[Mechanisms of perioperative corneal abrasions: alterations in tear film proteome]

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.

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.

Effect of General Anesthesia Duration on Recovery of Secretion and Biochemical Properties of Tear Fluid in the Post-Anesthetic Period

Changes in the biochemical composition of the tear film is a critical risk factor for the development of chronic perioperative dry eye syndrome, because increasing the duration of general anesthesia did not affect the dynamics of tear secretion recovery, but slowed down normalization of its structure and antioxidant activity in the post-anesthetic period.

Mitochondria-Targeted Antioxidant SkQ1 Prevents Anesthesia-Induced Dry Eye Syndrome

Dry eye syndrome (DES) is an age-related condition increasingly detected in younger people of risk groups, including patients who underwent ocular surgery or long-term general anesthesia. Being a multifactorial disease, it is characterized by oxidative stress in the cornea and commonly complicated by ocular surface inflammation. Polyetiologic DES is responsive to SkQ1, a mitochondria-targeted antioxidant suppressing age-related changes in the ocular tissues. Here, we demonstrate safety and efficacy of topical administration of SkQ1 at a dosage of 7.5 μM for the prevention of general anesthesia-induced DES in rabbits. The protective action of SkQ1 improves clinical state of the ocular surface by inhibiting apoptotic and prenecrotic changes in the corneal epithelium. The underlying mechanism involves the suppression of the oxidative stress supported by the stimulation of intrinsic antioxidant activity and the activity of antioxidant enzymes, foremost glutathione peroxidase and glutathione reductase, in the cornea. Furthermore, SkQ1 increases antioxidant activity and stability of the tear film and produces anti-inflammatory effect exhibited as downregulation of TNF-α and IL-6 and pronounced upregulation of IL-10 in tears. Our data suggest novel features of SkQ1 and point to its feasibility in patients with DES and individuals at risk for the disease including those subjected to general anesthesia.