Chitosan microparticles for delivery of proteins to the retina

Neuroprotective Effect of Tauroursodeoxycholic Acid (TUDCA) on In Vitro and In Vivo Models of Retinal Disorders: A Systematic Review

BACKGROUND

Tauroursodeoxycholic acid (TUDCA) is a naturally produced hydrophilic bile acid that has been used for centuries in Chinese medicine. Numerous recent in vitro and in vivo studies have shown that TUDCA has neuroprotective action in various models of retinal disorders.

OBJECTIVE

To systematically review the scientific literature and provide a comprehensive summary on the neuroprotective action and the mechanisms involved in the cytoprotective effects of TUDCA.

METHODS

A systematic review was conducted in accordance with the PRISMA (The Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Systematic literature search of United States National Library of Medicine (PubMed), Web of Science, Embase, Scopus and Cochrane Library was performed, which covered all original articles published up to July 2022. The terms, "TUDCA" in combination with "retina", "retinal protection", "neuroprotection" were searched. Possible biases were identified with the adopted SYRCLE's tool.

RESULTS

Of the 423 initially gathered studies, 24 articles met inclusion/exclusion criteria for full-text review. Six of them were in vitro experiments, 17 studies reported in vivo data and one study described both in vitro and in vivo data. The results revealed the effect of TUDCA on different retinal diseases, such as retinitis pigmentosa (RP), diabetic retinopathy (DR), retinal degeneration (RD), retinal ganglion cell (RGC) injury, Leber's hereditary optic neuropathy (LHON), choroidal neovascularization (CNV), and retinal detachment (RDT). The quality scores of the in vivo studies were ranged from 5 to 7 points (total 10 points), according to SYRCLE's risk of bias tool. Both in vitro and in vivo data suggested that TUDCA could effectively delay degeneration and apoptosis of retinal neurons, preserve retinal structure and function, and its mechanism of actions might be related with inhibiting apoptosis, decreasing inflammation, attenuating oxidative stress, suppressing endoplasmic reticulum (ER) stress, and reducing angiogenesis.

CONCLUSION

This systematic review demonstrated that TUDCA has neuroprotective effect on in vivo and in vitro models of retinal disorders, reinforcing the currently available evidence that TUDCA could be a promising therapeutic agent in retinal diseases treatment. However, well designed clinical trials are necessary to appraise the efficacy of TUDCA in clinical setting.

Controlled growth factor delivery via a degradable poly(lactic acid) hydrogel microcarrier synthesized using degassed micromolding lithography

Controlled and targeted delivery of growth factors to biological environments is important for tissue regeneration. Polylactic acid (PLA) hydrogel microparticles are attractive carriers for the delivery of therapeutic cargoes based on their superior biocompatibility and biodegradability, uniform encapsulation of cargoes, and non-requirement of organic solvents during particle synthesis. In this study, we newly present controlled growth factor delivery utilizing PLA-based hydrogel microcarriers synthesized via degassed micromolding lithography (DML). Based on the direct gelation procedure from the single-phase aqueous precursor in DML, bovine serum albumin, a model protein of growth factor, and fibroblast growth factor were encapsulated into microparticles with uniform distribution. In addition, by tuning the monomer concentration and adding a hydrolytically stable crosslinker, the release of encapsulated cargoes was efficiently controlled and extended to 2 weeks. Finally, we demonstrated the biological activity of encapsulated FGF-2 in PLA-based microparticles using a fibroblast proliferation assay.

Co-delivery of glial cell-derived neurotrophic factor (GDNF) and tauroursodeoxycholic acid (TUDCA) from PLGA microspheres: potential combination therapy for retinal diseases

Retinitis pigmentosa (RP) is a group of genetically diverse inherited disorders characterised by the progressive photoreceptors and pigment epithelial cell dysfunction leading to central vision impairment. Although important advances in the understanding of the pathophysiologic pathways involved in RP have been made, drug delivery for the treatment of ocular disorders affecting the posterior segment of the eye is still an unmet clinical need. In the present study, we describe the development of multi-loaded PLGA-microspheres (MSs) incorporating two neuroprotectants agents (glial cell-line-derived neurotrophic factor-GDNF and Tauroursodeoxycholic acid-TUDCA) as a potential therapeutic tool for the treatment of RP. A solid-in-oil-in-water (S/O/W) emulsion solvent extraction-evaporation technique was employed for MS preparation. A combination of PLGA and vitamin E was used to create the microcarriers. The morphology, particle size, encapsulation efficiency and in vitro release profile of the MSs were studied. Encapsulation efficiencies of GDNF and TUDCA for the initial multiloaded MSs, prepared with methylene chloride (MC) as organic solvent and polyvinyl alcohol (PVA) solution in the external phase, were 28.53±0.36% and 45.65±8.01% respectively. Different technological parameters to optimise the formulation such as the incorporation of a water-soluble co-solvent ethanol (EtOH) in the internal organic phase, as well as NaCl concentration, and viscosity using a viscosizing agent (hydroxypropyl methylcellulose-HPMC) in the external aqueous phase were considered. EtOH incorporation and external phase viscosity of the emulsion were critical attributes for improving drug loading of both compounds. In such a way, when using a methylene chloride/EtOH ratio 75:25 into the inner organic phase and the viscosity agent HPMC (1% w/v) in the external aqueous phase, GDNF and TUDCA payloads resulted 48.86±1.49% and 78.58±10.40% respectively, and a decrease in the initial release of GDNF was observed (22.03±1.41% compared with 40.86±6.66% of the initial multi-loaded formulation). These optimised microparticles exhibited sustained in vitro releases over 91 days. These results suggest that the microencapsulation procedure optimised in this work presents a promising technological strategy for the development of multi-loaded intraocular drug delivery systems (IODDS).

Intravitreal hydrogels for sustained release of therapeutic proteins

This review highlights how hydrogel formulations can improve intravitreal protein delivery to the posterior segment of the eye in order to increase therapeutic outcome and patient compliance. Several therapeutic proteins have shown excellent clinical successes for the treatment of various intraocular diseases. However, drug delivery to the posterior segment of the eye faces significant challenges due to multiple physiological barriers preventing drugs from reaching the retina, among which intravitreal protein instability and rapid clearance from the site of injection. Hence, frequent injections are required to maintain therapeutic levels. Moreover, because the world population ages, the number of patients suffering from ocular diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy (DR) is increasing and causing increased health care costs. Therefore, there is a growing need for suitable delivery systems able to tackle the current limitations in retinal protein delivery, which also may reduce costs. Hydrogels have shown to be promising delivery systems capable of sustaining release of therapeutic proteins and thus extending their local presence. Here, an extensive overview of preclinically developed intravitreal hydrogels is provided with attention to the rational design of clinically useful intravitreal systems. The currently used polymers, crosslinking mechanisms, in vitro/in vivo models and advancements are discussed together with the limitations and future perspective of these biomaterials.

Chitosan-Polycaprolactone Core-Shell Microparticles for Sustained Delivery of Bevacizumab

The current therapy for treating neovascular age-related macular degeneration requires monthly intravitreal injection of angiogenesis inhibitors such as bevacizumab or ranibizumab via a 31-gauge needle to inhibit choroidal neovascularization. However, repeated intravitreal injections are associated with poor patient compliance and potential side effects. Microparticle-based injectable devices have shown great promise to address this issue by sustained delivery of protein therapeutics, but critical barriers remain, including limited loading capacity and steady long-term release without compromising the anti-angiogenic activity of drugs. Addressing these challenges, we developed a unique method for synthesizing biodegradable polymer-based core-shell microparticles with sizes around 10 μm, high physical integrity, and uniform size. Subsequent electrostatic and physical interactions to control protein diffusion were designed for the core-shell microparticles to effectively increase the capacity of drug loading to 25%, reduce burst release by almost 30%, and extend the period of drug release from 3 to 6 months. Remarkably, the microparticles enabled a longer-term drug administration and maintained high drug potency up to 6 months in vitro, representing significant advancement compared to conventional microparticle-based delivery platforms or currently commercialized devices. Additionally, the microparticles presented minimal toxicity to human retinal cells in vitro with over 90% cell viability, and they also exhibited good injection feasibility through 31-gauge needles in an ex vivo porcine eye model. These results warrant further studies to evaluate the clinical potential for treating posterior ophthalmic diseases as well as other conditions or injuries requiring long-term local drug administration.

Polysaccharides in Ocular Drug Delivery

Polysaccharides, such as cellulose, hyaluronic acid, alginic acid, and chitosan, as well as polysaccharide derivatives, have been successfully used to augment drug delivery in the treatment of ocular pathologies. The properties of polysaccharides can be extensively modified to optimize ocular drug formulations and to obtain biocompatible and biodegradable drugs with improved bioavailability and tailored pharmacological effects. This review discusses the available polysaccharide choices for overcoming the difficulties associated with ocular drug delivery, and it explores the reasons for the dependence between the physicochemical properties of polysaccharide-based drug carriers and their efficiency in different formulations and applications. Polysaccharides will continue to be of great interest to researchers endeavoring to develop ophthalmic drugs with improved effectiveness and safety.

Chitosan and its derivatives as vehicles for drug delivery

Chitosan and its derivatives as vehicles for drug delivery can achieve the purpose of sustained release and controlled release for drugs, improve the stability of drugs, and reduce adverse drug reactions. So, the bioavailability of drugs can be enhanced. Therefore, chitosan and its derivatives have become a hotspot in the field of drug delivery. Their characteristics as drug delivery vectors were introduced, the types and applications were summarized. The development direction of chitosan and its derivatives in this field was also forecasted.

Overexpression of the X-Linked Inhibitor of Apoptosis Protects Against Retinal Degeneration in a Feline Model of Retinal Detachment

Retinal detachment is an acute disorder in humans that is caused by trauma or disease, and it can often lead to permanent visual deficits that result from the death of photoreceptors in the retina. The final pathway for photoreceptor cell death is apoptosis and necroptosis. The X-linked inhibitor of apoptosis (XIAP) has been shown to block both of these cell death pathways. This study tested the effects of XIAP on photoreceptor survival in a feline model of retinal detachment. The study was performed in 12 cats, divided into two experimental groups. Six animals received a subretinal injection of adeno-associated virus (AAV) carrying XIAP, and six animals received AAV carrying green fluorescent protein (GFP) as a control. Three weeks after viral delivery, retinas were detached by injecting C3F8 gas into the subretinal space. Optical coherence tomography revealed that the retinal detachments resolved within 3-6 weeks as the gas was slowly resorbed. Analysis of histological sections through the plane of the detachment showed significant preservation of the photoreceptor layer in AAV-XIAP-treated animals compared to AAV-GFP-treated animals at 9 weeks after the detachment. XIAP-treated detached retinas were similar to intact controls. These studies support the potential for XIAP therapy in the treatment of human retinal detachment.

Recent perspectives on the delivery of biologics to back of the eye

INTRODUCTION

Biologics are generally macromolecules, large in size with poor stability in biological environments. Delivery of biologics to tissues at the back of the eye remains a challenge. To overcome these challenges and treat posterior ocular diseases, several novel approaches have been developed. Nanotechnology-based delivery systems, like drug encapsulation technology, macromolecule implants and gene delivery are under investigation. We provide an overview of emerging technologies for biologics delivery to back of the eye tissues. Moreover, new biologic drugs currently in clinical trials for ocular neovascular diseases have been discussed. Areas covered: Anatomy of the eye, posterior segment disease and diagnosis, barriers to biologic delivery, ocular pharmacokinetic, novel biologic delivery system Expert opinion: Anti-VEGF therapy represents a significant advance in developing biologics for the treatment of ocular neovascular diseases. Various strategies for biologic delivery to posterior ocular tissues are under development with some in early or late stages of clinical trials. Despite significant progress in the delivery of biologics, there is unmet need to develop sustained delivery of biologics with nearly zero-order release kinetics to the back of the eye tissues. In addition, elevated intraocular pressure associated with frequent intravitreal injections of macromolecules is another concern that needs to be addressed.

Novel Spray Dried Glycerol 2-Phosphate Cross-Linked Chitosan Microparticulate Vaginal Delivery System-Development, Characterization and Cytotoxicity Studies

Chitosan microparticulate delivery systems containing clotrimazole were prepared by a spray drying technique using glycerol 2-phosphate as an ion cross-linker. The impact of a cross-linking ratio on microparticle characteristics was evaluated. Drug-free and drug-loaded unmodified or ion cross-linked chitosan microparticles were examined for the in vitro cytotoxicity in VK2/E6E7 human vaginal epithelial cells. The presence of glycerol 2-phosphate influenced drug loading and encapsulation efficacy in chitosan microparticles. By increasing the cross-linking ratio, the microparticles with lower diameter, moisture content and smoother surface were observed. Mucoadhesive studies displayed that all formulations possessed mucoadhesive properties. The in vitro release profile of clotrimazole was found to alter considerably by changing the glycerol 2-phosphate/chitosan ratio. Results from cytotoxicity studies showed occurrence of apoptotic cells in the presence of chitosan and ion cross-linked chitosan microparticles, followed by a loss of membrane potential suggesting that cell death might go through the mitochondrial apoptotic pathway.