Dendrimer-Triamcinolone Acetonide Reduces Neuroinflammation, Pathological Angiogenesis, and Neuroretinal Dysfunction in Ischemic Retinopathy

Frontier applications of retinal nanomedicine: progress, challenges and perspectives

The human retina is a fragile and sophisticated light-sensitive tissue in the central nervous system. Unhealthy retinas can cause irreversible visual deterioration and permanent vision loss. Effective therapeutic strategies are restricted to the treatment or reversal of these conditions. In recent years, nanoscience and nanotechnology have revolutionized targeted management of retinal diseases. Pharmaceuticals, theranostics, regenerative medicine, gene therapy, and retinal prostheses are indispensable for retinal interventions and have been significantly advanced by nanomedical innovations. Hence, this review presents novel insights into the use of versatile nanomaterial-based nanocomposites for frontier retinal applications, including non-invasive drug delivery, theranostic contrast agents, therapeutic nanoagents, gene therapy, stem cell-based therapy, retinal optogenetics and retinal prostheses, which have mainly been reported within the last 5 years. Furthermore, recent progress, potential challenges, and future perspectives in this field are highlighted and discussed in detail, which may shed light on future clinical translations and ultimately, benefit patients with retinal disorders.

Targeting endothelial ERG to mitigate vascular regression and neuronal ischemia in retinopathies

Retinopathy of prematurity (ROP) and diabetic retinopathy (DR) are ocular disorders in which a loss of retinal vasculature leads to ischemia followed by a compensatory neovascularization response. In mice, this is modeled using oxygen-induced retinopathy (OIR), whereby neonatal animals are transiently housed under hyperoxic conditions that result in central retina vessel regression and subsequent neovascularization. Using endothelial cell (EC)-specific gene deletion, we found that loss of two ETS-family transcription factors, ERG and FLI1, led to regression of OIR-induced neovascular vessels but failed to improve visual function, suggesting that relevant retinal damage occurs prior to and independently of neovascularization. Turning our attention to the initial stage of OIR, we found that hyperoxia repressed ERG expression in retinal ECs of wild type mice, raising the possibility that oxygen-induced ERG downregulation promotes vessel regression during the initiation of OIR-induced pathology. We therefore developed a murine model of EC-specific ERG overexpression and found it sufficient to prevent hyperoxia-induced vascular regression, neuronal cell death, and neovascularization in the OIR model. Importantly, ERG overexpression also improved visual function in OIR-challenged mice. Moreover, we show that both ERG and FLI1 are downregulated in the retinal vessels of human patients with early stages of DR, suggesting that neovascular disorders of the eye may share common mechanisms underlying pathological retinal capillary regression. Collectively, these data suggest that the regulation of vascular regression by EC-expressed ETS transcription factors may be adapted towards novel therapeutic approaches for the prevention and/or alleviation of ocular neovascular disorders.

Vaccines for immunological defense against traumatic brain injury

Traumatic brain injury (TBI) and subsequent neurodegeneration is partially driven by chronic inflammation both locally and systemically. Yet, current clinical intervention strategies do not mitigate inflammation sequalae necessitating the development of innovative approaches to reduce inflammation and minimize deleterious effects of TBI. Herein, a subcutaneous formulation based on polymer of alpha-ketoglutarate (paKG) delivering glycolytic inhibitor PFK15 (PFKFB3 inhibitor, a rate limiting step in glycolysis), alpha-ketoglutarate (to fuel Krebs cycle) and peptide antigen from myelin proteolipid protein (PLP139-151) was utilized as the prophylactic immunosuppressive formulation in a mouse model of TBI. In vitro, the paKG(PFK15+PLP) vaccine formulation stimulated proliferation of immunosuppressive regulatory T cells and induced generation of T helper-2 cells. When given subcutaneously in the periphery to two weeks prior to mice sustaining a TBI, the active vaccine formulation increased frequency of immunosuppressive macrophages and dendritic cells in the periphery and the brain at day 7 post- TBI and by 28 days post-TBI enhanced PLP-specific immunosuppressive cells infiltrated the brain. While immunohistology measurements of neuroinflammation were not altered 28 days post-TBI, the vaccine formulation improved motor function and enhanced autophagy mediated genes in a spatial manner in the brain. Overall, these data suggest that the TBI vaccine formulation successfully induced an anti-inflammatory profile and decreased TBI-associated inflammation.

Teaser

In this study, a vaccine formulation was generated to develop central nervous specific immunosuppressive responses for TBI.

Microglia in retinal angiogenesis and diabetic retinopathy

Diabetic retinopathy has a high probability of causing visual impairment or blindness throughout the disease progression and is characterized by the growth of new blood vessels in the retina at an advanced, proliferative stage. Microglia are a resident immune population in the central nervous system, known to play a crucial role in regulating retinal angiogenesis in both physiological and pathological conditions, including diabetic retinopathy. Physiologically, they are located close to blood vessels and are essential for forming new blood vessels (neovascularization). In diabetic retinopathy, microglia become widely activated, showing a distinct polarization phenotype that leads to their accumulation around neovascular tufts. These activated microglia induce pathogenic angiogenesis through the secretion of various angiogenic factors and by regulating the status of endothelial cells. Interestingly, some subtypes of microglia simultaneously promote the regression of neovascularization tufts and normal angiogenesis in neovascularization lesions. Modulating the state of microglial activation to ameliorate neovascularization thus appears as a promising potential therapeutic approach for managing diabetic retinopathy.

Innovative Nanotechnology in Drug Delivery Systems for Advanced Treatment of Posterior Segment Ocular Diseases

Funduscopic diseases, including diabetic retinopathy (DR) and age-related macular degeneration (AMD), significantly impact global visual health, leading to impaired vision and irreversible blindness. Delivering drugs to the posterior segment of the eye remains a challenge due to the presence of multiple physiological and anatomical barriers. Conventional drug delivery methods often prove ineffective and may cause side effects. Nanomaterials, characterized by their small size, large surface area, tunable properties, and biocompatibility, enhance the permeability, stability, and targeting of drugs. Ocular nanomaterials encompass a wide range, including lipid nanomaterials, polymer nanomaterials, metal nanomaterials, carbon nanomaterials, quantum dot nanomaterials, and so on. These innovative materials, often combined with hydrogels and exosomes, are engineered to address multiple mechanisms, including macrophage polarization, reactive oxygen species (ROS) scavenging, and anti-vascular endothelial growth factor (VEGF). Compared to conventional modalities, nanomedicines achieve regulated and sustained delivery, reduced administration frequency, prolonged drug action, and minimized side effects. This study delves into the obstacles encountered in drug delivery to the posterior segment and highlights the progress facilitated by nanomedicine. Prospectively, these findings pave the way for next-generation ocular drug delivery systems and deeper clinical research, aiming to refine treatments, alleviate the burden on patients, and ultimately improve visual health globally.

Biomaterial strategies for regulating the neuroinflammatory response

Injury and disease in the central nervous system (CNS) can result in a dysregulated inflammatory environment that inhibits the repair of functional tissue. Biomaterials present a promising approach to tackle this complex inhibitory environment and modulate the mechanisms involved in neuroinflammation to halt the progression of secondary injury and promote the repair of functional tissue. In this review, we will cover recent advances in biomaterial strategies, including nanoparticles, hydrogels, implantable scaffolds, and neural probe coatings, that have been used to modulate the innate immune response to injury and disease within the CNS. The stages of inflammation following CNS injury and the main inflammatory contributors involved in common neurodegenerative diseases will be discussed, as understanding the inflammatory response to injury and disease is critical for identifying therapeutic targets and designing effective biomaterial-based treatment strategies. Biomaterials and novel composites will then be discussed with an emphasis on strategies that deliver immunomodulatory agents or utilize cell-material interactions to modulate inflammation and promote functional tissue repair. We will explore the application of these biomaterial-based strategies in the context of nanoparticle- and hydrogel-mediated delivery of small molecule drugs and therapeutic proteins to inflamed nervous tissue, implantation of hydrogels and scaffolds to modulate immune cell behavior and guide axon elongation, and neural probe coatings to mitigate glial scarring and enhance signaling at the tissue-device interface. Finally, we will present a future outlook on the growing role of biomaterial-based strategies for immunomodulation in regenerative medicine and neuroengineering applications in the CNS.

Intraocular drug delivery systems for Diabetic retinopathy: Current and future prospective

In pharmaceutical research and development, novel drug delivery systems represent a significant advancement aimed at enhancing the efficacy of therapeutic agents through innovative delivery mechanisms. The primary objective of these systems is to transport therapeutic compounds to specific target sites, such as tumors and afflicted tissues, with the dual purpose of mitigating side effects and toxicity associated with the drugs while concurrently augmenting therapeutic effectiveness. Numerous innovative drug delivery strategies have been scrutinized for their applicability in the context of targeted ocular drug delivery. Diverse novel carriers, including but not limited to implants, hydrogels, metal nanoparticles, Nano-liposomes, micelles, solid lipid nanoparticles (SLN), emulsions, and biodegradable nanoparticles, have been harnessed to facilitate the controlled release of pharmaceutical agents to the retina and vitreous. These carriers offer distinct advantages, such as enhanced intraocular drug delivery, precise control over drug release kinetics, heightened stability, and superior entrapment efficiency. This comprehensive review seeks to elucidate the current strides made in the realm of carriers and their contemporary applications in treating diabetic retinopathy (DR). Furthermore, it underscores these carriers' pivotal role in achieving efficacious intraocular drug delivery. Additionally, this article explores the various administration routes, potential future advancements, and the multifaceted challenges confronting the domain of novel carriers in treating DR. In conclusion, novel formulations are introduced to surmount the challenges associated with intraocular drug delivery.

Recent advances in the treatment and delivery system of diabetic retinopathy

Diabetic retinopathy (DR) is a highly tissue-specific neurovascular complication of type 1 and type 2 diabetes mellitus and is among the leading causes of blindness worldwide. Pathophysiological changes in DR encompass neurodegeneration, inflammation, and oxidative stress. Current treatments for DR, including anti-vascular endothelial growth factor, steroids, laser photocoagulation, and vitrectomy have limitations and adverse reactions, necessitating the exploration of novel treatment strategies. This review aims to summarize the current pathophysiology, therapeutic approaches, and available drug-delivery methods for treating DR, and discuss their respective development potentials. Recent research indicates the efficacy of novel receptor inhibitors and agonists, such as aldose reductase inhibitors, angiotensin-converting enzyme inhibitors, peroxisome proliferator-activated receptor alpha agonists, and novel drugs in delaying DR. Furthermore, with continuous advancements in nanotechnology, a new form of drug delivery has been developed that can address certain limitations of clinical drug therapy, such as low solubility and poor penetration. This review serves as a theoretical foundation for future research on DR treatment. While highlighting promising therapeutic targets, it underscores the need for continuous exploration to enhance our understanding of DR pathogenesis. The limitations of current treatments and the potential for future advancements emphasize the importance of ongoing research in this field.

Recent Updates on Nanocarriers for Drug Delivery in Posterior Segment Diseases with Emphasis on Diabetic Retinopathy

In recent years, various conventional formulations have been used for the treatment and/or management of ocular medical conditions. Diabetic retinopathy, a microvascular disease of the retina, remains the leading cause of visual disability in patients with diabetes. Currently, for treating diabetic retinopathy, only intraocular, intravitreal, periocular injections, and laser photocoagulation are widely used. Frequent administration of these drugs by injections may lead to serious complications, including retinal detachment and endophthalmitis. Although conventional ophthalmic formulations like eye drops, ointments, and suspensions are available globally, these formulations fail to achieve optimum drug therapeutic profile due to immediate nasolacrimal drainage, rapid tearing, and systemic tearing toxicity of the drugs. To achieve better therapeutic outcomes with prolonged release of the therapeutic agents, nano-drug delivery materials have been investigated. These nanocarriers include nanoparticles, solid lipid nanoparticles (SLN), nanostructured lipid carriers (NLC), dendrimers, nanofibers, in-situ gel, vesicular carriers, niosomes, and mucoadhesive systems, among others. The nanocarriers carry the potential benefits of site-specific delivery and controlled and sustained drug release profile. In the present article, various nanomaterials explored for treating diabetic retinopathy are reviewed.

Subconjunctival therapy by cubic liquid crystalline nanoparticles to deliver Triamcinolone acetonide for the management of diabetic Retinopathy: In vivo evidences

The expression of inflammatory markers and vascular endothelial growth factor (VEGF) was found to be upregulated in various posterior ocular disorders, including diabetic retinopathy (DR). Effective delivery of therapeutic agents to the retina poses a significant challenge in ophthalmic drug delivery due to biological ocular barriers. Triamcinolone acetonide (TA) was selected as the model corticosteroid drug targeting cytokines and VEGF in DR. However, despite TA's low molecular weight and hydrophobicity, which enable it to bypass the conjunctival epithelial barrier, it doesn't efficiently exert its effect at the target site. Nanocarriers have emerged as a solution to enhance drug delivery to the retina and improve bioavailability. This study aimed to compare the effects of Triamcinolone-loaded cubic liquid crystalline nanoparticles (TA-cubic LCNPs) and TA-Suspension in an experimental DR model administered via the subconjunctival (SCJ) route. The results demonstrated that TA-cubic LCNPs enhanced TA periocular delivery efficacy by reducing inflammatory and VEGF markers through the advanced glycation end products (AGE)/protein kinase C pathway. They were identified as promising nano-carriers, exhibiting potential for targeted delivery to the retina.

Nanomaterial payload delivery to central nervous system glia for neural protection and repair

Central nervous system (CNS) glia, including astrocytes, microglia, and oligodendrocytes, play prominent roles in traumatic injury and degenerative disorders. Due to their importance, active pharmaceutical ingredients (APIs) are being developed to modulate CNS glia in order to improve outcomes in traumatic injury and disease. While many of these APIs show promise in vitro, the majority of APIs that are systemically delivered show little penetration through the blood-brain barrier (BBB) or blood-spinal cord barrier (BSCB) and into the CNS, rendering them ineffective. Novel nanomaterials are being developed to deliver APIs into the CNS to modulate glial responses and improve outcomes in injury and disease. Nanomaterials are attractive options as therapies for central nervous system protection and repair in degenerative disorders and traumatic injury due to their intrinsic capabilities in API delivery. Nanomaterials can improve API accumulation in the CNS by increasing permeation through the BBB of systemically delivered APIs, extending the timeline of API release, and interacting biophysically with CNS cell populations due to their mechanical properties and nanoscale architectures. In this review, we present the recent advances in the fields of both locally implanted nanomaterials and systemically administered nanoparticles developed for the delivery of APIs to the CNS that modulate glial activity as a strategy to improve outcomes in traumatic injury and disease. We identify current research gaps and discuss potential developments in the field that will continue to translate the use of glia-targeting nanomaterials to the clinic.

Next-generation nanomaterials: advancing ocular anti-inflammatory drug therapy

Ophthalmic inflammatory diseases, including conjunctivitis, keratitis, uveitis, scleritis, and related conditions, pose considerable challenges to effective management and treatment. This review article investigates the potential of advanced nanomaterials in revolutionizing ocular anti-inflammatory drug interventions. By conducting an exhaustive analysis of recent advancements and assessing the potential benefits and limitations, this review aims to identify promising avenues for future research and clinical applications. The review commences with a detailed exploration of various nanomaterial categories, such as liposomes, dendrimers, nanoparticles (NPs), and hydrogels, emphasizing their unique properties and capabilities for accurate drug delivery. Subsequently, we explore the etiology and pathophysiology of ophthalmic inflammatory disorders, highlighting the urgent necessity for innovative therapeutic strategies and examining recent preclinical and clinical investigations employing nanomaterial-based drug delivery systems. We discuss the advantages of these cutting-edge systems, such as biocompatibility, bioavailability, controlled release, and targeted delivery, alongside potential challenges, which encompass immunogenicity, toxicity, and regulatory hurdles. Furthermore, we emphasize the significance of interdisciplinary collaborations among material scientists, pharmacologists, and clinicians in expediting the translation of these breakthroughs from laboratory environments to clinical practice. In summary, this review accentuates the remarkable potential of advanced nanomaterials in redefining ocular anti-inflammatory drug therapy. We fervently support continued research and development in this rapidly evolving field to overcome existing barriers and improve patient outcomes for ophthalmic inflammatory disorders.

The Evolution of Triamcinolone Acetonide Therapeutic Use in Retinal Diseases: From Off-Label Intravitreal Injection to Advanced Nano-Drug Delivery Systems

Ophthalmic drug delivery to the posterior segment of the eye has been challenging due to the complex ocular anatomy. Intravitreal injection of drugs was introduced to deliver therapeutic doses in the posterior segment. Different posterior segment diseases including age-related macular degeneration, diabetic macular edema, retinal vein occlusions, uveitis, and cystoid macular edema, among others, have been historically treated with intravitreal corticosteroids injections, and more recently with intravitreal corticosteroids drug implants. Triamcinolone acetonide (TA) is the most frequently used intraocular synthetic corticosteroid. Using nanoparticle-based TA delivery systems has been proposed as an alternative to intravitreal injections in the treatment of posterior segment diseases. From these novel delivery systems, topical liposomes have been the most promising strategy. This review is oriented to exhibit triamcinolone acetonide drug evolution and its results in treating posterior segment diseases using diverse delivery platforms.

Nanoparticle-based targeting of microglia improves the neural regeneration enhancing effects of immunosuppression in the zebrafish retina

Retinal Müller glia function as injury-induced stem-like cells in zebrafish but not mammals. However, insights gleaned from zebrafish have been applied to stimulate nascent regenerative responses in the mammalian retina. For instance, microglia/macrophages regulate Müller glia stem cell activity in the chick, zebrafish, and mouse. We previously showed that post-injury immunosuppression by the glucocorticoid dexamethasone accelerated retinal regeneration kinetics in zebrafish. Similarly, microglia ablation enhances regenerative outcomes in the mouse retina. Targeted immunomodulation of microglia reactivity may therefore enhance the regenerative potential of Müller glia for therapeutic purposes. Here, we investigated potential mechanisms by which post-injury dexamethasone accelerates retinal regeneration kinetics, and the effects of dendrimer-based targeting of dexamethasone to reactive microglia. Intravital time-lapse imaging revealed that post-injury dexamethasone inhibited microglia reactivity. The dendrimer-conjugated formulation: (1) decreased dexamethasone-associated systemic toxicity, (2) targeted dexamethasone to reactive microglia, and (3) improved the regeneration enhancing effects of immunosuppression by increasing stem/progenitor proliferation rates. Lastly, we show that the gene rnf2 is required for the enhanced regeneration effect of D-Dex. These data support the use of dendrimer-based targeting of reactive immune cells to reduce toxicity and enhance the regeneration promoting effects of immunosuppressants in the retina.

SENP6-Mediated deSUMOylation of VEGFR2 Enhances Its Cell Membrane Transport in Angiogenesis

Angiogenesis is a significant pathogenic characteristic of diabetic microangiopathy. Advanced glycation end products (AGEs) are considerably elevated in diabetic tissues and can affect vascular endothelial cell shape and function. Regulation of the vascular endothelial growth factor (VEGF)-VEGF receptor 2 (VEGFR2) signaling pathway is a critical mechanism in the regulation of angiogenesis, and VEGFR2 activity can be modified by post-translational changes. However, little research has been conducted on the control of small ubiquitin-related modifier (SUMO)-mediated VEGFR2 alterations. The current study investigated this using human umbilical vein endothelial cells (HUVECs) in conjunction with immunoblotting and immunofluorescence. AGEs increased Nrf2 translocation to the nucleus and promoted VEGFR2 expression. They also increased the expression of sentrin/SUMO-specific protease 6 (SENP6), which de-SUMOylated VEGFR2, and immunofluorescence indicated a reduction in VEGFR2 accumulation in the Golgi and increased VEGFR2 transport from the Golgi to the cell membrane surface via the coatomer protein complex subunit beta 2. VEGFR2 on the cell membrane was linked to VEGF generated by pericytes, triggering the VEGF signaling cascade. In conclusion, this study demonstrates that SENP6 regulates VEGFR2 trafficking from the Golgi to the endothelial cell surface. The SENP6-VEGFR2 pathway plays a critical role in pathological angiogenesis.

Modulation of cGAS-STING signaling by PPARα in a mouse model of ischemia-induced retinopathy

In ischemic retinopathy, overactivated retinal myeloid cells are a crucial driving force of pathological angiogenesis and inflammation. The cyclic GMP-AMP synthase (cGAS) and stimulator of interferon genes (STING) signaling are key regulators of inflammation. This study aims to investigate the association of cGAS-STING signaling with ischemic retinopathy and the regulation of its activation. We found that protein levels of cGAS and STING were markedly up-regulated in retinal myeloid cells isolated from mice with oxygen-induced retinopathy (OIR). Knockout of Sting and pharmacological inhibition of STING both alleviated retinal neovascularization (NV) and reduced retinal vascular leakage in OIR. Further, Sting knockout and STING inhibitor also alleviated leukocyte adhesion to retinal vasculature and infiltration into the retina as well as microglial activation in OIR. These results suggest that cGAS-STING signaling played a pathogenic role in retinal myeloid cell activation and NV in ischemic retinopathy. To identify the regulation of cGAS-STING signaling in OIR, we evaluated the role of transcription factor peroxisome proliferator-activated receptor α (PPARα). The results demonstrated that PPARα was down-regulated in OIR retinas, primarily in myeloid cells. Furthermore, Pparα knockout significantly up-regulated cGAS and STING levels in retinal CD11b+ cells, while PPARα agonist inhibited cGAS-STING signaling and cytosolic mitochondrial DNA (mtDNA) release, a causative feature for cGAS activation. Knockout of Sting ameliorated retinal NV, hyperpermeability, and leukostasis in Pparα-/- mice with OIR. These observations suggest that PPARα regulates cGAS-STING signaling, likely through mtDNA release, and thus, is a potential therapeutic target for ischemic retinopathy.

Curing inflammatory diseases using phosphorous dendrimers

Different types of water-soluble phosphorous dendrimers have been synthesized and display many different biological properties. It has been shown in particular that phosphorous dendrimers of first generation functionalized with azabisphosphonate terminal functions are able to stimulate the human immune system ex vivo. These dendrimers are internalized by monocytes within a few seconds, and induce their anti-inflammatory activation. The presence of the dendrimers induces also the inhibition of the differentiation of monocytes into osteoclasts, the maturation of dendritic cells, and inhibits the proliferation of the proinflammatory CD4⁺ T lymphocytes. Finally, after 2-3 weeks of culture of peripheral blood mononuclear cells, amplifications by several tens of natural killer cells is observed. In view of all these properties, the influence of these azabisphosphonate-dendrimers has been tested in vivo with several animal models, against different chronic or acute inflammatory diseases, such as multiple sclerosis, rheumatoid arthritis, uveitis, and psoriasis, but also against myeloid leukemia, a hematological cancer. The hematological safety has been demonstrated in mice, as there is no platelet aggregation, no hemolysis, and no disturbance in the hematological formula. The safety of the azabisphosphonate-dendrimer has been assessed also with non-human primates (cynomolgus monkeys) which received repeated injections, as a de-risking pre-clinical test. Biochemical, hematological, and all immunological parameters in peripheral blood remained within a normal physiological range throughout the study, and all survived well. Other phosphorous dendrimers also display anti-inflammatory properties in vivo, in particular dendrimers functionalized with mannose derivatives, which prevent acute lung diseases when given orally (per os) to mice. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease.