame oil) is a formulation in Persian medicine (PM) for pain relief in migraine. An oleogel preparation of reformulated traditional chamomile oil was prepared and then standardized based on chamazulene (as a marker in essential oil) and apigenin via gas chromatography (GC) and high-performance liquid chromatography (HPLC) methods, respectively. A crossover double-blind clinical trial was performed with 100 patients. Each patient took two tubes of drug and two tubes of placebo during the study. Visual analog scale (VAS) questionnaires were filled in by the patients and scores were given, ranging from 0 to 10 (based on the severity of pain) during 24 h. Other complications like nausea, vomiting, photophobia, and phonophobia were also monitored. There was 4.48 ± 0.01 μl/ml of chamazulene and 0.233 mg/g of apigenin in the preparation (by correcting the amount with extraction ratio). Thirty-eight patients in the drug-placebo and 34 patients in the placebo-drug groups (a total number of 72 patients as per protocol) completed the process in the randomized controlled trial (RCT). Adapted results from the questionnaires showed that pain, nausea, vomiting, photophobia, and phonophobia significantly (p < 0.001) decreased by using chamomile oleogel on the patients after 30 min. Results supported the efficacy of chamomile oleogel as a pain relief in migraine without aura.

Role of poly-beta-amino-esters hydrolysis and electrostatic attraction in gentamicin release from layer-by-layer coatings

Layer-by-layer (LbL) deposition is a versatile technique that has been employed in numerous industrial applications i.e. biomaterials, drug delivery and electronics to confer peculiar properties to the system. When LbL is employed for drug delivery, the active molecule is sandwiched between layers of polyelectrolytes and the release is controlled by the diffusion of the drug through the layers and the possible hydrolysis of the coating (delamination). Poly-beta-amino-esters (PBAEs) are a class of hydrolysable polyelectrolytes that have been widely used in DNA delivery and for LbL on medical devices. Their use allowed the controlled release of antibiotics and other bioactive compounds from the surface of medical devices without cytotoxic effects. The general accepted consensus is that drug released from LbL coating assembled using PBAEs is the results of the polymer hydrolysis; however, no attention has been paid to the role of the electrostatic attraction between PBAE and the other polyelectrolyte utilised in the LbL assembly. In this work, we prepared LbL coatings on the surface of silica nanoparticles entrapping gentamicin as model drug and demonstrated that the drug release from PBAEs containing LbL coatings is predominantly controlled by the electrostatic attraction between opposite charged electrolytes. The positive charge of PBAE decreased from pH = 5 to pH = 7.4 while alginate negative charges remained unchanged in this pH range while PBAE hydrolysis kinetics was faster, as determined with Gel Permeation Chromatography (GPC), in acidic conditions. When PBAE were employed in the LbL construct higher levels of drug were released at pH = 7.4 than at pH = 5; additionally, replacing PBAE with chitosan (the charge of chitosan is not influenced in this pH range) resulted in comparable gentamicin release kinetics at pH = 5.

New model of proliferative vitreoretinopathy in rabbit for drug delivery and pharmacodynamic studies

Blinding retinal diseases become more epidemic as the population ages. These diseases, such as diabetic retinopathy and macular edema, are of chronic nature and require protracted drug presence at the disease site. A sustained intravitreal porous silicon delivery system with dexamethasone (pSiO₂-COO-DEX) was evaluated in a new rabbit model of proliferative vitreoretinopathy (PVR) in a real treatment design. In contrast to the pretreatment design model, pSiO₂-COO-DEX was intravitreally injected into the eyes with active inflammation. Subretinal injection of vascular endothelial growth factor (VEGF) and Matrigel induced a late-onset vitreoretinal inflammation that gradually developed into PVR. This method mimics the human disease better than PVR induced by either intravitreal cell injection or trauma. The pSiO₂-COO-DEX intervened eyes had minimal PVR, while balanced saline solution or free dexamethasone intervened eyes had significantly more PVR formation. In addition, adding VEGF to the Matrigel for subretinal injection induced greater inflammation and retinal neovascularization in comparison to only Matrigel injected under the medullary ray. Clinical and pathological examinations, including fundus fluorescein angiography and optical coherence tomography, confirmed these changes. In the current study, neither subretinal injection of Matrigel or subretinal injection of VEGF and Matrigel induced choroidal neovascularization. However, the current PVR model demonstrates a chronic course with moderate severity, which may be useful for drug screening studies.

Modern Therapeutic Approaches for Noninfectious Ocular Diseases Involving Inflammation

Dry eye disease, age-related macular degeneration, and uveitis are ocular diseases that significantly affect the quality of life of millions of people each year. In these diseases, the action of chemokines, proinflammatory cytokines, and immune cells drives a local inflammatory response that results in ocular tissue damage. Multiple therapeutic strategies are developed to either address the symptoms or abate the underlying cause of these diseases. Herein, the challenges to deliver drugs to the relevant location in the eye for each of these diseases are reviewed along with current and innovative therapeutic approaches that attempt to restore homeostasis within the ocular microenvironment.

Controlled Release of Dexamethasone From an Intravitreal Delivery System Using Porous Silicon Dioxide

PURPOSE

The current study aims to evaluate a porous silicon-based drug delivery system meant for sustained delivery of dexamethasone (Dex) to the vitreous and retina.

METHODS

Dexamethasone was grafted covalently into the pore walls of fully oxidized porous silicon particles (pSiO2-COO-Dex), which then was evaluated for the pharmacological effect of the payload on cultured ARPE19 cells before intravitreal injection. The Dex release profile was investigated in a custom designed dynamic dissolution chamber to mimic the turnover of vitreous fluid in rabbit eyes. Ocular safety, in vivo release, and pharmacodynamics were evaluated in rabbit eyes, and the human VEGF-induced rabbit retinal vascular permeability model.

RESULTS

Loading efficiency of Dex was 69 ± 9 μg per 1 mg of the pSiO2-COO-Dex particles. Dynamic in vitro release demonstrated a sustained mode when compared to free Dex, with the drug half-life extended by 5 times. The released Dex was unaltered and biologically active. In vivo drug release in rabbit eyes revealed a mode similar to the release seen in vitro, with a vitreous half-life of 11 days. At 2 and 4 weeks after a single intravitreal injection of pSiO2-COO-Dex particles (mean 2.71 ± 0.47 mg), intravitreal 500 ng of VEGF did not induce significant retinal vessel dilation or fluorescein leakage, while these events were observed in the eyes injected with empty pSiO2 particles or with free Dex. The retinal vessel score from fluorescein angiography for the control eyes was double the score for the eyes injected with pSiO2-COO-Dex. No adverse reaction was observed for the eyes injected with drug-loaded pSi particles during the course of the study.

CONCLUSIONS

The porous silicon-based Dex delivery system (pSiO2-COO-Dex) can be administered safely into vitreous without toxicity. Dex release from the porous silicon particles was sustained for 2 months and was effective against VEGF-induced retinal vessel reaction.

Acetylcholinesterase immobilization and characterization, and comparison of the activity of the porous silicon-immobilized enzyme with its free counterpart

The physically adsorbed acetylcholinesterase on mesoporous silicon surface is presented. The catalytic behavior of immobilized enzyme was assessed by spectrophotometric bioassay. The immobilization enhanced the reusability, shelf life and thermal as well as pH stability

A successful prescription is presented for acetylcholinesterase physically adsorbed on to a mesoporous silicon surface, with a promising hydrolytic response towards acetylthiocholine iodide. The catalytic behaviour of the immobilized enzyme was assessed by spectrophotometric bioassay using neostigmine methyl sulfate as a standard acetycholinesterase inhibitor. The surface modification was studied through field emission SEM, Fourier transform IR spectroscopy, energy-dispersive X-ray spectroscopy, cathode luminescence and X-ray photoelectron spectroscopy analysis, photoluminescence measurement and spectrophotometric bioassay. The porous silicon-immobilized enzyme not only yielded greater enzyme stability, but also significantly improved the native photoluminescence at room temperature of the bare porous silicon architecture. The results indicated the promising catalytic behaviour of immobilized enzyme compared with that of its free counterpart, with a greater stability, and that it aided reusability and easy separation from the reaction mixture. The porous silicon-immobilized enzyme was found to retain 50% of its activity, promising thermal stability up to 90°C, reusability for up to three cycles, pH stability over a broad pH of 4–9 and a shelf-life of 44 days, with an optimal hydrolytic response towards acetylthiocholine iodide at variable drug concentrations. On the basis of these findings, it was believed that the porous silicon-immobilized enzyme could be exploited as a reusable biocatalyst and for screening of acetylcholinesterase inhibitors from crude plant extracts and synthesized organic compounds. Moreover, the immobilized enzyme could offer a great deal as a viable biocatalyst in bioprocessing for the chemical and pharmaceutical industries, and bioremediation to enhance productivity and robustness.

A sustained intravitreal drug delivery system with remote real time monitoring capability

Many chorioretinal diseases are chronic and need sustained drug delivery systems to keep therapeutic drug level at the disease site. Many intravitreal drug delivery systems under developing do not have mechanism incorporated for a non-invasive monitoring of drug release. The current study prepared rugate porous silicon (pSi) particles by electrochemical etching with the current frequency (K value) of 2.17 and 2.45. Two model drugs (rapamycin and dexamethasone) and two drug-loading strategies were tested for the feasibility to monitor drug release from the pSi particles through a color fundus camera. The pSi particles (k=2.45) with infiltration loading of rapamycin demonstrated progressively more violet color reflection which was negatively associated with the rapamycin released into the vitreous (r=-0.4, p<0.001, pairwise). In contrast, pSi with K value of 2.17 demonstrated progressive color change toward green and a weak association between rapamycin released into vitreous and green color abundance was identified (r=-0.23, p=0.002, pairwise). Dexamethasone was covalently loaded on to the fully oxidized pSi particles that appeared in vitreous as yellow color and fading over time. The yellow color decrease over time was strongly associated with the dexamethasone detected from the vitreous samples (r=0.7, p<0.0001, pairwise). These results suggest that engineered porous silicon particles may be used as a self-reporting drug delivery system for a non-invasive real time remote monitoring.

STATEMENT OF SIGNIFICANCE

The current study, for the first time, demonstrated proof of concept that engineered porous silicon photonic crystal may deliver therapeutics in a controlled fashion while at the same time might offer a noninvasive remote monitoring of its payload release in a living eye. Porous silicon photonic crystal changes color which is in association with its payload release into vitreous. With further optimization, the color change may be harnessed to inform eye care professionals of real time drug concentration in the eye and allow them to make informed decision to re-dose the patients.

Pharmacological approaches to retinitis pigmentosa: A laboratory perspective

Retinal photoreceptors are highly specialized and performing neurons. Their cellular architecture is exquisitely designed to host a high concentration of molecules involved in light capture, phototransduction, electric and chemical signaling, membrane and molecular turnover, light and dark adaption, network activities etc. Such high efficiency and molecular complexity require a great metabolic demand, altogether conferring to photoreceptors particular susceptibility to external and internal insults, whose occurrence usually precipitate into degeneration of these cells and blindness. In Retinitis Pigmentosa, an impressive number of mutations in genes expressed in the retina and coding for a large varieties of proteins leads to the progressive death of photoreceptors and blindness. Recent advances in molecular tools have greatly facilitated the identification of the underlying genetics and molecular bases of RP leading to the successful implementation of gene therapy for some types of mutations, with visual restoration in human patients. Yet, genetic heterogeneity of RP makes mutation-independent approaches highly desirable, although many obstacles pave the way to general strategies for treating this complex disease, which remains orphan. The review will focus on treatments for RP based on pharmacological tools, choosing, among the many ongoing studies, approaches which rely on strong experimental evidence or rationale. For perspective treatments, new concepts are foreseen to emerge from basic studies elucidating the pathways connecting the primary mutations to photoreceptor death, possibly revealing common molecular targets for drug intervention.

Surface engineering of porous silicon microparticles for intravitreal sustained delivery of rapamycin

PURPOSE

To understand the relationship between rapamycin loading/release and surface chemistries of porous silicon (pSi) to optimize pSi-based intravitreal delivery system.

METHODS

Three types of surface chemical modifications were studied: (1) pSi-COOH, containing 10-carbon aliphatic chains with terminal carboxyl groups grafted via hydrosilylation of undecylenic acid; (2) pSi-C12, containing 12-carbon aliphatic chains grafted via hydrosilylation of 1-dodecene; and (3) pSiO2-C8, prepared by mild oxidation of the pSi particles followed by grafting of 8-hydrocarbon chains to the resulting porous silica surface via a silanization.

RESULTS

The efficiency of rapamycin loading follows the order (micrograms of drug/milligrams of carrier): pSiO2-C8 (105 ± 18) > pSi-COOH (68 ± 8) > pSi-C12 (36 ± 6). Powder X-ray diffraction data showed that loaded rapamycin was amorphous and dynamic drug-release study showed that the availability of the free drug was increased by 6-fold (compared with crystalline rapamycin) by using pSiO2-C8 formulation (P = 0.0039). Of the three formulations in this study, pSiO2-C8-RAP showed optimal performance in terms of simultaneous release of the active drug and carrier degradation, and drug-loading capacity. Released rapamycin was confirmed with the fingerprints of the mass spectrometry and biologically functional as the control of commercial crystalline rapamycin. Single intravitreal injections of 2.9 ± 0.37 mg pSiO2-C8-RAP into rabbit eyes resulted in more than 8 weeks of residence in the vitreous while maintaining clear optical media and normal histology of the retina in comparison to the controls.

CONCLUSIONS

Porous silicon-based rapamycin delivery system using the pSiO2-C8 formulation demonstrated good ocular compatibility and may provide sustained drug release for retina.