The Effect of Silica Nanoparticles on Human Corneal Epithelial Cells

SCO-pH: Microfluidic dynamic phenotyping platform for high-throughput screening of single cell acidification

Studies on the dynamics of single cell phenotyping have been hampered by the lack of quantitative high-throughput metabolism assays. Extracellular acidification, a prominent phenotype, yields significant insights into cellular metabolism, including tumorigenicity. Here, we develop a versatile microfluidic system for single cell optical pH analysis (SCO-pH), which compartmentalizes single cells in 140-pL droplets and immobilizes approximately 40,000 droplets in a two-dimensional array for temporal extracellular pH analysis. SCO-pH distinguishes cells undergoing hyperglycolysis induced by oligomycin A from untreated cells by monitoring their extracellular acidification. To facilitate pH sensing in each droplet, we encapsulate a cell-impermeable pH probe whose fluorescence intensities are quantified. Using this approach, we can differentiate hyperglycolytic cells and concurrently observe single cell heterogeneity in extracellular acidification dynamics. This high-throughput system will be useful in applications that require dynamic phenotyping of single cells with significant heterogeneity.

Extracellular vesicles promote silica nanoparticle aggregation that inhibits silica-induced cytotoxicity

Amorphous silica has been approved as a food and pharmaceutical additive. However, its potential to enhance the carcinogenicity of epithelial cells is incontrovertible. With their expanded surface area per unit mass and distinctive cellular incorporation, nano-sized silica particles (nSPs) exhibit heightened cytotoxicity compared to micrometer-sized counterparts. The precise effect of nSPs on the generation of small extracellular vesicles (sEVs) within endosomes after cellular uptake remains unclear. In the present study, we explored the secretion of sEVs from cells and their functional implications following exposure to nSPs. Our findings demonstrate that nSP50 exposure not only induced epithelial-mesenchymal transition (EMT) but also promoted the maturation of multivesicular endosomes (MVEs) along with the secretion of sEVs in A549 cells. Inhibition of sEV secretion using GW4869 and apoptosis activator 2 exacerbated nSP50-induced EMT, indicating that sEV secretion may suppress EMT. Analysis of the function of sEV in a cell-free system revealed that co-incubation of sEVs with nSP50 led to the formation of micrometer-sized aggregates, which exhibited limited uptake efficiency within A549 cells. These results strongly suggest that the secretion of sEVs plays a protective role against the cytotoxicity attributed to nSP50 exposure.

Recent Advances in Nanotechnology for the Treatment of Dry Eye Disease

Dry eye disease (DED) incidence is continuously growing, positioning it to become an emergent health issue over the next few years. Several topical treatments are commonly used to treat DED; however, reports indicate that only a minor proportion of drug bioavailability is achieved by the majority of eye drops available on the market. In this context, enhancing drug ability to overcome ocular barriers and prolonging its residence time on the ocular surface represent a new challenge in the field of ocular carrier systems. Therefore, research has focused on the development of multi-functional nanosystems, such as nanoemulsions, liposomes, dendrimers, hydrogels, and other nanosized carriers. These systems are designed to improve topical drug bioavailability and efficacy and, at the same time, require fewer daily administrations, with potentially reduced side effects. This review summarizes the different nanotechnologies developed, their role in DED, and the nanotechnology-based eyedrops currently approved for DED treatment.

In vitro and in vivo toxicity of thiolated and PEGylated organosilica nanoparticles

This study comprises the comprehensive toxicological assessment of thiolated organosilica nanoparticles (NPs) synthesised from 3-mercaptopropyltrimethoxysilane (MPTS). We investigated the influence of three different types of nanoparticles synthesised from 3-mercaptopropyltrimethoxysilane: the starting thiolated silica (Si-NP-SH) and their derivatives prepared by surface PEGylation with PEG 750 (Si-NP-PEG750) and 5000 Da (Si-NP-PEG5000) on biological subjects from in vitro to in vivo experiments to explore the possible applications of those nanoparticles in biomedical research. As a result of this study, we generated a comprehensive understanding of the toxicological properties of these nanoparticles, including their cytotoxicity in different cell lines, hemolytic properties, in vitro localisation, mucosal irritation properties and biodistribution in BALB/c mice. Our findings indicate that all three types of nanoparticles can be considered safe and have promising prospects for use in biomedical applications. Nanoparticles did not affect the viability of HPF, MCF7, HEK293 and A549 cell lines at low concentrations (up to 100 µg/mL); moreover, they did not cause organ damage to BALB/c mice at concentrations of 10 mg/kg. The outcomes of this study enhance our understanding of the impact of organosilica nanoparticles on health and the environment, which is vital for developing silica nanoparticle-based drug delivery systems and provides opportunities to expand the applications of organosilica nanoparticles.

Recent progress of nanomedicine in managing dry eye disease

Background

Dry eye disease (DED) is a commonly reported ocular complaint that has garnered significant attention in recent research. The global occurrence of DED ranges from 5% to 50%, impacting a substantial proportion of individuals worldwide with increasing frequency. Although topical administration remains the mainstream drug delivery method for ocular diseases, it suffers from drawbacks such as low bioavailability, rapid drug metabolism, and frequent administration requirements. Fortunately, the advancements in nanomedicine offer effective solutions to address the aforementioned issues and provide significant assistance in the treatment of DED.

Main text

DED is considered a multifactorial disease of the ocular surface and tear film, in which the integrity of tear film function and structure plays a crucial role in maintaining the homeostasis of the ocular surface. The conventional treatment for DED involves the utilization of artificial tear products, cyclosporin, corticosteroids, mucin secretagogues, and nonsteroidal anti-inflammatory drugs. Furthermore, nanomedicine is presently a significant field of study, with numerous clinical trials underway for various nanotherapeutics including nanoemulsions, nanosuspensions, liposomes, and micelles. Notably, some of these innovative nanoformulations have already received FDA approval as novel remedies for DED, and the advancement of nanomedicine is poised to offer enhanced prospects to solve the shortcomings of existing treatments for DED partially.

Conclusions

This article provides an overview of the latest advancements in nanomedicine for DED treatment, while the field of DED treatment is expected to witness a remarkable breakthrough shortly with the development of nanomedicine, bringing promising prospects for patients worldwide suffering conditions.

Hypermethylation and low expression of FANCC involved in multi-walled carbon nanotube-induced toxicity on ARPE-19 cells

Multi-walled carbon nanotube (MWCNT) exposure was observed to cause damages on the viability of ocular cells, however, the underlying mechanisms remain not well understood. Epigenetic alterations that regulate gene expression have been identified as a major responsiveness to environmental challenge. Thus, the aim of this study was to screen methylation-regulated genes involved in MWCNT exposure. The Illumina Human Methylation 850 K array was employed to determine the genome-wide DNA methylation profile of human retinal pigment epithelial cell line (ARPE-19) exposed to 50% inhibition concentration of MWCNTs (100 μg/ml) for 24 h or without (n = 3 for each group). Then, the transcriptome data obtained by high-throughput RNA sequencing previously were integrated with DNA methylome to identify the overlapped genes. As a result, the integrative bioinformatics analysis identified that compared with controls, FA complementation group C (FANCC) was hypermethylated and downregulated in MWCNT-exposed ARPE-19 cells. Quantitative real-time polymerase chain reaction analysis confirmed the mRNA expression level of FANCC was significantly decreased following MWCNT treatment and the addition of DNA methylation inhibitor 5-Aza-deoxycytidine (10 μM) reversed this decrease. Pyrosequencing analysis further validated the hypermethylation status at the 5'-untranslated promoter region of FANCC (cg14583550) in MWCNT-exposed ARPE-19 cells. Protein-protein interaction network and function analyses predicted that FANCC may contribute to MWCNT-induced cytotoxicity by interacting with heat shock protein 90 beta family member 1 and then upregulating cytokine interleukin-6 and apoptosis biomarker caspase 3. In conclusion, the present study links the epigenetic modification of FANCC with the pathogenesis of MWCNT-induced retinal toxicity.

Drug delivery methods based on nanotechnology for the treatment of eye diseases

One of the most difficult tasks among the numerous medication delivery methods is ocular drug delivery. Despite having effective medications for treating ocular illness, we have not yet managed to develop an appropriate drug delivery strategy with the fewest side effects. Nanotechnology has the potential to significantly address the drawbacks of current ocular delivery systems, such as their insufficient therapeutic effectiveness and unfavourable side effects from invasive surgery or systemic exposure. The objective of the current research is to highlight and update the most recent developments in nano-based technologies for the detection and treatment of ocular diseases. Even if more work has to be done, the advancements shown here might lead to brand-new, very practical ocular nanomedicines.

Nonivamide inhibits proliferation of human corneal epithelial cells by inducing cell cycle arrest and oxidative stress

Nonivamide, an agonist of transient receptor potential vanilloid type 1 (TRPV1), is widely used as a riot control agent, police incapacitant spray and pesticide. Although generally considered non-fatal, eye discomfort and even ocular injuries caused by such products are common. Little research has been conducted on the effects of nonivamide on corneal epithelial cells. Cell viability, impedance, flow cytometry, western blotting, and real-time fluorescence analyses were performed to investigate the effects of nonivamide on human corneal epithelial cells (HCE-T cells). We found that nonivamide impaired proliferation at subtoxic doses (100 μM and 200 μM) in HCE-T cells. Next, we described the mechanisms of action of nonivamide. Nonivamide caused cell cycle arrest by increasing p21 and decreasing cyclin D1. TRPV1 was activated by nonivamide, leading to an influx of Ca2+. Enhanced Ca2+ influx partially contributed to oxidative stress. Mitochondrial membrane potential (MMP) also decreased. All combined stress resulted in the inhibition of cell proliferation in HCE-T cells. In summary, nonivamide inhibited the proliferation of HCE-T cells at sub-toxic doses by inducing cell cycle arrest and oxidative stress. Our data demonstrate the corneal toxicity of nonivamide and explain the mechanisms underlying nonivamide-induced corneal injury.

Bioactive silica nanoparticles target autophagy, NF-κB, and MAPK pathways to inhibit osteoclastogenesis

Spherical 50 nm silica-based nanoparticles (SiNPs) promote healthy bone homeostasis and maintenance by supporting bone forming osteoblast lineage cells while simultaneously inhibiting the differentiation of bone resorbing osteoclasts. Previous work demonstrated that an intraperitoneal injection of SiNPs in healthy mice - both young and old - increased bone density and quality, suggesting the possibility that SiNPs represent a dual action therapeutic. However, the underlying mechanisms governing the osteoclast response to SiNPs have yet to be fully explored and defined. Therefore, the goals of this study were to investigate the cellular and molecular mechanisms by which SiNPs inhibit osteoclastogenesis. SiNPs strongly inhibited RANKL-induced osteoclast differentiation within the first hours and concomitantly inhibited early transcriptional regulators such as Nfatc1. SiNPs simultaneously stimulated expression of autophagy related genes p62 and LC3β dependent on ERK1/2 signaling pathway. Intriguingly, SiNPs were found to stimulate autophagosome formation while inhibiting the autophagic flux necessary for RANKL-stimulated osteoclast differentiation, resulting in the inhibition of both the canonical and non-canonical NF-κB signaling pathways and stabilizing TRAF3. These results suggest a model in which SiNPs inhibit osteoclastogenesis by inhibiting the autophagic machinery and RANKL-dependent functionality. This mechanism of action defines a novel therapeutic strategy for inhibiting osteoclastogenesis.

Effects of In Vitro Combination of Nitric Oxide Donors and Hypochlorite on Acanthamoeba castellanii Viability

Purpose

To investigate the combined anti-Acanthamoeba effects of nitric oxide (NO) donors and hypochlorite to maximize amoebicidal outcomes while minimizing damage to human corneal epithelial cells (HCECs).

Methods

Acanthamoeba castellanii and primary cultured HCECs and keratocytes were treated with sodium hypochlorite (NaOCl), NO donors (sodium nitroprusside [SNP] and sodium nitrite [NaNO2]), or a combination of hypochlorite and NO donors. The viability of A. castellanii, HCECs, and keratocytes was assessed. Minimal inhibitory concentration (MIC) and fractional inhibitory concentration of NaOCl and NO donors were determined. The activation of mammalian targets of rapamycin (mTOR) and ERK and the expression of nitrite reductase and Nrf2 were assessed in HCECs using Western blot analysis. The cysticidal effects of combined NaOCl and NO donors were also evaluated.

Results

A dose-dependent toxicity was observed in A. castellanii, HCECs, and keratocytes when treated with NaOCl and SNP. The range of tested NaNO2 concentrations showed no significant toxicity to HCECs; however, dose-dependent toxicity to A. castellanii was observed. The MIC of NaOCl against HCECs and A. castellanii was 8.0 mg/mL. The MIC of NaNO2 and SNP was 500 mM and 10 mM in both HCECs and A. castellanii, respectively. Weak attenuation of the mTOR and ERK phosphorylation was observed and Nrf2 expression decreased slightly after exposure of HCECs to 2.0 mg/mL NaOCl. For the combination treatment, NaOCl (0.125 mg/mL) was selected based on the safety of HCECs and the toxicity of A. castellanii. A more potent anti-Acanthamoeba effect and HCEC toxicity were observed when NaOCl was combined with SNP rather than NaNO2.

Conclusions

Combined NaOCl and NO donors had a stronger anti-Acanthamoeba effect compared to either drug alone.

Translational Relevance

This study demonstrates that the combined use of various drugs for the treatment of Acanthamoeba infection can enhance the anti-Acanthamoeba effect while minimizing the toxicity of the individual drug.

Effect of Magnetic Microparticles on Cultivated Human Corneal Endothelial Cells

Purpose

To investigate effects of magnetic microparticles on movement of magnet controlled human corneal endothelial cells (HCECs).

Methods

Immortalized HCEC line (B4G12) and primary culture of HCECs were exposed to two commercially available magnetic micro- or nanoparticles, SiMAG (average size 100 nm) and fluidMAG (average size <1000 nm). Cell viability assays and reactive oxygen species production assays were performed. Cellular structural changes, intracellular distribution of microparticles, and expression levels of proteins related to cellular survival were analyzed. Ex vivo human corneas were exposed to microparticles to further evaluate their effects. Magnetic particle-laden HCECs were cultured under the influence of a neodymium magnet.

Results

No significant decrease of viability was found in HCECs after exposure to both magnetic particles at concentrations up to 20 µg/mL for 48 hours. However, high concentrations (40 µg/mL and 80 µg/mL) of SiMAG and FluidMAG significantly decreased viability in immortalized HCECs, and only 80 µg/mL of SiMAG and FluidMAG decreased viability in primary HCECs after 48 hours of exposure. There was relative stability of viability at various concentrations of magnetic particles, despite a dose-dependent increase of reactive oxygen species, lactate dehydrogenase, and markers of apoptosis. Ex vivo human cornea study further revealed that exposure to 20 µg/mL of SiMAG and fluidMAG for 72 hours was tolerable. Endocytosed magnetic particles were mainly localized in the cytoplasm. The application of a magnetic field during cell culture successfully demonstrated that magnetic particle-loaded HCECs moved toward the magnet area and that the population density of HCECs was significantly increased.

Conclusions

We verified short-term effects of SiMAG and fluidMAG on HCECs and their ability to control movement of HCECs by an external magnetic field.

Translational Relevance

A technology of applying magnetic particles to a human corneal endothelial cell culture and controlling the movement of cells to a desired area using a magnetic field could be used to increase cell density during cell culture or improve the localization of corneal endothelial cells injected into the anterior chamber to the back of the cornea.

Nanotechnology based drug delivery systems for the treatment of anterior segment eye diseases

Diseases affecting the anterior segment of the eye are the primary causes of vision impairment and blindness globally. Drug administration through the topical ocular route is widely accepted because of its user/patient friendliness - ease of administration and convenience. However, it remains a significant challenge to efficiently deliver drugs to the eye through this route because of various structural and physiological constraints that restrict the distribution of therapeutic molecules into the ocular tissues. The bioavailability of topically applied ocular medications such as eye drops is typically less than 5%. Developing novel delivery systems to increase the retention time on the ocular surfaces and permeation through the cornea is one of the approaches adopted to boost the bioavailability of topically administered medications. Drug delivery systems based on nanotechnology such as micelles, nanosuspensions, nanoparticles, nanoemulsions, liposomes, dendrimers, niosomes, cubosomes and nanowafers have been investigated as effective alternatives to conventional ocular delivery systems in treating diseases of the anterior segment of the eye. This review discussed different nanotechnology-based delivery systems that are currently investigated for treating and managing diseases affecting the anterior ocular tissues. We also looked at the challenges in translating these systems into clinical use and the prospects of nanocarriers as a vehicle for the delivery of phytoactive compounds to the anterior segment of the eye.

High-Capacity Mesoporous Silica Nanocarriers of siRNA for Applications in Retinal Delivery

The main cause of subretinal neovascularisation in wet age-related macular degeneration (AMD) is an abnormal expression in the retinal pigment epithelium (RPE) of the vascular endothelial growth factor (VEGF). Current approaches for the treatment of AMD present considerable issues that could be overcome by encapsulating anti-VEGF drugs in suitable nanocarriers, thus providing better penetration, higher retention times, and sustained release. In this work, the ability of large pore mesoporous silica nanoparticles (LP-MSNs) to transport and protect nucleic acid molecules is exploited to develop an innovative LP-MSN-based nanosystem for the topical administration of anti-VEGF siRNA molecules to RPE cells. siRNA is loaded into LP-MSN mesopores, while the external surface of the nanodevices is functionalised with polyethylenimine (PEI) chains that allow the controlled release of siRNA and promote endosomal escape to facilitate cytosolic delivery of the cargo. The successful results obtained for VEGF silencing in ARPE-19 RPE cells demonstrate that the designed nanodevice is suitable as an siRNA transporter.

Recent achievements in nano-based technologies for ocular disease diagnosis and treatment, review and update

Ocular drug delivery is one of the most challenging endeavors among the various available drug delivery systems. Despite having suitable drugs for the treatment of ophthalmic disease, we have not yet succeeded in achieving a proper drug delivery approach with the least adverse effects. Nanotechnology offers great opportunities to overwhelm the restrictions of common ocular delivery systems, including low therapeutic effects and adverse effects because of invasive surgery or systemic exposure. The present review is dedicated to highlighting and updating the recent achievements of nano-based technologies for ocular disease diagnosis and treatment. While further effort remains, the progress illustrated here might pave the way to new and very useful ocular nanomedicines.

Application of Mesoporous Silica Nanoparticles in Cancer Therapy and Delivery of Repurposed Anthelmintics for Cancer Therapy

This review focuses on the biomedical application of mesoporous silica nanoparticles (MSNs), mainly focusing on the therapeutic application of MSNs for cancer treatment and specifically on overcoming the challenges of currently available anthelmintics (e.g., low water solubility) as repurposed drugs for cancer treatment. MSNs, due to their promising features, such as tunable pore size and volume, ability to control the drug release, and ability to convert the crystalline state of drugs to an amorphous state, are appropriate carriers for drug delivery with the improved solubility of hydrophobic drugs. The biomedical applications of MSNs can be further improved by the development of MSN-based multimodal anticancer therapeutics (e.g., photosensitizer-, photothermal-, and chemotherapeutics-modified MSNs) and chemical modifications, such as poly ethyleneglycol (PEG)ylation. In this review, various applications of MSNs (photodynamic and sonodynamic therapies, chemotherapy, radiation therapy, gene therapy, immunotherapy) and, in particular, as the carrier of anthelmintics for cancer therapy have been discussed. Additionally, the issues related to the safety of these nanoparticles have been deeply discussed. According to the findings of this literature review, the applications of MSN nanosystems for cancer therapy are a promising approach to improving the efficacy of the diagnostic and chemotherapeutic agents. Moreover, the MSN systems seem to be an efficient strategy to further help to decrease treatment costs by reducing the drug dose.

Nanoparticles in ocular applications and their potential toxicity

Nanotechnology has been developed rapidly in recent decades and widely applied in ocular disease therapy. Nano-drug delivery systems overcome the bottlenecks of current ophthalmic drug delivery and are characterized with strong biocompatibility, stability, efficiency, sustainability, controllability, and few side effects. Nanoparticles have been identified as a promising and generally safe ophthalmic drug-delivery system based on the toxicity assessment in animals. Previous studies have found that common nanoparticles can be toxic to the cornea, conjunctiva, and retina under certain conditions. Because of the species differences between humans and animals, advanced in vitro cell culture techniques, such as human organoids, can mimic the human organism to a certain extent, bringing nanoparticle toxicity assessment to a new stage. This review summarizes the advanced application of nanoparticles in ocular drug delivery and the potential toxicity, as well as some of the current challenges and future opportunities in nanotoxicological evaluation.

Silica nanoparticles: Biomedical applications and toxicity

Silica nanoparticles (SiNPs) are composed of silicon dioxide, the most abundant compound on Earth, and are used widely in many applications including the food industry, synthetic processes, medical diagnosis, and drug delivery due to their controllable particle size, large surface area, and great biocompatibility. Building on basic synthetic methods, convenient and economical strategies have been developed for the synthesis of SiNPs. Numerous studies have assessed the biomedical applications of SiNPs, including the surface and structural modification of SiNPs to target various cancers and diagnose diseases. However, studies on the in vitro and in vivo toxicity of SiNPs remain in the exploratory stage, and the toxicity mechanisms of SiNPs are poorly understood. This review covers recent studies on the biomedical applications of SiNPs, including their uses in drug delivery systems to diagnose and treat various diseases in the human body. SiNP toxicity is discussed in terms of the different systems of the human body and the individual organs in those systems. This comprehensive review includes both fundamental discoveries and exploratory progress in SiNP research that may lead to practical developments in the future.

Feasibility of Silicon Quantum Dots as a Biomarker for the Bioimaging of Tear Film

This study investigated the fluorescence and biocompatibility of hydrophilic silicon quantum dots (SiQDs) that are doped with scandium (Sc-SiQDs), copper (Cu-SiQDs), and zinc (Zn-SiQDs), indicating their feasibility for the bioimaging of tear film. SiQDs were investigated for fluorescence emission by the in vitro imaging of artificial tears (TheraTears^®), using an optical imaging system. A trypan blue exclusion test and MTT assay were used to evaluate the cytotoxicity of SiQDs to cultured human corneal epithelial cells. No difference was observed between the fluorescence emission of Sc-SiQDs and Cu-SiQDs at any concentration. On average, SiQDs showed stable fluorescence, while Sc-SiQDs and Cu-SiQDs showed brighter fluorescence emissions than Zn-SiQDs. Cu-SiQDs and Sc-SiQDs showed a broader safe concentration range than Zn-SiQDs. Cu-SiQDs and Zn-SiQDs tend to aggregate more substantially in TheraTears^® than Sc-SiQDs. This study elucidates the feasibility of hydrophilic Sc-SiQDs in studying the tear film's aqueous layer.

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

Background

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

Methods

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

Results

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

Conclusions

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

Graphical Abstract

Supplementary Information

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

Comparison of cytotoxicity effects induced by four different types of nanoparticles in human corneal and conjunctival epithelial cells

The impact of particulate matter (PM) on ocular surface health has attracted increased attention in recent years. Previous studies have reported that differences in the chemical composition of PM can affect the toxicological response. However, available information on the toxic effects of chemical components of PM on the ocular surface is insufficient. In this paper, we aimed to investigate the toxicity effects of chemical components of PM on the ocular surface, focusing on the effects of four different types of nanoparticles (NPs) in human corneal epithelial cells (HCECs) and human conjunctival epithelial cells (HCjECs), which include titanium dioxide (TiO2), carbon black (CB), zinc dioxide (ZnO), and silicon dioxide (SiO2). We found that the in vitro cytotoxic effects of CB, ZnO, and SiO2 NPs are dependent on particle properties and cell type as well as the exposure concentration and time. Here, the order of increasing toxicity was SiO2 → CB → ZnO, while TiO2 demonstrated no toxicity. Moreover, toxic effects appearing more severe in HCECs than HCjECs. Reactive oxygen species (ROS)-mediated oxidative stress plays a key role in the toxicity of these three NPs in HCECs and HCjECs, leading to apoptosis and mitochondrial damage, which are also important contributors to aging. Sirtuin1 (SIRT1) as an NAD+-dependent protein deacetylase that seems to play a potential protective role in this process. These findings implied that ROS and/or SIRT1 may become a potential target of clinical treatment of PM- or NP-related ocular surface diseases.

Retinal cytotoxicity of silica and titanium dioxide nanoparticles

The retina plays a key role in human vision. It is composed of cells that are essential for vision signal generation. Thus far, conventional medications have been ineffective for treating retinal diseases because of the intrinsic blood-retinal barrier. Nanoparticles (NPs) are promising effective platforms for ocular drug delivery. However, nanotoxicity in the retinal tissue has not received much attention. This study used R28 cells (a retinal precursor cell line that originated from rats) to investigate the safety of two commonly used types of NPs: silica nanoparticles (SiO₂NPs, 100 nm) and titanium dioxide nanoparticles (TiO₂NPs, 100 nm). Cellular viability and reactive oxygen species generation were measured after 24, 48, and 72 h of exposure to each NP. Cellular autophagy and the mTOR pathways were evaluated. The retinal toxicity of the NPs was investigated in vivo in rat models. Both types of NPs were found to induce significant dose-dependent toxicity on the R28 cells. A significant elevation of reactive oxygen species generation was also observed. Increased autophagy and decreased mTOR phosphorylation were observed after SiO₂NPs and TiO₂NPs exposure. The diffuse apoptosis of the retinal cellular layers was detected after intravitreal injection.

Nanotechnology for Topical Drug Delivery to the Anterior Segment of the Eye

Topical drug delivery is one of the most challenging aspects of eye therapy. Eye drops are the most prevalent drug form, especially for widely distributed anterior segment eye diseases (cataracts, glaucoma, dry eye syndrome, inflammatory diseases, etc.), because they are convenient and easy to apply by patients. However, conventional drug formulations are usually characterized by short retention time in the tear film, insufficient contact with epithelium, fast elimination, and difficulties in overcoming ocular tissue barriers. Not more than 5% of the total drug dose administered in eye drops reaches the interior ocular tissues. To overcome the ocular drug delivery barriers and improve drug bioavailability, various conventional and novel drug delivery systems have been developed. Among these, nanosize carriers are the most attractive. The review is focused on the different drug carriers, such as synthetic and natural polymers, as well as inorganic carriers, with special attention to nanoparticles and nanomicelles. Studies in vitro and in vivo have demonstrated that new formulations could help to improve the bioavailability of the drugs, provide sustained drug release, enhance and prolong their therapeutic action. Promising results were obtained with drug-loaded nanoparticles included in in situ gel.

Effects of Nonporous Silica Nanoparticles on Human Trabecular Meshwork Cells

PRECIS

Silica nanoparticles (SiNPs), which are potential drug carriers for glaucoma treatment, may induce mild dose-dependent cytotoxicity but not so severe as to compromise a mammalian target of rapamycin (mTOR) pathway in immortalized trabecular meshwork (TM) cells.

PURPOSE

Nanoparticle-based ophthalmic drug delivery is a promising field of drug development. In this study, we evaluated the effect of nonporous SiNPs on human TM cells.

METHODS

TM cells were exposed to different concentrations (0 to 100 µg/mL) of SiNPs (50, 100, and 150 nm) for up to 48 hours. Transmission electron microscopy confirmed the intracellular distribution of SiNPs. Cellular viability assay, reactive oxygen species generation, autophagy, and activation of the mTOR pathway were evaluated. Histologic analysis of the TM structure was performed after intracameral injection of SiNPs (0.05 mL of 200 µg/mL concentration) in rabbits.

RESULTS

SiNPs were taken up by TM cells and localized in the cytoplasm. Neither nuclear entry nor mitochondrial damage was observed. SiNPs induced a mild but dose-dependent increase of lactate dehydrogenase. However, neither increase of intracellular reactive oxygen species levels nor apoptosis was observed after SiNPs exposure. Significant coactivation of autophagy and the mTOR pathway were observed with exposure to SiNPs. Aqueous plexus structure was well maintained without inflammation in rabbits after SiNPs exposure.

CONCLUSIONS

SiNPs induce mild and dose-dependent cytotoxicity in TM cells. However, the toxicity level is not enough to compromise the mTOR pathway of TM cells and histologic structure of the aqueous plexus tissue.

Pharmaceutical-loaded contact lenses as an ocular drug delivery system: A review of critical lens characterization methodologies with reference to ISO standards

Therapeutic contact lenses for ocular drug delivery have received considerable interest as they can potentially enhance ocular bioavailability, increase patient compliance, and reduce side effects. Along with the successful in vitro and in vivo studies on sustained drug delivery through contact lenses, lens critical properties such as water content, optical transparency and modulus have also been investigated. Aside from issues such as drug stability or burst release, the potential for the commercialization of pharmaceutical-loaded lenses can be limited by the alteration of lens physical and chemical properties upon the incorporation of therapeutic or non-therapeutic components. This review outlines advances in the use of pharmaceutical-loaded contact lenses and their relevant characterization methodologies as a potential ocular drug delivery system from 2010 to 2020, while summarizing current gaps and challenges in this field. A key reference point for this review is the relevant ISO standards on contact lenses, relating to the associated characterization methodologies. The content of this review is categorized based on the chemical, physical and mechanical properties of the loaded lens with the shortcomings of such analytical technologies examined.

Activation of kelch-like ECH-associated protein 1/nuclear factor erythroid 2-related factor 2/antioxidant response element pathway by curcumin enhances the anti-oxidative capacity of corneal endothelial cells

Fuchs endothelial corneal dystrophy is one of the most common indications for corneal transplantation, and impaired anti-oxidative function is observed in corneal endothelial cells (CECs). Curcumin is well-known for its anti-oxidative property; but, no study has examined the effect of curcumin on anti-oxidative therapeutic roles in corneal endothelial disease. In our experiments, oxidative stress 0.25 mM tert-butyl hydroperoxide for 2 h was induced in immortalized human CECs pretreated with curcumin. Cell behavior and viability, reactive oxygen species production, and the protein expression of the kelch-like ECH-associated protein 1 (Keap1)/nuclear factor erythroid 2-related factor 2(Nrf2)/antioxidant response element (ARE) pathway were examined; the Keap1/Nrf2/ARE pathway is crucial anti-oxidative pathway of curcumin. The results showed that pretreatment with 12.5 μM curcumin significantly reduced the ROS production and improved the survival of CECs under oxidative stress. In addition, curcumin pretreatment significantly increased the expression of nuclear Nrf2, and the productions of superoxide dismutase 1 and heme oxygenase-1, which were the target anti-oxidative enzymes of the Keap1/Nrf2/ARE pathway. Our findings showed that curcumin enhanced the growth and differentiation of CECs under oxidative stress. The activation of Keap1/Nrf2/ARE pathway by curcumin was crucial for CECs to improve their anti-oxidative capacity.

Issues currently complicating the risk assessment of synthetic amorphous silica (SAS) nanoparticles after oral exposure

Synthetic amorphous silica (SAS) is applied in food products as food additive E 551. It consists of constituent amorphous silicon dioxide (SiO₂) nanoparticles that form aggregates and agglomerates. We reviewed recent oral toxicity studies with SAS. Some of those report tissue concentrations of silicon (Si). The results of those studies were compared with recently determined tissue concentrations of Si (and Si-particles) in human postmortem tissues. We noticed inconsistent results of the various toxicity studies regarding toxicity and reported tissue concentrations, which hamper the risk assessment of SAS. A broad range of Si concentrations is reported in control animals in toxicity studies. The Si concentrations found in human postmortem tissues fall within this range. On the other hand, the mean concentration found in human liver is higher than the reported concentrations causing liver effects in some animal toxicity studies after oral exposure to SAS. Also higher liver concentrations are observed in other, negative animal studies. Those inconsistencies could be caused by the presence of other Si-containing chemical substances or particles (which potentially also includes background SAS) and/or different sample preparation and analytical techniques that were used. Other factors which could explain the inconsistencies in outcome between the toxicity studies are the distinct SAS used and different dosing regimes, such as way of administration (dietary, via drinking water, oral gavage), dispersion of SAS and dose. More research is needed to address these issues and to perform a proper risk assessment for SAS in food. The current review will help to progress research on the toxicity of SAS and the associated risk assessment.

Emerging Nano-Formulations and Nanomedicines Applications for Ocular Drug Delivery

Ocular diseases can deteriorate vision to the point of blindness and thus can have a major impact on the daily life of an individual. Conventional therapies are unable to provide absolute therapy for all ocular diseases due to the several limitations during drug delivery across the blood-retinal barrier, making it a major clinical challenge. With recent developments, the vast number of publications undergird the need for nanotechnology-based drug delivery systems in treating ocular diseases. The tool of nanotechnology provides several essential advantages, including sustained drug release and specific tissue targeting. Additionally, comprehensive in vitro and in vivo studies have suggested a better uptake of nanoparticles across ocular barriers. Nanoparticles can overcome the blood-retinal barrier and consequently increase ocular penetration and improve the bioavailability of the drug. In this review, we aim to summarize the development of organic and inorganic nanoparticles for ophthalmic applications. We highlight the potential nanoformulations in clinical trials as well as the products that have become a commercial reality.

Surface functionalized mesoporous silica nanoparticles for intravitreal application of tacrolimus

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

Targeted delivery of mitomycin C-loaded and LDL-conjugated mesoporous silica nanoparticles for inhibiting the proliferation of pterygium subconjunctival fibroblasts

Pterygium is a degenerative disease that characterized by excessive fibrovascular proliferation. To reduce the recurrence rate, surgery is the main strategy, in combination with adjacent procedures or adjunctive therapy. One of the most common adjunctive agents, mitomycin C (MMC), is known as an alkylating agent that inhibits fibroblast proliferation but is limitedly applied in pterygium due to various complications. A previous study demonstrated that activated pterygium subconjunctival fibroblasts overexpressed low-density lipoprotein (LDL) receptors. In this study, we designed and synthesized MMC-loaded mesoporous silica nanoparticles conjugated with LDL (MMC@MSNs-LDL) to deliver MMC into activated pterygium fibroblasts in a targeted manner. The MMC loading efficiency was approximately 6%. The cell viability test (CCK-8 assay) revealed no cytotoxicity for the empty carrier MSNs at a concentration of ≤1 mg/ml after administration for 48 h in subconjunctival fibroblasts. Primary pterygium and normal human subconjunctival fibroblasts with or without stimulation by vascular endothelial growth factor (VEGF) were treated as follows: 1) 10 μg/ml MMC@MSNs-LDL for 24 h (MMC concentration: 0.6 μg/ml); 2) 0.2 mg/ml MMC for 5 min then cultured for 24 h after MMC removal; and 3) normal culture without any drug treatment. At 24 h, the anti-proliferative effect of MMC@MSNs-LDL in activated pterygium fibroblasts was similar to that of MMC (cell viability: 46.2 ± 5.5% vs 40.5 ± 1.1%, respectively, P = 0.349). Furthermore, the cytotoxicity of MMC@MSNs-LDL to normal fibroblasts with or without VEGF stimulation was significantly lower than that of traditional MMC (cell viability: 75.6 ± 4.4% vs 36.0 ± 1.5%, respectively, P < 0.001; 84.7 ± 5.5% vs 35.7 ± 1.3%, P < 0.001). The binding of fluorescently labeled MMC@MSNs-LDL in fibroblasts was assessed using confocal fluorescence microscopy. The uptake of targeted nanoparticles in fibroblasts was time dependent and saturated at 6 h. VEGF-activated pterygium fibroblasts showed more uptake of MMC@MSNs-LDL than normal fibroblasts with or without VEGF activation (both P < 0.001). Our data strongly suggest that MMC@MSNs-LDL had an effective antiproliferative role in activated pterygium fibroblasts, with reduced toxicity to normal fibroblasts compared to traditional application of MMC. LDL-mediated drug delivery might have great potential in the management of pterygium recurrence.

The Application of Nanomaterials in Cell Autophagy

Autophagy is defined as separation and degradation of cytoplasmic components through autophagosomes, which plays an essential part in physiological and pathological events. Hence it is also essential for cellular homeostasis. Autophagy disorder may bring about the failure of stem cells to maintain the fundamental transformation and metabolism of cell components. However, for cancer cells, the disorder of autophagy is a feasible antitumor idea. Nanoparticles, referring to particles of the size range 1-100 nanometers, are appearing as a category of autophagy regulators. These nanoparticles may revolutionize and broaden the therapeutic strategies of many diseases, including neurodegenerative diseases, tumors, muscle disease, and so on. Researches of autophagy-induced nanomaterials mainly focus on silver particles, gold particles, silicon particles, and rare earth oxides. But in recent years, more and more materials have been found to regulate autophagy, such as nano-nucleic acid materials, nanofiber scaffolds, quantum dots, and so on. The review highlights that various kinds of nanoparticles have the power to regulate autophagy intensity in stem cells of interest and further control biological behaviors, which may become a reliable treatment choice for disease therapy.

Sustained Nitric Oxide-Providing Small Molecule and Precise Release Behavior Study for Glaucoma Treatment

Incidence ofglaucoma, a severe disease leading to irreversible loss of vision, is increasing with global aging populations. Lowering intraocular pressure (IOP) is the only proven treatment method for glaucoma. Nitric oxide (NO) is an emerging material targeting the conventional outflow pathway by relaxing the trabecular meshwork (TM). However, there is little understanding on the NO level effective in IOP lowering without toxicity. Here, we report a novel long-term NO-releasing polydiazeniumdiolate (NOP) that enables lowering IOP via the conventional outflow pathway. NOP is composed of carbon-bound polydiazeniumdiolate, a stable NO donor moiety. NO release was monitored with accurate parameters by real-time detection of gas and analysis of the accumulated release profile. Based on the NO release information, the selected safe level of NOP exhibited effective TM relaxation and a potential IOP lowering effect in vivo without side effects. This work provides new insights into nitric oxide release behavior that should be considered for glaucoma treatment.

Safety Assessment of Nanomaterials to Eyes: An Important but Neglected Issue

The production and application of nanomaterials have grown tremendously during last few decades. The widespread exposure of nanoparticles to the public is provoking great concerns regarding their toxicity to the human body. However, in comparison with the extensive studies carried out to examine nanoparticle toxicity to the human body/organs, one especially vulnerable organ, the eye, is always neglected. Although it is a small part of the body, 90% of outside information is obtained via the ocular system. In addition, eyes usually directly interact with the surrounding environment, which may get severer damage from toxic nanoparticles compared to inner organs. Therefore, the study of assessing the potential nanoparticle toxicity to the eyes is of great importance. Here, the recent advance of some representative manufactured nanomaterials on ocular toxicity is summarized. First, a brief introduction of ocular anatomy and disorders related to particulate matter exposure is presented. Following, the factors that may influence toxicity of nanoparticles to the eye are emphasized. Next, the studies of representative manufactured nanoparticles on eye toxicity are summarized and classified. Finally, the limitations that are associated with current nanoparticle-eye toxicity research are proposed.

In Vitro Cytotoxicity of Zinc Oxide Nanoparticles in Cultured Statens Seruminstitut Rabbit Cornea Cells

The possibility of eye exposure for workers participating in manufacturing of nanoparticles or consumers using products containing nanoparticles has been reported, but toxicity studies on the eye are scarce. In this study, cytotoxicity of five nanoparticles including silver, ceria, silica, titanium and zinc were tested using Statens Seruminstitut Rabbit Cornea (SIRC) cells. When cells were treated with nanoparticles with concentrations of 1–100 μg/mL for 24 hr, zinc oxide nanoparticles showed higher toxicity to cornea cells. LC₅₀ of zinc oxide nanoparticles was less than 25 μg/mL but those of other nanoparticles could not be calculated in this test, which means more than 100 μg/mL. Generation of reactive oxygen species was observed, and expression of apoptosis related biomarkers including Bax and Bcl-2 were changed after treatment of zinc oxide nanoparticles, while no other significant toxicity- related changes were observed in cornea cells treated with Ag, CeO₂, SiO₂ and TiO₂ nanoparticles.

Effect of Nitric Oxide on Acanthamoeba castellanii

Purpose

Acanthamoeba keratitis is a well-known intractable corneal infectious disease. We investigated the anti-Acanthamoeba effect of exogenous nitric oxide (NO).

Methods

Acanthamoeba castellanii was axenically cultured and exposed to various concentrations of NO donors, such as sodium nitrite, sodium nitroprusside (SNP), and NO-releasing silica nanoparticles (coated in branched polyethylene imine, size:100 nm), for 1 to 7 days (sodium nitrite and SNP: 0, 0.1, 1, 10, 100, and 1000 μM; silica nanoparticles: 0, 6.25, 12.5, 25, 50, and 100 μg/mL). Human corneal epithelial cells (HCECs) were cultured and exposed to sodium nitrite, SNP (0, 0.1, 1, 10, 100, and 1000 μM), and silica nanoparticles for 1, 2, and 3 days.

Results

Sodium nitrite and SNP showed a dose-dependent inhibitory effect on A. castellanii viability. A more prominent inhibitory effect was observed with SNP (less than 10% of organisms survived at 7-day culture with 1000 μM) compared with sodium nitrite. However, more cytotoxicity on HCEC was observed with SNP. NO-releasing silica nanoparticles were successfully internalized into the amoebic cytoplasm and accumulated in large vacuoles. Although blank silica nanoparticles had no inhibitory effect on A. castellanii viability, NO-releasing silica nanoparticles showed a dose-dependent amoebicidal effect. Furthermore, no cystic transformation of A. castellanii was observed under a phase contrast microscope or transmission electron microscope after exogenous NO treatment.

Conclusions

Our results demonstrated the anti-Acanthamoeba effect of exogenous NO. This finding suggests that NO-releasing drug platforms, including nano-carriers, can be a promising therapeutic strategy for Acanthamoeba keratitis.

In Situ Gel of Triamcinolone Acetonide-Loaded Solid Lipid Nanoparticles for Improved Topical Ocular Delivery: Tear Kinetics and Ocular Disposition Studies

Triamcinolone acetonide (TA), an intermediate acting corticosteroid, is used in the treatment of posterior ocular diseases, such as inflammation, posterior uveitis, and diabetic macular edema. The objective of this investigation was to prepare TA-loaded solid lipid nanoparticles (TA-SLNs) and in situ gel (TA-SLN-IG) formulations for delivery into the deeper ocular tissues through the topical route. TA-SLNs were prepared by hot homogenization and ultrasonication method using glyceryl monostearate and Compritol® 888ATO as solid lipids and Tween®80 and Pluronic® F-68 as surfactants. TA-SLNs were optimized and converted to TA-SLN-IG by the inclusion of gellan gum and evaluated for their rheological properties. In vitro transcorneal permeability and in vivo ocular distribution of the TA-SLNs and TA-SLN-IG were studied using isolated rabbit corneas and New Zealand albino rabbits, respectively, and compared with TA suspension, used as control (TA-C). Particle size, PDI, zeta potential, assay, and entrapment efficiency of TA-SLNs were in the range of 200⁻350 nm, 0.3⁻0.45, -52.31 to -64.35 mV, 70⁻98%, and 97⁻99%, respectively. TA-SLN-IG with 0.3% gellan gum exhibited better rheological properties. The transcorneal permeability of TA-SLN and TA-SLN-IG was 10.2 and 9.3-folds higher compared to TA-C. TA-SLN-IG showed maximum tear concentration at 2 h, indicating an improved pre-corneal residence time, as well as higher concentrations in aqueous humor, vitreous humor and cornea at 6 h, suggesting sustained delivery of the drug into the anterior and posterior segment ocular tissues, when compared to TA-SLN and TA-C. The results, therefore, demonstrate that the lipid based nanoparticulate system combined with the in situ gelling agents can be a promising drug delivery platform for the deeper ocular tissues.

Distinct autophagy-inducing abilities of similar-sized nanoparticles in cell culture and live C. elegans

Nanomaterial-induced autophagy has raised increasing concerns. A variety of nanomaterials, conventional or recently emerged, have the capability of inducing autophagy. As a consequence, it is becoming a popular belief that induction of autophagy is a common response of cells upon exposure to nanoscale materials. In order to clarify whether the "nanoscale" size is the determining factor for the nanomaterials to induce autophagy, we utilized in vitro cultured cells and an in vivo Caenorhabditis elegans (C. elegans) model to systemically investigate the autophagy-inducing ability of nanomaterials. We selected four types of representative nanomaterials with similar sizes, namely silicon nanoparticles (SiNPs), CdTe quantum dots (QDs), carbon dots (CDs) and gold nanoparticles (AuNPs). We demonstrated that, unlike most other nanomaterials tested, no autophagosome formation was detected in cultured cells or in live C. elegans with SiNP treatment. The expression of autophagy-related genes and the lipidation of LGG-1/LC3 in cells and C. elegans also remained unchanged after the treatment of SiNPs. In addition, the ability of the nanomaterials to induce autophagy appeared to correlate with those to incur subcellular organelle damage. Together, our studies demonstrate that SiNPs do not induce autophagy in vitro or in vivo in the selected model organisms and cell lines, thus clarifying that the "nanoscale" size is not the determining factor for the nanomaterials to induce autophagy. The results also suggest that the autophagy-inducing ability of most nanomaterials could be merely a reflection of their detrimental effect on cellular structures.

Local Delivery and Sustained-Release of Nitric Oxide Donor Loaded in Mesoporous Silica Particles for Efficient Treatment of Primary Open-Angle Glaucoma

Nitric oxide (NO) donors are ideal drug candidates for reducing intraocular pressure in the treatment of glaucoma. However, poor cornea penetration, short duration of efficacy, and narrow therapeutic index of most NO donors obstruct their clinical applications in glaucoma treatment. This study reports a novel NO donor delivery system based on mesoporous silica nanoparticles that can readily overcome the above difficulties and deliver the NO-donating drug sodium nitroprusside to the target tissues (trabecular meshwork and Schlemm's canal). Mesoporous silica nanoparticles loaded with sodium nitroprusside can produce more exogenous NO and sustain higher NO concentration in animal eye models, which significantly extend the duration of intraocular pressure reduction from 3 to 48 h with only 1/40 of the dose of sodium nitroprusside solution. These findings open up the possibility of mesoporous silica nanoparticles loading sodium nitroprusside for effective management of ocular hypertension.

Metal-organic frameworks induce autophagy in mouse embryonic fibroblast cells

Autophagy is the lysosomal-dependent degradation process of intracellular substances in adaptation to environmental or developmental changes. It plays an essential role in maintaining cellular homeostasis while its dysfunction is involved in various human diseases. The regulation of autophagy has attracted more and more attention with the promise for improving treatment of diseases as a potential therapeutic target. Metal-organic frameworks (MOFs), as emerging biomaterials, have been investigated in the biological and biomedical fields in recent years. Therefore, it is interesting and significant to study the effects of MOFs on living cells from safety aspects as well as the therapeutic viewpoint, especially their effects on autophagy which have not been reported yet. In this study, the effects of Fe-MIL-101_NH2 on mouse embryonic fibroblasts (MEFs) were investigated and the potential applications of these nanoparticles in the regulation of autophagy were explored. Our results demonstrated that Fe-MIL-101_NH2 induced cytoprotective autophagy in MEFs instead of cytotoxicity. The activation of autophagy kept reactive oxygen species from accumulating, which protected MEFs from apoptosis. Further exploration of the possible mechanisms of MOF-induced autophagy revealed that the inhibition of mTOR pathway as well as the enhancement of Becline1 and Atg5 contributed to autophagy induction. Our study uncovered the autophagic effects and mechanistic insights of MOFs, which will be beneficial and meaningful to the safety evaluation and the reasonable and effective usage of MOFs.

Health Concerns of Various Nanoparticles: A Review of Their in Vitro and in Vivo Toxicity

Nanoparticles (NPs) are currently used in diagnosis and treatment of many human diseases, including autoimmune diseases and cancer. However, cytotoxic effects of NPs on normal cells and living organs is a severe limiting factor that hinders their use in clinic. In addition, diversity of NPs and their physico-chemical properties, including particle size, shape, surface area, dispersity and protein corona effects are considered as key factors that have a crucial impact on their safe or toxicological behaviors. Current studies on toxic effects of NPs are aimed to identify the targets and mechanisms of their side effects, with a focus on elucidating the patterns of NP transport, accumulation, degradation, and elimination, in both in vitro and in vitro models. NPs can enter the body through inhalation, skin and digestive routes. Consequently, there is a need for reliable information about effects of NPs on various organs in order to reveal their efficacy and impact on health. This review covers the existing knowledge base on the subject that hopefully prepares us better to address these challenges.

Toxicity of silicon dioxide nanoparticles with varying sizes on the cornea and protein corona as a strategy for therapy

The human cornea is exposed directly to particulate matter (PM) in polluted air. This exposure can cause eye discomfort and corneal injury. Ultrafine PM (diameter <100 nm) is thought to be particularly harmful to health, but there is limited research investigating its toxicity to the eye. In this study, we evaluated toxicity differences among 30-, 40-, 100- and 150-nm silicon dioxide nanoparticles (SiO₂ NPs) on the cornea. A 24-hour in vitro exposure of primary human corneal epithelial cells (hCECs) to ultrafine (30 and 40 nm) SiO₂ NPs produced toxicity, as evidenced by cell membrane damage, reduced cell viability, increased cell death and mitochondrial dysfunction. In vivo exposure to the same nanoparticles produced observable corneal injury. These effects were more severe with ultrafine than with fine (100 and 150 nm) SiO₂ NPs. Common antioxidant compounds, e.g., glutathione, did not protect the cornea from SiO₂ NP-induced damage. However, foetal bovine serum (FBS) did significantly reduce toxicity, likely by forming a protective protein corona around the nanoparticles. This finding suggests that FBS (or its derivatives) may be a useful clinical therapy for corneal toxicity caused by ultrafine particulates.

Sorbitan ester nanoparticles (SENS) as a novel topical ocular drug delivery system: Design, optimization, and in vitro/ex vivo evaluation

We explored the potential of two types of sorbitan ester nanoparticles (SENS) as novel tools for topical ocular drug delivery. The optimized SENS formulation (SENS-OPT) consisted of nanoparticles (NPs) of 170.5 nm, zeta potential +33.9 mV, and cyclosporine loading of 19.66%. After hyaluronic acid (HA) coating, the resulting SENS-OPT-HA NPs had a particle size of 177.6 nm and zeta potential of -20.6 mV. The NPs were stable during 3 months of storage at different temperatures and did not aggregate in the presence of protein-enriched simulated lacrimal fluid. There was no toxicity to cultured human corneal epithelial (HCE) cells when exposed to NPs up to 0.4% (w/v). Both NPs were effectively internalized by HCE cells through active mechanisms. Endocytosis of SENS-OPT NPs was caveolin-dependent whereas SENS-OPT-HA NP endocytosis was mediated by HA receptors. HA-receptor-mediated endocytosis may be responsible for the higher cellular uptake of SENS-OPT-HA NPs. After cyclosporine incorporation into the NPs, corneal penetration of this immunosuppressive drug by loaded SENS-OPT NPs was 1.3-fold higher than the commercial reference formulation Sandimmun®. For cyclosporine-loaded SENS-OPT-HA NPs, the penetration was 2.1-fold higher than for Sandimmun®. In ex vivo stimulated lymphocytes, both formulations demonstrated the same reduction in IL-2 levels as Sandimmun®.

HER2-Targeted Multifunctional Silica Nanoparticles Specifically Enhance the Radiosensitivity of HER2-Overexpressing Breast Cancer Cells

We investigated the effects of targeted functionalized silica nanoparticles on the radiosensitivity of cancer cells. Better control of the local concentration of silica nanoparticles may facilitate their use as an adjuvant in conjunction with ionizing radiation to target cancer cells while preventing damage to normal cells. Hyperbranched polyamidoamine (PAMAM) was grafted onto the surface of amorphous silica nanoparticles to functionalize them. The PAMAM-coated silica nanoparticles (PCSNs) were then conjugated with fluorescent dyes. Anti-HER2 antibodies were covalently attached to the labeled PCSNs. The HER2-overexpressing SK-BR3 breast cancer cell line was incubated in medium containing the PCSN probes. After incubation; the cells were exposed to X-ray radiation. Cells were counted in all samples using cell proliferation assays; and apoptotic cells were detected. The cell survival results showed that the combination of the targeted PCSN probes and radiation reduced the survival rate of SK-BR3 cells to a greater extent than when either PCSN probes, PCSNs or radiation were applied individually. The results also showed an increase in apoptosis in the SK-BR3 cells that internalized the PCSN probes and were then irradiated. Based on these data, PCSN probes act as specific radiosensitizing agents for HER2-overexpressing cells.

Safety of Nonporous Silica Nanoparticles in Human Corneal Endothelial Cells

Nonporous silica nanoparticles (SiNPs) are promising drug carrier platforms for intraocular drug delivery. In this study, we investigated the safety of three different sizes of SiNPs (50, 100, and 150 nm) in a human corneal endothelial cell (HCEC) line, B4G12. The HCECs were exposed to different concentrations (0, 25, 50, and 100 µg/ml) of three sizes of SiNPs for up to 48 h. Cellular viability, autophagy, lactate dehydrogenase (LDH) assay, and mammalian target of rapamycin (mTOR) pathway activation were evaluated. Intracellular distribution of the SiNPs was evaluated with transmission electron microscopy (TEM). TEM revealed that the SiNPs were up-taken by the HCECs inside cytoplasmic vacuoles. No mitochondrial structural damage was observed. Both cellular viability and LDH level remained unchanged with up to 100 µg/mL of SiNP treatment. Autophagy showed a significant dose-dependent activation with 50, 100, and 150 nm SiNPs. However, the mTOR activation remained unchanged. Human corneal tissue culture with 100 µg/ml concentrations of SiNPs for 72 h revealed no significant endothelial toxicity. In vivo corneal safety of the SiNPs (0.05 ml intracameral injection, 200 mg/ml concentration) was also verified in rabbit models. These findings suggested that 50, 100, and 150 nm SiNPs did not induce acute significant cytotoxicity in corneal endothelial cells at concentrations up to 100 µg/mL. However, long-term toxicity of SiNPs remains unknown.

An Evaluation of the in vivo Safety of Nonporous Silica Nanoparticles: Ocular Topical Administration versus Oral Administration

Nonporous silica nanoparticles (SiNPs) have potential as promising carriers for ophthalmic drugs. However, the in vivo safety of ocular topical SiNPs remains unclear. This study investigated the in vivo safety of oral and ocular topical applications of 100 nm-sized SiNPs in Sprague-Dawley rats. The rats were divided into the following four groups: low-dose oral administration (total 100 mg/kg of SiNPs mixed with food for one week), high-dose oral administration (total 1000 mg/kg of SiNPs mixed with food for one week), ocular topical administration (10 mg/ml concentration, one drop, applied to the right eyes four times a day for one month), or a negative control (no SiNP treatment). The rats were observed for 12 weeks to investigate any signs of general or ocular toxicity. During the observation period, no differences were observed in the body weights, food and water intakes, behaviors and abnormal symptoms of the four groups. No animal deaths occurred. After 12 weeks, hematologic, blood biochemical parameters and ophthalmic examinations revealed no abnormal findings in any of the animals. The lack of toxicity of the SiNPs was further verified in autopsy findings of brain, liver, lung, spleen, heart, kidneys, intestine, eyeballs, and ovaries or testes.