The Protective Effect of Topical Spermidine on Dry Eye Disease with Retinal Damage Induced by Diesel Particulate Matter2.5

Spermidine mitigates blue-light-induced corneal injury by alleviating oxidative stress and restoring autophagy impairment

This study investigated the protective efficacy of spermidine on corneal epithelium exposed to photodamage from artificial blue light (BL). After six weeks of BL exposure, the rabbit cornea exhibited epithelial injury and delayed wound healing accompanied by downregulation of spermidine, as identified through metabolomic analysis. Pathways related to autophagy and the antioxidant response were implicated in this process. In vitro, spermidine mitigated BL-induced reductions in viability and proliferation of human corneal epithelial cells, decreased cell death, and enhanced colony formation. Spermidine also partially reversed BL-induced mitochondrial dysfunction, oxidative stress and autophagy impairment. Furthermore, topical administration of spermidine eye drops reduced epithelial injury in the rabbit cornea under BL exposure, demonstrating benefits in promoting cell proliferation, accelerating wound healing, and maintaining antioxidant capacity and autophagy.

Impact of particulate matter and air pollution on ocular surface disease: A systematic review of preclinical and clinical evidence

PURPOSE

Exposure to particulate matter (PM) and air pollution has been implicated in the etiology of ocular surface diseases (OSD). The purpose of this systematic review is to evaluate and synthesize peer-reviewed literature on the impact of PM exposure on the ocular surface, integrating results from preclinical in vitro and in vivo studies with clinical findings to provide a comprehensive understanding of molecular mechanisms, physiological effects, clinical implications, and potential therapies to target acute and chronic PM-induced ocular toxicity.

METHODS

A systematic literature search was performed using PubMed and EMBASE over the period from 2009 to 2024 following the recommendations for the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) reporting guidelines. 102 studies were identified that met the inclusion/exclusion criteria. All studies were assessed for the risk of bias and qualitative data were analyzed.

RESULTS

Preclinical studies using models of corneal and conjunctival cells found that exposure to PM and similar air pollutants resulted in apoptosis, primarily via inflammatory and oxidative stress pathways as well as allergic and immune responses. Animal models resulted in phenotypes reminiscent of that of dry eye disease, presenting with reduced tear volumes and ocular surface damage. These results were corroborated by clinical studies, which reported that patients commonly presented with symptoms of itching, burning, and irritation, and ocular surface signs correlated with a diagnosis of dry eye disease, conjunctivitis, and allergic eye disease.

CONCLUSIONS

This systematic review provides a comprehensive summary of our current understanding of PM exposure on the ocular surface, highlighting the correlation between exposure to PM and ocular surface dysfunction.

Recommendations for nutritional supplements for dry eye disease: current advances

Dry eye disease (DED) represents a prevalent ocular surface disease. The development of effective nutritional management strategies for DED is crucial due to its association with various factors such as inflammation, oxidative stress, deficiencies in polyunsaturated fatty acids (PUFAs), imbalanced PUFA ratios, and vitamin insufficiencies. Extensive research has explored the impact of oral nutritional supplements, varying in composition and dosage, on the symptoms of DED. The main components of these supplements include fish oils (Omega-3 fatty acids), vitamins, trace elements, and phytochemical extracts. Beyond these well-known nutrients, it is necessary to explore whether novel nutrients might contribute to more effective DED management. This review provides a comprehensive update on the therapeutic potential of nutrients and presents new perspectives for combination supplements in DED treatment.

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.

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.

MSC-Derived Small Extracellular Vesicles Attenuate Autoimmune Dacryoadenitis by Promoting M2 Macrophage Polarization and Inducing Tregs via miR-100-5p

Background

Mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) have been increasingly proved as promising immunomodulators against some autoimmune disorders. However, the possible effect and the underlying mechanism of MSC-sEVs in autoimmune dry eye have been rarely studied.

Methods

Small extracellular vesicles from human umbilical cord mesenchymal stem cells (hUC-MSC-sEVs) were subconjunctivally injected to rabbit dry eye model, and their preventive or therapeutical effects were assessed by recording the clinical and histological scores. Quantitative real-time PCR (Q-PCR), western blot and flow cytometry were performed to evaluate the immunomodulatory effects of hUC-MSC-sEVs on macrophages and T regulatory cells (Tregs) both in vivo and in vitro, and the in vitro T cell proliferation was detected by Bromodeoxyuridine (BrdU) assay. In addition, high expression of miR-100-5p in hUC-MSC-sEVs was identified by Q-PCR, and the functional role of sEVs-miR-100-5p on macrophages was explored by a series of co-culture experiments using sEVs derived from hUC-MSCs transfected with miR-100-5p inhibitor.

Results

We firstly demonstrated that hUC-MSC-sEVs had the preventive and therapeutical effects on rabbit autoimmune dacryoadenitis, an animal model of Sjögren’s syndrome (SS) dry eye. Further investigation revealed that hUC-MSC-sEVs administration effectively elicited macrophages into an anti-inflammatory M2 phenotype and elevated the proportion of Tregs both in vivo and in vitro, which contributed to reduced inflammation and improved tissue damage. Importantly, hUC-MSC-sEVs-educated macrophages with M2-like phenotype exhibited strong capacity to inhibit CD4+ T cell proliferation and promote Treg generation in vitro. Mechanistically, miR-100-5p was highly enriched in hUC-MSC-sEVs, and knockdown of miR-100-5p in hUC-MSC-sEVs partially blunted the promotion of hUC-MSC-sEVs on M2 macrophage polarization and even attenuated the effect of hUC-MSC-sEVs-educated macrophages on T cell suppression and Treg expansion.

Conclusion

Our data indicated that hUC-MSC-sEVs alleviated autoimmune dacryoadenitis by promoting M2 macrophage polarization and Treg generation possibly through shuttling miR-100-5p. This study sheds new light on the application of MSC-sEVs as a promising therapeutic method for SS dry eye.

Research Progress and Potential Applications of Spermidine in Ocular Diseases

Spermidine, a natural polyamine, exists in almost all human tissues, exhibiting broad properties like anti-aging, autophagy induction, anti-inflammation, anti-oxidation, cell proliferation activation, and ion channel regulation. Considering that spermidine is already present in human nutrition, recent studies targeting supplementing exogenous sources of this polyamine appear feasible. The protective role of spermidine in various systems has been illuminated in the literature, while recent progress of spermidine administration in ocular diseases remains to be clarified. This study shows the current landscape of studies on spermidine and its potential to become a promising therapeutic agent to treat ocular diseases: glaucoma, optic nerve injury, age-related macular degeneration (AMD), cataracts, dry eye syndrome, and bacterial keratitis. It also has the potential to become a potent biomarker to predict keratoconus (KC), cataracts, uveitis, glaucoma, proliferative diabetic retinopathy (PDR), proliferative vitreoretinopathy (PVR), and retinopathy of prematurity (ROP). We also summarize the routes of administration and the effects of spermidine at different doses.

Is the Sex Difference a Clue to the Pathomechanism of Dry Eye Disease? Watch out for the NGF-TrkA-Piezo2 Signaling Axis and the Piezo2 Channelopathy

Dry eye disease (DED) is a multifactorial disorder with recognized pathology, but not entirely known pathomechanism. It is suggested to represent a continuum with neuropathic corneal pain with the paradox that DED is a pain-free disease in most cases, although it is regarded as a pain condition. The current paper puts into perspective that one gateway from physiology to pathophysiology could be a Piezo2 channelopathy, opening the pathway to a potentially quad-phasic non-contact injury mechanism on a multifactorial basis and with a heterogeneous clinical picture. The primary non-contact injury phase could be the pain-free microinjury of the Piezo2 ion channel at the corneal somatosensory nerve terminal. The secondary non-contact injury phase involves harsher corneal tissue damage with C-fiber contribution due to the lost or inadequate intimate cross-talk between somatosensory Piezo2 and peripheral Piezo1. The third injury phase of this non-contact injury is the neuronal sensitization process with underlying repeated re-injury of the Piezo2, leading to the proposed chronic channelopathy. Notably, sensitization may evolve in certain cases in the absence of the second injury phase. Finally, the quadric injury phase is the lingering low-grade neuroinflammation associated with aging, called inflammaging. This quadric phase could clinically initiate or augment DED, explaining why increasing age is a risk factor. We highlight the potential role of the NGF-TrkA axis as a signaling mechanism that could further promote the microinjury of the corneal Piezo2 in a stress-derived hyperexcited state. The NGF-TrkA-Piezo2 axis might explain why female sex represents a risk factor for DED.

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.