Oxidative stress markers dynamics in keratoconus patients' tears before and after corneal collagen crosslinking procedure

Evaluation of Ocular and Systemic Oxidative Stress Markers in Ocular Rosacea Patients

Purpose

To investigate oxidative stress markers in tears and serum of patients with ocular rosacea and to examine their association with both ocular surface parameters and cutaneous rosacea subtypes.

Methods

This prospective study includes rosacea patients with ocular involvement and healthy controls. We performed ophthalmological examination of all participants and collected tear breakup time (TBUT), Schirmer, Meibomian gland dysfunction (MGD) and Ocular Surface Disease Index (OSDI) scores. We quantified the total antioxidant status (TAS), total oxidant status (TOS), and arylesterase (ARE) levels from tear and serum samples, and calculated the oxidative stress index (OSI). We also classified patients into phymatous, erythematotelangiectatic, papulopustular subtypes.

Results

We included 90 ocular rosacea patients and 30 healthy controls. Oxidative stress (TOS, OSI) levels were significantly higher (P < 0.01) and antioxidant levels (TAS, ARE) were significantly lower (P < 0.01) in both tear and serum samples of ocular rosacea patients as compared to controls. We found a significant positive correlation between the tear and serum values regarding oxidative stress parameters (P < 0.05). Besides, OSI was negatively correlated with TBUT and positively correlated with MGD score (meiboscore) and OSDI (P < 0.05). The Schirmer score was not correlated with OSI. No difference was found between the cutaneous subtypes with respect to TAS, TOS, ARE, and OSI results.

Conclusions

In this study, we identified oxidative stress markers in the serum and tears of ocular rosacea patients and showed their correlation with clinical signs of MGD, suggesting that oxidative stress contributes to ocular rosacea pathogenesis and that oxidative stress could be an indicator of MGD severity.

The research progress on the molecular mechanism of corneal cross-linking in keratoconus treatment

Keratoconus (KC) is a corneal anomaly that is manifested in a limited cone-like bulge with corneal thinning. Many molecules in the cornea change during the development of KC, including various components of the extracellular matrix, cytokines, cell connection, and cell adhesion-related proteins. Several treatment options are available, with corneal cross-linking (CXL) being the treatment of choice for early KC. However, postoperative complications have been reported in some CXL patients, mainly caused by corneal epithelial resection. Despite the fact that some novel approaches have helped to reduce some of the initial post-operative issues, their effectiveness seems to be inferior to that of the original CXL. To keep effectiveness while avoiding these negative effects, it is necessary to study the mechanism of CXL in KC treatment at the molecular level. This article provides a review of the molecular mechanism of CXL in the treatment of KC from four aspects: enzyme activity, signal transduction pathway, corneal-related proteins, and other KC-related molecules, further confirming the feasibility of CXL treatment of KC, providing new ideas for improving CXL.

Role of Oxidative Stress in Ocular Diseases: A Balancing Act

Redox homeostasis is a delicate balancing act of maintaining appropriate levels of antioxidant defense mechanisms and reactive oxidizing oxygen and nitrogen species. Any disruption of this balance leads to oxidative stress, which is a key pathogenic factor in several ocular diseases. In this review, we present the current evidence for oxidative stress and mitochondrial dysfunction in conditions affecting both the anterior segment (e.g., dry eye disease, keratoconus, cataract) and posterior segment (age-related macular degeneration, proliferative vitreoretinopathy, diabetic retinopathy, glaucoma) of the human eye. We posit that further development of therapeutic interventions to promote pro-regenerative responses and maintenance of the redox balance may delay or prevent the progression of these major ocular pathologies. Continued efforts in this field will not only yield a better understanding of the molecular mechanisms underlying the pathogenesis of ocular diseases but also enable the identification of novel druggable redox targets and antioxidant therapies.

Oxidative Stress in the Anterior Ocular Diseases: Diagnostic and Treatment

The eye is a metabolically active structure, constantly exposed to solar radiations making its structure vulnerable to the high burden of reactive oxygen species (ROS), presenting many molecular interactions. The biomolecular cascade modification is caused especially in diseases of the ocular surface, cornea, conjunctiva, uvea, and lens. In fact, the injury in the anterior segment of the eye takes its origin from the perturbation of the pro-oxidant/antioxidant balance and leads to increased oxidative damage, especially when the first line of antioxidant defence weakens with age. Furthermore, oxidative stress is related to mitochondrial dysfunction, DNA damage, lipid peroxidation, protein modification, apoptosis, and inflammation, which are involved in anterior ocular disease progression such as dry eye, keratoconus, uveitis, and cataract. The different pathologies are interconnected through various mechanisms such as inflammation, oxidative stress making the diagnostics more relevant in early stages. The end point of the molecular pathway is the release of different antioxidant biomarkers offering the potential of predictive diagnostics of the pathology. In this review, we have analysed the oxidative stress and inflammatory processes in the front of the eye to provide a better understanding of the pathomechanism, the importance of biomarkers for the diagnosis of eye diseases, and the recent treatment of anterior ocular diseases.

Assessment of serum catalase, reduced glutathione, and superoxide dismutase activities and malondialdehyde levels in keratoconus patients

BACKGROUND

The aim of this study was to investigate the relationship between keratoconus disease and the antioxidant activities of catalase (CAT), reduced glutathione (GSH) and superoxide dismutase (SOD) and the level of the oxidative stress marker malondialdehyde (MDA) in serum.

METHODS

The study included 50 patients diagnosed with keratoconus and 53 healthy age- and sex-matched control subjects. The keratoconus patients were grouped according to the four keratoconus stages based on the modified Krumeich keratoconus classification system. The CAT, GSH and SOD activities and MDA levels in the serum samples collected from the patient and control groups were compared.

RESULTS

The mean serum CAT, GSH, SOD and MDA levels in the keratoconus group were determined to be 0.075 (0.074-0.078)U/L, 0.002 (0.001-0.006) mmol/ml, 1.56 (1.51-1.62)U/L and 1.69 (1.65-1.99) mmol/L, respectively, and those in the control group were determined to be 0.024 (0.013-0.037)U/L, 0.029 (0.018-0.049) mmol/ml, 4.13 (4.01-4.17) U/L and 0.74 (0.65-0.82) mmol/L. The serum GSH levels and SOD activity were significantly lower in the keratoconus group (p < 0.001 for both) than in the control group while the CAT activity and MDA levels were significantly higher (p < 0.001 for both).

CONCLUSION

The low serum GSH levels and SOD activity and the high CAT activity and MDA levels observed in this study suggest the presence of oxidative stress and inadequate antioxidant defence mechanisms in keratoconus patients. The studied parameters may offer auxiliary markers for use in the diagnosis and treatment of the keratoconus disease and in its potential therapeutic targets in the future.

Pathogenesis of keratoconus: NRF2-antioxidant, extracellular matrix and cellular dysfunctions

Keratoconus (KC) is a degenerative disease associated with cell and extracellular matrix (ECM) loss that causes gradual thinning and steepening of the cornea and loss of vision. Collagen cross linking with ultraviolet light treatment can strengthen the ECM and delay weakening of the cornea, but severe cases require corneal transplantation. KC is multifactorial and multigenic, but its pathophysiology is still an enigma. Multiple approaches are being pursued to elucidate the molecular changes that underlie the corneal phenotype to identify relevant genes for tailored candidate searches and to develop potential biomarkers and targets for therapeutic interventions. Recent proteomic and transcriptomic studies suggest dysregulations in oxidative stress, NRF2-regulated antioxidant programs, WNT-signaling, TGF-β, ECM and matrix metalloproteinases. This review aims to provide a broad update on the transcriptomic and proteomic studies of KC with a focus on findings that relate to oxidative stress, and dysregulations in cellular and extracellular matrix functions.

The Pathomechanism, Antioxidant Biomarkers, and Treatment of Oxidative Stress-Related Eye Diseases

Oxidative stress is an important pathomechanism found in numerous ocular degenerative diseases. To provide a better understanding of the mechanism and treatment of oxidant/antioxidant imbalance-induced ocular diseases, this article summarizes and provides updates on the relevant research. We review the oxidative damage (e.g., lipid peroxidation, DNA lesions, autophagy, and apoptosis) that occurs in different areas of the eye (e.g., cornea, anterior chamber, lens, retina, and optic nerve). We then introduce the antioxidant mechanisms present in the eye, as well as the ocular diseases that occur as a result of antioxidant imbalances (e.g., keratoconus, cataracts, age-related macular degeneration, and glaucoma), the relevant antioxidant biomarkers, and the potential of predictive diagnostics. Finally, we discuss natural antioxidant therapies for oxidative stress-related ocular diseases.

[Histological changes in keratoconus and wound healing after corneal cross-linking]

BACKGROUND

Keratoconus is classified as a corneal ectasia and is a multifactorial disease. In those affected, mostly adolescent patients visual deterioration occurs due to the development of irregular astigmatism. Treatment by corneal cross-linking (CXL) has been indicated in progressive disease for several years.

OBJECTIVE

To present the pathophysiology and histological changes in keratoconus as well as wound healing processes after CXL and their potential complications.

MATERIAL AND METHODS

Histological changes in keratoconus as well as wound healing processes after CXL and their potential complications are presented based on histological examination of corneal specimens with keratoconus with and without a condition after CXL. Relevant literature and own data are analyzed and discussed.

RESULTS

Besides inflammatory processes, atopic and genetic dispositions play a role in the development of keratoconus. The histological characteristics of keratoconus include changes in the epithelium, Bowman's layer and stroma. Wound healing processes after CXL include healing of the surface epithelium and transient loss of keratocytes and nerve fibers.

CONCLUSION

Keratoconus shows characteristic histopathological changes, such as epithelial irregularities, stromal thinning and breaks of Bowman's layer, whereas the endothelium and Descemet's membrane remain unchanged (apart from cases of corneal hydrops). After CXL wound healing processes can be followed primarily in vivo by confocal microscopy. Complications after CXL are rare. Persistent loss of keratocytes can be clinically manifested as a visually relevant scar.

Oxidative and antioxidative stress markers in keratoconus: a systematic review and meta-analysis

PURPOSE

To conduct a systematic review and meta-analysis on the levels of oxidative stress markers and antioxidants in keratoconus compared to healthy subject.

METHOD

The PubMed, Cochrane Library, Embase, Science Direct and Google Scholar databases were searched on 1st June 2020 for studies reporting oxidative and antioxidative stress markers in keratoconus and healthy controls. Main meta-analysis was stratified by type of biomarkers, type of samples (tears, cornea, aqueous humour and blood) and type of corneal samples (stromal cells, epithelium and endothelium).

RESULTS

We included 36 articles, for a total of 1328 keratoconus patients and 1208 healthy controls. There is an overall increase in oxidative stress markers in keratoconus compared with healthy controls (standard mean deviation (SMD) = 0.94, 95% confidence interval (95% CI) 0.55-1.33), with a significant increase in reactive oxygen and nitrogen species (1.09, 0.41-1.78) and malondialdehyde (1.78, 0.83-2.73). There is an overall decrease in antioxidants in keratoconus compared with healthy controls (-0.63, -0.89 to -0.36), with a significant decrease in total antioxidant capacity/status (-1.65, -2.88 to -0.43), aldehyde/NADPH dehydrogenase (-0.77, -1.38 to -0.17), lactoferrin/transferrin/albumin (-1.92, -2.96 to -0.89) and selenium/zinc (-1.42, -2.23 to -0.61). Oxidative stress markers were higher in tears and in cornea of keratoconus than in aqueous humour, and antioxidants were decreased in tears, aqueous humour and blood without difference between sample type. Oxidative stress markers increased in stromal cells and antioxidants decreased in endothelium.

CONCLUSION

Oxidative stress markers and antioxidants were dysregulated in keratoconus, involving an imbalance of redox homeostasis in tears, cornea, aqueous humour and blood.

Systemic oxidative stress biomarkers in patients with vitreomacular traction syndrome

PURPOSE

To evaluate whether the systemic oxidative stress biomarkers increased in patients with vitreomacular traction syndrome (VMT).

METHODS

This study compared 25 patients diagnosed with VMT with 20 healthy controls. As a biomarker of systemic oxidative stress, malondialdehyde (MDA) was measured. Total oxidant status (TOS) and total antioxidant status (TAS) were measured to evaluate the systemic oxidant status.

RESULTS

Serum MDA values were significantly higher among the patients (p < 0.001). The ideal cut-off value for MDA was determined to be 22.1 µmol/L, with 80% sensitivity and 75% specificity. The between-group differences were not statistically significant for TOS or TAS (p = 0.326 and p = 0.698, respectively).

CONCLUSION

Increased MDA levels suggest that systemic oxidative stress may play a role in VMT.

Preliminary Study on the Tears Oxidative Stress Status and Sleep Disturbances in Irritable Bowel Syndrome Patients

According to the latest gastrointestinal disorders diagnostic criteria (ROME IV), the irritable bowel syndrome (IBS) is mainly characterized by the presence of abdominal pain and changes in intestinal transit. However, both sleep impairments and oxidative status changes (in patients' sera, mucosal level, and other body fluids) were reported IBS. Thus, in this study, we aimed to evaluate several aspects regarding the oxidative stress status in patients' tears as well as sleep disturbances by comparison with the intensity of IBS symptoms, as assessed by the visual analogue scale for irritable bowel syndrome (VAS-IBS). Ten IBS patients and fourteen healthy sex- and age-matched volunteers were recruited from the Oftaprof Ophthalmological Clinic (Iași, Romania). Visual analogue scale for irritable bowel syndrome and the Pittsburgh Sleep Quality Index (PSQI) questionnaires were administered to all the patients. Tear samples were collected using the Schirmer test procedure and were subjected to biochemical analysis-superoxide dismutase and glutathione peroxidase activities, malondialdehyde, and total soluble proteins levels were determined. Standard statistical analysis was applied. We found significant differences in oxidative stress marker dynamics in IBS patients as compared to healthy age- and sex-matched controls: increased superoxide dismutase activity (p = 0.02), increased malondialdehyde (p = 0.007), and total soluble proteins levels (p = 0.019). We found no significant differences in tear glutathione peroxidase activity in IBS patients as compared to healthy age- and sex-matched controls (p = 0.55). Furthermore, we observed that the oxidative stress tear markers are correlated with gastrointestinal symptoms severity (as evaluated by VAS-IBS) but not correlated to the sleep quality index and items (as evaluated by PSQI), with significant differences according to patient sex and IBS subtype stratification. In this way, this study brings additional evidence of the oxidative stress role in IBS pathology alongside the evaluation of tear fluid molecular dynamics in IBS for the first time in our best knowledge.