Tear nanoDSF Denaturation Profile Is Predictive of Glaucoma

Primary open-angle glaucoma (POAG) is a frequent blindness-causing neurodegenerative disorder characterized by optic nerve and retinal ganglion cell damage most commonly due to a chronic increase in intraocular pressure. The preservation of visual function in patients critically depends on the timeliness of detection and treatment of the disease, which is challenging due to its asymptomatic course at early stages and lack of objective diagnostic approaches. Recent studies revealed that the pathophysiology of glaucoma includes complex metabolomic and proteomic alterations in the eye liquids, including tear fluid (TF). Although TF can be collected by a non-invasive procedure and may serve as a source of the appropriate biomarkers, its multi-omics analysis is technically sophisticated and unsuitable for clinical practice. In this study, we tested a novel concept of glaucoma diagnostics based on the rapid high-performance analysis of the TF proteome by differential scanning fluorimetry (nanoDSF). An examination of the thermal denaturation of TF proteins in a cohort of 311 ophthalmic patients revealed typical profiles, with two peaks exhibiting characteristic shifts in POAG. Clustering of the profiles according to peaks maxima allowed us to identify glaucoma in 70% of cases, while the employment of artificial intelligence (machine learning) algorithms reduced the amount of false-positive diagnoses to 13.5%. The POAG-associated alterations in the core TF proteins included an increase in the concentration of serum albumin, accompanied by a decrease in lysozyme C, lipocalin-1, and lactotransferrin contents. Unexpectedly, these changes were not the only factor affecting the observed denaturation profile shifts, which considerably depended on the presence of low-molecular-weight ligands of tear proteins, such as fatty acids and iron. Overall, we recognized the TF denaturation profile as a novel biomarker of glaucoma, which integrates proteomic, lipidomic, and metallomic alterations in tears, and monitoring of which could be adapted for rapid non-invasive screening of the disease in a clinical setting.

Comparative lipidomic analysis of inflammatory mediators in the aqueous humor and tear fluid of humans and rabbits

INTRODUCTION

Ocular inflammation is a key pathogenic factor in most blindness-causing visual disorders. It can manifest in the aqueous humor (AH) and tear fluid (TF) as alterations in polyunsaturated fatty acids (PUFAs) and their metabolites, oxylipins, lipid mediators, which are biosynthesized via enzymatic pathways involving lipoxygenase, cyclooxygenase or cytochrome P450 monooxygenase and specifically regulate inflammation and resolution pathways.

OBJECTIVES

This study aimed to establish the baseline patterns of PUFAs and oxylipins in AH and TF by their comprehensive lipidomic identification and profiling in humans in the absence of ocular inflammation and comparatively analyze these compounds in the eye liquids of rabbits, the species often employed in investigative ophthalmology.

METHODS

Ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was used for qualitative and quantitative characterization of lipid compounds in the analyzed samples.

RESULTS

A total of 28 lipid compounds were identified, including phospholipid derivatives and PUFAs, as well as 22 oxylipins. Whereas the PUFAs included arachidonic, docosahexaenoic and eicosapentaenoic acids, the oxylipins were derived mainly from arachidonic, linoleic and α-linolenic acids. Remarkably, although the concentration of oxylipins in AH was lower compared to TF, these liquids showed pronounced similarity in their lipid profiles, which additionally exhibited noticeable interspecies concordance.

CONCLUSION

The revealed correlations confirm the feasibility of rabbit models for investigating pathogenesis and trialing therapies of human eye disorders. The identified metabolite patterns suggest enzymatic mechanisms of oxylipin generation in AH and TF and might be used as a reference in ocular inflammation studies.

[Inflammatory metabolites of arahidonic acid in tear fluid in UV-induced corneal damage]

The ultraviolet (UV) B-induced damage of the eye surface of experimental animals (rabbits) includes loss of corneal epithelium, apoptosis of keratocytes and stromal edema. These changes are accompanied by clinically and histologically manifested corneal inflammation, neutrophil infiltration, and exudation of the anterior chamber of the eye. According to mass spectrometric analysis, UV-induced corneal damage is associated with pronounced changes in the lipid composition of tears, including a decrease in the amount of arachidonic acid and prostaglandin E2 and an increase in the concentrations of prostaglandin D2 and its derivative 15d-PGJ2. In addition, it is accompanied by an alteration in the levels of hydroxyeicosate tetraenic acid derivatives, namely upregulation of 12-HETE and downregulation of 5-HETE. The revealed changes indicate the activation of metabolic pathways involving 5-lipoxygenase, 12-lipoxygenase, cyclooxygenase 1 and 2, and prostaglandin-D-synthase. These findings contribute to understanding mechanisms of UV-induced keratitis and point on feasibility of selective anti-inflammatory therapy for improving corneal regeneration after iatrogenic UV damage.

Iatrogenic Damage of Eye Tissues: Current Problems and Possible Solutions

Visual system is at high risk of iatrogenic damage. Laser ocular surgery, the use of powerful illumination devices in diagnostics and surgical treatment of eye diseases, as well as long surgeries under general anesthesia provoke the development of chronic degenerative changes in eye tissues, primarily in the cornea and the retina. Despite the existence of approaches for prevention and treatment of these complications, the efficacy of these approaches is often limited. Here, we review the mechanisms of iatrogenic damage to eye tissues at the cellular and biochemical levels. It is well recognized that oxidative stress is one of the main factors hindering regeneration of eye tissues after injuries and, thereby, aggravating iatrogenic eye disorders. It is accompanied by the downregulation of low-molecular-weight antioxidants and antioxidant enzymes, as well as changes in the expression and redox status of proteins in the damaged tissue. In this regard, antioxidant therapy, in particular, the use of highly effective mitochondria-targeted antioxidants such as SkQ1, is considered as a promising approach to the prevention of iatrogenesis. Recent findings indicate that the most efficient protection of eye tissues from the iatrogenic injury is achieved by preventive use of these antioxidants. In addition to preventing corneal and retinal cell death induced by oxidative stress, SkQ1 contributes to the restoration of innate antioxidant defense of these tissues and suppresses local inflammatory response. Since the timing of routine medical manipulations is usually known in advance, iatrogenic damage to the ocular tissues can be successfully prevented using mitochondria-targeted therapy.

Mitochondria-targeted antioxidant SKQ1 protects cornea from oxidative damage induced by ultraviolet irradiation and mechanical injury

Background

Cornea protects the eye against natural and anthropogenic ultraviolet (UV) damage and mechanical injury. Corneal incisions produced by UV lasers in ophthalmic surgeries are often complicated by oxidative stress and inflammation, which delay wound healing and result in vision deterioration. This study trialed a novel approach to prevention and treatment of iatrogenic corneal injuries using SkQ1, a mitochondria-targeted antioxidant approved for therapy of polyethiological dry eye disease.

Methods

Rabbit models of UV-induced and mechanical corneal damage were employed. The animals were premedicated or treated with conjunctival instillations of 7.5 μM SkQ1. Corneal damage was assessed by fluorescein staining and histological analysis. Oxidative stress in cornea was monitored by measuring malondialdehyde (MDA) using thiobarbituric acid assay. Total antioxidant activity (AOA) was determined using hemoglobin/H₂O₂/luminol assay. Glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities were measured using colorimetric assays.

Results

In both models corneas exhibited fluorescein-stained lesions, histologically manifesting as basal membrane denudation, apoptosis of keratocytes, and stromal edema, which were accompanied by oxidative stress as indicated by increase in lipid peroxidation and decline in AOA. The UV-induced lesions were more severe and long healing as corneal endothelium was involved and GPx and SOD were downregulated. The treatment inhibited loss of keratocytes and other cells, facilitated re-epithelialization and stromal remodeling, and reduced inflammatory infiltrations and edema thereby accelerating corneal healing approximately 2-fold. Meanwhile the premedication almost completely prevented development of UV-induced lesions. Both therapies reduced oxidative stress, but only premedication inhibited downregulation of the innate antioxidant activity of the cornea.

Conclusions

SkQ1 efficiently prevents UV-induced corneal damage and enhances corneal wound healing after UV and mechanical impacts common to ocular surgery. Its therapeutic action can be attributed to suppression of mitochondrial oxidative stress, which in the first case embraces all corneal cells including epitheliocytes, while in the second case affects residual endothelial cells and stromal keratocytes actively working in wound healing. We suggest SkQ1 premedication to be used in ocular surgery for preventing iatrogenic complications in the cornea.

Suppression of Light-Induced Oxidative Stress in the Retina by Mitochondria-Targeted Antioxidant

Light-induced oxidation of lipids and proteins provokes retinal injuries and results in progression of degenerative retinal diseases, such as, for instance, iatrogenic photic maculopathies. Having accumulated over years retinal injuries contribute to development of age-related macular degeneration (AMD). Antioxidant treatment is regarded as a promising approach to protecting the retina from light damage and AMD. Here, we examine oxidative processes induced in rabbit retina by excessive light illumination with or without premedication using mitochondria-targeted antioxidant SkQ1 (10-(6’-plastoquinonyl)decyltriphenyl-phosphonium). The retinal extracts obtained from animals euthanized within 1–7 days post exposure were analyzed for H₂O₂, malondialdehyde (MDA), total antioxidant activity (AOA), and activities of glutathione peroxidase (GPx) and superoxide dismutase (SOD) using colorimetric and luminescence assays. Oxidation of visual arrestin was monitored by immunoblotting. The light exposure induced lipid peroxidation and H₂O₂ accumulation in the retinal cells. Unexpectedly, it prominently upregulated AOA in retinal extracts although SOD and GPx activities were compromised. These alterations were accompanied by accumulation of disulfide dimers of arrestin revealing oxidative stress in the photoreceptors. Premedication of the eyes with SkQ1 accelerated normalization of H₂O₂ levels and redox-status of lipids and proteins, contemporarily enhancing AOA and, likely, sustaining normal activity of GPx. Thus, SkQ1 protects the retina from light-induced oxidative stress and could be employed to suppress oxidative damage of proteins and lipids contributing to AMD.