Systemic and Intravitreal Delivery of Dendrimers to Activated Microglia/Macrophage in Ischemia/Reperfusion Mouse Retina

Recent Advances in Nanomedicine for Ocular Fundus Neovascularization Disease Management

As an indispensable part of the human sensory system, visual acuity may be impaired and even develop into irreversible blindness due to various ocular pathologies. Among ocular diseases, fundus neovascularization diseases (FNDs) are prominent etiologies of visual impairment worldwide. Intravitreal injection of anti-vascular endothelial growth factor drugs remains the primary therapy but is hurdled by common complications and incomplete potency. To renovate the current therapeutic modalities, nanomedicine emerged as the times required, which is endowed with advanced capabilities, able to fulfill the effective ocular fundus drug delivery and achieve precise drug release control, thus further improving the therapeutic effect. This review provides a comprehensive summary of advances in nanomedicine for FND management from state-of-the-art studies. First, the current therapeutic modalities for FNDs are thoroughly introduced, focusing on the key challenges of ocular fundus drug delivery. Second, nanocarriers are comprehensively reviewed for ocular posterior drug delivery based on the nanostructures: polymer-based nanocarriers, lipid-based nanocarriers, and inorganic nanoparticles. Thirdly, the characteristics of the fundus microenvironment, their pathological changes during FNDs, and corresponding strategies for constructing smart nanocarriers are elaborated. Furthermore, the challenges and prospects of nanomedicine for FND management are thoroughly discussed.

PET imaging for the early evaluation of ocular inflammation in diabetic rats by using [18F]-DPA-714

Ocular complications of diabetes mellitus (DM) are the leading cause of vision loss. Ocular inflammation often occurs in the early stage of DM; however, there are no proven quantitative methods to evaluate the inflammatory status of eyes in DM. The 18 kDa translocator protein (TSPO) is an evolutionarily conserved cholesterol binding protein localized in the outer mitochondrial membrane. It is a biomarker of activated microglia/macrophages; however, its role in ocular inflammation is unclear. In this study, fluorine-18-DPA-714 ([18F]-DPA-714) was evaluated as a specific TSPO probe by cell uptake, cell binding assays and micro positron emission tomography (microPET) imaging in both in vitro and in vivo models. Primary microglia/macrophages (PMs) extracted from the cornea, retina, choroid or sclera of neonatal rats with or without high glucose (50 mM) treatment were used as the in vitro model. Sprague-Dawley (SD) rats that received an intraperitoneal administration of streptozotocin (STZ, 60 mg/kg once) were used as the in vivo model. Increased cell uptake and high binding affinity of [18F]-DPA-714 were observed in primary PMs under hyperglycemic stress. These findings were consistent with cellular morphological changes, cell activation, and TSPO up-regulation. [18F]-DPA-714 PET imaging and biodistribution in the eyes of DM rats revealed that inflammation initiates in microglia/macrophages in the early stages (3 weeks and 6 weeks), corresponding with up-regulated TSPO levels. Thus, [18F]-DPA-714 microPET imaging may be an effective approach for the early evaluation of ocular inflammation in DM.

Chitosan as a promising materials for the construction of nanocarriers for diabetic retinopathy: an updated review

Diabetic retinopathy (DR) is a condition that causes swelling of the blood vessels of the retina and leaks blood and fluids. It is the most severe form of diabetic eye disease. It causes vision loss in its advanced stage. Diabetic retinopathy is responsible for causing 26% of blindness. Very insufficient therapies are accessible for the treatment of DR. As compared to the conventional therapies, there should be enhanced research on the controlled release, shorter duration, and cost-effective therapy of diabetic retinopathy. The expansion of advanced nanocarriers-based drug delivery systems has been now employed to exploit as well as regulate the transport of many therapeutic agents to target sites via the increase in penetration or the extension of the duration of contact employing production by enclosing as well as distributing tiny molecules in nanostructured formulation. Various polymers have been utilized for the manufacturing of these nanostructured formulations. Chitosan possesses incredible biological and chemical properties, that have led to its extensive use in pharmaceutical and biomedical applications. Chitosan has been used in many studies because of its enhanced mucoadhesiveness and non-toxicity. Multiple studies have used chitosan as the best candidate for manufacturing nanocarriers and treating diabetic retinopathy. Numerous nanocarriers have been formulated by using chitosan such as nanostructured lipid carriers, solid lipid nanoparticles, liposomes, and dendrimers for treating diabetic retinopathy. This current review elaborates on the recent advancements of chitosan as a promising approach for the manufacturing of nanocarriers that can be used for treating diabetic retinopathy.

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.

A new era in posterior segment ocular drug delivery: Translation of systemic, cell-targeted, dendrimer-based therapies

Vision impairment and loss due to posterior segment ocular disorders, including age-related macular degeneration and diabetic retinopathy, are a rapidly growing cause of disability globally. Current treatments consist primarily of intravitreal injections aimed at preventing disease progression and characterized by high cost and repeated clinic visits. Nanotechnology provides a promising platform for drug delivery to the eye, with potential to overcome anatomical and physiological barriers to provide safe, effective, and sustained treatment modalities. However, there are few nanomedicines approved for posterior segment disorders, and fewer that target specific cells or that are compatible with systemic administration. Targeting cell types that mediate these disorders via systemic administration may unlock transformative opportunities for nanomedicine and significantly improve patient access, acceptability, and outcomes. We highlight the development of hydroxyl polyamidoamine dendrimer-based therapeutics that demonstrate ligand-free cell targeting via systemic administration and are under clinical investigation for treatment of wet age-related macular degeneration.

Selective drug delivery to the retinal cells: Biological barriers and avenues

Retinal drug delivery is a challenging, but important task, because most retinal diseases are still without any proper therapy. Drug delivery to the retina is hampered by the anatomical and physiological barriers resulting in minimal bioavailability after topical ocular and systemic administrations. Intravitreal injections are current method-of-choice in retinal delivery, but these injections show short duration of action for small molecules and low target bioavailability for many protein, gene based drugs and nanomedicines. State-of-art delivery systems are based on prolonged retention, controlled drug release and physical features (e.g. size and charge). However, drug delivery to the retina is not cell-specific and these approaches do not facilitate intracellular delivery of modern biological drugs (e.g. intracellular proteins, RNA based medicines, gene editing). In this focused review we highlight biological factors and mechanisms that form the basis for the selective retinal drug delivery systems in the future. Therefore, we are presenting current knowledge related to retinal membrane transporters, receptors and targeting ligands in relation to nanomedicines, conjugates, extracellular vesicles, and melanin binding. These issues are discussed in the light of retinal structure and cell types as well as future prospects in the field. Unlike in some other fields of targeted drug delivery (e.g. cancer research), selective delivery technologies have been rarely studied, even though cell targeted delivery may be even more feasible after local administration into the eye.

IGFBPL1 is a master driver of microglia homeostasis and resolution of neuroinflammation in glaucoma and brain tauopathy

Microglia shift toward an inflammatory phenotype during aging that is thought to exacerbate age-related neurodegeneration. The molecular and cellular signals that resolve neuroinflammation post-injury are largely undefined. Here, we exploit systems genetics methods based on the extended BXD murine reference family and identify IGFBPL1 as an upstream cis-regulator of microglia-specific genes to switch off inflammation. IGFBPL1 is expressed by mouse and human microglia, and higher levels of its expression resolve lipopolysaccharide-induced neuroinflammation by resetting the transcriptome signature back to a homeostatic state via IGF1R signaling. Conversely, IGFBPL1 deficiency or selective deletion of IGF1R in microglia shifts these cells to an inflammatory landscape and induces early manifestation of brain tauopathy and retinal neurodegeneration. Therapeutic administration of IGFBPL1 drives pro-homeostatic microglia and prevents glaucomatous neurodegeneration and vision loss in mice. These results identify IGFBPL1 as a master driver of the counter-inflammatory microglial modulator that presents an endogenous resolution of neuroinflammation to prevent neurodegeneration in eye and brain.

Next-Generation Nanomedicine Approaches for the Management of Retinal Diseases

Retinal diseases are one of the leading causes of blindness globally. The mainstay treatments for these blinding diseases are laser photocoagulation, vitrectomy, and repeated intravitreal injections of anti-vascular endothelial growth factor (VEGF) or steroids. Unfortunately, these therapies are associated with ocular complications like inflammation, elevated intraocular pressure, retinal detachment, endophthalmitis, and vitreous hemorrhage. Recent advances in nanomedicine seek to curtail these limitations, overcoming ocular barriers by developing non-invasive or minimally invasive delivery modalities. These modalities include delivering therapeutics to specific cellular targets in the retina, providing sustained delivery of drugs to avoid repeated intravitreal injections, and acting as a scaffold for neural tissue regeneration. These next-generation nanomedicine approaches could potentially revolutionize the treatment landscape of retinal diseases. This review describes the availability and limitations of current treatment strategies and highlights insights into the advancement of future approaches using next-generation nanomedicines to manage retinal diseases.

Innovative Strategies for Drug Delivery to the Ocular Posterior Segment

Innovative and new drug delivery systems (DDSs) have recently been developed to vehicle treatments and drugs to the ocular posterior segment and the retina. New formulations and technological developments, such as nanotechnology, novel matrices, and non-traditional treatment strategies, open new perspectives in this field. The aim of this mini-review is to highlight promising strategies reported in the current literature based on innovative routes to overcome the anatomical and physiological barriers of the vitreoretinal structures. The paper also describes the challenges in finding appropriate and pertinent treatments that provide safety and efficacy and the problems related to patient compliance, acceptability, effectiveness, and sustained drug delivery. The clinical application of these experimental approaches can help pave the way for standardizing the use of DDSs in developing enhanced treatment strategies and personalized therapeutic options for ocular pathologies.

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.

Dendrimers and Derivatives as Multifunctional Nanotherapeutics for Alzheimer's Disease

Alzheimer's disease (AD) is the most prevalent form of dementia. It affects more than 30 million people worldwide and costs over US$ 1.3 trillion annually. AD is characterized by the brain accumulation of amyloid β peptide in fibrillar structures and the accumulation of hyperphosphorylated tau aggregates in neurons, both leading to toxicity and neuronal death. At present, there are only seven drugs approved for the treatment of AD, of which only two can slow down cognitive decline. Moreover, their use is only recommended for the early stages of AD, meaning that the major portion of AD patients still have no disease-modifying treatment options. Therefore, there is an urgent need to develop efficient therapies for AD. In this context, nanobiomaterials, and dendrimers in particular, offer the possibility of developing multifunctional and multitargeted therapies. Due to their intrinsic characteristics, dendrimers are first-in-class macromolecules for drug delivery. They have a globular, well-defined, and hyperbranched structure, controllable nanosize and multivalency, which allows them to act as efficient and versatile nanocarriers of different therapeutic molecules. In addition, different types of dendrimers display antioxidant, anti-inflammatory, anti-bacterial, anti-viral, anti-prion, and most importantly for the AD field, anti-amyloidogenic properties. Therefore, dendrimers can not only be excellent nanocarriers, but also be used as drugs per se. Here, the outstanding properties of dendrimers and derivatives that make them excellent AD nanotherapeutics are reviewed and critically discussed. The biological properties of several dendritic structures (dendrimers, derivatives, and dendrimer-like polymers) that enable them to be used as drugs for AD treatment will be pointed out and the chemical and structural characteristics behind those properties will be analysed. The reported use of these nanomaterials as nanocarriers in AD preclinical research is also presented. Finally, future perspectives and challenges that need to be overcome to make their use in the clinic a reality are discussed.

Targeted Microglial Attenuation through Dendrimer-Drug Conjugates Improves Glaucoma Neuroprotection

Retinal microglial/macrophage activation and optic nerve (ON) microglial/macrophage activation are glaucoma biomarkers and potential therapeutic targets for this blinding disease. We report targeting of activated microglia by PAMAM dendrimers in a rat glaucoma model and neuroprotection by N-acetylcysteine-conjugated dendrimer (D-NAC) conjugates in a post-injury rescue experiment. Intravitreally delivered fluorescently labeled dendrimer (D-Cy5) conjugates targeted and were retained in Iba-1-positive cells (90% at 7 days and 55% after 28 days) in the retina following intraocular pressure (IOP) elevation, while systemically delivered D-Cy5 targeted ON cells. A single intravitreal D-NAC dose given 1 week after IOP elevation significantly reduced transcription of pro-inflammatory (IL-6, MCP-1, IL-1β) and A1 astrocyte (Serping1, Fkbp5, Amigo2) markers and increased survival of retinal ganglion cells (39 ± 12%) versus BSS- (20 ± 15%, p = 0.02) and free NAC-treated (26 ± 14%, p = 0.15) eyes. These results highlight the potential of dendrimer-targeted microglia and macrophages for early glaucoma detection and as a neuroprotective therapeutic target.

Ocular barriers as a double-edged sword: preventing and facilitating drug delivery to the retina

In recent decades, the growing of the aging population in the world brings increasingly heavy burden of vision-threatening retinal diseases. One of the biggest challenges in the treatment of retinal diseases is the effective drug delivery to the diseased area. Due to the existence of multiple anatomical and physiological barriers of the eye, commonly used oral drugs or topical eye drops cannot effectively reach the retinal lesions. Innovations in new drug formulations and delivery routes have been continuously applied to improve current drug delivery to the back of the eye. Unique ocular anatomical structures or physiological activities on these ocular barriers, in turn, can facilitate drug delivery to the retina if compatible formulations or delivery routes are properly designed or selected. This paper focuses on key barrier structures of the eye and summarizes advances of corresponding drug delivery means to the retina, including various local drug delivery routes by invasive approaches, as well as systemic eye drug delivery by non-invasive approaches.

Targeted drug delivery to the retinal pigment epithelium: Untapped therapeutic potential for retinal diseases

The retinal pigment epithelium (RPE) plays a crucial part in sight-threatening diseases. In this review, we shed light on the pivotal implication of the RPE in age-related macular degeneration, diabetic retinopathy and retinopathy of prematurity; and explain why a paradigm shift toward targeted RPE therapy is needed to efficiently fight these retinal diseases. We provide guidance for the development of RPE-specific nanotherapeutics by giving a comprehensive overview of the possibilities and challenges of drug delivery to the RPE and highlight successful nanotherapeutic approaches targeting the RPE.

CD38 deficiency protects the retina from ischaemia/reperfusion injury partly via suppression of TLR4/MyD88/NF-κB signalling

PURPOSE

This study aimed to explore cellular localisation of CD38 in the retina and evaluate the role and potential mechanism of CD38 deficiency in retinal ischaemia/reperfusion (I/R) injury.

METHODS

Six-to eight-week-old male CD38 knockout (KO) and wild-type mice in C57BL/6 background were used. Immunostaining was performed to determine the cellular localisation of CD38 in the retina. Haematoxylin and eosin staining and immunostaining of Brn3a were used to evaluate the retinal I/R injury. Western blotting was performed to detect toll-like receptor 4 (TLR4), myeloid differentiation primary response 88 (MyD88), p-p65, ionised calcium-binding adapter molecule 1, Sirtuin1 (Sirt1), Ac-p65, and pro-inflammatory cytokines protein expression.

RESULTS

CD38 was highly expressed in mouse retinal microglia and astrocytes/Müller cells. CD38 deficiency reduced I/R-induced retinal damage and retinal ganglion cell death. Following retinal I/R injury, TLR4, MyD88, nuclear factor-κB p-p65 (NF-κB p-p65), pro-inflammatory cytokines and CD38 protein levels were also upregulated. After I/R injury, retinal inflammation factors IL-1β, IL-6, and TNF-α mRNA and protein levels were increased. IL-1β, IL-6, and TNF-α were reduced in CD38 KO mice after I/R injury. Retinal I/R injury induced the activation of microglia, but this effect was also suppressed by KO of CD38. Additionally, retinal I/R induced a significant increase in Ac-p65 protein levels and decrease in Sirt1 protein levels, while this effect was greatly attenuated by KO of CD38.

CONCLUSION

CD38 deficiency protects the retina from I/R injury by suppressing microglial activation partly via activating Sirt1-mediated suppression of TLR4/MyD88/NF-κB signalling.

Broad-Spectrum Theranostics and Biomedical Application of Functionalized Nanomaterials

Nanotechnology is an important branch of science in therapies known as “nanomedicine” and is the junction of various fields such as material science, chemistry, biology, physics, and optics. Nanomaterials are in the range between 1 and 100 nm in size and provide a large surface area to volume ratio; thus, they can be used for various diseases, including cardiovascular diseases, cancer, bacterial infections, and diabetes. Nanoparticles play a crucial role in therapy as they can enhance the accumulation and release of pharmacological agents, improve targeted delivery and ultimately decrease the intensity of drug side effects. In this review, we discussthe types of nanomaterials that have various biomedical applications. Biomolecules that are often conjugated with nanoparticles are proteins, peptides, DNA, and lipids, which can enhance biocompatibility, stability, and solubility. In this review, we focus on bioconjugation and nanoparticles and also discuss different types of nanoparticles including micelles, liposomes, carbon nanotubes, nanospheres, dendrimers, quantum dots, and metallic nanoparticles and their crucial role in various diseases and clinical applications. Additionally, we review the use of nanomaterials for bio-imaging, drug delivery, biosensing tissue engineering, medical devices, and immunoassays. Understandingthe characteristics and properties of nanoparticles and their interactions with the biological system can help us to develop novel strategies for the treatment, prevention, and diagnosis of many diseases including cancer, pulmonary diseases, etc. In this present review, the importance of various kinds of nanoparticles and their biomedical applications are discussed in much detail.

An intravitreal implant injection method for sustained drug delivery into mouse eyes

Using small molecule drugs to treat eye diseases carries benefits of specificity, scalability, and transportability, but their efficacy is significantly limited by a fast intraocular clearance rate. Ocular drug implants (ODIs) present a compelling means for the slow and sustained release of small molecule drugs inside the eye. However, methods are needed to inject small molecule ODIs into animals with small eyes, such as mice, which are the primary genetic models for most human ocular diseases. Consequently, it has not been possible to fully investigate efficacy and ocular pharmacokinetics of ODIs. Here, we present a robust, cost-effective, and minimally invasive method called "mouse implant intravitreal injection" (MI3) to deliver ODIs into mouse eyes. This method will expand ODI research to cover the breadth of human eye diseases modeled in mice.

Myeloid lineage contributes to pathological choroidal neovascularization formation via SOCS3

Background

Pathological neovascularization in neovascular age-related macular degeneration (nAMD) is the leading cause of vision loss in the elderly. Increasing evidence shows that cells of myeloid lineage play important roles in controlling pathological endothelium formation. Suppressor of cytokine signaling 3 (SOCS3) pathway has been linked to neovascularization.

Methods

We utilised a laser-induced choroidal neovascularization (CNV) mouse model to investigate the neovascular aspect of human AMD. In several cell lineage reporter mice, bone marrow chimeric mice and Socs3 loss-of-function (knockout) and gain-of-function (overexpression) mice, immunohistochemistry, confocal, and choroidal explant co-culture with bone marrow-derived macrophage medium were used to study the mechanisms underlying pathological CNV formation via myeloid SOCS3.

Findings

SOCS3 was significantly induced in myeloid lineage cells, which were recruited into the CNV lesion area. Myeloid Socs3 overexpression inhibited laser-induced CNV, reduced myeloid lineage-derived macrophage/microglia recruitment onsite, and attenuated pro-inflammatory factor expression. Moreover, SOCS3 in myeloid regulated vascular sprouting ex vivo in choroid explants and SOCS3 agonist reduced in vivo CNV.

Interpretation

These findings suggest that myeloid lineage cells contributed to pathological CNV formation regulated by SOCS3.

Funding

This project was funded by NIH/NEI (R01EY030140, R01EY029238), BrightFocus Foundation, American Health Assistance Foundation (AHAF), and Boston Children's Hospital Ophthalmology Foundation for YS and the National Institutes of Health/National Heart, Lung and Blood Institute (U01HL098166) for PZ.

The Emerging Role of Topical Ocular Drugs to Target the Posterior Eye

The prevalence of chronic fundus diseases is increasing with the aging of the general population. The treatment of these intraocular diseases relies on invasive drug delivery because of the globular structure and multiple barriers of the eye. Frequent intraocular injections bring heavy burdens to the medical care system and patients. The use of topical drugs to treat retinal diseases has always been an attractive solution. The fast development of new materials and technologies brings the possibility to develop innovative topical formulations. This article reviews anatomical and physiological barriers of the eye which affect the bioavailability of topical drugs. In addition, we summarize innovative topical formulations which enhance the permeability of drugs through the ocular surface and/or extend the drug retention time in the eye. This article also reviews the differences of eyes between different laboratory animals to address the translational challenges of preclinical models. The fast development of in vitro eye models may provide more tools to increase the clinical translationality of topical formulations for intraocular diseases. Clinical successes of topical formulations rely on continuous and collaborative efforts between different disciplines.

Dendrimer-Coated Gold Nanoparticles for Efficient Folate-Targeted mRNA Delivery In Vitro

Messenger RNA (mRNA) is not an attractive candidate for gene therapy due to its instability and has therefore received little attention. Recent studies show the advantage of mRNA over DNA, especially in cancer immunotherapy and vaccine development. This study aimed to formulate folic-acid-(FA)-modified, poly-amidoamine-generation-5 (PAMAM G5D)-grafted gold nanoparticles (AuNPs) and to evaluate their cytotoxicity and transgene expression using the luciferase reporter gene (FLuc-mRNA) in vitro. Nanocomplexes were spherical and of favorable size. Nanocomplexes at optimum nanoparticle:mRNA (w/w) binding ratios showed good protection of the bound mRNA against nucleases and were well tolerated in all cell lines. Transgene expression was significantly (p < 0.0001) higher with FA-targeted, dendrimer-grafted AuNPs (Au:G5D:FA) in FA receptors overexpressing MCF-7 and KB cells compared to the G5D and G5D:FA NPs, decreasing significantly (p < 0.01) in the presence of excess competing FA ligand, which confirmed nanocomplex uptake via receptor mediation. Overall, transgene expression of the Au:G5D and Au:G5D:FA nanocomplexes exceeded that of G5D and G5D:FA nanocomplexes, indicating the pivotal role played by the inclusion of the AuNP delivery system. The favorable properties imparted by the AuNPs potentiated an increased level of luciferase gene expression.

Protective Effects of Oroxylin A on Retinal Ganglion Cells in Experimental Model of Anterior Ischemic Optic Neuropathy

Nonarteritic anterior ischemic optic neuropathy (NAION) is the most common cause of acute vision loss in older people, and there is no effective therapy. The effect of the systemic or local application of steroids for NAION patients remains controversial. Oroxylin A (OA) (5,7-dihydroxy-6-methoxyflavone) is a bioactive flavonoid extracted from Scutellariae baicalensis Georgi. with various beneficial effects, including anti-inflammatory and neuroprotective effects. A previous study showed that OA promotes retinal ganglion cell (RGC) survival after optic nerve (ON) crush injury. The purpose of this research was to further explore the potential actions of OA in ischemic injury in an experimental anterior ischemic optic neuropathy (rAION) rat model induced by photothrombosis. Our results show that OA efficiently attenuated ischemic injury in rats by reducing optic disc edema, the apoptotic death of retinal ganglion cells, and the infiltration of inflammatory cells. Moreover, OA significantly ameliorated the pathologic changes of demyelination, modulated microglial polarization, and preserved visual function after rAION induction. OA activated nuclear factor E2 related factor (Nrf2) signaling and its downstream antioxidant enzymes NAD(P)H:quinone oxidoreductase (NQO-1) and heme oxygenase 1 (HO-1) in the retina. We demonstrated that OA activates Nrf2 signaling, protecting retinal ganglion cells from ischemic injury, in the rAION model and could potentially be used as a therapeutic approach in ischemic optic neuropathy.

Recent trends in drug-delivery systems for the treatment of diabetic retinopathy and associated fibrosis

Diabetic retinopathy is a frequent microvascular complication of diabetes and a major cause of visual impairment. In advanced stages, the abnormal neovascularization can lead to fibrosis and subsequent tractional retinal detachment and blindness. The low bioavailability of the drugs at the target site imposed by the anatomic and physiologic barriers within the eye, requires long term treatments with frequent injections that often compromise patient's compliance and increase the risk of developing more complications. In recent years, much effort has been put towards the development of new drug delivery platforms aiming to enhance their permeation, to prolong their retention time at the target site and to provide a sustained release with reduced toxicity and improved efficacy. This review provides an overview of the etiology and pathophysiology of diabetic retinopathy and current treatments. It addresses the specific challenges associated to the different ocular delivery routes and provides a critical review of the most recent developments made in the drug delivery field.

Systemic dendrimer nanotherapies for targeted suppression of choroidal inflammation and neovascularization in age-related macular degeneration

Inflammation and neovascularization are key pathological events in human age-related macular degeneration (AMD). Activated microglia/macrophages (mi/ma) and retinal pigmented epithelium (RPE) play an active role in every stage of disease progression. Systemic therapies that can target these cells and address both inflammation and neovascularization will broaden the impact of existing therapies and potentially open new avenues for early AMD where there are no viable therapies. Utilizing a clinically relevant rat model of AMD that mirrors many aspects that of human AMD pathological events, we show that systemic hydroxyl-terminated polyamidoamine dendrimer-triamcinolone acetonide conjugate (D-TA) is selectively taken up by the injured mi/ma and RPE (without the need for targeting ligands). D-TA suppresses choroidal neovascularization significantly (by >80%, >50-fold better than free drug), attenuates inflammation in the choroid and retina, by limiting macrophage infiltration in the pathological area, significantly suppressing pro-inflammatory cytokines and pro-angiogenic factors, with minimal side effects to healthy ocular tissue and other organs. In ex vivo studies on human postmortem diabetic eyes, the dendrimer is also taken up into choroidal macrophages. These results suggest that the systemic hydroxyl dendrimer-drugs can offer new avenues for therapies in treating early/dry AMD and late/neovascular AMD alone, or in combination with current anti-VEGF therapies. This hydroxyl dendrimer platform but conjugated to a different drug is undergoing clinical trials for severe COVID-19, potentially paving the way for faster clinical translation of similar compounds for ocular and retinal disorders.

The utility and risks of therapeutic nanotechnology in the retina

The clinical application of nanotechnology in medicine is promising for therapeutic, diagnostic, and surgical improvements in the near future. Nanotechnologies in nano-ophthalmology are in the early stages of application in clinical contexts, including ocular drug and gene delivery systems addressing eye disorders, particularly retinopathies. Retinal diseases are challenging to treat as current interventions, such as intravitreal injections, are limited by their invasive nature. This review examines nanotechnological approaches to retinal diseases in a clinical context. Nanotechnology has the potential to transform pharmacological and surgical interventions by overcoming limitations posed by the protective anatomical and physiological barriers that limit access to the retina. Preclinical research in the application of nanoparticles in diagnostics indicates that nanoparticles can enhance existing diagnostic and screening tools to detect diseases earlier and more easily and improve disease progression monitoring precision.

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

Diabetic retinopathy (DR) is the leading cause of blindness in working-age adults. Severe visual loss in DR is primarily due to proliferative diabetic retinopathy, characterized by pathologic preretinal angiogenesis driven by retinal ischemia. Microglia, the resident immune cells of the retina, have emerged as a potentially important regulator of pathologic retinal angiogenesis. Corticosteroids including triamcinolone acetonide (TA), known for their antiangiogenic effects, are used in treating retinal diseases, but their use is significantly limited by side effects including cataracts and glaucoma. Generation-4 hydroxyl polyamidoamine dendrimer nanoparticles are utilized to deliver TA to activated microglia in the ischemic retina in a mouse model of oxygen-induced retinopathy (OIR). Following intravitreal injection, dendrimer-conjugated TA (D-TA) exhibits selective localization and sustained retention in activated microglia in disease-associated areas of the retina. D-TA, but not free TA, suppresses inflammatory cytokine production, microglial activation, and preretinal neovascularization in OIR. In addition, D-TA, but not free TA, ameliorates OIR-induced neuroretinal and visual dysfunction. These results indicate that activated microglia are a promising therapeutic target for retinal angiogenesis and neuroprotection in ischemic retinal diseases. Furthermore, dendrimer-based targeted therapy and specifically D-TA constitute a promising treatment approach for DR, offering increased and sustained drug efficacy with reduced side effects.

Houttuynia cordata Thunb rescues retinal ganglion cells through inhibiting microglia activation in a rat model of retinal ischemia-reperfusion

AIM

To determine whether Houttuynia cordata Thunb (HCT) can increase the survival of the retinal ganglion cells (RGCs) and inhibit microglia activation following retinal ischemia-reperfusion (RIR) injury.

METHODS

Rat model of RIR was induced by transient elevation of the intraocular pressure (IOP). HCT was orally administered for 2d before the performance of retinal RIR model and once a day for the next 14d. After 14d of RIR injury, the rats were sacrificed for further analysis. Survival RGCs were stained with haematoxylin and eosin (H&E). Apoptosis of RGCs was detected by TUNEL staining. Retinal function was examined by flash-electroretinography (F-ERG). Retinal microglia were labeled using Iba-1, one specific marker for microglia. The mRNA expression levels of inducible nitric oxide synthase (iNOS), tumor necrosis factor alpha (TNF-α), and interleukin 1 beta (IL-1β) were assessed by quantitative real time reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

Systemic HCT treatment significantly reduced RGCs death by H&E staining and exhibited an anti-apoptotic effect as assessed by TUNEL staining at day 14 after RIR injury. HCT greatly improved the retinal function as examined by F-ERG. The number of activated microglia significantly increased after RIR injury, which was significantly attenuated by HCT treatment. Besides, RIR injury induced a strong upregulation of pro-inflammatory genes TNF-α, iNOS and IL-1β mRNAs at day 14 post injury, which was suppressed by HCT.

CONCLUSION

Neuroprotective effects of HCT encourage the survival of RGCs through inhibiting microglia activation due to RIR injury. Together these results support the use of HCT as promising therapy for the ischemic events of the retina diseases.

Rescue the retina after the ischemic injury by polymer-mediated intracellular superoxide dismutase delivery

Oxidative stress is a hallmark of the pathophysiogenesis of retinal ischemia. The direct delivery of antioxidant enzymes such as superoxide dismutase (SOD) into retinal cells provides a promising option for the down-regulation of oxidative stress in retinal ischemia, however, efficient intracellular protein delivery remains a major challenge for this application. Here, a boronic acid-rich polymer was used for the intracellular delivery of SOD both in vitro and in vivo. The polymer assembled with SOD into uniform nanoparticles with high binding affinity, and transported the cargo protein into several cell lines with maintained bioactivity and low cytotoxicity. We investigated the intraocular biodistribution, therapeutic efficacy and safety of the SOD nanoformulation in a retinal ischemia/reperfusion (I/R) injury model. After intravitreal injection, the nanoparticles rapidly diffused through the vitreous and penetrated into retinal ganglion cells (RGCs). Compared to free SOD, the nanoformulation exhibited much enhanced therapeutic efficacy with reduced RGC apoptosis and protected retinal function. Enzymatic results confirmed that the SOD nanoformulation reduced malondialdehyde expression and increased glutathione level in the ocular tissues, and thereby down-regulated oxidative stress and prevented RGC loss. Overall, this work offers a new therapeutic option for the treatment of retinal ischemic disorders by direct delivery of antioxidant proteins.

Recent advances in intraocular and novel drug delivery systems for the treatment of diabetic retinopathy

Introduction: Diabetic retinopathy (DR) is associated with damage to the retinal blood vessels that lead eventually to vision loss. The existing treatments of DR are invasive, expensive, and cumbersome. To overcome challenges associated with existing therapies, various intraocular sustained release and novel drug delivery systems (NDDS) have been explored.Areas covered: The review discusses recently developed intraocular devices for sustained release of drugs as well as novel noninvasive drug delivery systems that have met a varying degree of success in local delivery of drugs to retinal circulation.Expert opinion: The intraocular devices have got very good success in providing sustained release of drugs in patients. The development of NDDS and their application through the ocular route has certainly provided an edge to treat DR over existing therapies such as anti-VEGF administration but their success rate is quite low. Moreover, most of them have proved to be effective only in animal models. In addition, the extent of targeting the drug to the retina still remains variable and unpredictable. The toxicity aspect of the NDDS has generally been neglected. In order to have successful commercialization of nanotechnology-based innovations well-designed clinical research studies need to be conducted to evaluate their clinical superiority over that of the existing formulations.

Nanotechnological strategies for systemic microbial infections treatment: A review

Systemic infections is one of the major causes of mortality worldwide, and a shortage of drug approaches applied for the rapid and necessary treatment contribute to increase the levels of death in affected patients. Several drug delivery systems based in nanotechnology such as metallic nanoparticles, liposomes, nanoemulsion, microemulsion, polymeric nanoparticles, solid lipid nanoparticles, dendrimers, hydrogels and liquid crystals can contribute in the biological performance of active substances for the treatment of microbial diseases triggered by fungi, bacteria, virus and parasites. In the presentation of these statements, this review article present and demonstrate the effectiveness of these drug delivery systems for the treatment of systemic diseases caused by several microorganisms, through a review of studies on scientific literature worldwide that contributes to better information for the most diverse professionals from the areas of health sciences. The studies demonstrated that the drug delivery systems described can contribute to the therapeutic scenario of these diseases, being classified as safe, active platforms and with therapeutic versatility.

Dendrimers as Modulators of Brain Cells

Nanostructured hyperbranched macromolecules have been extensively studied at the chemical, physical and morphological levels. The cellular structural and functional complexity of neural cells and their cross-talk have made it rather difficult to evaluate dendrimer effects in a mixed population of glial cells and neurons. Thus, we are at a relatively early stage of bench-to-bedside translation, and this is due mainly to the lack of data valuable for clinical investigations. It is only recently that techniques have become available that allow for analyses of biological processes inside the living cells, at the nanoscale, in real time. This review summarizes the essential properties of neural cells and dendrimers, and provides a cross-section of biological, pre-clinical and early clinical studies, where dendrimers were used as nanocarriers. It also highlights some examples of biological studies employing dendritic polyglycerol sulfates and their effects on glia and neurons. It is the aim of this review to encourage young scientists to advance mechanistic and technological approaches in dendrimer research so that these extremely versatile and attractive nanostructures gain even greater recognition in translational medicine.

Nanoparticle-microglial interaction in the ischemic brain is modulated by injury duration and treatment

Cerebral ischemia is a major cause of death in both neonates and adults, and currently has no cure. Nanotechnology represents one promising area of therapeutic development for cerebral ischemia due to the ability of nanoparticles to overcome biological barriers in the brain. ex vivo injury models have emerged as a high-throughput alternative that can recapitulate disease processes and enable nanoscale probing of the brain microenvironment. In this study, we used oxygen-glucose deprivation (OGD) to model ischemic injury and studied nanoparticle interaction with microglia, resident immune cells in the brain that are of increasing interest for therapeutic delivery. By measuring cell death and glutathione production, we evaluated the effect of OGD exposure time and treatment with azithromycin (AZ) on slice health. We found a robust injury response with 0.5 hr of OGD exposure and effective treatment after immediate application of AZ. We observed an OGD-induced shift in microglial morphology toward increased heterogeneity and circularity, and a decrease in microglial number, which was reversed after treatment. OGD enhanced diffusion of polystyrene-poly(ethylene glycol) (PS-PEG) nanoparticles, improving transport and ability to reach target cells. While microglial uptake of dendrimers or quantum dots (QDs) was not enhanced after injury, internalization of PS-PEG was significantly increased. For PS-PEG, AZ treatment restored microglial uptake to normal control levels. Our results suggest that different nanoparticle platforms should be carefully screened before application and upon doing so; disease-mediated changes in the brain microenvironment can be leveraged by nanoscale drug delivery devices for enhanced cell interaction.

Nanoparticulate Drug Delivery to the Retina

Retinal diseases, such as age-related macular degeneration and diabetic retinopathy, are the leading causes of blindness worldwide. The mainstay of treatment for these blinding diseases remains to be surgery, and the available pharmaceutical therapies on the market are limited, partially owing to various biological barriers in hindering the delivery of therapeutics to the retina. The nanoparticulate drug delivery system confers the capability for delivering therapeutics to the specific ocular targets and, hence, potentially revolutionizes the current treatment landscape of retinal diseases. While the research to date indicates the enormous therapeutics potentials of the nanoparticulate delivery systems, the successful translation of these systems from the bench to bedside is challenging and requires a combined understanding of retinal pathology, physiology of the eye, and particle and formulation designs of nanoparticles. To this end, the review begins with an overview of the most prevalent retinal diseases and related pharmacotherapy. Highlights of the current challenges encountered in ocular drug delivery for each administration route are provided, followed by critical appraisal of various nanoparticulate drug delivery systems for the retinal diseases, including their formulation designs, therapeutic merits, limitations, and future direction. It is believed that a greater understanding of the nano-biointeraction in eyes will lead to the development of more sophisticated drug delivery systems for retinal diseases.

Dendrimer-conjugated glutaminase inhibitor selectively targets microglial glutaminase in a mouse model of Rett syndrome

Background: Elevated glutamate production and release from glial cells is a common feature of many CNS disorders. Inhibitors of glutaminase (GLS), the enzyme responsible for converting glutamine to glutamate have been developed to target glutamate overproduction. However, many GLS inhibitors have poor aqueous solubility, are unable to cross the blood brain barrier, or demonstrate significant toxicity when given systemically, precluding translation. Enhanced aqueous solubility and systemic therapy targeted to activated glia may address this challenge. Here we examine the impact of microglial-targeted GLS inhibition in a mouse model of Rett syndrome (RTT), a developmental disorder with no viable therapies, manifesting profound central nervous system effects, in which elevated glutamatergic tone, upregulation of microglial GLS, oxidative stress and neuroimmune dysregulation are key features. Methods: To enable this, we conjugated a potent glutaminase inhibitor, N-(5-{2-[2-(5-amino-[1,3,4]thiadiazol-2-yl)-ethylsulfanyl]-ethyl}-[1,3,4]thiadiazol-2-yl)-2-phenyl-acetamide (JHU29) to a generation 4 hydroxyl PAMAM dendrimer (D-JHU29). We then examined the effect of D-JHU29 in organotypic slice culture on glutamate release. We also examined GLS activity in microglial and non-microglial cells, and neurobehavioral phenotype after systemic administration of D-JHU29 in a mouse model of RTT. Results: We report successful conjugation of JHU29 to dendrimer resulting in enhanced water solubility compared to free JHU29. D-JHU29 reduced the excessive glutamate release observed in tissue culture slices in a clinically relevant Mecp2-knockout (KO) RTT mouse. Microglia isolated from Mecp2-KO mice demonstrated upregulation of GLS activity that normalized to wild-type levels following systemic treatment with D-JHU29. Neurobehavioral assessments in D-JHU29 treated Mecp2-KO mice revealed selective improvements in mobility. Conclusion: These findings demonstrate that glutaminase inhibitors conjugated to dendrimers are a viable mechanism to selectively inhibit microglial GLS to reduce glutamate production and improve mobility in a mouse model of RTT, with broader implications for selectively targeting this pathway in other neurodegenerative disorders.

Drug Delivery to the Posterior Segment of the Eye: Biopharmaceutic and Pharmacokinetic Considerations

The treatment of the posterior-segment ocular diseases, such as age-related eye diseases (AMD) or diabetic retinopathy (DR), present a challenge for ophthalmologists due to the complex anatomy and physiology of the eye. This specialized organ is composed of various static and dynamic barriers that restrict drug delivery into the target site of action. Despite numerous efforts, effective intraocular drug delivery remains unresolved and, therefore, it is highly desirable to improve the current treatments of diseases affecting the posterior cavity. This review article gives an overview of pharmacokinetic and biopharmaceutics aspects for the most commonly-used ocular administration routes (intravitreal, topical, systemic, and periocular), including information of the absorption, distribution, and elimination, as well as the benefits and limitations of each one. This article also encompasses different conventional and novel drug delivery systems designed and developed to improve drug pharmacokinetics intended for the posterior ocular segment treatment.

Dense hydroxyl polyethylene glycol dendrimer targets activated glia in multiple CNS disorders

Poor transport of neuropharmaceutics through central nervous system (CNS) barriers limits the development of effective treatments for CNS disorders. We present the facile synthesis of a novel neuroinflammation-targeting polyethylene glycol-based dendrimer (PEGOL-60) using an efficient click chemistry approach. PEGOL-60 reduces synthetic burden by achieving high hydroxyl surface density at low generation, which plays a key role in brain penetration and glia targeting of dendrimers in CNS disorders. Systemically administered PEGOL-60 crosses impaired CNS barriers and specifically targets activated microglia/macrophages at the injured site in diverse animal models for cerebral palsy, glioblastoma, and age-related macular degeneration, demonstrating its potential to overcome impaired blood-brain, blood-tumor-brain, and blood-retinal barriers and target key cells in the CNS. PEGOL-60 also exhibits powerful intrinsic anti-oxidant and anti-inflammatory effects in inflamed microglia in vitro. Therefore, PEGOL-60 is an effective vehicle to specifically deliver therapies to sites of CNS injury for enhanced therapeutic outcomes in a range of neuroinflammatory diseases.

Angiotensin II and aldosterone activate retinal microglia

Microglial cells are important contributors to the neuroinflammation and blood vessel damage that occurs in ischemic retinopathies. We hypothesized that key effectors of the renin-angiotensin aldosterone system, angiotensin II (Ang II) and aldosterone, increase the density of microglia in the retina and stimulate their production of reactive oxygen species (ROS) as well as pro-angiogenic and pro-inflammatory factors. Two animal models were studied that featured up-regulation of Ang II or aldosterone and included transgenic Ren-2 rats which overexpress renin and Ang II in tissues including the retina, and Sprague Dawley rats with ischemic retinopathy and infused with aldosterone. Complementary studies were performed in primary cultures of retinal microglia from neonatal Sprague Dawley rats exposed to hypoxia (0.5% O₂) and inhibitors of the angiotensin type 1 receptor (valsartan), the mineralocorticoid receptor (spironolactone) or aldosterone synthase (FAD286). In both in vivo models, the density of ionized calcium-binding adaptor protein-1 labelled microglia/macrophages was increased in retina compared to genetic or vehicle controls. In primary cultures of retinal microglia, hypoxia increased ROS (superoxide) levels as well as the expression of the NADPH oxidase (NOX) isoforms, NOX1, NOX2 and NOX4. The elevated levels of ROS as well as NOX2 and NOX4 were reduced by all of the treatments, and valsartan and FAD286 also reduced NOX1 mRNA levels. A protein cytokine array of retinal microglia revealed that valsartan, spironolactone and FAD286 reduced the hypoxia-induced increase in the potent pro-angiogenic and pro-inflammatory agent, vascular endothelial growth factor as well as the inflammatory factors, CCL5 and interferon γ. Valsartan also reduced the hypoxia-induced increase in IL-6 and TIMP-1 as well as the chemoattractants, CXCL2, CXCL3, CXCL5 and CXCL10. Spironolactone and FAD286 reduced the levels of CXCL2 and CXCL10, respectively. In conclusion, our findings that both Ang II and aldosterone influence the activation of retinal microglia implicates the renin-angiotensin aldosterone system in the pathogenesis of ischemic retinopathies.

Leveraging the interplay of nanotechnology and neuroscience: Designing new avenues for treating central nervous system disorders

Nanotechnology has the potential to open many novel diagnostic and treatment avenues for disorders of the central nervous system (CNS). In this review, we discuss recent developments in the applications of nanotechnology in CNS therapies, diagnosis and biology. Novel approaches for the diagnosis and treatment of neuroinflammation, brain dysfunction, psychiatric conditions, brain cancer, and nerve injury provide insights into the potential of nanomedicine. We also highlight nanotechnology-enabled neuroscience techniques such as electrophysiology and intracellular sampling to improve our understanding of the brain and its components. With nanotechnology integrally involved in the advancement of basic neuroscience and the development of novel treatments, combined diagnostic and therapeutic applications have begun to emerge. Nanotheranostics for the brain, able to achieve single-cell resolution, will hasten the rate in which we can diagnose, monitor, and treat diseases. Taken together, the recent advances highlighted in this review demonstrate the prospect for significant improvements to clinical diagnosis and treatment of a vast array of neurological diseases. However, it is apparent that a strong dialogue between the nanoscience and neuroscience communities will be critical for the development of successful nanotherapeutics that move to the clinic, benefit patients, and address unmet needs in CNS disorders.

Neuroimmune responses in the developing brain following traumatic brain injury

Traumatic brain injury (TBI) is one of the leading causes of both acute and long-term morbidity in the pediatric population, leading to a substantial, long-term socioeconomic burden. Despite the increase in the amount of pre-clinical and clinical research, treatment options for TBI rely heavily on supportive care with very limited targeted interventions that improve the acute and chronic sequelae of TBI. Other than injury prevention, not much can be done to limit the primary injury, which consists of tissue damage and cellular destruction. Secondary injury is the result of the ongoing complex inflammatory pathways that further exacerbate tissue damage, resulting in the devastating chronic outcomes of TBI. On the other hand, some level of inflammation is essential for neuronal regeneration and tissue repair. In this review article we discuss the various stages of the neuroimmune response in the immature, pediatric brain in the context of normal maturation and development of the immune system. The developing brain has unique features that distinguish it from the adult brain, and the immune system plays an integral role in CNS development. Those features could potentially make the developing brain more susceptible to worse outcomes, both acutely and in the long-term. The neuroinflammatory reaction which is triggered by TBI can be described as a highly intricate interaction between the cells of the innate and the adaptive immune systems. The innate immune system is triggered by non-specific danger signals that are released from damaged cells and tissues, which in turn leads to neutrophil infiltration, activation of microglia and astrocytes, complement release, as well as histamine release by mast cells. The adaptive immune response is subsequently activated leading to the more chronic effects of neuroinflammation. We will also discuss current attempts at modulating the TBI-induced neuroinflammatory response. A better understanding of the role of the immune system in normal brain development and how immune function changes with age is crucial for designing therapies to appropriately target the immune responses following TBI in order to enhance repair and plasticity.

Therapeutic implications of nanomedicine for ocular drug delivery

Delivering therapeutics to the eye is challenging on multiple levels: rapid clearance of eyedrops from the ocular surface requires frequent instillation, which is difficult for patients; transport of drugs across the blood-retinal barrier when drugs are administered systemically, and the cornea when drugs are administered topically, is difficult to achieve; limited drug penetration to the back of the eye owing to the cornea, conjunctiva, sclera and vitreous barriers. Nanomedicine offers many advantages over conventional ophthalmic medications for effective ocular drug delivery because nanomedicine can increase the therapeutic index by overcoming ocular barriers, improving drug-release profiles and reducing potential drug toxicity. In this review, we highlight the therapeutic implications of nanomedicine for ocular drug delivery.

Effect of mannose targeting of hydroxyl PAMAM dendrimers on cellular and organ biodistribution in a neonatal brain injury model

Neurotherapeutics for the treatment of central nervous system (CNS) disorders must overcome challenges relating to the blood-brain barrier (BBB), brain tissue penetration, and the targeting of specific cells. Neuroinflammation mediated by activated microglia is a major hallmark of several neurological disorders, making these cells a desirable therapeutic target. Building on the promise of hydroxyl-terminated generation four polyamidoamine (PAMAM) dendrimers (D4-OH) for penetrating the injured BBB and targeting activated glia, we explored if conjugation of targeting ligands would enhance and modify brain and organ uptake. Since mannose receptors [cluster of differentiation (CD) 206] are typically over-expressed on injured microglia, we conjugated mannose to the surface of multifunctional D4-OH using highly efficient, atom-economical, and orthogonal Cu(I)-catalyzed alkyne-azide cycloaddition (CuAAC) click chemistry and evaluated the effect of mannose conjugation on the specific cell uptake of targeted and non-targeted dendrimers both in vitro and in vivo. In vitro results indicate that the conjugation of mannose as a targeting ligand significantly changes the mechanism of dendrimer internalization, giving mannosylated dendrimer a preference for mannose receptor-mediated endocytosis as opposed to non-specific fluid phase endocytosis. We further investigated the brain uptake and biodistribution of targeted and non-targeted fluorescently labeled dendrimers in a maternal intrauterine inflammation-induced cerebral palsy (CP) rabbit model using quantification methods based on fluorescence spectroscopy and confocal microscopy. We found that the conjugation of mannose modified the distribution of D4-OH throughout the body in this neonatal rabbit CP model without lowering the amount of dendrimer delivered to injured glia in the brain, even though significantly higher glial uptake was not observed in this model. Mannose conjugation to the dendrimer modifies the dendrimer's interaction with cells, but does not minimize its inherent inflammation-targeting abilities.

Rapidly purified ganglion cells from neonatal mouse retinas allow studies of mitochondrial morphology and autophagy

Retinal explants and mixed primary cultures are currently used to investigate retinal ganglion cells (RGCs) pathophysiology and pharmacology, but information on yield, quality and quantity of contaminant cells for the available RGCs enrichment techniques is lacking. Here we compare two methods of mouse primary RGCs purification and show that mitochondrial and autophagy parameters can be measured in rapidly purified RGCs. RGCs were purified from P0 mouse eyes using two methods based on the surface antigen Thy1. In a two-step immunopanning purification, a subtraction plate bound macrophage antiserum removed contaminant macrophages and endothelial cells; unbound RGCs were then affinity selected using a plate-bound antiThy1 antibody. In an immunopanning-magnetic separation, macrophage-antiserum bound cells were first subtracted and then RGCs were positively selected using an antiThy1 antibody bound to a magnetic column. The two-steps immunopanning yielded low amounts of 90% pure RGCs, whereas RGCs represented 30% of the 6-fold more cells collected by immunopanning-magnetic separation. RGCs purified with both methods could be microelectroporated to image expressed mitochondria and autophagosomes fluorescent probes and to show that expression of pathogenic Optic atrophy 1 mutants causes mitochondrial fragmentation. Thus, these two methods purify primary mouse RGCs amenable to studies of cell morphology, mitochondrial biology and autophagy.

Preferential and Increased Uptake of Hydroxyl-Terminated PAMAM Dendrimers by Activated Microglia in Rabbit Brain Mixed Glial Culture

Polyamidoamine (PAMAM) dendrimers are multifunctional nanoparticles with tunable physicochemical features, making them promising candidates for targeted drug delivery in the central nervous system (CNS). Systemically administered dendrimers have been shown to localize in activated glial cells, which mediate neuroinflammation in the CNS. These dendrimers delivered drugs specifically to activated microglia, producing significant neurological improvements in multiple brain injury models, including in a neonatal rabbit model of cerebral palsy. To gain further insight into the mechanism of dendrimer cell uptake, we utilized an in vitro model of primary glial cells isolated from newborn rabbits to assess the differences in hydroxyl-terminated generation 4 PAMAM dendrimer (D4-OH) uptake by activated and non-activated glial cells. We used fluorescently-labelled D4-OH (D-Cy5) as a tool for investigating the mechanism of dendrimer uptake. D4-OH PAMAM dendrimer uptake was determined by fluorescence quantification using confocal microscopy and flow cytometry. Our results indicate that although microglial cells in the mixed cell population demonstrate early uptake of dendrimers in this in vitro system, activated microglia take up more dendrimer compared to resting microglia. Astrocytes showed delayed and limited uptake. We also illustrated the differences in mechanism of uptake between resting and activated microglia using different pathway inhibitors. Both resting and activated microglia primarily employed endocytotic pathways, which are enhanced in activated microglial cells. Additionally, we demonstrated that hydroxyl terminated dendrimers are taken up by primary microglia using other mechanisms including pinocytosis, caveolae, and aquaporin channels for dendrimer uptake.

Pediatric oral formulation of dendrimer-N-acetyl-l-cysteine conjugates for the treatment of neuroinflammation

N-Acetyl-l-cysteine (NAC) commonly used as an antidote in acetaminophen poisoning has shown promise in the treatment of neurological disorders such as cerebral palsy (CP). However, NAC suffers from drawbacks such as poor oral bioavailability and suboptimal blood-brain-barrier (BBB) permeability limiting its clinical success. It was previously demonstrated that intravenous administration of dendrimer-NAC (D-NAC) conjugates have shown significant promise in the targeted treatment of neuroinflammation, in multiple preclinical models. Development of an oral formulation of D-NAC may open new administrative routes for this compound. Here, we report the gastrointestinal stability, in vitro transepithelial permeability, and in vivo oral absorption and pharmacokinetics in rats of a pediatric formulation of D-NAC containing Capmul MCM (glycerol monocaprylate) as a penetration enhancer. D-NAC was stable for 6 h in all five simulated gastrointestinal fluids with no signs of chemical degradation. The apparent permeability (P_app) of D-NAC increased 9-fold in the formulation containing Capmul. The area under the curve [AUC]_0-∞ of D-NAC with Capmul increased by 47% when compared to D-NAC alone. These results indicate that an oral pediatric formulation containing D-NAC and Capmul can be an effective option for the treatment of neuroinflammation.

Activated Microglia Targeting Dendrimer-Minocycline Conjugate as Therapeutics for Neuroinflammation

Brain-related disorders have outmatched cancer and cardiovascular diseases worldwide as the leading cause of morbidity and mortality. The lack of effective therapies and the relatively dry central nervous system (CNS) drug pipeline pose formidable challenge. Superior, targeted delivery of current clinically approved drugs may offer significant potential. Minocycline has shown promise for the treatment of neurological diseases owing to its ability to penetrate the blood-brain barrier (BBB) and potency. Despite its potential in the clinic and in preclinical models, the high doses needed to affect a positive therapeutic response have led to side effects. Targeted delivery of minocycline to the injured site and injured cells in the brain can be highly beneficial. Systemically administered hydroxyl poly(amidoamine) (PAMAM) generation-6 (G6) dendrimers have a longer blood circulation time and have been shown to cross the impaired BBB. We have successfully prepared and characterized the in vitro efficacy and in vivo targeting ability of hydroxyl-G6 PAMAM dendrimer-9-amino-minocycline conjugate (D-mino). Minocycline is a challenging drug to carry out chemical transformations due to its inherent instability. We used a combination of a highly efficient and mild copper catalyzed azide-alkyne click reaction (CuAAC) along with microwave energy to conjugate 9-amino-minocycline (mino) to the dendrimer surface via enzyme responsive linkages. D-mino was further evaluated for anti-inflammatory and antioxidant activity in lipopolysaccharides-activated murine microglial cells. D-mino conjugates enhanced the intracellular availability of the drug due to their rapid uptake, suppressed inflammatory cytokine tumor necrosis factor α (TNF-α) production, and reduced oxidative stress by suppressing nitric oxide production, all significantly better than the free drug. Fluorescently labeled dendrimer conjugate (Cy5-D-mino) was systematically administered (intravenous, 55 mg/kg) on postnatal day 1 to rabbit kits with a clinically relevant phenotype of cerebral palsy. The in vivo imaging study indicates that Cy5-D-mino crossed the impaired blood-brain barrier and co-localized with activated microglia at the periventricular white matter areas, including the corpus callosum and the angle of the lateral ventricle, with significant implications for positive therapeutic outcomes. The enhanced efficacy of D-mino, when combined with the inherent neuroinflammation-targeting capability of the PAMAM dendrimers, may provide new opportunities for targeted drug delivery to treat neurological disorders.

Protective effects on the retina after ranibizumab treatment in an ischemia model

Retinal ischemia is common in eye disorders, like diabetic retinopathy or retinal vascular occlusion. The goal of this study was to evaluate the potential protective effects of an intravitreally injected vascular endothelial growth factor (VEGF) inhibitor (ranibizumab) on retinal cells in an ischemia animal model via immunohistochemistry (IF) and quantitative real-time PCR (PCR). A positive binding of ranibizumab to rat VEGF-A was confirmed via dot blot. One eye underwent ischemia and a subgroup received ranibizumab. A significant VEGF increase was detected in aqueous humor of ischemic eyes (p = 0.032), whereas VEGF levels were low in ranibizumab eyes (p = 0.99). Ischemic retinas showed a significantly lower retinal ganglion cell number (RGC; IF Brn-3a: p<0.001, IF RBPMS: p<0.001; PCR: p = 0.002). The ranibizumab group displayed fewer RGCs (IF Brn-3a: 0.3, IF RBPMS: p<0.001; PCR: p = 0.007), but more than the ischemia group (IF Brn-3a: p = 0.04, IF RBPMS: p = 0.03). Photoreceptor area was decreased after ischemia (IF: p = 0.049; PCR: p = 0.511), while the ranibizumab group (IF: p = 0.947; PCR: p = 0.122) was comparable to controls. In the ischemia (p<0.001) and ranibizumab group (p<0.001) a decrease of ChAT⁺ amacrine cells was found, which was less prominent in the ranibizumab group. VEGF-receptor 2 (VEGF-R2; IF: p<0.001; PCR: p = 0.021) and macroglia (GFAP; IF: p<0.001; PCR: p<0.001) activation was present in ischemic retinas. The activation was weaker in ranibizumab retinas (VEGF-R2: IF: p = 0.1; PCR: p = 0.03; GFAP: IF: p = 0.1; PCR: p = 0.015). An increase in the number of total (IF: p = 0.003; PCR: p = 0.023) and activated microglia (IF: p<0.001; PCR: p = 0.009) was detected after ischemia. These levels were higher in the ranibizumab group (Iba1: IF: p<0.001; PCR: p = 0.018; CD68: IF: p<0.001; PCR: p = 0.004). Our findings demonstrate that photoreceptors and RGCs are protected by ranibizumab treatment. Only amacrine cells cannot be rescued. They seem to be particularly sensitive to ischemic damage and need maybe an earlier intervention.

Maternal dendrimer-based therapy for inflammation-induced preterm birth and perinatal brain injury

Preterm birth is a major risk factor for adverse neurological outcomes in ex-preterm children, including motor, cognitive, and behavioral disabilities. N-acetyl-L-cysteine therapy has been used in clinical studies; however, it requires doses that cause significant side effects. In this study, we explore the effect of low dose N-acetyl-L-cysteine therapy, delivered using a targeted, systemic, maternal, dendrimer nanoparticle (DNAC), in a mouse model of intrauterine inflammation. Our results demonstrated that intraperitoneal maternal DNAC administration significantly reduced the preterm birth rate and altered placental immune profile with decreased CD8⁺ T-cell infiltration. Furthermore, we demonstrated that DNAC improved neurobehavioral outcomes and reduced fetal neuroinflammation and long-term microglial activation in offspring. Our study is the first to provide evidence for the role of CD8⁺ T-cell in the maternal-fetal interface during inflammation and further support the efficacy of DNAC in preventing preterm birth and prematurity-related outcomes.

Dexmedetomidine preconditioning protects against retinal ischemia/reperfusion injury and inhibits inflammation response via toll-like receptor 4 (TLR4) pathway

BACKGROUND

Retinal ischemia/reperfusion (I/R) injury is one of significant cause of visual dysopia and causes inflammatory response. Dexmedetomidine is widely applied to general/local anaesthesia and has been reported to have extensive anti-inflammatory effect. However, the role of dexmedetomidine in retinal I/R injury is currently unknown. This study investigates the effect of dexmedetomidine preconditioning on retinal I/R injury and explore the related signal mechanism toll-like receptor 4 (TLR4) pathway.

METHODS

Retinal I/R injury model were established with SD rats through periocular injection. Retinal damage was quantified by measuring the thickness of retinal layers, cell counts of retinal ganglion cells (RGCs) and electroretinography (ERG). Apoptosis of retinal cell was detected by TUNEL assay. Protein and mRNA expression of glial fibrillary acidic protein (GFAP) were measured by western blot and real-time quantitate PCR. Bax, Bcl-2 and nuclear factor-κB (NF-κB) in retinas were detected by western blot.

RESULTS

ERG and HE staining showed that dexmedetomidine preconditioning significantly inhibited the histologic damage induced by I/R injury, which expresses apparent concentration dependent. TUNEL demonstrated that apoptosis of retinal cells were reduced by dexmedetomidine. The expression of NF-κB and GFAP were decreased compared I/R blank group.

CONCLUSION

Dexmedetomidine preconditioning suppresses retinal I/R injury and shows effective anti-inflammatory effect by inhibiting TLR4/NF-κB expression.