A mouse dry eye model induced by topical administration of the air pollutant particulate matter 10

Impact of Airborne Exposure to PM10 Increases Susceptibility to P. aeruginosa Infection

The effects of exposure to airborne particulate matter with a size of 10 μm or less (PM10) on C57BL/6 mouse corneas, their response to Pseudomonas aeruginosa (PA) infection, and the protective effects of SKQ1 were determined. C57BL/6 mouse corneas receiving PBS or SKQ1 were exposed to control (air) or PM10 for 2 weeks, infected, and the disease was documented by clinical score, PMN quantitation, bacterial plate count, RT-PCR and Western blot. PBS-treated, PM10-exposed corneas did not differ at 1 day postinfection (dpi), but exhibited earlier (3 dpi) corneal thinning compared to controls. By 3 dpi, PM10 significantly increased corneal mRNA levels of several pro-inflammatory cytokines, but decreased IL-10, NQO1, GR1, GPX4, and Nrf2 over control. SKQ1 reversed these effects and Western blot selectively confirmed the RT-PCR results. PM10 resulted in higher viable bacterial plate counts at 1 and 3 dpi, but SKQ1 reduced them at 3 dpi. PM10 significantly increased MPO in the cornea at 3 dpi and was reduced by SKQ1. SKQ1, used as an adjunctive treatment to moxifloxacin, was not significantly different from moxifloxacin alone. Exposure to PM10 increased the susceptibility of C57BL/6 to PA infection; SKQ1 significantly reversed these effects, but was not effective as an adjunctive treatment.

Effect of Exposure to Particulate Matter on the Ocular Surface in an Experimental Allergic Eye Disease Mouse Model

In response to the escalating concern over the effect of environmental factors on ocular health, this study aimed to investigate the impact of air pollution-associated particulate matter (PM) on ocular allergy and inflammation. C57BL/6 mice were sensitized with ovalbumin (OVA) topically and aluminum hydroxide via intraperitoneal injection. Two weeks later, the mice were challenged with OVA and exposed to PM. Three groups-naive, OVA, and OVA-sensitized with PM exposure (OVA + PM) groups-were induced to an Allergic Eye disease (AED) model. Parameters including clinical signs, histological changes, inflammatory cell infiltration, serum OVA-specific immunoglobulins E (IgE) levels, mast cells degranulation, cellular apoptosis and T-cell cytokines were studied. The results demonstrate that exposure with PM significantly exacerbates ocular allergy, evidenced by increased eye-lid edema, mast cell degranulation, inflammatory cytokines (IL-4, IL-5 and TNF-α), cell proliferation (Ki67), and serum IgE, polymorphonuclear leukocytes (PMN), and apoptosis and reduced goblet cells. These findings elucidate the detrimental impact of PM exposure on exacerbating the severity of AED. Noticeably, diminished goblet cells highlight disruptions in ocular surface integrity, while increased PMN infiltration with an elevated production of IgE signifies a systemic allergic response with inflammation. In conclusion, this study not only scientifically substantiates the association between air pollution, specifically PM, and ocular health, but also underscores the urgency for further exploration and targeted interventions to mitigate the detrimental effects of environmental pollutants on ocular surfaces.

Mechanisms of PM10 Disruption of the Nrf2 Pathway in Cornea

We have previously shown that PM10 exposure causes oxidative stress and reduces Nrf2 protein levels, and SKQ1 pre-treatment protects against this damage in human corneal epithelial cells (HCE-2). The current study focuses on uncovering the mechanisms underlying acute PM10 toxicity and SKQ1-mediated protection. HCE-2 were pre-treated with SKQ1 and then exposed to 100 μg/mL PM10. Cell viability, oxidative stress markers, programmed cell death, DNA damage, senescence markers, and pro-inflammatory cytokines were analyzed. Nrf2 cellular location and its transcriptional activity were determined. Effects of the Nrf2 inhibitor ML385 were similarly evaluated. Data showed that PM10 decreased cell viability, Nrf2 transcriptional activity, and mRNA levels of antioxidant enzymes, but increased p-PI3K, p-NFκB, COX-2, and iNOS proteins levels. Additionally, PM10 exposure significantly increased DNA damage, phosphor-p53, p16 and p21 protein levels, and β-galactosidase (β-gal) staining, which confirmed the senescence. SKQ1 pre-treatment reversed these effects. ML385 lowered the Nrf2 protein levels and mRNA levels of its downstream targets. ML385 also abrogated the protective effects of SKQ1 against PM10 toxicity by preventing the restoration of cell viability and reduced oxidative stress. In conclusion, PM10 induces inflammation, reduces Nrf2 transcriptional activity, and causes DNA damage, leading to a senescence-like phenotype, which is prevented by SKQ1.

Consequences of exposure to particulate matter on the ocular surface: Mechanistic insights from cellular mechanisms to epidemiological findings

Exposure to air pollutants, especially in the case of particulate matter (PM), poses significant health risks throughout the body. The ocular surface is directly exposed to atmospheric PM making it challenging to avoid. This constant exposure makes the ocular surface a valuable model for investigating the impact of air pollutants on the eyes. This comprehensive review assembles evidence from across the spectrum, from in vitro and in vivo investigations to clinical studies and epidemiological studies, offering a thorough understanding of how PM10 and PM2.5 affect the health of the ocular surface. PM has been primarily found to induce inflammatory responses, allergic reactions, oxidative stress, DNA damage, mitochondrial impairment, and inhibit the proliferation and migration of ocular surface cells. In toto these effects ultimately lead to impaired wound healing and ocular surface damage. In addition, PM can alter tear composition. These events contribute to ocular diseases such as dry eye disease, blepharitis, conjunctivitis, keratitis, limbal stem cell deficiency and pterygium. Importantly, preexisting ocular conditions such as dry eye, allergic conjunctivitis, and infectious keratitis can be worsened by PM exposure. Adaptive responses may partially alleviate the mentioned insults, resulting in morphological and physiological changes that could be different between periods of short-term and long-term exposure. Particle size is not the only determinant of the ocular effect of PM, the composition and solubility of PM also play critical roles. Increasing awareness of how PM affects the ocular surface is crucial in the field of public health, and mechanistic insights of these adverse effects may provide guidelines for preventive and therapeutic strategies in dealing with a polluted environment.

Atmospheric pollutant black carbon induces ocular surface damage in mice

The threats of air pollution to human health have been gradually discovered, including its effects on eyes. The purpose of the study is to investigate the potential correlation between ocular surface exposure to black carbon and ocular surface structural damage as well as tear film dysfunction. To achieve this goal, 60 6-8-week-aged male BALB/C mice were randomly divided into 4 groups (n = 15). 0.5 mg/ml (group A), 1 mg/ml (group B), 5 mg/ml (group C) black carbon suspension droplets and PBS solution (group D) were used in the right eyes, 4 μl per time of three times per day. Tear break-up time, corneal fluorescein staining scores, and tear volume were assessed before treatment (day 0) and on days 4, 7, 10, and 14 after treatment. On day 14, the mice were sacrificed, and corneal and conjunctival tissues were collected for histological analysis. As the exposure time increased, there were no significant changes in the measured parameters from PBS-treated group of mice (P > 0.05). However, in the black carbon-treated group, there were significant decreases in tear film break-up time, significant increases in corneal fluorescein staining scores, and significant reductions in tear secretion (all P < 0.05). After 14 days, H&E staining of the corneal epithelium showed that in the PBS-treated group of mice, the corneal epithelial cells were neatly arranged, with no inflammatory cell infiltration, while in the black carbon-treated group, the corneal epithelium was significantly thickened, the basal cell arrangement was disrupted, the number of cell layers increased, and there was evidence of inflammatory cell infiltration. In the ultrastructure of the corneal epithelium, it could be observed that the black carbon-treated group had an increased amount of corneal epithelial cell detachment compared to the PBS-treated group, at the same time, the intercellular connections were looser, and there was a decrease in the number of microvilli and desmosomes in the black carbon-treated group. The results indicate that the ocular surface exposure to black carbon can result in a decrease in tear film stability and tear secretion in mice. Moreover, it can induce alterations in the corneal structure.

Urban Particulate Matter Triggers Meibomian Gland Dysfunction

Purpose

The meibomian gland (MG), as the largest modified sebaceous gland, is potentially damaged by urban particulate matter (UPM) based on epidemiological evidence, but the specific experimental mechanisms remain unknown. This study investigated the effects of UPM on MG dysfunction (MGD) in rodent models.

Methods

Female C57BL/6J mice received eye drops containing UPM suspension or PBS for 14 days. The proliferative capacity and progenitor of MG were evaluated by immunofluorescence. Cell apoptosis was confirmed by TUNEL assay, along with the analysis of caspase family expression. Lipid accumulation was visualized by Oil Red O staining and LipidTox staining. Ductal hyperkeratinization, neutrophil infiltration, and pyroptosis activation were detected through immunostaining. The relative gene expression and signaling pathway activation were determined by Western blot analysis.

Results

Administration of UPM caused MGD-like clinical signs, manifested as distinct corneal epithelial erosion, increased MG orifice occlusion, and glandular dropout. UPM exposure significantly induced progenitor loss, cellular apoptosis, and lipogenic disorder in MG, by reducing P63/Lrig1 expression and increasing cleaved caspase-8, -9, and -3 and meibum lipogenic protein (HMGCR/SREBP-1) expression. UPM-treated mice exhibited ductal hyperkeratinization and neutrophil recruitment. Simultaneously, pyroptosis was motivated, as indicated by the heightened expression of NLRP3 and the cleavage of caspase-1 and -4 and gasdermin D, as well as the increase in IL-1β and IL-18 downstream. The underlying pathological mechanisms of UPM involve the phosphorylation of mitogen-activated protein kinase and nuclear factor-κB.

Conclusions

These results provided direct evidence for the toxicity of UPM in MG. UPM-induced activation of pyroptosis and mitogen-activated protein kinase/nuclear factor-κB signaling pathway might account for the inflammatory MGD.

Particulate matter-mediated oxidative stress induces airway inflammation and pulmonary dysfunction through TXNIP/NF-κB and modulation of the SIRT1-mediated p53 and TGF-β/Smad3 pathways in mice

Exposure to particulate matter is currently recognized as a serious aggravating factor of respiratory diseases. In this study, we investigated the effects of particulate matter (PM) on the respiratory system in BALB/c mice and NCI-H292 cells. PM (0, 2.5, 5 and 20 mg/kg) was administered to mice by intra-tracheal instillation for 7 days. After a 7 day-repeated treatment of PM, we evaluated inflammatory cytokines/cell counts in bronchoalveolar lavage fluid (BALF) and conducted pulmonary histology and functional test. We also investigated the role of TXNIP/NF-κB and SIRT1-mediated p53 and TGF-β/Smad3 pathways in PM-induced airway inflammation and pulmonary dysfunction. PM caused a significant increase in pro-inflammatory cytokines, inflammatory cell counts in bronchoalveolar lavage fluid. PM-mediated oxidative stress down-regulated thioredoxin-1 and up-regulated thioredoxin-interacting protein and activation of nuclear factor-kappa B in the lung tissue and PM-treated NCI-H292 cells. PM suppressed sirtuin1 protein levels and increased p53 acetylation in PM-exposed mice and PM-treated NCI-H292 cells. In addition, PM caused inflammatory cell infiltration and the thickening of alveolar walls by exacerbating the inflammatory response in the lung tissue. PM increased levels of transforming growth factor-β, phosphorylation of Smad3 and activation of α-smooth muscle actin, and collagen type1A2 in PM-exposed mice and PM-treated NCI-H292 cells. In pulmonary function tests, PM exposure impaired pulmonary function resembling pulmonary fibrosis, characterized by increased resistance and elastance of the respiratory system, and resistance, elastance, and damping of lung tissues, whereas decreased compliance of the respiratory system, forced expired volume and forced vital capacity. Overall, PM-mediated oxidative stress caused airway inflammation and pulmonary dysfunction with pulmonary fibrosis via TXNIP pathway/NF-κB activation and modulation of the SIRT1-mediated TGF-β/Smad3 pathways. The results of this study can provide fundamental data on the potential adverse effects and underlying mechanism of pulmonary fibrosis caused by PM exposure as a public health concern. Due to the potential toxicity of PM, people with respiratory disease must be careful with PM exposure.

Heavy metal deposition and parameter change of soft contact lenses by exposure to particulate matter : Parameter change of SCL due to exposure to PM and heavy metal deposition

BACKGROUND

Particulate matter (PM) is known to contain heavy metals and be harmful to the tissues and organs of the human body including the eyes. As such, in this study, the deposition of heavy metals from PM on soft contact lenses was examined, and changes in the lens parameters were further investigated.

METHODS

Six types of soft contact lenses were exposed to captured PM10 for eight hours. The central thickness, water content, refractive power, and oxygen transmissibility of each contact lens were measured after analyzing the amounts of six heavy metals adsorbed on the contact lenses.

RESULTS

Lead, manganese, barium, arsenic, vanadium, and cadmium were detected in the captured PM, and only lead was adsorbed on all soft contact lenses except senofilcon C. The largest deposition was 23.21 ± 0.70 (10- 3)µg/lens of the lead on lotrafilcon B. The oxygen transmissibility of nelfilcon A exhibited statistically significant changes, however, it was within the ISO standard tolerance. Nevertheless, changes in the central thickness, water content, and refractive power of each soft contact lens were not statistically significant.

CONCLUSIONS

This study revealed that a considerable amount of lead in PM10 was adsorbed on soft contact lenses. Amongst lens parameters, only oxygen transmissibility changed significantly. Thus, wearing soft contact lenses under high PM10 concentration might affect the physiology of the eyes.

PM10 and Pseudomonas aeruginosa: effects on corneal epithelium

Purpose

In vivo data indicate that mouse corneas exposed to PM10 showed early perforation and thinning after infection with Pseudomonas aeruginosa. To understand the mechanisms underlying this finding, we tested the effects of PM10 and the mitochondria targeted anti-oxidant SKQ1 in immortalized human corneal epithelial cells (HCET) that were challenged with Pseudomonas aeruginosa strain 19660.

Methods

Mouse corneas were infected with strain 19660 after a 2 week whole-body exposure to PM10 or control air and assessed by clinical scores, slit lamp photography and western blot. HCET were exposed to 100μg/ml PM10 for 24h before challenge with strain 19660 (MOI 20). A subset of cells were pre-treated with 50nM SKQ1 for 1h before PM10 exposure. Phase contrast microscopy was used to study cell morphology, cell viability was measured by an MTT assay, and ROS by DCFH-DA. Levels of pro-inflammatory markers and anti-oxidant enzymes were evaluated by RT-PCR, western blot and ELISA. Reduced glutathione (GSH) and malondialdehyde (MDA) levels were evaluated by assay kits.

Results

In vivo, whole body exposure to PM10 vs. control air exposed mouse corneas showed early perforation and/or corneal thinning at 3 days post infection, accompanied by increased TNF-α and decreased SOD2 protein levels. In vitro, PM10 induced a dose dependent reduction in cell viability of HCET and significantly increased mRNA levels of pro-inflammatory molecules compared to control. Exposure to PM10 before bacterial challenge further amplified the reduction in cell viability and GSH levels. Furthermore, PM10 exposure also exacerbated the increase in MDA and ROS levels and phase contrast microscopy revealed more rounded cells after strain 19660 challenge. PM10 exposure also further increased the mRNA and protein levels of pro-inflammatory molecules, while anti-inflammatory IL-10 was decreased. SKQ1 reversed the rounded cell morphology observed by phase contrast microscopy, increased levels of MDA, ROS and pro-inflammatory molecules, and restored IL-10.

Conclusions

PM10 induces decreased cell viability, oxidative stress and inflammation in HCET and has an additive effect upon bacterial challenge. SKQ1 protects against oxidative stress and inflammation induced by PM10 after bacterial challenge by reversing these effects. The findings provide insight into mechanisms underlying early perforation and thinning observed in infected corneas of PM10 exposed mice.

The miR-183/96/182 cluster is a checkpoint for resident immune cells and shapes the cellular landscape of the cornea

PURPOSE

The conserved miR-183/96/182 cluster (miR-183C) regulates both corneal sensory innervation and corneal resident immune cells (CRICs). This study is to uncover its role in CRICs and in shaping the corneal cellular landscape at a single-cell (sc) level.

METHODS

Corneas of naïve, young adult [2 and 6 months old (mo)], female miR-183C knockout (KO) mice and wild-type (WT) littermates were harvested and dissociated into single cells. Dead cells were removed using a Dead Cell Removal kit. CD45+ CRICs were enriched by Magnetic Activated Cell Sorting (MACS). scRNA libraries were constructed and sequenced followed by comprehensive bioinformatic analyses.

RESULTS

The composition of major cell types of the cornea stays relatively stable in WT mice from 2 to 6 mo, however the compositions of subtypes of corneal cells shift with age. Inactivation of miR-183C disrupts the stability of the major cell-type composition and age-related transcriptomic shifts of subtypes of corneal cells. The diversity of CRICs is enhanced with age. Naïve mouse cornea contains previously-unrecognized resident fibrocytes and neutrophils. Resident macrophages (ResMφ) adopt cornea-specific function by expressing abundant extracellular matrix (ECM) and ECM organization-related genes. Naïve cornea is endowed with partially-differentiated proliferative ResMφ and contains microglia-like Mφ. Resident lymphocytes, including innate lymphoid cells (ILCs), NKT and γδT cells, are the major source of innate IL-17a. miR-183C limits the diversity and polarity of ResMφ.

CONCLUSION

miR-183C serves as a checkpoint for CRICs and imposes a global regulation of the cellular landscape of the cornea.

The impact of particulate matters on apoptosis in various organs: Mechanistic and therapeutic perspectives

Ecological air contamination is the non-homogenous suspension of insoluble particles into gas or/and liquid fluids known as particulate matter (PM). It has been discovered that exposure to PM can cause serious cellular defects, followed by tissue damage known as cellular stress. Apoptosis is a homeostatic and regulated phenomenon associated with distinguished physiological actions inclusive of organ and tissue generation, aging, and development. Moreover, it has been proposed that the deregulation of apoptotic performs an active role in the occurrence of many disorders, such as autoimmune disease, neurodegenerative, and malignant, in the human population. Recent studies have shown that PMs mainly modulate multiple signaling pathways involved in apoptosis, including MAPK, PI3K/Akt, JAK/STAT, NFκB, Endoplasmic Stress, and ATM/P53, leading to apoptosis dysregulation and apoptosis-related pathological conditions. Here, the recently published data concerning the effect of PM on the apoptosis of various organs, with a particular focus on the importance of apoptosis as a component in PM-induced toxicity and human disease development, is carefully discussed. Moreover, the review also highlighted the various therapeutic approaches, including small molecules, miRNA replacement therapy, vitamins, and PDRN, for treating diseases caused by PM toxicity. Notably, researchers have considered medicinal herbs a potential treatment for PM-induced toxicity due to their fewer side effects. So, in the final section, we analyzed the performance of some natural products for inhibition and intervention of apoptosis arising from PM-induced toxicity.

The environment and dry eye-manifestations, mechanisms, and more

Dry eye disease (DED) is a multifactorial condition that often presents with chronic symptoms of pain (that can be characterized as "dryness," "burning," and "irritation," to name a few) and/or fluctuating or poor-quality vision. Given its multifactorial nature, several pathophysiologic mechanisms have been identified that can underlie symptoms, including tear film, ocular surface, and/or corneal somatosensory nerve abnormalities. Research has focused on understanding how environmental exposures can increase the risk for DED flares and negatively impact the tear film, the ocular surface, and/or nerve health. Given that DED is a common condition that negatively impacts physical and mental functioning, managing DED requires multiple strategies. These can include both medical approaches and modulating adverse environmental conditions, the latter of which may be a cost-effective way to avoid DED flares. Thus, an understanding of how environmental exposures relate to disease is important. This Review summarizes research on the relationships between environmental exposures and DED, in the hope that this information will engage healthcare professionals and patients to consider environmental manipulations in their management of DED.

Isolation and Identification of a Novel Anti-Dry Eye Peptide from Tilapia Skin Peptides Based on In Silico, In Vitro, and In Vivo Approaches

Tilapia skin is a great source of collagen. Here, we aimed to isolate and identify the peptides responsible for combating dry eye disease (DED) in tilapia skin peptides (TSP). In vitro cell DED model was used to screen anti-DED peptides from TSP via Sephadex G-25 chromatography, LC/MS/MS, and in silico methods. The anti-DED activity of the screened peptide was further verified in the mice DED model. TSP was divided into five fractions (TSP-I, TSP-II, TSP-III, TSP-IV, and TSP-V), and TSP-II exerted an effective effect for anti-DED. A total of 131 peptides were identified using LC/MS/MS in TSP-II, and NGGPSGPR (NGG) was screened as a potential anti-DED fragment in TSP-II via in silico methods. In vitro, NGG restored cell viability and inhibited the expression level of Cyclooxygenase-2 (COX-2) protein in Human corneal epithelial cells (HCECs) induced by NaCl. In vivo, NGG increased tear production, decreased tear ferning score, prevented corneal epithelial thinning, alleviated conjunctival goblet cell loss, and inhibited the apoptosis of corneal epithelial cells in DED mice. Overall, NGG, as an anti-DED peptide, was successfully identified from TSP, and it may be devoted to functional food ingredients or medicine for DED.

Airborne Exposure of the Cornea to PM10 Induces Oxidative Stress and Disrupts Nrf2 Mediated Anti-Oxidant Defenses

The purpose of this study is to test the effects of whole-body animal exposure to airborne particulate matter (PM) with an aerodynamic diameter of <10 μm (PM10) in the mouse cornea and in vitro. C57BL/6 mice were exposed to control or 500 µg/m3 PM10 for 2 weeks. In vivo, reduced glutathione (GSH) and malondialdehyde (MDA) were analyzed. RT-PCR and ELISA evaluated levels of nuclear factor erythroid 2-related factor 2 (Nrf2) signaling and inflammatory markers. SKQ1, a novel mitochondrial antioxidant, was applied topically and GSH, MDA and Nrf2 levels were tested. In vitro, cells were treated with PM10 ± SKQ1 and cell viability, MDA, mitochondrial ROS, ATP and Nrf2 protein were tested. In vivo, PM10 vs. control exposure significantly reduced GSH, corneal thickness and increased MDA levels. PM10-exposed corneas showed significantly higher mRNA levels for downstream targets, pro-inflammatory molecules and reduced Nrf2 protein. In PM10-exposed corneas, SKQ1 restored GSH and Nrf2 levels and lowered MDA. In vitro, PM10 reduced cell viability, Nrf2 protein, and ATP, and increased MDA, and mitochondrial ROS; while SKQ1 reversed these effects. Whole-body PM10 exposure triggers oxidative stress, disrupting the Nrf2 pathway. SKQ1 reverses these deleterious effects in vivo and in vitro, suggesting applicability to humans.

Influence of Light-EmittingDiode-Derived Blue Light Overexposure on Rat Ocular Surface

We aim to investigate the effect of overexposure to blue light on the rat ocular surface and explore the potential mechanisms. 450 nm light-emitting diode (LED) derived light at 1000 lux was used to irradiate SD rats, 12 hours a day, for consecutive 28 days. Rats in the control group were exposed to 400 lux white light at the same time (in an indoor environment). Tear film breakup time (TBUT), tear volume, and corneal fluorescein staining scores were used to measure the changes to the ocular surface. Expressions of nuclear factor-κB (NF-κB), inhibitor-κB (I-κB), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α) were measured by real-time PCR, and the activation of the NF-κB pathway was detected by Western blotting, respectively. Cornea ultrastructure was examined by TEM and optical microscope on day 28. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of NF-κB signaling pathway, was used to measure the inhibition of blue light injury. The above indexes were detected again when compared with the solvent-treated group. On day 28, compared with day 0, the TBUT of the blue light group was significantly shorter, and the score was significantly higher. The amount of tear secretion changed slightly with time. HE and PAS staining revealed significantly decreased corneal epithelial cell layers and increased goblet cells after 28-day irradiation of blue light. Disarranged stromal cells, vacuoles in the basal nuclei, and decreased desmosomes were also found in the blue light group. Significantly increased levels of NF-κB, IL-6, TNF-α, and the ratio of phosphorylated NF-κB p65 (pNF-κB p65) to total NF-κB p65 implied blue light-induced damage and pathway activation. In addition, PDTC significantly reduced the phosphorylation of NF-κB activated in blue light-treated corneas and alleviated the ocular surface changes caused by blue light. Finally, our results demonstrated that long-term blue light exposure in rats could cause ocular surface changes and manifest as dry eye. Inflammation and activation of the NF-κB pathway may play a role in the pathogenesis.

The Extracts of Dendrobium Alleviate Dry Eye Disease in Rat Model by Regulating Aquaporin Expression and MAPKs/NF-κB Signalling

Dry eye is one of the most common ocular surface diseases caused by tear film instability and ocular surface damage due to an abnormal quality or quantity of tears. Inflammatory factors can initiate relevant transduction signalling pathways and trigger the inflammatory cascade response, resulting in ocular surface inflammation. It has been shown that the active ingredients in Dendrobium, such as polysaccharides, alkaloids and phenols, have anti-inflammatory, anti-tumour and immunity-boosting effects, and Dendrobium officinale extract can improve glandular secretion function, increase salivary secretion and increase the expression level of water channel protein in salivary glands in patients with dry eye syndromes. We investigated the in vitro cytoprotective effect of Dendrobium extracts in sodium chloride induced hyperosmotic conditions in human cornea keratocytes (HKs). Results showed that Dendrobium officinale Kimura et Migo water extract (DOW) and Dendrobium loddigesii Rolfe water extract (DLW) could upregulate the expression of aquaporins (AQP)5 protein, thus exerting a repairing effect by promoting cell migration. Furthermore, oral administration of DOW and DLW enhanced tear production in rats and exerted a protective effect on ocular surface damage. DOW and DLW could upregulate the expression of AQP5 and mucin (muc)5ac proteins in the lacrimal gland and reduce the inflammatory response. DOW and DLW inhibited the activation of the corresponding mitogen-activated protein kinases (MAPK) and NF-KB pathway, thereby playing a role in improving dry eye symptoms. This study provides a new perspective on dry eye treatment, and DOW and DLW may be potential therapeutic agents for dry eye.

Particulate matter 2.5 promotes inflammation and cellular dysfunction via reactive oxygen species/p38 MAPK pathway in primary rat corneal epithelial cells

PURPOSE

Numerous studies have linked particulate matter 2.5 (PM_2.5) to ocular surface diseases, but few studies have been conducted on the biological effect of PM_2.5 on the cornea. The objective of the present study was to evaluate the harmful effect of PM2.5 on primary rat corneal epithelial cells (RCECs) in vitro and identify the toxic mechanism involved.

MATERIALS AND METHODS

Primary cultured RCECs were characterized by pan-cytokeratin (CK) staining. In PM2.5-exposed RCECs, cell viability, microarray gene expression, inflammatory cytokine levels, mitochondrial damage, DNA double-strand break and signaling pathway were investigated.

RESULTS

Exposure to PM_2.5 induced cytotoxicity and morphological changes in RCECs. In addition, PM_2.5 markedly up-regulated pro-inflammatory mediators but down-regulated the wound healing-related transforming growth factor-β. Furthermore, PM_2.5 promoted mitochondrial reactive oxygen species (ROS) production and mediated cellular damage to mitochondria and DNA, whereas these cellular alterations induced by PM_2.5 were markedly suppressed by a potential ROS scavenger. Noteworthy, removal of ROS selectively down-regulated the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and the activation of the nuclear factor-κB (NF-κB) p65 in PM_2.5-stimulated cells. Additionally, SB203580, a p38 MAPK inhibitor, markedly suppressed these PM_2.5-mediated cellular dysfunctions.

CONCLUSIONS

Taken together, our findings show that PM_2.5 can promote the ROS/p38 MAPK/NF-κB signaling pathway and lead to mitochondrial damage and DNA double-strand break, which is ultimately caused inflammation and cytotoxicity in RCECs. These findings indicate that the ROS/p38 MAPK/NF-κB signaling pathway is one mechanism involved in PM_2.5-induced ocular surface disorders.

SIRT1 Protects Against Particulate Matter-Induced Oxidative Stress in Human Corneal and Conjunctival Epithelial Cells

Purpose

Sirtuin1 (SIRT1) as a hot therapeutic target for oxidative stress–associated diseases that has been extensively studied. This study aimed to determine the changes in SIRT1 expression in particulate matter (PM)–induced corneal and conjunctival epithelial cell damage and explore potential drugs to reduce PM-associated ocular surface injury.

Methods

Immortalized human corneal epithelial cells (HCECs) and human conjunctival epithelial cells (HCjECs) were exposed to an ambient PM sample. Cytotoxicity was evaluated by water-soluble tetrazolium salt–8 assay. SIRT1 expression was measured by Western blot analysis. Reactive oxygen species (ROS) production, cell apoptosis, mitochondrial function, and cell senescence were assessed by using 2ʹ,7ʹ-dichlorofluorescein diacetate assay, annexin V apoptosis assay, tetramethylrhodamine ethyl ester assay, and senescence β-galactosidase staining, respectively.

Results

PM-induced cytotoxicity of HCECs and HCjECs occurred in a dose-dependent manner. Increased ROS production, as well as decreased SIRT1 expression, were observed in HCECs and HCjECs after 200 µg/mL PM exposure. In addition, PM induced oxidative stress-mediated cellular damage, including cell apoptosis, mitochondrial damage, and cell senescence. Interestingly, SRT1720, a SIRT1 activator, increased SIRT1 expression and decreased ROS production and attenuated PM-induced cell damage in HCECs and HCjECs.

Conclusions

This study determined that SIRT1 was involved in PM-induced oxidative stress in HCECs and HCjECs and found that ROS overproduction may a key factor in PM-induced SIRT1 downregulation. The SIRT1 activator, SRT1720, can effectively upregulate SIRT1 expression and inhibit ROS production, thereby reversing PM-induced cell damage. This study provides a new potential target for clinical treatment of PM-associated ocular surface diseases.

Impact of Air Pollution on the Ocular Surface and Tear Cytokine Levels: A Multicenter Prospective Cohort Study

Purpose

To assess air pollution-induced changes on ocular surface and tear cytokine levels.

Methods

As a prospective multicenter cohort study, 387 dry eye disease (DED) participants were recruited from five provinces in China and underwent measurements of ocular surface disease index (OSDI), Schirmer’s I test (ST), tear meniscus height (TMH), tear film break-up time (TBUT), corneal fluorescein staining (CFS), meibomian gland (MG) function, and tear cytokines. The associations between ocular surface parameters and exposure to particulate matter (PM), ozone (O₃), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) for 1 day, 1 week, and 1 month before the examination were analyzed in single- and multi-pollutant models adjusted for confounding factors.

Results

In the multi-pollutant model, the OSDI score was positively correlated with PM with diameter ≤2.5 μm (PM_2.5), O₃, and SO₂ exposure [PM_2.5: β (1 week/month) = 0.229 (95% confidence interval (CI): 0.035–0.424)/0.211 (95% CI: 0.160–0.583); O₃: β (1 day/week/month) = 0.403 (95% CI: 0.229–0.523)/0.471 (95% CI: 0.252–0.693)/0.468 (95% CI: 0.215–0.732); SO₂: β (1 day/week) = 0.437 (95% CI: 0.193–0.680)/0.470 (95% CI: 0.040–0.901)]. Tear secretion was negatively correlated with O₃ and NO₂ exposures but positively correlated with PM_2.5 levels. Air pollutants were negatively correlated with TBUT and positively related with CFS score. Besides SO₂, all other pollutants were associated with aggravated MG dysfunction (MG expression, secretion, and loss) and tear cytokines increasement, such as PM_2.5 and interleukin-8 (IL-8) [β (1 day) = 0.016 (95% CI: 0.003–0.029)], PM with diameter ≤10 μm (PM₁₀) and IL-6 [β (1 day) = 0.019 (95% CI: 0.006–0.033)], NO₂ and IL-6 [β (1 month) = 0.045 (95% CI: 0.018–0.072)], among others. The effects of air pollutants on DED symptoms/signs, MG functions and tear cytokines peaked within 1 week, 1 month, and 1 day, respectively.

Conclusion

Increased PM_2.5, O₃, and SO₂ exposures caused ocular discomfort and damage with tear film instability. PM₁₀ exposure led to tear film instability and ocular injury. PM, O₃, and NO₂ exposures aggravated MG dysfunction and upregulated tear cytokine levels. Therefore, each air pollutant may influence DED via different mechanisms within different time windows.

Effect of Aucubin-Containing Eye Drops on Tear Hyposecretion and Lacrimal Gland Damage Induced by Urban Particulate Matter in Rats

Exposure to particulate matter is a causative factor of dry eye disease. We aimed to investigate the beneficial effect of eye drops containing aucubin on dry eye disease induced by urban particulate matter (UPM). Dry eye was induced in male SD rats (6 weeks old) by topical exposure to UPM thrice a day for 5 d. Eye drops containing 0.1% aucubin or 0.5% aucubin were topically administered directly into the eye after UPM exposure for an additional 5 d. Tear secretion was evaluated using a phenol red thread tear test and corneal irregularity. The oxidative damage in the lacrimal gland was evaluated using TUNEL and immunohistochemical staining. The topical administration of aucubin significantly attenuated UPM-induced tear hyposecretion (control group: 9.25 ± 0.62 mm, UPM group: 4.55 ± 0.25 mm, 0.1% aucubin: 7.12 ± 0.58 mm, and 0.5% aucubin: 7.88 ± 0.75 mm) and corneal irregularity (control group: 0.00 ± 0.00, UPM group: 3.40 ± 0.29, 0.1% aucubin: 1.80 ± 0.27, and 0.5% aucubin: 1.15 ± 0.27). In addition, aucubin also reduced the UPM-induced apoptotic injury of lacrimal gland cells induced by oxidative stress through the increased expression of HMGB1 and RAGE. These findings indicate that the topical administration of aucubin eye drops showed a beneficial effect against UPM-induced abnormal ocular changes, such as tear hyposecretion and lacrimal gland damage. Therefore, our results reveal the pharmacological activities of aucubin in dry eye disease.

The effects of short-term and long-term air pollution exposure on meibomian gland dysfunction

We aim to assess the effects of different air pollutants on meibomian gland dysfunction (MGD). As a prospective multicenter study, 864 patients were recruited from four different regions (i.e., coal, oil, steel, and living). The oil region had a significantly lower temperature and higher O₃ and SO₂ concentrations than other regions. Notably, participants in oil region presented with more frequent and serious MGD signs and higher cytokine levels (median interleukin 6 [IL-6] in oil: 2.66, steel: 0.96, coal: 0.38, living: 0.56; IL-8 in oil: 117.52, steel: 46.94, coal: 26.89, living: 33; vascular endothelial growth factor [VEGF] in oil: 25.09, steel: 14.02, coal: 14.02, living: 28.47). The short-term fluctuations of cytokine levels were associated with the changes in gas levels (PM_2.5 and IL-8: β = 0.016 [0.004–0.029]; O₃ and IL-6: β = 0.576 [0.386–0.702]; O₃ and IL-8: β = 0.479 [0.369–0.890]; SO₂ and VEGF: β = 0.021 [0.001–0.047]). After long-term exposure, lid margin neovascularization (r = 0.402), meibomian gland (MG) expression (r = 0.377), MG secretion (r = 0.303), MG loss (r = 0.404), and tear meniscus height (r = − 0.345) were moderately correlated with air quality index (AQI). Individuals in oil region had more serious MGD signs and higher cytokine levels. MGD is susceptible to long-term exposure to high AQI.

Topical Porphyrin Antioxidant Protects Against Ocular Surface Pathology in a Novel Rabbit Model for Particulate Matter-Induced Dry Eye Disease

Purpose: Particulate matter (PM) is a primary cause for the development of acute and chronic dry eye disease, especially irritant-induced conjunctivitis. The purpose of the present study was to determine the effects of fine atmospheric PM on the rabbit ocular surface, and determine the protective effects of a synthetic antioxidant, manganese(III) tetrakis(1-methyl-4-pyridyl) porphyrin (Mn-TM-2-PyP), in vitro and in vivo. Methods: Rabbit corneal epithelial cells (SIRC) were exposed to increasing concentrations of PM to determine the effects on cell motility and viability. The in vivo effects of topically instilled PM were tested in New Zealand White rabbits. Comprehensive ophthalmic exams and corneal fluorescein staining were performed. Results: Exposure to PM resulted in dose-dependent cell death and impaired cellular motility; Mn-TM-2-PyP protected against PM-induced cytotoxicity and significantly increased SIRC cell motility. In vivo, exposure to PM (5 mg/ml, topical, 3 times daily for 7 days) resulted in signs of dry eye, notably hyperemia, increased corneal fluorescein staining, and decreased tear volumes. Mn-TM-2-PyP significantly improved hyperemia and corneal fluorescein readouts but had no effect on tear production. Lifitegrast (Xiidra^®) showed similar pharmacologic efficacy to Mn-TM-2-PyP. Conclusion: Overall, these data provide evidence that PM induces phenotypes of ocular surface disease responsive to antioxidant and immunosuppressant therapy. To our knowledge this is the first report of a large animal model to study PM-induced ocular surface disease. The present work provides standardized experimental paradigms for the comprehensive in vitro and in vivo testing of novel therapeutic approaches targeting PM-induced conjunctivitis and dry-eye.

Necroptosis Contributes to Airborne Particulate Matter-Induced Ocular Surface Injury

In this study, we explored the role of necroptosis in the pathogenesis of ocular surface injury caused by airborne particulate matter (PM). Human corneal epithelial (HCE) cells and mouse ocular surface were treated with PM exposure and compared with non-exposed groups. The expression of necroptosis-related proteins was measured by immunoblotting in HCE cell groups. Cell damages were detected using CCK-8, flow cytometry, and immunofluorescence staining. In the mouse model, hematoxylin and eosin (H&E) staining and corneal fluorescein sodium staining were assessed. In addition, the expression of inflammatory cytokines and mucin were examined via Enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining and/or quantitative RT -PCR (qRT-PCR), both in vitro and in vivo. Our research showed that PM exposure may trigger HCE cell damage via necroptosis. Necrostatin-1(Nec-1), one of the specific inhibitors of necroptosis, can markedly reduce PM-induced HCE cell damage. HCE cell damage markers included decreased cell viability, increased intracellular reactive oxygen species (ROS) levels, and loss of mitochondrial membrane potential. At the same time, Nec-1 inhibited the increased inflammatory cytokines and the decreased mucin expression caused by PM exposure in HCE cells. Nec-1 also reduced corneal inflammation and mucin underproduction in mouse ocular surface after PM exposure. Our study demonstrated that necroptosis is involved in the pathogenesis of PM exposure-related ocular surface injury, including inflammation and insufficient mucin production in the cornea, which can be rescued by inhibitor Nec-1. This suggests Nec-1 could be a novel therapeutic target for ocular surface disorders, especially dry eye disease, which is caused by the exacerbation of airborne PM pollution.

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

Saponins of Korean Red Ginseng May Protect Human Skin from Adipokine-Associated Inflammation and Pigmentation Resulting from Particulate Matter Exposure

Background: Exposure to airborne particulate matter (PM) is an ever-increasing concern worldwide. Strategies to counter the detrimental effects that follow cutaneous exposure to PM, such as induction of pigmentation, inflammation, and alterations in adipokine profile, need to be investigated further. Korean red ginseng (KRG) extracts and individual ingredients have been demonstrated to play an effective role in suppression of ROS, inflammation, and resultant skin aging. In addition, recent investigations revealed that Rg3 and Rf saponins work as antimelanogenic agents. In this study, we investigated whether saponins of KRG can protect against or reverse the PM-induced detrimental effects. Methods: The biological effects of PM and saponins were evaluated both in vitro and ex vivo. Cell viability and intracellular ROS levels were determined in normal human epidermal melanocytes (NHMs), human epidermal keratinocytes (NHKs), and their cocultures. Experiments to demonstrate the protective properties of saponins against consequences of exposure to PM were performed. Melanin assay, quantitative real-time PCR, and Western blotting were carried out to determine the effects on melanogenesis and the implicated molecular signaling pathways. Results: Exposure to PM resulted in decreased keratinocyte viability, which was coupled with augmented oxidative stress. These changes were attenuated by treatment with saponins. PM exposure resulted in increased expression of leptin, which was reduced by saponins. Moreover, PM exposure led to increased melanin production in a coculture model, which was mitigated by treatment with saponins. Treatment with saponins resulted in a decrease in matrix metalloproteinase (MMP) levels after exposure to PM. Conclusion: Saponins of KRG can protect the skin from the harmful effects of PM exposure by reducing levels of ROS, leptin, inflammatory cytokines, and melanin.

A Novel Rat Model of Dry Eye Induced by Aerosol Exposure of Particulate Matter

Purpose

The purpose of this study was to introduce a novel dry eye rat model induced by aerosol exposure of particulate matter (PM).

Methods

A total of 30 female Sprague Dawley (SD) rats divided into 3 groups: the control group, the low-level exposed group, and the high-level exposed group. The rats in the experience groups were directly exposed to PM samples in the exposure chamber over 14 days. The clinical observation, including tear volume, corneal fluorescein staining, breakup time (BUT), inflammation index, corneal irregularity score, and corneal confocal microscopy. Eyeballs were collected on day 14 for hematoxylin and eosin (H&E) staining and PAS staining. TUNEL assay, CD45, and Ki67 immunostaining was performed and corneal ultrastructural changes were detected by electron microscopy. IL-1β, TNF-α, IFN-γ, and NF-κB Western blot analysis were used to observe the possible pathogenesis.

Results

In the PM-treated groups, the number of layers in the corneal epithelium and corneal nerve fiber length were significantly decreased compared with that of the control group. The number of corneal epithelial microvilli and chondriosome/desmosomes were drastically reduced in PM-treated groups. Confocal microscopy and CD45 immunohistochemistry showed inflammatory cell infiltration in the PM-treated groups. PM caused apoptosis of corneal and conjunctival epithelial cells while leading to abnormal epithelial cell proliferation, meanwhile, conjunctival goblet cells in the PM-treated group were also significantly reduced. PM significantly increased the levels of IL-1β, TNF-α, IFN-γ, and p-NF-κB-p65 in the cornea.

Conclusions

Aerosol exposure of PM can reduce the stability of tear film and cause the change of ocular surface, which is similar to the performance of human dry eye, suggesting a novel animal model of dry eye.

Experimental Models, Induction Protocols, and Measured Parameters in Dry Eye Disease: Focusing on Practical Implications for Experimental Research

Dry eye disease (DED) is one of the major ophthalmological healthcare challenges worldwide. DED is a multifactorial disease characterized by a loss of homeostasis of the tear film, and its main pathogenesis is chronic ocular surface inflammation related with various cellular and molecular signaling cascades. The animal model is a reliable and effective tool for understanding the various pathological mechanisms and molecular cascades in DED. Considerable experimental research has focused on developing new strategies for the prevention and treatment of DED. Several experimental models of DED have been developed, and different animal species such as rats, mice, rabbits, dogs, and primates have been used for these models. Although the basic mechanisms of DED in animals are nearly identical to those in humans, proper knowledge about the induction of animal models is necessary to obtain better and more reliable results. Various experimental models (in vitro and in vivo DED models) were briefly discussed in this review, along with pathologic features, analytical approaches, and common measurements, which will help investigators to use the appropriate cell lines, animal, methods, and evaluation parameters depending on their study design.

Peucedanum japonicum Thunberg and Its Active Components Mitigate Oxidative Stress, Inflammation and Apoptosis after Urban Particulate Matter-Induced Ocular Surface Damage

We previously demonstrated that urban particulate matter (UPM) exposure decreases the migration activity and survival of human corneal epithelial cells (HCECs). Herein, we investigated the potential to improve the corneal wound-healing ability of Peucedanum japonicum Thunb. leaf extract (PJE) and its active components on UPM-induced ocular surface damage in vitro and in vivo. PJE effectively assisted wound healing without altering HCEC survival and enhanced catalase (CAT), heme oxygenase 1 (HO1) and glutathione peroxidase 1 (GPX1) antioxidant gene expression. A corneal wound was uniformly induced on the right eye in all experimental animals and divided into eight groups such as two control groups (wounded right eye group-NR and non-wounded left eye group-NL), UPM treated group and PJEs (25, 50, 100, 200, 400 mg/kg) treated groups. Corneal abrasion model rats exposed to UPM showed delayed wound healing compared to unexposed rats, but wound healing was dose-dependently enhanced by PJE oral administration. Seventy-two hours after wound generation, inflammatory cells, apoptotic cells and interleukin-6 (IL-6) expression were increased substantially after UPM exposure, but PJE treatment significantly reduced the wound to an almost normal level while enhancing re-epithelialization without changing corneal thickness. Next, we tried to identify the key molecules for enhancing wound healing through fractionation. The major compounds in the fraction, confirmed by high-performance liquid chromatography (HPLC), were chlorogenic acid (CA), neochlorogenic acid (NCA) and cryptochlorogenic acid (CCA). Each type of CA isomers showed slightly different half maximal effective (EC50) and maximal effective (ECmax) concentrations, and their mixtures synergistically enhanced HCEC migration. Thus, corneal abrasion wound recovery after UPM exposure improved after PJE treatment, and the active PJE components were identified, providing an important basis to develop therapeutics for ocular surface damage using PJE.

Phenotypic and transcriptomic changes in the corneal epithelium following exposure to cigarette smoke

Cigarette smoke extract (CSE), a complex mixture of compounds, contributes to a range of eye diseases; however, the underlying pathophysiological responses to tobacco smoke remain ambiguous. The purpose of the present study was to evaluate the cigarette smoke-induced phenotypic and transcriptomic changes in the corneal epithelium with a view to elucidating the likely underlying mechanism. Accordingly, for the first time, we characterized the genome-wide effects of CSE on the corneal epithelium. The ocular surface of the mice in the experimental groups was exposed to CSE for 1 h per day for a period of one week, while mice in the control group were exposed to preservative-free artificial tears. Corneal fluorescein staining, in vivo confocal microscopy and scanning electron microscopy were performed to examine the corneal ultrastructure. Transcriptome sequencing and bioinformatics analysis were performed followed by RT-qPCR to validate gene expression changes. The results indicate that CSE exposure disrupted the structural integrity of the superficial epithelium, decreased the density of microvilli, and compromised the corneal epithelial barrier intactness. RNA-seq revealed 667 differentially expressed genes, and functional analysis highlighted the enhancement of several biological processes such as antioxidant activity and the response to oxidative stress. Moreover, the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis showed that glutathione metabolism and drug metabolism cytochrome P450 were the most relevant pathways contributing to the effects of CSE on the corneal epithelium. Protein-protein interaction (PPI) network analysis illustrated that GCLC, NQO1, and HMOX1 were the most relevant nodes. In conclusion, the present study indicates that CSE exposure induces changes in the phenotype and genotype of the corneal epithelium. The antioxidant response element is essential for counteracting the effects of cigarette smoke on this tissue layer. These results shed novel insights into how cigarette smoke damages this ocular surface.

Forgotten but not gone: Particulate matter as contaminations of mucosal systems

A decade ago, environmental issues, such as air pollution and the contamination of the oceans with microplastic, were prominently communicated in the media. However, these days, political topics, as well as the ongoing COVID-19 pandemic, have clearly taken over. In spite of this shift in focus regarding media representation, researchers have made progress in evaluating the possible health risks associated with particulate contaminations present in water and air. In this review article, we summarize recent efforts that establish a clear link between the increasing occurrence of certain pathological conditions and the exposure of humans (or animals) to airborne or waterborne particulate matter. First, we give an overview of the physiological functions mucus has to fulfill in humans and animals, and we discuss different sources of particulate matter. We then highlight parameters that govern particle toxicity and summarize our current knowledge of how an exposure to particulate matter can be related to dysfunctions of mucosal systems. Last, we outline how biophysical tools and methods can help researchers to obtain a better understanding of how particulate matter may affect human health. As we discuss here, recent research has made it quite clear that the structure and functions of those mucosal systems are sensitive toward particulate contaminations. Yet, our mechanistic understanding of how (and which) nano- and microparticles can compromise human health via interacting with mucosal barriers is far from complete.

Pollen shells and soluble factors play non-redundant roles in the development of allergic conjunctivitis in mice

PURPOSE

We aimed to clarify the role of particulate allergen exposure to the conjunctiva in the development of allergic conjunctivitis.

METHODS

We administered ragweed pollen suspension, pollen extract, pollen shell, particulate air pollutants, and their combinations to the mouse conjunctiva five days a week without prior sensitization. Clinical signs were scored. Histological changes, cellular infiltrations, mRNA expressions, lymph node cell recall responses, and serum immunoglobulin levels were assessed. Immune cell-depleting antibodies and ST2 knockout mice were used to investigate the cellular and molecular requirements.

RESULTS

Pollen suspension, but not the extract or shell alone, induced robust eosinophilic conjunctivitis, accompanied by a proliferative response of epithelial cells. A combination of pollen extract and shell completely restored eosinophil accumulation. In addition, eosinophilic conjunctivitis was induced by a mixture of particulate air pollutants and pollen extract. Mechanistically, eosinophil accumulation was ameliorated by deficiency of the IL-33 receptor ST2 and abolished by depleting CD4⁺ T cells. Pollen shells, but not the extract, induced IL-33 release from conjunctival epithelial cells in vivo.

CONCLUSIONS

Our results indicate the non-redundant roles for the allergens' particulate properties and soluble factors in the development of allergic conjunctivitis.

A Novel Rabbit Dry Eye Model Induced by a Controlled Drying System

Purpose

To establish an environment-induced dry eye model in rabbits using a controlled drying system (CDS).

Methods

Rabbits were randomly divided into two groups. The rabbits in the dry group were housed in the CDS, in which the relative humidity, airflow, and temperature were controlled at 22% ± 4%, 3 to 4 m/s, and 23°C to 25°C for 14 days. The rabbits in the control group were housed in a normal environment at the same time. A Schirmer test, fluorescein staining, and lissamine green staining were performed. On day 14, the eyeballs and lacrimal glands were processed for evaluating the corneal epithelial thickness, inflammatory cell infiltration index, goblet cell density, and expression of the MUC5AC protein and caspase-3 protein. The mRNA expression of the involved inflammatory genes was analyzed.

Results

The CDS was able to maintain a dry environment, in which the tear production decreased, and the ocular surface staining increased over time in the rabbits. In the dry group, the corneal epithelium became thinner, inflammatory cells were noted, goblet cells and MUC5AC proteins decreased, and the increased levels of caspase-3 proteins and inflammatory cytokines were observed in the ocular surface tissues and lacrimal glands.

Conclusions

This CDS could create a dry environment, in which the rabbits exhibited a pathological change in dry eye similar to that in humans.

Translational Relevance

This model would be helpful in offering a platform to identify and test candidate therapies for environment-induced dry eye and to explore its underlying mechanisms.

L-carnosine mitigates interleukin-1α-induced dry eye disease in rabbits via its antioxidant, anti-inflammatory, antiapoptotic, and antifibrotic effects

OBJECTIVE

To elucidate the implications of L-carnosine on interleukin-1α (IL-1α)-induced inflammation of lacrimal glands (LGs).

MATERIALS AND METHODS

Forty rabbits were divided equally into four groups: control group (G1), IL-1α (G2), L-carnosine (G3), and L-carnosine plus IL-1α (G4). Several clinical, histopathological, immunohistochemical, morphometric, and biochemical investigations were performed, followed by statistical analysis to diagnose the presence of dry eye disease (DED).

RESULTS

The LGs of G2 rabbits showed degeneration of the acinar cells, increased deposition of collagen fibers, and marked immunoexpression of FasL; elevated levels of interferon-γ, tumor necrosis factor-α, transforming growth factor-β1, and malondialdehyde; and decreased levels of glutathione peroxidase, superoxide dismutase, catalase, and reactive oxygen species compared with those of G1 rabbits. In contrast, administration of L-carnosine to G4 rabbits revealed marked improvement of all previously harmful changes in G2 rabbits, indicating the cytoprotective effects of L-carnosine against IL-1α-induced inflammation of LGs.

CONCLUSIONS

IL-1α induced inflammation of LGs and eye dryness via oxidative stress, proinflammatory, apoptotic, and profibrotic effects, whereas L-carnosine mitigated DED through antioxidant, anti-inflammatory, antiapoptotic, and antifibrotic effects on LGs. Therefore, this work demonstrates for the first time that L-carnosine may be used as adjuvant therapy for the preservation of visual integrity in patients with DED.HighlightsIL-1α induced dry eye disease through its oxidative stress, proinflammatory, apoptotic and profibrotic effects on the lacrimal glands of rabbit.L-carnosine has antioxidant, anti-inflammatory, antiapoptotic and antifibrotic effects.L-carnosine mitigated IL-1α induced dry eye disease via elevating the levels of FasL, IFN-γ, TNF-α, TGFβ1 and MDA as well as reducing the levels of antioxidants (GPx, SOD, and catalase) and ROS in the lacrimal glands of rabbit.L-carnosine could be used as a novel adjuvant therapy for the treatment of dry eye disease.

Association between ambient temperature, particulate air pollution and emergency room visits for conjunctivitis

BACKGROUND

Numerous studies have confirmed the association of ambient temperature and air pollution with a higher risk of morbidities, yet few have addressed their effect on the ocular system. The purpose of this study was to assess the association between temperature, air pollution, and emergency room visits for conjunctivitis.

METHODS

In this case-crossover study, the records of all emergency room visits to Soroka University Medical Center (SUMC) from 2009 to 2014 were reviewed for patients with conjunctivitis. Daily exposure to fine and coarse particulate matter and temperature were determined by a hybrid model involving satellite sensors. Mean relative humidity was obtained from the Ministry of Environmental Protection meteorological monitoring station located in Beer-Sheva.

RESULTS

Six hundred one patients were diagnosed with conjunctivitis in the SUMC emergency room. We discovered a positive association between temperature increments and incidence of conjunctivitis. The strongest effect was found during summer and autumn, with an immediate (lag0) incidence increase of 8.1% for each 1 °C increase in temperature (OR = 1.088, 95%CI: 1.046-1.132) between 24 and 28 °C in the summer and 7.2% for each 1 °C increase in temperature (OR = 1.072, 95%CI: 1.036-1.108) between 13 and 23 °C in the autumn. There was no statistically significant association between fine and coarse particulate matter and conjunctivitis incidence.

CONCLUSION

Temperature increases during summer and autumn are significantly associated with an increased risk of conjunctivitis. Conjunctivitis is not associated with non-anthropogenic air pollution. These findings may help community clinics and hospital emergency rooms better predict conjunctivitis cases and will hopefully lead to improved prevention efforts that will lower the financial burden on both the individual and the public.

Association of the Indoor Environment With Dry Eye Metrics

Importance

The ocular surface is continuously exposed to the environment. Although studies have focused on associations between outdoor environmental conditions and dry eye, information on associations between the indoor environment and dry eye is lacking.

Objective

To determine associations between the indoor environment and dry eye.

Design, Setting, and Participants

This prospective cross-sectional study sample of 97 veterans with a wide range of dry eye metrics was recruited from the Miami Veterans Affairs Healthcare eye clinic from October 19, 2017, to August 30, 2018. Dry eye metrics were first evaluated in the clinic, followed by indoor home environmental metrics within 1 week using a handheld particle counter. Data were analyzed from October 19, 2017, to August 30, 2018.

Main Outcomes and Measures

Symptoms of dry eye were assessed with standardized questionnaires. Dry eye signs were assessed via standard examination. Indoor environmental metrics included temperature, humidity, and particulate matter mass and count.

Results

Of the 97 participants included in the analysis, 81 (84%) were men, with a mean (SD) age of 58.2 (11.9) years. Dry eye symptoms were in the moderate range with a mean (SD) Ocular Surface Disease Index (OSDI) score of 31.2 (23.6). Humidity was associated with worse symptoms and signs, including OSDI score (r = 0.30 [95% CI, 0.07-0.49]; P = .01), inflammation (r = 0.32 [95% CI, 0.10-0.51]; P = .01), Schirmer score (r = -0.25 [95% CI, -0.45 to 0.02]; P = .03), eyelid vascularity (r = 0.27 [95% CI, 0.05-0.47]; P = .02), and meibomian gland dropout (r = 0.27 [95% CI, 0.05-0.47]; P = .02). In multivariate analyses, particulate matter of 2.5 μm or less (PM2.5) was associated with dry eye metrics when adjusted for demographic characteristics, comorbidities, medications, and interaction variables. For example, a 1-unit increase in instrumented PM2.5 level was associated with a 1.59 increase in the OSDI score (95% CI, 0.58-2.59; P = .002), a 0.39 reduction in Schirmer score (95% CI, -0.75 to -0.03; P = .04), a 0.07 increase in meibomian gland dropout (95% CI, 0.01-0.13; P = .02), and a 0.06 increase in inflammation (95% CI, 0.02-0.11; P = .009).

Conclusions and Relevance

When adjusting for humidity, this study found that increased particulate matter exposure was associated with worse dry eye metrics. Humidity was positively associated with dry eye metrics, potentially because higher humidity increases microbial growth and particulate matter size and mass.

New application for assessment of dry eye syndrome induced by particulate matter exposure

Dry eye syndrome (DES) is a multifactorial condition characterized by insufficient tear lubrication and eye irritation. Air pollutants, including particulate matter (PM), are an emerging threat to human health causing DES and other diseases. However, the pathogenic mechanisms of DES induced by PM exposure remain to be fully elucidated. Recent studies have attempted to create DES animal model using PM exposure. In this study, we explored a novel in vivo exposure model of DES, utilizing an inhalation device (aerosol exposure system) to reproduce the natural exposure to atmospheric PM. Rats were exposed to urban PM (UPM) using this aerosol system for 5 h per day over 5 days. Tear volume in UPM-exposed rats decreased significantly, whereas corneal irregularity and lissamine green staining significantly increased following UPM exposure. Additional effects observed following UPM exposure included apoptosis in the corneal epithelium and a decrease in the number of goblet cells in the conjunctiva. UPM also affected the stability of the tear film by disrupting its mucin-4 layer. In conclusion, aerosol exposure systems have proven effective as assessment tools for DES caused by PM.

Toxicological effects of urban particulate matter on corneal and conjunctival epithelial cells

Exposure to urban particulate matter (UPM) is a high-risk factor for various ocular surface diseases, including dry eye syndrome. However, the effects of UPM on corneal and conjunctival epithelium damage have not been fully elucidated. In this study, we investigated the toxicological effects of UPM exposure at high concentrations by using in vitro cultures. The cell viability, mucin expression, and the secreted inflammatory mediators of corneal and conjunctival epithelial cells was observed at 24 h after exposure to UPM. The progression of cell cycle was also examined by flow cytometry at 24 h after exposure to UPM. UPM reduced cell viability in a dose-dependent manner and increased cell population in S and G2 phase. The expression of mucin-1 was attenuated by UPM exposure, but that of mucin-4 was not. UPM increased interleukin (IL)-6 release and decreased IL-8 release. The intensity of 2',7'-dichlorofluorescein diacetate (DCF-DA) was highest at 4 h of UPM exposure. In conclusion, these results suggest that UPM causes the disruption of corneal and conjunctival epithelium by decreasing cell viability, altering cell cycle, disrupting mucin, and regulating inflammatory mediators.

Different adverse effects of air pollutants on dry eye disease: Ozone, PM2.5, and PM10

To date, there have been no well-organized clinical studies evaluating which air pollutants affect dry eye disease (DED). In this study, we investigated changes in the clinical parameters of DED according to exposure to outdoor air pollutants, including PM_2.5 (particulate matter with an aerodynamic diameter of less than 2.5 μm), PM₁₀ (less than 10 μm), and ozone. A prospective observational study was conducted on 43 DED patients who had used the same topical eye drop treatment between 2016 and 2018 in South Korea. Ocular surface discomfort index (OSDI) score, tear film break-up time (TBUT), corneal fluorescein staining score (CFSS), and tear secretion were measured during each visit. Air pollution data of ambient PM₁₀, PM_2.5, and ozone, based on the patients' address, were obtained, and mean concentrations were computed for one day, one week, and one month before the examination. The relationships between air pollutants and DED were analyzed in single- and multi-pollutant models adjusted for demographic and clinical factors. In the multi-pollutant model, the OSDI score was positively correlated with ozone and PM_2.5 exposure [ozone: β(exposure for 1 day/1 week) = 0.328 (95% CI: 0.161-0.494)/0.494 (0.286-0.702), p < 0.001/<0.001, per 1 ppb increase; PM_2.5: β(1 day/1 week) = 0.378 (0.055-0.699)/0.397 (0.092-0.703), p = 0.022/ = 0.011, per 1 μg/m³ increase], and tear secretion decreased with increased ozone exposure [ozone: β(1 week/1 month) = -0.144 (-0.238 to -0.049)/-0.164 (-0.298 to -0.029), p = 0.003/ = 0.017, per 1 ppb increase]. Interestingly, increased PM₁₀ exposure was only associated with decreased TBUT [β(1 day/1 week/1 month) = -0.028(-0.045 to -0.011)/-0.029(-0.046 to -0.012)/-0.023(-0.034 to -0.006), p = 0.001/ = 0.001/ = 0.018, per 1 μg/m³ increase]. Tear secretion and CFSS were not associated with PM₁₀ exposure. Increased ozone and PM_2.5 exposure led to aggravated ocular discomfort, and increased PM₁₀ concentration aggravated tear film stability in patients with DED. Thus, each air pollutant may aggravate DED via different mechanisms of action.

Particulate Matter Induces Tissue OxInflammation: From Mechanism to Damage

Significance: Oxidative stress and oxidative damage are central hypothetical mechanisms for the adverse effects of airborne particulate matter (PM). Activation of inflammatory cells capable of generating reactive oxygen and nitrogen species is another proposed damage pathway. Understanding the interplay between these responses can help us understand the adverse health effects attributed to breathing polluted air. Recent Advances: The consequences of PM exposure on different organs are oxidative damage, decreased function, and inflammation, which can lead to the development/exacerbation of proinflammatory disorders. Mitochondrial damage is also an important event in PM-induced cytotoxicity. Critical Issues: Reactive oxygen species (ROS) are generated during phagocytosis of the particles, leading to enhancement of oxidative stress and triggering the inflammatory response. The activation of inflammatory signaling pathways results in the release of cytokines and other mediators, which can further induce ROS production by activating endogenous enzymes, leading to a positive feedback loop, which can aggravate the effects triggered by PM exposure. Future Directions: Further research is required to elucidate the exact mechanisms by which PM exposure results in adverse health effects, in terms of the relationship between the redox responses triggered by the presence of the particles and the inflammation observed in the different organs, so the development/exacerbation of PM-associated health problems can be prevented.

Long-Term Exposure to Urban Particulate Matter on the Ocular Surface and the Incidence of Deleterious Changes in the Cornea, Conjunctiva and Retina in Rats

We investigated the time-dependent deleterious ocular changes induced by urban particulate matter (UPM) in vitro and in vivo. UPM treatment decreased human corneal epithelial cell migration and survival. Fluorescein scores were consistently increased by UPM application for 16 weeks. One week of rest at 2 or 4 weeks led to a recovery trend, whereas two weeks of rest at 8 weeks induced no change. UPM treatment decreased the tear film break-up time at 2 weeks, which was thereafter maintained until 16 weeks. No changes were found after periods of rest. UPM-treated eyes exhibited greater corneal epithelium thickness than normal eyes at 2 weeks, which recovered to normal at 4 and 8 weeks and was significantly decreased at 16 weeks. Apoptotic cell number in the epithelium was increased at 2 weeks, which remained constant except at 8 weeks. IL-6 expression in the cornea of the right eye continually increased for 16 weeks, and significant recovery was only observed at 8 weeks after 2 weeks of rest. Ocular pressure was significantly increased in the right eye at 12 and 16 weeks. Topical UPM application to the eye induced deleterious changes to various closely related parts of the eye.

Toxicity and mechanism of mesoporous silica nanoparticles in eyes

The study on the safety of nanomaterials in eyes is still in its early stages. In this study, we put our focus on the effect of one important nanoparticle feature - large surface area - to assess eye safety. To this end, mesoporous silica nanoparticles (MSiNPs) were for the first time employed as a model to evaluate their toxicity in eyes. The porosity of the MSiNPs endows them with a large surface area and the ability to attach to surrounding chemical or biological molecules, further enhancing their surface reactivity and toxic effects. Therefore, to better mimic MSiNP exposure in real environments, we also introduced other hazardous substances such as silver ions (Ag+) to the system and then investigated their synergistic nanotoxicity. Our results showed that the exposure to MSiNPs-Ag+ and even Ag+ at a safe dose, resulted in more significant toxicity than the MSiNPs alone, as evidenced from cell viability, apoptosis, reactive oxygen species (ROS) production, and DNA damage experiments. RNA-Sequencing analysis revealed that the mRNA surveillance signalling pathway plays a unique role in regulating MSiNPs-Ag+-induced cytotoxicity. Besides this, severe corneal damage and dry eye were observed in rat models upon exposure to MSiNPs-Ag+ compared to MSiNPs. Most importantly, we also proposed a protein corona-based therapy to treat MSiNP-induced corneal disease, where the corneal damage could be rescued by fetal bovine serum (FBS) treatment.

Dry eye induced by exposure to cigarette smoke pollution: An in vivo and in vitro study

Exposure to cigarette smoke (CS) pollution has previously associated with dry eye symptoms but without detailed experimental data and elucidation of the mechanism. We aimed to evaluate the effects of CS on the ocular surfaces of mice and the extraction of DMSO lipid-soluble cigarette smoke particles (DCSP) on cultured human corneal epithelial cells (HCECs), and explore to elucidate the probable mechanism. C57BL mice were exposed to CS challenging. In vivo clinical evaluations, including corneal fluorescein staining, tear film break-up time, and confocal microscopic observations, were performed before exposure and post-exposure. At the end of the in vivo study, changes in corneal and conjunctival histology, corneal ultrastructure, and conjunctival goblet cell intensity were examined, expression of TUNLE and Ki67 in tissue were also detected. In vitro, cell confluence and caspase3/7 were assessed in DCSP treated HCECs. Production of TNF-α, IL-1β and IL-6, activation of NF-κB and Ki67 were evaluated by means of ELISA and Western blot respectively in HCECs cultured with 0.6 μL/mL DCSP. We found that longer-term CS exposure induced dry eye symptoms in mice. Additionally, corneal and conjunctival epithelial damage occurred, the corneal ultrastructure changed, and the density of goblet cells decreased. Apoptosis and Ki67 increased in both the conjunctiva and the cornea of CS-exposed animals. Furthermore, although DCSP inhibited the proliferation of HCECs, expression of Ki67 increased and apoptosis was only induced significantly by 2.0 μL/mL DCSP. The release of IL-1β and IL-6, activation of NF-κB were prompted by DCSP. The results indicated that CS is toxic to the ocular surface of mice and HCECs. Longer-term CS exposure in mice stimulates ocular surface changes that resemble those observed with dry eye. The mechanism may relate to inflammation and activation of NF-κB. In this study, we established a novel animal model to study dry eye, with the experimental data and elucidation of mechanism facilitating further research.

IRF4 and STAT3 activities are associated with the imbalanced differentiation of T-cells in responses to inhalable particulate matters

Background

Particulate Matter (PM) is known to cause inflammatory responses in human. Although prior studies verified the immunogenicity of PM in cell lines and animal models, the effectors of PM exposure in the respiratory system and the regulators of the immunogenicity of PM is not fully elucidated.

Methods

To identify the potential effector of PM exposure in human respiratory system and to better understand the biology of the immunogenicity of PM, We performed gene-expression profiling of peripheral blood mononuclear cells from 171 heathy subjects in northern China to identify co-expressed gene modules associated with PM exposure. We inferred transcription factors regulating the co-expression and validated the association to T-cell differentiation in both primary T-cells and mice treated with PM.

Results

We report two transcription factors, IRF4 and STAT3, as regulators of the gene expression in response to PM exposure in human. We confirmed that the activation of IRF4 and STAT3 by PM is strongly associated with imbalanced differentiation of T-cells in the respiratory tracts in a time-sensitive manner in mouse. We also verified the consequential inflammatory responses of the PM exposure. Moreover, we show that the protein levels of phosphorylated IRF4 and STAT3 increase with PM exposure.

Conclusions

Our study suggests the regulatory activities of IRF4 and STAT3 are associated with the Th17-mediated inflammatory responses to PM exposure in the respiratory tracts, which informs the biological background of the immunogenicity of particulate matters.

Relationships Between Short-Term Exposure to an Indoor Environment and Dry Eye (DE) Symptoms

Air composition influences Dry Eye (DE) symptoms as demonstrated by studies that have linked the outdoor environment to DE. However, there is insufficient data on the effect of short-term exposure to indoor environments on DE symptoms. We conducted a prospective experimental research, in which an older building served as an experimental site, and a newer building served as the control site. Indoor air quality was monitored in both buildings. One-hundred-and-ninety-four randomly selected individuals were interviewed in the afternoon exiting the buildings and de-identified responses were recorded. Self-reported DE symptoms were modeled with respect to experimental and control buildings, adjusting for potential confounders. The experimental site had 2-fold higher concentration of airborne particulate matter (24,436 vs. 12,213 ≥ 0.5 µm/ft3) and microbial colonies (1066 vs. 400/m3), as compared to the control building. DE symptoms were reported by 37.5% of individuals exiting the experimental and 28.4% exiting the control building. In the univariate analysis, subjects exiting the experimental building were 2.21× more likely to report worsening of DE symptoms since morning compared to the control building (p < 0.05). When adjusting for confounders, including a history of eye allergy, subjects from the experimental building were 13.3× more likely to report worsening of their DE symptoms (p < 0.05). Our findings suggest that short-term exposure to adverse indoor environmental conditions, specifically air pollution and bioaerosols, has an acutely negative impact on DE symptoms.

Polygonum cuspidatum stem extract (PSE) ameliorates dry eye disease by inhibiting inflammation and apoptosis

[Purpose]

Here, we aimed to determine the effect of Polygonum cuspidatum stem extract (PSE) on exorbital lacrimal gland-excised rat models and hyperosmotic stress-stimulated human conjunctival cells (HCCs).

[Methods]

Seven week old male Wistar rats were divided into six groups. Only the rats in the control group (NOR, n=5) did not undergo surgery. Three days after the surgery, the exorbital lacrimal gland-excised rats were randomly allocated to five groups: (1) vehicle-treated dry-eyed rats (DED, n=5); (2) PSE (10 mg/kg) treated DED rats (PSE-10, n=5); (3) PSE (100 mg/kg) treated DED rats (PSE-100, n=5); and (4) PSE (250 mg/kg) treated DED rats (PSE-250, n=5). In addition, the HCC line was co-treated with hyperosmolar media (528 mOsm) and PSE (1-100 μg/ml).

[Results]

PSE treatment restored the tear volume and goblet cell density by inhibiting severe corneal irregularities and damage. The treatment with PSE significantly attenuated the hyperosmolar stress-induced inflammation and cell death through the suppression of mRNA expression levels of Tumor necrosis factor-α (TNF-α), Interleukin-6 (IL-6), Interleukin-1β (IL-1β), and Interferon-γ (IFN-γ), and the expression of Bcl-2-associated X protein (Bax) as well as the activation of caspase-3 in vitro.

[Conclusion]

The inhibitory effects of PSE treatment on dry eye disease indicate the potential of nutritional intervention by PES against inflammatory diseases without adverse effects.

Polydatin Inhibits NLRP3 Inflammasome in Dry Eye Disease by Attenuating Oxidative Stress and Inhibiting the NF-κB Pathway

Polydatin (also named pieceid, (E)-piceid, (E)-polydatin, trans-polydatin, or 3,5,4'-trihydroxystilbene-3-b-D-glucoside) is a monocrystalline compound isolated from the root and rhizome of Polygonum cuspidatum Sieb. et Zucc. (Polygonaceae). A previous study showed that polydatin has antioxidant and anti-inflammatory effects. However, the effect of polydatin in dry eye disease (DED) has not been elucidated. DED rat models were induced by exorbital lacrimal gland-excision. In vivo, the present study showed that the excision of lacrimal glands induced changes such as reduced tear fluid, severe corneal irregularity, damage, tear film break, and goblet cell loss as well as increased inflammation cytokine and NLRP3 expression in conjunctival tissue. However, these changes were restored by polydatin eye dropping. In vitro, polydatin inhibited hyperosmolar stress-induced inflammation through attenuation of the translocation of NF-κB to the nucleus and the mRNA expression of TNF-α, IL-6, IL-1β, and MMP9. In addition, the hyperosmolar stress-induced NLRP3 inflammasome pathway and ROS production were inhibited by polydatin. Our findings provided insight into the effect of polydatin as a candidate reagent for the treatment of DED.

Urban air pollution induces redox imbalance and epithelium hyperplasia in mice cornea

The aim of the study was to evaluate the time course of the effects of urban air pollutants on the ocular surface, focusing on the morphological changes, the redox balance, and the inflammatory response of the cornea. 8-week-old mice were exposed to urban or filtered air (UA-group and FA-group, respectively) in exposure chambers for 1, 2, 4, and 12 weeks. After each time, the eyes were enucleated and the corneas were isolated for biochemical analysis. UA-group corneas exhibited a continuous increase in NADPH oxidase-4 levels throughout the exposure time, suggesting an increased production of reactive oxygen species (ROS). After 1 week, an early adaptive response to ROS was observed as an increase in antioxidant enzymes. After 4 weeks, the enzymatic antioxidants were decreased, meanwhile an increase of the glutathione was shown, as a later compensatory antioxidant response. However, redox imbalance took place, evidenced by the increased oxidized proteins, which persisted up to 12 weeks. At this time point, corneal epithelium hyperplasia was also observed. The inflammatory response was modulated by the increase in IL-10 levels after 1 week, which early regulates the release of TNF-α and IL-6. These results suggest that air pollution alters the ocular surface, supported by the observed cellular hyperplasia. The redox imbalance and the inflammatory response modulated by IL-10 play a key role in the response triggered by air pollutants on the cornea. Taking into account this time course study, the ocular surface should also be considered as a relevant target of urban air pollutants.

Global Associations of Air Pollution and Conjunctivitis Diseases: A Systematic Review and Meta-Analysis

(1) Background: As the most common eye disease diagnosed in emergency departments, conjunctivitis has caused serious health and economic burdens worldwide. However, whether air pollution may be a risk factor for conjunctivitis is still inconsistent among current evidence. (2) Methods: We searched the literature on the relationship between air pollution and conjunctivitis in multiple English databases before 18 March 2019. Meta-analysis, meta-regression, and funnel plots were used to integrate the data, identify the sources of bias, and determine the publication bias, respectively. (3) Results: A total of 2450 papers were found, 12 of which were finally included. The pooled relative risk for each 10 μg/m³ increase of air pollution on conjunctivitis was 1.0006 (95%CI: 0.9993–1.0019) for CO, 1.0287 (1.0120–1.0457) for NO₂, 1.0089 (1.0030–1.0149) for O₃, 1.0004 (0.9976–1.0032) for PM_2.5, 1.0033 (0.9982–1.0083) for PM₁₀, and 1.0045 (0.9908–1.0185) for SO₂. In the subgroup, PM_2.5 and O₃ had a greater impact on conjunctivitis risk in women than in men, and people <18 years old than those ≥18 years old. Relative humidity significantly modified the risk of O₃ on conjunctivitis (p = 0.023), explaining 45% of the between-study heterogeneity. (4) Conclusion: Globally, air pollution has considerable health risks for conjunctivitis. Females and the youth were more vulnerable to PM_2.5, NO₂, and O₃. Reductions of air pollution levels are still warranted to protect the vulnerable populations.

Achyranthis radix Extract Improves Urban Particulate Matter-Induced Dry Eye Disease

Dry eye disease (DED) is a multifactorial inflammatory disease that severely impairs patients' quality of life. Particulate matter comprises a harmful mixture of particles less than 10 μm in size, which on contact with the eye, causes inflammation in the cornea/conjunctival epithelium, threatening eye health and triggering the onset of DED. Achyranthis radix is an ingredient of traditional medicine generally used for treating osteoporosis, trauma, and thrombosis in Asian countries. However, the effect of Achyranthis radix on eye health has not been elucidated. In this study, we evaluate the protective effect of Achyranthis radix hot water extract (ARE) in a rat model of urban particulate matter (UPM)-induced DED. UPM with or without ARE were topically administered on both eyes thrice daily for 10 days. ARE induced tear secretion and improved corneal irregularity. Additionally, ARE treatment protected the corneal epithelial cells from UPM-induced apoptosis. It also restored rMuc4 expression in the cornea and increased goblet cell density in the conjunctiva. These results are suggestive of the potential of ARE as a topical therapeutic agent for treating DED.