Suppression of phagocytic cells in retinal disorders using amphiphilic poly(γ-glutamic acid) nanoparticles containing dexamethasone

Vesicular Drug Delivery Systems: Promising Approaches in Ocular Drug Delivery

Ocular drug delivery poses unique challenges due to the complex anatomical and physiological barriers of the eye. Conventional dosage forms often fail to achieve optimal therapeutic outcomes due to poor bioavailability, short retention time, and off-target effects. In recent years, vesicular drug delivery systems have emerged as promising solutions to address these challenges. Vesicular systems, such as liposome, niosome, ethosome, transfersome, and others (bilosome, transethosome, cubosome, proniosome, chitosome, terpesome, phytosome, discome, and spanlastics), offer several advantages for ocular drug delivery. These include improved drug bioavailability, prolonged retention time on the ocular surface, reduced systemic side effects, and protection of drugs from enzymatic degradation and dilution by tears. Moreover, vesicular formulations can be engineered for targeted delivery to specific ocular tissues or cells, enhancing therapeutic efficacy while minimizing off-target effects. They also enable the encapsulation of a wide range of drug molecules, including hydrophilic, hydrophobic, and macromolecular drugs, and the possibility of combination therapy by facilitating the co-delivery of multiple drugs. This review examines vesicular drug delivery systems, their advantages over conventional drug delivery systems, production techniques, and their applications in management of ocular diseases.

Poly (γ) glutamic acid: a unique microbial biopolymer with diverse commercial applicability

Microbial biopolymers have emerged as promising solutions for environmental pollution-related human health issues. Poly-γ-glutamic acid (γ-PGA), a natural anionic polymeric compound, is composed of highly viscous homo-polyamide of D and L-glutamic acid units. The extracellular water solubility of PGA biopolymer facilitates its complete biodegradation and makes it safe for humans. The unique properties have enabled its applications in healthcare, pharmaceuticals, water treatment, foods, and other domains. It is applied as a thickener, taste-masking agent, stabilizer, texture modifier, moisturizer, bitterness-reducing agent, probiotics cryoprotectant, and protein crystallization agent in food industries. γ-PGA is employed as a biological adhesive, drug carrier, and non-viral vector for safe gene delivery in tissue engineering, pharmaceuticals, and medicine. It is also used as a moisturizer to improve the quality of hair care and skincare cosmetic products. In agriculture, it serves as an ideal stabilizer, environment-friendly fertilizer synergist, plant-growth promoter, metal biosorbent in soil washing, and animal feed additive to reduce body fat and enhance egg-shell strength.

Poly-γ-glutamic acid nanoparticles as adjuvant and antigen carrier system for cancer vaccination

Vaccination is an innovative strategy for cancer treatment by leveraging various components of the patients' immunity to boost an anti-tumor immune response. Rationally designed nanoparticles are well suited to maximize cancer vaccination by the inclusion of immune stimulatory adjuvants. Also, nanoparticles might control the pharmacokinetics and destination of the immune potentiating compounds. Poly-γ-glutamic acid (γ-PGA) based nanoparticles (NPs), which have a natural origin, can be easily taken up by dendritic cells (DCs), which leads to the secretion of cytokines which ameliorates the stimulation capacity of T cells. The intrinsic adjuvant properties and antigen carrier properties of γ-PGA NPs have been the focus of recent investigations as they can modulate the tumor microenvironment, can contribute to systemic anti-tumor immunity and subsequently inhibit tumor growth. This review provides a comprehensive overview on the potential of γ-PGA NPs as antigen carriers and/or adjuvants for anti-cancer vaccination.

Intraocular nano-microscale drug delivery systems for glaucoma treatment: design strategies and recent progress

Glaucoma is a leading cause of irreversible visual impairment and blindness, affecting over 76.0 million people worldwide in 2020, with a predicted increase to 111.8 million by 2040. Hypotensive eye drops remain the gold standard for glaucoma treatment, while inadequate patient adherence to medication regimens and poor bioavailability of drugs to target tissues are major obstacles to effective treatment outcomes. Nano/micro-pharmaceuticals, with diverse spectra and abilities, may represent a hope of removing these obstacles. This review describes a set of intraocular nano/micro drug delivery systems involved in glaucoma treatment. Particularly, it investigates the structures, properties, and preclinical evidence supporting the use of these systems in glaucoma, followed by discussing the route of administration, the design of systems, and factors affecting in vivo performance. Finally, it concludes by highlighting the emerging notion as an attractive approach to address the unmet needs for managing glaucoma.

Polymer- and lipid-based nanocarriers for ocular drug delivery: Current status and future perspectives

Ocular diseases seriously affect patients' vision and life quality, with a global morbidity of over 43 million blindness. However, efficient drug delivery to treat ocular diseases, particularly intraocular disorders, remains a huge challenge due to multiple ocular barriers that significantly affect the ultimate therapeutic efficacy of drugs. Recent advances in nanocarrier technology offer a promising opportunity to overcome these barriers by providing enhanced penetration, increased retention, improved solubility, reduced toxicity, prolonged release, and targeted delivery of the loaded drug to the eyes. This review primarily provides an overview of the progress and contemporary applications of nanocarriers, mainly polymer- and lipid-based nanocarriers, in treating various eye diseases, highlighting their value in achieving efficient ocular drug delivery. Additionally, the review covers the ocular barriers and administration routes, as well as the prospective future developments and challenges in the field of nanocarriers for treating ocular diseases.

Nanoparticles for the treatment of glaucoma-associated neuroinflammation

Recently, a considerable amount of literature has emerged around the theme of neuroinflammation linked to neurodegeneration. Glaucoma is a neurodegenerative disease characterized by visual impairment. Understanding the complex neuroinflammatory processes underlying retinal ganglion cell loss has the potential to improve conventional therapeutic approaches in glaucoma. Due to the presence of multiple barriers that a systemically administered drug has to cross to reach the intraocular space, ocular drug delivery has always been a challenge. Nowadays, studies are focused on improving the current therapies for glaucoma by utilizing nanoparticles as the modes of drug transport across the ocular anatomical and physiological barriers. This review offers some important insights on the therapeutic advancements made in this direction, focusing on the use of nanoparticles loaded with anti-inflammatory and neuroprotective agents in the treatment of glaucoma. The prospect of these novel therapies is discussed in relation to the current therapies to alleviate inflammation in glaucoma, which are being reviewed as well, along with the detailed molecular and cellular mechanisms governing the onset and the progression of the disease.

Synthesis and Characterization of Novel Succinyl Chitosan-Dexamethasone Conjugates for Potential Intravitreal Dexamethasone Delivery

The development of intravitreal glucocorticoid delivery systems is a current global challenge for the treatment of inflammatory diseases of the posterior segment of the eye. The main advantages of these systems are that they can overcome anatomical and physiological ophthalmic barriers and increase local bioavailability while prolonging and controlling drug release over several months to improve the safety and effectiveness of glucocorticoid therapy. One approach to the development of optimal delivery systems for intravitreal injections is the conjugation of low-molecular-weight drugs with natural polymers to prevent their rapid elimination and provide targeted and controlled release. This study focuses on the development of a procedure for a two-step synthesis of dexamethasone (DEX) conjugates based on the natural polysaccharide chitosan (CS). We first used carbodiimide chemistry to conjugate DEX to CS via a succinyl linker, and we then modified the obtained systems with succinic anhydride to impart a negative ζ-potential to the polymer particle surface. The resulting polysaccharide carriers had a degree of substitution with DEX moieties of 2–4%, a DEX content of 50–85 μg/mg, and a degree of succinylation of 64–68%. The size of the obtained particles was 400–1100 nm, and the ζ-potential was −30 to −33 mV. In vitro release studies at pH 7.4 showed slow hydrolysis of the amide and ester bonds in the synthesized systems, with a total release of 8–10% for both DEX and succinyl dexamethasone (SucDEX) after 1 month. The developed conjugates showed a significant anti-inflammatory effect in TNFα-induced and LPS-induced inflammation models, suppressing CD54 expression in THP-1 cells by 2- and 4-fold, respectively. Thus, these novel succinyl chitosan-dexamethasone (SucCS-DEX) conjugates are promising ophthalmic carriers for intravitreal delivery.

Optimization of fermentation conditions, purification and rheological properties of poly (γ-glutamic acid) produced by Bacillus subtilis 1006-3

This study aimed to investigate the optimal fermentation condition, purification and rheological properties of extracellular polymers produced by Bacillus subtilis 1006-3. An optimum temperature of 30.2 °C, inoculation amount of 6.1%, and pH of 8.2 were determined via Response Surface Methodology. The result of amino acid analysis and gel electrophoresis indicated that the obtained polymer contained only glutamic acid, with a wide molecular weight range. This polymer was finally determined as γ-PGA by infrared spectroscopy. The γ-PGA solution displayed a behavior of pseudoplastic non-Newtonian fluid with shear thinning properties, which can be described by the Ostward-de Waele power law model. The apparent viscosity of γ-PGA solution increased with the increase in its concentration from 1% to 10%. The deviation in pH from neutral value, and the addition of NaCl or MgCl₂ can reduce the apparent viscosity of γ-PGA solution, and it was more sensitive to Mg²⁺ than to Na⁺ addition. At the concentration of 4, 6, and 8%, γ-PGA solution showed predominantly viscous response in the range of 0.1-100 rad/s angular frequency (G″>G'). These results indicated the potential application of the γ-PGA as a thickening agent.

Distribution of polymeric nanoparticles in the eye: implications in ocular disease therapy

Advantages of polymeric nanoparticles as drug delivery systems include controlled release, enhanced drug stability and bioavailability, and specific tissue targeting. Nanoparticle properties such as hydrophobicity, size, and charge, mucoadhesion, and surface ligands, as well as administration route and suspension media affect their ability to overcome ocular barriers and distribute in the eye, and must be carefully designed for specific target tissues and ocular diseases. This review seeks to discuss the available literature on the biodistribution of polymeric nanoparticles and discuss the effects of nanoparticle composition and administration method on their ocular penetration, distribution, elimination, toxicity, and efficacy, with potential impact on clinical applications.

Polypeptide and glycosaminoglycan polysaccharide as stabilizing polymers in nanocrystals for a safe ocular hypotensive effect

Improved ocular delivery of a poorly soluble anti-glaucoma drug, acetazolamide (ACZ), in a stable nanosuspension (NS) was the main target of the study. The anionic polypeptide, poly-γ-glutamic acid (PG) and the glycosaminoglycan, hyaluronic acid, were used to stabilize ACZ-NS prepared using the antisolvent precipitation (AS-PT) coupled with sonication technique. To endue in site biocompatibility with high tolerability, soya lecithin (SL) phospholipid has been also combined with polyvinyl alcohol (PVA). NS with uniform PS in the range 100-300 nm, high ζ > ±20 mV, and enhanced saturation solubility were produced. Targeting solvent removal with control on future particle growth, post-production processing of NS was done using spray drying. The carriers' composition and amount relative to ACZ-NS were optimized to allow for the production of a redispersible dry crystalline powder. Particles crystallinity was confirmed using X-ray powder diffraction (XRPD) and differential scanning calorimetry (DSC) in liquid and spray dried NS. The modified Draize test proved the safety and tolerability following application to rabbit eyes accompanying an efficient ocular hypotensive activity using a steroid glaucoma model.

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.

Poly-Gamma-Glutamic Acid Functions as an Eective Lubricant with Antimicrobial Activity in Multipurpose Contact Lens Care Solutions

In order to perform the multiple functions of disinfection, cleansing, and storage, preservatives are often added to contact lens care solutions. The disadvantage of adding preservatives is that this often causes various eye conditions. However, lens care solutions would not be able to disinfect in the absence of such preservatives. In addition, comfort is an important issue for contact lens wearers due to the long periods of time they are worn. It has been shown that lower friction coefficients are correlated with increased comfort. We have previously developed a multipurpose contact lens care solution in which poly-gamma-glutamic acid (γ-PGA) was the main ingredient. In this study, we investigated the antimicrobial activity and lubricating property of our care solution. We showed that there was a synergetic effect of γ-PGA and chlorine dioxide on antimicrobial activity. We also demonstrated that γ-PGA functioned as a lubricating agent. Our results provided evidence of γ-PGA acting as a multi-functional polymer that could be applied in contact lens care solutions.

Feasible protein aggregation of phosphorylated poly-γ-glutamic acid derivative from Bacillus subtilis (natto)

Poly-γ-glutamic acid (PGA) was modified with phosphorylating agents such as sodium metaphosphate and potassium metaphosphate in the culture medium of Bacillus subtilis (natto). The highly phosphorylated PGA derivatives were prepared and investigated for their chemical and physicochemical properties. The PGA derivatives had approximately 7% (W/W) inorganic phosphorus and characteristic absorbance PO₂^- bands at 1082cm^-1 and 1260cm^-1 by Fourier Transform Infrared Spectroscopy. The derivative modified by sodium metaphosphate (J-5) was easily hydrated in water and had extremely low viscosity. The shear rate-induced transition leading to the decrease of viscosity was not observed in J-5 whereas the derivative modified by potassium metaphosphate (J-6) as well as unmodified PGA (J-1) showed the typical decrease of viscosity. In circular dichroism (CD) measurement of J-5, there was a significant loss of the negative chirality CD signal, implying that protein aggregation occured at decreasing pH from 6.2 to 4.4. The thioflavin T fluorescence intensity of the aqueous solution in the J-5 was extremely high despite the absence of heat-treatment. The results indicate that the J-5 is the likeliest type of aggregation by β-sheet cross-linking which is relevant to protein diseases like Alzheimer's disease.

Nanoengineering of therapeutics for retinal vascular disease

Retinal vascular diseases, including diabetic retinopathy, neovascular age related macular degeneration, and retinal vein occlusion, are leading causes of blindness in the Western world. These diseases share several common disease mechanisms, including vascular endothelial growth factor (VEGF) signaling, hypoxia, and inflammation, which provide opportunities for common therapeutic strategies. Treatment of these diseases using laser therapy, anti-VEGF injections, and/or steroids has significantly improved clinical outcomes. However, these strategies do not address the underlying root causes of pathology, and may have deleterious side effects. Furthermore, many patients continue to progress toward legal blindness despite receiving regular therapy. Nanomedicine, the engineering of therapeutics at the 1-100 nm scale, is a promising approach for improving clinical management of retinal vascular diseases. Nanomedicine-based technologies have the potential to revolutionize the treatment of ophthalmology, through enabling sustained release of drugs over several months, reducing side effects due to specific targeting of dysfunctional cells, and interfacing with currently "undruggable" targets. We will discuss emerging nanomedicine-based applications for the treatment of complications associated with retinal vascular diseases, including angiogenesis and inflammation.

Imaging retinal ganglion cells: enabling experimental technology for clinical application

Recent advances in clinical ophthalmic imaging have enhanced patient care. However, the ability to differentiate retinal neurons, such as retinal ganglion cells (RGCs), would advance many areas within ophthalmology, including the screening and monitoring of glaucoma and other optic neuropathies. Imaging at the single cell level would take diagnostics to the next level. Experimental methods have provided techniques and insight into imaging RGCs, however no method has yet to be translated to clinical application. This review provides an overview of the importance of non-invasive imaging of RGCs and the clinically relevant capabilities. In addition, we report on experimental data from wild-type mice that received an in vivo intravitreal injection of a neuronal tracer that labelled RGCs, which in turn were monitored for up to 100 days post-injection with confocal scanning laser ophthalmoscopy. We were able to demonstrate efficient and consistent RGC labelling with this delivery method and discuss the issue of cell specificity. This type of experimental work is important in progressing towards clinically applicable methods for monitoring loss of RGCs in glaucoma and other optic neuropathies. We discuss the challenges to translating these findings to clinical application and how this method of tracking RGCs in vivo could provide valuable structural and functional information to clinicians.

Poly-γ-glutamic acid: production, properties and applications

Poly-γ-glutamic acid (γ-PGA) is a naturally occurring biopolymer made up of repeating units of l-glutamic acid, d-glutamic acid or both. γ-PGA can exhibit different properties (conformational states, enantiomeric properties and molecular mass). Owing to its biodegradable, non-toxic and non-immunogenic properties, it has been used successfully in the food, medical and wastewater industries. Amongst other novel applications, it has the potential to be used for protein crystallization, as a soft tissue adhesive and a non-viral vector for safe gene delivery. This review focuses on the production, properties and applications of γ-PGA. Each application of γ-PGA utilizes specific properties attributed to various forms of γ-PGA. As a result of its growing applications, more strains of bacteria need to be investigated for γ-PGA production to obtain high yields of γ-PGA with different properties. Many medical applications (especially drug delivery) have exploited α-PGA. As γ-PGA is essentially different from α-PGA (i.e. it does not involve a chemical modification step and is not susceptible to proteases), it could be better utilized for such medical applications. Optimization of γ-PGA with respect to cost of production, molecular mass and conformational/enantiomeric properties is a major step in making its application practical. Analyses of γ-PGA production and knowledge of the enzymes and genes involved in γ-PGA production will not only help increase productivity whilst reducing the cost of production, but also help to understand the mechanism by which γ-PGA is effective in numerous applications.

One-step electrodeposition of self-assembled colloidal particles: a novel strategy for biomedical coating

A novel biomedical coating was prepared from self-assembled colloidal particles through direct electrodeposition. The particles, which are photo-cross-linkable and nanoscaled with a high specific surface area, were obtained via self-assembly of amphiphilic poly(γ-glutamic acid)-g-7-amino-4-methylcoumarin (γ-PGA-g-AMC). The size, morphology, and surface charge of the resulting colloidal particles and their dependence on pH, initial concentrations, and UV irradiation were successfully studied. A nanostructured coating was formed in situ on the surface of magnesium alloys by electrodeposition of colloidal particles. The composition, morphology, and phase of the coating were monitored using Fourier transform infrared spectroscopy, energy-dispersive X-ray spectroscopy, scanning electron microscopy, and X-ray diffraction. The corrosion test showed that the formation of the nanostructured coating on magnesium alloys effectively improved their initial anticorrosion properties. More importantly, the corrosion resistance was further enhanced by chemical photo-cross-linking. In addition, the low cytotoxicity of the coated samples was confirmed by MTT assay against NIH-3T3 normal cells. The contribution of our work lies in the creation of a novel strategy to fabricate a biomedical coating in view of the versatility of self-assembled colloidal particles and the controllability of the electrodeposition process. It is believed that our work provides new ideas and reliable data to design novel functional biomedical coatings.

Intravitreal drug delivery in retinal disease: are we out of our depth?

INTRODUCTION

With the ever-increasing global burden of retinal disease, there is an urgent need to vastly improve formulation strategies that enhance posterior eye delivery of therapeutics. Despite intravitreal administration having demonstrated notable superiority over other routes in enhancing retinal drug availability, there still exist various significant physical/biochemical barriers preventing optimal drug delivery into the retina. A further complication lies with an inability to reliably translate laboratory-based retinal models into a clinical setting. Several formulation approaches have recently been evaluated to improve intravitreal therapeutic outcomes, and our aim in this review is to highlight strategies that hold the most promise.

AREAS COVERED

We discuss the complex barriers faced by the intravitreal route and examine how formulation strategies including implants, nanoparticulate carriers, viral vectors and sonotherapy have been utilized to attain both sustained delivery and enhanced penetration through to the retina. We conclude by highlighting the advances and limitations of current in vitro, ex vivo and in vivo retinal models in use by researchers globally.

EXPERT OPINION

Various nanoparticle compositions have demonstrated the ability to overcome the retinal barriers successfully; however, their utility is limited to the laboratory setting. Optimization of these formulations and the development of more robust experimental retinal models are necessary to translate success in the laboratory into clinically efficacious outcomes.

Experimental uveitis can be maintained in rabbits for a period of six weeks after a safe sensitization method

PURPOSE

New treatments against long-lasting uveitis need to be tested. Our aim was to develop a six-week model of uveitis in rabbits.

METHODS

Rabbits were presensitized with an s.c. injection of Mycobacterium tuberculosis H37RA emulsified with TiterMax Gold adjuvant. Uveitis was induced at day 28 and 50, by intravitreal challenges of antigen suspension. Ocular inflammation was assessed till euthanasia at day 71 after s.c. injection of M. tuberculosis H37RA by: (a) the number of inflammatory cells in aqueous humor (AH); (b) the protein concentration in AH; (c) the clinical score (mean of conjunctival hyperaemia, conjunctival chemosis, oedema and secretion); (d) the microscopical score (mean presence of fibrin and synechiae, aqueous cell density and aqueous flare grade, as scored by slit lamp).

RESULTS

At the sites of presensitization injection, rabbits presented flat nodules which progressively vanished. The first challenge induced a significant increase in the four parameters (p < 0.05 the Wilcoxon/Kruskal-Wallis test). The AH contained 764 ± 82 cells/µl and 32 ± 0.77 mg protein/ml. During the following days, inflammatory parameters decreased slightly. The second intravitreal challenge increased inflammation (3564 ± 228 cells/µl AH and 31 ± 1 mg protein/ml), which remained at a high level for a longer period of time.

CONCLUSION

We developed a model of long-term uveitis, which could be maintained in rabbits for at least six weeks. Such a model could be used to test the efficacy of either new drugs or various drug delivery systems intended to deliver active agents during a few months.

Single-walled carbon nanohorns as drug carriers: adsorption of prednisolone and anti-inflammatory effects on arthritis

Prednisolone (PSL), an anti-inflammatory glucocorticoid drug, was adsorbed on oxidized single-walled carbon nanohorns (oxSWNHs) in ethanol-water solvent. The quantity of adsorbed PSL on the oxSWNHs was 0.35-0.54 g/g depending on the sizes and numbers of holes on the oxSWNHs. PSL was adsorbed on both the outside and the inside of the oxSWNHs, and released quickly in a couple of hours and slowly within about one day from the respective places. The released quantity in culture medium strongly depended on the concentration of the PSL-oxSWNH complexes, suggesting that PSL adsorbing on oxSWNHs and PSL in the culture medium were in concentration equilibrium. The local injection of PSL-oxSWNHs into the tarsal joint of rats with collagen-induced arthritis (CIA) slightly retarded the progression of the arthritis compared with controls. By histological analysis of the ankle joint, the anti-inflammatory effect of PSL-oxSWNHs was also observed.